CA1191703A - Combustion turbine combustor having an improved heavy- oil fuel preparation zone - Google Patents
Combustion turbine combustor having an improved heavy- oil fuel preparation zoneInfo
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- CA1191703A CA1191703A CA000410230A CA410230A CA1191703A CA 1191703 A CA1191703 A CA 1191703A CA 000410230 A CA000410230 A CA 000410230A CA 410230 A CA410230 A CA 410230A CA 1191703 A CA1191703 A CA 1191703A
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- zone
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Abstract
ABSTRACT OF THE DISCLOSURE
A combustor for a combustion turbine comprises an enclosure having apertures for enabling the flow of gases into the enclosure, a zone for mixing and vaporizing heavy oil fuel, fuel injecting means in the downstream end of the fuel mixing zone, and means for supporting combus-tion of the fuel mixture in a combustion zone downstream of the mixing zone. The fuel injecting means is prefer-ably a multiple-point fuel injector and where combustion is by catalyst, a catalytic element is preferably struc-tured in at least two segments.
A combustor for a combustion turbine comprises an enclosure having apertures for enabling the flow of gases into the enclosure, a zone for mixing and vaporizing heavy oil fuel, fuel injecting means in the downstream end of the fuel mixing zone, and means for supporting combus-tion of the fuel mixture in a combustion zone downstream of the mixing zone. The fuel injecting means is prefer-ably a multiple-point fuel injector and where combustion is by catalyst, a catalytic element is preferably struc-tured in at least two segments.
Description
1 49,686 COMBUSTION TURBINE COMBUSTOR HAVING AN
IMPROVED HEAVY-OIL FUEL PREPARATION ZONE
CROSS-REFERENCES TO RELATED APPLICATIONS
Canadian Patent Application No. 405,430, entitled "Combustion Turbine Combustor Having An Improved Fuel-Rich Fuel Preparation Zone" and filed June 17, 1982 by D. E. Carl, et al.
Canadian Patent Application No. 409,000, entitled "Combustion Turbine Comb-ustor Having A Heavy Oil Fuel Preparation Zone With Boundary Protection"
and filed August 9, 1982 by D. E. Carl, et al.
BACKGROUND OF THE INVENTION
The present invention relates to combustion turbines and combustors employed therein and more particularly to an improved fuel preparation zone structure for a pre-mixed, pre-vaporized combustor.
In general terms, the typical prior art combus-tion turbine comprises three sections: a compressor sec-tion, a combustor section, and a turbine section. Air drawn into the compressor section is compressed, increasing its temperature and density. The compressed air from the compressor section flows through the combustor section where the temperature of the air mass is further increased.
From the combustor section the hot pressurized gases flow ~7~
, '7~3~3
IMPROVED HEAVY-OIL FUEL PREPARATION ZONE
CROSS-REFERENCES TO RELATED APPLICATIONS
Canadian Patent Application No. 405,430, entitled "Combustion Turbine Combustor Having An Improved Fuel-Rich Fuel Preparation Zone" and filed June 17, 1982 by D. E. Carl, et al.
Canadian Patent Application No. 409,000, entitled "Combustion Turbine Comb-ustor Having A Heavy Oil Fuel Preparation Zone With Boundary Protection"
and filed August 9, 1982 by D. E. Carl, et al.
BACKGROUND OF THE INVENTION
The present invention relates to combustion turbines and combustors employed therein and more particularly to an improved fuel preparation zone structure for a pre-mixed, pre-vaporized combustor.
In general terms, the typical prior art combus-tion turbine comprises three sections: a compressor sec-tion, a combustor section, and a turbine section. Air drawn into the compressor section is compressed, increasing its temperature and density. The compressed air from the compressor section flows through the combustor section where the temperature of the air mass is further increased.
From the combustor section the hot pressurized gases flow ~7~
, '7~3~3
2 49,6~36 into the turblne section where the energy of the expanding gases is transformed into rotational motion of the turbine rolor .
A typical com'oustor section compr'ses a plural-ity of combustors arranged in an annular array about thecircumference of the combustion turbine. In conventional combustor technology pressurized gases flowing from the compressor section are heated by a diffusion flame in the combustor before passing to the turbine section. In the diffusion flame technique, fuel is sprayed into the up-stream end of the combustor by a nozzle. The flame is maintained immediately downstream of the nozzle 'oy strong aerodynamic recirculation. The lack of thorough mixing of the fuel results in pockets of high fuel concentration and correspondingly high combustion reaction temperatures (approximately 4500R) in Ihose pockets. Because the reaction temperature is hlgh, hot gases flowing from the combustion reaction must be diluted downstream by cool (approximately 700R) air so as to prevent damage to tur-bine components positioned downstream. In addition, theflame diffusion technique produces emissions with signifi-cant levels of undesirable chemical compounds including NOX and CO.
