Process control systems for energy efficiency

Although process control systems only use a small percentage of the total amount of energy consumed in a typical industrial unit, they directly affect how efficiently all the plant and machinery on the site works. So making sure your process control system is well tuned and working correctly is very cost-effective and can lead to substantial energy savings.

The performance of a control system declines over time as the system becomes de-tuned. Tuning it regularly means that it continues to work as well and efficiently as possible. Tuning - or 'optimising' - a process control loop involves adjusting the controller so that it responds more quickly to changes in the process. Tuning requires no capital investment and it is easy to measure the cost-savings from doing so quickly.

Automatic control

One of the signs that a control system has become de-tuned is when operators frequently override automatic controls and switch to manual operation, which is much less efficient. You should check at key times - such as shift changes - that operators haven't set systems to manual operation unnecessarily.

Staff training

Making sure your staff are trained to recognise and deal with tuning problems in control systems themselves can reduce the number of calls for maintenance and get processes back to normal quickly.

Monitoring

You should monitor your production processes regularly to help you identify where systems have become inefficient. You should look out for signs that your controls need tuning. These include:

• Excessive or variable energy use. Check that the specific energy consumption per unit of product is consistent. If you measure the energy used per unit of product at different times, but when throughput is the same, this will help determine whether energy use is consistent.
• Over-purification or over-specification of the product. This can occur when the system is using incorrect settings so that it over-reacts to small changes.
• Control disturbances. These can happen if your system isn't set up to compensate automatically for external changes - such as a drop in pressure - before it sets off plant alarms or safety trips.
• Time delays and dead time. Fine tuning the controller can help to avoid dead time caused by the slow response of the system to changes.

As well as highlighting where systems need attention, monitoring also helps you to establish where you could put in place energy-saving measures in the future.