Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/1074336
14 WET NEWS FEBRUARY 2019 | wwtonline.co.uk Overcoming the issues of transporting dewatered sludge T he recent Water 2020 re- port published by Ofwat encourages sludge trading markets between operators in order to move sludge from a company where it is expensive to treat to one that is cheaper. Ofwat's modelling suggests that if its proposed changes are implemented, around 30 per cent of all sludge could move between different water companies. Wherever it ends up, this sludge will need to be pro- cessed. The proposed changes will make it increasingly neces- sary to transport dewatered sludge over long distances, for example to a thermal processing energy plant. However, a long pipeline does not have to be a barrier to efficient sludge transfer. The SEEPEX Smart Air Injection (SAI) combines the advantages of two conveying technologies to transport dewatered sludge with high dry solids content over long distances in an ener- gy-efficient manner. Dewatered sludge – or other highly viscous media – is intro- duced into the pipeline using a progressive cavity pump, form- ing compacted material that is split into 'plugs' and pushed down pipelines of up to 1,000 metres using compressed air. The future of sludge transfer This alternative to conventional means of handling dewatered sludge has already been • INSIGHT PUMPS AND PUMPING SYSTEMS With Ofwat seeking to promote sludge trading to secure best value, efficient transportation solutions are required Lesley Eaton, business development and marketing manager, SEEPEX UK installed at a number of plants throughout Europe, and has generated a rapid return on investment. It is an interesting option for the UK's sludge treat- ment centres, as not only can the SAI transfer dewatered sludge over distances of up to 1,000 metres but it is also eco- nomical because the total investment and running costs are comparatively low. SAI is being integrated into one of the UK's largest water companies later this year, as an energy-efficient, high-perfor- mance alternative to conven- tional sludge-handling systems. The customised pumping solu- tion is being engineered to fulfil the plant's specific require- ments and to be configured at the location for optimum energy consumption. Out with the old Until now, long-distance trans- fer of dewatered sludge has been carried out by belt and screw conveyors and bucket ele- vators, which require a lot of maintenance, o"en made costly by the need for working at heights if silos are filled. In addition, these systems are frequently open to the envi- ronment, which can result in unpleasant odours and rehydra- tion by rainwater, and complica- tions on vertical or inclined transportation. As an alterna- tive, closed piping can be used in conjunction with multi-stage progressive cavity (PC) pumps and piston pumps, which are suitable for highly viscous media and high pressures. However, because of the high discharge pressures, these require comparatively high investment costs for higher pressure-rated pipework and valves (in some cases more than 100 bar). Piston pumps in par- ticular also require significant maintenance (incurring down- time), may suffer from hydraulic oil leaks and have relatively high drive power and energy consumption. This was proven at Thames Water, where piston pumps were replaced by SEEPEX PC pumps, lowering the discharge pressures and reducing energy consump- tion by over 50 per cent. Plant-specific solution Unlike traditional methods, the SEEPEX Smart Air Injection uses a combination of progressive cavity pump technology and dense-phase pneumatic convey- ing. A solid 'plug' of dewatered sludge is formed by an open hopper pump with auger feed screw, which is then transported onwards by means of pulsed compressed air injection that is pressure-controlled via an algo- rithm optimised for the application. The pneumatically trans- ported sludge plug is lubricated with boundary layer liquid, for example dilute polymer solu- tion. This reduces friction in the pipework and improves the energy efficiency of the system as a whole. The combination of pump and dense-phase pneumatic conveying permanently reduces the pressure in the entire pipe- line to below 10 bar which is generated by the pump to set the sludge plug in motion. Once the static friction force has been overcome, the sludge plug is moved by pulsed controlled compressed air, which again reduces the discharge pressure in the pipework. Adjusting system parame- ters, such as polymer and air volumes, at the location makes it possible to set a plant-specific, energy-optimised operating point. Smart systems The reduction in friction losses and the discharge pressure requirements mean that pumps fitted with Smart Conveying Technology (SCT) can be used for long-distance, high-viscosity transfer duties. Pump mainte- nance time is minimal (rotor sta- tor replacement in less than an hour), as pipework removal is not required for maintenance. The lower discharge pressure additionally ensures an increased service life for the components, which is further extended by SCT whereby the stator can be adjusted to main- tain pumping performance as performance drops. Additionally, in the auto- mated SAI system, process monitoring can be integrated into existing automation and control systems via conven- tional interfaces. All func- tional components, sensors and actuators are part of the scope of supply, and are inte- grated into the control so"- ware SAI, which is optimised for the respective application. The SEEPEX Smart Air Injection system