Control strategies bring cost benefits

8 min read

The terms of the 1997 Kyoto Protocol, coupled with rising energy costs, has led to a radical rethinking about how pumping efficiencies can be improved using control strategies. Pump control specialist Retroflo has responded with a ‘breakthrough' system-wide pump control technology, as company founder and operations director Andy Laundon explains.

Figure 1. The pump control room at a Northumbrian Water Sewage Pumping Station. Retroflo technology was fitted as part of a major refurbishment project at the pumping station.
Figure 1. The pump control room at a Northumbrian Water Sewage Pumping Station. Retroflo technology was fitted as part of a major refurbishment project at the pumping station.
Figure 2. The pump room at a Northumbrian Water Sewage Pumping Station. Retroflo technology was fitted as part of a major refurbishment project at the pumping station.
Figure 2. The pump room at a Northumbrian Water Sewage Pumping Station. Retroflo technology was fitted as part of a major refurbishment project at the pumping station.
Figure 3. Byzak project manager Ian Gibson checks data on the Retroflo RPC_2000 touch screen. Ian oversaw a 10-week refurbishment programme that included installing the Retroflo system to control new pumps and VSDs.
Figure 3. Byzak project manager Ian Gibson checks data on the Retroflo RPC_2000 touch screen. Ian oversaw a 10-week refurbishment programme that included installing the Retroflo system to control new pumps and VSDs.
Figure 4. Blockages occur in the pumping of any non-constant flows, such as sewage, because of the gradual build-up of debris on pump impellers. Blockages can lead to costly call-outs and disruption to the flow.
Figure 4. Blockages occur in the pumping of any non-constant flows, such as sewage, because of the gradual build-up of debris on pump impellers. Blockages can lead to costly call-outs and disruption to the flow.
Figure 5. The Retroflo system has virtually eliminated ragging blockages at sewage pumping stations where it is in operation.
Figure 5. The Retroflo system has virtually eliminated ragging blockages at sewage pumping stations where it is in operation.
Figure 6. Another blockage that has occurred because of gradual build-up of debris on the pump impeller. Such blockages can be costly.
Figure 6. Another blockage that has occurred because of gradual build-up of debris on the pump impeller. Such blockages can be costly.
Figure 7. Retroflo has virtually eliminated blockages at sewage pumping stations.
Figure 7. Retroflo has virtually eliminated blockages at sewage pumping stations.
Figure 8. The RPC_2000 combines hardware components with intuitive software that has been specifically designed for easy retrofitting or new installations.
Figure 8. The RPC_2000 combines hardware components with intuitive software that has been specifically designed for easy retrofitting or new installations.
Figure 9. The RPC_2000 touch screen allows easy access to the systems intuitive features.
Figure 9. The RPC_2000 touch screen allows easy access to the systems intuitive features.

Currently, fast changing energy and environmental legislation is one of the biggest drivers of pumping sector innovation. Moreover, new EU directives recognize increased demand for the introduction of a systemic approach to the ways in which pumps are used and controlled. It is clear that the well-established component-based approach does not take into account the potential energy and efficiency savings from monitoring and controlling all the parts that make up a pumping installation.

A systemic approach

Tyne & Wear, UK-based Retroflo has developed a patented pump control technology that takes just such a systematic approach to the traditional problems associated with pumping non-constant fluids. Using the full range of pumping data available, the company's RPC_2000 system delivers substantial energy-savings whilst dramatically reducing pump blockages. This success has been achieved by continuously monitoring the pump's characteristics dynamically over a range of wet well levels and pump speeds.

The results are impressive. At pumping installations operating the system, there has been a minimum 12% energy cost reduction. This, combined with little or no operator call outs, plus cleaner wells and the security of consented flow, has enabled pumping installations to operate at optimum efficiency – often for the first time.

It is this growing need for reduced operational expenditure and improved carbon management that has been the driving-force behind the company's project. A recent study by the US Department of Energy concluded that with pumping stations accounting for around 25% of the world's electric motor energy, the pumping sector offers the greatest opportunity for energy efficiency improvements in industry. In addition, it is now well established that component improvements alone will offer only small reductions, whereas a systematic approach can provide potential energy and operational savings of between 30-40%.

