Some confusion has arisen with regards to classing biochar as an active carbon or charcoal with regards to shipping and hazardous goods regulations.
Black Earth Products has sold and shipped biochar all over Australia and internationally since 2010 without a single product issue. All of our packaged product is shipped with a minimum 25% moisture content. All our biochar is exposed to oxygen and stored for a minimum of two weeks before sale. We class our product as a packaged soil improver with regards to all transportation regulations.
Black Earth Products Material Safety Data Sheet (MSDS) was prepared by process engineers James Joyce & Associates Pty Ltd and is available here >>>>
Black Earth Products approached Hugh McLaughlin Ph.D., P.E. as an independent expert with regards to the production, handling and transportation of biochar.
Hugh McLaughlin is an expert in the area of biochar properties, biocarbon processing, chemical manufacturing processes and chemical process safety. He has many years of experience developing new processing technologies and implementing those technologies on a commercial scale. Since 2009, he has served as Director of Biocarbon Research for Alterna Biocarbon, Inc., while maintaining his consulting practice at a reduced scope due to corporate obligations.
Considerations relevant to the storage and shipping of Biochar
Hugh McLaughlin, PhD, PE, Director of Biocarbon Research
Alterna Biocarbon website >>>>
December 3, 2012
Every so often, someone manages to get a bag of biochar to start smouldering or build up an elevated temperature during storage, and suddenly the world thinks every bag of biochar needs to be feared like a bomb itching to explode. While it is possible to get biochar to burn, its behaviour during storage and shipping are quite well understood and entirely safe, assuming certain steps are taken to eliminate the potential scenarios that lead to the elusive but undesirable misbehaviour.
As a starting point, biochar is basically a “charcoal-like material” that is intended for use as a soil amendment. Having made that connection, biochar is neither “charcoal” nor is it “activated carbon”. Both charcoal and activated carbon have circumstances that require precautions during storage and shipment, and since biochar shares many properties with charcoal and activated carbon, it is appropriate to apply such precautions to biochar. Once the precautions are addressed, and they will be delineated in the discussion that follows, biochar is no more unstable or dangerous than the compost it is often mixed with.
The one property biochar, charcoal and activated carbon all share is their manufacture under conditions of elevated heat and reduced oxygen – in order to create the “char” backbone of graphitic structures that results in all three materials being black. This conversion process, called “pyrolysis”, removes many non-carbon atoms and yields a more carbon-rich material through a process correctly called “carbonisation”. Any char, no matter if it is intended as a fuel (charcoal), an adsorbent (activated carbon) or a soil amendment (biochar) will react with oxygen the first time it is exposed to it. This initial exposure results in oxygen molecules adsorbing on the internal surfaces of the char and forming surface oxides. The formation of these surface oxides is accompanied by the generation of a small but significant amount of heat. Depending on how large the pile of char is, the heat has to be accounted for, since chars can also be excellent insulators and keep the heat in the pile, resulting in it increasing in temperature.
Notable, it is only the first time a char is exposes to oxygen, typically the first time it is intimately contacted with air. After that initial contact and the uptake of oxygen on those sites inside the char that “adsorb” molecular oxygen from the air, the char does not repeat the process. The sites are full, the appropriate sites within the char are “oxidised”, and the oxygen uptake and heat generation do not occur again.
Biochars that have significant adsorption capacity and activated carbons also exhibit the ability to adsorb water vapour, but the heat generation of this hydration is far less than the heat developed during the initial exposure of fresh char to air. In the manufacture of many biochars, water is used to cool the hot char after it is produced at elevated temperatures. Such a step, especially if it is done at the same time that the char is exposed to air, results in the excess heat of the hot char, the heat generated by oxidation, and the heat of hydration all being removed by the vaporisation of excess water into steam. Once the wetted aerated char is cooled down, it is completely passivated to any potential self-heating scenarios.
So when do chars represent a self-heating risk – essentially only if they are made, isolated, and cooled down without significant exposure to either air or water. This can occur when char are made in retorts that are sealed as they are cooled down, or the char is cooled without contacting it with water and packaged as it exits the carbonisation reactor. For large industrial processes, if the biochar is packaged in sealed 200-l drums or one cubic meter sacks, the char may develop heat when it is finally exposed to air. The classic example of this is the fast-pyrolysis chars produced by processes such as Dynamotive and others. These chars are made under conditions of no oxygen and remain reactive until they are passivated by exposure to air and cooled to remove the heat of adsorption associated with the oxygen uptake.
There are additional circumstances that allow activated carbon to be more reactive than chars, but this results from properties that activated carbons possess and biochars do not. “Activation” is a separate processing step where a char is “activated” using either steam or carbon dioxide at very high temperatures or the addition of chemicals. In addition, some activated carbons have additional chemicals added to increase the treatment capacity, a process called impregnation. Depending on the specific activated carbon and the material that is being adsorbed, it is possible for vapour-phase activated carbon to generate heat during adsorption service. Notably, this is not in storage or during shipment, it is when the activated carbon being used as the industrial adsorbent it was designed to function as.
Similarly, charcoal and some coals, especially if they have excessive volatiles, may have concerns when they are shipped in large quantities. In virtually all cases, bone-dry materials are exposed to a source of moist air and some of the moisture condenses in the fuel, liberating the heat of condensation. If there are volatiles present that vaporise under the mild temperature increase, then the volatiles may initiate a combustion event and everything escalates from there. Please note that several things are necessary: bone-dry fuel containing easily vaporised volatiles, a source of moisture and large volumes to retain the heat of condensation. That is why ships monitor the temperature of fuel piles and wet them down if they start developing heat.
In summary, if a biochar has been exposed to air and contains any significant amount of water vapour (above 10 weight percent is plenty), then the material does not have any self-heating reactions possible under conditions of storage and shipment. Furthermore, if the biochar is sitting in a container and not sealed in a manner that implies that it have never seen any air, then the biochar will not suddenly change its mind and start reacting with either air or moisture – it has been rendered stable and will remain so. By comparison, the plastic bag or cardboard box may represent a risk of fire, if the biochar doesn’t extinguish any such blaze first.
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