Temperature is a fickle business

Infrared thermometry

The petrochemical industry, for example, relies heavily on accurate temperature measurement to achieve a delicate balance between productivity and plant reliability.

The New Zealand Refining Company operates a number of large furnaces in many stages of the production of petrol. Infrared radiation thermometry is one proven method for obtaining reliable temperature measurements of the furnaces and the process tubes within.

Infrared thermometry allows the temperature of an object to be measured at a distance, by collecting the infrared radiation emitted by the object and converting the measured signal to temperature.

The technology has been around for a long time and it is generally known industry-wide that the measurements are not particularly accurate.This is largely because infrared radiation is both emitted and reflected, but it is only the emitted radiation that depends on temperature. The additional reflected radiation causes a higher temperature on the thermometer.

This is a common problem in many industries where non-contact radiation thermometry is used; for example, the plastics, ceramics and metal processing industries. The problem is not unique to high-temperature industries. It also affects the food industry, which is reliant on accurate temperature readings to determine the safe storage of perishable food products.

Mike Tosio, inspection engineer of the New Zealand Refining Company is only too aware of the consequences of unreliable temperature measurements.

“The furnaces we use have very high metal wall temperatures which can be critical for design life. Tubes within the furnace could cost in excess of $1m for one of our largest furnaces.

“If we are to accurately predict how long the plant will last for, it’s crucial to get as close as possible with our temperature readings. Getting it wrong can be both costly in regards to replacement, and hazardous to workers if, for example, the tubes were to fail. Additionally an unplanned shutdown is very costly in production losses.”

In order to obtain much more accurate results, the NZ Refining Company is now utilising the skills offered by the Measurement Standards Laboratory at Industrial Research.

Industrial Research’s Peter Saunders says their furnace radiation modelling relies on a sound understanding of physical processes and mathematical methods.

“It’s a benefit that industry is beginning to recognise as they understand that high quality measurement leads to better plant control, reduced risk and increased profitability.”

Mike Tosio says the service gives increased confidence that safe and efficient operating parameters are being maintained. It also means less time shutting down the plant to investigate what’s wrong because they’re able to know beforehand what the requirements are.

“Essentially, it allows us to operate more efficiently by being able to better predict plant and tube life.”