FR2553097A1 - INSTALLATION FOR TREATING COMBUSTIBLE MATERIAL AND METHOD OF OPERATION - Google Patents

Abstract

1. Plant for treating a combustible material by circulating hot gases, comprising an elongated reaction chamber (1) having a flat bottom (13) and provided at an upstream end (2) with means for loading the material in the form of a layer (4) which moves along the flat bottom (13) as far as a downstream end (12) for discharging the treated material, the reaction chamber (1) being associated with at least one circuit for circulating hot gases through the layer (4) of material, which circuit has means (18) for introducing the hot gases above the layer (4) of material and means (6) for sucking the gases through at least one permeable section (15) arranged in the bottom (13), at least on the downstream side, which plant comprises an element (8) for controlling the flow of the treated material at an adjustable rate, which element is located so as to project in relation to the plane of the bottom (13) at the downstream end (16) of the latter, a means for measuring the temperature of the gases sucked in below the layer (4) of material at the downstream end (12) of the bottom (13) and a means for adjusting, via the control element (8), the rate at which the treated material is discharged, in accordance with the variations in the measured temperature t of the gases with respect to a predetermined level t' corresponding to the optimum operating conditions.

Description

Installation for treating a combustible material and its mode of

operation.

  The subject of the invention is a plant for treating a combustible material, and in particular a gasification apparatus for coal or vegetable matter and also covers control methods.

  treatment carried out in an installation of this type.

  Apparatuses for pyrolysis or gasification of combustible materials by hot gas circulation are already known comprising an elongated reaction chamber having a planar bottom on which the material charged at an upstream end forms a layer moving to the downstream end of the The reaction chamber is associated with a circulation circuit of hot gas through the layer of materials having means for introducing hot gases over the layer for example by means of A burner and gas suction means through the layer of material by at least one permeable portion in the bottom In a gasification apparatus, as described, for example, in French Patent No. 7831,356 the bottom is provided with two permeable z nees constituted by grids, a z is placed in the upstream half of the chamber corresponding to the drying and the pyrolysis of the material and a z 8 placed on the downstream side corresponding to the gasification of the material after pyrolysis The pyrolysis gases sucked by a box located below the upstream grate are recycled into the burner placed above the downstream end of the the chamber, so as to produce the temperature necessary for the gasification, the gases produced by it being sucked by

  a box placed below the downstream grid.

  The reaction chamber described in this patent has a ho25 rice background. However, it may be advantageous to tilt the bottom more or

  less depending on the desired operating conditions.

  Indeed, when the bottom is inclined at a large angle that depends on the friction between the material and the bottom and may be greater than 45 ', the material loaded by an opening opening above the upstream end 30 of the bottom advances under the action of its own weight up to a hopper

  discharge located at the downstream end of the chamber.

  On the other hand, in the embodiment described in patent N 7837356, the bottom of the chamber is substantially horizontal or slightly inclined so that the advancement of the material can not occur naturally and is effected by means of a thrust member such as a piston placed below the loading port and animated, reciprocating movements of slow advance and fast retreat to give the

  material a substantially constant forward speed.

  The reaction chamber opens at its downstream end into a recovery hopper whose edge must normally be separated from the grid 5 by a weir-forming surface and whose length must be sufficient to maintain a minimum thickness of material above the grid. in view of the angle formed by the natural slope of discharge of the material at the downstream end of the layer Indeed, when the grid is not covered with a layer of material of sufficient thickness to produce a 10 certain pressure loss, we can see a phenomenon of firing producing preferential currents of hot gas through the grid.

  On the other hand, the downstream part thereof can also be exposed directly to the gas from the burner if it is placed too close to the edge of the discharge hopper, the slope may spill irregularly. This therefore results in a risk of overheating of the grid, the longevity

  depends on the temperatures to which it is exposed.

