Patent Application
20100257837
The subject matter disclosed herein relates to power generation and more particularly to power generation in hybrid power plants.
Power plants using steam turbines often include gas turbine engines. The gas turbine engines may be used during a cold start up of the plant and to increase power generation during plant operation. In a hybrid plant, the exhaust from gas turbine engines may be incorporated into the thermal cycle of the plant to increase the efficiency of steam generation. The operational specifications of gas turbines including, for example, exhaust temperatures, fuel consumption, and emissions affect the efficiency of a hybrid plant.
According to one aspect of the invention, a system comprises a first heat recovery steam generator (HRSG) having an upstream intake duct portion, a first gas turbine engine connected to a first exhaust duct operative to output exhaust from the first gas turbine engine to the upstream intake duct portion of the first HRSG, and a second gas turbine engine connected to a second exhaust duct operative to output exhaust from the second gas turbine engine to the upstream intake duct portion of the first HRSG.
According to another aspect of the invention, a system comprises a first heat recovery steam generator (HRSG) having an upstream intake duct portion, a first gas turbine engine connected to a first exhaust duct operative to output exhaust from the first gas turbine engine to the upstream intake duct portion of the first HRSG, a duct burner portion operative to heat the output exhaust of the first gas turbine engine, and a second gas turbine engine connected to a second exhaust duct operative to output exhaust from the second gas turbine engine to the upstream intake duct portion of the first HRSG.
According to yet another aspect of the invention, a system comprises a first heat recovery steam generator (HRSG) having an upstream intake duct portion and a downstream intake duct portion, a first gas turbine engine operative to output exhaust to the upstream intake duct portion of the first HRSG, wherein the exhaust from the first gas turbine engine is operative to heat the first HRSG to a first temperature, a second gas turbine engine operative to output exhaust to the upstream intake duct portion of the first HRSG wherein the exhaust from the second gas turbine engine is operative to heat the first HRSG to a second temperature.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Hybrid plants include a heavy frame and aeroderivative gas turbine engine connected to a generator(s) to produce power. The aeroderivative gas turbine engine may be used, for example, during periods of peak power consumption to augment the power produced by a steam turbine. Hybrid power plants having steam turbines and gas turbine engines may incorporate heat recovery steam generators (HRSGs) that use the heat from the exhaust gas of the aeroderivative gas turbine engine to generate additional steam that powers the steam turbine. The use of the exhaust gas from the aeroderivative gas turbine engine increases the efficiency of hybrid plants at part loads and may reduce fuel consumption and pollution during loading and unloading of the power plant.
During a cold startup of a typical plant, operation of the heavy frame gas turbine engine in a condition appropriate for preheating the cold HRSG results in undesirable levels pollutant emissions. The use of an aeroderivative gas turbine engine at operating parameters that reduce the exhaust temperature to a level appropriate for preheating the cold HRSG efficiently decreases undesirable pollutant emission levels.
During a cold start up sequence for a hybrid plant, the exhaust from the aeroderivative gas turbine engine is used to preheat the HRSG. Preheating the HRSG starts with a cold HRSG that is gradually heated by exhaust from the aeroderivative gas turbine engine until the HRSG reaches a normal operating temperature. Operating the aeroderivative gas turbine to preheat the HRSG reduces the time the heavy frame operates at low loads and results in lower total power plant emissions of undesirable pollutants. The parameters used to define operating temperatures at startup and normal operation of the HRSG are typically defined by the designed specifications of a particular plant and the associated system components. For example, the design of the steam turbines of the plant often defines the specifications used to operate the HRSG. Systems for efficiently preheating and operating a hybrid plant are described below.
The system 100 may operate in a number of different modes including, for example, cold plant start up, normal operation, and peak output operation and turndown operation. In an exemplary cold plant startup sequence, the system 100 begins with a cold, non-operating plant. The light frame gas turbine engine 106 is started, with the upstream intake duct damper 118 and the downstream intake duct damper 120 closed. The bypass stack 122 is open. Ambient air is received by the air inlet 112, mixed with fuel, and combusted in the light frame gas turbine engine 106. The alternator/generator 116 may be brought online, and the power from the alternator/generator 116 sent to the grid 105. The exhaust from the light frame gas turbine engine 106 is output by the bypass stack 122. The upstream intake duct damper 118 is opened, and the bypass stack 122 is closed-routing the exhaust from the light frame gas turbine engine 106 to the upstream intake duct portion 101 of the HRSG 102. The exhaust from the light frame gas turbine engine 106 begins preheating the HRSG 102 and/or a steam turbine.
