Environmental Engineering Reference
In-Depth Information
heating is more expensive than MP steam, the use of the MP steam is first maximized. In the
temperature range above the MP steam level, the heating duty has to be supplied by the
furnace flue gas. The flue gas flowrate is set as shown in the graph via drawing a sloping line
starting from the MP steam to theoretical flame temperature Ttft.
If the process pinch temperature is above the flue gas corrosion temperature, the heat
available from the flue gas between the MP steam and pinch temperature can be used for
process heating. This will reduce the MP steam consumption.
In summary the GCC is one of the basic tools used in pinch technology for the selection
of appropriate utility levels and for targeting for a given set of multiple utility levels. The
targeting involves setting appropriate loads for the various utility levels by maximizing
cheaper utility loads and minimizing the loads on expensive utilities.
Normally, we have a choice of many hot and cold utilities. Using the entropy balance
equation for an open system we can conclude and generally recommend to use hot utilities at
the lowest possible temperature while we generate it at the highest possible temperature to
generate work. And for the cold utilities it is recommended to use it at the highest possible
temperature. These recommendations are best explained using the grand composite curve.
T-tft
(C)
T*
MP
CW
Refrigeration
H
Figure 17. Grand Composite Curve for Utility Selection-2
