GB2069861A

GB2069861A - Fluidized bed gasifier

Info

Publication number: GB2069861A
Application number: GB8103928A
Authority: GB
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1980-02-19
Filing date: 1981-02-09
Publication date: 1981-09-03
Also published as: GB2069861B; IN152976B; ZA811073B

Abstract

A fluidized bed 2 has heating coils 4 within a bed of coal to be gasified. A combustion system 10 for the char produced by the gasifier is provided and its products of combustion flow through the bed heating coils, thus supplying heat to the bed. A steam generator 15 receives the output of the heating coils so that the heat from the output of the coils can be utilized to generate low pressure, superheated steam which is conducted to the fluidized bed to both fluidize and react with the bed producing a medium BTU gas free of nitrogen. Initially burner system 10 burns any auxiliary fuel until bed 2 produces sufficient char. <IMAGE>

Description

SPECIFICATION Fluidized bed gasifier The present invention relates to the gasification of a bed of carbonaceous material by the heating of the bed indirectly by means of a slagging burner connected to coils in heat exchange relation with the bed. The bed is fluidized by steam produced by the residual heat flowing from the coils after passing through the bed. More particularly, the invention relates to producing a medium BTU fuel gas from a carbonaceous bed indirectly heated by a slagging burner firing the char produced from the bed and fluidized by steam generated by heat flowing from the bed heating coils.

It is well known to gasify carbonaceous material, principally coal of all grades, to produce medium BTU fuel gas. When carbonaceous material can be gasified in the presence of little or no nitrogen, and at substoichiometric conditions, the produced gas will include H2O, CO, CO2, and hydrogen as well as sulfur compounds if the carbonaceous material contains sulfur.

The gas produced by this method will have a heat content within a range including 300 BTU per scf and can be readily separated from undesirable constituents for substantially clean use in industrial processes. The sulfur compounds and other undesirable constituents can be cleaned from the gas produced by well-known processes which will not be presently considered.

The process of gasification of beds of carbonaceous material can be facilitated by fluidizing the bed.

Various gaseous fluids have been utilized in fluidizing these beds. Further, oxygen-enriched gaseous fluids have been generated to produce a useful fuel gas which is low in nitrogen. In this art, it is desirable to fluidize the bed while producing a nitrogen-free gasification of the carbonaceous bed.

If the gasification process can utilize separate combustion of the char in the bed to sustain the gasification of the bed, generate steam for fluidizing the bed, and utilize any residual heat from the steam generation for raising the temperature of the combustion airforthe char burner, the resulting system will not only be simpler than the present art but will conserve energy beyond present expectations. For example, there will be no need for a separate generator for an oxygen-enriched gas for substoichiometric combustion of the bed of carbonaceous material.

According to one aspect of the invention there is provided apparatus for gasifying carbonaceous material in a vessel which enables the material to be heated by coils within the material and fluidized by a gaseous fluid, comprising heat exchange coils mounted in direct contact with a bed of the carbonaceous material, a burner connected to the coils and adapted to burn both char produced by the gasification of the bed and other fuels in producing slag-free products of combustion through the coils, a steam generator connected to the output of the coils to receive and utilize the heat of the products of combustion discharged by the coils to produce low-pressure superheated steam, means for connecting the steam output of the generator to the lower portion of the vessel in which the carbonaceous bed is mounted to fluidize the bed and promote gasification of the bed, and means for conducting the gas of medium BTU content per scf from the gasification of the carbonaceous material of the bed.

This invention contemplates a slagging burner which will initially supply products of combustion from the burning of any available form of fuel to produce the heat required to initiate the gasification of a bed of carbonaceous material such as coal. The burner may be established at a location separate from the bed to be gasified and produces nonslagging products into heating coils in contact with the bed to be gasified. The temperature of the products of combustion leaving the burner is normally maintained less than 2000"F to avoid adhering to surfaces by any solid particles which remain in the products of combustion. Upon production of char by the bed, the char will be utilised as fuel for the burner to produce the gasifying heat. Products of combustion discharged from the slagging burner are conducted to heating coils disposed inside the fluidized bed.Heat is supplied to the bed through those heating coils. Products are discharged from the coils to a steam generator where steam is produced, such low pressure, superheated steam being conducted to the bed forfluidizing the bed during its gasification.

Apparatus and process embodying the invention are hereinafter described, by way of example, with reference to the accompanying drawing.

The drawing diagrammatically represents apparatus including a fluidized bed of carbonaceous material heated by a burner and supplied steam for fluidizing the bed and including the present invention.

The drawing shows apparatus to carry out the invention in a very brief form. It will be evident that the invention will be adequately disclosed although the drawing is diagrammatic in nature.

The main feature of the apparatus of the drawing is a gasifiervessel 1.

In this vessel is mounted the bed 2 which is to be converted into the medium BTU gas by means of the carbon/steam reaction. The produced gas is passed from the bed through conduit 3. Any removal of undesirable constituents from the produced gas is carried out by equipment downstream of gasifier vessel 1 and is not a part of the present disclosure.

