Wood chip drying in connection with combined heat and power or solar energy in Finland

Abstract

Abstract. 20% of the Finnish district heating (DH) power plant fuels are wood-based and the share is increasing. The wood fuel demand probably exceeds the potential supply in the future. The wood fuel drying with waste heat is one profitable opportunity to gain more wood fuel. If the drying energy can be produced with lower primary energy use than combusting the fuel directly, the drying potentially improves the system efficiency. In this study, the drying feasibility in the connection of a combined heat and power (CHP) system, possibly with solar collectors, is calculated. The wood fuel heating can be increased profitably by 6%, using the heat from CHP for drying only when the marginal cost of the heat is low enough, i.e. the electricity price is high enough and there is free capacity after the DH demand. Although the drying is profitable, a larger heat storage can also increase the annual result similarly. The best investment choice depends on the plant properties. Here the optimal system enables 20% DH production cost savings. Solar heat may be profitable, when the solar heat has a 2-3% share of the annual heat demand. However, the dryer or larger storage tank are more profitable investments.

Pre-feasibility study of supply systems based on artificial drying of delimbed stem forest chips

“…The drying unit can be, e.g., of batch or silo type or alternatively a belt dryer (Brammer and Bridgwater 1999). Utilizing low-grade, waste heat -of which large amounts are available from many process industries -could significantly reduce energy consumption and the profitability of artificial drying (Li et al 2011;Holmberg 2007;Rinne et al 2014). In winter, the surface of freshly harvested timber is often icy or snowy, which can raise the moisture content of wood chips significantly.…”

“…In addition, laws mandating the physical dimensions of freight transport vehicles were changed on 1 October 2013 in Finland (Valtioneuvoston asetus 407/2013) and the new legislation enables higher gross weights as well as larger load capacities. It favours increasingly transport of fresh wood material (Laitila et al 2016) and may also increase interest in artificial drying of forest chips in the generation of heat and in combined heat and power production, especially if waste heat streams can be used as a heat source for drying (Holmberg 2007;Rinne et al 2014).…”