GB2075360A

GB2075360A - Water-cooled fluidised bed distributor plate

Info

Publication number: GB2075360A
Application number: GB8110194A
Authority: GB
Original assignee: Foster Wheeler Energy Corp
Current assignee: Foster Wheeler Energy Corp
Priority date: 1980-04-09
Filing date: 1981-04-01
Publication date: 1981-11-18
Also published as: SE8101964L; JPS599830B2; ZA812159B; JPS5716784A; NL8101701A; NL188816C; GB2075360B; NL188816B; CA1151474A

Abstract

In fluidized bed heat exchangers a distributor plate assembly (24) located at the base of the bed consists of a plurality of horizontal, spaced tubes (40) connected by a plurality of elongated fins (42). A plurality of air distributors (50) extend perpendicular to the plate assembly and respectively register with through openings formed in the fins (42) for receiving air and discharging the air in an upward direction to fluidize particulate material above the plate assembly. The lengths of the air distributors (50) are such that the plate assembly (24) is insulated from the high temperatures occurring in the fluidised bed and water is passed through the tubes of the plate assembly to cool it. <IMAGE>

Description

SPECIFICATION A fluidized bed heat exchanger This invention relates to a fluidized bed heat exchanger and more particularly, to such a heat exchanger having an improved, fluid cooled, air dis tribution plate assembly for supporting fluidizable particulate material.

The use of fluidized beds has long been recog nized as an attractive way of generating heat. In a typical fluidized bed arrangement, air is passed through a bed of particulate material, which usually includes a mixture of inert material, a fuel material such as high sulfur bituminous coal, and an adsor bent material for the sulfur released as a result of the combustion of the fuel material. As a result of the air passing through the bed, the bed behaves like a boil ing liquid which promotes the combustion of the fuel. The basic advantages of such an arrangement include a relatively high heat transfer rate, substantially uniform bed temperature, combustion at rela tively low temperatures, ease of handling the fuel materials, a reduction in corrosion and boiler fouling and a reduction in boiler size.

In the fluidized bed combustion process, in order to insure capture by the adsorbent of the sulfur released during combustion of the fuel, the bed temperature has to be maintained at a relatively high value (normally 15000-15500F). This requires the bed-supporting plate to be constructed of an expensive material, such as stainless steel, which will withstand these temperatures. However, even when a material such as stainless steel is used, the large differential expansion involved and the thermal gradients occurring across the surface of the plate reduce the life of the plate considerably. As a result, the plate has to be frequently replaced, which is costly both from a material and a labor standpoint, and which results in a considerable amount of down-time.Also, in arrangements, using watercooled walls, the difference in temperatures between the walls and the bed-supporting plate result in border seal junction problems.

It is therefore an object of the present invention to provide a fluidized bed heat exchanger in which a bed-supporting plate assembly is provided which can be fabricated from a low alloy material and yet enjoys an increased life when compared to plates of similar, or even more expensive, materials utilized in similar prior art arrangements.

It is a further object of the present invention to provide a fluidized bed plate exchanger of the above type in which the bed-supporting plate assembly is formed by a plurality oftubes through which a cooling fluid is passed to lower the temperature of the plate.

It is a further object of the present invention to provide a fluidized bed heat exchanger of the above type which has an air distribution system that insu latex the bed-supporting plate assembly from the high operating temperatures of the bed.

It is a further object of the present invention to provide a fluidized bed heat exchanger of the above type in which a stagnant area of particulate materials is provided immediately above the bed-supporting plate assembly for insulating the latter against the relatively high opemting temperatures in the bed.

It is a still further object ofthe present invention to provide a fluidized bed heat exchanger of the above type in which the fluidizing air for the bed is introduced at an area extending above the plane of the bed-supporting plate to provide for an insulating space immediately above the latter plate.

Toward the fulfillment of these and other objects, the system of the present invention comprises a plate assembly adapted to support a bed of particulate material and formed buy a plurality of tubes through which a cooling fluid is passed. The tubes are connected by elongated fins having a plurality of openings extending therethrough for receiving a plurality of hollow elongated air distributors extending perpendicular to the plate. Each air distributor has an inlet at one end for receiving air and an outlet at its other end for discharging the air in an upward direction into the bed to fluidize the bed material.

