GB2109096A

GB2109096A - Locomotive boiler fired by fluidised bed combustion

Info

Publication number: GB2109096A
Application number: GB08122822A
Authority: GB
Inventors: Duncomb Wallace Walker
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-07-24
Filing date: 1981-07-24
Publication date: 1983-05-25
Also published as: GB2109096B

Abstract

A locomotive boiler containing a special firebox section 1 to use the fluidised bed combustion process to burn solid fuel comprises one or more separate open bottom water cooled chambers 21 or one or more separate open bottom sections of the firebox through which the combustion gases pass before entering small bore tubes 8 forming the remainder of the boiler heating surface. Water tubes 20 which pass through the firebox are provided as an additional heating surface. The passage provided for gas flow from the firebox section to the separate water cooled chambers or separate sections of the firebox is such that gas flow within the firebox section is always vertical or near vertical from the fluid bed surface. One, two or three parallel runs of return tubes can be provided connecting gas transfer chambers at each end of the boiler. <IMAGE>

Description

SPECIFICATION A new type of locomotive boiler for firing by fluidised bed combustion.

This invention is concerned with boilers of the locomotive type and provides for a new design of locomotive type boiler to burn coal or other solid fuel or liquid or gaseous fuels using the Fluidised Bed Combustion process.

Sketch I shows a typical traditional locomotive type boiler which has been used for many years in land based boiler installations and is essentially similar to locomotive type boilers used in Traction Engines, Steam Rollers and Railway Engines.

In order that the novelty and importance of this invention of a new type of locomotive type boiler can be clearly demonstrated the traditional type of locomotive boiler will first be described in some detail as follows with reference to Sketch I and Sketch II.

SKETCH I TYPICAL LOCOMOTIVE TYPE BOILER.

(1) Is the boiler firebox which is rectangular in plan view and usually has a greater length than width. The top plate of the firebox may be flat as shown or of semi-circular or elipsoidal form. The firebox has an open bottom into which firebars or other form of grate can be fitted.

(2) Is the external boiler shell which is normally semi-circular at the top but may be flat or elipsoidal. The boilder shell has flat sides extending downwards to form a water space (3) between the shell sides and the firebox sides.

(4) Is a flat end plate closing off the external boiler shell (2) at the rear end forming an extension of the water space (3) adjacent to the rear of the firebox.

(5) Is a flat end plate partially closing off the boiler shell (2) at the front and forming an extension of the water space (3) adjacent to the front of the firebox.

The flat end plate (5) contains a large dia.

aperture into which is fitted a cylindrical boiler shell extension (6). The boiler shell extension (6) is open at its rear end and closed off at its front end by a circular tube plate (7).

A number of small bore tubes (8) extend from the upper portion of the firebox front plate through the lower portion of the cylindrical shell extension (6) into the tube plate (7).

(9) is the normal water level within the boiler which is above the firebox (1) and above the small bore tubes (8) and extends along the length of the boiler from the rear end plate (4) to the front tube plate (7). (10) is the boiler steam space above the water level (9). (11) is a flat plate which joins the firebox (1) to the boiler shell (2) and to the end plates (4) and (5) closing off the bottom of the water space (3). (12) is a circular smoke box extension attached to the front of the cylindrical shell (6) and has an exhaust gas connection (13) located at the top. The smoke box extension is normally lined with an insulating material as shown at (14). (15) is a fixed grate on which coal or other solid fuel is burnt. Air for combustion passes up through the grate as indicated at (16).

Approximately 50% of the heat liberated by the combustion process is transferred to the boiler water, mainly by radiation through the walls and roof of the firebox (1). Hot gases from the combustion process pass from the firebox (1) into the small bore tubes (8) giving up further heat to the boiler water in traversing the length of the small bore tubes. The cooled combustion gases discharge into the smoke box extension (12) and pass through the exhaust gas connection (1 3) to a suitable chimney arrangement.

(17) is an aperture through the water space (3) through which coal is fed onto the grate (15) and through which additional air for combustion can be supplied.

SKETCH II TYPICAL LOCOMOTIVE TYPE FIR EBOX FITTED WITH AN OIL OR GAS BUR NER.