  There is also a risk of overheating when the front part of the material layer consists almost entirely of ash which produces no cooling of the gases. It is therefore customary to regulate the operating conditions so as to keep within the the

  material covering the grid at the downstream end of the chamber a minimum proportion of charcoal may reduce the temperature of the gas and therefore the risk of heating of the grid through the endothermic reaction of formation of carbon monoxide Of course, this proportion of residual carbon must be reduced to the minimum necessary so as not to excessively reduce the gasification yield.

  When adjusting the operating conditions, it is obviously necessary to take into account the characteristics of the installation and the treated material and one can play on a certain number of parameters such as the debit bit, the temperature of the gases produced by the burner above

  the charge or the flow rates and velocities of the aspirated gases to achieve the desired operating conditions.

  The temperature produced by the burner above the charge should normally be as high as possible, but it is also necessary to avoid a too rapid fusion of the ash which would hinder evacuation. Experience shows that the upstream temperature of the gases above the charge must be

the order of 1150 C.

  The thickness to be given to the layer, which depends in particular on the

  material characteristics and the inclination of the bottom must be sufficient, as indicated, to produce the necessary pressure drop and depends on the suction conditions It has also been seen that the downstream temperature of the gases having passed through the load should be limited, if possible, so as not to degrade the grid while keeping a good gasification efficiency and experience shows that it is useful to maintain a temperature of about

700 below the downstream grid.

  It is possible empirically to determine the optimum operating conditions of a gasification plant, but unless it is provided with a movable hearth which complicates the installation a great deal, until now there were no simple means of controlling operating conditions during operation and, in fixed hearth furnaces, it is necessary either to maintain a relatively high carbon content at the downstream end of the furnace, which reduces the yield, or to spread towards the downstream the point of discharge of the material with respect to the end of

  the grid, resulting in an elongation of the oven.

  The object of the invention is to overcome these drawbacks by means of a device which makes it possible, in particular, without undue complication and without the use of a moving hearth, to control the end of the treatment process, in particular by avoiding a rise in the temperature of the gases at level of

  the grid which would lead to excessive heating thereof.

  According to the invention, the reaction chamber is provided with a spill control member of the treated material, projecting above the level of the bottom of the chamber at the downstream end thereof and provided with means for controlling the spill. continuous evacuation of the treated material with an adjustable flow rate. According to a preferred feature, the installation comprises a means for measuring the temperature of the gases sucked beneath the layer of material at the downstream end of the bottom and a control means for controlling the discharge of the flow. discharging the treated material, as a function of the variations of the measured gas temperature with respect to a determined level corresponding to the optimum operating conditions. In a particularly advantageous embodiment, the body 35 for controlling the discharge of the material is constituted by a roller extending transversely to the downstream end of the bottom, rotatably mounted about an axis parallel to the latter and whose upper part overflows above the bottom so as to be an obstacle to the advancement of the material.

  The roll is provided on its periphery with hollow portions capable of taking off a determined quantity of material at each revolution of the roll, the latter being associated with an adjustable speed rotating drive means constituting the means for adjusting the flow rate of the roll. evacuation of the material.

  In a first embodiment, the reaction chamber has a bottom inclined to the horizontal of an angle less than that causing the natural advancement of the material and is associated with a means of pushing the material to a surface. substantially constant forward speed In this case, the discharge flow of the discharge control member being set for optimum operating conditions as a function of the forward speed of the layer of material, the downstream temperature of the gases above the layer at the downstream end and, in the event of exceeding a reference temperature corresponding to the desired degree of treatment, a decrease in the evacuation rate of the treated material determining a desired increasing the height of the layer and lowering the measured downstream temperature to the reference level,

  the discharge rate is then reduced to its normal value.

  In another embodiment, the reaction chamber has a

  bottom inclined relative to the horizontal of an angle greater than that causing the natural advancement of the material under its own weight and spill control member projecting above the bottom to a height substantially equal to that of the material layer and which depends on the loading dump by the upstream port and the evacuation flow of the treated material.

