Efficient use of steam in heat exchanger


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Efficient use of steam in heat exchanger

  1. 1. OUTLINE Introduction What is steam Types of steam Heat exchanger Steam in heat exchanger Basic ways to improve heat transfer Ways to improve steam efficiency Problems in steam equipment Conclusions References
  2. 2. INTRODUCTION The dramatic jump in petroleum prices over the recent years has created much impetus to reduce operating costs at chemical process plants. The plant’s steam resource is often a primary provider of heat to a process. So using steam efficiently helps reducing operation cost thereby generating savings.
  3. 3. STEAM Steam is the gas formed when water passes from the liquid to the gaseous state Steam is one of the most common and effective heat transfer mediums used in industry They are mainly used in heat exchangers, turbines, strippers, and chemical reaction vessels
  4. 4. TYPES OF STEAM WET STEAM Wet steam applies to steam when a portion of its water molecules have given up their energy (latent heat) and condense to form tiny water droplets Also known as saturated steam Mixture of water in the liquid state (tiny droplets) and gaseous state (steam)
  5. 5. DRY STEAMDry steam applies to steam when all its water molecules remain in the gaseous stateKnown as superheated steamIts a transparent gasSuperheated steam and liquid water cannot coexist under thermodynamic equilibrium
  6. 6. WET STEAM VS. DRY STEAMWET STEAMRapid, even heating through latent heat transferHigh heat transfer coefficientOriginates from waterUsed for heating, cooking, drying or other procedures in industriesDRY STEAMLow heat transfer coefficientTemperature may be extremely highSensible heat used to transfer heatExclusively used in turbines
  7. 7. HEAT EXCHANGER Heat exchanger an equipment built for efficient heat transfer from one medium to another The media are separated by a solid wall so that they never mix They are widely used in refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, and natural gas processing counter-current and co-current flow
  8. 8. STEAM IN HEAT EXCHANGERSaturated steam is used in heat exchanger because it has high heat transfer coefficientHeat transfer with saturated steam utilizes the latent heat of steam, releasing a large amount of energy as it condensesProvision is made for condensate recovery
  9. 9. BASIC WAYS TO IMPROVEHEAT TRANSFERTemperature difference between the steam and process fluid should be highUsing saturated steam instead of superheated steam improves efficiency and minimizes operation costHigher the flow rate, higher will be the heat transferHigh conductivity of heat exchanger material helps in better heat transferLarger the surface area of conducting interfaces, greater the heat transfer rate
  10. 10. WAYS TO IMPROVE STEAMEFFICIENCYSTEAM TRAPSSteam traps are a type of automatic valve that filters out condensate (condensed steam) and non-condensable gases such as air without letting steam escapeThey need to be monitored for leakage and other faultsReplacing faulty traps minimizes loss of steam and improves efficiency
  11. 11. CONDENSATE RECOVERYThe condensate from traps can be returned to the boilerThis helps in reducing boiler fuel needsReducing boiler fuel needs through condensate recovery leads to less air pollution by lowering CO2, NOx and SOx emissionsINSULATING STEAM SYSTEMDespite high cost, insulation reduces heat lossHelps save energyMONITORING LEAKSChecking the steam distribution lines and valves for leakage and fixing them could save energy and enhance efficiencySTEAM METERINGSteam metering provides accurate steam usage statisticsIt can be a useful troubleshooting tool
  12. 12. PROBLEMS IN STEAMEQUIPMENTWATER HAMMER (STEAM HAMMER)Steam first supplied to steam distribution piping or steam- using equipment, a metallic and repetitive bang, bang, bang, or even sometimes a violent boom accompanied by vibration may be heardCaused by high levels of accumulated condensate inside the equipment
  13. 13. Water hammer causes a momentary abrupt pressure change of over 10MPa inside the pipingCan severely damage piping and equipment
  14. 14. FIXING ITRapid discharge of condensate is critical from a preventative maintenance standpointThe speed of condensate discharge combined with how smoothly the process occurs are two extremely important factors in the fight against water hammer in steam-using equipmentProper design and orientation of the equipment
  15. 15. STALLOccurs when the necessary pressure differential across a drainage device such as a trap becomes negativeCondensate is no longer discharged from the drainage device and instead pools inside the heat exchangerLinked to the following problems - ruptured heaters, water hammer, uneven heating temperatures
  16. 16. FIXING ITIncreasing trap inlet (primary) pressureReducing trap outlet (secondary) pressure
  17. 17. CONCLUSIONSBy proper use of steam, operational cost can be minimized and high efficiency is achievedCondensate recovery and recycling back to boiler helps reducing boiler fuel needs thereby minimizing pollutionDamage to equipment can be averted by properly regulating the steamUsing steam intelligently lowers carbon emission
  18. 18. REFERENCEShttp://www.tlv.com/global/SG/steam-theoryJames R. Risko, optimize the Entire Steam System, CEP June 2008, 31-32James R. Risko, Understanding Steam Traps, CEP Feb 2011, 21- 26James R. Risko, Handle Steam More Intelligently, CHEMICAL ENGINEERING www.che.com Nov 2006, 44-48