(18) is an oil or gas burner which is arranged to fire into the firebox (1 ) through the aperture (17).

A refractory floor (19) is used to protect the grate (15) from the radiant heat or can be used to replace the grate entirely.

The Fluidised Bed Combustion process consists of burning coal or other solid fuel or liquid or gaseous fuels in a bed of sand or other inert material such as crushed refractory. The mixture of fuel and bed material is fluidised by the upward passage of combustion air through the mixture, the air being injected by means of special nozzles in a base plate on which the mixture of fuel and bed material normally rests. The principle of a Fluidised Bed in operation is shown in Sketch Ill.

In order to take advantage of the characteristics of the Fluidised Bed Combustion process when this process is used to fire boilers it is necessary to arrange for part of the boiler heatingLsurface to be immersed within the bed. When this is done, high and consistent rates of heat transfer are obtained which results in more heat being transferred in a given volume of apparatus than with conventional firing. In addition the high rate of heat absorption from within the bed means that the combustion temperature of the fuel can be maintained at around 800 to 900"C. This is particularly important when firing coal as the fusion temperature of the coal ash is not attained, consequently the ash remains soft, of small particle size and not liable to impede the fluidisation process.

When using the Fluidised Combustion pro cess it is a matter of extreme importance to provide for a situation whereby the velocity of the combustion gases leaving the surface of the Fluid Bed is maintained in a substantially vertical direction.

If the gas velocity is constrained to adopt a horizontal or near horizontal direction in the space above the Fluidized Bed Surface then a number of significant disadvantages will exist.

(A) The particle matter of the bed and of the fuel in the bed will be entrained in the horizontal or near horizontal gas flow with a consequent tendency for a substantial proportion of the bed and fuel to migrate in the direction of the gas flow.

(B) The migration of the bed as described in (A) above leads to a variation in bed depth with a consequent variation in resistance to the fluidising air flow through the bed. This can progress to a state where there is severe blowing away of the bed at the shallow end and no effective fluidisation at the deep end.

(C) The gas flow acting across the bed surface will also entrain bed material including the fuel particles which may be unburnt or partially unburnt and the entrained material will be deposited elsewhere in the boiler or discharged from the boiler into the chimney system. This will significantly decrease the boiler efficiency and may require frequent cleaning of the boiler to remove deposited material.

Even when the gas flow velocity from the surface of the Fluidised Bed is maintained in a substantially vertical direction there is a considerable entrainment of ash and fine bed material. In any boiler employing small bore tubes which are horizontally inclined to extract heat from the combustion gases leaving the Fluidised Bed Combustion process- it is desirable to have some means of extracting the majority of entrained material before the combustion gases enter the small bore tubes.

From the above it will be appreciated that to use the Fluidised Bed Combustion process in the boiler firebox (1) as shown in Sketch I where the line 'X X' indicates the normal level that would be attained by a Fluidised Bed would not be practicable.

The new design of locomotive type boiler which is the subject of this invention incorporates a special arrangement of the firebox section which provides for boiler heating surface in the form of small bore tubes to be so positioned as to pass through the volume of the bed when the bed is being fluidised.

The special arrangement of the firebox section also provides for a substantially vertical gas velocity being maintained from the surface of the fluidised bed and for a means whereby a significant amount of entrained material may be extracted from the combustion gases before the gases enter the small bore tubes which form the secondary heating surface.

The means for achieving the above are by using one or more separate water-cooled chambers, alternatively one or more watercooled division walls within the firebox section.

In addition to the above this new design of locomotive boiler incorporates a further feature which is, that the small bore tubes which convey the combustion gases from the firebox section or from the separate water-cooled chambers to the exhaust gas outlet may be arranged either in one substantially horizontal pass which is conventional or in two or three substantially horizontal and parallel passes which is novel in a locomotive type boiler.

The particular features of this invention as outlined above will now be described in details and illustrated by means of various sketches.

SKETCH IV SPECIAL LOCOMOTIVE TYPE BOILER.

