Patent Abstract:
A gas turbine engine assembly including improved means for cooling the combustor to preclude thermal failure of the combustor and to preclude NO x  formation. The system includes a liquid pump driven by the turbine shaft and supplying a cooling fluid to an annular chamber defined around the central combustion chamber of the combustor. The cooling fluid is thereby placed in heat exchange relation to the combustor to absorb heat from the combustion products within the combustion chamber and convert the fluid to a relatively higher energy condition, whereafter the fluid in its high energy condition is injected into the combustion chamber for mixture with the combustion products and delivery with the combustion products to the turbine inlet. The cooling liquid may totally fill the annular cooling chamber around the combustion chamber or may partially fill tie cooling chamber, or the cooling fluid arriving at the cooling chamber may already be in a gaseous state so that the cooling chamber is totally filled with a vapor.

Full Description:
This is a division of U.S. patent application Ser. No. 08/550,893, filed Oct. 31, 1995 now U.S. Pat. No. 5,694,761, which is a continuation of U.S. patent application Ser. No. 08/087,974, filed Jul. 7, 1993 now U.S. Pat. No. 5,461,854. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to gas turbine engines and more particularly to improved methods and apparatus for cooling the combustor and combustion gases of a gas turbine engine. 
     It is important to provide cooling for the combustor and combustion gases of a gas turbine engine in order to maintain the combustor, turbine, and combustion gas conduits of the engine below the temperature at which thermal failure occurs and to also limit the formation of nitric oxide (NO x ). Various methods and apparatus have been utilized in the past to achieve combustor and combustion gas cooling including passage of cooling air over and through the combustor, the injection of steam into the combustor cooling air, the injection of a water spray into the combustor cooling air, and various combinations of these methodologies and apparatuses. Whereas these prior art methodologies are useful in lowering the temperature of the combustor and combustion gases, the cooling is achieved through losses in the overall engine system since the work required to deliver the primary coolant, air, is excessive, and the quantity of energy recoverable with the small steam and/or water injection rates permitted is negligible. 
     SUMMARY OF THE INVENTION 
     This invention is directed to the provision of an improved gas turbine engine assembly. 
     More specifically, this invention is directed to the provision of an improved combustor for a gas turbine engine assembly. 
     Yet more specifically, this invention is directed to the provision of an improved method and apparatus for cooling the combustor and combustion gases of a gas turbine engine assembly. 
     The invention discloses a method of cooling the combustor and combustion gases of a gas turbine engine assembly of the type including a turbine and a combustor arranged to receive a fuel/air mixture and generate products of combustion within the combustor for delivery to the turbine. 
     According to the invention, a fluid is delivered to the combustor by a pump and is placed in heat exchange relation with the combustion products within the combustor so that thermal energy is absorbed from the combustion products by the fluid, and the fluid is thereafter injected into the combustion products for delivery with the combustion products to the turbine. This methodology allows combustor cooling to be achieved with a minimum of energy loss in the total system, thereby maximizing the overall efficiency of the total system. 
     In one embodiment of the invention, liquid is delivered to the combustor where it is placed in heat exchange relation with the combustion products before being injected into the combustion gases as liquid. 
     In a further embodiment of the invention, liquid id delivered to the combustor where it is placed in heat exchange relation with the combustion products before being injected into the combustion gases as gas or vapor. 
     In a further embodiment of the invention, gas or vapor is delivered to the combustor where it is placed in heat exchange relation with the combustion products before being injected into the combustion gases as gas or vapor. 
     According to a further feature of the invention methodology, the combustor has a central combustion chamber for containing the combustion products and an annular cooling chamber in surrounding relation to the central combustion chamber and having apertures communicating with the central combustion chamber; the step of placing the fluid in heat exchange relation with the combustion gases comprises delivering the fluid to the annular cooling chamber in its low energy liquid phase; condition; the conversion of the fluid to a higher level of energy occurs in the annular cooling chamber; and the step of injecting the fluid into the combustor comprises passing the fluid in its relatively high energy condition through the apertures and into the central combustion chamber. 
