Patent Application
20130213054
The invention relates to a gas turbine inlet system and, more particularly, to a gas turbine inlet system including a solid-state heat pump.
Gas turbine engines generally include a compressor for compressing an incoming air flow (gas turbine inlet air or GT inlet air). The air flow is mixed with fuel and ignited in the combustor for generating hot combustion gases. The combustion gases in turn flow to a turbine. The turbine extracts energy from the gases for driving a shaft. The shaft powers the compressor and generally another element such as an electrical generator.
At higher ambient temperatures, the output of a gas turbine can drop due to the lower density of compressor inlet air. Prior systems have performed inlet air conditioning with the help of evaporative coolers, which become less effective as the ambient temperature falls or humidity increases. Inlet chillers have also been used to cool the inlet air in water scarce regions but have a disadvantage of higher operation and maintenance costs. Traditionally, fuel heating is achieved with an external heat source or low grade heat from the bottoming cycle.
It would be desirable to provide a system that effects inlet air conditioning and reduces the power output lapse versus the ambient temperature. It would also be desirable to utilize the fuel stream as the sink to thereby improve the heat rate of the plant due to the fuel heating effect.
In an exemplary embodiment, a gas turbine inlet system is provided for a gas turbine including a compressor that compresses gas turbine inlet air for combustion in a combustor that outputs products of combustion to drive a turbine. The inlet system includes a main inlet air passage that carries the gas turbine inlet air to the compressor, a heat pump, and a fuel passage that carries fuel to the combustor via the heat pump. A diverted inlet air passage is connected to the main inlet air passage and diverts a fraction of the gas turbine inlet air through the heat pump and back to the main inlet air passage. Heat from the gas turbine inlet air in the diverted inlet air passage is exchanged via the heat pump with the fuel in the fuel passage.
In another exemplary embodiment, a gas turbine inlet system includes a first passage that delivers inlet air to a compressor, a second passage that delivers fuel to a combustor, and a heat pump that transfers heat from the inlet air to the fuel by consuming electric power.
In still another exemplary embodiment, a method of delivering air and fuel in a gas turbine includes the steps of diverting gas turbine inlet air from a main inlet air passage to a heat pump; carrying fuel through the heat pump; transferring heat from the gas turbine inlet air to the fuel in the heat pump; returning cooler air to the main inlet air passage for delivery to a compressor; and delivering hotter fuel to a combustor.
In a further exemplary embodiment, the gas turbine inlet system includes the heat pump, an inlet air passage that carries the gas turbine inlet air to the compressor at least partially via the heat pump, a fuel passage that carries fuel to the combustor, and an exit air passage that carries compressor exit air to the combustor. Heat from the gas turbine inlet air in the inlet air passage is exchanged via the heat pump with one of the fuel in the fuel passage or the compressor exit air.
The gas turbine inlet system of the described embodiments utilizes a heat exchanger or solid-state heat pump such as a thermionic or thermoelectric device to transfer heat from a source (GT inlet air) to a sink (fuel stream) by consuming electric power. The heat transfer causes the GT inlet air temperature to drop and the fuel temperature to increase with favorable effects on both output and heat rate.
The inlet system 20 includes a main inlet air passage 22 that carries the GT inlet air to the compressor 12. A fraction of the GT air is diverted from the main inlet air passage 22 via a diverted inlet air passage 24 connected to the main inlet air passage 22. The fraction of diverted GT air is directed to a heat exchanger 26. An analysis has showed favorable results with 25% of air diverted, but any amount of air could be diverted. Preferably, the heat exchanger 26 is a solid-state heat pump, e.g., using thermionic or thermoelectric devices to transfer heat from a source to a heat sink.
A fuel passage 28 carries fuel to the combustor via the heat pump 26. The heat pump 26 consumes electric power to transfer heat from the inlet air stream (source) to the fuel stream (heat sink).
Downstream of the heat pump 26, the relatively cooler GT inlet air returns to the main inlet air passage 22 via the downstream portion of the diverted inlet air passage 24. As shown in
The relatively hot fuel is carried directly to the combustor 14. In an exemplary application, the fuel upstream of the heat exchanger is generally about 80° F., and the fuel downstream of the heat exchanger 26 is greater than 80° F. For gas turbine and steam turbine combined cycle operation, the temperature may be 365° F.
The decrease in GT inlet air temperature results in higher mass flow, which causes a corresponding increase in turbine output. The increase in fuel temperature provides a heat rate benefit. Due to the fast response of the system, the improvements in output and heat rate are nearly instantaneous. Since the thermionic/thermoelectric cooling effect is dependent on the electrical supply, the system can be easily controlled and integrated with the existing control systems, and dependency on external heat sources for fuel heating can be minimized. Additionally, the system is quiet and reliable as the heat pump operates silently and is essentially maintenance free. Still further, the increase in turbine output more than offsets the electrical energy needed to power the heat pump.
With this structure, advantageously, cooling the inlet air to the upstream (e.g., stage 1) compressor 112 serves to increase compressor efficiency, and as a consequence, parasitic compressor power is reduced thereby improving the net plant output. Additionally, by heating the compressor exit air from the downstream compressor (e.g., stage 2 compressor), the heat rate of the gas turbine is increased due to the higher combustor inlet temperature.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. For example, the system can be operated intermittently to provide the power boost required in transient events like during under-frequency grid code compliance. Also, the duct design can be refined further for minimum pressure loss and maximum heat transfer. Still further, the heat pump can be used in reverse (by reversing the direction of electric current flow) to heat the inlet air for IBH (inlet bleed heat) applications. Though the cost of present devices for such applications is prohibitive, future improvements in device efficiencies might prove to be practical.
