FR2505350A1 - Fixed bed gasifier for combustible solids - having air cooled combustion chamber and combustion air preheating (BR 20.4.82) - Google Patents

Abstract

A gasifier for combustible solids operates on the down draft principle employing as a primary source of combustion air preheated air which has been passed through an external combustion chamber cooling coil and entering via circumferential tuyeres. Excess air may be passed through the coil to enable the requirements of cooling and combustion to be satisfied independently. Additional combustion air is injected direct into the centre of the combustion chamber. To facilitate maintenance the combustion chamber and cooling coils are constructed in replaceable modules. Appts. is used for the gasification of wood, vegetable refuse or any carboniferous material of mineral or vegetable origin. Air injection into the centre of the combustion chamber ensures that the lightest temperatures are encountered away from the walls of the combustion chamber.

Description

 Fixed bed reverse fired solid fuel gazelators.

 The present invention relates to solid fuel gasifiers with fixed bed and reverse draft.

 There are already known fuel gasifiers intended to supply combustible gases from various solid fuels such as wood, vegetable or mineral charcoal, plant waste, etc.

Such gasifiers are described for example in patents BE-A- 457,333, BE-A- 457,257 and BE-A- 456,978 (FORSCHUNGSANS
TALT PROF. JUNKERS) and in the patent application FR. 79/28681 (PILLARD).

 The objective of the present invention is to improve gasifiers of this type, in particular as regards the airlock for the introduction of fuels, the injection of combustion air, the cooling of the combustion chamber, the rotating hearth and disposal of the ashes.

A gasifier according to the invention is of the known type, with a fixed bed and with reverse draft, comprising a vertical combustion chamber which is surmounted by a drying and pyrolysis chamber and an airlock for loading fuels, which combustion is disposed above a rotating hearth which carries in its center a chimney which is located coaxially in said combustion chamber and which comprises means for injecting air into said combustion chamber and in which the wall of said combustion chamber is surrounded by a cooling coil
The combustion chamber of a gasifier according to the invention comprises both an injection of peripheral combustion air which is constituted by peripheral nozzles which open into the upper part of said chamber and an injection of axial air which is constituted by nozzles which are placed in the vicinity of the top of said axial chimney, at a level much lower than that of the peripheral nozzles.

 The wall of the combustion chamber includes a stainless steel wear ring formed by several superimposed sections which can be replaced separately and a layer of coils of a coil which surround said shell, which coil is formed by several sections mounted in parallel. between a fresh air intake manifold and a heated air rejection manifold.

 The axial chimney comprises a central tube in which circulates combustion air and two tubes coaxial with said central duct which delimit two annular conduits which communicate with each other at their upper end, and cooling air circulates in these two annular conduits , the fresh air rising through the internal annular duct and descending through the external annular duct.

 The axial chimney is detachably fixed on the rotating floor. It has a coating consisting of a layer of thin anti-wear refractory concrete.

 The rotating floor comprises a framework formed by radial beams between which are placed independent plates in the form of circular sectors carrying an anti-abrasive tefracary coating.

 The fuel loading airlock has a lower door which pivots in a horizontal plane and further comprises a lever actuated by a jack which keeps said door closed by pressing in the center thereof.

 The fuel loading airlock has a double vertical wall defining an annular space open at both ends.

 The result of the invention is an improved solid fuel gasifier.

 By injecting combustion air at two different levels, a concentration of the hottest area is avoided and the gelling is better. In addition, the hottest area is peeled from the wall of the room.

 Thanks to the cooling of the external wall and the central chimney by a circulation of cold air independent of the combustion air, we can circulate a greater cooling air flow and we obtain a more efficient cooling, a better temperature and gasification control and the possibility of cooling even if the combustion air supply has to be stopped.

 The construction of the ferrule which serves as the internal wall of the combustion chamber and of the rotating hearth in separate elements facilitates maintenance.

 The following description refers to the accompanying drawings which show, without any limiting specification, examples of a solid fuel gazelifier according to the invention.

 Figure 1 is an axial vertical section of a gasifier according to the invention.

 Figure 2 is a top view of the rotating floor.

 Figure 3 is a section on III-III of Figure 2.

 Figures 4 and 5 show alternative embodiments of the disposal of ash.

 Figure 6 shows an alternative embodiment of the rotary drive of the rotary hearth.

 FIG. 1 represents a gasifier 1 of solid fuels of the fixed combustion bed type and with reverse draft. It is a fixed industrial gasifier intended to supply combustible gases to power a fireplace or gas engines. This device can also be used as a carbonizer in which a moderate oxidation is carried out which transforms a solid fuel into coal and gas.

