WO1999010094A1

WO1999010094A1 - Discharge of solid particulate material from a bulk vessel containing such material

Info

Publication number: WO1999010094A1
Application number: PCT/GB1998/002534
Authority: WO
Inventors: Philippus Jacobus Meyer
Original assignee: Sasol Technology (Proprietary) Limited; Sasol Chemicals Europe Limited
Priority date: 1997-08-21
Filing date: 1998-08-21
Publication date: 1999-03-04
Also published as: AU8870498A

Abstract

A method of discharging solid particulate material from a bulk vessel or container containing the material, comprises discharging the material from the vessel or container through an annular first discharge passageway in or adjacent a floor of the vessel or container. Simultaneously material is discharged from the vessel or container through a second discharge passageway in or adjacent the floor.

Description

DISCHARGE OF SOLID PARTICULATE MATERIAL FROM A BULK VESSEL CONTAINING SUCH MATERIAL

THIS INVENTION relates to the discharge of solid particulate material from a bulk vessel containing such material. It relates in particular to a method of discharging such material, and to an installation for effecting such discharge. It relates still more particularly to a method of discharging ash from a fixed bed coal gasifier, and to a fixed bed coal gasifier installation.

According to a first aspect of the invention, there is provided, broadly, a method of discharging solid particulate material from a bulk vessel or container containing the material, which method comprises discharging solid particulate material from the vessel or container through an annular first discharge passageway in or adjacent a floor of the vessel or container; and simultaneously discharging solid particulate material from the vessel or container through a second discharge passageway in or adjacent the floor.

While the process can, at least in principle, have broader application for discharging any solid particulate material from a bulk vessel, the solid particulate material may, in particular, be ash produced in a fixed bed coal gasifier, such as a LURGI (trade name) fixed bed coal gasifier. The vessel will thus be a gasifier defining a gasification chamber. Thus, according to a second aspect of the invention, there is provided a method of discharging ash from a fixed bed coal gasifier, which method comprises discharging ash from a gasification chamber of a fixed bed coal gasifier, through an annular first discharge passageway adjacent a floor of the gasification vessel; and simultaneously discharging ash from the chamber through a second discharge passageway adjacent a floor of the gasification chamber.

The second discharge passageway may also at least partly be of annular form, and at least a portion thereof may be located concentrically within at least a portion of the first passageway, when seen in plan view. Portions of the first passageway may be located at different levels, as may be portions of the second passageway. Additionally, at least a portion of the first passageway may be located at a different level to at least a portion of the second passageway.

The discharging of the material or ash through the first passageway may be effected by passing at least one primary scraper or plough over a stationary material or ash collection surface in the first passageway, with the primary plough urging the material or ash inwardly or outwardly along the collection surface. The movement of the primary plough over the surface may be effected by rotating it about a vertical axis extending centrally along the first passageway.

The discharging of the material or ash through the second passageway may be effected by rotating a first discharge or grate component relative to a second stationary discharge or grate component, with the second passageway being provided between the discharge or grate components. In particular, the second stationary discharge or grate component may be centrally located, with the first discharge component thus rotating around the second discharge or grate component. The material or ash may pass downwardly along a first annular portion of the second passageway, then radially outwardly along a second portion of the second passageway, before passing downwardly again through a third annular portion of the second passageway and which joins the first passageway. The radially outward distribution or passage of the material or ash along the second portion of the passageway may be effected by means of a secondary plough or scraper protruding outwardly from the second discharge or grate component into the second portion of the passageway.

The primary plough may, in particular, be attached to the rotating first discharge or grate component.

It will be appreciated that when the first and second passageways are not provided in the floor of the vessel, container or gasifier but adjacent it, ie above the floor, a further material discharge opening or passageway will be provided in the floor below the first and second passageways .

According to a third aspect of the invention, there is provided, broadly, a bulk material vessel installation, which comprises a vessel having a floor and wall(s) protruding peripherally upwardly from the floor; an annular first discharge passageway through which solid particulate material can be discharged, in or adjacent the floor of the vessel; a second discharge passageway through which solid particulate material can simultaneously be discharged, in or adjacent the vessel floor; and control means for controlling the rate of discharge of solid particulate material through the first and second passageways .

As indicated hereinbefore in respect of the process according to the first aspect of the invention, the installation can, at least in principle, have broad application for discharging any solid particulate material from a bulk vessel; however, the solid particulate material may, in particular, be ash produced in a fixed bed coal gasifier, so that the vessel is thus a gasifier defining a gasification chamber.

