Equipment Sizing
Preliminary Equipment Sizing for
Capital Cost Estimation
The Need for Equipment Sizing
Before one can carry out capital cost
estimates on process equipment, the
process engineer must carry out a
preliminary sizing of the equipment.
Although each process will have some
unique pieces of equipment there are
some general categories applicable to
most designs
Equipment Types
Towers
Heat Exchangers
Instrumentation
Tanks
Vessels
Pumps
Compressors
Fired Heaters
Others
Towers
Size (height and
diameter),Pressure,Temperature
Number and Types of Trays
Height and Type of Packing
Materials of Construction
Unique Characteristics, Swaged
Columns
Heat Exchangers
Type;Vapour-Vapour,VapourLiquid,Condenser,Vapourizer,Evaporators
Process Duty, Area, Temperature and
Pressure for all streams
Type, Shell and Tube, Air-Cooler, Tube and
Tube etc. Cooling Towers
Number of Shells and and Tube passes
Materials of Construction
Instrumentation
Pressure, Temperature, Flow and Level
Analytical, Gc, IR etc
Computer Control, Central or
Distributed
Tanks
Type of Tank and Service, Standard API,
Floating roof, Blanketed etc.
Materials of Construction
Vessels including Reactors
Height/Length,Diameter,Orientation
Pressure, Temperature
Materials of Construction
Pumps
Flow,Discharge Pressure,Temperature
ΔP,Driver Type, Shaft Power
Type of pump, Centrifugal,
Reciprocating, number of stages
Materials of Construction
Compressors
Actual Inlet Flow
Rate,Temperature,Pressure,Driver
Type,Shaft Power
Type of Compressor, Centrifugal, Single
or Multi-Stage,Reciprocator
Materials of Construction
Fired Heaters
Type,Tube Pressure,Tube
Temperature,Duty,Fuel
Materials of Construction
Other Equipment
Filter,Blenders,Mixers, Kneaders
Centrifugal Separators,Crystallizers
Crushers and Grinders,Dust Collectors
Electrostatic Precipitators
Conveyors
(This is by no means an exhaustive list)
Sizing Procedures - Towers
Flow Sheet Simulators such as PRO/II ®
and HYSYS ® have built in sizing
routines for most type of mass transfer
devices such as Fractionation Towers
and Liquid-Liquid Extraction Towers.
Unique devices such as Rotating Disk
Contactor would require a specific
procedure.
Towers Continued
For Fractionations, the designer must
determine the number of theoretical
stages required for a certain reflux and
boil-up rate in order to achieve the
required separation. The appropriate
type of Mass Transfer device must be
chosen, I.e. Trayed Tower, Packed
Tower etc.
Towers Continued
If a trayed tower is selected, the type of
trays must be specified, bubble-cap,
seive or valve trays. For packed towers
the type of packing must be selected.
There are many types of towers, Simple
Absorbers, Rectified Absorbers,
Reboiled Strippers, Steam Strippers etc.
Heat Exchangers
The most common type of heat
exchanger is the shell and tube. Shell
and tube exchangers come in many
configurations, however as in the case
with fractionators most simulators such
as HYSYS ® can carry out a rigourous
exchanger design. Condensers and
Thermosyphon Reboilers are tedious
calculations best done by a computer.
Heat Exchangers - Continued
For unique types of heat exchangers
separate sizing procedures may be
required. Often the designer must rely
on a vendor for a good preliminary
design sizing. Realistic sizing and easy
of maintenance are two important
considerations.
Instrumentation
For the purpose of preliminary
estimates instrumentation is usually
costed simply as a factor of major
capital.
Instrumentation (Process Control) has
become increasingly more sophisticated
and costly.
Instrumentation continued
Although a factor approach may be
suitable for a preliminary estimate, a
better definition is required for a
definitive estimate. Some units have a
very sophisticated plant-wide
supervisory control which is based on
complex computer technology.
Tanks
It is no longer satisfactory to only
consider the amount of material that
must be stored and the appropriate
materials of construction, environmental
considerations have a significant effect
on the design of tanks. Inventory
instrumentation has become more
sophisticated as well. Often one will
have to rely on a vendor.
Vessels
This category covers a wide range of
equipment from reactors to flash drum,
overhead accumulators, flare drums etc.
Some of this equipment can be readily
sized by heuristic residence time
considerations. Reactor design can be
a simple residence time consideration,
or a very complex design problem.
Vessels continued
CSTRs are usually a relatively simple
vessel with an agitator, although heat
removal problems may complicate the
design. Other reactors are considerably
more complex, for example catalytic
fluid bed cracker reactors and
regenerators, and trickle phase
reactors.
Pumps
The major concern with pump sizing is
selecting the particular type of pump for
the service. Although centrifugal pumps
are the most common, other types are
often required, reciprocating, gear
pumps and so on. You will be provided
with a spread-sheet for the sizing of
pumps.
Compressors Expanders
Flowsheet simulators such as HYSYS ® have
routines that are to be used for sizing
compressors (and expanders).
One common error that students in the
design course make is specifying a
compressor to move liquid. Compressors are
used for vapour, pumps for liquids.
Compressors can be destroyed by slugs of
liquid in the feed.
Fired Heaters
This is a relatively complex sizing
problem, and fortunately we don’t have
to deal with it in the design exercise.
Direct fired reboilers are not
uncommon, particularly in the
petroleum industry, however we have
avoided the need for such a unit in the
design project
Others
There are a great deal of unit
operations that fall into this category, all
with their own unique sizing
procedures. Solids handling is a fairly
broad field, as is the equipment used
for bioseparations.