Increasing environmental awareness has resulted in more stringent emission standards for ~x and CO. The more stringent standards are leading to developmen~ of improved combustor technologies. One such improvement is a premixing, prevaporizir.g combustor. In this type of combustor, fuel is sprayed into a fuel preparation zore where it is thoroughly mixed to achieve a homogeneous con~
centration which is everywhere within definite limits of the mean concen~ration. Additionally, a certain amount of the fuel is vaporized in ~he fuel preparation zone. Fuel combustion occurs at a point downstream 'rom the fuel
A typical com'oustor section compr'ses a plural-ity of combustors arranged in an annular array about thecircumference of the combustion turbine. In conventional combustor technology pressurized gases flowing from the compressor section are heated by a diffusion flame in the combustor before passing to the turbine section. In the diffusion flame technique, fuel is sprayed into the up-stream end of the combustor by a nozzle. The flame is maintained immediately downstream of the nozzle 'oy strong aerodynamic recirculation. The lack of thorough mixing of the fuel results in pockets of high fuel concentration and correspondingly high combustion reaction temperatures (approximately 4500R) in Ihose pockets. Because the reaction temperature is hlgh, hot gases flowing from the combustion reaction must be diluted downstream by cool (approximately 700R) air so as to prevent damage to tur-bine components positioned downstream. In addition, theflame diffusion technique produces emissions with signifi-cant levels of undesirable chemical compounds including NOX and CO.
Increasing environmental awareness has resulted in more stringent emission standards for ~x and CO. The more stringent standards are leading to developmen~ of improved combustor technologies. One such improvement is a premixing, prevaporizir.g combustor. In this type of combustor, fuel is sprayed into a fuel preparation zore where it is thoroughly mixed to achieve a homogeneous con~
centration which is everywhere within definite limits of the mean concen~ration. Additionally, a certain amount of the fuel is vaporized in ~he fuel preparation zone. Fuel combustion occurs at a point downstream 'rom the fuel
3~ preparation zone. T!le substantially uniform fuel concen-~ration achieved :l 'he fuel preparation zone results in a uniform reaction tempe~ature which may be limited to 3 49,686 appro,~l!ra e'y 'OGOF to 3000F. Due to -the uniformity and -thoroughness of combustion, the premixing, prevaporizing combustor produces Lower levels of NOy and CO than does a conventional combustor using the same amount of fuel.
To date, premixing, prevaporizing combustors have generally been fueled by clean fuel oils, such as No.
2 fuel oil, as opposed to heavy oil fuels. A clean fuel oil is characterized by low ash content, low nitrogen content and a low boiling point, so that the fuel will readily vaporize in a fuel preparation zone operating at normal temperatures. Heavy oil is generally avoided as a fuel due ~o the problems which typically accompany lts use.
Heavy oils are characterized by the short auto-ignition times of the longer hydrocarbon chains, making flashba-k a greater problem in heavy oils than in clean oils. Elashback is the propagation of flame from the point of combustion back into the fuel preparation zone.
If permitted to continue uncorrected, the presence of flame in the fuel preparation zone will damage the com-bustor to the extenl that the turbine must be shut down and the combustor repaired or replaced. Because of the higher boiling points, it is often impractical to com-pletely vaporize a heavy oil. Furthermore, fully mixing a heavy oil p-ior to combustion typically causes substantial deposition of coke on the walls surrounding the fuel pre-para~ion zone. Deposits of coke on the walls of a combus-tor create flow obstructions and create irregular gas flow patterns within the combustor, inhibiting performance of the combustor. On the other hand, failure to mix a heavy oil prior to combustion produces a non-uniform fuel con-centration which can result in extremely high reaction temperatures and damage to combustor components, espe-cially to a catalytic element in a catalytic combustor.
~ence, the known prior art combustors do not ap-pear to meet the need for a premixing, prevaporizing combustor capable of successfully utilizing heavy oil ' ( 3 IL3
To date, premixing, prevaporizing combustors have generally been fueled by clean fuel oils, such as No.
2 fuel oil, as opposed to heavy oil fuels. A clean fuel oil is characterized by low ash content, low nitrogen content and a low boiling point, so that the fuel will readily vaporize in a fuel preparation zone operating at normal temperatures. Heavy oil is generally avoided as a fuel due ~o the problems which typically accompany lts use.
Heavy oils are characterized by the short auto-ignition times of the longer hydrocarbon chains, making flashba-k a greater problem in heavy oils than in clean oils. Elashback is the propagation of flame from the point of combustion back into the fuel preparation zone.