It will be seen that apart from the special firebox section the general configuration of the boiler is similar to that shown in Sketch i, hence the same numerals are used to identify the-similar parts and abbreviated descriptions are used: (1) is the boiler firebox section.

(2) is the external boiler shell.

(3) is water space around the firebox section and around the separate chamber (21).

(4) is a flat end plate.

(5) is a flat end plate.

(6) is the cylindrical shell extension.

(7) is the front tube plate.

(8) are the small bore tubes extending from the separate chamber (21) to the front tube plate (7).

(9) is the normal water level.

(10) is the steam space.

--(11) is the flat joining plate.

(12) is the smoke box extension.

(13) is the exhaust gas connection.

(14) is insulating material.

(20) is additional boiler heating surface in the form of small bore tubes, each of which extends from low level on one side of the firebox section (1) to high level on the opposite side of the firebox section. Two rows of small bore tubes (20) are fitted to provide a symetrical arrangement and a significant length of the lower portion of each tube is immersed in the Fluidised Bed - the bed level being indicated at (24). Boiler water will flow through the tubes by natural circulation from low level to high level and the heat absorbed by the water passing through the tubes will maintain the combustion temperature within the Fluidised Bed at around 900"C.

(21) is a separate open-bottom chamber of the same height and width as the firebox (1) but only of sufficient length of accommodate a man for inspection or repair work. The small bore tubes (8) are connected to the chamber (21) instead of to the firebox section (1) as in Sketch I.

(22) is a series of large bore tubes which provide an exhaust gas passage from the central area of the roof of the firebox section (1) to the roof of the separate chamber (21).

(23) is the air distributor plate located at the bottom of the firebox section (1) through which air is supplied for combustion and fluidisation.

(24) is the level of the bed when being fluidised.

(25) is an inclined tube through which coal or other solid fuel is supplied to the bed. It should be noted the solid fuel feed tube (25) can also be vertical and extend from the roof of the firebox section (1) through the steam space (10) and through the boiler shell (2).

Also provision can be made by a means not shown for liquid or gaseous fuels to be directly injected into the fluidised bed.

(26) is a bed material collection hopper located at the bottom of the separate chamber (21).

Combustion gases leave the Fluidised Bed surface at (24) and travel in a substantially vertical direction towards the roof of the firebox section (1) and then pass through the large bore tubes (22) to discharge vertically downwards into the separate chamber (21).

The velocity of the gases entering the chamber (21) will be relatively high but will diminish rapidly owing to the greater cross sectional area of the chamber. However, the entrained material in the gases will tend to continue downwards due to the greater density of such material and will not be re-entrained as the slow-moving gases turn through 90 to enter the small bore tubes (8). The material will continue to fall and will be collected at the bottom of the chamber (21) in a collection hopper (26).

SKETCH V.

Is essentially the same design of boiler as shown in Sketch IV except that the roof of the firebox section (1) is modified to a 'top hat' section (1 a) across the width from which the large bore tubes (22) take the exhaust gases into the separate chamber (21). This arrangement has an advantage in that the vertical height for the gases leaving the Fluidised Bed (24) is extended and the 'top hat' section of the firebox roof will act as a stiffener for the total roof in withstanding the effect of the boiler steam pressure.

SKETCH VI.

Is essentially the same design of boiler as shown in Sketch IV except that there is no separate water-cooled chamber (21). The firebox section (1) is divided into two separate chambers (1A) and (1B) by a vertical screen of small bore tubes (27). The tube screen (27) connects a horizontal header (28) located at the bottom of the firebox section with the water space above the roof of the firebox section. The horizontal header (28) connects with the water space (3) on each side of the firebox section and provides a supply of cooling water to the tube screeen (27). The cooling water rises by natural circulation through the tubes forming the tube screen-(27) due to heat absorbed from the Fluidised Bed Combustion process and discharges from the tubes above the firebox section roof.

As shown in Sketch VI the tube screen wall (27) is of membrane construction, i.e. each tube (29) is attached to the adjacent tube by a continuously welded metal fin (30) which is also welded to the firebox roof and to the header top between the tubes and to the firebox wall at each side, thus forming a fully gas-tight screen.

