It should come as no surprise that operating your pump at the best efficiency point (BEP) results in optimal operation. But what does operation off BEP really mean in terms of reliability, efficiency, and cost? The short answer is that a pump that is not optimized to its system is less reliable, less efficient, and more costly. For this reason, pump optimization can offer real improvements in essential areas, like performance and safety, while having a very short payback period.
Unfortunately, many industrial pumps are operating away from their best efficiency point. End users find themselves in this situation for multiple reasons, such as conservatism in initial design or changes to required system output. Modifying equipment to better suit system needs has become more common as end users seek ways to reduce in ongoing equipment costs and remain competitive in their respective markets. The resulting energy savings and energy efficiency also support decarbonization goals.
Pumps are an essential component of systems across all industries that handle fluids. Pump systems are energy intensive, making them a key area of opportunity for energy reduction. This is especially true for high energy equipment that is continuously running. Major areas where energy savings can be achieved include:
- Providing more efficient equipment
- Optimizing new and existing equipment to its system, and
- Maintaining that efficiency beyond initial installation.
Many end users and suppliers emphasize efficiency when purchasing new equipment. This is an important factor when designing new units or systems; however, most equipment in our plants is already in service and not scheduled for replacement in the short term. Understanding actions that improve efficiency and reduce energy usage of existing installations can save millions of dollars a year and has the collateral benefit of achieving safer, more reliable operation.
System Optimization
While some efficiency gains can be made in the pump design itself, a large portion of the energy savings available is in optimizing the equipment for its system. In cases where pumps are oversized, a downstream valve needs to be throttled to increase system resistance and force the pump to operate back on its curve at the desired flow rate. The friction added to the system by the throttled valve wastes horsepower across the valve and reduces valve life. This wasted horsepower is energy that could be saved.
Operating away from the best efficiency point impacts more than just energy. Empirical data collected on pump reliability, as illustrated in the Weibull curve, shows that reliability decreases significantly as pump operation moves away from BEP. Operation at less than 80% of BEP or more than 110% of BEP is almost two times more likely to fail; operation at less than 70% of BEP or more than 115% of BEP is ten times more likely to fail.
Fortunately, optimizing the pump to its system is an achievable goal. Many end users will default to pump replacement when they find themselves in this situation. However, this does not always guarantee greater reliability and rarely provides the best value for the investment in time and capital.
Advancements in technology allow us to make hydraulic modifications more efficiently and effectively. With advancements in laser scanning, we can capture the geometry of critical components and develop 3D models that can be used to apply and test modifications. With advanced modeling, such as computational fluid dynamics (CFD), we can accurately predict the outcome of proposed modifications and develop new hydraulic designs. And with advancements in parts manufacturing, such as 3D-printed patterns and 5-axis machining, we can supply newly designed parts with shorter lead times and higher quality.
Making the choice to redesign instead of buying new has many benefits:
- No System Changes Required: New equipment requires altering the footprint of the installation, including costly and time-intensive changes to the baseplate and piping
- Shorter Lead Times: Because fewer components need to be manufactured and no system changes are required, the project can be completed in a much shorter schedule
- Better System Match: Most new pumps are chosen as a “best fit” from existing pump lines. Developing custom hydraulics for the specific application at hand can produce a better fit with more efficient operation
- Reduced Carbon Footprint: Extending the useful life of existing equipment helps reduces material waste and greenhouse gas emissions related to manufacturing and shipment of new equipment.
- Reduced Risk: Unless the pump is a bad actor, its many years of operation have already proven that it is well-suited for the service. Any design weaknesses can be identified and resolved by looking at historical data and applying new technologies. New equipment introduces many unknowns that will only be revealed after installation and start-up.
Case Study in Application Optimization
Five 50-year-old, 4-stage descaling pumps were consuming too much power and not producing enough output for a major steel manufacturer. The pumps had been repaired many times, but the actual hydraulic performance had never been analyzed.
One of the pumps was sent to Hydro’s Performance Test Lab for baseline performance testing. The test showed that the pump was underperforming and could not meet the 1850psi required pressure at the 2000gpm rated flow. It was determined that repeated refurbishments over the pump’s 50-year life had resulted in changes to critical hydraulic dimensions, affecting equipment performance.
The information from performance testing was paired with analysis using computational fluid dynamics (CFD). A new hydraulic design was developed that would increase the performance of the pumps. This design would require reconfiguring the casings, designing new impellers, and rebuilding the pump shaft.
