Straw from grain can be used as energy source in heat and power production.
The present data refer to heat and power production at Masnedø heat and power plant (Denmark) in 1999. The plant is dimensioned to 10 MW electricity and 23 MJ heat/sec and is primarily fired with straw (about 40.000 t/year). The main production processes are following: 1) straw bales (about 0.5 t each, 10-20% water content) are delivered to the plant in trucks and stored (capacity 1000 t) 2) straw is transported by a crane and conveyor lines to two vertical "snails" where the straw is cut into pieces 3) the loose straw is transported to the fire chamber through an air tight channel and burnt 4) heat from the fire is used to produce steam which is used to produce electricity in a turbine, 5) steam is condensed and returned to the furnace, 6) condensation heat is transferred to a heat accumulation tank 7) heat is distributed to district heating network when needed. The plant is equipped with electrical filter for reduction of fly ash emission but no SOx and NOx filtration system has been implemented. Slag is returned to agricultural land and used as fertilizer (nutrient content, see below). Fly ash is deposited (due to a high content of heavy metals). The plant's production is determined by heat demand. Production is determined by heat demand.
Data on straw, water and oil consumption and data on heat/electricity production and slag/ash generation have been derived from Masnedø heat and power plant's green account 2002. Data are derived from 1999 where input from other biomass than straw was relatively low (10% in terms of mass). As an approximation, all biomass entering the plant has been considered as straw. Data on emissions to air have been determined from emission factors (Energistatistik, 2002 and Gasteknisk Center, 2003).
All processes related to heat and power production (including administration and local wastewater treatment) are included. Use and disposal of chemicals has not been included. Inputs and output of seawater (for cooling purposes) has not been considered. Solid waste generation (except slag and ash generation) has been ignored. Emissions of VOC and heavy metals to air have been ignored due to lack of data. The plant is established in 1996 and represents modern technology.
All straw used for heat and power production was fired at de-central plants like Masnedø in 1999. However, central units are currently being installed and an increasing ratio of straw is fired in central plants (about one forth in 2004).
Masnedø heat an power plant is a medium sized de-central plant which provides a reasonable representation straw/biomass fires plants in Denmark. Central plants are installed with desulfurication and denoxification units and the emissions of SOx and NOx per produced units of heat and power are supposedly somewhat lower at these types of plants (no data available at the moment).
Data on air emissions are derived from a broad spectrum of plants in Denmark (Gasteknisk Center, 2003) and are representative for production in Demark at decentral plants.
Data on emissions to are validated (Gasteknisk Center, 2003). Other data are not.
1) Phosphor (P): 0.8 -2.1% (w/w), sulphur (S): 0.1 - 0.7% (w/w) calcium (Ca): 6-13% (w/w) nitrogen: 0.05 - 0.08 (w/w). Videncenter for halm og flisfyring (1999).
Energistatistik (2002): Energistyrelsen.
Videncenter for halm og flisfyring (1999): Halmasker, kemisk sammensætning (videblad nr. 146).
Videncenter for halm og flisfyring (1998): Halm til energiformål - Teknik, miljø og økonomi.
Data URL: http://www.lcafood.dk/processes/energyconversion/heatandpowerfromstraw.htm