Fundamentals of Distillation Column Control
The appropriate pressure profile within a distillation column is determined by process needs. Failure to maintain proper pressure at all points can result in energy waste, inefficient operation, product loss and quality issues, and, in certain situations, even safety risks. That is why pressure measurement is one of the most crucial elements for distillation process control — and why a column normally has many, and sometimes redundant, sensors to detect pressure in different zones.
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The pressure instruments must operate safely and reliably in order to maintain the desired pressure profile. This necessitates careful selection, calibration, and upkeep. So, in this post, we'll look at the problems that can arise while measuring pressure in distillation columns, as well as possibilities, selection criteria, and safety.
The output of a pressure sensor in a column is generally sent by an impulse line or a remote diaphragm seal with capillary tube to a ground-level pressure transmitter. To reach the transmitter, this impulse line or capillary tube may travel a great distance, such as from the top of a 100-foot tower to ground level. The transmitter is normally housed in an enclosure to protect it from the elements. However, because the capillary tube is frequently exposed to the environment, it experiences temperature fluctuations.
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The density of the fill fluid in an impulse tube or capillary is affected by changes in ambient temperature from day to night and from season to season. Because pressure transmitters are designed to assume the density of the fill fluid in a remote capillary leg is constant, these changes have a negative impact on the dependability of the pressure measurement.
Contents in Fundamentals of Distillation Column Control
Levels of control
Classification and pairing of variables
Control objectives and constraints
Dynamic responses
Material and energy balances
Separation
Pressure control
Material balance control
Temperature control
References
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