 The gasifier 1 comprises a vertical combustion chamber 2 of axis z zl, which is surmounted by a coaxial enclosure 3 forming a chamber for drying and pyrolysis of the fuel.

The enclosure 3 is surmounted by a loading airlock 4 making it possible to introduce solid fuels into the enclosure 2 without gas leakage.

 The combustion chamber 2 is arranged above a rotating hearth 5.

 A peripheral opening 6 separates from the rotary hearth the lower edge of the wall of the combustion chamber. This opening serves as an outlet for the gases which penetrate into an annular box 7 surrounding the combustion chamber and which exit from the appliance through a conduit 8.

 The rotary hearth 5 carries in its center a chimney 9 which is located coaxially in the combustion chamber. The wall of the combustion chamber 2 is surrounded by a cooling coil 10.

 In gasifiers of this type already known, the cooling coil 10 is traversed from bottom to top by combustion air which is preheated and which is then injected by peripheral nozzles into the top of the combustion chamber.

 Likewise, the central chimney comprises at the lower part an inlet for cold combustion air which is then injected into the chamber by nozzles situated at the top of the chimney, which is then substantially at the same level as the peripheral nozzles.

 In a gasifier according to the invention, the coil 10 and the chimney 9 are cooled by air which is not used for combustion, so that the two functions are separated and it is possible cool more efficiently and continue to cool even if the combustion air supply has to be stopped.

 Part of the combustion air is injected into the top of the combustion chamber by radial injection nozzles 11 which are supplied by an annular manifold 12.

 Another part of the combustion air is injected into the center of the chamber by nozzles 13 which communicate with a duct 14 located in the axis of the chimney 9, which duct is supplied with air by an air inlet 15 comprising a rotating joint. The nozzles 13 can be located on one or more levels.

 According to a characteristic of the invention, the height of the chimney 9 is less than that of the combustion chamber and the central nozzles 13 are located at a level lower than that of the peripheral nozzles 11. This two-level arrangement makes it possible to reduce further the material of the bed, peel off the hot area from the walls and avoid too much concentration of the hottest area.

 The wall of the combustion chamber has an internal wear ring 16 made of stainless steel sheet. This ferrule is composed of several superimposed sections 16a, 16b ... 16n which can be replaced separately, which facilitates maintenance. The ferrule 16 is surrounded by a layer of turns of the coil 10. The coil 10 consists of several sections. For example in the case of the figure, it is composed of four sections 10a, 10b, 10c 10d which are mounted in parallel between a manifold 17 for the arrival of fresh air and a manifold 18 for the outlet of heated air.

 The calories contained in the heated air can be recovered in an exchanger but this heated air is independent of the combustion air circuit which supplies the nozzles 11 and 13.

 The axial chimney 9 comprises an axial tube 14 and two other coaxial tubes 19 and 20 which delimit between them two annular conduits which communicate with each other at their upper end.

 Cooling air is injected into the lower end of the internal annular duct by a duct 21 and a rotating joint. The fresh air rises through the internal annular duct and descends through the external annular duct, the end of which is open.

 The construction of the coil 10 composed of several sections in parallel makes it possible to circulate a high flow of air with a relatively low pressure drop and to obtain good cooling, with a cooling fan having a relatively low power.

 The cooling of the central chimney by a flow and return circuit of cooling air independent of the combustion air makes it possible to obtain a very good cooling of the latter.

 The chimney 9 has a flange 22 which is fixed, in a removable manner, for example by bolts 23, on the rotary hearth 5, so that the central chimney can be taken out to maintain it.

 The central chimney 9 further comprises an external coating 24 which is constituted by a layer of special anti-wear and refractory concrete, having a relatively small thickness, of the order of a few centimeters, so that it is well cooled.

 The loading lock 4 is a vertical enclosure comprising two coaxial walls 25 and 26 which delimit between them an annular space 27 open at its two ends. Wedges 28 keep the two enclosures centered coaxially.

 The upper end of the airlock 4 is closed by a first door 29 articulated around a horizontal axis 30. This door is operated by a lever 31 which is itself actuated by a jack 32.

 The lower end of the airlock 4 is closed by a second door 33 which is articulated around a vertical axis 34, so that the door 33 pivots around the axis 34 while remaining in a horizontal plane and sliding against a peripheral seat 35 which is cut into a knife shape.

 The movement of the door 33 around the axis 34 is controlled by a second cylinder, not shown.

 It can be seen in FIG. 1 that the upper part of the cylindrical enclosure 3 has a lateral flaring 36 allowing the housing of the door 33 when the latter is open.