Tje Fluidised Bed (24) is contained within the firebox section (1A) and the combustion gases pass to the separate open bottom section (1 B) via the large bore tubes (22) and from section (1 B) to the small bore tubes (8).

SKETCH VII.

Is a modified design of the tube screen wall used to divide the firebox into two separate chambers (1A) and (1 B) as shown in Sketch VI. In this design the large bore tubes (22) are not employed and the combustion gases pass from the Fluidised Bed contained in section (1A) of the firebox to the open bottom section (1B) by means of apertures (31) located at the top of the tube screen (27. The apertures (31) are formed by terminating each metal fin (30) at a short distance from the roof of the firebox section, thus leaving a gap at this point between each of the tubes (29).

SKETCH VIII.

Is a further modified design of the tube screen wall used to divide the firebox section into two separate chambers (1A) and (1 B).

Instead of using a metal fin to join adjacent tubes over their length, as in Sketches VI and VII, the tubes are arranged to be touching over the greater part of their length and for each alternate tube to be off-set at the top and the bottom. The gap formed by the offset at the bottom is closed either by a limited length metal fin or by a high temperature refractory material at (32). The gap formed by the offset at the top (33) is left open, thus allowing the combustion gases from the Fluidised Bed Combustion process in the firebox section (1A) to pass between the tubes and flow into the open bottom section (1 B).

An alternative method of employing this design of tube screen is for the gap formed by the offset tubes at the top to be closed in a similar manner to that at the bottom (32), thus presenting a fully gas-tight screen, and for large bore transfer tubes (not shown) to be provided to take the exhaust gases from the section (1A) to the section (1 B) similar to those shown at (22) in Sketches IV and V.

SKETCHES IX AND X.

These sketches show how the firebox sections can be arranged to contain a number of separate open-bottom sections (1A), (1B), (1C) and (1 D) using two or three bottom headers (28), (28A) and (28B) and associated tube screens (27), (27A) and (27B), thus providing for a number of direction reversals of the combustion gases after leaving the Fluidised Bed section (1A) before entering the small bore tubes (8).

As shown in Sketches IX and X the tube screen walls are to the design shown in Sketch VII with the gap (31) for the combustion gas passage being at the top of the first tube screen wall (27), at the bottom of the second tube screen wall (27A) and at the top of the third tube screen wall (27B).

It will be readily appreciated that it is possible to use the tube screen wall design as shown in Sketch VIII with the gap for combustion gas passage alternatively at the top and bottom of the screen walls as described in the preceeding paragraph, alternatively to use a gas-tight tube screen wall as shown in Sketch VI or described as an alternative in connection with Sketch VIII to divide the firebox sections (1A) and (1B) with large bore tubes (22) to pass the combustion gases from section (1A) to (1B) and to use tube screen walls with a gap alternatively at the bottom and the top to form the successive separate open-bottom sections (1 C) and (1 D) .

SKETCH Xl.

This shows how the separate chamber section shown in Sketches IV and V can be extended to provide two separate open-bottom chambers (21) and (21A) by using large bore connecting tubes (34) at low level to connect the chambers (21) and (21A) and thus provide a passage for the combustion exhaust gases from the Fluidised Bed at (24) to the small bore tubes at (8).

It will be appreciated that this design can be extended to provide a number of separate open-bottom chambers by using a combination of large bore transfer tubes similar to (22) at the top and low level large bore tubes similar to (34) at the bottom to pass the combustion gases through successive separate chambers to the small bore tubes (8).

SKETCH XII.

This shows how the locomotive type boiler with a special firebox section such as described in Sketch VII can be provided with a second pass of small bore tubes (8A) to increase the heat transfer surface presented to the combustion gases after leaving the firebox section (1 B). The combustion gases leave the first row of small bore tubes (8) and turn through 180 in a refractory lined transfer chamber (35) and enter the second row of small bore tubes (8A). The combustion gases leave the small bore tubes (8A) and discharge intp a refractory lined smoke box (36) and from the smoke box to a chimney via the exhaust gas connection (13).

