PUMP USED AS TURBINE IN SMALL HYDROPOWER STATIONS



Investigation of Pump as Turbine Performance in Small Hydropower Stations

a.Nourbakhsh1 , Sh.Derakhshan2

1. Professor, Department of Mechanical Engineering, University of Tehran, Tehran 14147, Iran

2. M.S. Student, Department of Mechanical Engineering, University of Tehran, Tehran, Iran

Abstract:The major problem for installation of new small hydropower stations is specific cost expressed in $/KW installed capacity. Part of the solution of this economic problem is to substitute the conventional turbines by simple and inexpensive machines such as reversible centrifugal pumps.

Based on our experimental tests described in this paper a centrifugal pump can operate properly as a turbine, but of course with lower efficiency comparing to the conventional turbines. From an economical point of view, using a pump instead of a turbine can thus be recommended for power stations under approximately 500 KW installed capacity.

Pump manufacturers do not normally provide the performance curves of their pumps for working sturdiness. Therefore, establishing a correlation proper the passage from the "pump" performance to "turbine" once is important for selecting the proper machine in this study several empirical methods existing in the literature for predicting the best efficiency point of pumps running as turbines are presented and compared. However each of these of methods is applicable only for particular cases. Therefore a great interest for future research in this field is to investigate a theoretical way for predicting a pump's behavior operating as a turbine. This paper describes the principles of a theoretical method which can be used in general cases.

Key-words: pump as turbines- best efficiency point-small hydropower-discharge- power-head

1 Introduction

Small hydroelectric power stations became attractive for generating electrical energy after the oil price crisis of the seventies. However cost per KW energy produced by these stations is higher than the hydroelectric power plants with large capacity. Numerous publications in recent years emphasize the importance of using simple turbine in order to reduce the cost of produced electrical energy.

There is need for installation small hydroelectric power stations many developing countries. Based on our literature survey, approximately 200 known hydraulic potentials are available in Iran and can be used in case those projects will come feasible [1].

We considered the idea of using pumps as hydraulic turbines an attractive and important alternative. Pumps are relatively simple machine, are easy to maintain and are readily available in most developing countries. From the economical point of view, it is often stated that pumps working as turbines in the range of 5 to500 KW allow capital payback periods of tow years or less which is considerably less than that of a conventional turbine.

In this paper we report our experiments on using pump as a turbine which was curried in a complete laboratory model of mini hydropower plant.

2 Classification

There are several method proposed by different organization for classification of hydropower stations according to their powers, heads and flow rates. In table.1 the classification according to Latin American Energy Organization (OLADE) is presented.

In some countries and also in Iran, micro, mini and small hydropower plants are generally called under a common name "small hydro power plants".

Table.1.OLADE small hydropower classification

|Head (m) |Power Range | |

| |(KW) |Hydropower Station|

| | | | | |

|High |Medium |Low | | |

| | | |Up to 50 |Micro Hydropower |

|H>50 |15-50 |H100 |20-100 |H130 |25-130 |Hb>1

The values of (a) and (b) are dependent mainly on specific speed and efficiency of pump.

Therefore it can be concluded that each of above equations proposed by the mentioned authors is valid only for some particular cases.

6 Conclusions

In the turbine mode of a pump the output of turbine is more than the input power of pump. And the pump in turbine mode works in higher head and discharge. The pump operates without problem in different rotational speed and various head and discharge. The efficiency is same in both of pump and turbine mode and little more than the pump mode. With slightly impeller and the other component of pump modification, the efficiency will increase. Of course the pumps with higher specific speed present better efficiency and the propeller pumps with the adjustable impeller blades enable wide working region with higher efficiency. There doesn't exist the exactly formula or theory method for prediction of the turbine performance of pump. But with more try it is possible.

References:

[1] Nourbakhsh, A, and Jahangiri, G.(1992). Inexpressive small hydropower stations for small areas of developing countries, pp.313-319. conference on Advances in Planning, Design and Management of Irrigation Systems as Related to Sustainable Land use, Louvain, Belgium.

[2] Stepanoff, A.J. (1957). Centrifugal and axial flow pumps, John Wiley and Sons, New York.

[3] Williams, A. (1995). Pumps as turbines a user's guide, pp.34, intermediate Technology publications, London.

[4] Gantar, M. (1988). Propeller pumps running as turbines, pp 237-248, conference on Hydraulic Machinery, Ljubljana, Slovenia.

[5] Wong, W. (1987). Application of centrifugal pumps for power generation, pp. 381-348, World Pumps.

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Flow (m3/h)

Head (m)

1000

100

10

0

100000

10000

1000

100

0

Single-impeller pumps

Cross-flow

Kaplan

Francis

Pelton

KW OUTPUT

EFFICIENCY

HEAD

RPM=CONSTANT

HEAD, EFFECIENCY, KW OUTPUT

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