Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2000-11-01
2002-10-15
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039120, C060S039182
Reexamination Certificate
active
06463741
ABSTRACT:
This application claims priority under 35 U.S.C. §119 and/or 365 to Appln. No. 199 52 885.3 filed in Germany on Nov. 3 1999; the entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The invention relates to a method for operating a power plant, which contains a gas turbine set.
BACKGROUND OF THE INVENTION
It is known to utilize the high exhaust-gas temperatures of gas turbine sets for the generation of synthesis gas. In this context, water is evaporated in a waste-heat boiler by means of the exhaust-gas heat of the gas turbine set. The steam thus obtained is intermixed, in a reactor likewise heated by the exhaust gas of the gas turbine, with a hydrocarbon-containing crude fuel, for example natural gas. When the temperature is sufficiently high, a low-calorie synthesis gas is obtained in the reactor from the crude fuel and the steam and contains as essential constituents the components comprising steam, hydrogen, unconverted crude fuel, carbon dioxide and carbon monoxide. A reactor gas emerges from the reactor, which reactor gas consists, in a varying composition, of synthesis gas, crude fuel and unconsumed steam and which can be burnt in a combustion chamber of the gas turbine set. The combustion of such low-calorie gases affords advantages in terms of pollutant emissions, in particular of nitrogen oxides, since the flame temperatures are lower. The high hydrogen fraction at the same time ensures stable combustion. The large fraction of ballast materials in the reactor gas results in high fuel mass flows and therefore high specific power outputs of the gas turbine set.
Power plants of this type with chemical recuperation of the exhaust-gas heat offer high efficiencies. However, a thorough conversion of crude fuel and steam into synthesis gas requires a comparatively high temperature level. This is afforded, at least approximately, precisely in the exhaust gas of modern gas turbine sets with sequential combustion which have a plurality of combustion chambers at different pressure stages. Additional firing upstream of the waste-heat boiler which may be necessary in some cases in order to achieve the necessary reactor temperature can have small dimensions. This makes the practical use of chemical recuperation of the exhaust-gas heat in gas turbine sets with sequential combustion attractive.
SUMMARY OF THE INVENTION
The object on which the present invention is based, in a power plant in which the exhaust-gas heat of a gas turbine set is utilized for the generation of synthesis gas, is to utilize in the best possible way the potentials of such an operation method for efficiency and power output.
It is therefore proposed, according to the invention, that a method for operating a power plant, which power plant contains at least one gas turbine set with at least one combustion chamber of a highest pressure stage and with at least one combustion chamber of at least one lower pressure stage, and in which method a hot gas is first expanded from a combustion chamber of a high pressure stage in a turbine, at the same time delivering mechanical power, and is introduced into a combustion chamber of a lower pressure stage, an expanded hot gas of the gas turbine set flowing through a waste-heat boiler, in which waste-heat boiler a steam quantity is generated, this steam quantity being introduced into a reactor installed in the waste-heat boiler, into which reactor a quantity of a hydrocarbon-containing crude fuel continues to be introduced, and a reactor gas consisting at least partially of synthesis gas being generated in the reactor from the steam quantity and from the crude fuel, which reactor gas is burnt at least partially in at least one combustion chamber of the gas turbine set, be designed in such a way that the synthesis gas is introduced, at least for a predominant part, into a combustion chamber of as high a pressure stage as possible and is burnt there. Combustion chambers of lower pressure stages are fired preferably directly by means of the crude fuel.
The essence of the invention is, therefore, in a power plant with a waste-heat boiler, to design the waste-heat boiler initially in a way known per se as a reactor for the generation of synthesis gas. Modern gas turbine sets with sequential combustion, which have at least two combustion chambers operating at different pressures, are particularly suitable for the generation of synthesis gas in a waste-heat boiler because of the high exhaust-gas temperatures which can be achieved. Steam is generated in the waste-heat boiler and is combined with a hydrocarbon-containing crude fuel in a reactor heated by the exhaust gas. A reactor gas is obtained there, which, when the reactor temperature is sufficiently high, consists essentially of hydrogen, carbon dioxide, carbon monoxide and steam not consumed for the generation of synthesis gas and, when the reactor temperature is comparatively low, of unconverted crude fuel, the inert steam constituting a ballast component of the reactor gas. According to the invention, in a gas turbine set with sequential combustion, the reactor gas is introduced, at least for a large part, into the combustion chamber of the highest pressure stage, insofar as the gas quantity is capable of being converted there. Combustion chambers of low pressure stages are operated preferably directly by means of a crude fuel which does not necessary have to be identical to the crude fuel supplied to the reactor for the generation of synthesis gas, but in the majority of cases will be because of practical considerations. The entire generated reactor gas quantity is introduced preferably into the combustion chamber of highest pressure and is burnt there, as long as the production rate of the reactor gas does not exceed the gas quantity capable of being utilized in the combustion chamber of highest pressure. The reactor gas is thus introduced at the highest possible pressure into the working process of the gas turbine set. The efficiency of a power plant with chemical recuperation of the exhaust-gas heat which is operated according to the invention far exceeds that of a power plant with steam injection and comes very close to that of a combined cycle plant in which the apparatus is appreciably more complicated.
Optimization of the efficiency of a chemically recuperated gas turbine set with sequential combustion is therefore achieved, with the exhaust-gas heat utilized as fully as possible, the generated reactor gas is burned as far as possible in the combustion chamber of the highest pressure stage. When, for example, methane or natural gas with a high methane content is used as crude fuel, it proves beneficial, in this respect, if possible to set the variable mass ratio of steam and crude fuel at a value of 5 parts of steam to one part of methane. When the hot-gas temperature in the combustion chamber of the highest pressure stage reaches a specific limit value, which is determined′, for example, by the permissible material temperatures of the components in the hot-gas path or, by the operating concept of the gas turbine plant, no further fuel can be utilized in the combustion chamber of the highest pressure stage. Reactor gas generated beyond the quantity capable of being utilized in the combustion chamber of the highest pressure stage is introduced into a combustion chamber of a lower pressure stage, preferably into a combustion chamber of the next lower pressure stage, and is burned there. Thus, in a further operating state, the combustion chambers of the two highest pressure stages are operated with reactor gas, specifically the combustion chamber of the highest pressure stage exclusively or for a predominant part and the combustion chamber of the second highest pressure stage for the fraction to be covered by the production of reactor gas and for the rest with crude fuel, while, where appropriate, further combustion chambers of lower pressure stages are operated at least predominantly with the crude fuel so as to operate with optimum efficiency. Reactor gas which can no longer be utili
Alstom (Switzerland) LTD
Burns Doane Swecker & Mathis L.L.P.
Kim Ted
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