Thus, according to a fourth aspect of the invention, there is provided a fixed bed coal gasifier installation, which comprises a gasifier having a floor, a roof spaced from the floor, and a circular cylindrical wall between the floor and roof, with a coal inlet in the roof and an ash outlet in the floor, and with the vessel defining a coal gasification chamber; an annular first ash discharge passageway, adjacent the floor, through which ash can be discharged from the gasification chamber; a second ash discharge passageway, adjacent the floor, through which ash can also be discharged simultaneously from the gasification chamber; and control means for controlling the rate of discharge of ash through the first and second passageways.

As hereinbefore described, the second discharge passageway may also at least partially be of annular form, and at least a portion thereof may be located concentrically within at least a portion of the first discharge passageway, when seen in plan view. The wall may be of circular cylindrical form, with a support component, providing an upwardly directed material or ash collection surface, protruding radially inwardly from the wall, and located in the first passageway. The control means may include a first rotatable discharge or grate component, which is rotatable about the vertical axis of the first passageway, and at least one outer or primary plough or scraper protruding from the first discharge or grate component and adapted to direct material inwardly from the collection surface as the first discharge or grate component rotates .

The second passageway may be defined between the first discharge or grate component and a second stationary central discharge or grate component. The second passageway may comprise a more-or-less annular first portion, a second portion extending radially outwardly from the lower end of the first portion, and a third annular portion in communication with the second portion. The second stationary central discharge or grate component may comprise a central pillar and at least one stationary inner or secondary plough protruding outwardly from the pillar into the second portion of the passageway.

The control means thus comprises a grate which includes the first rotatable grate component and the second stationary central grate component.

A plurality of the outer ploughs, staggered or spaced apart about the rotational axis of the first grate component, may be provided. Similarly, a plurality of the stationary inner ploughs, staggered or spaced apart about the pillar, may be provided.

The central pillar may include a gasification agent passageway, extending along its length, with the lower end of the passageway being open at the lower end of the pillar and being connected, by means of a conduit, to a supply of the gasification agent; at least one gasification agent outlet at or in proximity to the upper end of the pillar protruding into the gasification chamber, with this outlet being in communication with the first portion of the second passageway; and at least one further gasification agent outlet in the pillar between its ends, the further outlet being in communication with the first passageway.

The first grate component may comprise a hollow support structure rotatable about the pillar, with the further gasification agent outlet in the pillar being in communication with the hollow interior of the first grate component; an outer shield covering at least a portion of the support structure; and at least one gasification outlet in or adjacent the outer shield, for discharging gasification agent from the inside of the support structure into the gasification chamber as the first grate component rotates about the pillar. The outer surface of the outer shield of the first grate component may taper upwardly inwardly from the outer ploughs. The angle which the outer surface forms with the horizontal may be greater than the angle of repose of coal ash.

In particular, the outer surface of the first grate component may be staggered or stepped when seen in vertical cross-section, with each step or layer comprising a plurality of outer shield plates arranged circumferentially in abutting or overlapping relationship and sloping upwardly inwardly. The different layers of shield plates thus together constitute the outer shield. A circumferential gasification agent opening may then be provided at each step or layer such that gasification agent passes underneath the lower edges of the outer shield plates of each step or layer. Breaker ribs may be provided on portions of the pillar and the first grate component which define between them the first portion of the second discharge passageway.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings.

In the drawings,

FIGURE 1 shows a vertical sectional view of part of a fixed bed coal gasifier installation according to the invention; and FIGURE 2 shows, in part section, a three-dimensional view of the grate of Figure 1, with portions omitted for clarity.

In the drawings, reference numeral 10 generally indicates a fixed bed coal gasifier installation, according to the invention.

The installation 10 includes a gasifier, generally indicated by reference numeral 12. The gasifier 12 comprises a circular section cylindrical outer wall 14, as well as a similar cylindrical inner wall 16 spaced from the outer wall 14 such that a cavity or space 18 is provided between the walls 14, 16. In use, a suitable cooling medium, such as water, will circulate through the space 18.

The upper ends of the walls 14, 16 are closed off with a roof (not shown) fitted with suitable coal feed means (not shown) such as a valve operated chamber for feeding coal in batchwise fashion, from atmospheric conditions to high pressure, by pressurizing and de-pressurizing cycles.

