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MIXING, WEIGHING & CONVEYING PLANT OVERHAUL MAXIMISES BIOGAS YIELDS
Following an upgrade of its reception tank and digester mixing system, Eco Verde Energy (EVE) has put a once troublesome Anaerobic Digestion (AD)+ plant firmly back on track. Landia equipment has been integral to the project...
he Holton AD plant in Suffolk, which receives around 65% of its feedstock from the adjacent Bernard Matthews poultry facility, had seen biogas production drop significantly, and eventually to a complete halt for a much needed overhaul. Initially, the primary digester (2700m3
T ) was
drained down, discovering, as expected, faults with the mixers, but also a broken stanchion. Later, further inspections revealed that there was damage to the roof of the digester, so the decision was taken to postpone operations for a complete maintenance revamp. Eco Verde’s Site Manager at Holton, Kris Martin, said: “At one point, the site was being run remotely, but it has now benefitted from a complete review of operations. When we shut down for the maintenance overhaul, trying to get shipshape became more challenging, due to some suppliers not being able to assist...” Matters took a significant turn for the better though when Martin made contact with Landia, about whom he’d heard good reports. “They’re a pump and mixer company, and there are plenty of those,” he said, “but unlike some others, they actually listened and clearly wanted to try and understand how a solution could be found. As soon as they first came to the site, there was a good vibe. Linking up the mixing operation from the reception tank, through the feeding module, and then on to the digesters, and finally through to the pasteurisers, wasn’t going to be easy, but rather than just try and sell us equipment, Landia were keen to find a way to help make the Holton plant perform as it should.” New submersible mixers (5.5kW) from Landia have been installed for the reception tank, which unlike the previous units, can be easily lifted up on a crimped rail system for inspection to remove any plastics and perform standard maintenance. For the feeding module, which is batch-fed from the reception tank, a Landia Chopper
26 FEBRUARY 2024 | PROCESS & CONTROL
Pump has replaced the failed unit. The external knife system (combined with the addition of a new shredder propeller) ensures that particles are continuously reduced in size, and that solids cannot enter the pump’s casing. The primary digester was first upgraded to replace the failed units with Landia mixers. By utilising a pre-existing hatch system that provides easy access, these new 18.5kW mixers were installed with minimal disruption to the biogas process, and can likewise be easily serviced without causing downtime. The secondary digester is now served with a system that comprises the proven Landia chopper pump, fitted with venturi nozzles to provide truly comprehensive mixing. When the primary digester meets the right level, the feedstock is automatically transferred to the secondary digester. The simple, but highly effective combination of submersible mixers, chopper pumps, and the venturi nozzles work to constantly recirculate the mixture of liquid and gas, even though it only typically has to run in 10-minute intervals, rather than mixers at many plants that run flat-out 24/7.
At the end of the process, in order to meet the legal requirements of a feedstock that
Kris Martin (pictured), said: “We now have a proper maintenance schedule in place, and unlike in the past, no problems or delays in the availability and delivery of parts.”
contains animal bi-products, there are now two (25m3
) Landia pasteurisers, which heat the
final effluent to the required temperature of 70˚C. The pasteurisers are supplied as complete processing units (tank, chopper pump, and controls), to break down the food waste effluent and any remaining solids. Each tank from Landia is made with a double stainless-steel tank wall that acts as a heating jacket. From here, heat is transferred by circulating hot water, meaning that a heat exchanger is not always required. Post- pasteurisation, with the maximum possible amount of gas extracted, the final digestate from Holton makes a nutrient-rich fertiliser. Martin said: “Nothing on this site is now off- the-shelf. Paul Broadhurst (from Landia) and I have put this all together step-by-step. It’s not been easy, but we’ve worked through it with a very healthy rapport and that all-important common goal of wanting something to work and work well for the long-term. It’s a world away from the daily hassles that we had previously.”
In addition to its primary feed from the Bernard Matthews’ plant, the Holton site also receives effluent from the local Adnams brewery and distillery, plus various fats and oils from nearby food processing plants. This variety of intake then takes careful managing to maintain a steady feed for the biogas plant. Martin continued: “With the Landia submersible mixers at the front end, we’ve gradually developed a constant, homogenous feed, which provides excellent stability for the remainder of the process and our drive to maximise biogas yields.”
At 1.1MW, the new-look Holton biogas plant can provide most of Bernard Matthews' 1.4MW energy needs, with a grid connection in place for times if/when the facility is on shutdown.
Landia
www.landia.co.uk
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