Biomass offers intergrated solutions in Australia
by the CADDET Australian National Team

In Australia, biomass promises to play a major role, not only in meeting the federal governments new requirements on power generation from renewable sources, but also in solving other important environmental and waste-disposal problems.

This deposit of sawmillwaste is a potential source for electricity generation

Introduction

The Australian government is introducing programmes which will require the electricity industry to achieve a significant increase in the contribution of renewable energy generators. It is expected that an increase of at least 900 GWh/year will be required.

It seems likely that biomass generation will make an important contribution to this increase. Apar t from large-scale hydro power, biomass is the largest source of renewable energy used in Australia at the moment. Electricity generated from the very large quantities of cheap waste materials in the agricultural and forestry sectors could provide a dual answer to the need for more electricity from renewable sources, and the chronic problem of how to dispose of unwanted residue.

Sugar Waste

Currently, the dominant fuel in the Australian biomass industry is bagasse, the fibrous waste left over from crushing sugar cane. Bagasse has always been used as boiler fuel to provide process heat and motive power in sugar mills. About 60 years ago mills also started to generate electricity, mainly for their own needs. Bagasse currently fires 14% of Australias cogeneration capacity, with 302.8 MWe  installed.

Until recently, very little of the surplus electricity p roduced in the sugar mills was exported to the grid. Howeve r, in the last two ye a rs, sugar mills in New South Wales (NSW) have taken advantage of Australias Green Power scheme, and the premium price that customers pay for renewable energy through electricity retailers. Recent upgrades at the Broad water and Harwood mills in northern NSW have incorporated greater generating capacity into the plants, with Broadwater exporting about 3 MW in to the grid. Broadwater has plans to expand its capacity to 30 MW.

Other Australian sugar mills are investing in a move into electricity generation for a retail market. The Rocky Point sugar mill in southern Queensland has received a grant under the Australian Greenhouse Offices Showcase programme to upgrade its plant to a capacity of 30 MW and to export the bulk of this electrcity to the grid. The upgrade, estimated to cost $35 million (where $ is the Australian dollar), will include new boiler and turbo-generator technology and more energy- efficient processing equipment to maximise electricity production.

To supply electricity on this scale ye a r- round, the Ro cky Point mill will have to use fuel sources other than just bagasse. As a by-product of the sugar production cycle, bagasse is produced in huge quantities - about 10 million tonnes each year - but is available for only six months of the year. Waste fuels such as municipal green waste , macadamia nut shells and timber residues from sawmills are being considered to augment the fuel supply.

A new technology is also being developed by the University of Southern Queensland that would collect the leaves of sugar cane, which are currently either burnt before harvest in cooler areas or returned to the soil as organic matter in hotter climates. Research by the Sugar Research Institute in Mackay, Queensland, indicates that 80% of the residual field biomass could be recovered by technologies such as this one, which could more than double the cogeneration potential of the existing cane crop.

Estimates made by the Sugar Research Institute suggest that there is enough waste bagasse current ly produced in Australia to provide fuel for an additional 3,000 MW. What is needed to ta ke advantage of this fuel is significant investment in plant equipped to generate electricity on this scale. At the moment, the purchase price for electricity is too low to support the significant plant upgrades in existing sugar mills that would be necessary to generate 3,000 MW. The new renewable energy measures introduced by the government will drive up the purchase price for electricity from renewables and so the economics of investing in technology upgrades will be more attract i ve .

Wood waste

Significant research has been carried out into gasification techniques for wood waste. A research team led by Dr Paul Fung has been developing a wood gasifier with a new gas microturbine developed in the USA. This gasifier with microturbine technology is being developed in units ranging in size from 30-200 kW, suitable for areas where wood waste is plentiful, cheap and located close to the plant. As with electricity produced in the sugar industry, the greatest benefit would be gained from cogeneration plants in industries that can use process heat, such as dairies, food processing plants and abattoirs.

There are already some plants in Australia using wood waste and existing technology. A timber kiln at Kempsey in NSW has used wood waste for about 15 years to generate electricity and process heat for kiln drying. Bega Cheese in southern NSW fires a 12 MW th boiler on sawdust from Orbost in Victoria, to produce electricity and process heat. The wood waste for these plants is left over from milling timber for building products, where as much as 65% of sawn logs is waste, presenting a huge waste disposal problem.

Another source of timber waste is the residue from farmed or plantation forestry. Although th e re are at present, very few short rotation forestry crops being grown in Australia specifically for electricity generation, there is a large quantity of wood waste, as thinnings from managed commercial plantations, that is best used as fuel. The quantity of woodwaste from this source is set to rise, since a programme to triple the national plantation area by 2010 has been in place since 1996.

Wood-coal co-firing

Using all of this waste for electricity generation will require additional infrastructure, in the form of either smaller embedded cogeneration plants linked to the grid, or other larger plants. One option - co-firing wood waste with coal - has the advantage of using existing infrastructure. In a recent successful pilot project in NSW, by Macquarie Generation, waste from native cypress pine forests, harvested for building material, was co-fired with coal at Liddell power station. The pilot project has resulted in on-going generation using wood waste. Waste will provide about 5% of the fuel mix for the steam boiler plant, producing an estimated 100 GWh/year of electricity.

New synergy

All of these current uses of biomass are based on the principle of getting something of value from something that would otherwise be wasted. But a new way of exploiting the synergy of fered by biomass - between meeting energy demands and providing solutions to other environmental problems - has emerged in Western Australia.

A consortium including Western Power Corporation recently won a grant under the federal government's Renewable Energy Commercialisation Program to further develop technologies to turn mallee into eucalyptus oil, activated carbon and electricity.

Mallee is a short, robust type of eucalypt, native to many parts of Australia. It has been cleared from much of the area where it formerly grew, to make way for agriculture, but is now being re-established to regenerate farming land. Mallee can be coppiced regularly and could, therefore, provide a cost-effective source of biomass.

The demonstration plant will use mallee as a feedstock for producing eucalyptus oil and activated carbon, and for generating electricity in a 1 MW plant. It is hoped that the project will succeed to the point where farmers are encouraged to increase their mallee plantations for sale as fuel. It is also an encouraging sign that projects are emerging where innovative combinations of products and markets are being grouped to provide a number of benefits.

For more information contact the CADDET Australian National Team in Moonah, Tasmania.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.