(61a) The Design and Revamp of Cooling Water Networks
AIChE Spring Meeting and Global Congress on Process Safety
2013
2013 Spring Meeting & 9th Global Congress on Process Safety
16th Topical on Refinery Processing
Tutorial On Utilities, Water, and Offsites - YP Tutorial
Tuesday, April 30, 2013 - 8:00am to 9:00am
Cooling Water
Networks
G.T.Polley, M.Picon Nunez & E.Tamakloe
Dept. of Chemical
Engineering, University of Guanajuato, Mexico
In Reality:
Simulations
can be set up quickly
Analysis
quite simple
Significant Benefits - power reduction, capital cost saving,
fouling mitigation
Topics:
Design Principles
Flow Simulation
Design
Principles
?
Cooling Towers:
Individual
Plants ? Plant Regions ? Centralized System
Packaged Units ? Specialist Suppliers
Selected with
future expansion in mind
Thermal
Performance well modeled using E-Ntu Method
Minimum
wetting required. So, system may have flow set by cooling tower rather than
process plant
Maximum water
return temperatures apply (function of water chemistry)
· Piping
Dominates
Capital Cost
Set with
allowance for plant expansion
Equations for
economic pipe size
Capital Cost : diameter to power 3
Installation
: again diameter to power 3
Function of
Plant Layout ? not use of temperature driving force
· Heat Exchanger Sizing
Must be
undertaken in ?system context?
Cannot
arbitrarily set pressure drop or cooling water temperature rise
Pressure drop : function of square of volumetric throughput
FLOW
SIMULATION
Components of pressure drop:
?
Gravitational head
?
Frictional losses
?
Momentum changes
Implications:
?
MOMENTUM EFFECTS INDEPENDENT OF FLOW
PATH
?
GRAVITATIONAL EFFECTS INDEPENDENT OF
FLOW PATH (Provide flow initiated)
Gravitation
?
Initiation of flow may require
provision of back pressure ? restriction at cooling tower return
?
Vacuum can be pulled in heat
exchangers ? checks for vapor blocking are required
Friction
?
Great advantage in using equation
based on Volumetric Flow Rate rather than velocity
?
Velocity can vary along specific flow
path ? but volume flow remains constant
Frictional Components are additive:
Pipe + Valve + Heat Exchanger + Valve
Kleg
= 2Kvalve + Kexchanger + Kpipe
Pressure Drop Across Branches
are Equal
Revamping Cooling
Water Networks
Occasions arise when it is necessary to reduce load
on cooling tower.
Example: installing new plant into existing factory
and do not want expense of new cooling tower.
Best Option:
Improve integration of plants in order to reduce demand for cooling
water.
Problem: Load
on existing exchangers is reduced, hot stream inlet temperature fall, outlet
temperatures also fall : streams are now ?over-cooled?
Identifying ALL Options:
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