Page 92 - Design of Simple and Robust Process Plants

4.1 Process Synthesis 77
these properties must be determined for all chemicals involved in the process. This
includes the reactants and products, as well as solvents, any solid materials such as
ion exchangers or adsorbers, catalysts, and utilities (water, air, nitrogen, oxygen,
heating and cooling media) and construction materials, including insulation and
gaskets. Be aware that the process also covers cleaning activities; thus, it is required
that substances used during cleaning, washing and regeneration (e.g., solvents,
regeneration materials, water) be included.
The reactivity properties must be documented, and the constraints for the design
determined. For example:
. Do not heat exchange two substances which are classified as incompatible, as
the heat exchangers might leak.
. Operate outside an explosion range.
. Avoid materials of construction in sections which might lead into a compat-
ibility problem with process streams.
. Pyrophoric materials are not a preferable choice.
Mechanical sensitivity testing is divided into sensitivity to mechanical shock, and fric-
tion. These mechanical sensitivity conditions are to be avoided, and may lead to the
constraint of a design. On occasion, the sublimation of shock-sensitive solids might
be the cause of a major accident.

4.1.2.4 Environmental requirements
These have a growing impact on the design of processes, and are subject to mov-
ing targets as Society places more emphasis on this aspect over time, with
strongly evolving global directions. The emission of pollutants will have to be
absolutely minimized. The requirements will not be limited to steady-state condi-
tions, and more emphasis will be placed on occasional situations. The drive for
sustainable technology will enforce the industry to select more efficient routes
from a sustainability perspective (Graedel and Allenby, 1995). Eco-profiles (APME,
1997) will be required, and standards such as ISO14040/43 will have to be applied
to these studies. The sustainability studies must be performed during the technol-
ogy selection stage of a process, but the results achieved in the process synthesis
need to confirm these data. Sustainability is improved either by the selection of a
more efficient route, or by process efficiency through integration between pro-
cesses.
Add-on techniques to comply with emission requirements are generally available,
but are still subject to improvements. The challenge is to prevent these emissions
rather than to apply techniques of abatement.
An approach by which environmental losses may be attacked is illustrated in Fig-
ure 3.8 of Chapter 3, the sequential actions being to:

. Prevent/minimize
. Recycle in process/reuse in process
. Recycle between processes
. Destroy with recovery