Carbon dioxide removal in indirect gasification - SGC

SGC Rapport 2013:277
case is the case that has the largest differences compared to traditional biogas
upgrading as there is low methane content and high content of hydrogen and carbon
monoxide in the gas, table 7.
Table 7. The 100 MW gas mixtures and flow rate on a dry-gas basis.
100 MWth
100 MWth
Pre-methanation Post-methanation
Component (Vol-%) (Vol-%)
CO2 35.4 47.6
CH4 24.5 48.8
CO 9.5 0.1*10 -3
H2 29.6 2.0
C2Hx
C6H6
6.4*10 -4
2.4*10 -6
7.9*10 -4
0
N2 1.1 1.6
O2 0 0
Gas flow (Nm 3 /h) 20 400 15 700
As can be seen in the table, there is about 35% CO2 in the gas mixture before
methanation and 48% after methanation. The gas mixture before methanation
contains 30% hydrogen and 10% carbon monoxide as well as trace amounts of
ethylene and benzene. After the methanation, the CO is reduced to trace amounts
while there is still 2% hydrogen in the mixture as well as trace amounts of C2Hx
which is about 10% of both ethane and acethylene while 80% is ethylene. For the
purpose of these calculations all C2Hx has been considered as ethane or ethylene.
The cases have been constructed using the MILENA and OLGA gasification and
gas purification as already stated. The methanation has been modeled based on
the TREMP set-up and using information in the open literature with respect to operating
conditions energy is exported [2]. In the current set-up heat is also used
for biomass drying from 50% to 25% moisture content using 4.5 MJ/kg of water
[88]. The cases simulated are quite close to the process lay-out in Figure 11 but
for clarity figure 23a and 23b contains the two alternatives considered here.
48 Svenskt Gastekniskt Center AB, Malmö – www.sgc.se