  In this case, the temperature of the gases is constantly

  below the layer of material at the downstream end of the bottom and, if a reference temperature of the desired degree of treatment is exceeded, an increase in the evacuation flow rate controlling an increase in the content is controlled. carbon content of the material at the downstream end and a lowering of the measured temperature to the reference level, the evacuation flow then being brought back to its normal value.

  However, the invention will be better understood with reference to embodiments given by way of example and shown in the accompanying drawings. FIG. 1 represents schematically, in longitudinal section,

  the treatment chamber of a gasification plant.

  Figure 2 is an enlarged detail view of the downstream discharge end of the material.

  FIG. 3 is a schematic representation of a longitudinal

other type of gasifier.

  FIG. 1 diagrammatically shows a gasifier consisting of a treatment chamber 1 of elongate shape, provided with a bottom 13 inclined with respect to the horizontal and extending between a feed inlet 2 and a hopper 16 for discharging the treated material, placed at the two ends, respectively upper and lower, of the elongate chamber 1. The reduced-piece material introduced through the inlet 2 moves along the inclined bottom 13 of the chamber for example under the action of a piston 3 which is driven by a ram 31 reciprocating in advance and recoil, the advance being at a slow speed adjustable and the retreat at a higher speed of such so that the material moves in a practically continuous movement, at a medium speed V. The material thus forms above the bottom 13 a layer 4 which can

  it has a variable thickness and whose front portion 44 forms a slope 45 limited by the downstream end 12 of the bottom 13 and whose inclination depends no.20 aamment physical characteristics of the material after treatment.

  Opposite the slope 45 and above the discharge hopper 16, the chamber 1 forms a hood 17 in which is placed a burner 18 The hot gases produced by the burner 18 are spread in the treatment chamber 1 above of the material and are sucked therethrough by two caissons 51 and 61 connected to suction circuits, respectively 5 and 6 and respectively limited by two grids 14 and 15 forming permeable portions of the bottom 13 respectively placed on the upstream side and on the downstream side of it. In this way, the hot gases produced by the burner 18 pass through the layer of material 4 and the slope 45 in a substantially transverse direction and produce above the gate 14 the drying and then the pyrolysis of the combustible material which is transformed into charcoal and then converting it to gas above the grate 15 the gas produced being

sucked by the box 61.

  The downstream part of the bottom 13 between the boundary of the caisson 15 and the edge of the hopper 16 forms a weir 12 whose length determines the position of the slope 45 and consequently the thickness of material traversed

  by the gases sucked by the grid 15.

  According to an essential characteristic of the invention, it is

  this place a roll 8 which is provided on its periphery with groove-shaped recesses 81 which extend over the entire length of the roll.

  It is rotatably mounted with an axis 80 parallel to the bottom 13 and perpendicular to the axis of the chamber 1, that is to say to the direction of displacement. The axis 80 of the roller 8 may be placed for example, at the bottom 13, the weir 130 forming a cylindrical housing for the lower part of the roll 8, the upper part of which thus extends above the bottom 13. On the other hand, the roll 8 is rotated by a motor 10 82 with an average angular speed for which the discharge rate of the material taken by the grooves 81 corresponds to the average speed V of advancement of the material along the bottom 13 In this way, by adjusting the rotational speed of the roller 8, the discharge rate of the material can be varied and therefore accelerate or, on the contrary, slow the advancement of the downstream portion 44 of the layer of material so that, depending on the speeds of the roller 8, the slope 45 oscillates between two

  positions 46 and 47 indicated schematically in FIG.

