It's 'hell' for pumps

Pumps are increasingly being required to deliver accurate, uninterrupted flow, with minimal maintenance in hostile environments, such as those encountered in desert regions, within nuclear plants, as well as at plants handling highly aggressive chemicals.

Many of the toughest applications for pumps are not immediately evident from location or nature of the plant as highlighted by a Clariant’s Gerstofen plant in Bavaria, Germany, which processes Montan waxes for use in car and shoe polishes.

But, in what the supplier described as “every production engineer’s nightmare”, the Clariant Produkte operation includes a transfer system that has to convey a foaming, corrosive medium at a pressure of more than 4 bar and temperatures of 130°C. Volumes vary between 300 and 2,000 litres/hour, while there is also a legal requirement to use hermetically sealed pumps.

Corrosive medium
Explaining these ’pump-hell’ conditions, Franz Kovanetz, production engineer at Clariant, said: “Montan wax is recovered from bitumen-containing lignite and processed in several stages to obtain the end product. We have operating conditions here under which some pump designs would fail very quickly.

“We need pumps that can convey relatively low volumes of a highly corrosive medium with up to 20% entrained gases at high pressure. And, because it’s molten wax at a high temperature, and we need them to be maintenance-free for a continual manufacturing process.”

The process had created severe problems for the plant engineers until the installation of Richter MPB peripheral pumps, which can deliver low flow rates at high delivery heads. These demands, claims Richter, are not “economically covered” by standard centrifugal pumps.

The hermetically sealed pumps have a magnetic power coupling, which equates to no seals and virtually maintenance-free operation. Varying volumes can be coped with efficiently via frequency control, the equipment maker also claims.

We need pumps that can convey relatively low volumes of a highly corrosive medium with up to 20% entrained gases

The reduced life cycle costs of the peripheral pumps give Clariant a considerably longer service life and the maintenance costs are substantially lower, said Kovanetz, who added: “Given the expected service life of four years, we are assuming a cost advantage of several thousand euros for each pump.”

The challenging and dangerous nature of applications in the nuclear power industry, were evident recently during the virtual meltdown of the Fukushima plant in Japan. Despite a backlash against the industry in some countries, pumps makers are continuing to supply nuclear projects around the world.

Glasgow-based ClydeUnion Pumps claims to offer a unique safety pump design, called the TWL, that meets the need for improved safety in the nuclear industry. The high-temperature and high-pressure design requires no external services.

The design is much more robust when dealing with catastrophic events, such as the recent Japanese tsunami, claims ClydeUnion, which has recently won a $15-million order for six main feed water pumps and associated kit in China.

The equipment is for the Fuqing 3 & 4 nuclear power plant in Fujian Province in southwest China, the Scottish company has reported (see panel, above).

Elsewhere, the sheer size of the pumps and the need for corrosion resistance were the challenges faced by KSB of Frankenthal, Germany, for an order for a gas liquefaction plant in Ras Laffan, Qatar one of the biggest seawater cooling plants in the world.

To meet the increased demand for cooling water, the operator is replacing the existing pumps with pumps of the same design but with a significantly higher output. Each of the new 18m-tall, 70-tonne pumps is driven by a low-speed, 4,000kW, 12-pole, 6,000V motor.

The single-flow tubular casing pumps with mixed flow impeller made entirely of seawater-resistant duplex stainless steel deliver around 140,000m3 of water per hour at a head of 58m. The first pump will leave KSB’s Frankenthal, Germany, factory for Qatar at the end of December. By the end of June 2012, all pump units will have left for their destination.

While the San Francisco Bay area is a milder environment, the local water utility’s Tesla Portal Disinfection station is required to disinfect 288 million gallons of water per day using 12.5% NaOCL (sodium hypochlorite), which has corrosive and ’gasing off’ characteristics that present problems for many pumps and metering equipment.

The pump was found to perform without any failure or component wear in a range of operating scenarios

As the diaphragm pumps used at the Tesla unit were prone to vapour lock and pulsation issues, check valves plus vibration and pulsation dampeners had to be installed for each pump at a cost of $450 per pump, while extra maintenance costs were incurred to just to release vapour locks. The utility, therefore, recently switched to using seepex progressive cavity (PC) pumps, which were found to meter well without instrumentation or analysers and need no accessories to prevent vapour lock.

Following the introduction at Tesla, a further 24 new seepex pumps have now been ordered for another of San Francisco’s chlorination facilities at Sunol Valley as part of a capital improvement programme.

Back in the UK, another pumps challenge was presented by the rigorous conditions found in ultrasonic cleaning machines supplied by Guyson International. The Yorkshire company’s portfolio includes solvent-based systems for precision engineering, electronics, aerospace and metal-finishing applications.

The combination of handling volatile, near-boiling-point solvents with a very low suction head had resulted in very low pressures at the pump inlet with NPSHa (net positive suction head) levels occurring of typically less than one metre. On many types of pump this causes severe cavitation, leading to regular failures.

Guyson has, therefore, selected a magnetically coupled centrifugal pumps in PVDF (polyvinylidene fluoride) construction from the Finish Thompson DB range, to avoid potential failures of the main circulation pumps on some models of its solvent cleaning machines.

The DB pump was found to perform without any failure or component wear in a range of operating scenarios that included dry-running, starved suction by closing the suction valve and dead-heading by closing the discharge valve.