Refuse-derived fuel (RDF) is a type of fuel made from different kinds of waste, such as household trash, industrial waste, or waste from businesses.
The World Business Council for Sustainable Development explains that certain waste and by-products can be used as fuel in cement kilns. These materials replace some traditional fuels like coal, but only if they meet strict requirements. Sometimes, these materials must be processed first to become suitable for use in cement production.
RDF is mostly made up of parts of waste that can burn, such as non-recyclable plastics (excluding PVC), paper, cardboard, labels, and other materials like corrugated cardboard. These materials are separated using methods like screening, air separation, and sorting out metals, glass, stones, and other unwanted materials. They are then cut into small, uniform pieces or pressed into pellets to create a consistent material. This material can be used as a replacement for fossil fuels in places like cement plants, lime plants, coal-fired power plants, or in steel furnaces. If it follows guidelines from CEN/TC 343, it can be called solid recovered fuel (SRF).
Other sources describe the characteristics of these materials:
There is no single, exact way to classify or define these materials. Even government groups have not created clear rules about their type or composition. The first efforts to create standards for these fuels began in Germany (Bundesgütegemeinschaft für Sekundärbrennstoffe) and at the European level (European Recovered Fuel Organisation). These efforts, led mainly by producers of alternative fuels, are correct because only clearly defined standards for the composition of these materials can ensure consistent production and use worldwide.
Early steps in classifying alternative fuels:
Solid recovered fuels are a type of RDF because they are made to meet standards like CEN/343 ANAS. A detailed review now exists about how SRF and RDF are produced, their quality standards, and how they are used for energy recovery, including data on the quality of SRF in Europe.
History
In the 1950s, tires were first used as refuse-derived fuel in the cement industry. In the mid-1980s, the Westphalian cement industry in Germany began using “Brennstoff aus Müll” (BRAM), which means “fuel from waste.”
At that time, reducing costs by replacing fossil fuels was a main goal because the industry faced strong competition. Since the 1980s, the German Cement Works Association (Verein Deutscher Zementwerke e.V. (VDZ, Düsseldorf)) has been recording 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. By 2015, this use had increased to nearly 62%.
Refuse-derived fuels are used in specialized waste-to-energy facilities. These facilities process waste-based fuels with lower energy content of 8–14 MJ/kg and sizes up to 500 mm to produce electricity and thermal energy (heat/steam) for district heating systems or industrial uses.
Processing
Materials like glass and metals are removed during waste processing because they cannot burn. Metals are taken out using magnets, and glass is separated with screening machines. Next, an air knife helps divide lighter materials from heavier ones. Light materials have more energy value and are used to make RDF. Heavier materials are usually sent to landfills. The leftover material can be sold as a mixture or pressed into fuel pellets, bricks, or logs for other uses, either on their own or in recycling processes. RDF or SRF is the burnable part of household and similar waste, created using methods like mechanical sorting or biological drying in mechanical-biological treatment (MBT) plants. During RDF/SRF production in MBT plants, some burnable material is lost as waste, leading to discussions about whether making and using RDF/SRF is more efficient than burning leftover waste directly in incineration plants.
When making RDF pellets from shredded SRF, drying is often needed. Moisture levels must drop below 20% to create strong, energy-rich pellets. Drying RDF requires a lot of energy, so using a low-cost heat source is better.
Producing RDF may involve these steps:
• Breaking open or shredding bags
• Manually sorting to remove non-burnable materials, PVC, or other unwanted items
• Screening by size
• Using magnets to remove metal
• Separating non-metallic metals with eddy current machines
• Using air classifiers to sort by weight
• Shredding into larger pieces
• Separating materials using infrared technology
• Drying
• Pressing into pellets
• Mixing to make the material uniform
End markets
Refuse-derived fuel (RDF) can be used in many ways to create electricity or replace fossil fuels. It can be used with traditional fuels in coal power plants. In Europe, RDF is used in the cement kiln industry, where strict air pollution rules from the Waste Incineration Directive apply. The main challenge for using RDF or solid recovered fuel (SRF) in cement kilns is the total chlorine (Cl) content. On average, commercially produced SRF has a chlorine content of 0.76 percent by weight on a dry basis (± 0.14% w/wd, 95% confidence). RDF can also be used in plasma arc gasification systems and pyrolysis plants. If RDF can be burned cleanly or meets the Kyoto Protocol standards, it may provide funding through the sale of unused carbon credits on the open market via a carbon exchange. However, the use of municipal waste contracts and the reliability of these solutions is still a new concept, so RDF's financial benefits may be uncertain. The European market for RDF production has grown quickly due to the European landfill directive and landfill taxes. RDF exports from the UK to Europe and other regions are expected to reach 3.3 million tonnes in 2015, which is about 500,000 tonnes more than the previous year.
