Experimental Study And Exergy Analysis Evaluation Of Steam-oxygen Gasification Process Of Semi-coke In Bubbling Fluidized Bed Based On The TBCFB System

The proposal of double carbon targets will accelerate the transformation of China’s energy to safety,cleanliness,high efficiency and low carbon.China’s energy resource endowment of"rich coal,short of oil and short of gas"and China’s huge demand determine that it is difficult to change the energy structure overnight.In order to realize the clean and efficient conversion and utilization of coal with low carbonization,the bubbling fluidized bed gasifier of triple-bed circulating fluidized bed technology(TBCFB)proposed by Tsutsumi,University of Tokyo,Japan,gives full play to the advantages of its hierarchical conversion and improves the energy utilization efficiency of coal,among which the gasification of semi-coke in bubbling fluidized bed gasification is an important link.It is of great significance to study the gasification operation conditions to obtain the synthesis gas with high added value for realizing the high-quality and efficient conversion and utilization of coal.In this paper,firstly,the gasification experiment study of semi-coke steam-oxygen is carried out in bubbling fluidized bed gasification device in TBCFB.The effects of different steam/semi-coke mass ratio(S/C),oxygen equivalence ratio(ER)and semi-coke gasification under catalyst on gasification indexes such as volume fraction of synthesis gas,H2 yield,low calorific value of gas(LHV)and carbon conversion rate were investigated.When the gasification temperature is 800℃,S/C increasing from 0.3 to 2.1,the volume fraction of H2increases and the volume fraction of CO decreases.With the increase of S/C,the yield of H2and the conversion of carbon both increased at first and then decreased.When the S/C ratio is1.5,the gasification performance is the best,and the H2 yield and carbon conversion rate in the synthesis gas reach the maximum of values 21.14g/kg and 10.58%,respectively,and the low calorific value of the tail gas at this time is 104.18 k J/Nm~3;When the S/C ratio is kept constant at 1.5,with the increase of ER,the volume fraction of CO in synthesis gas gradually decreases,the volume fraction of H2 increases first and then decreases,the volume fraction of CO2 shows an upward trend,and the volume fraction of CH4 basically remains unchanged.When the ER ratio increases,both the H2 yield and the carbon conversion rate increase at first and then decrease.When ER is 0.3,the maximum H2 yield and carbon conversion rate in synthesis gas are 5.46 g/kg and 35.36%,and the low calorific value is 80.43 k J/Nm~3,and the optimal ER is0.30.When the catalyst is introduced,the reaction rate of semi-coke gasification can be significantly increased,and the catalytic activity of steam-oxygen gasification of semi-coke is(K2CO3-Na2CO3)>K2CO3>Na2CO3.And potassium carbonate and sodium carbonate catalyst can improve H2 yield,carbon conversion rate and low calorific value of tail gas.The gasification effect is the best when 5%K2CO3-5%Na2CO3-loaded semi-coke is gasified,the gasification quality is significantly improved,and the calorific value of the synthesis gas reaches 103.39 k J/Nm~3,the maximum H2 yield is 23.00 g/kg,which is four times that of non-catalyst gasification,and the maximum carbon conversion rate is 51.71%.Through the experimental study of semi-coke gasification,the gasification law of semi-coke in fluidized bed reactor is obtained,which provides a reference for the industrial application of triple-bed circulating fluidized bed pyrolysis gasification device.Secondly,this article introduced Taking the steam-oxygen gasification experiment of semi-coke carried out in TBCFB system as the research object,the exergy value distribution and target exergy efficiency of gas produced by semi-coke gasification under different S/C,ER and catalyst were explored using the exergy analysis method.The results show that when S/C increases from 0.3 to 2.1,the contribution relationship of each component gas to the exergy value of syngas is H2>CO>CH4>CO2;When S/C is 1.5,the total exergy value and target exergy efficiency of syngas can reach the maximum.When ER increases from 0.25 to 0.40,the contribution order of each component gas to the exergy value of syngas is CO>H2>CO2>CH4;When ER is 0.30,the maximum target exergy efficiency is 12.33%.Adding catalysts K2CO3 or Na2CO3 both can obviously improve the gasification effect of semi-coke and increase the exergy value and target exergy efficiency of gasification syngas.When semi-coke supports composite catalyst 5%K2CO3-5%Na2CO3 is applied,the gasification effect of semi-coke can be the best.The exergy analysis makes a systematic and comprehensive evaluation of the semi-coke gasification process from the point of view of energy quality,which provides guidance for high-quality utilization of coal.