FR2468832A1 - IMPROVEMENTS IN DEVICES FOR PERFORMING A REACTION, SUCH AS A COMBUSTION, BETWEEN A SOLID AND A GAS - Google Patents

Abstract

Reactions are carried out between gases and solids in fluidized beds established above perforated supports 228, 248 and where, for example, combustion and desulfurization are carried out, the presence of an inert and non-combustible material such as sand and quartz pebble 230, 250 used to renew by attrition the active surface of a sorbent such as limestone combining with SO2, baffles 252 opposing the entrainment of solids out of the beds whose heights and the fluidization conditions are carefully adjusted with the aid of ascent devices 264 and descent 260, 266.

Description

246883 '

  "Improvements to devices and methods for carrying out a reaction, such as combustion,

between a solid and a gas. "

In the prior art, coal burners with desulfurization in a fluid bed are known, using sorbents such as limestone. However, these devices of the prior art have proved unsatisfactory. They appeared to be characterized by ineffective use of sorbents, inadequate removal of sulfur unless

we resign ourselves to such ineffective use of outlets

  bants that it is not economically acceptable, and by a practical inability to use many materials

  sorbents available. The use of more tender limestones

dres results in fragmentation and training

  particles by the gases before the sorbent is suitable

  kindly reacted; the use of harder limestones

  due to the formation of a sulfate coating which decreases reactivity. The limestone in large particles that the devices of the prior art allow to discharge has forced the specialists responsible for the design of the installations to use a greater spacing of the steam tubes, the

  result being an increased cost price of the boilers.

  Efforts to burn coal in fluid bed combustion devices have encountered problems both when walking at a speed below maximum capacity and during the warm-up period for start-up; many specialists in the prior art have recognized this. One approach to solving the problem of reduced speed walking has been to use quite a number of combustion devices and to completely interrupt the operation of at least one of these multiple unitary devices. Another approach has consisted in simply alternating frequently enough periods of operation and shutdown of a single combustion device. Such solutions

  require the provision of complicated auxiliary equipment

  ques, inconvenient to use, allowing only a small

ble variation of the running speed between full power

  and combustion at reduced power, or else have been

  characterized by a reduction in walking speed ratio

undesirably low, or make it impractical to reduce

  the operating regime unless the costs entailed by restarting operations accompanied by

wasted time; It goes without saying that many of these in-

  can be observed when adopting a solution

  particular tion given. The prior art has also led to giving up the use of excess air allowing the

  cooling of the bed during a period of operation-

reduced walking.

In accordance with the present invention, it has been discovered

  than a gas (such as the products of the combustion of

  good) can be allowed to react with a solid substance (such as limestone) in a fluid bed device, the reaction being carried out with good efficiency and high yield if the gas, when it is allowed to enter the fluid bed is forced to follow a course modified by chicaces or similar arrangements in such a way

  that the gas cannot, by shock on the solid, the frac-

  turing and fragmenting it into particles if said solid is itself chosen such that its attrition rate

  by wear in the bed-is suitably large (by "con-

  venably large ", we mean a production pace of

  microfragments superior to the formation pace of a re-

  clothing, for example calcium sulphate), if enough material ("stone") which has not easily broken up has been incorporated into the fluid bed, so as to maintain a desired bed height, if means of discharge by overflow are provided for regulating

  the depth of the bed, such that

  tervian by friction movements in the bed, this

  which results in a constant formation of very small parts

  particles ("microfragments"), and if solid is added at a rate calculated so as to satisfy the desired degree of reaction. Particles formed by attrition in the bed are extremely small (their diameter is, for example, 3 microns), and they are produced as a result of a surface friction effect as noted in the art previous ("Experimental and Engineering Support of the FBC program", DL Kearns et ai., Westinghouse Research'Labs, Pittsburgh, Pennsylvania, Monthly report NO 14 in the United States EPA, Contract 6802-2132, January

  1977). (Gas emitted at the orifices of a dispenser

  tor without baffles allowed to move around enough

quickly so that the entrained particles collide violently

lie and shatter into small fragments, the particle size of the fragments thus produced being very large, and a good number of the particles thus formed being too small to remain in the bed but being however too large to effectively absorb S02 during their entrainment out of the bed .)

  We have discovered that it is possible to carry out a

che at reduced diet very effective in a device of

fluidized combustion, free from all the above drawbacks

mentioned devices of the prior art, if it is pre-

  seen two areas in which portions of the materials

  components of the bed can be kept and stored

born, a first portion being a lower part of

the actual combustion area in a fluidized bed, located

  underside of cooling tubes in the upper part

re from the combustion zone and a dry conservation zone

  trimmed to which and from which material

  the bed can be transferred from the first

first area and up to the first area so, respectively-

ment, lower the material levels below the cooling tubes or raise the level in the cooling tubes, adequate cooling of the bed

  being realized when its level is located below the tu-

  bes, blowing through excess air, the depth

  deur below said tubes being such that the first conservation and storage area can be allowed to operate in the manner of a combustion device to

fluid bed even when the depth is not greater

of. The invention has the additional advantage of improving

much improved preheating, a new requirement which raised a difficulty (use of larger burners

  and more expensive, and undesirable production of soot and hy-

unburnt drocarbons), as well as making it convenient to preheat with various energy sources (including

  gaseous fuels, liquids, solids, and electricity).

  It has been discovered that if combustion is predicted (or-

  normally in oxygen from primary air) without sorbent present in an upstream fluidized zone (in slow current, so that the constituent material of

  matrix does not leave the bed), and if a treatment is provided

  With a sorbent (for example, limestone) or another treatment, in a fluidized area arranged downstream, it is possible to achieve flexibility of operation.

considerably improved and in optimal conditions.

It is possible to operate the combustion zone, with many coals, at higher temperatures, which improves the fuel and system efficiency, and also without causing (because of the absence of lime) a corrosive corrosion. from the surface of the exposed water tubes

  to the flames. This also makes it possible to set values

their optimal the fuel to air ratios and the

  content of particulate fragmented solids (matter and di-

  mensions) chosen and used in each area. A com-

  busting carried out in the manner just described also makes possible optimal elimination of carbon monoxide and nitrogen oxides. The combustion efficiency is increased to the maximum when the combustion bed is admitted

  to operate at the highest possible temperature,

  below the ash melting temperature,

  and in the presence of an excess of air at the level of the bed of com

bustion or downstream of this bed; NO formation is minimized by operating the combustion bed at a similarly high temperature, and also by allowing the nitrogen oxide associated with the volatile substances to be chemically reduced to molecular nitrogen in the downstream bed in the presence of charred substance and a small excess of oxygen; carbon monoxide formation is minimized by performing combustion with an excess of air, at a temperature above 7770C; elimination of

  sulfur dioxide is maximized by making it work

  operate the downstream bed at 8430C 2800 in the presence of an excess of oxygen; the presence of the carbonized substance necessary to reduce the NOx associated with volatile substances

is favored by the combustion of coal in an atmosphere

reducing sphere prevailing in the combustion bed; the

omitting a sorbent in the combustion zone

  puts the tubes to higher temperatures without risking excessive corrosion of the surface of said tubes licked by the flames; and the higher temperatures of the heated fluid thus permitted also allow

  increase the efficiency and effectiveness of the system.

  The invention can be better understood using the

additional description which follows and using the drawings

  appended hereto, which relate to embodiments of the invention chosen by way of non-limiting examples, of course. Fig. 1 of these drawings shows diagrammatically, part in elevation and part in vertical section, the mode

for producing a device according to the present invention-

considered to be the most advantageous.

  Fig. 2 shows in longitudinal section a nozzle and a portion of a water vapor tube used in the

embodiment shown in fig. 1.

  Fig. 3 shows in vertical section a portion of a bubbling cap installed in the dispenser assembly

median of the embodiment shown in fig. 1.

  Fig. 4 shows in elevation, and partially in vertical section, a bubbling cap and a portion of the

  upper distributor assembly of embodiment

presented fig. 1.

Fig. 5 shows in vertical section a dilated joint

ble used to mount the lower distributor plate

in the embodiment shown in fig. 1.

Fig. 6 is a diagram of the circulation system of

  water used in the embodiment shown in fig. 1.

  Fig. 7 shows in side elevation, partially

in vertical section and partially with rear portions

  chées, an arrangement used to dry, then grind char-

  and then transport it to the installation

presented fig. 1. Fig. 8 shows in side elevation, and for the

  mostly in vertical section, a limestone pot used

  sand to remove lime from the installation

shown in fig. 1.

  Fig. 9, finally, schematically represents an ins-

tallation for the combustion and desulfurization of coal.

  An embodiment is described below in detail.

  preferred of the present invention.

  There is shown fig. 1, schematically, a three-bed combustion desulfurization device 1-5, all three fluidized; this device is generally designated by the reference 200. A metal casing 202 surrounds refractory layers 204 and 206 which are respectively of a lower density and a higher density. he

  a complete installation is thus established which reposes

  stands on supports 208. Metal distribution plates

Liques 210, .212 and 214 extend transversely to the in-

  envelope 202 to define the bottom bottoms

  ors of three fluidized beds, namely a lower bed for storing sand, a median combustion bed, and a

upper desulfurization bed.

  The lower bed 210 is located above Pune bedroom.

  bre of insufflation supplied by a wind box 216 and allowing fluidization air to penetrate through the lower distributor plate 210 into the sand bed resting on this plate 210. Multiple bubbling caps 218 s' extend through the plate 210 (on which extends an insulating panel, not shown, serving to avoid hot zones) which is

  e4 itself held in place by expandable seals 219.

  Through the casing 202 and above the caps

218 extends a line 220 which serves to remove cen-

  coarse dres and to be transferred to a hopper not shown

smelled, equipped with filter bags, the material

excess bed linen.

  The median combustion bed is established above a

  insufflation chamber 227 for supplying air

  bustion and fluidization down to this middle bed. Multiple bubbler caps 224 extend through a distributor plate 212 and a water jacket 225 which serves to cool the plate 212 to prevent it from curling. An insulating layer 228 rests on the plate 212

  around each of the caps 224, and a layer of pier-

  res 230 (which are actually rough fragments of

  quartz with a grain size of approximately 9 mm to

about 25 mm in diameter) covers the 228 insulation.

