Environmental Engineering Reference
In-Depth Information
Figure 3. Simplified schematic of the proposed gasification process with energy recovery.
The waste enters the gasification reactor together with the gasification air and a stream of
steam, supplied to push the hydrogen production. Once imposed the gasification temperature,
the amount of required gasification air is evaluated. The gasification solid residues leave the
reactor from the bottom, while the syngas exits from the top. Syngas is cooled down to an
assumed temperature - recovering the heat to produce superheated steam - before entering a
wet scrubbing for the removal of undesirable compounds. Actually the removal process is
simulated only from a thermodynamic point of view, considering the syngas further cooling
and its moisture content saturation, at the temperature assumed at the exit. Then the syngas is
fed to a boiler together with combustion air, which is evaluated on the basis of the assumed
combustion temperature. The energy released in the combustion is in large part recovered in
the boiler to produce superheated steam. This steam, together with the amount of steam
produced in the first syngas cooler, expands in a steam turbine, down to the condenser
pressure, producing power output. The exhausts exiting from the boiler are further cooled
down in order to produce the amount of process steam required by the gasification reactor.
Table 6. Main operating parameters assumed for the waste
gasification with energy recovery.
Gasification temperature [°C] 875
Gasification pressure [bar] 1
Steam supplied to process gasification [kgH
2
O/kgC] 0,11
Unreacted carbon [%]
4,60
Syngas temperature at the exit of first cooler [°C]
150
Syngas temperature at the exit of scrubbing [°C]
80
Syngas combustion temperature [°C]
850
Steam maximum temperature [°C]
400
Steam maximum pressure [bar]
40
Steam cycle condenser pressure [bar]
0,25
Temperature of exhausts after last cooling [°C]
150
The main operating parameters assumed for the simulations are reported in table 6. Table 7
shows the simulation main results and the details of calculated syngas characteristics. Table 8
reports the gasification and energy recovery cycle synthetic results. The overall process efficiency
is calculated as the ratio between the power output an the energy entering with the waste.
