Page 266 - Design of Simple and Robust Process Plants

252 Chapter 7 Optimization of an Integrated Complex of Process Plants
state situation. Complexes are growing in size, and although there is a master plan
(particularly for grass-root sites), this will always be subject to change. During the
design of a complex, sufficient flexibility must be provided to cope with these uncer-
tainties. Independent of these uncertainties in design capacity, there will also be
operational variations among the different plants, and these need to be absorbed
during operation of the integrated complex.

7.2
Chemical Complexes

Chemical complexes for base chemicals (which are considered as a global market)
in general emphasize the existence of a certain production chain, and this depends
on the activities of a specific company.

7.2.1
Nitrogen-based Complexes

These incorporate fertilizer-producing companies which, in general, operate a
production train starting from natural gas (CH 4 ) and air to produce H 2 , and N 2 with
CO 2 as by-products. The chain continues with ammonia production (NH 3 ), from
which extend nitric acid (HNO 3 ) and ammonium nitrate (NH 4 NO 3 ) production.
Urea (NH 2 CONH 2 ) is also often produced in this scheme. [PB1]

7.2.2
Hydrocarbon-based Complexes

These are the producers of different types of plastics. Here, selected hydrocarbon
feedstocks such as liquid petroleum gas (LPG), naphtha, and gas oil are converted
into different products such as ethylene, propylene pyrolysis gasoline (also called
pygas, a C 6 ±C 8 fraction) and a C 4 fraction containing butenes and butadiene. The C 4
stream may be fed to a butadiene extraction process for its recovery, while the
remaining iso-butene can be converted to methyl tert-butyl ether (MTBE). Ethylene
and propylene poly-olefinics are produced from the monomers. From pygas, ben-
zene is recovered, and this may be converted with ethylene to ethyl benzene, next to
styrene, and finally into polystyrene. Many other chemicals can be produced in this
chain, including the co-production of styrene and propylene oxides from ethyl ben-
zene and propylene, ethylene oxides, and ethylene glycols based on ethylene. For a
typical flowsheet, see Figure 7.1.