CA1208910A - Vapor generating system having a plurality of integrally formed gasifiers extending to one side of an upright wall of the generator - Google Patents

Abstract

VAPOR GENERATING SYSTEM HAVING A PLURALITY OF
INTEGRALLY FORMED GASIFIERS EXTENDING TO ONE SIDE
OF AN UPRIGHT WALL OF THE GENERATOR

ABSTRACT OF THE DISCLOSURE
A vapor generating system in which a furnace section is provided that is formed by four upright walls. A plurality of openings are formed in one of the walls, and a plurality of gasifiers extend adjacent said one wall and surround the openings so that the respective interiors of the gasifiers communicate with the openings. A bed of absorbent material is supported in each gasifier for adsorbing the sulfur generated as a result of the gasification of fuel introduced into the gasifier, and air is passed through the bed of adsorbent material to fluidize said material so that, upon combustion of said fuel, a substantially sulfur-free product gas is produced which passes from the gasifier, through the openings and into the furnace section.

Description

P89~
VAPO~ GENE:RAIING S~'STE~l HAVIN(; A Pl,URALITY O~
I~TEGR~LLY ~OR~D GP~SIFIERS EXTENDING ~O ONE SIDE
0~ AN UPRIGHT WALI. O~ THE GENERATOR

BACKGROUN~ O~ THE II~VENTION
This invention relates to a vapor generating system ~nd, more par~icularly, to such a system in which a vapor gPnerator burns a relatively low B~U produc~ gas essenti211y free o sulfur which is yenerated by a gasifier located integxal with the ~ap~r generator.
The Environmental Pr~ection Agency and various s~ate ~- . agencies have esta~lished standards of performance that .. . . . . ~ . .
de~ine maximum allowable sulux dioxide emission levels ~ar fossil ~ueled power sta~ions. I~ response to these sta~dards, .. . .
a genèration of stack gas clean up e~uipment has been designed ~o xemove or scrub sulfur di~xide frQm ~he steam generat~r ~lue gases prior to release into the atmosphere. Since lar~e volumes of gas with dilute sulfur dioxide concentra,ions are enountered at the steam generat3r exitt the s~ack gas clean up equipment becomes large an~ expensive.
Instead o~ con'rolling sul~ur dioxide emissions by treating the stack gases it is advant~ge~us to remove sul.u~
. .~ , .
- from the fuel prior to combustion in the steam generator,.
since at this stage the volume of gases reguiring treatme~
is signi~icantly reduced. To this end a gasification proeess has evol~ed that involves the partial combustion o ~uel, such as particulate coal, or heavy ~uel oil in a fluidized bed o~ lime particles~ Desul~urization is accomplished through reaction with the lime particles and a combustible off-gas is produced t~at is ducted to a steam generator where combustion is completea in commercially available gas ~urners.

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However, in these systems, hot gas ducting has to be provided, along with a cyclone separator in the case of particulate coal, to pass the product gas from the gasifier to the steam generator. However, this equipment is expensive and, in addition, since the cyclone separators were less than completely efficient~ the coal particles would enter the furnace and cause an appreciable build up of carbon. There-fore, the gasifier had to be designed to burn the carbon, which often compromised the efficiency of the system.

SU~MARY OF THE INVENTION
Accordingly, the present invention seeks to proyide a vapor generating system in which sulfur is removed from the fuel prior to combustion in the vapor generator.
Further, the present invention seeks to provide a system of the above type in which a chemically active fluidized bed is provided for producing a product gas sub-stantially free of sulfur which is passed to the vapor generator.
~ till further, the present invention seeks to provide a system of the above type in which the sulfur free product gas is generated in a gasifier and passed to the vapor generator without the use of ducting and~or cyclone separators.
A still further aspect of the present invention see~s to provide a system of the above type in~which two-stage combustion is achieved, with sulfur removal in the gasifier, and combustion of the gas together with the carbon parti-culate in the furnace.
The present invention still further provides a system of the above type in which a gasifier is formed integrally with the vapor generator, and is supported in the same manner as the vapor generator.

Toward the ~ulfillment of these and other aspects, the system of the present invention comprises a vapor generator including an upright furnace section. A plurality o vertically spaced gasifiers are respectively provided adjacent one o~ the walls and each supports a bed of ad-sorbent material for the sulfur generated as a result of the combustion of fuel introduced into the bed. Air is passed through the bed of a~sorbent material to fluidize the materia~ so that, upon combustion of the fuel, a sub-stantially sulfur-free product gas is produced. The gasifiers communicate with the interior of the furnace section so that the product gas from the gasifier passes into the furnace section for combustion.