Similar insulation 229 che is fixed (by means not shown) on the lower bottom of the water jacket 225, and is used to minimize heat loss by transmission to the water in the jacket 225. Au -above the bubbling caps 224 is arranged a pipe 232

  of coal supply which deposits coal at the lower part

  upper part of the combustion bed, just above the bubbling caps 224. (Such a supply of coal under the bed makes it possible to use coal fines in the charge which otherwise, that is to say if one carried out the supply on the bed, would be blown and carried out of the bed without burning there. A supply on the bed would also have the disadvantage of making difficult the operation of the bed in another

  position only at full load, i.e. with covered sand

  to the top of the steam tubes 234. At low levels

  sand, and with a supply of charcoal to the bed, the charcoal would fall as far as the steam tubes, and an agglomeration of unburnt charcoal would soon

  settle down. The inability to function at re-

sand in the middle bed would prevent the use of preferred low-running methods

  and restart as described below).

Above the line 232 and across from the combustion bed extend water vapor tubes

234, the ends of which are mounted in metal sheets

  tube ports 235 (one of which is shown in point-

tillé) which define collectors for the introduction of water into the tubes and for the exit of water and steam from said tubes. These tubes 234 are spaced apart and occupy 25% of the volume limited by the envelope in the area between the upper row of tubes and the

lower row of tubes.

The upper desulfurization bed is arranged above a perforated tube 236 for supplying secondary air; this tube is pierced with two rows of holes 238 inclined downwards

at an angle of 300 to distribute the secondary air over

under the upper bed; a third run is planned

  hole 240 on the lower generatrix of the tube to expel by blowing any particles that could have entered the tube. Above tube 236 is arranged

  a water jacket 242 which is used to cool the plate

tributary 214 to prevent it from curling. Baffles 244 (one shown) are used to maintain the speed of circulation of the cooling water at a value large enough to avoid the establishment of zones

  overheated rooms which could cause damage.

  Multiple splash caps 246 extend through the

  towards water jacket 242 and plate 214. A cou-

Che insulation 248 rests on the plate 214 around each

one of the caps 246, and a layer of stones 250 (the same materials as for the stones 230) covers the insulation 248 and the caps 246. A similar layer of insulation

  249 is fixed to the lower bottom of the water jacket 242.

  This latter insulation serves the same purpose as that provided on

-30 the distributor plate and on the water jacket of the mete bed-

  dian. (250 stones are used to allow gases from

  caps 246 to be distributed laterally on the device

tributor, thus making them enter the upper bed

  laughing at a speed low enough to avoid a

  Exaggerated fragmentation of limestone particles). At-

above the upper bed are arranged three rows of tubes 252 used to return particles to the bed. Each tube forming part of the middle row is placed directly above a corresponding tube forming

  part of the bottom row, but each of the tubes

  The part of the upper row is placed midway between each adjacent pair of tubes belonging to the two lower rows. This arrangement avoids the possibility of

line of sight opening at any angle

  only through the bundle of tubes, and has the effect that any particle ejected out of the bed must necessarily strike one of the tubes before leaving the bed, which reduces

its speed and reduces the risk of flying particles

up to the freeboard. (A similar bundle of tubes can usefully be arranged above the second bed, i.e. the combustion bed). The 252 tubes are

supported near their ends and in posi-

  tations spaced along their length by tales per-

drilled holes 254 (only one of which is shown), which are themselves supported from the casing 202 by rods 256. Above the tubes 252 extends a pipe 258 for supplying limestone which serves to deposit limestone in the desulfurization bed to a level just

above the upper row of tubes 252. The calcare-

  re falls from an exit tee 259 from the tube 258 through an interval (not shown) formed in the

  bundle of tubes 252; without this interval, some

  limescale could be too large to not-

pass through the bundle of tubes. A column of des-

  cente 260 of limestone cooperates with a limestone pot (not

shown.fig. l but shown in fig. 8) used for many

  fix the level of limestone just above the tubes 252 and remove the worn limestone from the installation. Hot desulphurized gases exit via a flue pipe 262 which can transfer them to a boiler in which they transfer their sensible heat, then to a battery of filter bags to separate any ash or other particles that may have escaped from the upper bed; they are

  Analogously sent to a chimney.

An ascent column 264 and a descent column 266 make it possible to transfer the material constituting the bed from the lower bed to the middle bed and vice versa, in order to carry out preheating and to put the engine into reduced operating mode (these two operations being described in more detail below). The ascent arrangement 264 comprises an ascent pipe 268 which, when a door 270 is opened by a control device 272 (shown in dotted lines because it is arranged outside the envelope 202), allows the removal of bed material from the lower bed and its blowing, under pressurized air injected through a tube 274, into the bed

  median through a door 276, which is maintained normally

  Lately closed by the effect of gravity to prevent filling of the lift pipe with bed material when it is not in use, but which opens in response to the thrust of the bed material blown from the lower bed. The normal level of

material of the bed so that the device

  bustion operates at its 100% capacity is located just above the tallest steam tubes, as shown in fig. 1. Reinforced fittings 278 and 279 are used at the elbows for the passage of the bed material in order to avoid excessive wear on the wall of the tube of the

lift column.

The descent arrangement 266 comprises a descent pipe 280 which, when a door 282 is opened by a control device 284 (shown in dotted lines because it is mounted outside the envelope), allows bed material which has entered the pipe

  from the middle bed to be transferred by a screw of ali-

  ment to the lower bed. In normal operation, the downcomer 280 should be filled with bed material acting as a pressure-resistant seal so that air from an insufflation chamber 227 is not able to prevent

  the material of bed to descend in this con-

  pick. A reinforced connector 281 is arranged where the connection

  pick 280 makes a sharp bend to prevent wear

driving too quickly at this bend.

  Particular details of construction of the installation shown in fig. 1. Each

  boiler tube 234 has a nozzle 288 (fig. 2) em-

sleeved in that of its ends which is connected to the water intake manifold. The purpose of this nozzle is to

allow water to enter a tube

  fear and to flow into it, such flow only occurring

not just in the lower tubes because the pressure

  hydrostatic ion is greater for them. If water stops flowing in a tube, it may very quickly overheat. With the nozzle, the resistance

primary flow is pressure loss (or pressure

  sion) through the nozzle, which is the same for all the tubes, so that the lower tubes cease to provide the water with a flow path substantially

easier.

  Fig. 3 shows a bubbling cap 224 arranged in the central distributor plate 212. This cap 224 comprises an end piece 290 and a proper cap 292, or cap. The end piece 290 is fitted through a hole drilled in the plate 212 and through a tube placed in the water jacket 225 (not shown in fig. 3

  see fig. 4 concerning the same construction of a capu-

  splash pad arranged in the upper bed). Just at-

  four holes 294 are drilled under the cap 292

  spaced apart (only three of which are shown) formed in the side wall of the end piece 290. The cap

  292 has an annular shoulder 296 which acts in the

  lesson of a parasol on holes 294 to prevent sand (or, in the upper bed, limestone and sand) from falling into the holes and "crying" onto the

  bed below when the burner is off. In fact

  lity, such a runoff poses a much less acute problem in the upper bed because there are stones V0 providing protection against such a runoff of sand and limestone. The diameter of the shoulder 296 is chosen so that an angle has measured from the edge

  lower outer shoulder to the inter-

  ne lower of one of the holes 294 (fig. 3) is lower

  at the angle of rest (or collapse) of the sand (or the calcare-

  re), which is the angle formed by a pile of material in part

  cules with the base on which it rests. The angle of re-

pos for the sand used in the installation shown in fig. 1 is equal to 370. In fact, to calculate the angle oc, it is first necessary to subtract, from the diameter of the hole 294, the diameter of the particles, then to choose a shoulder diameter which, when draw a line from the edge of the shoulder to the bottom of hole 294 minus the

  diameter of a particle (as shown in Fig. 3), give

ra an angle smaller than the angle of rest. We can cal-

set the angle a in this way because it has been observed that a simple layer (or monolayer) of particles cannot

fall into one of the holes.

  Splash caps 218 and 246 are similar

  to the bubbling caps 224, to their dimensions.

All bubbler caps can be removed from their respective distributor plates for easy replacement. Each bubbling cap 246 of the upper bed is fitted through a tube 298 (fig. 4) placed in a water jacket 242 and is wedged there by a ferrule 300. A half-connector 251 is threaded at the bottom of the end piece 290 to fix it in the hole. With the exception of the ferrule 300 and the half-union 251, the bubbling cap 246 is kept relatively isolated from the tube 298

and of the water jacket 242 in order to allow that said ca-

  bubbling plug can heat up to a temperature

rature higher than that of the dispenser, to break up any tar or other volatile substances likely to accumulate on the caps during the setting

  market. Because this combustion function of the sub-

volatile stances shortens the useful life of the

bubbling plugs, the possibility of replacement fa-

ckle of said caps without the need for replacement

  placing the distributor is a valuable advantage.

Fig. 5 shows an expandable seal 219 for the lower distributor plate 210. Such a seal 219 comprises a

L-shaped element 302 which is bolted with no play

  table on the external underside of plate 210 by

* 304 bolts (only one of which is shown). A corner

re en fer 306 is subject to the envelope 202 and extends inwardly through the refractory layers 204 and 206 into the space between the plate 210 and 1 '

  element 302. The angle iron 306 extends the length of the plate 210 in the direction extending out of the plane of the paper, just like the

does element 302. However, spaced saw cuts 308 (only one of which is shown in FIG. 5) are cut from angle 306 to allow lateral expansion of the angle under the effect of heating, in particular at the outer edge of the iron angle. When

  plate 210 expands in the direction of the arrows (visi-

  wheat fig. 5) when the burner works, a space is met

  swam for this expansion because the outer edge of the angle 306 is itself spaced from the bolt 304 and because, correspondingly, the outer edges of

  the plate 210 and the element 302 are spaced from the refraction

shutter 206. Seals 219 thus prevent the plate 210 from

  curl. A bolt 304 mutually secures the plate

that 210 and the element 302 by providing a sufficient seal

fisante to minimize gas leakage through the joint, the tightening achieved, however, being loose enough to allow free lateral movement of the plate and the L-shaped element relative to the angle. Joints 219 secure the plate 210 to the casing 202

  on at least three sides. We can foresee, on the fourth-

on my side, either another joint 219, or a groove made

  in the inner wall of the envelope.

