Environmental Engineering Reference
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case the designs of the selected options come to a dead end prematurely, one has
to revisit the abandoned options at an earlier level.
7.7 DIVISION IN SUBPROCESSES
Design at the second level deals with the division of the process into certain
subprocesses.
a.
Scope
A division into subprocesses makes sense (among others) when a subpro-
cess has:
A feed or product that has commercial value and can be traded on the market.
It makes the subprocess an independent economic entity and less sensitive to
what happens in other subprocesses.
A special technology, operating under a license from another company.
Confidential in-house technology that the owner does not want to share with
co-owners of the process.
A different mode of operation, e.g., batch processing, requiring intermediate
storage between subprocesses.
A different location than the other subprocesses. For example, it is better to
collect, chop, and dry biomass close to the different harvesting areas, while
further processing is best done at a central location, thereby avoiding trans-
portation of useless moisture along with the feed.
b.
Knowledge
An analysis of existing processing technologies for the (intermediate) products
at hand is made to see if splitting is desirable and if competitors have done this
and in what ways.
c.
Synthesis
The synthesis activities at the level of subprocess formation consist of:
Identifying candidate subprocesses and conversion technologies with associ-
ated intermediate feeds and products
Ordering the subprocesses and connecting them by streams, considering
recycle structures
Developing an input
output diagram for each subprocess, which forms a
basis for further design, similar as for the main process
-
Figure 7.8 shows an example of the split of a process into three subprocesses.
Two subprocesses run in parallel, each converting a different feed into the
same product (e.g., wood and natural gas to syngas), though with a different
composition. The intermediate product (syngas) can be sold on the market if
the joint capacity of subprocesses 1 and 2 exceeds the demand of subprocess
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