BRIEF DESCRIPTION OF THE DRAWINGS:
The above description, as well as further aspects, features and advantages of the present invention will be more fully appreciated by reference to the following de-tailed description of the presently preferred by nonetheless illustrative embodiment in accordance with the present invention when taken in conjunction with the accompanying drawings in which:
Fig. 1 is a schematic sectional view of the steam genexatingJgasifying system of the present invention;
Fig. 2 is an enlarged sectional view depicting a portion of the system of Fig~ l; and Fig. 3 is a cross-sectional view taken along the lines 3-3 of Fig. 2.

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DESCRIPTION O~ THE PREFERRED EMsoDIMENT

Referring specifically to Fig. 1 of the drawings, the reference numeral 10 refers in general to a vapor generator utilized in ~he system of the present invention which includes a lower furnace section 12, an intermediate furnace section 14, and an upper furnace section 16. The boundary walls defining the furnace sections 12, 14 and 16 include a front wall 18, a rear wall 20 and two sidewalls extending between the front and rear wall, with one of said sidewalls being re erred to by the reference numeral 21.
Although only shown schematically for the convenience of presentation, it is understood that each of the walls 18, 20 and 21 are formed of a plurality of tubes having continuous fins extending outwardly from diametrically opposed portions thereof, with the fins of adjacent tubes being connected together in any known manner, such as by welding, to ~orm a gas-tight structure.
The lower portions of the front wall 18 and the rear wall 20 are sloped inwardly from the intermediate furnace section 14, as shown by the reference numerals 18a and 20a, respectively, so tha~ the lower furnace section 12 is in the form of a hopper.
Four integral gasifiers 22, 24, 26 and 28 are located to the side of the generator 10 and adjacent the front wall 18.
The gasifiers 22, 24, 26 and 28 include vertical wall portions 30, 32, 34 and 36 respectively, extending in a parallel spaced relation to the front wall 18, to define a chamber 38 which communicates with a plurality of refractory aligned openings 40 formed alony the lower portion of the front~,wall 18. A
plurality of nozzles 42 are supported by a vapor generator wind-box support structure 44 extending intermediate the front wall ''i'~..'

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1~ and the wall portions 30 and 32, with the discharge endof each nozzle extending within a corresponding opening 40.
A preheater 46 is provided in a heat exchange relation with a duct 48 which receives air from an external source and conveys the preheated air to a windbox 50 which surrounds the gasifiers 22, 24, 26 and 28. The la~er gasifiers are spaced apart vertically so ~ha~ the preheated aix from the windbox 50 enters each gasifier through a grate forming ~he floors of the gasifiers as will be described la~er~ A series of dampers 51 are provided in the duct 48 for controlling the flow of air ~ through.*he-.-.latter.duct, the windbox 50 and into the gasLfiers 22, 24, 26 and 28 as shown by the solid flow arrows. F~rther detail~ of the axrangement and operation of the gasifiers 22, ~4, 26 and 28 will be described later.
. A duct ~ ~ranches from ~he duct 48 and is connected to the vapor generator windbox support structure 44 in suc~ a manner so as to direct a portion of the air from the duct 48 i~o and through the openings 40 in the front wall 18. A series ~
dampers 53 are pro~ided in the duct 52 for con~rolling ~e flow o air through the latter duct~
A heat recovery area, shown in general by the referens~e numeral S4 is provided ad~acent the upper furnace secti~ ~.6 in gas flow ~0~ n i.cation therewith and includes a vesti~e section 56 and a convection section 580 . The convection section 58 includes a ~ront ~all 6~, rear wall 62 and two sidewalls 64, with one of the lat~e~
being shown in Fig. 1. It is understood that the rear wall 62, the sidewalls 64 and the lower portions of the front wa~ ~0 are all ormed of a plurality of vertically extendin~, ~inned interconnected tubes in a similar manner to that of the fuxnace sections, and that screen openings are provided in the upper portion of the wall 60 to permit communication between the vestibule section and the convection section 58.

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A partition wall 66, also formed by a plurality of fin-ned intexconnected tubes, is provided in the convection section 58 to divide the latter into a fron~ gas pass 68 and a rear gas pass 70. ~n economizer 72 is disposed in the lower por-tion of the rear gas pass 70, a primary superheater 7~ is disposed immediately above the econo~izer, and a ban~ of reheater tubes 76 is provided in ~he front gas pzss 68.
A platen superheater 78 is provided in the upper furnace ,section 16 and a finishing superheater 79 is provided in the vestibule section 56 in direct fluid communication with the platen superheater 78. --A plurallty of division walls, one of which is show~
by the r~ference numeral 80, extend in the upper furnac~ sec-tion 16 with each wall being formed by a plurality of i~ter-connec~ed tubes. Each division wall 80 penetra~es a portion of the tubes of the rear wall ~0 and extends upwardly wi~hin the upper furnace section 16 as shown~
A roof 82 is disposed in the upper portion of the va~or ` generator 10 and consists o~ a plurAlity of tubes having f~ns connected in ~he mannar described above but ex~ending horizon-tally across the generator 10~ The roof 82 is top suppor~d to an upper support structure (not shown) b~ a plurality of support members 84 to permit thermal expansion of'the en~ire s~ructure including the vapor genexator 10 and the gasifiers 22, 24, 26 an~ 28 in a downward direction, as viewed in ~he drawing.
The gasifiex 22 is shown in detail in Figs. 2 and 3, it being understood that the other gasifiexs 24, 26 and 28 are all constructed and arranged in an identical manner. The aasi-fier 22 includes a gasifyi~s section 86 and a regeneratins sec~tion 88 separated by a vertical wall 90 extendin~ in a s~aced, parallel relation to the wall 30. A grate 94 forms tlle floor of the gasifier 22 and is adapted to receive a plurality of ~-shaped air distributor pipe assemblies 96 ~thich receive air from the nd~c)x 50 ~n~ in .r~duces the 2ir in,o tne g2s~ ying section 8 6 c~ nd ,he regener~ting se~ .iC?n 8 8 . AAS be . ~er sho~ ig . 3, each pipe ~sse~nbly 96 inclu~es c ~Jer,icâl ~ipe g62 which ex,ends throush an oper~ins in the sr2~e 34 and ~ ~o~izonLa~
pil~e 96~ connec.e~ in registry with ~,he ve-~Licc~ e.
ticul2 .e cc~ ,l L eeder 9 8 ~ is supp~-~e~
. on the ~ron~ up~ight wall oS eac~ g~.si::ier 22, 24, 2~, and 28 fo-con-,_inuc~usly disch?rirlg p~r,icul2. .e C~21 on.o ~be llu~ di~ed 3~ed in each g2si:~ier . ~ltern~tely; ~ lity o o~ 1 distribu~or 10 pipe asse~r~lies (n,o . shown~ cc)u~ d ex~end through c~ther c)penings in -~he gra~e g4 bel~w ~he gasi~yin~ sec ~ion 8 6 with each ~ssembly be~ ng c:onnected ,o ^c sc)urce 0c ~ or s~lpplying s~urce to the g si~iers.
~ A feeder 100 extends throush 2 siQeW~ll of the gasifier 22 and is adap,ed to feed an a~sorbent, such 25 l~mestone, in.o the ga~i~yi~S sec~ic~ 8~.
. . ~ divider wall 1~ is disposed in .he 92sifying section 86 ~o divide it in~c cha~ber ~6a and 86b (~ig. 3~P The di~i~er wall 102 extends fr~m the ~artition ~0 (Fig~ 2~ to an area ~ ~paced from the opposite wall ~o de ine 2 ~2s52ge ~6c t~ig. 2) communicatin~ with the ch~mbers 86a zn~ 86b.
An inlet ~lo, 106 and an o~leL S1OL 108 are ~ormed in the pzrtition ~0 ~Sith ,he forSner comr.~nlca.ing gasifyi~g ch~mber 86~ with the regener2ting section 8~ ænà the 12,ber com-muicating ~h~ s2sifying chaS~ber 86b ui.n Lhe regenera~iny secticn.;
As a result of this 2rrzngement 2 mi~ture o~ limestone and ~uel continuclly flows from the s~sifying ch~mbex ~6~, 2round the ~assage 86c, throu~h the sasiCying ch2mber 86a and the slot 1~6 2nà into bhe regenera.ins secti~n 88 znd, from the .
latter seo,ion, Lhr~ugh the slct 108 2no into the gasif~ing cha~er ~6h f~r rec~rculation.
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~ A discharge manifold 110 communicates with the u~Per .
portion of the xegenerating section 88 to disch2rge the sulfurgas produced in the regenerating section to external sulLUr recovery equipment tnot shown). Towards this end the manifolds 110 from each gasifier 2~, 2~, 25 and 28 can be connected as shown by the dot-dashed line in Pig. 1 to provide a single source o~ the sulfur gas.
Since the gasifiers 24, 26 and 28 are arranged and operate in a manrler identical to the gasilier 22, they will not be described in detail. In this context it is noted that the horizontal and vertical wall portions forming the gasifiers 22, 24, 26 and 28 can be water cooled as in the case of the other walls discussed above, i.e., they can be formed by a plurality of finned interconnected water tubes.
In operation, the temperature in each fluidized be~
in the gasi~ying sections 86 of ~he gasifiers 22, 24, 26 and 2 8 i5 malntained at a predetermined elevated value Csuch a~
1600F) by control of the fuel entering their respectiYe beds.
Air from the windbox 50, via the preheater ~6 and the duct 48, is admi~ted into the gasifying section 86 of each gasifier through the air distributor pipe assemblies ~6 i~ substo~chio-metric proportions to limit the amount of combustion and heat release.
Partial combustion o~ the fuel enterina the gasif~ing section 86 with approximately 25 to 30~ stoichio~etric air furnishes sufficient heat to parti~lly combu~t the fuel and, when oil is used, to vaporize and crack the remaining oil. This partial combustion results in the formation of hydrogen sul~ide which reacts with the fluidized bed of lime to form c~lcium sulfide and water vapor. The gaseous product of this ~rocess is an essentially sulfur free and vanadium free fuel ~as which ~z~
rises in the gasifylng section 86 and exits the latter section via spaces fQrmed between the adjacent walls 30, 32,

