The pulp and paper industry represents a large and growing portion of the world’s economy. Specifically, the pulp industry has maintained a strong tailwind for a few years now for several reasons. According to Pöyry’s World Fibre Outlook, the steady growth of the global tissue paper market, together with the tightening supply of recovered paper, dramatic changes in China’s papermaking fibre furnish and enforced recyclables ban, and the strong global economy have all contributed to the present state of the pulp market.

For now, the long-term fundamentals of the packaging, tissue, and pulp markets look reasonably solid, and market imbalances have not distorted the overall positive sentiment of the industry. Although the wave of digitalisation currently sweeping the globe may appear to threaten the pulp and paper industry, the sector continues to grow, albeit at a slower rate than in previous years. While graphic paper has been on the decline for several years, the growing demand in other sectors - such as packaging, tissue paper and pulp for hygiene products - is stepping up to fill the gap.

Despite this, the industry faces challenges - not least the pressure to make wise capital investments, meaning mills need to focus on extending asset lifecycle and improving operational efficiency by new means.

According to McKinsey’s report ’Pulp, Paper and Packaging in the Next Decade’, the industry is experiencing the most substantial transformation it has seen in many decades. The key challenge is cost optimisation and within the operations field, that is being addressed with its own digital transformation.

There are significant opportunities for the sector to benefit from digital technologies to bridge the gap that has traditionally existed between information technology (IT) and operations technology (OT). By applying data analytics, artificial intelligence and machine learning to the growing volume of production data that is available, producers can transform the resulting improved visibility into actionable business insights to improve operational efficiency all along the value chain. One such solution connecting IT and OT comes through the ABB Ability™ digital platform.

When it comes to gaining valuable business insights from data utilising connected digital solutions, ABB Ability™ offers many applications for pulp and paper, including advanced process control (APC). APC helps industries attain operational and financial targets by increasing throughput and reducing energy use.

The benefits of APC solutions for pulp mills include the opportunity to stabilise, improve process operations, and minimise the variation of key variables while considering process constraints. These operational benefits translate into financial gains due to increased throughput and minimised energy and raw material use.

ABB Ability™ Advanced Process Control for pulp mills provides monitoring, predictive analytics and robust closed loop process control to optimise mill operations. The solution stabilises the process, reduces chemical usage and coordinates the numerous loops to incur optimum on-specification product quality at minimum variance. This technology is of particular value in the pulp and paper industry, where many processes are notoriously difficult to measure, and provides a better opportunity to model things that cannot directly be measured.

To understand how APC can optimize pulp mills, we are focusing on how it positively affected the lime kiln operations at one mill in Europe. The work on the pulp mill in Europe centered on the lime kiln.

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Criteria	Achieved improvement
Reduction in Cold End Temperature variation	58%
Reduction in Oxygen variation	26%
Reduction in energy consumption	5.02%
Reduction in residual carbonate variation	62%

^{In addition to MPC, the latest technologies - ranging from data access, analytics and visualisation to advanced modeling algorithms - are leveraged in ABB Ability™ APC to help customers optimise operations and drive their mill to its desired targets.}

Calcination is a highly interactive, multi-variable process, characterised by non-linear dynamics, subprocesses with time scale that vary from seconds to hours and a vastly varying feed that makes the optimisation and efficient control of a lime kiln a challenging problem. Furthermore, the complex operating conditions often result in multiple objectives (environmental, energy and efficiency) that are often conflicting in nature to be managed adequately.

Because of the nature of the kiln where operating conditions exceed 1,000 degrees Celsius and significant quantities of dust are produced, most sensors are unreliable and frequently provide false signals that hamper real-time control. Other common disturbances in a lime kiln include varying density of the lime mud feed, varying production demands due to upsets in the cooking section and varying properties of the fuel, which makes designing robust control all the more difficult. Safety is of utmost concern, as poor control could lead to hazardous situations with the production of the dangerous carbon monoxide, and even lead to explosions.

Designing robust supervisory control and advanced control logic that coordinate the existing regulatory control system of a lime kiln is demanding yet essential. The potential benefits that can be achieved through dynamic control are vast. First and foremost is the significant increase in fuel savings or energy efficiency, which provides an immediate economic benefit. Stable lime quality will greatly improve the cooking process and result in less off-spec pulp production. The lifetime of the lime kiln will also increase, lowering the maintenance costs associated with refractory repairs, ring formation, and other effects of poor temperature regulation. Finally, the environmental costs of treating flue gas can also be reduced.

The lime kiln control architecture is typically built on a set of basic instrumentation, on-line analysers, regulatory control logics (PID), and supervisory control logic. APC would further optimise the existing control system by coordinating their functioning by calculating optimal setpoints.

Another feature of the installation was the utilisation of ABB Ability™ Collaborative Operations. Utilising IOT infrastructure, Collaborative Operations provides a new breed of connected services that leverage the vast amount of information available today. Advanced data processing and analytical applications uncover trends, data patterns and relationships to improve operations, lower service costs and reduce downtime. Problems that once required experts to travel to the site can often be resolved remotely via collaboration operation centers. Condition monitoring, machine learning, and data analytics enable a small team of ABB experts to monitor and optimise a large installed base of equipment effectively.

Collaborative Operations is a way of operating that allows both supplier and papermaker personnel to operate on the same information and communication backbone. This enables ABB and the customer experts to remotely monitor and optimise critical equipment and production processes, together, and improve overall plant performance.

Through the application of ABB Ability™ APC and Collaborative Operations, significant improvements can be achieved. For the European lime kiln, the process was stabilised and optimised with APC, which resulted in significant cost savings while maintaining all process parameters within operational constraints. Furthermore, over time, benefits such as reduction in makeup lime requirements and reduction in maintenance downtime were also observed. The application of ABB Ability™ Collaborative Operations enabled continuous monitoring and sharing of key performance indicators with all stakeholders, through which the performance was sustained and further optimised over time.

Digitalisation through the ABB Ability™ platform is not limited to lime kilns and has found applications across the various processes in pulp and paper mills. Improving the pulp quality in the cooking process, minimising water consumption in the washing process, minimising chemical consumption in the bleaching process, improving the runnability of paper machines are a few areas where the ABB digital solutions have been successfully implemented.

ABB’s extensive and worldwide experience in implementing pulp mill optimization and control packages is proven with more than 500 systems installed since 1969. The process expertise coupled with this extensive experience has resulted in new and improved advanced process control (APC) solutions for pulp mills packaged under the OPT800 suite.