Capacitance sensor solves foam level measurement problem

14 June 2016

William Grant & Sons Distillers are the producers of Glenfiddich single malt whisky which has been created, since 1866, at the Dufftown Distillery in Scotland.

The recipe today is the same today as it was 150 years ago, although the process itself has seen some improvement. Recently the company turned to Siemens to inject some modern technol¬ogy into the operation. 

The challenge facing the distillery was that prior to vapourisation in the wash stills, foam is produced. If the level of that foam gets too high, it results in an unwanted situation where boiling high levels of froth mix with the low wines from the first stages of distillation.

The foam can be controlled simply by turning off the burners until it dissipates. However, it is important to know precisely when to turn the burners off, and when it is appropri¬ate to turn them back on again. Because foam is neither liquid nor air, it has traditionally been impossible to detect with level measurement equipment such as floats or vibrating forks.

It was not possible for the distillers to automate the wash still operation, unless it was able to reli¬ably detect the level of the foam within the stills.

The Siemens Pointek CLS200 provided a solution. These capacitance level switches are suited to use in an application where the material being measured has a low dielectric value. Although traditional capaci¬tance devices measure voltage drop or current flow, and are affected by changes in material properties, Pointek sensors monitor the effect of capacitance based on fre¬quency change. Because even small level changes create large changes in frequency, the result is better resolution and accuracy.

The instrument has a high frequency oscillator with the sensor encapsulated in the probe tip. The sensitive tip is an accurate and repeatable switch point, and the probe is unaffected by material build-up, humidity or moisture. In addition, the device is said to be easy to install and calibrate.
To solve the longstanding foam detection problem, technicians at the distillery installed the instruments on the neck of each wash still. Now, when foam reaches the tip of the instrument probe it is detected and the burners are automatically turned off. When the froth level diminishes enough to clear the sensor the device will then restart the burners.

This more reliable foam level detection solution allows the distillery to deal effectively with the foam produced in the wash stills, helping to prevent spills as well as protecting the process.

Further, because the burners only operate when they are needed, the distillate is more consistent. The new solution also reduces both staff and maintenance requirements, freeing operators for other duties, and allowing production to continue through weekends too.

Commenting on the solution, Willie Thomson from the Duff¬town Distillery said: “This technology helps us ensure quality product and enhance efficiency. It is an ideal meeting of our time-honoured traditions with modern technology.”

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