ANDRITZ’s flexible air system operation mode control “DUO POWER - C” keeps emissions in check

Tissue and MG paper machines are designed to produce at their top capacity, known as the dry limit of the system. However, when running with lower basis weights, the required dryness capacity is much lower, which is why a more flexible drying process can be beneficial to improve operating parameters like temperature and blowing speed across different production modes.

ANDRITZ has been granted a patent for its new system, “DUO POWER - C”, a method for controlling the hood air system operation mode in the tissue paper plant. The focus of this innovation is on the control of process hood air in the duo-type hood-air system, which is widely used, particularly in Europe, the Americas and the Middle East. It results from the application of the ANDRITZ R&D team’s extensive expertise and know-how in tissue drying technology and is relevant for systems based on natural gas, Syngas, hydrogen or electricity.

This comprehensive method for controlling the air system operation mode can be applied to both new and existing tissue machines and is equally applicable to MG paper machines.

Counting the reward in energy and emissions

Greater energy efficiency and lower emissions are the reward for implementing the solution. They reduce costs, including taxation on CO₂ emissions in many countries, and ensure the environmental impact of the process is minimized.

So, what is the technology behind this revolution?

ANDRITZ’s European business leader for hood, air and energy systems Luca Linari explains: “In partnership with our R&D specialists and a confidential Italian customer, we have been able to demonstrate that the implementation of additional dampers in the hood air system, along with the remote control of the standard dampers, allows for selective operation of the hood air system directly from the Distributed Control System (DCS) in three different working modes: standard parallel, direct cascade, and special reverse cascade.”

The most common configuration depends on how the tissue machine is specialized and the market it serves. In high-performance tissue machines, particularly where higher basis weights of 22-25 gsm are produced, the hood configuration is generally standard parallel or direct cascade. The special reverse cascade mode might be preferred for low grammage tissue production of 12-15 gsm, which includes most facial tissue and toilet tissue grades, where the burner of the wet-half hood remains active, and the dry half-hood burner can be modulated to decrease the hood’s thermal input, which would otherwise be redundant.

Significant downtime reduction

ANDRITZ s “DUO POWER - C” flexible solution integrates all three hood-air system operating modes which can be activated through the simple action of specifically placed regulating devices (the dampers) which avoid significant machine downtime. The new control logic optimizes the drying process, increases the overall energy efficiency of the tissue plant, and lowers emissions based on the specific product type, frequency of grade change and other production needs.

“The new system can be manual or semi-automatic, with the operator deciding when to switch configurations based on information from various sensors,” says ANDRITZ’s Global Product Manager for hood, air and energy systems Marco Cattani. “In drying limit mode, the burners in the hood operate close to full power, normally between 400 and 450 degrees Celsius, providing the best range to minimize emissions. In speed limit mode, full power of the burner is not necessary to achieve a temperature of, say, 250 degrees Celsius, which also results in lower emissions, in this case thanks to lower fuel consumption. In either scenario, the necessary temperature to ensure thermal cleaning of dust would of course be maintained.”

Installing the “DUO POWER -C” system on existing machines requires evaluation of the factory layout to ensure the necessary space is available. It is not a major project, however, and typically takes less than a week to install the system, depending on the layout. Upgrading conventional systems involves adding some ductwork, dampers, upgrading system logic, and installing instruments such as temperature probes and pressure transmitters. If space is available, the system can be installed with the machine running, reducing downtime to just a few days.

The greatest benefit

For adapting existing machines or adding to new machines, the investment or additional cost is paid back very quickly. The system provides great flexibility, especially for machines producing a wide range of grammages. The benefits for installing the system on MG machines with a wide range of basis weights are similar.

The market's need for emission and energy consumption reduction is clear as deadlines for net-zero approach, for example. Customers can set targets to show their commitment to reducing emissions but, crucially, this system represents a valid step towards achieving those targets and gives credibility to stated intentions. The reduction in energy consumption for low basis weights could be up to 5 percent, and the reduction of emissions can be remarkable, depending on various parameters.

ANDRITZ's patented “DUO POWER – C” solution for controlling the air system operation mode in tissue plants represents a significant, low-risk advancement in tissue drying technology. It offers flexibility, energy efficiency, and emission reduction, making it a valuable solution with the ability to benefit tissue and MG paper manufacturers worldwide.