Digital evolution across the recovery island

We are in the middle of a massive digital transformation in all areas of our lives – at home, at work, even in our cars – as digitalization fully enters our lives. The pulp industry has by no means been ignored, and now there are already promising results being seen at pulp mills as the latest in Metris Digital Solutions from ANDRITZ bring major advantages to process islands.


“This is not simply the case of jumping on the digital bandwagon,” says Li Liao, Vice President, Automation and Digitalization – SMART Products, at ANDRITZ. “Far from it; digitalization in the pulping process is already bringing major benefits to our customers.”

And digitalization of the pulping process really is all about customer benefits. Liao continues, “We know our customers really well, and they are not looking for anything fancy or trendy just because they are digital. They are looking for clear solutions that bring added value, for instance, on how to reduce operating expenses and optimize performance mill-wide.”

ANDRITZ has combined its world leading expertise in core pulping technology with the latest in digital innovations that together have proven to reduce emissions and operating costs at the same time as increasing productivity, safety, and chemical recovery of a recovery island. Under the umbrella of ANDRITZ autonomous solutions, there is now a rapid evolution taking place at the heart of the pulping process.

ANDRITZ has been implementing digitalization across the whole pulping process including all recovery islands: recovery boiler, white liquor plant, evaporation plant, and power boiler. Liao says, “ANDRITZ has core expertise, know how, and decades of experience across the whole pulping process. This is why we have full confidence in applying digitalization; we have all the background knowledge we need to create full autonomy across all the recovery islands and then to integrate into the whole mill production process.”

Liao compares the digitization process at pulp mills to the structure of an onion, “First of all, there is the core ANDRITZ pulp and paper process, and then we add the different layers of autonomy and digital optimization. This step-by-step process of autonomy of each of the islands gives us the ultimate aim of linking all the processes together on the way to full autonomy.”


ANDRITZ has created four steps as a way of achieving full autonomy of the pulping process:

The first level of digitalization in a process island is Operator Assistance, which uses the latest Metris AVA (Advanced Visual Analysis) machine vision technology along with smart sensors to fully inform the operator of what is happening in the process. “A good analogy of this first step is to think about the latest cars. Some cars now, via cameras and sensors, can inform a driver of lane position or distance to the next car, allowing the driver to know where he/she is in relation to the lanes on the road. But it’s still “hands on wheel” and the responsibility for safe driving here still rests with the driver,” says Liao.

“This is the same with the process islands; the information that comes back via AVA visualization and smart sensors allows the operator to know exactly how the process is performing, so adjustments can be made accordingly.”

The next step is Partial Automation utilizing Metris ACE (Advanced Control Expert) solutions, which bring together all the information about what is happening in the process and then allowing automatic advanced process control to take place. “At this stage, using the driving of a car again as an example, this is where basically the car can drive itself. In the case of the process islands, based on the information collected, ACE enables automatic functions to take place in tuning and managing the processes. There are different ACE systems placed across all the recovery islands,” says Liao.

Conditional Automation is the third step on the way to full autonomy, where the introduction of robotic technology takes away some of the human activity that takes place in the mill field work. “This is an important step in the automation process where we take certain tasks that are carried out by field personnel and replace them where possible with robotic technology,” says Liao. “This is key when we are enabling a much safer operation across the recovery islands, as well as bringing in a more stable operation.

“This step is where we can free people from the field carrying out manual work in inhospitable environments, as well as avoid a lot of people sitting in the control room analyzing data.”

The fourth step to the full autonomy of a mill is the High Automation stage. This is where the whole system is connected via Metris Digital Twin, and where the mill can be completely optimized all of the time. When connected to a Digital Twin, process islands are capable of self-optimizing control ready for fully autonomous operation. Liao says, “This is the ideal situation where the Digital Twin from each of the process islands is captured in one platform, making the mill one organic, fully linked operation.”


ANDRITZ already has many years of experience in the collection of data using smart sensors, along with its AVA and ACE technologies implemented for autonomous operations across the recovery islands. Now with the implementation of Digital Twin along with the latest in robotic technology, ANDRITZ brings cutting edge autonomous solutions to the market for recovery boilers, white liquor plants, evaporation plants, and power boilers.

Recovery boiler



The main purpose of the recovery boiler is to burn black liquor, generate energy and recover chemicals. For autonomous solutions ANDRITZ focuses on four main areas: capacity, cleanability, safety, and emissions. The central focus on each of these areas is how stepwise autonomy can bring value to the recovery boiler operation with the benefits of increased stability and availability, improved safety, increased productivity, and lower emissions.

ANDRITZ provides the following autonomous solutions for the recovery boiler:

Increased capacity:

AVA Recovery Boiler Toolbox is the base of all autonomy in the recovery boiler, where it continuously monitors the status of the combustion in the boiler using smart sensors to feed back data, allowing operators to make decisions.

Combustion ACE automatically fine-tunes and adjusts the liquor feeding and air distribution controls with the integrated AVA data. The operator still needs to tune few parameters in the process.

Digital Twin continuously calculates the best setpoints for the combustion ACE to achieve full autonomy. The capacity of the boiler will be automatically calculated, allowing for fully optimized boiler operation.

Improved cleanability:

Metris HEWI smart sensors continually monitor the ash load on the superheaters and check for fouling.

Sootblowing ACE, using data from HEWI, provides a dynamic sequence to clean foulings and control the sootblowers when and where needed.

The Digital Twin continually calculates the best setpoints for the sootblowing ACE to achieve full autonomy.

