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AEROTHERMAL completes 65m3 thermal hydrolysis vessel for new anaerobic digestion site

AeroThermal Ltd today (12 December 2017) announced that its 65m3 Thermo-Pressure Hydrolysis (TPH) vessel has been completed and has left its factory in Poole en route to a new bio-waste anaerobic digestion site in the Midlands.

The TPH vessel is a key component at the new facility and has been provided in partnership with Jones Celtic Bioenergy.The technology pre-treats food waste and other bio-waste organics prior to going to mesophilic anaerobic digestion.

The TPH operates in cycles of 2-2.5 hours each processing over 20 tonnes of bio-waste. The bio-waste, inclusive of packaging, is shredded to <50mm prior to transfer to the vessel. There it is sterilised firstly by being put under vacuum, then under high temperature saturated steam for 30-45 minutes while the drum rotates depending on the process requirements.

This hydrolyses the cellulosic material and after the process is complete, the product exits the vessel as a pumpable liquid. This is then separated into the predominant organic fraction which goes into anaerobic digesters producing high yields of biogas, which will be upgraded and injected into the national gas grid.

AeroThermal has demonstrated that pre-treating food and packaging waste in utilizing the TPH process before anaerobic digestion significantly increases methane generation and substantially reduces the amount of material requiring disposal.

The TPH vessel left Poole at the end of November in four sections. It will then be reassembled, with commissioning in February and hot commissioning later in the year. Christian Toll, AeroThermal’s CEO, said:

“In our in-house lab, we have conclusively proven that there are significant advantages in applying thermal hydrolysis as per the AeroThermal method to a wide range of municipal organics. This includes its flexibility in efficiently separating it from food waste, while ultimately recovering feedstock for anaerobic digesters for energy production.

“We are proud to have developed this system in partnership with Jones Celtic, and we are looking forward to our autoclave generating significant quantities of green energy from food waste.”


Aerothermal today (15 September 2017) announced that it had designed, manufactured, delivered and installed a new, state-of-the-art eight metre oven to a global aerospace supplier, the first of its type in the world.

What makes the oven unique is the entire side-on opening, with a door running the full eight metre width, whilst at the same time maintaining an exceptionally high level of temperature uniformity.

The oven, which is 1.75m high, enables two components to be loaded at one time with an innovative loading mechanism. A trolley carries the components into the oven, with a gap of half a metre between the external tracks and the internal fixturing. This gap was required to enable the doors to close. The trolley then cantilevers across the gap, thanks in part to the unique design of its axels.

An additional challenge was the temperature conformity and accuracy needed by the customer. The maximum temperature difference across the part was specified to be no greater than +/- 2.5oC, to a maximum temperature of 175oC to be maintained for a number of hours to facilitate the heat treatment of highly specialised CNC machined aluminium components.


Aerothermal delivered an oven with an accuracy of better than +/- 2oC, exceeding the client’s requirements. It achieved this using a multizone heating system on the top and bottom, with four different banks of heater cassettes and four fans, to ensure temperature uniformity. The cassettes were sheathed electrical heaters and produce 240kW.

The oven is made of a steel structural frame and steel panelling. It is also highly insulated, to the extent that it is possible to touch the vast majority of the oven wall at a temperature marginally above that of ambient whilst the oven is in operation. This has the added benefit that energy usage is minimised.

Aerothermal also designed, and built in-house, a plc control system, with two controllers; one for the air temperature; one for the parts’ temperatures. Though not needed for this application, it is possible to accelerate the air temperature very quickly.

When the manufacturing process is complete, the oven’s temperature is reduced by using a power-assisted ambient cooling system, through external ducts.

It also contains an interior isolator pull-string alarm, and lights and windows to ensure safety. It was delivered and installed in one piece to the customer.


Ian Toll of Aerothermal said: “This was a challenge. We had to design the oven, with a unique side-loading mechanism, from a blank sheet of paper. On top of this it needed to operate within a very tight accuracy in temperature. By working in partnership with the client, we were able to deliver and install an effective and efficient oven as part of a busy production line. We got there!”

