Online viscometer optimises starch coating

The XL7 online viscometer from Hydramotion has solved a long-standing viscosity measurement problem for the paper recycling operation of leading Australian packaging manufacturer Amcor

With its world headquarters in Melbourne, Australia, Amcor offers a broad range of plastic, fibre, metal and glass packaging products, along with packaging-related services.

The company was Australia's first established paper and cardboard recycling company, and remains a leading recycler of paper and cardboard products.

Viscosity measurement used to be a problem at the Amcor Fibre Packaging plant in Port Botany, Sydney, which receives and processes around 50% of the waste paper collected in New South Wales.

Since the paper is 100% recycled the base sheet is coated with starch before the final drying stage to give it the necessary strength.

Amcor uses a refined acidified wheat starch slurry, which is cooked at 140C, and stored in a service tank, from where it is pumped up to the size press and applied to the paper.

The excess is pumped back into the service tank, making a closed-loop system.

The viscosity of the starch directly affects the degree of penetration and hence the efficiency of starch usage.

For some grades the starch has to penetrate the paper, so a lower viscosity is required, while other grades are optimised by providing a surface coating to the sheet, requiring less penetration and therefore higher viscosity.

The aim is to ensure uniform viscosity during production and hence the most efficient use of starch.

In the past Amcor could only check starch viscosity by conducting spot tests with a rotational viscometer.

At best these tests were only done four times a week, so it was impossible to tell whether process problems were starch-related or had some other cause.

There was a clear need for continuous viscosity monitoring using an online instrument.

Blade-type viscometers were tried, but these proved unreliable.

They tended to block up and needed constant cleaning, so bypass lines had to be installed to enable them to be cleaned on the run.

The weekly maintenance required was both time-consuming and highly inconvenient.

Acting on a recommendation from another paper mill in Australia, Amcor consulted Hydramotion.

After some discussion a Hydramotion XL7 online viscometer was installed on the discharge side of the service tank pump in order to monitor the mixture of fresh and recirculated starch, to detect the viscosity effects resulting from loss of heat, starch degradation and contaminants leaching from the paper sheet.

As soon as the XL7 came on-line, Amcor was able to measure viscosity continuously in real time without interruption.

Encouraged by the successful results, the company went on to install a second XL7, this time on the fresh starch line exiting the cooker/converter, to monitor cooking efficiency.

"Both installations were very easy," commented Paul Chappell, Technical Manager at Amcor: "These devices are extremely easy to use - basically just plug them in and that's it.

We run ours back to a PLC and trend starch viscosity online on each of our two paper machines".

With the benefit of continuous real-time data from the Hydramotion viscometers it has been possible to make significant improvements in process control.

"We have been able to troubleshoot starch cooking faults and over usages as a direct result of the data provided by these devices" said Paul Chappell: "The benefits gained are in starch uniformity and efficiency.

In Australia the cost of wheat and therefore starch is rising, and these are operational costs to us.

We always aim to reduce costs of manufacture where we can, and these devices have enabled us to optimise and reduce our starch consumption".

By careful selection of instrument location cleaning has been reduced to a single, once-a-year operation which can be carried out alongside routine servicing of the lines.

No other maintenance has been required.

"The performance has been excellent - we have not had any issues to date with these devices," Chappell added: "The operators have come to trust them and use them to optimise the process".

The XL7 was chosen for its ease of use and negligible maintenance requirements.

The transducer, which can be installed in any location and in any orientation, has a single solid-rod sensor with no moving parts, giving minimal risk of material entrapment.

Measurements are unaffected by gas outbreak, flow rate, plant vibration or the presence of solid particles.

Outputs include a 4-20mA analogue viscosity signal and an optional RS232 serial data link for continuous viscosity monitoring and control.

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