| China’s coal-based energy consumption structure is determined by the resource endowment of "rich coal,lack of oil and gas",and its dominant position cannot be changed in a short term.Coal gasification is the key to affect the efficiency pollutants and greenhouse gas emissions of coal-based system.How to determine the gasification paths,rationally utilize sensible heat of syngas and reduce the energy consumption of oxidant preparation are the key to improve the gasification efficiency.This thesis analyzed the regularity of energy conversion efficiency in different gasification paths and the mechanism of irreversible destruction reduction.The coal-steam staged gasification with thermo-chemical regenerative unit is proposed,and the experimental study of coal-steam staged gasification method is carried out.The integration of energy system with high efficiency and low carbon emission based on this gasification method are presented and analyzed.In the mechanism analysis of gasification process,the thermodynamic equilibrium model is used,and the cold gas efficiency and gasification efficiency of different gasification paths are analyzed.The exergy efficiency of different gasification paths is investigated,and the irreversible destruction distribution in gasification process are defined.Furthermore,the coupling relationship between the exergy benefit of syngas and the reduction of irreversible destruction is established.The results showed that the energy conversion efficiency of steam gasification is better than that of other gasification routes when considering the energy consumption of oxidant preparation.The gasification efficiency of steam gasification can reach 88%.Reducing the content of O2/CO2 can effectively reduce the irreversible destruction of oxidant preparation.The irreversible destruction reduction benefit of oxidant preparation in steam gasification can reach 20%,and the exergy benefit of syngas of steam gasification can reach 32%.From the point of view of choosing reasonable gasification path and sensible heat utilization way of syngas,this thesis put forward a staged gasification method with thermochemical regenerative unit.Steam was as the only gasification agent in this method,and the sensible heat of syngas would be sent back into gasification process through the thermochemical regeneration.The results showed that the novel gasification method has significant advantages in improving coal utilization efficiency.Its cold gas efficiency,thermal efficiency and exhaust efficiency of gasification process can reach 91.1%,91%and 85.5%respectively.The results of exergy analysis showed that compared with coal-slurry gasification,the novel method avoids energy consumption in air separation and reduces the exergy destruction of oxygen preparation by 3.5 percentage points;thermochemical regeneration unit can effectively reduce the irreversibility of gasification process by 4 percentage points.The reduction of energy level difference and process heat change in the novel gasification method are the main reasons for the reduction of irreversibility.The experimental platform for coal pyrolysis process and coke-steam gasification process was established.The mechanism and model of coal pyrolysis were described.Based on the vertical tube experimental platform,the pyrolysis products of lignite,long flame coal,gas coal and lean coal were prepared,and the thermodynamic characteristics of pyrolysis process(product composition,coke formation rate)were analyzed.The reaction mechanism and model of coke gasification process were described,and the key process characteristics were verified by experiments on a fixed-bed reactor experimental platform.The results showed that the cold gas efficiency of the novel method is higher than the traditional gasification.The integrated coal gasification combined cycle power generation system based on the novel gasification method was established.the results showed that the H2/CO produced is as high as 1.2,and the cold gas efficiency is 8.2 percentage points higher than the traditional IGCC system,and the overall power generation efficiency is improved by 4.1 percentage points.Also,the carbon capture was integrated with the novel IGCC.The efficiency of this system can be reduced to 42.4%when the CO2 capture rate is about 50%,which is comparable to that of the traditional IGCC system without carbon capture.Besides,a new coal-to-natural gas system based on the novel gasification and direct methanation technology was presented and studied.The results showed that compared with the traditional coal-to-natural gas system,the energy consumption of SNG products in the new coal-to-natural gas system decreases from 84 GJ/t to 60.5 GJ/t.The SNG energy conversion efficiency increases from 61.3%to 71.7%,and the thermal efficiency of the whole plant increases from 64.1%to 73.1%.In addition,the energy consumption of CO2 separation in the novel system has been reduced from 15.3 kJ/mol to 11.7 kJ/mol.This system realized a high efficiency of coal utilization and low energy consumption in CO2 capture. |
