Gasifier

Abstract

A gasifier may include a chamber wall defining a gasification chamber configured to allow gasification of feedstock material. The gasifier may also include an ash grate disposed in the gasification chamber. The gasifier may further include a rotary crusher disposed in the gasification chamber above the ash grate. The rotary crusher may include at least one crushing element. The rotary crusher may be configured to break apart, between the at least one crushing element and an opposing surface, the feedstock material responsive to rotation of the rotary crusher.

Claims

1. A gasifier comprising: a chamber wall defining a gasification chamber configured to allow gasification of feedstock material; an ash grate disposed in said gasification chamber; a rotary crusher disposed in said gasification chamber above said ash grate; a rotatable shaft coupled with said rotary crusher; and a camming mechanism configured to move said rotatable shaft and said rotary crusher axially with respect to said gasification chamber, and wherein said rotary crusher includes at least one crushing element, wherein said rotary crusher is configured to break apart, between said at least one crushing element and an opposing surface, said feedstock material responsive to rotation of said rotary crusher, and wherein said rotary crusher is configured to contemporaneously rotate and move axially within said gasification chamber.

2. The gasifier of claim 1, wherein said rotary crusher comprises a crusher base configured to support said at least one crushing element, and wherein said crusher base is dome-shaped.

3. The gasifier of claim 1, wherein said ash grate is fixed in said gasification chamber.

4. The gasifier of claim 1, wherein said opposing surface is a surface of a portion of said chamber wall.

5. The gasifier of claim 1, wherein said chamber wall defines a cavity, and further comprising: an element disposed at least partially within said cavity, and wherein said opposing surface is a surface of said element.

6. The gasifier of claim 5, wherein said element is replaceable.

7. The gasifier of claim 5, wherein said element is composed of a different material than said chamber wall.

8. The gasifier of claim 5, wherein said element is composed of firebrick.

9. The gasifier of claim 5 further comprising: a wall retainer arranged to retain said element in place.

10. The gasifier of claim 1, wherein said rotary crusher includes at least one gas nozzle configured to introduce gasification gas into said gasification chamber.

11. The gasifier of claim 10 further comprising: a rotatable shaft coupled with said rotary crusher, and wherein said rotatable shaft is configured to provide fluid communication between said at least one gas nozzle and a source of said gasification gas.

12. The gasifier of claim 1 further comprising: a drive assembly coupled with said rotatable shaft, wherein said drive assembly includes a drive unit and a gearbox, and wherein said drive assembly is configured to rotate said rotatable shaft.

13. The gasifier of claim 1 further comprising: an actuation mechanism coupled with said rotatable shaft, wherein said actuation mechanism is configured to move said rotatable shaft and said rotary crusher axially with respect to said gasification chamber.

14. The gasifier of claim 13, wherein said actuation mechanism is configured to move said rotatable shaft and said rotary crusher independently of said camming mechanism.

15. A waste processing apparatus comprising: a pyrolyser configured to decompose waste to produce feedstock material; and a gasifier comprising: a chamber wall defining a gasification chamber configured to allow gasification of said feedstock material; an ash grate disposed in said gasification chamber; a rotary crusher disposed in said gasification chamber above said ash grate; a rotatable shaft coupled with said rotary crusher; and a camming mechanism configured to move said rotatable shaft and said rotary crusher axially with respect to said gasification chamber, and wherein said rotary crusher includes at least one crushing element, wherein said rotary crusher is configured to break apart, between said at least one crushing element and an opposing surface, said feedstock material responsive to rotation of said rotary crusher, and wherein said rotary crusher is configured to contemporaneously rotate and move axially within said gasification chamber.

16. The waste processing apparatus of claim 15, wherein said feedstock material comprises pyrolysis char, and wherein said pyrolyser is configured to produce pyrolysis gas.

17. The waste processing apparatus of claim 15, wherein said pyrolyser includes: a heating vessel defining a heating chamber; and a rotary pyrolysis tube disposed at least partially within said heating chamber of said heating vessel, wherein said rotary pyrolysis tube is configured to heat said waste to produce said feedstock material.

18. The waste processing apparatus of claim 17, wherein said rotary pyrolysis tube is configured to convey said feedstock material to said gasifier.

19. The waste processing apparatus of claim 17 further comprising: a feed assembly configured to receive and convey said waste to said rotary pyrolysis tube.

