13 Pump economy

Pump economy

This chapter is all about pump economy and begins with a general discussion with regards to the purpose and extent of economic optimisation, both in connection with the planning of new plant and also with respect to existing plant. It should be emphasized that it is important that the complete fluid transport system, including the secondary costs are considered in the optimisation. Usually it is the piping and energy costs which are two most dominant factors in pumping plant service life cost. Energy costs are greatly dependent upon the choice and methods of control and regulation. Economic optimisation thus involves additional aspects, which are dealt with in more detail in the chapter about Flow regulation.

The section dealing with economic assessment criteria reviews the various methods of evaluation of alternative pump plant proposals. It is important, when assessing the profitability of an investment, to consider the rate of increase of energy costs in comparison to general inflation, together with the investment returns which can be gained by introducing energy conserving remedies.

An important characteristic of pumping plant, from an economical point of view, is its efficiency factor, i.e. the efficiency with which it converts the debitable energy, usually electrical energy, into hydraulic energy. This is especially pertinent, since efficiency factors normally have extremely low values. Reasons for low efficiency factors are discussed and suggestions for improvement are presented. The secondary costs for the main process, of which the pump unit constitutes a part, can be considerable if factors such as process adaptation and available capacity are not considered when designing the plant. The most precious form of energy in connection with pumping is hydraulic energy, which motivates attention in respect of the parameters which, in the first hand, determine the hydraulic power requirements and thereby also the energy consumption.

Certain components in a pumping plant can be optimised individually, which greatly assists the optimisation procedure. For existing plant the majority of feasible optimisations are of a partial character.

Obviously there are different prerequisites for economic optimisation depending upon the type, size and process for which the pumping plant is intended. This chapter is a generalisation offering, in special sections, practical advice
in respect of cost reductions for the majority of pumping applications.