 The equipment of the airlock 4 comprises> in addition, a lever 37 which is supported in the center of the door 33 when the latter is closed and which keeps the latter pressed in a sealed manner against the seat 35. The lever 37 is articulated around an axis 38 and it is maneuvered by a third jack 39.

 The lower door 33 which moves in a horizontal plane by sliding against the seat, allows the pieces of fuel which would have remained on the door to be swept by the seat and there is no risk of a piece being trapped between the door and the seat.

 The lever 37 which bears against the door 33 avoids the deformation of the latter and produces a sealed contact of the door on its seat.

 The double wall 26, 27 is intended to avoid the risks of sudden gas backflow into the airlock 4. In fact, when the airlock 4 has been filled with fuel and the door 33 is opened, the fuel which fills the airlock 4 forms a plug which tends to create a depression in the airlock, hence a call for gas to fill this depression when the plug has passed through the lower door.

 The annular space 27 which is open at its two ends allows pressure balancing and avoids the depression of the airlock 4 and therefore the risk of a sudden return of the gases in the airlock causing a "sudden" pressure on the gas outlet circuit.

 The references 40 and 41 represent a couple emitting receiver of radiation, for example a transmitter and a receiver of microwaves or ultrasound, which are arranged opposite one another, on either side of the drying enclosure 3, at a level which corresponds to the minimum level of the fuel bed, that is to say the level requiring the loading of the device with fuel.

 The receiver 41 receives the radiation beam when the top of the bed has unmasked it and it emits a signal which can act on an alarm and / or automatically control the opening of door 33 to recharge the device. Such a detector operates in a hot and corrosive atmosphere more faithfully than a mechanical detector.

 FIG. 2 represents a top view of the floor 5 of a gasifier according to the invention. Figure 3 is a section on III-III of Figure 2.

 The sole 5 has a central hub 42 onto which is welded a frame formed by radial beams 43 for example of eight inverted U beams. On these beams are placed independent steel plates 44 having the form of circular sectors which occupy the space between two beams. The adjacent plates are separated from each other by a large clearance 45 allowing free expansion of the plates. The plates 44- are welded to the hub 42. The plates 44 are retained by flat bars 46 which are placed above the beams 43 and plates 44 and which are fixed to the beams by rods 47 so that there has a clearance 48 of the order of 2 mm between the plates 44 and the flat bars 46.

 The floor 5 further comprises a coating 49 of abrasion-resistant refractory concrete, which is shown in Figure 3 and which is removed in Figure 2. This coating 49 is composed of sectors separated by radiating expansion joints 50 having a width of several millimeters.

 The plates 44 have a peripheral edge 50 raised upwards having a thickness substantially equal to that of the covering 49.

 Equidistant ends of tube 51 are welded to the outside of the flange 50.

 FIG. 1 represents a variant, in which the rim 50 is slightly flared towards the outside and has a height greater than the thickness of the covering 49, so that the sole 5 has a hollow shape. FIG. 1 shows a fixed scraper 52 in the form of a spoon, which discharges the ashes outside the sole towards a lifting worm 53.

 The structure of the sole which has just been described has the advantage of eliminating the deformations of the sole.

 For small and medium-sized gasifiers, the rotary hearth is driven by a pulley 54 wedged on an axial hollow shaft 55 which extends down the axial chimney 9. The pulley 55 is driven by a motor 56.

 FIG. 6 represents a variant, in the case of large diameter gasifiers. The rotating floor 5 has, on its underside, a peripheral raceway 74 which rolls on rollers 75.

 The number of bearing rollers 75 is arbitrary. The underside of the rotary hearth 5 further comprises a circular drive path 74a, whether or not adjacent to the raceway 74. The drive path 74a is constituted for example by a conical or cylindrical toothed ring.

 The drive is carried out either by one of the rollers which can comprise a conical or cylindrical member which meshes with the toothed crown 74a, or by a toothed pinion or by an endless screw or a ratchet wheel or any other drive system equivalent. In the case of Figure 6, a roller 75a and a pinion 79 are mounted on a shaft 80 driven by a motor.

 FIG. 6 represents an axial chimney 9 which is rotated by the hearth 5. The flange 22a, which is integral with the chimney, is not fixed to the hearth. It is hampered in rotation by studs 23a which are integral with the frame of the sole.

 A clearance in height el is left between the underside of the flange 22a and the top of the sole. Likewise, a radial clearance e2 is left between the hub of the hearth and the external wall.

 The ashes fall onto an inclined wall 57 or into a cone and they are taken up by a stainless steel lifting screw 53 driven by a motor 58. A double-door airlock makes it possible to isolate the ash evacuation circuit.

