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It’s feasible for residents to pyrolyse their own waste

heru unit

At the end of the first Back to the Future film, Doc Brown picks out a few bits of rubbish from a bin to power his newly adapted DeLorean time machine. This vision of deriving power from waste was conjured up in 1985, as the environmental lobby started to influence popular culture. Fast forward 30-odd years and a version of the idea has been fashioned into reality – only this time to heat the home.

The Home Energy Recovery Unit (HERU) is the brainchild of Nik Spencer, an entrepre­neur with more than 25 years’ experience in the waste industry. With the help of Brunel University, he has developed a small boiler than can pyrolyse all sorts of waste – from plastic to food and nappies – and runs on a 13A fuse.

After ‘cooking’ the waste at the right temper­ature, the resulting char is slowly burned to provide energy, leaving nothing but a small amount of ash and oil that can be safely flushed down the home’s drain.

heating pipes original

heating pipes original

Considering the difficulties that large-scale pyrolysis plants face, including environ­mental concerns, it seems too good to be true. But Spencer is not short of ambition: he wants to revolutionise the waste industry and has an answer for every potential prob­lem.

“The dream for me is that, when the youngster is about to jump in a car to drive off to McDon­ald’s, the parents shout out the door, ‘don’t forget to bring your rub­bish home’,” says Spencer. “It’s no longer waste, it’s a resource.”

He came up with the idea in 2008 but put it on hold after speaking to a pyrolysis expert, who pointed out that to process waste successfully, it has to be dried and shredded first. This would clearly make the process too complicated for the household.

“The whole concept behind HERU is that it has to be as simple to use and as robust as a wheelie bin. I thought that, in 20 or 30 years’ time, will we be running round the streets with dustcarts collecting material, only to put it into energy-from-waste (EfW) plants?”

According to a lifecycle study by Brunel Uni­versity, by the time one tonne of cardboard has been collected from homes, sent to a MRF, bundled into a container and shipped round the world to mills thousands of miles away, around three tonnes of carbon has been used. This is why using the material directly in the home makes such sense to Spencer.

nappies after pyrolysis

nappies after pyrolysis

The breakthough came when he teamed up with Dr Hussam Jouhara at Brunel, whose expertise with heat pipes has helped to over­come the ‘shredding and drying’ problem. This led to a series of working prototypes that have been supported by the Innovate Energy Game Changer fund. The Government thinks the technology has the potential to shake up the energy market radically.

Spencer’s inspiration came from 188-year-old train technology: “I looked at the Stephen­son engine, and how he took the heat from the furnace through the water and then created the steam to drive the Rocket.”

With Brunel, Spencer developed four thin steel pipes which run through the middle of the waste in the pyrolysis chamber. There are also a series of pipes around the outside and a couple along the bottom.

heru schematic

heru schematic

HERU system flow chart

The pyrolysis method breaks down waste using high temperatures in the absence of oxygen. A small amount of water is turned into vapour, which flushes oxygen out of the system. Pyrolysis then starts and, after about seven hours, the material has been turned into char. As soon as pyrolysis is finished, a grate inside lifts up automatically with the hot char in. Air is then let in at a regulated rate and combustion takes place spontaneously. “It glows like a barbecue,” says Spencer. The exhaust gases then pass through a heat exchanger unit, before a gas filtration cleans the exhaust prior to being vented. The system is then easy washed with water. The process does not destroy batteries, should they mistakenly be put in the system, and any residual metal can be easily separated.

“If you take a normal pyrolysis chamber, you might have to heat it up to 700°C on the out­side in order to get the heat transferred into the waste in the middle of the chamber.

“If you’ve got a nappy in the middle, it will partially pyrolyse – it retains moisture and you can’t get the temperature high enough. This is why normally you have to dry and shred the waste.

“All you do is put a little bit of water in those pipes in the bottom, and a 3kW dishwasher heating element to heat that water which vapourises it, hits the top of the pipes and con­denses down. It creates a thermal cycle. With this method, you get a uniform 300°C through­out the chamber.”

For Spencer, who has a prototype working in his own home, having a device that does not get hotter than an oven is a key selling point. Keep­ing the process at this temperature also does not break down sufficient amounts of hydro­carbons so that they turn into large amounts of gas. Some pyrolysis oil is produced, and there has been extensive testing done to prove it can be safely flushed into the sewer.

“The way to think of it is that, if you take a dinosaur buried in the northern hemisphere, you get a lot of coal and not too much oil or gas,” he explains. “Bury the same thing in Texas, you get a lot of oil and gas and not much coal.”

Current models are producing around 2.5kW for every 1kW put in. By contrast, Spen­cer points out that sending waste to EfW means you lose around 70-75% of energy by the time the electricity is transmitted back to the plug on your wall.

There is an obvious question to ask at this point: how can a home pyrolysis machine meet the necessary environmental standards? “We have done a huge amount of work on this,” says Spencer. “We have to assume the material that is going in is still defined as ‘waste’. If material is waste, it comes under regulation 8 of the Environmental Permitting Regulations (Eng­land and Wales) 2010 and the amendments in 2013.

“The HERU falls under ‘the following facili­ties are not regulated: the disposal or recovery of household waste from a domestic property within the curtilage of the property by a person other than an establishment or undertaking…’

“It basically means that, as long as you’re not receiving waste from outside and, as the home­owner, you are using your waste within your own curtilage, it falls outside of the permitting regulations. So, at the moment, helping your neighbours by taking their waste to heat your home would technically not be legal.”

Spencer is looking to launch the HERU com­mercially in early 2020. By the end of this year he hopes to have 10 machines ready to go for full trials – Stratford upon Avon District Coun­cil, Rugby Borough Council and the City of London have asked to try one. If the HERU is a success, what will this mean for resources policy in the UK? Will recycling rounds be a thing of the past?

“I think it sits right at the top of the waste hierarchy because it is waste prevention in its finest form,” claims Spencer. “If you have a product and you can use it to produce your hot water instead of using electricity from fossil fuels, then it isn’t waste.”

In the film, Doc Brown’s DeLorean was fitted with its ‘Mr Fusion’ garbage-eating reactor in 2015. Reality may be lagging behind fiction, but perhaps we are finally travelling back to the future.

Spencer: A life in waste

nik spencer 400 by 400

nik spencer 400 by 400

Nik Spencer came into the waste industry in the early 1990s when he started producing bedding for racehorses made from recycled paper. The business grew and his company, Bettabedding, started collecting paper from homes around Stratford upon Avon and Solihull in 1991. This, Spencer believes, was first kerbside recycling company in the UK.

He sold the collections business to Biffa in the mid-1990s and went on to set up another kerbside recycling business, WCR. This was spurred by the incoming Landfill Directive.

Spencer eventually successfully lobbied the then environment secretary Michael Meacher to extend recycling credits to private companies, not just councils and charitable organisations.

His next step was to branch into municipal vehicle hire, and says he “got in with” Dennis Eagle and Mercedes. The result was a fleet of 180 RCVs on hire to local authorities.

WCR was sold in 2006, and Spencer went on to launch Pure Recycling, a 150,000 tonnes a year MRF using technology discovered from a trip to the US. Kier bought Pure Recycling in 2010 and Spencer stayed on as a director on the environmental board for three years.


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