Steam quality from a boiler
Steam quality from a boiler
(OP)
Does anyone know of a good method to calculate the quality of steam leaving the disengagement space of a waste heat boiler? The boiler recovers heat from reactor effluent and produces steam to cool the process gas.
I am looking for a method on how to figure out how much water is entrained in the steam.
Thanks
I am looking for a method on how to figure out how much water is entrained in the steam.
Thanks





RE: Steam quality from a boiler
RE: Steam quality from a boiler
This seems to sound to me like a way of measuring the quality. I need a way to calculate this. How about an empirical method?
Anyone know of any books/articles about something similar to this?
RE: Steam quality from a boiler
If the upstream condition is denoted as "1" and the downstream condition is denoted as "2", then
X1 = (h2-hf1) / hfg1, where
X1 = quality of steam at high pressure
hf1 = enthalpy of saturated liquid at high pressure
hfg1 = enthalpy of vaporization at high pressure
h2 = enthalpy of (superheated) throttled steam at low pressure
h2 is looked up in a steam table based upon the temperature reading from the throttling calorimeter.
I hope this helps.
RE: Steam quality from a boiler
RE: Steam quality from a boiler
RE: Steam quality from a boiler
Sorry if I was a little unclear in making it sound like I was at the plant. I found out this morning that it's not so much to help the operation of this boiler, but to be able to provide a value of the steam that will be produced before the boiler is even in operation.
RE: Steam quality from a boiler
RE: Steam quality from a boiler
*grumble grumble*
RE: Steam quality from a boiler
You need to use the Souders-Brown equation to calculate entrainment in your system. Go to Amistco.com, they explain it nicely.
Regards
Ahmed Vawda
Process Engineer
Al Khaleej Sugar - Dubai
avawda@aksugar.co.ae
RE: Steam quality from a boiler
I have been looking, but have not been able to find anything that will allow me to estimate this rate. There are so many variables involved in that, that it may be impossible to calculate. Splashing within the boiler, surface tension, gas velocity, distance from where the droplet forms to the outlet, etc. etc. etc. all affect the quality. I am not aware of a method to calculate how much all of these things contribute.
RE: Steam quality from a boiler
What is the steam used for? If it is only for process use, the normal boiler discharge of 99.5% quality should be OK if your header trapping stations are properly designed (big connections to prevent the condensate from "flying over" the drip pot).
But, if the steam goes to a turbine, it must be very dry.
Doesn't the boiler have an internal separator?
RE: Steam quality from a boiler
We are pretty sure that boiler manufacturers make this calculation, but so far we have not found anyone who is willing to give us the method of doing this calculation.
If I could calculate the amount of entrained liquid, then my problem would be solved (I think).
RE: Steam quality from a boiler
I doubt you'd get an accurate number from just manufacturer's data. Too many desk-bound assumptions. You simply have to go measure it. It's just one of those things. Plus, the manufacturer won't know anything about the field conditions (effectiveness of insulation, velocity, water chemistry, etc).
Whenever I have to convince a client he has a quality problem, I measure it at the boiler, half-way down the main, and at the user. Works every time.
Yours truly,
Steam Ejector P.E.
Serving the Western Hemisphere
RE: Steam quality from a boiler
I agree that there is no more accurate way of doing this than measuring it, but I need a way to calculate what this should be, even before the boiler is built. If a client comes to us wanting to know if they should spend the extra money to install a mesh mist-pad or other type of droplet eliminator, then we should be able to tell them whether it is worth their money or if it is not.
Canoman
RE: Steam quality from a boiler
You mention that the situation is bad enough to cause knocking in the piping. This problem may or may not be originating in the boiler. If the steam line is not adequately insulated and/or the piping does not have adequate drip legs and traps, then condensation accumulating in the piping downstream of the boiler can cause knocking. This can occur even if the quality of the steam leaving the boiler is 100%.
RE: Steam quality from a boiler
We've gotten a little off topic here. My main concern is figuring out how to calculate a steam quality for a designed, but not existing boiler. How can I do a somewhat accurate calculation to figure out the quality of steam that a newly designed boiler *should* produce? We are almost certain that boiler manufacturers have a way of doing this since steam quality needed for some pieces of equipment is so crucial. We just can't figure out how they do it, and they are not willing to disclose that information.
RE: Steam quality from a boiler