Vulnerabilities in Boiler and Steam Drum Level Control Technology

Technologies historically used for boiler and steam drum level control rely on inference or buoyancy to determine the level. This in itself leaves them vulnerable to process dynamics (specific gravity, pressure, temperature, etc.) or limits their ability to precisely manage the level for improved fuel economy. Although corrections can be applied to mitigate the effects, the variables that need to be accounted for increase the level control’s installation, hardware and calibration complexity, which has the unintended consequence of introducing new avenues for error.

The hardware and calibration complexity and vulnerability to process conditions introduce additional costs and potential errors in any given level measurement technology.

The hardware and calibration complexity and vulnerability to process conditions introduce additional costs and potential errors in any given level measurement technology.

Magnetrol® has produced the “Steam Generation Cycle and Condensate Recovery Process Optimization Kit” to help improve boiler and steam drum level control and increase efficiency throughout the steam generation cycle. The kit includes a white paper that identifies key areas where cost-effective instrumentation solutions can improve control. Here is an excerpt from the white paper on the vulnerabilities of various technologies for boiler and steam drum level control:

Eliminating potential sources of error (including human error) as related to an instrument’s fundamental technology is the first step in optimizing boiler/steam drum level control. A quick peek at various technologies reveals their shortfalls as related to boiler/steam drum level control:

  • Differential Pressure – a complex system of tubing, condensate pot and transmitter(s) based on inference requiring up to 12 process parameters to properly calibrate. External inputs and corrections are applied to ensure accuracy.
  • Buoyancy (displacer) – accuracy from startup to operational temperatures is not achievable due to displacer being designed for the specific gravity at operational conditions. Calibration and mechanical wear may introduce errors over time.
  • Buoyancy (mechanical switch for on/off control) – a low-cost solution for smaller boilers; however, introduction of larger volumes of sub-cooled liquid could affect performance and increase fuel consumption as compared to a continuous type measurement.
  • RF Capacitance – based on the dielectric constant of the process medium. The dielectric constant of water/condensate changes as a function of temperature, introducing unnecessary errors. Requires in-situ calibration.
  • Conductivity – high upfront and probe maintenance costs as compared to other technologies. Not a continuous measurement. Resolution is contingent on the proximity of adjacent conductivity probes across the measurement span; vulnerable to scale accumulation and fouling.

Guided Wave Radar (GWR), on the other hand, is a continuous measurement technology that has the distinct advantage of not being vulnerable to changes in process conditions that affect the aforementioned measurement techniques. Since its performance and accuracy are not contingent on the specific gravity and/or inference, it excels in measuring the actual liquid level in all conditions encountered in the boiler/steam drum. Furthermore, GWR does not require external inputs or calibration to achieve specified performance — accuracy is inherent to the technology. This effectively eliminates the introduction of errors during the calibration process or from external sources, i.e., pressure and temperature. A reduction in the number of variables affecting the measurement provides a high degree of data certainty allowing operators to better maintain the Normal Water Level (NWL) in the boiler/steam drum for optimal water/steam separation throughout a variety of process conditions.

GWR provides the reliable measurement that is needed for improved boiler and steam drum level control. With better level control, an operation can reduce heat rate, environmental impact, fuel and water consumption, water treatment and maintenance costs in commercial and heavy industries where steam generation is essential to the production processes. To learn more, visit steamgen.magnetrol.com.

steam generation

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