When choosing the type of biomass to use as a feedstock for a biogas or bioethanol plant, one of the overriding questions is: What is the most profitable? A new tool developed by Aarhus University, the Knowledge Centre for Agriculture and Agro Business Park will – in a simple way – help you to calculate that. The tool can also be used to analyse various scenarios before carrying out investments or adaptations in existing value chains.

The modelling tool is described and illustrated with a couple of sample cost calculations in a report published by DCA - Danish Centre for Food and Agriculture at Aarhus University.

Owners and potential investors in biogas or bioethanol plants need answers to specific questions: Should you focus on using local resources or should the biomass be imported from outside the local area? Is it actually worth buying biomass from outside the local district? What form should the biomass take for the best economy?

After the actual data for a biogas plant have been entered, the newly developed modelling tool will help you to estimate the economic and environmental costs. The tool has been developed with financial support from Central Denmark Region and can analyse the value of a biomass throughout the processing chain – from harvest in the field to conversion to energy at the power station.

The tool can help optimise the mobilisation of biomass with the minimum of environmental impact and energy loss at a reasonable price and quality.

Two concrete examples

The mathematical model analyses four different factors:

• quantity of available biomass in a given catchment area over time as the basis for supply management

• the logistics of the supply chain from field to power plant

• key parameters as the basis for decision-making on deliveries and price negotiations

• capacity, direct resource consumption of biomass management, environmental impact, etc.

Calculations can be carried out for the five main types of biomass: straw, straw bedding, meadow grass, beets and manure. The model takes into account the factors and costs involved in the various stages of the chain from harvest, transport from the field and storage to any subsequent treatment (e.g. briquetting) and gas yield at the power plant.

In the report, the tool is demonstrated via two concrete cases in the planning stage: Måbjerg Energy Concept and Biocenter Gudenaa where specific costs are entered based on certain assumptions. The numbers in the report are examples of calculations and should not be interpreted as absolute costs.

The Måbjerg example is based on two different scenarios. In one scenario, the straw is transported as big bales from the field, via temporary storage on a farm, to the Måbjerg plant. In the second scenario, the straw is turned into briquettes on decentralised briquetting facilities before being transported to Måbjerg.

Optimised use of biomass

Sensitivity analyses based on the Måbjerg case show that the briquetted straw needs to be transported more than 150 km for it to be become economically attractive to use briquettes instead of big bales when only transportation costs are taken into account. The value of the briquettes is, on the other hand, higher for a biogas plant or ethanol plant than the value of big bales because the briquettes, in contrast to bales, do not require further processing.

- The more energy a product contains the longer it can be transported from an economic point of view. The market is therefore expected to adapt so that wet biomass (slurry) will remain a local resource while moist biomass (e.g. beets or straw bedding) can be transported longer distances. Straw briquettes can potentially be transported the furthest – making them candidates for the national or North European market, according to the report.

- The tool can be used as a pawn to meet the political ambitions for Denmark to become a non-fossil-fuel society by year 2050 by providing important information for investors and insight into the supply of biomass and price negotiations. The model tool can in this way optimise the use of biomass with minimal environmental impact and energy loss at a reasonable price and quality, write the authors of the report.

The report (in Danish) "Modelværktøj – Biomasse fra marken til værket", DCA report no. 50, December 2014 can be downloaded here.

For further information please contact: Senior Researcher Claus Aage Grøn Sørensen, Department of Engineering, e-mail: claus.soerensen@eng.au.dk, telephone: +45 8715 7638, mobile: +45 2282 7547