| Abstract |
In geothermal steam applications such as steam separators, flash tanks, and condensers, accurate level measurements can be challenging because of dynamic process conditions. Process densities, which vary from what was initially specified, will result in measurement inaccuracies with traditional d/p (differential pressure) level instruments as well as mechanical level measurement technologies such as displacers. In steam separator and condenser applications, pressures and temperatures change and, as they do, the accuracy of the level measurement is impacted because of the changes to fluid properties as an example specific gravity/density, especially during startups, severe process transients, and operational upsets. Moving parts associated with mechanical technologies (displacers) and wet legs associated with d/p instruments can be maintenance intensive, for example, if wet legs plug or flash. Displacers, floats, and magnetic level indicators all have moving parts which can degrade over time or get “hung up” and require maintenance, re-calibration, and/or additional validation. Specifically, low level in condensers can cause condensate pump cavitation which leads to severe pump damage if left unchecked. In steam separators, high level can result in water carryover to the steam header exposing the steam turbine to potentially catastrophic damage, unplanned outages, and revenue losses. Accurate level measurement when optimized with level control on steam separators, flash tanks, condensers, and cooling tower basins assures maximum run time for the power producer. When selecting a level technology for an application several considerations are: 1) the process conditions and their variability 2) desired accuracy, and 3) the costs- of the instrument, its installation, and the maintenance costs over the life time of the device. Guided Wave Radar (GWR’s) measurement technology operates independently of process density and requires less calibration and compensation than a d/p instrument for that device to provide an accurate level measurement. The advanced design of high temperature-high pressure (HTHP) GWR probes makes them an excellent solution for steam applications. If steam pressures fluctuate significantly, the velocity of the GWR’s microwave energy may change and affect the accuracy of the radar measurement. Dynamic steam vapor compensation is available to address this issue and make GWR an excellent technology for geothermal level measurement applications. The use of radar for level measurement addresses many of the issues with other technologies - moving parts, wet legs, and required calibration- while operating independently of density. Still, depending on vapor space conditions, the speed at which the radar’s microwave energy propagates may change, which would affect the level measurement. While vapor space conditions are relatively constant, a vapor dielectric constant is configured in the radar to compensate for the slower speed of the microwave propagation. This is commonly referred to as static vapor dielectric compensation. Should the vapor space conditions change due to operating conditions and/or fluctuating demands and therefore pressures, the speed of microwave propagation changes dynamically. Static vapor dielectric compensation may not be sufficient for accurate level measurement. Innovative dynamic vapor space dielectric compensation continuously calculates the vapor dielectric and compensates for changing microwave speed thereby improving level measurement performance and accuracy. A large geothermal operator in California realized significant savings as a result of reduced maintenance costs and operational downtime for each GWR that replaced a d/p level instrument or mechanical level device. |