CA1311132C - Method for driving a gas turbine - Google Patents

Method for driving a gas turbine

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Publication number
CA1311132C
CA1311132C CA000564983A CA564983A CA1311132C CA 1311132 C CA1311132 C CA 1311132C CA 000564983 A CA000564983 A CA 000564983A CA 564983 A CA564983 A CA 564983A CA 1311132 C CA1311132 C CA 1311132C
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CA
Canada
Prior art keywords
gases
turbine
air
fuel
passing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA000564983A
Other languages
French (fr)
Inventor
Juan Antonio Garcia-Mallol
Michael Gerard Alliston
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Foster Wheeler Energy Corp
Original Assignee
Foster Wheeler Energy Corp
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Filing date
Publication date
Application filed by Foster Wheeler Energy Corp filed Critical Foster Wheeler Energy Corp
Priority to CA000564983A priority Critical patent/CA1311132C/en
Application granted granted Critical
Publication of CA1311132C publication Critical patent/CA1311132C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Abstract

METHOD FOR DRIVING A GAS TURBINE

Abstract of the Disclosure A method for driving a gas turbine in which air is passed through a bed of particulate material including fuel with the quantity of air being insufficient for complete combustion of the fuel but sufficient to generate a com-bustible off-gas. Additional air is added above the fluidized bed to complete the combustion of the fuel and produce flue gases. The off-gas is discharged from the vessel and is combusted to raise the temperature of the flue gases before they are passed to a turbine.

Description

METHOD FOR DRIVING A GAS TURBXNE

Backqround of the Invention This invention relates to a method of driving a gas tur-bine, and more particularly, to such a method utilizing a combined fluidized bed boiler and gasifie~ For generating gases to drive the turbine.
Combustion systems utilizing fluidized beds as the pri-mary source of heat generation are well known. ID these arrangements, air is passed through a bed of particulate material, including a fossil fuel such as coal and an adsor-bent for the sulphur generated by the combustion of the coal, to fluidize the bed and promote the combustion of the fuel at relatively low temperatures. When the combustor is pressurized, the hot gases produced by the fluidized bed can be used to drive a turbine Eor the generation of electrical power.
One of the characteristics of a fluidized bed combustion bed process is a relatively low gas temperature which is necessary in order to keep the pollutant emissions low.
However, this results in a compromise in -the combined boiler-turbine cycle efficiency since the turbine can be operated with gas temperatures well in excess of the maximum permi-tted in a fluidized bed boiler. Hence, in order to increase the temperature of the gas entering the turbine to improve the cycle efficiency, it has been proposed to gasify a slip stream of the fuel feed in a separate vessel. This fuel gas stream is then combined with the flue gases from the boiler in a burner to raise the temperature of the latter gases to acceptable levels. ~owever, this require-ment of an additional gasifier considerably adds to the cost of the process and is thus undesirable.
Summary of the Invention It is therefore an object of the present invention to provide a method for generating qases for driving a turbine which eliminates the cost of a separate gasifier.

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It is ~ further objec~ of the p~esen~ invention to p~ovide a method of the above -type in which a fluidized bed boiler is provided which has a gasifier section which generates gases that are partially combusted, and extracts a portion of them so that, when recombined witll the flue gases from the boiler in a burner, the gases attain an elevated temperature consistent with the optimum operation of the gas turbine.

Toward the fulfillment of these and other objects, the present invention provides a me-thod of operating a gas turbine comprising tlle steps of passing air through a bed of particulate material including fuel disposed in a vessel, the velocity of said air being su~ficient to fluidize said particulate material and promote the combustion of said fuel, and the quantity of said air being insufficient for complete combustion of said fuel but sufficient to generate combustible off gases, adding additional air to said vessel at a location above said f luidized bed and below said outlet to complete said fuel combustion, said off gases and the flue gases from said combustion being at a first temperature effective to minimize pollutant emissions, said flue gases passing through the length of said vessel and entraining a portion of said particulate material before discharging from an outlet in the upper portion of said vessel, separating the entrained particulate material from said -3a-flue gases in a separa-tor, passing said separated flue gases from said separator directly to a burner, discharging a portion of said off gases from an outlet of said vessel located upstream of said location where said addition~l air is added, separating the entrained particulate material from said off gases in a separator, passing said separated off gases directly to a burner, burning said separated off gases and said separated flue gases to raise their temperatures to a second temperature effective to drive a turbine, and then passing said gases to a turbine.

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Brief Description of the Drawings The above brief description, as well as further objects, fea-tures and advantages of the present invention will be more ~ully 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 conjunction with the accompanying drawings in which:

Fig. l is a schematic view of the components utilized in the method of the present invention; and Fig. 2 is a view similar to Fig. l but showing an alternate embodiment of the present invention.