AeroThermal produces a wide and varied range of thermal processing equipment, the majority of which is custom designed and manufactured as being part of the company’s specialism.

Autoclaves quadruple gas yield from black bag municipal waste

Aerothermal Group announced today (29 October 2015) that pre-treating black bag municipal waste in an autoclave before sending it to anaerobic digestion could increase methane generation by over 300% and substantially reduce the amount of material requiring disposal.

The announcement comes on the back of new research carried out by Dr. Zhengjian Wang (Senior Research Manager) and Dr. Nigel Baily (Technical Director and Principle Engineer) at Aerothermal’s state-of-the-art test facility in Poole.  

As part of the research, experiments were conducted in triplicate on two waste streams. The first waste stream consisted of a sample of MSW feedstock with large items removed.  Tests on this demonstrated how much extra material can go to the anaerobic digestion (AD) system as well as the increased gas yield per tonne of material fed to the AD system.  The second waste stream was a sample of MSW feed stock used to demonstrate the improvements that autoclaving can achieve on a like-for-like basis.  

The two waste samples were each divided into four portions.  One portion of each waste was processed each day, four days per week.  50% of each was processed via the autoclave route and the other half was processed via a non-autoclave route.  

After loading, the autoclave was initially evacuated using a vacuum pump to remove incondensable gases which were filtered out in activated carbon filter beds.  The autoclave was then brought up to pressure and temperature (6.2 bars abs/160oC) by the injection of steam and when the temperature had equalised throughout the autoclave the load was left to “cook” for 45 minutes.

Twelve cylindrical constantly stirred tank anaerobic digesters, each of which has a working volume of 1.8 litres, were used for this trial.  To start the process 1.8 litre of seed inoculums was first added into each digester. When the digesters reached the required temperatures a daily feeding, semi-continuous operating regime was started according to defined organic loading rates.

The biogas production was monitored every day and the gas composition was measured once per week. The pH of the digestate was monitored daily.  A weekly composite digestate sample for each single digester was collected and the properties such as DS, VS, ammonia and VFAs were analysed once per week.

Test results on the first waste stream (where large items had been removed) revealed that autoclaving gives a gas yield of about 150m3/tonne which is more than double the target of 65m3/tonne of waste.  Autoclaving also greatly increased the fraction of the waste that could be digested, as well as the gas yield from each kilogram of waste sent to the digesters which substantially reduced the amount of material requiring disposal.

Tests on the second (like-for-like) waste stream revealed that autoclaving gives a substantial improvement in gas yield, achieving again a figure in excess of 150m3/tonne of waste processed with a HRT of 27 days.

Both waste streams showed autoclaved materials were less susceptible to the development of high VFA concentrations than un-autoclaved material and steam consumption was in close agreement with predictions.

Christian Toll, AeroThermal’s CEO, said: “We’re very excited that our research has proved autoclaving can make black bag municipal waste disposal more efficient, cost effective and less damaging to the environment. A win-win in anybody’s book!  Now we’ve got the scientific proof, we’re looking forward to working with waste disposal companies across the UK and beyond to help them use autoclaves to improve the way they dispose of their waste.”

18ft diameter autoclave moves to UTC Aerospace Prestwick

Aerothermal Group and AIC Group today (21 September) announced that they have successfully completed the move of an 18ft diameter autoclave from Scunthorpe to UTC Aerospace’s Prestwick facility.

The autoclave is so large that the move required the Highways Agency to make special arrangements for the transfer.

This is a major milestone in the contract to provide UTC with a custom-built state-of-the-art autoclave, won by Poole-based companies AIC Group and Aerothermal Group.

The autoclave is the first of its size in the UK and will enable UTC Aerospace Systems’ Prestwick Scotland facility to maintain, repair and overhaul larger nacelles systems fitted to the next generation of wide-bodied aircraft.  

The autoclave will be operational by the end of 2015.  It will run on AIC’s Autoclave Management and Control System (AMCS) which provides significant production efficiencies and energy savings as well as aerospace compliant QA reports. The autoclave will be maintained by AIC in a 10-year programme which includes their world class 24/7 technical support.

