Heat and power production from straw (Produktion af kraftvarme fra halm)

Straw from grain can be used as energy source in heat and power production.

Process description

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 collection and treatment

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). 

Technical scope

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.

Representativity

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.

Validation

Data on emissions to are validated (Gasteknisk Center, 2003). Other data are not.

Inputs and outputs

Inputs and outputs associated with heat and power production from straw (10-20% water content) Data are provided per ton of straw applied.

		Unit	Quantity
Inputs	Straw	t	1.0
	Water	liter	75
	Diesel oil	liter	0.18
	Heat (own prod.)	MJ	40
	Electricity (own prod.)	kWh	110
Outputs	Products
	Electricity	kWh	850
	heat	GJ	8.7
	Air emissions
	CO2 (fossil)	g	687
	SO2	g	680
	NOx	g	1900
	CO	g	910
	HCl	g	670
	N2O	g	20
	Dioxin	ug	0.32
	Slag and ashes
	Fly ash (deposit)	kg	8.3
	Slag (return to farmland)1)	kg	54

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).

References

Energistatistik (2002): Energistyrelsen.

Gasteknisk Center (2003): "Miljøforhold kortlagt decentral fraftvarme". Nyhedsbrev fra Dansk Gasteknisk Center (August).

Masnedø Kraftvarmeværk, Green account 2002 (in Danish).

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. 

Administrative information

Data URL: http://www.lcafood.dk/processes/energyconversion/heatandpowerfromstraw.htm
Version no.: 1.00
Author: Per H. Nielsen, The Institute for Product Development
Data entry: Data have been entered in this format by Per H. Nielsen.
Data completed: February 2004.