Energy savings and efficiency are a growing concern for most industrial companies, not only fitting into decarbonization strategies, but also significantly increasing plant profitability.
In any industry that handles fluids, pumps are essential. Pump systems account for 40% of industrial fluid system energy usage and are a key area where gains can be made by:
- Providing more efficient equipment
- Ensuring system optimization
- Maintaining efficiency beyond initial installation
Many users focus on procuring high efficiency equipment. This is an important factor when designing new systems; however, most plant equipment is already in service with remaining useful life. For older facilities, pumps were likely purchased under outdated standards with little attention paid to energy usage. Understanding how to 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
A large portion of available energy savings is not in pump design but in pump operation. Few systems are optimized for operation at the best efficiency point (BEP), where both efficiency and reliability are highest.
Most systems have "too much pump" putting more flow into the system than required. For desired flow, a downstream valve is throttled to increase system resistance and force the pump back on its curve to a lower flow rate. Throttling the valve wastes horsepower and reduces valve life - energy that could be saved. A pump can be optimized by using affinity laws, which predict performance changes based on changes to speed or impeller diameter.
For systems with a single operating point, a change in diameter is usually chosen because it requires less investment. Diameter changes are not as straightforward as speed changes, so partnering with an experienced company that supports modifications with computational fluid dynamics is important. Lab testing is recommended to verify performance and produce a new certified curve.
For systems with multiple operating points, a variable frequency drive (VFD) facilitates operation at BEP for any flow. Beyond higher cost and space limitations, upgrading to a VFD risks excitation of a natural frequency as operation at multiple speeds increases the number of acting forcing frequencies. An engineering study is recommended when upgrading to a VFD.
As an example of optimization, boiler feed pumps at a petrochemical plant were optimized by Hydro through an underfile modification. The plant was designed with two 100% pumps installed in parallel, but increased system output dictated that both pumps operate to meet the new demand. This change led to operation at a flow much lower than BEP, resulting in fluid recirculation and repeated failures. The impeller modification improved reliability, saved energy, and allowed the unit to operate a single pump with an installed spare. By operating one pump at a higher efficiency, an estimated $95,000 is saved annually.
Maintaining efficiency
The importance of maintaining efficiency upon equipment installation is often overlooked. Efficiency reduces during operation as internal recirculation increases. Maintaining design clearances is essential to limit this recirculation. The greatest influence on clearance degradation is excessive tolerances.
Stringent tolerances are critical because rotating and stationary components that are not on a common centerline will wear at an accelerated rate. Concentricity of bores and registers, face perpendicularity to these bores, rotor TIR, and shaft alignment must all be kept in tight control.
Attention to detail, strict acceptance criteria, and experienced personnel are all part of the blocking and tackling needed to maintain efficiency. This requires choosing a qualified partner for refurbishment and training internal maintenance crews to best-in-class standards. Understanding that a low first cost is dwarfed by high unavailability, maintenance, and energy costs associated with the "cheap fix" is critical for increased plant profitability.
For more information, visit hydroinc.com or call (832) 720-8691.