George Willacy, John Reilly and Giles Perryman examine the benefits of the modular and flexible Refgas advanced gasification system for converting biological waste – in particular wood waste – into energy
RG650 gasifier unit (background) and two generator engines (foreground)
The Refgas advanced gasification system generates renewable energy using waste products as a feedstock. It is able to remain a cost-effective solution due to the low tonnage of feedstock required per unit, its modular design and the easily-controlled processes. In addition, units can be used to target the recovery of specific fractions of waste stream, therefore complementing other waste management options, such as reuse and recycling.
Refgas was established nearly three years ago to develop and produce moderate scale renewable energy facilities. Refgas has developed an advanced gasification 'combined heat and power' (CHP) system to ensure the efficient production of renewable energy. Refgas headquarters and demonstration facility (which utilizes a RG650 unit) are based in north Wales, UK, while the Asia office is based in Western Australia.
Smaller-scale for wider application and reduced carbon emissions
Refgas CHP advanced gasification facilities produce renewable energy from feedstock volumes as low as 5000 tonnes per annum. Using biological feedstocks (e.g. timber and wood waste, refuse derived fuel, compost residues, animal manures, sewage cake, etc.) the system produces renewable energy '24/7' whether the sun is shining, the wind is blowing or the waves are breaking.
Provided the feedstock meets a number of criteria, the material can be processed. The specifications for the feedstock include a particle size less than 100mm, a low moisture content and contamination of non-biological material of less than 30%. Therefore a wide range of feedstocks, some of which are considered waste, can be utilized for energy production. Sources of feedstocks include; sawmills, waste management facilities, alternative waste treatment facilities, waste water treatment plants, or any large scale producer of biological waste.
The relatively small tonnage of feedstock required for the units ensures that the proximity principle is followed – ensuring both transport distances for feedstock and electricity transmission losses are minimized, therefore guaranteeing further environmental benefits and reduced carbon emissions.
Modular and flexible design
Refgas produces two sizes of unit. Ideal for specialist applications, the RG650 unit requires approximately 5000 tonnes per annum of feedstock to produce 1 MW of CHP (approximately 0.65 MW of electricity), while the larger RG2000 requires 15,000–20,000 tonnes per annum to produce 4 MW of CHP (approximately 2 MW of electricity). Both units are modular and can be 'multiplied up' for greater power production.
The RG650 has been designed so that each unit is housed within three standard shipping containers which allows for simple transport, establishment and, if required, relocation of the unit to an alternative site in the future. Typically, the smaller RG650 unit has uses for smaller, remote or island communities facing waste and energy generation issues or remote resources activities (e.g. fly-in fly-out mine sites, etc.). The Gasifier produces little noise and the generator engines are contained within sound-reducing containers to reduce the noise to low background levels.
The RG2000 units are designed for applications that require higher energy production or need to process a higher tonnage. Units can be combined within a facility to increase capacity and each unit can be 'tailored' to process different wastes and maximize the efficiency of handling systems and energy production.
The process
The physical characteristics required for the feedstock are:
- a particle size between 50-100 mm; loose shredded material can be processed
- moisture content less than 30%, however wetter feedstocks can be dried using excess heat from the unit to reduce the moisture content
- non-biomass/organic content (e.g. plastics) less than 30%.
Existing Refgas facilities receive feedstocks that have already undergone physical processing (when required) to meet the feedstock specifications.
The advanced gasification process used is a down-draft system – designed for even heat distribution and reduced tar production – which ensures a high quality gas is created along with highly efficient energy production. The feedstock is heated to 1000°C in a controlled oxygen atmosphere, giving off syngas (which is drawn off). There are no other emissions from the Gasifier, other than the syngas for the energy generation and ash/char, there is no stack or chimney.
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| Feedstock examples: 1. Loose RDF | 2. Baled RDF |
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| 3. Shredded waste wood | 4. 'Dirty' wood waste |
Thermal refuse derived fuel (RDF) gasification is very different from incineration technology. The chemical reactions in gasification reduce RDF into simpler molecules, whereas incineration creates more complex substances, including dioxins and furans – these substances are generally destroyed in gasification.
New gas clean-up technology ensures that the gas produced is suitable to be used in an internal combustion engine which generates electricity. The only gaseous emissions are from the generators' exhaust gases and these are much lower than the required European standards. It should be noted that the emissions produced by the combustion of syngas are far less harmful than those produced by other carbon-based fuels, including natural gas, gasoline, diesel oil and coal.
Ash makes up approximately 5%–10% of the feedstock. However, this proportion can increase if the feedstock contains any inert material (e.g. glass, ceramics, metals, gravel, etc.) as inert materials are unaffected by the process. Depending upon the type and quality of the feedstock, the ash can be used as a soil conditioner due to its very high carbon content or can be disposed of to landfill.
The facility utilizes approximately 10% of the energy it produces for its operation and to communicate the systems operational activities back to a central office or to Refgas, so ensuring the smooth, efficient operation of the units. The remaining 90% of energy can be fed into an electric grid to provide revenue, or used internally by an organization that has a demand for the electricity produced.
The next Refgas project is based at a Corus Steel site in the north west of England, and will include five RG2000 units. The facility will have a 20WM CHP capacity (10MW of electricity) and the power will be utilized by the steel works.
Economics
The Refgas units provide a cost-effective solution for the production of renewable energy. The detailed costs and returns for a unit are obviously dependent upon a number of local factors. However, within the economic environment of the UK, a standard RG2000 unit has a payback period of approximately five years. Financial modelling for the Australian market indicates a payback period of seven to 10 years, allowing for borrowings and a return on investment.
Environmental sustainability
The overall benefit of gasification as an advanced technology, is one of increased environmental sustainability which involves a number of issues:
- reliance on renewable energy,
- reducing waste disposal,
- conserving natural resources,
- responsible consumption.
The Refgas advanced gasification units provide a flexible modular approach to the efficient generation of renewable energy by utilizing feedstocks which have previously been considered as waste materials.
George Willacy is managing director at Refgas Ltd, John Reilly is a director at Refgas Australia Ltd and Giles Perryman the business development manager at Refgas Australia.
e-mail: george@refgas-uk.com, reillyjohn@bigpond.com, refgas@askwm.com
Case study: University of East Anglia, UK
After assessing the available systems, the University of East Anglia (UEA) selected Refgas to provide them with a renewable power station that will reduce their carbon emissions by more than a third. UEA had previously constructed a number of low-energy buildings and generates 60% of its own electrical power on-site. This is carried in the most efficient way, by utilizing CHP – heating buildings with the waste heat from the power generation.
The Refgas units will provide electricity and heat to be used on the UEA campus and will utilize locally sourced woodchips as the feedstock, ensuring the production of 100% renewable energy. Equally important, the plant should pay for itself within five years and then provide self-sufficient energy for the University which is not linked to the grid, world energy or carbon prices.The residual ash produced by the Refgas units will be used a fertilizer for the plantations that produce the woodchips.
The UEA facility has already received its first Refgas RG2000 unit, which has been installed and is waiting to be commissioned. This unit will produce 4 MW of CHP (i.e. 2 MW of electricity and 2 MW of heat), while the project has the option to install an additional RG2000 unit at the facility in the future. A BBC news report about the facility can be viewed at our website: www.refgas-uk.com .
'Energy from waste will become increasingly important as we seek to reduce the impact we have on the environment. We can reduce the amount of waste sent to landfill and we can reduce our reliance on fossil fuels for energy,' stated George Willacy, chairman of Refgas.
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