Citation

Wilen, C., Stahlberg, P., Sipila, K., and J. Ahokas, Pelletization and combustion of straw. Energy From Biomass and Wastes 10: 469-484, 1987.

Abstract

Finland's annual straw harvest is about 4 mill. t. Only 2.2 mill. t of this can be utilized with the present harvesting methods. About 1.8 mill. , i.e. 0.5 Mtoe, of this could be used as a fuel, primarily in the grain-growing regions of Southern and Western Finland.

A study of straw pelletization technology and of the combustion of pellets has been carried out. Experiments were also made on the drying of straw in storage facilities. Production costs of pellets and costs of produced heat compared to other fuels were evaluated in a technoeconomic study. Pelletizing experiments with a portable pelletizing unit indicated that straw can be pelletized without thermal drying over a fairly wild range of moisture content. The moisture content of straw to be pelletized should be less than 20%, i.e., about the same as that of straw stored in bales. If the straw must be harvested and baled in a moister straw, it can be dried in a cold-air drier. The size of the chopped straw has a significant effect of the pelletizability of straw and on the energy consumption during pelletization. Handling and storage properties of straw pellets are also dependent on the moisture content of straw.

Combustion experiments with straw pellets were performed in screw stokers (10 - 30 kW) designed for peat pellets and wood chips. Combustion experiments were also carried out in a fluidized bed (300kW) combusted and gasification experiments in a fixed bed gasifier with the object of producing fuel gas. The combustion of straw pellets has been monitored in practice at several farms during the heating season 1984-1985. The results were very positive and the annual efficiency of heating high.

The production costs of straw pellets vary over a wide range depending primarily on the straw harvesting method. Straw can be pelletized either in a portable pelletizing unit or in conjunction with some existing commercial operation, for example green fodder drying or sugar milling. The annual consumption of pellets at farms is on average 13-26t. The price of straw pellets should be 66-116 USD/t to be competitive with that of light fuel oil. The price of straw pellets made on a farm in a portable unit is about 54-84USD/t. The price of commercially manufactured pellets varies from about 74 to 100 USD/t, depending on the proportion of fixed costs in the price of the product.

Country, State, District, etc.

Finland

Language

English

Material

wheat straw, barley straw, rye straw, oat straw

Use category

energy production