The gasifier 12 also includes an inwardly tapering outer floor 20 which is attached to the lower end of the wall 14, as well as an inner floor 22 which is attached to the wall

16. The space 18 is thus maintained between the floors 20, 22. In the zone where the floor 22 is attached to the wall 16, a support component, generally indicated by reference numeral 24, is provided. The support component 24 has a horizontally located circumferentially extending radially inwardly protruding portion 26, providing an upper horizontal ash collection surface 28, as well as a portion 30, also extending circumferentially, located between the inner periphery of the portion 26 and the upper end of the floor 22.

An inner stationary support structure, generally indicated by reference numeral 32, protrudes inwardly from the floor 22 and has a cylindrical component 34 through which extends a gasification agent feed line or conduit 35 which leads from a supply of the gasification agent. The gasification agent is thus typically a mixture of oxygen and steam. A support plate 36 is mounted on the support structure 32 and the component 34.

The installation 10 also includes a grate, generally indicated by reference numeral 40, located inside the wall 16, at the lower end of a gasification chamber 42 defined by the wall 16.

The grate 40 comprises a first outer rotatable grate component, generally indicated by reference numeral 43, as well as a second stationary inner grate component, generally indicated by reference numeral 44.

The stationary grate component 44 comprises an upright pillar 46 mounted to the support plate 36. The pillar 46 has a central gasification agent passageway 48 which has an inlet at the lower end of the pillar, with the inlet being in communication with the gasification feed line 35; however, the upper end of the passageway 48 is closed off with a venturi structure 50 to prevent ash intrusion into the passageway 48. The structure 50 comprises end plates 52 closing off the upper end of the passageway 48 against ash intrusion, and provided with a gasification agent outlet 54 for discharging gasification agent from the passageway 48 into a zone below a protective cap 56, with gasification agent then passing outwardly into the gasification chamber 42 along the lower peripheral edge of the cap 56, as indicated by arrows 58. A venturi 57 is located below the end plates 52, for creating a flow induced low pressure and serving to extract gasification agent leaking between the stationary inner grate component 44 and the outer rotatable grate component 43.

A number of circumferentially staggered stationary inner ploughs 60 protrude outwardly from the pillar 46. Breaker ribs 62 are provided around the upper portion of the pillar 46, ie the portion thereof between the ploughs 60 and the end cap structure 50.

A plurality of vertically and circumferentially spaced gasification agent passageways 64 are provided in the pillar 46 below the ploughs 60.

The outer rotatable grate component 43 comprises a hollow rotatable support structure 66 rotatably mounted to the pillar 46 by means of thrust bearings 68 and journal bearings 70 and 72. The support structure 66 includes a ring gear 74 engages a pinion gear (not shown) mounted to an output shaft of a gearbox (not shown) driven by a variable speed electric motor (not shown) for driving the grate component 42 to rotate, typically at between 2 and 12 rph. Two sets of the pinion gears, gearboxes and motors are provided.

The interior of the support structure 66 is in communication with the passageways 64 in the pillar 46. The outer surface of the grate component 43 is of conical form, being stepped or staggered, so as to provide four 'layers', generally indicated by reference numerals 76, 78, 80 and 82 respectively, with the layer or portion 76 having the largest diameter and the layer or portion 82 having the smallest diameter. Each step or layer 76 to 82 comprises a plurality of circumferentially arranged outer shield plates 84 located in abutting or overlapping relationship. The shield plates 84 in each layer or step slope upwardly inwardly. The angle of the outer surface of the grate component 42, as defined by the shield plates 84, is in the region of 55° to the horizontal, ie greater than the angle of repose of ash which is about 35° to the horizontal. By 'angle of repose' is meant the angle of maximum incline at which a heaped mass of loose coal ash will be stable with no particles sliding down this incline.

The shield plates 84 in the layers or portions 76 and 78 are mounted to a lower support ring 83 forming part of the grate component 43, while the shield plates in the layers or portions 80 and 82 are mounted to an upper support ring 85 also forming part of the grate component 43. Each support ring typically comprises three segments which are attached together.

Circumferentially extending gasification agent outlets are provided in the grate component 43 such that the gasification agent can flow underneath the lower edges of the outer shield plates 84 at each level or step, as indicated by arrows 86. The configuration of the shield plates thus ensures the gasification agent flow and also prevents ash intrusion into the grate component 43. An additional circumferential gasification agent outlet 88 is provided at the upper end of the grate component 43 so that gasification agent can also be distributed therethrough as indicated by arrow 90.

Additionally, gasification agent can pass between the rotating support structure 66 and the stationary pillar 46, via a join line 92, also to be discharged through the venturi 57 and the structure 50.

