Modeling Drying and Energy Performance of Industrial Through-Dryers

Abstract

A model of an industrial through-dryer for production of tissue paper was developed. The model can be used to predict the performance of a dryer section of an industrial through-drying machine consisting of one or more through-drying rolls separated by free draw sections. Roll diameters, wrap angles, machine speed, basis weight, initial paper moisture ratio, operating pressure differentials, drying air temperatures, and drying air humidity are input parameters to the model. Based on the input information, the model predicts paper drying rate, paper moisture ratio, paper temperature, exhaust air humidity, exhaust air temperature, and air flow rate as a function of time, which at a given machine speed is equivalent to a certain position in the machine direction of the dryer. The model also includes a description of the fabric and along with the paper properties the model also predicts fabric drying rate, fabric moisture ratio, fabric temperature, and fabric air humidity as a function of time (or position). Air, vapor, and enthalpy fluxes were integrated over the residence time of each through-drying roll in order to retrieve the average flow rate and air properties of the air leaving each roll. These data were then used in a steady-state description of the air system of each roll, which means that, for given drying conditions, natural gas consumption in the burners and the fan power associated with each roll can be predicted. The model was used to study how the different operating conditions affect the energy demand and economics of the through-drying process.

The simulation results indicate small differences in total drying cost for different operating conditions. Reduction of fabric water was shown to have a relatively large impact on overall drying cost. Reducing the initial fabric moisture ratio from 0.019 to 0.012 kg water/kg dry solids reduced total operating costs by approximately 3.3%.

Keywords:

• Industrial dryer
• Machine
• Modeling
• Through air drying
• Through-drying

Notes

^a Based on data by Lang. ^[11]

^a Drying cost defined as cost for natural gas and fan power. Fan efficiency was set to 70%.