HCl Removal by hydrated lime
In 2011, the EPA announced new Utility Boiler MAT limits. These limits included a maximum HCl emission of 0.002 lbs/MMBtu and boilers must meet this limit by early 2015. Hydrated lime, especially in conjunction with a baghouse, is effective for controlling HCl (and HF).
Historically, hydrated lime scrubbing by dry sorbent injection has been used to control HCl in industrial applications including industrial incinerators and waste to energy facilities. The byproduct formed is calcium chloride.
2HCl(g) + Ca(OH)2 (s) -> CaCl2(s) + 2H2O (g)
Lab, pilot and full scale testing has shown that HCl removal is secondary to SO3 removal. For that reason, Utilities must plan for good SO3 removal (<5 ppm) in order to commence HCl control.
For units without a wet scrubber, DSI using hydrated lime for HCl control is an excellent option for meeting 2015 MATS requirements. DSI systems are required significantly less capital than dry or wet scrubbers and can be a cost-effective solution for units that are not currently scrubbed. If hydrated lime is injected post-APH, there is little competitive reaction from flue gas SO2, so utilization is improved.
Mississippi Lime hydrated lime has been used to successfully mitigate HCl from full scale coal-fired Utility boilers. In systems that contained significant (>20 ppm) or low (<5 ppm) amounts of SO3 in the untreated flue gas, Mississippi Lime hydrated lime products were able to reduce HCl levels below 1 ppm (or 0.001 lbs/MMBtu) at the outlet of the respective unit's baghouse. Several reports on our hydrated lime test programs are included in the Links section of this website.