3~ and 36 as shown ~y the dashed flow arrows in Fig. 1. The gases then enter the chamher 38 and p255 throu~h nozzles A2.
Secondary air from the duct 52 enters the openinSs 40, burning the gases to co~pletion in the in~ermediate ~urnace section 14 in a conventional manner. The capacity for sul~ur reten~ion by the gasifying section 86 is maintained by the continuDus remo~al of the sulfated lime and the replenishment of this material with sulfur-free lime through the feeder 100. q'he sulfated lime, along with the spent fuel particles is dis-charged ~rom each gasifier 22, 24, 26 and 28 in a convent~onal manner, such as by a drain pipe, or the li~e ~not shown).
Air from the windbox 50 is also admitted into the regenerating section 88 through he pipe assemblies 96, am~ the calcium sulfide formed in tAe gasifying section 8~ is circ~lated through the regenera ing section 8g as discussea a~ove, to convert the calcium sulfide to calcium oxide wh~e produc~g an off-gas with a high sulfur dioxide concentration. As the calcium sulfide is transferred into the o~ygen ~icb regenel~ting section 99 pxeferably at about 1900F, the foll~wing react~vn takes place:
CaSO4~CaS+ 2 > ~CaO t 2SO2 ~ he sulfur dioxide formed by the above rea~o~ exits from the re~enerating sectiGn 88 o each gasifier 22, 2~, ~6 and 28 through their respective discharge manif~Lds 110, ~s combined as discussed above and is rec~vered by e~ernal ~quip-ment from the gas stream in the form of elemental s~l~ur, while calcium oxide is recirculated back ~o the gasifying section 86 for re-use as a sulfur absorbent.

