Friday, June 12, 2015

10 Easy Biomethane Lessons

Lesson 1. The Real Biomethane Definition

The definition of biomethane is quite a difficult one, because there are competing definitions. According to the general dictionaries dotted around the web, the term "biomethane" is interchangeable with the word "biogas".

However, in technical use among energy professionals and commentators, this is not correct. Biomethane is really a particular pure form of biogas, which is only produced after high quality further purification of raw biogas. This purification is usually referred to as "biogas upgrading", and this is performed in an "upgrader".

Lesson 2.  What is a Biogas Upgrader?

A biogas upgrader is a particular type of gas treatment unit that is used to concentrate the methane in biogas to natural gas standards (those being the high purity levels of "natural gas" as produced by capturing fossil fuel reserves). These upgrading treatment systems remove carbon dioxide, hydrogen sulphide, water, and other contaminants found in tiny (trace) quantities, from the biogas, to meet standards for "natural gas" quality, as issued by the gas grid distribution companies.



One technique for doing this utilizes what is known as amine gas treating, to purify biogas to become biomethane.

To put it simply, it can be used interchangeably with natural gas in gas distribution grids.

Amine treating is not the only way to produce biomethane from biogas, and recently membranes have been developed which perform this function very efficiently.

Lesson 3. Cutting Through the Confusion which Surrounds Biomethane Use in Transport

At this point I can hear my readers saying: "Haven't I also read about biomethane buses as well as biogas powered engines, so what's the difference". To understand the nuances of meaning in the different uses of these words, a distinction must be drawn between basic treatment of raw biogas, which is needed, for example for use in a biogas combined-heat-and-power (CHP) plant to run a gas-engine, and the more technologically advanced treatment needed to produce natural gas quality (biomethane).

Lesson 4. How Corrosion Problems Affect Raw Biogas Use

Suitably corrosion resistant gas-engines can be powered by untreated raw biogas, but put that biogas through a normal vehicle engine, and the life of the engine will suffer, hence both biogas and biomethane is used to fuel transport vehicles. But, the degree of ruggedisation needed for raw biogas use as a transport fuel is greater (and the engines are more costly), than the use of biomethane which is equivalent to using compressed natural gas CNG.

It is both environmentally preferable and economically justifiable to distribute this CNG made from biogas. Rather than using the term of CNG though, the energy industry is starting to use the term bio SNG, for biogas Synthetic Natural Gas. Bio SNG is best distributed together with natural gas in the existing gas grid.

Lesson 5. Injection of Accredited Quality Biomethane into Gas Grids

The production of renewable gas, at accredited biomethane quality, is injected into the nearest gas main, and paid for by the local gas supplier company. The biomethane price paid will vary according to the market and any green subsidies available locally. The large scale production of renewable biomethane now coming on-stream, is produced through anaerobic digestion (biogas), followed by methanation to create bio SNG, or by gasification.


Lesson 6. Biogas Treatment for Grid Injection

Biogas has, most of the time until now, been used directly in biogas cogeneration plants. This already requires desulphurisation and de-humidifying in order to avoid corrosion in the CHP.

However, to be able to feed biogas into the natural gas network, or use it as a transport fuel a more comprehensive method of treatment is necessary. Added to the need for drying and desulfurization, the carbon dioxide must be removed, and chemical conditioning undertaken to obtain gas quality properties which meet the specifications for natural gas.

This biomethane is more and more, being injected into the natural gas network, and converted to electricity and heat through a CHP unit. Efficiency of heat production is best served when the gas is burnt at a place close to where the thermal energy can be used. A good use would be, for example, in heating a swimming pool, as these have an almost constant year-round, and large, heat demand.

Lesson 7. Technological Advances in Gasification (A Competing technology for Gas Grid Injection)

We mentioned gasification technologies earlier and these are well established for conventional feedstocks for example, as coal and crude oil. The technology used in these processes has been advancing rapidly in recent years, producing a second generation of gasification technologies. These include gasification of, waste wood, forest and agricultural residues, energy crops and may also extend to black liquor.

