For water and wastewater plant operators, opportunities to better manage the energy use of pump systems is an area of great interest. This equipment accounts for a large share of a facility’s total electricity consumption.
The following article describes how advancements in ultrasonic flow meter technology provide an enhanced solution for monitoring flow rate in water distribution systems, for pump efficiency checks and in sewage pumping stations, among other applications.
Demands on Plant Operators
In today’s uncertain economic environment, water and wastewater plants strive to be efficient, cost-effective and reliable. Every facility needs to maximize performance and availability. Environmental regulations have become more rigorous, operating costs have increased and technology has advanced.
Some of the specific demands on operations include:
- maximize pumping reliability
- minimize energy consumption
- optimize maintenance procedures
- reduce life cycle costs
- ensure environmental compliance
- achieve long-term sustainability
Critical Role of Pump Systems
Pump systems play a significant role in a wide range of water and wastewater operations. Ideally, they should always operate at the flow rate at the point of highest efficiency—but that is almost never the case. The average pump efficiency in industrial applications is estimated to be below 40 percent. By evaluating the actual operating point of pumps and correcting performance problems, plant operators can improve availability and reduce maintenance and repair costs.1
Pumps tend to consume large amounts of electricity, so it is important that they run at the required speed and not any faster. A study by the Electric Power Research Institute (EPRI) estimated that, on average, pumping accounted for 80 percent of total electricity use in public water systems. Additionally, raw water pumping to a treatment facility, along with treated water pumping to distribution systems, are large energy-consuming processes.2
Importance of Flow Measurement
Pumping, lift and well stations are integral parts of water and wastewater networks. Flow measurement at these sites is crucial, as the quantities fed to the treatment plant or delivered through the distribution system have to be monitored. As heavier rainfall becomes more widespread, sewage levels at pumping stations can rapidly reach critical levels and monitoring pump flow rates can help operators take appropriate measures.
All too often, water and wastewater plants lack the right tools to accurately measure flow. Many facilities are fitted with outdated flow meters, which no longer function properly due to age, condition and other factors. The effort and cost to remove these devices from the line can be prohibitive. In order to determine whether flow exceeds the capacity within any of their pumps, operators may rely on course flow data derived from calculating the rate of change in sump levels.
In a perfect world, flow measurements could be obtained on all pumps. This often proves impractical, yet vital for understanding overall pump efficiency. Most facilities have two primary flow measurement challenges: accuracy and cost. The goal is to correctly match the right flow meter to the right application to achieve the best performance for the lowest purchase price and total cost of ownership.
Flow meters installed downstream of pumping stations can provide valuable real-time data, which is processed to yield actionable information to operators and engineers.
For instance, comparing flows at various points in the system can show if a major leak has occurred. Data from flow meters can also be used to balance loads during pump operation, as it is often found that pump speed set points can be lowered while still maintaining sufficient flow—saving energy, reducing maintenance and increasing pump life.
Why Use Ultrasonic Meters?
Many plant operators now choose noninvasive ultrasonic flow measurement solutions. Ultrasonic meters can work whenever contact with the measured fluid is not possible. Designed for easy clamp-on installation, these instruments can be used for metering points on sewage networks and wastewater treatment plants, especially for retrofit situations. They are designed to have no moving or wetted parts, no pressure loss, offer a large turndown ratio and may provide maintenance-free operation.
Transit time ultrasonic flow meters are used in the vast majority of liquid flow application due to their ability to obtain accuracy. This technique measures the difference between the travel time of an ultrasound wave going with the fluid flow and against the fluid flow. The time difference is used to calculate the velocity of the fluid traveling in a closed-pipe system. The transducers employed in transit time measurements operate alternately as transmitters and receivers. Transit time measurements are bidirectional and are most effective for fluids that have low concentrations of suspended solids and are sonically conductive.
Transit-time ultrasonic flow meters also have diagnostic capabilities that other meter designs lack.
Clamp-on ultrasonic flow meters can be quickly installed without cutting or tapping the pipe. They reside outside the process line and can make it easier to perform routine monitoring of pump efficiency, which helps staff to identify maintenance concerns such as worn impellers or blockages.
Clamp-on ultrasonic flow meters can be an alternative to traditional mechanical meters, which may be subject to deteriorating accuracy caused by wear and tear.
The need for mechanical meters to be periodically tested, recalibrated and repaired means they have to be removed, requiring users to either replace the meter with a temporary device or cease abstraction until the meter is refitted back into the line.
Plant operators may choose to employ portable ultrasonic flow meters to verify the accuracy of existing metering technology, and thus extend the life of their equipment assets.
Latest Technology Advances
The newest generation of clamp-on ultrasonic flow meters can be used for a host of data logging tasks, providing the baseline and load profile information needed to optimize pump system efficiency, while also reducing energy consumption and costs.
The meters allow multiple parameters, including flow rate and total, signal strength and alarms, to be logged with a time/date stamp and sent to a programmable logic controller (PLC) or remote terminal unit (RTU). The data can be retrieved locally at a station site to assist with troubleshooting or maintenance.
Some ultrasonic flow meters offer helpful diagnostics that take the guesswork out of isolating process or application problems.
Users are alerted to out-of-specification flow conditions and can access a history with the most recent alarm, error and event codes.
In addition, ultrasonic meters can provide connectivity to process control systems via standard industry protocols like Modbus RTU, Modbus TCP/IP, BACnet MS/TP, BACnet/IP and EtherNet/IP. They can even support an encoder output for use with cellular endpoints for connecting to advanced metering analytics (AMA) cloud software.
With this solution, interval measurements are collected and uploaded to the cloud on a regular schedule to help in tracking and analyzing volumetric water usage.
In the water and wastewater industry, the flow meter best suited for pump-related applications will result in improved equipment performance and reliability, reduced energy consumption and lower operating costs.
Superior value in terms of ease of installation and low cost of ownership make clamp-on ultrasonic flow meters a solid choice for many water and wastewater treatment facilities.
1. Kernan, D. Pumps 101: Operation, Maintenance and Monitoring Basics. Retrieved from https://www.gouldspumps.com/ittgp/medialibrary/goulds/website/Literature...?
2. Carns, K. (2005, November), EPRI Solutions, “Bringing Energy Efficiency to the Water & Wastewater Industry: How Do We Get There?” Paper presented at WEFTEC 2005,