Effect of HCl on chain grate-rotary kiln gas purification system and its emission reduction measures
In addition to NOx and SO2,the gaseous pollutants in the gas of the chain grate-rotary kiln also contain a certain proportion of HCl,which will have a significant negative impact on the gas purification system and affect the pellet production efficiency.The generation mechanism of HCl in the gas of the chain grate-rotary kiln is analyzed,the influence of HCl on the gas purification system is studied,and corresponding improvement measures are proposed.The results show that 95.85％of the chlorine comes from various raw material of iron ore concentrates.In addition,the main reason for the poor operation of the active coke sulfur and denitrification system is that HCl in the gas reacts with NH3 in the ammonia injection area to generate a large amount of NH4Cl crystals.In actual production,the following HCl emission reduction measures can be taken:reducing the use of high-chlorine raw materials to achieve source reduction,using slaked lime as a calcium additive to produce alkaline pellets to inhibit the formation of HCl,and spraying alkaline solution in the exhaust drying section of the chain grate where HCl is concentrated.Under the alkali solution spraying measure,when n(Na)/n(Cl)(the ratio of the amount of substance)is 2.6,the HCl removal rate is only 48.7％,and its emission reduction efficiency is low and cannot meet the production needs.When calcium solvent is added,the proportion of slaked lime is 1.5％,and the conversion rate of chlorine in the raw material into HCl is only 8.2％.The implementation of SNCR and embedded SCR coupled pre-denitrification process in the chain grate-rotary kiln production line can remove NOx from the gas before HCl is generated,basically isolating the contact between HCl and NH3.For newly built chain grate-rotary kiln production lines,planning and configuring a combination of a pre-denitrification system and an activated coke desulfurization system can avoid the negative impact of HCl in the gas and achieve ultra-low emissions of pellet gas.
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