How do you reconcile PROCESS

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1 Advantage Hydra-Cell Pumps The importance of pumps in the world of chemical processing and manufacture is self-evident. Many processes cannot run without them. The cost of pump failure in downtime and lost production, also in some cases worries about safety, may be very high. Costs associated with the pump itself - not only buying the pump and standby, but operational costs such as energy consumption, maintenance, repairs and replacement, may be far from negligible How do you reconcile the need to constrain pump costs with the need to avoid pump failure? Dr Ing Friedrich-Wilhelm Hennecke, former pump chief at BASF and a leading authority on process pumps, gave some good basic advice when interviewed by this journal last year (CEW June 2006). "A company can save money," he said, "by buying cheap pumps and doing no maintenance. At least for a short time, for long-term this will cause high costs for repairs and loss of production. The best way is to select the right pump (flow LCC comparison survey (1) rate, head) of good quality and run it properly, with regular maintenance." There is certainly plenty of choice. At the Achema exhibition in Frankfurt in May 2006, for example, no fewer than 160 suppliers were offering their products in the halls devoted to process pumps. However, selection is not always easy. In the more straightforward applications where (to take an ideal set of conditions) the liquid to be pumped is clean water at ambient temperature and the operating pressure is no more than about 10 bar, many types of pump could perform satisfactorily. Choice will probably be governed Figure 1: Pump life cycle costs (LCC), comparison example (pumps recommended for 1.4 m 3 /hr flow rate) F-W Hennecke March 2006 by cost but even in these conditions, according to Dr Hennecke, this should never just mean purchase cost. The true cost of a pump, defined as Life Cycle Cost (LCC), is the total cost of the pump from purchase to scrapping. This will include purchase of the pump, motor and auxiliary devices, installation and commissioning, energy consumed during the lifetime of the unit, supervisory labour costs, maintenance, repair, downtime and consequential loss of production, environmental cost, decommissioning and disposal. In practice some of these elements (e.g. downtime) are very difficult to calculate in advance, while one or two others may not be significant. But costs such as energy, maintenance and repair can be crucial in assessing LCC and making sensible comparisons between one type of pump and another. The concept of life cycle costs is one of Dr Hennecke's ongoing interests. While still at BASF, he co-edited the landmark 'Guide to Pump Life Cycle Costs' published jointly in 2001 by Europump and the Hydraulic Institute in the USA. In 2005 he carried out a comparative investigation into the lifetime costs of five different types of pump, presenting the results in March Four of these pump types are well known in the process industries. The fifth type, viz., the Hydra-Cell is less well known, but in Chemical Engineering World JANUARY

2 Limiting factors include pressure, temperature, solid content, hazardous fluids and pump pulsation. Dr Hennecke's research into LCC was very detailed (a full copy of his report, published in the journal Paper Technology, may be downloaded from the Wanner International web site Among its general conclusions he noted that the Hydra-Cell was the most economic pump overall 'within the pressure and Figure 2: Hydra-Cell pump - simple construction some respects it is the most remarkable, and in many applications it has proved a valid and less costly alternative to types of pump more familiar to plant engineers. The types of pump considered by Dr Hennecke were: the centrifugal pump the side-channel pump the peristaltic pump. the membrane piston pump the Hydra-Cell pump Each of these is generically different from other types of pump. With the exception of the Hydra-Cell, which is manufactured by Wanner Engineering, all the types investigated are produced by more than one company. For his comparative study, Dr Hennecke approached a prominent manufacturer of each type, requesting the company to select its most appropriate model for given operating requirements in three flow capacities. Also to supply data on routine maintenance needs, expected time between repairs, costs of spare parts and labour. All the information was provided by the pump manufacturers themselves. The scope of the investigation covered flow rates of 1.4, 4.2 and 8.4m 3 /hr and pressures of 5, 10, 50, 75 and 100 bar. In practice, not all the pump types are suited to operation in all circumstances. flow ranges considered.' And it was not restricted by pressure considerations or the type of fluid it could handle. The side-channel pump was comparable, within its pressure range, but could only handle clean fluids. "The LCC of the peristaltic pump", he commented, "is increased by its high consumption of replacement tubes", while "Membrane piston pumps are very efficient, but their investment cost and the cost of spare parts and labour when changing membranes are extremely high". Centrifugal pumps "are for low pressures and high flow rates". For pressures above 10 bar, irrespective of flow rate, only positive Chemical Engineering World JANUARY

