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Lecture Chemical process control - Chapter 21

a | Chapter 21 Process Monitoring 21.1 Traditional Monitoring Techniques 21.2 Quality Control Charts 21.3 Extensions of Statistical Process Control 21.4 Multivariate Statistical Techniques 21.5 Control Performance Monitoring 1 Introduction Chapter 21 Process monitoring also plays a key role in ensuring that the plant performance satisfies the operating objectives. The general objectives of process monitoring are 1. Routine Monitoring. Ensure that process variables are within specified limits. 2. Detection and Diagnosis. Detect abnormal process operation and diagnose the root cause. 3. Preventive Monitoring. Detect abnormal situations early enough so that corrective action can be taken before the process is seriously upset. 2 Chapter 21 Traditional Monitoring Techniques Limit Checking Process measurements should be checked to ensure that they are between specified limits a procedure referred to as limit checking. The most common types of measurement limits are 1. High and low limits 2. High limit for the absolute value of the rate of change 3. Low limit for the sample variance The limits are specified based on safety and environmental considerations operating objectives and equipment limitations. In practice there are physical limitations on how much a measurement can change between consecutive sampling instances.