TGA and Drop Tube Furnace Investigation of Alkali and Alkaline Earth Metal Compounds as Coal Combustion Additives
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- 作者：Katherine Le Manquais ; Colin Snape ; Jim Barker ; Ian McRobbie
- 刊名：Energy & Fuels
- 出版年：2012
- 出版时间：March 15, 2012
- 年：2012
- 卷：26
- 期：3
- 页码：1531-1539
- 全文大小：310K
- 年卷期：v.26,no.3(March 15, 2012)
- ISSN：1520-5029
文摘
Even though alkali and alkaline earth metal compounds are well-known catalysts for the combustion of coal, there has been no significant investigation into the importance of the anion across a broad selection of salts. The results described here compare the burnout of bituminous coal samples containing 21 Group I and II compounds on a thermogravimetric analyzer, thereby furnishing a wide-ranging systematic evaluation of anion effects for the first time. A variety of acetates, bicarbonates, carbonates, chlorides, hydroxides, nitrates, and sulfates were studied. Testing was also extended to a drop tube furnace (DTF), so that individual combustion additives could be assessed under conditions more similar to those found in a pulverized fuel (PF) boiler. All of the catalysts were subsequently found to increase the rate of TGA char combustion, but establishing definitive carbon burnout improvements proved to be more difficult on the DTF. This was probably due to a combination of the experimental variability associated with this setup, poor additive-coal contact, and the intrinsic volatility of the tested salts, particularly sodium carbonate鈥檚 removal at high temperatures and the loss of calcium nitrate in an oxidizing environment. Despite these uncertainties, the attained DTF reactivity ranking was quite similar to that of thermogravimetric analysis (TGA). The alkali chlorides were identified as the most active additives, with their higher melting points possibly enhancing both their retention and the catalyst鈥揷oal contact achieved during devolatilization. However, the burnout improvements associated with the other Group I salts appeared to be limited by the propensity of the cations to interact with the coal matrix, while the activities of the less effective Group II compounds seemed to be restricted by their higher ionization energies and different bonding.