Variable speed drives

With an estimated three quarters of all pumps over-sized by 20% to secure the consented flow of a pumping installation, the use of variable speed drives (VSDs) is playing a substantial role in energy reduction. Where VSDs are used, a small reduction in pump speed can significantly reduce energy costs. For example, reducing a pump motor's speed by 20% can equate to a near 50% power reduction. However, while process control and energy conservation are the two primary reasons for VSD application, there are associated problems.

Often, the greater incidence of blockages and higher maintenance costs of running VSDs can outweigh the energy-saving benefits. Many operators of non-constant fluid installations opt for the tried-and-tested fixed speed pumping option, rather than variable speed constant level pumping – they sometimes lack faith in VSDs being able to deliver trouble-free consented flow.

Fixed speed pumping also has problems. Cycling pumps on and off results in frequent high electric current surges, increasing energy costs and pump component wear. Not only that, such batch type pumping can cause network problems through process flow surges.

 The RPC_2000 has been specifically designed to overcome such problems. The system recognizes that every pumping station is different, not only physically, but also in terms of its operating requirements for consents and storage, population served, and position within a network. These variables are calculated, and processes are automated to achieve VSD energy-saving benefits, whilst ensuring consent security. In turn, this results in lower energy consumption because the pumps are either running more slowly, or less frequently – with a consequent increase in pump asset life.

 This new technology, we believe, represents a ‘revolution' in pump control systems. Moreover, it is the first in the world, we think, to offer pre-blockage detection, consent security, intelligent flushing cycles, periodic efficiency testing and asset data storage, all within a single system. The concept was no ‘Eureka!' moment, rather a clear idea of how a pumping installation could work efficiently, using the extensive knowledge gained over many years in the industry.

Previously, the tendency would be to install larger pumps to compensate for drop off in performance and wear over time, and those pumps would invariably be operated at full speed. Now customers can install correctly sized pumps with the comfort that as-new performance will be maintained. Also, automated early warnings of wear can be provided, which allows preventative maintenance regimes to be adopted.

Application examples

An appreciation of the issues relating to securing a consented flow for a wastewater pumping station helps in understanding the system's concept. Typically, the pass forward flow of the station, the basis for the consented flow, is calculated by taking the population of its catchment and applying industry guidelines for per capita contributions (litres/head/day). Infiltration factors are applied and any trade effluent flow is added in order to determine the design Dry Weather Flow rate. This figure is further factored to allow for surface water contributions. The final figure defines the pass forward flow.

Anywhere a consented flow is stipulated by the regulatory authorities, blockages are a major concern because of the risk of untreated or undiluted sewage being discharged into the watercourse. According to Environment Agency figures, the UK's water industry caused 19% of serious water pollution incidents in 2007. Under the Urban Waste Water Treatment Regulations of 1994, water companies are subject to tough penalties should it be proven that a pumping station not delivering its consented flow caused sewage pollution.

Bob Dixon, Pumping Station Framework Manager for Northumbrian Water (NW) in the UK, has been involved with Retroflo's projects from the outset and fully understands the issues relating to pumping stations. The utility provides 2.6 m customers in the NE of England with water and wastewater services. It is also investing £249 m between 2005 and 2010 to upgrade its vast sewerage network. Retroflo's technology is part of this significant investment.

Explains Bob: “NW provided a platform to put the projects in place. We have over 800 pumping stations, many inherited from local authorities, and we undertook a process of identifying what work needed to be done through asset surveys. The biggest issue identified was blockages.”

Blockages occur in the pumping of any non-constant flows, such as sewage, because of the gradual build-up of debris on the pump impellers. Any blockage results in time-consuming and costly call-outs, often entailing the lifting of the pump from the wet well to carry out maintenance.

The RPC_2000 uses a Pre-Blockage Detection facility to overcome this problem. An initial analytical process records the pump's characteristics across the range of well levels and pump speeds. The system also constantly compares benchmark data against current data to determine the criteria of the unblocking cycle: i.e. reverse direction, its speed and duration, and the number of self-cleanse sequences made prior to pump trip.

The result, explains Bob Dixon, is a vast improvement: “We have virtually eliminated blockages at one of our pumping stations that experienced frequent blockages before Retroflo was installed.”

A wide range of equipment

The successful installation of this technology in two pumping installations led our team to realise that the system had a far broader reach than first imagined. When the system proved patentable, it was decided to invest in the R&D of a standardized instrument that could be programmed for site-specific conditions. The result is this new approach to a pumping control system. The next step was to design a solution applicable to a wide range of manufacturers' equipment (both pumps and drives) that could either be incorporated in new installations, or integrated into existing systems.