Fig. 6 shows a portion of a circulatory system

  tion of water for a 200 combustion and de-

  sulfurization. Food water enters the system through a return line 328 and is pumped by a circulation pump 312 which delivers it through a line 314 into the intake manifold (not shown because it is located on the side of the burner which is at

  the opposite of that shown in fig. 6) feeding the tu-

  bes of steam 234, after which this water passes through said steam tubes 234, then into the outlet manifold 316 and exits through a pipe 318. Steam is separated from the water in the outlet manifold 316 and exits therefrom a pipe providing steam, 320. A pipe

  322 transfers a portion of the water from the circulating pump

  culation to a water jacket 242 used to cool the upper distributor plate. Water comes out of this jacket 242 through a pipe 324 which brings it back to the outlet manifold 316 from which it comes out through a pipe 318. Although the pipes are not shown, an arrangement

  similar is provided for the water jacket 225 (not shown

smelled fig. 6). A steam drum 326, separate device

ready placed along the combustion and desulphurisation installation 200, supplies water to the system to make up the water which is lost as a result of production

  steam in the combustion system and for guarantee

  firing that there will always be enough water to ensure proper operation of the pump 312. The steam drum 326 has a pipe 328 for supplying drinking water and

  an outlet pipe 330, the latter serving to supply

  supply water to the pump 312. An assembly 332 comprising a float valve supplies additional water which can be admitted into the steam drum through a pipe 328 each time the water level in this drum drops to below a certain height. Line 334 is used

  to drown the steam tubes 234 with water for an in-

emergency terruption in case of danger, in order to pocket a

  overheating of said tubes. A 336 solenoid valve

automatically reads an intake of this flood water

for such an emergency interruption. A conduct of-

wind 338 communicates the steam drum with the steam flow line 320 to avoid establishment

positive or negative vapor pressure in the drum

  steam circuit 326. The water circuit for the combustion-desulphurization installation is established in parallel with the water circuit of the boiler (not shown) as follows. The line ensuring a return of water to line 328 is also connected to the water supply to the boiler, and the steam line admitting steam to the steam installation, which is connected to the line 320, is also connected to the steam outlet of the boiler. If we now want to consider the system used to supply coal to the combustion and desulphurization installation 200, FIG. 7 shows a variable speed screw device 348, a coal dryer 340, a grinder 342, a rotary lock 368 air, and a coal pot 344. Coal from a hopper 346 passes through the device feed 348 with screw and falls into a dryer 340 by a chute 341 from which it falls into a trough 350 affecting in cross section a partially semicircular shape and in which is placed a rotating shaft 352 carrying at each end a grinding wheel 353 ( only one of which is represented); between these two grinding stones extend bars 354. One of the bars 354

supports smaller cross dowels 356 (me-

  about 25 mm long) which are mutually

spaced at intervals of approximately 6 mm serving to hold

  make larger pieces of charcoal while not leaving

  serve smaller pieces of charcoal and fines. At the base of the trough 350 is fixed a hot air pipe 358 (260-370oC) which introduces this hot air into the trough 350 through a perforated distributor plate 359 in order to fluidize the smaller particles and to heat, by the shock of the jet, the larger ones. This air is first heated by passing it through a coil (not shown) placed in the combustion bed. A cover 360 closes the trough 350. A vent 361 allows the exhaust of hot air and all gases likely to be emitted by the coal. Rotary mounting promotes drying of

  coarse pieces of charcoal, when the food is made

  tation with only large fragments of charcoal (for example, charcoal for heating stoves, in pieces measuring approximately 32 x 6 mm), by shaking the pieces, which has the effect of eliminating pockets of moisture which without

this could remain between pieces of coal.

When using the dryer to dry a charcoal containing

  ning at the same time coarse fragments and fines (for example, nuts and dust with a particle size ranging between 38 and 0.6 mm), the displacement of the raking pins 356 eliminates the coarse pieces, which do not require drying as thoroughly as fines, which allows the remaining charcoal to be dried in

a fluidized state. Charbors containing up to 15% oil

  Moisture can be treated by the dryer using air which, in accordance with safety requirements, is at a temperature well below the explosion point of the coal gases, because of the relatively long duration of the residence time (typically 15 seconds) of coal in the trough, which allows air to access a relatively large proportion of the surface of the coal, the result

  being to favor a good transfer of heat to coal.

On the side of the trough 350 located opposite the screw feeder 348 is arranged an outlet lip

  362 which is placed at the end of a radius at 150 au-

below a horizontal radius, and which directs the dried coal to a pipe 364 and from there to a grinder 342 (designed to allow crushing of the coal up to a particle diameter corresponding to 95% of particles of less than 13 mm , with 50% of particles remaining on a standard sieve with square openings measuring approximately 2.36

  mm side), from where it falls into a rotary air lock 368.

A vent 369 prevents the establishment of a pressure upstream of said air lock, and is put in communication with

the atmosphere.

Pockets of crushed charcoal are then allowed to fall from the air lock 368 into a charcoal pot 344 in which is mounted a perforated distributor plate 370 below which an air intake duct 372

  introduces fluidizing air into the pot through

  towards said plate 370. A coal outlet pipe 374 extends from the pot above the plate 370 and is connected to the pot by a convergent nozzle 375 which

facilitates pneumatic transfer of carbon by a

  pick 374 which brings this coal to the supply line 232 (fig. 1) of coal to the combustion installation 200 and

desulfurization.

  The purpose of the charcoal pot is to attenuate the fluctuations in the charcoal feed rate, fluctuations which in the absence of such a pot would be observed when the rotary airlock empties each pocket. Such fluctuations would increase the risk of a blockage in the coal supply line, thereby decreasing the safety and reliability of operation of the system, and would also decrease its ability to transport relatively large pieces of coal (up to 13 mm) in line 374 of

  32 mm in diameter without any obstruction.

  A pipe. 374 of larger diameter would then be born

stop to properly transfer such large mor-

hides. However, a larger diameter coal transfer line requires larger quantities of air to operate pneumatically, which in turn results in a greater risk of the combustion device malfunctioning, increasing the danger of blowing through the bed when the height of this bed is at its minimum depth. These blows carry with them the coal fines (passing through a standard No. 28 mesh screen, having openings

0.59 mm square) in the supply line

  carbon, and adversely affect the yield

  combustion burner. We can amortize as

  follows fluctuations in the pattern of outflow

tie of coal. The charcoal pot is dimensioned so as to allow vigorous fluidization. In other words, a value of the speed of flow of the fluidizing air through the pot is chosen such that it is equal

  at least three times the minimum fluidization speed.

  coal. This results in particles of char-

* good fly to the space above the

  level of the upper surface of the bed in the charpot

Well; those of the particles which fly away as far as

- 18

in the vicinity of the converging 375 are drawn to

in this converge and are blown into the pipe

  te 374 of coal and to the combustion and desulfurization device 200. Without fluidization, the coal feed rate would be appreciably modified as a result

  slight variations in bed height that occur

  inevitably feels due to the jerks in the supply of combustible material but, with a fluidization, one can note that the speed of supply to the convergent depends on the spurts of splashes from the bed, which are independent of the jerks. A blow tube 376

  helps to provide an advantageous equalization of the e-

flow by eliminating all accumulations of material likely to occur, failing this precaution,

in convergent 375.

The charcoal pot can also be used to split the main stream of charcoal into a number of smaller, equal feed streams, each serving to feed a bed area of equal dimensions. Such current sharing is necessary for fluid bed combustion devices whose bed area exceeds approximately 0.93 square meters. The coal pot performs such a current-sharing function by placing the number

  required outlet ports (one for each portion of over-

face of 0.93 m2) on the perimeter of the pot, each of these orifices being identical to the arrangement with convergent 375,

  with pipe 374 and with blow tube 376.

(Means of an even more advantageous design would consist in moving the rotary airlock 368 to air to place it between the supply screw 348 and the dryer 340, and by allowing heated air, leaving the dryer by a vent 361, to act as air for transporting charcoal which is allowed to enter the charcoal pot through a pipe 372 before entraining the charcoal towards the fluid bed combustion device. This eliminates the loss of heat and fuel loss associated with establishing a vent communicating with the atmosphere

to let the gases escape from the dryer, and remove

  also undermines the ntcess-ity of providing any particle collector system which would otherwise be necessary

  with a system using a vent communicating with the

  mosphere. Fig. 8 shows a limestone pot 378, similar to the charcoal pot 344. The aforesaid pot 378 is connected to the descent column 260 of limestone by a vertical tube 380 which extends from top to bottom centrally inside

  from the envelope 382 of the pot. Inside this envelope

  pe 382 is also arranged with a perforated distributor plate

384 placed below the lower mouth of the tube

  tical 380. Above plate 384 there is a plate

that obturatrice.d'orifice 386, which plate 386 is vertically adjustable using a handle 388 and a threaded shaft 390 to adjust the dimensions of the lower orifice of the vertical tube 380 opening into the casing 382. At a level above the mouth 381 of the tube

vertical 380 is arranged an outlet assembly 392 which connects

  cord the casing 382 to a pipe 394 for evacuating

limestone. An air supply tube 396 is directed in a

  lesson in blowing air into outlet fitting 392 to facilitate pneumatic transport of used limestone using a pipe 394 leading to a hopper

  (not shown) equipped with a battery of filter bags

  ge. Below the plate 384 is arranged an air inlet pipe 398 which sends fluidizing air through the plate 384. The envelope 382 rests on

  supports 400. The limestone pot fulfills an ana-

logue to that of the coal pot; in other words, it is used to transport solids smoothly and without interruptions in

  a pipe with the smallest practically possible diameter

  sible. It is also used to cool the sorbent from its

bed temperature (around 8430C) up to a fairly low temperature (below 2040C) can safely sorb the used sorbent up to the battery of bags

  filters. It is still used to operate the tube

  plunging tical 380 which brings the sorbent in the manner of a pressure-maintaining joint making it possible to establish the

  pressure prevailing in the limestone pot at a suf-

  setting (typically equal to about 0.07 bar) for trans-

take the used sorbent to the hopper fitted with a drum

  filter bags, thus eliminating the need to arrange a mechanical seal in the tube

descent containing sorbent at a high temperature.

  (According to Walker et al., Combustion, February 1979, page 31, no device enabling these functions to be fulfilled, namely those of a cooler in a supply line.

  lowering of bed material, is not present-

ment available).

