NW Pump & Valve has designed a vacuum sludge pumping system which has found favour with United Utilities, solving problems at some difficult sitesNW Pump & Valve of Barrow in Furness, Cumbria, has been specifying, supplying and installing pumps for its blue-chip customers in the Northwest of England for the past 11 years. During this time, the company has specified the Gorman Rupp Ramparts pump range for a variety of applications - from the nuclear industry to waste-water treatment.
From supplying and installing bespoke pumping systems, including M&E and minor civil works, NW has widened its scope to include design. Engineering director John Fletcher says: "Some of the problems of our United Utilities customers started to assume a common pattern. We were being asked to look at and resolve problems associated with sludge handling, and in response, the Air-Driven Diaphragm (ADD) pumping system began to evolve.
"Our design capabilities have allowed us to tailor each package to site conditions, with environmental and health and safety risks being designed out of the system as far as possible," Fletcher adds.
This system comprises the Gorman Rupp Ramparts ADD pump, the Plusair air compressor and a unique control system that enables the system to be operated locally or remotely by telemetry, for example by SCADA system. There are several major advantages to the customer of using this system:
- Because the system is run on air rather than hydraulically, there is no risk of oil spills, and no need for a bunded area
- The efficiency of the design reduces air consumption and energy usage by responding to changing sludge conditions
- The system has few moving parts - longevity and reliability are ensured by the efficiency and robustness of the pump design and control
- Due to the air operation and accessibility of the component parts, there are no confined-space safety issues
- The system is also fully compliant with United Utilities C&I requirements, and can be tailored to suit specific utility or commercial standards
"Our experience in working under the CDM regulations has enabled us to focus our design activities on the elimination of risk elements and taking environmental considerations into account. This hopefully will assist United Utilities in their Sustainability Procurement Strategy," he adds.
The rugged internal and external design of the Gorman Rupp Ramparts Air Driven Diaphragm pump allows the pump to cope with the most demanding environments and operating conditions. It can handle corrosive (pH4) and abrasive pumping media, and is capable of overcoming the high-wear problems commonly associated with this type of pump. The externally positioned check valve assemblies enable ease of cleaning and servicing.
One of the best selling points of this pump is that it is environmentally friendly. The air cylinder offers virtually no resistance as the pump moves through its discharge stroke. This means energy savings, smooth action, a longer diaphragm life and reduced consumption of air.
This pump is capable of operating dry on suction lifts up to six metres and handling a solids content of up to 70%. The stroke rate, discharge stroke time, suction drive pressure and discharge drive pressure can all be adjusted independently. The vertical orientation of the diaphragm and flow-through layout of the check valve and body allow concentrated slurries and sludge, plus a large solid content, to be handled, making this pump ideal for sludge handling operations.
The multi-functional compressor supplies clean, dry air to the pump. It can be regulated to suit the viscosity of the liquors pumped, minimising energy input and giving running cost savings
The control system comprises software developed by NW Pump & Valve. The unique dual controller (electro-pneumatic) combines both the electrics and pneumatics logic software to hardware interface to give a variable and flexible pumping system. The PLC controller uses a combination of touch screen and keypad, which offers the operator maximum flexibility in data entry and system control.
Woolton WwTW, Liverpool
NW was asked by United Utilities to install five ADD systems at Woolton WwTW, Liverpool, in 2002. The prime considerations for United Utilities on this site were safety and the severe vandalism problem. The ADD package was considered suitable due to the rugged design and the fact that the pumps are pneumatically driven - hence no electrics that could be tampered with. Each of the five pumps works independently, drawing sludge from the primary settling tanks and sending it to the dewatering tanks. A custom-built controller and timer was also tailored to the operator's schedule on site. The pumping system has now been in place on this site for more than three years and has demonstrated longevity of service, safety, reliability and environmental benefits.
Also in 2002, NW was asked to design and install a replacement auto de-sludge pumping system at Middleton WwTW, near Morecambe, Lancashire. The system included the addition of a SCADA interface for remote control of the pumping system. For this site, United Utilities chose the ADD system for its reliability and longevity, its ease of serviceability as well as environmental considerations. The design of the system, with components well above ground level, eliminated the confined space working that had been necessary for servicing and repair. The rugged construction of the pump has also ensured longevity of service in a harsh coastal environment.
Kevin Hodgson, senior controller at United Utilities (Morecambe Bay District), has been very pleased with the ADD pump system installed at Middleton. Hodgson reported that the bellmouth outputs from the previous system were continually getting blocked. The submersible pumps had to be removed from the wet well to remove blockages - with associated time and health and safety issues.
"By installing this package, we were hoping to achieve a greater level of efficiency and easier maintainability," he says. "The ADD package has proved to be easier to maintain. The previous system required two operatives, but the ADD system is simple and easy for one operator to maintain.
"The design is very robust and is safer and easier to work on. The SCADA element allows ease of operation and monitoring. We can now carry out trend analysis of flow, sludge condition and pumping parameters. The system is a vast improvement on the previous one and to date, has given three years of trouble-free operation."
Franklaw WwTW, Preston
In January 2004, a trial ADD system was installed by NW at Franklaw WwTW, near Preston. The concerns of United Utilities for this site were to improve the efficiency of the existing sludge pumping system, which comprised hydraulically operated pumps. These pumps required frequent downtime in order to carry out maintenance and servicing, and the environmentally damaging leakage of oil was also a major headache. United Utilities accepted NW's solution of the ADD pump package, with its benefits of longevity, ease of maintenance, and no oil contamination issues. NW was able to install one system on a trial basis, with a further three systems to be installed on successful completion of the trial.
The concept of this system was to build into it an operator interface that would vary the suction pressure, discharge pressure and pump stroke rate to enable the operator to tailor each pump's operation to suit the product. The pump monitors stroke rate using piston movement sensors. Suction pressure and discharge pressure is monitored using a pressure cell mounted in the pump outlet line. Each pump has the facility to be selected for use individually via the operator interface.
On satisfactory completion of the six-month trial period, NW was asked to install a further three units at Franklaw. Ken Longshaw, operations manager at the site said the main problem with the previous system was its inefficiency.
"The pumps were unable to meet process output needs, creating a large sludge tankering requirement," he said. "The system was also very problematic in that it was constantly failing. By installing the ADD system, we were hoping to improve efficiency and reliability. Environmental and health and safety issues were also very important in our decision, for example, with this system there is no hot oil at high pressure.
"During the trial, the single ADD system was monitored closely. In terms of health and safety and the environment, we found there were vastly improved operating conditions for the operators. There is now no working at height, noise or need for guarding, no slippery floors and no need for a bund.
"We also monitored priming capabilities from all storage tanks and time to fill press, as well as the condition of the cake. The system met all expectations; time to fill press was reduced by half. The cake produced was drier, and as dry cake is easier to transport, this gives transportation cost savings."
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