  In a reaction chamber with a low inclined bottom, the average speed of advancement of the material layer 4 is determined by the piston 3 and remains substantially constant as long as the piston speed is not modified. average rotation of the roller 8 for which the discharge rate of the ashes through the grooves 81 corresponds to the average speed of advance of the downstream portion 44 of the layer and which depends on the piston speed small account, obviously, the varia25 the physical characteristics of the material during processing, especially the density and settlement For this average roller speed, the discharge slope takes the average position 45 If the speed of rotation of the roller is decreased, the flow rate The evacuation also decreases and this results in a braking effect, the roller constituting an obstacle 30 which must be crossed by the material. The slope then takes the position 46 indicated in dashes. In the figure and which is substantially tangent to the roller 8 and whose inclination depends on the angle (D) natural discharge of ash On the other hand, when increasing the speed of rotation of the roller, the discharge rate of ashes becomes greater than the arrival rate which corresponds to the average speed of advance and the slope takes the position 47 of slightly concave shape, indicated in dotted line

in Figure 2.

  As a result, the minimum thickness h of material traversed by the gases at the lower end of the grid 15 can vary between two values h 1 and h 2 corresponding to the end positions 46 and 47 of the slope according to the speed given to the roller 8 Thus, by controlling the discharge of the material and the discharge rate through the roller 8, there is a means for varying the height h of material passed through the gases and therefore the cooling thereof, the operating conditions being adjusted, as stated, so that the ash conserves at the end of treatment a minimal proportion of carbon determining

  a lowering of temperature by endothermic reaction.

  It has been found empirically that, under normal operating conditions and the roller being driven at a speed which corresponds to the average speed of advancement of the material, it could be considered that the height h of material covering the downstream end of the grid was in the order of twice the height e of the roll portion protruding above the bottom 13, therefore, in the case where the axis 80 of the roll 8 is placed

  substantially in the plane of the bottom 3, the roll 8 will be given a diameter of the order of the height of material that it is desired to keep above the grid. Of course, this depends essentially on the properties of the material and the a possibility of adjusting the height of the roller axis 80 could be provided.

  To maintain the temperature of the gases above the grid at the desired level, it is therefore advantageous to use a regulating device for controlling the speed of rotation of the roller 8 as a function of the temperature of the gases. This device may comprise a comparator. 9, receiving the temperature measured by a sensor 91 placed below the gate 15 to compare it with a reference temperature t '. Depending on the result of this comparison, the comparator 9 sends an order to an adjustment member 83. the rotational speed of the roller driving motor 82 When the measured temperature t substantially exceeds the reference temperature t ', the comparator 9 sends to the regulating member 83 a deceleration order of the roller 8 which allows the Increasing the through-layer height and therefore the cooling of the gases When the temperature difference is judged normal, the comparator issues an order

  back to normal speed of roller 8.

  Normally, if the device is properly adjusted, the temperature measured below the grid should not fall abnormally below the reference level. If the comparator detects an abnormal temperature drop that results in a drop in efficiency, then

  act on the speed of advancement of the material by means of the piston 3.

  Of course, the relative proportions of charcoal and ash remaining at the end of the treatment depend on the nature of the fuel which can produce a proportion of ash ranging from 5 to 20%. The operating conditions being determined according to the nature of the fuel and characteristics of the installation, the control device according to the invention makes it possible to control the degree of progress of the treatment and the temperature of the gases sucked so as to avoid excessive heating of the grid 15 Thanks to the security provided By means of the control water of the spill, it is therefore possible to reduce as much as possible the carbon content of the ashes and consequently reach an optimal gasification yield. However, the device which has just been described also has other advantages. Thus, the ashes in molten form, on the surface 45 of the slope, a crust which will be broken and easily discharged by the roller. Furthermore, it is possible to place in the front wall 17 of the treatment chamber 1 a porthole 19 which makes it possible to observe the discharge of the material onto the roll 8. Thus, it will be possible to recognize the presence of unconverted coal particles entrained in the grooves 81 of the roll and, in this case, play on the speed of rotation thereof to slow the advancement of the material so as to obtain a complete conversion It is possible to obtain a virtually complete depletion of the carbon content

  in the combustible material at the end of the gasification zone.

  Similarly, we can monitor and avoid the formation of sticky ash that could hinder the progression of the material and go up to

  the obstruction of the treatment chamber 1.

