Influence of Phosphorus on Alkali Distribution during Combustion of Logging Residues and Wheat Straw in a Bench-Scale Fluidized Bed

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• 作者：Alejandro Grimm ; Nils Skoglund ; Dan Bostr枚m ; Christoffer Boman ; Marcus 脰hman
• 刊名：Energy & Fuels
• 出版年：2012
• 出版时间：May 17, 2012
• 年：2012
• 卷：26
• 期：5
• 页码：3012-3023
• 全文大小：574K
• 年卷期：v.26,no.5(May 17, 2012)
• ISSN：1520-5029

文摘

The influence of phosphorus on the alkali distribution in fluidized (quartz) bed combustion using two different typical biomasses (logging residues and wheat straw) was studied. Phosphoric acid (H₃PO₄) was used as an additive. The produced ash fractions were analyzed for morphology and elemental composition by scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), and crystalline phases by powder X-ray diffraction (P-XRD). For both fuel assortments tested, a reduction of volatilized deposit and fine particle-forming matter, containing mainly KCl, was achieved by adding phosphorus. For the wheat straw, this effect was considerable at medium and high phosphorus addition. As a consequence, an increased amount of potassium was found in the coarse ash particle fractions, principally as CaKPO₄, KMgPO₄, and CaK₂P₂O₇, at the same time that the levels of HCl and SO₂ in the flue gases increased. Generally, the addition of phosphorus to the studied biomasses changed the alkali distribution from being dominated by amorphous K-silicate coarse ash fractions and fine particulate KCl, to a system dominated by crystalline coarse ash of K鈥揅a/Mg-phosphates and fine particulate K₂SO₄. This implies that the fouling and high-temperature corrosion observed in industrial-scale combustion of problematic biofuels can possibly be reduced by employing additives rich in reactive phosphorus, on the condition that the higher concentrations of acidic gases can be tolerated. In order to achieve these effects, the relationship between alkali and alkaline-earth metals (i.e., (K + Na)/(Ca + Mg)) in the overall fuel ash must be considered. With respect to this, the formation of low-temperature-melting alkali-rich phosphates should not be promoted, to avoid potential increases in bed agglomeration tendencies and phosphorus release from the bed.