ARF07 - Optimization of switchgrass management for commercial fuel pellet production

| Alternative Renewable Fuels - Project Summaries 2006 |

Researcher:

Roger Samson, Stephanie Bailey Stamler, and Claudia Ho Lem REAP - Canada

Objectives:

To evaluate and optimize switchgrass production to create a new biomass energy resource for the emerging agri-fibre pellet fuel heating industry in Ontario. This will be accomplished through the following project activities:

1. Assessing actual production costs and yields of switchgrass grown on two commercial farms in Ontario. This includes costs associated with actual crop establishment, land rental, maintenance and harvest costs from switchgrass crops grown in two counties in Ontario.
   

2. Evaluation of strategies to reduce the harvest and delivery costs of switchgrass to pellet plants. This includes a field performance assessment of baling and bulk harvesting of switchgrass.
   

3. Assessment of the impacts of fall harvesting regime versus fall cutting and spring baling on yield and chemical composition of switchgrass. This includes assessments in differences in harvested yield, field losses and biomass composition of conventional late-fall harvested switchgrass and fall-cut and swathed material left in windrows over the winter and spring harvested.
   

4. Combustion tests of switchgrass pellets in commercial boilers. This includes a comparative assessment of fall vs. spring harvested switchgrass biomass and its fuel quality and combustion performance in a commercial boiler.

Expected Benefits:

To advance understanding of strategies to optimize switchgrass cultural management and its suitability as fuel for commercial boilers. This will greatly enhance investment decisions by farmers and agribusiness in this emerging new industry.

Summary of Research Results:

This project identified that a late fall mowing of the grass prior to the onset of winter followed by spring baling has considerable promise. The major advantages are:

• provides a higher overall recovery (21%) of biomass than spring mowing and harvesting systems which was attributed to less winter breakage by wind storms and lower machine harvest losses
• ensures harvesting of dry material which is suitable for pelleting without further energy required for drying;
• promotion of earlier soil warming and better field support for farm machinery in
  the spring by promoting earlier drying of the field;
• biomass combustion quality is improved compared to fall harvesting as overwintering grass leached undesirable elements (e.g. potassium was reduced by 70%)

Combustion trials indicated that both late fall and spring harvested material were suitable fuel for use in commercial boilers. Spring harvested switchgrass had less potential to produce fine aerosols because of lower levels of undesirable chemical compounds (eg. K). The energy content of the fall and spring harvested fuels was similar with approximately 18.8GJ/tonne and approximately 4-5% ash. Combustion trials conducted by NRCAN indicated that switchgrass pellets produced from both late fall and spring harvested material were suitable fuel for use in commercial boilers. No major concerns were identified regarding combustion emissions with the switchgrass fuel samples tested in a 1 MW commercial boiler.

The direct switchgrass establishment costs (Year 1) were estimated at approximately $857.36/ha. An assumed 12-month operating loan at 6.0% incurred an additional cost of $51.44/ha for an overall establishment cost of $908.80/ha or $90.88/ha amortized over 10 years. Switchgrass production costs were divided into two categories, crop maintenance, accounting for 56% of the cost and, harvest and delivery representing 44% of the cost (Table 1). A major cost problem identified was that rising land rents in Southern Ontario are causing land rental costs to be an important cost driver in grass pellet fuel production.

Table 1: Estimated annual production and baled harvest costs from Nott Farms (Production Years 2-10)

The use of more marginal farmland, bulk harvesting methods, and production of fuel briquettes were promising means to reduce production costs appreciably. Harvesting costs could be reduced 52% by switching to a bulk harvesting system which costs $9.84/tonne. Briquetting had the potential to reduce densified fuel costs by $25.21-$28.01 tonne through lower processing costs and reduced transport distance to plants. These integrated strategies reduce plant gate costs for densified overwintered switchgrass fuels from $146.75 to approximately $105.53/ODT or $5.61/GJ.