The light frame gas turbine engine 106 is designed to operate efficiently and with low pollution emissions while outputting exhaust gas at a temperature within the preheat temperature specifications of the HRSG 102 and the associated steam turbine. Once the HRSG 102 is preheated to a temperature threshold that is associated with the exhaust temperature of the light frame gas turbine engine 106, the heavy frame gas turbine engine 104 is started. The heavy frame gas turbine engine 104 operates efficiently at an exhaust temperature that is higher than the light frame gas turbine engine 106 and outputs a higher temperature exhaust into the upstream intake duct portion 101 of the HRSG 102. Once the heavy frame gas turbine engine 104 is operating at a desired frequency the alternator/generator 114 may be brought online and deliver power to the grid 105, the light frame gas turbine engine 106 may be shut down, and the upstream intake duct damper 118 is closed. The heavy frame gas turbine engine 104 exhaust continues to preheat the HRSG 102. Once the HRSG 102 is preheated to a desired temperature, the HRSG 102 may produce steam for the steam turbine 108. In normal operation, the steam turbine 108 may receive steam from another boiler (not shown) in the system 100, and the heavy frame gas turbine engine 104 may be shut down. Alternatively, the heavy frame gas turbine engine 104 may remain running and provide power to the grid 105 and exhaust gas to heat the HRSG 102.
In peak operation, the light frame gas turbine engine 106 may be used with the alternator/generator 116 to provide additional power to the grid 105. In peak operation the heavy frame gas turbine engine 104 is operating efficiently; turning the alternator/generator 114, and outputting exhaust to the upstream intake duct portion 101 of the HRSG 102. The light frame gas turbine engine 106 is started with the upstream intake duct damper 118 and the downstream intake duct damper 120 closed and the bypass stack 122 open. Once the light frame gas turbine engine 106 is operating at a desired output, the downstream intake duct damper 120 is opened and the bypass stack 122 is closed—routing exhaust from the light frame gas turbine engine 106 to the downstream intake duct portion 103 of the HRSG 102.
When the light frame gas turbine engine 106 and the heavy frame gas turbine engine 104 are each operating at an efficient output level, the exhaust temperatures of the gas turbine engines are dissimilar. Typically, the exhaust temperature of the light frame gas turbine engine 106 operating at a desired efficiency is lower than the temperature of the heavy frame gas turbine engine 104 operating at a desired efficiency. Routing the cooler exhaust of the light frame gas turbine engine 106 to mix with the hotter exhaust of the heavy frame gas turbine engine 104 at the upstream intake duct portion 101 of the HRSG 102 is undesirable since the cooler exhaust of the light frame gas turbine engine 106 reduces the effectiveness of the hotter exhaust of the heavy frame gas turbine engine 104. As the exhaust from the heavy frame gas turbine engine 104 flows down stream through the HRSG 102, the exhaust cools by creating steam in the HRSG 102. Eventually, the exhaust from the heavy frame gas turbine engine 104 reaches a temperature that effectively matches the temperature of the exhaust of the light frame gas turbine engine 106. The region where the exhaust from the heavy frame gas turbine engine 104 reaches a temperature that effectively matches the temperature of the exhaust of the light frame gas turbine engine 106 is the input region for the downstream intake duct portion 103 of the HRSG 102.
Thus, the exhaust of the heavy frame gas turbine engine 104 mixes with the exhaust of the light frame gas turbine engine 106 at a similar temperature in the downstream intake duct portion 103 of the HRSG 102. Routing the exhaust of the light frame gas turbine engine 106 to mix with the exhaust of the heavy frame gas turbine engine 104 in the HRSG 102 in a region where the temperatures of the exhaust are matched, allows the heavy frame gas turbine engine 104 and the light frame gas turbine engine 106 to operate at efficient output levels; providing power to the grid 105 and efficiently contributing exhaust gas to the HRSG 102.
The embodiments described above show exemplary systems. Other embodiments may include a variety of combinations of gas turbine engines, HRSGs, and steam turbines. The embodiments are not limited for example, to one or two HRSGs, but may include any number of HRSGs, gas turbine engines, and associated equipment. The terms light frame and heavy frame gas turbine engine are not limiting and used for illustrative purposes. For example a heavy frame gas turbine engine having desired design specifications may be substituted for a light frame gas turbine engine. Likewise, a light frame gas turbine engine may in some applications be substituted for a heavy frame gas turbine engine or any other gas turbine engine that may also be in the aero-derivative branch of gas turbine engines.
The functions shown in
In operation, the cold plant startup sequence of the system 300 of
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