If permitted to continue uncorrected, the presence of flame in the fuel preparation zone will damage the com-bustor to the extenl that the turbine must be shut down and the combustor repaired or replaced. Because of the higher boiling points, it is often impractical to com-pletely vaporize a heavy oil. Furthermore, fully mixing a heavy oil p-ior to combustion typically causes substantial deposition of coke on the walls surrounding the fuel pre-para~ion zone. Deposits of coke on the walls of a combus-tor create flow obstructions and create irregular gas flow patterns within the combustor, inhibiting performance of the combustor. On the other hand, failure to mix a heavy oil prior to combustion produces a non-uniform fuel con-centration which can result in extremely high reaction temperatures and damage to combustor components, espe-cially to a catalytic element in a catalytic combustor.
~ence, the known prior art combustors do not ap-pear to meet the need for a premixing, prevaporizing combustor capable of successfully utilizing heavy oil ' ( 3 IL3
4 49,686 fuels. ;~Ieatry oil fuels, not widely used in the past be-cause o the problems des~ribed above, are attractive as an alternative source of energy.
SUMMARY_ F THE_INVFNTIOM
Accordingly, a combustion turbine combustor comprises an enclosure or basket having apertures îor permitting the flow of compresso1- discharye gases into the enclosure, a zone disposed within the enclosure downstream of at least one of the ape~tures for mixing and vaporizing the fuel prior to initiation of combustion, fuel injection means di;,posed within the enclosure in the downstream end of the mixin~ zone, and a combus-tion zone having means for supporting combustion of the fuel mixture. The downstream position of the fuel injection means reduces co~e deposi-tion on the combustor walls and shortens the dwell time of the fuel mi~ture in the combustor prior to initiation of combustion. Use of a mul_iple-point fuel injector maxi-mizes îuel mi~ing in the short space provided therefor.
Combustion may be by flame or by catalyst. When combus-tion is by catalyst, a catalytic element is preferablystructured in t~o elements to reduce the potential îor damage due to an imbalance in fuel concentration.
BRIEF DESCRlPTIOM OF T~E DR~.WTNGS
Figure l schematically shows a catalytic comblls-tor arranged to operate a gas turbine in accordance withthe principles of the invention;
Figure 2 shows an elevational view of a catalytic combustor disposed as shown schematically in Figure 1;
Figure 3 shows a sectior of the combustor of 3C Figure 2 arranged in accorc;ance w~th the principles of the invention;
Figure a shows a cross-section of the combustor of Figure 3;
Figure 5 shows an alternate embodiment of the combustion means of Figure 3.
~9,6~6 D~-SC~ rN-C~ 0~ THE PREEER~ED E BODIr~ENT
More oa-ticularly, there is shown in Figure 1 a generalized schematlc representation of a combustion tur-bine combustor and combustor control system. A turbine or general~y cylindrical catalytic combustor 10 is combined with a plurality of like combustors (not shownj to supply hot motive gas to the inlet of a turbine (not shown) as indicated ~y reference character 12. The combustor ~i~
includes a catalytic unit 1' which supports catalytic combustion (oxidation) of fuel-air mixture flowing through the com~ustor 10.
The combustor 10 includes a zone 11 irto which 6c~.~0~
fuel, such as oil, is injected by~nozzle /means 16 from a fuel valve 17, where fuel-air mixin~ occurs in preparation lS for entry into the catalytic unit la. Typically, the îuel-air mix temperature (for example 800F) required for cataly~ic reaction is higher than the temperature (for example 700~) of the compressor discharge air supplied to the combustors from the enclosed space outside the combus-tor sheils. The deficiency in air supply temperature intypical cases is highest during startup and lcwer load operation.
A primary combustion zone 18 is accordingly provided upstream rom the fuel pre~aration ~one 11 within the combustor 10. Nozzle means 20 are provided for in-jecting fuel from a primary fuel valve 22 into the primary combustion zone 18 where conventional flame combustion is supported by primary alr enterirg the zone 18 from the space within the turbine casing through o enings in che combustor wall.
As a result, a hot gas flow is supplied to the fuel preparation zone '1 where it can be mixed with the fuel and air mixture to provide a heated îuel mi~ture at a sufficiently high temperature to enable proper catalytic unit operation. In this ar;^angement, the fuel injected by the nozzle means 16 for com'oustion in the catalytic unit is a secondary uel îlow. The secondarv fuel flow is :!d~ 3 6 49,6a6 mixed with secondary air and primary combustion products, which su?ply the preheating needed to raise the tempera-ture of the mixture to the level needed for entry to the catalytic unit.
It should be noted that a combustor structured according to the principles of the invention is not limit-ed to the catalytic structure described herein. Other combustors structured according to the principles of the invention include catalytic combustors having no primary combustion zone for preheating the gas flow and non-catalytic combustors. A non-catalytic combustor structured consistent with the principles of the invention comp.ises nozzle means injecting fuel into a fuel preparation zone for fuel-air mixing. Combustion of the fuel-air mixture occurs at a flameholder or in an open section in a co~us-tion zone downstream of the fuel preparation zone, produc-ing a hot gas flow which is supplied to the turbine inlet.
