Liquid Pumps and their End Uses
Pumping liquids is fundamental to the smooth operation of life in all aspects. From the central heating and water supply in our homes, sewage and waste water treatment in our cities through extraction and processing of raw materials to manufacture of finished products, pumps play a fundamental role.
Moreover, the importance of pumps in economic terms should not be underestimated. Globally the industry is worth almost $40 billion and some individual examples taken from utilities and industry should demonstrate their key role:
- On a 650 MW combined cycle generating station, a total of 18-20 pumps may be used in applications as diverse as boiler feed, condensate extraction, circulating cooling water and for utility service. The total value of pumps employed is around $4 million.
- On a 1 GW supercritical coal fired station, as many as 40-45 pumps will be used including applications for slurry handling for flue gas desulphurisation units. The total value of the pumps can be around $11-12 million (excluding the turbines used for e.g. boiler feed) and where sea water rather than river water is used for cooling, the prices will be considerably higher because of the requirement to use stainless steel 316 or duplex stainless.
- By contrast a 1700 MW pressurised water nuclear reactor for power generation may require up to 150 pumps with a value of up to $140-150 million. Unit values can range from $12,000 for utility service pumps to $20 million for specialist reactor coolant pumps.
- Much higher numbers of pumps are used in oil refineries. A 300k barrels per day oil refinery could have up to 600 to 650 pumps with a value of around $150 million.
- Similarly, chemical plants can have large numbers of pumps although, given the vast range of products, numbers are highly variable. Unit values also tend to be much lower since the operating conditions (e.g. temperature, pressure) are usually less onerous than in refineries.
Depending upon the application/end use sector, the number, type, configuration, size and materials or the pumps used can vary considerably. Hence in a chemical plant, air operated diaphragm pumps may be used for unloading raw materials, centrifugal pumps for supplying raw materials to the reactors and for transfers between the processing units, metering pumps for adding small quantities of reactants and/or catalyst and eccentric screw pumps for handling waste products or slurries of an intermediate/final product.
The toxicity, flammability and corrosive/erosive nature of the liquid being pumped will determine whether a sealed, magnetic drive or canned motor pump is used and the material in which it is made. Materials used can range from basic ductile cast iron to exotics such as zirconium and titanium depending upon the service.
Pump configurations can vary depending upon factors such as space available, pump location in relation to the liquid to be pumped, volatility of the pumped liquid and extent to which the liquid may contain solids. Pump designs are available to cover these and most other situations e.g. in line/close coupled pumps where space is limited, vertical line shaft pumps for high lift applications, self-priming pumps for liquids containing high proportions of air and side channel pumps for volatile liquids such as LPG.
Careful attention to impeller design can assist in handling liquids containing stringy or fibrous material e.g. open style impellers, and where solids content is particularly high, it may be appropriate to use eccentric screw pumps. Note also that in pumping applications, the international standards applied can differ.
In the process units of a refinery, the pumps will typically be specified to meet API (American Petroleum Institute) standards which are designed to cope with the high temperature, high pressure environment. However, for non-critical and/or utility applications, ISO or ANSI (the American equivalent of ISO) may be sufficient. In a chemical plant, by contrast, ISO/ANSI standards would be sufficient for all but the most demanding processes.
Pumps used in West European municipal water supply and waste water/sewage handling pumps will also meet the relevant ISO standards. It should be noted that in some developing countries, these standards may or may not be applied.
There are cases, for example in biofuel manufacture, where pumps used in the processing of the raw material are purchased at the lowest cost possible and, if necessary, replaced at the end of the growing season for the raw material. The astonishing diversity of pump types, designs and materials mirrors the wide range of applications where pumping is required. Even as new transformational technologies are developed, e.g. solar power, geothermal energy, shale gas extraction using hydraulic fracturing (“fracking”) etc., the ability of society to exploit these depends heavily on whether the pump industry can respond to the challenges that each presents. The fact that the US now enjoys abundant supplies of cheap natural gas, that most of Iceland’s power comes from geothermal sources, and that the viability of solar power is being proven in Spain and the western United States, all testify to the demands made of the pump industry and our success in finding solutions.