Research On Entrained-flow Gasification Reaction Characteristics Of Coal With High Ash Melting Point

Coal will continue to be the dominant energy of China's energy supply and consumption for a long time.Entrained flow coal gasification technology is one of the core technologies for clean coal technology.However,the existing entrained flow bed coal gasification uses liquid slag discharge,which seriously restricts the use of a large number of coal with high ash fusion point in China.The technology of solid slag discharge in fluidized bed coal gasification can solve the shortage of liquid slag discharge in coal with high ash fusion point,so the in-depth study on the reaction characteristics and mechanism of coal gasification under the condition of solid slag discharge at high ash fusion point is helpful to promote the development of the technology,which has important practical significance to realize the clean and efficient utilization of coal resources with high ash fusion point in China.This paper chooses the typical high ash fusion point of huainanzhuji coal and three component differences of low ash fusion point of coal,delves into the high CO ₂atmosphere,reaction mechanism and the characteristics of low ash fusion point coal char,high ash fusion point coal char gasification reaction kinetics model established,the resolution of high ash fusion point entrained flow bed gasification solid slag discharge process operating conditions,the design of 500 t/d high ash fusion point entrained flow bed gasification solid sludge discharge system and its technological process.The main research contents and results are as follows:?1?The thermal gravimetric analyzer was used to investigate the reaction characteristics of coal char with high and low ash fusion points in different reaction temperatures and gas concentrations in CO₂ atmosphere.The dynamic characteristics of char-CO₂ reaction were analyzed based on the classical volumetric model,core shrinking model and random pore model.The results showed that:with the increase of CO₂ concentration,the number of activated CO₂ molecules per unit volume increased,and the char-CO₂ reactivity increased at both high ash fusion point and low ash fusion point.At 900?to 1100?temperature range,high ash fusion point and low ash fusion point coal char reaction rate increases with temperature and CO₂,coal char in a chemical reaction kinetics control area,high ash fusion point coal char gasification reaction activation energy?88.49-89.88 k J/mol?higher than that of low ash fusion point coal char gasification reaction activation energy?64.42-80.41 k J/mol?,reactive high and low for sample:Laos coal char>Zhun Dong coal char>Nei Meng coal char>Huai Nan coal char;When the gasification temperature is higher than1100?,the reaction rate of coal char with low ash fusion point no longer increases or even decreases,and the gasification reaction changes from dynamic control to internal diffusion control.As the temperature continue to increase the gasification reaction of char with low ash fusion point changes from internal diffusion control to external diffusion control.The gasification reaction of coal char with high ash fusion point is controlled by reaction dynamics within the range of temperature.Compared with the volumetric model and core shrinking reaction model,the random pore model can more accurately predict the char-CO₂ reaction rate of huainan coal with high ash fusion point.?2?The gasification characteristics of huainan zhuji gas flow bed with high ash fusion point under different O/C molar ratios and different temperatures were investigated in a 20kg/h autothermal gasification experimental facility.The microstructure and secondary reactivity of coal ash after gasification were analyzed by means of particle size analysis,scanning electron microscopy?SEM?and thermogravimetric analysis.The results show that:with the increase of O/C mole ratio,the gasification reaction temperature increases and the carbon conversion rate increases.When the O/C mole ratio exceeds 1.0,too much oxygen leads to the decrease of the active components?CO,H₂?in syngas,and the decrease of syngas production rate,cold gas efficiency and heating value.When the O/C molar ratio was1.0,huainan coal gasification characteristics were the best,the corresponding gasification temperature was 1300?,and the volume concentration of CO and H₂in syngas was 72%.After the gasification reaction under the condition of O/C molar ratio 1.0,a small part of the coal ash at the gasification furnace ash hopper was found to melt,the fusion part was generally in the tens of microns,and no obvious fusion was found in the rest part,which can realize solid slag discharge.Under these conditions,the gasification reaction activation energy of coal ash separated by cyclone separator was 103.26k J/mol higher than that of raw coal?89.88k J/mol?,and the reactivity of coal ash was reduced.?3?This paper design 500 t/d high ash fusion point coal solid slag-discharge gasification process,including powder and pulverized coal pneumatic transport,entrained flow bed coal gasification,solid slag-discharge gasifier,syngas purification,gasifier heat recovery and other processes and main operating condition.The results show that the energy utilization efficiency of the system is 96.5%when the gasification temperature is 1300?,the gasification pressure is 3.6 MPa,the coal input is 500 t/d,the carbon conversion rate is 90%,and the O/C molar ratio is 0.95.The flow chart of primary process pipe and instrument is drawn,and the layout of main equipment in gasification process is suggested,which provides reference for the engineering design of solid slag discharge in high ash fusion point gas flow bed.