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Combining fiber monitoring and advanced process control delivers real energy and fiber savings to papermakers

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Pulp and papermakers can now benefit from the combination of deeper fiber insight, bundled with the use of new multi-variable advanced process control (APC) tools, to produce fibers with more consistent tailor-made properties.

This can help any paper machine run better simply by keeping specs perfectly in the target range, enabling big savings in energy and fiber costs, while optimizing refining, blending and more.

By Håkan Österholm and Carl-Magnus Tjeder, ABB Global Product Managers 
 

Today, the available capabilities to get deeper, actionable insight into the true characteristics of the fibers that pulp and paper makers are processing is far greater than ever before. As an example, instead of relying mainly on traditional freeness measurements that were previously taken perhaps once per day or at best once per shift, a wide range of robust online monitoring tools give operators a much clearer, continuously updated ‘picture’ of the true, real-time morphology of the fibers they are processing.

Besides allowing much more frequent and accurate online freeness measuring, the digital testing equipment gives detailed new data on morphology characteristics – like fiber lengths, fines percentages and degree of fibrillation. Such data can now be accurately collected, analyzed, and acted upon using the power of multi-variable process control to improve almost any pulp or paper operation.

To be clear, we are certainly not forgetting about the well-established CSF and S-R freeness testing methods or any other standard TAPPI or ISO method; we are just adding more detailed fiber property information to give us a higher level of understanding.

With this information made available online, we are now able to apply automated closed loop control. This advanced process control (APC) allows us to solve highly-complex, multi-variable challenges, providing tighter quality control in an automatic and consistent way. This helps the paper machine run better and keeps the specs in a narrower range to meet targets with less refining energy – while reducing the need for manual operator intervention.

Making the move to auto pilot

These latest advances mean we are truly able to move to an auto-pilot system on furnish lines where the data can be used to precisely control the refiners. This way we can apply the exact amount of refining energy needed to get the properties we require in the pulp or paper, but not more. Since you can meet the specs with a tighter distribution – without overshooting them just to be on the ‘safe side’ – very large cost savings in refining energy, and even fiber consumption, can be made.

Trust is established with the operators because the traditional measurements are provided alongside the new fiber property measurements, with APC supporting predictions of measured and manipulated process variables. Hence operators get additional information of what is happening at any moment and are also made aware of what is going to happen, reducing manual interventions and maximizing automatic control utilization on stock preparation in the mill.


  
  
  
  
Manual testing can be a tedious process to get reliable results. Standard freeness testing starts with one liter of pulp suspension being poured into a drainage chamber (1). The bottom lid (2) is then opened to measure the volume passing through the side discharge (3), which determines the freeness of the sample. The advantage of using an automatic freeness analyzer is that the sample is handled the same way every time, both in the preparation stage and in all the tests.

Virtual Measurements help estimate potential fiber strength

The new fiber characteristic insights, coupled with our ability to crunch big data concerning process variables like flow, consistency, temperature, refining energy, etc., now allow us to generate what we call Virtual Measurements (VMs). This enables us to recreate information relevant and tangible to the paper maker, such as an accurate estimate of potential tensile strength of the fibers.



 
 
 
 
This model is adaptive and based on all the key signals coming in. Every time a new physical measurement is done, the model is adjusted and calibrated, giving a continuous predicted Virtual Measurement reading.

Based on the deep domain expertise in APC and monitoring systems that ABB possesses, we have created a mature, robust, adaptive software framework that supports these Virtual Measurements. They are not theoretical; they are real world, reliable measurements that serve the process just as traditional physical sensors do.

Multi-variable control delivers the perfect mix

By taking more measurements, more frequently – and in which we have high confidence – allows us to deploy true multi-variable control to fiber processing. As the name implies, multi-variable control lets us get the optimal combined fiber properties by managing all the variables that influence the result.

A very simple analogy could be a water tap with a hot/cold mixer. Previously, in older days, we had one hot water tap and one cold water tap, and we tried to get the right flow and temperature coming out of the tube by manually adjusting both. But the modern single tap mixer adjusts both the temp and flow to achieve the desired result, quickly and easily.

