Automatic maceral analysis of low-rank coal (brown coal)

Abstract

In the nomenclature system for the macerals of low-rank coal, which has been established by ICCP and already world-wide adopted, one of the macerals, huminite, is divided into three maceral subgroups depending on preservation extent of plant materials. Each of these three maceral subgroups includes several macerals which are also subdivided into maceral-type and further maceral variety, according to their gelification. On the other hand, in the liptinite and inertinite groups of brown coal, there are not so well distinguished physico-chemical differences between macerals of the same group. They are, therefore, not so finely divided as in bituminous coal. In order to save time, and also to avoid personal error, the automatic maceral analysis is regarded indispensable, especially for practical purposes. In the automatic analysis, the reflectance is measured at some fixed intervals (point to point), and the maceral type is then identified from the distribution pattern obtained. However, because the difference of the reflectance for each huminite subgroup is not so significant, the identification of macerals by means of reflectance measurement alone must be uncertain and impossible. It is well known, however, that the higher the reflectance of a maceral, the lower its fluorescence intensity is. Providing the difference between both optical intensities is adequately expressed, it might therefore quite easily be expected that the difference between each subgroup can be emphasized and that their identification becomes easier. In the above-mentioned figure of fluorescence intensity to reflectance ( F o n − R o n), the boundary between macerals is defined by application of Fourier series expansion, and the maceral type of bounded part is identified depending on the several parameters adopted as criteria for each maceral. Comparing the results obtained by automatic analysis with those by manual operation, the hit ratio of identification of huminite maceral amounts to more than 90%. For inertinite and liptinite macerals a similar ratio was established. It could therefore be conclusively said that the automatic maceral analysis of brown coal could be completed using the difference between reflectance and fluorescence intensity.