Measurement of RDF and SRF properties: biogenic content
The biomass part of RDF and SRF has a monetary value under several greenhouse gas protocols, such as the European Union Emissions Trading Scheme and the Renewable Obligation Certificate program in the United Kingdom. Biomass is considered carbon-neutral because the carbon dioxide released when it burns is reabsorbed by plants during their growth. The burned biomass part of RDF/SRF is used by stationary combustion operators to lower their reported carbon dioxide emissions.
Several methods have been created by the European CEN 343 working group to measure the biomass part of RDF/SRF. The first two methods (CEN/TS 15440) were the manual sorting method and the selective dissolution method; a comparison of these two methods is available. Another method, which is more costly, uses principles from radiocarbon dating. A technical review (CEN/TR 15591:2007) explaining the carbon-14 method was published in 2007, and a technical standard for the carbon dating method (CEN/TS 15747:2008) was published in 2008. In the United States, a similar carbon-14 method is already included in the standard method ASTM D6866.
Although carbon-14 dating can measure the biomass part of RDF/SRF, it cannot directly measure the biomass's calorific value. Knowing the calorific value is important for green certificate programs like the Renewable Obligation Certificate program. These programs give certificates based on the energy produced from biomass. Several research papers, including one commissioned by the Renewable Energy Association in the UK, have shown how carbon-14 results can be used to calculate biomass calorific value.
Quality assurance of RDF and SRF properties: representative laboratory sub-sampling
There are big challenges in making sure the quality of RDF/RSF is correct, especially in finding out their exact heat-related properties when they burn. This is because RDF/RSF have a mix of different materials, making their composition uneven. New methods help take small samples from a 1 kg sample down to grams or milligrams for testing using tools like bomb calorimetry or TGA. These methods can help get a representative sample, but they are less effective for measuring chlorine levels. New studies show that the theory of sampling might be suggesting more work is needed than is actually required to get a good sample.
Regional use
In 2009, Italy faced a waste management problem in Campania, near Naples. To solve this, the Acerra incineration facility was built for over €350 million. The incinerator burns 600,000 tons of waste each year. The energy produced from the facility is enough to power 200,000 households each year.
The first full-scale waste-to-energy facility in the United States was the Arnold O. Chantland Resource Recovery Plant, built in 1975 in Ames, Iowa. This plant produces RDF, which is sent to a local power plant as additional fuel.
The city of Manchester, in the northwest of England, is working to award a contract for RDF that will be made by proposed mechanical biological treatment facilities as part of a large PFI contract. The Greater Manchester Waste Disposal Authority recently reported that there is strong interest in initial bids for RDF, which is expected to be produced in amounts up to 900,000 tonnes each year.
In spring 2008, Bollnäs Ovanåkers Renhållnings AB (BORAB) in Sweden opened a new waste-to-energy plant. This facility turns municipal solid waste and industrial waste into refuse-derived fuel (RDF). About 70,000 to 80,000 tonnes of RDF are produced each year and used to power the nearby BFB-plant, which provides electricity and district heating to the citizens of Bollnäs.
In late March 2017, Israel opened an RDF plant at the Hiriya Recycling Park. The plant will process about 1,500 tonnes of household waste daily, totaling around 500,000 tonnes of waste each year. It is expected to produce 500 tonnes of RDF daily. The plant is part of Israel’s effort to improve waste management.
In October 2018, the UAE’s Ministry of Climate Change and Environment signed a contract with Emirates RDF (BESIX, Tech Group Eco Single Owner, Griffin Refineries) to build and operate an RDF facility in Umm Al Quwain. The facility will process 1,000 tonnes of household waste daily from Ajman and Umm Al Quwain, serving 550,000 residents. The RDF will be used in cement factories to replace some traditional fuel sources like gas or coal.