Four approaches for the year-round operation of wood-fired heating plants with low pollutant emissions

Abstract

Fluctuations in heat demand and low heat demand in summer make it difficult to operate wood boilers all year round at high efficiency and low pollutant emissions. Therefore, today's wood-fired heating plants are often equipped with an auxiliary fossil fuel boiler. This paper investigates technical approaches to operate wood heating plants without additional fossil heat while avoiding unfavorable operation with high pollutant emissions. To evaluate these concepts, the dynamic behavior of wood-fired heating plants is modelled. The model includes one to four wood boilers, an auxiliary fossil fuel boiler, the heat demand, a stratified heat storage tank and the control system. The simulation reveals that the fossil share can be eliminated by large boiler output ranges and the use of several wood boilers in cascade. High storage capacities and large boiler output ranges enable low pollutant emissions and low cool down losses of the wood boilers. By doubling the storage capacity from 30 to 60 min of the nominal boiler output, reductions of the annual emissions of carbon monoxide and particulate matter of 17% and 8% are observed. Mitigating heat demand peaks can reduce pollutant emissions of heating plants with small storage capacity.