The air distributors extend from the plate for a length sufficient to insulate the plate from the relatively high temperatures in the bed.

The above brief description, as well as further objects, features, and advantages, of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred but nonetheless illustrative embodiment in accordance with the present invention, when taken in connection with the accompanying drawings in which: Fig. 1 is a vertical sectional view of the fluidized bed heat exchanger of the present invention; Fig. 2 is an enlarged partial sectional view of a portion of the bed-supporting plate assembly of the heat exchanger of Fig. 1; Fig. 3 is an enlarged plan view depicting a portion of the bed-supporting plate assembly of the heat exchanger of Fig. 1; and Figs. 4-8 are enlarged vertical sectional views of alternative embodiments of the air distributors utilized in the heat exchanger of Fig. 1.

Referring to Fig. 1 of the drawings, the reference numeral 10 refers in general to an enclosure forming a major portion of a fluidized bed heat exchanger which may be in the form of a boiler, combustor or any similar type device. The enclosure 10 consists of a front wall 12, a rear wall 14, and two sidewalls, one of which is shown by the reference numeral 16. Each wall is formed by a plurality of vertically-extending tubes 18 disposed in a spaced, parallel relationship and connected together by a plurality of elongated fins 20 extending for the entire lengths of the tubes and connected to diametrically opposed surfaces of the tubes 18, in a conventional manner.The upper portion of the enclosure 10 is not shown for the convenience of presentation, it being understood that it consists of a convection section, a roof and an outlet for allowing the combustion gases to discharge, also in a conventional manner.

A bed of particulate material, shown in general by the reference numeral 22, is disposed within the enclosure 10 and rests on a plate assembly 24 extending horizontally in the lower portion of the enclosure. The bed 22 can consist of a mixture of discrete particles of inert material, fuel material, such as bituminous coal, and an adsorbentforthe sulfur released by the combustion of the fuel material.

An air plenum chamber 26 is provided immediately below the plate assembly 24 and an air inlet 28 is provided through a lower extension of the rear wall 14 in communication with the chamber 26 for distributing air from an external source (notshown) to the chamber. A pair of air dampers 30 are suitably mounted in the inlet 28 for pivotal movement about their centers in response to actuation of external controls (not shown) to vary the effective opening in the inlet and thus control the flow of air into the chamber 26. Since the dampers 30 are of a conventional design, they will not be described in any further detail.

A bed light-off burner 32 is mounted through the front wall 12 immediately above the plate assembly 24 for initially lighting off the bed 22 during startup.

A plurality of overbed feeders 34,36 and 38 are provided which extend through the side walls 16.

The feeders 34,36 and 38 receive relatively fine particulate coal from inlet ducts or the like, and are adapted to feed the relatively fine coal particles onto the upper surface of the bed 22 in a conventional manner. it is understood that the feeders 34,36 and 38 could be located at a level below the upper surface of the bed 22, and that feeders identical to the feeders 34,36 and 38 can also be provided through one or more ofthefrontwalls 12, the rear walls T4 and the other sidle wall 16.

The details of the plate assembly 24 are shown in Figs. 2 and 3. The assembly 24 consists of a plurality of spaced parallel tubes 40 extending in a horizontal fashion between the walls 12,14 and 16. The tubes 40 are connected together to form an integrastruc- ture by a plurality of plates, or fins, 42 extending for the entire length of the tubes 40 and connected thereto at diametrically opposite surfaces Withe tubes.As shown in Fig. 2, a plurality of horizontal support plates 44 extend from the fins 20 forming the rear wall 14 and are connected to the endmost fin 42 of the plate assembly 24, it being understood that a similar arrangement is provided in connection with the walls 12 and 14 to support the plate assembly 24 in the position shown. The connections between the fins 42 and the tubes 40, between the endmost fins 42 and the support plates 44, and between the support plates 44 and the fins 20 can be made in any known manner such as by the weldments shown or by other known fabricating techniques, such as key ing, rolling, braising, pinning, tacking, etc.

A plurality of air distributors 50 extend through a plurality of spaced openings extending through the fins 42. The distributors 50 are in the form of verti cally disposed tubular members that are welded to the fins 42 and extend upwardly from the fins for a predetermined distance into the bed 22 of particulate material. The lower end of the distributors 50, as viewed in Fig. 2, project only slightly from the lower surface of the fins 42 and receive air from the chamber 26. After passing through the length of the distributors 50, the air discharges outwardly into the fluidized bed at the predetermined distance from the plate assembly 24. As a result, a dormant layer of particulate material is formed between the upper surface of the plate assembly24 and the upper ends ofthe distributor 50 for reasons that will be discussedin detail later.

Referring again to Fig. 1, a pairof horizontal head ers4Gare shown in Fig. 1 which are connected in fluid communication to the tubes 18 forming the front wall 12 and the rear wall 14, it being understood tnat similar headers are provided in communication with the upper ends of the walls and with both ends of the side walls 16. As a result,afiuidto be heated can be sequentially or simultaneously passed through the walls 12, 14 and 16 to pick up the heat from the fluidized bed in a conventional manner. A header 48 is provided adjacent each side wall 16 in communication with the corresponding ends of the tubes 40 of the plate assembly 24 to enable cooling fluid to be passed through these tubes.It is understood that the cooling fluid for the headers 48 can either be provided from the same source as the fluid passing through the walls 12, 14 and 16, or from a separate source.

In operation, the dampers 30 associated with the air inlet 28 are opened and air is distributed up through the chamber 26, towards the plate assembly 24 and into the inlet ends of the distributor 50. The air then flows upwardly through the lengths of the distributor 5U before it discharges from the outlet ends of the distributor into the bed 22 ata plane above the plane of the plate assembly. Thus, that portion ofheparticulate material in the bed 22 extending immediately above the outlet ends of the distributor 50 is fluidized while the portion extending betweenihe latter ends and the upper surface of the plate assembly 24 remains dormant, or stagnant.

The light-off burner 32 is then fired to heatthe material inthe bed until the temperature of the material reaches a predetermined level, atwhich time particu late fuel is discharged from the feeders 34,36 and 38, and onto the upper surface ofthe bed 22 as needed to insure a continuous replenishing of the fuel material as it burns off.

After the bed 22 has been fluidized and has reached a predetermined elevateritemperature in accordance with the foregoing, the light-off burner 32 is turned off while the feeders 34, 36 and 38 con ti nue to distribute particulate fueltothe upper surface of the bed in accordance with predetermined Bed rates. As a result ofthe foregoing, the dormant layer of particulate material extending between the upper surface of the pbte assembly 24 and the outlet endsofthedistributor50 actsasan insulator for the plate 24. Spent fuel material, primarily in the form of ashes, can be discharged from an outlet (not shown) extending from the plate assembly 24 and through one of the walls 12, 14 or 16.

Cooling fluid, preferably water, is passed between the headers 48 and through the tubes 40 of the plate assembly 24 to reduce the temperatures of the latter assembly and fluid to be heated is passed simultaneously, or in sequence, through the tubes 18 forming the walls 12,14 and 16to add heatfromthe fluidized bed to the fluid before it is passed to external apparatus for further processing.

As a result of the unique arrangement of the present invention the plate assembly 24, including the tubes 40, the fins 42 and the distributors 50, can be fabricated of a relatively low cost, low alloy material and yet will enjoy a relatively long life when compared to plates of more expensive, heat-resistant material that are not so insulated and cooled.

Figs. 4-7 each depict an alternate embodiment of an air distributor that can be utilized in the plate assembly 24. Referring to Fig. 4, the reference numeral 54 refers to a distributor which is formed by a straight tube 56 which is mounted through an opening 52 in a fin 42, and a separate horizontal branch tube 58 extending over the upper end portion of the tube 56 in communication therewith. This arrangement results in a horizontal discharge of air into the bed 22 from the ends of the tube 58 in two opposite directions.

The embodiment of Fig. 5 is similar to that of Fig. 4 but is in the form of a single piece, T-shaped distributor 60 which consists of a single member having a vertical portion 62 and a horizontal portion 64 in communication therewith which function in a similar manner to the embodiment of Fig. 4.

The embodiment of Fig. 6 is similar to that of Fig. 5 and is in the form of a distributor 66 having a vertical tube 68 and a arrow-shaped head portion 70 formed integral with the vertical tube. The head portion 70 receives air from the upper end portion of the tube 68 and discharges the air in two opposite, silghtly downwardly directions.