Sketch XIIA shows the transfer chamber (35) can also be in the form of a fully watercooled chamber set within the cylindrical shell extension (6). Access to the inside of the water-cooled chamber for inspection or repair would be via a refractory lined access door as shown at (37).

SKETCH XIII.

Is essentially the same design of boilder as shown in Sketch XII except that the boiler is provided with a third pass of small bore tubes (8B) to further increase the heat tansfer surface presented to the combustion gases.

As shown, the boiler has a refractory lined chamber at (37) which contains a gas-tight division plate protected by refractory material at(38). The portion of the chamber below the division plate (37) is a transfer chamber to conduct the combustion gases from the tubes (8) into the tubes (8A). The portion of the chamber above the division plate (37) is a refractory lined smokebox which provides the means for conducting the exhaust gas from the tubes (8B) to a chimney via an exhaust gas connection (13). (39) is a refractory lined transfer chamber which conducts the exhaust gases from the tubes (8A) into the tubes (8B).

It will be appreciated that the multi pass arrangement of small bore tubes, as shown in Sketches XII and XIII, can be used in a special locomotive type boiler having any of the special firebox sections described as a feature of this invention.

It will be appreciated that the boiler described in Sketch XIII can employ a watercooled chamber, as described in Sketch XII, to conduct the exhaust gases from tubes (8) to (8A) and if desired a further water cooled chamber to conduct the exhaust gases from tubes (8A) to (8B).

In addition it will be further appreciated that any of the special locomotive boilers designed in accordance with this invention can be fired with either liquid or gaseous fuels using conventional burners, the conventional burners firing into the special firebox section (1) or (1A) as the case may be, through an aperture located as at (17) in Sketch II.

SUMMARY.

A special design of locomotive type boiler having a firebox section designed for Fuildised Bed Combustion by virtue of providing additional heating surface in and above the Fluidised Bed.

The design also provides for one or more separate open-bottom water-cooled chambers or one or more separate open-bottom sections of the firebox through which the combustion gases pass before entering the small bore tube heating surface. The arrangement provides for a substantially vertical exhaust gas flow in the firebox section containing the Fluidised Bed and a means for extracting entrained matter from the exhaust gases before the exhaust gases enter the small bore tubes.

The design also provides for installing one, two or three substantially horizontal and parallel rows of small bore tubes for the exhaust gases to traverse before leaving the boiler.

The means for conducting the exhaust gases from one row of tubes to another row of tubes may be by chambers external to the boiler shell or by water-cooled chambers within the boiler shell.

In addition to be fired by Fluidised Combustion of solid, liquid or gaseous fuels, the special design of locomotive boiler may also be fired by liquid or gaseous fuels using conventional burners.

Claims

1. A locomotive type boilder for steam or hot water generation containing a special firebox section for utilising Fluidised Bed Combustion connected to separate open bottom chambers or separate open bottom sections of the firebox for exhaust gas flow.

2. A boiler as claimed in claim (1) in which the special firebox section contains additional tubular heating surface for extracting heat from the Fluidized Bed Combustion process.

3. A boiler as claimed in claims (1) and (2) which is provided with one or more separate open bottom chambers adjacent to the special firebox section.

4. A boiler as claimed in claims (1) and (2) where the special firebox section contains one or more open bottom sections in addition to the section provided for the Fluidised Bed Combustion process.

5. A boiler as claimed in claim (3) where gas flow from the special firebox section is conducted to a first separate open bottom chamber by means of exhaust gas pipes connected to the roof section of the firebox section and to the roof section of the first separate open bottom chamber.

6. A boiler as claimed in claim (5) where the exhaust gases pass from the first separate open bottom chamber into a series of horizontal small bore tubes connected to the end plate of the first open bottom chamber.

7. A boiler as claimd in claim (3) where gas flow from a first separate open bottom -hsmber is conducted to a second adjacent opn bottom chamber by means of exhaust gas pipes connecting the first open bottom chamber to the second open bottom chamber at low level.

8. A boiler as claimed in claim (7) where the exhaust gases pass from the second open bottom chamber into a series of horizontal small bore tubes connected to the end plate of the second open bottom chamber.

