Are you thinking about growing hemp? One of the most significant questions is how you will dry your material. Here we explain how to build a hemp kiln dryer.
Now that the farm bill has passed, you might be thinking about growing hemp. If you do, you will find it fun, engaging and an extraordinary amount of work. It is, after all, farming. Farmer’s hands look the way they do for a reason.
You have many decisions ahead of you. How will you irrigate? How will you germinate? Plant? Monitor for males? However, the most significant questions you face are how you will harvest and how you will dry your material. We will tackle those questions one by one in this series. We will begin at the end. Because before you know how many seeds to buy and acres to plant, you need to be sure you have the capacity to dry your crop.
Air drying is great. It keeps terpenes intact, and customers prefer this method for a number of products. You will need space, labor, and cooperative weather. You will also need heaters and dehumidifiers depending on your climate.
We like to use both air drying and kiln drying. These methods provide flexibility. One can relieve pressure from the other. Having a kiln dryer is very handy. Ours is small, but it puts out between 400-500 lbs of dry material per day. The dryer cost about $15,000 in materials including freight. Consumables were $1 per pound for electrical and gas. If you have natural gas that number should be lower.
Advantages of having your own kiln dryer
Using a drying service costs about $6 or so per pound. Adding hard and soft costs of having one’s dryer, we were about half that price – and we fully amortized the dryer in that calculation. We see two disadvantages and three advantages to having our own dryer. The disadvantages are noise and space. A big farm should handle both. A small farm might not.
The advantages – 1) We dry to our own specs. Some, but not all services do so. 2) We dry as needed. Drying services often want large volumes delivered at set times. We can feed the dryer as we progress, in small manageable chunks. 3) We control our destiny. Drying services fill up and we want to be in control of that variable.
Hemp needs to be turned over as it dries to prevent hot spots and to dry evenly. We used Oast floor panels from Hops Harvester. The concept is a three-tier dryer column blowing warm/hot air into a chamber in the bottom. Three louvered screen layers are above that. The raw material is dumped into the top. Crews returned to the field for another run. When they return, they drop the top layer to the middle layer, then deposit new material in the top. At the next harvest round, layer 2 drops to tier 3, tier 1 to tier 2, etc. Each drop turns the material over for uniform drying.
Build a Hemp Kiln Dryer
Hops Harvester designs a modular system so you can create a dryer sized for your needs. Dryers can use 2, 4 or 6 panels per tier. 6 panels is the maximum number per tier. If you need more, you will need to build a second unit. Our design used six oast panels per tier, for a total of 18 4′ x 4′ panels. That is 96 SF per tier, and it was just undersized to do about 5 acres. Calculate your needs based on acreage and air-drying capacity. We will add 1 or 2 units for 2019.
Roughly 24 hours after the first load went into the top layer it is done. We place totes in the heat chamber and drop the finished material into totes, then into super sacks. Once you fully load your drier, you just keep feeding the top layer every turn of the harvest crew. By the time you empty each load, it will have been in the oven 24 hours if you keep a consistent schedule.
You will find your own sweet spot in terms of scheduling. Raw green hemp flower should not sit overnight, as composting can begin. You will know if you are cutting it close by sticking your hand in a tote that has
been staged. If it is warm in the center, you are flirting with decomposition. So we only used freshly harvested hemp. The morning crew of 4-6 could prepare a load in 2-3 hours. We targeted 700-750 lbs of wet hemp per cycle. If the crew starts at 7, load #1 is loaded at 10. #2 is at 1:00 and #3 is at 4 pm. That way the dryer stays full and running 24/7.
Our dryer uses a centrifugal fan blowing through a propane burner, then through a transition into the heat chamber. We kept temps at 95F which worked with our long warm harvest season. Consequently, you might need to increase that temperature if weather dictates.
If you are reasonably good with electrical wiring, you can do most of this yourself. However, we learned many things about the system which would make it much easier to install. I would recommend a burner technician to tune the gas regulators and valves. It is money well spent.
To build a hemp kiln dryer, determine the number of panels you need per tier. They will help you select a fan and burner to work with your capacity.
We added a feed to get totes to the top layer and a catwalk to help load it uniformly. Both were critical for heavy usage. Ours is outside, so we added a roof. That was essential as well.
View videos of the dryer in action: