Solid Fuel Combustion Apparatus

Abstract

Combustion apparatus for burning solid fuel in particulate or divided form includes a plurality of air-permeable floor elements e.g., trays or membranes arranged within a housing. Each element is provided for supporting a fluidized bed of the solid fuel and in one form is inclined to assist the passage of material along the element. In another form of apparatus each element is horizontal and the passage of material along the tray is effected by the buildup of a hydraulic gradient between the feed end and the discharge end of each element. Gas-operated means are located adjacent the discharge end of one element and to feed end of an adjacent element, and are provided for transferring solid material from one element to an adjacent element. The elements may be in side-by-side relationship or they may be arranged one above the other, adjacent trays being either oppositely inclined relative to one another or horizontal and mutually parallel.

Description

This invention relates to apparatus for the combustion of solid fuels in particulate or divided form when in a fluidized bed, and in particular to the combustion of such fuel using a gaseous fluidizing medium, for example air, for the formation of the fluidized bed.

In the case where a large diameter bed is required, especially when the bed is shallow, it has been found that a fluidized bed ceases to be satisfactory as a means of contacting gas and solids under controlled conditions. This is especially true where uniform distribution of the solid feed through the system is important and where the fuel feed undergoes highly exothermic or endothermic reaction or where volatile primary reaction products react with the fluidizing gases.

One disadvantage of a large diameter shallow fluidized bed is that of insufficient lateral movement of the solid material. Such movement can be applied to the system by means of mechanical stirrers, although the use of such devices is limited.

It is an object of the invention to obviate the above mentioned disadvantages. For this purpose, according to the invention combustion apparatus includes a housing, a gas-permeable floor element located in the housing and adapted in use to support a fluidized bed of solid material in particulate or divided form, a gaseous fluidizing medium inlet means, a solid material inlet in the housing, a gaseous fluidizing medium outlet in the housing, and a heat exchanger located within the housing, wherein the invention comprises a plurality of said gas-permeable floor elements located within the housing, each element including a feed end and a discharge end, and gas-operated means in the form of a well adapted to raise said solid material from a location adjacent the discharge end of one element to the feed end of an adjacent element whereby material is deposited on the adjacent element.

Conveniently the floor elements may be in the form of inclined trays, and may be arranged at the same mean level and mutually parallel in the housing such that the discharge end of one element is adjacent the feed end of an adjacent element.

The trays may be positioned in close adjacency in the housing, adjacent trays being oppositely inclined relative to one another. Alternatively the trays may be horizontally disposed within the housing.

As an alternative the trays may be arranged at different levels with respect to one another within the housing, each tray being either oppositely inclined relative to the tray directly beneath it or horizontal.

The said gas-operated means may be in the form of a well, the solid material being caused to flow into and out of said well.

Conveniently the solids material feed to the apparatus may be introduced at the bottom of one or more of the said wells for the purpose of mixing and increasing the contact time between the solids material and the fluidizing gas; alternatively solids material may be introduced through a side wall of the said housing and deposited one or more of the trays.

Reference will now be made to the accompanying drawings in which:

FIG. 1 is a schematic plan view of a first embodiment of combustion apparatus according to the invention;

FIG. 2 is a schematic side view of a first embodiment of a detail of combustion apparatus of FIG. 1;

FIG. 3 is a schematic side view of a second embodiment of a detail of combustion apparatus of FIG. 1;

FIG. 4 is a schematic cross section of a second embodiment of combustion apparatus according to the invention;

FIG. 5 is a schematic cross section of a third embodiment of combustion apparatus according to the invention;

FIG. 6 is a schematic cross section of a fourth embodiment of combustion apparatus according to the invention; and

FIG. 7 is a schematic cross section of a fifth embodiment of combustion apparatus according to the invention.

In FIG. 1 a combustion apparatus for the fluidized bed treatment of solid materials includes a housing 1 having a rectangular cross section in which is located an air-permeable floor comprising a plurality of side-by-side trays 2- 10 separated by an assembly of baffles 11 to 18, which latter are so arranged that each tray 2- 10 is in material flow connection with only one other tray.

Each tray is inclined to the horizontal so as to induce a directional movement in any material introduced on the tray. The arrangement of the tray inclination is such that the lower or discharge end of any tray is located in the vicinity of the higher or feed end of the tray on to which it is to feed material.

The arrangement of the trays 2- 10 is such that the trays are all situated at a common mean level. Furthermore, the layout of the baffles, in conjunction with the inclinations of the trays defines a continuous flow path for material introduced onto the reactor. The arrows of FIG. 1 indicate the directions of material travel along the various trays.

The material is transferred from the discharge end of any tray to the feed end of the tray with which it is in flow communication by air-operated means schematically represented in FIG. 1 by a hatched rectangle 19, and described in detail in relation to FIG. 2 or 3.

In the embodiment shown in FIG. 2, the arrangement 19, includes a well 20 having one vertical wall 21 connecting with the lower end of one tray, a second vertical wall 22 connecting with the upper end of the adjacent tray and a floor 23 connecting the two walls. A baffle 24 extends into the well the lower end of the baffle being spaced from the floor 23. The floor 23 includes an inclined portion 25 connecting with the wall 21 and an air-permeable portion 26 connecting with the wall 22.

In operation the material at the lower end of a tray falls into the well 20, the inclined portion 25 guiding the material to the air-permeable portion. An airflow inlet schematically represented by the arrow 27 enters the well through the permeable floor portion and lifts material falling into the well upwards to deposit same on to the higher end of the adjacent tray.

Conveniently, the supply of material for combustion, is distributed to each tray, and is conveniently fed pneumatically to the air-operated means so that the air of the pneumatic feed contributes to the airlift. The coal feed to the well 20 is represented by the arrow 28.

The unburnt coal and ash resulting from combustion flows down the associated tray by gravity to the lower end of the tray where it discharges into the well associated with this particular lower end. Fines material, which is elutriated from the bed is collected in a conventional cyclone or cyclones (not shown) and returned to the wells by means of dip legs (not shown) from the cyclones.

Ash removal from the system is effected from one or more wells, prior to the coal feed and any fines return positions.

Heat exchange from the combustion of material to a working fluid is conveniently effected by an assembly of heat exchange tubes (not shown) which are located within the beds, said tubes running parallel to the direction of ash movement lengthwise of the trays.

When it is desired to maintain consistent material flow under conditions of bed segregation on the trays 2 to 10 the well arrangement of FIG. 3 may be used. In this arrangement a baffle 29 is provided in each well. Each baffle 29 extends downwards to a predetermined distance above the floor of the adjacent tray lower end, and extends upwards to a level which is a predetermined distance below the required bed height. A short air-permeable floor portion 30, which extends across the full width of the tray, connects with the vertical wall 21. In use the flow of material under the baffle 29 is controlled by variation of the airflow rate through the floor portion 30 so that a continuous stream of material is caused to flow over the top of the baffle 29. In the FIGS. 2 and 3 the level of the beds in the trays is shown by the dashed lines 31 and 32 in the upper and lower trays respectively.

In the embodiment shown in FIG. 1 the trays are inclined but the invention also includes combustion apparatus wherein such trays are horizontally disposed in the housing.

The above described combustion apparatus is of particular application to fluidized combustion in shallow beds. The reactor may also be applied to a process in which low (shallow) beds are desirable and where exothermic or endothermic reaction occurs between the solid feed and the fluidizing gas.

The apparatus of FIG. 4, includes a housing 1 with a top 2, a base 3, end walls 4 and 5 and sidewalls 6 (only one shown). An air permeable floor or membrance 7 extends across the lower region of the housing 1. The upper end of the membrane 7, which is inclined to the horizontal, connects with a gas-permeable element 8, which is itself connected to the end wall 4. The lower end of the membrane 7 is connected to a vertical wall 9 extending between the sidewalls 6. The mounting of the membrane 7 is such as to form a wind box 10. An opening 11 is provided in the end wall 4 for the admission of air into the wind box 10.

A second air permeable floor or membrane 12 is located above and spaced from the membrane 7. The membrane 12 is inclined to the horizontal in the opposite sense to the inclination of the membrane 7. The upper end of the membrane 12 is connected to a vertical wall 13 and the lower end of the membrane 12 is connected to a vertical wall 14 adjacent to the inner edge of the element 8. The bottom edge of the wall 13 extends between the sidewalls 6.

A horizontal wall 15 extends from the wall 9 to the end wall 5, this wall 15 being spaced from the lower edge of the wall 13. The wall 15 defines with the lower portion of the wall 5, and upper portion of the wall 9 a well 16, and with the lower portion of the wall 5, the lower portion of the wall 9 and the base 3, a wind box 17. The wall 15 has a permeable portion 18 through which air from the wind box 17 can enter the well 16. An air inlet 19 communicates with the wind box 17.

