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- Åmand, Lars-Erik, 1957, et al.
(author)
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Co-combustion of municipal sludge with wood/coal in CFB--enrichment of phosphourous and cadmium in ashes
- 2003
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In: In Proceedings of the 17th International Fluidized Bed Combustion Conference--FBC2003 held in Jacksonville, Florida, USA May 18-21, 2003. - 0791836754
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Conference paper (peer-reviewed)abstract
- Municipal sludge, originating from two wastewatertreatment plants in Sweden, has been burned together withwood pellets or bituminous coal in a circulating fluidised bed (CFB) boiler equipped with a secondary cyclone and bag filter for fly ash removal. Such co-combustion is an alternative to mono-combustion of sludge. The sludge is burned in either mechanically dewatered or pre-dried form. The mechanically dewatered sludge was fed with a pump, but pre-dried sludge could be fed by the fuel feed system normally used for coal. Both types of sludge were burned with either wood-pellets or coal as main fuel under identical operating conditions, typical for a CFB boiler. The focus was on ash balances and on analysis of fuels and ashes to obtain concentrations of relevant species. The presence of phosphorous (P) is of special interest in relation to trace elements, such as mercury (Hg), cadmium(Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni) andzinc (Zn). For this reason a comparison has been made between these trace elements and phosphorous in the various ashes and the original sludge as well as other sources of phosphorous thatcould be used for agricultural purposes. The results show that sewage sludge and fly ash, after combustion of sludge, contain similar amounts of phosphorous as other phosphorous sources for agricultural use, but the levels of trace elements in relation to phosphorous (Hg, Cd, Pb, Cr, Cu) are higher than in animal manure and artificial fertilizer and higher than the present limits in Sweden.
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- Åmand, Lars-Erik, 1957, et al.
(author)
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Co-combustion of pulp and paper sludge with wood -- emissions of nitrogen, sulphur and chlorine compounds
- 2003
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In: In Proceedings of the 17th International Conference on Fluidized Bed Combustion--FBC2003 held in Jacksonville, Florida, USA, May 18-21, 2003. - 0791836754 ; 17:FBC2003-097
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Conference paper (peer-reviewed)abstract
- Sludge from wastewater treatment plants in five Swedish pulp and paper mills has been burned together with wood in a circulating fluidised bed (CFB) boiler. The sludge was either mechanically dewatered or pre-dried. The mechanically dewatered sludge had to be fed with a pump, but the pre-dried sludge could be fed by the fuel feed system normally used for coal, wood chips or wood pellets. In parallel to the combustion tests in the CFB boiler the sludges were also investigated as single fuels in a small laboratory FB. The Swedish pulp and paper industry produces three major fractions of sludge: pure fibre sludge, sludge produced by employing a precipitation species like ironaluminiumsulphate, and finally, sludge subjected to biological cleaning. The way of production of the sludge influences its content of, for example, nitrogen, sulphur and chlorine, but the composition of the sludge is also influenced by the pulp and paper process. The present measurements show that the concentrations of nitrogen, sulphur and chlorine in the sludge have a great impact on the corresponding gaseous emissions from combustion. Actions to prevent these emissions could be necessary, depending on the origin of the sludge and treatment process used. In the present project all sludges were burned with wood-pellets as the main fuel under identical operating conditions, typical for a CFB boiler. Wood pellets were chosen as a well defined, low-polluting fuel that makes comparison of emissions from the sludges clear. Co-combustion with wood-pellets has the advantage of enabling operation also with wet sludges that cannot be used as single fuels without pre-drying. No actions were taken to improve sulphur and chlorine retention, by for example adding limestone. From a combustion point of view the co-combustion works well with low levels of carbon monoxide present in the flue gas and no light hydrocarbons.
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