Migration And Distribution Of Alkali And Alkaline Earth Metal Elements And Energy Optimization In Coal Gasification System

Coal gasification is the key technology of efficient and clean utilization of coal.However,the release and migration of alkali and alkaline earth metal elements(AAEM)in coal during conversion process cause a range of problems.In this paper,the release characteristic of AAEM and the distribution of AAEM in gasification system are studied by experiments.And the heat energy comprehensive utilization of coal gasification system combined with saline waste water recovery is simulated and optimized by using the process system optimization method.The release characteristics of AAEM during ashing,pyrolysis and gasification of coal are carried on the muffle furnace and high frequency furnace reactor respectively.Results show that the release rate of AAEM increased with increasing temperature.The temperature effects more on the release of K and Na than that on Ca and Mg,and the release rate of K and Na is larger than C.a and Mg.The release of AAEM mainly occurs at the initial stage of gasification and pyrolysis,and the release rate of Ca and Mg in gasification is larger than pyrolysis process.The distribution and enrichment characteristics of AAEM in coal gasification system are studied by analyzing samples from the OMB CWS,GE CWS and Shell pulverized coal gasification plant.Results show that the distributions of AAEM elements in coal water slurry gasification system are as follows:coarse slag>fine slag>waste water.The distributions of AAEM in Shell gasification system are as follows:coarse slag>fly ash>fine slag>waste water.K and Na are mainly concentrated in fine slag in coal water slurry gasification system while K and Na are mainly enriched in fly ash in Shell pulverized coal gasification system.Ca and Mg do not show obvious enrichment tendency.The heat energy comprehensive utilization of gasification system combined with saline waste water recovery are studied by simulation and calculation.Results show that when the high temperature black water recycling ratio is 0.5,the new process can improve the total thermal efficiency from 90.65%to 93.58%while the steam gas ratio of syn-gas increases from 0.80 to 0.99.The consumption of recirculating cooling water is cut by 45.64%.Moreover,the discharged waste water is reduced by 25.09%through evaporation process.