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Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants

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Precast concrete tanks vs stelel meme

We recently received the following Press Release which inspired this article in which we discuss the relative merits of precast concrete vs steel biogas tanks for anaerobic digestion plants (i.e. Glass/ Epoxy Coated Steel Tanks).

Quite possibly when you read the article which follows you will, like us, say. “That’s interesting. Why is it that every biogas plant I’ve seen in the last 10 years has the same looking steel biogas reactor tanks?”

“Why is it that the anaerobic digestion and biogas industry is dominated by steel biogas reactor tanks which are hidden behind aluminium profile sheeting and thick insulation for heat retention when in other industries, such as water treatment, the dominant tank material is concrete?”

The thought-provoking Press Release which follows seemed to us to be unique. Read it and our discussion below, and see if you agree… YOUR COMMENTS ARE APPRECIATED.


Press Release:

The Oval AD Tank Solution by Whites Concrete

A special elliptical tank (rectangular in shape with the corners formed into a radius) made from precast concrete panels supplied by Whites Concrete (part of the Naylor Group) has recently been installed for a new Anaerobic Digestion plant in Lincolnshire.

Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants depicted in image.

A Precast Concrete Biogas Tank for an Anaerobic Digestion Plant

This AD plant is one of an increasing number of successful biogas plants operated by a leading multi-disciplinary construction, engineering and operating group, Whites Concrete. The company has also provided a circular Sealwall tank for the farm, which uses cattle manure as its main feedstock.

The elliptical tank, approximately 30m by 10m and 4m high, comprises 68 precast concrete panels, whilst the circular sealwall tank is constructed with 30 units: – both now providing a very robust storage solution, without the need for in-situ concrete, which can reduce construction time by up to 50%.

Whites Concrete’s pre-cast panels can also be utilised to maximise silage storage, such as a new silage clamp at Sherburn in Elmet, constructed in 3 compartments with a capacity of 4500 tonnes. 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 from the bulk density could be safely resisted by the units. via Whites Concrete-Naylor


A telephone call to Michael Wright, the Director responsible for Whites Concrete, revealed the following additional information about the precast concrete units used:

  1. Each precast concrete wall unit stands alone with external counterforts to enable the wall unit to act as a vertical cantilever requiring minimum temporary propping during erection.
  2. The precast units use conventional reinforcement, with appropriate cover for the exposure conditions, and are neither pre-tensioned or post-tensioned, so there are no concerns about the tendons becoming corroded. (Some alternative precast concrete tank designs have been criticised because, in the event of tendon corrosion, failure can occur suddenly and without warning.)
  3. Each Sealwall unit is jointed using a tried and tested compressible hydrophilic jointing method. Stainless steel fixings hold the precast units together, making a visibly robust system.
  4. The wall units are factory cast to very high quality standards, and designed to the exacting requirements of the Water Retaining Concrete Code of Practice BS8007, and Eurocode EC1992. This ensures that the high temperature gradient stresses across the walls during winter weather, while the contents of the biogas reactor remains suitably warm to hot, are allowed for by the provision of the necessary anti-crack steel on the outer surface of the concrete units.
  5. Similar precast concrete designs have been in use for many years in the sewage and industrial effluent treatment industry and have proved their super longevity.

 


The reason for including the above list is that it shows that the use of precast concrete for tanks of this type is an existing proven technology which could be in much more widespread use for all large biogas reactor tanks.

The Reasons Why the Option of Precast Concrete vs Steel Biogas Tanks is Worth Considering by AD Plant Designers

Image showing Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants

Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants

Technical Advantages of Concrete Tanks versus Glass Coated Mild Steel Tanks

Reinforced concrete has the following advantages over steel as the material for these anaerobic digestion/ digester tanks, (and tanks in general) as follows:

