| Gasifier is the key of entrained flow coal gasification technology.The traditional entrained flow gasifier has the problem of serious sensible heat loss and low thermal efficiency.In order to solve this problem,a two-stage combined coal gasification process with chemical heat recovery was proposed.The steam and CO2 in the high-temperature syngas of the first stage is gasified again with the coal in the second stage fixed bed.The sensible heat of the high-temperature section is recovered,and the invalid components(steam and CO2)in the syngas are utilized Compared with the traditional processes of water quenching,syngas quenching and waste heat boiler,the sensible heat recovery process is more concise,the equipment investment cost is smaller,and the effective gas content and cold gas efficiency in the syngas can be improved.So it has a broad application prospect.In this work,the reaction characteristics of coal in gasification syngas at high temperature were explored based on the second fixed bed of the two-stage combined gasifier.The characteristics of high-temperature pyrolysis reaction,water gas shift reaction and coal char gasification reaction were investigated.Moreover,the gasification reaction characteristics of coal in gasification syngas on different scale devices were also evaluated.The main contents are listed as follows:(1)The release characteristics of pyrolysis gas product generated from different coals at 1100-1600? were evaluated based on the fixed bed reactor.In the range of 1100-1600?,the main gas product of coal pyrolysis is only CO.With the increase of temperature,the release rate of CO increases gradually.CO is mainly formed by the carbothermal reaction of oxygenated compounds and carbon elements in coal.The initial reaction temperature is about 1300 ?,1400?,1550? respectively when adding 20%SiO2,Al2O3,CaO.At 1600 ?,the CO formation rate is 3.72,2.61 and 2.42 mLˇmin-1ˇg-1 respectively.SiO2 reacted with carbon to form SiC,and Al2O3 finally forms AIN in N2.The reaction product of CaO was not detected because the gaseous Ca formed at the experimental temperature escaped with the gas products and was not in the solid residue.The temperature,rate and amount of CO generation are mainly related to the type and content of minerals in coal,but less to the coal rank.(2)The water gas shift reaction(WGSR)of gasification syngas in short residence time(1?2 s)and high temperature(700?1300?)was studied.The effect of coal ash and coal char on WGSR was studied.It was found that the CO conversion was close to zero when the temperature below 1100?.As the reaction temperature reached 1300?,reverse water gas shift reaction can occur in syngas,but it did not reach the chemical equilibrium state.Coal ash had promoting effect on WGSR.However,this behavior was limited by uneven gas distribution and coal ash sintering.When coal ash was used as medium,the CO conversion of syngas grew 2.3 percentage points compared with the blank test at 1100?.Coal char had a similar promoting effect on WGSR to coal ash.The influence of particle size for coal char on WGSR is significant.The effect of coal char particle size on shift reaction had a better value.The surface area and promoting effect decreased by enlarging the size of coal char particle.Small particle size can also contribute to low promoting effect due to uneven gas distribution.Under the experimental conditions,the coal char with particle size of 0.8-1.5 mm had the most significant promotion effect,and the CO conversion of syngas at 700? was 1.7 percentage points higher than that of the blank test.(3)Coal-char gasification reaction in different mixture atmosphere(H2O,CO2,Hz,and CO)was conducted in a fixed-bed tube reactor at atmospheric pressure.The effects of H2 and CO on CO2-gasification and steam-gasification reactions were evaluated at 1100-1400?.The results demonstrated that H2 promoted the steam-gasification reactivity of coal char,especially at low temperatures.The inhibition effect of CO on steam gasification was apparent at 1100-1200?.H2 promoted the CO2 gasification of coal char at 1000? but inhibited it above 1300?.CO inhibited CO2 gasification at 1100-1400?.The random-pore model was suitable for all experimental conditions.(4)The coal gasification reactivity in the gasification syngas was tested in a fixed-bed tube reactor and a two stage combined gasifier hot-state experimental device at atmospheric pressure.The effect of reaction temperature,raw gas composition,coal amount on gaseous products composition and carbon conversion rate was explored.The flow rate of CO increased significantly,while the flow rate of H2 increased a little under the tubular furnace experimental conditions.The the flow rate of CO2 decreased a little.The effective gas(CO+H2)concentration of syngas could be enhanced after the reaction and reached the highest extent(3.3%)in the experimental conditions.The results indicated that the inhibition impact of CO and H2 and the competitive effect between H2O and CO2 were obvious.The maximum coal reaction rate in the mixture gas was only 55%and 67%of the maximum coal reaction rate in pure gasification agent(H2O,CO2)in 1100? and 1300?,respectively.The random pore model was also suitable for the experimental conditions.However,the volumetric reaction model and core shrinking model were not well in fitting the data.In the hot-state experiment,the gasification agent conversion efficiency was similar to the results of tubular furnace.The experimental results of small-scale device can be extended for large-scale device. |
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