New pump technology aids plant efficiency

Changing requirements in pharmaceuticals manufacturing are driving pump manufacturers to develop new techniques and improve the economy and efficiency of dosing and proportioning systems

Reciprocating positive displacement process pump technology is a proven method for the in-line proportioning and dosing of liquids and provides the highest levels of accuracy and repeatability available. The factors affecting the choice of a metering or dosing pump as opposed to other pump types are normally associated with the pump's precision over a range of flows, and the fact that the capacity is not influenced by pressure fluctuations within the process.

The metering pump is very adaptable and its design makes it ideal for the continuous, in-phase metering of single or multiple liquid systems at varying rates. It is the only pump with two flow adjustment methods, speed and stroke length, that can be used independently or simultaneously to optimise performance.

It is the application that will always determine the type of pump to be used. Having established the nature of the medium, it is necessary to consider other parameters such as delivery volume and pressure, temperature, flow characteristics, vapour pressure, solids content, corrosiveness, toxicity and hygiene.

The correct material for the pumphead is selected according to the properties of the pumped medium. For toxic materials or exacting applications where security and safety are priorities, a diaphragm pumphead is usually the first choice. For less demanding applications, a plunger pumphead will normally suffice.

The standard plunger pumphead, consisting of a housing, displacement plunger, seal arrangement, pump valves and suction/discharge side connections, is commonly used where high pressures and high flow rates are encountered. The simple design and small number of components allow a low dead volume and high volumetric efficiency.

Mechanically coupled and hydraulically actuated diaphragm pumpheads are one of the areas of focus for new developments in metering pump technology. Available in a wide variety of materials, diaphragm pumpheads are now capable of accommodating hazardous, toxic and dangerous liquids at variable flow rates and pressures. For environmental and safety reasons the market is moving towards diaphragm pumps and away from the traditional plunger design.

Bran + Luebbe's hydraulically actuated double diaphragm pumpheads incorporate diaphragms made from either PTFE or stainless steel, and are capable of handling pressures of 1000 bar and above. All these pumphead designs incorporate a diaphragm failure indicator to give warning of a problem. This design of leak-free pumphead will continue to provide continuous service even in the event of one diaphragm failing.

chemical resistance

Diosynth, a sub-business unit of Akzo Nobel, based in Fife, UK, manufactures intermediates for active pharmaceuticals. It has switched to double diaphragm metering pump technology from plunger type pumps for handling thionyl chloride, a chlorinating agent used in organic synthesis. Thionyl chloride is a particularly reactive and corrosive liquid that reacts in moist air to produce sulphur dioxide and hydrogen chloride gases.

The replacement metering pump incorporates a hydraulically actuated double diaphragm pumphead with Halar coating and PTFE valves, and is leak-free and resistant to chemical attack.

Traditionally the options for high pressure and hazardous proportioning and metering applications have been limited to reciprocating fixed stroke positive displacement, high speed, or multi-stage type centrifugal pumps. All these have their limitations, not least in respect of regular maintenance, frequent replacement of worn parts, product leakage and high running costs.

The introduction of a hydraulically actuated, double diaphragm pump capable of handling pressures of 1000 bar and above leak-free, is changing this situation. The Novaplex pump contains modular phased pumpheads that provide a smooth product flow across a wide operating range, including low speeds. Comprising various gear sizes in combinations between one and seven, a choice of diaphragm materials and variable flow rate, its modular build accommodates the widest possible range of duties for all critical pressure processes.

By employing low-maintenance reduction gears, energy consumption is minimised and almost silent operation is ensured. Each gear segment contains a separate crankshaft element, and the use of roller bearings makes it possible to have speeds ranging from zero to maximum, even at extremely high suction pressures. Users also get the benefit of diaphragms giving a long service life; 5,000 hours are the norm, although 20,000 hours have been attained.

Metering pumps are capable of dosing and proporioning a wide variety of materials, including slurries and suspensions containing abrasive particles. What must be taken into account is the impact the material will have on the pump's components, together with previous experience of the medium being handled.

Metering pumps are used in a wide range of applications for single point or multi-ingredient dosing. Single point dosing typically involves the addition of a specific medium, such as a dye, chemical or fragrance, accurately and in proportion on a continuous basis. Multiple liquid applications can be handled on a single multi-head machine, with the individual liquids metered independently to predetermined points in the process or brought together to create a blend.

This can involve any range of liquids in any range of flows and in any proportion, using a multiple headed pump unit to take the recipe and blend the components together. Each of the components is blended in the correct proportions, in the correct order and place to obtain the desired mix.

Process and metering pump technology is not standing still and Bran + Luebbe continues to invest considerable research and development resources into exploring new concepts with a view to improving overall performance and efficiency. In addition to its work in double diaphragm development, it has been concentrating on increasing the efficiency of gears. The spin-off from this is that less power is required to drive them, enabling users to reduce their energy costs.

The company's recently developed H4 provides users with a new high efficiency horizontal gear box containing state-of-the-art sealing technology. This new gear design offers the benefits of low oil temperature, reduced leakage potential, stroke adjustment forces and lifecycle costs. Furthermore, the housing, pump yoke and stroke adjuster mechanism come as a single, integrated unit, enabling several units to be joined together in a horizontal assembly.

The introduction of off-line diagnostics allows maintenance engineers to look at the pump while in use to determine its performance and pre-empt any failures by taking remedial action; furthermore the pump can be shut down when convenient to avoid costly downtime.

Diaphragm pumps are supplied with diagnostics fittings, consisting of a pressure sensor and gearbox mounted impulse device as standard. A p-V diagram of each pump cylinder is produced, via the sensor probe linked to a laptop PC with PCMCIA data acquisition board, for analysis of the pressure curve versus time, or piston stroke contained on the diagram (figure 1).

The system also allows for comparisons with flow measuring devices and improves quality control and documentation for production tests, e.g. NPSHR-tests. Clearly, where large and complex units are in operation and the process is of a critical nature, preventative maintenance through off-line diagnostics becomes an attractive proposition.

changing requirements

The changing requirements in pharmaceuticals and chemicals manufacturing are forcing pump manufacturers to examine current technologies with a view to developing new techniques and making use of more exotic materials for components. At the same time, there is a push for more economical and efficient dosing and proportioning systems.

Although the basic concept of a dosing and proportioning system is very much a standard, the market is diverse and the demands of each industry are different. The skills of the pump manufacturer lie in determining how and where its components are customised for each application. The onus is on the pump manufacturer to offer its engineering resources to customers to provide solutions and not just a commodity.