US1393738A - Cement-kiln plant and method of operating- the same - Google Patents

Description

I. E. BELL.

CEMENT KTLN PLANT AND METHOD oF oPERATlNG THE sANE.

APPLICATION FILED AUG.2, 191B.

Z l li Patented 0011. 18, 1921.

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Patented Oct. 18', 1921.

l. E. BELL.

CEMENT KTLN PLANT AND NETHon 0F OPERATING THE SAME.

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CEMENT KILN PLANT ANDMETHOD 0F OPERATING THE SAME.

I. E. BELL.

APPLICATION FlLED/AUG.2,I9I8.

Patented Oct. 18, 1921.

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CEMENT KILN PLANT AND METHOD 0F OPERATING THE SAME. APPLICATION FILED Auf-L2, 1918.

FIG- 7 Luid Arron/vm1 UNITED STATES PATENT OFFFI@ JOI-IN E. BELL, OF BROOKLYN, NEW YORK.

CEMENT-KILN PLANT AND METHOD 0F OPERATING THE SAME.

To all whom t may concern.'

`true and eXact description, reference being had tothe accompanying drawings, which form a part thereof, n

My present invention comprises improvements in the construction, arrangement and method of operating cementkiln systems in which the hot y gases leaving the cement kilns are passedk through so-called waste heat boiler furnaces in which the heat contained in the gases is partially absorbed and utilized. My invention relates particularly to a system in which a plurality of rotary cement kilns are used. The general object of the invention is to provide a plant construction and arrangement and method of operating same which will be simple and reliable, and will give a desirably high efficiency without entailing prohibitive costs of installation, operation and maintenance.

The heating of steam generating boilers by the hotgases leaving industrial furnaces of many kinds, including rotary cement kilns, has been often proposed, and has been practised with success in some instances, but the effective utilization of the heat contained in the hot gases issuing from rotary cement kilns presents special diliiculties, and so far as I am aware no satisfactory plan of utilizing the gaseous products from a vbattery of rotary cement kilns in heating steam generating boilers has been developed prior to my present invention.

rllhe special difficulties standing in the way of the effective utilization of the hot gases from rotary cement kilns in waste heat boiler furnaces include or arise from various factors or circumstances. There are usually several rotary cement kilns in each battery or unit, the average number of kilns in each such unit in this country being perhaps siX or seven. The volume of heated gas issuing from each kiln is relatively large. The volume of gas and thefrequent necessity for cutting out portions of the plant for cleaning and repairs, as well as on account of irregularities in the output capacity required, make it desirable to associate with lea/ch `ib a-tteiyof kilns :a plurality lof waste Patented Oct. 1 8, 1921.

Application filed August 2, 1918. Serial No. 247,923.

heat boiler units. Practical operating considerations make it necessary that the plurality of kilns for each unit or battery, and the corresponding waste heat boilers, be connccted by a common fiue system, so that any one kiln or any one boiler furnace may be cutout of service without necessarily interfering with the operation of the rest of the system. The hot gases leaving the cement kilns .carry with them a relatively large amount of flue dust, consisting mainly of particles of the finely ground stone from which the cement is made, and both the amount of this dust, and the difficulties to which it gives rise, are augmented by the fact that the draft must be ample to give a high velocity of gas flow past the heat absorbing surfaces of the waste heat boiler portion of the system, this high velocity being necessary to insure a desirably high operating efficiency. The draft loss, or drop in pressure head, in the kilns proper is comparatively small and forms but a small fraction of the total draft or drop in pressure head necessary to move the burning gases and products of combustion through the system as a whole. This makes it difficult to obtain, and to preserve under the varying conditions of operation, the necessary substantial uniformity of draft in the different kilns. The relatively large total draft required and the relatively high temperature, ordinarily about 1500o F., at which the hot gases leave the kilns, makes it both difficult and especially important to keep the air leakage into the flue system at a practical minimum because of the injurious effectk on the plant efficiency of such leakage. lllie leakage itself works against the efliciency in two ways; it increases the draft consumption and thereby increases the difficulty of maintaining the proper draft, and by lowering the temperature of the heated gases, it materially and directly reduces the efficiency of the waste heat utilizing apparatus.