The description hereinafter is directed expressly to a catalytic combustor but applies equally well to a non-catalytic type combustor.
In Figure 2 there is shown 3 structurally de-tailed catalytic combustion system 30 embodying the prin-ciples described for the combustor 10 of Figure 1. ~hus, the combustion system 30 generates hot combustion products which pass through stator vanes 31 to drive turbine blad~s (not shown). A plurality of combustion systems 30 are disposed about the rotor axis within a turbine casing 32 to supply the total hot gas flow needed to drive the tur-bine.
In accordance with the prirciples of the inven-tion, combustor 30 in_ludes a combustor basket 40, a cata-lytic unit 36 and a t~ansition duct 38 which directs the hot gas to the annular --pace through which it passes to be directed against the turbine blades. ~he combustor 30 further comprises a fuel preDaration ~one internal to the combustor baske; 40 at reference charact-r 34.
3~7(~3 7 ~9,686 A fuel preparation zone of a combustor is shown in section in Figure 3. The fuel preparation zone 42 comprises a fuel injector means 44 positioned in the downstrea.m end oE the fuel preparation zone 42. Placing the fuel injector means 44 at the downstream end oi the zone ~12, rather than at the upstream end as typically found in prior art combustors, improves the reliability and performance of the combustor when the combustor is fueled with heavy oil.
The downstream position of the fuel injector means 44 eliminates a prelimina.ry mixing section of the fuel preparation zone of prior ar-t combustors. The pre-liminary mixing section is an open space between the fuel injector and a static mixing structure, which structure could be either a flameholder, a catalytic element or a separate mixing structure. The introduction of heavy oil fuel into the preliminary mixing section can result in substantial coke deposition on the walls of the fuel preparation zone, obstructing gas flow and inhibiting performance of the combustor. The downstream position of the fuel injector means 44 reduces the dwell. time of the fuel mixture in the fuel preparation zone 42. The reduced dwell time reduces coke deposition by the heavy oil fuel and also reduces the potential .for autoignition, or flash-back, due to the shorter period of time between fuelinjection and fuel ignition. Due to the downstream position of the fuel in-jector means 44, the low degree of mixedness of the fuel mixture prior to combustion can result in the problems associated with an imbalance in fuel concentration. One approach to minimizing this problem is to use a multiple-point fuel injector means 44 to yield substantial fuel mixing immediately upon injection. The structure for one form of multiple-point fuel injector means is depicted in Figure 3 and Figure 4.
~ 4g,686 As showr. ln Figure 3 and Figure 4, the uel injector 'L4 comprises a plurality of truncated cone-like s-tructures ~5, dispose~ with axes parallel to the combus-tor axis of flow. Fuel is injected .rom a feeder tube ~8 protruding through an opening 50 in the truncated end of each cone a6, whereupon the fuel is atomized by air flow, shown by the arrow at 52, passing tnrough the opening 50.
The air flow 52 is accelerated through ~he opening 50, thereby substantially vaporizing and mixing the fuel iO injected by the tubes a~3.
The fuel feeder tubes 48 communicate fuel from a fuel manifold, such as an outer fuel manifold 5a and an inner fuel manifold 56, the two manifolds being concen-trically disposed. A single fuel supply line 5~ supplies fuel from a fuel valve (reference character 17 of Fig. l) to the dual fuel manifolds 54, 56. Hence, by appropriate structure of the fuel injector means 44, potential negative effects of the downstream position of the fuel injector means are diminished, permitting use of heavy oil fuels in a premixing, prevaporizing combustor.
Incomplete mixing of the fuel-air mixture can also cause problems within the catalytic unit (36 of Fig.
2) positioned downstream of the fuel injector means 44.
Pock-ts of high fuel concentration resulting from incom-plete fuel mixing tend to react to a higher temperature corresponding to that consentration, which temperature may exceed the maximum temperature which the single cat~lytlc element of typical prior art combustors is capable of withs-tanding without damage.
To minimize tr.e risk of damage to the catalytic unit, the catalytic element of the present combustor is structured in two segments. In this configuration, the fuel-air mixture undergoes only ?artial reaction within the first catalytic segment 60, ensuring that the reaction temperature remains within he li.nitations o~ the catalytic element. ~ space 62 between the î~rst segment 60 and the second catalytic segment 6a permits co;npiete Cuel mixing .3 ~ 49,686 before combustion is completed within -the second catalytic segment 6~. The dual catalytic element struc-ture thereby reduces the sens~tivity o the catalytic unit to incom-plete fuel mixing, fu~ther improviny performance of a premixing, prevaporizing combustor fueled with heavy oil.
