Wood Chip Production Technology and Costs for Fuel in Namibia

摘要

This work has been done in the project where the main target is to evaluate the technology and economy to use bush biomass for power production in Namibia. The project has been financed by the Ministry for Foreign Affairs of Finland and the Ministry of Agriculture, Water and Forestry of the Republic of Namibia. The target of this study is to calculate the production costs of bush chips at the power plant using the current wood chip production technology and to look possibilities to develop production technology in order to mechanize production technology and to decrease the wood chip production costs. The wood chip production costs are used in feasibility studies, in which the technology and economy of utilization of wood chips for power generation in 5, 10 and 20 MW electric power plants and for power generation in Van Eck coal fired power plant in Windhoek are evaluated. Field tests were made at Cheetah Conservation Farm (CCF) in Otjiwarongo region. CCF is producing wood chips for briquette factory in Otjiwarongo. In the field tests it has been gathered information about this CCF semi-mechanized wood chip production technology. Also new machines for bush biomass chip production have been tested. A new mechanized wood chip production chain has been designed on the basis of this information. The wood chip production costs for the CCF semi-mechanized and the new production chain have been calculated. The target in the moisture content to produce wood chips for energy is 20 w-%. In the semi-mechanized wood chip production chain the work is done partly manually, and the supply chain is organized into crews of 4.8 men. The wood chip production chain consists of manual felling and compiling, drying, chipping with mobile chipper and manual feeding and road transport by a tractor with two trailer unit. The CCF production chain works well. The chipping and road transport productivity in the semimechanized production chain is low. New wood chip harvesting machines, such as chainsaw, brush cutter, lawn mover type cutter, rotator saw in skid steer and Nisula harvester head for felling, were tested at CCF. The most effective felling device in the tests appeared to be rotary saw in the skid steer. Based on these tests it was designed a new totally mechanized production chain. The working phases in this mechanized production chain are felling with a rotary saw in skid steer, compiling with a grapple fork in skid steer, drying in the heaps, chipping with a mobile chipper with a loader and road transport with a tractor trailer. This new production chain is not fully tested in Namibia. The calculated harvesting and road transport costs of wood chips with the designed new mechanized production chain are about 15% lower than those of the semi-mechanized production chain. The wood chip production costs at power plant with the new mechanized production chain are 170.5 N$/wet ton (4.4 Euros/MWh) for 5 MWe power plant, 181.4 N$/wet ton (4.7 Euros/MWh) for 10 MWe power plant and 192.3 N$/wet ton (4.9 Euros/MWh) for 20 MWe power plant. The average road transport distance in the calculation is 30 km for a 5 MWe, 40 km for 10 MWe and 50 km for 20 MWe power plants. The wet ton and MWh units are presented in 20 w-% moisture content.