The specific object of the invention may be said to be such a construction and method of operating a cement kiln system comprising a plurality of kilns and a plurality of waste heat boiler furnaces, that the proper draft conditions may be maintained in the various kilns and in the various waste heat boiler furnaces by means of a common collecting and distributing flue system of such character as to facilitate the temporary cutting .Out ofservice Voran individuel )Q19 9F Fig. l. f

boiler furnace, and without an undesirably large loss of efficiency due to heat radiation from the lue system or air leakage into the same, and without entaling a prohibitively high .cost of construction, maintenance and operation.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a `better understanding of the invention, however, and the advantages attending it reference should be had to the accompanying drawings and descriptive Vmatter in which I have illustrated and described preferred constructions and methods of operation embodying my invention.

Of the drawings:

Figure l. is a somewhat diagrammatic plan with parts brokenv away and in section of a cement kiln system constructed in accordance with the present invention.

Fig. 2 is a partial section on the line 2-2 ot Fig. l.

Fig. 3 is a of Fig. 1.

Fig. t is a section on the line 4-4 ot partial section on the line 3 3 Fig.` 5 is a view taken similarly to Fig. 1 illustrating a modified system.

Fig. 6 is a section on the line 6-6 oit Fig. 7 isa view taken generally similar to Fig. 1 illustrating a third construction'.

Fig. 8 is a partial section on the broken line 8 8 of Fig, 7.

lIn the system illustrated in Figs. 1 to a, inclusive, there are seven rotary cement kilns A of ordinary construction, and each adapted to discharge the heated gases issuing from its upper end into a common collecting or bus channel E. which also serves to supply heating gases through branches E to three separate steam generating boiler furnaces F. As shown, the upper or discharge end of each of the slightly inclined kilns A opens directly' into an individual chamber or kiln head B. Each kiln head B discharge either through a port C into the base of a corresponding individual stack C, or through a passageway D into the common orbus channel E. Provisions are made for ellecting a removable closure ot each of the two outlets from the chamber B, since ordinarily one ot these outlets must be closed when the other is open. The removable closure for the stack connection is formed, as shown, by means o'l removable closure bars C2 disposed to cross a restricted portion C3 fof the stack, preferably located immediately above the top ot' the port C. It is not necessary to describe 'this closure in detail since its specilic construction forms no part of the present invention and istfully disclosed, moreover, in my Patent-No. '1,311,435, `granted 'July 29,

1919. The passage D, leading from each chamber B to the bus channel E is shown as generally horizontal, but is formed with its bottom wall in two portions which are inclined downwardly away from the opposite sides of a restricted throat portion of the channel. A kerl D', formed in the wall of the channel D, at its throat portion, is normally illed by a U shaped body J when flow through the passage D is permitted, and when flow through the passage D is cut oit, the kerf D is filled by the edge of a plate like damper or cut-off which then extends across the throat portion of the channel, as shown at JA in Fig. 6. The member J may be proportioned and arranged to partially obstruct and 'thus further restrict the thro-.tt

portion Aof the corresponding passage D when this is desirable. The joints between the side walls of the kerl and the member. J or JA, filling the kerf are normally sealed by luting them with clay. This special construction of damper or cut-olf valve while novel with me is not claimed herein.y but is disclosed and claimed in my Patent lllat. granted July 29,1919. The restriction of the passages D at their throat portions insures a high gas velocity through the throat portions, preventing liue dust from lodging in these restricted portions, and the inclination ot' the portions of the bottom wall of each passage D at each side of the throat, minimizes the accumulation thereon of flue dust. The shape and capacity of the lower portions of the chambers aresuch as to permit considerable accumulations ot flue dust therein without interference with the operation of the system, and these accumulations can be' removed from time to time through suitabh7 disposed cleanout doors (not shown). The restriction of each passage D at its throat exerts an important influence on the dra ft conditions, and the extent to which the throat is restricted depends upon the draft controlling effect desired as is hereinafter explained.

vThe bottom wall of the channel is inclined so that the flue dust deposited thereon tends to go to one lower corner of the channel at which open distributed inlets I to dust removing'conveyer pipes I ruiming along the bottom of the channel. The passages E by which the channel E is connected to the ditferent boiler furnaces proper are each 'forme-:l

cleanout doors at the 'botbomfof'thefurnace l economizer.

