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Plastics: smaller-scale plants are the future

The recent policy emerging from China of rejecting plastic wastes imports has the potential to provide short-term challenges within the UK. We currently export around 500,000 tonnes of plastics each year to China, so alternative arrangements are going to be necessary.

A logical alternative is, in the absence of other markets, to manage this waste through our growing energy-from-waste (EfW) infrastructure.

So for the long-term, the single closed door in China will open others that will provide more long-term opportunities, benefiting the UK, local communities and the environment globally. Simply recovering energy from plastics through combustion is a reasonable short-term option, but there’s the potential to generate a range of products - more valuable than energy alone - which also fits better with the goal of creating a circular economy.

In the UK, the deployment of the next generation of energy from waste technologies has often been discussed, with gasification and pyrolysis often mooted as the future of thermal conversion of waste. However, several high-profile failures across the UK have damaged the confidence in these technologies. Traditional combustion facilities are well established at a more regional scale (greater than 60 kilotonnes per annum) and the issues have come from organisations looking to make commercial gains from large-scale operations, whereas recent studies have suggested that these technologies are more suitable at smaller, town-scale solutions.

Large volumes of waste plastics - and the mixed low-grade plastics that are rejected for use in traditional recycling - can be used as fuels in combustion processes, or used as feedstock for producing energy-rich gases, liquid fuels and chemicals. Thermal processing of wastes under gasification or pyrolysis conditions offers a more flexible approach than combustion. This kind of thermal treatment plant would produce regular supplies of high-quality products usable for heating and power - which even could be used to run the fleet of vehicles collecting the waste plastics.

Even greater value is contained in the oil, with a range of uses in the petrochemical industries, and use as aviation and HGV fuel. CO2 emissions from such a process would be significantly lower than using virgin materials (like crude oil).

At Cranfield University we are working on a project with Syngas Products in Dorset and WestAfricaENRG in Nigeria, funded by Innovate UK. This is focused on a pilot of a small-scale thermochemical plant which uses plastic-rich waste materials as a feedstock for a one megawatt pyrolysis facility, aiming to demonstrate the commercial feasibility of processing wastes in this way, and to produce high-value liquid fuels and chemical products. Evidence from the research strongly supports the principle that this type of local facility would cope with the average mix of waste from households and industry.

The project is exploring the feasibility of such a process in developing countries, which face different waste management and energy supply challenges to those seen in the UK. In Nigeria, the electricity connection is sporadic and unreliable, which is typical across many African countries, hence there is an inherent reliance on costly diesel back-up generators as primary sources of electricity generation. Low-grade plastics, in the context of Nigeria, could provide a ‘greener’ fuel for these generators, thus adding security to the power supply and reducing the reliance on pure fossil-fuels in addition to stimulating development of more MRFs in Nigeria.

The missing ingredient needed for making the transition to this circular plastic waste model is investor confidence and a commitment from the UK Government along with supported industry demonstration of gasification and pyrolysis technologies.

There are signals that this is already happening. The Government has registered its interest in finding alternative fuels for aviation and HGVs. The Energy Technologies Institute (ETI), a public-private partnership between global energy and engineering companies and the UK Government, has invested £8 million into a small-scale waste gasification plant in the West Midlands using sorted household waste.

Once operational, the plant will open up 25 permanent jobs and generate 1.5 megawatts, enough power for 2,500 homes, as well as 40 tonnes of gas for conversion into power, and waste heat for heating a local swimming pool. Its compact and localised scale is its strength, making it possible to integrate with heat networks in towns and provide heat and power to local institutions, hospitals and factories.

Evidence of the success of the ETI plant and other local facilities will be invaluable in the coming years, and vital for being able to say, once and for all, that shipping waste overseas was just an old-world solution.

(UPDATED 6.2.18 to correct the total tonnage in the opening sentence)

Stuart Wagland is senior lecturer in energy and environmental chemistry at the Centre for Bioenergy & Resource Management, Cranfield University


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