Precautions For Drying Hemp In A Hemp Pellet Production Plant

Date: 08/12/2020 08:36:35 From: wood-pellet-plant.com Clicks:

What are the considerations for drying hemp? The first question is: What part of the plant? Drying the flower for CBD production is significantly different than drying the straw, which is significantly different than drying the fiber after it has been separated from the hurd, which is significantly different than drying the seeds. The flower is extremely delicate, and the oils can be damaged by heat, whereas the straw and hurd can be dried similarly to wood chips or oriented strands for oriented strand board, depending on end use. Other considerations include the following.

Dryer Material

What material can you use for the fabrication of your dryer? Food-grade typically requires stainless steel. It’s possible the construction of the dryer will be determined by the final use of the hemp and time of year harvested. Harvesting the whole straw for energy after overwintering in the ground solves many problems, including a lower average moisture content. The hemp will be less corrosive, and the final pellets will have a reduced chance of slagging when used for fuel. Carbon steel should be adequate for this ideal harvest. Overwintering will not be practical in all situations, however, especially if the straw or hurd is a byproduct of seed or CBD production. Stainless steel is required if torrefaction is the end goal.

Surface and Bound Moisture

Hemp has potential for both, but most likely will only have bound moisture. The drying medium must not flash the surface dry, but gradually warm the whole particle, driving moisture from the inside out. This can be done with a high-moisture drying atmosphere with high wet bulb temperature, such as created in a recycled exhaust gas system. This particular piece of the puzzle is still under experimentation for drying the flower for CBD extraction. Stay tuned.

Safety

Is this item on OSHA’s combustible dust list? Not yet. It will very likely be added in time, as hemp has a similar Btu content to wood. Depending on dryer type, method and temperature of the drying medium, drying in a low-oxygen environment will be the safest option. A very simple way to create a low oxygen environment is to recycle the exhaust gases.

Susceptibility to Radiant Energy

As an organic material, hemp straw, flower and seed will be susceptible to getting a “sunburn,” so care should be taken to reduce the presence of a visible flame.

Conveyance

Any portion of the hemp plant has relatively low density and is capable of being pneumatically conveyed. This opens up the possibility of concurrent-flow, rotary-drum dryers as well as fluid-bed dryers and flash dryers. All dryers perform better with uniform material, but it is crucial to the functioning of the latter two styles. Mechanical conveying, such as in a belt dryer, is an acceptable dryer as long as the product is uniform and the other drying criteria has been met.

Energy Use

Is natural gas or propane available? Do you need to use electric heat? Can you use waste heat from another process? Are you concerned with energy usage? Recycling exhaust gases will reduce energy use, but the initial system will cost more. Likewise with using waste heat—the system will likely cost more to purchase, but will potentially have a quicker return on investment.

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