HELSINKI UNIVERSITY OF TECHNOLOGY
ABSTRACT OF THE MASTER'S THESIS


Author: Matti Pellinen
Title of the thesis: Energy Supply Alternatives for Mechanical Forest Industry
Title in Finnish: Mekaanisen metsäteollisuuden energianhankinnan vaihtoehdot
Date: April 26 1996
Number of pages: 75+30
Department: Faculty of Mechanical Engineering
Professorship: Ene-47 Department of Energy Engineering
Supervisor: Prof. Carl-Johan Fogelholm
Instructor: DI Ismo Nousiainen
Keywords: bark, bioenergy, biomass, boiler, diesel, heat, heat production, Organic Rankine Cycle, PGI system, sawmill, small-scale power plant
Mechanical forest industry produces a lot of biomass by-products like bark, sawdust and wood chips. By-products are often enough for generating the heat needed in a sawmill or a veneer factory. Cogenerating heat and electricity is however rare.

The temperature needed for lumber drying in sawmills, is only 120 Degree C. On the other hand, the heat load of the drying units is rather stabile. Small-scale power plants, utilising sawmill by-products, could produce heat and electricity in sawmills, if it would be economically feasible.

In this work different choices for supplying heat and electricity to the sawmill are investigated. One option is a hot water boiler burning different fuels. A novel possibility is to build a small-scale cogenerating power plant with a net thermal output of 1-20 MW. These plants may also use by-products or other fuels, in which case the by-products can be sold. The processes investigated here are: small-scale steam power plant, biomass gasifying diesel, pyrolysis oil diesel, wood-fired gas turbine (PGI system), Organic Rankine Cycle and gas turbine using natural gas. A model was created to research the various options and their costs for different sizes of sawmills. These are compared to the standard option of buying electricity and to use bark in a hot water boiler for generating heat.

A primary boiler using bark and a secondary boiler using heavy fuel oil is the most common and often the most economic solution. However, it is cheaper to use wood chips instead of bark when production is 15 000 m3/a or less. In this case bark must be disposed of or sold. If production is 300 000 m3/a or more, it could be economically feasible to use small scale steam power plant or ORC-process for cogeneration.

In case the investments become 20 % lower it would be economically feasible to use small scale steam power plant already at a production level of 200 000 m3/a and ORC-process with 130 000 m3/a of lumber production. This would mean 17 power plants or 27 ORC-processes producing up to 110 MW electricity, in Finland.
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