According to the embodiment of Fig. 7, a distributor72 is provided which consists of a vertical tube 74 having an arcuate-shaped tube 76 connected to its upper end to form a double elbow-T arrangement which discharges the air in a pattern similar to that of the embodiment of Fig. 6.

The distributor 78 of the embodiment of Fig. 8 consists of a single integral tube 80 having its upper end bent, or otherwise curved toward the horizontal and slightly downwardly. This results in a single air discharge pattern which extends in a direction slightly downwardly from the horizontal. This type of distributor is capable of imparting circulation to the bed or can be designed with directional characteristics capable of spreading the bed particulate across the bed or moving larger particles or ashes.

It is understood that other variations can be made in the foregoing without departing from the scope of the invention. For example, insulating or refractory materials may be provided in the area extending between a plane defined by the outlet ends of the distributors 50 and the upper surface of the plate assembly 24 instead of the dormant particulate material. In this case, the distributors 50 would act as anchors for the insulation or refractory material.

Claims

1. Afluidized bed heat exchanger comprising a plurality of spaced parallel tubes, a plurality of elongated fins extending between said tubes and connected thereto to form a plate assembly, said plate assembly extending in a substantially horizontal plane to support a bed of particulate material, means for passing a cooling fluid through said tubes, a plurality of holes extending through said plate assembly, a plurality of air distributors extending perpendicular to said plate assembly, each distributor having an inlet which registers with a corresponding hole and at least one outlet, and means for introducing air into the inlets of said distributors, said air passing through said distributors and discharging from said outlets to fluidize the particulate material disposed above said outlets, the outlets of said distributors being spaced from said plate assembly for a length sufficient to enable the particulate material extending below said outlets to insulate said plate assembly from the relatively high temperatures in said bed.

2. The heat exchanger of claim 1 wherein said fins extend from two diametrically-opposed surfaces of each tube.

3. The heat exchanger of claim 2 wherein each fin is connected to two tubes along opposite edges of said fin.

4. The heat exchanger of claim 1 or3wherein said fins are welded to said tubes.

5. The heat exchanger of claim 1 wherein each distributor extends within a hole for the entire thickness of said fin.

6. The heat exchanger of claim 1,3 or 5 wherein said distributors are welded to said fins.

7. The heat exchanger of claim 1 wherein the holes extend through said fins in a spaced relation along the lengths of said fins.

8. The heat exchanger of claim 1 wherein said air introducing means comprises a chamber disposed immediately below said plate assembly, said chamber having an inlet connected to a source of air.

9. The heat exchanger of claim 8 further comprising damper means associated with said inlet for controlling the flow of air into said chamber.

10. The heat exchanger of claim 1 wherein each distributor is in the form of a vertically extending tube adapted to discharge air in an upward direction from its upper end.

11. The heat exchanger of claim 1 wherein each distributor is in the form of a vertically extending tubular portion extending from said plate assembly and adapted to receive said air, and a substantially horizontally extending tubular portion communicating with said vertically extending tubular portion and adapted to discharge said air in opposite directions from its ends.

12. The heat exchanger of claim 1 wherein each distributor is in the form of a vertically extending tubular portion extending from said plate assembly and adapted to receive said air, and two angularly extending tubular portions communicating with said vertically extending tubular portion, said angularly extending tubular portions adapted to discharge said air in opposite directions from said vertically extending tubular portion.

13. The heat exchanger of claim 12 wherein each of said angularly extending tubular portions extends slightly downwardly from the horizontal.

14. The heat exchanger of claim 1 wherein each distributor is in,the form of a tube having a vertical portion extending from said plate assembly and adapted to receive said air and a substantially horizontally extending portion formed integral with said vertical portion and adapted to discharge said air.

15. The heat exchanger of claim 14wherein said substantially horizontally extending portion is adapted to discharge said air in a direction slightly downwardly from the horizontal.

16. The heat exchanger of claim 1 furthercomprising a plurality of upright walls surrounding said plate assembly to form a chamber for housing said particulate material.

17. The heat exchanger of claim 16 wherein said particulate material contains fuel which upon combustion, releases heat energy, and further comprising means for adding additional particulate fuel material to said chamber.

18. The heat exchanger of claim 16 or 17 wherein said walls are formed by a plurality of upright tubes through which water is passed to transferthe heat from said bed.

19. A heat exchanger substantially as described herein with reference to the accompanying drawings.