Production process

Refining upgrades in times of AI

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Refining upgrades in times of artificial intelligence. This is shown by Valmet thanks to its innovative refining concept, which guarantees high performance, automated processes and constant process and quality control.

The innovative smart intelligence has been designed to improve the sustainability of the refining process and save on working costs, thereby always keeping the quality of final products high to the standards required by the customers.

The 2020 Aticelca Congress was the occasion to focus on this issue, which was addressed by Juha-Pekka Huhtanen, Valmet, Process Technology Manager Stock Preparation, Research & Technology, Microfibrillated

Smart refining is based on three main pillars:

  1. high-performance refiners
  2. automation for measurements, controls and process optimization
  3. online dialogue with process and quality data.

High-performance refiners

OptiFiner Pro manufactured by Valmet is a latest generation refiner, which unlike other refiners works based on a completely different flow principle.

It features two entries, i.e. two power supplies that provide for the same quantity of fibre introduced in the rotor of the refiner. The fibrous paste then goes through the holes of the rotor and enters the refining area, to then come out of it refined through the empty spaces of the stator; there is only one exit.

The loading of this refiner is managed through a servo motor that quickly and accurately regulates each individual gap between the rotor and the stator.

This refiner uniformly distributes fibers in individual gaps in the entire refining area, thereby transferring the mechanical energy to the fibrous paste more effectively. All fibers are uniformely processed in the airgap between the blades, with this contributing to an increase in the percentage of fibers that undergo proper refining.

Thanks to an improved through-flow of fibers, refining intensity can be increased without damaging the fibers and the time spent by the paste inside the refiner is shorter. For these reasons, the refiner is smaller and the rotor has a smaller diameter.  As a consequence, there is a lower vacuum power, which leads to significant energy savings.

A comparison of SR developments based on the specific refining power: with the same pastes, the energy parameters detected in a traditional plant in a mill with conic refiners are higher, if they are compared with the results of the experiment made with the high-capacity refiner.

Data from the refining plants of the mills has shown that this high-capacity refiner enables to minimize energy consumption up to 20% of the actual energy required during the refining stage, if one compares it with the energy of the other refiners under the same working conditions.

This refiner joins the new double disc refiners which, with decades of innovations and developments, have reached their current good performance in terms of productivity, quality and energy efficiency.

Today’s refiners feature a tangential entry for the optimized distribution of the entry paste flow, hence an increase of their hydraulic capacity up to 50% compared to previous DD. A better centring of the floating rotor provides for better refining results and less wear of the blades. An improved loading system based on variable frequency improves the stability of the quality of refined fiber and optimizes the refiner’s loading and unloading stages.

Automation for measurements, controls and process optimization

The refiner’s task is not only to develop the ingoing fibrous paste to achieve the right refining grade, but also to manage the quality of the fibers and, consequently, of the paper.

During refining, the development of fiber fibrillation, the refiner’s cutting action and the formation of fines are interrelated. It is, therefore, necessary to know and measure the morphology of the paste fibers to optimize the refining process.

This morphology can be viewed through a tool called Fiber Furnish Analyzer, which, besides measuring freeness, incorporates the technology for the analysis of fiber images and provides details on a microscale of said morphology and the properties of the paste fibers.

For each sampling point, it provides systematic answers with a series of measurements that can be used by the controls of the refiners and the operators for a more comprehensive overview of the refining operation. This is a very valid tool, if it is used in closed loop of analysis and control of the entire refining process.

The online analyzer enables to constantly measure and analyze consistency, which must be perfect, fiber length, refining grade, as well as all the technological factors that characterize refined fibers.

These values then feed the algorithms of the refining control loop, which, based on the targets set by the operators and the refined fibers, adjusts the specific energy of the refiners so as to produce the the ideal quantity and quality of the refined paste and not to waste residual energy.

Analyzers enable to view and better understand the reason why fibers’ resistance potential is higher when the fibers are not destroyed and maintain an ideal level of refining intensity. This is shown by the video pages of a real refining process analyzed. The analysis of the videos shows that less load on the motor and energy make it possible to obtain longer fibers and higher resistance to the paste.

The fiber analyzers’ measurements and controls in different points make it possible to expand the refining system to wards the holistic optimization of paste preparation (figure 6). Virtual sensors can also be used. These enable to create predictive models from certain measured values, like fibrillation, fiber length, etc. These values can be processed and enable to predict the resistance properties of the paste and the paper.

This predictive control model enables to simultaneously control the target values of several parameters and optimize more objectives, including the refining process, the final paste and the properties of paper or cardboard. This helps reduce process instability, improve quality and reduce total production costs.

The controlled variables are always defined by process and product needs. These include the specific energy of each refining line, paste dosage, capacity and consistence values, chemicals and starch, drainage in the forming section and presses.

The results of the optimization process, including results in paste preparation to paper, consist in savings in raw materials and energy, the decrease in number of breakdowns of paper machines and the possibility to increase their working speed. The constant inflow of information on paste and final paper resistance values enables a better control of final product quality.

A real experience consisted in the fact that, before the installation of smart automation, the Gaussian curve of the average resistance values at the exit of a refining plant. After installing the control predictive control model, the distribution of resistance probability values is down to a minimum, as shown by the green Gaussian curve.

At this point, with minor variations it was possible to set a slightly lower target value, indicated by the red Gaussian curve, to hedge against the possibility that lower resistance values are within the specifications required for the final product. This enabled to save raw materials and energy.

Another real example of reduction of process variability.

With this optimization process the paper mill has managed to reduce fiber length variability by over 50%. As a consequence, during paste preparation also variability decreased by over 50% and the paste in the paper machine became more uniform and constant, thus improving machine runnability and the stability of the quality of the final product.

Online dialogue with process and quality data

Industrial internet applications based on new technologies, like Cloud services and advanced analytics, enable paper manufacturers to compare process, quality and economic data coming from different operating systems present in the paper mill, ranging from laboratory data to DCS and ERP systems data.

A meaningful dialogue with the collected and transferred data enabling new solutions for a more rapid management of the entire paper mill process. The resulting advantage is higher process stability and the reduction of response time for problem solving.

The main results of industrial internet solutions can be classified in three main types:

– reduction of raw materials and energy costs

– reduction of downtime times and less machine breakdowns

– better product quality.

The production or maintenance manager, or a process specialist no longer has to go to the refining section, the control room or the operator panel to check what is happening during a refining process, but he can constantly check the corresponding data wherever he is from his tablet or smartphone. The videopages of the refining process can be customized based on the operator’s needs, thereby visualizing the most important and significant parameters of the refining process, including maintenance values. A single check is enough and this can be done wherever the operator is.

The Performance Center is yet another support for paper and cardboard manufacturers. Through a remote connection and the work by a team of experts, the Center provides services to support the paper mill staff and optimize processes.

The Performance Center can provide three different types of services:

  1. remote monitoring and optimization for improved equipment use and productivity through active monitoring and optimization;
  2. expert support upon request for problem resolution and indications on the actions needed to solve them;
  3. analytics as a service, for improved productivity, quality and efficiency through big data, with enhanced analyses and methodologies and tools useful to identify in advance problems and their causes, which cause process variations.

Thanks to the tools used, the measurements detected and the feedbacks from the fibers, which are used for process control and optimization, have become valuable information for the quality of the final product and the efficiency of the paper machine.

Once the desired quality levels on the paper machine are reached and optimized in terms of energy consumption, use of raw materials and production costs, i.e. the costs of starch and chemicals, it is possible to further improve process efficiency, innovate the product and study possible savings on production costs.

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