Power plants – Combustion products used as motive fluid – Multiple fluid-operated motors
Reexamination Certificate
2000-03-31
2001-08-07
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Multiple fluid-operated motors
C060S736000, C122S00700A
Reexamination Certificate
active
06269626
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to gaseous fuel heating by a regenerative fuel heating system in a combined cycle cogeneration power plant.
Conventionally, a preferred combined cycle cogeneration power plant configuration includes at least one combustion turbine (which is also referred to as “gas turbine”) driving an electrical generator for receiving combustion fuel, a combustion turbine having a multi-stage compressor for compressing ambient air, a combustion turbine having a combustor for the combustion process, and a combustion turbine having turbine blades for expanding the gaseous combustion product through the turbine blades. A heat recovery steam generator (HRSG) receives the gaseous combustion product from the combustion turbine for generating motive steam and includes a superheater, reheater, evaporator, economizer, preheater and steam/water evaporator drums. A steam turbine which drives an electrical generator for accepting motive steam from the HRSG, includes an extraction port for extracting steam for the process, an induction port for accepting induction steam, a reheat port for accepting reheat steam from the HRSG and a condensing port to release exhausted steam into condenser.
It is generally recognized that the most significant technique for improving efficiency of power plant generation is by means of a combined cycle cogeneration power plant system. Increasing power plant efficiency and power output have been a continuous goal throughout the power industry. One such goal has been in the area of fuel heating in the combined cycle cogeneration power plant.
Several known prior art systems have sought to improve plant efficiency and power output by means of preheating fuel by utilizing economizer water from the HRSG, preheating fuel by utilizing exhaust gas from the combustion turbine, preheating fuel by a second heat recovery system in the combustion turbine exhaust gas flow path or preheating fuel by recovering hot air or steam from a combustion turbine engine.
One approach described in U.S. Pat. No. 4,932,204 recovers heat available in the exhaust gas by increasing the water flow through the economizer section of the HRSG to a rate in excess of that required to match the steam production rate in the evaporator section. The excess water flow is withdrawn from the HRSG at a temperature approaching the evaporator temperature and used to preheat fuel delivered to the combustion turbine.
Another approach is taught by U.S. Pat. No. 5,357,746, which preheats fuel by utilizing exhaust gas from the combustion turbine by a second heat recovery system, using waste heat from the combustion turbine that is not recoverable from the first heat recovery system.
Yet another approach is taught by U.S. Pat. No. 5,826,430, which preheats fuel by using heated coolant such as steam or air returning from the gas turbine engine.
Still another approach is taught by U.S. Pat. No. 5,845,481, which preheats fuel by a fuel line disposed in heat transfer relationship within the exhaust gas from the combustion turbine so that the fuel may be heated by the exhaust gas prior to being introduced into the combustor.
Such prior art systems have failed to recognize that the most efficient power plant has already been achieved through a combined cycle cogeneration power plant configuration. In addition, such prior art systems have all failed to recognize that there would be no additional energy recoverable without imposing penalties on the most efficient combined cycle cogeneration power plant.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a combined cycle cogeneration power plant as well as a conventional power plant with a fuel heating system which provides a better overall efficiency than those of which have been realized heretofore.
It is another object of the invention to provide a combined cycle cogeneration power plant with a fuel heating system which recovers useful thermal energy from the HRSG steam/water evaporator drum surface blowdown which is currently released to surrounding environment.
It is still another object of the invention to provide heat exchangers of a fuel heating system for recovering waste thermal energy from the HRSG steam/water evaporator drum surface blowdowns to provide higher plant efficiency to the most efficient design basis of the thermodynamic cycle of the combined cycle cogeneration power plant.
It is yet another object of the invention to provide a combined cycle cogeneration power plant with heat exchangers in cascaded heat exchange relationship for providing cascaded heating capability of the combustion fuel prior to injecting the same into the combustion chamber of a combustion turbine.
It is a further object of the invention to provide a combined cycle cogeneration power plant with a regenerative fuel heating system which eliminates high thermal energy release into the atmosphere and provides effective means of mitigating thermal discharge impact to the surrounding environment.
It is a still further object of the invention to provide a combined cycle cogeneration power plant with a regenerative fuel heating system which recovers currently-being-wasted steam and condensate from the HRSG steam/water evaporator drum surface blowdown and preheats gaseous fuel prior to injecting the same into the combustion chamber.
The regenerative fuel heating system of the present invention provides a higher efficiency than prior art systems of a combined cycle cogeneration power plant by recovering currently-being-wasted thermal energy within the thermodynamic cycle of a power plant.
In accordance with an aspect of the present invention, a regenerative fuel heating system in a combined cycle cogeneration power plant includes heat exchangers for receiving and preheating the combustion fuel in heat exchange relationship with waste thermal energy prior to injecting the combustion fuel into the combustor, the heat exchangers having at least a first inlet and at least a first outlet through which the combustion fuel can be supplied and the preheated combustion fuel can be injected into the combustor, and having at least a second inlet and at least a second outlet through which the thermal waste energy can be supplied and discharged after heat exchange relationship with the combustion fuel. These heat exchangers can be configured in cascaded heat exchange relationship for providing cascaded heating capability of the combustion fuel prior to injecting into the combustor.
In accordance with another aspect of the present invention, a regenerative fuel heating system in a combined cycle cogeneration power plant includes a heat exchanger for accepting thermal energy from the HRSG high pressure high temperature steam/water evaporator drum surface blowdown to preheat the combustion fuel, another heat exchanger for recovering an intermediate and/or a low pressure and temperature steam/drum surface blowdowns from the HRSG to control the desired fuel temperature prior to cascading into the high pressure, high temperature heat exchanger.
Traditionally, the heat recovery steam generator (HRSG) includes superheaters, reheaters, evaporators, economizers, preheaters and steam/water evaporator drums. The HRSG is connected to the exhaust of a combustion turbine to recover gaseous combustion product to generate motive steam as a final product to be used by a steam turbine or as a process steam for the industries. The motive steam is produced by a gradual process of changing fluid phase from a liquid phase (feedwater to HRSG) to a vapor phase by heat transfer through the preheater, economizer, evaporator and superheater. Each evaporator includes a steam/water evaporator drum directly connected to each evaporator for accepting two phase flow (liquid and vapor) in which the vapor phase and the liquid phase become as a separate phase.
All steam/water evaporator drums need to be blowndown continuously to mitigate or avoid collecting impurities and scale concentration in the drum as steam is transported and used. These impurities and scales are in
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Kim Ted
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