Predictive cruise control on pulp lines

When we bring all these insightful new tools together – including faster and more accurate fiber morphology tests, virtual measuring, and multi-variable control algorithms – we get valuable real-time predictive powers. This means we have the capability to make future forecasts, both short term and long term, of where we are taking the process and how we’ll do it, such as what actuators we will employ.

Another analogy for this could be with the cruise control function on a car that is climbing a hill. But, instead of applying more gas when the car is actually already on the hill, by using predictive power of an APC solution, the car can sense when a hill (or other disturbance) is coming and will proactively accelerate before it has started climbing the hill. This both saves fuel and gives a smoother ride, at the desired speed.

In a paper or pulp mill, APC gives us the visibility to see what process fluctuations are coming up ahead and adjusting in advance, rather than reacting after an upset has already begun.

Of course, just like when using cruise control on a new car for the first time, it takes time for the operators to gain confidence in multi-variable APC. This is perfectly normal and reasonable. That's why our operator-focused approach works to make them feel comfortable every step of the way, so they can see where we want to take the process and are with us. And delivering APC as a service also means we are there before, during and after implementation. This is a major factor in building operator trust and confidence.

Staying in range with adaptive cruise control

Taking the cruise control analogy a little further, one can imagine that if we let the car deviate a little bit from the specific speed target, the controller is able to minimize fuel consumption. By not strictly maintaining an exact speed when going uphill, we can save some fuel. And, when going downhill, having a speed range rather than too tight a target, we can avoid dissipating energy into wasted heat, which may happen if we apply the brakes if we are going faster than a specific target.

Now think of this within the context of a fiber line. With time, adaptive APC that simultaneously adjusts many variables to get the perfect resulting output gives us an even greater ability: moving from specific quality targets to a target range. And staying inside that range keeps costs in terms of energy, fibers, and perhaps even water and chemicals as low as possible.

To determine if a paper or pulp mill is ready to augment their control strategy, an automatic process control readiness assessment first needs to be made. This is done at the mill by ABB experts who explore the processes, typically the refining and approach flow control circuits on the paper machine. Since the high level control is dependent on the performance of these lower levels, this is necessary to remove or correct any possible weak links, which is normally not very difficult. Once everything is checked out and corrected, automatic control can then start to be used.

  
 

High impact areas

Concrete examples of where we can apply APC to furnish management in pulp and papermaking include:

  • Refining, for reducing energy and fiber costs and improving end paper sheet properties.
  • Fiber fractionation, to take the guesswork out of separating fiber lengths and instead rely on the exact measurements the new testing methods provide. This can also be used for validation of the fractioning equipment, to make sure what it claims is actually true.
  • Stock blending, to optimize mixing of various fiber species and sources, including recycled broke, for optimal strength properties. It can also measure and adjust for variations in incoming fiber properties to get a smoother, more consistent fiber blend to the PM headbox.

The end result: Full control of furnish

The combined power of better online fiber measuring with Advanced Process Control of multi-variable process streams, and the development of Virtual Measurement methods that truly represent the fiber properties that the papermaker values, is a big step forward.

By providing new fiber insight that was not available in the past and applying adaptive modelling to the key insights to provide something concrete and specific to the paper maker – like a virtual measurement of fiber strength – APC can better tackle multi-variable papermaking challenges.

With time, trend prediction can help build operator trust for future process variables and control actions – resulting in fewer manual interventions and smoother operation. The system can also monitor the process line KPIs and alert users not only when something is clearly wrong, but already earlier when trends indicate some attention is required.

Although we fully realize that ‘optimize’ is a vastly overused word, in this case we truly can say that papermakers have powerful new ways to optimize their operations: to get the best outputs, automatically and adaptively through the use of more frequent, reliable data while obtaining the lowest raw material usage.


To learn more about wood fiber morphology and the science and technology of fiber analysis and processing, you can download ABB’s 140-page Fiber Guide free of charge here.

 

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