Improved Multi-Zone Kiln Control

[drying]

Previously, a question was asked if there were any improvements in TDAL kiln control.  An improved multi-zone kiln control system has been developed and validated by several applications on Southern Pine.  This method was made possible by derivation of the Delta T mathematical model for batch drying that relates the lumber moisture to the temperature drop (delta t or TDAL) and to the drying time.  In order to remove the error from the (delta t/TDAL) process variable, the model must be differentiated with respect to time for each zone to convert to drying rate.  This process eliminates the error in the (delta t/TDAL) term, and supplies a comparison parameter (drying rate) that is comparable from zone-to-zone and charge-to-charge.  Thus true zone control is achieved for multi-zoned kilns.  In addition,  by continuously calculating  and displaying  zone drying rates, the Fiber Saturation Point (FSP) of each zone is detected,  which enables the correct amount of heat  applied to each zone and at the proper time.  This reduces over drying of the driest zones and under-drying of the wettest zones.  As a result, production rate is increased by reducing total kiln drying time, lumber quality is improved by significantly reducing over-drying, and energy is saved as a result of these improvements.