     According to a further feature of the invention, the turbine engine assembly includes a shaft driven by the turbine engine assembly includes a shaft driven by the turbine and a pump driven by the shaft and the fluid is delivered to the combustor by the pump. 
     The invention also provides an improved combustor for generating combustion products for delivery to a gas turbine. The improved combustor includes a central combustion chamber defining a central axis; a burner positioned to deliver products of combustion to one end of the chamber; a discharge at the other end of the chamber for delivering the combustion products to the turbine; and annular cooling chamber in surrounding relation to the central combustion chamber; an entry opening in the cooling chamber for receipt of a cooling liquid; and a plurality of apertures communicating the cooling chamber with the central combustion chamber. This combustor construction allows the cooling fluid to be placed in heat exchange relation to the combustor so that thermal energy is absorbed from the combustion products within the combustor before the fluid is injected in to the combustor through the apertures interconnecting the cooling chamber and central combustion chamber. 
     According to a further feature of the invention, the combustor is positioned with its central axis generally vertical; the burner is proximate the lower end of the combustion chamber; the discharge is proximate the upper end of the combustion chamber; and the entry opening in the cooling chamber is proximate the lower end of the combustion chamber. This specific arrangement and orientation of the combustor facilitates the placement of the cooling fluid in heat exchange relation to the combustion chamber. 
     The invention also provides an improved gas turbine engine assembly. The improved gas turbine engine assembly includes a turbine driving a shaft; a combustor operative to generate products of combustion for delivery to the turbine; a source of cooling liquid; and a pump driven by the turbine shaft, having an inlet connected to the liquid source, and having an outlet connected to the combustor. This arrangement allows a cooling liquid to be delivered to the combustor by a pump driven by the turbine, to improve the overall efficiency of the assembly. 
     According to a further feature of the invention, the combustor includes a central combustion chamber and an annular cooling chamber in surrounding relation to the central combustion chamber and connected to the combustion chamber by a plurality of apertures; the pump outlet is connected to the cooling chamber of the combustor by conduit means; and the assembly further includes a heat exchanger in the conduit means the heat exchanges receiving the discharge of the turbine. This arrangement allows the energy content of the cooling fluid to be increased by utilizing the waste products of the turbine. 
     According to a further feature of the invention, the assembly further includes means for delivering further energy to the fluid flowing through the conduit means. In the disclosed embodiment of the invention, the energy delivery means comprises a boiler arranged in the conduit interconnecting the pump to the cooling chamber of the combustor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, partially cross sectional view of a gas turbine engine assembly according to the invention; 
     FIG. 2 is a somewhat schematic view of the gas turbine engine assembly of FIG. 1; 
     FIG. 3 is a somewhat schematic view of a modified form of the gas turbine engine assembly according to the invention; and 
     FIG. 4 is a somewhat schematic view of a still further modified form of the gas turbine engine assembly according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Each of the invention embodiments is of the type including a turbine  10  of know form having an inlet  10   a  and outlet  10   b ; a combustor  12  arranged to deliver products of combustion to inlet  10   a  of the turbine and thereby drive the turbine; a compressor  14  drive by shaft  16  of the turbine and including an inlet  14   a  connected to a source of fuel and an outlet  14   b  for delivering the fuel in pressurized form to the combustor; and a compressor  18  driven by shaft  16  and having an connected to a source of air and an outlet  18   b  for delivering pressurized air to the combustor for mixture with the fuel from compressor  14  to provide a fuel/air mixture for combustion in the combustor to produce combustion products for delivery to the turbine to drive the turbine. 
     The invention provides an improved combustor  12  as well as an improved means of cooling the combustor. 