Dimensions and other specifications are given below.

  cations of an installation in accordance with the embodiment described above, and which has been chosen to provide an amount of energy equal to 1356 therms / hour / m2. The

  steam overpressure (pressure in addition to the pressure at-

mospheric) is less than or at most equal to 1 bar. The horizontal surface area of the central distributor plate 210 is equal to 1.858 m2 (0.9144 m, 0.0508 m x 1.8288 m, 0.1016 min) for an energy output equal to 2520 thermies / hour. When the lower bed is filled, its depth (in the packed state, not fluidized) is equal to 0.1778 meters;

to make it} we use a sand whose particles

  measure 850 microns (standard sieve with mesh No. 20).

  The depth of the middle bed varies from 0.1524 m to 0.2921 m and uses sand of the same dimensions as for the lower bed. The upper bed has a depth of 0.1524 m and uses a sand comprising 90% of particles corresponding to a standard sieve with mesh No. 6 (3.33 mm) and 50% of particles remaining on a standard sieve with mesh No. 10 ( 1.65 mm), plus fragments of limestone

  measuring approximately less than 16mm and more than 8mm. The cal-

  this is of type 1360 which can be purchased from the Monmouth Stone Co., h Monmouth, Illinois, United States of America. The coal is a Peggs Run bituminous coal for heating homes, calibrated approximately 32 mm x 6 mm, containing 3.25% sulfur and having a calorific value equal to 7639 therms / ton, which can be purchased at the Peggs Run Coal

  Co., h Shippingport, Pennsylvania, United States of America.

  The distance between the bubbling caps 224 and the lower part of the bundle of steam tubes 254 is equal to 152 mmo (This allows the burner to operate without blowing in the coal feed line. When implementing this mode

of realization, we observe a blowing when the depth

  deur of material of the middle bed is less than 76 mm, this depth being measured from the top of the bubbling caps 224. The fact of giving this depth a value of 152 mm, instead of being satisfied

minimum velocity of 76 mm, allows to establish a coefficient

safety cient to guard against blowing da

  to an inadvertent loss of material

  of the bed during operation of the installation

tion). The freeboard of the middle bed is 762 mm, and for the upper bed the freeboard is 457 mm. We choose

these dimensions of freeboards to prevent a no-

sand and sorbent table, respectively. The overall height of the combustion-desulfurization device 200 is equal to 2.54 m. All of the splash caps 218, 224 and 246 are spaced 76.2 mm apart between centers, which results in 172 per square meter. They are placed closer to the walls than shown in fig. 3, in order to obtain a

  well uniform fluidization throughout the extent of the bed.

  The ends for the bubbling caps on the upper bed are 25.4 mm (IPS) and the caps are .4 mm NPT; each of these elements is 12.7 mm in the two lower beds. The shoulder 296 measures 48.3 mm in diameter. The radial spacing 291, between the end piece 293

for the upper bed and the tube 298 which surrounds it is suitable

approximately 2.5 mm. The holes 294 drilled in the case of the middle distributor plate measure 4.88 mm

  of diameter; the equivalent holes for the distribution plate

  upper scorer measure 10.16 mm in diameter. The

  250 quartz pebbles constitute a layer of which the

thickness is 50.8 mm above the top of the caps

- 22

  246. Although only one coal supply line 232 has been shown, in reality two are used, each placed centrally on a bed area of 0.93 m2. The supply line 232 is made of 31.75 mm IPS tube, the steam tubes 234 measure 38.1 mm in diameter

outside, and the secondary air lines 236 (of which only

  one has been shown) measure 101.6 mm outside diameter. Holes 238 are 12.7mm along both sides, spaced 177.8mm between centers, and holes 240

  are 6.35 mm and are spaced 88.9 mm between centers.

  The spacing of the steam tubes is 165.1 mm

in the horizontal direction, and 71.1 mm in a di-

  rection at 300 from the horizontal. The limestone supply pipes 258 measure 38.1 mm in outside diameter. The 252 tubes measure 19.05 mm outside diameter. The

252 tubes are spaced 34.93 mm between axes, and

kill rows also spaced 34.93 mm between axes. The riser pipe 268, the sinker pipe 280 and the limestone sinker pipe 260 are all 50.8 mm IPS. The gear ratio at reduced speed is 30 to 1. The preheater 223 is of the type with a pipe heated by propane combustion and represents 15% of the

heating capacity of the combustion plant 200

desulfurization. The apparent density of refractory 204 is equal to 800 kg / m3 and its thickness is equal to 63.5 mm; the apparent density of refractory 206 is equal to 2240 kg / m3 and its thickness is equal to 38.1 mm. Regarding the coal pot, the air intake pipe 372 is a 38.1 mm IPS tube, the air blowing tube 376 is a 9.53 mm tube, the outlet convergent 375 is off center

and its two inlet and outlet sections measure respectively

  63.5 mm and 31.75 mm in diameter. Regarding

  surrounds the limestone pot, the air intake pipe 398 is made of 38.1 mm IPS tube, the air supply tube 396 measures 9.53 mm in diameter, and the convergent 392,

  offset, measures 63.5 mm x 38.1 mm, while the conduct-

outlet 396 is made of 38.1 mm IPS tube.

  With regard to building materials, the ascent pipe 268, the descent pipe 280, the limescale pipe 260, and the stop tubes

  252 are made of 316 alloy of the type known as stainless steel

corn. The secondary air lines 236, the coal supply line 232, and the ends for the bubbling caps are made of alloy 304 of the so-called stainless steel type. The casing 202, the boiler tubes 234,

  the water jackets 225 and 242, the three distribution plates

  the charcoal pot 344 and the limestone pot 378 are

carbon steel workbenches. The caps for the capu-

  splash pads are made of 304 alloy of the so-called stainless steel type. Air supply tubes 376 and 396

are made of copper.

  The operation of the system is described below.

  Sand is used to fill the middle bed to a depth of approximately 292 mm. Type 1360 limestone, crushed to an average particle diameter equal to 850 microns (mesh screen No. 20) is brought through a supply line 258 to fill the upper bed to a

depth of about 152 mm.

  The start-up of a cold combustion appliance requires preheating carried out as follows: fluidizing air is supplied from a blower (not shown) via a wind box 216 the middle bed , it being admitted that it has been previously filled

  of material of this bed, is emptied using the-

  descent arrangement 266 until the level of the bed is established below the inlet of the descent pipe, so that the boiler tubes 234 cease to be covered with bed material (this material remains under a thickness of approximately

  152 mm). Air from the windbox 216 and not-

  health through bubbling caps 218 acts

to distribute and spread the material of the bed

  deposited by the downpipe, and is directed to the tra-

  towards the storage or accumulation bed when either

  the ascent pipe, i.e. the downhill pipe

in order to keep the material evenly distributed

  constituting the lower bed. When the level of the bed

  dian is lowered to 152 mm, one interrupts the flow of fluidizing air. We start pump 312

  water circulation. Then start the preheating

  for 223, placed at a certain distance below the

distributor plate 212 in order to achieve uniform heating

shape of the middle bed. The flames generated in the burner

  their preheater are cooled to approximately 9270C by secondary air before they are admitted

h exit the burner to avoid overheating of the

  splash pads 224. Hot gases coming out of the burner-

preheater 223 heats the material of the middle bed to about 5380C in about an hour, after

which one adds charcoal during one minute with fluidisa-

tion (to facilitate further preheating), then

  takes preheating for about 15 minutes, until

until the bed temperature reaches about 7320C.

PFor the boiler tubes are not in contact with the material of the middle bed, they do not extract

no heat from said bed, and, because the material

riau constituting said bed is heated while it is not fluidized (in other words, when the bed operates at

fixed bed), the surface developed for the cal-

  heat loss ass from the bed is reduced,

  so that the bed material can be heated

fairy using a fairly small preheater.

  When the temperature of the middle bed has reached 7320c, the operation of the hot preheater is interrupted.

  propane. Combustion air is injected with fluidization

  tion, coming from a blower, using a wind box 222 and bubbling caps 224 in order to fluidize

the middle bed. The flow of combustion air and fluidi-

  sation is controlled and regulated by a valve (not shown

  t) so as to give this flow a value of 31.25 m (measured under normal conditions of temperature and pressure) per minute and per square meter of bed area, which corresponds to a surface speed equal to h

  approximately 2.29 meters per second in the upper bed

  h 8450C. The coal feed screw 348 and the

  transport air presser (not shown) supplying air to the coal pot via the intake pipe 372 and to

  the output (not shown) of the rotary device supplied

  limestone are then turned on, and coal is thus brought from the hopper 346 using the screw feeder 348, the dryer 340, the grinder 342, the rotary air lock 368, pot of coal 344

then to the middle bed via line 374.

The coal mixes with the bed material

hot and burning. Efficient fluidization produces good-

  distribution of the coal from the coal supply pipe, and this results in a homogeneous mixture of the coal and the material of the bed. The heat released from the combustion of the coal heats the bed until the temperature of this middle bed approaches

their desired 9820C. (A setting at a lower temperature

may be necessary to avoid the formation of sco-

ries or bottom ash when using coals with low ash melting points, and a higher temperature setting may be provided when using

  coal with more difficult combustion, less reactivity

  t, and at higher ash melting points). We take

  catches the temperature of the middle bed to reach a too high value in part thanks to the cooling effects

steam tubes 234, which are splashed by the material

  riau constituting a fluidized bed, and in part thanks to the effect of a control thermocouple arranged in the middle bed and which serves to regulate the temperature established in the middle bed thanks to an adjustment of the speed of the supply device 348 screw, which has the effect of acting on the fuel / air ratio in the middle bed. One can, typically, under these conditions, operate

the burner with 100% excess air.

  -When the coal supply begins, we put

  when moving the supply of limestone to the upper bed, at a

  Ca / S predetermined port, as explained below.

The limestone, in fragments measuring less than 15.9 mm and more than 7.9 mm, flows from a limestone hopper-silo

  (not shown) and through the feeding device

one rotary; said fragments are pneumatically trans-

  to the upper bed via the limestone supply pipe 258. The flow at which limestone is thus supplied

  is determined by the speed of rotation of the a-

  limestone supply, which speed is controlled by the flow rate of the screw device 348 for the supply of coal,

  in order to establish a predetermined value of the Ca / S ratio.