Ian Toll, founding director of Aerothermal Group, said: “We have achieved a major milestone in this project and it was fantastic to see the autoclave begin its installation in UTC. We are still firmly on track to see the autoclave operational in the coming months.”

Nigel Clifford, Sales Director of AIC Group, said: “Manufacturing an autoclave requires complex engineering design skills. And moving one of 18ft diameter was also a challenge. However we have overcome these challenges and are confident that the autoclave will soon be working efficiently on large engine nacelles.”

Steve Callan, Managing Director of UTC Aerospace Systems – Aerostructures Prestwick Service Centre, said: “We are committed to maintaining the high quality capabilities and services our customers expect.  This new autoclave better positions us to be a leader in the new large engine nacelle products that have begun entering the market. It further demonstrates our dedication to meeting our customers’ requirements and supporting them into the future.”


Aerothermal Group today (7 July) announced that pre-treating sewage sludge in an autoclave increased methane generation by 47%, according to a new research report, “Effect of Autoclaving on Anaerobic Biodegradation of Sewage Sludge”, by Dr. Zhengjian Wang & Dr. Nigel Baily.  

Three batches of dewatered sewage sludge cakes from three different sources were separately treated by autoclaving at 160⁰C (5.2 bar gauge) for 45 minutes at the company’s Poole facility. A biochemical methane potential (BMP) test was carried out on both autoclaved and un-autoclaved sewage sludge samples.

A semi-continuous anaerobic digestion experiment was also conducted on both autoclaved and un-autoclaved sewage sludge samples using organic loading rates of 5 kg VS/m³/day with a hydraulic retention time of 15 days.

Stable conditions for digesters treating the autoclaved and the un-autoclaved sludges were achieved at this loading rate. Also at this loading rate, bio-methane production from digesting the autoclaved sludge was up to 47% more than that from treating the un-autoclaved sludge.

The experiments were carried out in duplication for each tested sample. Two inoculum control digesters were also run alongside, fed with seed sludge and tap water only. The inoculums were prepared by screening (1mm mesh) out large inert and undigested substrates.

Three batches of sewage sludge cakes were collected and separately autoclaved at a temperature of 160⁰C (5.2 bar gauge) for 45 minutes. After autoclaving, the sludge masses were increased 1.3 – 1.5 times due to the addition of water (from steam condensing). Also after autoclaving, the sludge had a more homogenous slurry-like appearance (brown in colour) and was less odorous.

It was concluded that stable digester operation is possible at a loading rate of 5 kg VS/m³/day, and under these conditions, an autoclaving pre-treatment for anaerobic digestion of sewage sludge cake could increase bio-energy production by over 45% and facilitate the easy co-processing of multiple ‘problematic’ streams, such as screenings and scum.

Christian Toll, AeroThermal’s CEO, said: “We are very excited that we have proven that the British designed and built, AeroThermal hydrolysis system, is  an efficient way to produce a higher yield of methane gas, through autoclaving of sewage sludge cakes, to potentially be used as a source of green energy and at the same time go some way to solving the waste problem which is so damaging to our environment.”

New contract R&D facility for AeroThermal Group

AeroThermal Group, pioneers in developing innovative solutions from aerospace through to green energy from waste, announced today that its new contract R&D Facility is now open to carry out comprehensive testing in Poole, Dorset.

The laboratory specialises in the examination of the anaerobic biodegradation potential of different waste materials with or without pre-treatment in the AeroThermal pilot scale autoclave.

AeroThermal has a team of specialists who use a range of high tech equipment, and are led by Dr Nigel Bailey and Dr Zhenjiang Wang. It has 36 laboratory-scale constantly stirred digesters available and provides various services, including:

•  Bio Methane Potential (BMP) testing

•  Semi-continuous anaerobic digestion testing

•  pH measurement

•  DS & VS testing

•  Biogas composition

•  COD

•  VFA

•  Ammonia Nitrogen and Total Nitrogen analysis

Dr Bailey, AeroThermal’s Technical Director, said: “Anaerobic digestion can be a key technology in solving the waste conundrum. However how to maximise the energy output while controlling by-products such as ammonia are not yet clearly understood by many in the industry. This new capability can help waste companies evaluate how to efficiently deploy AD and deal with increasing volumes of landfill-bound rubbish.”

