Page 292 - Sustainability in the Process Industry Integration and Optimization

I n d u s t r i a l A p p l i c a t i o n s a n d Ca s e S t u d i e s 269

A case study of a whisky distillery by Smith and Linnhoff (1988;
see also Caddet, 1994) provides another example of how Pinch
Technology and Heat Integration can reduce energy use and increase
energy efficiency. In this case it was found that steam was being used
below the Process Pinch, resulting in an overall increase in utility
usage. The steam was related to use of a heat pump, so the steam
used below the Process Pinch was eliminated by reducing the size of
that heat pump. Although the steam now had to be used for process
heating above the Process Pinch, the overall energy costs were
reduced owing to the reduction in compressor duty.
Another study involving a whisky distillery was made by Kemp
(2007). The hot utility requirement for the process examined was
8 MW, and the Process Pinch was at 95°C. The main hot utility
requirements were steam for the distillation system and hot air for
the drying system. Kemp showed that the form of the Grand
Composite Curve and the temperature of the Pinch could be
exploited for heat pumping, and he also suggested that the process
would benefit from the introduction of a Combined Heat and Power
(CHP) scheme for improved Process Integration and energy
efficiency. The site’s power demand was 12 MW, so there were two
possibilities for providing both the power and the heat demands
from the same utility system. First, a gas turbine that produced
12 MW of power would also supply about 30 MW of high-grade heat
from the exhaust. The second option involved the use of back-
pressure steam turbines, but these would produce nearly 100 MW,
much more than what was required. Another advantage of a gas
turbine was that its exhaust could be used for drying purposes.
Figure 11.10 shows the final configuration of the utility system
matched to the GCC. Most of the necessary heat was provided by the
gas turbine exhaust and the existing thermo compressors. The
existing package boilers were used to provide steam for the thermo
compressors. The efficiency of this part of the system was increased
by using waste heat from below the Pinch to preheat the boiler feed
water. Waste heat boilers driven by the exhaust from the gas turbine
provided additional steam.
Many processes in the food and drink industry make use of
chilling and refrigeration systems. Pinch Technology and Heat
Integration have also been used to increase the efficiency of these
systems. For example, Fritzson and Berntsson (2006) studied a
Swedish slaughtering and meat-processing plant. Their analysis of
the plant’s subambient temperature section employed the method
proposed by Linnhoff and Dhole (1992) for low-temperature process
changes that involve shaftwork targeting. Figure 11.11 shows the
plant’s Exergy Grand Composite Curve (EGCC). There is a large gap
between the EGCC and the utility curve, which indicates low
efficiency in the use of available shaftwork. Improvements in this
area could result in a 15 percent reduction in energy demand.