20. The waste processing apparatus of claim 15, wherein said gasifier is configured to produce syngas, and further comprising: an oxidiser in fluid communication with said gasifier, wherein said oxidiser is configured to receive, from said gasifier, said syngas and pyrolysis gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described by reference to the following drawings, in which:

(2) FIG. 1 schematically shows waste processing apparatus according to an embodiment of the invention;

(3) FIG. 2 schematically shows a further view of the waste processing apparatus of FIG. 1;

(4) FIG. 3 shows a gasifier for the waste processing apparatus of FIG. 1

(5) FIG. 4 shows the camming mechanism of the rotary crusher of the gasifier of FIG. 3;

(6) FIG. 5 shows the camming mechanism of FIG. 4 rotated through 180; and

(7) FIG. 6 shows the jacking mechanism of the rotary crusher of the gasifier of FIG. 3.

DETAILED DESCRIPTION

(8) FIG. 1 shows waste processing apparatus 100 comprising a feed assembly 200, a pyrolyser 300 including a rotary kiln or rotary pyrolysis tube 302 and a heating vessel 400, a gasifier 500 and an oxidiser 600.

(9) In use, waste is received in the feed assembly 200 and conveyed into the rotary pyrolysis tube 302 of the pyrolyser 300 where it is decomposed under the action of heat to form pyrolysis char and pyrolysis gas. The rotary pyrolysis tube 302 is disposed within the heating chamber 404 of the heating vessel 400, and heat is transferred to the rotary pyrolysis tube 302 from hot gases received within the heating chamber 404. The pyrolysis char and pyrolysis gas exit the rotary pyrolysis tube 302 to enter the gasifier 500, where the pyrolysis char is gasified by the introduction of oxygen and/or steam to produce syngas and ash. The pyrolysis gas and syngas flow together from the gasifier 500 to the oxidiser 600 (see FIG. 2), where the gas is combusted to produce hot gas. The hot gas is redirected to the heating chamber 404 of the heating vessel 400 to heat the rotary pyrolysis tube 302. The hot gas is then directed from the heating chamber 404 to a separate heat recovery unit, such as a steam turbine for power generation.

(10) Ash formed in the gasifier and collected in the oxidiser and heating chamber is collected in an ash bin (not shown) of an ash collection unit by a number of ash feed ducts 702, 704.

(11) As shown in FIG. 3, the gasifier 500 comprises an interface conduit 502 and a gasification vessel 504. The interface conduit 502 is arranged to receive pyrolysis char and pyrolysis gas from the outlet end of the substantially horizontal pyrolysis tube 302 of the pyrolyser, and to provide the pyrolysis char and pyrolysis gas to the vertically-oriented gasification vessel 504. The interface conduit 502 is coupled to the pyrolysis tube 302 by an outlet rotary seal so that both are sealed from the external atmosphere.

(12) The gasification vessel 504 comprises a refractory-lined chamber wall 510 having an upwardly tapering frustoconical wall portion 512, a top wall portion 514 and a base wall 516 defining between them a gasification chamber 518. The top wall portion 514 has a central conical inlet duct 520 aligned with the central vertical axis A of the gasification chamber 518 and arranged to introduce pyrolysis char and pyrolysis gas into the gasification chamber 518 in a generally downward direction through an inlet opening 522.

(13) The top wall portion 514 further comprises a gas outlet duct 523, opening into the gasification chamber 518 at an annular outlet opening 524, for discharging pyrolysis gas received in the gasification chamber 518 and syngas from the gasification chamber 518. The gas outlet 523 is in communication with an oxidiser inlet of the oxidiser 600 via a gas exhaust pipe 562 (FIG. 2).

(14) The conical inlet 520 projects into the centre of the chamber 518 so that the annular outlet opening 524 is above the level of the inlet opening 522.

(15) The top wall portion 514 of the chamber wall 510 forms a baffle structure 525 between the inlet duct 520 and the gas outlet duct 523, around which pyrolysis gas entering the gasification chamber 518 from the inlet duct 520 must flow to be discharged from the gas outlet 523. In this embodiment, the baffle structure 525 partly forms the inner walls of both the inlet duct 520 and the gas outlet duct 523, and is in the form of an annular projection projecting downwardly into the gasification chamber 518.

(16) The gasifier 500 has a flow path between the inlet duct 520 and the gas outlet 523 that extends through the gasification chamber 518. The flow path has an inlet portion which extends downwardly from the inlet opening 522 and turns upwardly within the gasification chamber to an outlet portion which extends upwardly towards the annular outlet opening 524 and the gas outlet duct 523. In this embodiment, the flow path is constrained to turn upwardly around the baffle structure 525.

