Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-12-07
2002-10-01
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S728000, C062S333000
Reexamination Certificate
active
06457315
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to systems and methods for increasing the power produced by a gas turbine or combustion turbine for driving a mechanical device or for power generation. More particularly, it provides a more efficient refrigeration method and apparatus for cooling turbine inlet air to enhance its power output and overall combustion efficiency.
2. Background of the Invention
As used herein, the terms turbine, gas turbine and combustion turbine may be used interchangeably in reference to the same or similar process or system. Gas turbines are widely used in all phases of industrial applications. They are utilized as a source of shaft power to drive compressors, aircraft, and other rotating equipment. They are also coupled to electrical power generators for the generation of electricity extensively in either a simple cycle or a combined cycle power plant. Gas turbines typically consist of an intake air filtration, a compressor for compressing inlet air, a combustion chamber for mixing and igniting the compressed air with fuel to form a compressed hot gas for expansion to a turbine section to generate power. The work extracted from the high temperature gas, after partially used for air compression, will be available for output load. The exhaust gas from the turbine section, which contains a high level of heat energy, can be introduced into a waste heat recovery section, e.g. the heat recovery steam generator (HGSG) in a combined cycle power plant, or in some cases, discarded.
The performance of a combustion turbine system operated under the cycle described above is generally proportional to the mass flow rate of the inlet air to the gas turbine compressor, and is therefore largely affected by ambient air conditions. At high ambient temperatures, the available work produced from a gas turbine decreases due to a reduction in the mass flow of air through the system. And ironically, power demand often reaches the peak in most gas turbine applications during the hottest days when the operational efficiency of the turbine is at the lowest. Thus, an inlet air cooling system is commonly adopted to reduce the intake air temperature for minimizing the impact on turbine output, and to augment power output even during hot days when it can be installed cost effectively.
Various methods and apparatus for cooling gas-turbine inlet air are available in the art. For example, U.S. Pat. No. 5,930,990 to Zachary, et al. discloses an apparatus for achieving power augmentation in a gas turbine through a wet compression where water is sprayed to the inlet air to induce “latent heat inter-cooling.” Further, a liquid coolant fuel, as exemplified by the disclosure in U.S. Pat. No. 5,806,298, is introduced at the inlet of the air compressor, which vaporizes and cools the air to enhance power output of a gas turbine. Others utilize either a direct or an indirect evaporative cooler where the heat of hot air is transferred into the circulating water, leading to partial vaporization of water. However, the temperature reduction achieved with an evaporative cooler is limited to the daily fluctuating wet bulb temperatures in the areas. An evaporative cooling apparatus may not be applicable for warm and humid areas. Moreover, it often requires a high level of maintenance and relies on the quality and availability of a water source.
It is also readily common to introduce an external refrigeration system to chill the inlet air temperature far below that achievable by an evaporative cooler. This approach permits the turbine to operate at a fairly constant and optimal output regardless of the ambient air conditions. Although chilling the air to near 32° F. is possible, a minimum temperature considered suitable for inlet air chilling in a gas turbine application is usually set above 42° F. This prevents moisture contained in the inlet air from freezing and depositing on the inlet guide vanes or compressor blades as the static air temperature decreases further while it accelerates into the compression chamber. U.S. Pat. No. 5,457,951 discloses the use of liquefied natural gas as a refrigerant to improve the capacity and efficiency of a combined cycle power plant. Liquid nitrogen, as disclosed in U.S. Pat. No. 5,697,207, was also proposed to gain additional power from a gas turbine generator. However, the availability of this type of cold refrigerant is extremely limited. In most areas where a cold refrigerant is not readily available, a refrigeration system is proposed.
In all refrigeration systems, the refrigeration process depends on the absorption of heat at a low temperature which is achieved by the expansion and evaporation of a liquid refrigerant. Refrigeration systems are distinguished by how the refrigerant vapor is liquefied to repeat the cycle. There are two major types of refrigeration systems in commercial practice today, namely absorption refrigeration and mechanical refrigeration. In a typical absorption refrigeration system, a refrigerant vapor from the evaporator is dissolved in a liquid absorbent to form what is commonly referred to as a “solution pair” in an absorber. The solution pair is transferred to a desorber, or regenerator, where heat energy is applied to desorb the refrigerant in the form of a vapor, which is fed to a condenser. The two most commonly used absorption refrigeration systems are ammonia water and aqueous lithium bromide units. U.S. Pat. No. 5,555,738 improves combined-cycle power plant efficiency by operating an ammonia refrigeration cycle driven by the waste heat from the gas turbine to lower the inlet air temperature. Although absorption refrigeration systems are known and utilized commercially, continuous efforts have been devoted to improving their performance. A multiple effect generator is described in U.S. Pat. Nos. 4,183,228; 4,742,693, and 4,441,3332 to improve the efficiency of an absorption refrigeration circuit. U.S. Pat. Nos. 4,283,918 and 4,413,479 introduce a third fluid, which is at least partially immiscible to allow separation of refrigerant at absorption temperature, in the absorption refrigeration cycle. Other improvements include those described in U.S. Pat. Nos. 4,055,964 and 5,816,070. These systems are driven by heat energy and are relatively inefficient and inflexible unless reliable waste heat or inexpensive fuels are readily available.
In a mechanical refrigeration system, the refrigerant vapor is mechanically compressed to a high pressure and is then cooled to total condensation. This type of system has prevailed in industrial installations as a result of the improvement in efficiency. Depending upon temperature requirements, availability, and economics, various pure component refrigerants are commercially available, including light hydrocarbons, ammonia, water, and newly discovered chlorinated fluorocarbons (CFC's). For instance, an inlet air chilling apparatus using water vapor compression is described in U.S. Pat. No. 5,632,148 to achieve power augmentation of a gas turbine. For the modest cooling goal of inlet air chilling, the CFC refrigerants may be most appealing. However, their usage has become increasingly restricted due to environmental regulations. Conventional mechanical refrigeration using a single component refrigerant capable of achieving much colder refrigeration tends to be less efficient. Besides, the need of additional power to drive the compressor reduces the advantages of inlet air chilling.
An enhanced refrigeration system has also been attempted by combining both mechanical refrigeration and absorption refrigeration. For instance, U.S. Pat. No. 5,038,572 discloses a combined refrigeration method and apparatus for an improved efficiency, wherein mechanical refrigeration is alternately connected in series with an aqueous lithium bromide refrigeration. A combustion-powered compound refrigeration system is disclosed in U.S. Pat. No. 4,873,839 to reduce the energy consumption of a refrigerati
Chen Jong Juh
Elliot Douglas G.
Jain Pallav
Lee Rong-Jwyn
Yao Jame
Freay Charles G.
IPSI LLC
Jensen, Esq. William P.
Shook Hardy & Bacon L.L.P.
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