THE ENERGY INDUSTRY TIMES - JANUARY 2017 Technology 15 Pioneering enzyme process improves waste recycling DONG Energy is building the world’s first commercial full-scale wasteto energy bio plant in Northwich, UK. The plant will use enzyme treatment to convert household, municipal and some commercial waste into biogas, as well as recyclable plastics and metals. Thomas Dalsgaard Although recycling performance has improved in recent years, tens of thousands of tonnes of waste are still sent to landfills every year. There is a pressing need for effective and efficient waste treatment facilities that can recover valuable materials and energy from waste. To reduce the costs for local authorities at a time when budgets are under pressure, there is a need to manage waste efficiently. While many recognise DONG Energy’s leading role in the British offshore wind sector, supplying increasing amounts of renewable energy to the UK while simultaneously bringing down the overall cost of offshore wind technology, waste management technology is also now a key focus. Last year witnessed a significant landmark as DONG Energy took the first steps towards entering the UK’s waste and resources market. It is an important milestone for the business, but it also occurs at an exciting time for the sector as new recycling and resource recovery technologies emerge with the potential to revolutionise the UK’s waste landscape and putting it on a greener footing. DONG Energy is taking its place in this movement towards better, cleaner waste management by building the world’s first commercial full-scale bio plant in Northwich. The plant secured planning approval from Cheshire West and Chester Council’s planning committee in February 2016 and construction is now well under way. The facility will accept household, municipal and some commercial waste from surrounding areas in the North West and North Midlands, which – through enzyme treatment – will be converted into biogas, as well as recyclable plastics and metals. DONG Energy will finance, construct and operate the plant, which is due to be operational in 2017. Around 150 workers will be engaged during the peak phase of construction, with an average of 75 at any given time. The plant will also require around 24 full-time local employees to operate it once finished. The pioneering new technology that will be used at the plant is called REnescience. It is safe and reliable, and has been proven since 2009 at a demonstration plant in Copenhagen. Significantly, it does not involve incineration, pyrolysis, gasification or advanced thermal treatment. The REnescience process takes place at a low temperature, at ambient pressure (meaning that the processing vessels are not pressurised) and is safe and gentle. Anaerobic digestion is also a well-proven technology operating at hundreds of sites in England, from farms to food processing facilities as well as other waste treatment facilities. When compared to most traditional waste treatment processes, REnescience is capable of a higher capture rate of organic materials and can help to achieve higher recycling rates. REnescience also increases recycling rates from the remaining solid materials, reducing the overall need for other treatment and disposal methods. Most importantly, depending on the composition of the waste (which can vary over the year), it almost completely eliminates the amount of waste that eventually goes to landfill. The new facility will be able to receive 120 000 tonnes of waste every year, roughly equivalent to the waste produced by 110 000 UK households. Waste will be supplied by FCC Environment, which already collects household rubbish in the region. While there are various local and central government initiatives to encourage more recycling, there is still an immediate medium-term problem that needs to be addressed as household recycling rates in England are currently at just under 45 per cent, with tens of thousands of tonnes of waste still being sent to landfills annually. There is a pressing need for effective, efficient and green waste treatment facilities that can recover valuable materials and generate clean energy. At first, when the residual waste is brought to the Northwich plant it is treated with enzymes and warm water so that a greater volume of the recyclable material and other resources can be extracted. This process occurs without any up-front waste shredding or crushing, because the enzymatic process targets the organic material effectively, even in mixed, unsorted waste. This helps to avoid most of the dust, odour, noise and pollution issues that can occur when waste is shredded. The process sees enzymes mixed together with warm water and waste inside a sealed vessel, where they are able to interact with and break down all of the organic matter. This allows for the organic or biodegradable material (food, paper, card, etc.) to be efficiently extracted from the other waste, concentrating it into a bioliquid. This means that no separate shredding or incinerating is required at the plant. Through this process, cleaned metals and some other solid plastics are recovered separately for recycling, together with another stream of clean, solid recovered fuel for onward use elsewhere. In addition to these items, inert materials such as sand, gravel and glass, are recovered for reuse as aggregates. These processes are all carried out inside the one building. Once this separation process is complete, the separated organic material is recovered as a thin bio-liquid, which is digested by bacteria within a sealed anaerobic digestion vessel to produce biogas. The biogas, which is captured, can then be used to fuel gas engines on site, generating renewable energy and heat. Between 5 and 6 MW of electricity will be produced by these gas engines via their individual electrical generators. Ensuring that the facility is as sustainable as possible, a small amount of this energy will be used to power the operations itself. This will leave around 5 MW, enough to power around 9500 households, to flow into the national electricity grid for use by consumers and industrial users. Producing the same amount of electricity in a modern gas-fired power station, for example, would release 15 000 tonnes of carbon dioxide equivalent (CO2e) per year, a statistic which demonstrates the project’s importance in the UK’s shift to a low-carbon economy. Heat from the gas engines will also be utilised on-site to maintain the required temperature for the REnescience bioreactors and to heat the buildings when needed. This makes the facility more energy efficient. The refuse derived fuel (RDF) from the Northwich plant will have a high calorific value, making it suitable for use elsewhere in energy recovery plants or cement kilns, which need high temperatures to operate. Meanwhile, the digestate, a compost-like output left over after the anaerobic digestion phase, can be used for land restoration. The facility is carefully designed to control any odours. Waste will be delivered in enclosed vehicles, unloading into a waste bunker that is fully enclosed inside the building. Since the REnescience process removes the biodegradable material, which is the component that can make waste smell, the final output has a low potential for odour. However, the air in the waste treatment building will be extracted so that fresh air from outside is continuously and gently sucked into the building, ensuring that potentially odorous air will be cleaned through an odour control system before being released. REnescience breaks with today’s practice of waste disposal and collection by centralising the sorting of the waste and doing so in a more environmentally friendly way. This project is yet another example of complex, high-tech, green engineering at its best, once again the UK’s firm commitment to renewable energy. Thomas Dalsgaard is Executive Vice President, DONG Energy. Artist’s impression of the Northwich plant REnescience process diagram DONG Energy’s patented technology REnescience is a groundbreaking way to generate value from waste
Energy Industry Times January 2017
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