A comparison of the original and proposed performance curves indicated that the improved performance would provide significant energy savings. These savings could justify the cost of the project for the mill. By performing this upgrade, they would be able to operate three pumps in parallel instead of four, saving them 16.9% (over $800k USD) on the current energy costs year-after-year.
All five pumps have now been re-engineered by Hydro and are exceeding the customer’s expectations. This redesign has saved the mill millions of dollars in new equipment replacement costs and continues to provide savings from reduced energy requirements.
Pump on Test Stand
Maintaining Efficiency
Optimizing the pump to its system is an excellent starting point, but this efficiency must be maintained upon installation. One of the biggest factors in diminishing efficiency is increased internal recirculation. As internal recirculation increases, the total fluid discharged to the system decreases. The equipment then needs to produce more flow to make up for the fluid lost to internal recirculation and deliver the required total output.
Internal recirculation is controlled by close clearance areas, such as wear rings or bushings. Maintaining the design clearance of these components is essential. The greatest influences on premature wear are lax tolerances, poor assembly practices, and material choices.
Stringent tolerances are critical to ensure that rotating and stationary components share a common centerline. Any offset between components increases the risk of contact and accelerated wear. To ensure centerline compatibility, circularity and concentricity of critical bores and perpendicularity of critical faces is essential. Rotor TIR must be limited and adjoining shafts must be in parallel and angular alignment. Fit-ups cannot be excessive to limit any offset of the component inside its fit. Multistage elements should be assembled vertically; if this is not possible, measures must be taken to avoid a stack-up of fit tolerances.
Many of the factors that affect accelerated wear are not a function of pump design. Attention to detail, strict acceptance criteria, and experienced personnel are all part of the blocking and tackling that must be done to maintain efficiency. This requires choosing a qualified partner for equipment refurbishment and training internal maintenance crews to best-in-class standards. Understanding that a low first cost is dwarfed by the high unavailability, maintenance, and energy costs associated with the “cheap fix” is a critical first step for increased plant profitability.
Case Study in Extending Efficiency & Life
When a steel mill in Pennsylvania experienced repeated failures of its descaling pumps, Hydro was brought in to determine the root cause of the failure and provide engineered upgrades to extend the mean time between repair (MTBR).
The decision to seriously address the continued failures was cemented when a recently repaired 10-stage descaling pump failed upon start-up. This latest of five back-to-back failures caused the mill to struggle with making production, placing it on the verge of shutting down.
Despite the urgent nature of the repair, the mill was determined not to cut corners and risk suffering another pump failure. They recognized that the repeated “repairing-in-kind,” where the pump was returned to the original condition without addressing the root cause of the failures, was the reason that they were struggling with low reliability and high risk to production. They engaged Hydro to correct the design defects and build a more reliable piece of equipment.
A forensic analysis was completed which identified several material and assembly issues that were affecting pump life. Applying state-of-the-art technology, Hydro was able to not only increase reliability, but also realize energy savings over the life of the pump.
During the inspection of the first failed pump, it was discovered that one of the impeller rings had broken loose and passed through the pump. The failed wear ring caused significant internal damage. Analysis of the ring led Hydro to conclude that the wear ring was improperly heat treated. The material was being through-hardened to achieve the specified surface hardness; this process often results in a brittle material that can fail under stress.
To provide the necessary hardness without compromising the ductility of the material, a 410 martensitic steel with a laser-deposited weld overlay was provided as an upgraded material. This process provides the same surface hardness as through-hardening without the brittleness and susceptibility to stress cracking. In parallel with this, tolerances and fit-ups were tightened to best-in-class standards, ensuring better centerline compatibility of all components and reducing the risk of contact and wear. These actions together ensured that the internal clearances would remain at design for a much longer period of time, maintaining design efficiency and rotor stiffness and damping.
This upgrade resulted in an extension in the mean-time-between-repairs (MTBR) from two years to more than five years.
Cracked Impeller Ring
Laser Deposit Welding of Impeller Hub
Conclusion
Reducing parasitic energy losses and increasing energy efficiency in your pumping systems does more than just help you reduce your energy usage and carbon footprint. It also provides you with a competitive edge by reducing operating costs, eliminating downtime events, and increasing mean-time-between-repair for pumps, motors, and valves.
By identifying opportunities for improvement through field testing and engineering analysis, developing modifications that optimize pumps to their systems, and building our equipment in a way that ensures efficiency is maintained, we ensure operation that is both sustainable and reliable.