     The invention combustor has a generally cylindrical configuration and defines a central vertical axis  20 . Combustor  12  includes cylindrical outer wall  12   a ; a circular upper wall  12   b ; a circular lower wall  12   c ; an inner cylindrical wall  12   d  defining a central cylindrical combustion chamber  22  and concentrically coacting with outer wall  12   a  to define an annular cooling chamber  24 ; a plurality of apertures  12   e  in inner wall  12   d  providing communication between annular cooling chamber  24  and central combustion chamber  22 ; a central discharge aperture  12   f  in upper wall  12   b ; an opening  12   g  in lower wall  12   c  within annular cooling chamber  24 ; and a burner  26  positioned centrally in lower wall  12   c . Apertures  12   e  are arranged in vertically spaced rows with each row including a plurality of circumferentially and equally spaced apertures. The rows of apertures begin in the midregion of inner wall  12   d  and extend upwardly to a topmost row proximate discharge aperture  12   f , that is, there are no apertures in the lower region  12   h  of inner wall  12   d.    
     Burner  26  provides a pre-combustor for combustor  12  in the sense that the actual combustion process takes place within burner  26  utilizing air delivered to the burner from compressor  18  via a conduit  28 , and fuel delivered to the burner from compressor  14  via conduit  30 . The fuel and air are mixed within the burner and combusted within the burner to define flame front  32  within central combustion chamber  22 . Burner  26  may take various forms and, for example, may include a housing  26   a  an electrode  26   b  supplied by electrical conductors  34  and functioning in a known manner to combust the fuel and air mixture within housing  26   a  for delivery into combustion chamber  22  to form flame front  32 . Burner  26  may, for example, comprise a gas, coal or fuel oil burner available from Maxon Corporation of Muncie, Indiana as Part No. WR-3. It will be understood that whereas the initial combustion of the fuel/air mixture occurs within burner  26 , post combustion also occurs within combustion chamber  22 . Discharge opening  12   f  of the combustor is connected via hood  36  and conduit  38  to inlet  10   a  of turbine  10  so that the products of combustion generated within combustion chamber  22  are delivered to the turbine inlet to drive the turbine. 
     The cooling of the combustor is accomplished by cooling chamber  24  in coaction with pump  40  and conduit  42 . Pump  40  is a liquid pump and may take various forms, including a gear pump, a lobe pump, a rotary pump or a centrifugal pump. A centrifugal pump is illustrated and includes an inlet  40   a  connected to a source (not illustrated) of liquid such as water and an impeller  40   b  mounted on shaft  16  and including a circumferentially spaced series of curved vanes  40   c . It will be understood that when the impeller is driven by shaft  16 , liquid is drawn in through inlet  40   a  from the liquid source, passes between the vanes of the impeller, and is thereafter thrown outward by centrifugal force for passage through pump outlet  40   d  and into conduit  42 . 
     Conduit  42  extends from pump outlet  40   d  to the inlet opening  12   g  in the cooling chamber of the combustor so that cooling liquid from pump  40  is conveyed by conduit  42  to annular cooling chamber  24 . 
     During steady state operation of the gas turbine engine assembly, fuel and air id delivered to the combustor via conduits  30  and  28  respectively for combustion in the combustor to form flame front  32  within central combustion chamber  22  of the combustor, the combustion products from the combustion chamber are delivered via conduit  38  to the inlet of the turbine to drive the turbine, and the turbine shaft drives pump  40  and compressors  14  and  18  to provide continuous delivery of fuel and air to the combustor and to further provide delivery of a cooling fluid to annular cooling chamber  24  of the combustor via conduit  42 . 
     The behavior of the cooling fluid in annular cooling chamber  24  will vary depending upon the pressure and temperature at which fluid id delivered to the cooling chamber. For example, and as shown in FIGS. 1 and 2, water may be delivered to cooling chamber  24  in a steady state manner at 30 bars and 300° Kelvin, in which case, assuming combustion chamber  22  is operating at 25 bars and 2,300° Kelvin at flame front  32  with an arbitrary combustion rate of 150 kilowatts, the gas turbine engine assembly can be sized such that water can be maintained in the lower end of the annular combustion chamber, below lowermost aperture  12   e , to form annular water bath  44 . Water bath  44  absorbs energy from the combustion products within the combustion chamber through inner wall  12   d  with the result that the water is converted to a vapor or steam phase  46  which forms in cooling chamber  24  above bath  44  and thereafter passes through apertures  12   e  and into combustion chamber  22  where it mixes with the combustion products within the combustion chamber and passes with the combustion products through hood  36  and conduit  38  to the inlet of the turbine to drive the turbine. 
     The energy absorbed from the flame front by the annular body of water  44  (representing the energy required to change the water from a liquid to a gas phase) together with the cooling effect of the vapor as it passes through apertures  12   e  and joins the combustion products within the combustion chamber, has the effect of reducing the temperature of the combustion products leaving the combustor through aperture  12   f  to approximately 1140° kelvin, This temperature is low enough to ensure that the combustor does not suffer thermal failure and is further low enough to ensure that there is no significant NO x  formation within the combustor. 
     The modified gas turbine engine assembly shown in FIG. 3 is generally similar to the assembly shown in FIGS. 1 and 2 with the exception that the assembly in FIG. 3 further includes a heat exchanger  50  positioned in conduit  42  and arranged to receive the discharge from outlet  10   b  of the turbine through conduit  52  and place the discharge products from the gas turbine in heat exchange relation to the cooling fluid flowing through conduit  42 , whereby to add energy to the fluid so that the fluid arriving at inlet  12   g  of the combustor has a higher energy content than the fluid leaving pump  40 . 
     As with the assembly of FIGS. 1 and 2, the nature and behavior of the fluid within cooling chamber  24  may be selectively varied by selective variation of the temperature and pressure under which the cooling fluid is delivered to the cooling chamber through conduit  42 . For example, water may be delivered to heat exchanger  50  in a steady state manner at 100 bars and 300° Kelvin, and thermal energy may ideally be added to the water so that it enters conduit  42   b , for delivery to cooling chamber  24  at 100 bars and 584° Kelvin. When the water enters inlet  12   g  at 100 bars and 584° Kelvin, cooling chamber  24  is totally filled with water, and again assuming combustion chamber  22  is operating at 25 bars and 2300° Kelvin at flame front  32  with an arbitrary combustion rate of 150 kilowatts, the gas turbine engine assembly can be sized such that thermal energy is absorbed through wall  12   d  from flame front  32  so as to cool the flame front and raise the temperature of the water. In this embodiment, with the given parameters, water passes through apertures  12   e  in a still liquid form and undergoes a phase change immediately upon entering combustion chamber  22  whereby to extract further energy from the flame front by virtue of the energy required to change the water to a gas or vapor, whereafter the gas or vapor passes out of the combustion chamber through discharge opening  12   f  for delivery with the combustion products to the inlet of the gas turbine. As with the assembly shown in FIGS. 1 and 2, the combined effect of the energy absorbed by the water residing in annular cooling chamber  24 , together with the energy required to accomplish the phase change of the water as it passes through openings  12   e  and encounters the flame front, has the effect of lowering the combustor temperature to a point (for example, 1140° Kelvin at discharge aperture  12   f ) where thermal failure of the combustor is prevented and not significant NO x  forms. 
     It should be understood that, in the embodiment of FIG. 3, the cooling flow rate can be increased such that coolant can pass through apertures  12   e  in liquid form whereafter some of the liquid can pass to a vapor and some of the liquid can flow downwardly by gravity to absorb energy and remove fuel contaminants whereafter the liquid can be removed through a drain port  12   i . For example, the liquid flowing outwardly through drain port  12   i  can be at 490° kelvin and 25 bars. Supplying excess liquid to the combustor and allowing the excess liquid to flow downwardly in the combustor for discharge through drainage port  12   i  has a washing down effect and specifically, and depending upon the fuel employed, removes fuel bound metals such as lead, nickel and vanadium, minerals such as calcium and sulphur, and combustion products such as coke, ash and soot. 
