Production process

How to avoid paper web breakage

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Bringing efficiency to a system, a production line or a plant means making the best use of available resources while respecting the timing, yield and quality of the process. In terms of paper production, it can mean avoiding web breakage and consequent machine downtime. Today there are more tools available for collecting and analysing data.

When we talk about improving the efficiency of a plant we think of new technologies to be added to the production process. In reality, this is not necessarily the case. Efficiency means being able to make the best use of available resources without affecting the quality and yield of the process. Avoiding web breaks is an ideal way of optimising the production line. In order to do this, digitalisation now gives paper mills an additional weapon: data. Jukka Luoto, product manager Industrial Internet at Valmet, spoke about this at the Aticelca 2021 Congress.

Searching for the cause

Web breaks are a problem that paper manufacturers have always had to deal with. The standard approach to this issue is to try to understand what happened, starting by investigating trends to see if there was any abnormal behaviour immediately before the break; anomalies that could then justify the event.

In reality, Luoto explains, there are countless factors that could cause a break-up. «There may even be situations where you have to analyse 1,000 trends before you can find the cause» he says. As you can imagine, this is time-consuming and not at all efficient.

There are already some technologies on the market that can help paper mills. For example, «there are systems for monitoring breaks using camera technology, which help to identify the position of the break and allow the behaviour of the web to be explained before the event. And web inspection systems to identify dirt and holes, and to understand how defects can interact with breaks, both in the machine direction and in the transverse direction. The breakage log is a systematic method of finding possible correlations between breaks, in terms of location and timing of circumstances. And finally, the alarm of the automation system, which is able to suggest what went wrong».

The trends that these different systems reveal will provide information on the behaviour of the process variables. Usually, explains the manager, it is necessary to make an analysis of all these systems. To make the operation more consistent and precise, «Valmet has therefore developed an application that collects all the data from the different measuring instruments and equipment, and highlights the most important anomalies and the variables that are, in some way, correlated with failures».

The value of the Industrial Internet

In the case of an event like web breakage there is also an economic consequence that should not be underestimated. Of course, says Luoto, the mill’s operating costs remain the same – energy, personnel, chemicals and other costs – but you have to consider that web breakage means stopping the machines – and therefore production – with inevitable losses of time and money. The maths are soon in. «If we consider a testliner machine, with a width of 7,840 mm, a speed of 1,400 m/min and a production of 90 gsm, and in terms of profit we are talking about 100 EUR per tonne of paper produced; we can calculate that an increase of even just 2% in PM efficiency would bring an extra annual profit of 1 million EUR.» It is on these issues of system efficiency that Valmet Industrial Internet is intervening with a long-term performance development programme. «We are not only suppliers of equipment and automation systems” adds Luoto “we have over 200 process experts in the world and thanks to the combination of technology, automation and services, in 2020 alone we remotely solved 322 problematic cases and supported 60% of the events with our professionals». 

Detecting anomalies

In the area of process control, the Austrian company has therefore developed new intelligent control methods and more sensitive sensors. In particular, explains Luoto, «the Web break anomaly detector is a useful application for identifying process tags that fall outside the analytically defined optimal operating range. The detector helps to understand the anomalies with respect to this range and, consequently, the increased risk of breakage. The optimal operating range is delineated by the historical data collected on speed, weight, thickness, etc. The most significant anomalies are statistically determined. The optimum operating range is delineated by the historical data collected on speed, grammage, thickness, etc. Statistically, the most significant anomalies that emerge are collected in an anomaly history index and serve to indicate the conditions that lead to web breakage. The history tool, therefore, together with our know-how, will help the mill to analyse paper breaks and identify their causes».

Valmet’s application allows the list of breaks to be displayed on its main page. The data can be filtered by month, by type of downtime – i.e. their reason – or by type of production. It is also possible to filter the tags of a specific process area. The list of breaks that occurred shows the duration, with start and end time of the event, and what type of production was in progress at the time of the break.

The application allows you to easily view any deviations from the optimal range of the specific tag under consideration – a range that, by the way, varies depending on the state of the process at the particular moment you decide to consider; in essence, the limits are constantly changing because the process itself is changing. The application indicates: the upper and lower limit of each tag, therefore its optimal range, the deviation from these parameters or anomalous behaviour – the only time the system does not measure process anomalies is during production changes – and the entire pre-break session. The most interesting elements are precisely the deductions that can be made by analysing the tags showing the abnormal behaviour recorded just before the event. This makes it possible to verify what happened at that time and thus to have an indication of what caused the breakage. By selecting an event, the application displays the description, unit and scale of the tags. It is also possible to choose a period of 4, 8 or 24 hours before the break and thus see what happened on the line during that time.

Luoto gives the practical example of a break on a paper machine. «Analyses carried out using the historian’s instrument showed that just before the web broke, there was a sharp increase in the flow rate of wet starch.» «A phenomenon,» he explains, «which, when so sudden, can easily cause the web to break.» «The tool also makes it possible to calculate various tag statistics and to analyse the co-variance of the starch flow rate and, from this, to see how a more moderate increase in starch flow rate could prevent breakage».

The case study

Valmet’s application has been successfully used by a paper mill producing coated topliners with a PM of 3,861 mm width and an annual production of over 300 thousand tons. Luoto says that although there were few cases of web breakage recorded by the mill, the problem was the long downtime involved and the time it took to return to the desired production quality. «The customer was able to see the benefits of the web break anomaly detector tool in his day-to-day operations because it gave him a new way to analyse breaks and find their causes. The application has already identified elements that have led to a reduction in the amount of breakages from 15 to 20%» and above all, explains the manager, «it shows elements that were not even considered before.» Thanks to the use of the application, together with the experience of process experts from both Valmet and the mill itself, the mill has achieved an efficiency improvement of 1% per year, equivalent to a saving of 300,000 EUR.

Ultimately the Web break anomaly detector helps to identify the causes of breakage through data collected from different sources, increasing process stability and machine efficiency.

Anti-breakage solutions: systems and services

As well as being a supplier of automation equipment and systems, Valmet offers a range of web-based production management tools for paper mills that allow a tailor-made efficiency plan to be implemented. «Valmet Industrial Internet solutions are customised for each mill» explains Jukka Luoto. And in the specific case of the web break phenomenon, they combine applications such as Data discovery, Dynamic centreline advisor, Web break anomaly detector that detects process anomalies, Trending tool that defines trends, and Web break logbook that records breaks. The main equipment and measurements can then include the Web monitoring system to monitor the web, the Web inspection system to inspect the web, as well as different types of analysers, QCS measurements and felt profile measurements.

In addition to the applications, the company has developed a range of services that mills can turn to, including performance agreements and the Valmet Performance Center with on-demand expert support, up-to-date applications, ongoing reporting and on-site paper technology support. The Valmet customer portal, on the other hand, is the collaboration tool between the company and its business customers where they can find attachments, expert opinions, training material and applications. «This type of solution will ensure that the levels of digitisation are activated and the up-to-date equipment and knowledge that are crucial to the success of projects are implemented» concludes Luoto.

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