What to consider when building your anaerobic digestion plant

11 January 2018

Good plant design and separation of equipment may help prevent losses and lead to competitive and sustainable insurance premiums.

Recent claims in the anaerobic digestion (AD) industry have led to a focus on whether developers are taking the correct planning considerations into account when building their AD plants.

By reviewing the risks prior to construction and incorporating mitigations within the design and build of the plant, developers will be able to demonstrate an improved risk which will be viewed favourably by insurers.

Considering risk mitigation during the design phase can avoid the eventuality of losses. For example, if you have wide separation between key plant items, you may save your plant from total loss by allowing the fire brigade get to the site in time and to contain the fire to a smaller section of the plant. It is easier and cheaper to replace an engine, for example, than the entire plant.

The majority of build and maintenance contractors recognise that it is good practise to build biogas plants using experienced contractors; to install well-recognised plant and machinery with a proven track record, and to manage risks with, for example, good operational housekeeping. While all good engineers will undertake to design and build a suitable plant, often little consideration is given to plant design should a fire occur.

In the UK, fire risk assessments are primarily concerned with personnel safety, and workers’ ability to escape a fire, whereas a property insurer’s objective will be to try to reduce exposure to building and machinery losses from fire.

A specialist engineering insurance company takes into account the hazards within a design, and considers how to reduce the exposure. Additionally, it looks at the following:

  • Are the buildings of a two-hour fire resistance?
  • Is the separation between the buildings and plant of sufficient size to reduce the chances of fire spreading?
  • If the worst happens, how quickly can the fire brigade arrive, and what fire water supplies are on site?

Often, biogas site buildings are not constructed from two-hour fire resistance materials; a case recognised by insurers. Where this is the case, the guidance is to increase the separation between buildings and plant by a distance of 30m. If the building is constructed of materials with a two-hour fire resistance, this distance can be reduced to 15m.

In the event of an AD plant having a mechanical failure or container spillage a lot of valuable digestate is at risk of being wasted. To mitigate the loss, the digestate can be pumped into a lagoon whilst the problem is fixed and reused afterwards.

The principal advantages of constructing a lagoon are the low cost and speed of construction. However, there have been incidents wherein a lack of consideration for the angles and ratio of the lagoon’s banks and the suitability of the soil composition have caused ‘mini-landslides’ of digestate that risk contaminating neighbouring properties and publicly owned waters.

In order to minimise this risk, when constructing a lagoon, the banks should have slopes not surpassing an incline ratio of one vertical to three horizontal (1:3), to enable proper access during compaction of the subgrade, liner and fill.

Cleaning up digestate spills can be expensive and laborious. A spill may not only cause an inconvenience; it could affect neighbouring land too. When insuring an AD plant, the environmental impairment liability policy should include specialist environmental cleaning costs for accidental digestate loss with a high enough liability limit to cover damage to neighbouring and cleaning costs for the site of the AD plant.

Each AD plant will be unique and will present its own specific risks which will require consideration and mitigation, whether through design changes or insurance solutions. A specialist renewable energy broker will be able to provide technical expertise to advise on managing risks and developing bespoke insurance solution that provides the most effective solution for the AD plant.

For further information please contact Flynn Linard, Account Handler on +44 20 7459 5578 or email flynn_linard@jltgroup.com

This blog is compiled for the benefit of clients and prospective clients of companies of the JLT group of companies (“JLT”). It is not legal advice and is intended only to highlight general issues relating to its subject matter; it does not necessarily deal with every aspect of the topic. Views and opinions expressed in this document are those of JLT unless specifically stated otherwise. Whilst every effort has been made to ensure the accuracy of the content of this document, no JLT entity accepts any responsibility for any error, or omission or deficiency. If you intend to take any action or make any decision on the basis of the content of this document, you should first seek specific professional advice. The information contained within this document may not be reproduced and nothing herein shall be construed as conferring to you by implication or otherwise any licence or right to use any JLT intellectual property.