Mechanism of Through Air Drying of Paper: Application in Hybrid Drying

Abstract

During through air drying the internal sheet drying history develops as a succession of local moisture content profiles in the sheet thickness dimension. These profiles were determined by interrupting the through drying of 180 g/m 2 6-ply sheets, then quickly delaminating and determining the moisture content of each 30 g/m 2 ply. On the through flow inlet side of the sheet, large moisture differences, about 0.4-0.6 kg/kg dry per 30 g/m 2 ply, develop and move into the interior of the sheet provided that local moisture content is in the range 0.45-1.75 kg/kg. On the through flow exit side, moisture gradients only become significant for moisture content below about 1.25 kg/kg. From the through flow exit side of the sheet much of the water is removed by diffusion to the flow entry side where most evaporation into the through flow occurs. The kinetics of through drying reflect the interaction between these two mechanisms, local evaporation into the through flow and thickness direction diffusion. The moisture diffusivity-moisture content relation controls this balance. In any combination with cylinder drying to give some kind of hybrid dryer, through drying should be at the dry end where air permeability is highest and cylinder drying rate is lowest.

An experimental simulation model for coated paper drying

“…The difference between the relevant corresponding values is about 10%. Simulation results were in accordance with (Hashemi et al, 2003) and the difference between the experimental and simulation results is less than 10%, as shown in Figure 17. In their work, paper was formed as a stack of three plies.…”

“…x,t D = coefficient of moisture diffusion into the base paper, which is a function of moisture content and temperature (Hashemi et al, 2003).…”

Comparative evaluation of the performance of an improved solar-biomass hybrid dryer

“…In such cases, farm residues (biomass) can be utilized to provide additional energy in farm crop processing thereby increasing the value addition of the farmers' agricultural business. Research and development activities in solar drying are geared towards developing more efficient solar dryers with backup auxiliary biomass heating (Hashemi et al, 2003;Hossain, 2008;Leon and Kumar, 2008;Lokeswaran and Eswaramoorthy 2013;Agrawal and Sarviya 2014).…”

Drying of paper: A review 2000–2018

“…McGill University has also been active in developing the TAD technology. [145][146][147][148][149][150] Several studies were focused on the variation in grammage and formation that will lead to uneven flow through the sheet, uneven drying and poor quality parameters. To quantify this a drying nonuniformity index was developed and measured for different parameters.…”

“…[147,149] The moisture content for TAD drying of a 6-ply 180 g/m 2 sheet was studied by interrupting the drying and separating the sheets. [148] Sack paper with a basis weight of 100 g/m 2 was dried in a TAD experimental rig but with a high pressure drop of 8 kPa. [150] One conclusion from these studies was that in order to implement the TAD process and avoid high-pressure drops for drying of heavier grades would be to use the cylinder dryer for the first part of the drying and the TAD-process for the final stages of drying.…”