  1. Concrete has better inherent anti-corrosion characteristics than steel. The length of life of a steel tank depends upon the longevity of the protective coatings. Once the protective layers of a steel tank are penetrated, even at small points of damage, a corrosion cell develops and the risk of a rapid onset of leaks then occurs. Steel tank manufacturers seldom warrant the life of their products beyond 10 years, and that period is often conditional on active maintenance to identify any points of corrosion and take remedial action on any exposed metal or areas of chipped coatings. Concrete tank designs are carried out to the buyer’s specified lifetime, and “design life” can exceed 100 years. By comparison, is a steel tank really a “permanent” structure at all?
  2. Concrete is a Better Insulator than Glass Coated (and Epoxy Coated) Steel (although additional insulation may be needed for some AD plants). The normal practice for precast concrete reactor tank walls is to leave them exposed on the surface, and readily available for inspection for the start of any leaks. This is unlike insulated GCS (steel) tanks, where the structural tank walls are hidden behind insulation materials and aluminium profiled sheeting, and unseen damage may have occurred during installation.
  3. Concrete Can be Drilled at any Time to Make Openings (for example for replacement Digestor Digestate Mixers to be retrofitted if needed. The same cannot be said for steel tanks due to concerns about creating bare steel and corrosion points at any new openings.
  4. Reinforced Concrete is Inherently a More Sustainable Material than Steel for this Type of Construction. This is a subject which can be debated long and hard. In different applications of concrete versus steel construction the sustainability case may go either way. However, when used in biogas digester tanks, the author considers that the extended life of a concrete structure as opposed to the much shorter life of a steel tank renders the concrete option the most sustainable.

So, there are many advantages to concrete as a material for biogas plant tanks, and yet the advantages go further. There are also additional advantages to precasting the concrete, as discussed next:

Advantages of Precasting Concrete vs In-situ Cast Concrete

  1. Casting in factory conditions permits high quality standards from a highly trained specialist workforce, and economies of scale are present where a continuous production line exists for many clients.
  2. No need to transport shuttering the often large distances to the site, and reduces the need to work at height when fixing reinforcement up to 4m off the ground.
  3. None of the problems which can occur to concrete curing conditions for in-situ cast walls constructed out in the open in all weather conditions.
  4. Precast construction is far more rapid than in-situ construction of concrete, saving money both on construction site staff overheads and on lead in times for the AD plant operator.

The above all tend to reduce the cost of precast concrete, leading us to our final section in which we discuss the relative costs of concrete vs steel biogas tanks for anaerobic digestion plants:

Cost of Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants

Image showing Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants precast wall units

At this point we would be expecting our readers to be asking. OK. But what about the relative costs of Concrete vs Steel Biogas Tanks…

For biogas reactor tanks up to about 4 m deep it is considered by the precast concrete manufacturers that their tank would be cheaper to build overall. They also point out that to compare build-cost alone would not be reasonable, because a precast product which was to last even 10 years longer that an alternative steel tank would be of much greater value to the client. Experts point out that there are very many examples of similar concrete structures still in use after 60 years or more of service.

For taller tanks above 4 m depth, which are not yet common in the UK and Europe, Glass/ Epoxy Coated (GC) Steel Tanks (which take their loading in tension around the circumference and can be built 10 m or more high) would naturally win on cost, and construct-ability.

According to Tracy Taylor, Product Manager, Whites Concrete:

“Precast can be applied to meet numerous design criteria and, in addition to tanks, can be used in a wide variety of applications: vertical walls, horizontal panels in King-post Walls, roofs, and spillway walls to name but a few. The modular  nature of precast means installation is faster and there is no waiting for it to gain its design strength. As with any construction, early involvement is always an advantage, but precast will always offer more options – and will reduce the overall cost of a project.”

The last word on the pre-cast concrete to GC Steel cost comparison comes from Michael Wright who said:

“Our recent successful projects show that precast concrete can compete and win as the design material for AD plant tanks. As the AD plant market matures with more of these tanks being built we expect to see many more precast tanks used as biogas reactor tanks in the future“.

Press Release contact Details:

Whites Concrete

www.naylor.co.uk

concrete@naylor.co.uk

Whaley Road, Barugh Green
Barnsley, South Yorkshire
S75 1HT England

+44 (0)1226 320814

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17 Responses to Concrete vs Steel Biogas Tanks for Anaerobic Digestion Plants

  1. MichaelDwemo August 24, 2017 at 12:10 pm #

    provide your data for concrete insulation values. It is necessary to demonstrate the concrete heat loss, because this does not show concrete as a heat loss.