  The horizontal or slightly sloped gasifier which has just been described is well suited to the treatment of materials with a relatively low ash content of the order of 5%, such as, for example, wood.

  In the case of materials of vegetable origin containing a significant proportion of ash, for example of the order of 20%, as in the case of the compacted rice husk, it is preferable to use a gasogen whose bottom is inclined at a large angle substantially corresponding to the natural discharge angle of the material such that it advances under the action of its own weight, without the use of a thrust means, the thickness and the rate of advancement of the layer of dependent material

  then the feed rate and the discharge rate.

  Such a gasifier has been shown by way of example in FIG. 3. The reaction chamber 1 is then provided with an inclined bottom 13.

  a large angle, of the order of 45 and is provided, above the upper end 11 of the bottom 13, an inlet port 2 through which opens a chimney 21 for introducing the material continuously.

  At the downstream end 12 of the bottom 13, is placed a roller 8 which may be provided, as described above, with fluting 81, but which protrudes above the level of the bottom 13 over a height. 10 substantially corresponding to that of the layer of material at its entrance

  In this way, the material introduced by the inlet orifice 2 forms a layer of substantially uniform thickness up to the discharge roller 8.

  It can be seen that a difference with respect to the previous embodiment lies in the fact that the thickness of material traversed by the gases remains substantially constant. On the other hand, in the case described now, the material contains a significant proportion of ash and by Therefore, by varying the discharge rate thereof, the carbon content of the material above the grid 15 can be varied sufficiently to affect the temperature of the gases measured above. below

of the grid.

  Thus, as in the previous case, a sensor of

  temperature 91 placed below the downstream end of the gate 15 and connected to a comparator 9 which drives the motor 82 of the roller via a member 83 for adjusting the speed of rotation.

  When the comparator 9 detects an abnormal rise in temperature above the reference temperature t ', the comparator 9 determines an increase in the rotational speed of the roller and consequently the ash discharge rate. These are immediately replaced by the material upstream and advancing under the action of

  This material, having undergone a less thorough treatment, has a higher carbon content which determines a lowering of the temperature to the desired level. The comparator 9 then reduces the speed of the roll to normal speed.

  Conversely, if the comparator 9 detected a lowering of the temperature corresponding to an insufficient treatment of the material, the comparator 9 could slow down the roll and consequently the evacuation flow of the material which would then undergo further processing.

  lowering the carbon content and raising the temperature of the gases sucked up to a normal level, the rotational speed of the

  roll is then returned to its normal value.

  It can be seen that the device according to the invention makes it possible to adapt to very different operating conditions and one could obviously imagine other variants.

  In addition, the devices which have been described by way of example could be replaced by equivalent means. Thus, the material spill control roller 8 could be provided, in place of the flutes 81, helical threads to form a worm which would be placed in the bottom of a bucket The material would then move parallel to the axis of the roller, that is to say transversely to the direction of the bottom 13, the evacuation is producing in this case also, it would be possible to adjust the ash discharge rate and consequently to control, to a certain extent, the operation of the installation by acting on the

  speed of rotation of the worm-shaped roller.

Claims (12)

