One of the main topics of cotton growing season conversation all across the Cotton Belt has been way too much or way too little water and what to do about it. This month, I want to talk about water in cotton and handling that seed cotton in the gin. All cotton gins are equipped to handle too much water by some type of seed-cotton drying, and most are equipped to handle too little water by some type of moisture restoration.
Drying and/or moisture restoration both can significantly affect fiber quality, must be properly handled, and every ginner out there worth his salt already knows that. I hope every ginner has nothing but smooth running, dry harvested, well-moduled cotton with good covers that have been properly stored and handled, and life is good.
However, for those unfortunates, who, through no fault of their own, are having to deal with significant amounts of wet cotton, and by wet cotton, I mean seed cotton in the range that is spoiling or going to spoil if stored for very long or whose seed is soft and doesn’t crack when you bite on it – I want to talk about some basic drying facts.
Not everyone agrees on the best way to dry seed cotton as there are at least a dozen or more drying systems or system variations that are currently being used in U.S. cotton gins. However, any effective drying system must mechanically open up and keep open the seed cotton to allow heated air to move through the fiber and carry away moisture. In addition, any effective system must allow enough time for this moisture transfer to take place.
USDA-ARS Laboratory tests have shown that heated air at 200 degrees moving through individual locks of seed cotton at 1,200 feet per minute can take fiber moisture from 20 percent to 8 percent in 10 seconds. The point is that it does not take very long or very hot air to dry wet fiber under very open, ideal conditions. However, wet cotton does not come into the gin under ideal conditions and is very difficult to open mechanically.
The only tools with which a ginner has to compensate is to either increase mechanical separation, increase drying time or increase temperature or some combination of these. The machinery arrangement is fixed, so drying time can’t be changed. Cotton feed rate can be decreased, which might help the feed works initially open up the seed cotton a little better – improving drying.
The primary tool a ginner has to use is turning up the drying temperature. Other laboratory research has shown that seed cotton coming into the gin at 18 percent fiber moisture and dried twice at temperatures between 350 and 400 degrees had the same fiber length, uniformity, strength and short fiber content as the same seed cotton ginned at 6 percent fiber moisture and ginned with no heat. The point here is that cotton fiber will not get any hotter than about 200 degrees as long as there is moisture to evaporate and high drying temperatures don’t do any harm other than to your fuel bill.
Once the free moisture is gone, around 5 or 6 percent fiber moisture, then the fibers themselves start heating, and high drying temperatures start doing permanent fiber damage. So, if wet cotton hits your gin this fall, slow down as much as is necessary, turn up the heat as much as your billfold will allow and don’t worry about fiber quality.
You won’t do any more damage than what has been done already by the excess moisture. But hopefully all you have is already dry cotton – so you can keep those drying temperatures and fuel bills low and enjoy the rest of the season.
– Ed Hughs is Director of the Southwest Ginning Research Laboratory in Mesilla Park, N.M. Contact him at (575) 526-6381 or firstname.lastname@example.org.