It’s one of the most commonly asked questions posed to the UNTHA team. So, our alternative fuel experts have got their heads together to elaborate on this complex question…

What is RDF?

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 80 and 400mm – 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. We can supply this entire package with UNTHA’s turnkey Alternative Fuel Production (AFP) system.

What is SRF?

Solid Recovered Fuel (SRF) on the other hand, is a much more refined resource, produced to a defined quality specification, usually from C&I waste, or other complex materials such as carpets, pulper ropes, production waste or mattresses. Once the result of a sophisticated pre and post-shredding operation, the UNTHA XR can now produce this on-spec fuel in a single pass. 

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 technology can of course be configured to suit varied end user specifications, but a particle size of less than 30mm,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.

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. 

So, what is the difference between RDF and SRF?

The main difference is how refined and processed the final product is. SRF is a more time consuming process, but the resulting material is very usable as fuel across the rest of industry. RDF on the other hand is less refined and typically not as ‘efficient’ as fuel. Also, due to the separation of recycles generated in SRF another revenue stream can be created. 

For more information on this topic, please visit our dedicated landing page on RDF/SRF manufacturing.