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Turning Vented Steam Back Into Water and Heat
Condensate recovery condensers capture steam that would otherwise vent to atmosphere and return it as hot water and usable heat. The sources are familiar to any plant engineer: the plume from a flash tank, exhaust from a turbine or steam-driven pump, vapor driven off a process heater, and utility steam left over after a heating header. Each pound condensed returns treated water, the chemicals in it and the energy spent heating it, and it removes a visible plume from the roof.
Four duties sit under this topic. Exhaust steam condensers handle low-pressure steam from turbines, pumps and engines, often with oil carryover. Flash steam condensers take the vapor released when high-pressure condensate drops to receiver pressure. Process vapor condensers deal with steam from cooking, evaporation or drying that has picked up product and noncondensables. Utility steam condensers recover steam from heating headers, tracing and dump lines.
What they share is a cooling side that is usually a water stream the plant can use, which makes the condenser a water heater as much as a condenser.
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Exhaust, Flash, Process and Utility Steam
Flash and utility steam are the cleanest members of the family. The vapor is essentially pure steam with a little air, and the condensate goes straight back to the boiler house. The design questions are the flash rate, which depends on the pressure drop the condensate takes, and the backpressure the condenser imposes on traps upstream. A flash condenser that adds backpressure can hold condensate in upstream heat exchangers and cut their capacity elsewhere in the plant.
Exhaust steam often carries lubricating oil and must be condensed at very low backpressure so the turbine or pump keeps its output. Process vapor is the dirtiest: it may carry sugars, proteins, fatty acids or fines from a cooker or evaporator, plus noncondensables, and its condensate may be unfit for boiler return without treatment. For process vapor, cleanability and inert venting outrank thermal rating as design issues.
Which Recovery Duty Applies
Classify the steam by source and cleanliness, then decide where the condensate and the heated water go. Clean flash or utility steam with condensate returning to the deaerator is a straightforward rating with a close approach. Exhaust steam needs oil separation ahead of the boiler and a low pressure drop. Process vapor needs a cleaning plan and a route for condensate that may be contaminated. The repeated mistake in this family is rating to average flash load when traps discharge in slugs, which leaves the condenser venting steam at every peak.
U-Tube or Gasketed Plate & Frame
A U-Tube shell and tube condenser with steam on the shell side and water in the tubes rides out thermal shock from slugs of hot condensate, takes up expansion without a bellows, and has a removable bundle for cleaning. It is the safer choice for exhaust steam and process vapor. A Gasketed Plate & Frame exchanger gives a very close temperature approach, which raises the heated-water temperature and the energy credit, and plates can be added as load grows. Its gaskets limit steam pressure and temperature, and its narrow channels dislike oily or product-laden vapor, so it fits clean flash and utility steam best.
Measured Return on Recovered Condensate
Recovered condensate cuts makeup water, treatment chemicals and the fuel needed to heat cold makeup, and each of those savings is easy to meter.
Removing vent plumes clears roof areas, ends corrosion around vent outlets and stops the visible steam that neighbors and inspectors notice.
Water Chemistry and Materials
Condensate is low in dissolved solids but can be aggressive: dissolved carbon dioxide forms carbonic acid that attacks carbon steel, and air in-leakage adds oxygen pitting. Stainless tubes are common on the steam side, while copper alloys appear on some water heating duties but are avoided where amine treatment chemicals travel with the steam. Erosion at the steam inlet from wet flash vapor justifies an impingement plate on shell and tube units. Water-side scaling depends on the heated stream's hardness and outlet temperature.
Data That Sizes Any Recovery Condenser
Provide the steam source, its pressure and flow including peaks, the upstream condensate pressure if the duty is flash, any oil or contaminants present, allowable backpressure, and the cooling water flow with inlet temperature and required outlet temperature. Say where the condensate goes, since a deaerator, a hot well and a drain each set a different outlet requirement.