  Gases leaving the middle bed pass through the bubbling caps 246 and the upper bed, and leave the combustion-desulphurization installation 200 by a

  line 262. When the temperature of the upper bed reaches

  complexion 8430C, operating temperature set point

* onment of the upper bed, corresponding to the temperature

for which the desulfurization efficiency is the best

re, a thermocouple arranged in the upper bed causes the opening of a mod-ulation valve (not shown) at the blower supplying the combustion air, which results in a secondary air blowing in the

freeboard 237 of the middle bed through the con-

236 secondary air supply line. The second air flow

  daire is continuously modulated to maintain

843 C the temperature of the upper bed.

Solids in particles too small to be able to

  remain in the middle bed, including ashes,

  bant, small particles of carbon, are blown through the bubble caps 246 and are captured in the upper bed, where the combustion of small carbon fragments continues for a few moments before they are blown out of the upper bed and of the installation

of combustion via line 262.

Particles too coarse to be able to be blown

  flies out of the upper bed will cause the level of this bed to rise, causing material to be removed

  in excess by a limestone overflow pipe 260.

  If after the bed has reached its desired temperature

the steam pressure of the system is

  below the required value, the burner automatically adapts

  only in the following way to increase the amount of heat it produces. Material of the bed

  from the lower bed is blown, thanks to the function-

lift 264 up to the bed

median. This slowly increases the contact of the material

  bed stitutive with the steam tubes 234, which has the effect of increasing the heat loss from the bed, the result being a momentary drop in the temperature of the middle bed. The device (thermocouple) for perceiving the temperature of the middle bed causes an increase in the rate of supply of coal by the screw device 348 for the supply of coal, in order to maintain the charging temperature at its previous setting point. This process is

  continues in such a way that the level of the bed is elevated

  at the same time that the coal feed rate is increased

raw, until the steam tubes are complete-

covered. At this stage, approximately 2/3 of the combustion heat is collected at the tubes

  of steam 234, the remaining heat being eliminated at the

  Calf from the boiler, and excess air in the mete bed

dian represents a proportion of 5 h 30%. The ascent pipe should blow enough of the bed material

slowly to avoid extinction of the middle bed,

  ie to allow the growth of the flow of supply of chai'bon. to be fast enough to compensate for the effects of

  cooling by the material supplied.

  The 200 combustion-desulphurisation installation

bare to operate at this maximum value of its capacity until the vapor pressure reaches a set point P2 which determines the actuation of the downcomer 266 and which also determines a slow transfer

  material in the middle bed to the bed

  servation and accumulation, which results in

reduce the heat transfer up to the ventilation tubes

  can 234 and possibly, in response to the thermocouple of the middle bed, to decrease the coal feed rate. Reduced heat transfer at the vapor tubes 234 in turn causes the vapor pressure to drop below the set point P2. At this stage, the downcomer 266 is put out of action. In most cases, the burner is then in equilibrium: the coal feed rate, the bed depth, the production

  all remain constant.

In some cases, when, for example, there is a large amount of vapor stored in the system such that the vapor pressure changes very slowly in response to variations in the shape of the combustion pipe, the down pipe may have been out of action for too long, causing too much bed material to transfer to the storage bed, and possibly could cause a drop in vapor pressure below of a

lower adjustment point P1, lower than P2. At this point

  de, the lifting device 264 is actuated until, if necessary, the level of the middle bed is such

  that steam production meets the needs of

  fear, and until the vapor pressure remains between Pl and P2. At this point, again, further adjustments to the

  level of the middle bed is not necessary as long

  while the demand for steam remains constant. However, if the steam demand is modified, by causing one or the other of the two aforementioned adjustment points to be crossed, the ascent pipe or the descent pipe is put into action until the system itself

  finds balance again. In this way, the ins-

combustion-desulfurization plant is continuously

  modulated from full capacity to around% of full capacity. Such a mode of operation

is called "modulation mode".

  If the steam demand drops below the% level, a further decrease in the depth of the material

  in the middle bed would be unable to produce new

decreases in steam production and, in fact, would be impracticable since the inlet of the pipe

descent 266 does not allow removal of material

  support of the middle bed below the depth of 152 mm.

In this case, the vapor pressure continues to rise and possibly exceed a set point P4 (upper

  to P2) which causes the shutdown of the combustion plant 200

tion-desulfurization. Such a stop results in the interruption

  operation of device 348 the supply of char-

good, dryer 340, shredder 342, rotary air lock

368, and the limestone supply device. After 15 se-

  condes, sufficient time for there to be no more solids in the coal pipe 374 and in

the limestone pipe 258, the air compressor

  port and the blower supplying the combustion air are stopped. The combustion-desulphurization installation 200 thus remains stopped until the vapor pressure drops below a set point P3 (located between

  P2 and P4), to which it is restarted according to a success-

transfer of elementary operations opposite to that of

shutdown operations. As long as the

  steam production capacity is less than 50% of the

  nominal capacity, 200 combustion-desul-

  furation continues to operate cyclically and

  however the vapor pressure is subject to flow

kills between P3 and P4. This operating mode is called "cyclic mode". During operation in cyclic medium, the combustion-desulphurization installation

can be kept stopped for periods of a

up to an hour before it cools below the temperature at which coal combustion easily resumes. It takes approximately three minutes of operation to heat the bed and thus bring it back to its setting point, at a rate of coal supply equal to 2/3 of that which corresponds to the rate

full capacity. By this means, an attenuation is achieved.

  operating speed with a ratio of 30 to 1. If the demand for steam averages less than 1/30 of full capacity for a period of time greater than or at least one hour, the device (such as a thermocouple) sensitive to the temperature of the middle bed makes it possible to note that the temperature of this bed has become lower than the re-ignition temperature, and it prohibits the supply of coal to the installation until that the use of the preheater has brought the bed back to its minimum ignition temperature. It is possible, if this appears necessary, to reach gait slowdown values greater than 30: 1 by using more extensive insulation around the middle bed.

Another mode of operation depending on the mode of modu-

  lation consists in resorting to a servo-control of the combustion air flow at the rate of supply of coal. This increases the thermal efficiency of the system by minimizing the proportion of excess air, and thus the heat losses to the chimney, but this requires more complex adjustment controls than when using the method described above consisting essentially of always maintain

constant air flow.

Another operating mode, called "low nitric oxide mode", makes the necessary arrangements for the combustion bed to operate stoichiometrically.

  (typically, at an equivalence ratio of 0.85), however

  as long as the upper bed is allowed to operate at a slightly excess air rate (typically 3%), and so that tertiary air can be added above the bed

  desulfurization-thanks to the use of an aerody mixer-

namic (not shown) allowing to establish an atmosphere

  re containing 20 to 30 do of air at the outlet of the installation

  tion of combustion-desulfurization. It will be necessary to

  grow the freeboard above the upper bed, in order to

  allow adequate combustion of hydrocarbons (and also

  if carbon monoxide) unburnt. The purpose of this

method is to minimize emissions of nitric oxide (No)

  from the burner, while still obtaining a good

  combustion and good pollution characteristics

  tion and with regard to SO2, CO and various hydrocarbons.

  Operation of the combustion bed under conditions

  stoichiometric slows down the rate of combustion of the

  coal particles, which has the effect of increasing the

  carbon in the combustion bed and also in the decay bed

  sulfurization. Previously, researchers (Beer et al., "NO Reduction by Char in Fluidized Combustion", Proc. Of the 5th Conf. On Fluidized Bed Combustion, Washington, DC,

  December 1977) demonstrated that the presence of small pro-

portions of carbon in a bed is sufficient to decrease

er very strongly the level of NO emitted from a fluid bed. Other technicians (Horio et al., "A Model Study

  of the Development and Low NOx Fluidized-Bed Coal Combus-

  tors ", Proc. of the 5th Conf. on Fluidized Bed Combustion, Washington, DC, December 1977) found that a device

  two-stage fluid bed combustion is particularly

This is very effective in performing a NO mixing operation with carbon, which results in a chemical reduction of NO with the formation of molecular nitrogen. The oxygen level in the upper bed must be chosen and fixed at an optimal value making it possible to satisfy both the requirements of desulfurization (which is favored by an atmosphere with a high oxygen content) and those of a reduction of NO (which is favored by a low content atmosphere

  oxygen, although the presence of small proportions of o-

xygene [typically corresponding to 3% excess air]

  is acceptable for the NO reduction operation).

Since it is impossible to operate the system with a small proportion of excess air according to the cyclic mode, this cyclic mode does not allow to succeed

at low NO levels.

  Periodically, depending on the rate of depletion in

solids or accumulation of solids in the system, di-

  Parts of this system should be checked for an inventory or balance of solids, and appropriate action should be taken as follows:

The accumulation of particles is not normally observed

  coarse cules in the middle bed, unless large particles of mineral matter are brought with the coal. In such a case, the operation of the burner is periodically interrupted, after which the descent pipe 266 is actuated, all the material constituting the bed is blown into the lower bed in addition to a depth of 152 mm in the bed. upper, after which all the material in addition to a thickness of 178 mm in the lower bed is removed by the overflow 220. The material

  coarse can be removed by sieving, after which

  channel the remaining material to the bed, or else all of the excess can be sent to the hopper supplying the battery with filter bags for disposal. The use of

  conservation bed and accumulation as a place of elimination

tion allows to cool the excess material from

  the bed temperature (about 9820C) up to a temperature

  ture allowing it to be transported and stored safely (temperature below 2040C) by allowing fluidizing air to enter the combustion-desulphurization installation at the level of a wind box

216 until the lower bed is at low temperature

erasure, and at this point we open the valve

  overflow control via overflow line 220.

When the removal of excess material is completely finished, the burner can resume its

normal running.

