Thursday, August 22, 2019

New pump makes anaerobic digester more sustainable

May 1, 2019 by  
Filed under News & Business

farming family who installed a new anaerobic digestate pump say the decision is helping to make their renewable energy enterprise sustainable for the long term.

Esther Rudge farms with husband Henry and their son Monty at Ballingham Court, Herefordshire. The anaerobic digester runs on by-products from the 130ha business which includes 200 ewes, 70 stabiliser-cross cows and 40 Herefords – as well as apples, pears, cereals and maize.

The previous pump was unable to handle the 11% dry matter thickness of the digestate being discharged from the digester. This was causing disruption to the farm’s 80kW biogas plant, which exports most of its green energy to the National Grid.

“Börger quickly helped us out with a temporary solution until a larger unit could be installed,” says Mrs Rudge, whose son Monty now principally manages the plant since joining the business after studying agriculture at Harper Adams University, Shropshire.

‘Reliable processing’

“We were already very pleased with their Powerfeed system and Multichopper macerator at the front-end of our process – so it was perhaps no surprise that their additional pump was also of very good quality.”

The Powerfeed mixes and homogenises the feedstock of fruit, manure, maize and chicken litter – regardless of variability. The system guarantees safe and reliable processing of solids from four tonnes per hour, up to nine tonnes per hour, if required.

“Despite the inevitable foreign objects, such as wood, that get caught up in straw, the Powerfeed will handle it – and at the next stage of the process, the Multichopper macerator will sort it out properly.”

Beyond the mixer – and connected by a Börger circulation pump – the P500 Multichopper benefits from a tough, perforated disk chopper with central high-performance rotating blades, enabling throughput volumes of up to 400m3/h (1760 usgpm).

Control system

Bespoke controls ensure the system is fully automated. The pump provides continuous feed for a 10m3 buffer tank. As the tank approaches it capacity, the system typically performs a 5-minute feed cycle, pumping the feedstock through the macerator and into the digester.

The time taken for a feed-cycle can be adjusted for certain feedstocks in order to maintain gas levels. This system prevents any fluctuations in temperature that would prevent the digestion process from operating at optimum levels.

Load and flow sensors monitor the equipment remotely so that the operator can see at a glance via a smartphone or computer whether the set-up is working properly. Operating at around 1 Bar, with no great head of pressure to overcome, it is a gentle, carefully managed system.

It is now two years since the AD plant was commissioned. And with the new pump now taking care of the discharge, Mrs Rudge believes the farm business is now sustainable enough to hand on to the next generation when the time comes.

Tighter restrictions

“Our investment in AD will no doubt continue to be a learning, fine-tuning part of our farm life, but we’ve achieved our aim of becoming increasingly sustainable – and generating a new income stream. There’s the bonus too of producing very good fertiliser.

“We’re almost landlocked here by the River Wye – halfway between Ross-on-Wye and Hereford – with poor road links and ever-tightening restrictions on what we can and can’t do, so it was vital to our future that we became as sustainable and self-sufficient as possible.”