Speaker
Description
In Japan, woody biomass power generation is increasing due to the Feed-in Tariff (FIT) scheme. However, woody biomass power generation suffers from low energy efficiency. Therefore, improving energy efficiency through combined heat and power (CHP) generation is being considered. Preferential treatment under the FIT program for small-scale facilities (generating less than 2 MW) has begun, and the introduction of gasification CHP systems, suitable for small-scale applications, is advancing. However, gasification imposes stringent requirements on fuel, leading to difficulties in procuring it and soaring fuel prices that cause business failures. Fuel chips for gasification require minimal fines and a uniform, relatively larger particle size. Large chippers designed for paper mill chips can produce a large proportion of relatively large chips. However, not only do these chips fuel applications compete with paper applications, but the production scale also far exceeds the demand of small-scale gasification CHP plants, leading to price increases. Conversely, medium- and small-sized chippers, which produce quantities suitable for small-scale gasification CHP, tend to generate more fine particles and struggle to produce relatively large chips. This fact necessitates screening to select chips suitable for fuel production, further contributing to fuel price increases. Therefore, a medium-sized drum-type chipper was modified to produce chips suitable for gasification CHP. Preliminary test results showed that chips produced by a commercially available medium-sized drum-type chipper met the ISO P31s specification. However, compared with the chip requirements specified by various gasification CHP boiler manufacturers, the chips contained too much fine material and lacked sufficient larger chips. We therefore conducted development and testing to reduce fine material and enable the production of larger chips. To reduce fine particles, the number of blades was reduced from 6 to 3. To produce larger-sized chips, the rotor speed and feed rate were optimized. Using a chipper equipped with a standard drum and a chipper equipped with a prototype drum featuring 3 blades, and two types of screens, we conducted chipping operations on sets of 10 Japanese red pine logs with a butt diameter of less than 30 cm and a length of 2 m. We observed the operations and collected samples of the produced chips. Each condition was tested three times. After returning to the laboratory, the samples were dried in the oven, weighed to determine water content, and then sieved. The particle size analysis showed that reducing the number of blades significantly decreased fine particles and increased the proportion of larger chips; however, this still fell slightly short of the gasification CHP boiler manufacturers' requirements.
| Keywords | blades; rotor; feeder; size |
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