Lesson 8. Syngas from Gasification

When gasification takes place the output is normally known as "syngas". Syngas undergoes further synthesis to create biomethane. This for example can take the form of, Fischer Tropsch products including the possible conversion of biomethane into diesel fuel, biomethanol, BioDME (dimethyl ether), or gasoline using catalytic conversion of dimethyl ether, or biomethane (Synthetic Natural Gas) (SNG). Syngas can also be used for heat production, and it is increasingly being used for generation of mechanical and electrical power using gas motors or gas turbines.

Lesson 9. Biomethane in America

We provide news here from NGVAmerica, which is a US national organization dedicated to:
… the development of a growing, profitable, and sustainable market for vehicles powered by natural gas or biomethane. NGVAmerica represents more than 200 companies, environmental groups, and government organizations interested in the promotion and use of natural gas and biomethane as transportation fuels. Our member companies are those that produce, distribute, and market natural gas and biomethane across the country; manufacture and service natural gas vehicles, engines, and equipment; and operate fleets powered by clean burning gaseous fuels."


Lesson 10. Biomethane in the UK


The UK has subsidies which are currently being been made available for biomethane upgrading under the (Renewable Heat Incentive RHI) and/ or for the "Renewable Heat Incentive" scheme, which has been on-sale since March 2011.

The UK government has just announced that the initial part is solely for non-domestic applications.
The key aspects are that:

"… the owner of the installation, or the producers of the biomethane for injection, are the people to whom the payments claimed are paid to, and payments will be made over a 20 year period".

Conclusion

By reading this article, and our 10 Lessons, you will have learnt a lot about "biomethane". We think that this will be a very useful knowledge for you to have, because biomethane production, with injection into the local natural gas supply grid, is here to stay. 

After-all how many other businesses create a product for which there is unlimited demand, and once connected into the gas grid needs no selling! Simply read the meter of the flow into the gas grid and charge the gas supply company!

Monday, May 25, 2015

6 High Demand Anaerobic Digestion and Biogas Plant Products

In this article we have identified 6 popular anaerobic digestion and biogas plant products, which with the rising rate of biogas plant installation, has meant that these products are in high demand to ensure the proper running of an ever increasing number of anaerobic digestion plants.


(If you have suggestions for products that you think we should add, just add them to this page via our commenting facility below.)

1. pH/Redox measurement by Hach Lange

It is important to measure pH and Redox potential is all anaerobic digestion plant fermenters, other than perhaps some of the most basic un-mixed plastic membrane covered anaerobic digestion lagoons which are used in hot countries, and are not optimized or controlled. 

For all other plants this measurement is essential, and also needs to be reliable, and very accurate even if not re-calibrated over long periods. That's because the pH and redox information the device provides is used to adjust the operation of the fermenter. Get that wrong and the production of biogas can cease!

Keeping a biogas plant running at close to its full design gas yield, is done mostly through adjusting the feed material type and quantity day by day, and also at times, to decide on how much of any dosing chemicals must be supplied to bring the pH or Redox back within the optimum operating range. These adjustments are used to ensure that the micro-organisms in the digester are maintained in the chemical conditions in which they will thrive and produce the most biogas, at a high methane quality.

One company that has a pH/Redox monitoring instrument which is in high demand, and is designed for the extreme conditions found in biogas plant reactors is Hach Lange.

It is best to provide their technical details to describe this pH robe system. They state the following in their downloadable pdf file:

“The digital pHD electrode used to measure pH and redox is fully encapsulated so that it does not come into contact with the fluid being measured. A special, soil resistant salt bridge forms the direct contact to the fluid to enable the measurements to be made."

"In contrast to conventional membrane based electrodes, this electrode can be used for very long periods even in fluids with a high particulate content, e.g. digester water. The intervals between cleaning are especially long. Electrode poisoning, e.g. by any H2S that may be present, is prevented and dilution of the electrolytes is avoided.”

