4 replies to this topic

[USR]

I am currently looking for some operating and sizing philosophy for LP condensate flash vessel.The flash vessel is vented to the atmosphere via a U loop.It handles LP condensate from various users and LP condensate from the MP condensate flash vessel.Anyone having expertise in this field can share their experience.I know my post is not very explicit please feel free to ask any data needed.

Edited by USR, 21 February 2011 - 11:57 PM.

Here are attached a typical condensate flash drum. This system is very simple for operation and design. This drum work almost alone because the holdup level is defined by the height of the outlet pipe of condensate , the most import device is the pressure control valve. This control valve ensures a constant pressure in the condensate main collector. This equipment work at atmosphere pressure, for that reason is very ease to calculate. You can calculate this drum by the same way than a liquid-vapor separator (there are many bibliographies for that). You can estimate the vapor flow to the drum by calculating the flash in the control valve using simulation or equilibrium curve for steam. Once you get the vapor flow, calculate the critical velocity and define the diameter of the drum as 100% of the critical velocity. The holdup typical is around 400 to 600 mm.

Attached Files

•  Condensate Flash Drum.pdf   12.73KB   402 downloads

[fallah]

What about using RO (restriction orifice) instead PV in the sketch for simplicity?

Edited by fallah, 06 March 2011 - 08:03 AM.

[Art Montemayor]

The submitted drawing shows a Pressure Controller regulating a control valve on the (steam?) condensate inlet line. [In Chemical Engineering we deal with a lot of different "condensates" and I think we should try to be specific in at least that detail.] Steam condensate is formed by condensing a utility steam supply on heating demand or by a power generation system such as a steam turbine. Either way, ALL steam condensate formed in a process plant is collected and sent back to it boiler origin to complete the Rankine cycle. That means that LEVEL CONTROLLERS are used to monitor the creation of the condensate and used to regulate its transport to a convenient collection system for ultimate return to a boiler. A Pressure Controller is not the correct instrument for this application.

A Resistance Orifice (RO) is certainly not a correct device to use for this application either. Not only is not an instrument, it is a latent safety hazard in the steam condensation application I've just described. The RO CANNOT CONTROL and ensure that a safe and required condensate seal always exists upstream of it. That means that when all the condensate flows through the RO, a steam BLOW-THROUGH event will be generated, sending high pressure steam downstream to a low-pressure designed system. This certainly is not something to recommend for this application - unless further detailed and accurate basic data is furnished. But since USR is not being explicit, no recommendation can be given.

[fallah]

A Resistance Orifice (RO) is certainly not a correct device to use for this application either. Not only is not an instrument, it is a latent safety hazard in the steam condensation application I've just described. The RO CANNOT CONTROL and ensure that a safe and required condensate seal always exists upstream of it. That means that when all the condensate flows through the RO, a steam BLOW-THROUGH event will be generated, sending high pressure steam downstream to a low-pressure designed system. This certainly is not something to recommend for this application - unless further detailed and accurate basic data is furnished. But since USR is not being explicit, no recommendation can be given.

Above mentioned statements are generally right regarding RO usage in condensate lines.But i think in the sketch under discussion the condensate collector has certainly been fed through some LV or steam traps in upstream.Thus in this system steam BLOW-THROUGH could be a hazard firstly across LV or steam trap rather than RO.

Anyway,IMO a proper sized RO could be installed right at the inlet of flash drum to avoid flashing in the condensate collector provided that proper material would be considered its downstream against erosion due to two phase flow created by flashing.