GB2168908A

GB2168908A - A coal feed system for a fluidized bed reactor

Info

Publication number: GB2168908A
Application number: GB08525619A
Authority: GB
Inventors: Bimal K Biswas; Ernest L Daman
Original assignee: Foster Wheeler Energy Corp
Current assignee: Foster Wheeler Energy Corp
Priority date: 1984-12-19
Filing date: 1985-10-17
Publication date: 1986-07-02
Also published as: GB8525619D0; ES548320A0; ES8608921A1; AU4793885A; CA1261683A; CN85108257A; JPS61165506A; GB2168908B

Abstract

A coal feed system for a fluidized bed reactor in which a grate 20 is supported in a housing 14 and adapted to receive a bed 18 of particular material at least a portion of which is combustible. Air is passed through the grate and the particulate material to fluidize the particulate material. A relatively coarse particulate fuel material is distributed to the upper surface of the bed and a slurry containing a relatively fine particulate fuel material is distributed into the bed below the upper surface of the bed. The coal feed is separated in separator 30 having a grid 34 allowing finer particles in the form of a slurry to be fed via reservoir 50 into the bed. <IMAGE>

Description

SPECIFICATION A coal feed system for a fluidized bed reactor Background of the invention The present invention relates to fluidized beds and, more particularly, to a coal feed system for a fluidized bed reactor.

Fluidized bed reactors, in the form of combustors, boilers, steam generators, and the like have long been recognized as an attractive and effective means of generating heat. In these arrangements, air is passed through a bed of particulate material which normally consists of a mixture of inert material and a particulate fossil fuel such as coal, to fluidize the bed and to promote the combustion of the fuel. When the heat produced by the fluidized bed is utilized to convert water to steam, the fluidized bed system offers an attractive combination of high heat release, improved heat transfer to surfaces within the bed and compact boiler size.

In these type arrangements, the particulate fuel material must be continuously, or at least periodically, distributed into the bed to replenish the spent material expended in the combustion process. Many of these arrangements utilize in-bed feeding systems in which the particulate fuel material is introduced directly into the bed from a point below the upper surface of the bed. However, these in-bed systems present problems since the lateral transfer or distribution of the materials through the bed is relatively poor requiring a multiplicity of feed points to prevent hot spots or cool spots which increases the cost of the installation.

Other systems utilize a feeder for distributing the particulate fuel material from a position above the upper surface of the bed where it falls by gravity onto the latter surface. However, since a great majority of the commercial coal that is available is of a relatively large particle size range, which may extend from very small particles to and including particles that will pass through a two-inch screen, this ejection of the particulate fuel material onto the upper surface of the bed presents problems.

For example, the combination of the upwardly rising combustion gases and air passing through the bed will blow relatively small material out the top of the combustor before it is burned.

According to the present invention there is provided a fluidized bed reactor comprising a housing, grate means supported in said housing and adapted to receive on its upper surface a bed of particulate material at least a portion of which is combustible, means for passing air through said grate means and said particulate material to fluidize said particulate material, means for distributing a relatively coarse particulate fuel material to the upper surface of said bed and means for distributing a slurry containing a relatively fine particulate fuel material into said bed below the upper surface of said bed.

The coal feed system in the fluidized bed reactor of the present invention allows an optimum distribution of a particulate fuel material of a relatively large particle size range to be achieved.

In the system of the present invention the particulate fuel material is separated into a relatively coarse material which is distributed to the upper surface of the bed and a relatively fine material which is distributed into the bed at a point below the upper surface of the bed. The relatively fine material may be entrained by water in the separation process to form a slurry which is injected into the bed.

The system of the present invention minimizes escape of the relatively fine material from the bed and increases the combustion and sulfur capture efficiency of the fluidized bed.

The invention will now be described with reference to the accompanying drawing which is a partial sectional partial schematic view of the reactor of the present invention.

Referring to the drawing, the reference numeral 10 refers in general to the fluidized bed reactor of the present invention in the form of a boiler consisting of a front wall 12, a rear wall 14, and two sidewalls, one of which is shown by the reference numeral 16. The upper portion of the boiler 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 from the boiler, in a conventional manner.

A bed of particulate material, shown in general by the reference numeral 18 is disposed within the boiler 10 and rests on a perforated grate 20 extending horizontally in the lower portion of the boiler. The bed 18 can consist of a mixture of discrete particles of inert material and fuel material such as bituminous coal.

