In the last blog post, we talked about how the buildup of fines and red dog can reduce dryer capacity for screen dryers. In this post, we want to continue the discussion and look for a way to tell if you are losing capacity.
Here is the most obvious way to see if you are losing capacity: You will see the moisture leaving the dryer increasing over time, requiring you to reduce the discharge speed to achieve the desired moisture target (the grain has to stay in the dryer longer for the same inlet moisture). The normal temptation here would be to increase the temperature to get the rate back up again, but this could have implications for quality.
For example, at the beginning of the week let’s say the average discharge rate was 30, and at the end of the week, the discharge rate has fallen to 24 because of buildup. This results in a 20 percent loss in throughput.
The reduction in capacity can also have an impact on electrical consumption—as you could see higher electrical usage from increased power usage by the fans, due to higher back pressure. This can negatively affect product quality as well, as the increase in air velocity contributes to faster moisture removal over a shorter period of time, possibly further stressing the kernels.
In order to get back to full capacity it is usually necessary to have a shutdown period while you wash down the upper portion of the dryer.
Obviously, it is not always possible to shutdown and clean when trying to keep up with the incoming product in the peak of the drying season, but as often happens there is a trade off from continuing to run with less than full capacity.
Also, remember that you will want to pay particular attention at the start of the season when high moisture product may require you to clean more frequently.
It may be a bit hard to believe, but we have actually seen cases where a dryer has lost up to 50 percent of its capacity! We don’t want to see this happen to anyone so in this post, and the next one, we will talk a little bit about maintaining dryer efficiency.
Let’s start with the basics. Maintaining maximum air flow is the key to efficient performance. Because drying grain involves hot air passing through the grain, anything that reduces this air flow impacts performance.
With screen dryers, a great deal of moisture is expelled from the top few feet of the dryer. Much of the easy-to-dry product such as fines, broken kernels, chaff (red dog or bees wings) loses the bulk of its moisture here. These particles then tend to get pushed through the screen to the outside where they build up as a wet mess and stick to and plug the screens—thereby reducing air flow.
Over time, this wet section will steadily move further and further down the dryer as the screens in the higher portion above it plug up. This process gradually reduces the effective capacity of the dryer, and when drying capacity is lost, drying efficiency is reduced.
One way to slow this process is to clean the product ahead of drying. This will reduce the broken, fines, and red dog (bees wings) which tend to plug the screens.
This entry was posted in Control Technology, Moisture Sensors and tagged agriculture, bees wings, canada farming, canada grain dryer, coffee, corn, dryer master, drying, farming, grain dryer, grain moisture, midwest grain, north america grain, red dog.