 FIG. 4 represents a first alternative embodiment in which the downstream end of the conduit 59 containing the screw 53 pours into a hopper 60 through a first door 61 which pivots about a vertical axis 62 under the action of a cylinder. The hopper 60 has> at its lower end, a second door 63 actuated by a second cylinder. The hopper 60 therefore forms an airlock which is placed after the screw. A lever 64 actuated by a jack presses in the center of the door 61 to keep it closed in a sealed manner.

 FIG. 5 represents a second variant in which the upper end of the conduit 59 communicates with a small hopper 65 which pours into an ashtray 66. The hopper 65 forms an airlock which comprises a first door 67, which pivots about an axis 68 perpendicular to its plane and which is kept closed by a lever 69 which is supported in the center of the door. The hopper 65 has a second door 70 which closes the communication between the hopper and the ashtray.

 According to a third variant which appears in FIG. 1, the ashtray 66 is housed in a box which has a sealed door and the upper end of the duct 59 communicates with this box through a chute 72 which is closed by a second door 78. In in this case, the box 71 forms an airlock.

 According to another variant shown in FIG. 7, the ash evacuation airlock comprises a first horizontal door 81 which pivots about a vertical axis 82 and which is kept closed by a lever 83 which is supported in the center of the door.

The door 81 is located at the outlet of a chute 84 which opens into a small hopper 85 situated upstream of the inlet of the conduit 59 containing the screw 53. The airlock comprises a second door located at the outlet of the conduit 59.

Claims (11)

 1. Solid bed fixed reverse reverse flow gasifier (1) of the type comprising a vertical combustion chamber (2) which is surmounted by an enclosure (3) for drying and pyrolysis and an airlock (4) loading fuel, which combustion chamber is disposed above a rotating hearth (5) which carries in its center a chimney (9) which is located coaxially in said combustion chamber and which comprises means for injecting l air in said combustion chamber and in which the wall of said combustion chamber is surrounded by a cooling coil (10), characterized in that said combustion chamber comprises both an injection of peripheral combustion air which is constituted by peripheral nozzles (11) which open into the upper part of said chamber and an axial air injection which is constituted by nozzles (13) which are placed in the vicinity of the top of said axial chimney (9), at a nivea u lower than that of the peripheral nozzles.  2. A gasifier according to claim 1, characterized in that the wall of the combustion chamber comprises a wear ring (16), of stainless steel, formed of several superposed sections (16a ... 16n), which can be replaced. separately and a layer of turns of a coil (10) which surround said ferrule, which coil is formed by several sections (lova, 10b, 10c, 10d) mounted in parallel between a manifold (17) of fresh air intake and a manifold (18) for rejecting the heated air.  3. Gasifier according to any one of claims 1 and 2, characterized in that said axial chimney (9) comprises a central tube (14) in which circulates combustion air and two tubes (19, 20) coaxial with said central duct which delimit two annular ducts which communicate with each other at their upper end, and cooling air circulates in these two annular ducts, the fresh air rising through the internal annular duct and descending through the external annular duct.  4. Gazelficator according to claim 3, characterized in that said axial chimney (9) is fixed, in a removable manner, on said rotating hearth.  5. A gasifier according to any one of claims 3 and 4, characterized in that said central chimney comprises a coating (24) consisting of a layer of refractory anti-wear concrete, of small thickness.  6. Gazelficator according to any one of claims 1 to 5, characterized in that said rotary sole comprises a framework formed by radial beams between which are placed independent plates in the form of circular sectors carrying an anti-abrasive refractory coating.  7. Gasifier according to any one of claims 1 to 6, characterized in that said airlock (4) for loading fuels comprises a lower door (33) which pivots in a horizontal plane and further comprises a lever (37 ) actuated by an actuator (39) which keeps said door closed by pressing in the center thereof.  8. A gasifier according to any one of claims 1 to 7, characterized in that said airlock (4) for loading fuels comprises a vertical double wall (25, 26) delimiting an annular space (27) open at both ends.  9. A gasifier according to any one of claims 1 to 8, characterized in that said enclosure (3) for drying and pyrolysis comprises an emitter (40) and receiver (41) couple of radiations, placed opposite one of the other, on either side of the enclosure, at a level which corresponds to the level requiring recharging of the appliance with fuel.  10. A gasifier according to any one of claims 1 to 9, characterized in that the ash discharge circuit comprises an inclined wall or a cone (57) located under said rotary hearth (5), a lifting worm ashes (53), an ashtray (66) and two doors (61,63) or (67, 70) forming an airlock.  11. Gasifier according to any one of claims 1 to 10, characterized in that the rotary sole (5) comprises a peripheral raceway (74) which rolls on rollers (75) and a motorized drive system acting on the periphery of the sole.