Moisture Effects on An Energy Balance Developed for Using Forest Biomass as a Fuel

Energy associated with removing fuel moisture may be a large energy expenditure when using forest biomass as a fuel. This study analyzes the effects of fuel moisture on a net energy analysis (energy-out to energy-in ratio and percent overall energy balance efficiency) using three scenarios: 1) fuel moisture content (MC), 2) drying efficiency, and 3) drying efficiency coupled with stack gas recovery efficiency. The moisture effects on recovering energy in the form of usable heat, process steam, and electricity were analyzed. When burning wet wood, the energy-out to energy-in ratio and the energy balance efficiency decrease as fuel MC increases, and the out to in ratios are somewhat insensitive to changes in MC at low energy conversion efficiencies. In analyzing drying efficiency, it was assumed that the drying energy was supplied by energy sources other than the wood combustion system. The energy-out to energy-in ratio and energy balance efficiency increase curvilinearly for all energy conversion methods as drying efficiencies increase. The effects of coupling stack gas recovery and drying efficiency produced increases in the energy-out to energy-in ratio and energy balance efficiency over burning wet wood. The increases were more pronounced for high stack gas recovery and drying efficiencies.

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