There is more information about this popular product at:

2. pH Test Strips

pH test strips have been around for many years, but nowadays the technology behind the best of these strips enables the user to assess the pH value, and not just whether the liquid tested is acid or alkaline. They are still not as accurate as using a good quality pH probe, however, they can be very useful when an immediate assessment of approximate pH value is needed, and when there is no probe, such as the Hach Lange pH/Redox probe discussed in 1., above.

For that reason we have included pH Test Strips in this list of our "in demand" anaerobic digestion products.

Probably the best known test strips are those made by Merck in their Millipore range. They offer a large number of products for pH measurements with various methods of operation. These include pH indicator papers, and MColorpHast™ pH test strips, and pH indicator solution, however it is the simple test strips that are most used and can be an essential tool, especially when carrying out process troubleshooting site checks on anaerobic digestion plants.

For anyone that wishes to find out more about pH test strips by Merck we suggest the following link as a starting point:


3. NPL Biogas Analysis

NPL, once the UK's National Physical Laboratory is a private company which specialises in carrying out trace-level impurity analyses for gases, especially for biogas. Knowing what may be present in biogas as trace-level impurities is critical for the design of the gas-engine for power generation, and also increasingly for upgrading biogas to biomethane by removing these impurities.

The concentrations of both the trace-level impurities which cause corrosion and those that cause the build-up of hard silica materials on valves, and combustion cylinders, are assessed by using these tests. Also, very sticky tar-like substances within a gas-engine used for electrical power generation, can build-up, and trace-level gas impurity tests will when used skilfully by an expert, allow the need for pre-treatment of the biogas before it enters gas engines to be investigated, thus avoiding the risk of very expensive remedial maintenance on the power generation and biomethane upgrading system later.

Traceable gas standards containing each of the following components are available, from NPL as follows:

• Siloxanes (multi-component mixtures of the siloxanes most commonly found in biogas)
• Hydrogen sulphide
• Ammonia.

Further information on this in-demand service can be obtained from:


4. Prosonic Flow B 200 Ultrasonic Flowmeter

Almost all anaerobic digestion systems require the monitoring of flow, and it is particularly important to measure the flow and volume of the substrate feed continuously and accurately, so that the calorific value feed that is added is known, and can be controlled. The Prosonic Flow B 200 by Endress and Hauser Ltd is a well-known example of such a flowmeter.

An inexperienced biogas plant designer might think that a cheaper, vane type flowmeter would be satisfactory, but due to the presence of fibrous materials in the flow, these get caught around the vane of a cheap flowmeter and cause malfunction of the device. As a "non-intrusive" flowmeter the ultrasonic types are very well suited to biogas applications, and ATEX rated explosion proof versions are also available to avoid explosion risks where these occur.

Further details are available at:

5. Biogas Plant Mixer Systems

Biogas plant mixing systems have traditionally been under-specified for completely stirred mixed reactor type biogas plants. With inadequate stirring, their performance can be far below what would be achieved if well designed, good quality mixing, was installed and operated.

Anaerobic digestion operators can experience problems with the build-up of a hard cap of biomass floating on the surface. It can impede the circulation of biogas through this "hard crust", and as the crust can contain a large proportion of the organic material in the reactor, the rate of biogas production can be significantly reduced.

The installed mixers may be incapable of breaking up the "hard crust" and opening the top of a reactor to physically smash up a floating crust, means significant plant down-time, and loss of biogas production.

The Landia GasMix has not been around for even 18 months (time of writing is May 2015), and yet it is a biogas plant reactor mixing system that is in high-demand. Users report that once installed, and using the cleverly designed combination of biogas and substrate purging, hard crust accumulations can be broken up and re-submerged in not much more than half an hour of operation using this system. Once initial crust break-up and re-suspension has been achieved, the system is run on an automatic setting and runs for only short periods daily, to prevent any further significant build-up of floating material.

Further information of the Landia GasMix is available here:

6. Biogas Storage Covers and Vessels

If there is one thing that all biogas plants have in common is that they produce gas which must be stored, until needed. Suppliers of biogas storage covers and vessels, have been in increasing demand for their products, as the rate of anaerobic digestion plant construction has accelerated.

