Low saturated steam velocity
Low saturated steam velocity
(OP)
Hi,
I have a question regarding a new steam distribution line we are designing. We need to design a steam distribution line that will work both ways: during start up of the plant we need to guarantee a steam import flowrate of about 45t/h but then, under normal operation, it will drop to a steam export flowrate of about 3 t/h (desuperheated steam from a process boiler). The plant supplier will use the same line for both purposes. Due to pressure drop issues the line will be something between 8" and 10". Under normal operating conditions steam velocity will then be between 1 and 1.7 m/s. This is way below the recommended saturated steam velocity. What problems can arise from this situation? Higher losses due to excessive condesation? Will it help if we consider a higher degree of superheating at the outlet of the desuperheater? Does it justify creating a different line for normal operating conditions?
Regards,
sefmp
I have a question regarding a new steam distribution line we are designing. We need to design a steam distribution line that will work both ways: during start up of the plant we need to guarantee a steam import flowrate of about 45t/h but then, under normal operation, it will drop to a steam export flowrate of about 3 t/h (desuperheated steam from a process boiler). The plant supplier will use the same line for both purposes. Due to pressure drop issues the line will be something between 8" and 10". Under normal operating conditions steam velocity will then be between 1 and 1.7 m/s. This is way below the recommended saturated steam velocity. What problems can arise from this situation? Higher losses due to excessive condesation? Will it help if we consider a higher degree of superheating at the outlet of the desuperheater? Does it justify creating a different line for normal operating conditions?
Regards,
sefmp





RE: Low saturated steam velocity
If your steam user can take more superheat, you can raise the outlet temperature controller to give higher temperature.
Not knowing the distances involved nor the type of equipment that you will be using, you might put your temperature controller sensing unit at the end of the run, but that would only work if the flow is steady state and constant. Too much lag time if the flow is variable with this suggestion.
You could also calculate (or determine empirically) your temperature losses along the export route and put just enough superheat at your DSH outlet to enable the steam to arrive at the user approaching saturation. Seasonal temperature variations would have to enter into the design of that approach.
rmw
RE: Low saturated steam velocity
You are right, the DSH will work within 5 to 10 ºC of the steam stauration temperature. I was just wondering if it would be a good idea to use its adjustment to overcome the line size issue under export conditions. This is obviously easier than considering an independent line for steam export. After commissioning of the pant I will check the line losses and adjust the DSH accordingly. Maybe 5 to 10ºC is already enough.
sefmp
RE: Low saturated steam velocity
We at the same time take the 300 pound steam and reduce it to 175 steam + 50F-35F superheat for a 16 unit operation.