Behavior of Chlorine and Enrichment of Risky Elements in Bubbling Fluidized Bed Combustion of Biomass and Waste Assisted by Additives
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- 作者：Beatrice Coda ; Martti Aho ; Roland Berger ; and Klaus R. G. Hein
- 刊名：Energy & Fuels
- 出版年：2001
- 出版时间：May 2001
- 年：2001
- 卷：15
- 期：3
- 页码：680 - 690
- 全文大小：348K
- 年卷期：v.15,no.3(May 2001)
- ISSN：1520-5029
文摘
High contents of chlorine and alkalies restrict the use of biomass in energy production. Alkalichlorides vaporize during combustion. Chlorine tends to produce corrosive deposits and unacceptably high emissions of HCl and dioxins. Chlorine recovery and enrichment of Cl, Na, K, Ca,Al, and Si in coarse and fine fly ash were studied experimentally with two electrically stabilizedbubbling fluidized bed (BFB) reactors capable of reproducing the particle residence times existingin full-scale BFB plants. Feedstocks were fir (mixture of heartwood and bark), paper sludge, andblends of fir with agricultural waste or plastic waste. Sulfur concentrations of feed componentswere low (<0.5 wt %), while chlorine and potassium concentrations ranged widely (0.02-3.2 wt% for Cl and 0.07-3.1 wt % for K). Aluminum-containing additives (kaolin, bauxite and fly ashfrom a pulverized coal plant) and limestone were added to the feedstocks at various dosages toevaluate their influence on Cl behavior and enrichment of the elements of interest. HCl wasmeasured by FTIR and wet-absorption methods. Different ash samples (bed, cyclone and filterash) were characterized for their Cl content and the major ash-forming constituents. Cl wascompletely volatilized from bed ash and recovered only in coarse (cyclone) and fine (filter) fly ashfractions. Al-containing additives increased HCl formation and decreased Cl concentration inthe fly ash. In the case of Al-Si based additives, evidence was found of the formation of alkalialuminum silicates from alkali chlorides. The aluminum silicates were transferred mainly tothe coarse fly ash fraction. Al-based additives also seemed to liberate Cl from alkali chlorideswith reactions forming water-soluble alkali compounds. Limestone had the opposite effect to theAl-containing additives by binding Cl from gas phase to fly ash, but mainly to the coarse fly ashfraction. The results will be useful in optimizing the behavior of chlorine in bubbling bedcombustion of Cl- and alkali-containing biomass.