It’s one of the questions we’re most frequently asked by operators new to the Waste to Energy market. So here we attempt to explain, in simplest terms, how RDF and SRF differ.
Refuse Derived Fuel (RDF) is a relatively crude material, produced by shredding pre-sorted municipal solid waste (MSW). Before the MSW can enter the RDF production process, valuable commodities such as paper, metal, glass and wood should have been removed for recycling.
Then, a powerful single shaft shredder with foreign object protection – the UNTHA XR – shreds this pre-sorted material. A uniform particle size can be achieved – typically something between 3 and 16″ – depending on the client’s specific requirements.
Our configurable cutting system also produces a guaranteed particle size in three dimensions rather than just two, which satisfies the evolving requirements of modern WtE plants.
Some RDF manufacturers carry out little further treatment,however the more ‘savvy’ of producers aim to increase their profitability. By investing in additional separation equipment, a more efficient system can be built. This allows recyclates such as metals to be recovered and sold, which generates an additional revenue stream and increases the return on investment from this plant.
Solid Recovered Fuel (SRF)on the other hand, is a much more refined resource, produced to a defined quality specification. Usually manufactured from pre-sorted commercial and industrial (C&I) waste rather than MSW, this material is also pre-shredded with an XR. This produces a coarse fraction with approximately a 0.6-12″ particle size. This size-reduced material prevents blockages and ensures the more effective treatment of the ‘waste’ moving forward.
A number of additional separation technologies then further refine the material stream. For example:
- A series of magnets can extract ferrous metals
- A vibration screen or trommel can sift out soils and fines
- An air separation box (wind shifter) can remove large lumps of materials
- An eddy current separator can extract aluminium that could damage the secondary shredder.
The extra materials that are salvaged as part of this rigorous separation process can be sold for recycling, creating a further revenue stream for the SRF manufacturer and increasing the production margin.
Shredding technology can of course be configured to suit varied end user specifications, but a particle size of less than 1.2″, moisture content of <15% and a calorific value of 18-22MJ/kg appears to be the norm. Following this sophisticated SRF manufacturing process, the end product is a resource from which energy can be harnessed. It is used in cement kilns, paper mills and power stations as an alternative to fossil fuels.