VERGAS Ltd is a leading company in biogas storage systems, and specialises in the design, manufacture and installation of high quality flexible membrane biogas management equipment, worldwide.

The following is a link to VERGAS Ltd's website where further information on biogas storage covers and vessels is available:

Conclusion

We hope that this article has been useful. If it has, or even if it has not and you have suggestions on improvement you would like us to make, please provide us with feedback via the "commenting" facility below, or via our contact page.

Saturday, May 02, 2015

At Last EU Biofuels Cap Agreed and Should Now Allow Biogas from Waste to Thrive

"Waste Fed Biogas Plants" Should Now as Time Goes On, be Able to Throw Off the Critics Who Confuse them with Food Crop Based "Biofuel Biogas Plants"

The EU has at last agreed 7% cap on 'harmful' biofuels, and although many would say that this cap should have been set much lower, it is an important step away from one aspect of the use of anaerobic digestion, which has caused much damage, to the concept of gaining renewable energy from biogas plants, in the eyes of the public.

A example of an anti-biofuels campaign poster recently available on Twitter
About 15 years ago, when oil price rises had been inexorably rising for as long as anyone could remember, and the supply sources of oil looked increasingly insecure, governments began the renaissance of anaerobic digestion by subsidizing so called "biofuel" biogas plants.

The idea of biofuel is focused mainly on the production of diesel fuel, and the organic feedstock was almost entirely food crops.

It was seen as being "green", at first, but when in-depth and "whole-life" assessments were conducted on the balance of net energy produced by the crop use processes, and the fact that food prices have been rising as population demand raises consumption, the idea quickly began to look like nothing other than "greenwash".

The big hope that gave rise to the whole "biofuels" movement, was that the carbon emissions reduction benefits from it would be large, and would justify the use of food to make energy. But, sadly these gains have never materialised.

Worse still, in countries like the UK where biofuel subsidies were introduced late, and were lower than in Europe generally, waste material fed anaerobic digestion plants have often been mistakenly also tarred by the same brush, and perceived cynically as just another deceptive "green" lable.



Even today, objectors protest about proposed organic-waste-fed biogas plants, in the false belief that they will turn-out to be just the opposite! This is entirely due to studies conducted on biofuel production, and planning consents are being held-up, and even rejected, due to negative publicity related in fact to crop-fed biofuel plants, by hostile media and the public.

On this blog we have always been at pains to make the distinction between the very positive environmental (carbon emission reduction potential) of waste fed biogas production, as opposed to the poor record of crop-fed biogas production when used to make biofuels (mostly bio-diesel).

The main countries which did adopt biofuel production in a big way were, Germany and other central Eurpoean States, the US, and some South American countries. Most of these have been progressively reducing their subsidies for biofuels for some time. In fact, steep subsidy reductions in Germany have led close to stagnation, in the numbers of their biogas plants in recent years.

The 7% cap on 'harmful' biofuels will go hand-in-hand with further reduction in biofuel production subsidies, as governments seek to cut-back their national biofuel production, and to meet the new low target.

Hopefully, existing Agricultural Biogas Plants built for the creation of biogas for further processing into biofuel will, in the most part, be able to convert their operations to accept agricultural waste and continue in profitable operation as a result.

For those interested in reading more about the fall from grace of "biofuels", we suggest a visit to the following web pages for further reading:

EU agrees to burst biofuels bubble after 2020

After more than 10 years of debate, the European Parliament has today (28 April) agreed new laws to limit the use of crop-based biofuels across the continent.

The new rules effectively limit the use of biofuels in the transport sector at 7%, which count towards the 10% renewable energy target in transport by 2020.

The decision will prevent up to 320 million tonnes of CO2 - equal to Poland's total carbon emissions in 2012 - from entering the atmosphere. It has dually been welcomed by green groups and industry bodies alike.

Friends of the Earth Europe's biofuels campaigner Robbie Blake said: "Let no-one be in doubt, the biofuels bubble has burst.

