Changing Process Requirements

Adaptive Control Process control problems inevitably require on-hne tuning of the controller constants to achieve a satisfactory degree of control. If the process operating conditions or the environment changes significantly, the controller may have to be retuned. If these changes occur quite frequently, then adaptive control techniques should be considered. An adaptive control system is one in which the controller parameters are adjusted automatically to compensate for changing process conditions. 

Change process to adjust specific gravity to design value, or throttle pump to reduce horsepower requirements. This will not correct problem with some vertical turbine pumps that have a flat horsepower-required curve. 

The final design should meet process requirements (within reasonable expectations of error) at lowest cost. The lowest cost should include operation and maintenance costs and credit for ability to meet long-term process changes, as well as installed (capital) cost. Ex(mangers should not be selected entirely on a lowest-first-cost basis, which frequently results in future penalties. 

For moderate general process requirements at gauge pressures less than 2058 kPa (300 Ibf in ) and less than 177°C (350°F), tube-sheet holes without grooves are standard. For all other sei vices with expanded tubes at least two grooves in each tube hole are common. The number of grooves is sometimes changed to one or three in proportion to tube-sheet thickness. 

The issue that must be managed is the appropriate threshold to communicate the change and initiate appropriate approval processes. Tolls subject to regulatory requirements may use the regulatory guidance as the threshold for management of change processes other tolls must establish the threshold appropriate to process risks, quality systems, and business concerns. 

The uncontrolled type, in which there are small intermediate pressure process requirements with little change in demand. 

The performance curve can also be shifted to match the process requirements by variable inlet guide vanes. Located at the compressor inlet, these vanes change the direction of the velocity entering the first-stage impeller. By changing the angle at which these vanes direct the flow at the impeller, the shape of the head capacity curve can be changed. 

FCC is one of the cheapest conversion processes. Its inherent flexibility can assist a refiner in meeting changing product requirements in spite of the steady decline in feedstock quality. 

The condition of any soil represents a stage in the changing process of soil evolution. Soils develop, mature and change with the passage of time. Whereas the time required for a true soil to develop from the parent rock of the earth may be thousands of years, rapid changes can result in a few years when soils are cultivated, irrigated, or otherwise subjected to man s manipulation. The type of soil that develops from the parent material will depend upon the various physical, chemical and biological factors of the environment. 

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