A heat exchange or acceptor arrangement is provided within the housing 1. The heat exchanger comprises an assembly of tubes, for a heat exchange fluid such as water, the tubes are schematically represented by dashed lines 20 which illustrate the locus of the tubes.

The above described apparatus operates as follows:

Fuel to be combusted is introduced through an inlet 21 in one of the sidewalls 6 of the housing and falls on to the higher end of the membrane 7. A gaseous reaction media such as air is introduced through the opening 11 into the wind box 10 at such a volumetric throughput and pressure that fluidizing conditions are produced above the membrane 7 and the coal is caused to react with the air. Initially, the gaseous media is preheated in order to raise the temperature of the fuel to that required for combustion. By reason of the inclination of the membrane 7 any material on the membrane will travel along the membrane towards the lower end. The combustion of the fuel produces heat which is transferred to the fluid in the heat exchange arrangement. At the lower end of the membrane 7 the material (coal, coke, ash) falls into the well 16. A flow of air is introduced through the wall portion 18 from the wind box 17 to entrain this material and lift it upwards between the walls 5 and 13 and drop the lifted material onto the higher end of the upper membrane 12. The gases above the membrane 7 pass through the membrane 12 to produce fluidizing conditions above the membrane 12. As the material travels along the membrane 12 combustion of the fuel is completed and further heat is given to the upper bank of tubes of the heat exchange arrangement. At the lowermost end of the membrane 12 the material which is by now substantially wholly ash falls onto the element 8. Some of this ash is caused to pass out from the housing through an ash outlet 22, by a controllable flow of air through porous membrane 8, to maintain a constant recycle ash burden within the reactor. The flue gases arising from the combustion leave the housing through a flue 23.

In FIG. 5 those elements which are similar to those shown in FIG. 4 are identified by similar reference numerals. The embodiment of FIG. 5 essentially consists of three pairs of the oppositely inclined membranes 7 and 12 arranged one above the other, together with the associated wind box constructions for elevating the material travelling lengthwise of a membrane to the membrane immediately above. For convenience suffices A, B and C will be applied to elements associated with the successive pairs of membranes.

An arrangement of walls similar to that defined by the walls 9, 13, 15, 18 (in FIG. 4) is located at the lower end of each membrane so that material falling from the lower end of a membrane may be elevated, as previously explained, to the next higher membrane.

In the apparatus of FIG. 5, the ash which remains at the lower end of the uppermost membrane 12C is recycled as schematically shown by arrow 24. The air used for elevating material from a lower membrane to a higher membrane is introduced through inlet means 25 at the left-hand side of the drawing and through inlet means 26 at the right-hand side of the drawing, each of the inlet means communicating with associated inlets similar to the inlet 19 of FIG. 4.

Coal, coke or other fuel is introduced at an inlet 21 adjacent the higher end of the lowermost membrane 7A. With this arrangement the hottest part of the apparatus is within the chamber between the membranes 7A and 12A, so that as the gases travel upwards through the successive membranes, the gases are cooled. The fluid flow through the heat exchange arrangement is from the higher membrane downwards to the lowermost membrane 7A, with the outlet from the heat exchange arrangement 20 located adjacent to the lower end of the membrane 7A.

The gases passing through the membrane of FIG. 5 are progressively cooled by reason of the heat exchange with the heat exchange tubes 20, and are finally discharged from the apparatus at the flue 23.

In the apparatus of FIG. 5 the coal, coke or other fuel may be introduced onto any selected one of the membranes or onto more than one of the membranes.

In FIG. 6 those elements which are similar to those shown in FIG. 4 are identified by similar reference numerals. The embodiment of FIG. 6 is substantially the same as that shown in FIG. 4, but differs from the second embodiment of FIG. 4 in that the membrane 7' and the membrane 12' are horizontal. The passage of material along the membranes is effected by build up of a hydraulic gradient from the feed end to the discharge end. The term `hydraulic gradient` as used herein means a difference between the head of material at the feed end and the head of material at the discharge end, the latter being less than the first-mentioned head such that material passes from the feed end to the discharge end under the action of the head of material at the feed end.

