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The World Business Council for Sustainable Development provides a definition:
“Selected waste and by-products with recoverable calorific value can be used as fuels in a cement kiln, replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. Sometimes they can only be used after pre-processing to provide ‘tailor-made’ fuels for the cement process“
RDF consists largely of combustible components of such waste, as non recyclable plastics (not including PVC), paper cardboard, labels, and other corrugated materials. These fractions are separated by different processing steps, such as screening, air classification, ballistic separation, separation of ferrous and non ferrous materials, glass, stones and other foreign materials and shredding into a uniform grain size, or also pelletized in order to produce a homogeneous material which can be used as substitute for fossil fuels in e.g. cement plants, lime plants, coal fired power plants or as reduction agent in steel furnaces. RDF can be also further specified into e.g. tyre derived fuels (TDF) from used tyres, or solid recovered fuels (SRF)
Others describe the properties, such as:
- Secondary fuels
- Substitute fuels
- Solid recovered fuels (SRF)
- “Climafuel®” as trade name from Cemex
- “AF“ as an abbreviation for alternative fuels
- Ultimately most of the designations are only general paraphrases for alternative fuels which are either waste-derived or biomass-derived.
There is no universal exact classification or specification which is used for such materials. Even legislative authorities have not yet established any exact guidelines on the type and composition of alternative fuels. The first approaches towards classification or specification are to be found in the Federal Republic of Germany (Bundesgütegemeinschaft für Sekundärbrennstoffe) as well as at European level (European Recovered Fuel Organisation). These approaches which are initiated primarily by the producers of alternative fuels, follow a correct approach: Only through an exactly defined standardisation in the composition of such materials can both production and utilisation be uniform worldwide.
First approaches towards alternative fuel classification:
Solid recovered fuels are part of RDF in the fact that it is produced to reach a standard such as CEN/343 ANAS. A comprehensive review is now available on SRF / RDF production, quality standards and thermal recovery, including statistics on European SRF quality.
In the fifties of the last century tyres were used for the first time as refuse derived fuel in the cement industry. Continuous use of various waste-derived alternative fuels then followed in the mid-eighties with “Brennstoff aus Müll“ (BRAM) – fuel from waste – in the Westphalian cement industry in Germany.
At that time the thought of cost reduction through replacement of fossil fuels was the priority as considerable competition pressure weighed down on the industry. Since the eighties the German Cement Works Association (Verein Deutscher Zementwerke e.V. (VDZ, Düsseldorf)) has been documenting the use of alternative fuels in the Federal German cement industry. In 1987 less than 5% of fossil fuels were replaced by refuse derived fuels, in 2015 its use increased to almost 62%.
Refuse derived Fuels are used in a wide range of specialized waste to energy facilities, which are using processed refuse derived fuels with lower calorific values of 8-14MJ/kg in grain sizes of up to 500 mm to produce electricity and thermal energy (heat/steam) for district heating systems or industrial uses.
Materials such as glass and metals are removed during the treatment processing since they are non-combustible. The metal is removed using a magnet and the glass using mechanical screening. After that, an air knife is used to separate the light materials from the heavy ones. The light materials have higher calorific value and they create the final RDF. The heavy materials will usually continue to a landfill. The residual material can be sold in its processed form (depending on the process treatment) as a plain mixture or it may be compressed into pellet fuel, bricks or logs and used for other purposes either stand-alone or in a recursive recycling process.
RDF is extracted from municipal solid waste and other waste using a mix of mechanical and/or biological treatment methods.
The production of RDF may involve the following steps:
- Bag splitting/Shredding
- Size screening
- Magnetic separation
- Air classifier (density separation)
- Coarse shredding
- Refining separation by infrared separation
RDF can be used in a variety of ways to produce electricity. It can be used alongside traditional sources of fuel in coal power plants. In Europe RDF can be used in the cement kiln industry, where the strict standards of the Waste Incineration Directive are met. RDF can also be fed into plasma arc gasification modules & pyrolysis plants. Where the RDF is capable of being combusted cleanly or in compliance with the Kyoto Protocol, RDF can provide a funding source where unused carbon credits are sold on the open market via a carbon exchange.[clarification needed] However, the use of municipal waste contracts[clarification needed] and the bankability[jargon] of these solutions is still a relatively new concept, thus RDF's financial advantage may be debatable. The European market for the production of RDF have been grown fast due to e.g. the European landfill directive, or landfill taxes e.g. in UK and Ireland. Refuse derived fuel (RDF) exports from the UK to Europe and beyond are expected to have reached 3.3 million tonnes in 2015, representing a near-500,000 tonnes increase on the previous year.
