Process control systems for energy efficiency

The performance of your process control system may gradually decline over time because your operators override the system, or your equipment and plant develop faults. You may not be aware that the system is performing badly because maintenance schedules don't always include the right checks to identify problems. If your system is poorly-maintained, your processes won't be operating efficiently and your energy costs will be higher than necessary.

Indications that your system isn't performing well may include:

• operators setting controllers to manual when they should be on automatic mode
• inefficient operation
• too much variability
• frequent calls for repairs and maintenance

The maintenance approach itself may be the cause of many problems. If 'quick fix' breakdown maintenance is carried out in response to equipment failure, underlying problems may never be sorted out and can become permanent. A planned preventive maintenance strategy involves carrying out maintenance tasks regardless of whether a machine has broken down. This can also help you identify opportunities to enhance or upgrade your system.

Produce a maintenance manual and use a log book

If you have a good maintenance manual, you will be able to keep process control systems working well and make sure that you don't overlook routine maintenance tasks. You should include in the manual:

• details of all maintenance tasks, who is responsible for them, and how often they must be done
• schematic diagrams of all equipment and controls
• operating instructions including emergency shutdown procedures
• contact details for equipment manufacturers, and installation and maintenance technicians

You should always make sure the key parts of the system are working correctly. Carry out regular checks on:

• instruments - get faulty instruments repaired or recalibrated by qualified personnel
• measurement devices - correct problems caused by poor installation of sensors
• valves - check for 'sticky' valves which increase energy consumption

You should also keep detailed records of all your maintenance activity in a log book. This will help you when:

• dealing with problems that keep happening
• improving process control - for example by training operatives or replacing manual controls with automatic ones
• upgrading your equipment if it has reached the end of its useful life