The bed is heated by coils 4. At the same time, the bed is physically fluidized by the injection of steam which enters from the bottom of gasifier vessel 1 through conduit 5.

The heating medium introduced into coils 4 will be in the order of 1800-20000F and will supply indirect heating for the gasification of the carbonaceous material of bed 2.

The present invention contemplates utilizing a low pressure superheated steam for fluidizing bed 2. The use of steam forfluidizing the bed 2 while the bed 2 is heated by coils 4 will exclude nitrogen from the final product. It is evident that if steam can be utilized to both fluidize and produce a nitrogen-free gaseous product, the need for an oxygen-generating plant to supply an oxygen-enriched environment for the substoichiometric combustion of bed 2 will be unnecessary.

The heating medium for coils 4 is supplied by the products of combustion from burner 10. Burner 10 is capable of burning any number of fuels. Burner 10 is positioned remote from gasifier vessel 1 and is connected to coils 4 in vessel 1 by conduit 11. The products of combustion from burner 10 are expected to have a temperature in the range of 1800-2000"F.

It is anticipated that burner 10 can initially produce its products of combustion by any auxiliary source of fuel brought to the burner through conduit 12. Once bed 2 begins to gasify and produce char, this char is transported to burner 10 through a system represented by conduit 13. The operation will be selfsustaining for so long as carbonaceous material is continuously supplied to replenish gasifying bed 2.

The products of combustion which heat bed 2 are withdrawn from coils 4 through conduit 14. It is anticipated that sufficient heat will be available in these products of combustion to generate steam at 15. The low pressure, superheated steam from generator 15 is then conducted by conduit 5 to the bottom of gasifier vessel 1 for the fluidizing of bed 2. In the event that additional heat is required, supplemental fuel can be fired in the steam generator as indicated by conduit 16.

Finally, combustion air required by burner 10 is indicated as passing through heat exchanger 17 to remove all heat practicable from the output of steam generator 15. This heated combustion air is then transported through conduit 18to burner 10.

The embodiment of the invention is dominated by the gasifiervessel 1. The bed 2 is fluidized by the very medium which reacts with the bed to produce the medium BTU gas product.

Uniquely, the bed is indirectly heated by the products of combustion from burner 10, the burner initially fired by any available auxiliary fuel. Subsequently, as char is produced by bed 2, the char becomes a fuel for burner 10. At the same time, the air for combustion of burner 10 is heated by the products of combustion from the burner in heat exchanger 17.

Not to be overlooked is the important a range mentwhereby products of combustion from burner 10 are also used to produce steam in generator 15 which fluidizes and reacts with bed 2.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and inherent to the method an apparatus.

It will be understood that certain features and subcombination are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the invention.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted in an illustrative and not in a limiting sense.

Claims

1. Apparatus for gasifying carbonaceous material in a vessel which enables the material to be heated by coils within the material and fluidized by a gaseous fluid, comrising: heat exchange coils mounted in direct contact with a bed of the carbonaceous material; a burner connected to the coils and adapted to burn both char produced by the gasification of the bed and other fuels in producing slag-free products of combustion through the coils; a steam generator connected to the output of the coils to receive and utilize the heat of the products of combustion discharged by the coils to produce low-pressure superheated steam; means for connecting the steam output of the generator to the lower portion of the vessel in which the carbonaceous bed is mounted to fluidize the bed and promote gasification of the bed;; and means for conducting the gas of medium BTU content perscffrom the gasification of the carbonaceous material of the bed.

2. Apparatus according to Claim 1, including; a heat exchanger for combustion air connected to receive the products of combustion discharged from the steam generator; and means for flowing the air from the heat exchanger to the burner.

3. Apparatus according to Claim 1, including; means for supplying fuel other than char to the burner to initiate gasification of the bed of carbonaceous material; and means for substituting char to the burner as a fuel after the initiation of gasification.

4. Apparatus according to Claim 1, in which the carbonaceous material of the bed is coal.

5. Apparatus according to Claim 1, including, means for supplying the source of heat to the steam generator in addition to the heat from the products of combustion from the burner.

6. A process for gasifying carbonaceous material in the form of a bed within a vessel having coils in heat exchange within the bed and means for distributing fluids up through the bed, including; burning fuel other than char to generate slag-free products of combustion; passing the products of combustion from the burner through the coils within the bed to initiate gasification ofthe bed; passing the products of combustion from the coils into a steam generator to produce low pressure superheated steam; passing the steam as a fluidizing medium up through the bed to sustain the gasification of the bed; and passing the char from the bed gasification to the burner in substitution for the initial fuel supplied the burner.

7. The process of Claim 6, including; passing the products of combustion from the steam generator to a heat exchanger for raising the temperature of combustion air flowed to the burner.

8. Apparatusforgasifying carbonaceous mater ial, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

9. A process for generating carbonaceous material, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.