Page 341 - Sustainability in the Process Industry Integration and Optimization

318 Cha p te r F o u r tee n

with the fossil fuels. Renewable resources typically feature
availability distributed over certain areas, varying significantly with
time and location.
Another source of variability is the energy demands (for heating,
cooling, and power) of residential and business consumers, which
vary significantly with the time of day and period of the year. (The
notable exception is large-scale industries that operate continuous
processes; in this case, variations are less pronounced and can often
be either neglected or conveniently modeled using multiperiod
optimization.) Furthermore, the variations in consumer energy
demand are not synchronous but instead are displaced in time. For
instance, commercial and office buildings tend to have higher energy
demands during normal business hours, whereas residential
demands tend to increase after business hours.
These factors all make optimizing the design of energy conversion
systems using renewable resources more complex than when using
fossil fuels only. However, combining the supply and demand
streams of individual users may allow such systems to serve
industrial plants as well as residential customers and the service
sector (hotel complexes, hospitals). The design task is to account for
both the demand- and supply-side variability. One approach to
solving the task is to employ advanced PI methodology with time as
another problem dimension. A basic methodology along these lines
has already been developed for Heat Integration of batch processes
(Kemp and Deakin, 1989; Klemeš et al., 1994) and was recently
revisited by Foo, Chew, and Lee (2008). A further important step in
the direction of extending this methodology to Heat Integration of
renewables was taken by Perry, Klemeš, and Bulatov (2008), who
considered the integration of local energy sectors into extended total
sites involving residential and commercial processes and buildings
in addition to industrial ones. This work was further developed by
Varbanov and Klemeš (2010) to account for the integration of
inherently variable renewables.
Converting waste via thermal processing is an intriguing option
because it simultaneously reduces the demand for fossil fuels and
landfilling. Bébar et al. (2001, 2002) demonstrated a method for
efficiently utilizing the heat value of incineration products that
would partially compensate for the cost of thermal waste treatment.
The challenge of utilizing waste as an energy source is not variability,
as it is with renewables, since waste is relatively plentiful and
generated at significant rates. Rather, the main problems associated
with extracting energy from waste are technological. Municipal and
other solid wastes are typically incinerated (Bébar et al., 2001; Bébar
et al., 2002; Stehlik, 2009), a process that involves three principal
issues.
First, the incineration must ensure efficient combustion and
minimal emissions of pollutants; this is often achieved by co-firing