A large power generation plant on a coastal bay site in the United States needed to convert its cooling tower water system to a closed-loop design. The newly retrofitted closed-loop system is more efficient and reduces the thermal impact on the bay.
The problem
The owner of the plant invested several hundred million dollars in retrofit equipment to minimise the amount of cooling water drawn from the bay. The plant’s process and consulting engineers designed a closed-loop system which retrofits the piping already in place.
In the new design, the engineering team identified the need for liquid flowmeter placement at multiple locations to measure the flow of water as it passed through the system. Accurate liquid flow measurement is necessary not only for operational purposes to support the cooling towers but also to determine the system influence on the bay’s marine life.
The design team needed to find a flow measurement technology that provides accurate and dependable measurement in medium to large line sizes, which also could be installed easily within the existing piping layout. In addition, the flowmeter needed to be constructed of rugged materials resistant to seawater, which is highly corrosive over time.
The solution
After looking at various flow measurement technologies, the design team contacted the local McCrometer sales representative who collaborated with the applications group at McCrometer in California. The company specialises in flow measurement, and recommended the FPI magnetic flowmeter for its reliable performance, ability to support large line sizes and the ease of its hot tap installation.
The meters are suitable for service in small to large-scale liquid measurement applications such as cooling tower water systems at electric power generation plants. Thanks to the hot tap design, they are economical to use as installation costs can be reduced by up to 45%.
Whereas the total installed cost of conventional full bore meters goes up with increases in pipe diameter because of greater material costs and more complex installation, the FPI eliminates the need for heavy equipment or extensive manpower. Installation can occur without interrupting service, dewatering lines, cutting pipe, or welding flanges. The FPI combines the ease of hot tap installation with an accurate measurement across the full flow profile. It delivers accuracy that rivals the performance of full bore magnetic flowmeters at an economical price.
The power plant’s technicians installed several flowmeters on its newly retrofitted closed-loop system. The FPI is equally cost-effective for new or retrofit applications because of its compact insertion design that fits easily into limited access confined spaces. It can also be removed from pipes under pressure for easy inspection, cleaning or calibration verification without an expensive shutdown and re-start sequence, helping cut plant ownership costs.
The meters operate under the principle of Faraday’s Law to measure water velocity. The principle of operation states that a conductor such as water moving through a magnetic field produces a voltage which is directly proportional to the velocity of the water flowing through it.
The unique sensor features multiple electrodes across the entire pipe diameter. Electromagnetic coils installed inside of the sensor produce magnetic fields. Stainless steel electrode pairs installed on the outside of the sensor collect the induced voltage caused by the flowing water. The total of each voltage signal is transmitted to the converter electronics, where it is converted to an average flow velocity. The converter then multiplies the average flow velocity by the pipe’s cross-sectional area to create a volumetric flow rate.
Multi-electrode sensing provides accurate measurement without long upstream and downstream straight pipe runs. The FPI provides a large rangeability and the multi-electrode sensor design compensates for variable flow profiles, including swirl, turbulence, and low-flow conditions. The unique sensor configuration continually measures and reports the average flow rate over the full diameter of pipe for greater accuracy and repeatability.
Conclusion
Choosing the flowmeter best suited for an application will result in improved accuracy, repeatability, lowered maintenance costs and will promote a long-life for the flowmeter. Its superior value in terms of the cost of installation and the cost of ownership made the FPI an excellent flow measurement choice for this electric power generation plant. After installing the meters in the retrofitted closed-loop cooling water system, the results have been positive.
For more information contact Stuart Brown, UIC Instrumentation, +27 (0)31 468 2561, [email protected], www.uic.co.za
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