3 Figure 3: Hydra-Cell G25 pump delivering hot de-ionised water to control temperature in steam line displacement pumps were considered suitable, ruling out centrifugal, side channel and peristaltic types. The results showed that for these higher pressure applications the LCC of the Hydra-Cell pump was substantially lower in each case than that of its only real alternative, the membrane piston pump (see Figure 1). The basic Hydra-Cell design, which today is embodied in a range of models covering flows up to 138 litres per minute (8.3 m 3 /hour) and discharge pressures up to 170 bar, originated in the 1970s. It was then that William F. Wanner built his first seal-less pumps and joined with his son Bill, current CEO, in founding the company that remains the sole manufacturer. From the outset William Wanner determined to keep his design simple and also avoid the use of dynamic seals. He was targeting certain markets and applications and knew that seal wear was one of the most common causes of failure and high repair costs for existing positive displacement pumps more especially when they were handling chemicals and liquids carrying abrasives. Since these early days, the company has invested massively in design, development and sophisticated manufacturing technology. These programmes continue more strongly than ever. But the original concept still holds good. The Hydra-Cell pump (Figure 2) has no dynamic seals. It uses the principle of hydraulically balanced diaphragms, most models in the range have 3 or 5 diaphragms in a single head, producing a flow with very low pulsation. The diaphragms have a dual function. They are flexed in sequence from behind by liquid pressure in the hydraulic cells to provide the pumping action. They also act as a barrier, totally isolating the oil in the drive end of the pump from the chemical or other liquid being pumped. This allows the pump to handle many 'difficult' media including corrosives, abrasives, liquids with solids in suspension, Chemical Engineering World JANUARY

4 viscous products and thin nonlubricating liquids. The relatively few components in contact with the liquid medium, viz., pump head, diaphragms, inlet and outlet valves are offered in a wide range of suitably resistant materials. But tolerance of media is rarely the only consideration, and the Hydra-Cell pump has other valuable features. Any pump vulnerable to seal wear, or whose pumping action depends on narrow clearances between moving surfaces, begins with a disadvantage when handling certain types of liquid. In the cement industry for example, xylene (a by-product of wood and coal processing) is pumped to burner nozzles to be used as fuel. But it is toxic, non-lubricating and contains abrasive particles. It is not easy to pump. Cement plants tried various pumping solutions. A gear pump with good quality seals lasted for one week. Piston pumps also failed, and the required working pressure (25 bar) was too high for peristaltic pumps. Traditional metering pumps (hydraulic diaphragm pumps) could handle xylene, but pulsation would have been a problem and in any case the cost of those elaborately engineered pumps ruled them out for this application. As often happens, what made pump selection difficult was having to satisfy several potentially conflicting requirements simultaneously: pumping abrasive liquid that would damage seals; avoiding toxic leakage; pumping at pressure; delivering a smooth, even flow; ensuring reliability and satisfactory service life-and all without procuring at uneconomic prices. Pumping xylene safely, with no risk of seal leaks, is no problem for the sealless Hydra-Cell G25 pump; and the specified delivery pressure of 25 bar is well within the G25's pressure capability of 70 bar. Moreover, the G25 incorporates 3 sequentially-acting diaphragms within its single compact pump head, so that the steady stream of product delivered to the nozzles at 50 l/min is virtually pulse-free, with no need for pulsation dampeners. Proven reliability and their good lowmaintenance record provide further evidence of why the cement industries of several European countries continue to rely on G25 pumps for this work. Wanner engineers are sometimes asked how the flexible diaphragms of the Hydra-Cell cope with the high operating pressures to which they are exposed. The answer is that in normal operation the diaphragm never sees more than 2 psi pressure differential. Hydraulic balance is maintained between the fluids on either side of the membrane, so that the diaphragm itself comes under no stress even at high working pressures. A development by Wanner adds a further safeguard to the Hydra-Cell design. Its patented Kel-Cell technology protects the diaphragms from rupture under adverse inlet conditions such as the severe vacuum that might result from the accidental closure of a valve, or a suction filter becoming blocked. The pump can run dry indefinitely without damage. The drive mechanism, submerged in a reservoir of oil, is permanently lubricated and this arrangement means that power is transmitted through the drive train with minimal friction losses helping to account for the efficiency of the pump. The Hydra-Cell achieves efficiencies as high as 85 per cent, compared with 45 per cent for a typical centrifugal pump. In consequence, the pumps can often be fitted with a motor smaller than would be needed for pumps of another type for the same work output. Energy savings alone have enabled plants to recover the cost of a Hydra-Cell pump within a year. With their high efficiency and simple build-multiple diaphragms concentrated in a single head, Hydra-Cell pumps are remarkably compact in relation to their performance. Pune-based Comp Engineering & Export, a leading Indian manufacturer and exporter of spray drying systems, cites the small size and low weight of the Hydra-Cell, as well as its proven trouble-free operation, as important considerations when choosing to fit Hydra-Cell pumps as original equipment in its spray dryers. Operating pressures for these systems are generally between bar. Products sprayed include slurries and soap solutions and typical flow rates are from 15 to 50 l/min. Models most Figure 4: Pulsation comparison Hydra-Cell G10 v. Traditional metering pump (single head) Chemical Engineering World JANUARY

