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Feature Renewable energy It’s size that matters, not quantity


According to David Brown, managing director at Börger, specifying a pump for an AD plant is all about feedstock size rather than quantity. He explains how choosing macerating and pumping equipment robust enough to cope will help avoid AD systems breaking down


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hen it comes to sizing up the right pump and macerator for an Anaerobic Digestion (AD) application, Börger’s managing director David Brown will invariably find himself explaining to an interested party that... ‘a potato is a potato is a potato’. The point being, whether you are trying to harness one tonne of waste potatoes for your biogas plant or 20 tonnes of potatoes, it is the size, not the quantity, that will dictate the type of equipment that is required. “At Börger we have a product port- folio that can suit every AD feedstock from 2 tonnes per hour to 20 tonnes per hour at today’s super plants,” said Brown, “but we are receiving an increasing number of enquiries from small owner-operators who perhaps only want to process two to five tonnes - per week.


Industrial-size equipment “We always try to help, but those who have perhaps carried out tests in a lab- oratory with something bulky like potatoes say that they only want a small two inch pump, a two-inch mac- erator and a small auger feeder. Understandably they have a low volume and are trying to keep their costs down. Their mind is very much on the basis that industrial-size equip- ment isn’t required for this applica- tion, but, it is!”


Brown says that with every AD plant having its own quirks, those using a less bulky feedstock such as tomatoes will be at an advantage, as will those who choose pre-processed material, but away from the lab, scal- ing equipment down to suit lower vol- umes of waste should only go so far. Sufficient power to feed it, macerate and pump it is still required. He added: “The industry has reached a stage where we appear to have a ‘twenty grand (£20,000) gap’.


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Enquiries we receive from small scale projects, often experimental sites, often seem to reckon on a figure of around £5,000 for their pump and macerator needs. The reality is more like £16,000 for a basic entry-level system, but if you are really going to attack this prop- erly and sensibly, then for an auger feeder, an effective macerator, decent pump, controls, skid-mounted, deliv- ered, commissioned – and work with a reputable company that isn’t just going to walk away or lose interest the second you have a problem, then a figure of around £25,000 is far more realistic. At Börger, and I’m sure at any decent pump manufacturer, we aren’t going to sell anyone a system that does- n’t work!”


Industrial-size equipment is still required for small volumes says Börger’s MD David Brown (below)


so build the plant accordingly and it will work well.”


The Carrigbyrne Farmhouse Cheese Company did just this at its AD plant in County Wexford, Ireland, where it brought in a pump and a macerator from Börger to help process slurry and food waste. Börger had to guar- antee that its pump and macerator would meet the specific EU Animal By-Products legislation for a maxi- mum particle size of 12mm for treat- ment of waste at 70°C for 1 hour. The anaerobic digester at Carrigbyrne’s 198-acre dairy farm now produces 1100 cubic meters of biogas per day, supplying power for the cheese making process, to the farm, and to the Irish national grid.


‘The front-end of the AD plant is crucial. It must be able to handle the feedstock in its raw format or you are going nowhere fast - build the plant accordingly and it will work well’


In the UK, Brown is among many who would like to see more of the co- operative community model that is so prevalent in Germany, where farms and those with other feedstock work together. There’s shared investment in good quality technology and then shared benefits of what they have made commercially viable for all con- cerned, including the pump supplier. However, Börger has several suc- cessful installations to its name, where Brown says individual cus- tomers quickly grasped what was being proposed and why, took a long term view, and were soon up and run- ning with an AD plant, whilst others are still in limbo.


“The front-end of the AD plant is crucial,” he continued. “It must be able to handle the feedstock in its raw format or you are going nowhere fast -


Börger’s Powerfeed SSR for AD applications


Warts and all “Typically, size requirements are dic- tated to us,” said Brown. “Size 12, 8 or 6mm, but our advice would be to opt for a pump that can handle 20-30mm because even if the waste has been through a plate or multi-spindled mac- erator, it is only macerated in one direction, so in effect, that potato we’ve been referring to could become a series of long chips that will cause problems if you haven’t sized up your pump correctly. Away from the lab, an AD plant is warts and all. We’re told far too often that ‘our feedstock is nice clean food waste’, but the fact that can- teen waste will inevitably contain more than the odd knife and fork, never seems to reach the specification sheet. So if your pumping and macer- ating equipment isn’t industrially robust enough to cope, then you will very possibly have an AD system that breaks down and doesn’t work prop- erly. There are enough of those already.”


Börger Pumps T: 01902 798977 www.boerger.com


Enter 231 NOVEMBER 2013 Process & Control


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