Expert ForumsSteam and Thermal Systems

Topic: Why are we getting wet steam from the electric steam generator?

anonymous
We are facing a problem with an electric steam generator operating on a controller that limits the power allowed to be use by the generator. We get wet steam that causes us operating problems in a feed mill plant that requires only dry saturated steam. We want to understand the process of steam generation on Mollier diagram and estimate the quantity of water that is carried with steam. We also need to plan the revision of the steam network. That boiler operates between 105 and 110 psig with a modulating feed valve on water. It is a 12-stage boiler of up to 984 kW.
  • Avatar Veerasamy Venkatesan Forum Moderator 13 Posts

    Re: Why are we getting wet steam from the electric steam generator?

    There could be more than one reason to get wet steam from the electric steam generator.
     
    The basics of steam generation are to add enough heat to the water and convert the water into fully dry steam.  The process of phase change (liquid water to steam vapors) occurs at a constant temperature.  However, heat needs to be supplied to the water continuously at that constant temperature also until the phase change is completed.  This constant temperature is termed as the saturation temperature and the steam after it is fully converted into dry steam is called saturated steam.  If the water is not fully converted into steam, it is called partially saturated steam (or wet steam).  If more heat is added to the saturated steam, its temperature rises and it is called super heated steam. 
     
    The saturation temperature and the quantity of heat (also known as Latent heat of vaporization) required to make phase change into dry steam depends upon the pressure of the water at which the phase change is taking place.  Saturated steam could become wet steam again, when it loses its heat content (known as Enthalpy of steam) in the transporting pipeline due to radiation losses.
     
    Hence the problem of getting wet steam (or partially saturated steam) at user end could be due to the following:

        1.  The load controller of the electric steam generator may be having some problem, in the way it controls the heat input and the way the controller responds to meet the sudden surge in steam demand.
        2.  The generator design may not be having sufficient mist-eliminators in its steam accumulating/separator drum.
        3.  Steam transport piping may not be sufficiently designed to remove condensate formed in the pipeline.
       
    Hence, if a user needs dry steam at certain pressure, then the user should generate steam at a higher pressure than required and reduce it to the required pressure at the point of use.  When steam at a higher pressure is reduced to lower pressure, through a letdown valve, it actually becomes superheated steam at the lower pressure.  When steam is supplied at super heated condition, it ensures dry steam supply to the user.
     
    Further analysis of the problem to find the suitable remedy requires more details/site visit by a steam system engineer.   A qualified steam system engineer could be found from the US DOE website http://www1.eere.energy.gov/industry/saveenergynow/partners/ee_steam.cfm
    who could help further. 

  • Avatar Jim Murrant Community Member 1 Post

    Re: Why are we getting wet steam from the electric steam generator?

    A boiler is a covered container in which water or other fluid is heated after being subjected to pressure. The steam or hot fluid is then disseminated out of the boiler for its utilization in heating. A safety bulb is an integral part of a boiler, and is essential for the prevention of overheating and subsequent damage to the boiler that can be caused by a probable explosion. http://www.plumbarena.co.uk