Activities - Sunnea

Development activities

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Runnability boxes for the Paper and Board Machines

Increasing the speed of paper and board machines is often restricted by web flutter, wrinkles, quality defects, web breaks and problems with tail threading. The runnability problems are typically tried to be compensated by unnecessarily high draws which lead to an increase in web breaks, therefore reducing the efficiency and productivity of the machine.

Recent development work for runnability has concentrated in minimizing the fan power consumption of runnability devices and at the same time achieving excellent sheet stability.

Enhancing Heat Transfer Correlations for High-Temperature Impingement Drying in the Paper Industry

Existing empirical correlations found in the literature have demonstrated good prediction accuracy for impingement heat transfer coefficients at lower temperatures (approximately 100 °C). However, their accuracy diminishes at higher temperatures. In paper drying applications, impingement temperatures typically range from 300 to 700 °C, highlighting the need to enhance the existing heat transfer correlations in the high-temperature range

Heat recovery at Paper, Board and Tissue Machines

It is a well-known fact that a large part of energy required to produce paper or board is consumed in the dryer section, primarily as fresh steam in the cylinders. As most of the of this energy leaves the dryer section with the exhaust air, which carries away evaporated water, it is economically profitable to recover energy from this flow. In a modern PM up to 25-30 MW of heat energy can be recovered with good heat recovery systems and used for different purposes at the paper machine. Heat recovery provides substantial savings in energy, the payback time of heat recovery investment is usually less than one year. Therefore, energy management and conditions in which the drying occurs play an important role in identifying and improving the existing situation at paper and board machines.

Active Cooling tower

Evaporative cooling towers are based upon a very simple principle where energy is removed from the hot water in a direct contact with relatively cool and dry air. In a counterflow cooling tower the process consist of gas phase (air) flowing upwards, a liquid phase (water film) flowing downwards, and a large interface between these two phases. The key factors required for intensive heat and mass transfer in the cooling tower are large air to water interfacial contact area and high heat transfer coefficient. The main objectiveof the research is to determine the heat and mass transfer coefficients and the pressure drop of the different filling materials, and further how these depend on air and mass flow.

High Temperature Cylinder Drying

One of the weak points of multi-cylinder dryers is the low rate of heat transfer from steam to paper. Behind this are several natural, technical and economic aspects. At high rotational speeds, a layer of condensate forms on the inner surface of the cylinder, which dramatically reduces the rate of heat transfer from the steam to the cylinder shell. A cast iron dryer 30-45 mm thick is another barrier to heat transfer. Furthermore, significant resistance to heat flow occurs at the contact surface between the cylinder and the paper surface.The focus of the research is the analysis of improvements in heat transfer in drying cylinders by different cylinder interior design and high cylinder surface temperatures.

Influence of fabric Structure on the drying rate and cylinder-paper contact heat transfer coefficient

In a paper machine, drying fabrics are used to support the web as it passes through the dryer section. The main purpose of the fabric is to ensure a good thermal contact between the paper web and dryer surface and to maintain sufficient web tension in machine and cross directions.

The objective of the study is determination of the influence of dryer fabric’s structure and tension on the drying rate and contact heat transfer coefficient.