Suo - Mires and peat vol. 30 no. 3 | 1979

This work completes our previous thermo-gravimetric investigations of domestic solid fuels. In this part, we have mainly concentrated on the pyrolysis of less common fuels e.g. straw, stumps and rejected, old railway sleepers. These cannot, of course, be regarded as significant fuel sources but locally and we wanted to show that the kinetics of their pyrolysis shows no exceptional behaviour as compared with previous materials. Two peat samples were investigated because they differ from the other peat samples by their kinetic properties. The straw ash, however, has a surprisingly low melting point, which can be detected from the TG-curves. The utilization of used railway sleepers needs additional investigations, because the impregnating substances seem to evaporate in the course from the beginning to the end of the combustion. The safe use of the railway sleepers provides the determination of the toxicity of these substances.

• Tummavuori, Sähköposti: ei.tietoa@nn.oo
• Venäläinen, Sähköposti: ei.tietoa@nn.oo
• Nyrönen, Sähköposti: ei.tietoa@nn.oo

Gasification was studied at the Technical Research Centre of Finland in the 1950s. After the era of cheap oil, the research work on the gasification of domestic solid fuels was restarted in the fall of 1975. In a technico-economic study it was concluded that the most favourable short-term application alternatives were processes with sod peat or peat pellets as raw material and low-Btu fuel gas as products. The energy price of gas was calculated to be between those of light and heavy fuel oil so that in the size class of 10 MW and at a high efficiency of use the price of heavy fuel oil is approached in fixed bed gasification. Gasification tests were carried out on a co-current fixed bed reactor. It was found that peat with 50 % moisture content and with about 30 % content of fine material is suitable for gasification. The amount of gas generated per kg peat dry matter was 2.8 to 3.2 m3n. The chemical efficiency was about 70 % at its best. The total efficiency is considerably increas-ed if the sensible heat of gas can be utilized. Tests with fluidized bed gasification were also restarted in the Fuel and Lubricant Reserach Laboratory of the Technical Research Centre of Finland both on the PDU and pilot plant scale. For the time being, tests with the production of activated carbon from peat coke have been carried out on the pilot plant equipment, while the equipment will be modified after the PDU tests for the use in gasification tests. Fluidized bed gasification is an alternative of consideration when peat is gasified on a large scale. The production of both fuel and synthesis gas can be considered. The development of fluidized bed gasification on the basis of the peat combustion systems in fluidized bed is considered possible and necessary.

• Asplund, Sähköposti: ei.tietoa@nn.oo
• Salo, Sähköposti: ei.tietoa@nn.oo

The aime of the study is to determine whether the decomposition of organic matter and the activity of different groups of micro-organisms has changed in peat-lands where the ground-water table has been maintained at different depths for a considerable length of time. The study has been carried out in sample plots situated on Scots pine and Norway spruce swamps where the groundwater table has been maintained at depths of 10, 30 and 70 cm since 1960. The annual growth of the trees has been followed since the time when the experiment was established. It has thus been possible to examine the connection between tree growth and the numbers of different types of bacteria and the rate of decomposition of the organic matter. Experiments with NPK fertilizer were established in 1961—1962 on plots where corresponding ground-water table regulation had been carried out. The plots in North Finland were refertilized in 1965, and those further to the south in 1967—1969. Intensification of drainage on the sample plots established on spruce swamps has produced a considerable increase in stand growth (Fig. 1). Decomposition of cellulose in the peat has also increased (Fig. 2). Cellulose decomposition on the plots which have been efficiently drained is effective down to a depth of at least 50 cm. Fertilization increased stand growth most on those plots on the spruce swamp where the ground-water table had been maintained at a depth of 10 cm from the surface. Cellulose decomposition also became more effective on these plots. The nutrient reserves in peat which has been efficiently drained, have possibly been sufficient without any fertilizer addition. Fertilization has had a strong effect on stand growth on the pine swamps, the best results being obtained with a drainage depth of 30 cm. Fertilization has also had the strongest effect on cellulose decomposition in the plots on pine swamps where the ground-water table has been maintained at a depth of 30 cm. The numbers of aerobic, ammonification and proteolytic bacteria in the surface layer of the unfertilized peat have been the greater, the deeper the ground-water table (Fig. 5). Intensifying drainage has had the strongest effect on the number of ammonification bacteria. Fertilization, similarly, had the strongest effect on the number of ammonification bacteria. In other words, the activity of both the trees and the bacteria has been limited by a lack of nutrients, which fertilization has alleviated. Although drainage makes the conditions in the peat more aerobic, the number of anaerobic, bacteria has not decreased as the efficiency of drainage increased. Generally speaking, the higher the level of bacterial activity, the better the tree growth. Following changes in the number of different types of bacteria provides information about the decomposition of organic matter in the peat. However, this is not sufficient and chemical analyses are also required.

• Karsisto, Sähköposti: ei.tietoa@nn.oo