5 Figure 5: Size comparison Hydra-Cell G10 v. Traditional metering pump Performance (both pumps) Max flow: 1500 l/hr Max pressure: 80 bar frequently fitted are the Hydra-Cell G10 and G25, though occasionally a lower or higher flow rate Hydra-Cell pump has been used. No problems have been experienced and recently there has been some interest from customers of Comp's sister company Mojj Engineering Systems, which makes similar equipment for the Indian market. Proven applications of Hydra-Cell pumps in the process industries are numerous and diverse. As well as spray drying they include reverse osmosis, gas conditioning and cooling (Figure 3), pressure cleaning of filters, tanks and mixing vessels and transfer of product from storage tanks directly into process lines. Worldwide, a rapidly-growing area of application for Hydra-Cell pumps is metering and dosing. Hydra Cell pumps have long been used in this field for a variety of reasons, and it was not at first noticed that on more and more installations the pump had been chosen for its ability to deliver liquid in precise volumes. This trend was happening at the same time as rapid advances were being made in electronic control devices. Frequency inverters, for controlling the speed of an electric motor, simultaneously became far more accurate and less expensive. The essential point here is that the flow of a Hydra-Cell pump is directly proportional to pump speed and that this relationship is linear, exceeding the API 675 performance specification. In practical terms, it has become simple and inexpensive to automate a metering operation, while taking advantage of other Hydra-Cell features such as low pulsation. Compared with traditional metering pumps the Hydra-Cell has virtually pulse-free pulsation (Figure 4). Traditional (piston diaphragm) pumps built to comply with the API 675 standard have long been regarded as the 'true' type of metering pump. API 675 laid down standards of accuracy for metered flow, and also defined the construction features which were then judged the best means of setting, sustaining and readjusting flow within precise limits. But the basic technology is outdated and the resultant engineering is elaborate. Inevitably such pumps are big, heavy and expensive (Figure 5). To vary flow, they have an inbuilt mechanism that changes the actual or effective length of the piston stroke. Costly to automate, by adding an actuator, they are relatively slow to react to external signal. Two Hydra-Cell G10 pumps replaced a traditional single-piston metering pump delivering de-mineralised water with 30 per cent titanium dioxide into a process line at a German chemical plant. Plant engineers had considered replacing the original pump with a triplex (3- headed) pump to try to reduce pulsation, but the two Hydra-Cell pumps had overwhelming advantages. Pulsation is much lower, and even together they took less space, were cheaper to run, consumed less energy and cost less to buy. And the control system is simple. A flow meter monitors the process line, passing data to a computer, which controls the speed of the pumps via a frequency inverter and their drive motors. Flow is varied instantly and accurately on signal. Last year Wanner launched 'Hydra- Cell Metering Solutions', a new series of Hydra-Cell based pumps and control accessories specifically for metering and dosing applications. The company also announced the results of a 2-year programme of tests under controlled installation conditions. They showed that all the pumps (including the basic Hydra-Cell models) consistently exceeded API 675 standards for Linearity +/- 3 per cent, repeatability +/- 3 per cent and steady state +/-1 per cent. Full documentation is available. For more information: Hydra-Cell Pumps Sales and technical support in India Machinomatic Engineers, 102 Naigara Near Colaba South Post Office, Mumbai ,India Tel: symach@mtnl.net.in Chemical Engineering World JANUARY