ONLINE ELECTRICAL ENGINEERING STUDY SITE

What is Steam Flashing?

Flash steam is produced when high pressure water is reduced to low pressure in the steam trap, such that its temperature is higher than that of saturation temperature corresponding to lower pressure. Thus this high temperature water (condensate) contains much higher energy than corresponding to its saturated condition at the lower pressure.

This excess energy in the water (condensate) causes part of the water (condensate) to flash.
Flashing is the name given to formation of steam from the hot-condensate when the same is released at reduced pressure.

Whether Flash Steam is a Different Steam ?

Flash steam is similar to any other normal steam, but its name is given on the basis of how it is produced.

How the Generation of Flash Steam is Different from Normal Steam?

Flash steam is produced/generated, when a high pressure condensate before the steam trap is exposed to a large pressure drop during its exit.
Flash steam generation is an automatic phenomenon depending upon the condensate parameters (system parameters). Do not depend upon the primary or secondary source of fuel.
Where as normal steam is produced mainly from Boiler or waste heat recovery steam generator (HRSG).
Normal steam generation requires the firing of primary or secondary fuel in the Boiler or HRSG. steam flash Flashing of Steam
It is the Excess energy or enthalpy available (due to fall in pressure) will flashes/evaporate some portion of the water/condensate when pressure falls.
Amount of Flash steam produced is given by the formula:
hf at 6 bar = 697.22 kJ/Kg
hf at 0 bar = 417.5 kJ/Kg
hfg at 0 bar = 2258 kJ/Kg
Flash steam generation for the condensate for values as given in Figure 1 = 0.124 Kg of steam/per Kg of water or 12.4 %.
Principal of energy of conservation associated with the generation of Flash steam is described in the given below example:
Let the condensate (water) is at a pressure of 6 Bar(g) as shown in the Figure 1 above.
1 kg of condensate at 6 Bar(g) and at 165oC produces 0.124 kg of flash steam at atmospheric pressure. As the summation of mass of flash steam and condensate is equal to 1, therefore amount of condensate is (1- 0.124) = 0.876 kg.
steam flashing
Pressure in Bar(g)Saturation Temperature in oCSpecific Enthalpies kJ/Kg
hfhfghg
Inlet Condition or condition before the steam trap6165 697.12066.32763.5
Outlet Condition or condition after the steam trap0100 417.462258.02675.5
Therefore from the above table:
Total enthalpy at atmospheric pressure of saturated water is hf417.46 kJ/kg
Total enthalpy in atmospheric pressure of saturated water is hg2675.5 kJ/kg
Therefore at exit condition or lower pressure of 0 bar(g)
Condensate (water) total enthalpy (from fig:2)0.876 × 417 = 365.3A
Steam total enthalpy (from fig:2)0.124 × 2675.5 = 331.76B
Thus at the exit point or lower pressure, total enthalpy in water ( condensate) and steam is A + B = 697.1
Thus when law of conservation of energy principle applies to Flash steam it is proved that the energy associated with the condensate at the inlet of the steam trap is equal to the energy associated with the water at the outlet of the steam trap.
Misconception when visualising Flash Steam
First thing that strikes while visualising flash steam clouds, as if leaking of live steam. But usually the flash steam clouds are on account of hot condensate being passed to atmosphere through a steam trap.
Volume of Flash steam generated
Water is denser than steam, so the specific volume of steam is far more than that of water. Thus a small increase in the generation of flash steam results in many fold increase in volume of steam generated.
Larger or greater is the differential pressure between the trap inlet and out parameters larger is the amount of flash steam generated and larger its volume.

Flash Steam Effects

Following are the areas where Flash steam effect should be given due consideration other it may lead to water hammer:
  • Condensate-receiver tank vent sizing
  • Steam-traps discharge piping.
  • Condensate return line sizing.




Comments/Feedbacks






Closely Related Articles SteamSteam Dryness FractionSuperheated Steam and Steam Phase DiagramVapour Properties Mollier Chart Heat CapacitiesHow to Calculate Steam Consumption During Plant Start Up Effective Steam Distribution SystemWhat is Water Hammer?More Related Articles Steam Boiler | Working principle and Types of BoilerMethods of Firing Steam BoilerFire Tube Boiler | Operation and Types of Fire Tube BoilerWater Tube Boiler | Operation and Types of Water Tube BoilerSteam Boiler Furnace Grate Firebox Combustion Chamber of FurnaceFeed Water and Steam Circuit of BoilerBoiler Feed Water Treatment Demineralization Reverse Osmosis Plant DeaeratorCoal Combustion TheoryFluidized Bed Combustion | Types and Advantages of Fluidized Bed CombustionSteam Condenser of TurbineJet Condenser | Low Level High Level Ejector Jet CondenserSurface Steam Condenser Economics of Power GenerationCooling Tower Useful Terms and Cooling Tower PerformanceCooling Tower Material and Main ComponentsPower Plant Fire Protection SystemHydrant System for Power Plant Fire ProtectionMedium Velocity Water Spray or MVWS System for Fire ProtectionFoam Fire Protection SystemFire Detection and Alarm SystemGas Extinguishing SystemElectric Power GenerationPower Plants and Types of Power PlantThermal Power Generation Plant or Thermal Power StationHydro Power Plant | Construction Working and History of Hydro power plantNuclear Power Station or Nuclear Power PlantDiesel Power StationWhy Supply Frequency is 50 Hz or 60 Hz?Economiser in Thermal Power Plant | EconomiserMHD Generation or Magneto Hydro Dynamic Power Generation Cogeneration | Combined Heat and PowerThermoelectric Power Generators or Seebeck Power GenerationCost of Electrical EnergyGas Turbine Power PlantNuclear ReactorSolar ElectricitySolar Energy System | History of Solar EnergyTypes of Solar Power StationComponents of a Solar Electric Generating SystemWhat is Photovoltaic Effect?Staebler Wronski EffectWorking Principle of Photovoltaic Cell or Solar CellSolar CellCharacteristics of a Solar Cell and Parameters of a Solar CellSolar Cell Manufacturing TechnologyWhat is a Solar PV Module?What is Standalone Solar Electric System?Solar LanternEngineering Thermodynamics Part 1Science of Engineering Thermodynamics Part 2Basic Law of Conservation and First Law of Thermodynamics Carnot Cycle and Reversed Carnot CycleEnthalpy Entropy and Second Law of ThermodynamicsRankine CycleRankine Cycle and Regenerative Feed HeatingRankine Cycle for Closed Feed Water Heaters and Rankine Cycle CogenerationIdeal Verses Actual Rankine CycleRankine Cycle Efficiency Improvement TechniquesWind Energy Electricity GenerationTheory of Wind Turbine Wind Turbine | Working and Types of Wind TurbineBasic Construction of Wind TurbineNew Articles Principle of Water Content Test of Insulating OilCollecting Oil Sample from Oil Immersed Electrical EquipmentCauses of Insulating Oil DeteriorationAcidity Test of Transformer Insulating OilMagnetic Flux