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Fast-approaching targets push RDF to the fore

31 January 2012

Deadlines for reducing the levels of waste sent to landfill are fast-approaching.

The time is therefore ripe for the UK to take positive action with alternative fuel production. It is tempting during a period of continued economic difficulty to ignore EU landfill diversion initiatives whilst the country regains stability.

But whether or not individual businesses feel ready and able to exercise their corporate social responsibility and reduce their environmental impact, the unprecedented pressures on our industry – and the Government – to find alternative solutions for utilising waste, are not about to disappear.

It is now well over a decade since the EU Landfill Directive brought in tough new requirements for the UK to cut landfill volumes, or face hefty fines. Driven by the need to minimise landscape blight and the pollution of surface water, soil and air, the directive set mandatory targets for the UK to reduce the amount of biodegradable municipal waste being sent to landfill to 35% of 1995 levels, by 2020.

The Climate Change Act’s legally binding target, as I understand, also requires us to reduce UK CO2 emissions by at least 26% by 2020, and greenhouse gas emissions by at least 80% by 2050. When you consider that the UK has additionally signed up to the EU Renewable Energy Directive, which means we’re aiming for 15% of energy from renewables by 2020, there’s a lot to tackle.

But due to the UK’s attitude to the production of alternative fuels using mechanical biological treatment, things are getting quite exciting. Take Refuse Derived Fuel for example – advanced RDF processing methods, which shred and dehydrate municipal waste to produce a combustible pellet, are without doubt the way forward. By first recovering recyclable materials, extracting and cleaning heavy metals and removing organics for composting along the way, a product is created that can be burned for energy, instead of fossil fuels.

Due to the shredding technology now available to us in the UK, waste can pass through a rigorous size reduction process to ensure a homogenous material in terms of size and calorific value that releases a uniform quantity of heat, specific to the requirements of the end user.

For example, MSW with a bulk density of 250 – 400kg/m³ and up to 60 % moisture, can be fed mechanically into a pre-shredder. Better quality pre-shredders are designed to handle different types of waste and detect foreign objects, without incurring any damage to the machine and its cutters. At this stage it is possible to achieve a particle size suitable for a fluidised bed combustion plant such as a power station.

However for modern SRF-type fuels, further treatment is required to remove metals, organics and aggregates prior to secondary shredding. This can be done using ferrous separation and aggregate and organic screening. Revenue can be generated in normal waste recycling streams from salvaged materials such as aluminium and brass.

A windshifter – high pressure jet of air – then pushes lighter fractions onto an exit conveyor, whilst heavier residual items such as bricks or stones fall out. This light fraction residual can then be shredded using a sophisticated secondary shredder to produce a <30mm product which is metal and aggregate free, and meets the calorific requirements of 17-22Mj/kg.

Because incineration is involved, many people would choose to avoid this method of alternative fuel production. But modern technology actually results in a very clean, scientific and recycling-friendly approach, and once burnt for energy, the waste used to make RDF can be counted towards landfill diversion targets.

Quite rightly, the Government’s 2011 waste review highlighted ‘prevention’ as the priority within the UK’s waste hierarchy. But for as long as we continue to fill our black bags with household ‘rubbish’ – and whilst we carry on using fossil fuels – we must look at smarter ways to utilise our waste.

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