| For a long time,the issue of high energy consumption and high pollution in coal utilization has not been fundamentally solved,and to cope with global climate change,coal is also facing the challenge of carbon emission reduction.The development of low-carbon clean coal technology is one of the key challenges in building the future efficient,clean,low-carbon energy supply system.Coal gasification technology is a key process for the clean and low-carbon coal utilization,and it is the second largest exergy destruction process after combustion This dissertation took the novel gasification technology by decomposing C and H components as the object,and by means of exergy balance analysis and energy utilization diagram methodology,the chemical energy conversion mechanism and the component evolution laws of fuel were studied.On the basis,the simulation and mechanism experimental researches of the novel gasification were conducted,then the thermodynamic and kinetic characteristics of the key reaction processes were investigated.At last,the integrated innovation based on the novel coal gasification technology is carried out and the efficient and low-carbon utilization of coal is realized ultimately.First,the in-depth studies were conducted on chemical energy conversion and release characteristics of coal gasification and on the mechanism of the chemical reaction exergy destruction.Improving the conventional exergy balance analysis,this dissertation proposed the chemical exergy balance analysis method by distinguishing chemical energy from physical energy in an energy system.Aiming at the coal gasification processes,the chemical energy transformation and release laws were explored.Further a method for solving the exergy destruction of each chemical reaction in the gasification process was proposed by combining the chemical reaction kinetics with the coal gasification exergy analysis model Then the internal mechanism of chemical reaction was revealed by using the energy utilization diagram analysis methodology,and the schemes to reduce gasification exergy destruction were proposed.The study results showed that the carbon oxidation reaction was where the largest exergy destruction occurred.The gasification exergy destruction could effectively reduce by changing gasifying agent and it reached the minimun when CO2 was used.Based on the mechanism research,the gasification technology by decoupling C and H components was introduced,and the simulation of the novel gasification was eatablished.On the basis,the energy saving mechanism was analyzed,and the relationship between the overall cold gas efficiency and each subprocess efficiency of the novel gasification technology was discussed.The research results indicated that the overall cold gas efficiency could reach up to 86%,and the decisive factor affecting the overall cold gas efficiency was the carbon conversion of the char-CO2 gasification process.Furthermore,the experimental platform for gasification by decomposing carbon and hydrogen components was built to verifying the thermodynamic and kinetic characteristics of the key processes from coal,coking conditions,char reactivity and char-CO2 reaction conditions.On the basis,the design principles of each reactor were formulated,which gave grounds for further development of the novel gasification technology.The experimental results showed that the long-flame-coal was the most suitable coal for the novel gasification technology,and it recommended that the coking condition was 900?-3h and the char-CO2 gasification temperature was higher than 1150?.Under these conditions,the carbon conversion of char-CO2 gasification process was 98.6%,and the overall cold gas efficiency was 82.7%.Finally,the system integration researches based on the gasification technology by decomposing C and H component were studied.It showed that the energy efficiency of the separate chemical engineering and power generation systems based on the novel gasification had been improved compared with the separate systems based on the traditional gasification,which mainly came from the reduced exergy destruction of gasification In addition the series-parallel polygeneration system gave scope to the characteristic of decoupling CO and H2 of the novel gasificaiton,which lead to its energy saving ratio(7.1%)higher than that of the series polygeneration system by 1 percentage point.Further,the polygeneration system could still show the energy-saving effect when reducing 45%CO2 emission compared to the separe systems.The chemistry-electricity polygeneration systems based on gasification by decomposing C and H components showed a significant advantage of CO2 capture,which was an important direction for the development of low carbon clean coal technology in the future. |
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