Hi everyone, I’ve built a few (unpowered) seed dryers, but they are all similar, and small scale - ramp which heats up air, travels through mesh shelves, and out the chimney. These are great for small quantities of seed, but I’m wondering whether anyone has a really large-scale seed dryer design? We work with massive quantities of tree seeds of various sizes, so something more on the lines of a seed drying walk-in shed would work better. Thanks in advance. Beth.
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Hi Beth! Do you have electricity? Or does it need to be a passive solar drier?
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Passive. Plenty of heat and sunshine around, and no electricity option
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I don’t have any experience with walk-in seed drying sheds, but I know at ECHO Asia they have a portable seed drying frame with metal grates/shelves in it to dry larger amounts of seed. @Patrick_Trail do you have any ideas or input for Beth?
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Hi Beth,
Here in Senegal, we’ve built a large walk-in dryer for Moringa leaves. The top and sun-facing walls are made of roofing sheets painted black. We added a glass-topped tunnel at the inlet for additional heating.
It’s designed for use with the trolleys used by bakers, each holding up to 20 perforated baking sheets.
The original design was fully passive, using the updraft created in a large chimney (8-10 barrels stacked) to draw air through the tunnel. It worked adequately, but we soon found that we were able to get much faster drying times and higher throughput by adding fans. I was originally resistant to the idea (I love the elegance and adaptability of fully passive), but a fan or two has a huge impact on your ability to dry a lot of material by evacuating humid air from the dryer. A few panels are usually adequate, and with the quickly dropping cost of solar, this will usually be a relatively minor part of overall dryer costs. (The energy needs of fans are also quite small compared to those of electric heating element in commercial drying units). This dryer has been running well for us (now with the chimney replaced by an exhaust fan) for about 4 years.
For leaf products like moringa, we usually achieve completely dry leaves within 24 hours. Temps usually peak around 50 C, but this could be moderated fairly easily by changing some design elements. During rainy season when the sky is overcast and humidity is high, we rarely dry leaves because drying time stretches past our 24 hour standard, and we risk spoilage. For tree seeds, a somewhat slower drying time might be acceptable. Otherwise, you could perhaps achieve dryer air and faster drying times by heating the air with a low-smoke charcoal fire.
Incidentally, I’m involved in another project building an iteration of this dryer in Zim, up in the Vic falls area. It will be scaled up somewhat, with a ~ 12 m. x 1.8 m. drying tunnel and larger array of fans. I hope to be in country in May if you’d like to come up and see it in action.
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Thanks so so much, the photos and ideas are hugely appreciated. I’m interested why clear plastic was used rather than black plastic.
Amazing! Thank you!! I so appreciate the pictures and design ideas. We’re not working in hugely humid regions, so I’m hoping we can start without a fan, but will keep it in mind to add on if we notice spoilage/moulds/slow drying times. Also extremely keen to link up in May, will see if I can send you a private message with whatsapp number. Thanks again.
So glad to help, I look forward to seeing what you come up with for your context! I’ll connect by WA.
Just a note on the humidity in the dryer: We are in a similarly dry area here (humidity often in the teens during dry season), but even dry air will quickly become saturated inside a dryer if there is enough wet/moist material being dried. Once it is saturated, it becomes useless for drying product, since it has no more capacity to pick up moisture. Obviously, the faster you can move that saturated air out of the tunnel and replace it with dry air from outside, the faster your material can dry. That being said, how quickly your air becomes saturated will depend on the air temperature, humidity of the incoming air, the surface moisture of the product you are drying, how much product is in the dryer, and so forth. You may need a higher or (most probably) lower air circulation rate than we do.
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