Sorbent injection into a slipstream baghouse for mercury control: Project summary

A project led by the Energy and Environmental Research Center to test and demonstrate sorbent injection as a cost-effective mercury control technology for utilities burning lignites has shown effective mercury capture under a range of operating conditions. Screening, parametric, and long-term tests were carried out at a slipstream facility representing an electrostatic precipitator–activated carbon injection–fabric filter configuration (called a TOXECON™ in the United States). Screening tests of sorbent injection evaluated nine different sorbents, including both treated and standard activated carbon, to compare mercury capture as a function of sorbent injection rate. Parametric tests evaluated several variables including air-to-cloth (A/C) ratio, flue gas temperature, cleaning frequency, and dust loading to determine the effect on mercury control and systems operation. Long-term tests (approximately 2 months in duration) evaluated the sustainability of systems operation.The screening tests identified four sorbents that achieved greater than 90% mercury capture. Longer-term tests demonstrated mercury capture of 82% at sorbent injection rates of about 2–2.5 lb/Macf. Ash loading and A/C ratio affected the operation of the fabric filter. At lower ash loadings, A/C ratios as high as 6 ft/min could be sustained while operating with conventional bags, but higher ash loadings required the use of high-permeability bags to overcome pressure drop issues.