The support structure 66 includes an annular floor plate 93 immediately below the lower edges of the ploughs 60 so that ploughs act as scrapers as the plate rotates below them, in use .

An inner breaker ring 95, having ribs 94, is provided around an upper portion of the support ring 85, while an outer breaker ring 98, having ribs 96, is provided on the support structure 66.

Three circumferentially spaced outer ploughs 100 are attached to the outer grate component 42 and are arranged such that they pass with limited clearance over the ash collection surface 28 of the component 26.

A first ash discharge passageway 102 is defined between the wall 16/support component 24 and the grate component 43. The first ash discharge passageway 102 comprises a first annular portion 104 defined between the shield plates 84 of the grate component 43 and the wall 16, as well as a second portion 106 protruding radially inwardly from the lower end of the portion 104, along the surface 28 and along a wear plate 108.

The wear plate 108 protrudes inwardly from the component 26, and is provided with a collar portion 110, which is also fitted with breaker ribs 112.

The breaker ribs 62 and breaker ring 94 define between them a first cylindrical portion 116 of a second ash discharge passageway 114. The passageway 114 also has a second portion, generally indicated by reference numeral 118, protruding radially outwardly from the lower end of the portion 116, as well as a third annular portion, generally indicated by reference numeral 120, which is in communication with the portion 118.

The breaker rings 96, 112 define between them an annular ash discharge passageway, generally indicated by reference numeral 122, into which ash is discharged from the portion 106 of the passageway 102. The portion 120 of the passageway 114 also discharges ash into the ash discharge passageway 122.

It will be appreciated that ash discharged through the passageways 102, 114 and 122, which are thus in proximity to or adjacent the floors 22, falls into a floor zone of the gasifier 12 and is discharged through an ash outlet (not shown) provided at the lower end of the gasifier.

In use, the gasifier 12 is operated by feeding coal batchwise into the top thereof through the coal feed means while injecting gasifying agent as hereinbefore described continuously into the bottom of the reaction zone through the gasification agent outlets as hereinbefore described, thereby to gasify coal located in a slow moving bed within the gasification chamber 42. Ash is continuously withdrawn from the bottom of the gasification zone by the rotation of the gasifier component 43 which leads to the ploughs 100 continually rotating and discharging ash through the passageway 102. Simultaneously, ash is discharged through the passageway 114.

Typically, about 20% of the ash is removed through the passageway 114, and about 80% through the passageway 102. As the grate component 43 rotates, clinker crushing is performed between the breaker ribs 62, 94, between the shield plates 84 and the wall 16, and between the breaker ribs 96 and 112, as hereinafter described in greater detail. The shield plates 84 also protect the grate 40 against wear and high ash temperatures. By 'clinker' is meant a solid agglomerate of melted ash which needs to be crushed to enable it to be extracted from the gasifier.

About 10% of the total gasifying agent passes into the gasification chamber 42 underneath the end cap arrangement 50, about 10% along arrow 90, about 20% through the circumferential outlet underneath the lower edges of the outer shield plates 84 in the layer or portion 82, about 25% through the similar outlet in the layer or portion 80, and about 35% through the similar outlet in the layer of portion 78. The gasification agent also serves to cool the grate components, such as the outer shield plates 84, as it passes through the rotating grate component 43.

The ash withdrawal proportions through the passageways 102, 114 and the gasification agent proportions through the various outlets, as given above, are balanced according to the annular cross-sectional areas immediately above the agent outlets and the ash discharge passageways.

By, amongst others, controlling the rate of ash withdrawal, the interface (not shown) between a coal ash bed located towards the bottom of the chamber 42 and the coal bed which will thus be located above the interface, is maintained at a desired position. A fire bed thus constitutes this interface .

Ideally, for good gasifier control, the fire bed should be in a more-or-less horizontal line across the gasification zone, thereby indicating uniform or mass flow withdrawal of ash across the entire cross-section of the gasification chamber 42, ie uniform ash withdrawal with uniform ash particle velocity. In other words, the fire bed profile should, ideally, be stable, flat and in equilibrium. There should be no vertical movement or displacement of the fire bed, ie it should be located in a fixed position within the gasifier, and the fire bed thickness should be uniform across the gasification zone. The gasification agent should, ideally, move upwardly on a mass flow basis, ie be distributed uniformly throughout the cross-section of the reactor and have a uniform velocity throughout the cross-section.

