The unexpected ways in which factories are saving energy

Green-minded companies are using traditional energy-generation methods such as solar power and wind turbines to good effect. However, rather quirkier solutions that, all-in-all, contribute to the conservation of energy are beginning to emerge.

Government incentives to achieve carbon targets set out in the Paris Agreement of 2015, and dramatic price falls in renewable generating technologies, have combined to encourage businesses to cut their energy consumption and, in the process, reap savings on their bills and emissions. Likewise, government climate policies have encouraged the ‘greening’ not only of farming but also increasingly of manufacturing.

One innovative green-energy solution now being appropriated by businesses is to employ anaerobic digester (AD) plants to turn their organic process and industrial waste into electricity and heat. An AD is an airtight tank in which bacteria break down biodegradable materials into usable products, primarily biogas – a combustible mix of methane and carbon dioxide.

Technology in the form of ground- and air-source heat pumps, which rely on natural heat, is gradually displacing fossil fuels for heating or cooling homes and buildings in South Africa, Australia and the UK.

Another novel sustainable approach seen in southern hemisphere countries is the use of seawater to cool buildings, while cities in the northern hemisphere are taking water from lakes and rivers for the same purpose. Insulation has benefitted from use of new materials and the comeback of natural fibres such as wool and hemp. Management of energy consumption has advanced with the introduction of Internet of Things technology and is being augmented with cloud-based systems.

These innovative measures are being adopted in factories, offices, industrial parks and universities, for example, offering the benefits of reduced operating costs, predictability of energy bills and enhanced green credentials.

Organic waste from manufacturing processes is being transformed into a source of electricity and heat. Essentially, the organic waste is fed into an AD plant in which the ‘digestion process’ produces biogas, which is then burned to release heat. This heat turns water into steam, which turns the blades of a turbine generator to produce electricity.

In the UK, the confectionery arm of food giant Nestlé and the Scottish whisky industry are two prime users of anaerobic digesters, which they use to turn their organic waste into biogas, the first step to producing electricity. There is increasing strong interest from food and drink manufacturers in developing on-site AD plants to ‘digest’ their processing residues.

Nestlé’s factory in Fawdon, north-east England, manufactures well-known brands of confectionery such as Rolo, Caramac and Fruit Pastilles. The factory’s waste – consisting of rejected chocolates and sweets as well as leftovers such as starch and sugar – is dissolved into liquid by onsite cleaning processes to create a ‘chocolate soup’ (which is not as tasty as it sounds). The ‘soup’ is then fed into an AD and the resultant biogas is burned, creating steam for power generation and heating purposes.

Currently, this system meets 8 per cent of Fawdon’s power needs and has cut the factory’s carbon footprint by 10 per cent. It has also shaved £300,000 off the site’s energy bill and saved £200,000 in disposal costs. Andrew Griffiths, head of environmental sustainability at Nestlé UK, views the anaerobic digester as a pet, “a living thing with its own likes and dislikes, since it can get quite upset if its diet changes too quickly. It evolves and develops over time.”

Whisky, the third largest industry in Scotland after energy and financial services, makes up around 70 per cent of the entire Scottish food and drink sector and is valued at £5bn a year. The whisky distilleries use a hierarchy of measures to cut their energy bills and earn additional income. Traditionally, distilleries have converted the waste grains (known as draff) from the malting process into pellets, a protein-rich cattle feed sold to local farmers.

According to Zero Waste Scotland, the country’s whisky industry produces 1.6 billion litres of pot ale and 500,000 tonnes of daff a year. However, now the daff and sometimes the pot ale is increasingly being used to help power Scotland’s distilleries. AD plants fed with daff and pot ale produce biogas, which is burned to heat water to create steam, which turns turbine blades to produce power and heat.

A good example of the benefits of anaerobic digestion is seen in the Glendullan distillery, which in the first year of operating its new AD plant gained 6,000MWh of thermal energy – enough to reduce the distillery’s fossil fuel consumption by 25 per cent. This is just one of a number of AD initiatives Glendullan’s owner Diageo is implementing across its distillery sites in a £100m investment in renewable energy technology. Other well-known whisky producers, including William Grant & Sons (which owns Glenfiddich and Balvenie, among others) and Glenmorangie, are also employing AD plants.

The heat created by distillation and mashing is also often re-used in distilleries, usually to warm or re-heat water that is crucial to the whisky-making process. Diageo’s Roseisle distillery feeds its waste heat to two nearby malting facilities. However, the benefits need not be confined solely to the whisky-making process. For example the Bruichladdich distillery on Islay re-routes waste not only to heat water but also to heat its visitor centre, bottling hall and meeting rooms. At nearby Bowmore, heat from the distillery warms the community swimming pool next door.

