Title:
Heat exchanger utilizing adjoining fluidized beds
United States Patent 3893426


Abstract:
A heat exchanger in which a substantially vertical partition divides a housing into at least two adjoining chambers each of which support a bed of particulate fuel material. Air is passed through the beds to promote the combustion of the fuel material and to maintain the chambers at predetermined temperatures. The fuel material in one of the chambers is relatively coarse while the fuel material in the other chamber is relatively fine with the chambers communicating to permit circulation of portions of the fuel between the chambers.



Inventors:
BRYERS RICHARD W
Application Number:
05/454045
Publication Date:
07/08/1975
Filing Date:
03/25/1974
Assignee:
FOSTER WHEELER CORPORATION
Primary Class:
Other Classes:
110/245
International Classes:
F22B1/02; B01J8/26; B01J8/36; F22B31/00; F22B37/10; F23C10/00; F23C10/18; (IPC1-7): F22B1/02
Field of Search:
122/4D 110
View Patent Images:



Primary Examiner:
Sprague, Kenneth W.
Attorney, Agent or Firm:
Naigur, Marvin Wilson John De Luca John A. E. P.
Claims:
What is claimed is

1. A heat exchanger comprising a housing, at least one substantially vertical partition dividing said housing into at least two adjoining chambers, means for establishing a bed of relatively coarse particulate fuel material in one of said chambers, means for establishing a bed of relatively fine particulate fuel material in the other chamber, and means to pass air through each of said beds to promote the combustion of said fuel material and maintain said chambers at predetermined temperatures, said partition being formed by a plurality of finned tubes for circulating a heat exchange medium in a heat exchange relation to said beds, portions of said tubes being bent in a manner to form a plurality of slots in said partition to communicate said chambers and permit circulation of portions of said fuel between said chambers.

2. The heat exchanger of claim 1 wherein each of said bed establishing means comprises means to introduce said fuel material into its respective bed.

3. The heat exchanger of claim 1 wherein said air passing means comprises a perforated distribution plate supporting the bed of fuel material in each of said chambers, and means to pass air into said housing and upwardly through said plates.

4. The heat exchanger of claim 1 wherein said bed of relatively fine fuel material is maintained at a higher level than said bed of coarse fuel material.

5. The heat exchanger of claim 4 wherein said slots are located relative to said beds to permit the upper portion of said bed of relatively fine fuel material to spill over into said bed of coarse fuel material.

6. The heat exchanger of claim 1 wherein a portion of each wall of said housing is formed by a plurality of finned tubes for circulating a heat exchange medium in a heat exchange relation to said beds.

7. The heat exchanger of claim 1 further comprising a bundle of heat exchange tubes disposed in one of said beds for circulating a heat exchange medium in a heat exchange relation to said bed.

8. The heat exchanger of claim 7 wherein said bundle of heat exchange tubes are disposed in said bed of relatively fine fuel particles.

9. A heat exchanger comprising a housing, at least one substantially vertical partition dividing said housing into at least two adjoining chambers, means for establishing a bed of relatively coarse particulate fuel material in one of said chambers, means for establishing a bed of relatively fine particulate fuel material in the other chamber at a higher level than said bed of coarse material, and means to pass air through each of said beds to promote the combustion of said fuel material and maintain said chambers at predetermined temperatures, at least one opening extending through said partition at a level above the level of said bed of coarse material and below the level of said bed of fine material to permit passage of portions of said fine material to said bed of coarse material, and at least one opening extending through said partition at a level below the level of both of said beds to permit passage of portions of said coarse material to said bed of fine materials.

10. The heat exchanger of claim 9 wherein each of said bed establishing means comprises means to introduce said fuel material into its respective bed.

11. The heat exchanger of claim 9 wherein said air passing means comprises a perforated distribution plate supporting the bed of fuel material in each of said chambers, and means to pass air into said housing and upwardly through said plates.

12. The heat exchanger of claim 9 wherein a portion of each wall of said housing is formed by a plurality of finned tubes for circulating a heat exchange medium in a heat exchange relation to said beds.

13. The heat exchanger of claim 9 wherein said partition is formed by a plurality of finned tubes for circulating a heat exchange medium in a heat exchange relation to said beds, portions of said tubes being bent in a manner to form a plurality of slots in said partition to define said openings.

14. The heat exchanger of claim 9 further comprising a bundle of heat exchange tubes disposed in one of said beds for circulating a heat exchange medium in a heat exchange relation to said bed.

