|Torrefaction is a process that can be used to convert brown coal, biomass and other organic materials into valuable energy and beneficial products, involving the thermochemical treatment of carbonaceous material at 200°C to 400°C. It is carried out at atmospheric pressure or greater, and in the absence or near absence of oxygen. The process drives off water, releases volatiles and changes the structure of materials so they can be ground, blended and processed to create new value-added products. Torrefaction produces volatile vapours that are burned to create the heat needed to drive the process. For organic materials the final product is a residual solid, dry, blackened material which is commonly referred to as ‘torrefied biomass’ or ‘bio-coal’.|
While torrefaction technology has traditionally been used to process biomass for the creation of wood fuel pellets for use in co-fired power stations, there are other applications and potential markets that involve coal. Brown coal, in particular, is a suitable material for torrefaction because of its moisture content, potential for energy densification and inherent agricultural and soil amendment properties. Accordingly there are torrefaction opportunities such as coal to fertiliser and upgrading brown coal and biomass to form renewable energy Black Coal Equivalent (‘BCE’) fuels.
Coal based carbon fertiliser
The Australian agriculture industry consumes 5–6 million tonnes of chemical fertiliser annually, providing approximately 1 million tonnes of nitrogen (N), half a million tonnes of phosphorous (P) and two hundred thousand tonnes of potassium (K) (reference Fertilizer Australia Inc.). In excess of 50% of N:P:K products are imported. The industry also uses approximately 1 million tonnes of organic based products such as manures and compost.
Growing demand for biological and conservation farming systems is creating opportunities for products that recover and recycle nutrients in sustainable ways, thereby reducing reliance on chemical fertiliser, potentially replacing imported products and mitigating exposure to global supply and demand pricing issues. As a result, research into biological farming practices is on the rise, with a focus on soil health, carbon and food security.
Brown coal and other lignites are rich in humic materials and have potential to create high performance agricultural products, especially when combined with nutrients recovered and recycled from agricultural and bio-based waste streams (e.g. chicken manure and other animal wastes).
Coal based fertilisers are low cost, carbon-based soil enhancement products that can be manufactured by drying and crushing brown coal into fine particles, adding beneficial trace elements, and then granulating the outputs so they can be can be handled and delivered to soil with existing agricultural plant and equipment.
Since the colonisation of Australia, the average organic carbon content in agricultural soils has fallen from 5 per cent down to 0.5 per cent, affecting soil structure and crop productivity. Coal based fertilisers have the potential to build soil carbon through improved nutrient availability, increased plant growth and enhanced photosynthetic activity, leading to healthier soils and higher productivity. Other potential benefits offered by coal based fertilisers include reduced farm input costs and reduced greenhouse gas emissions from the manufacture of chemical fertilisers.
Research into biological farming systems is currently being done by universities throughout Australia, including Victoria. Torreco and Feeco Australia have been working with researchers at Monash University to develop granulated coal based fertilisers, which are currently under evaluation. High quality, dense granules have been produced at laboratory scale by Feeco Australia (refer to Figure 1 and Figure 2), based on the extensive granulation expertise developed by its parent company, Feeco International. Torreco and Feeco Australia have also produced granulated fertilisers based on Victorian brown coal for Australian Carbon Fertilisers, for evaluation in field trials.
|Figure 1: Product development – formation of granules (FEECO Australia).|
|Figure 2: Fertiliser granules suitable for application with standard agricultural delivery systems (FEECO Australia).|
|To date, positive results have been observed with coal based granulated fertiliser and soil amendments, suggesting the potential to achieve comparative yields at reduced input cost. There appear to be opportunities for Australian farmers to achieve competitive yields at a cost advantage over traditional applications of chemical fertiliser, with the potential to contribute to improved food security and sustainable farming practices.|
Feeco International has the technology expertise necessary for a commercial granulated fertiliser factory (see Figure 3). However, further field trials and product validation work is required to justify the investment in such a facility. Unfortunately, the laboratory-scale equipment used to produce granulated coal based fertilisers to date is too small to produce the quantities needed for large-scale field trials.
|Figure 3: The pilot demonstration facility is a precursor to commercial scale fertiliser production plants that can be scaled to produce granulated fertiliser products in volumes ranging between 15,000 and 200,000 tonnes per annum (FEECO International).|
|Feeco International is seeking local support for construction of a world class applied research and product development facility in Victoria, to support the commercial development of granulated fertilisers based on brown coal and other organic inputs. The envisaged industry extension facility would include a torrefaction / granulation pilot demonstration plant capable of manufacturing sufficient volumes of products for in-field trials and validation; this in turn would accelerate the creation of end market demand and help de-risk investment in commercial scale plants. Ancillary capabilities would include engineering plant and process design, customer services and support, access to specialised manufacturing, engineering and construction thereby providing a total ‘end to end’ solution and assistance for research into coal based fertiliser products and their transition from laboratory to market.|
The Latrobe Valley is potentially an ideal location for such a product development facility given the available infrastructure, abundance of coal and other inputs, close proximity to end markets for fertiliser and willingness of local industry to support economic development in the valley and wider Victorian region.
Upgrading brown coal to blended black coal equivalent fuels
Torrefaction can also be used to upgrade blends of brown coal and biomass to form black coal equivalent (BCE) fuels suitable for export (briquettes) and local energy markets.
In this application Torrefaction achieves four basic functions:
- Dewatering and energy densification: output has a higher energy content on a mass basis;
- Materials homogenisation: a wide variety of inputs can be changed to a common known output with little variability;
- Physical transformation: structure of inputs is changed to make them more suitable for granulation and briquetting, while reducing the propensity for spontaneous combustion; and
- Reduction of greenhouse gas emissions.
|Unlocking the value of Victorian brown coal and creating new export markets depends on the ability to densify its energy content, homogenise and physically upgrade the coal in a manner that is financially viable in current and emerging market conditions.|
Torrefaction is an enabling technology that addresses the opportunity to transform both brown coal and biomass into black coal equivalent products that will reduce greenhouse gas emissions and grow the local economy.
The ability to blend coal and biomass creates opportunities for products with a varying range of biomass content and therefore varying greenhouse gas emission profiles, ranging from 100% coal through to 100% biomass, depending on energy requirements and market demand.
Throughout Asia there is growing interest and demand for torrefied biomass fuel pellets and other low emissions fuels. The combination of torrefaction and production of biomass and brown coal based fuels in “transport friendly” form has the potential to add value to Victoria’s brown coal resources and create new products for export markets.
For further information please contact Torreco Pty Ltd by visiting their website www.ideaservices.com.au.