Improving Pump Performance at Multotec

A human of about 77 kg consumes approximately 2 300 kcal (9 623 kJ) per day. The human heart uses 420 kcal (1 758 kJ), ≈ 18 % of our requirements. It moves / transports nutrients and oxygen through our bodies. Pressure and heart rate (flow rate) change constantly to meet our environmental conditions… anger, love, excitement, exercise… 

Is a centrifugal pump or other devices displacing a fluid, any different? 

Healthy living and regular exercise strengthen your heart and improves its efficiency in moving blood through your body… leading to improved health... leading to a stronger heart… leading to improved health… 

Is an efficient pump any different? 

Focusing on centrifugal pumps, a study by (Jeswiet & Szekers, 2016) showed that in 2013 copper processing and concentration contributed to 48.6 % of the total global energy consumption for this mining segment. An increase to 64.2 % is expected by 2025. 

How much does pumping contribute to this? 

According to the same authors pumps contribute more than a ¼ of the electricity consumption (Table 1) of a typical mining plant. As listed in the same table an improvement in pump efficiency contributes significantly to lower production costs. 

Now, Pa = Q.Hm.Sm/ηm 

[Pa = Absorbed power of a slurry pump] 

What influences the energy required to make the pump do work? 

Q     Flow Rate = the higher the flow the more energy required. 
Hm     Dynamic head = the more resistance of the system the more energy required to move the fluid. 
Sm     Slurry specific gravity = the higher the density, the more mass to transport, the more power required to move the media. 
ηm     Slurry pump efficiency = The higher the efficiency the less energy is wasted to move the slurry - the closer the electric motor size can be to the absorb power of the pump. 

Let’s say the flow rate, dynamic head and specific gravity are set (a fixed operational condition). 

How can we then improve or reduce energy consumption? 

1.    Do not size a pump for “in case”. Engineers tend to be conservative and in many cases over engineer systems. Thus, if additional safety factors have been added to the plant design, friction losses, greater differential heads etc. adding some “meat” during pump selection increases pump size, pump costs and higher power requirements …. stick to your guns. 
2.    Meet the required duty point and increase electric motor power rating slightly to allow for wear. 
3.    Reduce the wear inside the pump. 
4.    Tighter tolerances between components. 
5.    Improve flow characteristics within the pump. 
6.    Reduce friction losses in bearing units, sealing arrangements etc. 
7.    Correct setting of impeller to volute. 

To reduce and improve we need to innovate. 

How can we as an equipment provider assist our clients? 

Well, Multotec Pumps recently developed the new MA range. We aim to be competitive in the market, reducing the cost of ownership for our clients. The MA range is not a “like for like” machine but designed from the ground up, using years of field experience. 

So how has the MA range pushed the boundaries? 

1.    Reduce wear 

Interface between the throat bush and impeller. Slurry circulates from high pressure to lower areas within the pump. The gap between impeller and throat bush is as small as possible to prevent or lessen flow. Pump out vanes on impeller and angled interface between impeller and throat bush (Table 2). 

Note: Cross flow from high to low pressure regions is also reduced by pump out vanes on the front and rear shrouds of the impeller and should be considered together with the angled gap between impeller and throat bush. 

Ceramic impeller and shaft sleeves 
Ceramic components can last up to 3 times longer. Material density of alumina is lower than steel with start-up current less due to a reduction in the moment of inertia. The drawback of ceramics is low impact resistance. Foreign particles such as nuts and bolts in the slurry will crack and chip the components on impact. 

2.    Efficiency 

Impeller 
A CFD (Computational Fluid Dynamics) optimised impeller vane design allows for smoother (less turbulent) transition from linear to radial flow in the impeller while reducing wear in most applications. The vane design has a curved leading-edge geometry (Francis type). 

The pump out vanes shape on the front and rear shrouds of the impeller are optimised to ensure more efficient expelling of slurry and sealing and contribute to higher pump efficiency over a wide operating range. 

The pump out vanes function to reduce the pressure between the discharges and inlet in the regions where the impeller interacts with the throat bush (front) and volute (back). The smaller size MA pumps have open impeller configurations. Open impellers have lower efficiencies but are less prone to blockage. To overcome reduced efficiency a five-vane configuration is employed. 

Alignment 
On older competitor designs, the frame plate liner insert (FPLI), volute and throat bush were clamped between the cover and frame plates. Alignment of these components is not always true to the centreline of the pump. This misalignment can affect the longevity of your other components, such bearing units, wear and pump efficiency. 

The MA pump incorporates the FPLI with the volute, fewer components, and the components bolts to the frame and cover plates through studs and bolts. This ensure all components are in line with the pump centre, consistent in fitment and performance.

Conclusion 

The basic slurry pump design has stayed the same for many years. Through research and development, incremental changes and improvements were made to pump designs. 
Usually the aim was to reduce cost of ownership (capital cost, energy consumption and maintenance), while fulfilling customer requirements. Focus on materials of construction (improve longevity), understanding fluid dynamics / behaviour (increasing pump efficiency) and component design (applied material and flow characteristic) differentiate the different Original Equipment Manufacturers from one another. 

References:
Jeswiet, J. & Szekers, A., 2016. Energy Consumption in Mining Comminution. Ontario, Elsevier B.V.. Vijfeijken, M. v. d., 2010. Mills and GMDs. International Mining, Issue October, p. 30.