Control of air toxin particulate and vapor emissions after coal combustion utilizing calcium magnesium acetate

• Published in: Resources, conservation and recycling conservation and recycling, 1996-04, Vol.16 (1), p.15-69
• Main Authors: Shuckerow, Judith Irene, Steciak, Judith Anne, Wise, Donald L., Levendis, Yiannis A., Simons, Girard A., Gresser, Joseph D., Gutoff, Edgar B., Livengood, C.David
• Format: Article
• Language: English
• Subjects: Acid rain; Air pollution; Air toxin; Calcium magnesium acetate; CMA; Coal; Combustion; Fly ash; Mercury vapor; Nitride oxide; Nitrous oxide; Sulfur dioxide
• ISSN: 0921-3449; 1879-0658
• DOI: 10.1016/0921-3449(95)00046-1

Major environmental issues are now coming to the forefront in all parts of the globe with increased public awareness of the human health effects and the possible effects on our global environment. Modern control technologies, when implemented, have significantly reduced air pollution emissions that are a result of coal combustion during this century. However, the emissions have not been completely eliminated. On this basis, a study was conducted to determine the efficacy of carboxylic calcium and magnesium salts (e.g., calcium magnesium acetate or CMA, CaMg 2 (CH 3CO 2) 6) for the simultaneous removal of SO 2 and NO x in oxygen-lean atmospheres. Experiments were performed in a high-temperature furnace that stimulated the post-flame environment of a coal-fired boiler by providing similar temperatures and partial pressures of SO 2, NO x, CO 2, and O 2. When injected into a hot environment, the salts calcined and formed highly porous ‘popcorn’-like cenospheres. Residual MgO and/or CaCO 3 and CaO reacted heterogeneously with SO 2, and oxygen to form MgSO 4 and/or CaSO 4. The organic components — which can be manufactured from wastes such as sewage sludge — reduced NO x to N 2 efficiently in a moderately fuel rich atmosphere. Dry-injected CMA particles at a Ca S ratio of 2, residence time of 1 s and bulk equivalence ratio of 1.3 removed over 90% of SO 2 and NO x at gas temperatures ≥950°C. When the furnace isothermal zone was ≤950°C, CaO was essentially inert in the furnace quenching zone, while MgO continued to sorb SO 2 as the gas temperature cooled at a rate of — 130°C/s. Hence, the removal of SO 2 by CMA could continue for nearly the entire residence time of emissions in the exhaust stream of a power plant. The composition of the calcined salts was used to interpret the results of a cenosphere sulfation model. The sulfation kinetics of Ca-containing calcined residues were found to be bounded by those of pure CaO and pure CaCO 3. The high solubility of the carboxylic acid salts makes them excellent candidates for wet injection. Fine mists of CMA sprayed in the furnace at temperatures between 850 and 1050°C, removed 90% of SO 2 at a Ca S molar ratio of 1, about half of the amount used in the dry injection experiments to achieve a similar SO 2 reduction. The NO x reduction chemistry was not affected by water when CMA was sprayed at a Ca S ratio of 1, i.e., the same reduction efficiency was achieved as with dry injection (25–30%). Thus, while a substantial degr