(17) An ash grate 526 is disposed within the gasification chamber 518 above the level of the base wall 516 and is mounted to the frustoconical wall portion 512.

(18) The frustoconical wall portion 512 has an annular recess 528 at its lower end above the ash grate 526 in which a replaceable wall section 530 composed of firebrick is received. The replaceable wall section 530 is retained in place by a replaceable annular wall retainer 532 that is releasably coupled to the ash grate 526 and abuts the radially inner surface of the replaceable wall section 530 to hold it in place.

(19) The gasifier 504 further comprises a rotary crusher 532 mounted on a shaft 534 extending through the base wall 516 and ash grate 526 of the gasifier 504 and coupled to an external drive unit 536. The shaft extends through a seal 544 received in an opening in the base wall 516. The rotary crusher 532 is disposed immediately above the ash grate 526 and has a generally dome-shaped base 535 to which a plurality of crushing elements or projections 536 are mounted. The crushing projections 536 protrude from the rotary crusher base 535 towards the replaceable wall section 530 and have a spherical cap.

(20) The rotary crusher 532 further comprises a plurality of nozzles 538 mounted on the base 535 and coupled to an external source of gasification gas (i.e. oxygen and/or steam) for introducing gasification gas into a bed of pyrolysis char (i.e. feedstock material for the gasifier 500) within the gasification chamber 518. Gas conduits (not shown) for the nozzles extend through the rotatable shaft 534 to which the rotary crusher 532 is mounted. In this embodiment, the nozzles 538 are directly mounted on the base 535, although it will be appreciated that in other embodiments the nozzles may be provided at the end of extension supports extending from the base 535 of the rotary crusher into the gasification chamber 518 so that, in use, gasification gas is introduced towards the centre of the bed of pyrolysis char.

(21) As shown in FIGS. 4 and 5, the shaft 534 for the rotary crusher 532 is keyed with a stub shaft 542 of the drive unit 536, and is configured to move axially with respect to the stub shaft 542 by way of a swash plate mechanism 540.

(22) The stub shaft 542 extends vertically upwardly from below a hollow gear box 537 of the drive unit 536 through the gear box 537 and towards the rotary crusher 532, and is driven to rotate by the hollow gear box 537. The shaft 534 for the rotary crusher 532 is keyed with the stub shaft 542 so that it is constrained to rotate axially with the stub shaft 542 but is axially movable relative to the stub shaft 542. A seal 544 for the shaft 534, which is received in a shaft opening in the base wall 516 of the chamber wall 510, supports a cam plate 546 having a top surface inclined with respect to the horizontal. A corresponding inclined swash plate 548 is mounted to the shaft 534 for the rotary crusher 532 so that it is constrained to rotate with the shaft 534 and is supported by the cam plate 546. Accordingly, as the stub shaft 542 rotates, the shaft 534 rotates and moves axially up and down as the swash plate 548 rides over the cam plate 546. FIG. 4 shows a lower position of the rotary crusher 532 corresponding to alignment between the swash plate 548 and cam plate 546, whereas FIG. 5 shows an upper position of the rotary crusher 532 corresponding to rotation of the shaft 534 by 180.

(23) The lower end of the stub shaft 542 below the hollow gear box 537 is provided with inlets 543 for receiving gasification gas for injecting into the gasifier chamber 518. The stub shaft 542 is hollow and is in fluid communication with the hollow interior of the shaft 534 for the rotary crusher so that, in use, gasification gas flows through the stub shaft 542, the shaft 534, and the base 535 and nozzle 538 of the rotary crusher 532 into the gasification chamber 518.

(24) As shown in FIG. 6, the drive unit 536 further comprises a jack 550 for selectively moving the stub shaft 542 and the shaft 534 for the rotary crusher vertically up and down in a jacking operation, independently of the swash plate mechanism 540. The jack 550 may be any suitable actuator, such as a hydraulic actuator. The drive unit 536 has a controller for selectively initiating a jacking operation based on a fixed schedule, a detected blockage in the bed of the gasifier, or on demand. The stub shaft 534 is configured to move vertically relative to the hollow gear box 537 of the drive unit 536, so that the gear box 537 remains stationary during a jacking operation.

(25) In use, pyrolysis char from the rotary pyrolysis tube 302 of the pyrolyser 300 is conveyed into the interface conduit 502 of the gasifier 500, and falls downwardly into the gasification chamber 518 through the downwardly extending inlet duct 520 to form a bed of pyrolysis char for gasification. At the same time, pyrolysis gas flows through the interface conduit 502 from the pyrolysis tube 302 and downwardly through the inlet duct 520 into the gasification chamber 518.

