Bio-Char

3 Pages of an Article published on Bio-Chars
Hugh McLaughlin PHD, PE
Paul S. Anderson PHD
Frank E. Sheilds
Thomas B. Reed PHD
6.2. Lump Charcoal from Commercial Sources
Conventional lump charcoal was a widespread product prior to WWII, but has been replaced by charcoal briquettes after the war. Currently, most charcoal briquettes are a mixture of powdered devolatilized coal, a small portion of raw or carbonized sawdust, and intentional ash additives – intended to create the “complete charcoal cooking experience.” All that lovely white ash, indicating the coals are ready for cooking, is limestone, straight from the mine.
Nowadays, lump charcoal is a boutique cooking fuel, which is gaining popularity and distributed almost anywhere outdoor cooking supplies are sold, including most hardware stores. It is generally made from clean wood scraps, such as residues from furniture making, and appears as solid lumps that still exhibit the grain of the original wood. While it is not inexpensive, lump charcoal is certainly affordable in the smaller quantities that a home garden might require to achieve recommended biochar levels in the soils of 3 to 10 weight percent of the soil mass in the root zone.
However, an underlying issue remains: Is lump charcoal a good candidate for use as a biochar? Furthermore, there are many varieties of lump charcoal, as can be investigated by visiting a web site called www.nakedwhiz.com. The site reviews the cooking properties of lump charcoals, but was a valuable resource by supplying over a dozen various lump charcoals for testing. This data set was augmented by a large number of varietal charcoals from Real Montana Charcoal, which makes small batches of charcoal from individual wood species. Thus, an additional survey was made of how charcoal varies as a function of the wood species when made within the same basic production process.
The lump charcoals were tested for total mobile matter, adsorption capacity, and relative density. The goal was to judge the relative variability of the charcoal properties and see if any one property could be inferred from another, such as lower density charcoals correlating with higher adsorption capacity per unit weight, etc. It should be noted that for this set of data, the Mobile Matter assay temperature was the coal volatile matter setpoint of 900 degrees Celsius, which removes a small increment of additional volatiles over the previously discussed 450-Celsius setpoint now proposed for the biochar modified proximate and ultimate analyses.
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Mobile matter is an important property in biochar for two reasons. First, there is evidence that mobile matter leaches into the soil and provides a soluble carbon source, which can cause a short-term nutrient deficiency for the plants by stimulating soil microbe growth that competes with the plants for available nitrogen. The mobile matter levels in lump cooking charcoal are a concern because the charcoal is expected to light without the addition of liquid charcoal starter. As such, in order to aid lighting, lump charcoal are often made under carbonization conditions that leave higher levels of low molecular weight volatiles in the charcoal and, thereby, achieve the desired lighting qualities.
Second, the elevated amounts of mobile matter are likely to disappear within a single growing season and not contribute to the long-term properties of the soil. As such, mobile matter portion in biochar is bought and paid for, but represents less long-term value as a soil amendment. Water and ash provide similarly reduced long-term value in the biochar, but most people recognize that situation and purchase accordingly.
In addition to the Mobile Matter assay, Adsorption Capacity was tested because that is a crucial property of biochar that is created at the time of manufacture and unlikely to improve over time. The results of testing 15 randomly selected commercial lump charcoals are shown in Figure 10.
In general, the best of the lump charcoals had adsorption capacities comparable with the biocarbons shown on the right of Figure 8, when the adsorption data is compared at the same adsorption temperature (done by the corresponding author, data not presented here). Unfortunately, the average lump charcoal mobile matter was over twice the average level of 10% for biocarbons shown in Figure 8. Furthermore, it is apparent from Figure 10 that one cannot infer the mobile matter or adsorption capacities based on the relative bulk density, although there appears to be a weak inverse correlation of adsorption capacity and bulk density.
Eighteen samples of Real Montana Charcoal were obtained and tested for adsorption capacity to see how the adsorption capacities vary from species to species of wood, holding constant the specific carbonization process. Figure 11 shows the Real Montana Charcoals adsorption capacity data, plotted in addition to the adsorption capacity data of Figure 10 for commercial lump charcoals.
As shown in Figure 11, selecting within a single carbonization method does reduce the variability of both the relative density and the adsorption capacity. Considering that the average Real Montana Charcoal adsorption capacity was 70% higher than for the selection of lump charcoals, and that only one other lump charcoal significantly exceeded the average of the Real Montana family, it is clear that there is value to be realized by testing lump charcoals for desired properties. Or in other words, the adsorption capacities have been found to vary as much as 700% (a seven-fold difference) between samples of commercial charcoals, and therefore their application into soils as biochars should be conducted with forethought and caution, including measurement of their individual properties prior to soil application.
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FIGURE 10: COMMERCIAL LUMP CHARCOAL PROPERTIES