Using non-recyclable waste as an energy source is one highly effective way of reducing the amount of waste that goes to landfill. Known as refuse derived fuel (RDF) or solid recovered fuel (SRF), residual waste is first processed; in some cases dried down to suitable moisture content for optimum outcomes; and then transported to energy from waste plants, pyrolysis plants and cement kilns.

The purpose of this article is to set out the key arguments that support drying and conditioning SRF, but first, we set out the definitions of ‘RDF’ and ‘SRF’.

RDF is a non-defined term which refers to waste that hasn’t undergone the proper processing associated with SRF. RDF is produced from domestic and commercial waste which includes biodegradable material and plastics. Non-combustible materials such as glass and metals are removed during the sorting process, and the residual material is then shredded into more homogenous particle size.

Typically, RDF is used to generate energy at recovery facilities where they produce electricity and hot water for communal heating systems.

SRF is a high-quality fossil fuel alternative produced mainly from non-hazardous commercial waste including paper, card, wood, textiles and plastic. SRF is a higher grade material than RDF since it has gone through additional processing to improve the quality and value of the fuel. Typically, SRF has a higher calorific value than RDF and is used in waste to energy plants, pyrolysis plants and cement kilns, to name a few. SRF is sampled and tested according to EU standards and produced under the regime of a quality assurance scheme of the producer.

Drying SRF and RDF, can, in the right circumstances where a residual heat source is available, lead to significant financial and environmental benefits. Lowering the moisture content of SRF reduces overall emissions with lower transport frequency and cost, easier handling and cleaner burning. The photo below shows a Stronga SRF dryer.

Production of SRF always goes hand-in-hand with recycling. Only the materials that cannot be recovered for recycling are fit to be used for SRF production, and because SRF production is complementary to recycling, the optimisation of recycling will therefore leave less material available SRF production.

However, full recycling of many waste streams is simply impossible due to the wide range of fractions present in the material. Optimised sorting facilities can recover up to 75% of the input waste steam, therefore leaving around 25% space for SRF production. By utilising a large percentage of MSW, the SRF process greatly reduces the need for landfill capacity while producing a clean, renewable fuel.

1. Provides a carbon-neutral, renewable fuel;
2. Recovers recyclables from the waste stream;
3. Converts RDF to clean-burning syngas using a proven fluidised bed gasification technology;
4. Supplies syngas to various facilities for co-firing with other fuels, such as biomass, or firing on a stand-alone basis;
5. Reduces fuel costs substantially relative to natural gas and syngas produced from coal or biomass, for example;
6. Produces syngas that can also be used as a feedstock for downstream production of chemical products, synthetic natural gas or liquid fuels.

Below is a photo of the world’s first SRF gasification plant - Lahti Energy’s Kymijärvi II power plant.

SRF provides for flexible use of the calorific value in waste.

SRF is stored and shipped as fluff or pellets and then latterly used in places where there is a need for a fuel and heat. SRF is used in various combustion processes that are designed to generate heat and/or power. As an example, the combined combustion of SRF together with biomass provides a great heat and power option for district heating and CHP plants. The efficiency of such processes is high, and while energy is needed to transform waste into SRF, the overall balance is still positive, ensuring SRF takes its place as a valuable fuel source.

By eliminating a huge percentage of waste going to landfill, SRF’s process greatly reduces landfill emissions of methane, a greenhouse gas 20X more powerful than carbon dioxide, and therefore significantly reduces the need for landfill space which is a finite resource.

SRF’s process captures all recyclable material from the waste stream for re-use. As an example, syngas produced by SRF is renewable and carbon neutral, and when replacing fossil fuels, it greatly reduces emissions of carbon dioxide.

SRF gives businesses access to an energy source at much lower cost than natural gas or syngas produced from other sources, such as coal or wood waste. Moreover, SRF can provide long-term, fixed price contracts, eliminating the price volatility of fossil fuels. Customers gain the benefit of an environmentally sound fuel at reduced cost, with price certainty. The benefits really add up.

In Tallin and the surrounding areas, roughly 220,000 tonnes of Municipal Solid Waste (MSW) are produced every single year. Instead of landfilling the waste, which has huge environmental and economic implications, the city is looking into more sustainable solutions.

The two options available to decision makers are (1) the incineration in a waste to energy plant; and (2) production of SRF to be used in a local cement plant. The latter cement plant option turns out to be more sustainable and financially viable solution, as the table below demonstrates.

Many industry sectors have a major heat or energy demand that can be covered by recycling waste streams. This waste only needs a transformation into a reliable, environmentally safe fuel with known characteristics. That fuel is SRF.

The cement industry is one of the first to fully endorse and utilise the potential of SRF. Cement kilns are currently the main user of it, and the benefits for the industry are twofold. Whereas the energy is recovered at the highest efficiency, inert materials become a substituent of the cement clinker.

SRF varies in moisture depending on a range of factors with the climate, weather and season being the most significant. Clearly, waste collected in a wet city like Bergen, Norway will have higher average moisture content than waste collected in most African countries. The moisture content of the SRF fed into the dryer will have a huge impact on drying performance; Stronga can help optimise the SRF dryer for your situation.

Drying SRF to the optimum moisture content is vital because if the material is too wet, let’s say over 40% moisture, the cement works will not accept it and the waste to energy plant will apply a per ton penalty. It is vital to remove moisture in a Stronga SRF dryer to reach the specified moisture content and therefore calorific value determined by the fuel-receiving client.

The photo below shows wet SRF in the FlowDrya infeed hopper, ready to be dried.

Target moisture depends entirely on the client’s fuel specification.

Waste to energy plants often have different pricing structures for high grade fuels so there will be a ‘sweet spot’ for the SRF producers / recycling companies. It is also important to remember that there are gates fees on the incoming material from local waste producers, local authorities etc. FlowDrya assists you to optimise the net price difference between incoming gates fee and the cost to dispose via SRF route (loose bulk or baled).

Clients investing in SRF drying systems from Stronga enjoy the control of consistently dry SRF and RDF waste. Drying SRF using residual heat from CHP, for example, leads to level and stable SRF fuel moisture content and calorific value. Over time, the financial and environmental implications delivering the correct profile SRF fuel really add up.

Stronga SRF drying systems are highly efficient and financially viable when the client has a residual heat source available. The objective of waste management facilities is to increase the calorific value of the SRF and thus to reduce the usage of CO² primary fuels. In addition to increasing calorific value, waste management facilities also benefit from:

• Reduced landfill costs
• Reduced transport costs
• Better control of your costs
• Optimised operational income and profit
• Reduced Energy from Waste (EfW) export costs
• Improved processing productivity (e.g. fuel baling etc.)
• Meeting client’s fuel specification requirements while avoiding penalties

Stronga SRF drying systems operate on a low temperature basis, ensuring safe and efficient drying of SRF with low fire risk compared to other dryers available in the market. Contact Stronga today to discuss the financial and environmental implications for your business, investing in SRF drying solutions.

Email – info@stronga.co.uk
Or call – 01992 519000

The photo below shows Stronga’s continuous SRF drying solutions.