CSD_PAR 101 - Drying Parameters - An Opening Discussion

Overview

What often appears “simple from afar”, can become much more “challenging up close”.

This can be said of the ear seed corn drying process. This is particularly true if your drying process utilizes a Double Pass Reversing (DPR) Dryer.

There are a number of parameters that either contribute to, or detract from, the methodical removable of moisture from ear seed corn. These all come into play and interact in the drying process. Ambient weather, ear corn physiology, dryer design, drying procedures and other factors all introduce “variability” that affect the drying process.

To achieve drying consistency and predictability, these variables must be managed by being controlled, compensated for or considered as part of the execution of the drying process.

In this article we will identify and discuss drying parameters, their effect on drying and the dryer operator’s options to mitigate their variability.

Controlled, Compensated, Considered

Predictability is “key” in the optimum management of the ear seed corn drying process.

Predictability is the ability to “know” that a bin of seed is dry when we arrive at the end of the drying process. It is also the ability to “know when” the bin of seed is “expected” to be dry at the beginning of the drying process.

Predictability is achievable by managing the drying process with consistency. We often express this concept by saying that ‘if the same seed is dried in the same dryer with the same drying procedures, it will dry in the same way'.

Sounds simple.

To achieve consistency, the dryer operator needs to first recognize and understand that there are numerous parameters and factors affecting the drying process that act as “variables” in the “formula” to achieve drying predictability.

Secondly the operator needs to know how to address each of them as they are encountered.

To achieve optimum consistency, variability needs to be held to a minimum. Some variability of parameters and factors are within the operator’s ability to either control or compensate for while other factors are not. Those that are not must be taken into consideration in the management of the drying process. An explanation of what is meant by Control, Compensate or Consider is given below.

Controlled - A Controllable parameter or factor would be one that the dryer operator is able to dictate. Examples include Fan-Burner System (FBS) heated air temperature or bin fill depth.

Compensated - A Compensated parameter or factor would be one that the dryer operator is able to compensate for by changing another parameter or factor that is controllable. An example of this might be compensating for high air volume humidity by increasing air temperature and/or air flow.

Considered - A Considered parameter or factor would be one that the dryer operator is neither able to control or compensate for. Uniformity of Bin Fill Depth is an example of this. Bin Fill Depth must be managed when the bin if first loaded. If at the end of the drying cycle the Bin Fill Depth is not uniform, it is not easy to correct or compensate for. The dryer operator must now take this adverse factor into consideration when predicting the final Drying Events of this bin.

Depending upon the level of automation, some parameters and factors may, or may not be, within the ability of the dryer operator to either control or compensate for.

Airflow would be a good example of this.

Without some form of airflow control via Fan Speed Control or Air Flow Control Doors, airflow is limited to the volumes defined by the basic dryer design.

The Benefit Of Predictability

Before we proceed further with the discussion of drying parameters, we will provide an example of the benefit of Predictability achieved through Consistency in the drying.

Maintaining Dryer Airflow Balance can be challenging. In a Double Pass Reversing (DPR) Dryer, it is necessary for there to be approximately the same number bins configured as UP Air as there are bins configured as Down Air. This “stands to reason” considering that a goal in managing the DPR dryer is to have similar airflow in all bins regardless of direction.

The state of the 24 Bin DPR dryer illustrated in Figure 1 is considered “balanced” in that there are 11 bins configured as Up Air Bins and 11 bins configured as Down Air Bins. Assuming the bins have uniform fill depths, the airflow through all the bins are approximately the same.

What is not readily apparent is “where the dryer is headed” regarding Airflow Balance. The number of bins on Up Air and Down Air at any given time “tells you where you are at”. The Remaining Hours on Up Air and Down Air “tells you where you are headed”.

Remaining Hours on Up Air and Down Air are values acquired by being able to “predict” when Drying Events such as Reversal and Shut Off will occur.

Consistency is needed for Predictability.

In reality, the 24 Bin DPR dryer illustrated in Figure 2 is headed toward and “unbalanced” condition.

Even though there are 11 bins configured as Up Air Bins and 11 bins configured as Down Air Bins, there is an “imbalance” in the Total Hours Remaining for Up Air Bins and Down Air Bins.

Unless corrective action is taken, there will soon be an excessive number of Down Air Bins resulting in non-uniform airflow and drying. Predictability is needed to be able to see this condition coming and take action to mitigate it before it gets “out of hand”.

Drying Parameter Categorized

We can separate drying parameters and factors that have an effect on the drying process into four basic categories as follows:

• Seed Characteristics
• Weather
• Dryer Design
• Drying Procedures

Seed Characteristics - This includes characteristics that are both “static” to the seed which are inherent to the seeds physiology and those that are “dynamic” to the seed such as those affected by the growing season (i.e. seed set) and harvest strategy (i.e. harvest moisture).

Weather - Primarily this is the dynamic nature of the moisture content of the air volume. Dryer air temperature is controlled via Fan-Burner Systems (FBSs), but moisture content must be compensated for or considered in the management of the drying process.

Dryer Design - Unlike people, all dryers are not created equal” . This is true of the fundamental dryer design which defines air flow velocities in ducts and tunnels. The design of these dryer components can affect air distribution between bins. Similarly the design of the bin “inlet to floor” area ratios will affect air dispersal through the seed piles and there are other dryer design nuances that effect dryer performance. Also, the design of the dryer sub-systems such as the heated air delivery system, airflow control and automation have significant impact on the dryer operator’s ability to control and/or compensate for variables in the drying parameters and factors.

Drying Procedures - The amount of “detail” there is in seed drying procedures and how consistent they are adhered to, has a significant effect on how the seed dries. This begins with bin loading practices, and includes procedures such as bin reversal decisions, dryer airflow balance management and many other seed drying procedures. These procedures all “come into play” in defining how consistent each bin of ear seed corn dries through the harvest seed drying operation.

Drying “Degrees Of Freedom”

The term “Degrees Of Freedom” can be simply defined as “independent variable factors affecting the range of states in which a system may exist”.

The more factors that are “free” and not controlled in a “system” the more dynamic the “system” becomes. Another way to express this concept would be ‘the fewer variable factors that a system has, the easier it is to manage’.

Applying this to the ear seed corn drying process, we can seed that with four basic categories of Drying Parameters, each having multiple parameters and factors that are variable that the number of “degrees of freedom” compounds.

These parameters and factors may at sometimes “work against each other” to counterbalance their individual effect and the drying process experience appears to be “typical”. At other times these parameters and factors “work with each other” to create a compounding effect that results in an “unusual” condition or issue with the drying process.

Drying Predictability “Windfall” Benefits

In the broader operational scope of seed corn production, predictability of the drying process benefits other areas of the harvest operations.

The Drying Operation is often considered the “bottleneck” of production “flow” during seed corn harvest. The Field Operation is often managed based on the availability of dryer bins and the Shelling Operation is subject to the rate of bins of seed completing the drying process.

The benefits of uniform and predictable dryer throughput have a significant impact on the efficiency of other operations happening concurrently in the seed corn production process.

Summary

From our introductory discussion of Drying Parameters, we see that there is “more than meets the eye” when it comes to the number of parameters and factors that are variables that can and need to be managed in the ear seed corn drying process.

The discipline to identify and address these variables with a goal to create consistency in the drying process will result in confidence and effectiveness in the overall management of your Dryer Operation.

Before we can manage these drying process parameters and factors, we must understand their effect on seed drying and the methods available to mitigate these effects. This will be the focus of our next SDU article CSD_PAR 201 - Drying Parameters Defined.

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