Carbon dioxide removal in indirect gasification - SGC

Percent by Volume
30%
25%
20%
15%
10%
5%
0%
LT-step
inlet CO
SGC Rapport 2013:277
HT-step
inlet CO
LT-step
outlet CO
0 100 200 300 400 500 600 700
Temperature (°C)
HT-step
outlet CO
Figure 10. Schematic representation of the water-gas shift reaction, adapted from
[27].
The first stage catalyst may tolerate sulphur, but the second stage catalyst will be
permanently deactivated by the presence of sulphur [28]. The general strategy for
tuning the SN is by splitting the gas stream upstream of the water-gas shift and
converting the CO in the stream passing through the reactor to as high a degree
as possible [29].
3.4 Process configurations
First of all, it should be realized that what gasifier technology to prefer (from the
ones mentioned above) and which oxidant to use is to a large extent depending on
the planned application of the gas. The first criterion for choosing gasification
technology is the desired plant size. After that the oxidant is chosen, depending on
the gas quality desired. If an energy dense gas is required, the oxidant of choice
would be oxygen and/or steam or indirect gasification. If downstream processes
are favoured by high pressures, the gasifier is usually pressurized to avoid (or at
least minimize) any compression of the gas.
The combination of gasifier, gas cleaning, gas conditioning, carbon dioxide removal
and SNG synthesis can be performed in many ways. Depending on the sulphur-tolerance
of the catalysts used, the sulphur removal may be performed upstream
or downstream the water-gas shift and/or the SNG synthesis. The CO2 removal
may also be performed either before or after the SNG synthesis. The upstream
removal will create higher temperature in the SNG synthesis. In Figure 11
some alternative process configuration has been suggested.
28 Svenskt Gastekniskt Center AB, Malmö – www.sgc.se
CO2
CO