Chemical Engineering January 2015 - 54

Stacked heat exchangers
* Suitable performance
* Safety requirements, such as the
need to ensure the proper distance
between the furnace and
oil-storage tanks
* Construction requirements, such
as the need to provide enough access
area to allow construction
equipment (such as cranes and
lifts) to maneuver around the
equipment
* Operation, inspection and maintenance
requirements, to ensure
easy accessibility for operators to
reach each component, system or
monitoring console
* Logistics requirements, to ensure
easy accessibility for service companies
and their vehicles, including
chemical-delivery trucks
If the team follows the basic rule
of seeking to minimize pipe length
wherever possible, it will undertake
efforts to minimize the length of
both process piping and utility piping.
To minimize the process piping
length, equipment must be placed
in the order of the process flow diagram
(PFD) arrangement. However,
the effort to minimize the utility
piping length often forces designers
to lay down the developed " string "
of equipment based on the PFD
along the perimeter of a circle with
shared utility units in the center.
Although other requirements (such
as those related to safety and logistics)
will usually result in changes
to this preliminary arrangement,
it will be a useful exercise to group
equipment components that are
using common utilities, in a first
attempt to minimize the utility
pipe lengths.
The designer not only needs to try
to minimize the pipe length but also
to minimize the pipe rack length
and the number of finger pipe racks.
Doing so requires effort to develop
common routes for different pipes,
as much as possible.
Safety requirements call for segregating
areas within a plot plan in
a way that groups equipment and
units with common hazardous characteristics.
To minimize the risk of
releasing flammable, toxic, or lethal
liquids from storage tanks, they
should be grouped based on hazardous
classification areas and then
put within different containments
or diked areas.
Figure 2. In many cases, it makes
good engineering sense to incorporate
vertical designs, to take advantage of
gravity-based flow, limited footprint area
in the facility, and other engineering
considerations
Control
cabinet
Centrifuge
Mezzanine
level
Chute
Truck for
dumped
sludge
Prevailing wind direction at the
target location also affects the location
of equipment. Thus, a furnace,
for instance, can be placed at the
edge of a plant against the direction
of the prevailing wind to make sure
any potential flammable leaked
fuel gases would move away from
the plant. This same logic is why
flares are typically placed far from
human activity.
Another group of safety considerations
could be better classified
as " nuisance issues. " For instance,
even though engineering controls
are often used to manage noise
and fugitive emissions, units that
are inherently noisy or odorous
should be placed in areas with little
human presence.
Construction requirements are
equally important during the development
of a plot plan. Ease-ofconstruction
rules typically call for
a plant with a regular shape, preferentially
with right angles.
Meanwhile, specific installation
requirements associated with certain
equipment must also be taken
into account. For example, air coolers
are usually installed in a horizontal
direction, at some height
above the ground. Such an installation
will require an additional support
structure. The added expense of
this typically leads the plot plan designer
to locate all the air coolers in
one location, to economize.
The concept of constructability
can affect the location of equipment,
too. For instance, a piece of equipment
may be placed relatively far
from the main part of the plant -
in a less-congested area against all
other requirements - to satisfy the
need for ease of access for construction
vehicles, such as large cranes.
Operation and inspection requirements
will also impact the location
of equipment. Such considerations
often require that operator-intensive
equipment be grouped and
placed in easily accessible areas.
There must be specific clearance
around each piece of equipment, to
provide enough room for operators.
Specific maintenance requirements
may require wider clearance
around one or all sides. For example,
a floating bundle shell-and-tube
heat exchanger needs a clearance of
about 1.5 times the tube length in
front of the heat exchanger as an
area for bundle removal. Similarly,
plate-and-frame heat exchangers
need enough clearance to allow for
plate removal.
Some equipment - raw material
tanks, silos of additives, chemicalinjection
skids that may need freChemiCal
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Chemical Engineering January 2015

Table of Contents for the Digital Edition of Chemical Engineering January 2015
