PUMPS
pumps. Piston diaphragm pumps are designed near 60 strokes per minute or less.
“ Maintenance of centrifugal slurry pumps may turn out to be considerable as compared with positive displacement pumps which require maintenance on an annual or semi-annual basis.
“ Efficiencies of positive displacement pumps may run as high as 90 %. Centrifugal pumps have a peak efficiency at their best efficiency point but actual efficiencies may be considerably lower.
“ Centrifugal pumps are the industry standard for pumping gland seal water to the large centrifugal pumps on tailings service, ball mill discharge, or other duties. A steady flow is vital to the service life of these large centrifugal pumps even as pressures vary due to gland wear, head tank level changes or other causes.“ A positive displacement pump although more costly initially provides a steady flow of water to the gland seals. Variations in head tank level or condition of the gland area do not change the flow. The positive displacement piston pump provides a constant flow for a given strokes per minute.
“ Feed pumps for plate and frame filter presses operate over a range of capacity and pressure. Generally, slurry is initially fed to the press at a high feed rate. As the press fills, the pressure builds up and the feed rate is reduced in steps as the pressure recommended for the press is attained. Feed material may continue to pack into the press for a short time and then the cycle is ended. The pump is stopped. The press is emptied and the cycle repeated.
“ Centrifugal pumps are a low capital cost option often found in filter press feed applications. Operations range from high capacity and low pressure to low capacity and high pressure. Little of the operation is at the best efficiency point. Damage to the centrifugal pumps occurs from cavitation or recirculation on either end of the operating range. In some instances the centrifugal pump incurs substantial damage from abrasive wear in just a few weeks.
“ Piston diaphragm pump operation ranges from full capacity and low pressures to low capacity and high pressure by varying the stroke rate of the pump. Pump efficiency remains constant during this transition. This is accomplished using a pressure transmitter and variable frequency drive.
“ Piston diaphragm pumps, while greater capital cost, can pump to a filter press without experiencing undue abrasive wear and while maintaining efficiencies greater than 90 %.”
Reciprocating piston pumps produce a pulsating flow. Pulsations can cause vibrations in piping, excessive acceleration head, and influences on downstream processes. Pulsation can be dealt with adequately with pulsation dampeners.
“ One type of dampener is the bladder type. Air or nitrogen is added to the top of the vessel above the bladder at 70 % to 80 % of the process pressure. The pressure above the bladder does not need to be adjusted as long as the operating pressure is fairly constant.
“ With varying pressures, as with a filter press feed operation, the bladder style is inadequate due to the changing pressures. An air cap dampener is preferable. Air within the vessel is compressed by the slurry and the pulsations are attenuated. Air or nitrogen needs to be added regularly to the discharge dampener to replace that carried out by the slurry.
“ The amount of residual pulsation is a function of the stroke volume of the pump, the operating pressure, the volume of the dampener, and a constant for the pump. A 10 % residual pulsation is a good value for most applications.
“ When transferring solids such as thickened tailings, or paste, hydraulically actuated piston pumps are often employed. These machines have two reciprocating pistons. No diaphragm is used. Material is fed to the machines by an auger. Efficiencies are typically less than a hydraulic piston diaphragm pump but they are capable of handling thicker solids than can be fed into a hydraulic diaphragm pump.
“ Piston diaphragm pumps( sometimes also called hydraulic membrane pumps) operate typically at efficiencies near 90 %. Materials need to be fluid enough to flow into the pump. Some materials are thixotropic and can be sheared with an auger such that they will flow into a piston diaphragm pump.
“ The dividing line between piston and piston diaphragm selection is near 70 % solids for many mineral slurries. One rule of thumb suggests that if the slurry is less than 45 % solids by weight it may be amenable to flow into a piston diaphragm pumps. Laboratory testing is
One of two hydraulic membrane pumps installed for backfilling service at a mine in Peru
recommended to confirm which style of pump to select.”
Concluding, Kesler notes:“ centrifugal pumps are the most common pumps and generally have the lowest capital cost. However, when one considers efficiency, abrasive wear, pressure per stage, water usage, energy consumption, down time and other factors; positive displacement pumps, and more specifically, piston-diaphragm pumps, are the better choice.”
In May, GIW Industries, leader in the design, manufacture, and application of heavy-duty, centrifugal slurry pumps, announced its 125th year in operation. The evolution began from a small foundry and machine shop in Augusta, Georgia in 1891, under the name Georgia Iron Works. GIW began building slurry pumps in 1914, closely examining clients’ most demanding applications and finding solutions became a successful way of operating. This hands-on approach has taken employees around the globe to wherever companies demand systems that expand the limits of moving slurry.
Although the GIW ® Minerals High-Volume Froth( HVF) Pump has been on the market for six years, the company has announced new updates that make this innovative pump even more beneficial to mining. Its revolutionary design helps remove excess air from the slurry process. This is remarkably valuable, as traditional pumps often struggle with air bubbles that can cause pumps— and operations— to come to a grinding halt.
Air injected into slurries creates bubbles.“ The small particles( of valuable mineral) adhere to the bubbles, allowing them to be extracted,” explains Richard Inglett, GIW Industries Product Manager. The problem in these applications, according to Inglett, is that a regular pump is meant to pump fluids, not air.
110 International Mining | SEPTEMBER 2016