Abstract
Biomass cogeneration plants in wood industry are usually designed to cover large share of site heat demand. However, plant capability to cover peak load in winter could lead to low utilisation of installed capacities at sites whit high seasonal heat demand fluctuations. At some sites, where income of sold electricity is essential for plant investment payback, non-cogeneration operation mode is applied and evacuation of surplus heat through air cooled heat exchangers is usual practice. Price increase of wood chips, as a consequence of increased demand, accompanied by implementation of sustainability criteria for biomass utilisation forced plant owners to reconsider existing business model and to find more efficient ways of biomass utilisation.
Based on analysis of operational pattern of existing 1 MW organic Rankine cycle plant in wood pellets processing industry in Croatia, configuration and parameters of an additional low temperature organic Rankine cycle have been investigated in order to find technically and economically optimal configuration. Taking into account time dependant variation of surplus heat of the high temperature cycle in the range of 1 to 3 MW and variation of ambient temperature, net output power of the low temperature cycle has been optimised. Off-design and part-load operating conditions have been also considered and results of analyses have been presented.