RAF Marham in Norfolk is home to the front-line squadrons of the RAF’s Tornado Force and the new fleet of F-35 Lightning stealth fighters. The airbase receives baseload electricity from an innovative sustainable generating power plant built by Future Biogas on behalf of the Defence Infrastructure Organisation (DIO) Utilities, the Crown Commercial Service Utilities & Fuels and EDF.

The Future Biogas site, situated four miles east of RAF Marham, generates up to 4.5MW of electricity from three gas engines. The biogas is produced by an on-site anaerobic digester, which is fed with locally grown crops and sugar-beet waste. Heat from the power generators is used to dry the waste residue from the AD process, which is used as a fertiliser on local fields, thereby creating a virtuous circle. It is a green, sustainable solution that undercuts mains electricity costs and benefits the local economy.

This clean-energy AD plant contributes to the Ministry of Defence’s Sustainable Development Strategy and delivery plan for 2011 to 2030. It saves the base £290,000 a year in electricity costs and has cut its carbon emissions by 14,000 tonnes. The project also has strategic importance because, by providing another source of electricity, it has increased the power resilience of RAF Marham. For DIO Utilities, the project proved cost-neutral and low-risk since the build, operation and maintenance of the AD plant and connection to RAF Marham fell to others.

Today, the manufacturing and agriculture sectors are increasingly adopting ground or air source heat pumps to not only reduce their fuel bills and environmental footprint but also to increase their green credentials. As a technology, heat pump systems offer not only heat, as their name suggests, but also active and passive cooling. Two examples from the UK are worth noting. The first of these is the Kensa Heat Pump factory and other enterprises based in the Mount Wellington Mine Renewable Energy Business Park of Cornwall, which use ground source heat pumps to capitalise on the mine’s subsurface heat. A large quantity of special plastic pipe – called a geothermal array – has been lowered into the mineshaft; a mixture of water and antifreeze is pumped downwards from the heat pump and what returns to the surface is warm water at between 12 and 20°C. The heat pump then upgrades this to a more usable 35 to 40°C for underfloor heating.

Richard Freeborn, owner of the Mount Wellington Mine Renewable Energy Business Park and founder of Kensa Heat Pumps, spells out the advantages: “This is the first building in Europe to use heat from the decay of radioactive isotopes, and it is working very well indeed. The heat energy extracted from the mine is 100 per cent renewable. The geothermal arrays require no servicing or maintenance and have a predicted life of over 100 years. The heat pumps are running at an incredible efficiency, thanks both to the warmth of the mine and the high standards of insulation in our manufacturing building.”

In Cambridgeshire, RAGT Seeds, one of Europe’s leading plant breeders, has installed a passive cooling system using heat-pump technology provided by Finn Geotherm to cool its greenhouses in summer. Before this installation, RAGT Seeds glasshouses had been known to reach 45°C (compared to the target temperature of 21-22°C). The traditional low-tech methods of painting the glass panels and using fans were proving ineffective, particularly during the hot summers of recent times. Finn Geotherm’s team of experts devised a bespoke passive cooling system, which circulates air at an ambient ground temperature from the ground loop. Cool air is circulated through 24 Jaga AVS fan-coil units – four per glasshouse – using a control system that is activated if the temperature increases by 1°C from the target range.

Passive cooling not only delivers the cooler temperatures needed by RAGT Seeds during summer, but also provides a ‘gentle summer breeze’ throughout the glass greenhouses. An unexpected benefit of the better-regulated greenhouse temperatures is enhanced plant growth, while in the future the company expects to be able to reduce its chemical inputs.

Guy Ransom, commercial director of Finn Geotherm, explains the benefits: “The installation at RAGT Seeds has not only revolutionised the way in which the company heats its glasshouses but also how it cools them too. The energy and cost savings are outstanding, with plant room meters showing a coefficient of performance of 3.9:1 to date, which is excellent.” Ransom adds, “A typical installation could show a payback on its entire cost within five years, with the return on investment continuing to provide another 15 years of income at no cost to the user.”

Coastal and inland cities with access to large bodies of water such as rivers and lakes can exploit their surroundings to cool the interior of buildings. Some coastal cities in the southern hemisphere – Cape Town in South Africa, Sydney in Australia and Antofagasta in Chile, for example – have seafloors that naturally drop to a great depth close to the coast, which would allow them to access seawater at just 5°C via insulated pipelines. This could drive both district cooling and large-scale water-from-air extraction units for drinking water.

The new Zeitz Museum of Contemporary Art Africa and its surrounding buildings in the port and central business district of Cape Town now make use of seawater cooling. Other major cities, including Paris, Toronto and London, make use of large local bodies of water such as lakes and rivers to cut the cost of their cooling bills using a similar approach. The City of Toronto’s water department, for example, installed an insulated water pipe to access cold waters near the bottom of Lake Ontario. During the northern summer and before arriving at the water purification plant, that cold water passes through a heat exchanger to provide district cooling to several office towers in the business district. In cases like this, water cooling has reduced the use of fossil-fuelled electricity for air conditioning.