Advanced engineering efficiency from 90 year-old pump station
05 May 2017
Thames Water is the UK’s largest water and wastewater services company, supplying around 2,600 million litres of tap water to over nine million customers across London and the Thames Valley.
One of Thames Water’s biggest abstraction facilities is the Littleton Raw Water Pump Station (RWPS) in Surrey, United Kingdom.
In an initiative to make Littleton the most cost-effective and reliable river abstraction system along the Thames, while retaining the site’s authentic personality, Thames Water collaborated with its partner, the Pump Management team of Boulting Group.
The Littleton pumping station was originally fitted with four 900mm discharge horizontal double suction axially split case pumps. Each individual pump had a capacity of 340ML per day. In the 1950s, three pumps were modified to electric motor drives and have been operating using this arrangement since.
Despite its successful history, the Littleton RWPS wasn’t operating at optimum efficiency. Improvements could be made to reduce loss of pump priming, minimise cavitation, simplify start up, maintenance and control procedures, reduce energy usage and therefore, operational costs.
After four years of successful projects with the Boulting Group, Thames Water invited the company to propose an upgrade to the Littleton RWPS, which would increase the performance of the site, while also making it more flexible, reliable and energy efficient. Thames Water was also keen to increase the average capacity from 400 to 750ML per day.
In addition, Thames Water wanted to implement an automated system with remote control function, which would allow a faster and more efficient pump start up procedure, while also making monitoring easier. In the existing system, operators had to go to the site and work for three to four hours to start up a pump, making the operation time-consuming and costly.
The final requirement was providing dual electrical power supply from the National Grid and up to 1.5MW of power supply from a photovoltaic (PV) system located in an adjacent field.
To address these requirements, the Boulting Group completed an holistic, objective site testing and evaluation process of the entire system, including Front End Engineering and Design (FEED). This resulted in a set of recommendations, including the upgrade of assets like switchgear, motors, drives and control systems.
Hydraulic redesign of impellers
The original impellers were limited in efficiency to around 80 percent. To improve the hydraulic performance and the priming process, Boulting Pump Management suggested a pump upgrade, including a complete redesign and manufacture of the pump impellers to help improve the net positive suction head (NPSH) characteristic and pump efficiency.
The specific design Boulting created for this project allows an improvement to 87 percent pump efficiency and increased reliability during start up and operation. Another benefit of the new design was the minimisation of cavitation and its damaging effects on the pump components.
Improved priming process
Poor priming also made the old system difficult to manage, time-consuming and expensive. To resolve the issue, the Boulting Group suggested the installation of a new and automated priming system that uses motive air vacuum ejectors and continuous water level monitoring.
To further increase priming reliability, the Boulting Group replaced the old packed glands with mechanical seals. This reduced leakage to virtually zero, making the system more reliable and adding an extra two percent to overall system efficiency.
Increased energy efficiency
The pump upgrade and refurbishing also meant an improvement in overall energy efficiency. In the new installation, the pumps, motors, drives and channel level will be automatically controlled to optimise the Specific Energy Consumption (SEC) of the system. Each component will be controlled individually and automated using Boulting PSOp (Pump System Optimisation), installed within SCADA managed Programmable Logic Controllers (PLCs).
The PSOp software was developed by Boulting Pump Management and has been used extensively in pump systems for Thames Water. It is able to continuously monitor and analyse the pump system, taking into account the known characteristics of each component in terms of performance. The system automatically identifies the speed the pump needs to operate at to achieve optimum efficiency. It also automatically detects how many pumps need to be running at any given time to ensure the lowest specific energy consumption.
In addition, the remote control feature of the Boulting PSOp software meant even further cost savings for the Littleton system. Whereas in the past, operators had to go on site and manually start the pumps, the new system reduces pump start up time by up to 96 percent.
Dual power supply
Another interesting feature of this project was the need to integrate dual power supply from the National Grid as well as a separate solar power photovoltaic system. So, the Boulting Group installed a High Voltage Switchboard that enables the pump station to use PV power when available and supplement it with grid power when necessary.
The unique character of the Littleton pump station comes from the beautifully designed pump room, created in the mid 1920s. To preserve the personality and historical character of the space, the Boulting Group suggested changing the layout of the system. This meant removing some equipment installed in the 1950s and several add-on pieces such as air ducts, as well as installing modern inverters, panels, transformers and control system in an adjacent room.
The original pumps are connected to new high performance motors and gearboxes, close to the oldest static steam driven pump, which will be kept as a museum piece.
By improving efficiency, reliability and performance and by integrating a renewable energy source, the new system will be highly energy-efficient. The upgrade aims to make the Littleton abstraction station one of the most modern and innovative in the UK.
The project will provide significant and sustainable benefits to Thames Water for decades to come. The annual energy savings resulting from this project are predicted to exceed 4.9 million kilowatt hours with an energy cost reduction close to £0.5 million.
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