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Chapter | 1  Introduction                                     17


             plant is 745 g/kWh compared to 770 g/kWh from a combustion-based sub-
             critical pulverized coal (PC) plant (Termuehlen and Emsperger, 2003, p. 23).
                Sequestration of CO 2 could become an important requirement for new
             power plants. On that note, a gasification-based power plant has an advantage
             over a conventional combustion-based PC power plant because CO 2 is more
             concentrated in the flue gas from an IGCC plant making it easier to sequestrate
             than that from a conventional PC plant where CO 2 is diluted with nitrogen.
             Table 1.5 compares the CO 2 emissions from different electricity-generation
             technologies.
                Biochar produced from pyrolysis of biomass offers a new alternative to
             carbon capture and sequestration (CCS) (see Section 5.8).


             1.3.2.2 Sulfur Removal
             Most virgin or fresh biomass contains little to no sulfur. Biomass-derived
             feedstock such as municipal solid waste (MSW) or sewage sludge contains
             sulfur, which requires limestone for capture. Interestingly, such derived feed-
             stock often contains some amounts of calcium, which intrinsically aids sulfur
             capture.
                Gasification of coal or oil has an edge over combustion in certain situa-
             tions. In combustion systems, sulfur in the fuel appears as SO 2 , which is
             relatively difficult to remove from the flue gas without adding an external
             sorbent. In a typical gasification process, 93 96% of the sulfur appears as
             H 2 S with the remaining as COS (Higman and van der Burgt, 2008, p. 351).
             One can easily extract sulfur from H 2 S by absorption. The extracted elemen-
             tal sulfur in a gasification plant is a valuable by-product.





               TABLE 1.5 Comparison of Emissions and Water Use for Electricity
               Generation from Coal Using Two Technologies
                                          PC                  Gasification
                                          Combustion          (IGCC)
               CO 2 (kg/1000 MWh)         0.77                0.68
               Water use (L/1000 MWh)     4.62                2.84
               SO 2 emission (kg/MWh)     0.68                0.045
               NO x emission (kg/MWh)     0.61                0.082
               Total solids (kg/100 MWh)  0.98                0.34
               Source: Recompiled from graphs by Stiegel (2005).
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