Integration in an IGCC
In contrast to most chemical applications for gasification, the presence of C02 in IGCC syngas is not only no problem but even beneficial, in that it increases the mass flow through the gas turbine and therefore contributes to the energy output. This fact allows the integration of the tail gas treatment of the Claus unit into the main AGR system in a manner that eliminates the SRU tail gas as an emission completely. The principle is shown in Figure 8-17. The tail gas from the Claus plant, which contains both H2S and S02, is hydrogenated and recycled back to the AGR, where the sulfur is again removed from the syngas. Clearly, for the economics of this system it is necessary to keep the recycle compression costs low. This puts a premium on the selectivity of the AGR, which in the IGCC scenario is in any case desirable, so as to keep the C02 in the recycle low. Furthermore, one needs to use an oxygen-blown Claus unit to avoid large quantities of nitrogen placing an unnecessary load on the recycle compressor. On the other hand, since the Claus tail gas is no longer an emission as such, there is no need to include more than one catalytic stage in the Claus unit itself. This type of integration has proved itself both in coal applications (Puertollano using an MDEA AGR) and for oil gasification (Sarlux using Selexol).
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CLEAN FUEL GAS Figure 8-17. Integration of Claus Unit in an IGCC |