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High levels of water removal

HRS Heat Exchangers’ digestate concentration system

What is your technology?

HRS Heat Exchangers’ digestate concentration system (DCS), which removes up to 80% of the water from digestate biofertiliser produced by anaerobic digestion (AD), while also increasing nutrient content.

How does it work?

The DCS superheats digestate in heat exchangers under vacuum before concentration.

Where would it ideally be used?

At any AD plant which produces a liquid digestate containing solids. It is particularly suitable for sites with limited digestate storage or on-farm plants looking to maximise the nutrients provided by digestate fertiliser.

How is it different?

Unlike conventional digestate dryers, which require a lot of heat, the DCS is extremely efficient in term of digestate concentration. The heat from the biogas combined heat and power is recovered and reused up to a maximum of four cycles, giving a high level of water removal per kW. The DCS can be retrofitted to any plant.

Where has it been used?

Willen Biogas in Middlesex and Kernal Export in Spain.

What benefits does it offer?

It reduces the handling, storage, transportation and application requirements to provide associated operational, overhead and capital cost savings. In some situations, such as plants treating food waste, water removed from the digestate can be added to the feedstock before digestion, creating a closed-loop system.

It also reduces odours and increases nutrient content by turning ammonia into ammonium sulphate. No additional heat and little additional water is required, and it qualifies for the Renewable Heat Incentive.


Cost is dependent on factors including the number of concentration effects installed and other options, but as a guide it is £200,000 to £1m depending on capacity.

Any savings?

Some examples from a 1.5MW plant include 60% reduction in tanker volumes, £20,000 a year savings in water costs and displacement of around 1,100 tonnes a year of artificial fertiliser.

What about maintenance?

Using corrugated tubular heat exchangers reduces maintenance requirements. Cleaning is by integrated ‘cleaning in place’ system while non-welded heat exchangers make it possible to inspect and clean the unit easily.

What is its life span?

The designed working life is 20 years.

How is it future-proofed?

The equipment is easy to upgrade and service, while efficiency benefits will justify its use throughout the lifetime of the plant.

Any future applications?

We are investigating other applications where the solid content of solutions needs to be increased and surplus process heat is available.

How many have you sold and where?

Three units are operational and we are in discussions with other potential customers.

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