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Finnish chemical company Kemira was experiencing poor performance from a dissolved oxygen (DO) measurement system, so replaced it with a Mettler Toledo system to help reduce maintenance costs.

Kemira specialises in fibre, chemical water treatment and water-separation technologies.

At its UK facility in Bradford, the company manufactures organic flocculants for use in the water-treatment industry.

The application in question is a copolymerisation involving acrylamide and a quaternary ammonium compound.

Monomers and polymer initiators are combined immediately prior to injection into the reactor, which is blanketed with nitrogen.

The polymerisation takes place as material enters the reactor.

At the reactor outlet the polymeric product passes through a series of cutting processes that break the solid material into small pieces ready for drying and packaging.

Oxygen acts as an inhibitor to the polymerisation.

This means that, if oxygen levels are not kept below a certain level, sufficient polymerisation will not take place.

If this happens, there is a risk of unreacted monomers entering the cutting system, causing reduced product quality, a potential environmental issue and undesirable process downtime.

Measurement of the dissolved oxygen level in the monomers is therefore critical in preventing out-of-spec material entering the reactor stage of the process.

Mettler Toledo was approached after Kemira experienced problems with its existing dissolved-oxygen measurement system.

They were seeing unexpected membrane failures in their DO equipment and generally poor membrane lifetime, lasting anything from a couple of weeks, down to only a few days in extreme cases.

Before a Mettler Toledo system was put in place, samples of the monomers were taken back to our lab so that the suitability of our dissolved oxygen membranes could be evaluated.

At the end of the trials no significant change or damage to the membranes was observed.

Following this successful evaluation, Kemira purchased a system to install on one of their monomer lines.

The system chosen comprised the Inpro 6800 DO sensor and M700 multi-parameter transmitter.

The M700 was selected because it would allow access to raw signal data and calibration statistics, which would help in Kemira’s management and long-term evaluation of the system.

The installation has now been in place for many months without any membrane problems and hence no maintenance requirement.

As a result, Kemira has recently purchased a second system, this time upgrading to the new Inpro 6850i digital sensor, allowing them to take advantage of Intelligent Sensor Management (ISM) technology.

ISM uses advanced diagnostics to provide real-time information on sensor conditions.

By using the predictive maintenance functions of the M700 transmitter, maintenance tasks at Kemira can be performed before a critical drop in sensor performance occurs.

The result is reduced maintenance costs with higher process availability.

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