However, with a known grate in which all the ash is extracted along the periphery of the gasification chamber, ie along the inner wall of the gasifier, the fire bed profile is normally unstable and non-symmetrical, ie does not have an equilibrium W-shaped profile. Additionally, the level of the fire bed is often not fixed or stable, and there is often extensive vertical variation in the position of the fire bed. The fire bed thickness varies across the diameter of the reactor, typically being relatively thin at the centre of the gasification chamber. Still further, although the gasification agent is normally distributed across the cross-sectional area of the gasification chamber at the bottom thereof, channelling of the gasification agent towards the periphery of the reaction chamber is experienced. In other words, an annular distribution of the gasification agent in a peripheral zone of the reaction chamber is experienced since ash is only extracted along the periphery. As indicated, the known grate only employs outer ploughs, ie ploughs moving along the periphery of the gasification chamber. The outer surface of the grate tapers upwardly inwardly at a general angle which is smaller than the angle of repose of coal ash. All these factors contribute to gasifier operation being difficult to control, and hence loss of gasifier efficiency is experienced with the known grate .

It is believed that, with the method and installation of the present invention, the fire bed profile will be stable and symmetrical, being of flattened -shape. In other words, it will have an equilibrium profile. It is also anticipated that the fire bed level will move within a restricted narrow vertical band and hence be stable, while it will also be of more uniform thickness. It is also expected that the gasification agent will be distributed upwardly on an approximated mass flow basis, while ash extraction will similarly take place on an approximated mass flow basis downwardly, when about 20% of the ash is removed through the passageway 114 and about 80% thereof through the passageway 102. It is believed that up to six of the outer ploughs 100 can be used while up to four of the stationary ploughs 60 can be used. Still further, the outer surface of the grate component 42, as provided by the shield plates 84, is about 55° to the horizontal, ie greater than the angle of repose of ash. This will promote ash, which abuts the shield plates 84, moving downwardly towards the periphery to be removed by the ploughs 100 rather than creating stagnant zones as is experienced with the known grate hereinbefore described.

As regards fire bed equilibrium, on evaluation of a theoretical single element of the fire bed, it is in equilibrium if the upward burning velocity (V_u) and the downward ash extraction velocity (V_d) thereof are equal in magnitude and opposite in direction. Thus, to obtain an in equilibrium fire bed, on evaluation of the total cross-sectional area of the fire bed, all the fire bed elements must be acted upon in the equilibrium manner described. This will ensure a stable, flat, uniform and in-equilibrium fire bed, which is characterized by uniform gasification agent distribution and uniform mass flow ash extraction.

It is thus clear that if V_d is greater than V_u or V_u is greater than V_d, the fire bed equilibrium will be subjected to an overall downward or upward movement, depending on which value is greater. With the known grate, 'orifice' extraction areas are created directly behind the rotating ploughs. With reference to a particular point in the periphery of the ash bed, the fire bed is thus displaced downwardly when that particular point falls within the 'orifice' area immediately behind the plough. However, as the plough then moves further away from that point, the fire bed again burns upwardly. Thus, the fire bed height or level varies continuously in a zig-zag fashion. In other words, the ash extraction pattern is characterized by a period of constant burning up of the fire bed (zero ash extraction with only crushing of the ash being performed between the grate and the wall of the gasification chamber) followed by a sudden extraction of ash ('orifice' extraction, zone of relaxation of forces) . This sudden ash extraction is of such a nature that the total of the fire bed burning up distance is equal to the downward ash extraction distance. This action is thus characterized by relatively high local extraction velocities .

The vortices created by this orifice extraction mechanism are opposite in direction to the rotational direction of the grate. The mechanism can thus be described as a localized 'hole' in which ash is extracted downwardly with decreasing vortex angular velocity from bottom to top.

The fire bed profile is still in equilibrium as regards V_d and V_u but the ash layer is not of uniform thickness/height due to the orifice extraction being effected only at the periphery. This is due to the fact that less ash is removed from the central area than is removed at the periphery with the known grate.

Moreover, in practice, it is found that the fire bed is often not in equilibrium, ie the rate at which the fire bed burns upwardly and the rate at which ash is extracted at a particular point is not balanced. This is due to, it is believed, local arching/bridging of an 'orifice' resulting in little or no extraction at that point, but still with constant burning up of the fire bed. This results in an unstable uncontrollable and ineffective fire bed. By 'arching' is meant the mechanical mechanism of ash particles or clinkers attaching together in such a way to inhibit or disturb the ash flow pattern. Chemical reaction can promote this phenomenon. By 'bridging' is meant two or more ash particles locking together, and is considered an extreme case of arching.