Each boiler furnace is provided With an individual draft producing fan ll, and interposed between each boiler furnace and the corresponding fan is an economizer or feed Water heater having its tubes transverse to the general direction ot iloiv of the heating gases. G represents cleanout doors for the removal of flue dust Jfrom the bottom of the rllhe Walls of the flue system connecting the difllerent kilns A, to the diiferent boiler furnaces F, must be lined with refractory material to withstand the high temperatures of the gases passing through them, and are advantageously formed with a relatively impervious and heat insulating jacket around a fire brick lining in order to reduce heat radiation loss and leakage of air into the flue system.

lhe clinker forming material, or finely crushed cement forming stone, is 'led into the upper ends or the various kilns A. by corresponding conveyer pipe portions l, arranged to pass one through each of the chambers B into the corresponding open kiln end. The tuel,V which may be coal, gas or oil for heating the kiln, and the air for supporting its combustion, are 'ted into the ends ot the kilns remote from the chambers B, and regulated in the usual manner, which, as it is .vell known, need not he illustrated or described herein.

ln the operation, the hot gases issuing out of the upper end of each oi" the kilns A pass into the correspondingchambers B at a temperature ot about 15000 F. From each chamber B the gases pass through the port C to the corresponding stack C, when thc passage D" is closed, or in the more normal condition When the stack C is sealed.` they pass through the then open passage D into the bus channel E. The gases flow through the channel E to the outlets E through which that channel communicates with the dii'lierent furnace chambers F. T he gases passing out olf the channel E, through each passage lll', tlovv through the corresponding boiler' furnace F and economizer 'Gr to the corresponding fan H., which discharges the cooled gases either directlv into the atmosphere, or into suitable discharge stack or conduit not Shown. ln any event the fans Hrcreate the draft relied upon to carry the burning gases and products of combustion through the kilns, the (lue system connecting the kilns to the boilers, and through the latter and the econoniizers Gr. rlhe eilective abstraction ci heat 'from the gases requires a comparatively high velocity of iloiv of the gases over the heating tubes of the boiler and economizer. To obtain this the boiler and econornizer tubes should be closely spaced. and the high velocity of ilovv., coupled with the restricted and tortuous character of the boiler and economiser llow paths result in a substantial ,loss ot pressure head or draft consumption in this portion of the apparatus. 'lhis high gas velocity is also desirable to minimize the lodging of flue dust on boiler and economiser tubes. 'lhe bores ot the kilns A are straight and large in diameter and on this account offer little resistance to the flow ot the burning and healing through them. ln consequence the draft consumption in thekilns is relatively small, and slight fluctuations in the pressure at the discharge end oiE a kiln produces a substantial and highly undesirable variation in the amount and character oi the combustion in the kiln. ln the cha-nnel l there is a. considerable longitudinal ilo'vv which varies different points owing to the distributed in-ilovv into this channel from the different kilns, and this variable longitudinal flow creates diierences in static pressure ditlerent points along the length of the latter., which react upon the dra-lt through the different kilns and tend to make the dra'lit conditions in the diiiiercnt kilns unequal. llfith the longitudinal llow in the channel E toward the end oi. the channel to which the furnaces F are connected the static pressure at that end oi the channel must be loiver than it is at the end oi 'the channel remote from the furnaces. Furthermore. the eliect ot friction and the increase in velocity of ilovv as the furnaces are approached. due to the distributive admission into the channel E along its length from the various kilns il, both tend to increase the difference between the static pressure at the end oit the channel E to which thc furnaces F are connected and the opposite end oi the channel. The disturbing effect ci the change ot velocity and the friction loss ln the channel E may advanta- ,tfeouslv compensated for to some extent hy ma.V g the cross section of the channel increase the end ol the channel to Which the turn es F are connected in approached; and in ll l l havo shoivn the section ot the conduit into -which the 'four kilns nearest the furnaces open larger in cross section than the section into which the other three kilns open. Practical pressure equilibrium cannot be obtained by this expedient.. houiever, even with all of the kilns continuously in regular operation. ll/lioreover. any such armroach to equilibrium as could be obtained under steady operating conditions, bv thus varying` the cross section ot the channel lt. would be destroyed. in practical operation, by disconnecting; any particular kiln A 'from the channel The variations in static pressure in the channel E could ybe made desirablv small. of course, by simply making the channel very large in. cross section. but this is not practically feasible because of the increase in cost ot construction in heat radiation, and in liability to the influir of air, resulting from a great increase in the size of this channel, and in many cases space conditions would themselves make such an enlargement in the cross section of the channel'E practically impossible of attainment.

