Page 106 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

84 Biomass Gasification, Pyrolysis and Torrefaction

The volume fraction of a gas can be found by noting that the volume that
1 kmol of any gas occupies at normal temperature and pressure (NTP) (at 0 C

3
and 1 atm) is 22.4 m . So, taking the example of hydrogen, the volume of
3
1 kmol of hydrogen in the gas mixture is 22.4 nm at NTP.
The total volume of the gas mixture is V 5 summation of volumes of all con-
3
stituting gases in the mixture 5 P ([number of moles (n i ) 3 22.4])/nm 5 22.4n.
The volume fraction of hydrogen in the mixture is volume of hydrogen/total
volume of the mixture:
22:4n H n h
V H 5 P 5 5 x H (iv)
22:4 n i n
Thus, we note that:
Volume fraction 5 mole fraction
The partial pressure of a gas is the pressure it exerts if it occupies the entire
mixture volume V. Ideal gas law gives the partial pressure of a gas component,
i,as
n i RT
P i 5 P a
V
The total pressure, P, of the gas mixture containing total moles, n,is
RT
P 5 n
V
So we can write:
n i p i v i
x i 5 5 5 (v)
n p V
Partial pressure as fraction of total pressure 5 mole fraction 5 volume fraction.
The partial pressure of hydrogen is P H 5 x H P.
The molecular weight of the mixture gas, MW m , is known from the mass
fraction and the molecular weight of individual gas species
X
MW m 5 ½x i MW i Š (vi)
where MW i is the molecular weight of gas component i with mole fraction x i .

SYMBOLS AND NOMENCLATURE
ASH weight percentage of ash (%)
C weight percentage of carbon (%)
specific heat of biomass (J/g K)
C p

C pθ specific heat of biomass at temperature θ C (J/g C)
specific heat of water (J/g K)
C w
pore diameter (m)
d pore
emissivity in the pores ( )
e rad
FC weight percentage of fixed carbon (%)