The precise structure and nature of the catalytic element is well known in the ?rior art and not critical to the operation of the combustor described herein.
As an alternative to the dual catalytic elemen~
structure, the outer annulus of the catalytic unit may be structured so as to induce turbulence in the fuel-air mixture flowing therethrough. This may be accomplished by varyiny the diameter of the catalytic unit along its length so as to ensure turbulence and resultant fuel mixing.
The catalytic unit 36 may be replaced by a flameholder unit 70, depicted in elevation in Figure 5, in a non-cata].ytic combustor. The flameholder unit 70 c:om-prises a flameholder 72 of any appropriace shape such as a sphere, an ignition means 74 for initiating the combustion reaction in response to command from a turbine control (not shown) and an ignition tube 76 for communicating between the ignition means 74 and the flamehol.der 72 and for structural support of the flameholder 72. The struc-ture of a flameholder unit, as presented generally above,is well known in tne prior art. It is noteworthy that the flameholder unit 70 adapts well to the characteristics of the invention described heretoîore.
An incompletely mixed -^uel-air mixture entering the flamenolder un t 70 does not pose a threat of damage to the flameholaer unit 70 as in the case of the catalytic unit 3~ properly structured flameholder is by nature a flow obstruction whose aercdynamic wake creates a well stirred reaction ~one. ~ence, pockets of hiyh fuel con-centrat on are thoroughly m_xed by Ihe flameholder 72. Inadditlon, the reducec. level Gf mixedr.ess upstream of the flameholder may act to stabi'ize the combustion reaction 3~
o 49, ~6 by preventincJ flashback. Thus, the principles of the in-vention apply to a non-catal~ytic combustor as well as to a catalytic co~bustor, en2bling both types of combustor., to operate by use of heavy oll fuel.
SUMMARY_ F THE_INVFNTIOM
Accordingly, a combustion turbine combustor comprises an enclosure or basket having apertures îor permitting the flow of compresso1- discharye gases into the enclosure, a zone disposed within the enclosure downstream of at least one of the ape~tures for mixing and vaporizing the fuel prior to initiation of combustion, fuel injection means di;,posed within the enclosure in the downstream end of the mixin~ zone, and a combus-tion zone having means for supporting combustion of the fuel mixture. The downstream position of the fuel injection means reduces co~e deposi-tion on the combustor walls and shortens the dwell time of the fuel mi~ture in the combustor prior to initiation of combustion. Use of a mul_iple-point fuel injector maxi-mizes îuel mi~ing in the short space provided therefor.
Combustion may be by flame or by catalyst. When combus-tion is by catalyst, a catalytic element is preferablystructured in t~o elements to reduce the potential îor damage due to an imbalance in fuel concentration.
BRIEF DESCRlPTIOM OF T~E DR~.WTNGS
Figure l schematically shows a catalytic comblls-tor arranged to operate a gas turbine in accordance withthe principles of the invention;
Figure 2 shows an elevational view of a catalytic combustor disposed as shown schematically in Figure 1;
Figure 3 shows a sectior of the combustor of 3C Figure 2 arranged in accorc;ance w~th the principles of the invention;
Figure a shows a cross-section of the combustor of Figure 3;
Figure 5 shows an alternate embodiment of the combustion means of Figure 3.
~9,6~6 D~-SC~ rN-C~ 0~ THE PREEER~ED E BODIr~ENT
More oa-ticularly, there is shown in Figure 1 a generalized schematlc representation of a combustion tur-bine combustor and combustor control system. A turbine or general~y cylindrical catalytic combustor 10 is combined with a plurality of like combustors (not shownj to supply hot motive gas to the inlet of a turbine (not shown) as indicated ~y reference character 12. The combustor ~i~
includes a catalytic unit 1' which supports catalytic combustion (oxidation) of fuel-air mixture flowing through the com~ustor 10.
The combustor 10 includes a zone 11 irto which 6c~.~0~
fuel, such as oil, is injected by~nozzle /means 16 from a fuel valve 17, where fuel-air mixin~ occurs in preparation lS for entry into the catalytic unit la. Typically, the îuel-air mix temperature (for example 800F) required for cataly~ic reaction is higher than the temperature (for example 700~) of the compressor discharge air supplied to the combustors from the enclosed space outside the combus-tor sheils. The deficiency in air supply temperature intypical cases is highest during startup and lcwer load operation.
A primary combustion zone 18 is accordingly provided upstream rom the fuel pre~aration ~one 11 within the combustor 10. Nozzle means 20 are provided for in-jecting fuel from a primary fuel valve 22 into the primary combustion zone 18 where conventional flame combustion is supported by primary alr enterirg the zone 18 from the space within the turbine casing through o enings in che combustor wall.
