This project was placed top priority because veneer drying is the bottleneck and the biggest item for energy consumption in plywood mills. During the past three years, the Forintek veneer drying manual was first upgraded. Our research capabilities in drying were significantly improved by the establishment of a mini-dryer and the installation of pilot scale veneer dryer. While the former allows for in-situ monitoring of moisture content change in veneer during drying, the latter can be used to simulate industrial dryers such as jet dryers or longitudinal dryers. Both are capable of testing the effects of such parameters as drying temperature, humidity and air flow. Based on the improved understanding from the experimental tests and theoretical analyses, initial computer models (VDRY-L and VDRY-J) have been developed to simulate the drying processes for longitudinal dryers and jet dryers, respectively.
The combination of laboratory studies and computer simulation led to effective mill studies to evaluate the existing drying technologies, to optimize the existing dryers without capital cost and develop future opportunities.
The key findings from these studies were:
Lab tests showed that temperature and airflow rates are dominant factors affecting drying rate for the whole drying process. While veneer drying increases as drying temperature and airflow rates are increased, higher temperatures and airflow rates both have a greater influence on drying rate at the early drying stages compared to the final stages.
Lab tests also showed that veneer can be dried at high rates under high humidity and temperature conditions. A combination of high temperature and humidity is a good drying mode to save energy and increase output.
Mill case studies showed that the sorting of green veneer prior to drying was poorly done. Lab tests showed that a probable reason for this was due to the inaccuracy of RF sensors used for measuring moisture content of green veneers. The RF accuracy significantly dropped when veneer moisture content exceeded 30%.
Mill case studies showed that a sensitivity analysis of drying parameters is a very useful method for determining effective measures for optimizing dryer performance.
Mill case studies showed that by using higher temperatures and humidity levels in the early drying stages and lower temperatures in the final stages, veneer production can be increased and drying energy can be reduced.
An impact analysis showed that mills can potentially save up to 10% in energy costs and increase production by 10% by optimizing dryer performance.
It is recommended that mills use the results and methodologies from this project as guidelines for optimizing dryer performance. Further research should be undertaken to improve green veneer moisture sorting. The current computer simulation models of drying should be calibrated and used as a quality control tool for determining optimum dryer parameter settings.