15. The heat exchanger of claim 14 wherein said bundle of heat exchange tubes are disposed in said bed of relatively fine fuel particles.

Description:
BACKGROUND OF THE INVENTION

This invention relates to a heat exchanger and, more particularly, to a heat exchanger employing two or more adjoining fluidized beds.

Fluidized beds have often been utilized to produce heat used in heat transfer applications such as the generation of steam or the like. In these arrangements, air is normally passed upwardly through a mass of particulate material including a particulate fuel, causing the material to expand and take on a suspended or fluidized state. Combustion of the fuel material produces heat which is transferred to a heat exchanger medium, such as water, passing through tubes, or the like, located proximate to the fluidized bed. Although use of the fluidized bed in this environment enjoys the advantages of an improved heat transfer rate, a lower combustion temperature, a reduction in boiler size, a reduction in corrosion and boiler fouling, and an increase in combustion efficiency, several limitations do exist. For example, the size of the particle fuel used in the beds must be within a relatively narrow range to avoid blockage of tube surfaces and air distribution plates by oversized fuel particles. Also, the presence of a relatively large tube surface in, or adjacent to, the fluidized bed requires a relatively high amount of energy during the early stages of start-up and fluidization.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a heat exchanger incorporating two or more adjoining fluidized beds which enjoy the advantages enunciated above, yet enables a relatively wide range of fuel particle sizes to be utilized.

It is a further object of the present invention to provide a heat exchanger of the above type in which the fluidized beds can be started and operated in a relatively efficient manner.

It is a still further object of the present invention to provide a heat exchanger of the above type in which the residence time of the fuel particles in the fluidized beds is extended to ensure complete combustion of a great percentage of the fuel particles.

Toward the fulfillment of these and other objects, the heat exchanger of the present invention comprises a housing, at least one substantially vertical partition dividing said housing into at least two adjoining chambers, means for establishing a bed of relatively coarse particulate fuel material in one of said chambers, means for establishing a bed of relatively fine particulate fuel material in the other chamber, means to pass air through each of said beds to promote the combustion of said fuel material and maintain said chambers at predetermined temperatures, and means communicating said chambers to permit circulation of portions of said fuel between said chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional, partial schematic, view of a heat exchanger employing features of the present invention;

FIG. 2 is a horizontal cross-section taken along the line 2--2 of FIG. 1; and

FIG. 3 is an enlarged partial, perspective view depicting a portion of the heat exchanger of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring specifically to the drawings, the reference numeral 10 refers in general to the heat exchanger of the present invention which includes an enclosure 12 of a refractory, or other type insulating material, having a closed bottom, or floor, portion and an open upper end portion which receives a funnel-shaped insert 13 having an outlet opening 13a.

Each wall of the enclosure 12 is lined with a wall 14 formed by a plurality of tubes 16, each of which has two external elongated fins 18 extending from diametrically opposite sides thereof, with the adjacent fins being interconnected to form a contiguous wall-like structure. Both ends of the tubes 16 of each wall 14 are connected to horizontal headers 20 for distributing a heat exchanger fluid, such as water, from an external source (not shown) to the walls 14, and collecting the fluid from each wall 14 after it has passed through the wall before being discharged from the enclosure or rerouted to another header 20 for further circulation.

A divider wall, or partition, 22 is disposed parallel to the side walls of the enclosure 12 and is spaced intermediate the walls to define two adjoining chambers 24 and 26. The wall 22 is also formed by a plurality of tubes 16 having interconnected fins 18, and a header 20 is connected to each end of the wall 22 so that water may be circulated through this wall in a manner similar to the circulation through the finned tube walls 14.

A pair of air distribution plates 28 and 30 are disposed in the chambers 24 and 26, respectively, and are adapted to receive air from an inlet 32 (FIG. 2) registering with the lower portion of the housing 12. The flow of air to the plates 28 and 30 is regulated by a pair of damper assemblies 34 and 36, respectively, disposed immediately below the plates.

The air distribution plate 28 is adapted to support a bed 40 of particulate material in the lower portion of the chamber 24, consisting of inert material, a said fuel material, and a sorbent material for the sulfur formed during combustion of the fuel if said fuel contains relatively large amounts of sulfur. Additional fuel for the bed 40 is introduced through a feeder tube 42 extending through the front wall of the enclosure 12 and the corresponding finned tube wall 14, and located proximate to the plate 28. The fuel in the bed 40 can be of a relatively small, or fine, size for reasons that will be explained later.