In FIG. 7 those elements which are similar to those shown in FIG. 5 are identified by similar reference numerals. The fifth embodiment shown in FIG. 7 is substantially the same as the third embodiment of FIG. 5 but differs from the third embodiment in that the membranes 7A', 12A', 7B', 12B', 7C', 12C' are all horizontal. As in the apparatus of FIG. 6 the passage of material along the membranes is effected by the build up of a hydraulic gradient from the feed end to the discharge end.

During the transit of the coal/coke/ash through the apparatus heat is given up to the heat exchanger tubes, whereby any fluid within the tubes is heated.

Claims

We claim:

1. Combustion apparatus comprising a housing, a gas-permeable floor element located in the housing and adapted in use to support a fluidized bed of solid material in particulate or divided form, a gaseous fluidizing medium inlet means, a solid material inlet in the housing, a gaseous fluidizing medium outlet in the housing, and a heat exchanger located within the housing, a plurality of said gas-permeable floor elements located within the housing, each element including a feed end and a discharge end, and gas-operated means in the form of a well adapted to raise said solid material from a location adjacent the discharge end of one element to the feed end of an adjacent element whereby material is deposited on the adjacent element.

2. Apparatus according to claim 1 wherein the floor elements are mutually parallel and are arranged at the same mean level within the housing, such that the discharge end of one element is adjacent the feed end of an adjacent element.

3. Apparatus according to claim 2 wherein the floor elements are positioned in close adjacency, adjacent elements being oppositely inclined relatively to one another, the lower end of each element forming the discharge end and the upper end of each element forming the feed end.

4. Apparatus according to claim 1 wherein the elements are arranged in close adjacency, the elements being horizontally disposed within the housing.

5. Apparatus according to claim 1 wherein the gas-operated means in the form of a well comprises a first wall connecting with the discharge end of an element, a second wall connecting with the feed end of an adjacent element, and a base interconnecting the first wall and the second wall, said base including an inclined portion connecting with the first wall and a gas-permeable portion connecting with the second wall.

6. Apparatus according to claim 5 wherein an inlet for solid material is provided in the base of the gas-operated means.

7. Apparatus according to claim 5 comprising a baffle extending into the gas operated means, the lower end of the baffle being spaced from the base of said means.

8. Apparatus according to claim 5, comprising a further baffle situated superjacent the discharge end of each floor element the baffle extending downwards to a predetermined distance above said end and extending upwards to a level which is a predetermined distance below the required bed height, and a short gas-permeable portion provided in each element adjacent the discharge end, whereby material flow under the further baffle is controlled by variation of gas flow rate through the portion so that a continuous stream of material is caused to flow over the top of the baffle.

9. Apparatus according to claim 1 wherein the floor elements are arranged at different levels with respect to one another.

10. Apparatus according to claim 9 wherein each element is oppositely inclined to the superjacent and the subjacent element.

11. Apparatus according to claim 9 wherein each element is horizontal and is parallel to the superjacent and the subjacent elements.

12. Apparatus according to claim 9 comprising an upper and a lower floor element, the lower element extending across the lower region of the housing, a gas-permeable member attached at one of its ends to an end wall of the housing end at the other end to the feed end of the lower element, a first vertical wall located within the housing, the discharge end of the lower floor element being connected to the first vertical wall.

13. Apparatus according to claim 12 comprising a second vertical wall extending between the side walls of the housing, and a third vertical wall adjacent the inner end of the gas-permeable member, the upper floor element being connected at its feed end to the second vertical wall and at its discharge end to the third vertical wall.

14. Apparatus according to claim 13 comprising a horizontal wall extending from the first vertical wall, and a gas-permeable portion in the horizontal wall, said horizontal wall together with the upper portion of the first vertical wall and the lower portion of the second vertical wall defining the gas-operated means in the form of a well.

15. Apparatus according to claim 12 comprising a material discharge outlet located above and adjacent the gas-permeable member, and a gas inlet located below and adjacent said member, the discharge end of the upper element being in a positional relationship with said member whereby, in use, material leaving the upper element falls onto the member and a part of the material is discharged through said outlet by means of the gas introduced through said gas inlet.

16. Apparatus according to claim 9 comprising two pairs of floor elements arranged one pair above the other.

17. Apparatus according to claim 16 wherein adjacent elements are oppositely inclined relative to one another.

18. Apparatus according to claim 16 wherein the elements are horizontally disposed within the housing.

19. Apparatus according to claim 16 comprising means provided on the uppermost element adapted for recycling material.