4 replies to this topic

[process85]

Hello everybody,

I know I am asking a very basic question but I am not able to find answer for these questions:

1)I have a MP steam header with Op. cond. 10kg/cm2g@220degC.There is a drip leg assembly provided on this header for removing the condensate formed.Drip leg assembly consists of a thermodynamic type steam trap and the downstream of this trap is connected to grade (Atmosphere.)
I need to fill data for the line upstream and downstream of this steam trap in line schedule.
My understanding is upstream conditions will be same as MP steam header condition, i.e vapor phase and Op. cond. as 10kg@220degC.
But I am confused about the conditions downstream of steam trap.
Kindly help me in providing this data.

2)I have a condensate pot which is operationg at 8kg/cm2g@150degC.There is a level gauge mounted on this condensate pot for which a drain connection with an isolation valve is provided.This level gauge drain is discharging to atmosphere.
I need to fill the data upstream and downstream of the isolation valve on level gauge drain.
My understanding is upstream conditions will be same as condensate pot conditions i.e liquid phase at 8kg@150degC.Downstream conditions will be mixed phase at 0kg@100degC.

Please help me provide answers to the above questions.

[Zauberberg]

If the steam trap discharges into atmosphere, you have zero (atmospheric) backpressure acting on the trap. That is the pressure downstream of the assembly.

The same philosophy is applied for the level gauge drain valve(s).

[process85]

If the steam trap discharges into atmosphere, you have zero (atmospheric) backpressure acting on the trap. That is the pressure downstream of the assembly.

The same philosophy is applied for the level gauge drain valve(s).

Thanks Zauberberg for your reply.
For pressure I am also aware will be zero or may be the back pressure that is due to the flow say may be 0.1kg.
But what I am not sure about is the temperature values and phase in both the scenarios.

[ankur2061]

Process 85

1. Considering that the downstream of the trap to atmosphere is a very short piece of pipe your line schedule should show the conditions as follows:

a. Operating Pressure: Atmospheric or 0 barg

b. Operating temperature: 100 deg C

2. For the condensate pot drain valve downstream again considering that the pipe piece to atmosphere is very short the line schedule should show:

a. Operating Pressure: Atmospheric or 0 barg

b. Operating temperature: 100 deg C

Remember that the condensate downstream of the trap as well as the drain valve is flashing to atmospheric pressure

Regards,
Ankur.

[Zauberberg]

Check the steam tables (attached) and you will see that, at 220 degC and 10 kg/cm2.g you can have only superheated steam - but not the condensate. So any condensate that can be collected inside the MP system must be colder than ~183 degC which is the saturation temperature.

The basic approach in determining the flash temperature (downstream of the trap/valve), is to perform isenthalpic flash calculation at the final flash/discharge pressure (~ 1 bara in your case). In other words, you set the initial conditions (e.g. 11 bara, 180 degC), look at the enthalpy of condensate, and then see what is the resultant temperature at 1 bara pressure, where enthalpy is equal to the initial conditions.

As Ankur has said, you are somewhere close to 100 degC, and the Excel workbook attached below can guide you to the final result.

Attached Files

•  XSteam Excel v2.6.xls   701.5KB   53 downloads