As a result, a hot gas flow is supplied to the fuel preparation zone '1 where it can be mixed with the fuel and air mixture to provide a heated îuel mi~ture at a sufficiently high temperature to enable proper catalytic unit operation. In this ar;^angement, the fuel injected by the nozzle means 16 for com'oustion in the catalytic unit is a secondary uel îlow. The secondarv fuel flow is :!d~ 3 6 49,6a6 mixed with secondary air and primary combustion products, which su?ply the preheating needed to raise the tempera-ture of the mixture to the level needed for entry to the catalytic unit.
It should be noted that a combustor structured according to the principles of the invention is not limit-ed to the catalytic structure described herein. Other combustors structured according to the principles of the invention include catalytic combustors having no primary combustion zone for preheating the gas flow and non-catalytic combustors. A non-catalytic combustor structured consistent with the principles of the invention comp.ises nozzle means injecting fuel into a fuel preparation zone for fuel-air mixing. Combustion of the fuel-air mixture occurs at a flameholder or in an open section in a co~us-tion zone downstream of the fuel preparation zone, produc-ing a hot gas flow which is supplied to the turbine inlet.
The description hereinafter is directed expressly to a catalytic combustor but applies equally well to a non-catalytic type combustor.
In Figure 2 there is shown 3 structurally de-tailed catalytic combustion system 30 embodying the prin-ciples described for the combustor 10 of Figure 1. ~hus, the combustion system 30 generates hot combustion products which pass through stator vanes 31 to drive turbine blad~s (not shown). A plurality of combustion systems 30 are disposed about the rotor axis within a turbine casing 32 to supply the total hot gas flow needed to drive the tur-bine.
In accordance with the prirciples of the inven-tion, combustor 30 in_ludes a combustor basket 40, a cata-lytic unit 36 and a t~ansition duct 38 which directs the hot gas to the annular --pace through which it passes to be directed against the turbine blades. ~he combustor 30 further comprises a fuel preDaration ~one internal to the combustor baske; 40 at reference charact-r 34.
3~7(~3 7 ~9,686 A fuel preparation zone of a combustor is shown in section in Figure 3. The fuel preparation zone 42 comprises a fuel injector means 44 positioned in the downstrea.m end oE the fuel preparation zone 42. Placing the fuel injector means 44 at the downstream end oi the zone ~12, rather than at the upstream end as typically found in prior art combustors, improves the reliability and performance of the combustor when the combustor is fueled with heavy oil.
The downstream position of the fuel injector means 44 eliminates a prelimina.ry mixing section of the fuel preparation zone of prior ar-t combustors. The pre-liminary mixing section is an open space between the fuel injector and a static mixing structure, which structure could be either a flameholder, a catalytic element or a separate mixing structure. The introduction of heavy oil fuel into the preliminary mixing section can result in substantial coke deposition on the walls of the fuel preparation zone, obstructing gas flow and inhibiting performance of the combustor. The downstream position of the fuel injector means 44 reduces the dwell. time of the fuel mixture in the fuel preparation zone 42. The reduced dwell time reduces coke deposition by the heavy oil fuel and also reduces the potential .for autoignition, or flash-back, due to the shorter period of time between fuelinjection and fuel ignition. Due to the downstream position of the fuel in-jector means 44, the low degree of mixedness of the fuel mixture prior to combustion can result in the problems associated with an imbalance in fuel concentration. One approach to minimizing this problem is to use a multiple-point fuel injector means 44 to yield substantial fuel mixing immediately upon injection. The structure for one form of multiple-point fuel injector means is depicted in Figure 3 and Figure 4.
~ 4g,686 As showr. ln Figure 3 and Figure 4, the uel injector 'L4 comprises a plurality of truncated cone-like s-tructures ~5, dispose~ with axes parallel to the combus-tor axis of flow. Fuel is injected .rom a feeder tube ~8 protruding through an opening 50 in the truncated end of each cone a6, whereupon the fuel is atomized by air flow, shown by the arrow at 52, passing tnrough the opening 50.
The air flow 52 is accelerated through ~he opening 50, thereby substantially vaporizing and mixing the fuel iO injected by the tubes a~3.
The fuel feeder tubes 48 communicate fuel from a fuel manifold, such as an outer fuel manifold 5a and an inner fuel manifold 56, the two manifolds being concen-trically disposed. A single fuel supply line 5~ supplies fuel from a fuel valve (reference character 17 of Fig. l) to the dual fuel manifolds 54, 56. Hence, by appropriate structure of the fuel injector means 44, potential negative effects of the downstream position of the fuel injector means are diminished, permitting use of heavy oil fuels in a premixing, prevaporizing combustor.
