Managing temporary grain piles
Nov. 7, 2013
Temporary grain piles require careful management to ensure that the quality of grain put into the pile remains the same. In most cases this requires a different mindset than grain put into permanent structures.
There are two very important issues in maintaining the grain in these temporary piles. The majority of these piles employ some type of cover. For both types the main method to try and maintain grain quality is aeration. Without covers it is impossible to protect the grain from weather. High quality aeration will help to limit the damage done by rain. If at all possible, the grain should be run through a cleaner prior to putting it into the storage pile. This makes it much easier to get proper aeration to the grain. In uncovered piles, a pressure system should be used to ensure that you are not drawing moisture down into the pile. I have talked about proper design in previous articles but it is good to cover the basic principles again.
The minimum amount of air supplied should be 1/10th to 2/10th CFM per bushel. The higher airflows will help to offset some of the moisture that is added to the grain pile from rain. But just supplying the amount of air is not enough by itself. The system must be designed to give a good uniform distribution to the grain pile. In the majority of cases, round perforated tubes will be used to supply the air. The size, number and spacing of the tubes is very important in getting good uniform air distribution. The best results will be obtained if the pipe velocities can be kept under 2,500 fpm (feet per minute). Higher velocities lead to higher static pressures and less air entering the pile at the entrance end of the tube. At 4,000 fpm you are adding 1 inch of static pressure to the fan.
The air velocity coming out of the pipe should also be in the range or 30 to 40 CFM per square foot of surface area. For a round pipe setting on the floor (base), you should use 80% of the surface area because part of the pipe is blocked by the surface it is resting on. As an example, an 18-inch diameter round pipe will have 1.75 square feet of cross section. At 2,500 fpm you could use a fan delivering 4,400 CFM of air. The surface area per foot of length is 3.77 square feet. At 40 CFM per foot of length you could supply a 30-foot-long pipe. At 30 CFM per foot you could supply a pipe 40 feet in length.
The spacing of the pipes is also another critical factor in providing uniform air distribution. With temporary piles of grain we do not have uniform depth. This complicates the ability to get uniform airflow if the system is not properly designed
If the perforated pipe is started too close to the edge of the pile, more air travels through the reduced depth than through the deeper grain mass in the center. You should therefore consider using solid pipe for the first three to five feet into the grain pile. The other factor is how close to put the pipes together throughout the length of the pile. The distance that the air travels vertical and horizontally added together should not exceed 1.5 times the hypotenuse. Let’s assume that the center of the pile is 30 feet in depth. We space the tubes 30 feet apart so the horizontal distance the air flows is 15 feet.
Adding the two together gives a figure of 45 feet. The hypotenuse for this example would be approximately 34 feet (34 x 1.5 = s 51). Let’s move farther down the pile to a depth of 10 feet. The two added together is 25 feet. The hypotenuse in this example would be 18 feet (18 x 1.5 =s 27). In both examples, the spacing of the pipes would be acceptable for making sure that all of the grain is receiving aeration.
Covered piles present a different challenge to aeration. The reason for covering the pile is to eliminate the affects of rain, snow and the outside elements. Part of the challenge of maintaining the grain is to ensure that the cover remains intact and does not allow outside moisture to enter the pile. The cover also increases the challenge of monitoring the condition of the grain.
The majority of the covered grain piles employ a down draft (suction) type of aeration system. This is done to keep the cover from being damaged in wind conditions. The other reason is just the sheer effort that is required to keep the cover in place if positive aeration is used. While this can be accomplished, it is much easier to use a down draft system that holds the cover down.
The important thing to consider when using the down draft system is how you will get the air properly distributed to the grain mass. If this is done properly, you will not need to worry about keeping the cover in place. You must consider how to keep the cover in place if you are not running the aeration system. We have all seen pictures of hundreds of tires lying on the cover, but you should consider the use of other methods if practical.
The labor cost of placing and removing the tires can be relative high. In extremely high winds, these may not be sufficient to keep the cover in place. Many of today’s covers have ropes sewn into the seams that can be used to tie the cover down. Depending on the wind conditions at your site, you may want to consider additional ropes or straps between the existing ones in the cover.
When using covers over the pile, how do we get air into the pile? Several companies use round perforated tubing under the covers to get air into the grain pile. This is a good practical method if properly designed. Remember that the same rules of velocity and distance apply in this case also. The fans can then be placed into the sidewall to pull the air through the grain and exit the fan or tied into tunnels or pipes on the bottom of the pile.
There are also systems that have perforated sidewalls and a center fill system. The fans are located so that all of the air comes through the sidewalls and exits through the center fill area. The biggest challenge here is to be sure that the entire grain mass is getting the proper amount of air. Round piles of this type are easier to work with than rectangular or round ones.
Even though you have cleaned the grain, installed a good aeration system and put a good cover on the pile, you still have to properly manage the system. Maintaining a weather type cover is a must. If rain or snow gets into the grain through a compromised cover, what should you do?
While one can see that at 40 degrees F you have an adequate number of days to move the grain, once the grain gets wet two things start to happen. As the moisture increases, the temperature also increases. You could rapidly see the grain going out of condition in just a matter of days if the cover is breached and rain or snow gets into the grain pile. If this happens, do you have a plan on how to handle this situation? Setting up a plan ahead of time may be the difference between limiting the amount of loss to a small percentage of the grain in storage or having a very expensive loss.
Paul Doubele of Canamer International recommends putting dampers on the intake air tubes. This makes it possible to direct all of the aeration air to the location closest to the breached area or one where increased temperatures are found. By doing this you have increased the airflow to that area, which may offset the problem of temperature increases and might even dry the grain that has been re-wetted. Doublele also considers some type of a filter on the tube intake to eliminate possible insect infestation.
In the event that you can’t adequately aerate the grain at the trouble spot, do you have some method of moving or isolating the grain from that area? While this could be a very difficult task, it might be the best approach to limit your potential loss.
Scott Chant of Dayton Safe Grain and Doubele agree that the most important part of managing your temporary grain pile is having a proper designed aeration system. Equally important is maintaining the integrity of the cover.
Harmon L. Towne is retired from Brock Manufacturing where he was vice-president of engineering and product development. He can be reached at firstname.lastname@example.org