In September 2008, when CEO of the Goulburn Valley Regional Waste Management Group (GVRWMG) Nick Nagle contacted Mr Paxton, the founder of biomass generation company Knetic Renewables (KRL), and asked if peach stones could be disposed of in an environmentally acceptable way, the company began to explore the possibility of using peach stones as a renewable energy source.

“There are only two other bioenergy systems using peach stones in the world – one in Turkey and one in Greece – so this is a very exciting project,” says Mr Paxton.

The project

A waste by-product of fruit processing, peach stones have been stockpiled on Victorian farms by the GVRWMG for over five years. The stones will now be used in a fuel blend for the renewable Shepparton Power Plant currently under construction in North Shepparton, Victoria, which is expected to be commissioned in March 2010.

After confirming that the stones could be used as biomass for a gasification plant, KRL established a materials handling facility north of Shepparton where the stones could be processed. This stockpile has been accumulating since November 2008.

Along with the peach stones, the power plant will be fuelled by locally supplied biomass resources such as wood waste from surrounding farming operations.

Project aims

The project has wide-ranging aims, including better waste management, improving the health of the region’s water catchments, providing employment and contributing to economic development in rural areas.

KRL hopes to demonstrate the application of Mobile Distributed Generation (MDG) technology – developed by KRL in Australia – to dispose of biomass waste in an environmentally friendly manner by producing electrical power at the Shepparton site.

The plant will be operated as a combined heat and power plant (CHP), which will benefit local industry operations and demonstrate a high conversion efficiency of biomass into electricity and waste heat.

The technology

The Shepparton Power Plant will use a highly efficient pyrolysis combustion process to generate electricity and heat to achieve efficiency rates of over 67 per cent.

The facility will use a waste heat recovery system, which will be fitted to the electricity generator, to allow the heat to be used for industrial processes.

The power generation plant will consist of a storage silo and material feed system, a gas production unit, gas scrubbing system, one reciprocating engine with electrical alternator rated at 22 kilovolt, and other auxiliary equipment including heat recovery equipment.

The generated electricity will be delivered to the local grid network with the waste heat to be used by local industry.

The plant is expected to generate 1.2 megawatts (MW) of electrical output per hour, and will mitigate CO2 emissions by approximately 9,600 tonnes per year. KRL has said that the biomass resources are such that they could provide 10 MW of electricity generation in the region.

The project also uses proprietary technology related to gas scrubbing to remove tar and contaminants from the synthesis gas. This gas scrubbing system catches the tar for processing and on sale to the veterinary industry.

The pyrolysis process

While the gasification system used in this project is a relatively new concept, the remainder of the equipment selected is well established, a decision which minimises any economic and technical risks associated with this project.

The pyrolysis process to be used at the plant will limit the amount of air, and conversely the amount of oxygen to 30 per cent of the stoichiometric value (the ratio of synthesis gas to air). This incomplete combustion releases a mixture of incompletely oxidised gases known as producer gas or synthesis gas. The producer gas may be used in a boiler, reciprocating engine, or gas turbine.

The process occurs in a closed reactor known as a gasifier at a temperature of 260 degrees Celsius and is completed when the temperature reaches 1,150 degrees Celsius. Depending on the type and source of the biomass, the producer gas may be accompanied by moisture, particulates in the form of fine ash, and tars which must be removed before the producer gas can be used as engine fuel.

The energy required to sustain the reaction is generated by the complete combustion of portions of the biomass fuel fed to the gasifier.

The gasification process coupled with heat recovery uses the energy of a low grade biomass fuel more efficiently than the standard boiler-steam turbine cycle. This is because a standard steam cycle based electric power generation plant only approaches 20–27 per cent efficiency using very low calorie fuels, with the remainder of the energy wasted.

In the steam cycle system approach, higher quality fuels are commonly used and the latent heat from the system is given up to a condenser/cooling tower as waste heat. In a gasification system, the producer gas is used to fuel an engine generator and waste heat from the generator is recovered and used for heating systems.

The CHP system that is being developed for the Shepparton peach site typically operates at around 67 per cent efficiency, depending on size, design, and the application of the system.

The electrical energy derived from the use of producer gas in a reciprocating engine will give an efficiency of around 36 per cent, with another 31 per cent being available as process heat for industrial use. Y

The site

The power plant site is located on property owned by the Goulburn Valley Water Authority in Shepparton, northern Victoria.

Road access to the site is reasonable and would support efficient transportation on site, while local biomass resources have been identified and are adequate for the fuel needs of the power plant.

Additionally, a good grid connection is available with adequate capacity to allow the generation of 1.2 MW of electricity. Construction, energy purchase and supply

Power Systems Australia, based in Campbellfield, Victoria, has been awarded the Engineering, Procurement and Construction contract for the project.

A Power Purchase Agreement with Diamond Energy in St Kilda, Victoria has been established, under which Diamond Energy will purchase all electricity and renewable energy credits for a period of ten years.

Environmental impact

The 1.2 MW power plant will mitigate the equivalent of 9,600 tonnes CO2 electric per year by producing electricity from renewable resources. The thermal efficiency of the power station starts at 36 per cent for electricity production only and rises to 71 per cent when the waste heat is utilised.

The emissions from the engine generator of the system are less than half that of a gas fuelled automotive engine.

Project successes and future outlook

Mr Paxton says “This project has significant Government and private backing.”

He adds that the company has received “tremendous support” from GVRWMG, Shepparton City Council, Goulburn Valley Water Authority, Foott Waste, SPC Ardmona, Dempster Farms and the Victorian Departments of Sustainability and Environment and the Department of Primary Industries.

The company has plans to establish similar projects elsewhere and subject to successful operation of this plant, is looking to develop another ten systems, predominantly in Victoria.

The company has applied for grant support from Sustainability Victoria.