Direct Contact or Open CondensersA presentation by:Farooq Ahmad Shah
What are Direct Contact Condensers?• Exhaust steam and cooling water come in direct contactand mix together.• Steam condenses suddenly achieving the temperature ofcooling water.• Condensate and cooling water are continuously takenout.• Used in special cases▫ When dry cooling towers are used▫ Geothermal power plants▫ Plants that use temperature differences in ocean waters• Mainly three types▫ Spray condenser▫ Barometric condenser▫ Ejector or jet condenser
Advantages vs. Disadvantages• Advantages▫ Heat exchange through direct contact, thus less waterquantity required.▫ Construction is simpler thus less costly.▫ Maintenance is simple and cheap.▫ Requires small floor space.• Disadvantages▫ If condensate contains impurities cannot be reused.▫ Low vacuum efficiency hence not suitable for largerplants.▫ More power required for air pump.
Spray Condenser• Modern direct contact condenser.• Water is sprayed into the steam.• Part of the condensate , equal to the turbineexhaust flow, is sent back as feedwater.• Rest is cooled in a cooling tower. Cooled water issprayed into the turbine exhaust, process isrepeated.• Continuously circulated cooling water must bepure.
• Mass balance• Energy balance• Cooling water to steam ratio• h2-h3 is larger since large latent heat ofvaporization where as h3-h5 is much smaller.Spray Condenser
• Early type of Direct–Contact Condenser.• The vacuum is obtained by an air pump that sucks airout from the top.• Baffles are used which increases the surface to volumeratio.• Has a long vertical tale pipe (at least 10.23m) making itdifficult to access.• The outlet of the tail pipe must be at least 6” below theminimum level of the water in the hot valve.• The condensate cannot be reused in boiler since it iscontaminated by cooling water.• No need of condensate pump.Barometric Condenser
• The cooling water is made tocascade down a series of baffles inthe form of water curtains orsheets.• The static head compresses themixture to atmospheric pressureand thus replaces the pump.• The steam condenses and themixture goes down a tail pipe to thehot well.• The larger the H the easier it is forthe condensate to flow down to thehot well.Barometric Condenser
Jet or Ejector Condenser• A kind of direct contactcondenser in which coolingwater and steam mix in aseries of combining cones.• Kinetic energy of steam isexpended to drain off thecondensate and cooling waterfrom the condenser.• It reduces the tail pipe heightin barometric condenser.• Removes the need of air pump.• The condensate cannot bereused in boiler since it iscontaminated by coolingwater.Parallel flowCounter flow
• Water enters from the top through nozzles. Its issurrounded by guide cones.• Steam entering from the side is guided on to thesurface of water through guiding cones.• Due to decreasing area of guide cones, potentialenergy is converted into kinetic energy.• Decrease in potential energy causes pressure dropresulting in suction.• Suction pulls more and more steam forcondensation.• Water and condensate then enter diverging section. Here velocity decreases andpressure increases.• Built up pressure enable the mixture of condensate and water to dischargedautomatically in the hot well.• A non return valve prevents sudden rush of water from hot well into the turbinein event of a failure in supply of injection.Jet or Ejector Condenser