I have discovered, Yand the essence of my invention, in its broader aspects, lies in this, that the disturbing effects in the kiln draft, due to variations in static pressure in a bus channel E of moderate and suitable dimensions, may be reduced to an extent not seriously objectionable by` the simple expedient of restricting `the passages D connecting the kilns tothe bus channel E, so that the drop in pressure, or draft consumed by the hot gases in flowing through these passages becomes substantially larger than the loss of pressure or draft consumption in the individual kilns, and larger than the fluctuations in pressure in the bus channel E.

' F or example, with such an arrangement as is illustrated in Fig. l, the variation in static pressure between the points in the channel E adjacent the endsx of the two kilns most remote from one another would be in practice something like .2 of an inch of water. The draft or pressure loss in each kiln would be in the neighborhood of .2 or .3 of an inch of water. Assume that the loss of head in the bus channel is only .l of an inch of water and the effective kiln draft is .2 of an inch of water, then if the kilns were in unrestricted communication with the channel E, and the pressure in the channel E. was such as to create the proper draft of .2 of an inch through the kiln A, nearest the furnace F, the draft through the kiln most remote from the furnaces F would be only Vbe more than 40% greater than the flow through the kiln most remote from the furnaces. By restricting the connection between the kilns and the channel E so that the draft consumed by the passage of the normal amount of gas through each of these restricted portions would be say of an inch, then the actual capacity of the two end flues would be in the rat-io of the square root of .4 to the square root of .5, and the crpacity of the flue nearest the furnace would then be only about 12% greater than the capacity of the more remote flue. By increasing the pressure drop through the restricted connections between the kilns and furnaces to an inch of water the change in capacity could be brought down to less than 5%. Practically a variation in draft of 5%, or even .10%, is not highly objectionable, as

such lagdraft variation can be compensated for, to a substantial degree, by adjustment of the air and fuel admission inlets to the remote ends of the kilns.

No provisions for varying or adjusting the restrictions or throttling effect afforded by the restricted portions of the various passages D need be provided. iu some cases, though where the passages D are throttled more or less, under different operating conditions as by means of dampers J partially obstructing the passages D, it is possible to obtain the desired draft equalization with a somewhat smaller total draft than is rcquired when the throttling effects, due to the restricted dimensions of the permanent walls of the throat portions of the passages D, are wholly relied upon. The effect of throttlin g communication between the various kiln heads and the common collecting flue E is, of course, to increase the total draft required. rl`he production of the extra amount of draft thus entailed is ordinarily not a serious matter. The extra draft does, of course, increase the tendency to air leakage, but it is to be noted that this tendency to increased leakage only exists with respect to the portions of the fiue and furnace system at the outlet sides of the kiln heads B, and does not exist in the kiln heads proper, where, because of the necessity of providing for the necessary motion of the kilns with respect to the kiln heads, it is most difficult to guard against leakage.

viVhile changes in the static pressure in the portion of the conduit to which the different boiler furnaces E are connected tend to disturb the distribution through the boiler furnaces, the disturbance in this case is much less serious than in the case of the kilns and can moreover be adequately compensated 'for by varying` the speed of operation` and hence the draft producing effects of the di fferent fans H when each boiler furnace is provided with an individual fan. lVhcre the arrangement of the furnace system is such as to minimize the static pressure variations at the inlets to adjacent waste heat boiler furnaces, as is the case with the arrangement shown in Figs. 5 and G, it is not practically necessary to provide an indi` vidual fan for each waste heat unit, and in Fig. 5 one pair of adjacent waste heat units F at the left of the figure are shown as provided with a common exhaust fan.

