What is the difference between GCV on an ARB basis and an ADB basis?
ARB (As Received Basis) and ADB (Air Dried Basis) are both common bases used for measuring the Gross Calorific Value (GCV) of coal or biomass, but they differ in how the moisture content is considered. Here is the key difference between the two:
1. ARB (As Received Basis)
Definition: ARB refers to the analysis done on a sample as it is received, with its natural or original moisture content intact. It includes the total moisture that is present when the sample is collected.
GCV on ARB: The GCV measured on an ARB basis takes into account all of the moisture and other components present in the sample as received. Thus, the GCV on ARB will generally be lower compared to ADB since the energy value is diluted by the moisture.
2. ADB (Air Dried Basis)
Definition: ADB refers to the analysis conducted on a sample that has been air-dried to remove most of the surface moisture. The sample still retains inherent moisture, but it is relatively reduced.
GCV on ADB: The GCV measured on an ADB basis is higher than ARB since the moisture content is reduced. This provides a more consistent measurement, as the majority of surface moisture that can significantly vary is removed.
Summary of Differences
Moisture Content:
ARB: Considers the total moisture as received, which includes surface and inherent moisture.
ADB: Considers the reduced moisture after air drying, mainly inherent moisture.
GCV Value:
ARB GCV: Lower, as it includes total moisture, leading to more dilution of the calorific value.
ADB GCV: Higher, as the moisture is partially reduced, resulting in a more concentrated energy value.
These differences are important because the moisture content affects the calorific value directly, and choosing the appropriate basis depends on what aspect of the fuel’s performance needs to be measured or reported.
Example:
Let’s say we have a sample of coal:
GCV (ARB Basis): 3,800 kcal/kg This value is measured considering the total moisture as the coal is received. The moisture is high, which lowers the energy content.
GCV (ADB Basis): 4,200 kcal/kg This value is measured after the coal has been air-dried, reducing some of the moisture content. As a result, the energy content per kilogram is higher compared to ARB.
Explanation: The GCV on an ARB basis (3,800 kcal/kg) is lower than on an ADB basis (4,200 kcal/kg) because the ARB includes all of the natural moisture present in the sample, whereas ADB considers less moisture after air drying.
