Optimizing water treatment efficiency at pulp and paper mills

Let’s take wastewater treatment as an example. Governments around the world are tightening environmental regulation, and many pulp and paper mills have stricter discharge limits over water pollutants in their permits. To ensure that the outlet effluent is within allowable discharge limits 24/7, continuous treatment process stability is required, which is not that easy to achieve.

“The loads of suspended solids, turbidity, and hard COD, which is particularly challenging for the mills, vary in the wastewater from hour to hour. The reality is that, in many cases, the treatment chemicals are fed into the process at a steady dosage flow. This leaves a lot of points in time where the chemicals are either underdosed or unnecessarily overdosed,” says Anders Ånäs, Manager, Global Digital Services at Kemira.

Adding to the challenge are the time-consuming quality control processes. Typically, basic monitoring and control requires manual work in collecting samples and analyzing them in a lab. This causes delays in the process.

“It can take several hours or even days before the plant personnel can react to a changed wastewater composition and take the needed corrective actions to adjust the chemical dosage and optimize the treatment process performance. As a result, the mills face unstable and at times poor effluent quality and, on the other hand, chemical wastage and unnecessary costs.”

At many mills, there are a lot of points in time where the water treatment chemicals are either underdosed or unnecessarily overdosed.

The same goes for the other water treatment applications at pulp and paper mills, starting from the incoming raw water treatment all the way to sludge dewatering. Fresh water that is taken into production from rivers and lakes contains seasonally varying levels of organic compounds, which makes maintaining a steady quality in the chemically purified water a challenge. Similarly, varying sludge composition makes it difficult to predict the performance of the dewatering process and to optimize both the sludge dryness and filtrate quality.

“Without an up-to-date view, you are unable to adapt to the fluctuating process conditions. There’s a lot to gain with improved process control and efficiency,” says Anders.

Digital services for optimized efficiency

Kemira has developed digital services that help optimize the performance of water treatment applications at pulp and paper mills. KemConnect™ Water Treatment services enable real-time monitoring and automated control of both raw water and wastewater treatment processes.

“The up-to-date view helps overcome many key challenges. The customizable KemConnect dashboard allows you to see at a glance the current levels of, e.g., COD, suspended solids, and turbidity in your process and how the current treatment is performing. Based on the real-time data, the mill personnel can make fact-based and timely decisions, leading to round-the-clock stable quality and optimized performance.”

The real-time view enables fact-based and timely decisions and leads to round-the-clock stable quality and optimized performance.

“Overall, thanks to the improved process control, there will be fewer situations where something goes unexpectedly wrong, and a sudden remedy is needed,” Anders Ånäs points out.

It is also possible to automate the chemical dosing adjustments in the treatment process, based on the real-time quality measurements and performance data. The algorithms for automated dosing as well as the patented portfolio of reliable online monitoring tools for chemical applications are built on Kemira experts’ extensive chemistry and application expertise and process know-how.

Automated dosing ensures that just the right dose of chemicals is used at the right time, further improving process efficiency. Application expertise plays a key role. “For example, determining the right measuring and chemical dosing points is crucial for getting the optimal results. Our experts work closely with the mill personnel for successful implementation and reliable service.”

Compliance and cost-savings

Optimized and cost-efficient water treatment processes are built with the combination of best-in-class application expertise, high-performing chemistry, and advanced digital services.

A mill producing specialty paper grades was able to further reduce suspended solids by 60% and COD by 30% in their wastewater treatment process after introducing treatment chemicals from Kemira together with the KemConnect solution for real-time control.

“Continuous operation stability secures effluent quality and ensures that the mill stays compliant with the strict discharge limits of environmental permits at all times. The coagulation and flocculation performance is monitored and controlled at multiple points throughout the wastewater treatment process. Based on the data, the operators can respond to changes without delay and with optimal use of chemistry,” Anders Ånäs explains and shares another case.

Real-time data helped a board mill overcome high seasonal variations in the incoming fresh water. The mill achieved a 50% increase in COD removal efficiency. Dissolved organic compounds cause issues e.g. with runnability and increase deposit risk at the paper machine, so stable raw water quality materializes as savings in operation costs.

“When you see your chemical applications in real-time, you can stay one step ahead and maintain optimized efficiency even in varying conditions. The process and performance data that cumulates over time provides additional insight and reveals opportunities for further improvement.”