Towards Net Zero: Feedstock Analysis for Regional Bioenergy & Biochar Planning
Early in October I gave a presentation to the Towards Net Zero: On-Farm Renewables & Biochar Forum in Manjimup, Western Australia. The presentation focused on using land use data for planning regional bioenergy and biochar production from pyrolysis and addressed both supply side (feedstock) analysis and demand side analysis. This article provides a case study on using land use data in feedstock analysis and estimating associated bioenergy and biochar production from pyrolysis associated with prefeasibility planning of multiple regional pyrolysis facilities. It will be of interest to those involved with resource recovery planning, bioenergy and biochar planning, facility planning, regional development and climate change adaptation.
Towards Net Zero: The role of bioenergy, pyrolysis and biochar
Achieving net-zero emissions is a critical goal to combat climate change and limit global warming. Net Zero means that the amount of greenhouse gases (GHGs) emitted into the atmosphere is balanced by the amount removed or offset. Achieving Net Zero will require a range of actions. Those actions which bioenergy and biochar directly relate to include:
Transitioning to renewable energy e.g. bioenergy.
Reducing GHG emissions from waste and management practices e.g. avoid burning of plantation forestry residues, crop stubble and other wastes.
Carbon capture and storage (CCS) e.g. biochar.
Bioenergy is obtained through the processing of biomass, which is material derived from previously living things. Anaerobic digestion (AD) and pyrolysis (PY) are increasingly being developed to generate bioenergy using a range of biomass feedstocks including plantation forestry and cropping residues and wastewater sludge/biosolids.
Figure 1 - Pyrolysis of biomass produces renewable bioenergy and biochar.
Pyrolysis (figure 1) involves burning biomass in a low oxygen environment, generally at temperatures of between 300 to 800 degrees Celsius. Pyrolysis can generate heat energy, syngas, biodiesel, biochar and wood vinegar as its primary outputs. The heat or thermal (th) energy can be used for functions such as heating liquids e.g. water and air and generating steam to run turbines to produce electricity (e). The syngas and biodiesel can also be burnt to produce energy.
Figure 2 - The Renergi pyrolysis facility is co-located at the Collie landfill facility in Western Australia and is expected to be able to process 8,000 tonnes of forestry waste per year once commissioned.
The most common form of industrial pyrolysis is undertaken using lignocellulosic biomass in the form of things such as woody plantation forestry residues and cropping residues e.g. straw. Increasingly wastewater solids are being viewed as a resource for pyrolysis, however the type of pyrolysis used is usually different to that used for lignocellulosic biomass.
Biochar or charcoal is a form of resistant carbon which is recognised by the IPCC as a Negative Emission Technology (NET) providing an approved carbon capture and storage mechanism. This is because emissions are avoided by converting biomass to a resistant form of carbon which can last in the soil for many hundreds and potentially over a thousand years. For these reasons one tonne of biochar has a much higher value than one tonne of biomass sequestered in a tree.
Indirectly, biochar can be used to reduce emissions through use in a range of management practices. For example, it can improve soil fertility thereby mitigating the need to use chemical fertilisers which can require large amounts of energy to produce and distribute and which can emit nitrous oxide (NOx), a GHG almost 300 times more potent than CO2.
Why use land use data for resource recovery planning?
Land use data* (figure 3) provides insights into how land and associated resources are used and managed. Analysis of land use data can provide insights into things such as:
- Sources and volumes of feedstock for use in processing or resource recovery facilities i.e. supply side analysis.
- Potential locations for processing facilities.
- Potential uses and users of products supplied from processing facilities i.e. demand side analysis.
*Land use data is mapped Nationally by individual States. See this blog article providing more information about Australia’s land use mapping system.
Figure 3 - Land use across Australia is mapped at scales suitable for regional and sub-regional resource recovery planning.
The analysis of feedstock sources and associated outputs, facility siting options and demand for outputs are critical elements of resource recovery planning. The analysis can be used for a range of planning applications (figure 4) including developing the conceptual business case, scoping, prefeasibility and feasibility planning and associated scenario modelling (optioneering) and multi-criteria analysis.
