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Compact for profit

The UK’s energy-from-waste (EfW) infrastructure might be trailing that of the continent, but things are changing.

Stricter landfill legislation is one factor, but we are now seeing better use of waste-derived fuels, as more incinerators and combined heat and power facilities come onstream. Industrial energy users, like the UK cement industry, are also benefiting.

Whether the ultimate destination is the domestic market or continental Europe, refusederived fuel (RDF) and solid recovered fuel (SRF) represent a significant opportunity. Estimates put the UK and Republic of Ireland potential for both types of fuel somewhere in the region of 26 million tonnes a year.

SRF and RDF have different uses. Generally produced from commercial waste, SRF delivers a high-quality alternative to fossil fuel. RDF is made from municipal waste – essentially the residue once all the recyclables have been removed – and consequently has a lower calorific value.

They have similar qualities when it comes to handling, storage and transportation, with shredding and screening required to recover a high-quality fraction.

SRF tends to be less dense because it is shredded down to a smaller fraction. RDF can be wetter because of the nature of the material within it, and is normally in fractions of 300mm or less.

Loose storage and transportation is not practical or financially viable. Compacting the material is essential, but making the right choice of baler to ensure an economic operation can be challenging.

Ideally, you should be looking at a fully automatic baler, with a continuous press feed and a capacity or throughput that is capable of matching your processing needs, which could increase. A typical operation will run 24/7 and expect to process between 15 and 40 tonnes an hour, depending on the loose feed density of the material being baled.

Compaction is a prime consideration. Taking what can be a very loose and friable material and compressing this into dense and uniform bales is important to ensure efficient use of storage and transportation. For this reason, twin-ram machines capable of delivering 150 tonnes press force, and doing this consistently over the life of the machine, are the best option, while for SRF a pre-press may also be required.

Flexibility is another factor. Uniform bales that maximise storage and container transportation are important, but there may also be requirements to change bale sizes and weight to suit clients.

While a good baler needs to be hard-wearing and fit for purpose, the material it handles is extremely abrasive, so liners may be required. The compacted material has a tendency to expand as the bale exits the machine, and the ejection aperture should be designed in a way to hold the material in place until the bale is tied off.

Tying systems are crucial too. Traditionally bales have been tied using steel wire – an expensive consumable and unacceptable for upstream fuel operations – even incurring a premium from EfW plants.

But a number of solutions are now available offering plastic strapping using recycled PET, which is around 40% cheaper than wire and, above all, combustible. If you expect to bale multiple waste streams, a dual tying head should be considered.

Finally a wrapping system using a UV-protected polythene film is needed. As well as ensuring the product is cleaner to store and transport, it will maintain bale integrity and the calorific value of the material while in storage.

Even with the right baler, a number of factors govern production efficiency. Loading and material flowing into the baler will affect bale density and integrity, so operator training is essential.

Materials tend to be dusty, so a sound cleaning regime, plus regular servicing and maintenance, are all vital to minimise downtime and should be factored into operational costs.

Despite the challenges, there is now emerging a far better alignment between the UK’s waste resources and energy policies. Getting the handling and processing issues right will ensure a profitable business for UK waste-derived fuels. 

Mark Smith is technical director at Middleton Engineering

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