Introduction - Biomass Gasification, Pyrolysis and Torrefaction - page 26

When the gasification product, CO, is burnt subsequently in adequate
oxygen, it releases the remaining 72% (283 MJ) of the heat. Thus, the CO
retains only 72% of the energy of the carbon.
We can also go for complete gasification of a biomass where the energy
recovery is 75

88% due to the presence of hydrogen and other hydrocar-
bons. The producer gas reaction is an example of gasification reaction, which
produces hydrogen and carbon monoxide from carbon. This product gas
mixture is also known as synthesis gas or syngas:
C

H 2 O - CO H 2 1 131 ; 000 kJ = kmol (1.7)

1 1

Utilization of heavy oil residues in oil refineries is an important applica-
tion of gasification. Low-hydrogen hydrocarbon residues are gasified into
hydrogen:

C n H m 1 ð n = 2 Þ O 2 5 nCO

1 ð

m = 2 Þ H 2 (1.8)

This hydrogen can be used for hydrocracking of other heavy oil fractions
into lighter oils.
The reaction between steam and carbon monoxide is also used for maxi-
mization of hydrogen production in the gasification process at the expense
of CO:

CO H 2 O - H 2 1 CO 2 41 ; 000 kJ = kmol (1.9)

1

1.6.5 Syngas Production
Syngas

80% CH 4 )u inga
steam methane-reforming reaction, instead of from solid carbonaceous fuel
alone. The reforming reaction is, however, not strictly gasification but a
molecular rearrangement:

is also produced from natural gas (

.

CH 4 1 H 2 O ð catalyst Þ- CO 3H 2 1 206 ; 000 kJ = kmol (1.10)

1

Partial oxidation of natural gas or methane is an alternative route for pro-
duction of syngas. In contrast to the reforming reaction, partial oxidation is
exothermic. Partial oxidation of fuel oil also produces syngas:
CH 4 1 1 = 2O 2 - CO 2H 2 36 ; 000 kJ = kmol (1.11)

1

1.6.6 Methanol Synthesis
Syngas provides the feedstock for many chemical reactions, including metha-
nol synthesis ( Eq. (1.12) ). Methanol (CH 3 OH) is a basic building block of
many products, including gasoline:

CO 2H 2 ð catalysts Þ- CH 3 OH (1.12)

1