Influence of Wood Moisture Content on the Heat Balances and Efficiencies of Concrete Pits During Steaming or Boiling Unfrozen Veneer Logs

Abstract

A model-based approach for determining the heat balances and efficiencies of concrete pits during steaming or boiling of unfrozen veneer logs presented. With the help of a personal 1D model, the heating durations of beech logs with a diameter of 0.4 m, initial temperature of 10°C, and moisture content of 0.4, 0.6, and 0.8 kg∙kg-1 were calculated at operating temperature of 80°C in the pit. Using the determined logs' heating times and our own stationary model of the heat balances of concrete pits during steaming or boiling logs, the change in the heat balances and efficiencies of a pit with working volume of 20 m3 and loading level of 45, 60, and 75%, depending on the logs' moisture content was calculated. It was found that the change of the logs' moisture content from 0.4 to 0.8 kg∙kg-1 at maximum possible loading level of 75% leads to a rise in the energy consumptions and heat efficiencies of the pit from 104.3 to 125.2 kWh∙m-3 and from 34.3 to 42.9%, respectively, during the steaming process, and also from 143.5 to 161.8 kWh∙m-3 and 24.9 to 33.2%, respectively, during the boiling process. Reducing the pit load level from 75 to 45% at 0.6 kg∙kg-1 causes a decrease in the pit efficiencies from 39.0 to 28.5% during the log steaming process and from 29.3 to 16.1% during the log boiling process.