How a 90-year-old pump station used engineering to reap maximum efficiency
05 April 2016
Thames Water is the UK’s largest water and wastewater services company, supplying about 2,600 million litres of tap water to more than 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.
Built between 1923 and 1925, the station preserves much of its original character. 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 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 340 megalitres per day. In the 1950s, three pumps were modified to electric motor drives and have been operating using this arrangement since.
The pump station is responsible for maintaining the water supply to one of the largest raw water reservoirs in the UK, providing fresh water to London and some neighbouring counties. It covers 707 acres and lies 13m above the surrounding area.
Despite its successful history and charming character, 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.
Thames Water sought 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 750 megalitres per day.
In addition, it 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, a holistic, objective site testing and evaluation process of the entire system, including Front End Engineering and Design (FEED), was carried out. This resulted in a set of recommendations, including the upgrade of assets like switchgear, motors, drives and control systems.
The initial scope of the project was slightly altered to minimise the loss of original aesthetics and to preserve the pump room character.
The original impellers were limited in efficiency to around 80 per cent. To improve the hydraulic performance and the priming process, a pump upgrade was suggested, 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 created for the project allows an improvement to 87 per cent 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, it was suggested installing a new and automated priming system that uses motive air vacuum ejectors and continuous water level monitoring.
To further increase priming reliability, the old packed glands were replaced with mechanical seals. This reduced leakage to virtually zero, making the system more reliable and adding an extra two per cent 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 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 PSOp software meant further cost savings for the Littleton system. Whereas in the past, operators had to go on site and manually start the pumps – a time-consuming and often unreliable operation – the new system reduces pump start-up time by up to 96 per cent.
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. A high voltage switchboard, which enables the pump station to use PV power when available and supplement it with grid power when necessary, was installed.
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, it was 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. After the most recent upgrade, the pump room will actually look more like the 1920s original, although the system will see a huge boost in reliability, flexibility and energy efficiency.
Thames Water originally estimated the upgrade would take at least two years but the project is expected to take only half that time, including the design, delivery and installation of the new system.
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 £500,000.http://www.engineersjournal.ie/2016/04/05/27935/http://www.engineersjournal.ie/wp-content/uploads/2016/04/aaapump2-1024x731.jpghttp://www.engineersjournal.ie/wp-content/uploads/2016/04/aaapump2-300x300.jpgChemenergy,software,United Kingdom