Page 101 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 3 Biomass Characteristics 79

3.6.4.1 As-Received Basis
When using the as-received (ar) basis, the results of ultimate and proximate
analyses may be written as follows:
Ultimate analysis: C 1 H 1 O 1 N 1 S 1 ASH 1 M 5 100% (3.22)

Proximate analysis: VM 1 FC 1 M 1 ASH 5 100% (3.23)
where VM, FC, M, and ASH represent the weight percentages of volatile
matter, fixed carbon, moisture, and ash, respectively, measured by proximate
analysis, and C, H, O, N, and S represent the weight percentages of carbon,
hydrogen, oxygen, nitrogen, and sulfur, respectively, as measured by ulti-
mate analysis. The ash and moisture content of the fuel is the same in both
analyses. “As received” can be converted into other bases.

3.6.4.2 Air-Dry Basis
When the fuel is dried in air, its surface moisture is removed while its inher-
ent moisture is retained. So, to express the constituent on an air-dry (ad)
basis, the amount is divided by the total mass less the surface moisture.
For example, the carbon percentage on the “ad” basis is calculated as:
100 C
C ad 5 (3.24)
100 2 M a
where M a is the mass of surface moisture removed from 100 kg of moist fuel
after drying in air. Other constituents of the fuel can be expressed similarly.

3.6.4.3 Total Dry Basis
Fuel composition on the “ad” basis is a practical parameter and is easy to
measure, but to express it on a totally moisture-free (td) basis, we must make
allowance for surface as well as inherent moisture, M i . This gives the carbon
percentage on a total db, C td :
100 C
C td 5 (3.25)
100 2 M i
where M is the total moisture (surface 1 inherent) in the fuel: M 5 M a 1 M i .

3.6.4.4 Dry Ash-Free Basis
Ash is another component that at times is eliminated along with moisture.
This gives the fuel composition on a daf basis. Following the aforementioned
examples, the carbon percentage on a “daf” basis, C daf , can be found.
100C
C daf 5 (3.26)
100 2 M 2 ASH
where (100 2 M 2 ASH) is the mass of biomass without moisture and ash.