3 replies to this topic

[victorvikram]

Dear All,

I have a question on estimating steam requirements for various sections in CDU. In calculating the column overhead temperature, I need to know the steam flow rate in the tower top section. The steam flow rate at the tower top section is the sum of steam flow rates available at different sections.

Steam flow rate (tower top) = Steam flow rate (Residue) + Steam flow rate (HGO) + Steam flow rate (LGO) + Steam flow rate (Kerosene).

I have been told that the steam required to produce a required product can be obtained from pilot plant data or by the use of correlations. I don't have access to pilot plant data, therefore, I have to rely on correlations to estimate the steam flow rates. Is there any journals or handbooks that I can refer to? Appreciate your feedback on this matter.

Thank you.

[kkala]

I can only express a thought, having never dealt with distillation towers, even though worked for several refinery Projects. A crude distillation tower is assumed, with reboiler and pumparounds (steam flow "balance" is not understood, but it may not be significant). Useful handbooks on the subject can be:
1. "Petroleum refinery engineering" by W. L. Nelson, McGraw-Hill, 1958. Enthalpies and specific heats of petroleum fractions are reported in Chapter 5; Heat balance of a Fractionating Tower can be found in Example 16.1 of Chapter 16, titled Fractionator and Towers.
2. "Petroleum Refinery Distillation" by R. N. Watkins, Gulf 1979. Heat & material balance Calculations for Towers can be found in Chapter 2, titled "Atmospheric Tower". This book seems more detailed, while Nelson provides a view of all refinery operations.
Both books are for understanding the basics; then a heat and material balance can be easier made through a simulator, after considering crude as a mixture of pseudo components.

Edited by kkala, 05 July 2011 - 05:00 AM.

[Padmakar Katre]

Hi Vikram,
Addition to Mr. Kkala's useful and to the point comments,steam flow rate as a starting point can be considered as recommended values (X lbs/h per ft3/h of the product rate) , increased steam flow will increase the front end distillation of products i.e. proper flash point and lesser overlap, but it will have serious consequces like
1. higher diameter of the fractionator due to increase in the vapor load inside the column,
2. increase pump around/ overhead condenser duties
3. Increased load on the sour water stripper unit due to increased thru'put.

Hope you understand this.

[chemsac2]

Victorvikram,

Elements of Petroleum Processing by Jones in chapter 6 has detailed CDU system design with solved examples.

As suggested by kkala, Petroleum Refinery Distillation by Watkins is alo very good book on CDU design.

Typical stripping steam rates for various side-draws in crude main fractionator are as below.


Product Steam required (lb/gal product)
Naphtha 0.2-0.5
Kerosene/diesel 0.2-0.6
Gas oil 0.1-0.5
Topped crude oil 0.4-1.2

Regards,

Sachin

Edited by chemsac2, 08 July 2011 - 05:40 AM.