Simulation of a direct combustion biomass power plant

In this paper an existing direct combustion biomass power plant located in Airasca near Turin (Italy) is studied. During the summer the rated output is 14 MWe while in winter the electricity production is reduced because of a steam extraction to generate 6 MWth of hot water for heating a nearby manufacturing plant. The biomass entering the travelling-grate combustor is primarily made of wood chips which are highly heterogeneous; this variability source together with a manual furnace control system causes quite strong fluctuations - about 10% - of steam flow rate and electric power consequently. The objective of this work is to analyse the relation between biomass input and steam generation, with special focus on moisture content and heating value, which are key drivers, unfortunately unknown. The ultimate aim is to try and make the combustion process less variable and therefore its control simpler. The whole plant was modelled with the commercial software GateCycle. The resulting steady state model was firstly used to study the natural evolution of the system when biomass changes occur (in terms of moisture content, density, chemical composition). Afterward, given a certain worsening in biomass quality, the model was employed to predict how the plant is expected to react to control actions intended to bring it back to its previous operating condition. Finally, different strategies were explored on a theoretical level to keep the plant power constant when biomass quality gets worse.