Method for exhaust waste energy recovery at the reciprocating gas engine-based polygeneration plant

A method for an exhaust waste energy recovery at a reciprocating gas engine-based polygeneration plant, comprising in combination:

• supplying said polygeneration plant with a methaneous gas selected from a group consisting of pipeline natural gas, biogas, landfill gas, coal-bed methane and renewable methane and used as a fuel in said gas engine;
• supplying the gas engine with a charging air pressurized by an air compressor and cooled upstream of the gas engine;
• burning a mixture of the fuel and the charging air in the gas engine producing a gas engine power output, as a main product of the polygeneration plant, and releasing a pressurized exhaust gas stream comprising a mixture of nitrogen, oxygen, carbon dioxide and water vapor at a high temperature;
• harnessing most of a hot thermal energy of the pressurized exhaust gas for production of a process steam in a waste heat recovery boiler installed at an outlet of the gas engine;
• using the process steam for production of a power output of a steam bottoming cycle;
• expanding the pressurized exhaust gas in a gas turbine installed downstream of said waste heat recovery boiler, resulting in recovering a kinetic energy and a remainder of a thermal energy of the pressurized exhaust gas for production of a power output of said gas turbine;
• using at least a part of the power outputs of said gas turbine and said steam bottoming cycle for driving said air compressor;
• and
• additionally comprising:
• supplying the polygeneration plant with said methaneous gas at a rate exceeding an amount of said fuel used by the gas engine;
• forming a pre-treated methaneous gas stream through drying and purifying a supplied methaneous gas as needed to meet a pre-treatment quality standard set up for the methaneous gas being liquefied;
• compressing the pre-treated methaneous gas up to a high pressure of at least 60barA by a methaneous gas compressor if necessary, resulting in forming a high-pressure methaneous gas stream;
• pre-cooling said high-pressure methaneous gas, thereby forming a pre-cooled high-pressure methaneous gas stream;
• reducing in temperature the pressurized exhaust gas that, escaped the waste heat recovery boiler, to a near ambient value with accompanied drainage of a formed condensate;
• drying the pressurized exhaust gas and following pre-cooling a dried pressurized exhaust gas to a temperature below 0° C. in a cold regenerator, forming a dried and pre-cooled pressurized exhaust gas stream upstream of said gas turbine;
• said expanding of the dried and pre-cooled pressurized exhaust gas in the gas turbine, resulting in producing the power output by said gas turbine and forming a deeply cooled non-pressurized exhaust gas stream discharged from the gas turbine;
• recovering a cold thermal energy of said deeply cooled non-pressurized exhaust gas first for a liquefying of the whole of said pre-cooled high-pressure methaneous gas in a gas liquefier and then for said pre-cooling of the dried pressurized exhaust gas in said cold regenerator;
• using a non-pressurized exhaust gas removed from the cold regenerator to an atmosphere for removing a water vapor captured during said drying of the pressurized exhaust gas;
• depressurizing a high-pressure liquefied methaneous gas escaped the said gas liquefier down to a selected low pressure, resulting in forming a low-pressure two-phase liquefied methaneous gas stream;
• separating said low-pressure two-phase liquefied methaneous gas stream, resulting in forming a low-pressure methaneous vapor stream and a low-pressure liquefied methaneous gas stream;
• using said low-pressure methaneous vapor as the fuel for the gas engine;
• using said low-pressure liquefied methaneous gas as a co-product of the polygeneration plant;
• and
• using a part of the power outputs of the gas turbine and the steam bottoming cycle for driving said methaneous gas compressor.