GWR level instruments are very practical for boilers, deaerators, feedwater heaters, LP/IP/HP heaters and other steam drums. Matt Brummer of Emerson backs up this observation with an analysis in Processing. They are particularly well suited to mounting in bridles, similar in orientation to existing sight glass installations. They are immune to changes in liquid density and temperature. Even in situations in which the DK of vapors is variable, the ability of GWR instruments to self compensate extends accuracy and reliability. In more general level measuring applications, having a probe to guide the microwave signal helps overcome some problems associated with non-contact radar and ultrasonic technologies such as ghost readings from mixer blades, heavy vapors, condensation, ladders and other internal obstructions. The ability for the signal to follow the guide provides a positive reading even in a variety of difficult applications. GWR level instruments are an excellent choice for many difficult applications, particularly those in which it is important to have precise level measurement in a challenging environment. One example A 900-MW CCGT plant in the southeastern U.S. was struggling with a level-controlling problem. It was using DP level instruments in a two-out-of-three (2oo3) voting scheme to keep its three boilers on an even keel. Under normal conditions it operates at 2,300 psi and 650ºF at the drums. During peak demand, production value is more than $1,000 per MW, so any unplanned shutdown costs hundreds of thousands of dollars per hour. Since the area was prone to occasional freezes during the winter, the DP instruments were protected in an enclosure with the impulse lines heat traced. Even with these precautions, the heat tracing was not fully effective, and the plant experienced multiple trips each winter. Getting the plant stabilized after a trip normally involved operator overtime to get things thawed and back in operation. These losses provided additional motivation to find an alternative. The plant changed all three boilers to instruments equipped with dynamic vapor compensation capabilities. The instruments were mounted in external bypass chambers, and the plant’s control system retained the 2oo3 voting scheme. The new configuration met all the ASME B31.1/BPV1 code requirements. After the installation, the plant survived the winter with no outages, or even near misses, related to boiler drum level measurement, allowing the instruments to pay for themselves after just one winter, according to the site engineering manager.

• Emerson Electric

• Gas Turbine

• Level Sensor

• Article