Chemical Engineering December 2016 - 80

with regard to the danger to people,
equipment and buildings from fire,
explosion and toxicity. The layout
may well have to be adjusted.
The Mond Index method [15] may
be used prior to (but not instead of)
the above assessments.
Step 8. Layout of piping and other
connections. The principal piping
and pipe routes are confirmed
during this step. Principal electrical
mains routes are also checked. Various
connecting arrangements are
considered and the most promising
ones are further optimized. Piping
models can be used as aids and
computerized versions can be used
to support optimization efforts. The
best layout arrangement should now
be selected and recorded.
Step 9. Critical examination of
plot layout. The proposed arrangement
should satisfy all of the obvious
requirements in light of all the
information available. It should be
examined formally by the various
disciplines to make sure less obvious
features (discussed below) have
not been omitted.
Specific aspects to examine include:
* Ease of operation
* Ease of maintenance
* Ease of construction
* Ease of commissioning
* Ease of escape and firefighting
* Safety of operators and other
personnel during
commissioning,
operation
maintenance
* Environmental impact
* Future expansion
3-D models can be good aids to
the review process, though they are
expensive to produce. Check lists to
assist with this process can be found
in Ref. 12.
The results of the critical examinations
carried out by the various disciplines,
and the results of the hazard
assessment, must be reconciled.
Carrying out such a multi-disciplinary
consultation is essential.
In some cases, it may be found
that the layout is impractical or even
impossible. When this occurs, it
will be necessary to rethink the
process design or even undertake
further laboratory and other development
work. In most cases, though,
the results of the critical examination
will mean adjusting the layout by
means of further iteration from
Step 2 onward.
74
construction,
and
FIGURE 3. The output of a typical 3-D plant layout model is shown here. This model of a solids-handling
facility was produced using CADWorx from Intergraph
Preliminary site layout
Step 10. Site data. Steps 1-9 will be
carried out for each separate plant
and storage area within the proposed
site. This will provide the size
and shape of each plot, will help to
define access requirements (for vehicles
and people during construction,
operation, maintenance and
emergencies), and will provide an
approximate evaluation of the separation
needed around each plant to
ensure proper hazard containment.
Using the process data of the
various plants, the layout engineer
should compile information related
to the site materials and utilities
PFDs, pedestrian and vehicular
traffic capacities (for both internal
and external movements), size and
shape of the plots, buildings, and required
utilities, central services and
amenities.
Step 11. Site layout. The PFD for
the site allows the various processes
to be positioned relative to one another.
The flow pattern may be modified
in order to isolate hazardous
processes and to accommodate the
proposed rail and road entry points
or wharf positions.
Next, services, such as the boiler
house and effluent plant, are added
in the most convenient positions,
subject to the provision that they are
not likely to be put out of action by
a disaster. The central buildings are
placed so that the distances traveled
by personnel who use them are minimized,
providing that these buildings
are in safe places.
After this, the road and rail systems
are marked in greater detail.
Try to keep the various types of traffic
segregated as far as is possible
and desirable. There should be access
from at least two directions to
all parts of the site, to allow for emergencies,
as shown in in Figure 4.
The size of the site is determined
from the area of individual plants,
storage areas and central buildings
plus
the
clearances between the
plants. It is also necessary to allow
ample space for things like parking,
loading and unloading, stores and
firefighting water storage. Typical
clearances, size and areas are given
in Ref. 12. During the development
of this layout, allowance must be
made for future plant expansion and
for general construction and other
access considerations.
It is essential to establish, within the
overall layout, all the important positional
relationships between elements
of the layout that must be maintained.
This consideration is crucial because
available sites may not conform in
shape or topography to the preliminary
layout and some compromises
and amendments to the layout are almost
certain to be needed. In light of
this, it must be known which relationships
can be relaxed to fit the plant in
the available space.
Simple drawings and paper cutouts
are very useful for site-layout
development. Physical and 3-D
computer
models
may
also
be
used especially to gauge the
visual impact.
Step 12. Hazard assessment of
site layout. The plots on the site
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