For most mineral processing applications, slurry pumps represent a key component. Too often, however, many plants will take a “fit and forget” approach to maintenance of these vital pieces of equipment—at least until a critical repair is needed. There can be severe cost penalties associated with this approach. Some of the most significant include reduced productivity, and higher than necessary energy and maintenance costs. A carefully planned and implemented optimization program can help alleviate these unnecessary costs.
Generally speaking, optimization leads to reductions in energy consumption, thereby resulting in lower operating costs. And while it is often the anticipated energy cost savings that are used to justify a slurry pump improvement project, the fact is, benefits often extend well beyond energy savings.
For example, shaft misalignment is responsible for up to 50% of all costs related to rotating machinery breakdowns. Accurately aligning shafts can prevent slurry pump breakdowns and reduce unplanned downtime that results in a loss of production.
The point at which the highest proportion of energy from the shaft of a pump is transferred to the fluid being pumped is the Best Efficiency Point (BEP) of that pump. At this point, internal forces in the pump are at a minimum. As the operating point of a pump moves away from the BEP, this energy transfer efficiency falls and axial and radial forces increase.
Although some energy loss is inevitable (for instance, friction at wetted surfaces, seal faces and within bearings) some of the energy that is not being transferred from the shaft to the fluid is wasted. Of this wasted energy, some is lost by internal recirculation within the pump and some as heat or vibration, or any combination of them. These are erosive forces, and so the relationship between reliability and energy efficiency is clear—as more energy is wasted, erosive forces increase in intensity, so reliability is reduced.
Energy Savings with Alignment Optimization in Pumps
A plant recently experienced high vibration levels on 12 pumps, resulting in excessive consumption of both energy and spare parts.
An SKF condition monitoring program with Microlog Analyzer showed that the high vibration levels were clearly due to misalignment. Using the SKF TKSA 40 system technicians corrected the misalignment to help improve the operation of the electric motors. Measuring energy consumption before and after alignment for the 12 pumps demonstrated an average of 8% energy savings (maximum of 20% in some cases) or approximately 180 MWh/year, along with reduced vibration levels and increased reliability.
In addition to higher maintenance costs, the costs of unreliability due to forced shut downs can be high. The costs of unplanned shutdowns vary, and in many cases are difficult to quantify.
The SKF Energy Monitoring Service—Pump Systems is designed to help pump operators track efficiency, as well as actual operating efficiency relative to BEP. Periodic measurements of pressure, flow and power for each pump being tracked provide the data needed for the analysis, which is conducted using SKF @ptitude software.
This is based on the company’s Operator Driven Reliability concept and provides plant operators with the information they need to establish the optimization opportunities available within their pump systems. In addition, it can be incorporated into any condition monitoring program. SKF recommends that condition monitoring programs be adapted to include this data because condition monitoring alone does not provide all of the information needed to assess the health of a pump: energy efficiency is a key component of the information needed.
Pump system optimization provides real opportunities for mine operators to improve reliability and to reduce costs. There are many tools and training courses available to help provide the knowledge needed to implement a program to realize these opportunities.
Where investment is needed to capture the benefit, the full array of cost savings should be estimated to provide a realistic return for that investment.
Given that energy costs are by far the largest component of the life cycle costs of owning a pump, plant operators owe it to themselves to assure the highest level of pump optimization attainable. By incorporating the right tools and services into their condition monitoring programs, plant operators can go a long way toward maximizing the energy efficiency of their pump operations.
MDX Technology Cuts Pump TCO by Millions
GIW Industries, a leader in the design, manufacture and application of heavy duty, centrifugal slurry pumps, announced that its installation of MDX pump technology at a major copper mine in Chile has resulted in a dramatic reduction of total cost of ownership (TCO) for those pump applications—amounting to millions of dollars in savings for the mining company.
Elias Aho, global sales and projects manager for GIW, said that a sulfide concentrator, owned by BHP Billiton, reports increased revenue of $8 million due to productivity increases, with an additional savings of $1 million in energy costs.
“TCO for slurry pumps includes not only the initial cost of the pump, but also factors such as wear life, annual cost of parts, labor, energy and downtime for maintenance,” said Aho. All of these factors are addressed by the advanced engineering, materials and technology provided by GIW MDX pumps.
The mine relies extensively on slurry pipelines to transport copper ore. But the hard rock slurry is brutal on pumps and equipment. Wear parts suffer under the constant abrasion of the ore, and most competitor pumps require frequent maintenance and replacements. The company had GIW installations for other applications and realized it was seeing greatly improved wear life with those pumps. The mine decided that replacing its lower-performing pumps with GIW MDX technology was the right move.
When the pump stops, the mill stops. And the cost of that downtime is dramatic at a large mining installation. For this mine, every hour of downtime represented $150,000. To replace a slurry pump, the mill has to be down for 10 hours. And with the previous pump, the mill engineers were performing pump replacement eight times per year.
But the application presented its own challenges: This mine operates the largest cyclone-feed pump in the world. However, working with GIW had advantages for the company. Because GIW operates its own foundry, it can produce parts cost- and time-effectively — even a pump as large as this one. The new GIW MDX pump, with an 84-inch impeller and weighing 100,000 lb, replaced the 150,000-lb competitor pump, providing a lighter, more durable pump that runs on significantly less energy.
The new MDX pump has already surpassed the mine’s goal of doubling the wear life of the pump. GIW engineers are now working on a program of continuous improvement, aiming to extend the pump’s wear life another 40% to 50%. By cutting its maintenance downtime in half, the mine has realized an $8 million increase in revenue. In addition, it has reduced its energy cost by an additional $1 million annually.
