Experimental Study On The Collaborative Reaction Of Sulfur And Mercury Under Coal Pyrolysis Atmosphere

At present,the emission standard of coal burning air pollutants in China is becoming more and more strict.Ultra-low emission control technology is vigorously promoted in coal-fired power plants all over the country,which brings about higher operation cost and more complex end-of-pipe treatment process of the main pollutant after coal burning.The content and concentration of mercury in coal-fired flue gas is low.Up to now,in China there is no commercial economic and efficient mercury removal technology for the coal-fired power plant.Air pollution control has risen as a national strategy,the control mechanism of mercury emissions from coal-fired flue gas starting from the combination of source control and process emission control will be developed,which can realize economic,efficient and cooperative control.The study shows that mercury removal through the process of coal pyrolysis is feasible for mercury removal before combustion.The mercury concentration of the flue gas generated by heat treatment before combustion will be greatly improved,but the amount of flue gas will be greatly reduced.At the same time,the sulfur in coal can also be removed in the heat treatment process before burning.As the previous study showed that sulfur and mercury in coal with high content of sulfur and mercury removal process had positive influence.The main form of mercury is Hg0 no matter in the pyrolysis or combustion process.H2S is the key component of sulfur in coal pyrolysis gas,and the vast majority of sulfurous gas in the flue gas is SO2,while H2S and SO2 can generate elemental S under certain condition.Elemental sulfur can generate HgS with elemental mercury.Based on the above theories,a new method of low sulphur-mercury emissions from coal combustion is proposed,which basic idea is that coal combustion process with high content of sulfur is divided into pyrolysis and combustion process.H2S and SO2 produce elemental sulfur,which further react with elemental mercury,by controlling sulfur pyrolytic product,and the final products will be released from coal pyrolysis gas,which most of the sulfur and mercury can be synergistically removed in the initial combustion process.Based on the above technical route,two sets of experiment system were set up,S-Hg reaction experiment system and H2S-SO2-Hg reaction experiment system.Firstly,under non catalytic and catalytic conditions characteristics and effect factors of S-Hg reaction were studied.The results showed that the reaction between S and Hg could be carried out at room temperature,but the reaction rate was low due to the lower temperature.As the temperature increased,the reaction rate between S and Hg increased.Adding aluminum catalyst could effectively promote the S-Hg reaction.Under non catalytic conditions,oxygen slightly increased the removal efficiency of elemental mercury.Under catalytic conditions,with the increase of oxygen concentration,the reaction efficiency of S-Hg increased obviously.CO2 and SO2 nearly has no effect on the S-Hg reaction.Secondly,the effect of mercury removal based on H2S-SO2-Hg combined reaction without catalytic,the characteristics of H2S-SO2-Hg reaction under catalytic conditions and the influence of many factors on the reaction were studied.The results showed that the rate of mercury removal based on combined reaction without catalytic was low overall and it is not suitable to applied in actual production because of its poor mercury removal effect.The rate of mercury removal and H2S-SO2 reaction were all in a high level under catalytic conditions,when the reaction temperature is 200?,too high temperature does not increase the degree of combined reaction.With the longer time,the reaction is more complete,however,when the time is more than 2s,it is no significantly enhancement on the efficiency.The influence on the rate of H2S-SO2 reaction was enormous with the change of molar ratio,which also impacted the effect of mercury removal,but the change was not larger than H2S-SO2 reactions.The reaction efficiency was highest when the molar ratio is 2.CO2 had no effect on the combined reaction.With the increase of O2 concentration,the rate of mercury removal showed an upward trend,and the trend of the rate of H2S-SO2 reaction was contrary.It should be considered that O2 concentration effected the tow partial reaction in practice.With the increase of the elementary mercury in the inlet,the ability of mercury removal decreased.