EU agrees 7% cap on 'harmful' biofuels

Pietro Caloprisco, senior policy officer at Transport & Environment, said: "After years of industry and member state lobbying, this agreement is far weaker than the Commission's original proposal. Nevertheless, it sends a clear signal that land-based biofuels have no future role to play in Europe."

'Shun food crops'

European representatives of the Green party were rather more scathing, calling the deal a "major missed opportunity".

Green climate spokesperson Bas Eickhout said: "Feeding crops into cars has fuelled rising food prices and rainforest destruction and the EU should not be further exacerbating these trends by promoting the use of agricultural land for fuel.

"We should be shunning the use of food crops for fuel altogether but a 7% 'cap' is clearly too high and will allow for further increasing the large share of climate-damaging biofuels in our fuel mix."

What do you think? Please comment below...



Friday, April 24, 2015

ENER-G Biogas CHP Technology Will Raise Small Commercial Anaerobic Digestion Plant Profitability

We are delighted to have been sent, (and publish) the following press release, which we believe is very good news for existing AD Plant owners, and also those considering jumping into the AD Renewable energy business.

If you are not quite sure what a CHP Unit is, let me just tell you that it stands for Combined Heat and Power Unit. If that still means nothing let me tell you that you are not alone! The renewable energy sector badly needs to come up some new ways of describing what CHP is!


Putting the jargon to one side. This CHP Unit takes the heat which, without it, would go into one of those cooling systems you see on the top of biogas power containers, you know those ISO Containers which contain those gas engines (electrical power generators) which hum away all day and night. It converts that heat in a heat exchanger, into hot water.

The hot water produced is the piped to a place where it can be used. That can be anything from heating the domestic radiators in homes, to providing hot water for an industrial process in a factory. 

With a CHP Unit, farmers can heat their own greenhouses, and barns, seeing an immediate reduction in their fuel bills, or export the hot water through pipes to neighbours. So, if the CHP Unit investment cost is low enough, the profitability of biogas plants will be improved wherever they are installed. This new CHP technology appears to fit all the technical requirements, so its uptake will depend on the price to buy these CHP Units.

PRESS RELEASE: 24 April 2015

New ENER-G biogas CHP technology warms up cash returns on small scale anaerobic digestion

ENER-G has turned up the heat on the anaerobic digestion market by launching a new sub 200kwth CHP unit that maximises financial returns on both the highest rate Renewable Heat Incentive (RHI) and Feed in Tariffs (FIT).
This will help to stem the shortfall from FIT digression following the 20% reduction in FIT rates last year and ongoing tariff reductions. ENER-G says that its new biogas CHP technology makes small scale anaerobic digestion viable for a wider customer base, particularly smaller farms and dairies, as well as industrial processors.
The new ENER-G E200 biogas CHP unit provides a thermal output of 195kWth (qualifying for the highest rate RHI  of 7.5p per kWth), together with an electrical output of 205kWe - at a total efficiency rating of 77.1%.
"Our UK design team have packed a mighty heat punch of 40.7% efficiency into the new E200, without compromising on high electrical efficiency of 37.6%," said ENER-G's Laurence Stephenson. "The heat efficiency for a unit of this size is unmatched in the market, which is critical in boosting RHI returns to bridge the shortfall from dwindling FIT rates.
"It will accelerate the pay back on investment - making anaerobic digestion feasible for smaller farms and other sites. This could provide a valuable lifeline for dairies, which are under huge financial pressure from falling milk prices."
ENER-G's UK R&D team has achieved the high thermal output by using a high efficiency turbo-charged MAN engine and then reducing the cooling level of exhaust gases to achieve a sub 200kWth heat output that falls below the threshold for highest rate RHI.
The  higher rate of RHI payment, available only to sub 200 kWth sites, provides  customers with an extra 1.6p per kWth compared to the next tariff band for sub 600kWth sites. This provides a guaranteed income over 20 years that increases with inflation.
FiTs are payable on electricity generated from a CHP unit of this size at the highest current rate of 10.13p per kWh..
At current rates, a typical farm or dairy operating the E200 on a 24-hour cycle at 92% availability would receive annual payments of £167,361 for FITs and £117,866 for RHI - amounting to a total guaranteed 20-year income of up to  £5.7 million. This would be around £455,340 more than the lifetime income from the lower band RHI tariff.
Government grants of up to £10,000 are available to UK farmers to undertake anaerobic digestion feasibility studies.
Laurence Stephenson added: "Many pre-accredited anaerobic digestion projects are stalling because of finance issues, particularly due to FIT digression. But with guaranteed higher rate returns from RHI, a typical small scale anaerobic digestion project should offer a payback within four years, providing a guaranteed profit stream thereafter. ENER-G's maintenance package guarantees a minimum 92% availability of power and heat production - providing added certainty in negotiating finance".
The ENER-G CHP system can be supplied in a container on a 'plug and play' basis - simplifying and speeding up the commissioning process, which must take place within 12 months of pre-accreditation approval.
For the past 30 years ENER-G has been European market leader in small scale CHP (4kWe to over 10MWe). The company has developed  over 170MW of  biogas power generation from AD, landfill, and associated gases. ENER-G provides a complete package - from design and manufacture of CHP systems - to installation, commissioning and finance - through to maintenance and service via its national engineering team. It also supplies pre-treatment technology required to clean and dry biogas from digestion processes, such as effluent and AD.
Further information is availabe at: www.energ.co.uk/chp

