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Are you overdrying your product simply to ensure that it is dry enough? An in-dryer moisture-content sensing and control system may offer a way to control your dryer based on the feed's moisture content without dead time in control response.
Industrial dryers - no matter how effective they are in drying solid materials - are incapable of maintaining product target moisture content (MC) at the lowest level practicable when evaporative-load changes to the dryer occur. Why? One big reason is that most dryers are controlled using moisture-content data obtained too late to be effectively used in a control system. Long dead times (time to detect an evaporative-load disturbance entering the dryer) produce proportionally wider moisture-content variations.
What does this mean for most dryer operators? Lack of effective moisture- content control forces operators to run at lower target moisture-content levels to avoid producing wet product. This is a costly practice that results in less production, higher energy costs and poorer product quality.
3 Most Common Problems with Moisture Sensing and Control
After viewing many drying operations over nearly 30 years, my experience has shown there are three common problems with currently used (PID-based) systems for moisture sensing and control. These problems prevent recovery of the above-mentioned productivity losses. They are:
* Long dead time due to a lack of timely, accurate and reliable moisture- content data upon which to make control decisions.
* Inadequate evaporative-load sensors, which result in problems sensing the moisture content of wet feed.
* Lack of a simple, precise method for continuously calculating a new process- variable setpoint to maintain the target moisture content following an evaporative-load change to the dryer.
Each of the three main problems and potential solutions will be discussed.
Inadequate Access to Timely Moisture-Content Data
Long dead time is one of the three major problems that prevent effective moisture-content control. This is not a new...