HEAT BALANCES OF CONCRETE PITS WHEN STEAMING OR BOILING UNFROZEN LOGS

Abstract

An approach to calculating the heat balance of concrete pits during the steaming or boiling of unfrozen logs intended for the production of peeled veneer is presented. Using our non-stationary model, the heating times of beech logs with a diameter of 0.4 m, initial temperatures of 0, 10, and 20 °C, and humidity of 0.6 kg.kg^-1 at an operating temperature in the pit of 80 °C were determined. Using the determined log heating times and our stationary model, the change in total energy required to perform the entire steaming or boiling process, as well as the energy needed for each of the individual components of the pit heat balance, was calculated. Computer simulations were performed for a concrete pit with overall dimensions of 7.4 × 2.8 × 2.5 m, a working volume of 20 m³, and a degree of filling with logs of 45%, 60%, and 75%. The total heat consumption for heating beech logs with a diameter of 0.4 m, an initial temperature tw0 = 10 °C, and a humidity of 0.6 kg∙kg^-1 at an operating temperature in the pit tm1 = 80 °C and a degree of filling f = 75% is equal to 114.7 kWh.m³ for log steaming and 152.7 kWh.m³ for log boiling. It was found that increasing the initial log temperature from 0 °C to 20 °C results in a decrease in the total energy consumption of the pit, from 122.8 to 106.3 kWh.m³ for the steaming process and from 159.7 to 145.4 kWh.m³ for the boiling process. Reducing the pit load from 75% to 45% would result in an increase in energy consumption in the pit from 114.7 to 157.0 kWh.m³ in the log steaming process and from 152.7 to 278.8 kWh/m³ in the log boiling process.