8 replies to this topic

[luuquocdai]

Hi all
Can you help me with this problem?
When I calculate Thermal Rating of Shell and Tube Heat Exchanger, I don't know how to define and calculate Liquid Critical Pressure.
You can see the attached file to get more details about my problem.
Can you show me the way to get this value?
Many thanks.
LuuQuocDai

[Padmakar Katre]

Hi all
Can you help me with this problem?
When I calculate Thermal Rating of Shell and Tube Heat Exchanger, I don't know how to define and calculate Liquid Critical Pressure.
You can see the attached file to get more details about my problem.
Can you show me the way to get this value?
Many thanks.
LuuQuocDai

Dear just upload the excel sheet with some background of the simulator/software you are using for thermal rating.

[MrShorty]

You may try reading The Properties of Liquids and Gases by Poling, Prausnitz, and others (I have the 4th edition in front of me, I know there's a 5th edition that may have newer information). Chapter 4 (section 3 in the 4th edition) discusses how to calculate pseudocritical properties for use in corresponding states type methods. Chapter 5 (section 6 in the 4th edition) discusses various ways to calculate true critical pressures. See if that helps.

[luuquocdai]

Here is my problem.
About Program which I use to calculate Thermo rating, now I am using HTRI program.
Dear Mr Shorty: Many thanks for your help, I got the book which you introduce to me.

Attached Files

•  untitled.jpg   206.74KB   56 downloads

[SSWBoy]

Presumably a process engineer would have provided you with enthalpy curves etc. for you to carry out your exchanger rating with? Why not ask them if you can get the critical pressure from their simulation.

[luuquocdai]

Dear SSWBoy
Do you have any diagrams or any curves like this?
If you have, could you share with me this curves.
Many thanks for your help.
With kind regards.
LuuQuocDai
23rd/Aug/2009

[daryon]

Hi, I'm a process engineer and have completed thermal design for a few S&T HTEX using HTFS Tasc+ (never HTRI), i've also generated a number of datasheets for S&T HTEX vendors to do thermal and mechanical design from. I have never specified critical properties of the fluids on the datasheets or in the thermal design software. I'm interested in what type of exchanger you are rating and a what the fluids are? I'm surprised you need critical properties; normally all need to calculate heat transfer coefficients & pressure drops is viscosity, thermal conductivity, specific heat capacity, and density.

[luuquocdai]

Dear Dragon
- The type of Heat exchanger which i calculated is AES type (follows TEMA type)
- The fluids:
In hot tube is Stripped Water
In cold shell is Sour Water
If you use HTRI Program to check Thermal Rating of Heat Exchangers, I'm sure that you have to define the properties of fluids in Shell and tubes.
I tried to use Simulation Program - ProII to get critical pressure and critical temperature, but I don't have enough data to complete simulation case.
If you have any ideals, please share with me.
I'm looking forwards your reply.
Thanks in advance.

LuuQuocDai
Email: luuquocdai@gmail.com
Tel: 0084988521012

[daryon]

Hi LuuQuocDai,

As you are dealing with water i think as a first pass you can use the critical properties of pure water:
Critical T = 647.13 K
Crtical P = 21,940 kPa
(source Perry's Chemcial Engienering Handbook Table 2-164)

The presence of CO2 and H2S in the water I think will change the critical properties slightly but this can possibly be ignored for the heat exchanger thermal design. If you're adding excess surface area to your calculated heat transfer area (typical to add 10 to 20%) then small inaccuarcies in the fluid phyiscal properties and resulting heat transfer coefficients will be catered for by this design margin.

I have access to HYSYS and have had a look at pure water critical properties compared to sour water as predicted by the Peng-Robinson property package (might not be the best for predicting water properties). HYSYS using P-R EOS predicts the following:

PURE WATER
Mole Fractions
H2O 1.00000000000000
H2S 0.000000000000000
CO2 0.000000000000000
True Tc [C] 374.148637002351
True Pc [bar_g] 220.186499588526


SOUR WATER
Mole Fractions
H2O 0.995000000000000
H2S 2.50000000000000e-003
CO2 2.50000000000000e-003
True Tc [C] 373.343662306650
True Pc [bar_g] 222.524770386953

Critical properties aren't that different, so it might well be O.k. to use vaules for pure water for both fluids.

Edited by daryon, 01 September 2009 - 03:37 AM.