THERMOCHEMICAL CONVERSION: (CO)GASIFICATION AND HYDROTHERMAL GASIFICATION - Biomass as a Sustainable Energy Source for the Future - page 301

Liquid Fuels:
FT diesel
Ethanol
Methanol
DME

Gaseous Fuels:
Hydrogen
Methane (SNG)
Ammonia

Torrefaction Gasiication

to
raw syngas

Gas cleaning
and
upgrading

Drying
sizing

Pyrolysis

Power:
Gas engine
Gas turbine
Fuel cell

FIGURE 10.1 Scheme for thermochemical conversion of biomass via gasification to multiple
products.

devolatilization is the thermal decompositionof themainorganic constituents into char,

permanent gases, and heavier hydrocarbons (also called tars); details of this process are
presented in Chapter 11. In the gasification step of the process, tars and char react further
with already evolved gases to produce more gases. Gasification is a thermochemical
conversion process and is performed at relatively high temperatures (typically in the
range of 700

—

1500 C). The pressure can range from atmospheric pressure up to 7 MPa.
During gasification, numerous chemical reactions occur. The most significant of
these are summarized in equations (RX. 10.1)

-

(RX. 10.13). In these reaction
equations, the carbonaceous residue, usually called char, is considered to consist
exclusively of carbon (C(s)) and tar, which is represented as C n H m :

-

Δ r H 0 298 =

mol −1

: :

Cs ðÞ +O 2 ! CO 2 − 394 kJ ð RX 10 1 Þ

Δ r H 0 298 = mol −1

Cs ðÞ + O 2 ! CO − 111 kJ ð RX : 10 : 2 Þ

½

Δ r H 0 298 = + 131 kJ mol −1 Cs ðÞ +H 2 O $ CO + H 2 ð RX : 10 : 3 Þ

Δ r H 0 298 = + 173 kJ mol −1

Cs ðÞ +CO 2 $ 2CO ð RX : 10 : 4 Þ

Δ r H 0 298 = mol −1

Cs ðÞ +2H 2 $ CH 4 − 75 kJ ð RX : 10 : 5 Þ

Δ r H 0 298 = mol −1

CO + O 2 ! CO 2 − 283 kJ ð RX : 10 : 6 Þ

½

Δ r H 0 298 = mol −1 H 2 + O 2 ! H 2 O − 242 kJ ð RX : 10 : 7 Þ

½

Δ r H 0 298 =

mol −1

: :

CO + H 2 O ! CO 2 +H 2 − 41 kJ ð RX 10 8 Þ

Δ r H 0 298 = + 206 kJ mol −1

CH 4 +H 2 O $ CO + 3H 2 ð RX : 10 : 9 Þ

C n H m tars ðÞ +nH 2 O ! nCO + n + m ð = 2 Þ H 2 ð RX : 10 : 10 Þ

C n H m tars ðÞ + nCO 2 $ 2nCO + m = 2H 2 ð RX : 10 : 11 Þ

C n H m tars ðÞ$ nC + n +m ð = 2 Þ H 2 ð RX : 10 : 12 Þ

C n H m tars ðÞ +4n ð − m Þ = 2H 2 O $ nCH 4 ð RX : 10 : 13 Þ