Benefits of growing fibre crops for bioenergy
Evaluating the economicsThe agronomics of kenaf have been covered by work carried out in the Ord, Burdekin and Murrumbidgee irrigation areas. What has not been investigated, according to A guide to kenaf production in Queensland [DAF Queensland], is post-farmgate handling and processing of the crop.
To date, there is no commercial processing facility in Australia. This is a major obstacle to industry development.
Feasibility studies need to be carried out to establish:
- markets with firm contracts and product specifications
- cost efficient harvest, handling and transport systems
- returns to primary producers.
While they are relatively new in Australia and local knowledge and experience is limited, kenaf and sunn hemp crops are commercially grown in the United States.
Grown as a rotation crop with sugar, they offer exciting potential to be used as a profitable complementary crop to improve the economic viability of the sugar industry in Australia.
Both summer crops for fibre and winter crops for seed have been grown on the Atherton Tablelands, Mackay and in the Burdekin where commercial yields of up to 15 tonnes/ha have been achieved.
As part of a research project funded by SRDC, Mackay Fibre Producers developed a business case for supplying sunn hemp in a large quantity. The business case examines:
- economics of the production system
- transporting the product
- flow-on benefits
- producing the crop
- handling the crop
- local infrastructure.
Read more about the Mackay pilot plant fibre-to-ethanol tests.
The waste product from production of the stalks is known as black liquor and is usually burned for fuel or chemical recovery or can be converted into fertiliser and feed binder.
Fibre seeds contain about 20% oil, which can be used for cooking and lubricants. The oil can be used in the manufacturing of soap, linoleum, paints and varnishes. Cattle feed in the form of a seed cake can be made from the residue after oil extraction.
Growing and harvesting fibre cropsKenaf, sunn hemp and industrial hemp can produce large amounts of biomass in as little as 60 to 90 days. The stalks are richer in cellulose fibre than wood.
Fibre crops can be grown in rotation with sugar cane, early season vegetables, tobacco and grains. In Australia, they are grown as a soil improvement or green manure cover crop. While kenaf is susceptible to root-knot nematodes, sunn hemp is nematode resistant making it valuable to rotate crops with when nematode counts are high.
They also fix large amounts of nitrogen (excluding industrial hemp), improve soil properties, reduce soil erosion, conserve soil and water, and recycle plant nutrients.
Experience to date has shown they are a relatively easy crops to grow.
The following guides to growing and harvesting kenaf, sunn hemp and industrial hemp have information on all aspects of production:
- A guide to kenaf production in Queensland, by DAF Queensland
- How to grow sunn hemp [PDF]
- Industrial hemp – a new crop for NSW [PDF] by NSW DPI.
Converting fibre crops to ethanolThe QUT Mackay Renewable Biocommodities Pilot Plant, hosted by the Mackay Sugar Racecourse Mill, converts plant material to ethanol, testing which physical and chemical conditions produce the most ethanol for the smallest cost. The pilot plant has tested sunn hemp and kenaf and found that 1 kg of kenaf or sunn hemp can produce about 18,000 kilojoules of energy—this is similar to bagasse. The technology aims to extract all the sugars from the fibres. By breaking down the fibres to release their sugars, then fermenting them, ethanol is produced.
The pilot plant converts biomass to ethanol in 3 main steps:
- treating the biomass with chemicals and steam to make it easier to break down
- using enzymes to make sugar molecules into even smaller ones
- using yeast to ferment the sugar into ethanol.
level 12, 10 Valentine Ave, Parramatta NSW 2150,
83 Castle Street, Dunedin, New Zealand, 9058
Phone: 1 800 751 806
2 George St, Brisbane QLD 4000
Phone: 07 3138 1551, 0437 541 295
Mackay Fibre Producers Group
Phone: 0429 377 162