May 23, 2017

Choosing the right pump for the job is key in the reduction of operational costs

After what seemed to be a robust growth of the pump industry over the past few years supported by infrastructure projects within the mining, power generation, water and waste water industries, seems to have hit a brick wall and slowed-down. This is partly because the industry’s 85- 90% business relies heavily on the mining sector which is currently facing a number of challenges – from declining commodity prices, projects being put on hold, new mineral tax laws as well as the strikes in the case of South Africa, explains Harry Steyn, BU Dewatering Manager at Xylem Water Solutions South Africa (Pty) Ltd.

Considering the above challenges as well as financial constraints, mine operators are compelled to keep costs down and – the type of pumps used can impact on operational costs, especially considering that pumping slurry, i.e. a liquid containing solid particles raises different requirements for a pump compared to just water.

Pumps wear hard and fast, it is therefore important to choose a pump that will impact positively on the balance sheet, taking into consideration that pumps need servicing as well as maintenance between intervals. Submersible slurry pumps since they are heavy and robust version of centrifugal pumps, capable of handling tough and abrasive duties can be the ideal solution for mines.

Submersible Slurry Pumps

Some slurry pump users may have limited knowledge of submersible slurry pumps. It is therefore imperative to examine the benefits offered by submersible pumps over dry and especially semi-dry mounted pumps (cantilever):

When operating directly in the slurry, the submersible slurry pump requires no support structure. It therefore occupies less space. The motor and volute are one integrated unit, compact and easy to install.

Submersible pump is operated underwater, it produces low noise or even silent operation. Motor cooled by surrounding liquid allows for up to 30 starts/ hour, resulting in smaller and more efficient sumps. In addition, it allows for flexible installation with several installation modes, all of which are either portable or semi-permanent, as well as the possibility to practice clean pump technology.

Steyn explains the main difference between slurry and waste water pumps, “it is in the parts that are in direct contact with the slurry and thus subject to wear by the slurry’s solid particles. Slurry pumps possess important factors for instance the Flygt slurry pumps possess a motor, cooling jacket, seal, impeller, inspection chamber, strainer, agitator as well as stand, making it unique and superior to other pumps”.

Effective cooling

Water cooling is superior to air cooling and gives the submerged motor a high power density and comparatively low temperature. The pump can be cooled in three ways depending on the slurry temperature and other circumstances:

-Pumps that work fully submerged in slurry, cooled by the ambient liquid. The slurry temperature may not exceed 40˚C.

– Pumps that work at times with the motor partially or totally un-submerged, can be equipped with a cooling jacket for internal cooling, where a cooling medium (glycol mixture) circulates (5100/ 5150).

– Pumps that often work in a low level, in hot slurry or are dry installed can be cooled using external supply of cooling liquid, connected to the cooling jacket.

Submersible Pump Seals- leakage and wear resistance

In conjunction with leakage rate, the most important feature for seals in slurry applications is the ability to resist wear from abrasive particles.

The seals for the slurry pumps are designed to cope with highly abrasive pump media. Only the seal rings are exposed to the media. Other parts of the seal, such as springs and torque locks are protected from wear, clogging and corrosion inside the seal housing.

In addition, an isolation zone takes the pressure of the mechanical seal.

Agitator- an important factor for submersible pump hydraulic parts.

The pump can be equipped with an agitator. The unique design of Flygt agitators create a strong vertical thrust, which forces settled solids into suspension. This makes the particles easier to transport and ensures a cleaner sump at the end of the pumping cycle.

When selecting a slurry pump, it is imperative that the characteristics of the slurry of the system including certain parameters are known, adds Harry Steyn.

Understanding the slurry parameters is key- for instance the following parameters must be determined when calculating a slurry pump application. The particle size and distribution; mass fraction of small particles; concentration of solids; density gravity; as well as the particle shape.

Slurry characteristics

Slurries can be divided into settling and non-settling types, depending on the slurry parameters.

Competitive pricing for pumps, availability as well as aftermarket service is important if pump manufacturers are to survive and add value in these tough times. For instance Xylem’s Flygt slurry pump is easily available at competitive pricing without compromising quality, you can rent or buy from Xylem in over 150 countries around the globe. In addition, the company is represented in every corner of the country to assist clients, and also supported by the rental division which offers a 50% discount rental discount if the pump problem cannot be fixed on site as well as for testing purposes before making a purchase or choosing the right product for your problem, explains Jonathan Höll, Application Engineer at Xylem Water Solutions South Africa (Pty) Ltd.

Mine operators should go for premier products that are well known in the market, and that will improve their turnaround time, that’s impacting positively on their operation costs, notes Jonathan Höll.

Despite the currently slump, the future looks bright and in 2017 as an organisation, with our RD continuously improving our product offering – we are certain that industry will also improve, concludes Harry Steyn.

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