Steam Drum Level Measurement Compensation through the use of Constant Head Chamber with Dynamic Compensation
Abstract
The level measurement for high pressure steam drum, using differential pressure (D/P) transmitters, has been challenging and sometimes problematic because condensate/steam densities vary significantly with the pressure and the temperature. One additional source of measurement error is the difference in temperature between the differential pressure transmitter’s reference legs. These factors could cause the level measurement to be off as much as 30% from the actual value for high pressure steam boilers, enough to exceed the tolerance established in the Safety Requirement Specification (SRS) for a Low-Low Steam Drum Level Safety Instrumented Function (SIF). The further the deviation from normal operating conditions, the greater the level measurement error. Because of this, the Low-Low Steam Drum Level SIF is not operative during the start-up, which is the riskiest operation mode. This paper presents the use of temperature - equalizing columns (Constant Head Chambers) to minimize the temperature difference between the transmitter reference legs, and drum level compensated measurements through the use of dynamic selection of D/P range vs % Level depending on the steam drum operating pressure or dynamic calculation of saturated liquid/steam properties in SIS Logic Solver. This paper also addresses the challenges of implementing this method to meet measurement accuracy and safety integrity level requirements.
Description
PresentationSubject
Steam Drum Level MeasurementCollections
Citation
Zhong, Lianwei; Wei, Cindy; Johnston, Henry (2018). Steam Drum Level Measurement Compensation through the use of Constant Head Chamber with Dynamic Compensation. Mary Kay O'Connor Process Safety Center; Texas &M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /193503.