Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-05-13
2001-01-09
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S655000, C060S673000
Reexamination Certificate
active
06170263
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of thermal energy conversion and, more particularly, to the conversion of low grade heat to a cooling load which may be used for auxiliary cooling needs in an integrated gasification system.
BACKGROUND OF THE INVENTION
Gas produced by the gasification process for integrated gasification power plants and industrial process applications needs to be cooled for effective gas treatment. Typically, the thermal energy of the raw gas is used in the combined cycle unit to improve the performance of the power cycle. Additional low grade heat, typically below about 150° C. (about 300° F.), is also normally available in the raw gas. However, this low grade heat is too low in temperature for steam generation for the bottoming cycle. Additional sources of low grade heat exist and are available in other sections of the integrated gasification unit, such as the air separation unit, the sulfur removal/recovery unit, heat recovery steam generator, and other subsystems. This low grade heat energy is normally rejected to the cooling water, or sometimes used for liquid heating duties, which have minor performance benefits.
BRIEF SUMMARY OF THE INVENTION
There has thus developed a need for a system and process which can use the previously un-utilized or underutilized low grade heat in the raw gas, preferably to enhance the thermodynamic efficiency of the integrated gasification system.
The invention provides a system and process whereby low grade heat recovered, for example by heat exchange, from various sections of, e.g., an integrated gasification system, is used to drive an absorption chilling cycle. The cooling load produced by this absorption chilling system may then be used for auxiliary cooling needs in the integrated gasification system. The use of previously un-utilized or underutilized low grade heat in the raw gas reduces auxiliary power requirements of cooling loads in the cycle, and thus enhances the thermodynamic efficiency of the integrated gasification system.
In accordance with a preferred embodiment of the present invention, there is provided a method of producing a cooling load, e.g., from low grade heat recovered from a gasification process, that comprises heating a working solution that is being pumping along a flow path, forming a rich stream and a lean stream from the heated working solution, condensing the rich stream to produce a liquid rich stream, throttling the rich stream to reduce the temperature thereof, evaporating the rich stream to produce a cooling load, mixing the rich vapor stream produced by the evaporating step with the lean stream to produce a mixed stream, and cooling the mixed stream in an absorber thereby to produce the working solution for the cycle to repeat. In a presently preferred system, the working solution is partly evaporated before the heating step with heat transferred from the lean stream.
Also in accordance with a preferred embodiment of the present invention an apparatus is provided for producing a cooling load, e.g., from low grade heat recovered from a gasification process, that comprises a first flow path; a pump for pumping a liquid working solution along the first flow path; means for heating the working solution flowing along the first flow path with heat from a source remote from the first flow path; a separator for forming a rich stream and a lean stream from heated working solution flowing thereinto from the first flow path; a second flow path for the rich stream exiting the separator; a third flow path for the lean stream exiting the separator; a condenser along the second flow path for condensing the rich stream to produce a liquid rich stream; a throttle valve along the second flow path for reducing a temperature of the liquid rich stream; and an evaporator along the second flow path for evaporating the rich stream to produce a cooling load. The second flow path and the third flow path are then joined to define the first flow path, downstream from the evaporator, for mixing the rich vapor stream produced by the evaporator with the lean stream flowing along the third flow path, to produce a mixed stream which is cooled by an absorber thereby to produce the working solution to be pumped by the pump. Also, the working solution is preferably pre-heated by the lean stream before being heated by the remote heat source.
The invention may thus be embodied in an integrated gasification system that includes a gasification and reforming system for receiving a fuel and converting the same to a hot raw gas, a gas cooling section for cooling the hot raw gas produced by the gas reforming section and an absorption chilling system for recovering low grade heat from at least the gas cooling system and producing a cooling load for auxiliary cooling, the absorption chilling system including that comprises a first flow path; a pump for pumping a liquid working solution along the first flow path; means for heating the working solution flowing along the first flow path with heat from a source remote from the first flow path; a separator for forming a rich stream and a lean stream from heated working solution flowing thereinto from the first flow path; a second flow path for the rich stream exiting the separator; a third flow path for the lean stream exiting the separator; a condenser along the second flow path for condensing the rich stream to produce a liquid rich stream; a throttle valve along the second flow path for reducing a temperature of the liquid rich stream; an evaporator along the second flow path for evaporating the rich stream to produce a cooling load; the second flow path and the third flow path being joined to define the first flow path, downstream from the evaporator, for mixing the rich vapor stream produced by the evaporator with the lean stream flowing along the third flow path, to produce a mixed stream which is cooled by an absorber thereby to produce the working solution to be pumped by the pump.
REFERENCES:
patent: 4982568 (1991-01-01), Kalina
patent: 5029444 (1991-07-01), Kalina
patent: 5095708 (1992-03-01), Kalina
patent: 5572871 (1996-11-01), Kalina
patent: 5649426 (1997-07-01), Kalina
patent: 5822990 (1998-10-01), Kalina
Anand Ashok Kumar
Chow Cedric
Ranasinghe Jatila
Stats David Andrew
General Electric Co.
Nguyen Hoang
Nixon & Vanderhye
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