The desirabilitjv of regulating draft conditions by throttling communication between the various kilns and the flue system into which they discharge is augmented by the fact that where the invention s used in connection with waste heat recovery systems added to existing installations, as well as in wholly new installations, a great variety of arrangements of kilns, boilers and connecting flues must be employed. Thus Figs. land 5 show plants differing materially from one another in their general layout, while Figs. 7 and 8 show a third arrangement diilering from 'the first two. ln Figs. 7 and 8 the collecting llue E eirtends over the kilns A, and the connections D tothe kiln heads B, yare at the same side of the latter, as are the kilns A; this arrangement being made necessary by the tact that space in `direction ol the length of the kilns is especially restricted. On account of the diversity in the plant layouts, which must be adopted in different cases, it is especially dillicult to attempt to approximate static pressure equalization in the collecting flue by tapering the latter, since the amount of taper which will give the best practical results cannot be theoretically determined, but must be determined experimentally or be based upon past experience. lt will be understood, of course, that the three diiierent layouts illustrated, while typical, represent by no means the various iorms or kinds ot arrangement which must be employed in practice.

lllhile in accordance with the provisions oic the statutes l have illustrated and described the best structural embodiments of my invention, and the best modes of practising it now known to me, those skilled in the art will understand that changes may be made in the `lorm of the apparatus, and method of operation disclosed, without departing l'rom the spirit of my invention as set forth in the appended claims. "lhose skilled in the art will also understand that certain lea-tures of my invention may sometimes be used with advantage without a corresponding use of other features.

llaving now describedmy invention, what I claim as newand desire to .secure by lietters Patent, is: l

l; The method ot operating a cement kiln plant comprising a plurality of rotary cement kilns, a waste heat boiler section and a flue into which the individual kilns open at points at varying distances from the boiler section, and which connects the series ol kilns to said boiler section which consists in throttling the connection between each kiln and the flue to such an extent as to make the pressure drop or draft consumption between each kiln and the flue greater than the total pressure drop or draft consumption in 'the tine and maintaining such draft conditions throughout the connected parts ol the system as will compensate for the resistance created by the throttling of saidv connections and bring about a sutlicient and an approximately even draft in the kilns.

2. ln a cement kiln plant comprising` a series of rotary cement kilns, a collecting hue, one or more waste heat boiler sections connected to the flue and a series of connecting flues leading from the kilns to the collecting due at points at varying distances from the boiler connections, the construction ot the collecting Jlue and ol the connecting lues from the kilns ci such normal tired proportions relative to each other that the loss of pressure head in each said connecting flue is greater than the loss of pressure head in the collecting flue and the draft in the kilns thereby maintained atV such approximation to uniformity as is necessary for their el'- ective working.

ln a cement kiln plant comprising a series of rotary7 cement kilns, a collecting flue, a plurality ol waste heat boiler sections connected to the flue at dilterent points along its length and each provided with an independent suction ifan to induce draft therein and a series of connecting lines leading from the kilns to the collecting ilue at points at varying distances trom the boiler connections, the construction ot the collecting tlue and ot the connectin lines from the kilns of such normal fixed proportions relative to each other that the loss ot pressure head in each said connecting flue is greater than the loss ol pressure head in the collecting flue and the dralt in the kilns thereby maintained at such approximation to unitormity is necessary lor their effective working.

ln a cement kiln plant comprising a series et rotary cement kilns, a collecting line, one or more waste heat boiler sections connected to the llue, a series or" connecting Illues leading` from the kilns to the collecting flue at points at varying distances from the boiler connections and gates for closing each connecting flue at will, kthe construction of collecting liuc and ol the connecting lines :trom the kilns oit such normal fixed proi I'ons relative to each other that the loss or pressure head in each said connecting flue is greater than the loss of pressure head in the collecting line and the draft in the kilns thereby maintained at such approximation to uniformity as is necessary for their effective working.

5. fi cement kiln` plant comprising a series or rotary cement kilns, a flue or chamber for each kiln into which it delivers its gas, a stack leading from each chamber, a common collecting line, one or more waste heat boiler sections connected to the collecting ilue, connecting llues leading from the stack chambers to the collecting flue and entering the same varying distances from the points where the boiler sections connect therewith, each ot said connecting tlues havsuch normal restricted and liz-,ted arcas as will about pressure drop therein in excess of the pressure drop in the collecting liu-e and thereby insure an approximation to uniform drat't in the kilns, and valves whereby the gases from the kilns can be directed to the stacks or collecting fines at will.

6. A furnace system comprising a plurality of rotary cement kilns, a stack and flue connection t0 said stack for each kiln, a col-y each kiln to they Collecting flue and valves for directing the gases from each -kilri to its stack or connecting flue at will, said connecting ilues leading ,to the collecting flue being structurally of such fixed restricted area with reference to the urea of the kilns 10 having mi inclined bottom and a dust collect- 15 ing chamber connecting therewith.

JOHN E. BELL.

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