Possibilities and evaluation of straw pretreatment

Biomass utilisation by cofiring of straw in a pulverised coal fire boiler is economically attractive compared to dedicated straw fired plants. However, the high content of potassium and chloride impedes utilisation of the fly ash, deactivates the de NOx catalysts in the flue gas cleaning system and may also lead to increased deposit formation.

A pretreatment process is required to solve the problems. In this paper two pretreatment processes are considred, one based on straw wash and another based on pyrolysis and char wash. To evaluate and compare the processes, laboratory and technical invetsigations were performed. The economy of both processes are favourable compared with seperate straw fired boilers, however, the removal efficiency of potassium of the pyrolysi based process is relatively low.

At the present level of invetsigations the straw wash process looks promising and commercially viable.