The growing need for energy and operational savings in the water industry has been the driving-force behind the Retroflo pump control system project. By far the largest emission area for water companies is power use, which represents 40-50% of carbon impact. The launch of the Retroflo’s award-winning RPC_2000 pump control system represents a breakthrough in pump control systems and is at the forefront of the water industry drive for reduced emissions.
Retroflo’s Research and Development Centre in Washington is dedicated to developing products and processes that work in tandem with water companies’ carbon strategies and their long-term commitment to achieve 25-30% reductions in carbon usage by 2020.
Changing legislation on energy and environmental issues are undoubtedly one of the biggest drivers of innovation in industry. A recent study by the US Department of Energy concluded that with pumping stations accounting for around 25% of the world’s electrical motor energy, the pumping sector now offers the largest opportunity for energy efficiency improvements in industry.
Retroflo’s RPC_2000 pump control system has been proven to optimise efficiencies and improve the reliability and longevity of pumps. In operation at various sites the system has recorded impressive results, including a minimum 12% energy saving and a CAPEX payback within 12 months. This combined with little or no operator call-outs, cleaner wells and the security of consented flow, has enabled pumping installations, in many cases for the first time, to operate at optimum efficiency.
Designed using a holistic rather than a traditional component-based approach to pump control, it is the first product on the market to offer Pre-Blockage Detection, Consent Security, Intelligent Flushing Cycles, Periodic Efficiency Testing, and Asset Data Storage, within a single system.
Initially developed in the UK, the RPC_2000 pump control system was successfully trialled and put into operation at several problematic pumping stations operated by Northumbrian Water. The success of these installations led to interest from the principal water companies in the UK, and the RPC_2000 is currently being put in operation by United Utilities and Scottish Water and undergoing trials by several other companies at home and abroad.
UK water companies invest more than £94 million per week in maintaining and improving services and as an energy intensive industry account for around one percent of the UK’s total carbon emission. It is therefore increasingly important for water companies to realise efficiencies.
The potential for the RPC_2000 pump control system to save energy and operational costs is huge. If you consider that water companies operate thousands of wastewater pumping stations across the UK, and Retroflo systems are saving on average £1 per hour on existing pumping costs per station, the scope for efficiencies is enormous.
The RPC_2000 pump control system can be retro-fitted to existing pumping stations and it is here that the potential for massive energy reductions with a small investment is best exemplified.
Prior to fitting Retroflo’s new pump control system , Northumberland Water’s Skinningrove sewage pumping station was an historically expensive and troublesome installation, despite relatively new pumps and Variable Speed Drives (VSDs). Frequent pump blockages meant numerous reactive maintenance call-outs to unblock the pumps. Retroflo’s new approach has virtually eliminated blockages at the station and delivered dramatic energy and operational savings
Located in an area of natural beauty on the North East coast, the pumping station was a concern because of the risk of discharges through pump blockages. Retroflo’s pump control system was specifically designed to control pumping stations as a whole, rather than just the components inside.
Through continuous dynamic monitoring of the pump characteristics over a range of wet well levels and pump speeds, the system was able to use the full range of pumping data available at Skinningrove to optimize the performance of the station.
Blockages occur in sewage pumping because of the gradual build-up of debris on pump impellers. This causes inefficient pump operation and eventually leads to a blockage, resulting in time consuming and costly call-outs.
During the first 12 month period from installation of the pump control system at Skinningrove, over 1000 successful pre-blockage detection routines were implemented. All returned the pumps to optimum performance, so no operator/maintenance intervention was required to remove blockages.
As the site was already fitted with variable speed drives (VSDs), the principal reason for installing the pump control system was blockage alleviation. However, by initiating pump reversal cycles on detection of partial blockages and returning the pump to optimum operating conditions, the improved pump performance equates to a 12% decrease in power during normal operation. At Skinningrove this has resulted in a savings of 0.45p every 12.2 sec.
A further benefit was a vast improvement in wet well condition because of the initiation of Retroflo's intelligent flushing cycle. This ensures that wells are kept cleaner, so alleviating solids settlement and septicity problems. This, in turn, reduces the threat of blockages to the pumps and reduces the need for routine cleansing.
The energy and operational savings derived from the installation of the RPC_2000 pump control system meant the capital expenditure of installing the system was repaid within the first year.
The cost-saving benefits of the Retroflo pump control system can best be described by looking at the historical problems associated with pumping non-constant fluids.A small blockage in the pump body means a greater risk of further debris passing through the pump, which tends to collect and add to the original problem.
Pre-modification at Skinningrove and many other sites, this happened until the pump could no longer deliver consent flow, or the pump protection caused tripping. This resulted in a breakdown requiring pump removal for costly un-blocking. Removing the smaller debris upon initial pick-up prevents the large build up.
Over a year, the pump control system has performed over 1000 Pre-Blockage Detection pump reversal sequences. Not all of these potential blockage events would have resulted in maintenance intervention - however each of the reversals allowed the pump to be returned to its efficient state automatically. Early stage blockages are eradicated, which also avoids any related H&S issues.
When in high level conditions, the pumps are controlled to maintain a forward flow to the works of 82 l/sec. Operating optimally, each pump works at around 96% speed reference to deliver 82 l/sec with slight variations. Over time, settlement intensifies and the pumps pick up debris.
Ordinarily, (when not in high level conditions), pre-blockage detection would detect these partial blockages and perform reversal cycles; however provided that consent flows are achieved, reversal cycles aren't implemented because of the increased risk of spillage.
Consequently, this debris continues to impede the pump's performance and the control system increases the speed of the under-performing pump to deliver the required 82 l/sec. The result is a pump operating at 100% speed reference (as opposed to 96%) to deliver the equivalent flow rate.
Theoretically, the decrease in power consumption from 100% pump speed to 96% pump speed can be calculated by applying the following equation:
where:
N1 = Full speed (%) = 100%N2 = New speed (%) = 96%kW1 = Full power (%) = 100%kW2 = New power (%) = ???%
kW2 = 100 X0.88 = 88%
kW2 = 88% a reduction of 12%
The calculation shows that a 4% reduction in speed is in fact a 12% reduction in power. Without pre-blockage eetection, and the facility to detect and counter partial blockages, when partially blocked the pumps will eventually be operated at maximum speed, resulting in increased operating costs. This situation would go undetected until a catastrophic blockage and breakdown occurs. Pre-blockage detection ensures that the pumps operate efficiently at all times, whilst also reducing the potential for breakdown.
Retroflo’s research and development centre is continually reviewing and updating the technology driving the Retroflo pump control system. As part of current development work is a feature that will benchmark efficiency and automatically select duty criteria based on these efficiencies. The added benefit of this feature will be further optimisation of the station and its power requirements. Retroflo’s RPC_2000 pump control system is at the vanguard of improving the water industry’s carbon management - a British innovation that has the potential to impact the industry globally.