Description of the Preferred Embodiments Referring specifically to the drawings, the reference numeral~10 refers to a fluidized bed boiler which contains a bed 12 of particulate material including fuel and a sorbent for absorbing the sulphur generated by the combustion of the fuel. A conduit 14 introduces air into the lower portion of the boiler 10 and the air passes through a perforated grate 16 and is thus evenly distributed through the bed 12 to .~`

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fluidize the ~aterial. An air compressor 15 operates in a conventional manner to supply pressurized air to the conduit 14. The quantity of the air is insufficient for complete combustion of the fuel but sufficient to generate a com-bustible off-gas. A branch conduit 14a extends from the conduit 14 and introduces air at a point above the fluidized bed 12 which is sufficient to complete the com-bustion of the fuel. Although not shown in the drawings it is understood that one or more feeders, or the like, are provided to introduce additional fuel and adsorbent material into the bed as needed and also provided are one or mo.e extraction units so that solid products do not accummulate in tne bed.
The gases not combusting in the bed combine with the gaseous products of combustion and with the air introduced ~Jia the conduit 14a to form a flue gas that passes through the length of the boiler before exiting from an outlet on the boiler 10 and into a conduit 18 which is connected to the inlet of a cyclone separator 20. An outlet conduit 22 is disposed between the air distribution grid ~late 16 and the point of introduction of the additional air from the ^L '~ 3~ ~J ~, conduit 14a and receives the combustible off-gas from an outlet of the boiler 10 and discharges it into a second cyclone separator 24.
The solid particulate separated from the gases in the separators 20 and 24 are discharged from their lower por-tions thereof into a conduit 26 which re-injects the par-ticulate material through a suitable inlet of the boiler 10 and back into the bed 12. The separated gas from the separators 20 and 24 pass, via condui~s 28 and 30, respec-tively, into two clean-up units 34 and 36, respectively, for effecting an ?dditional separation of any impurities or solid particles from the gases.
Two conduits 38 and 40 respectively connect the clean-up units 34 and 36 to a burner assembly 42 which functions in a conventional manner to ignite the gases in the presence of excess air in conduit 38 and therefore produces a product gas which is Eed, via a conduit 44, to a gas t~rbine 46.
The gas turbine 46 drives an electrical generator 48 in a con~entional manner, and the ~as outlet of the turbine is connected, via a conduit 50, to a waste heat boiler 52.
Feedwater enters the upper Portion of the waste heat boi.ler ~ 3 ~ f;~

52 via a conduit 54 and traverses the length of the boiler and is thus heated before passinq, via a conduit 56, to the fluidized bed boiler 10 and a superheater 58 disposed in the fluidized bed boiler 10. The superheated steam from the superheater 58 is directed, via a conduit 60, to other equipment for further use.
In operation, air from the compressor lS is passed, via the conduit 14, into the fluidized bed 12 in the boiler 10 at a velocity sufEicient to fluidize the bed 12 and promote the combustion of the particulate fuel material in the bed.
The gases not combusting in ~_he b^d comb.ine with the gaseous products of combustion and with the air introduced via the conduit 14a to form a flue gas that passes through the length of the boiler before exiting from an outlet on the boiler and into the conduit 18. During this passa~e, the flue gas entrains the relatively fine particulate material in the bed and is passed into the separator 20. The air introduced into the lower por-tion of the bed 12 in the manner just described is carefully controlled so that i.t is insufficient to completely combust the fuel in the bed but sufficient to generate a combustible off-gas. The branch -a-conduit 14a introduces additional air into an area ~f the boiler lO above the bed 12 in sufficient quantities to complete the combustion.
The conduit 22 receives the off-gas at a point upstream of the introduction of the additional air from the conduit 14a and this off-gas passes into the separator 24.
The gases in the separators 20 and 24 are sepa~ated from their entrained particulate material and the latter is rein-jected, via the conduit 26, back into the bed 12. The rela-tively clean gases from the separators 20 and 24 pass, viathe conduits 28 and 30, into the clean-uP units 3~ ~nd 36, respectively, for further clean-up, and the relatively pure gases then pass, via the conduits 38 and 40, into the burner assembly 42. At the burner assembly 42, combustion of the lS c~mbustible off-gas is achieved in the presence of the flue ~as and excess air in the conduit 38 to raise the tem perature of the gases before they pass, via the conduit 44 into the gas turbine 46.
The spent gases from the turbine pass, via the conduit 50, into the waste heat boiler, and exchanqe heat with feed-water passing through the boiler from the conduit 5~. The relatively hot feedwater from the boiler 52 passes, via the conduit 56, into the fluidized bed boiler 10 where it is converted to steam by passing through the superheater 58.
The superheated steam is then passed, via the conduit 60, to external equipment.
Since the embodiment of Fi~. 2 is similar to that of Fig. 1 and utilizes the same components as in the embodiment of Fig. 1 these components will be given the same reference numerals. According to the embodiment of Fig. 2 a second-stage turbine 46' is provided in series relationship withthe firc~-stage turbine 46, ~nd two burners 42 and 42' are provided and are connected~ via the conduits 38 and 40, to the clean-up units 34 and 36, respectively. A conduit 62 connects the gas outlet of the first-stage turbine 46 to the burner 42' and a conduit 64 connects the burner 42' to the second stage turbine 46' A bypass conduit 66 is provided for routing a portion of the gases from the clean-up device 36 to the burner 42 as in the previous embodiment.
Thus, according to the embodiment of Fig. 2 the gases from the first-stage turbine 46 pass through the conduit 62, the burner 42', the conduit 64 and into the second-stage turbine ~6', and the spent gases from the latter pass via the conduit 50, to the waste heat boiler 52. Otherwise the operation and function of the embodiment of the Fig. 2 is identical to that of Fig. lo It is understood that the fluidized bed boiler 10 can be of a "bubbling" type or a 'Ifast'' type. In the bubbling type a bed of particulate materials is supported by an air distribution plate, to which combustion-supporting air is introduced through a plurality of perforations in the plate, causing the material to expand and take on a suspended, or fluidized, state. The gas v210city is typically two -to three times that needed to develop a pressure drop which will support the bed weight (e.gA, minimum fluidiza-tion velocity), causing the ~ormation of bubbles that rise up through the bed and give it the appearance of a boiling liquid. The bed exhibits a well-defined upper surface.
When provided with high solids recycle, the bubbling bed can build up its fines content and operate as a circulating fluidized bed.
In a "fast" fluidized bed the mean gas velocity, as a fraction of the minimum fluidizing velocity, is increased ~ 3 ~ ~ _L ~

