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Down in the depths of the Peak District resides the largest battery breaking and recycling plant in the UK. Operated by HJ Enthoven & Sons, on the site of an historic lead mine, the Company recycles over 100,000 tonnes of industrial and automotive lead-acid batteries per year, and is one of the most environmentally responsible and efficient plants for lead recycling in the world. Given the toxic nature of the batteries, HJ Enthoven is aware of its environmental responsibilities and has invested considerable resources into ensuring that the local environment is not affected by its operations.
The breaking up of the batteries and the recovery processes involve crushing the complete battery and then separating out all the individual metals, plastics and chemicals. The first stage involves crushing the batteries in a high speed hammer mill, a process which breaks the components into small parts for subsequent separation.
The next stage of the process sees the crushed parts passing through primary and secondary rotating filter screens to separate acid, plastic and metallic fractions. The internal surfaces of the screens require continuous cleaning with internal high pressure jet-washing sprays to optimise the overall separation processes and removal of the lead sulphate sludges for recovery.
However, the external surfaces of the screens can become blocked and regular cleaning is required. Without effective high pressure washing of the screens' external surfaces, HJ Enthoven cannot achieve the required levels of material separation required to successfully operate the battery breaking aspect of its business.
The problem
Historically, external screen washing was performed using a single high pressure pump to feed the spray nozzles. However, the pumps used were not up to the demands of the breaking process and required frequent attention and maintenance, resulting in costly plant downtime. Having struggled with this situation for a number of years HJ Enthoven decided in 2005 to instigate a major review of this aspect of the process, in order to overcome these problems and reduce the associated costs.
The solution
It was at this time that Cat Pumps entered the scene, providing much needed information on spray nozzle performance curves. Working alongside HJ Enthoven's engineers, Cat Pumps brought its knowledge of high pressure pumping, gained on similar industrial applications, to the table. “In many respects, we took on a consultancy role,” says Cat Pumps UK general manager Brian Hubbard. “Over a period of several months, we undertook an evaluation of the pumping requirements in order to provide HJ Enthoven with a number of alternative solutions that addressed the many issues that emerged from our meetings. It was time well spent as we were able to demonstrate not just the technical capabilities of our pumps to operate in an extremely challenging environment for long period, but also our engineering design resources.”
After much consideration, which involved looking at proposals from other equipment suppliers, HJ Enthoven elected to go with Cat Pumps. They had demonstrated a clear understanding of the importance of the spray cleaning process to the breaking plant and had shown where cost savings could be made. It was in late 2007 when Cat Pumps received the go ahead to design a ‘ready to use’ skid based package consisting of three individual high pressure 6811K Series triplex plunger pumps, two duty and one standby, complete with motors, control panel, header tank and pulsation dampers.
The 6811K Series pumps feature 316 SSL block-style manifolds for strength and corrosion resistance and ceramic plungers which maximise seal life. To satisfy the demanding environment in which they operate at HJ Enthoven, the pumps were equipped with cast iron crankcases as well as incorporating special ported inlet manifolds which permit an external liquid flush.
According to Brian Hubbard the pumps offered higher levels of energy-efficiency than experienced in the past, so HJ Enthoven would get double the flow rate for similar electricity consumption. “We provided consultancy to help design the system and establish the pump requirements, balancing effective cleaning against water and energy consumption,” reports Brian Hubbard.
“Our pump package has the effect of doubling the output flow of the existing pump, enhancing the effectiveness of the process and also vastly increasing pump reliability and eliminating down-time. The inclusion of a standby pump provides built-in redundancy so the process could continue when any one of three pumps is out of service e.g. for routine inspection and parts replacement.”
The pumps feed a single pipeline into the spray heads which wash various screens which were previously prone to blinding. Motorised valves allow the plant operators to turn these individual areas on and off as required and set sequencing cycles. The pumps, which are capable of providing pressures up to 4,000 psi and giving a flow rate of 2.6 m3/hr, are required to operate 24 hours a day in a very demanding environment. The water supply comes from flooded mineshafts and contains dissolved carbonates, which can be a problem for some pumps but not for Cat Pumps.
In any application where high pressure pumping is required and a constantly smooth flow rate needs to be achieved, the triplex positive displacement pump is arguably the most economical choice. The triplex pump employs three synchronised plungers, which give it the ability to deliver a predictable, smooth and constant flow. The smooth flow greatly reduces the possibility of system failure caused by excessive pulsation. With Cat Triplex Pumps, the synchronised plungers can produce flows of 0.1–265 l/mi. at pressures up to 690 bar.
The results
HJ Enthoven installed and commissioned Cat Pumps' rig in early 2008 and after 12 months the performance has more than measured up to expectations. “We are now running the pumps ‘under PLC control’ incorporated into the auto start-up and shut-down sequence for the battery breaker,” comments Paul Grainger, engineering manager, HJ Enthoven & Sons. “Cat Pumps have provided a professional and friendly service, from the early design stages through commissioning and subsequent maintenance and support of the equipment.”
“Performance so far has been far better than anticipated,” he continues, “with pressure and flow satisfying our operating requirements. Overall there have not been any operational problems. We were advised by Cat Pumps in the initial stages that after 12 months continuous operation the pumps would require a routine service involving the replacement of seals and valves etc. When we inspected the pumps with Cat Pumps after more than 12 months, very little work was required, which even surprised Cat Pumps given the amount of work that they had been subjected to. We have been delighted with the performance of the equipment to date.”
Conclusion
Whilst the pump package meets the performance requirements in terms of pressure and flow, HJ Enthoven has been able to reduce substantially the costs incurred in pump maintenance, spare parts and downtime. In addition, the three pump set-up is far more efficient to run in terms of energy consumed.