Figure 4 - Example of infrastructure planning process (Source AusIMM)
Feedstock analysis
Most areas contain multiple feedstocks which can be used to generate bioenergy and biochar. These range from lignocellulosic material (e.g. wood, straw residues) to wastewater sludge. Collectively these are called biomass.
Spatial analysis of land use can be used to identify both point and diffuse sources of biomass. Point sources include municipal wastewater treatment plants, abattoirs, dairies, piggeries, breweries, feedlots’ landfills and so forth. There are around 20 point sources mapped in the Australian land use mapping system. Diffuse sources are many and range from plantation forestry (thinnings and harvest residues) and cropping (residues i.e. straw) in agricultural areas to tree and lawn clippings in urban areas. We have identified almost 50 diffuse land use sources. In this case study (figure 5) we used 15 which were summarised into two biomass categories: wood and straw. For each of these, sustainable yield estimates* were calculated.
**Not all crop residues are available for removal. A proportion must be left behind to provide soil cover to retain soil water, reduce erosion, maintain soil carbon levels or provide a source of animal feed (See Bulletin 4862 - Biomass scoping study - Opportunities for agriculture in Western Australia).
Figure 5 - Analysis of plantation forestry and cropping land use within 20km of potential facility location.
Biomass yield estimates can be readily applied to many diffuse sources using existing national datasets, such as those available from ARENA and other National and State agencies. This is generally suitable for regional and sub-regional scale pre-feasibility planning. Figure 6 provides a summary of the thermal energy generated by facility location and biomass source and the tonnes of biochar carbon able to be sequestered.
Figure 6 - Analysis of estimated bioenergy production (thermal) and biochar carbon sequestered by facility.
Demand analysis
Demand analysis for bioenergy and biochar will inform facility size and location. Figure 7 shows that the amount of electricity potentially able to be produced from pyrolysis of lignocellulosic biomass (wood and straw) could exceed existing demand from households in the towns analysed. Demand scenarios can also be undertaken to identify potential uses and demand for the biochar and associated compound fertilisers.
Figure 7 - Supply of bioenergy and biochar could potentially exceed demand for the facility catchments assessed.
Results
The prefeasibility study analysed a scenario where pyrolysis facilities were proposed in various regional locations. Lignocellulosic biomass within 20 kilometres of each of the 5 facility locations was assessed using land use and other data with the results for 5 presented in this article. The prefeasibility analysis indicated that for the locations and the scenario assessed:
The area of plantation forestry and cropping land use in the 20km catchments of the 5 locations was about 86,000 hectares. The sustainable yield of lignocellulosic biomass (wood/straw) from the land uses evaluated could generate sufficient bioenergy (electricity) via pyrolysis to meet the needs of the number of households located in each location (i.e. town).
A product of the pyrolysis process is biochar. The amount of biochar produced could be in the order 33,500 tonnes. This would sequester the same amount of carbon as about 5,500 hectares of trees.
The biochar could be sufficient to fertilise about 335,000 hectares of cropping or grazing land. Alternatively it could be used as a fertiliser and soil conditioner for forestry plantations, environmental plantations, urban greening initiatives, rehabilitation of civil works and mining, water management, restoration of degraded or contaminated land etc.
This scenario did not assess the avoided costs associated with burning plantation wood waste e.g. thinnings or burning crop residues or replacing nitrous oxide emitting chemical fertilisers with bio-based fertilisers such as biochar. Nor did it consider other benefits such as increased local jobs and business development.
Many other scenarios could be modelled. Another common scenario which could be considered includes the use of anaerobic digestions (AD) to process wastewater and other biomass to generate bioenergy as well as bio-based fertilisers and soil conditioners.
Conclusions
Land use and other spatial data provides insights into what is normally out of sight. It is available for most areas of Australia at a scale sufficient for regional and sub-regional scale planning. It can be used for a range of planning projects including net zero and carbon planning projects associated with:
Regional development.
Local government land use planning.
Renewable energy facilities planning.
Resource recovery planning.
Regional through to precinct scale planning.
The data can also be mashed with other datasets to pin point problems and opportunities and easily modelled to evaluate scenarios and options to ensure rigorous and informed decision making.
