The following issues were addressed in the project:
The project is based on combustion tests in the two Waste to Energy boilers at 20 MWth each owned by Borås Energy and Environment AB (BEM). Furthermore, results from the Waste Refinery Project “Reduced bed temperature in FB-boilers burning waste – part II” has been used as reference in some cases. At normal conditions the boilers are run on a fuel mixture containing 80 percent sorted industrial waste and 20 percent household waste. This fuel mixture consists mainly of paper, plastics and wood. In Borås the organic part of the household waste is sorted out and used for biogas production. With the addition of biomal, which consists of animal by-products crushed to a pumpable fuel, the chemical composition of the fuel mixture is changed to some extent.
The results from the combustion tests shows that biomal influences the chemical fuel composition, but also that there are large variations in the ordinary waste fuel composition as well. The most evident changes with addition of biomal are:
However, there were no changes in sodium, potassium, sulphur and chlorine, elements important for increased/reduced fuel related problems, derived from biomal.
The increase of calcium and phosphorus with biomal derive from bone and the calcium-phosphates influenced to some extent the sand/ash flows were the largest change was an increase in the amount of phosphorus and calcium. In addition a decrease of the amount of lead was seen in all ash flows. The calcium-phosphates were stable during combustion and no reactions of phosphorus with other elements were detected. The results from the trials in this project show that co-combustion of biomal had the following positive effects on the boiler performance:
The conclusion is that the boiler could be operated in a safe way with addition of biomal.