In-depot upgrading the quality of fuel chips for a commercial gasification plant

Uncertainties in quality and timely availability of feedstock are among major issues in planning an economically viable bioenergy enterprise. Reported studies in open literature on feedstock supply logistics are either the results of modeling or from laboratory scale investigation with limited usefulness to commercial operations. The objective of this research is to quantify the sensitivity of steam production rate in a commercial updraft gasifier to several critical feedstock quality attributes like moisture, ash, and particles size. The specific case study is a 7 MW thermal gasifier at the University of British Columbia that supplies process steam to campus facilities. The wood fuel is collected from a large number of urban waste wood sources, sorted, and blended in a recycling yard (depot) prior to delivery to the gasification plant. Several improvements in particle size uniformity, reduction in wood contamination with dirt, and dryness of the feedstock were made within a two-year period of recorded data (2013-2014). As a result, the overall percent of operating hours of the gasification plant increased from 75% to 94% while the average steam production increased by 30%. Most of the earlier variability in fuel properties was traced to the blending of dry fuel chips at a moisture content of 17% wet basis with a high moisture green wood at a moisture content of 40% wet basis.