Furthermore, an inner zone in the coal bed at the centre of the gasification zone is very stable, with a stabilized in-equilibrium fire bed in the upper part of the reaction chamber and whose equilibrium height is hardly influenced by grate speed and gasification agent supply variations, ie a stable but uncontrollable by grate performance, condition. The outer annular zone between the central zone and the wall of the reactor is, in contrast, an unstable zone in which the fire bed height is not in equilibrium, is not symmetrical on a vertical section and whose height changes randomly over the reactor height .

Furthermore, with the known grate as hereinbefore described, due to, amongst others, the flat angle of the outer surface of the grate, little or no primary crushing of clinkers is experienced, with only secondary crushing being experienced. This results in ineffective ash extraction and by-passing of the ploughs. By 'secondary crushing' is meant crushing performed between the lowermost shield plate ring or layer and the reactor shell or wall, while by 'primary crushing' is meant crushing performed between shield plate rings or layers located above the lowermost shield plate ring or layer, and the reactor shell or wall. With the known grate, the ineffective primary crushing is due to the fact that the angle which the outer surface of the grate forms with the horizontal, ie the grate angle, is smaller than the angle of repose of the ash. Additionally, a 'dead zone' is formed between the angle of repose of ash

(about 35° to the horizontal) and the grate surface angle

(typically 30° to the horizontal). This 'dead zone' provides a cushioning effect contributing to ineffective primary crushing. Thus, reliance is placed wholly on secondary crushing which is, however, ineffective. Additionally, there is a constant ash and clinker bridging problem, which causes a difference between the theoretical ash downward flow velocity and the actual ash withdrawal velocity experienced, depending on whether there is partial or total bridging. This bridging can be experienced up to 1 meter above the ploughs.

The nett result of these effects is that there are relatively small forces driving ash downwardly and inwardly, while there are considerable forces driving the ash upwardly and over the ploughs, ie by-passing the ploughs, causing extensive wear on the ploughs and bottom shield plates located below the ploughs. Additionally, horizontal forces acting on the 'orifice' area cause an increase in the amount of bridging/arching experienced in and around the 'orifice' area, ie a choking effect is thereby caused.

These factors contribute to providing a fire bed which is unstable, non-uniform, partially not in-equilibrium and which is uncontrollable by grate and gasification agent control as also hereinbefore described.

It is believed that with the grate 40, and with which peripheral as well as central ash extraction is effected, effective primary crushing, in which clinkers are crushed in stages, will be effected, due to the grate angle being greater than the angle of repose of ash. This applies to both the inner or central breaker rings 94, as well as the outer breaker or crusher rings constituted by the 'layers' 76, 78, 80 and 82 of outer shield plates 84. Additionally, there is no 'dead zone' since the grate angle, typically about 55° to horizontal, is greater than the angle of repose of ash which, as mentioned hereinbefore, is about 35° to the horizontal. The breaker rings are thus placed positively into the active or live ash region of the ash bed. It is also envisaged that little, if any, ash arching and clinker bridging will be experienced, resulting in little or no difference between the theoretical ash withdrawal velocity and the actual ash withdrawal velocity. If any bridging does take place, it is believed that it will be limited to a distance of no more than about 200mm above the outer ploughs 100, and that there will be very little or no segregation of ash and clinker particles. It is further believed that with the grate 40, gasification agent distribution will be substantially more uniform, and that there will thus be a more uniform upward velocity component of the fire bed, due to the agent being distributed in a less segregated mass flow moving ash bed both at the periphery and the centre of the grate 40.

Thus, with the grate 40, it is believed that there will be relatively large forces driving the ash downwardly and inwardly in the region of the ploughs 100, 60, while there will be relatively small forces driving ash upwardly and over the ploughs, resulting in less wear on the ploughs and the outer shield plates 84. Additionally, the wear is spread over all the shield plates, and there will in any event be a lower propensity for wear due to the fact that 20% of the ash passes through the ash passageway 114 and thus does not pass over the wear plates 84. There are substantially smaller horizontal forces acting on the 'orifice' area, resulting in a decrease in the amount of bridging/arching experienced in and around the 'orifice' area. It is to be appreciated that the rotating outer ploughs 100 as well as the stationary inner ploughs 60 create extraction of 'orifices' in both central and peripheral zones of the ash bed. It is believed that this will result in a much better approximation of idealized mass flow ash extraction and thus an improved fire bed profile as hereinbefore described. Additionally, the ash and fire bed of the gasifier 12 will generally be more stable, resulting in more effective gasifier operation.

