June 19, 2016
Reducing energy and maintenance costs in process equipment is always a good idea, especially now when government agencies and utility companies are offering incentive programs aimed at cutting electricity consumption. However, for complex systems, zeroing in on where and how to achieve savings isn’t always easy. For these situations, a systematic program of monitoring performance over a period of time can provide the answers that operators need.
As was pointed out in a previous article (“Capping Energy Costs: Improving the efficiency of industrial pump systems”, IPP&T, June, 2014), the key to minimizing the cost of operating pumps lies in making a good match between each machine’s performance characteristics and the requirements of the system where it is installed. Having pumps operate at or near their ‘best efficiency point’ (BEP) not only improves overall energy efficiency, but also results in smoother running, lower maintenance costs, fewer outages and longer pump lifetimes. However, in complex systems, predicting system characteristics over a full range of operating conditions can be difficult. As well, plant modifications, changes to the operating profile or even the slow accumulation of solids and corrosion products inside pipes over time can have significant effect on system performance. In practical terms, it can be extremely valuable to evaluate pumps’ performance in the field in order to make well-informed decisions about system operations and the potential for changes that will save energy and operating costs.
In-situ monitoring …
Specialist contractors, such as KSB’s Service Division, offer comprehensive pump system assessment and analysis services. The starting point is to install a number of sensors on each pump set (pump and motor) that will be assessed. These sensors will measure performance parameters such as intake and outflow pressures, flow volumes, vibration levels, power consumption and rotation speed under various operating conditions. Depending on the complexity of the system and the objectives of the assessment, it may also be useful to measure pressure, flow rate and fluid temperature at other locations around the piping system.
An essential feature of in-situ testing techniques is the ability to collect measurements over time. This is called data logging. Pump system problems have an annoying habit of happening when an operator is not present, the so-called ‘ghost failures that’ occur in the late hours of the night. Data logging can monitor multiple channels of information for long periods of time to capture these events as they occur. Examining data logger records collected over extended periods can also reveal trends that point to a gradual deterioration of pump or motor conditions. And most important, data logging makes it possible monitor the pump system over a range of operating conditions and to evaluate the exact duty point and duty cycles of the system. By comparing this information with the manufacturer’s pump curves, an experienced technician can accurately determine the actual in-service operating points of pumps. This analysis, in conjunction with on-site inspections, can help determine the actual running efficiency (as compared to the potential “best efficiency point”) and identify performance-robbing effects such as pump wear, pipe restrictions and intake suction problems.
… and analysis
The collection of running data is only the first step; it is in the interpretation and analysis of the data where the true value of pump assessment studies lie. The combination of accurate, relevant system performance data and the knowledge of experienced technicians make it possible to diagnose problems and find solutions that can improve efficiency, reduce wear and decrease downtime. The quantitative data from in-situ measurements can also be used to build a business case for making system changes that will improve operating efficiency.
Once the results are in, the analysts can recommend changes to the pump system that will significantly reduce energy and maintenance costs. These could involve the replacement of seriously over- or under-sized pumps with units that are better matched to the actual operating conditions. Adding variable frequency drives (VFDs) can enable the running speed of pumps to be changed in response to variations in the required flow rate, in effect shifting the BEP so that it lies closer to the required duty point. In-situ measurements can also detect problems at the pump intakes that are causing cavitation or rough running. Addressing these problems might require redesign of piping systems and sump structures.
Savings and affordability
In-situ pump system assessments are clearly valuable to pump operators who are confronted with unexpected equipment failures or unreasonable maintenance costs. They are also very helpful as a tool to find approaches that will reduce energy costs. In this area, there are a number of incentive programs offered by government agencies and electricity companies that will contribute a significant portion of the cost of both assessment studies and system modifications.
by Gary Zeidler, National Service Manager, KSB Pumps Inc.