Study On Coal Gasification And Chemical Looping Combustion Under The Pressure Of SCO2

The coupling chemical looping conversion process of coal gasification is a research hotspot nowadays.The gasification and chemical looping reaction under the pressure of sCO₂ accelerated the reaction rate and realized the liquefaction and capture of CO₂.In this paper,the chemical kinetics characteristics of coal gasification process under sCO₂pressure are studied,and the factors affecting the conversion efficiency and the capture rate of CO₂ liquefaction are analyzed.And came to the following conclusions:(1)The internal and external mass transfer coefficients at sCO₂ pressure were significantly larger than those at atmospheric pressure.The higher the pyrolysis temperature is,the faster the pyrolysis rate is.The higher the gasification pressure,the lower the internal efficiency factor and the higher the external efficiency factor.The internal concentration of gasifier,intrinsic reaction rate and apparent reaction rate of coal gasification under sCO₂ pressure are higher than those under normal pressure,and the gasification time is shorter.Due to the cross-linking of pores,the gasification rate extreme point under sCO₂ pressure is earlier than that under normal pressure.The increase of gasification temperature will accelerate the gasification process and lead to the advance of gasification rate extreme point.(2)When compressed air is used as gasification agent,the experimental results of bituminous coal show that the calorific value of crude gas is only about 3MJ/Nm³,and it is difficult to separate a large amount of N₂,which is not suitable for chemical looping combustion process.When pure oxygen and water vapor are used as gasifiers,their calorific values are similar,so they are suitable for chemical looping combustion transformation.(3)The efficiency of the sCO₂ system is slightly less than that of the atmospheric system and the calorific value is slightly higher than that of the atmospheric system.Taking bituminous coal from Xuzhou as research object,the best oxygen-coal ratio and water-coal ratio are 0.9 and 0.7 respectively for sCO₂ pressure gasification.When the MEO/coal ratio is above 45,the synthesis gas is fully oxidized and the MEO is surplus.The overall net efficiency of sCO₂ system is higher than that of normal pressure system,the liquid CO₂ capture efficiency is similar,the higher the pressure,the lower the net efficiency.(4)The concentration of O₂ in air separation system should be controlled to be over 90%,the cooling temperature of CO₂ liquefaction should be less than 28?,and the MEO/coal ratio should be no less than 45.At this time,the concentration of CO₂ in sCO₂logistics is more than 98%,so it is easy to realize liquefaction and capture.Pollutants such as sulfide,NOx and chloride can be dissolved directly in liquid CO₂ without further treatment.