(26) Some particulate material, such as ash, may be entrained with the pyrolysis gas entering the gasification chamber 518. The pyrolysis gas flows along the flow path within the gasification chamber described above between the inlet opening 522 of the inlet duct 520 and the annular outlet opening 524 of the gas outlet 523. Accordingly, the pyrolysis gas initially flows downwardly along an inlet portion of the flow path, and then turns upwardly within the gasification chamber 518 around the baffle structure 525. Whilst the light pyrolysis gas can turn upwardly to be drawn out of the gas outlet duct 523, the heavier particulate material entrained in the gas has too much downward momentum to turn upwardly within the gasification chamber, and therefore separates from the pyrolysis gas and falls towards the bed of pyrolysis char. In addition, the particulate material may be drawn downwardly by gravity.

(27) Gasification gas (i.e. oxygen and/or steam) is introduced into the bed of pyrolysis char through the nozzles 538 on the rotary crusher to fuel the gasification reaction, and the pyrolysis char is gasified to form syngas and ash. The syngas moves upwardly through the bed towards the annular outlet opening 524 and is discharged from the gasification chamber 518 via the gas outlet 523, together with the pyrolysis gas, for combustion in the oxidiser 600.

(28) The rotary crusher 532 is driven to rotate by the drive unit 536 during the gasification reaction. The crushing projections 532 agitate the pyrolysis char and crush agglomerated pyrolysis char against the replaceable wall section 530 to break it apart. The rotary crusher 532 is driven to rotate at a speed of five revolutions per minute (0.52 radians per second). Breaking apart the pyrolysis char increases the surface area of the pyrolysis char and therefore increases the efficiency of the gasification reaction. In addition, breaking apart the pyrolysis char can prevent blockages from forming in the bed due to the agglomeration of pyrolysis char, which could otherwise result in the gasifier (and the associated waste processing unit) being taken out of service.

(29) The rotary crusher 532 moves axially up and down once per revolution as the swash plate 548 rides over the cam plate 546. The axial movement of the rotary crusher 532 agitates the bed of pyrolysis char during gasification to break it apart. The drive unit controller selectively initiates a jacking operation in which the jack 500 drives the stub shaft 542, and thereby the shaft 534 and rotary crusher 532 axially up and down to agitate the bed of pyrolysis char. In this embodiment, the drive unit controller is configured to initiate a jacking operation on a fixed schedule, such as of once every five minutes. In addition, a jacking operation can be manually initiated, for example by a push button command, or a signal from a remote operating station, to the drive unit controller. For instance, an operator may selectively initiate a jacking operation when it is determined that there may be a blockage in the bed, for example when ash is discharged at an unusually low discharge rate. In other embodiments, the gasifier may be configured so that a jacking operation is initiated whenever a blockage in the bed or a bridged condition is detected. A blockage in the bed may be detected by monitoring the resistance to rotation of the rotary crusher (e.g. with a torque sensor or by monitoring the power consumption of the rotary crusher), or by monitoring an ash output rate of the gasifier. A bridged condition occurs when the bed becomes compacted at an intermediate level in the gasification chamber (i.e. above the rotary crusher 532), so as to form a cavity within the gasification chamber. The bridge condition is therefore a specific type of blockage. The bridged condition may be detected by monitoring an ash output rate of the gasifier. For example, the ash output rate may be significantly reduced when there is a bridge, whilst the rotary crusher may not experience significant resistance to rotation. The frustoconical wall 512 of the gasification chamber 518 also helps to prevent a bridged condition as the frustoconical wall 512 tends to divert material downwardly as it is radially outwardly compacted.

(30) The swash plate mechanism 540 and the jack 500 therefore provide means of agitating the bed of pyrolysis char during gasification to break apart pyrolysis char and prevent blockage.

(31) The replaceable wall section may experience increased wear relative the rest of the chamber wall 510 owing to the crushing action of the rotary crusher 532. During scheduled maintenance in which the gasifier is taken out of service, the replaceable wall section 530 is replaced by removing the wall retainer 532 and withdrawing the replaceable wall section 530 from the cavity 528. A replacement wall section 530 is then inserted into the cavity 528, and the wall retainer 532 is re-inserted to retain it in place.

(32) The provision of the cavity in the chamber wall, the replaceable wall section and the wall retainer therefore allow the portion of the wall that experiences the highest wear to be easily replaced.