Incomplete mixing of the fuel-air mixture can also cause problems within the catalytic unit (36 of Fig.
2) positioned downstream of the fuel injector means 44.
Pock-ts of high fuel concentration resulting from incom-plete fuel mixing tend to react to a higher temperature corresponding to that consentration, which temperature may exceed the maximum temperature which the single cat~lytlc element of typical prior art combustors is capable of withs-tanding without damage.
To minimize tr.e risk of damage to the catalytic unit, the catalytic element of the present combustor is structured in two segments. In this configuration, the fuel-air mixture undergoes only ?artial reaction within the first catalytic segment 60, ensuring that the reaction temperature remains within he li.nitations o~ the catalytic element. ~ space 62 between the î~rst segment 60 and the second catalytic segment 6a permits co;npiete Cuel mixing .3 ~ 49,686 before combustion is completed within -the second catalytic segment 6~. The dual catalytic element struc-ture thereby reduces the sens~tivity o the catalytic unit to incom-plete fuel mixing, fu~ther improviny performance of a premixing, prevaporizing combustor fueled with heavy oil.
The precise structure and nature of the catalytic element is well known in the ?rior art and not critical to the operation of the combustor described herein.
As an alternative to the dual catalytic elemen~
structure, the outer annulus of the catalytic unit may be structured so as to induce turbulence in the fuel-air mixture flowing therethrough. This may be accomplished by varyiny the diameter of the catalytic unit along its length so as to ensure turbulence and resultant fuel mixing.
The catalytic unit 36 may be replaced by a flameholder unit 70, depicted in elevation in Figure 5, in a non-cata].ytic combustor. The flameholder unit 70 c:om-prises a flameholder 72 of any appropriace shape such as a sphere, an ignition means 74 for initiating the combustion reaction in response to command from a turbine control (not shown) and an ignition tube 76 for communicating between the ignition means 74 and the flamehol.der 72 and for structural support of the flameholder 72. The struc-ture of a flameholder unit, as presented generally above,is well known in tne prior art. It is noteworthy that the flameholder unit 70 adapts well to the characteristics of the invention described heretoîore.
An incompletely mixed -^uel-air mixture entering the flamenolder un t 70 does not pose a threat of damage to the flameholaer unit 70 as in the case of the catalytic unit 3~ properly structured flameholder is by nature a flow obstruction whose aercdynamic wake creates a well stirred reaction ~one. ~ence, pockets of hiyh fuel con-centrat on are thoroughly m_xed by Ihe flameholder 72. Inadditlon, the reducec. level Gf mixedr.ess upstream of the flameholder may act to stabi'ize the combustion reaction 3~
o 49, ~6 by preventincJ flashback. Thus, the principles of the in-vention apply to a non-catal~ytic combustor as well as to a catalytic co~bustor, en2bling both types of combustor., to operate by use of heavy oll fuel.
Claims (9)
1. In a combustion turbine system, a combustor for heating compressor discharge gases to drive a turbine, said combustor comprising:
an enclosure for containing a combustion reaction, said enclosure being generally cylindrical and having apertures therethrough toward an upstream end to permit influx of compressor discharge gases which flow into said enclosure and exit through an open downstream end of said enclosure to a transition duct which leads to a turbine inlet;
a zone disposed within said enclosure downstream of at least one of the apertures in said enclosure where fuel is mixed with the discharge gases and vaporized prior to combustion;
multiple point fuel injecting means positioned in proximity to the discharge end of said mixing zone for injecting fuel into the flow of gases within said enclosure to create fuel mixing and vaporization sufficient substan-tially to avoid hot spots from fuel concentration yet adequately incomplete so that fuel contact with the mixing zone wall is avoided to prevent coking when the fuel is heavy oil; and a combustion zone disposed within said enclosure downstream of said mixing zone, said combustion zone having therein means for initiating and supporting combustion of the fuel mixture the temperature of gases flowing into the transition duct being thereby increased.
an enclosure for containing a combustion reaction, said enclosure being generally cylindrical and having apertures therethrough toward an upstream end to permit influx of compressor discharge gases which flow into said enclosure and exit through an open downstream end of said enclosure to a transition duct which leads to a turbine inlet;
a zone disposed within said enclosure downstream of at least one of the apertures in said enclosure where fuel is mixed with the discharge gases and vaporized prior to combustion;
multiple point fuel injecting means positioned in proximity to the discharge end of said mixing zone for injecting fuel into the flow of gases within said enclosure to create fuel mixing and vaporization sufficient substan-tially to avoid hot spots from fuel concentration yet adequately incomplete so that fuel contact with the mixing zone wall is avoided to prevent coking when the fuel is heavy oil; and a combustion zone disposed within said enclosure downstream of said mixing zone, said combustion zone having therein means for initiating and supporting combustion of the fuel mixture the temperature of gases flowing into the transition duct being thereby increased.
