Mercury Balances in Modern Cement Plants

National Emission Standards for Hazardous Air Pollutants (NESHAP) and Commercial and Industrial Solid Waste Incinerator (CISWI) regulations will require all cement plants in the U.S. to meet new mercury emission limits in the coming years. Toxic release inventory (TRI) reporting data indicate that over 50% of the cement plants operating in the U.S. would require some form of mercury emission reduction in order to meet the NESHAP standard. Mercury emission reduction has been the subject of many studies in the coal-fired electric utility industry. This work has improved our understanding of mercury reduction technologies. However, the cement industry presents some unique challenges for mercury reduction. The mercury balance in a modern cement plant with an in-line raw mill can be quite complicated. The process conditions, and therefore the mercury balance, can change quite drastically between mill running and mill down situations. These changes can be attributed to differing temperature profiles, gas compositions, and concentrations of material in the gas streams, among others. Understanding the mercury balance is a necessary first step in developing a mercury control strategy. This paper explores some of the issues and presents data around the cement plant mercury balance. Data from actual plant mercury balances will be used to demonstrate and explain some of the factors that influence these mercury balances. Areas of uncertainty and where additional research is required are also identified.