9. A boiler as claimed in any one of the claims (1) to (8) where the roof of the special firebox section contains an inverted channel section with exhaust gas pipes connected to one side of the channel section.

10. A boiler as claimed in claims (1) (2) and (4) where a first open bottom section of the firebox is separated from the section provided for Fluidised Bed Combustion by a vertical water cooled tubular wall.

11. A boiler as claimed in claim (1) where the exhaust gases pass from the firebox section provided for Fluidised Bed Combustion to the first open bottom section by means of exhaust gas pipes connected to the roof of the firebox section and to the roof of the first open bottom section.

12. A boiler as claimed in claim (11) where the exhaust gases pass from the first open bottom section of the firebox into a series of horizontal small bore tubes connected to the end plate of the open bottom section.

1 3. A boiler as claimed in claim (10) where the exhaust gases pass from the firebox section provided for Fluidised Bed Combustion to the first ope bottom section by means of spaces provided between the tubes forming the tubular division wall at the upper end of the wall adjacent to the roof of the firebox section.

14. A boiler as claimed in claim (4) and claim (10) where a second open bottom section of the firebox is separated from the first open bottom section of the firebox by a vertical water cooled tubular wall.

15. A boiler as claimed in claims (4) (10) and (14) where the exhaust gases pass from the first open bottom section of the firebox into the second open bottom section of the firebox by means of spaces provided between the tubes forming the tubular division wall at the bottom end of the wall adjacent to a horizontal header.

1 6. A boiler as claimed in claim (15) where the exhaust gases pass from the second open bottom section of the firebox into a series of horizontal small bore tubes connected to the end plate of the second open bottom section.

17. A boiler as claimed in claims (4) (10) and (14) where a third open bottom section of the firebox is separated from the second open bottom section by a vertical water cooled tubular wall.

18. A boiler as claimed in claims (4) (10) (14) and (17) where the exhaust gases pass from the second open bottom section of the firebox into the third open bottom section of the firebox by means of spaces provided be tween the tubes forming the tubular division wall at the upper end of the wall adjacent to the roof of the firebox section.

1 9. A boiler as claimed in claim (18) where the exhaust gases pass from the third open bottom section of the firebox into a series of horizontal small bore tubes connected to the end plate of the third open bottom section.

20. A boiler as claimed in claims (4) (10) (11) (12) (13) (14) (15) (16) (17) (18) and (1 9) where the tubular division walls may be of tangent or membrane construction.

21. A boiler as claimed in claim (20) where water supply to the tubular division walls is provided by means of horizontal headers connected with the water space on each side of the firebox section at low level.

22. A boiler as claimed in any of the foregoing claims where water circulation is maintained around the firebox and through the additional tubular surface within Fluidised Bed Combustion zone by natural circulation.

23. A boiler as claimed in claims (4) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20 and (21) where water circulation is maintained through the bottom horizontal headers and through the vertical tubular division walls by natural circulation.

24. A boiler as claimed in any of the foregoing claims where exhaust gases from the open botton chambers or open bottom sections of the firebox pass through at least one horizontal series of small bore tubes before being discharged to atmosphere.

25. A boiler as claimed in any of the foregoing claims which is provided with two or three separate parallel horizontal series of small bore tubes.

26. A boiler as claimed in claim (25) where the exhaust gases pass through a first series of horizontal small bore tubes and turn through 180 in a reversal chamber to pass through a second series of horizontal tubes before being discharged to atmosphere.

27. A boiler as claimed in claim (25) and claim (26) where the exhaust gases pass through the second series of horizontal tubes and turn through a further 180 in a reversal chamber to pass through a third series of horizontal tubes before being discharged to atmosphere.

28. A boiler as claimed in claims (26) and (27) where the reversal chambers are external to the boiler water space.

29. A boiler as claimed in claims (26) and (27) where the reversal chambers are contained within the boiler water space.

30. A boiler as claimed in claims (26) (27.) and (29) where one reversal chamber-is external to the boiler water space and one reversal chamber is contained within the boiler water space.

31. A boiler as claimed in any of the foregoing claims which may be provided with conventional oil and/or gas burners firing into the special firebox section above the Fluidised Bed Combustion zone.