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Dryer Optimization: Be Smarter Than Your Dryer - continued

Operations
Let’s discuss the physiology of grain. A basic understanding of the principles of heat, air, and time helps the operator to control and anticipate results from the drying process. With all current technology regarding controls as well as mechanical improvements in the drying process it is still undisputed that the general mechanics of removing water from grain is a function of the level of heat (BTU’s), the volume of air (total CFM), and the time to pass through the dryer (holding capacity). At a given drying temperature with a given volume of drying air a put through rate can be anticipated based on the retention time in the drying section of the dryer. It is important that the operator know this holding capacity as it reflects to length of time to affect a change in the output moisture from the dryer. Example: If it is known that heat holding of a dryer is 2,500 bushels and the dryer is discharging at 2,500 bushels per hour, the operator cannot expect to see the results of the initial or any additional adjustments in the operation of the dryer for at least one hour. Too often operators tend to rush their management decisions of the dryer resulting in longer than desired time to achieve target output.

As the operator is making changes to any of the dryer inputs it is important to reference the relationship between drying temperature and kernel temperature. In most cases it is the kernel temperature that you are ultimately trying to manage but very seldom do you have the ability to monitor this temperature throughout the drying process. The higher the kernel temperature the more susceptible the grain is to physiological damage. High kernel temperature results in faster migration of moisture to the atmosphere (higher capacity put through) but it will most likely result in a higher percentage of stress cracking and additional breakage of final product from mechanical handling through the facility. Reducing the temperature of a high temperature dryer to result in the most acceptable capacity rates for the facility will net more dry matter (drying shrink) and less total breakage to the final product (total shrink). Let it be noted that most United States grain facilities today consider shrink management as a total separate profit center in the overall operations of their business.

Humidity
One additional factor affecting the drying process is the outside relative humidity. Let it suffice to say that this variable is very difficult to manage. First of all, there is no way to control or predict what humidity levels will be at any given time. It is known that the higher the humidity of the outside air the less ability a given cubic foot of drying air has to carry water. Therefore if you are expecting a given CFM of air at a given temperature to remove a given amount of water in a set amount of time, you can expect that as the outside humidity increases so will the amount of time needed to dry. This can be offset by an increase in drying temperature which in turn taxes kernel temperature. This may sound like a chase your tail phenomenon but it should be noted that this effect normally is not a serious issue unless the humidity is 85 to 90 percent or higher. The operator should then be aware of the results and manage the discharge rates accordingly.

Drying temperatures and efficiencies are also an elusive subject. In fact, the higher the drying air temperature the greater ability the air has to remove water. Therefore, a reduction in drying air temperature to reduce fuel usage may not, in fact, use less fuel if the grain needs to remain in the dryer longer. Operator management should again focus on the optimum temperature to achieve the desired grain quality (managing kernel temperature) as well as an acceptable drying rate for the facility. Keep in mind here the mistake is often made to let dryer capacity be the leading factor in temperature choice. With today’s energy costs it is difficult to not let efficiencies become the next driving force. Align the operations of your dryer with the expected outcome of your facility and make your adjustments accordingly.

Expected outcomes of the facility will be determined by type of grain being dried and any specialty crops requiring extraordinary kernel temperature management. This can be varied with the initial moisture content of the incoming grain. Managing the uniformity of kernel temperature can be a positive tool as well. Some grain dryers are equipped with devices to turn or alter the flow of the grain to more uniformly maintain kernel temperature. As a result, the negative effects of cooling the grain with colder outside temperature can be diminished.

One final note to offer the operators as a tool to manage the effects of kernel temperature in today’s dryers is the effect of tempering the grain. It is argued that tempering grain is a function of hours in the drying process, not minutes in the drying column. When tempered properly, however, the results are very positive. The pro’s of tempering grain can result in less stress cracking, higher utilization of energy, reduction in dryer shrink, and increased capacities through the dryer. However, the major setback for this tool is that it requires downstream cooling of the grain as well as additional transfer between the drying process and long term storage. Today’s modern grain facilities often lack the design to manage the flow of grain in this fashion. With the rising costs of energy and the potential on the rise for higher standards of grain, further design research is warranted in this area.

Maintenance or Subsistence?
The value of maintenance of any piece of equipment has been argued successfully for all industries. The value of true maintenance versus just fixing to get by is often circumvented during the rush of the season or the time left in the day. Prioritizing levels of maintenance along with good record keeping can assist in achieving a true maintenance regime.

Inspections of the grain dryer should be based on four values. Cleanliness, Functionality, Integrity and Safety. It is recommended to prioritize these values consistent with the management and facility guidelines. If you apply these values to each aspect of the dryer from electrical, fuel, mechanical, and structure you will have a solid true maintenance program. Example: Cleanliness. Is the equipment or component clean? Functionality. Is the equipment or component functional? Integrity. Is the equipment or component in good working order? Safety. Is the equipment or component safe? Although these questions may seem academic, by requiring a simple yes or no response on a checklist forces the operator to take a black or white position and not compromise his response. Supervisors can then require action based on a yes or no answer consistent with the facility guidelines.

Now the supervisor or manager can apply set priorities. Example: Can equipment be safe but not clean? Can equipment lack integrity but be functional? Can equipment be functional, yet not safe? Some of the answers to these questions can be obvious, yet others force the supervisor to a call for action. We all want to require safety to be our number one priority and most cases advocate it in our daily routines. Lack of facts or knowledge of a problem is often the first excuse for an incident. If your true maintenance plan is intact you will avoid accidents, downtime, and more costly repairs.   Continued >>

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