T

QHmin

QHmin

FIG. 3.11.4 Division of a process into two thermodynamically separate systems.

the more fuel burned and the greater the flue gas emissions. Pinch technology can be used to improve energy efficiency through better integration and thus reduce flue gas emissions.

In addition, a design engineer can systematically direct basic modifications to a process to reduce flue gas emissions. For example, part a of Figure 3.11.7 shows a process grand composite. Because the process requires a high temperature, a furnance is required. Part a in Figure 3.11.7 shows the steepest flue gas line which can be drawn against the existing process. This line corresponds with the smallest flue gas flowrate, the smallest fuel consumption, and hence the smallest flue gas emissions.

Part b in Figure 3.11.7 shows the grand composite curve of the same process which has been modified specifically to open the temperature-driving forces in the high-temperature part of the process. The overall process duty is unchanged. However, the systematic modification of the process shown in part b of the figure allows a steeper flue gas line to be drawn leading to reduced flue gas emissions.

Composite Curves Grand Composite Curve

FIG. 3.11.5 Grand composite curve presenting the profile of the horizontal separation between the composite curves with a built-in allowance for ATmin.

Composite Curves Grand Composite Curve

FIG. 3.11.5 Grand composite curve presenting the profile of the horizontal separation between the composite curves with a built-in allowance for ATmin.

Grand Composite Curve

FIG. 3.11.6 Grand composite curve revealing where heat is transferred between utilities and the process.

Grand Composite Curve

FIG. 3.11.6 Grand composite curve revealing where heat is transferred between utilities and the process.

0 0

Post a comment