Retroflo Technical Director, Lee Bishton, played a key role in taking the project from concept, through R&D to the launch of the RPC_2000. Comments Lee: “I knew what an operator would want from a system. Our process was to use a collaborative approach – taking on board problems and coming up with solutions. Pump blockages, in particular, are an industry-wide problem. Solutions in the pumping industry seemed to exist at component level, but not system-wide. We were able to find the solution through adopting a holistic approach where all the characteristics of a wet well (level, flow, speed) are monitored and analyzed by a single system.”

In 2006, Lee began to write the control philosophy behind the innovation. The first implementation and testing of the system was carried out at a UK Northumbrian Water pumping station and was then rolled out to other NW sites. Despite every pumping station being different, what soon became apparent to the design team was that they were able to standardize the processes required to monitor and analyse pump speeds, wet well levels and flow in any given installation. “In effect,” says Lee, “we created a standard product that can be fitted or retrofitted to any pumping station.”

System benefits

At another mid-sized NW pumping station, on the Northumbrian coast, UK, the benefits of the system are clear to see. Since it became operational in January 2008, the station log lists a single reactive call-out, contrasting with the log for 2007, which records 49 call-outs.

Leading UK water industry contractor Byzak was appointed to NW's framework agreement for the refurbishment of pumping stations. Byzak is the approved Retroflo installer and has so far refurbished over 50 NW stations, with projects ranging from minor works to multi-million pound refurbishments.

Ian Gibson, a Project Manager for Byzak, oversaw a 10-week refurbishment programme at a NW site, which included installing the system to control new pumps and VSDs. Over his 14 years in the water industry, Ian has encountered the recurrent problems particular to pumping stations - principally frequent blockages and the resultant maintenance call-outs.

He explains: “The previous firm I worked for had two or three goes at sorting out the problems of troublesome stations - with little success. It's been good to be involved with this project. Working with NW and Retroflo on a day-to-day basis, I've seen the benefits of the system at the front-end. To be honest, I can't see how the industry can ignore it. It's what has been needed for a long time.”

The retrofit capability provides opportunities for dealing with historically problematic sites and the success of such installations has been demonstrated by greatly improved carbon management and reduced maintenance costs. At another NW station, in the Tees Valley, energy costs have been reduced by 20% following refurbishment and the installation of the system.

Life cycle costs

While it makes sense to focus on the system's pump control and pre-blockage facilities, the RPC_2000's inbuilt diagnostic tools incorporate several other features aimed at improving efficiencies and performance. Because pump installation costs typically account for about 10% of station expenditure, it is the life cycle costs that offer the greatest potential for savings.

For example, the RPC_2000's Intelligent Flushing Cycle uses historical data to predict the incoming flow rate, allowing the well to fill to a pre-set level before initiating a rapid well-emptying sequence. The benefits of this are twofold: dilution of settled solids in the well; and the rapid emptying of the well usually ensures that self-cleansing velocities are generated in the rising main, alleviating solids settlement and septicity problems.

Another feature is Periodic Pump Efficiency Testing. This monitors wear on pumps, alerting operators of maintenance issues should a pump begin to lose performance. While operational savings are mainly derived from lower energy costs and fewer call-outs, the benefits from improved asset lives cannot be ignored.

Potential savings

Future Water, The Government's water strategy for England, published in February 2008, highlights the need for innovation in reducing the UK water industry's approximate four million tonnes of greenhouse gas emission. In his introduction, Hilary Benn, UK Secretary of State for Environment, Food and Rural Affairs, states: “The way we pump, treat, and clean water has profound implications for energy use. The water industry is a major energy user, and there's a carbon impact here that simply has to be tackled.”

The RPC_2000 is, we believe, uniquely positioned to be at the vanguard of improving the industry's carbon management. The impressive figures produced by the system in operation clearly demonstrate the efficiencies associated with its use. What is also clear is that the RPC_2000 has the potential for wide application across the pumping sector at large. When this happens the savings could be huge.

The pump industry has taken note of the RPC_2000. Retroflo was a winner at the Institute of Engineering and Technology (IET) Innovation Awards, and was one of six companies short-listed for the Pump Industry Awards 2008 in the Technical Innovation of the Year category

Contact Andy Laundon Operations Director Retroflo Tyne & Wear, UK Tel: 0191 497 2840 Fax: 0191 419 1579, Web: www.retroflo.com