Artificial dewatering of peat. Part 6. Peat production methods for the mechanical dewatering process

Alternative peat production methods based on so called artificial (mechanical) dewatering have been studied in several countries for many decades. In Finland, a research program called the Artificial Dewatering of Peat (ADEWA) was carried out at the Technical Research Centre of Finland (VTT) during 1988 1992. Several techniques for wet peat mining were tested at the Combustion and Thermal Engineering Laboratory of VTT. In the ADEWA research program, a new peat production method, SLURRY COMP, was developed. The method is based, in its optimum form, on a modified ridge transporting method (Peco), on slurrying of milled peat from a stockpile ridge, pumping of the slurry through pipelines to the power plant, and, after chemical pretreatment, dewatering by pressing. Feasibility studies on wet milled peat and slurry production as well as pilot scale pumping tests of peat slurries have been carried out on the bog and under laboratory conditions. In these studies, slurrying of peat and pumping of that slurry have been established as the most viable method for production of raw material for the dewatering process. In the rheological studies, the DS contents of the slurries have been 4 7 % on the bog and 5 10 % in the laboratory. According to the pressure losses measured in the pipes of different sizes (inner diameters 140 400 mm), the optimal DS content of the slurry is about 7 8 % with the most common peats in Northern Finland, i.e. Carex (sedge) peat. The mining and slurrying technique (determining the particle size), peat type, pipe diameter, and flow velocity have a great influence on the flowing properties and pressure losses of peat slurry. Based on our present knowledge, the SLURRY COMP method produces fuel from sedge peat in Northern Finland at almost the same cost as the normal milling (HAKU) method. The production costs are about 48 53 mk/MWh and 44 50 mk/MWh with an annual production of 100 000 and 400 000 tons of dry solids. These amounts of dry peat meet the fuel requirements of the power plants with an electric output of 40 50 MW and 150 200 MW, respectively. The peat thus produced has a dry solids content of 35 %, which is adequate for the fuel used with pressurized combustion techniques