Solid fuel grade gasification-combustion dual bed poly-generation system and method thereof

A solid fuel grade gasification-combustion dual bed poly-generation system, comprising:

• a circulating fluidized-bed combustion boiler (1), a circulating fluidized-bed gasification boiler (2), a synthesized gas purification unit and a methanation unit;
• wherein a bottom of the circulating fluidized-bed combustion boiler (1) is provided with a combustion boiler slag outlet (7) and a combustion boiler fluidizing air inlet (5);
• the fluidizing air enters the combustion boiler fluidizing air inlet (5) and then flows to the circulating fluidized-bed combustion boiler (1) via a combustion boiler air distribution unit (6a), one part of the fuel enters the circulating fluidized-bed combustion boiler (1) via a combustion boiler fuel feeding opening (4a), flue gas generated during combustion enters at least a primary combustion boiler cyclone separation unit via a gas channel (8), the gas after separation is directly exhausted, while separated ash particles are returned back into the circulating fluidized-bed combustion boiler via a combustion boiler material return unit (10a), the heat generated during combustion is used to produce combustion boiler steam (46a) and the steam (46a) from combustion boiler is used for external supply and is supplied to the circulating fluidized-bed gasification boiler (2);
• the bottom of the circulating fluidized-bed gasification boiler (2) is provided with a semi-coke outlet (49) and gasification boiler fluidizing air inlets (11a, 11b);
• a gasifying agent for gasification is sent into the gasification boiler fluidizing air inlets (11a, 11b) and then flows into the circulating fluidized-bed gasification boiler (2) via a gasification boiler air distribution unit (6b), steam (44) in the gasifying agent comes from a combustion boiler steam (46a) and/or methanation unit, carbon dioxide is the carbon dioxide generated by the methanation unit, the other part of the fuel is fed into the circulating fluidized-bed gasification boiler (2) via a gasification boiler fuel feeding opening (4b), the semi-coke generated by gasification is discharged via a semi-coke outlet (49) and then sent into the combustion boiler fuel feeding opening (4a), the synthesized gas enters at least a primary gasification cyclone separation unit via a synthesized gas outlet on top of the circulating fluidized-bed gasification boiler, after separation the synthesized gas is sent into a synthesized gas purification unit, while the separated ash particles are sent back into the circulating fluidized-bed gasification boiler (2) and/or the combustion boiler fuel feeding opening (4a) via a gasification boiler material return unit (10b),
• the synthesized gas purification unit primarily washes and de-dusts the synthesized gas, uses water as a cooling media to chill the synthesized gas in a heat exchange mode, sends the cooled gas to the methanation unit, a sewage including oil and water is generated during the cooling process, performs oil-water separation on at least one part of the sewage including oil and water generated during cooling, and sends impurities expelled from the separation to the combustion boiler fuel feeding opening (4a) or the gasification boil fuel feeding opening (4b) or sends by-products obtained for further processing;
• the methanation unit converts the fed synthesized gas into synthesized natural gas through low-temperature methanol washing process and methanation process, sends carbon dioxides generated in the low-temperature methanol washing process to the gasification boiler fluidizing air inlets (11a, 11b) and the steam (44) as a side produced by the methanation process to the gasification boiler fluidizing air inlets (11a, 11b), or as a supplemental steam required by the methanation unit or discharges the stream for other purposes;
• wherein the synthesized gas purification unit comprises a cooling scrubber (16), a heat recovery boiler (19), a cooling unit (22), a first oil-water separator (25), a second oil-water separator (26) and a sewage settlement tank (36);
• the synthesized gas coming from the gasification boiler cyclone separator unit is sent into the cooling scrubber (16) or the heat recovery boiler (19),
• when the synthesized gas is sent into the cooling scrubber (16), the cooling scrubber (16), the heat recovery boiler (19) and the cooling unit (22) are connected in turn, wherein the cooling scrubber (16) primarily washes, de-dusts and chills the synthesized gas and then the cooled synthesized gas is sent into the heat recovery boiler (19), the heat recovery boiler (19) is also supplied with de-salted water (55) simultaneously, the de-salted water (55) exchanges heat with a synthesized water in the heat recovery boiler (19) and then as a cooling water is led to the cooling scrubber (16), the synthesized gas enters the cooling unit (22) after the heat exchange, the cooling unit (22) receives supernatant (38) as a cooling media from the sewage settlement tank (36) simultaneously, the synthesized gas flows out of the cooling unit (22) and then is sent into the methanation unit, the sewage expelled from the heat recovery boiler (19) and the cooling unit (22) in the heat exchange process is sent to the first oil-water separator (25) and the second oil-water separator (26) through respective pipes, the first oil-water separator (25) and the second oil-water separator (26) as well as the sewage settlement tank (36) are connected in turn, a part of the sewage undergoes separation in the first oil-water separator (25), the obtained product as a washing water is led to the cooling scrubber (16), and the impurities expelled by the first oil-water separator (25) and the second oil-water separator (26) are sent to the combustion boiler fuel feeding opening (4a) or sent to the gasification boiler fuel feeding opening (4b) or as side products are used for further process, a part of the sewage passes through the first oil-water separator (25) and the second oil-water separator (26) and then is collected in the sewage settlement tank (36), the supernatant (38) produced by the sewage settlement tank (36) is sent to the cooling unit (22), residual deposits (37) are sent out of the system for further process, and the rest of which is sent out of the system for sewage treatment (52),
• when the synthesized gas is sent into the heat recovery boiler (19), the heat boiler (19), the cooling scrubber (16) and the cooling unit (22) are connected in turn;
• the heat recovery boiler (19) is supplied with de-salted water (55) and supplied with the synthesized gas from the gasification boiler cyclone separation unit simultaneously, the de-salted water (55) exchanges heat with the synthesized water in the heat recovery boiler (19) to form steam, which as a gasifying agent is sent into the gasification boiler fluidizing air inlets (11a, 11b), after heat exchange, the gasifying agent is sent into the cooling scrubber (16), the cooling scrubber (16) primarily washes, de-dusts and chills the fed synthesized gas and then the cooled synthesized gas is sent into the cooling unit (22), the cooling unit (22) is also supplied with a supernatant (38) as a cooling media from the sewage settlement tank (36) simultaneously and the synthesized gas flows out of the cooling unit (22) and then is sent into the methanation unit, the sewage produced by the cooling scrubber (16) and the cooling unit (22) in the heat exchange process is sent to the first oil-water separator (25) and the second oil-water separator (26) through respective pipes the first oil-water separator (25) and the second oil-water separator (26) as well as the sewage settlement tank (36) are connected in turn, a part of the sewage is separated by the first oil-water separator (25) and the product as the washing water is led to the cooling scrubber (16), the impurities expelled by the first oil-water separator (25) and the second oil-water separator (26) are sent to the combustion boiler fuel feeding opening (4a) or sent to the gasification boiler fuel feeding opening (4b) or as by-products are used for further process, a part of the sewage passes through the first oil-water separator (25) and the second oil-water separator (26) and then is collected in the sewage settlement tank (36), the supernatant (38) produced by the sewage settlement tank (36) is sent to the cooling unit (22), and deposits (37) accumulated are sent out of the solid fuel grade gasification-combustion dual bed poly-generation system for processing and the rest of which is sent out of the solid fuel grade gasification-combustion dual bed poly-generation system for sewage treatment (52).