Think about everything that you find on a drilling rig, snubbing basket, coiled-tubing unit, or wireline truck. You’ll quickly realize how much we depend on instrumentation and control just to get oil and gas to the wellhead. Once it arrives, there are gathering lines, pipelines, refineries, and processing facilities that play a part in getting products to end-users. Process control is the key to getting it all done.
Process control in the Oil & Gas, Refining, and Petrochemical industries is hardly ever just a matter of efficiency and profitability. There is almost always a safety-sensitive element to the work that we perform.
Do you ever stop to think about how crucial process instrumentation is to our ability to see what is going on and intervene when needed?
Sometimes it can seem overwhelming just to keep up with all of the elements of our own job responsibilities. But it’s always a good idea to make time to familiarize ourselves with the big picture because we should know our facilities. And we should want to learn how what we do compares to other approaches in our own industry and others. An overview of the basics of process control operations helps us develop a better understanding of our own roles and a greater appreciation for the roles of others.
Process Control – The Basics
In large facilities, automation is the key to effective process control systems. We rely on instrumentation to monitor and manage variables like pressure, temperature, flow rates, and much more. To get the results that we want, we need the right valves and instrumentation components for our processes.
There are two basic functions that process instrumentation performs for us in our facilities. First, instrumentation must be able to measure and indicate accurate readings of the variables that they are monitoring. Second, process instrumentation must be capable of comparing those readings to predetermined standards. It must be capable of executing changes in the process to manipulate variables whenever they stray from set targets.
Our process control systems have to function effectively. So, both valves and instruments have to be appropriate for the tasks we ask them to perform and the specifications of the broader system they’re a part of. If we have the wrong valves or instruments, they won’t perform optimally. Similarly, if we use the right valves and instruments in the wrong applications the results will be sub-optimal.
Give the basics the respect that they deserve and your automated process control system will perform optimally. When your basics are anything less than ideal, that means that you are building on a foundation of sand.
5 Common Automatic Control Systems
Every process control loop is a custom-designed system. It has to meet the needs of the process, the facility, and many other considerations. In large and complex facilities, each of these process control systems might be used at different points. Knowing how to recognize each system and what each is best at helps you get a clear view of the big picture.
On/Off Control System
An on-off control system simply drives the manipulated variable from fully closed to fully open depending on the position of the controlled variable relative to the setpoint.
Gap Control System
A typical application of gap control is average level control. Gap control is somewhat like surge tank control, but the process variable is controlled around a set point.
PID Control System
The PID controller consists of proportional, integral, and derivative elements. It is widely used in feedback control in industrial processes.
Cascade Control System
A cascade control system is often used to reduce the effect of disturbances and upsets on the primary control objective. It consists of a primary and a secondary loop.
PLC Control System
A programmable logic controller is an industrial computer control system. It continuously monitors the state of input devices and makes decisions. These are based on a custom program to control the state of output devices.
PSA is a team of experts. Our ability to reverse-engineer and manufacture critical components assures a successful project.
At PSA, we’ve been helping our clients in the chemical, petrochemical refining, and gas distribution industries since 1974. We offer products and services that help you find, install, and maintain the valves and instrumentation that it takes to make your facility safe, efficient, and profitable.