In with the new
Resource thought it was time for an update on new waste technologies, and asked five experts to explain the various processes and costs, as well as critique government endeavours to encourage the fledgling techniques
Anaerobic digestion
Food waste recycling at one of ReFood's anaerobic digestion facilities
Philip Simpson, Commercial Director, ReFood
The anaerobic digestion (AD) process is often likened to processes used by the human stomach. Organic waste is processed in digester tanks in the absence of oxygen while bacteria breaks it down and produces methane gas, which is later used to produce energy. According to the latest AD annual report issued by Defra in August 2013, 110 AD plants have been constructed in the UK with a further 200 sites receiving planning consent. The exact technologies may vary from plant to plant, and increasingly many are looking at sending gas-to-grid.
ReFood is investing in two new AD plants and doubling the capacity of our existing AD plant in Doncaster. Between them, they will be able to process over 420,000 tonnes of food waste and the total investment in these sites in 2013/14 will be over £60 million. Gate fees depend on the type of material, but are typically in the range of £35 to £45 per tonne, half the cost of landfill.
The fact that Defra intends to step back from waste policy and leave it to the market is a concern, as best practice is likely to lose out to regulation on the cheap. This is a sensitive issue for food waste as it raises the potential for the risk of food waste going back into the feed supply chain. In an ideal world, we would like the government to introduce a phased ban on food waste to landfill. The report ‘Vision 2020: UK roadmap to zero food waste to landfill’ outlines that if all of the UK’s food waste was diverted from landfill, by 2020, every year, it would: save the economy over £17 billion; prevent 27 million tonnes of greenhouse gas; return over 1.3 million of valuable nutrients to the soil; and generate over one terawatt-hour (Twh) of electricity, enough to power over 600,000 homes.
As AD infrastructure grows, it will become easier and more cost effective for food waste to be diverted to AD rather than sent to landfill, and we are optimistic that we will see more of this happening. As global food resources come under greater stress, we expect people to take the issue of food waste more seriously and start to really understand its value as a resource.
Autoclaving
The AeroThermal one cubic metre working volume demonstration autoclave, which has run over 800 cycles with more than 65 mixtures of alternative waste material inputs
Ian C Toll, Director, AeroThermal Group
Autoclaving is a generic term for the application of heat and three-dimensional pressure. The process has been employed in industry around the world for over 70 years in such diverse applications as meat rendering, rubber vulcanisation, acrylic castings, windscreen laminating, advanced composite curing and now to break down the binders and lignin within organic materials. Quite simply, by placing food stuffs, paper, cardboard or sewage sludge into a heated pressure vessel, through the application of steam and physical movement, a solid can be reduced to that of a digestible pulp using thermal hydrolases.
Mixed waste streams such as municipal solid waste containing not only food, paper and cardboard but also bottles, cans and a range of plastics, can easily have the recyclable elements separated from the organic post process with the ‘earth like’ organic rich soup being used as a feedstock for AD. This process kills a hundred per cent of pathogens and, in addition, renders a wider range of material suitable for the digestion process, providing homogenised and stable feedstock.
At present, there are no commercial operating plants of this type anywhere in the world. A 75,000-tonne capacity plant, including autoclaves, anaerobic digesters, power generation and ancillary treatments would have a capital cost of between £22 and 25 million, and would be seeking a gate charge of circa £75 per tonne, with the balance of the income being derived from the sale of electricity through Renewable Obligation Certificates, Feed-in Tariffs and/or the Renewable Heat Incentive.
Government policy is obliging people to seek alternative means of treating waste through the Landfill Tax, which has clearly had an effect on the waste industry as a whole. However, the tax still remains too low to genuinely encourage new technologies. Perhaps the government should consider providing a financial guarantee to a council that is ready, willing and able to award a waste contract to a fledgling supplier but is reluctant to do so because the supplier does not have a full-size operational plant to demonstrate the process to the satisfaction of the authorities. Something has to give if the whole of the UK waste-to-energy issue is not going to be controlled by the five major waste management companies.
Mechanical Biological Treatment
Waste treatment at Viridor's MBT facility in Bredbury, Greater Manchester
Howard Ellard, Business Development Director, Viridor
One of a range of options for the treatment of residual waste, mechanical biological treatment (MBT) is a technology available for deployment between kerbside recycling and modern energy-from-waste (EfW) facilities. With a 2013 WRAP reported gate price of £66-£82 per tonne, the process is part of Europe’s largest public-private waste partnership at Greater Manchester, where Viridor utilises five MBT facilities.
MBT, often receiving residual municipal solid waste, utilises mechanical processes such as shredding, sieving, and screening to reduce the size of the waste and separate it into fine or organic, light, ferromagnetic metals, non-ferromagnetic metal and heavy residue fractions. The light material is incorporated into a high calorific value solid recovered fuel (HCV-SRF), and the heavy residue is reused as aggregate. The strategic policy and political objectives of individual authorities determine which technology, or mix of technologies, will best meet local requirements.