Measurement of the biomass fraction of RDF and SRF
The biomass fraction of RDF and SRF has a monetary value under multiple greenhouse gas protocols, such as the European Union Emissions Trading Scheme and the Renewable Obligation Certificate program in the United Kingdom. Biomass is considered to be carbon-neutral since the CO2 liberated from the combustion of biomass is recycled in plants. The combusted biomass fraction of RDF/SRF is used by stationary combustion operators to reduce their overall reported CO2 emissions.
Several methods have been developed by the European CEN 343 working group to determine the biomass fraction of RDF/SRF. The initial two methods developed (CEN/TS 15440) were the manual sorting method and the selective dissolution method. Since each method suffered from limitations in properly characterizing the biomass fraction, an alternative method was developed using the principles of radiocarbon dating. A technical review (CEN/TR 15591:2007) outlining the carbon-14 method was published in 2007, and a technical standard of the carbon dating method (CEN/TS 15747:2008) was published in 2008. In the United States, there is already an equivalent carbon-14 method under the standard method ASTM D6866.
Although carbon-14 dating can determine the biomass fraction of RDF/SRF, it cannot determine directly the biomass calorific value. Determining the calorific value is important for green certificate programs such as the Renewable Obligation Certificate program. These programs award certificates based on the energy produced from biomass. Several research papers, including the one commissioned by the Renewable Energy Association in the UK, have been published that demonstrate how the carbon-14 result can be used to calculate the biomass calorific value.
The first full-scale waste-to-energy facility in the US was the Arnold O. Chantland Resource Recovery Plant, built in 1975 located in Ames, Iowa. This plant also produces RDF that is sent to a local power plant for supplemental fuel.
The city of Manchester, in the north west of England, is in the process of awarding a contract for the use of RDF which will be produced by proposed mechanical biological treatment facilities as part of a huge PFI contract. The Greater Manchester Waste Disposal Authority has recently announced there is significant market interest in initial bids for the use of RDF which is projected to be produced in tonnages up to 900,000 tonnes per annum.
During spring 2008 Bollnäs Ovanåkers Renhållnings AB (BORAB) in Sweden, started their new waste-to-energy plant. Municipal solid waste as well as industrial waste is turned into refuse-derived fuel. The 70,000-80,000 tonnes RDF that is produced per annum is used to power the nearby BFB-plant, which provides the citizens of Bollnäs with electricity and district heating.
In late March 2017, Israel launched its own RDF plant at the Hiriya Recycling Park; which daily will intake about 1,500 tonnes of household waste, which will amount to around half a million tonnes of waste each year,with an estimated production of 500 tonnes of RDF daily. The plant is part of Israel's "diligent effort to improve and advance waste management in Israel."
- Cement kiln
- Isle of Wight gasification facility
- Mechanical biological treatment
- Mechanical heat treatment
- CEN/TC 343 - Published standards
- Velis C. et al. (2010) Production and quality assurance of solid recovered fuels using mechanical—biological treatment (MBT) of waste: a comprehensive assessment
- Williams, P. (1998) Waste Treatment and Disposal. John Wiley and Sons, Chichester
- European Committee for Standardization, list of published standards
- Arnold O. Chantland Resource Recovery Plant, www.city.ames.ia.us, Retrieved 29.11.06
- Healthy interest for Manchester waste-derived fuel contract, www.letsrecycle.com, Accessed 20.11.06
- Manchester seeks outlets for refuse-derived fuel, www.letsrecycle.com, Accessed 20.11.06
- BORAB - Waste-to-energy plant, Accessed 03.03.11
- Bioenergitidningen - New waste mill in Bollnäs, Accessed 03.15.11
- Israel Turning Garbage Dump into Energy Resource - Accessed 03.27.17
- Dirk Lechtenberg, Dr. Hansjoerg Diller "Alternative Fuels and Raw Materials Handbook for the cement & Lime Industry