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EQUIPMENT DESIGN:
BASIC CONCEPTS
GOALS:
u Definitions and Concepts
u Types of Design
u Design Methodology
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Input
Streams
Output
Streams
Operating
Parameters
Size
Parameters
EQUIPMENT
CHARACTERIZATION
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DEFINITIONS
u EQUIPMENT RATING:
e Given the input streams,operating parameters,and
size parameters,determine the equipment
performance and output streams
u EQUIPMENT SIZING:
e Given the input streams and the performance
specifications,estimate the economically important
size parameters using approximate methods
u EQUIPMENT DESIGN:
e Produce a design in enough detail to guide the
fabrication of the item of equipment
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Equipment Design Methodology
Set
Performance
Specifications
Determine
Operational
Constraints
Choose Equipment
Type and
Design Parameters
Perform Rating
Calculations
Satisfy Specs
& Constraints?
No
Iterate
Yes
Done
Try First
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EXAMPLE #1,REFLUX DRUM
PROBLEM,Design a reflux drum for a distillation column
u For a residence time of 15 minutes when half full,
u That has a length to diameter ratio L/D = 3.0,and
u Is horizontal.
OPERATING CONDITIONS:
u Flow rate out of drum is 5,000 Kg/hr
u Flow is 100% Ethanol (SG = 0.789)
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From Overhead
Condenser
DistillateReflux to Column
D
L
REFLUX DRUM
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u Holdup = (5000 kg/hr)(0.25 hr) = 1250 kg
u Density = (0.789)(1000 kg/m3) = 789 kg/m3
u Volume = (2)(1250 kg)/(789 kg/m3) = 3.17 m3
(To simplify the size calculations,neglect the holdup in the
dished heads of the drum.)
u Volume = 3.1416 (D2) L (but L = 3.0 D,so)
u D3 = 3.17/(3)/(3.1416) So,
u D = 0.695 m and L = 2.09 m.
DESIGN CALCULATIONS
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EXAMPLE #2,FLASH DRUM
PROBLEM,Design a flash drum that is
u To flash a stream that is 60 mol% ethylene and 40
mol% water at a flow rate of 800 kmol/hr,
u To produce a vapor that is 99% ethylene
u At a fractional recovery of ethylene of 99 %
u The flash drum is a vertical pressure with an L/D = 4.0.
OPERATING CONSTRAINTS:
u Low entrainment of water in the vapor
u 10 minute holdup of liquid when drum is 1/2 full
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VAPOR
LIQUID
Heating
or
Cooling
FEED
FLASH DRUM
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DESIGN PROCEDURE
uBASIC DESIGN VARIABLES,Pressure P and Heat
Duty Q..
u Guess values for P and Q,Do the adiabatic flash
calculation to determine V,L and their compositions and
temperature
u If the performance specifications are satisfied,proceed
to size the drum,If not iterate on P and Q.
u Size drum to satisfy entrainment,liquid holdup and L/D
constraints.
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SUMMARY
u For very simple situations,the design calculations are
explicit.
u For most situations,the design calculations involve a
trial-and-error search for those values of key design
variables that satisfy the performance specifications and
constraints.
u The details of the design methodology will differ from
one equipment type to another.
u The details of the design methodology may also differ
for different performance specifications for the same type
of equipment.