COMPACTING BIOMASS AND MUNICIPAL SOLID WASTES TO FORM AND UPGRADED FUEL

摘要

Biomass waste materials exist in large quantity in every city and in numerous industrial plants such as wood processing plants and waste paper collection centers. Through minimum processing, such waste materials can be turned into a solid fuel for combustion at existing coal-fired power plants. Use of such biomass fuel reduces the amount of coal used, and hence reduces the greenhouse effect and global warming, while at the same time it reduces the use of land for landfill and the associated problems. The carbon-dioxide resulting from burning biomass fuel is recycled through plant growth and hence does not contribute to global warming. Biomass fuel also contains little sulfur and hence does not contribute to acid rain problems. Notwithstanding the environmental desirability of using biomass waste materials, not much of them are used currently due to the need to densify the waste materials and the high cost of conventional methods of densification such as pelletizing and briquetting. The purpose of this project was to test a unique new method of biomass densification developed from recent research in coal log pipeline (CLP). The new method can produce large agglomerates of biomass materials called ''biomass logs'' which are more than 100 times larger and 30% denser than conventional ''pellets'' or ''briquettes''. The Phase I project was to perform extensive laboratory tests and an economic analysis to determine the technical and economic feasibility of the biomass log fuel (BLF). A variety of biomass waste materials, including wood processing residues such as sawdust, mulch and chips of various types of wood, combustibles that are found in municipal solid waste stream such as paper, plastics and textiles, energy crops including willows and switch grass, and yard waste including tree trimmings, fallen leaves, and lawn grass, were tested by using this new compaction technology developed at Capsule Pipeline Research Center (CPRC), University of Missouri-Columbia (MU). The compaction conditions, including compaction pressure, pressure holding time, back pressure, moisture content, particle size and shape, piston and mold geometry and roughness, and binder for the materials were studied and optimized. The properties of the compacted products--biomass logs--were evaluated in terms of physical, mechanical, and combustion characteristics. An economic analysis of this technology for anticipated future commercial operations was performed. It was found that the compaction pressure and the moisture content of the biomass materials are critical for producing high-quality biomass logs. For most biomass materials, dense and strong logs can be produced under room temperature without binder and at a pressure of 70 MPa (10,000 psi), approximately. A few types of the materials tested such as sawdust and grass need a minimum pressure of 100 MPa (15,000 psi) in order to produce good logs. The appropriate moisture range for compacting waste paper into good logs is 5-20%, and the optimum moisture is in the neighborhood of 13%. For the woody materials and yard waste, the appropriate moisture range is narrower: 5-13%, and the optimum is 8-9%. The compacted logs have a dry density of 0.8 to 1.0 g/cm{sup 3}, corresponding to a wet density of 0.9 to 1.1 g/cm{sup 3}, approximately. The logs have high strength and high resistance to impact and abrasion, but are feeble to water and hence need to be protected from water or rain. They also have good long-term performance under normal environmental conditions, and can be stored for a long time without significant deterioration. Such high-density and high-strength logs not only facilitate handling, transportation, and storage, but also increase the energy content of biomass per unit volume. After being transported to power plants and crushed, the biomass logs can be co-fired with coal to generate electricity.