With regard to the upper bed, each time that it is observed that the height of this bed falls below the minimum admissible value of 102 mm, the bed is filled to its optimum depth of 152 mm by the addition of coarse sand [particle size: 90% passing through a standard No. 6 mesh screen (3.33 mm square openings), 50% o remaining on a standard No. 10 mesh screen (1 square openings , 65 mm side)]. he

  also suitable, if it is observed that the height of the bed

greater than a maximum admissible depth of 229 mm, to allow transport air to enter the limescale container via line 398, in order to fluidize the solids which are on the distributor plate 384,

  which allows the material-having entered the cal pot-

cairn to be blown out of this limestone pot and

pumped back into the filter bag battery. The ori-

  fice 386 is adjusted to restrict the pace to

which of the bed material is allowed to penetrate

  trer in the lime pitcher, thus preventing the

excessively hot materials from said lime pitcher, and also preventing the establishment, in

  the limestone pot, excessive pressure which annihilates-

  the pressure sealing effect exerted by the material in the downcomer 260 and

  in the vertical tube 380. When the depth of the bed

  lower has been reduced to its desired height, cut the fluidization air intake to the limestone pot, and let the vertical tube 380, as well as the down pipe 260, remain full, or else they refills, after which we stop continuing to remove other

  material from the top bed, until it appears

  necessary reason to repeat the cycle.

  Other areas requiring periodic attention include

  take the bags from the wire bag battery

  trants, which must be cleaned to rid them

accumulation of dust by using one

  conch of the different operating modes conventionally used

  for cleaning such bags. It is considered preferable to temporarily interrupt the burner while cleaning the filter bag battery; even in completely full bed conditions, the filter bag battery can be cleaned

  before the middle bed has been cooled to a temperature

  below the ignition point of the coal. The hopper supplying the battery with filter bags must also be emptied periodically, where residues are collected, the settling or sedimentation chambers arranged inside the boiler may also require

cleaning operations.

  An interruption of the burner operation for prolonged periods, that is to say of a duration greater than one hour, should be started with the middle bed operating at its set temperature, after which it is stopped just the coal feed screw,

  which allows the combustion of the coal contained in said bed.

  Failure to burn this charcoal can result in clinker formation at a later restart. The combustion air is allowed to pass and the water circulation pump 312 operates. the burner is cold enough to avoid

distortion of the steam tubes 234 which could occur

re when the coolant circulation stops

dissement.

  We must establish a sufficiently large value for the

calcium / sulfur port, by an adequate adjustment of the pace

  of limestone, to produce at least enough micro-

  fragments (measured in mass per unit of time) to absorb

  ber S02 generated by combustion; otherwise the bed

  energy is lost. It is said that there is a loss of energy

of the desulfurization bed when a hardening of the particles

sulfation occurs at a faster pace

  that attrition of these particles by friction,

  tion which eliminates by wear of the material from

shot from the particle surface. The super hardening

  ficiel causes a decrease in the rate of attrition, which results in a more pronounced hardening by sulfation; a cycle is thus established which does not end until the attrition practically ceases. Once a bed has lost its energy, its purifying efficiency is

  finds it considerably diminished, unless the ratio

  Ca / S port is very strongly increased.

  Once a bed has lost its energy, the best is

  replace it with a bed of fresh sorbent, and

  firing with a higher Ca / S supply ratio.

The appearance of a loss of energy from the bed occurs

  accompanied by a decrease in the density of the micro-cloud

  fragments when getting out of bed, and a simulated increase

  tane of the depth accumulation pattern of the upper bed

  laughing. One can resort to the observation of one or 1'-

  Another of these effects is to prevent energy loss from the bed by increasing the rate of sorbent supply. As a variant, one can simply establish the Ca / S ratio at a higher level, so as to establish a safety margin beyond. the minimum allowable value; this avoids the risk of energy loss from the limestone bed

  without any measure of attrition.

Ideally, very soft sorb; utts should be used, so that none of the particles

  can never harden by sulfation, instead of continu-

  er to undergo attrition until they have become

  too small to be able to stay in bed. An increase

sation of the particle size of the sorbent brought in favor

  increases attrition, and allows the use of leavers which, without it, could prove to be inadequate. An upper limit of the size of the sorbent particles appears when the sorbent particles are too large, and therefore too few in number, to form gaps in the bed devoid of sorbent; one would expect fumes rich in S02 to escape

  from these intervals, thereby reducing the efficiency

  tee of the desulphurization purification operation.

  - Particles of harder sorbent may not

bir a complete attrition, but eventually they can-

  wind harden even more by sulfation, more particularly

  when they got smaller. By the-

  hardened particles stay in the bed, absorbing the

  classic portion of S02 (typically, one third of the pro-

  stoichiometric portion) before leaving the bed by discharging through the overflow 260. The SO2 eliminated by these particles directly reduces the required proportion of

  production of microfragments necessary to avoid per-

  energy of the bed, although the total limestone requirement

  higher than if you used a very soft limestone

  dre, for which no hardening by sul-

particle fatation.

  Therefore, in cases where a sor-

bant harder, the sorbent itself can serve two purposes:

as a solvent and as a gravel.

  Various modifications and variations are described below.

  your implementation of the invention.

With regard to modifications and variants relating more particularly to the embodiment

  preferred, it should be noted that the refractory layers

  res 204 and 206 can be replaced by a single layer of refractory having an intermediate apparent density (either diary or, for installations of a

  large capacity, by walls cooled with water.

The secondary air line 236 can be designed to re-inject solids, for example unburnt carbon

  collected, using a cyclone arranged upstream of the bat-

  series of filter bags. 250 stones can be replaced

  placed by other materials, such as alloy spheres of the so-called stainless steel type, or by using

  other constructions such as inverted channels if-

  killed above the bubbling caps and which serve to decrease the speed of the gases entering the bed to a value low enough to avoid splashing of particles. The baffle tubes 252 arranged above the upper it can be omitted, in particular if one

provides for an additional freeboard of sufficient extent.

The latter provision may also be adopted to replace

  place the baffle tubes arranged above the middle bed.

One can still use, instead of the preferred configuration, other configurations of baffle which prevent

  also the opening of a free line of sight.

  The down pipe 266 can be replaced by a vertical tube passing through a distributor assembly

to equip the middle bed, and ending in a valve

  constriction arranged just above the highest level of the accumulation and conservation bed. To actuate the downpipe, the throttle valve is opened by a predetermined quantity, sufficient however for the material of the middle bed to flow into the accumulation bed at a desired speed under the effect of the gravity, but less than the speed at which the

  ve rtical tube can be blocked with respect to the passage of the ma-

teriau constituting the bed, thus losing its characteristic

  making it constitute a pressure seal.

When the downcomer is made inactive, the throttle valve is allowed to return to its closed position. The use of such another mechanism of the downpipe type eliminates the need for the feed device. screw provided and shown for mounting

preferred of the downpipe type, but it requires adjustment

much more careful opening of the throttle valve-

to function properly, and is significantly more prone to malfunctions due to the

  presence of large particles in the middle bed.

  The embodiment of the splash cap chosen for the preferred device is simply one example among many others that could also be envisaged; the preferred cap has the advantage of being able to be

made simply and easily from common elements

available.

  A construction of the water-cooled type can be adopted for the lower distributor plate 210 as for the

  upper distributor plates, or other mechanisms making it possible to prevent such a plate from curling, for example by using bellows at the edge of the distributor plate. Distributors can be designed and produced so that they extend beyond the casing 202, and make them watertight to prevent leaks using flanges or flanges which can be fixed to

  outside of envelope 202, instead of attaching them to.

angles arranged inside the envelope, as

shown in fig. 1.

When using the 200 combustion device-

desulfurization to generate steam under high pressure

other methods can be used to

  cool dispensers. For example, one can use a separate cooling loop, allowing water to circulate. using a separate pump through the distributors, to a water / water heat exchanger, then return to the distributors. The other side of the exchanger

  of water / water heat can be cooled by

umentation intended for the boiler. This method avoids the

* overheating of the dispensers, which has the effect of

leinr thermal expansion and their tendency to swell

  doler, and also minimize the values of pressure and

  the corresponding structural requirements for distributors

goalscorers, and therefore reduce their weight and cost. The steam drum 326 is optional; alternatively, the inlet line 328 and the float valve assembly 332 can be attached directly to

the outlet manifold cover 316. The tubes on-

  drivers, if any, are located in France

  edge of the upper bed, when you can settle for a small

  tit degree of overheating, and in a modular device analogous to that shown in fig. 1, in the event that significant overheating is necessary. In the latter case, the superheater tubes are arranged in the same position,

  compared to the distributor, than that occupied by the

bes 234.

Other types of amassing devices can be used.

  born of coal, such as belt conveyors. The charcoal drier can be removed if coal with moderate humidity is used, in conjunction with an air sweep mill designed to allow circulation of drying air to dry the charcoal inside the mill . The agitator of the coal dryer 340 may be of a different type from that shown; for example, we

  can use a spiral element or a pair of spirals

  them in place of the transverse dowels 354. The other transverse dowels 356 are also optional, more particularly with a carbon which contains only

  few fines measuring less than about 6 mm. The temperature

re air admitted to. getting inside the dryer can

  be thermostatically adjusted to establish the temperature

  re optimum de-coal outlet which is equal to around 930C, whatever the humidity. This avoids the risk of overheating the coal, and the start of a fire.

  d-ns the dryer h. coal during periods of slowdown-

faint or stop working. Ceila also allows you to

  dry coals with a higher moisture content

at 15%, increasing the temperature up to more than 3700C

  the air admitted to enter the dryer. The heat

  necessary for drying can come from a burner

  arranged them in a pipe. and separately alimentirenbustld., instead of being generated in a coil immersed in the

  middle bed as described in connection with the mode of reaction

preferred reading.

  In the limestone pot, you can place a rotary valve

tive in the vertical tube 380 in order to prohibit the escape

Conveyor air to the upper bed instead of to the hopper of the filter bag battery, desired destination for this air. Such a

rotary valve replaces, in its effect, the effect of the ma-

  material contained in the overflow pipe 260 and in the vertical tube; it seals against pressure, makes the system less easy to unbalance, and also allows the use of higher pressures in limestone pots, hence the possibility of admitting larger

  * distances between the limestone pot and the bat hopper

series of filter bags.

The air supply tubes 396 and 376 are optional.

  tifs. The charcoal pot 344 is optional, and can be replaced by a simple transition tank in

which of the coal can fall and from which of the char-

  good is then blown back into the dispo-

  sitive 200 of combustion-desulfurization. In systems using more than one coal supply line, the above-mentioned transition tank advantageously affects a

circular in cross-section and has a circle

a large number of coal outlet pipes distributed around its periphery, these different pipes being supplied

  by a rotary distributor arranged in the center.

