How Does GCV Differ Between ARB and ADB?

the moisture content of the sample plays a critical role. This is where the concepts of ARB (As Received Basis) and ADB (Air Dried Basis) come into play. Both are used to calculate GCV, but they have notable differences based on how moisture is accounted for.

1. ARB (As Received Basis)

• What It Means: GCV on an ARB basis refers to the calorific value measured while the sample is in its natural state—exactly how it was received, with all its moisture content intact.

• Impact on GCV: Since ARB GCV takes into account both surface and inherent moisture, the value tends to be lower because the moisture essentially "dilutes" the energy potential of the fuel. In simple terms, the more water present, the less efficient the energy output.

2. ADB (Air Dried Basis)

• What It Means: GCV on an ADB basis is measured after the sample has been air-dried to remove most of the surface moisture, while still retaining the inherent moisture content. The air-drying process reduces the overall moisture content, giving a more consistent sample for energy analysis.

• Impact on GCV: Due to reduced moisture, the GCV on an ADB basis is generally higher compared to ARB. Less water means more concentrated energy content, hence providing a more realistic picture of the potential energy yield during combustion.

Key Differences:

• Moisture Content:

o ARB: Includes total moisture (both surface and inherent).

o ADB: Includes only inherent moisture, after removing surface moisture through air-drying.

• GCV Value:

o ARB GCV: Typically lower due to the dilution effect of total moisture.

o ADB GCV: Higher since it measures after some of the moisture has been removed, resulting in a more energy-dense calculation.

Illustrative Example:

• Suppose you have a sample of biomass:

o GCV (ARB Basis): 3,800 kcal/kg 

This value reflects the energy content considering all natural moisture, which lowers the effective energy.

o GCV (ADB Basis): 4,200 kcal/kg 

After air-drying the sample, the moisture content is reduced, which results in a higher energy content.

Why Does This Matter? The choice between ARB and ADB depends on your purpose. If you need to know the energy value for a sample as it is transported and stored (with all its moisture), then ARB is the appropriate measure. If you want a more controlled value for combustion analysis, ADB is more suitable since it considers reduced moisture.

In short:

• ARB: Reflects energy in its natural, "as-is" state. Lower GCV due to more moisture.

• ADB: Reflects energy after air-drying. Higher GCV with less moisture interference.