Page 134 - Design of Simple and Robust Process Plants

4.2 The Methodology of Process Synthesis 119
ently) included. The savings are based on realistic expectations (which are seldom at
100% capacity) and the highest energy prices.
The constraints as listed above are a primary condition for clever process integra-
tion. In particular, the operability and controllability of the operation ± next to safety
aspects ± are the major preconditions for these inter-process connections and need
to be included in the economics..

4.2.3.2 Integration of raw materials
The objective of inter-process integration is to achieve lower consumption of natural
resources, and this effort will continue to receive growing attention in light of the
sustainability of the environment. Indeed, this is one of the main drivers in the
building of integrated complexes. In the past, it has been the reduction in logistic
costs which has led to the integration of processes, with resultant large complexes.
This drive is now strengthened by a tendency to process less-purified streams
between plants in order to save on separation costs. Information on this subject has
been published to a limited extent, but has largely been targeted at specific applica-
tions.
It was Netzer (1997) who first drew broader attention to these opportunities, and
current practice is clearly evolving in that direction. The potential applications of
inter-process integration include:

. Streams that require large amounts of energy and capital to separate them
from components with similar properties ± propylene and propane, or ethyl-
ene and ethane separations are good examples. The application of less-puri-
fied olefin streams is found in the alkylation of benzene to produce cumene
and ethyl benzene. In these applications the receiving plants remove the ole-
fins and concentrate the alkanes; the concentrated streams are then re-sent
to the supplier olefin plant as valuable feed.
. When the receiving plant dilutes the raw material stream which has been
concentrated at the supplier plant. Examples are hydrolysis processes which
receive dried, raw material such as ethylene/propylene oxide, while the
stream is diluted again during hydrolysis. Other examples include the drying
of monomer streams before use in a watery emulsion polymerization reac-
tions.
. Cooling or condensation of a stream before delivery, while the receiving
plants re-heats the stream before usage.
. More interconnections will be created to achieve higher-efficiency operations,
an example being the integration of an ethyl benzene plant within an olefin
plant (Netzer, 1999).
The opportunities are at hand, particularly as there is a trend to produce chemicals
at complexes in order to minimize logistics costs. The above examples can be
extended, and most applications have been explored during revamping of processes
to find cheap solutions. The trend towards further process integration is clear.
A number of specific problems areas may be encountered with respect to
impurities: