Page 27 - Sustainability in the Process Industry Integration and Optimization

4 Cha p te r O n e

wind, water power), which significantly reduce the generation of
greenhouse gases. Implementing Combined Heat and Power (CHP)
systems (AEA Technology, 2000), rather than a separate power system
and heat system, can also substantially improve the efficiency of
energy supply. In addition, the overall situation can be improved by
certain fast-advancing technologies: heat pumps, compact heat
exchangers, fuel cells (FCs), and intensified technologies. Some of
these approaches are not yet fully commercialized but are gradually
becoming available. Some examples discussed in AEA Technology
(2000) are as follows:
• Advanced gas turbines for both utility and industrial
applications, including cogeneration (CHP).
• Fuel cells are electrochemical devices that may be fueled by
hydrogen, methane, or other organic fuels. High-temperature
FCs (MCFC and SOFC) can also use cleaned and conditioned
synthesis gas directly. These systems produce high-grade
heat (above 500ºC) in addition to electrical power, and they
are well suited to cogeneration. It is estimated that FCs
typically emit 25 percent less CO than a gas turbine. Yet
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further advances are required before their full application
becomes economically practical. One option is to integrate
CHP and FCs (Varbanov et al., 2006).
• Dividing-wall distillation technology (Triantafyllou and Smith,
1992; Hernández and Jiménez, 1999). This technology
involves the separation of three components (or groups of
components) in a mixture. In the past this would have
required two distillation columns, with heating and cooling
provided for each column. The dividing-wall technology
combines the separation process into a single vessel to yield
energy savings of about 30 percent and capital savings of
about 25 percent (MW Kellogg, 1998).
• Compact heat exchangers are generally made of thin metallic
plates rather than tubes. The plates form complex and small
flow passages that result in a large surface area for heat
transfer per unit volume. Multistream versions of these
exchangers can incorporate 12 or more streams. Compact
heat exchangers can yield energy savings and also reduce the
costs of capital and installation. In a case study at a U.K.
refinery, potential capital savings ranged from 69 to 84 percent
(EEO, 1993).
Cogeneration is being increasingly applied in most sectors. For
example, many oil refineries satisfy a large portion of their power
demands by on-site generation, with the balance being supplied by
externally purchased electricity. Usually all or almost all heating