The emergence of UK policy focused on enhanced recycling and landfill diversion means that for many local authorities, a firm focus on high levels of clean kerbside recycling combined with renewable energy generation through modern, economic EfW infrastructure is a platform designed for delivery. For others, more complex factors come into play, including policy requirements on specific recycling outcomes, or political commitments on EfW infrastructure. For those reasons and others, authorities may seek to incorporate MBT – liberating a range of recyclables and residues prior to recovering energy from what remains locally or, as is often the case, at regional
EfW infrastructure.
Looking ahead, the key driver for UK infrastructure will remain Landfill Tax, hopefully with clarity from next year’s budget. Whilst investment will continue in even higher levels of kerbside recycling combined with EfW, decisions on the deployment of MBT will continue to reflect local requirements.
Pyrolysis
The New Earth Solutions facility in Avonmouth uses a combination of pyrolysis and gasification
Rob Asquith, Planning and Permitting Director, NEAT Technology Group Ltd
Pyrolysis is the heat treatment of material without oxygen. Along with gasification, it is considered by DECC a form of renewable energy called advanced conversion technology (ACT). New Earth Solutions Group’s gasification and pyrolysis plant in Avonmouth near Bristol, the first of a number of such projects, uses ACT developed by sister company NEAT Technology Group (NEAT). At least three other UK ACT companies are currently building, each using very different designs. Two are for municipal solid waste (MSW) derived refuse-derived fuel (RDF), the third for material recovered from metal recycling (mainly plastic, rubber, etc, from scrap cars). There are also a number of research and development plants including NEAT’s Dorset R&D facility.
The pyrolysis stage of NEAT’s ACT converts RDF to energy-rich synthesis gas (syngas) and a carbon-rich, solid char. NEAT uses a ‘staged and separated’ approach, each pyrolysis unit feeding char to a separate gasifier into which steam and air are carefully introduced. Char gasification produces more syngas. The pyrolysis and gasifier syngas is used to generate electricity.
NEAT ACT costs per unit of electricity compare favourably to mass-burn energy from waste (EfW). Correspondingly, waste gate fees are competitive. ACT is supported under the Renewables Obligation and also has Strike Price under the government’s Contracts for Difference (CfD) proposals, reflecting ACT’s circular resource management potential as well as its proven renewable energy credentials.
Our main policy concern is that the new electricity market CfDs should fully reflect the position of small independent generators – which are potentially disadvantaged in the new system. The CfDs and the complementary Capacity Market mechanism should also be flexible, as emerging technologies, such as ACT, are very different to established sectors such as wind power, yet have great cost reduction potential as they mature. ACT’s potential benefits extend beyond the production of renewable electricity, which also should be recognised.
Given the right policies, by 2024, ACT could be delivering around one gigawatt of low-carbon energy and possibly making hydrogen or other products, having, in passing, helped end the UK’s reliance on exporting RDF.
Gasification
An internal viwe of the Energos plant in Sarpsborg, near Oslo, in Norway
Tony Grimshaw, Technical Director of Energos
Gasification technologies, in simple terms, turn all kinds of municipal solid waste (MSW) and commercial and industrial (C&I) waste into electricity. Gasification itself
is a very old process, which is now being applied to all varieties of waste with the advantage of modern process equipment.
This article was taken from Issue 75A typical feedstock would be a residual waste stream that has already had the recyclable materials removed. This MSW passes through the gasification chamber, where it is subjected to a high temperature. This process converts everything, apart from the ash, to a gas – referred to as syngas. The syngas is combusted, and the resultant flue gases are typically fed to a boiler to produce steam, which, in turn, produces electricity through a steam turbine. It is the fact that the ‘chemistry’ is carried out in the gas phase that results in the emissions to air being low.
Energos’s Isle of Wight facility was the first plant in the UK to utilise gasification for the treatment of waste. Other facilities that use gasification are now opening up, including the New Earth Solutions facility near Bristol (see left); a large Air Products plant (49 megawatts) is under construction in the Tees Valley. This project will generate electricity using the syngas in a gas turbine.
The government’s main support mechanism is through Renewable Obligation Certificates (ROCs), which will form part of the Electricity Market Reform from next year leaving the support at the same level. Incineration does not qualify for this support.
The fact that gasification plants are now being built to service competitively bid tenders, as has happened in Glasgow, demonstrates that the technology can be competitive (with ROCs) and can operate at commercially realisable gate fees.
Government could further support the industry by: restricting the quantity of waste, which is a valuable resource, being exported; and giving stability to the support mechanism to maintain investor confidence.
2014 will see several gasification plants near completion ready for operation in 2015/16. In the longer term, gasification of waste offers the opportunity to convert the syngas into other products.
