Control valves make a significant contribution to pressure drop.
Control valves location can create a need for additional pumps and compressors, and must be decided in order to size to the pumps and compressors.
IT is therefore necessary for the design engineers to understand the plant control philosophy even at the PFD stage and the PFD usually shows the location of control valves.
Objectives of process control operation
- Ensure stable process operation- 1. Particularly, keep the plant operating under safe conditions 2. Minimize damage to equipment due to variation in plant conditions
- Ensure operation meets product specification-1. Minimize impact of external disturbances- Example: Change in ambient temperature
- Optimize Process performance- 1. Minimize Process throughput 2. Minimize operating costs.
The final control element is usually a control valve
Exceptions: electric heaters, mixers and variable speed drives
The actuator is either a motor or a bellows that opens or closes the valves response to the signal.