BUREAU OF GEOLOGY


approximately 30 percent water content after wet oxidation (Mensinger,
et al., 1980 in Minnesota DNR, 1981, p. 30).
 Wet carbonization consists of heating a slurry of peat and water
(approximately three percent solids) to 300 to 4000F at 50 to 100 atmo-
spheres of pressure for 30 minutes. A "peat coal" with a heat value of
12,000 to 14,000 BTU/lb dry weight is obtained after the liquid is
removed (U.S. Department of Energy, 1979).
 Wet oxidation is an established process for the oxidation of many wet
organic materials. Air or oxygen is pressure fed to wet peat in a closed,
heated vessel. Combustion is rapid and is controlled by the rate of supply
of the oxygen or air. The process can be stopped after enough heat has
been generated to carbonize the remaining peat or can be carried to
completion to produce energy (U.S. Department of Energy, 1979).
 Solvent extraction reacts a heated peat-water slurry under pressure
with an organic solvent. The water is extracted from the peat by the
solvent. Subsequent to cooling, the absorbed water is stripped from the
solvent and after treatment is disposed of as waste.

 Fuel Uses

 DIRECT COMBUSTION

 Direct combustion of peat is a method of producing energy which has
been utilized on a commercial scale in Ireland, Finland and the Soviet
Union for several decades. The Soviet Union had installed an electric
power station fueled entirely by peat as early as 1914 (U.S. Department
of Energy, 1979).
 The U.S. Department of Energy has developed several criteria for fuel-
grade peat for use in its peat program. The criteria are: 1) heat value
greater than 8,000 BTU/lb (dry weight), 2) greater than 80 acres of peat
per square mile, 3) peat depth greater than four feet, and 4) ash content
less than 25 percent (Minnesota DNR, 1981). Hemic peats are generally
the most suitable for direct combustion usage. The more decomposed
peats (sapric) have been carbonized to a greater extent but often have
larger ash contents which reduces their fuel value. Fibric peats have been
less carbonized and thus have lower heating values.
 Direct combustion of peat is accomplished in boilers designed or retro-
fitted for either peat fuel entirely or mixed fuel feed. Boiler design must
accommodate the characteristics of peat fuel: low energy density, high
moisture content. Both of these characteristics result in increased cost
(approximately 50 percent greater) of the boiler and feed system com-
pared with a coal or oil fired boiler of the same capacity (U.S. Department
of Energy, 1979). Grate fired and fluidized-bed boilers require pelletized
or briquetted feed. Pulverized-fired boilers require peat ground to be par-
ticle size compatible with the combuster design.
 Direct combustion techniques can result in partial oxidation of the peat