Slow pyrolysis in Brista : AN EVALUATION OF HEAT AND BIOCHAR PRODUCTION IN SWEDEN

Abstract: This study is an analysis of the potential to have a slow pyrolysis power plant in Brista, Sweden. The study is investigating current technologies available and research and application of the pyrolysis products from the process. Pyrolysis has been known for over thousands of years. It has played an important part during the industrialization for producing coal in kilns. In recent years, the slow pyrolysis technology has started to become an area of interest because of the use and research surrounding the concept of biochar.Biochar is a term used to describe the char product of pyrolysis when biomass is used as a feedstock. The slow pyrolysis technology has a higher yield of char compared with other pyrolysis and carbonization methods. The biochar could be used as a soil enhancer to improve soil quality.Currently the biochar market is undeveloped and the concept is not well known in the general public. In Sweden there are no large scale slow pyrolysis processes for the production of biochar, in Europe there is some examples of slow pyrolysis power plant of various sizes. Slow pyrolysis has currently not been as profitable as traditional combustion of biomass. But it has the advantage to low grade feedstock sources and could become more profitable if the use and demand if biochar would increase.The profitability of establishing a slow pyrolysis plant is estimated by using the theoretical performance of such a plant. The slow pyrolysis processes used to create the model is based on the descriptions from the manufacturers Pyreg, Carbon Terra and BigChar. Data regarding the investment and operation cost of the plant is brought from manufacturers and other studies surrounding the slow pyrolysis concept. Different cost settings and fuel qualities for three different biomass types (Wood, forest residue and green garden waste) are applied to test the sensitivity of the process.The result of the study indicates the plants utilizing the green garden waste material will have the shortest payback period and return on investment. The green garden waste seem to be possible to use as a feedstock in a slow pyrolysis process to produce biochar of certifiable standard and large quantities are available in the area around Brista, but further research is needed.The larger reactor with a capacity of circa 3-5 MW had the highest return on investment and was not as sensitive to fluctuations of heat and biochar price as the smaller pyrolysis alternatives. The environmental benefit of establishing a slow pyrolysis power plant could not be determined. The char produced could work as a carbon sink if utilized as a soil enhancer. But the relatively small production capacity 0,5-5 MW makes the impact insignificant at a district level. But it could serve as a method to bring new research opportunities. New projects regarding biochar production in Sweden in under process and could bring new information that could improve the model of biochar production.