Water and Effluent Treatment Magazine
Issue link: https://read.utilityweek.co.uk/i/867569
SEPTEMBER 2017 WET NEWS 23 give the optimum return on investment so it is important that the pump is not treated as a standalone commodity. A thorough understanding of the product to be handled and the process requirements should be considered, with tailor-made packages oen providing the best solution. Back-mixing Minimising the energy use of equipment is desirable, and progressive cavity (PC) pumps compare well in this respect to other pump technologies with their ability to maintain flow even with varying pressures and variable sludge viscosities, which is specifically important when feeding heat exchangers to ensure the most efficient heat transfer for heating the sludge. Integrating pumps with complementary equipment, such as special live bottom silos, boundary layer injection systems and back-mixing technology, together with intelligent control systems, is crucial for reliability, performance and cost efficiency. Sludge cake pumps are large so it is vital that they are efficient in use and have accessible wearing parts for ease of maintenance when required. Anglian Water supplies more than six million homes and business customers in the east of England with clean water and treatment services. During AMP5, which ended in 2015, the company installed sludge reception centres and advanced energy generation using thermal hydrolysis at three locations within its area. It was important that these plants were as efficient as possible to provide the double advantages of reduced energy consumption and increased generation. Anglian Water installed Seepex PC pumps for efficient sludge transfer and mixing duties. PC pumps were chosen as they can handle both low and high viscosity products, can pump sludge with ds% up to 45%, and are not hindered by solid particles. In addition, their good discharge pressure capabilities enable long distance pumping, and their non-pulsating flow characteristics make them a popular choice for many wastewater applications. Open hopper pumps for high solids transfer (up to 30% dry solids in this case) and liquid transfer pumps formed part of the package, while a visit to an existing sludge treatment plant demonstrated how efficiencies in installation could be achieved, removing the need for conveyors in parts of the process. This was achieved by using customised pumps fitted directly to silo outlets which could back-mix sludge cake with dilution liquid to the required ds% needed for energy generation. Integrated controls pumps which transferred the sludge were identified as a limitation due to frequent maintenance requirements and the high pressures generated. While piston pumps can operate over a wide pressure range and can move viscous products over long distances, they do incur high operating and maintenance costs and have a very strongly pulsating flow. This is due to the pump action of filling and emptying a chamber of product which is then pushed through the pipe using a reciprocating action, requiring check valves to regulate and direct flow through the system. The pulsation creates a high operating pressure – at Reading, the piston pumps generated pressures of up to 64 bar and this would be likely to increase if the solids ds% was higher. Furthermore, they had hydraulic drives and drew absorbed power of 31kW. These factors, along with the high maintenance requirements, added up to a high operational cost for Thames Water. Rotary action In comparison, progressive cavity pumps are also able to operate over a wide pressure range and can move viscous and abrasive products over long distances. However, they have a different principle of operation and employ a rotary action via a series of cavities which are filled and emptied continuously as they are 'progressed' through the pump. This results in low pulsation that generates lower pressure in the pipework, and which can be further reduced by boundary layer injection due to smooth laminar product flow. PC pumps have lower operating and maintenance costs and, in this case, drew absorbed power of 18kW – a reduction of 40% compared to the piston pumps. Thames Water replaced the piston pumps, which transferred dewatered digested sludge from the energy generation plant to storage silos, with Seepex PC pumps. Seepex project managed the installation, working with Thames Water's approved contractors to deliver a turnkey system. The new pumps transfer higher ds% sludge with a lower energy demand, bringing the additional benefit of a reduction in the system's pressure rating, enabling de-rating of pipework and valves to suit. The pumps have been in use for more than two years, and have required no maintenance interventions throughout this time. The Seepex PC pump system has delivered a hat-trick of cost reductions compared to the piston pumps – lower sludge disposal costs, lower energy use and reduced maintenance costs. Lesley Eaton is business development and marketing manager at Seepex. The trend for water companies to treat only their own sludge is set to change link the liquid addition and back-mixing silo pumps to ensure optimised mixing. As well as lower capital costs, operating costs were reduced by using very small amounts of liquid injected constantly to the outlet of the pump. This produces a lubricating boundary layer around the sludge, reducing friction losses and hence operating pressure. The load on the pump is reduced and service intervals are extended by using this boundary layer system, made possible by the accurate dosing characteristic of PC pumps. Thames Water, with 15 million customers and 350 sewage treatment works (STW), treats more than 4.2 billion litres of sewage a year. Its strategy is to adopt treatment processes that maximise the generation of renewable energy and minimise the volume of residual sludge produced, and the company is using thermal hydrolysis of sludge before AD to achieve these aims, oen on existing STW. The company's STW at Reading aimed to reduce onward sludge transport costs by increasing the ds% of dewatered sludge from 22 to 25%. However, the piston "While process optimisation, economies of scale and deregulation will all play a part in the continued increase in energy gene- ration by the water industry, it is important not to overlook the importance of correct equip- ment selection" Lesley Eaton WATER MANAGEMENT SOLUTIONS ttpumps.com +44 (0) 1630 647200 CONTACT US FOR FURTHER INFORMATION Our innovative portfolio of sewage pumps are available with a range of impellers to handle all conditions, including: - The E-Flow and V-Flow range have an explosion proof motor, for use in Zone 1 applications. They are available with a single-channel or vortex impeller for excellent solids handling. Our range of WRAS approved valves are suitable for potable and clean water and include: - The Aquavault, a resiliant seat wedge gate valve used for pipeline isolation. - Swing Check Valve, used to prevent reverse flow. - The Aquabrake, an air valve, used to release gas to prevent pressure build-up. WATER AND SEWAGE PUMPS WRAS APPROVED VALVES - The Uniqa range of reliable, submersible electric pumps are energy efficient and have a vortex impeller and anti-clogging system to guarentee optimum performance. WET News.indd 1 08/08/2017 12:17:29 www.teekaycouplings.com tel: +44 (0)1494 679500