TABLE OF CONTENTS Target product quality and production levels can be maintained by continuously evaluating the performance of the process and the control system. The maximum throughput and operating efficiency of a plant are ultimately determined by the process design and equipment selection. However, in many cases a plant's operation is far from achieving the ultimate capability inherent in the plant design and equipment. For example, numerous studies done in the pulp and paper industry show that loop utilization ranged from 55% to 76%, depending on production area.
The reasons for process variation and poor control utilization can be attributed to one or more of the following:
Field measurement or final control element: analyzer and process measurement failures, noise, and repeatability errors; incorrect ranges and scan times; improper sensor and valve locations; damper or valve stick-slip; nonlinear installed damper and valve characteristics; and incorrect valve sizes
Process or control design: insufficient capacity, process changes, undersized units, and lack of lab feedback
Process interaction and mechanical problems
Process, lab, and raw material problems (more so for chemical than pulp and paper)
One of the main reasons such conditions exist is that the downsizing of support services in many plants has resulted in plants operating with a minimal staff for process control and instrumentation maintenance. Often there is only enough manpower available to fix the critical problems found today that are limiting production and affecting product quality. Under these circumstances, there is little time to study the process operation to...