Claims

CLAIMS :

1. A method of discharging solid particulate material from a bulk vessel or container containing the material, which method comprises discharging solid particulate material from the vessel or container through an annular first discharge passageway in or adjacent a floor of the vessel or container; and simultaneously discharging solid particulate material from the vessel or container through a second discharge passageway in or adjacent the floor.

2. A method according to Claim 1, wherein the second discharge passageway is at least partly of annular form, with at least a portion thereof being located concentrically within at least a portion of the first passageway, when seen in plan view.

3. A method according to Claim 2, wherein portions of the first passageway are located at different levels, as are portions of the second passageway, and wherein at least a portion of the first passageway is located at a different level to at least a portion of the second passageway.

4. A method according to Claim 2 or Claim 3, wherein the discharging of the material through the first passageway is effected by passing at least one primary scraper or plough over a stationary material collection surface in the first passageway, with the primary plough urging the material inwardly or outwardly along the collection surface, and with the movement of the primary plough over the surface being effected by rotating it about a vertical axis extending centrally along the first passageway.

5. A method according to any one of Claims 2 to 4 inclusive, wherein the discharging of the material through the second passageway is effected by rotating a first discharge component relative to a second stationary discharge component, with the second passageway being provided between the discharge components.

6. A method according to Claim 5, wherein the second stationary discharge component is centrally located with the first discharge component thus rotating around the second discharge component, and with the material passing downwardly along a first annular portion of the second passageway, then radially outwardly along a second portion of the second passageway, before passing downwardly again through a third annular portion of the second passageway and which joins the first passageway.

7. A method according to Claim 6, wherein the radially outward distribution or passage of the material along the second portion of the passageway is effected by means of a secondary plough or scraper protruding outwardly from the second discharge component into the second portion of the passageway.

8. A method according to any one of Claims 5 to 7 inclusive, wherein the solid particulate material is ash produced in a fixed bed coal gasifier, with the vessel being a gasifier defining a gasification chamber, and the discharge components being grate components.

9. A bulk material vessel installation, which comprises a vessel having a floor and wall(s) protruding peripherally upwardly from the floor; an annular first discharge passageway through which solid particulate material can be discharged, in or adjacent the floor of the vessel; a second discharge passageway through which solid particulate material can simultaneously be discharged, in or adjacent the vessel floor; and control means for controlling the rate of discharge of solid particulate material through the first and second passageways .

10. An installation according to Claim 9, wherein the second discharge passageway is also at least partially of annular form, with at least a portion thereof being located concentrically within at least a portion of the first discharge passageway, when seen in plan view.

11. An installation according to Claim 10, wherein the wall is of circular cylindrical form, with a support component, providing an upwardly directed material collection surface, protruding radially inwardly from the wall, and located in the first passageway, with the control means including a first rotatable discharge component, which is rotatable about the vertical axis of the first passageway, and at least one outer or primary plough or scraper protruding from the first discharge component and adapted to direct material inwardly from the collection surface as the first discharge component rotates .

12. An installation according to Claim 11, wherein the second passageway is defined between the first discharge component and a second stationary central discharge component, with the second passageway comprising a more-or-less annular first portion, a second portion extending radially outwardly from the lower end of the first portion, and a third annular portion in communication with the second portion, and with the second stationary central discharge component comprising a central pillar and at least one stationary inner or secondary plough protruding outwardly from the pillar into the second portion of the passageway.

13. A method of discharging ash from a fixed bed coal gasifier, which method comprises discharging ash from a gasification chamber of a fixed bed coal gasifier, through an annular first discharge passageway adjacent a floor of the gasification vessel; and simultaneously discharging ash from the chamber through a second discharge passageway adjacent a floor of the gasification chamber.

14. A method according to Claim 13, wherein the second discharge passageway is at least partly of annular form, with at least a portion thereof being located concentrically within at least a portion of the first passageway, when seen in plan view.

15. A method according to Claim 14, wherein portions of the first passageway are located at different levels, as are portions of the second passageway, and wherein at least a portion of the first passageway is located at a different level to at least a portion of the second passageway.

16. A method according to Claim 14 or Claim 15, wherein the discharging of the ash through the first passageway is effected by passing at least one primary scraper or plough over a stationary ash collection surface in the first passageway, with the primary plough urging the ash inwardly or outwardly along the collection surface, and with the movement of the primary plough over the surface being effected by rotating it about a vertical axis extending centrally along the first passageway.

17. A method according to any one of Claims 14 to 16 inclusive, wherein the discharging of the ash through the second passageway is effected by rotating a first grate component relative to a second stationary grate component, with the second passageway being provided between the grate components .