In a similar manner, the plate 30 supports a bed 44 of a mixture of particulate material in the chamber 26, similar in makeup to that of the material of the bed 40. An inlet tube 46 extends through a side wall of the enclosure 12 and its corresponding finned tube wall 14 at an elevated position relative to the plate 30 and is adapted to introduce additional particulate fuel material into the bed 44. The fuel material forming the bed 44 is of the same type as that in the bed 40 but is of a relatively large size for reasons also to be described in detail later. The particulate fuel material may be fed through the inlets 42 and 46 and to their respective beds 40 and 44 in any conventional manner, such as by pneumatic injection, gravity feed, or the like.

The beds 40 and 44 are fluidized, or maintained in a suspended state, by virtue of the air passing from the inlet 32 and through the distribution plates 28 and 30, with the air flow being regulated by the damper assemblies 34 and 36 so that it is high enough to fluidize the particulate fuel materail in each bed and obtain economical burning or heat release rates per unit area of the bed, while being low enough to avoid the loss of too many fine particles from the beds, and to allow sufficient residence time of gases to promote good sulfur removal by the abovementioned sorbent.

An overflow pipe 48 extends through a side wall of the enclosure 12 and its corresponding finned tube wall 14 and registers with the chamber 26 to maintain the bed 44 at a predetermined level which is lower than the level of the bed 40, for reasons that will be described later.

A tube bundle, shown in general by the reference numeral 50, is immersed in the bed 40 and consists of a plurality of spaced parallel tubes extending in a serpentine relationship with the inlet and outlet ends of each tube extending externally of the housing 12 for connection to a source of water and another component of the system, respectively, in a conventional manner. As a result, water passing through the tube bundle 50 will be heated by virtue of the heat generated in the bed 40.

According to one of the main features of the present invention, the divider wall 22 has two openings 52 and 54 formed therein with the opening 52 extending from approximately the upper level of the bed 44 to the upper level of the bed 40 and the opening 54 extending from approximately the plane of the distribution plates 28 and 30 to a point below the level of the bed 44.

The openings 52 and 54 are provided in the wall 22 in a manner better shown in connection with FIG. 3. In particular, two spaced portions of every other tube 16 forming the wall 22 is bent outwardly at an angle as shown by the reference numeral 16a, to provide a series of alternating solts 16b in that area vacated by the bent portions 16a. For the convenience of presentation, a portion of the bent portions 16a have been broken away in FIG. 3 to better show the slots 16b. Thus, each opening 52 and 54 is formed by a plurality of the slots 16b, which enables the particulate material to be circulated between the beds 40 and 44 for reasons detailed in the following operational description of the heat exchanger 10.

The bed 44 is initially ignited in any conventional manner which raises the temperature in both chambers 24 and 26 to a predetermined value after which the bed 40 is ignited. Air is passed from the inlet 32 through the plates 28 and 30 and controlled by the damper assemblies 34 and 36 to fluidize the beds and promote the combustion of the fuel material in each bed. The air passing throough the beds 40 and 44 combines with the combustion gases in each chamber 24 and 26 and passes outwardly from the enclosure 12 through the outlet 13a.

Water from an external source is passed into one or more of the lower headers 20 and is passed upwardly through the finned tube walls 14 and 22 where it is heated by the heat generated by the beds 40 and 44 before being passed collected in the upper headers 20 for further treatment or use.

The relatively large fuel particles in the bed 44 that are not completely spent in combustion, while floating on the surface of bed 44, will eventually become immersed upon sufficient size reduction and circulate downwardly in the bed 44 by the turbulent forces of the bed, and will pass through the opening 54 into the bed 40, where they will combine with the fine fuel particles in the bed 40 and normally be completely combusted in the latter bed. In a similar manner, that portion of the fine fuel particles not completely combusting in the bed 40 will pass through the opening 52 into the bed 44 for further combusting or circulating, as described above.

In this manner, the residence time of the large particulate fuel material is considerably increased in an unobstructed bed, ensuring complete combustion. Fine material is continuously circulated to a second bed where heat is extracted through an immersed tube bundle. As a result, a more efficient operation is achieved while permitting use of fuel particles of a relatively wide range.

Several variations may be made in the foregoing without departing from the scope of the invention. For example, the type and quantity of particulate material in the fluidized beds may be varied. Also, a booster fan or the like may be provided at the lower portion of one or more of the beds for promoting the circulation of particles in, and the passage of air through, the beds.

Of course, variations of the specific construction and arrangement of the heat exchanger disclosed above can be made by those skilled in the art without departing from the invention as defined in the appended claims.