ARB and ADB are very common terms for a veteran Coal Supplier/Trader/Consumer. Yet we find that certain coal consumers are not aware of the difference between these 2 terms.
For example, We receive inquiries for Coal, having specification of 7500 KCal/Kg GCV. Yet upon asking the Basis, the traders seems confused. As a result, more often than not a few traders sell coal by claiming it to be of higher GCV when infact the difference between the 2 sample is simply the way the information has been presented.
In short, a coal having GCV 7200 KCal/Kg and GCV 7600 KCal/Kg MAY be both similar. The difference might be only that the former has been quoted on ARB basis and the later on ADB basis.
ARB puts all variables into consideration and uses the total weight as the basis of measurement. ADB (air-dried) basis neglect the presence of moistures other than inherent moisture unlike ARB which uses total moisture. This results in different measured GCV on different Basis.