An air plenum chamber 22 is provided immediately below the grate 20 and an air inlet 24 is provided through the rear wall 14 in communication with the chamber 22 for distributing air from an external source (not shown) to the chamber. A pair of air dampers 26 are provided in the inlet 24 for controlling the flow of air into the chamber 22. The dampers 26 are suitably mounted in the inlet 24 for pivotal movement about their centers in a response to actuation of external controls (not shown) to vary the effective openings in the inlet and thus control the flow of air through the inlet and into the chamber 22. Since the dampers 26 are of a conventional design they will not be described in any further detail.Although not shown in the drawing, it is understood that a bed light-off burner is mounted through the front wall 12 immediately above the grate 20 for initially lighting off the bed 18 during startup.

A screen separator, shown in general by the reference numeral 30 is located externally of the boiler 10 and is adapted to receive particulate fuel material, such as coal, of a relative large particle size range from an external source (not shown) via a duct 32. The separator 30 includes a screen 34 which is sized so as to permit the relatively fine particles to pass through while preventing passage of the relatively coarse particles. As an example, the screen can be adapted to separate particles greater than 1,16 of an inch in diameter from those less than 1/16 of an inch. The particles on the screen 34 are washed by water from three spray bars 36 disposed adjacent the separator 30. The water aids in the separation process and entrains the relatively fine particles as they pass through the screen 34 into the lower portion of the separator 30.

A distributor 40 is mounted on the wall 12 of the boiler 10 and includes a hopper 42 for receiving the coarse coal particles from a duct 44 extending from the upper portion of the separator 30 above the screen 34. The distributor 40 operates to feed the coarse coal particles 34 by gravity, onto a rotating blade assembly 46 which operates to propel the coarse particles through an opening in the wall 12 into the interior of the boiler 10 and onto the upper surface of the bed 18.

A storage tank 50 is located externally of the boiler 10 and receives the slurry containing the fine particles from the separator 30, via a duct 52. A pump 54 extends between an inlet duct 56 connected to the tank 50 and an outlet duct 58, extending through the wall 12 to pump the slurry containing the fine particles from the tank 50 into the bed 18.

To start up the bed 18, the dampers 26 associated with the air inlet 24 are opened, and air is thus distributed upwardly through the chamber 22, through the perforations in the grate 20 and into the bed 18. This loosens the particulate material in the bed 18 and reduces material packing and bridging.

A light-off burner is fired to heat the material in the bed 18 until the temperature of the material reaches a predetermined level, at which time the separator 30 and the spray bars 36 are activated to separate the fine particles from the coarse materials. The distributor 40 and the pump 54 are activated to introduce the coarse materials to the upper surface of the bed 18 and the slurry containing the fine materials into the bed.

After the bed 18 has been fluidized and has reached a predetermined elevated temperature, the light-off burner is turned off while the distributor 40 and the pump 54 continue to distribute the particulate fuel to the bed 18 in accordance with predetermined feed rates.

It is thus seen that the present invention provides an effective yet simple method of insuring optimum distribution of particle fuel material of a relatively large particle size range.

It is a still further object of the present invention to provide a system of the above type which minimizes escape of the relatively fine materials from the bed.

It is a still further object of the present invention to provide a system of the above type in which the combustion and sulfur capture efficiency of the fluidized bed are increased.

It is understood that if the reactor of the present invention is used for steam generation, a plurality of heat exchange tubes carrying water may be routed through the interior of the boiler 10 in a conventional manner with these tubes being omitted in the drawing for the convenience of presentation.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

Claims

1. A fluidized bed reactor comprising a housing, grate means supported in said housing and adapted to receive on its upper surface a bed of particulate material at least a portion of which is combustible, means for passing air through said grate means and said particulate material to fluidize said particulate material, means for distributing a relatively coarse particulate fuel material to the upper surface of said bed and means for distributing a slurry containing a relatively fine particulate fuel material into said bed below the upper surface of said bed.

2. The reactor of claim 1, further comprising separator means for receiving particulate fuel material of a relatively large particle size range and separating the fuel material into relatively coarse and relatively fine particles.

3. The heat reactor of claim 2 wherein said separator means includes a screen for receiving said particulate fuel material and allowing said relatively fine particles to pass therethrough.

4. The reactor of claim 3 further comprising means for discharging water onto said screen to promote the separation of said coarse particles from said fine particles and for forming a slurry containing said fine particles.

5. The reactor of Claim 4 wherein said second mentioned distributing means comprises a pump for pumping said slurry containing said fine particles into said bed.

6. A reactor as claimed in Claim 1 substantially as herein described with reference to the accompanying drawing.