Page 43 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

22 Biomass Gasification, Pyrolysis, and Torrefaction

6. Total water consumption in a gasification-based power plant is much
lower than that in a conventional power plant (Table 1.5), and such a
plant can be designed to recycle its process water. For this reason, all
zero-emission plants use gasification technology.
7. Gasification plants produce significantly low amounts of major air pollutants
like SO 2 ,NO x , and particulates. Figure 1.8 compares the emission from
a coal-based IGCC plant with that from a combustion-based coal-fired
steam power plant and a natural-gas-fired plant. It shows that emissions
from the gasification plant are similar to those from a natural-gas-fired
plant.
8. An IGCC plant produces lower CO 2 per MWh than that by a combustion-
based steam power plant.

1.5.1 Comparison of Gasification and Combustion
For heat or power production, the obvious question is why a solid fuel
should be gasified and then the product gas is burnt for heat, losing some
part of its energy content in the process. Does it not make more sense to
directly burn the fuel to produce heat? The following comparison may
answer that question. The comparison is based in part on an IGCC plant and
a combustion-based steam power plant, both generating electricity with coal
as the fuel.

1. For a given energy throughput, the amount of flue gas obtained from
gasification is less than that obtained from a direct combustion system.
The lower amount of gas requires smaller equipment and hence results
in lower overall costs.

0.2

0.15

0.1
No x
So x
0.05
PM
0
Coal combustion Intergrated Natural-gas
gasification based combined
combined cycle cycle
FIGURE 1.8 Comparison emission of pollutants from power plants using coal-based steam
power plant, IGCC plant and natural-gas based combined cycle plant. (Drawn in an arbitrary
scale for comparison.)