We would love to hear about your experiences with biogas plant CHP generally, and specifically for this and any other Anaerobic Digester Sites, of which you are aware. Just add a comment, and we will publish your non-spammy comments.

Tuesday, April 21, 2015

Clever Re-use of Pre-cast Concrete in World War II Hangar for AD Plant Feed Storage

Whites Concrete has recently provided an innovative storage solution for the "Northern Crop Driers" Anaerobic Digestion Plant, and we think that the way in which this new use has been found for a historic World War II aircraft hangar, will interest many people.

Based south east of York at the former RAF Melbourne, Northern Crop Driers has successfully utilised pre-cast panels from Whites Concrete to maximise silage storage for its AD plant. 
Leading manufacturers of dried grass horse feeds that are virtually identical to fresh grass, Northern Crop Driers needed a clamp capable of storing 6,000 tonnes of silage in an old hangar at its Melrose Farm base. With a roof height limiting the maneuverability of machinery to compress the stored material, 
Whites Concrete were called upon to create a design that would use the space to full effect, keeping silage dry and clean whilst ensuring that load demands would meet the bulk density. The safely stored maize, grass silage (plus some sugar beet), and slurry from sister company Melrose Pigs, provides feedstock for the 500kW AD plant. 
Pam Dear from the family-owned and run business said: “Investing in an AD plant made perfect sense here because it brings everything together.
With our pigs and grass drying business, we knew we could generate our own green electricity, but first we had to bring in a whole year’s worth of crop, so getting our storage facility right was crucial”. 
Whites Concrete worked closely with Northern Crop Driers to initially provide two designs, including one with metalwork, but 4m concrete panels were ultimately chosen as the best solution. Pam Dear added: “We were determined to utilise every inch of the hangar to give us 6,000 tonnes of storage, so Whites’ expertise in materials and load-bearing requirements was invaluable”. 
Over a period of one month, 150No 4m high (1m wide) Whites Concrete panels were installed at the 750-acre Melrose Farm, where grass, home grown maize and supplies from neighbouring farms combine with the pig slurry to produce enough power for everything required on site, with excess sold on to the grid. L-shape Groundwall panels from Whites Concrete were considered the most suitable option so as not to create any additional load bearing onto the existing structure of the old hangar. 
Ideal as push-walls to resist machinery loads, extreme heights of storage and areas where heavy traffic will be working, Groundwall is hygienic, as well as far quicker and more economical than block or in-situ concrete. 
Pam Dear continued:
 “Despite being a higher cost, the pre-cast concrete panels from Whites Concrete are actually much cheaper to install. We produce high quality horse feed from 100% natural, home grown grass, which takes up a good chunk of power to dry out, so in the not too distant future we also hope to harness the heat from our AD plant for that part of our business. Going into AD production has given us more stability. It is helping both of our businesses grow and shows that we are serious about sustainability”. 

