Optimering av sotningsfrekvens i biobränsleeldad CFB-panna : panna 5, Mälarenergi AB, Västerås

Abstract: During the past 30 years the fuels for energy production in heating and power plants have changed. Fossil fuels have decreased in usage whereas bio fuels in Sweden have increased with 60% since the 1970's. Different fuels affects combustion and the release of various substances and particles into the flue gas. This is caused by the diverse components and chemical structures of fossil fuels and bio fuels. When the flue gas leave the combustion chamber and enters the path to the chimney particles in the gas are being transported out of the combustion chamber. When particles encounter surfaces either a reaction between the particles and the materials of the surface takes place or a new layer builds on top of the surface. These layers of particles decrease the efficiency of the boiler. In order to remove the particles from the surfaces through witch heat is being transferred different soot methods are used. One of the common soot methods is soot blowing, where hot steam is blown through a nozzle causing the layers to crack and remove from the surfaces. The purpose of this work was to optimise the soot blower frequency in boiler 5, Mälarenergi AB, in Västerås, Sweden. Boiler 5 is a CFB-boiler with bio fuel combustion. Today different soot intervals are used. The interval frequency is of importance to the growth rate of the layer on the surfaces. Data from a period of six moths were studied in order to conclude when and where in the boiler the soot blowers were active and cleaning. The results were analyzed and compared to measurements of heat transfer through the surfaces. In the supra heaters the most commonly used interval was intervals of 24 hours, and in economiser and in the air pre heater intervals of 8 hours was more common. Calculations and comparisons show that an increase of soot frequency from 24 hour intervals to 8 hour intervals in the supra heaters is profitable. The results from the economiser and the air pre heater have not been conclusive since there is lot of fluctuations in the measurement that affect the results. In order to conclude the optimal cleaning interval for economiser and air pre heater more studies are acquired.