Design And Optimization Of Parallel Type Of Polygeneration Systems Of Liquid Fuels And Power Based On Co-gasification Of Coal And Biomass

Energy and environmental issues are related to human survival and development.As a conventional energy source,fossil energy has still occupied an irreplaceable status comparing with the new energy sources.The three major fossil energy sources,such as coal,oil,and natural gas,occupy an absolute advantage in China's energy consumption market.However,China's energy distribution characteristic of"rich coal,lean oil,and low gas"has made China's large amount of petroleum resources dependent on imports.In order to balance the energy structure,taking advantage of abundant coal resources to produce liquid fuel is an effective way to optimize China's energy structure.From the perspective of power production,the traditional thermal power generation technology mainly burns raw coal,and its disadvantages are serious environmental pollution and low energy utilization efficiency.As a clean and efficient coal based power generation technology,IGCC has obvious advantages in both thermal efficiency and environmental friendliness.Considering the sustainability and reproducibility of energy,coal,as a non-renewable energy,will eventually run out.Therefore,the mixed utilization of coal resources and renewable biomass resources can not only prolong the use cycle of coal resources,but also effectively reduce the emission of CO₂ and other greenhouse gases.Based on the above technical flaws,it is feasible to couple FTS process with IGCC power generation technology using coal and biomass mixed gasification as the source process and polygeneration as the technical guideline.In this study,based on the comprehensive cascade utilization of physical and chemical energy,a parallel polygeneration system of synfuels and power based on co-gasification of coal and biomass was established,and the thermodynamic characteristics of the polygeneration system were analyzed.The subsystems of the polygeneration mainly include co-gasification of coal and biomass unit,primary purification unit,synthesis gas conversion unit,secondary purification unit,FTS unit,oil refining unit,IGCC power generation unit.The system model and logistics accounting model were established by using Aspen Plus-Excel software,and the thermal efficiency,coal saving rate and carbon capture rate of the polygeneration system were calculated and analyzed under different biomass mass fraction and different FTS diversion ratio.Based on the first law of thermodynamics and the conservation of materials and energy,the thermal efficiency and coal saving rate of the polygeneration system were calculated.The feedstock is 3000 t/d and the syngas shunting ratio of FTS side is assumed as 0.2,0.4,0.6,0.8,respectively.The results show that when the biomass mass ratio is 0.2 of the feedstock,the polygeneration can obtain the highest thermal efficiency which is 46.39%,46.51%,46.59%,47.49%,respectively under each of the assumed shunting ratios.This is due to the optimal synergy effect when the biomass mixing ratio is 0.2.When the mass fraction of biomass exceeds 0.2,because the biomass itself has a high volatile content and a low fixed carbon content,the synthesis gas flow is reduced,and the effective components?CO,H₂?and the calorific value of the synthesis gas are reduced.The synergistic effect of co-gasification weakened,and the thermal efficiency of the system showed an overall decline,but the system still had a high thermal efficiency before the biomass ratio was 0.3.Under the premise of the same biomass mass fraction,the thermal efficiency of the polygeneration system gradually increased with the increase of the diversion ratio of syngas on the FTS side.When the biomass mass fraction exceeds 0.5,the change of the synthesis gas split ratio on the FTS side has a greater effect on the thermal efficiency of the system.Increasing the split ratio of the FTS side synthesis gas can improve the system thermal efficiency.For the study of coal saving rate,when the biomass mass fraction is less than 0.2,the coal saving rate increases with the increase of the biomass mass fraction,and the polygeneration system has a better coal saving rate under the specific FTS split ratio of each group.When the biomass content is 0.2,corresponding to the four groups of FTS split ratios of 0.2,0.4,0.6,and 0.8,the coal saving rates are 12.4%,12.27%,12.41%,and 12.57%,respectively.When the biomass mass ratio is more than 0.2,the syngas shunting ratio of FTS side has an obvious effect on the coal saving ratio.Thus under specific biomass mass ratio,the coal saving ratio of polygeneration systems can be improved by increasing the syngas shunting ratio of FTS side.In the research of environmental protection contribution,carbon capture rate and carbon emission rate are mainly used as research indicators.The results show that the total carbon capture rate of the polygeneration system increases gradually with the increase of biomass mass fraction under the specific FT synthesis shunt ratio.When the biomass mass fraction is less than 0.6,the carbon capture rate increases rapidly with the gradual increase of biomass mass fraction,and the system makes a greater contribution to environmental protection.When the biomass mass fraction exceeds 0.6,the increasing rate of carbon capture gradually slows down as the biomass mass fraction gradually increases.The CO₂ emission rate of the entire system gradually decreases with the increase of the biomass mass fraction.This is because under a specific FT synthesis split ratio,the total synthesis gas flow rate and the molar fraction of CO in the system are gradually decreasing.Eventually,the synthesis gas allocated to the IGCC unit will gradually decrease as the biomass mass fraction increases.When the shunt ratio of syngas on the FTS side is less than 0.4,the carbon emission rate decreases significantly with the increase of biomass mass fraction.When the synthesis gas split ratio of the FTS side exceeds 0.4,the carbon emission rate decreases significantly only when the biomass mass fraction is less than 0.2,and the carbon emission rate keeps unchanged when it exceeds 0.2.