Control of toxic metallic emissions formed during the combustion of Ohio coals. Final report, September 1, 1993--August 31, 1994

Abstract

Portions of this document may be illegible in electronic image products. Images are produced from tbe best available original document. EXECUTIVE SUMMARYThe objective of the projec "Control of toxic metallic emissions formed during the combustion of Ohio coals" was to characterize metallic emissions fiom representative coals and develop strategies for their control. Though metallic emissions fiom coal combustors have been extensively studied, more studies need to be performed to better characterize the interaction of various species which is required for the selection and design of sorbents for effective control of these emissions. Furthermore, this characterization is important as the 1990 Clean Air Act Amendments (CAAA) have targeted a list of air toxics for fbrther regulation under Title 111. Eleven metallic species and their compounds -antimony, arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, mercury, nickel and selenium are in this list, and most of them are prevalent in coal. Major sources (industries emitting 10 tons per year of any single air toxic or 25 tons per year of any combination) will be initially targeted, and many utilities and industrial facilities using coal fall in this category. The other feature of the 1990 CAAA is that USEPA has been instructed to set stiingent technology based standards, and therefore control techniques have to be developed. Some coals are rich in sulfbr, and utilities using these coals will have to use some form of Flue Gas Desulfbrization (FGD). A technique for FGD is the use of calcium based sorbents, and the degree of metals capture of these sorbents under different conditions will be researched.The objective of the first year of the study was to understand the evolution of metallic aerosol size distributions and the capture characteristics of various sorbents. Also, the metallic emissions resulting fiom the combustion of two seams of Ohio coals were to be characterized. Studies on the evolution of the metallic aerosol size distributions have been completed and the use of silicon and calcium based sorbents for capture of lead species has been examined. Co-injection of metallic compounds along with organometallic silicon indicated a high degree of capture of lead in a certain 1 temperature regime. Preliminary results with Calcium based sorbents also indicate capture of metallic species. To gain a krther understanding of the capture processes, in situ optical diagnostic studies were performed in collaboration with researchers at the National Institute of Standards and Technology. Spectroscopic studies (laser induced fluorescence coupled with particle scattering) were performed to help understand the mechanisms of metallic species capture. Characterization of metallic emissions from the combustion of Ohio coals is in progress. Several modeling efforts have also been initiated. A detailed thermodynamic equilibrium model to predict metallic species capture rates has been developed and a number of simulations have been carried out to establish conditions fo...