The Mogden plant was built in 1936 for the West Middlesex (UK) drainage district to replace 28 small sewage treatment works. Over the years it has been expanded, still within the original site boundaries, to now treat the effluent of approx. 1.8 million people.
The plant produces some 96,000 tonnes of sludge cake every year all of which is recycled to land. Chiswick, Wembley, Edgware, Ruislip, Harrow, Staines and Hampton mark the limits of its catchment, with the River Thames the southern boundary. It has a capacity to treat 810 million litres of liquid waste each day. It’s a large site with large maintenance demands and Thames Water required an appropriate maintenance plan to be established to keep the new pumps at their optimum performance.
The starting situation
The seepex pumps in use at Mogden are used for a variety of applications from small dosing pumps with liquid polymers to large transfer pumps. Most however are used in the sludge treatment processes from mechanical thickening to pasteurisation and they handle a variety of different sludges at varying densities and temperature. Each pump is specified particularly for its duty with consideration to all the varying factors to ensure the pumps are left to operate at their optimum efficiency with minimal downtime.
Mogden is also the home of the monstrous seepex N300-36 sludge surface transfer pumps which transfer 180 m³/hr of sludge 16 km to another treatment plant. These pumps are fitted with massive 250 kW energy efficient electric motors and provide a combination of flow and pressure unmatched worldwide.
16 weeks to implement, that’s record breaking, a project team of 30 spanning all departments within the company designed, manufactured and delivered these giant pumps. At 11 m long and almost 7 tons in weight they represent a new milestone in the development of progressive cavity pumps enabling the company to penetrate markets that are traditionally associated with large piston pump technology.
The core to the progressive cavity pump, the rotor, was manufactured from one single piece of tool steel which initially consisted of a billet weighing 1.7 tons and finally ended up at 0.7 tons and almost 6 m long and within accuracies of 0.2 mm. The stator concept utilised, considered aspects of Health and Safety relating to manual handling, during both assembly and future servicing whilst ensuring optimum pump performance.
The solution
seepex were asked to offer its excellent service capabilities to assist Thames Water with planned and reactive maintenance to some of the more specialised seepex progressive cavity pumps and associated grinders. The service had to be comprehensive, cost effective and reliable in order to meet the high demands of running the third largest effluent treatment plant in Europe.
seepex started by delivering this service by means of a monthly service visit to check and maintain just 28 of the 55 pumps and to take care of any maintenance interventions identified as a result of the checks. Such was the success, measured by the reduced sludge pump downtime site was now enjoying, seepex were quickly asked to add to the list of pumping equipment it was responsible for.
The benefit
Since their installation in 2003 these massive pumps have been pumping sludge 16 km day in and day out without the use of any spare parts.
3.5 years down the line with no significant failures to report, seepex now has responsibility for all of the seepex pumps at the site and also all of the pumps at Mogdens‘ sister site Iver South in Slough. seepex had proved it was much, much more than a pump supplier and that the service consultation package offered delivers less repairs, less down time, less usage of parts and more importantly reduced costs of ownership.
seepex UK are contracted to carry out planned and preventative maintenance to a total of 68 progressive cavity pumps and grinders at two sites ranging from polymer dosing pumps to massive sludge transfer pumps. Checks are thorough. Dry run, over pressure, wear, drive condition and efficiency are all checked on a monthly basis. Wear rates are predicted as a result of these checks and preventative interventions are carried out before downtime occurs and when required they are carried out within one working day, on site. As a result neither site has experienced any unplanned downtime due to sludge pump failure since the agreements were put in place.
