Study Of Entrained Flow Gasification By Two-stage Oxygen With High Ash Fusion Temperature Coal

Large scale entrained flow gasification technology is the development direction of current coal gasification technology and the most promising method of coal conversion technology.It is widely concerned by power plant and coal chemical industry for its highly efficiency,clean and high compatibility.Amounts of the power coal of China have high ash fusion temperature（AFT）and high content of ash,and they are difficult on using as the fuel in the main entrained flow gasification technologies with slagging around the world.In order to keep stable slagging,more flux should be added or the gasification temperature should be increased.As a result of that,a great waste of energy and increasing cost seriously limit the gasification technology promotion and use in China.Therefore,it is of great significance to develop the entrained flow gasification technology with dry slag using Chinese coal with high AFT,which is very important for the promotion and application of large-scale and high efficient clean coal gasification.In this thesis,the kinetic study of high AFT coal char-H₂O/CO₂,and the coal water slurry or pulverized coal entrained flow gasification with dry slag by two-stage oxygen supply were systematically studied with experiments and mathematical models.And then a new process design of coal-water supply pressurized entrained flow gasification with dry slag by two stage oxygen supply was summarized and presented.Firstly,a modified Thermax 500 thermogravimetry analysis was used to conduct the kinetic experiments of high AFT coal char-H₂O/CO₂,under different temperature,pressure and concentration of reacting gas.Based on the experimental results,a kinetic model under wide temperature range was modeled,which includes effect of temperature,pressure and diffusion.The results show that,the temperature effect is most important factor affecting the rate of gasification reaction.As the partial pressure of reacting gas increasing,the rate of gasification reaction increases,but the increasing rate slows down when the partial pressure of reacting gas is high.Besides,the rate of char-H₂O reaction is about as 5 times large as that of char-CO₂ reaction.The mean intrinsic activation energy and the average n-order coefficient are 226.23 kJ/mol and 0.44 for the reaction of char-CO₂,172.24 kJ/mol and 0.54 for the reaction of char-CO₂.Secondly,a coal water slurry entrained flow gasifier with dry slag by two-stage oxygen supply（20 kg/h）testbed was set up and one-dimensional kinetic model was matched.During the experiments,the effect of O/C molar ratio,non-second oxygen and second oxygen supply were studied.The one-dimensional kinetic model was based on the energy conservation equation,chemical reaction balance,element conservation and material conservation.The experimental and simulated results are analyzed and showed.As the molar ratio of O/C is larger than 0.95,the entrained flow gasification technology with dry slag by second-stage oxygen began to have a better gasification result than the entrained flow gasification technology with non-second stage oxygen.Specifically,when the molar ratio of O/C was 1.1,the effective syngas fraction and carbon conversion of second-stage water gasification were 80.2%and 93.24%,respectively.The one-dimensional kinetic model can simulate the experimental results well,the average error of each parameter is not more than 1.6%,and the best reaction condition can be obtained by simulating the best reaction condition.Some key data can be obtained by the model,such as cold gas efficiency of 69.56%,the coal consumption of 594.82 kg/kNm³,the average particle residence time of 1.85s and so on.Thirdly,a modified pulverized coal entrained flow gasifier with dry slag by two-stage oxygen supply（about 15 kg/h）testbed was set up and a two dimensional CFD model was concerned.During the experiments,the effect of O/C molar ratio,the ratio between second oxygen and total oxygen,coal types were studied.Besides,the best experimental result was also simulated with the model.The results show that,when the O/C molar ratio is increasing,the gasification results of non-second oxygen and second oxygen supply experiments are both increasing,such as carbon conversion,effective syngas fraction and gasification temperature.When the O/C molar ratio is fixed,with the ratio between second oxygen and total oxygen increasing,the fraction of H₂ would increase obviously,the fraction of CO₂ would decrease firstly,then increase,the fraction of CO is just contrary,and the temperature would decrease.Considering the need of stable dry slag,the best experimental condition was chosen as 0.82 of O/C molar ratio and 10%of the ratio between second oxygen and total oxygen,which shows the effective syngas fraction and carbon conversion of second-stage water gasification are 79.20%and 92.04%.The two dimensional CFD model figures effectively the distribution of temperature,pressure,velocity,turbulence intensity and gas composition in the gasifier,which can effectively explain the effect of second stage oxygen supply.The absolute error of the effective syngas fraction between model and experiment is-0.70%,but the error of temperature is relatively high.In addition,for the entrained flow gasification with dry slag by two-stage oxygen supply,the pulverized coal type technology fits the needs of low oxygen supply and high CO concentration,the coal water slurry type technology fits the needs of high oxygen supply and high H₂ concentration.Last,based on the material balance with 840t/d coal water slurry pressurized entrained flow gasification with dry slag by two stage oxygen supply simulated by one dimensional kinetic model,a new design was modeled.The results show that,when using the LJ coal as the slurry fuel,the best operation condition is 1.13 of O/C molar ratio,20%of the ratio between second oxygen and total oxygen and 50%of the molar ratio of between second O₂ and second oxygen supply.The simulated results of effective syngas fraction and flux are 80.33%and 60666.94Nm³/h,meanwhile,the gasification temperature is between1331¹450℃.In addition,some key data was also calculated,such as 94.96%of carbon conversion,6.37s of mean particle residue time,576.92kg coal and 386.08 Nm³ oxygen comsumption with 1000 Nm³ CO+H₂ generation.