Bagasse and cane trash | Biomass Producer – Bioenergy information for Australia's primary industries

Producing biomass: Biomass types: Crop residue: Bagasse and cane trash

Bagasse is the fibrous residue left over when sugarcane is squeezed for its juice.

Economics and productivity

Australia’s sugar industry has used bagasse to meet its electricity and heat requirements for over 100 years. Today, bagasse is a major contributor in the bioenergy sector – accounting for over 60 per cent of Australia’s dedicated bioenergy capacity (Clean Energy Council). There are projects also working towards using bagasse as a biomass for ethanol production. Local and international feasibility studies are assessing whether incorporating sugarcane trash into both power and ethanol generating system can increase productivity. Australian sugar mills burn bagasse on site to generate heat and electricity.

Bagasse is the fibrous residue left over when sugarcane is squeezed for its juice Credit: Econnect Communication

The amount of electricity generated from bagasse could be greatly increased if sugar mills and associated power plants were modernised into more efficient operations, and if more effort was made to gather all of the cane trash which could be used in electricity generation – currently only 50% of the cane biomass available for use is collected (Clean Energy Council, PDF 73 kB). The dry and green leaves and tops represent about one-third of the total mass for commercial sugarcane. Dry leaf trash has about double the net heat energy of bagasse and about three times that of green leaves and tops. This can be used to generate extra electricity which can be fed back into the grid for a profit. The Clean Energy Council’s fact sheet, Using Bagasse for Bioenergy [PDF, 73 kB], notes a premium can be paid for this surplus electricity because sugar milling seasons often coincide with peak demand loads. An extensive project in Brazil, implemented by the United Nations Development Programme, Biomass power generation: sugarcane bagasse and trash [PDF, 5.2 MB], assessed the feasibility and benefits of harvesting sugarcane trash. A similar project, which looked at the supply chain for the sugarcane industry supply chain for the sugarcane industry was also undertaken in Australia by AgriFutures Australia.

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Benefits

The Clean Energy Council’s fact sheet outlining the benefits of bagasse [PDF, 73 kb] claims that using bagasse to generate heat and electricity at sugar mills offers many unique benefits:

Mills are self sufficient in terms of energy they consume
It removes the need for transporting the bagasse away
Extra electricity produced can be fed back into the grid for a profit
Energy from bagasse generates less greenhouse gas emissions than conventional fossil-fuel generation
If bagasse were left to rot, it would break down and release greenhouse gases, particularly methane, which is 27 times more dangerous to the ozone than carbon dioxide
It plays an important role in helping Australia achieve its Renewable Energy Target

Researchers from the Queensland University of Technology assessed whether using cane trash could potentially provide a new source of revenue for growers [PDF, 256 kB]. They assessed six value-adding products for risk and revenue generation. Low risk/low reward

Generating electricity using bagasse
Harvesting cane tops immediately before the cane harvest for cattle feed
Producing furfural as a commodity chemical from bagasse
Producing ethanol from weak-acid hydrolysis and fermentation of bagasse

Medium risk/ high reward

Biodiesel production form hydrothermal liquidifcation of bagasse
Production of pulp and ligin in a biorefinery using bagasse

The analyses suggested that the medium risk/high reward options were financially viable with internal rates of return in the order of 13-35% from plants producing biodiesel or lignin and pulp from bagasse. Supplementation of the feedstock with trash improved the expected returns.

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Harvesting cane trash

Harvesting and collecting sugarcane trash along with cane is known as whole-of-crop harvesting.Two strategies used for whole-of-crop harvesting are described in Chapter 2 of the Sustainable Biomass Supply Chain for the Mallee Woody Crop Industry report published by AgriFutures Australia, 2012. These are:

Green cane harvest, where all material (cane and trash) is harvested at the same time and transported to the mill
Conventional green cane harvest, where the cane is harvested and then the trash is collected post harvest.

The report claims that by using a ‘chopped cane’ harvester, growers can harvest cane and collect remaining leaf and trash at the same time. The report also claims the challenge for whole-of-crop harvesting is in the logistical problems of harvesting and transporting increased volumes of material.

Sugarcane being harvested Credit: Econnect Communication

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Transporting cane trash

Transport chains are a key link in an agricultural commodity system supply chain and an efficient transport system is critically important for efficient agricultural commodity marketing (Chapter 3, Sustainable Biomass Supply Chain for the Mallee Woody Crop Industry, AgriFutures Australia, 2012).Sugarcane that is harvested in Australia is delivered to mills via road and/or rail. Transport from the siding to the factory by road and/or rail transport (including the cost of railway infrastructure) is 30-40% of the total milling cost.Chapter 3 of AgriFutures Australia’s report on Sustainable Biomass Supply Chain for the Mallee Woody Crop Industry, provides an overview of the transport supply chain for sugar cane and highlights ways that segments can become more efficient.

Sugarcane locomotives Credit: Econnect Communication

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Storing bagasse

Bagasse needs to be properly stored so that it doesn’t rot or spontaneously combust. When bagasse is left to rot, it breaks down and releases greenhouse gases, particularly methane, which is 27 times more dangerous to the ozone than carbon dioxide. Wet cellulose, which is the principal component of bagasse, ignites more easily than dry cellulose. The Queensland University of Technology is leading a project addressing the spontaneous combustion of bagasse, which is a fundamental problem of safely storing bagasse (sugar cane fibre residue) in large stockpiles. Researchers are applying a mathematical model to predict temperature and moisture profiles of large stockpiles. The model will help maximise storage capacity while minimising the risk of spontaneous combustion not only for bagasse but other biomass materials too, including woodchip, grain and composting industries. The Queensland Department of Environment and Heritage Protection provides a guideline for managing impacts from the bulk storage of bagasse [PDF, 158 kB]. The guideline helps with minimising the risk of environmental harm arising from the establishment and management of bagasse storage areas. It provides information about actions that can be taken to minimise the impact of bagasse storages off site and on the surrounding community and environment. Control measures are provided to reduce the risk of the following: