Comparison of sorbents based on Ca(OH)2 for removing HCl from flue gas

Abstract

Due to EU climate change policy are coal-fired heating and power plant switching their fuel to biomass one. Emissions of flue gas from biomass are more environmentally friendly in general, but emissions of HCl and HF are increasing, and BAT limits are quite low for them. The possible solution is installation of technology DSI (Dry sorbent injection), especially with connection with bag house filter flue gas treatment. Powder of calcium hydroxide is one of suitable solution. Although the chemical composition is same, there are a huge differences in consumption between another types of Ca(OH)2. This article describes two most selling types of Ca(OH)2 in the Czech republic from the lime works in Štramberk (vz.1) and Čertovy schody (vz.2). This article is divided into laboratory part, where characterized both examples, and experimental part – operational test in the heating plant technology. The results of laboratory part were same for both examples in their thermal characteristic (thermogravimetry and DTA) and real density. Elementary and matter composition were quite similar, only sample 1 was a little bit contaminated by CaCO3 from original material. There was big difference in BET specific area – 14.8 m2·g-1 by sample 1 example and 41.273 m2·g-1 by sample 2. Sample 1 had the most of pore volume in pores with diameter 20-80 nm, the second one on had a more developed pore structure through the whole particle, Operational tests in same constructed CFB boilers were realized during two months in the same conditions. Control system of the heating plant mange cleaning technologies by emission limits, input fuel mixture was for both boilers same. Most of focused parameters were same, only data from DSI system were for each sorbent different. Efficiency of removing HF were for both sorbents same around 99%, for HCl around 85%. Consumption sample 1 was 80.63 m3 and 37.74 m3 of sample 2. When comparing the laboratory and operational parts, higher consumption of sample 2 can be caused by more developed porous structure and a larger specific BET surface. This may be due to the purity of the original material (CaCO3), which was also higher in sample 2, as well as the production technology of the sorbents.