Paramount in industry is the maintenance of the on-stream reliability of equipment - a task that seems straightforward in principle but is not necessarily simple in practice. Ensuring such reliability often entails cooling certain portions of operating equipment so that equipment components are not damaged or degraded excessively. Stated differently, on certain components, higher equipment operating temperatures tend to accelerate equipment degradation and reduce equipment reliability. While some equipment may be cooled with air, many processes use cooling water to keep the equipment sufficiently cool so as to provide reliable long-term service.
In some applications, measuring the equipment temperature in strategic locations is a viable approach to detect when the equipment is being stressed. When the equipment requires more protection, both the equipment temperature and the flow of cooling water may be monitored. Detection of low cooling water flow can alert the operator to a problem sooner than the temperature measurement, so the operator can take appropriate action before the equipment temperature has time to rise. In many applications, normal cooling water flow may be much higher than the minimum cooling water flow requirement. Setting the flow alarm trip well above the minimum flow - but below the normal flow - can give the operator even more time to react to a potential problem.
There are a number of flowmeter technologies that commonly are applied to process cooling water service. They include differential pressure, magnetic, vane, variable area and vortex shedding flowmeters. These flowmeters typically offer sufficient accuracy to ensure that sufficient cooling water is maintained to protect equipment. Here is a closer look at each type.
Magnetic Flowmeters. Magnetic flowmeters use Faraday’s Law to measure the voltage generated when a conductor moves through a magnetic field. In magnetic flowmeters, a nonconductive liner isolates the conductor (cooling water) that flows through the magnetic field produced by the flowmeter. The voltage generated at the electrodes by cooling water flowing through the magnetic field is proportional to the cooling water flow rate. Magnetic flowmeters are widely used and offer the advantage of being obstruction-less, so they are not subject to plugging.
Variable area flowmeters have a moving float that is subject to plugging. In addition, variable area flowmeters with glass tubes are subject to damage due to breakage as well as internal coating that may adversely affect the ability to see the float. Nonetheless, variable area flowmeters are widely applied as economical flow indicators in many cooling water applications.
Utilizing flowmeters to measure and subsequently monitor cooling water flow can be paramount to maintaining the integrity and on-stream reliability of equipment by ensuring that certain components are not damaged or degraded excessively due to high temperature. There are many flowmeter technologies available to measure cooling water flow, the more common of which are described above. Flowmeter selection for a given application is dependent upon factors such as the desired accuracy, cooling water quality, desired features and cost. In making this selection, be sure to remember the importance of keeping equipment cool because the cost of equipment damage is often many times more expensive than the cooling water flowmeter.