Wood volatile matter content

Charcoal yields and the volatile matter content of the charcoal produced decrease with increasing temperature (see figure 2). For willow wood the required diarcoal yield of 0.38 kg/kg dry feed can be obtained at a temperature of 350-400 C, giving a product with a volatile matter content of 30-50 wt,%. In this temperature range 46-60% (LHV-basis) of the energy content of the feedstock is retained in the charcoal. 

C/min. These experiments show the considerable importance of moisture content regarding mass and energy flows the other characteristics are of secondary importance. The results lead to the development of a phenomenological modelling of mass and energy flows of the total volatile matter produced through wood carbonization in retort kilns, based on the logistic symmetric function. 

Figure 2 Evolution of the total volatile matter mass flows according to the moisture content of beech wood samples (anhydrous - HO, wet - H37) (heating rate 2 C/min).

The major fact resulting from the analysis of mass flow from wood carbonization is the general and considerable effect of moisture content on the process. The effect on the factor M of the symmetric logistic function (maximal mass of volatile matter produced at an infinite time) is expected the water present in wood is evaporated and constitutes a part of the volatile matter. It is thus natural to observe a factor M higher for wet wood samples (H37) than for anhydrous samples (HO). 

The cause of this difference could be a possible combined effect of the thermal conductance and the gas permeability. The thermal conductance is the lowest for blocks 16 poplar (see table I) and the permeability to gases is the lowest for poplar. These two factors combined could contribute to delay and slow down the production of volatile matter for blocks 16 of poplar. However, we must stress the fact that the difference between these blocks 16 poplar and the other samples is not that big, although significant in the case of factor a, the difference is S to 6 min for anhydrous wood samples, 20 to 30 min for wet wood samples, when moisture content generates differences between anhydrous and wet samples of the order of 60 min. 

Another approach has been developed in the field of mineral coal research in coke production. This approach is based on the volatile contents of the non-thermally treated material and of the char. As a result of the process of carbonization, the whole volatile matter of wood must be eliminated, except the residual volatile matter contained in the char. Consequently, the theoretical mass yield of carbonization is the ratio between the non volatile matter of the wood on one hand and the non volatile matter of the char on the other hand. The formula is [7] ... 

If the coal used for briquette is rich in volatile matter, the coal has to be carbonized first. Carbonized briquettes are superior to uncarbonized briquettes for the same reasons that charcoal is preferred to fuel wood. The sulfur content is also reduced during carbonization as the sulfur is converted to hydrogen sulfide gas. 

Table I shows the major physicochemical characteristics of wood firom the four main French regions. It highlights the, in some cases striking, differences in the composition of oak wood according to its geographical origin (10). Wood in the Limousin group stood out considerably firom the other types, due to their concentration of extractable, non-volatile substances, especially phenolic compounds. From this point of view, there is relatively little difference between the other regions. Among file four regions considered, oak firom the Center had the lowest content of coloring matter.

As expected, the factor M (maximal mass of matter volatilized) is significantly influenced by the moisture content of wood. The difference between anhydrous and wet wood samples is naturally explained by the quantity of water which has to be evaporated, contributing to an increase of the value of M for the symmetric logistic functions for wet wood samples (H37),... 

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