    • radimin August 30, 2017 at 2:38 am #

      O.K. That is a good point. For a concrete tank design the buyer would need to check that a bare concrete surface would be of low-enough heat loss to maintain the digester at the required temperature throughout cold winter.

  2. Gregorydyday August 27, 2017 at 2:58 am #

    The the biogas production is a danger. People are already constantly in touch with normal biological systems already in nature, animals, air, and the risk of contracting parasites.
    The scientist should not bring new organisms of bio gas manufacture to humans. It is big risk of new sickness.

  3. OscarDealt August 28, 2017 at 7:16 pm #

    Outside the biogas industry there has been a trend away from steel tanks to concrete. Look at the Wastewater Treatment Industry. They’don’t very often use glass coated steel.

  4. Diego Lob September 5, 2017 at 12:16 am #

    How you can avail benefits associated with concrete when so few are specified? This is helpful to the biogas plant contractor but how does the plant purchaser ensure a concrete tank. I presume concrete tank materials are a proven way to truly ensure a long-life? How many examples can you give to back-up that?

  5. Dawanna October 9, 2017 at 12:52 pm #

    Most tanks that are made in Nigeria, are structurally made from steel. Why would an architect or designer choose one material over the other? That’s becausee concrete buildings offer many safety advantages over steel skeleton structures. Compared to steel, concrete can last well in very high temperatures for long periods, and offers excellent protection from fire.

  6. Tain Kuo October 12, 2017 at 2:08 pm #

    The reasons for steel are many. See this – “construction speed quickly, light steel structure building system, don’t need the tie bar, do not need to make a template, cast-in-site concrete floor, do not need to temporary support, in this way, can greatly speed up the construction site of the assembled. Therefore the construction cycle of Light steel structure system, can shorten 50% ~ 75% than the traditional structure mode, can greatly shorten the occupied period of investment funds, increasing the service efficiency of funds.”

  7. Rob Peck October 13, 2017 at 11:55 am #

    In-depth article. Good. This does not look like a biogas plant. What is it?

    • radimin October 16, 2017 at 2:01 am #

      Rob Peck – Yes. It is a biogas plant. I guess you are more familiar with the look of steel tank biogas plants?

  8. Dan Cox October 15, 2017 at 9:06 am #

    Reasoning seems good. What is the design life that these concrete tanks are designed for?

  9. Zach Sullivan October 21, 2017 at 7:11 pm #

    I really enjoyed the writing. Concrete vs steel biogas tanks. Really looking forward to read more. Will read on….

  10. Sunshine L. October 22, 2017 at 9:49 am #

    You are my inspiration. How do you do it? I have few web blogs and very sporadically post to them.

    It takes sooooo long to think of great topics, write the articles, and publish. You seem to manage it and this time its concrete vs steel. Which will win-out?. Awe to you guys.

  11. A Millar October 22, 2017 at 11:59 pm #

    I loved your comparison of these materials. How long do you think the steel and the concrete will actually last for? Thanks Again. Really Great.

  12. Arson Peters October 25, 2017 at 10:46 am #

    Nice writing. Very few people are writing on this important topic. Concrete tanks are long lasting. Concrete tanks are here to stay.

  13. Verna October 27, 2017 at 2:39 am #

    This is an interesting comparison. Have you any comments on how this would apply to a biogas tank in Russia? Это интересное сравнение. Есть ли у вас какие-либо комментарии относительно того, как это применимо к биогазовому танку в России?

  14. Roberto October 31, 2017 at 9:08 pm #

    I thought this page was very useful and well-written.

    Why not do a compare like this for plastic GRP biogas digester tanks though?

    I would come back to read that.

  15. Bockayan November 2, 2017 at 4:56 am #

    In my book the stainless steel versus concrete reverses everything you ever learn about steel versus concrete construction sustainability. Usually, for mild steel it is fairly obvious that it is going to corrode no matter how well it is corrosion protected at the start. But, can it really be true that stainless steel will practically last pretty close to “forever”? I am very sceptical about that.

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