Improved safety:

AVA Smelt Flow Tool visually monitors the buildup of smelt in the spouts on the recovery boiler smelt deck. AVA Charbed Tool monitors the height level of the charbed.

Robotic solutions to free operators from working in a dangerous work environment. Added value comes from operators being free to concentrate on other important operational tasks.

Metris WLA leakage advisor monitoring the potential risks of water leakage.

Reduced emissions:

As all processes have been stabilized and optimized via autonomous solutions, emissions from the boiler will also be reduced accordingly.

White liquor plant



The main function of the white liquor plant is to create high-quality white liquor for the cooking process from the green liquor obtained from the other recovery islands. The key is to make sure the plant runs as efficiently as possible by using the minimum amount of heat in the lime kiln. Digitalization and autonomy of the process allows the reduction of any excessive heat consumption and therefore reduces fuel consumption while optimizing the quality of the end product, white liquor.

ANDRITZ provides the following autonomous solutions for the white liquor plant:

Smart sensors, AVA measurements, and digital advisers act as the “eyes and ears” of the white liquor plant. AVA provides data from the inside of the lime kiln, monitoring the shape and size of the flame. AVA also provides visualization of the kiln bed and distribution of lime pellets.

Two of the latest smart sensor measurement tools developed by ANDRITZ are the LimeDry Solids Analyzer, which measures the moisture of lime mud fed to the kiln, and the Residual Carbonate Analyzer, a quality measurement tool for measuring the residual carbonate level of the burnt lime coming out of the kiln. The digital advisor provides lime kiln condition monitoring, checking on the health of the lime kiln.

Kiln & Gas ACE and Recaust ACE process controls utilize new measurements from level one together with traditional instrumentation. With these, we can partially automate and optimize the process operation in recausticizing, lime reburning, and biomass gasification.

Robotics are engaged in the operation of a residual carbonate analyzer, sampling the lime from the kiln on a regular basis, leading to improved health and safety of operators, at the same time as enabling a high amount of data points.

Digital Twin works closely with ACE by directing the automatic process control instead of being carried out by a human operator. The Digital Twin has the ability to look around and decide on smart setpoints, thus optimizing the process to the full. Digital Twin also has the ability to look ahead and decide on the next setpoints according to the data gathered from the process.

Evaporation plant



An evaporation plant is utilized to produce a stable, high-solids black liquor stream for efficient combustion in the recovery boiler. Evaporator plant operators often face questions such as: How do I run the plant to minimize operational costs to the full? What rate should I run at to meet the set targets? How soon or often should I wash? What is the maximum capacity I can get right now?

ANDRITZ has accepted these challenges and is developing autonomous solutions for evaporator plant operation that center on how to add value. In the first step, machine vision technology (AVA) collects valuable data and information, supporting the operator in controlling operation and decision making. Amongst others, ANDRITZ offers a soap separation camera and turpentine level camera for the evaporation plant.

The second level of autonomous operations, Evaporation ACE, combines the knowledge and information gathered through machine vision and traditional instruments, thus providing better control of key parameters like dry solids, production rate, storage tank inventory, and fouling indication. Therefore, Evaporation ACE helps in optimizing the evaporation plant’s productivity.

A step further takes the Digital Twin. The implementation of the Digital Twin continuously solves the actual and ideal heat and mass balance continuously. It produces real-time data and predictions that can be fed to ACE controllers. One example of the use of Digital Twin in the evaporation plant is washing prediction. Washing the evaporator units is crucial for the evaporation plant to run efficiently. The status of the units is derived from the heat and mass balance that is automatically solved by Digital Twin. With Digital Twin more accurate data can be obtained than by using traditional instruments, allowing operators to plan the operation ahead of time:

Digital Twin data can also feed data to ANDRITZ Smart sequences that can dynamically:

  • Decide which unit should be washed based on cleanliness status and the operational situation
  • Provide a preventative opportunity wash
  • Optimize washing when a bottleneck occurs

The aim of an autonomous evaporation plant is to support customers in maximizing reachable capacity, optimize flows based on feed and product tank levels, and minimize steam consumption, which result in higher productivity and reduced operational costs.


The main purpose of the power boiler is to efficiently produce power while keeping the emissions within environmentally safe limits. Today, there is a constant need to improve and optimize boiler performance and decrease the operating and maintenance costs.

Metris BOA – developed by ANDRITZ – is a web app that utilizes live data as well as historical data from the plant to optimize and analyze power plant processes and monitor the equipment installed. Tailored operation advisor apps will actively support the operator in increasing the efficiency of the boiler, detect opportunities to improve consumption values, and help start processes according to operational needs. Furthermore, automatically generated performance reports comparing current data with data from previous periods provide information at a glance for overall management of the power plant. The ANDRITZ Metris BOA platform will be integrated into the control architecture as a third layer of automation and control together with the boiler protection and plant automation systems (DCS).

The software architecture is based on micro-services with standardized communication channels. This makes it possible to tailor Metris BOA to the user’s needs.

With the Metris BOA smart solutions, ANDRITZ provides a solution to optimize the following key factors:

  • Optimizing performance
  • Increasing reliability
  • Reducing operating costs
  • Optimizing the use of resources

“This is not simply the case of jumping on the digital bandwagon. Far from it; digitalization in the pulping process is already bringing major benefits to our customers.”

Li Liao

Vice President, Automation and Digitalization  – SMART Products



  • Increased safety
  • Higher availability
  • Improved efficiency
  • Better transparency of operations
  • Optimized productivity leading to stable processes
  • Reduced operational costs
  • Optimized use of resources
  • Reduced time on maintenance
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