A review of an alarm history has identified that the bad actors include level, pressure, and temperature alarms that are associated with a liquid-phase, continuous, stirred-tank reactor. The chemical reactions are exothermic, and the CSTR is used at different times to make two products, A or B.The

Question

A review of an alarm history has identified that the bad actors include level, pressure, and temperature alarms that are associated with a liquid-phase, continuous, stirred-tank reactor. The chemical reactions are exothermic, and the CSTR is used at different times to make two products, A or B. The low-level and low-pressure alarm violations occur mainly during shutdown operations, whereas high temperature alarms for the jacket cooling water occur primarily when product B is produced. Devise a strategy for reducing these bad actor alarms.

Accepted Answer

Because these nuisance alarms tend to occur for different known-process conditions, a state-based alarming strategy is warranted (Guideline :
State-based alarming can greatly improve alarm management by eliminating nuisance alarms. It involves automatic adjustment of alarm limits to accommodate different process conditions, such as startups, shutdowns, changes in feedstocks or production rates (Hollifield and Habibi, 2007)).
In particular, different alarm levels are required for the three reactor conditions. For example, the following alarm limits could be employed with variables expressed in %.

Condition	Level (high)	Level (low)	Pressure (high)	Cooling water temperature (high)
Product A	90%	10%	85%	75%
Product B	90%	10%	85%	85%
Shutdown/ empty	5%	0%	10%	30%

Production of B involves a more exothermic reaction and thus tends to result in a higher cooling water temperature. When the reactor is shut down and evacuated, the level alarm settings are reduced to very low values. In particular, if reactor is not completely evacuated, the alarm sounds if the liquid level exceeds 5%. The state-based alarm settings eliminate many of the nuisance alarms.

Question 10.2: A review of an alarm history has identified that the bad act...

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