  l.Installation of treatment of a combustible material by circu   a hot-gas outlet comprising an elongate reaction chamber (1) having a planar bottom (13) and provided at an upstream end (2) with means for loading the material in the form of a layer (4) moving along from the bottom plane (13) to a downstream end (12) of discharge of the treated material, the reaction chamber (1) being associated with at least one hot gas circulation circuit through the sock (4) of material, comprising means (18) for introducing the hot gases above the layer (4) of material and means (6) for suction of the gases through at least one permeable portion (15) formed in the bottom (13), at least on the downstream side, characterized in that the reaction chamber (1) is provided with a control member (8) 81e of the spill of the treated material, projecting above it from the bottom level (13) to the downstream end (16) of the latter and provided with means for the continuous evacuation of the material re treated, with an adjustable flow rate.   2 treatment plant according to claim 1, characterized in that it comprises a means for measuring the temperature of the gas sucked below the layer (4) of material at the downstream end (12) of the bottom (13). ) and adjusting means, by the control member (8) of the discharge rate of the treated material, according to the variations of the   measured temperature t of gases with respect to a determined level corresponding to the optimum operating conditions.   3 treatment plant according to claim 1, characterized in that the control member 181 e spill of the material 25 is constituted by a roller (8) extending to the downstream end (12) of the bottom   (13), transversely to the axis of the chamber (1) rotatably mounted about an axis and whose upper part overflows above the bottom so as to constitute an obstacle to the advancement of the material (4).   4 Treatment plant according to claim 3, characterized in that the roller (8) is provided on its periphery with parts   hollow means (81) capable of taking a determined quantity of material at each revolution of the roll (8), the latter being associated with a means (82, 83) for rotationally rotating at an adjustable speed constituting the means for controlling the flow rate; evacuation of the material.   5 Treatment plant according to claim 1, characterized in that the hollow portions (51) for sampling the material consist of grooves formed on the periphery of the wheel.   water (8) parallel to its axis and capable of digging the material passing through the layer (4) to pour it on the other side of the axis of the roller (8).   6. Processing plant according to claim 1, characterized in that the hollow portions (81) for sampling the material are constituted by helical threads forming a worm on the periphery of the roll (8) and determining the evacuation. material with adjustable flow in a direction transverse to that of the bottom (13).   7 treatment plant according to claim 3, characterized in that the means for adjusting the discharge rate of the material comprises a device (9) for controlling the speed of rotation of the roller (8) as a function of the downstream temperature. of gas measured below of the layer (4) of material.   8 improvement to a treatment plant according to claim 7, characterized in that the control device 9 of the speed of rotation of the roller 8 comprises a temperature sensor 91 placed in the suction box 61 below the grid 15, a comparator 9 of the measured temperature t with a displayed temperature t 'and a member 83 for adjusting the speed of the drive means 82 of the roller 8, controlled by the comparator 9 to control a variation of the rotational speed of the roller 8 with respect to a reference value in the direction that can be determined according to the operating conditions, the   return of the measured temperature t to the displayed temperature t '.   9 -Installation treatment according to one of claims 1 and   2, characterized in that the reaction chamber (1) has a bottom (13) inclined relative to the horizontal, at an angle less than that causing the natural advancement of the material and is associated with a means (3) thrusting the material at a substantially constant forward speed.   10 treatment plant according to one of claims 1 to   8, characterized in that the reaction chamber has a bottom (13) inclined relative to the horizontal by an angle greater than that causing the natural advancement of the material under its own weight and that the control member 181 e of the spill projecting above the bottom (13) over a height (e) substantially equal to that of the layer of material.   11 A method of controlling the degree of treatment of a combustible material in a treatment plant according to claim 9, characterized in that, the discharge rate of the body (8) of con-   With respect to the speed of advance of the layer of material, the temperature of the spill was adjusted for optimal operating conditions and the downstream temperature of the gas below the material layer (4) was continuously measured. the downstream end (12) and if a reference temperature t 'corresponding to the desired degree of treatment is exceeded, a decrease in the discharge rate of the treated material is controlled, determining an increase in the height of the the layer and lowering the measured downstream temperature t up to the reference level t ', the evacuation flow then being brought back to its normal value.   12 A method for controlling the degree of treatment of a combustible material in an installation according to claim 10, characterized in that the discharge rate of the spill control member (8) being adjusted for operating conditions. the continuous temperature of the gases below the layer (4) of material at the downstream end (12) and in case of exceeding a reference temperature corresponding to the desired degree of treatment is permanently measured. an increase in the evacuation flow rate determining an increase in the carbon content of the material at the downstream end (12) and a lowering of the measured downstream temperature to the reference level, the evacuation die being then brought back to its normal value.