2 replies to this topic

[Aditya000333]

Dear all ,
I want to learn how to calculate dew point calculation for my main fractionator in delayed Coker unit with continuous varying feed to unit and fluctuating steam injection into system

[latexman]

AI generated this answer.  A simulator is what I would recommend using.

 

A multicomponent dew point calculation involves iteratively assuming a temperature and calculating K-values for each component, then determining the liquid-phase mole fractions using the equation Xi = Yi / Ki. The dew point is reached when the sum of all liquid-phase mole fractions (ΣXi) equals one. For non-ideal mixtures, this involves solving complex equilibrium equations, often using Newton's method or other root-finding algorithms to find the correct temperature. 

The Dew Point Calculation Process (Iterative Method)

1. Assume a Temperature: Start by assuming a trial temperature for the mixture. 
2. Determine K-values: At the assumed temperature and given pressure, calculate the equilibrium K-value (Ki) for each component, where Ki = Yi / Xi (vapor mole fraction divided by liquid mole fraction). For non-ideal systems, these values are found using fugacity coefficients. 
3. Calculate Liquid Phase Compositions: Using the K-values, determine the mole fraction of each component in the liquid phase (Xi). 
4. Check the Sum of Liquid Compositions: Sum the calculated liquid mole fractions (ΣXi). 
5. Adjust Temperature:
   • If ΣXi = 1 (within a defined tolerance), the assumed temperature is the dew point. 
   • If ΣXi > 1, the assumed temperature is too high, so you must lower it. 
   • If ΣXi < 1, the assumed temperature is too low, so you must raise it. 
6. Repeat: Repeat steps 2-5 until the condition ΣXi = 1 is met. 

Key Equations and Concepts

• K-value: 

  The ratio of vapor phase mole fraction to liquid phase mole fraction: Ki = Yi / Xi. 
• Liquid phase mole fraction (Xi): 

  For a given component, Xi = Yi / Ki. 
• Summation condition: 

  The dew point is the temperature where the sum of all liquid-phase mole fractions equals one: ΣXi = 1. 
• Non-Ideal Systems: 

  For non-ideal mixtures, the calculation becomes more complex and often requires methods such as:

  • Poynting equations: for liquid-phase pressure effects. 
  • Fugacity coefficients: to account for deviations from ideal behavior. 
  • Newton's method: for solving the set of non-linear equations, which is a common root-finding technique for complex equilibrium problems. 

[breizh]

Hi,

Another resource for your application is Google.

 

Attached an excel sheet for this type of calculation.

 

Breizh

Attached Files

•  Bubble & Dew points calculation.xlsx   17.42KB   35 downloads