WATER & WASTE TREATMENT DON’T WASTE TIME AND MONEY
hardly blame a local distributor for supplying something off the shelf for a site in its hour of need – but the vast majority of today’s equipment suppliers like to work with manufacturers to find better, robust solutions that are truly designed for the job. A quick-fix might do the job in certain
applications, but not for food waste. So that we can provide the right, long lasting, reliable equipment, that is also actually far, far cheaper in the long-run, we always ask for key information about the pH of the tank’s contents; the dissolved solids, abrasiveness – and much more – in order to help our customers bring about the right solution. I had to read one part of the article a few
Paul Davies, from mixer and pump manufacturer Landia, explains why stainless steel mixers are a much better option than cast iron mixers in food waste applications
food waste application at a biogas plant. The article then gives a rosy description about how these failing cast iron mixers have been replaced by... another brand of cast iron mixers! I despair of course because I don’t think you
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have to be a certified, professional engineer to know that with food waste’s typical low pH, stainless steel mixers should be used. What a waste of time and what a waste of
money to address the same low pH problem with more cast iron that is doomed to fail – yet
ometimes, I do despair. I’ve just read a glowing article about how some cast iron mixers – not surprisingly – failed in a
the article isn’t shy of telling the reader just how wonderful and fluffy this all is for the environment. In a short space of time, they no doubt won’t be showing us the pictures of the failed mixers on their merry way to the scrapheap. At a time when there is at last such a strong
recognition to make the best possible use of precious resources, why do such short-sighted decisions like this continue? Perhaps it is because some need or believe they need a new mixer, ‘right now’ – or they shy away from stainless steel because it will cost more? Often it is no more the case that people buy what they’ve had before. In these situations, one can
times to believe what it was saying. Yes, some applications are super-aggressive – but here it was proudly stating that hopefully, a new mixer wouldn’t have to be replaced... ’within a year’. Not exactly what you’d call a sound, value for money investment! The vast majority of our pumps and mixers have a 20-25-year lifetime. Furthermore, the photos show the new
mixers being lowered down inside the tank. As soon as there is a problem – which is inevitable, the whole biogas process will have to stop so that those failing mixers can be retrieved. This presents numerous health and safety issues, as well as a costly disruption to the process. Mixers mounted outside the tank are so much better, safer and easier to service. As we head towards 2022, there is still huge
room for improvement in mixer and pump specification for food waste/biogas plants. It’s a very tough environment, so best not purchase equipment that is going to get eaten alive.
Landia
www.landia.co.uk
MAXIMISING OUTPUT FOR HYDRO APPLICATION
Riventa has been monitoring a hydro-turbine for a major water supplier in England, to see if its maximum possible electrical output was being maintained. At a key site, river water is pumped to a break tank at the top of a hill, from where it can either overflow or run
down the hill to a large reservoir below - or be directed to a hydro-turbine with the same outfall. Riventa were tasked with monitoring the efficiency of the turbine in question – a fixed speed machine (1016 rpm) that operates without any human intervention. Using inlet guide vanes, its load is controlled via flow rate modulation. Riventa’s FREEFLOW hardware and software system was installed to show immediately whether a proposed
change was effective or not. The system also tracked any savings associated with a change and the financial consequences of it. Originally rated with a best efficiency of 84%, the maximum detected was 82%. However, the turbine was found
to spend less than 10% of its time above 80%. Significant differences in power generated for the same flow rate were also observed. For example, at 925l/s, the power generated varied between 185-260kW,
showing an efficiency variation of 58-82% - thus demonstrating instances when 40% more power was generated for the same flow rate. Working closely alongside its customer, Riventa looked at how to schedule the turbine for the best return within the operational constraints of the overall water
network. In highlighting whether scheduling changes were effective or not, the FREEFLOW system provided real-time tracking of any savings associated with a specific change. The turbine was found to operate at an annualised average of 73% efficiency, but if increased to 80% this would translate to at least £11,000 per year savings –
based on little or no capital investment. Steve Barrett, managing director for Riventa, commented: “This is a good example of how we can help identify opportunities to maximise output from a hydro application – with the same technology that we bring to pump and blower installations to help improve efficiencies, create energy savings and prolong the lifetime of assets.”
www.riventa.com NOVEMBER 2021 | PROCESS & CONTROL 45
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