The combustion-desulfurization device 200 provided for the preferred embodiment has a capacity of 2,520 therms / hour. In fact, the design of such an installation can be adapted to a very wide range of

dimensions, from industrial facilities generated

drant 250 therms / hour to installations intended

  born to supply steam to power plants and

  with a nominal power of around 2,500,000 ther-

mies / hour. The characteristics of the water vapor

  pick in the steam tubes 234 depend on the applica-

  tion envisaged. For the equipment of power plants, where the highest values of temperature and steam pressure are desired due to their effect on thermal efficiency, it is possible to obtain steam temperatures as high as 6500C approximately, under supercritical pressures. This is about

  jQ the steam temperatures obtained in boilers

  classic eras equipped with fireplaces as well

heavy oil-than coal or conventional fireplaces-

fluidized beds, -and can reduce consumption by 5 to 10 eo

normal fuel for such systems, while extending the useful life of the boilers and improving their maintenance conditions. As reported in the specialized technical literature (John Stringer, "Materials for Fluidized Bed Combustors", 3rd Annual Conference on Materials for Coal Conversion and Utilization, NBS, Gaithersburg, Maryland, USA, October 1978, page 154, et al .), the mechanism leading to a

corrosion of surfaces licked by flames, which

that at present limited the maximum temperatures of the vapor generated in boilers equipping power stations, is not observed in combustion installations in fluidized bed, mainly because the alkaline substances released in apparatuses of conventional types operating at high temperatures are not released in fluidized bed systems, where temperatures are lower. However, fluidized bed combustion devices are the site of corrosion phenomena on surfaces exposed to flames, due to

  the presence of calcium sulphate deposited in the form of

  clothes on the steam tubes. This form of corro-

  Zion is eliminated by the use of sand, rather than sorbent, near the steam tubes in the combustion-desulfurization device 200 according to the

present invention; in fact, said sand prevents the formation

  corrosive sulphate coating, thus allowing

operate the boiler at certain temperatures

caused by factors other than corrosion of surfaces exposed to flame. In larger systems, the burners should be constructed according to the principles of modular systems in order to avoid excessive stresses imposed on the steam tubes and distributors as a result of the establishment of too large ranges. To increase the capacity of the system,

  the area of the beds should be increased, in cross section

versale, '- of one square meter for 1356 therms / hour. The

  burner height should only be increased to the extent

  re o the lateral speeds in the insuffla-

tion 227, 237 and in the freeboard above the upper bed

  are kept low enough to avoid

dragging of the material of the bed. It suits

increase the diameters of the proportional pipes-

the capacity of the burner. An exception concerns the coal supply pipes: they should always be around 32 mm in diameter, such a pipe being necessary for each square meter of bed area. Feeds can be used above the bed, with larger coal particles and larger coal feed lines, or spreading or dispersing devices, if the steam tubes are arranged with space wide enough at the

coal entry plan to allow injection

  direct action of the carbon particles without them

  collide with said tubes. We don't have to increase the diameter

  neither bubbling caps nor that of the heating tubes

  diere, although the diameters of the steam tubes can be significantly increased for greater mechanical strength when their lengths must extend over greater spans than those intended for installation

described above with reference to fig. 1.

  Any type of charcoal can be used, with characteristics (odor, sulfur content, humidity,

tendency to agglutination, ash content, etc.)

  conches. Residual fuels can also be burned

  res, containing a high proportion of inert material, such as dust or oil shale, as well as low reactivity fuels such as coke embers. In the first case, it may prove necessary to move all or part of the bundle of steam tubes in order to move at least some of them away from the zone subjected to splashes of material constituting the middle bed for this, one can either remove tubes 234, or move them to a position high enough that they no longer risk receiving such splashes when the depth of the bed is at its minimum depth. Other fuels can also be used, including wood chips or fragments, as well as heavy oil and

  natural gas. For these fuels, it may be necessary to

stop using a particular method to in-

throw the fuel into the bed at intervals

  fairly close times; such methods have been de-

  written in the prior art. The possibility of use

  of these fuels would make the ins

  tallation whatever the price fluctuations or

  temporary shortages of a given type of fuel.

  The combustion of heavy oil in the desulfurization combustion plant 200 may also prove preferable.

  to the combustion of this fuel in standard boilers

  especially if the sulfur content of this oil

  is regrettably high; it is also possible to lower the concentration of nitric oxide in the flue gases without having to use a scrubber, and it is also possible to considerably raise the maximum temperature of the steam produced without risking severe corrosion of the surfaces exposed to the action flames or gases very

hot combustion.

  One can also arrange the installation 200 of combus-

  tion-desulphurization inside the firebox of a boiler, or else construct it in the form of a separate unit (of the so-called "Dutch hearth" type) such as that shown in fig. 1. In this case, it is also possible to provide the possibility of supplying the burner-boiler system with

  various fuels, by operating the device

  tif 200 combustion-desulphurization with only com-

solid fuel, by removing the flue 262 from the boiler and installing a gas burner instead

or heavy oil, which allows the use of

  tion of these latter fuels when necessary

  to be. It is thus possible to give to the global system

greater reliability, acquired it is true at the price of

  ne decrease in thermal efficiency and steam production capacity compared to the system in which the gas (or heavy oil) is injected into the middle bed.

A wide variety of limestones, including do-

lomites, are adequate; approximately half of all calcium carbonates appear adequately

subject to attrition to be usable. We can also

  if using synthetic sorbents, consisting of lime which has been ground until particles are obtained

measuring at most 10 microns.

None of the following: dimensions of

  beds, geometry of steam tubes, cap spacing

splash pads, materials used for the construction of the combustion-desulfurization device, is not really critical, although certain choices may lead to a deterioration in performance if the optimal conditions have not been adopted. In particular, the use of greater depths of the middle bed increases the violence

of bubbling and then, to improve the yield of com-

bustion, appropriate arrangements must be made

  than greater heights of freeboards, the reinjection

tion of fly ash, or the use of a cell

  separate where the combustion of particles can be carried out

  carbon, as well as the preheating of the air

bustion. The use of greater depths of the desulfurization bed has less serious effects and can even, in fact, improve desulfurization and denitrification as long as one uses splash baffles, arranged above the upper bed, there is no need to plan for a large increase in

  the height of the corresponding freeboard.

  We can start the installation by leaving

operate the propane burner until the bed

  dian reaches a temperature of 5930C; at this time, we

  extinguishes the preheating burner and you can start the

  normal heat from coal heating; we can omit the elementary operation of adding charcoal

  for one minute to participate in preheating.

  The degrees of size of the parts can be varied

  sand and sorbent cules, as long as the ca-

  The fluidization and mixture formation characteristics remain adequate and make it possible to avoid the establishment of overheated zones and the formation of clinker. It is also possible to vary the amount of heat released per unit area, for example by + 25%, or even more, provided that all appropriate precautions are taken to prevent defluidization, at low speeds, or

  excessive carbon losses at extremely high diets

vés. We can resort to a reinjection of voluminous ash

to improve the rate of carbon use and help

der desulfurization, the particles being injected either in the primary air stream or in the stream

secondary air.

We can use coal particle sizes other than those specified above, without losing sight of that an excess of fines (passing through a sieve

standardized with nc 28 mesh, i.e. with openings

measures about 0.59 mm per side) can increase the difficulties of obtaining high combustion yields

  it may even result in an obstruction of the dis-

superior tributary.

We can use a combustion device 200

  desulfurization to heat, in tubes 234, other fluids such as air to be used in ovens or ovens, or compressed air usable to make

operate gas turbines to generate energy

  electricity by implementing combined cycles; he can

  also to supply mixed installations,

  which is required to produce both electric-

summer and heat.

  Another operating variant consists in using

ser the combustion-desulfurization device shown in fig. 1 in the manner of the carbonaceous burner described in US Pat. No. 4,051,791 concerning an arrangement

  for the combustion of coal, granted October 4, 1977.

  Fig. 9 shows such use of the device

  combustion-desulfurization in a system comprising a pyro-

  lyser 400, a cyclone 402 separating carbonic matter

  a combustion-desulfurization device 404, a cy-

  clone 406 ash separator, and a postbr 4040

  coal and limestone are pneumatically brought to the pyro-

  lyser 400 through a line 412. Coal is py

  rolyzed in the pyrolyzer 400 so as to form a substantial

this carbonized into fairly fine particles (passing through a standard No. 4 mesh screen, with square openings measuring approximately 4.7 mm per side) while producing volatile substances, including hydrogen sulfide (or hydrogen sulfide , H 2S). The limestone is pyrolyzed in the pyrolyzer so as to form lime (CaO)

  which performs a purification by combining with the sulfide of hy-

  drogen, contained in the stream of volatile substances, by carrying out a reaction according to the following chemical equation: H2S + CaO - CaS + H2O (1)

The calcium sulfide is then conducted, with the substance

  this carbonized and volatile substances, via a pipe 414 into a cyclone 402 for separating carbonized substance, where gases are separated from the solids, then by

  a pipe 416 to the combustion stage 418 of the device

  positive 404 combustion-desulfurization (which may be of the type described above with reference to FIG. 1, the lower accumulation bed and the vapor tubes of which have been omitted: these are tubes 234). Gases from said

cyclone 402 separator of carbonized substance are transferred

  res to the postbraleur 408 via a line 420. The carbonized substance is then burned in stage 418 of the combustion device, allowed to operate at a temperature of 982 to 10930C (preferably around 10380C). Calcium sulfide is brought back by oxidation in the form of lime by excess air in the combustion device, the reaction in question taking place according to the equation CaS + 3/2 2 - Cao + S02 (2) The sulfur dioxide released during this lime regeneration, and the sulfur dioxide released by the combustion of

carbonized substance, are then engaged in a reacti-

  is purified by the action of lime in a desulfurization stage 422 (allowed to operate at a temperature between 7880C and 8710C, preferably at 8430C; the purification yield to remove B02 falls rapidly at temperatures above 8710C) part of

combustion-desulfurization device 404; this reaction

  tion is carried out according to the following chemical equation: CaO + 802 + 1/2 02> CaSO4 (3)

The lime participating in reaction (3) is brought to the state

  desulfurization age 422, via a pipe 424, in the form of limestone in proportion to the initial content of

  sulfur in coal and the degree of desulfurization required.

  The used sorbent which is in too coarse fragments to

be able to be blown out of the combustion device 404

  desulphurization left the desulphurization stage 422 by a line 426 leading to a place of discharge such as an ash hopper (not shown). The spent sorbent consists of a mixture of CaO and CaSO4; this is

  an inert material that can be disposed of without treatment

  later, or with little treatment.