2. A combustor according to claim 1 wherein said multiple fuel injecting means is located substantially adjacent to and upstream of said combustion means so that the residence time of the fuel within said combustor prior to combustion is held sufficiently short to avoid auto-ignition when heavy oil is used as a fuel.
3. A combustor according to claim 2 wherein said means for supporting combustion comprises a catalytic combustion element within said combustion zone.
4. A combustor according to claim 3 wherein the catalytic element is arranged in at least two segments separated by a space so that partial combustion and fuel mixing occurs in the first segment and combustion is completed in the succeeding segment.
5. A combustor according to claim 2 wherein said means for supporting combustion comprises a flame-holder disposed within said combustion zone.
6. A combustor according lo claim 3 wherein said multiple-point fuel injecting means comprises:
a plurality of adjacent atomizing structures having longitudinal axes parallel to the combustor axis of flow, one end of each of said structures being open to the downstream direction, the opposite end of each of said structures having at least one aperture to permit the flow of gases into each said structure; and means for communicating fuel to the aperture end of each of said structures.
a plurality of adjacent atomizing structures having longitudinal axes parallel to the combustor axis of flow, one end of each of said structures being open to the downstream direction, the opposite end of each of said structures having at least one aperture to permit the flow of gases into each said structure; and means for communicating fuel to the aperture end of each of said structures.
7. A combustor according to claim 6 wherein each said atomizing structure comprises a truncated cone structure with an open base disposed downstream within said fuel preparation zone.
8. A combustor according to claim 6 wherein said communicating means comprises:
at least one fuel manifold structure arranged to communicate fuel among the several atomizing structures;
a fuel supply line for communicating fuel from a fuel valve to each said fuel manifold structure; and a plurality of fuel feeder tubes for delivering fuel from said fuel manifold into the aperture at the upstream end of each said atomizing structure.
at least one fuel manifold structure arranged to communicate fuel among the several atomizing structures;
a fuel supply line for communicating fuel from a fuel valve to each said fuel manifold structure; and a plurality of fuel feeder tubes for delivering fuel from said fuel manifold into the aperture at the upstream end of each said atomizing structure.
9. A combustor according to claim 5 wherein said multiple-point fuel injecting means comprises:
a plurality of adjacent atomizing structures having longitudinal axes parallel to the combustor axis of flow, one end of each of said structures being open to the downstream direction, the opposite end of each of said structures having at least one aperture to permit the flow of gases into each said structure; and means for communicating fuel to the aperture end of each of said structures.
a plurality of adjacent atomizing structures having longitudinal axes parallel to the combustor axis of flow, one end of each of said structures being open to the downstream direction, the opposite end of each of said structures having at least one aperture to permit the flow of gases into each said structure; and means for communicating fuel to the aperture end of each of said structures.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31709781A | 1981-11-02 | 1981-11-02 | |
| US317,097 | 1981-11-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191703A true CA1191703A (en) | 1985-08-13 |
Family
ID=23232105
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000410230A Expired CA1191703A (en) | 1981-11-02 | 1982-08-26 | Combustion turbine combustor having an improved heavy- oil fuel preparation zone |
Country Status (3)
| Country | Link |
|---|---|
| JP (2) | JPS5880422A (en) |
| CA (1) | CA1191703A (en) |
| IT (1) | IT1153574B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5000004A (en) * | 1988-08-16 | 1991-03-19 | Kabushiki Kaisha Toshiba | Gas turbine combustor |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61258929A (en) * | 1985-05-10 | 1986-11-17 | Hitachi Ltd | Fuel controller for gas turbine |
| JPH0674892B2 (en) * | 1987-06-10 | 1994-09-21 | 株式会社日立製作所 | Combustion control method and apparatus for multi-stage combustor |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE7802205L (en) * | 1977-03-04 | 1978-09-05 | Johnson Matthey Co Ltd | IMPROVEMENTS IN AND REGARDING CATALYSIS |
-
1982
- 1982-08-26 CA CA000410230A patent/CA1191703A/en not_active Expired
- 1982-09-01 IT IT23079/82A patent/IT1153574B/en active
- 1982-09-02 JP JP15181182A patent/JPS5880422A/en active Pending
-
1986
- 1986-01-07 JP JP19286U patent/JPS61135170U/ja active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5000004A (en) * | 1988-08-16 | 1991-03-19 | Kabushiki Kaisha Toshiba | Gas turbine combustor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5880422A (en) | 1983-05-14 |
| IT8223079A0 (en) | 1982-09-01 |
| IT1153574B (en) | 1987-01-14 |
| JPS61135170U (en) | 1986-08-22 |
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