Saturday, October 11, 2014

5 Most Critical Factors in the Design of Every Biogas Plant - Xergi List

The five design factors which can make or break the success of a Biogas Plant Project, is a list inspired by a pdf available on the Xergi website. Our interpretation of their list follows:

The 5 most essential aspects of the design of any anaerobic digestion plant can be listed as:

1. A High Degree of Flexibility

Biogas plants are complex even without consideration of the fact that the feed materials are waste products. They vary not only seasonally, but according to market forces and what the waste producer is doing in their business at any time. Not only that, as any biogas plant operator will tell you, it is necessary to feed the digester with the right mix of "woody" and "green" at all times.

If you perfer to view this on the YouTube website click here for this Xergi Biogas Top Design Success Factors video.

So, all biogas plant designs need to come with a huge dose of flexibility across just about any parameter that you consider. This is essential, when it comes to providing a plant which will be sufficiently adaptable to the clients needs throughout the lifetime of the biogas plant.

2. Dosing Equipment With The Ability To Handle All Types Of Feed Materials

No biogas plant can work well for long unless the operator is able to set the relative feed materials (substrate) proportions and overall input flows to what is needed for the good of the biomass in the digesters at any time, and for the equipment to reliably deliver that dose.

In most processes the input (raw material) is known (because it is bought-in to a specification). Waste deliveries to an AD Plant are the complete opposite. Nothing is the same for two days running when it is waste that is the raw material and is collected from the public and businesses.

This is a challenge for dosing equipment designers, and not all of them are up to scratch on the ability of their pre-treatment of waste arriving at the biogas plant to sort, mix, and break the material down into a transportable/ pump-able quantity of biogas plant feed accurately, and daily over long periods in-between maintenance dates.

3. Adopting an Ideal Process Temperature

Thermophilic AD Plants provide optimum gas yields within the shortest period of time (average particle residence time in the reactor), so it is important for the economic benefit of the biogas project that the best rates of reaction are achieved, and by experience a company like Xergi is well versed in balancing demanding cost factors for choice the best process operating temperature.

4. High Efficiency Mixing

Mixing demands are hard to meet in the fermentation process, as the mixture has a comparatively high viscosity, and fibrous materials can cause reduced equipment availability.

Within the biogas industry there are many ways to achieve biogas reactor mixing, some solutions are generic and have been around for many years. But, many of the best now, which are now avialable are compartaively cheap to run and provide the closest approximation to perfect mixing, are proprietory.

Xergi for example has its own in-house mixing technology to ensure that the mixing function is reliably available to provide something like the features of a fully-mixed reactor (fermenter).

5. Remote Control of Operating Systems

Biogas plants need to be readily accessible by remote control to operational managers 24/7, including at times while off-duty. Production of power has to continue all the time, so remote control must not only be available, but capable of being used easily on multiple computing device types, including from a small smartphone 

For further information visit the Xergi website here:

Sunday, October 05, 2014

Many UK Anaerobic Digester Planning Applications Still Public Relations Disaster

Objections are Understandable After UK AD Plant Leaks
New anaerobic digestion plant projects are being put forward for planning permission in increasing numbers in the UK, but many are facing heavy local opposition.

In fact it isn't unreasonable to label many of these planning applications as a public relations disaster. 

In this post we have highlighted just three biogas plant applications to provide a flavour for the public reactions received. In the first example, it is clear that the residents of the quiet market town of Whitchurch in Shropshire are very concerned about the possible negative impacts of this anaerobic digestion project.

1000 sign petition against Whitchurch anaerobic digester -

"1000 sign petition against Whitchurch anaerobic digester. - One of the group's campaigners Sue Whitson said:
“We have been collecting signatures against the proposed digester for some weeks now and have had petitions in a number of business premises in the town as well as collecting signatures on-line."
In the article it becomes clear that an incident at an AD Plant not far away, is on the minds of many of the people of Whitchurch. We reported upon that tank collapse and digestate leak here:
"So far, Whitchurch Town and Parish Councils have objected to the plans on the grounds of potential smell and negative environmental impacts.
Planning experts always say that the secret to avoiding objections to any controversial project is early consultation, and spending time with the locals to make the case for the AD Plant and allay fears, if necessary modifying your proposals before the full application for planning permission is submitted. The next link suggests that this may be the approach being used in this case, but it is unclear whether the plannign application has yet been made:

More than 120 Wimblington people have their say on Fengrain ... - Wisbech Standard
"Wisbech Standard - GALLERY: More than 120 Wimblington people have their say on Fengrain ...Wisbech Standard - Public meeting about the Anaerobic digestion for Fengrain, Held at Wimblington parish hall. Left: Mick Knight resident and organiser of the meeting. Cllr David Connor, Chairman David Green,Speaker Charlie Graham-Cameron.Picture: Steve Williams.and more »"
Clearly, the UK anaerobic digestion industry needs to do better with its public relations. That the public are against this AD Plant going ahead is evident from the following quotation from the article:
"Mr Barclay revealed the result of the contrasting petitions he put on his website for and against the digester – 151 voted against it, 11 people were in favour."
Finally, there are yet more biogas plant planning permission problems currently evident in the following example:
Developer appeals over green belt anaerobic digestion plant refusal - PlanningResource (subscription)
"Place North West - Developer appeals over green belt anaerobic digestion plant refusal. The developers behind a planned anaerobic digestion plant on a green belt site in Greater Manchester have appealed against a council's decision to turn down the application. Ramsbottom: developer to appeal energy plant refusal. The application, for the ...Controversial digestion plant developers lodge appeal against refusal. Bury Times: Appeal launched for Ramsbottom energy plant. Place North Westall 2 news articles »"
However, it is clear that there will be many more AD Plants built in the near future throughout the UK if the following news, of a regulation that has been simplified, is anything to judge by:

Changes to UK's waste regulations favour anaerobic digestion industry - Renewable Energy Focus

"Changes to UK's waste regulations favour anaerobic digestion industry: Renewable Energy Focus - Biogas producers will no longer need to pay for permits or waste handling controls to use fruit and vegetable by-products in the anaerobic digestion (AD) process, the Environment Agency confirmed earlier this week.1 This resolves a long-standing ...and more »"
Taking the above reports into account does we suggest fully justify our view that many current UK Anaerobic Digester Planning Applications are still a Public Relations disaster. Does anyone have any suggestions as to how this situation can be improved?

Wednesday, October 01, 2014

Rise in Biogas Plant Blockages Causes Financial Losses at Food Waste AD Plants

As governments and biogas plant operators have woken up to the amount of food waste that modern societies produce, there has been a trend for existing biogas plant operators to start accepting food waste as an additional feed source.

But, that has been causing big trouble for many biogas plant operators. It is causing many plant pumping failures, and big losses to these businesses due to time-consuming plant downtime while clogged pipework is dismantled and rebuilt.

There is a solution to this so read-on to find out what it is!

The Food Waste Problem

By "food waste", we mean all kinds of waste from food processing plants to out-of-date supermarket food packets, and this may also include restaurant and office canteen waste. These are wastes which until 20 years ago, in many countries would have been fed to pigs, or rendered down into various types of cattle feed.

Watch our video below, in which we explain the problem! (Please try not to get too emotional while watching!!)

(If this video does not display well on you device, it can also be wtached by clicking here: )

It was concern about the risks of infection spreading, such as "Foot and Mouth" and "BSE", that these types of wastes were deemed to cause if consumed as part of the food chain, which has lead to them becoming a "waste" and age-old practices for re-use of unwanted food, being banned. By preventing their consumption, the waste had to go somewhere, and has been resulting in huge tonnages which have been being landfilled to the detriment of landfills.

On the face of it, food waste should not be landfilled, and to do so is a huge waste of resources, because all the energy locked-up up in food makes it absolutely the best type of feedstock to use because it is the highest in calorific value. But, when an anaerobic digestion plant changes its feed material to food waste it also starts accepting a highly variable type of waste, and one which can vary greatly in viscosity and will almost always include a substantial amount of foreign matter, especially pieces of plastic and plastic film.

Existing Biogas Plant Pumps Are Often Not Suitable

Anaerobic Digestion plants built originally for manure and agricultural wastes/ energy crop digestion, and by some accounts also those designed by "experts" to accept food waste, are usually equipped with high solids passing centrifugal subtstrate pumping systems to deliver the feed into the digesters, and to remove it after digestion.

Such, "standard" pumps are being found inadequate and furthermore, as pipework starts to clog up, the flow rate from such pumps tends to drop, allowing yet more material to build-up within the pipework and eventually pumping stops when the pipe flow resistance overloads the pump system and all pumping ceases, until pipes and pumps are manually cleaned out.

To compound the problem, many AD Plants were never designed for the pipes to be dismantled and in such cases pipe replacement may be necessary.

The Solution

Pump experts recommend positive displacement pumps as the solution to this problem in combination with chopper or macerator pumps. An example is the Verderflex peristaltic pump series which when correctly installed is designed to reliably transport the chopped slurry from holding tanks and through the system to the digesters tank(s). This usually will be via a heat exchanger to raise the substrate’s temperature to a level suitable for efficient digestion, before it enters the AD plant digester tanks. The same type of pump may also be recommended for the outlet from the digester.

The Silver Lining Once Food Waste Problems are Solved!

With the right pump systems installed, biogas plants are capable of producing substantially more biogas from the higher calorific value food waste, so once upgraded pumping systems are working reliably, the pant operator can benefit from a significantly improved income from increased biogas energy sales.

For further information on peristaltic pumps and anaerobic digestion plant susbtrate/ digestate pumping, we sugest that you might do well to visit the Verder website at:

A case study pdf is also available on the Verder website, here:

Anaerobic Digestion Community Website