above that for the bubbling bed, so that the bed surface becomes more difEused and the solids entrainment from the bed is increased. According to this process, fluidized bed densities between 5 and 20~ volume of solids are attained which is well below the 30~ volume of solids typical of the bubbling fluidized bed. The formation of the low density fast fluidized bed is due to its small particle size and to a high solids throughput, wilich require high solids recycle.
The velocity range of a fast fluidized bed is between the solids terminal, or free fall, velocity and a velocity beyond which the bed would be converted in'c a pneumatic transport line.
The high solids circulation required by any circulating fluidized bed makes it insensitive to fuel heat release pat-terns, thus minimizing the variation of the tempera-ture within the steam generator, and therefore decreaslng the nitrogen oxides formation. Also, the high solids loading improves the ~fficiency of the mechanical device used to separate the gas from the solids for solids recycle. The resulting increase in sulphur adsorbent and fuel residence times reduces the adsorbent and fuel consumption.

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Several advantages result from the methods of the pre-sent invention. For example, a fluidized bed boiler, with the inherent advantages discussed above is utilized and is operated at the op-timum temperature of 1600 F while elimi-nating the need for utilizing a separate gasifier to raise the tempera~ure of ~he gases to the requisite temperature required by ~he turbine. This is achieved by generating a combustible off-gas in the lower portion of the boiler and utilizing this gas to raise the temperatUre of the flue gases exiting from the boiler. Thus, a relatively efficient operation is achieved.
Other modifications, changes and substitutions are intended in the foregoing disclosure and, in some instances, some features of the invention can be employed without a correspon~ing use of other features. Accordingly, it is appro~riate that the appended claims be construed broadly and in a manner consistent with the scope of the invention therein.

Claims (5)

1. A method of operating a gas turbine comprising the steps of passing air through a bed of particulate material including fuel disposed in a vessel, the velocity of said air being sufficient to fluidize said particulate material and promote the combustion of said fuel, and the quantity of said air being insufficient for complete combustion of said fuel but sufficient to generate combustible off gases, adding additional air to said vessel at a location above said fluidized bed and below said outlet to complete said fuel combustion; said off gases and the flue gases from said combustion being at a first temperature effective to minimize pollutant emissions, said flue gases passing through the length of said vessel and entraining a portion of said particulate material before discharging from an outlet in the upper portion of said vessel, separating the entrained particulate material from said flue gases in a separator, passing said separated flue gases from said separator directly to a burner, discharging a portion of said off gases from an outlet of said vessel located upstream of said location where said additional air is added, separating the entrained particulate material from said off gases in a separator, passing said separated off gases directly to a burner, burning said separated off gases and said separated flue gases to raise their temperatures to a second temperature effective to drive a turbine, and then passing said gases to a turbine.
2. The method of claim 1 wherein said flue gases and said off gases are burned in the same burner.
3. The method of claim 1 wherein said flue gases and at least a portion of said off gases are respectively passed to separate burners.
4. The method of claim 3 wherein the respective gases from said separate burners are passed to a first stage and a second stage turbine, respectively.
5. The method of claim 1 further comprising the step of exchanging heat between the spent gases from said turbine and feedwater to raise the temperature of the feedwater, and passing the feedwater to said fluidized bed boiler to convert said heated feedwater to steam.
CA000564983A 1988-04-25 1988-04-25 Method for driving a gas turbine Expired - Fee Related CA1311132C (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA000564983A CA1311132C (en) 1988-04-25 1988-04-25 Method for driving a gas turbine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA000564983A CA1311132C (en) 1988-04-25 1988-04-25 Method for driving a gas turbine

Publications (1)

Publication Number Publication Date
CA1311132C true CA1311132C (en) 1992-12-08

Family

ID=4137899

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000564983A Expired - Fee Related CA1311132C (en) 1988-04-25 1988-04-25 Method for driving a gas turbine

Country Status (1)

Country Link
CA (1) CA1311132C (en)

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