     The embodiment of the gas turbine engine assembly seen in FIG. 4 is similar to the embodiment seen in FIG. 3 with the exception that apparatus  54  is interposed in conduit  42  in a manner which allows apparatus  54  to receive the cooling fluid output of heat exchanger  50  through conduit  42   c  before the cooling fluid is delivered to cooling chamber  24  through conduit  42   b . Apparatus  54  may, for example, comprise a boiler fired by a separate source of energy, such as gas, so that apparatus  54  serves to add further energy to the fluid flowing through conduit  42 . 
     As with the embodiment of FIGS. 1 and 2 and the embodiment of FIG. 3, the nature and behavior of the fluid in cooling chamber  24  may be selectively modified by selectively varying parameters of the system. For example, the pump parameters may be chosen such that water leaves the pump at 330 bars and 300° Kelvin; heat exchanger  50  parameters may be chose such that water leaving the heat exchanger is at 300 bars and 584° Kelvin; and the boiler parameters may be chosen such that superheated steam or water vapor leaves boiler  54  and thereafter enters cooling chamber  24  through inlet  12   g  at 673° Kelvin and 300 bars. With these parameters, cooling chamber  24  is totally filled with water vapor or gas, and as the vapor or gas resides in the cooling chamber  24 , it absorbs energy from the flame front through inner wall  12   d  whereby to raise the temperature of the vapor or gas in the cooling chamber, whereafter the gas or superheated vapor passes through apertures  12   e  to join the flame front of r passage out of the discharge aperture  12   f  and passage with the combustion products to the inlet of the turbine. 
     As with the embodiment of FIGS. 1 and 2, and the embodiment of FIG. 3, the combined action of the energy absorbed by the vapor residing in cooling chamber  24  and the cooling effect of the vapor as it passes through apertures  12   e  to joint the flame front, has the effect of reducing the combustor temperature to a temperature below the thermal failure temperature of the combustor and below the temperature at which any significant NO x  formation takes place. As with the embodiment of FIGS. 1 and 2, and the embodiment of FIG. 3, the temperature of the combustion products leaving the combustion chamber through apertures  12   f  may be controlled to approximately 1140° Kelvin, assuming combustion chamber  22  is operating a 25 bars and 2300° Kelvin at flame front  32 , with an arbitrary combustion rate of 150 kilowatts. 
     In each of the invention embodiments, it will be seen that the cooling the combustor is accomplished without the use of cooling air. It will further be seen that, in each case, energy is absorbed from the flame front in a two-stage process with the first stage comprising the absorption of energy by the cooling fluid in chamber  24  through inner wall  12   d  and the second stage comprising the further cooling of the flame front as the fluid in cooling chamber  24  passes through apertures  12   e  to joint the flame front. 
     The invention will be seen to provide a simple and efficient means of maintaining the combustor below the temperature at which thermal failure and NO x  formation occurs without substantially interfering with flame ignition or maintenance, and with out elevating the carbon monoxide, level unburned hydrocarbon, or fuel consumption of the engine. Specifically, the invention methodology, level requiring only a relatively low energy consumption pump to provide the cooling needs of the combustor as opposed to the relatively high energy air compressors of the prior art, has the effect of increasing the net turbine work output since the energy required to produce the required cooling effect is significantly reduced as compared to systems in which the cooling is achieved utilizing air or a combination of air, water injection and/or steam injection. 
     Whereas preferred embodiments of the invention have been illustrated and described in detail, it will be apparent that various changes may be made in the disclosed embodiments without departing from the scope or spirit of the invention. For example, although the invention has been described with reference to a liquid or a gas utilized as the cooling substance, the cooling substance may also in certain applications, comprise a suitable alkali metal or Newtonian fluid, and the term substance as used in the claims is intended to include a liquid, gas alkali metal, or Newtonian fluid.

Technology Classification (CPC): 5