The oversupply of organic fertilizers causes an urgent need for alternative treatments of manure. CO2 neutral electricity is produced from poultry manure, a renewable fuel which is relatively dry and has a heating value of 6-8 MJ/kg. The electricity production from manure saves emissions from fossil fuel combustion, resulting in a reduced environmental impact in the impact category climate change. Moreover, as manure contains a large amount of ammoniacal N, and due to nitrification and denitrification processes, land spreading of poultry manure causes larger emissions of NH3, N2O and NOx than combustion. Electricity production from manure therefore outperforms land spreading in the impact categories terrestrial acidification, particulate matter formation, marine eutrophication and photochemical oxidant formation. The fluidized bed combustor of BMC in the Netherlands generates zero waste, as the ash is recovered as a PK fertilizer, which is odorless, dry, sterile and has a lower mass and volume than the manure, making it more suitable for export to regions with a high P demand. The ash causes however technological problems, such as agglomeration and deposition.

Agglomeration of ash in fluidized bed combustors may result in defluidization and subsequent downtime of the installation. Previous research has shown that Ca-based additives can prevent agglomeration, but the added amount was determined arbitrarily and testing occurred only on lab scale or pilot scale. This paper presents a statistical approach, based on a newly developed agglomeration index, to calculate the amount of CaO that should be added (in the form of a Ca-based mineral, e.g., CaCO 3 ) to the fluidized bed in order to prevent agglomeration. The agglomeration index is based on an understanding of the reactions occurring in the ash, for instance, the formation of potassium silicates with low melting points, and the formation of calcium phosphates and calcium silicates with high melting points. Full-scale testing of partial replacement of silica sand by calcite (CaCO 3 ) as fresh bed material showed that the increased CaO concentration in the ash, with respect to normal operation, appears to reduce both wall and in-bed agglomeration problems. As a measure for agglomeration risk, differential bed pressure variations were statistically analyzed. In the test periods during which CaCO 3 was added, the bed pressure variations were smaller and less frequent, and the severity of agglomeration was thus reduced. The proposed strategy can be applied for fuels that are commonly perceived as difficult or unsuited for fluidized bed combustion, and also for other additives than CaCO 3 , e.g., Al-based minerals.

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