Simulation of Radiata Pine Veneer Drying: Thermal Energy Consumption and Efficiency
Veneer drying consumes over 60% of the total thermal energy demand in manufacturing of plywood and laminated veneer lumber. In order to understand the veneer drying process and manage the energy supply, a mathematic model was developed to simulate the radiata pine veneer drying thus energy consumption and efficiency can be predicted as a function of distance through the drier length.
The drier is a continuous, air jet impinging type with six layers and three rows of veneers, and for each layer, there are two layers of jet boxes, one above and one beneath the veneer layer. The input parameters for the drying simulation include drier zone temperature, dryer zone humidity, air impinging velocity, veneer conveying speed, veneer thickness and initial moisture content. The simulation results show that thermal energy consumption is in 170 to 490 kWh/m³ veneer with efficiencies of 40 to 65% for eight drying schedules used. The results also illustrate that the whole drying process along the drier length consists of a constant drying-rate period followed by two falling-rate periods. Both energy consumption and efficiency are high in the constant drying stage and decreasing in the falling drying stage. Veneer moisture content is the most significant factor contributing to the drying energy consumption and efficiency. The model is validated from drying operations in a commercial LVL plant in New Zealand. Close agreement between the simulation and actual results gives confidence in employing the model to optimise the drying operations and improve the energy efficiency in veneer drying.