Page 225 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

202 Biomass Gasification, Pyrolysis and Torrefaction

TABLE 7.2 Typical Gasification Reactions at 25 C

Reaction Type Reaction
Carbon Reactions
R1 (Boudouard) C 1 CO 2 22CO 1 172 kJ/mol a
R2 (water gas or steam) C 1 H 2 O2CO 1 H 2 1 131 kJ/mol b
R3 (hydrogasification) C 1 2H 2 2CH 4 2 74.8 kJ/mol b
R4 C 1 0.5 O 2 -CO 2 111 kJ/mol a
Oxidation Reactions
R5 C 1 O 2 -CO 2 2 394 kJ/mol b
R6 CO 1 0.5O 2 -CO 2 2 284 kJ/mol c
R7 CH 4 1 2O 2 2CO 2 1 2H 2 O 2 803 kJ/mol d
R8 H 2 1 0.5 O 2 -H 2 O 2 242 kJ/mol c
Shift Reaction
R9 CO 1 H 2 O2CO 2 1 H 2 2 41.2 kJ/mol c
Methanation Reactions
R10 2CO 1 2H 2 -CH 4 1 CO 2 2 247 kJ/mol c
R11 CO 1 3H 2 2CH 4 1 H 2 O 2 206 kJ/mol c
R14 CO 2 1 4H 2 -CH 4 1 2H 2 O 2 165 kJ/mol b
Steam-Reforming Reactions
R12 CH 4 1 H 2 O2CO 1 3H 2 1 206 kJ/mol d
R13 CH 4 1 0.5O 2 -CO 1 2H 2 2 36 kJ/mol d
a Higman and van der Burgt (2008), p. 12.
b Klass (1998), p. 276.
c Knoef (2005), p. 15.
d Higman and van der Burgt (2008), p. 3.

energy applications. While we cannot do much about the inherent moisture
residing within the cell structure, efforts may be made to drive away the
external or surface moisture. A certain amount of predrying is thus necessary
to remove as much moisture from the biomass as possible before it is fed
into the gasifier. For the production of a fuel gas with a reasonably high
heating value, most gasification systems use dry biomass with a moisture
content of 10 20%.
The final drying takes place after the feed enters the gasifier, where it
receives heat from the hot zone downstream. This heat preheats the feed and