Carbon dioxide removal in indirect gasification - SGC

SGC Rapport 2013:277
The most apparent difference between the two gas compositions, the major
components aside, is the benzene concentration which is zero after the
methanation. Looking at the carbon dioxide content of the gas this is increased
with methanation because of the stoichiometry of the methanation reaction
producing fewer gas molecules. Out of the 100 MWth entered into the system, 89
MWth is left after gasification and 80 MWth is left after gasification and gas
cleaning. Additional losses are acounted for in the water-gas shift, CO2 separation
and gas compression. The CO2-separations have been performed at normal
operating pressure for the respective processes. Simulations of CO2-separation
performed at high pressure with the technology at hand displayed either a high
methane loss or an unreasonably high recycle power consumption to lower the
methane loss. The gas composition after separation in the pre-methanation case
is displayed in Table 14a for the water scrubber case and Table 14b for the amine
scrubber case.
Table 14a. Gas compositions and other properties in the 100 MWth case after upgrading
pre-methanation with water scrubbing, on a dry-gas basis.
After separation After methanation
Component (Vol-%)
CO2 1 1.8
CH4 36.8 90.5
CO 14.3 1.8*10 -2
H2 44.8 3.2
C2Hx
C6H6
6.4*10 -4
2.1*10 -6
7.9*10 -4
0
N2 2.6 4.6
O2 0.5 0
Methane slip (% of inlet) 1 N/A
Propane required for Wobbe indexLHV
45.5 (kg/Nm 3 ) N/A 0.11
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