Solid Recovered Fuel

Solid Recovered Fuel (SRF) is a type of Waste Derived Fuel but is distinct from Refuse Derived Fuel (RDF) in that its quality as a fuel is far superior. It is typically used in processes that require a high quality, small particle size, high Calorific Value, low Moisture Content material – such as Cement Kilns and new-generation ATT plants. There is a move in the UK towards the production of pellets from SRF for subsequent use in industrial processes.

Picture of loose SRF, source Geminor all rights reserved

Context

Solid Recovered Fuel (SRF) is a type of Waste Derived Fuel but is distinct from Refuse Derived Fuel (RDF) in that its quality as a fuel is far superior. It is typically used in processes that require a high quality, small particle size, high Calorific Value, low Moisture Content material – such as Cement Kilns and new-generation ATT plants. There is a move in the UK towards the production of pellets from SRF for subsequent use in industrial processes.

Data for Cement Kilns in UK suggests that around 400,000 tonnes of SRF was used as a WDF in 2019 and 2020.

Solid Recovered Fuels are covered by international technical specifications which set, amongst other parameters, the chemical and physical parameters of an SRF . For the purposes of legislation, though, SRF remains a waste (unless stringent End of Waste Criteria can be met) and so users of the fuel have to comply with the IED which has superseded WID.

Composition of Solid Recovered Fuel

The composition of SRF is defined in the international specification set out above, but often an SRF in the UK can be a more refined RDF rather than something that complies entirely with the specification standard. The main chemical parameters that vary between an RDF and SRF are Calorific Value and Moisture Content, and the table below shows a comparison between RDF and SRF based upon a range of specification sheets for illustration.

Measure	Units	RDF	SRF
Net Calorific Value	MJ/kg (as received)	10 - 15	>18.5
Moisture	wt% (dry basis)	<25	<15
Biomass Content	wt% (dry basis)	>65	>65
Ash Content	wt% (dry basis)	<20	<15
Sulphur	wt% (dry basis)	<0.5	<0.5
Nitrogen	wt% (dry basis)	<0.8	<0.8
Lead	mg/kg	<100	<80
Chlorine CI	wt% (dry basis)	<0.1	<0.6
Zinc	wt% (dry basis)
Sodium and Potassium	wt% (dry basis)
Mercury	mg/kg	<1	<0.6
Nickel	mg/kg	<100	<100
Thallium	mg/kg	<10	<10
Ferrous and non-ferrous metals	wt% (dry basis)	<3	<1
Non combustible material	wt% (dry basis)	<10	<5
Glass	wt% (dry basis)	<2	<1
Dust <1mm	wt% (dry basis)	<5	<5
Bulk Density (loose)	kg/m3	100 - 175	185
Particle Size (max dimension)	mm	300	<40

Chlorine is a particular issue due to its tendency to form Hydrochloric Acid in an energy recovery process, which then requires specific abatement/clean-up technologies. With limited such arrangements in Cement Kilns this means that they generally have a lower tolerance for Chlorine closer in spec to an SRF. In addition, the use of any Waste Derived Fuel in Cement Kilns has the potential to impact the final quality of the cement produced, and so the composition is critical in the decision to use it in such an application in terms of the ash content of the SRF fuel.

Background to Export of Refuse Derived Fuel and Solid Recovered Fuel

The movement of WDF from the UK, primarily in the EU, commenced in c.2010 and progressively grew up until around 2016 driven by supply-demand and landfill tax in the UK and the economics and spare capacity of EfW plants in the EU. From around 2017 tonnages for export started to drop, with more pronounced drops from 2018 as the supply-demand patterns changed in the UK, some EU countries started to implement taxation on EfW and the cost and complexities of transportation following Brexit increased. The two charts below show the overall patterns of export and whilst the data clearly shows the drop in RDF tonnage, the tonnage of SRF shows a more stable export position from 2018 of around 400,000 tonnes a year.

CIWM Presidential Report 2018 – RDF Trading in a Modern World	RDF and SRF Export - analysis of EA data by Monksleigh
CIWM Presidential Report (2018) Showing Grow in RDF and SRF Export	Analysis by Monksleigh of RDF and SRF Exports from England from EA Data

Moving Refuse Derived Fuel and Solid Recovered Fuel from the UK abroad requires compliance with the Transfrontier Shipment Regulations (TFS) and in simple terms requires an application for movement to be made to the relevant authorities that requires a number of key measures to be satisfied before this can occur. It also requires the user of the fuel to be classified as an R1 facility.

Annual SRF Export from England

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Month on Month Export

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Year on Year Differences

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Exporters

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Nascent SRF Pellet Market

Increasingly the market is considering further refinement (including reducing moisture and increasing NCV) of SRF to produce a high quality fuel pellet for ease of storage, haulage, and introduction into a Cement Kiln, with some companies seeking to achieve End of Waste Criteria classification that would then enable the material to be used in other applications as a blended substitute for coal. There are three main organisations pursuing this approach in the UK market at the present time, each with a different 'brand name' for their pellet:

N+P (Subcoal®)

N+P have been producing a pellet in their operation in the Netherlands and are in the process of producing their Subcoal® pellets in their first plant in the UK in Teeside, with plans to expand to this at their recently acquired facility at Crayford

Waste Knot (SIRF Pellets)

Waste Knot's SIRF pellet is to be produced in their first plant, which is under construction in Middlesborough

Eco-PowerFuels (Eco Power Pellets)

Eco-PowerFuels have been producing their Eco-Power Pellets in their facility in Humberside and in January 2021 was reported to have signed a contract to supply Tarmac's Tunstead Cement Kiln