08.08.2015   BIOMASS NOW - SUSTAINABLE GROWTH AND USE

Discussion of catalytic steam tar reforming pathway

Figure 11 shows simple pathway of the woody biomass gasification process with Ni/BCC catalyst. The woody biomass was first pyrolysis to form gas, tar and char at 923 K. Both useful gas and tar passed through the catalyst particles. Tar was dissociatively adsorbed onto a nickel site where nickel catalyzed dehydrogenation occurs. With steam injection tar would be cracked and reformed follow the mechanism.

The chemistry of coal (biomass) gasification is usually depicted to involve the following reactions of carbon and steam [29]. The standard enthalpy change (gram molecules) at 298 K is shown for each reaction. The most important reactions are listed in Table 1[29-31]

Process Ah!?98 (kJ/mol)

Steam reforming

CH4 + H2O = CO + 3H2

+ 206

(7-1)

CnHm + иНЮ = nCO + n + (m/2)H

+1175a

(7-2)

CO2 reforming

CH4 + CO2 = 2CO + 2H2

+ 247

(7-3)

Gasification

C + H2O ^ CO + H2

+ 131.3

(7-4)

C + 2H2O ^ CO2 + H2

+ 90.2

(7-5)

C + CO2 ^2CO

+ 172.4

(7-6)

Water-gas shift reaction

CO + H2O ^ CO2 + H2

— 41.1

(7-7)

Methanation

2CO + 2H2 ^ CH4 + CO2

— 247.3

(7-8)

CO + ЗН2 ^ CH4 + H2O

— 206.1

(7-9)

CO2 + 4H2 ^CH4 + H2O

— 165.0

(7-10)

C + 2H2 ^ CH4

— 74.8

(7-11)

a for nC7Hi6

Table 1. Synthesis gas reactions