Posted October 1997
Many wood-processing industries are used to simply dumping their woodwastes, causing significant environmental pollution. At the same time, these industries buy in fuel oil. In Indonesia and Malaysia a trend is now emerging to establish integrated wood-processing complexes, where woodwastes from processing are being used to supply energy for the complex, making the units both more efficient and more economical, and minimising pollution.
One example is the Indonesian plywood manufacturing company PT Siak Raya Timber, located in Pekanbaru, Sumatra, Indonesia. The company employs 6,000 people and produces a yearly average of 160,000 m3 of plywood and secondary processing plywood products. In addition, an affiliated woodworking factory produces about 50,000 m3 per annum of downstream products. The raw materials used for these products come mainly from company-owned forests in central Sumatra. In the process, a lot of residues are produced. As yet the company generates electricity using diesel gensets, but it has decided to install an energy plant, using its own wood residues as fuel, to meet its heat and power requirements.
Cost reduction and reduced environmental impact will be achieved by replacing the existing diesel engines by the new energy plant fuelled by wood residues, generating 5.55 MW of electricity for captive use. In this way, expected increased expenditure on fossil fuels is also avoided. Contracts have been signed with European equipment suppliers. This is slightly more expensive locally manufactured equipment, but it is assumed that reliability and efficiency are higher, thus minimising the operation and maintenance costs.
For this project, the EC-ASEAN COGEN programme has carried out a pre-investment study. Operating staff are to receive special training and the plant will be monitored after implementation.
The turnkey-supplied plant will consist of the following main components:
Excluding civil and structural works, the total investment cost for the equipment on a turnkey basis is US$ 5.6 million. Based on the present diesel consumption and price, the annual savings in diesel purchase will be more than US$ 1.7 million. The expected pay-back period is around three years after commissioning.
At present, 6% of Denmark's total energy consumption is covered by biomass energy, representing 75% of the country's renewable energy production. Denmark is an agricultural country and generates large amounts of straw (2.3 Mt/a or 46 PJ) and animal wastes (3 Mt/a or 26 PJ), which are increasingly being used as sources of energy. Straw presses have been developed that efficiently process the straw into bales of standard sizes, which are used in 8,000 on-farm heating systems (0.39 Mt/a) and, increasingly, purchased by electric utilities for power generation (0.26 Mt/a) and/or district heating (0.28 Mt). Electricity generation from straw is set to expand further, as the Danish power utilities have signed contracts for 1.4 Mt/a.
Though only 12% of the country is forested, 70% of all wood residues from forestry, or 5.1 PJ, is being used for energy purposes. The majority of these residues are chipped in situ using mobile equipment. All industrial woodwaste (0.15 Mt/y or 13.2 PJ) is already pelletized and used as an energy source. The main use for both wood chips and wood pellets is in district heating plants that previously used coal.
Municipal solid waste (MSW) is also increasingly being used for energy. Households separate organic from non-organic waste. The organic waste is used in biogas digester plants which generate heat and electricity from the biogas. Combustible waste accounts for 10 PJ out of 80 PJ of heat delivered by district heating systems. By 2000, all combustible wastes will be used for energy purposes, mainly in cogeneration facilities. All waste incineration and district heating units above 1 MW will be converted to cogeneration units by the same deadline.
In reaction to the 1973 oil shock, Denmark put emphasis on energy conservation and fuel substitution (from oil to natural gas and biomass) to reduce the country's dependence on oil imports. Individual heating systems were replaced by more efficient district heating systems. An energy tax was introduced on oil and coal to keep consumer prices high. Tax earnings were invested in energy-saving equipment and research into modern biomass systems. Cogeneration district heating plants were converted to use straw, wood chips and waste. Burning straw in the field was prohibited in 1990. The issue of global warming led to the introduction of a CO2 tax in combination with incentives for decentralized electricity generation using renewables. Other incentives are funding of up to 30% of the cost of biomass-fired boilers and biogas plants, and support for research into modern biomass energy crops and systems.
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