The Challenge
Wastewater collection via sewerage systems has proven challenging for Welsh Water due to the country’s mountainous topography. Many customers are situated within valleys, necessitating the use of sewage pumping stations (SPSs) that vary greatly in size and pumping capacity.
Until recently, the majority of the 1,861 SPSs belonging to Welsh Water had no system in place to measure flow. Those that did had been fitted with full-bore electromagnetic flow meters, many of which were no longer functioning properly due to age, condition and other factors. In order to determine whether inflow was exceeding capacity within any of their pumps, the company relied on course flow data derived from calculating the rate of change in sump levels.
If a markedly high sump level was observed, an operator was required to travel to the site to investigate whether the pumps were performing correctly, or a spill was genuinely occurring. This method was not operationally efficient and posed a significant environmental risk, particularly in storm conditions.
The Solution
To combat this issue, a team from Welsh Water was tasked with finding a low-cost way to provide accurate and reliable flow metering in retrofit SPS applications. Siemens was one of several process instrumentation suppliers asked to propose a potential solution. This was because Siemens had previously provided the company with numerous electromagnetic flow meters for new installations as well as a number of clamp-on ultrasonic flow meters for large pipes.
Welsh Water engaged their approved contractor, Celtic Process Control, to survey 80 SPSs identified as being high-risk to property or people in the event of a malfunction. These were then surveyed using a Siemens portable SITRANS FS290 clamp-on ultrasonic flow meter. Parameters and diagnostics were recorded by the meter at each location, allowing the technicians to determine at a later time which sites were suitable for permanent equipment and facilitating the subsequent installation process. The SITRANS FS290 proved capable of providing a true picture of the flow at locations where no previous metering existed.
Survey results confirmed the SITRANS FS220, would be appropriate for permanent installation at a number of SPSs. This clamp-on flow meter was recommended to Welsh Water for a number of reasons, including:
Cost savings. The SITRANS FS220 offers basic yet high-performance measurement functionalities at a significantly lower cost than other flow solutions, especially when overall civil, mechanical and operational costs were taken into consideration. This was particularly important to Welsh Water given the large number of sites that required metering.
Time savings. Because the SITRANS FS220 is non-intrusive, no cutting of the pipe is necessary and installation can be completed in only a few hours, as compared to 2-5 days installation for electromagnetic meters.
Improved accuracy. Calculating sump level rate of change typically results in an accuracy rate of 5-10 % but is not feasible during periods of excessive inflow and storm overflow. In contrast, the SITRANS FS220 uses patented transit-time sensors that demonstrate a consistently high accuracy of 1-2% of rate accuracy.
Ease of use. The SITRANS FS220 features straightforward product configuration and a user-friendly design for simplified operation and maintenance.
Recognizing that the SITRANS FS220 was an ideal fit, Welsh Water ultimately selected Siemens as the supplier of clamp-on instrumentation for their large-scale retrofit project. SITRANS FS220 flow meters were installed on the majority of the high-risk SPSs and are now performing accurate measurement of sewage flow. The meters have made it possible to monitor each SPS remotely, eliminating the need to send operators out into the field to verify flows. This allows operational staff to be more effectively deployed. In addition, the SITRANS FS220 provides a comprehensive and trustworthy audit trail for the governmental body that oversees spillage incidents. The clamp-on technology also makes it easier to perform routine monitoring of pump efficiency, which helps staff in more quickly identifying maintenance concerns such as worn impellers, blockages and faulty non-return valves (NRVs).
Having observed the value of the SITRANS FS290 during the initial site survey, Welsh Water also decided to order 10 portable units for distribution across maintenance depots. Now they are readily available to personnel whenever and wherever they may be needed for diagnostic and operational purposes.
“Our experience with Siemens has been outstanding every step of the way,” said Carle Redwood, Senior Innovation Engineer with Welsh Water. “From the very inception of the SPS retrofit project, Celtic Process Control and Siemens partnered with us to provide the best possible solutions, support and service, and with their help our operations are now becoming more efficient than ever.”
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