Experimental And Simulation Research On Coal Gasification Mechanism And Gasification Process

Energy is one of the motivity of the society and economy development. In China, coal is the primary energy supply. Development of Clean Coal Technology (CCT) is the way to protect the energy safety now and hereafter. This thesis focuses on the coal gasification, one of the most important CCTs, and both fundamental research and application research were conducted. In the fundamental research, coal gasification behavior, including coal reactivity, coal surface structure development at atmospheric pressure, coal pressurized pyrolysis characteristics and high rank coal catalysis characteristics, were analyzed. While in the application research part, major gasifier process models based on Aspen Plus and gasification based substitute natural gas (SNG) production technology were developed and simulated to predict the operation performance.Coal gasification behavior is critical in the gasifier design and operation. It is found that pyrolysis pressure influences the volatile evolution process, and the volatile evolution process in different temperature range is closly related to the pyrolysis products and the coal (char) thermal properties and then makes a different char physical surface. The optimum pressure exists which produces a more developed physical structure and this reveals the balance between surface tension and the viscosity. Because of the enlargement of volatile-char reaction time and the increase of char secondary pyrolysis reaction, system pressure also influences char chemical structure, which shows the grow of the skelecton and the decrease of the oxygen contained function group with pressure increase. It is also found that char reactivity is closely related to char surface structure by introducing fractal shringking core model. The characteristics of char from different carbon conversion reveals that char from different rank coal go through different development regime, the high rank coal char shows little trend to interspace development while the low rank coal char physical surface structure experieces the first grow up stage and then the ruin which is inclined to spacial development. The fractal dimensions variations of different pore radius range were found which could be explained by the pore enlargement and breakage. Also, ash plays a key role in char physical structure development, especially for low rank coal. The catalysis effect of AAEM and transition metal salts in high rank coal gasification was also investigated. It is found that, there is less correlation between addtion amont and catalysis effect and different catalysis have different application temperature.In order to verify the performance and the design method of typical coal gasifier process model based on ASPEN PLUS was developed, including the detailed fixed bec gasifier model, fluidized bed gasifier model and entrained flow gasifier model. The detailec gasifier model combines the coal gasification reaction process in the gasifier and the laten heat recovery process and it is shown that different gasifier have different operatior performance, which determines the gasifier application and its operation economy.At last, in view of the trend in China energy supply adjustment, the current substitute natural gas (SNG) production technologies were reviewd. Based on the SNG productior research and development in the world, improvements on Exxon Catalytic Coa Gasification Process (CCG) were proposed. Simulation shows the improved CCG process SNG yield is 0.703 Nm3/kg Coal. Also, it is found that biomass is more suitable for catalytic gasification to produce SNG, and a novel biomass based direct SNG productior process was proposed. The simulated SNG yield is 0.320 Nm3/kg biomass.