Comparison of possible supply chains for forestry derived biomass for bioenergy in New Zealand
In many countries residual woody biomass from forest operations is a significant resource for bioenergy. In New Zealand this is also the case, with forest residue resources up to 4.1 million green tonnes (1.64M odt) per annum, of which only a small proportion is utilized. Lower quality K grade logs that are exported unprocessed are a further significant potential resource with a long run supply of a further 5.4M green tonnes per annum.
Getting this material into the energy market at a cost competitive price will require the refinement of fledgling biomass supply chains. For forestry derived biomass to play a greater role in New Zealand’s drive to a low carbon future the supply chain for this resource must be optimised, with costs being as low as reasonably possible. This report covers analysis of forest residue harvesting systems, including the use of aggregation hubs and the effect of screening, storing and drying on the cost of process heat delivered by a biomass fueled boiler.
The lowest cost fuel and heat energy found in this analysis is that derived from chip logs from a conventional forest via a hub that does chipping, storage and drying ($11.19 per GJ of heat)*. The next lowest cost materials are from residuals produced at landings via a hub that does full processing including hogging ($11.92). Next cheapest is landing residues which are taken direct from forest to heat plant and do not go via a hub ($12.93).
The use of hubs can reduce the cost of fuel and heat. Hubs can provide a place to store and improve fuel quality via a system where the biomass is screened, sized and dried. The value of the use of hubs is affected by the specifics of each resource and the site specifics of the demand being met, including transport distance from where the biomass is produced to where it is finally used.
A suggested system incorporating a hub is one where the material delivered to a hub is subsequently;
- screened to remove fines, dirt and oversize
- stored under cover
- stored on a floor that has passive air inlet pipes
- stored for a period of 2 to 3 months, less being preferable
The cost of operating a hub that includes these features was estimated at around $6.00 per tonne or $0.67 per GJ assuming the material coming out of the site has reached a moisture content of 40% wet basis (8.9 GJ per tonne) over a storage period of 3 months.
Chip logs direct to the user with chipping at the boiler site is the next lowest cost, followed by material derived from a short rotation forest (16-year rotation) with the material going via a hub that includes chipping. This assumes wood with a moisture content of 54% or can be obtained from these logs.
More data is available in the report. All costs results are dependent on the transport distances assumed in the calculations.
* currency in the report is New Zealand dollar (~0.6 USD)