Power plant integrating coal-fired steam boiler with air turbine

A power plant comprising the combination of:

• a steam turbine, a coal-fired steam boiler having a radiant section including a combustion zone and steam generating tubes and a convection section provided with tubes for heating compressed air by indirect heat exchange with flue gas;
• compressor means wherein air is compressed for passage to said convection section;
• air turbine means driven by expansion of air compressed by said compressor means then heated in said convection section and passed to the inlet of said turbine means;
• said turbine means being arranged to produce useful power;
• conduit means for passing air turbine exhaust to said combustion zone as preheated combustion air;
• and conduit means for removing steam from said boiler and passing the same to the inlet of the steam turbine;
• said radiant section containing platens, said platens comprising a steam superheating section or a steam superheating section plus a steam reheating section effective to permit partial substitution of such service in the convection section by compressed air heating service whereby the temperature of said compressed air is raised to at least about 1450.degree. F.

A power plant comprising the combination of:

• a steam turbine, a steam boiler fired by a non-premium quality fuel and having a radiant section including a combustion zone and steam generating tubes and a convection section provided with tubes for heating compressed air by indirect heat exchange with flue gas;
• compressor means wherein air is compressed for passage to said convection section;
• air turbine means driven by expansion of air compressed by said compressor means then heated in said convection section and passed to the inlet of said turbine means, said compressor means being driven by said turbine means or by auxiliary means;
• said turbine means being arranged to produce useful power;
• conduit means for passing air turbine exhaust to said combustion zone as preheated combustion air;
• and conduit means for removing steam from said boiler and passing the same to the inlet of the steam turbine;
• said radiant section containing platens, said platens comprising a steam superheating section or a steam superheating section plus a steam reheating section and absorbing a sufficient percentage of heat for said services to release the convection section for compressed air heating service whereby the temperature of said compressed air is raised to at least about 1450.degree. F.

A power plant comprising the combination of:

• a steam turbine, a coal-fired steam boiler having a radiant section including a combustion zone and steam generating tubes and a convection section provided with tubes for heating compressed air by indirect heat exchange with flue gas;
• compressor means wherein air is compressed for passage to said convection section;
• air turbine means driven by expansion of air compressed by said compressor means then heated in said convection section and passed to the inlet of said turbine means, said compressor means being driven by said turbine means or by auxiliary means;
• said turbine means being arranged to produce useful power;
• means for recovering heat from air turbine exhaust to preheat boiler combustion air and conduit means for removing steam from said boiler and passing the same to the inlet of the steam turbine;
• said radiant section containing means for steam superheating or for steam superheating plus steam reheating effective to absorb a sufficient percentage of heat for said services to release the convection section for compressed air heating service whereby the temperature of said compressed air is raised to at least about 1450.degree. F.

In a method of operating a power plant comprising a coal-fired steam boiler/steam turbine power cycle, the improvement which comprises:

• integrating an air turbine with said cycle to provide a combined power cycle by heating compressed air by indirect heat exchange with flue gas in the convection section of said boiler, passing the hot compressed air to the inlet of the air turbine and expanding it in the air turbine;
• maintaining a radiant/convection heat split in the boiler which avoids coal ash fusion substantially;
• using a lower percentage of heat for generating steam of the same temperature and pressure;
• using remaining available heat in the radiant section for steam superheating or for steam superheating plus steam reheating thereby reducing such services in the convection section and allowing the convection section to carry out compressed air heating service so as to heat the compressed air to a temperature of at least about 1450.degree. F.;
• and
• passing air turbine exhaust as preheated combustion air to the boiler.

In a method of operating a power plant comprising a coal-fired steam boiler/steam turbine power cycle, the improvement which comprises:

• integrating an air turbine with said cycle to provide a combined power cycle by heating compressed air by indirect heat exchange with flue gas in the convection section of said boiler, passing the hot compressed air to the inlet of the air turbine and expanding it in the air turbine;
• maintaining a radiant/convection heat split in the boiler which avoids coal ash fusion substantially;
• using a lower percentage of heat for generating steam of the same temperature and pressure;
• transferring radiant heat from the coal firing along with convective heat from the flue gas available after provision for air heat duty raising the air to at least about 1450.degree. F., to tubes in the boiler to produce high pressure superheated steam;
• and
• passing air turbine exhaust as preheated combustion air to the boiler.

In a method of operating a power plant comprising a coal-fired steam boiler/steam turbine power cycle, the improvement which comprises:

• integrating an air turbine with said cycle to provide a combined power cycle by heating compressed air by indirect heat exchange with flue gas in the convection section of said boiler, passing the hot compressed air to the inlet of the air turbine and expanding it in the air turbine;
• maintaining a radiant/convection heat split in the boiler which avoids coal ash fusion substantially;
• using a lower percentage of heat for generating steam of the same temperature and pressure;
• providing platens in the radiant section of the boiler for steam superheating or for steam superheating plus steam reheating which assume a portion of such services of the convection section so as to enable the convection section to have a compressed air heat duty in the range of about 20 to 33% of the total heat absorbed in the boiler thereby heating the compressed air to a temperature of at least about 1450.degree. F.;
• using low level heat in the convection section to heat boiler feed water and removing flue gas from the convection section at a temperature in the range of about 275.degree. F. to 400.degree. F.;
• and
• passing air turbine exhaust as preheated combustion air to the boiler.