11 replies to this topic

[ProcessEng_12]

Hello all!!

Could anyone please help me in calculating the energy balance across steam let down valve?

In our plant we reduce the steam at 41kg/cm2 absolute 334 degree Celsius to 18kg/cm2 absolute. I want to calculate the temperature of 18kg/cm2 steam.

 

[Zauberberg]

Use Steam tables. Letdown is an isenthalpic operation.

 

http://www2.spiraxsa...team-tables.asp

 

Find enthalpy at p1 and T1, then use the calculated enthalpy and p2 to calculate T2.

[breizh]

https://www5.eere.en...amo_steam_tool/

Another tool if needed  (equipment calculator).

To keep in your toolbox.


Breizh

Edited by breizh, 17 May 2015 - 02:04 PM.

[fallah]

chemengg99,

 

The steam flow through a PRV is a constant enthalpy process in which the temperature would drop when the pressure does, mostly due to the expansion; then the energy is balanced across the valve as "enthalpy in" is equal to "enthalpy out".

 

To calculate the outlet temperature you can follow the procedure mentioned by Zauberberg...

[Bobby Strain]

Do they still publish Mollier diagrams for steam? You should get one.

 

Bobby

[Supriyo Mukherjee]

Dear Chemengg 99,

 

Follow the following steps.

1. Download steam & water properties addin- IAWFPS available in internet and Cheresources.

2. Integrate with your excel spreadsheet.

3. Using syntax of add in calculate enthalpy of 41 kg/cm2 and 334 degree Celsius steam.

4. Now for outlet condition of 18 kg/cm2 steam assume a temperature and calculate enthalpy.

5. Iterate or goal seek for the assumed temperature at 18 kg/cm2  now to make the enthalpy calculated in point 4 same as that calculated     in point 3.

6. This will give you your answer with certain deviation  as you are considering isenthalpic enpansion here. But I think that will do.

 

Regards,

 

Supnit

[samayaraj]

Dear Chemengg

 

Find attached the excel sheet to find the temperature of depressurized steam. This excel sheet contains inbuilt steam data already. Enable Macros before using this excel sheet. 

 

Throttling process is a constant enthalpy process, hence the enthalpy of steam in/out of the pressure reducing valve is same. Based on the inlet steam pressure P1 & temperature T1 you can find the enthalpy H using function h_pt(P1, T1) and with the same enthalpy H and downstream pressure P2 you can calculate the temperature T2 using function t_ph(P2, H).

 

For your reference, there are examples given in adjacent sheets to know more about the functions.

 

#Samayaraj

Attached Files

•  Temp of depressurized steam.xls   461.5KB   94 downloads

Edited by samayaraj, 14 May 2015 - 01:33 AM.

[farid.k]

sorry to ask..what if i simply simulate with hysys? put the valve and set the delta P. does it sound faster and easier to find the temperature at the outlet?

[samayaraj]

Ya farid, it's an instant solution...

[ProcessEng_12]

 

Zauberberg:

 

Thanks

[ProcessEng_12]

 

Supnit:

 

Thanks

[ProcessEng_12]

Fallah:

 

Thanks

..