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Quotes - Engineering - Sales| DUTY | TYPICAL SERIES | COOLANT | DECIDES LIFE |
| Process Cooling | WU / CHXS | Tower or chilled water | Fouling |
Industrial Process Cooling
Removing Heat From a Process Stream
Process cooling covers everything from a small equipment jacket to a main plant cooling duty. The coolant is usually tower water, chilled water or a glycol loop, and the process side is whatever the plant makes or uses.
Fouling decides the real service life. Tower water is open to atmosphere, biologically active and concentrating dissolved solids as it evaporates. Whatever the thermal calculation says, the exchanger's useful life is set by how well the fouling side can be cleaned.
Put the fouling stream in the shell. On a U-tube bundle the cleanable side is the shell side, because nothing rigid passes a 180 degree bend. Where tower water is the dirtier of the two streams, it belongs on the shell side even though the instinct is to put cooling water in the tubes.
Seasonal variation is larger than most designs acknowledge. Tower water supply temperature follows wet bulb, so the hot humid day is the design case and winter is the control problem. Size for summer and check the behaviour at the cold end of the range.
Fouling allowance is a design decision. Over-generous allowance produces excess surface, which means lower velocity when clean, which encourages the deposition it was meant to cover. Use your own water quality history rather than a default table.
Process Cooling Selection
Both streams, both pressure drops, and an honest fouling allowance.
Duty Inputs
- Process stream: Flow, in and out temperatures
- Coolant: Type, flow, supply temperature
- Pressure drop: Allowable each side
- Fouling: From experience where possible
Series
- WU for general duty
- CHX and CHXS for small loops
- OC where the process fluid is oil
- GC for hot gas streams
- Removable bundle for cleaning
Design Notes
- Fouling stream on the shell side
- Size for summer supply temperature
- Check winter control behaviour
- Bundle pull clearance
- Velocity high enough to discourage deposition
Related
Fouling Is the Whole Game on Cooling Duty
Clean on Condition, Not on the Calendar
Trend the approach temperature or the overall heat transfer coefficient over time. When it degrades past a threshold you have set, clean. Plants that adopt this almost always find they clean less often and lose less production than plants working to a fixed schedule.
It also gives you a real basis for deciding when a bundle has reached the end of its life, rather than replacing on age or on a hunch.
Velocity Discourages Deposition
Below a certain velocity, particles settle and deposits build. An oversized exchanger runs slower than a correctly sized one at the same flow, which is why excessive fouling allowance is self-defeating.
Pass count is how tube-side velocity is bought. Where the flow is low relative to the surface needed, more passes raise velocity into a useful range at a pressure drop cost worth paying.