  The remaining sorbent is transferred from bed 422

  and out of the system to a cyclone 406 or to a device

tif for collecting particles arranged downstream of the oven

(not shown) to which the post-burner 408 is attached.

  The material contained in bed 418 of the

combustion, consisting mainly of CaO, is recycled

key to the pyrolyzer, via line 428, and there

  ve converted to CaS following reaction (1). It is enough

therefore made provision for an additional supply, via a line 412, of fresh limestone brought to the pyrolyzer to compensate for the losses and replace the limestone which became inactive after a certain number of cycles through the pyrolyzer and the bed of the combustion device . This extra can

be practically zero if the limestone retains its reactivity

tee, insofar as the circulating current acts at the

way of a sulfur transporter and doesn't actually serve-

  to remove sulfur from the system. On the other hand, sorbent added to the desulfurization bed 422 removes

  actually sulfur from the system, by implementing

  vre of the reaction (3). The partially exhausted or worn sorbent in the bed of the combustion device is not wasted or lost, but is transferred by a line 430 to the upper desulphurization bed, where it is used to absorb S02 before being discharged to the using a pipe 426.

Ashes and hot combustion gases are trans-

from the desulphurization bed via a line 432 to an ash separation cyclone 406 from which the ash-free gases are then transferred via a line 434 to the post-burner 408 where they are mixed with

  volatiles from cyclone 402 of separation

  tion of carbonized substances; in this post-burner, the resulting gas mixture is burnt at very low temperatures

  high (for example, around 16500C).

A problem that arises when you want to operate -

  ner the bed of the combustion device at temperatures close to 10400C results from a possibility of sintering

sorbent, sintering lowering its reactivity after a

any number of cycles, and also a possibility of training

  tion of slag or bottom ash from the ashes, which

  is observable when some types of coal are used.

  Therefore, it may be better to operate-

ner the bed of the combustion device at lower temperatures, for example between about 890 and

  9820C, to avoid these problems (and to acquire a-

  additional advantages consisting of a lower emission of alkaline substances and an easier solution of the problems of corrosion of surfaces subjected to the action of flames), but the conversion efficiency of the cal sulphide

cium in lime in the combustion bed can also be found

  worm decreased at these lower temperatures, although the

degree of conversion may still be sufficient to

  put a recycling to the pyrolyzer. Another problem is this: if the temperature is too low, CaS can be converted to CaSO4 and not to CaO, and CaS04 can form an eutectic with CaO and thus produce a slag or clinker. To avoid having to release a large proportion of CaS, which could cause H2S to form at the disposal site,

  then add a post-milking station 436 to the system

is lying. Instead of throwing partially used sorbent

to the desulphurization bed via a line 430, one trans-

then carries the sorbent through a pipe 438 to the station

tion 436, where it is treated (for example, by washing in hot carbonated water as taught by GP Curran et al. in their publication "The Conoco Process for Hot Desulfurization of Fuel Gas: A Progress Report", Conoco Coal Development Co., which was reported in "Proceedings of the Fourth International Conference on Fluidized-Bed Combustion", December 9-11, 1975, Conference held under the aegis of Miter Corp., McLean, Virginia, USA;

  pages 239-263) to obtain a sufficient stone

  significantly poor in CaS. Due to the fact that the amount of sorbent to be subjected to post-treatment is

  relatively small, such post-processing can be con-

  flabbergasted as an economically viable alternative

and can replace high temperature regeneration.

The combustion desulfurization device 404, which the

  whether or not post-processing is used, is preferably

Rence admitted to operate in the manner of an adiabatic fluid bed device in which the combustion stage is cooled by excess air (typically, 150%) rather than by indirect cooling by tubes which

  are immersed in it. Secondary air, supplied by a pipe

te 442, cools the gases leaving the bed of the combustion device 418 to a temperature for which the desulfurization bed operates under the best conditions. Additional information regarding regeneration of the sorbent can be found in US Patent No. 3,870,480

(granted to Moss).

  An alternative embodiment of the combustion device

  desulfurization 404 for the system shown in fig. 9 consists in using a bundle of tubes immersed in the bed of the combustion device 418 to transport cooling air instead of operating the bed in the manner of an adiabatic fluid bed combustion device with air excess added to combustion air. This modification would reduce

  very substantially the dimensions of the burner 404, substantially

  this charred and cyclone 406 ash separator.

However, when choosing this variant, it must be taken into account that the tubes can become very hot and can therefore become subject to strong corrosion. Another variant eliminates recirculation line 428, after which the limestone is brought into

  the system in such a way that it only goes through it once. This simplifies the problem of handling materials, but increases the

  proportion of residues that must be treated in a post-treatment 436 reactor when

considers it necessary to use such a reactor.

When using each of the above variants

  mentioned from the system shown in fig. 9, it is necessary to use an attrition-resistant sorbent, otherwise the sorbent would be driven out of combustion zone 418, or could even be fragmented into such small particles as the substance-separating cyclone could no longer effectively separate them (there

  cyclone 402), and in this case the sorbent cannot-

  be in the form of CaS through the post-burner 408 and the

  associated furnace, such a presence of contaminated CaS

  possibly eliminating the solid residues collected at the exit of this oven to the point of making them unfit for

  land rotation without additional treatment.

* The use of attrition resistant sorbents may

  limit the possibility of supplying suitable materials

quats, and increase their cost prices. If the same sorbent is used in both lines 412 and 424, which would be the normal trend, the attrition resistance of the sorbent in the desulfurization bed 422 would cause

loss of bed activity, resulting in increased

  consumption of sorbent while reducing its

  purifying efficiency, as has been described

  pos of the operation of the combustion device 400-

  desulfurization for the production of steam.

We can avoid these problems, and use sorbents

  subject to attrition in the same way as in dispo-

combustion-desulphurisation sitives intended for the production of steam, if a separate desulphurization bed is interposed on the course of the pipe 420. It is then advisable that

  sorbent be added to the contents of this desulfurization bed

is separated, and not to the content of the pyrolyzer 400, from which the spent sorbent would be transferred, via a line 416, to the

  dispositid 404 combustion-desulfurization. In the dis-

  positive separate from desulfurization, volatile substances

  leaving cyclone 402 for separation of carbon substances

would penetrate through a distributor plate arranged at the bottom of the container, and come out

by an exhaust pipe arranged in the upper part

of said container. The outgoing circulation current

bant would be established in reverse, in order to cause a

  counter-current reaction. The provision should

  separate desulphurization tif is dimensioned wide enough-

so that conditions of the fixed bed type are established there, so as to minimize attrition inside this reactor. Specialists can easily imagine many other variations. For example, in a system

245883Z

  with an additional desulfurization reactor

  on the route of line 420, it may be advantageous to provide a third distributor plate

  and a third bed to complete the equipment of the device.

  tif 404 of combustion. Carbonaceous substances should be burnt in the lower bed (as in the installation shown in fig. 9) and sorbent (mainly consisting of CaS) should be converted to CaO in the middle bed, while the elimination of S02 (depending on the

  reaction 3) is carried out in the third bed, occu-

pant the highest level. Under these conditions, it must-

  would be possible to minimize the corrosion of air tubes on their surfaces exposed to the action of flames or very hot gases, because the sorbent, whose presence in the vicinity of these tubes has been shown to cause

  this type of corrosion would thus be far removed.

  The invention described and claimed herein

  request is also interesting to apply in dispo-

  single bed combustion devices. In such arrangements

tifs, the fluidization speed should be between 5 times and 10 times the minimum fluidization speed (while in twin-bed type installations, the fluidization speed should be between 2 and 4 times the speed fluidization

minimum).

Certain features described and claimed in the present application may also prove to be interesting.

to be used in dedicated combustion devices

provided with a separate desulfurization bed, or for burning

fuels other than coal.

Claims (10)

1. Fluidized bed combustion device, which   device is characterized in that it comprises essential- ment: means perforated with openings and defining a support for fluidizing the content they support, envelope-type means for defining with said support a combustion zone, heat transfer means through which it is possible to pass fluid in order to remove heat produced by combustion, said heat transfer means being spaced above said support in order to provide beneath them a first preservation or accumulation zone whose depth allows combustion in fluidized bed of a content placed on said support without contact of a sedimented bed between the surface of said content and none of said heat transfer means,   means of conservation or accumulation defi- establishing a second conservation or accumulation zone,   means for selectively transferring materials   rials from said first storage area to said second storage area, and means for selectively transferring material from said second storage area to   said first conservation area.   2. Combustion device according to claim 1, characterized in that said second zone and said pre-   first zone are arranged in series said second zone   being arranged upstream of said first zone.   3. Fluidized bed combustion device according to claim 1, which device is characterized in that it comprises second means perforated with openings and defining a support for the fluidization of a content   which they support, said second perforated means of opening   tures defining, jointly with the envelope type means and said perforated opening means, said   second conversation or accumulation zone.   4. Combustion device according to claim 1, characterized in that it comprises fuel introduction means for introducing fuel, into said first preservation or accumulation zone, situated so as to introduce said fuel to a   substantial distance below the top of said pre-   better conservation or accumulation area. 5. Combustion device according to claim 4, characterized in that said means for the introduction of fuel are means for the introduction of coal. 6. Arrangement according to claim 5, characterized in that said means for the introduction of fuel   are located at a distance between 76 and 152- milli-   meters below the top of said first conservation or accumulation area 7. Combustion device according to claim 3, characterized in that it is prAvu, inside said second preservation or accumulation zone and at a predetermined height, means for the outlet of solids, so that incombustible solids accumulating in the combustion zones can, be transferred to said second conservation zone, be cooled there by air, and be discharges through said means for the exit of solids.   8. Combustion device according to claim 4, characterized in that it comprises a desulfurization zone comprising means perforated with openings, and which define a support for the fluidization of a sorbent supported by the-   said perforated means, and envelope type means arranged around said support, said desulfurization zone being arranged in series and downstream with respect to said combustion means. 9. Combustion device according to claim 3, characterized in that the combustion zone and said second conservation or accumulation zone are defined   by common envelope type means.   10. Combustion device according to claim 4, characterized in that said second conservation zone   tion or accumulation, said combustion means, and said desulfurization zone are defined by means of common envelope type.