Dryer in Matraville plant is made of 2 zones and has 8 decks. Dryer Chain speed is calculated by dividing Board-line speed with 16 (each deck accommodates 2 boards)
Ideal Dryer Chain speed for 1312RE board manufactured at 30 m/min Board-line speed is 1.875 m/min. Ideal Dryer Chain speed for 1312FR board manufactured at 22 m/min Board-line speed is 1.375 m/min. This means that gap between boards in the Dryer is approximately up to 500 mm when Board-line speed is changed but Dryer Chain speed is not. This change in gap will affect temperature profile of the Dryer. TIC9000 and TIC9020 will maintain calculated temperature but heat exchange between hot air and board will be reduced prompting Dryer to close natural gas valve resulting in reduction to the inlet temperature. Due to reduced heat exchange, outlet temperature will climb up. Excessive temperature at the exit of the Dryer very often results in board calcination. There is no strict point determined as for what exact temperature results in calcination but it is commonly accepted that outlet (exit) temperature in Dryer Zone 2 must not exceed 120oC for extended period of time.
Graph demonstrates different temperature profiles for different conditions:
Temperature profiles presented in the graph on the left side were recorded in our plant under different Dryer conditions (Dryer loading).
It is important to note that readings for TIC9000 and TIC9020 are identical under all four different conditions. These values are NOT MEASURED but rather CALCULATED. Dryer will change natural gas valve opening in order to achieve required temperature (Set Point). These changes will greatly affect inlet and outlet temperatures.
Dryer inlet and outlet temperatures for Zone 1 and Zone 2 can be monitored in Conductor NT.
Dryer inlet and outlet temperatures for Zone 1 and Zone 2 can be monitored in Conductor NT .
Introduction of excessive gap in the Dryer will reduce our abilities to control inlet and outlet temperatures greatly.
All above temperatures are for the air flowing through the Dryer – NOT FOR THE BOARD ITSELF. Board temperature is much lower due to the evaporation process. Generally speaking – board is protected form calcination as long as there is moisture inside the core and evaporation is not finished.
Every change to settings made during Core Mix and Drying phase is recorded in Conductor NT. This is an excellent opportunity to analyse changes and their impact on the outcome.
Two changes of this type have been recorded and scrutinized to find out reasons for success or failure. These are changes performed on 03/11/2007 and on 16/01/2008. First change resulted in some loss of product due to calcination (delamination and soft edges). Amount of rejected product was just under 300m2. This is also the first change of this type that was closely scrutinized in terms of additional testing of the product at the Dry End Transfer. Second change was successful and additional testing returned all positive results.