Centrifugal pumps high-energy

Garbers, A. W. and A. K Wasfi, Preventing Cavitation in High Energy Centrifugal Pumps, Hydrocarbon Processing, V. 69, No. 7, 1990. 

In all of the above equations, is assumed to be constant and uniform throughout the flow field. In most items of bioprocess equipment, however, there is a spatial distribution of energy dissipation. The definition of an average or a maximum energy dissipation rate is notoriously difficult in the case of bioprocess equipment such as high pressure homogenisers, centrifuges, pumps and microfiltration units which all have complex flow fields. 

As liquids are essentially incompressible, less energy is stored in a compressed liquid than a gas. However, it is worth considering power recovery from high-pressure liquid streams (> 15 bar) as the equipment required is relatively simple and inexpensive. Centrifugal pumps are used as expanders and are often coupled directly to pumps. The design, operation and cost of energy recovery from high-pressure liquid streams is discussed by Jenett (1968), Chada (1984) and Buse (1985). 

The centrifugal pump operates over a very wide range of flows and pressures. For low heads but high flows the axial pump is best suited. Both the centrifugal and axial flow pumps impart energy to the fluid Iw the rotational speed of the impeller and the velocity it imparts to the fluid. 

The impeller is the working part of a centrifugal pump. The function of the impeller is to increase the velocity or kinetic energy of the liquid. The liquid flows into the impeller, and leaves the impeller, at the same pressure. The black dot shown at the top of the impeller in Fig. 23.6 is called the vane tip. The pressure at the vane tip is the same as the pump s suction pressure. However, as the high-velocity liquid escapes from the impeller and flows into the volute, its velocity decreases. The volute (which is also called the diffuser) is shaped like a cone. It widens out in the manner illustrated in Fig. 23.7. As the liquid flows into the wider section of the volute, its velocity is reduced, and the lost velocity is converted—well, not into pressure, but into feet of head. 

When pressures in an oil reservoir have fallen to the point where a well will not produce by natural energy, some method of artificial lift must he used. Oil-well pumps are of three general types (I) pumps located a( the bottom of the hole run by a string of rods, (2) pumps at the bottom of the hole run by high-pressure liquids, and (3) bottom-hole centrifugal pumps. Another method involves the use of high-pressure gas to lift the oil from tile reservoir. 

A similar evaluation relevant to the comparison of efficiency and resulting energy costs with high speed centrifugal pumps, gives a clear indication in favour of the PDP. In a particular case of application, based on an energy price level of 0.12 DM/KWh, the break even point has been reached already after one and a half years. 

Centrifugal pumps work by giving the fluid kinetic energy and then converting this to injection work. They are generally high-flow-rate, low-pressure-rise devices. 

This is an example of Bernoulli s equation in action. A steam vacuum ejector (jet) works in the same way. Centrifugal pumps and centrifugal compressors also work by converting velocity to pressure. Steam turbines convert the steam s pressure and enthalpy to velocity, and then the high velocity steam is converted into work, or electricity. The pressure drop we measure across a flow orifice plate is caused by the increase of the kinetic energy of the flowing fluid as it rushes (or accelerates) through the hole in the orifice plate. 

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