AeroThermal has run several hundred scientific trials on different waste streams, and its team has now written nearly 100 internal research reports. The company has already completed waste trials for a number of major waste companies and fast food restaurants.


New research published today by AeroThermal Group shows that pre-treating food waste with a combination of steam and pressure, in a machine known as an autoclave, will double the throughput of an anaerobic digester and significantly reduce the amount of ammonia concentrations by denaturing proteins. The trials have been run over 580 days to date.

This increase in performance of the digesters was maximised when the autoclave operated at a temperature of 140oC and the digesters were run at an Organic Loading Rate (ORL) of >5kgVS/m3/day.

The experiments have shown that autoclaving has the effect of producing a feedstock for AD which allows stable digestion at very high loading rates, without the addition of trace elements which could be harmful to the environment.  

Stable operations have been achieved at a loading rate as high as 10 kg VS/m3/day with food waste autoclaved at 140oC, while the un-autoclaved feedstock digesters entirely failed at a loading rate of 5 kg VS/m3/day.

Such significant increases in digester performance can be attributed to the denaturing of protein during the autoclaving pre-treatment, which has the effect of reducing the quantity of ammonia generated.  

There is a small loss in gas generation due to this denaturing of protein and the caramelisation of sugars but autoclaving at 140OC is probably the optimum temperature as only limited caramelisation will occur and any potential gas loss is more than offset by the advantages of operating stably at higher loading rates.

For the plant operator, this means that by using an autoclave, they can potentially double the throughput of the plant and in doing so, they would double revenues for only a marginal increase in operating costs, since the autoclave uses waste heat from the CHP process.  This can only make for an attractive proposition to food waste AD plant operators, in a market where gate fees continue to fall.  

The autoclave can easily facilitate the co-processing and blending of different types of waste, since it pasteurises, homogenises and hydrolyses the feedstock in one simple and highly effective process.  

Christian Toll, AeroThermal’s CEO, said: “In the past there has been a lot of speculation on the efficacy of pre-treating food waste by an autoclave. This long term series of experiments has shown conclusively that using an autoclave will double the throughput of anaerobic digesters.

“This could have a huge impact on every organisation running a digester, as fitting an autoclave into the process, a relatively straightforward process, could revolutionise the world of anaerobic digestion.”

With this ground breaking technology, AeroThermal have previously won the title of ‘Most Innovative Product and Process’ at the prestigious ADBA and Lets Recycle awards.  

The AD team at AeroThermal is lead by Tony Kimber BSc (Hons), CEng, who has over 30 years experience and has been responsible for the D&B of approx 60 AD plants, successfully managing EPC contracts and leading multiple site delivery teams. 

AeroThermal’s comprehensive testing facility at its laboratory and demonstrator autoclave in Poole, Dorset, is lead by Dr Nigel Bailey MA PhD and Dr Zhenjiang Wang BSc Hons PhD. They use a range of high tech equipment and provide a number of services to the industry, including the examination of waste properties and the evaluation of the anaerobic biodegradation of wastes.


AeroThermal troubleshoots digester processes, analyses plant performance and advises options for plant optimisation.  

They have  36 laboratory-scale, constantly stirred, digesters available for contract research and provide services such as Biologic Methane Potential (BMP) testing, semi‐continuous anaerobic digestion testing,  pH, DS & VS testing, biogas composition, COD, VFA, NH-N and TKN analysis, for any kind of organic wastes or wastewater.

The company has run several hundred scientific trials on many different types of wastes, some in conjunction with Southampton University. The AeroThermal team has now written over 100 reports and has completed waste trials for a number of major waste companies including Biffa, Shanks, Viridor, and New Earth Solutions amongst others.

This programme of experiments builds on AeroThermal’s work on the EU funded Valorgas project, in conjunction with Southampton University, where optimisation of food waste AD plant performance was explored.