Impeller for a centrifugal pump, a centrifugal pump and a use thereof

Abstract

An impeller for a centrifugal pump, the impeller includes a front shroud, a rear shroud, and one or more working vanes therebetween, the front shroud having a front face opposite to the face having the working vanes, the rear shroud having a rear face opposite to the face having the working vanes, the front shroud having an outer circumference and a plurality of front pump-out vanes attached to the front face of the front shroud, the rear shroud having a plurality of rear pump-out vanes attached to the rear face of the rear shroud,the front pump-out vanes being dimensioned in accordance with an equation:Σi=1z(li) / D>8, whereZ is the number of front pump-out vanes,l is the vane length measured along the leading surface of each front pump-out vane,D is the outer diameter of the front shroud.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to EP Patent Application 14165689.2, filed Apr. 23, 2014, the contents of which is hereby incorporated herein by reference.BACKGROUND[0002]1. Field of the Invention[0003]The present invention relates to an impeller for a centrifugal pump, a centrifugal pump and a use thereof. The present invention relates especially to a novel closed impeller structure for a centrifugal pump. The centrifugal pump utilizing the impeller of the present invention is suitable for pumping both clean liquids and solids-containing liquids like for instance fibrous suspensions of pulp and paper or board industry.[0004]2. Background Information[0005]Energy saving, in other words efficiency, is an important factor in the development and design of all kinds of machines and machine elements including centrifugal pumps and their impellers. It has always been a known fact that the work the impeller of a centrifugal pump subjects to the ...

AI Technical Summary

Benefits of technology

The present invention aims to improve the construction of centrifugal pumps, especially at the lower end of the speed range, to increase efficiency and meet the EU efficiency curve. This involves shaping the impeller to raise its efficiency and designing the pump-out vanes to prevent leakage flow and act in an energy-efficient manner.

Problems solved by technology

It has always been a known fact that the work the impeller of a centrifugal pump subjects to the fluid it pumps is not totally converted to kinetic and / or potential energy but a part of it is wasted in phenomena taking place between the fluid and both the rotary impeller and the static pump volute or volute casing.

In other words, small sized pumps have a low specific speed.

However, since the specific speed of a centrifugal pump correlates to efficiency, it has been understood now when studying the pumps having a low specific speed that they have low efficiency due to two impeller-related factors having a relatively high impact to efficiency.

Also, without any measures the pressure affects the shaft sealing, and has to be limited for preventing the sealing from deteriorating.

However, because they are normally much smaller, the pressure they develop cannot overcome that developed by the working vanes.

At its worst there is a significant recirculating leakage flow from the pressure side of the impeller back to the suction side of the impeller through the gap between the front shroud of the impeller and the volute casing.

However, as the wear ring has a certain operating clearance, the wear ring must be replaced, when the clearance becomes excessive.

The flow restriction created by the tight clearance between the stationary and rotating wear ring faces causes very high local velocities and hence a high wear rate.

If the fluid to be pumped contains abrasive particles, wear rings, because they are subject to a very high flow velocity, will have an unacceptably short life span, even when made of hard materials or when their surfaces have been specifically treated in view of wear.

Thus the use of a wear ring is not desirable when pumping liquids containing solids.

The disadvantage of known pump-out vanes is that they consume considerable amount of power while controlling leakage.

An impeller with wear rings loses efficiency rapidly as the rings wear.

It is not uncommon to have several outages to replace wear rings over the life of a single impeller when wear rings are used in an aggressive solids application.

A further known disadvantage of closed impellers is that the smooth front and back shrouds (not having pump-out vanes), rotating in close proximity to the casing walls, generate disc friction that lowers the efficiency of the pump relative to that found in open impeller designs.

Yet another disadvantage is that the closed impeller is more easily plugged.

Large solids that might otherwise be broken up by the grinding action generated by a rotating open impeller and the stationary casing wall, can easily become lodged in the eye of a closed impeller.

This may create a mechanical or hydraulic imbalance that has the potential to damage the pump, or at the least causes a pre-mature outage to remove the blockage.

In other words, there are two separate methods of restricting internal recirculation that can lower the efficiency of the pump and generate a lot of unwanted heat to the fluid to be pumped.

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