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Referring again to Fig. 1, the combustion gases produced as a result of the combustion of the sulfur-free product gases from the gasifiers 22, 24, 26 and 28 in the intermediate furnace section 14 pass upwardly to the upper furnace section 16 and through the heat recovery area 54 before exiting from the front gas pass 68 and the rear gas pass 70. As a result, the hot gases pass over the platen superheater 78, the finishing superheater 79 and the primary superheater 74, as well as the reheater 76 and the economizer 72 to add heat to the fluid flowing through these circuits. The hot gases then pass through the air preheater 46 to preheat the air entering the duct 48.
Although not shown in the drawings for clarity of present-ation, it is understood that suitable inlet and outlet headers, downcomers and conduits, are provided to place the tubes of each of the aforementioned walls and heat exchangers as well as the roof in fluid communication to establish a "once--through"
flow circuit for heating the entering wa-ter to vapor. To this end, feedwater from an external source is passed through the economlzer 72 to raise the temperature of the water before it ~ is passed through the walls of the gasifiers 22, 24, 26 and 28 and, from the latter walls to the divisional walls 80. From the latter walls, the heated water is passed to inlet headers (not shown) provided at the lower portions of the furnace walls 18, 20 and 21. All of -the water flows upwardly in series through the walls 18, 20 and 21 to raise the temperature of the water further, i.e., subcritical or to convert at least a portion of same to vapor, i.e., supercritical, before it is collected in suitable headers located at the upper portion of the vapor generator 10. The fluid is then passed downwardly through suitable downcomers, or the like, and then directed through ~8~

heat recovery area 54 after which it is collected and passed through the roof 82. From the roof 82, the fluid is passed via suitable collection headers, or the like, to separators (not shown) which, during start-up, separate the vapor portion of tne fluid from the li~uid portion thereof. The liquid por-tion is passed from the se~ar2tors to a drain manifold and heat recovery circuitry (not shown) for further treatment, and the vapor portion of the fluid in the separators is passed directly into the primary supexheater 74. From this latter 1~ the fluid is spray attemperated after which it is passed to the platen superheater 78 and the finishing superheater 7g before it is passed in a dry vapor state to a turbine, or the like. After start-up, the separators merely act as trans~r headers.
It is understood that the arrangement of the present invention is egually applicable to a natural circu~ation sys~em utilizi~g a steam dxum or drums in a conventional manner.
As a result o~ the foregoing a sulur-free product is ~x~duced and is introduced directly into ~he Y~pOX generator without the need for hot gas ducting and cyclone separators_ Also, the furnace can be designed to accept and burn a cert~
amount of solid particulat~ carbon which is entrained in th~
yasas exiting from the gasifier; thus eliminating the neces~
o burnins ~his carbon in the gasifier.
A latitude of modification, change and substitution is intended in the foregoing disclosure and in so~e instances some eatures o~ the invention will be employed without a corresponding use of other features. According, it is appropriate that the appended clai~s be construed broadly and in a manner consistent with the spirit and scope of ~he invention therein.

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An integral generator/gasifier system comprising a vapor generator including a furnace section formed by four upright walls, a plurality of openings formed in at least one of said walls, a plurality of vertically spaced gasifiers extending adjacent said one wall and surrounding said open-ings, so that the respective interiors of said gasifiers communicate with said openings, means for introducing fuel to each gasifier, means in each gasifier for supporting a bed of adsorbent material for the sulfur generated as a result of the gasification of said fuel, and means for passing air through said bed of adsorbent material to fluidize said material so that, upon gasification of said fuel, a substantially sulfur-free product gas is produced which passes from said gasifier, through said openings and into said furnace section, such that combustion of the gas and unreacted carbon occurs.

2. The system of Claim 1 wherein each gasifier includes means for generating the adsorbent containing said sulfur to produce a sulfur gas.

3. The system of Claim 1 wherein said fuel is coal which is introduced into said fluidized bed.

4. The system of Claim 1 wherein said fuel is oil which is injected into said fluidized bed.

5. The system of Claim 1 wherein said gasifiers are spaced from said one wall of said furnace section to form a gas chamber for receiving gas from said gasifiers and directing said gas to said openings.

6. The system of claim 5 further comprising a plurality of nozzles extending from said gas chamber into said openings for receiving said gas from said gasifiers and introducing it to said furnace section.

7. The system of claim 1 further comprising a windbox surrounding said gasifiers.

8. The system of claim 7 further comprising a source of air, and duct means for passing said air to said windbox.

9. The system of claim 8 further comprising means for passing the combustion gases from said furnace section in a heat exchange relation to said air before said air is passed to said windbox.

10. The system of claim 1 wherein said upright walls of said furnace section and the walls of said gasifier are formed by a plurality of tubes for receiving water to heat said water to vapor.

11. The system of claim 1 wherein said gasifiers are each integrally formed with a sorbent regenerator.

12. The system of claim 1 further comprising means for top supporting said gasifiers and vapor generator to permit thermal expansion in a downward direction.