Wooden fuel pellets : raw material composition, mechanical strength, moisture content, particle size distribution and processing

There are many factors that affect the quality of wooden fuel pellets, from raw materials to pellet production process. Among the factors, raw materials compositions, mechanical durability, moisture contents, and particle size distribution were studied. Experimental raw materials of different percent weights were introduced to industrial fuel pellet production, micro-chips in part-1 experiment and peat in part-2 experiment. Pellets made from these experimental raw material mixtures were tested for their mechanical strength (also known as durability) according to Swedish standards SS 187180 in Part 1 experiment, and European Technical Specification CEN/TS 15210-1 in Part 2 Experiment. Moisture contents of these pellets were also determined. In part-1 experiment, particle size distributions of raw materials and final micro- chips pellets were analyzed. Mapping of pellet production process, bio-energy combine power and heating plant integrated with pellet production were illustrated along with descriptions on major processes. Selected process parameters (i.e. feed rate, drying temperature, milling temperature, pellet machine temperature) for Part 2 experiment were extracted from an industrial program, PGIM signal explorer, and combine with experiment results, thereafter analyzed with statistical methods and by use of SIMCA-P program. The results show that more fresh chips in raw material mixtures give better mechanical strength for micro-chips pellets. For pellets with 80% fresh chips and 20% mature chips in raw materials composition, high durability came from low drying temperature and low feed rate. For peat pellets with 20% peat and 80% fresh chips in raw materials composition, high durability came from high drying temperature, high feed rate, relatively higher pellet moisture content and slightly lower pellet machine temperature. The high and low are relative and based on the experiment results.Validerat; 20101217 (root