The high quality of the digestate at Melrose Farm is also proving a winner, with its valuable nutrients producing healthier grasses. It has helped make a big reduction on bought-in fertiliser. Following the success of the silage clamp, 
Northern Crop Driers has since extended the storage facility by an additional 4,000 tonnes, installing a further 90 No 3m high pre-cast concrete panels from Whites Concrete to create 10,000 tonnes of silage space for the AD plant. 
These extra panels are from Whites Concrete’s Rockwall range, which achieves a finished concrete strength in excess of 60N for any above or below ground construction.
 “Moving into AD is a very good fit with our business model”, concluded Pam Dear.
“We produce 100% natural horse feeds and bedding, and now we generate our own on-site green power, with a payback of just five to six years”. 
Historical Note:  RAF Melbourne was a Royal Air Force station during the Second World War. In the late 1940s the airfield was used by Armstrong Whitworth Whitleys of 10-Squadron as a relief landing ground for RAF Leeming near Northallerton, just south of Darlington. The squadron continued with operation until March 1945. 
 It lost 109 aircraft. Unusually, Melbourne was equipped with FIDO (Fog Investigation and Dispersal Operation). This made the RAF station a popular diversion airfield for other squadrons returning from operations to Yorkshire. The [smoke making] device consisted of two pipelines situated along both sides of the runway, through which fuel was pumped, and then out through burner jets positioned at intervals.
Although very large volumes of fuel were consumed, FIDO more than made up for the costs involved by reducing aircraft losses
This very much follows the ethos of Anaerobic Digestion. Re-use of existing facilities certainly avoids carbon emissions, and in this case the solution chosen also avoids changing the historic structure, by any more than is essential. Well done, Northern Crop Driers, and Whites Concrete!

Tel: 01924 464 283
k whites[@]longley.uk.com
Ravensthorpe Road, Thornhill Lees, Dewsbury, West Yorkshire, WF12 9EF

Tuesday, February 24, 2015

Confronting the Fear of a Biogas Digester Turning Sour

Nobody talks about what happens when a biogas digester turns sour. It's costly, can mean turning away clients, and the extra hydrogen sulphide produced can be very dangerous...

We must start confronting the fear of a Biogas Digester Turning Sour!


As more and more biogas plants are built, many organisations and plant operators will be tasked with the responsibility for reliable operation of these intricate pieces of equipment. There is a danger that unless the biogas industry airs its past errors in public, the anaerobic digestion industry will be set back by lack of understanding of the nature of the problems that can occur if biogas plants are not continually monitored and well run.

It is perfectly natural for a young industry, such as this to want to move forward and not talk about past mistakes, but on the other hand it is only by understanding the past that repeating past errors can be avoided.

For that reason, in this article we will discuss that most unpleasant outcome of poor or inexperienced biogas plant operation, which is known as a digester turning sour.

What is actually meant by this term, is when a biogas reactor is allowed to diverge sufficiently from its target pH, and intended alkalinity concentration for the methanogens (methanogenic organisms) to be killed (in effect poisoned), and other unwanted organisms to thrive. Significant quantities of dangerous hydrogen sulphide are likely to be produced in such circumstances.

To describe this as a "fearful event", is not an overstatement. The consequences in terms of lost production from a biogas plant in these circumstances are substantial. In fact it is quite possible that plant managers and/ or operators will have faced disciplinary action due to such events.

Those that sell these plants naturally like to provide the impression that these plants run themselves.  While they may appear to do so when run by experienced operators, behind the scenes there is always activity. Biogas plants should never be considered to be "black boxes" in which waste enters and methane leaves like clockwork. It simply cannot be like that!

These are complex biochemical reactors. Those that study biochemistry and microbiology will appreciate that there are at least three stages taking place, each of which has to progress successfully before biogas is produced. Phase changes are needed from solids to liquid to gas, and the right healthy micro-organisms need to be present at every stage.

The equipment can fail in a multitude of ways. Sensors can lose calibration, but still appear to be working. Pumps can, at times appear to be running but are in fact delivering no flow.

A delicate balance needs to be maintained and while it is, all goes well. However, feed materials are always changing both in their nature, and seasonally. This means that regular monitoring of digester health is always absolutely essential, and beyond that so is a proactive plant operator needed, to ensure that manual and automatic adjustments are carried out, hour by hour, day by day, year in, year out.

Wise biogas plant designers/contractors install automatic equipment and train operating and maintenance staff, to maintain that delicate balance, as a matter of routine.

But, it is vital that management and staff at every biogas facility remain vigilant, because should a digester fail and turn sour it is a lengthy procedure to bring it back to health. The worst case scenario is that the whole digester tank has to be dug out, and the whole biological commissioning process started again. The consequences of this in terms of cost, the ability to comply with contractual duties, and lost goodwill, are massive. Not to mention the dangers of the likely odour escape, the health and safety of personnel, and the risk of polluting the local environment while disposing of the contents of a "sour" reactor, which hardly need stressing.

Short of that, in most cases when it happens, it is caught in time to implement procedures to bring the reactor back to a healthy condition, while retaining the substrate in-situ. This is a slow process and may take 4 weeks or more to achieve even the recommencement of substrate feeding feed, even at a low fow rate.

Subsequently, over some weeks, the feed flow rate must be progressively increased. This must be done rapidly enough to encourage the growth of a healthy compliment of fermentation micro-organisms, but never so rapidly as to cause organic overload. Organic overload could push the reactor back into the chemical conditions which caused the problem originally, so care is needed throughout.

Once the bulk of the methanogenic organisms are lost, for example, they must be replaced. The methanogens are slow growing and have to be teased back into health, over a long period when no treatment can take place. In short, the microbiologcal system has to be allowed its own time, to recover itself, and that process cannot be rushed.

In view of the large loss of revenue and inevitable disruption which would be caused to the waste producers if their waste could not be removed by the biogas plant operator, the avoidable event of a sour digester needs to be continually borne in-mind by all those involved in the industry.

Monitoring and control systems are improving all the time in reliability and sophistication, so with time the threat is becoming easier to manage. However, the AD industry must never forget the consequences of a sour digester.

It is only when organisations in this industry continuously confront the fear of a sour digester, which should be instilled in the culture of all biogas companies, that it can be avoided. That mildly felt apprehension, needs to be ever-present throughout the company from the managing director, at all levels down to the pump fitter.

Some "fear" should especially be felt by the accountant/ maintenance budget holders who might otherwise require that essential maintenance be deferred to improve company cash-flow, just for a few months, but with dire consequences.

Paradoxically, it can be the best run biogas companies which fall hardest. It is perfectly possible for a site team to make biogas plant operation look to higher-management to be simple, and by achieving reliable plant operation for many years, to result in a loss of understanding of the duties of the plant operational staff. This is easy to creep-up on an organisation over time, and after many staff changes.

A gradual erosion of respect for the work of the site operational staff, can easily lead to corner-cutting. This can reduce monitoring and maintenance, while the site staff suffer in silence, mending and managing on reduced man-hours, and pared-back budgets. Eventually, if not corrected, this can result in a crisis, and a large plant failure.

Yes. Even the very best run companies can fall prey to this...

So, our conclusion is that the "black box" concept of a biogas plant, must always be held in-check by a willingness not to brush this age-old problem of biogas plant operation "under the carpet". You can never switch-on a biogas plant and walk away!

Instead, all in the anaerobic digestion industry must in their own ways, continuously remain open to the fear of biogas plant micro-organism failure (a "sour" digester), when operating conditions stray a long way away from healthy conditions for the unseen microbial populations, which are essential for plant operation.

Achieve that, and the problem doesn't actually recur - and the biogas industry will thrive.