The present invention relates generally to a power plant with an industrial gas turbine engine, and more specifically to a process for retrofitting an industrial gas turbine engine for increased power and efficiency.
Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
Single shaft gas turbine engines are limited in power and efficiency when pressure ratios and firing temperatures are raised to the point where the last turbine stage is loaded to where Mach numbers reach the maximum aerodynamic capability. In these cases, the engine has limited capability to be upgraded for either power or efficiency. In some cases, the two shaft engine configuration is coupled to a larger free spinning turbine with the generator on the low speed shaft to create an upgrade in power. This also has limitations in total flow and is limited in the maximum pressure ratio that the unit could sustain.
In the present invention, existing single shaft turbine engines are retrofitted with a low speed turbine coupled to a low speed compressor that is aerodynamically coupled in front of the existing compressor, now deemed the high compressor, where the existing turbine (now deemed the high pressure turbine) is coupled to the low speed turbine. Further enhancements to the cooling systems enhance the ability to increase the firing temperature of the existing section of the gas turbine and elevate the overall power rating and efficiency.
A process for retrofitting an industrial gas turbine engine in which a new independently operated low spool shaft with a power turbine and a low pressure compressor is installed with the low pressure compressed air being directed into an inlet of the high pressure compressor. A variable area turbine vane assembly is added to the power turbine and a variable inlet guide vane to the low pressure compressor. In another embodiment, a power turbine that drives an electric generator is retrofitted by using the power turbine to drive a low pressure compressor that feeds low pressure air to an inlet of the high pressure compressor, and relocates the electric generator to the high speed shaft on a cold end of the compressor. Regenerative or closed loop cooling can also be used to increase efficiency by bleeding off air from the compressor, cooling the air and then pressurizing the air further in order to pass through stator vanes for cooling, where the spent cooling air is then discharged into the combustor upstream of the flame. Air for cooling can be bled off from a middle stage of the compressor or from the exit end of the compressor. Or, ambient air from atmosphere can be used with an external compressor to further compress the air to P3 level followed by intercooling prior to cooling of the stator vanes.
The present invention is a process for retrofitting an industrial gas turbine engine of a power plant for increased power and efficiency.
In the present invention, existing single shaft turbine engines 10 like that shown in
Further enhancements to the cooling systems enhance the ability to increase the firing temperature of the existing section of the gas turbine and elevate the overall power rating and efficiency. The retrofit-able upgrade consists of several optional elements. Most or all of the cooling air used to cool turbine airfoils is discharged into the combustor upstream of the flame instead of into the hot gas path of the turbine in order to improve the efficiency of the engine. In one embodiment, some of the turbine airfoil cooling air can be discharged through trailing edge exit holes and into the hot gas stream with most of the spent cooling air being discharged into the combustor. Passing cooling air through the turbine airfoil for cooling and then discharging most or all of the spent cooling air is referred to as a closed loop cooling where the cooling circuit in the turbine airfoil is a closed loop instead of an open loop in which all of the cooling air is discharged out from the airfoil and into the hot gas stream through film holes or exit holes in the airfoil.
The first upgrade element is to introduce a low speed turbine (LST) 21 directly driving a low speed compressor (LSC) 22 is coupled aerodynamically to the existing single shaft industrial gas turbine engine (IGTE) 10. The existing industrial gas turbine exhaust system is removed and replaced with a close coupled turbine section featuring a variable area low pressure turbine stator vane (turbine 21 with variable turbine inlet guide vanes 25). This variable turbine stator vane 25 is used in conjunction with the low compressor variable geometry, Inlet guide vane and variable geometry Stator guide vanes part of compressor 22, to control the low shaft speed and to simultaneously match the low speed and the high speed compressor for aerodynamic performance (
The discharge of the low pressure compressor 22 is connected aerodynamically to the inlet of the existing compressor 11 through a compressed air line 23, now the high pressure compressor 11, boosting the overall pressure ratio of the engine. The generator connected to the original gas turbine is now defined as being on the high speed shaft, as the new turbine 21 and compressor 22 make the low speed shaft.
The existing gas turbine has the exhaust diffuser removed and is close coupled to the new low pressure gas turbine 21 with the variable area turbine stator vane 25. The flow discharging the existing gas turbine 13 now enters the low pressure gas turbine 21 which passes through the variable area turbine stator vane 25 and passes across the low speed turbine and out the new exhaust system (
The retrofit in this configuration can increase the existing industrial engines overall pressure ratio significantly, a range from 1.1 to even over 7×, thus greatly enhancing the engines mass flow and power output. The upgrade including the new low pressure gas turbine 21 may entail removing one or more of the front high pressure compressor blading stages 11A to optimally match the pressure ratio split between the low pressure and high pressure compressors 11A and 22 (
An alternate embodiment of this invention is to retrofit a two shaft gas turbine, where the high speed shaft has a compressor 11 and turbine 13 on one shaft, and a low speed turbine (Power turbine) 15 driving a generator 14 or mechanically driven equipment (Pump, process compressor etc.) as shown in the
In the process for retrofitting the prior art IGT engines in
The second upgrade elements are cooling system retrofits and are also available to be created alone, or in combination with the low speed spool retrofit. This use of regenerative (closed loop) cooling for the first several rows of cooled turbine vanes in the now high speed turbine 13 are implemented where the existing turbine stator vanes with cooling flow discharges into the gas path (such as through film cooling holes or exit holes) are replaced by stator vanes that collect the post cooling coolant and return it into the combustor 12 upstream of the flame. The use of the regenerative or closed loop cooling increases the thermal efficiency of the engine, and further enhances the overall power and efficiency coupled with the low speed compressor 22 and turbine shaft (
The cooling system if upgraded alone, would source cooling air from one of several places. This first option would be from ambient air such as that in
In the
A second approach is shown in
A fifth case the fully compressed air from the main compressor is extracted and cooled and then further compressed,
In each of these cases the externally compressed cooling air is created at a pressure significantly over the main compressor 11 discharge pressure, commonly designated P3. This intercooled and over pressurized coolant provides optimized low temperature high pressure coolant to the turbine stator vanes to provide cooling of the vanes to the desired level while the captured cooling flow exiting the vane exists with positive pressure margin to pass it into the combustor shell to mix with the existing compressor discharge air.
This configuration of closed loop air cooing (meaning most or all of the airfoil cooling air is discharged into the combustor instead of the hot gas stream through the turbine) optimized thermal efficiency and augments power by increasing the overall flow through the combustor while preventing coolant form diluting the main hot gas stream. By closed loop cooling of the turbine airfoil, the present invention means that most or all of the spent cooling air passing through the turbine airfoils is discharged into the combustor instead of being discharged into the hot gas stream.
In the cases where the regenerative turbine vane cooling implemented on the HPT is coupled with the low spool turbine and compressor, the cooling air source could be from the LPC discharge, or from an intermediate LPC bleed, HPC bleed or the HPC compressor discharge.
This application claims the benefit to U.S. Provisional Application 62/299,248 filed on Feb. 24, 2016 and entitled PROCESS FOR RETROFITTING AN INDUSTRIAL GAS TURBINE ENGINE FOR INCREASED POWER AND EFFICIENCY.
This invention was made with Government support under contract number DE-FE0023975 awarded by Department of Energy. The Government has certain rights in the invention.
Number | Date | Country | |
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62299248 | Feb 2016 | US |