Power plants – Combustion products used as motive fluid
Reexamination Certificate
1998-10-15
2001-04-17
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039120
Reexamination Certificate
active
06216436
ABSTRACT:
TECHNICAL FIELD
The present invention relates to power generation plants and particularly to a method of employing a Kalina bottoming cycle in an integrated gasification combined cycle power plant.
BACKGROUND OF THE INVENTION
Integrated gasification combined cycle (IGCC) power generating plants have demonstrable lower costs, improved reliability and improved efficiencies. The IGCC process relies on two-stage combustion with clean-up between the stages. The first stage includes a gasifier for partial oxidation of fossil fuel, i.e., coal, heavy fuel oils or the like, whereas the second stage utilizes a gas turbine combustor for burning the fuel gas produced by the gasifier to complete the combustion process. For example, it has been demonstrated that inherent fuel processing losses associated with fossil fuel gasification, in conjunction with the combined cycle, can deliver superior cycle efficiency. In a simple combined cycle power generating system, there is provided a gas turbine, one or more steam turbines, one or more generators and a heat recovery steam generator. The gas turbine and steam turbine may be coupled to a single generator in a tandem arrangement or multi-shaft combined cycle systems may be provided having one or more gas turbines, generators and HRSGs for supplying steam through a common header to a separate steam turbine generator unit. In the combined cycle, heat from the gas turbine exhaust is provided in heat exchange relation with a working fluid in the heat recovery steam generator for powering the steam turbines and, hence, generating electricity or mechanical work.
In recent years, there have been substantial improvements in thermodynamic cycles employing multi-component working fluids and a combination of absorption, condensation, evaporation and recuperative heat exchange operations to reduce irreversible losses typical of conventional Rankine cycles. Generally, these improved thermodynamic cycles are known as Kalina cycles and afford demonstrable and substantial improvements in thermodynamic cycle efficiency. Kalina cycles use two interactive subsystems. The first subsystem involves a heat acquisition process for a multi-component working fluid comprising, for example, preheating, evaporating, superheating, regenerative feed heating and power generation. The second subsystem consists of a distillation/condensation subsystem (DCSS). The efficiency improvements of the Kalina cycle over the Rankine cycle are a result of the use of a multi-component working fluid, preferably an ammonia/water mixture, the components of which have different boiling points at the same pressure. The compositions of the vapor and liquid streams change at different points throughout the cycle and the sub-systems enable closer matching of the enthalpy-temperature characteristics of the working fluid and the heat source used to evaporate the working fluid and the heat sink used to condense it.
In the heat acquisition subsystem, the Kalina system closes the mismatch between the enthalpy-temperature characteristics of the heat source and working fluid as the working fluid passes through the boiler. These energy losses, typical of the Rankine cycle, are reduced by taking advantage of the changing temperature-enthalpy characteristics of the multi-component working fluid as it evaporates.
In the second subsystem, i.e., the DCSS of the Kalina cycle, the spent working fluid after expansion through the turbine, is too low in pressure and too high in ammonia concentration to be directly condensed at the temperature of available coolant. The working fluid therefore can only be partially condensed and a lean solution is mixed with a two-phase precondensed flow from a recuperative heat exchanger, thereby forming a lower concentration of ammonia/water mixture which can be fully condensed at available coolant temperature. The lean condensate is subsequently distilled recuperatively against the turbine exhaust to regenerate the working composition for the heat acquisition subsystem. The Kalina cycle has been the subject of a number of patents including U.S. Pat. Nos. 4,586,340; 4,604,867; 5,095,708 and 4,732,005, the disclosures of which are incorporated by reference. The continued quest for increased efficiencies in power generation equipment has resulting in combining the Kalina bottoming cycles in an integrated gasification combined cycle power generating system in accordance with the present invention.
BRIEF SUMMARY OF THE INVENTION
The present invention combines an integrated gasification combined cycle power system with a Kalina bottoming cycle to afford increased power output and system efficiencies. Particularly, the present system employs a gasification system including a gasifier, with gas cooling and clean-up units. The power portion of the present system includes a gas turbine, a heat recovery vapor generator with a Kalina cycle bottoming unit, vapor turbines, electric generator units and an optional air separation unit. Basically, the present invention uses thermal energy streams from the gasification system and/or the optional air separation unit to heat the working fluid in the Kalina bottoming cycle units at appropriate locations to supplement the thermal energy supplied from the gas turbine exhaust, thereby maximizing the benefit of integration of thermal streams resulting in improved net plant electrical output and thermal efficiency. In one aspect of the present invention, heat available from the high temperature cooling section of the gasification system is recovered and placed in heat exchange relation with the multi-component working fluid of the combined cycle to augment the thermal energy supplied to the working fluid by the gas turbine exhaust. A low temperature cooling section of the gasification system is also used to preheat the condensed multi-component working fluid prior to supplying the working fluid to the heat recovery vapor generator.
In a preferred embodiment according to the present invention, there is provided in an integrated gasification combined cycle power generating system having a plurality of turbines, including first and second vapor turbines and a gas turbine for driving one or more generators for generating electricity or mechanical work, and a fuel gasifier for generating fuel gas for the gas turbine, a method of operating the system comprising the steps of (a) generating fuel gas from the fuel gasifier, (b) providing a heat recovery fluid from the fuel gasifier, (c) supplying the fuel gas from the fuel gasifier to a combustor for the gas turbine to drive the gas turbine, (d) expanding a working fluid through the first vapor turbine, (e) reheating the expanded working fluid from the first vapor turbine, (f) expanding the reheated working fluid through the second vapor turbine, (g) condensing the working fluid exhausted from the second vapor turbine, (h) passing the condensed working fluid in heat exchange relation with hot exhaust gases from the gas turbine for flowing heated working fluid to the vapor turbines and (i) additionally heating the working fluid supplied the vapor turbines by passing the working fluid in heat exchange relation with the heat recovery fluid.
In a further preferred embodiment according to the present invention, there is provided in an integrated gasification combined cycle power generating system having a plurality of turbines, including first and second vapor turbines and a gas turbine for driving one or more generators for generating electricity or mechanical work, and a fuel gasifier for generating fuel gas for the gas turbine, a method of operating the system comprising the steps of (a) generating fuel gas from the fuel gasifier, (b) providing a heat recovery fluid from the fuel gasifier, (c) supplying the fuel gas from the fuel gasifier to a combustor for the gas turbine to drive the gas turbine, (d) expanding a working fluid through the first vapor turbine, (e) reheating the expanded working fluid from the first vapor turbine, (f) expanding the reheated working fluid through the second vapor turbine, (g) condensi
Anand Ashok Kumar
Ranasinghe Jatila
Smith Raub Warfield
Evora Robert Z.
Freay Charles G.
General Electric Co.
Nixon & Vanderhye
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