18. A method according to Claim 17, wherein the second stationary grate component is centrally located with the first grate component thus rotating around the second component, and with the ash passing downwardly along a first annular portion of the second passageway, then radially outwardly along a second portion of the second passageway, before passing downwardly again through a third annular portion of the second passageway and which joins the first passageway.

19. A method according to Claim 18, wherein the radially outward distribution or passage of the ash along the second portion of the passageway is effected by means of a secondary plough or scraper protruding outwardly from the second grate component into the second portion of the passageway.

20. A fixed bed coal gasifier installation, which comprises a gasifier having a floor, a roof spaced from the floor, and a circular cylindrical wall between the floor and roof, with a coal inlet in the roof and an ash outlet in the floor, and with the vessel defining a coal gasification chamber; an annular first ash discharge passageway, adjacent the floor, through which ash can be discharged from the gasification chamber; a second ash discharge passageway, adjacent the floor, through which ash can also be discharged simultaneously from the gasification chamber; and control means for controlling the rate of discharge of ash through the first and second passageways.

21. An installation according to Claim 20, wherein the second discharge passageway is also at least partially of annular form, with at least a portion thereof being located concentrically within at least a portion of the first discharge passageway, when seen in plan view.

22. An installation according to Claim 21, wherein the wall is of circular cylindrical form, with a support component, providing an upwardly directed ash collection surface, protruding radially inwardly from the wall, and located in the first passageway.

23. An installation according to Claim 22, wherein the control means comprises a grate which includes a first rotatable grate component and a second stationary central grate component, with the first grate component being rotatable about the vertical axis of the first passageway, and with a second passageway being defined between the first grate component and the second grate component.

24. An installation according to Claim 23, which includes at least one outer or primary plough or scraper protruding from the first grate component and adapted to direct ash inwardly from the collection surface as the first grate component rotates.

25. An installation according to Claim 24, wherein the second passageway comprises a more-or-less annular first portion, a second portion extending radially outwardly from the lower end of the first portion, and a third annular portion in communication with the second portion, while the second stationary central grate component comprises a central pillar and at least one stationary inner or secondary plough protruding outwardly from the pillar into the second portion of the passageway.

26. An installation according to Claim 25, wherein a plurality of the outer ploughs, staggered or spaced apart about the rotational axis of the first grate component, and a plurality of the stationary inner ploughs, staggered or spaced apart about the pillar, are provided.

27. An installation according to Claim 26, wherein the pillar includes a gasification agent passageway, extending along its length, with the lower end of the passageway being open at the lower end of the pillar and being connected, by means of a conduit, to a supply of the gasification agent; at least one gasification agent outlet at or in proximity to the upper end of the pillar protruding into the gasification chamber, with this outlet being in communication with the first portion of the second passageway,- and at least one further gasification agent outlet in the pillar between its ends, the further outlet being in communication with the first passageway.

28. An installation according to Claim 27, wherein the first grate component comprises a hollow support structure rotatable about the pillar, with the further gasification agent outlet in the pillar being in communication with the hollow interior of the first grate component; an outer shield covering at least a portion of the support structure; and at least one gasification outlet in or adjacent the outer shield, for discharging gasification agent from the inside of the support structure into the gasification chamber as the first grate component rotates about the pillar.

29. An installation according to Claim 28, wherein the outer surface of the outer shield of the first grate component tapers upwardly inwardly from the outer ploughs, with the angle which the outer surface forms with the horizontal being greater than the angle of repose of coal ash.

30. An installation according to Claim 29, wherein the outer surface of the first grate component is staggered or stepped when seen in vertical cross-section, with each step or layer comprising a plurality of outer shield plates arranged circumferentially in abutting or overlapping relationship and sloping upwardly inwardly, with the different layers of shield plates thus together constituting the outer shield, and a circumferential gasification agent opening being provided at each step or layer such that gasification agent passes underneath the lower edges of the outer shield plates of each step or layer.

31. An installation according to any one of Claims 25 to 30 inclusive, wherein breaker ribs are provided on portions of the pillar and the first grate component which define between them the first portion of the second discharge passageway.

32. A novel method of discharging solid particulate material from a bulk vessel or container containing the material, substantially as described and illustrated herein.

33. A bulk material vessel installation, substantially as described and illustrated herein.

34. A method of discharging ash from a fixed bed coal gasifier, substantially as described and illustrated herein.

35. A fixed bed coal gasifier installation, substantially as described and illustrated herein.