Artikkelit kirjoittajalta Dan Asplund

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

Different kinds of waste waters can be purified by peat. The right choice of peat quality and its correct handling may be the qualification for reaching the optimum result, i.e. the use of one and the same peat quality for all kinds of purification purposes is not possible. In the present paper, the subject is confined to discussing removal of heavy metals and oils from waste waters, as we have advanced the furthest in these fields and also because peat applies most economically to the purification of relatively small and special flows of waste water. Compared with other sorbents and adsorbents, one of the greatest advantages of peat is its price per removed impurity. At the University of Sherbrooke in Canada, a process has been developed for the removal of heavy metal ions. In this process metal ions are removed in a 2 mm thick continuously moving peat filter. Prior to this phase, the pH of waste water has been changed or sodium sulphide has been added to it. By means of this test equipment, waste waters containing mercury, copper, zinc, iron and chromium have been purified, the removal percentage being from 98 to 99 %. Five units of this process have already been sold. In an investigation carried out at the Technical Research Centre of Finland, the influence of a number of variables, such as particle size, bed thickness, bed density, heat treatment, peat quality, emulsion stability, on the purification degree, oil-binding capacity, headloss and changes in the bed have been investigated. A 98 % removal was reached by means of a 0.05 ... 0.2 m thick peat bed depending on other process parameters, and the oil-binding capacity has been from 0.1 to 0.2 l oil/l peat (corresponding to about 1 ... 2 kg oil/kg peat). An initial difficulty caused by the shrinkage of the bed has been reduced by choosing a better peat quality and optimum conditions. In a peat filtering process either equipment with a fixed bed or continuously running equipment can be used. A modification of the last-mentioned piece of equipment is being developed at the Technical Research Centre of Finland. Cost estimates indicate that a peat filter is favourable alternative in many cases. Furthermore, there are cases where the purification possibility in general is concerned, e.g. many pollution cases, rather than the economical aspects. Provided the production of filtering peat can be started by some enterpriser, there is every probability that even equipment manufacturers will be found.

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