3 replies to this topic

[LexiTran]

I'm doing a project that design LPS for hydrotreating, but I have a problem of calculating the diameter and the area of the LPS. The diameter and the area of the LPS are so small.

I got the density of the hydrogen sulfide = 6.17 g/L by using formula PV = ZnRT and crude oil was 54.54 lb /ft^3 (0.874*62.4 lb/ft^3). From the density of both crude oil and H2S, I calculated the maximum velocity which was 1.3042 ft/s. Then I calculated the Volume which was using a formula PV=ZnRT to find the Volume then divide by day, 24 hrs and 3600s to look for the volumetric flow rate. To find the Area, I took Volumetric flow rate / maximum velocity, and then I calculated the diameter of the LPS by knowing Area. From what I said above, I got Area = 0.037 ft^2 and the diameter was 0.108 ft.

I just want to know where I did wrong, why my number was so small for LPS. Thanks for all of your help.


Lexi

[Art Montemayor]

Lexi:

I don’t think we should all have to struggle with what you state and try to guess at what you are thinking. I think that is YOUR responsibility – if you want concise, clear, and accurate advise and comments. I’m not referring to a “language barrier”; I’m referring to the bad presentation of data and equally bad description of what you are trying to describe. Bear in mind that we “can’t read your mind” and we don’t have the slightest clue of what you could be up against. You should describe what it is that you have as a problem and then describe what is giving you a problem(s) and ask a specific question. Let me show you how your mental process is not organized by my remarks in RED:

“I have a problem of calculating the diameter and the area of the LPS”
There is an external surface area, an internal surface area, and a superficial cross-sectional area of a cylindrical vessel (which I have to presume you are using). What area are you referring to?

“From the density of both crude oil and H2S, I calculated the maximum velocity which was 1.3042 ft/s”
How did you calculate the answer? What relationship did you use? What factors? What reference?
By the “maximum velocity”, do you mean the top velocity of the feed? Of the vapor? Of the liquid phase? Or do you mean the Maximum Allowable Superficial Vapor Velocity inside the separator?

“To find the Area, I took Volumetric flow rate / maximum velocity”
What do you mean by “volumetric flow rate”? The flow rate of the feed? The flow rate of the vapor? The flow rate of the liquid? Again, you are forcing us to guess and speculate at what you are trying to say.

“I just want to know where I did wrong”
What you have been doing wrong is not organizing your thoughts and writing them down clearly and specifically so that others can understand what you are trying to state. This mental and writing process is a major pre-requisite in ALL languages – not only English.

I’m going to gamble and guess that you are trying to separate a mixture of crude oil and hydrogen sulfide by using a vapor-liquid separator. If so, you are immediately confronted with the realities of Stokes Law and the related Souders – Brown Relationship. In the Souders – Brown Relationship you are required to employ an empirical constant, “K”, that is dependent on several factors (which you have failed to state or take into consideration). Please go to the following thread in this same Student Forum and download the workbook found in Post #4:

http://www.cheresour...x...


Read the entire workbook and learn WHAT is being done and WHY. This workbook is not for doing your thinking for you. It is only for carrying out the mundane mathematical exercise. YOU have to understand why you are applying the referenced equations and what is the logic of employing them. You are also responsible for the accurate and logical input into the workbook. Use the correct units and the correct “K”. I cannot over-emphasis that the workbook will not do your thinking for you. YOU will always have to furnish that.

[LexiTran]

Let me re-state what I said on the previous posted. For my project, there was a 30642168 lbs of crude oil and H2S that entered to the LPS and I have to caculate how much H2S evaporate from the LPS and how much Hydrocarbon go to the next part, fractionator.

First, I want to calculate the area, diameter of the LPS. I calculated Maximum Superficial Vapor Velocity, which was 1.3042 ft/s. Then I calculated the area of of cross sectional area which was 0.036 ft2 then the diameter.

I hope I would state little bit clear. Thanks for your advise and help.


Lexi

[Art Montemayor]

Lexi:

You still have not addressed the critical points I raised:

1. How did you calculate the answer? What relationship did you use? What factors? What reference?
2. What do you mean by “volumetric flow rate”? The flow rate of the feed? The flow rate of the vapor?

Have you tried using the Workbook I've made available to you? Have you read through the various sections? Do you understand the importance of applying an appropriate "K" value?

If you show your calculations and the steps employed to arrive at the final answer, we can better analyze to see if you are making any logic or application mistakes. You state you have "30642168 lbs of crude oil and H2S". This doesn't mean much to a process engineer because it is a quantity, not a RATE. You must obtain a design flow rate in order to use the Souders - Brown relationship and obtain an allowable velocity (which is a rate!).

You must accept a position of being critical of any suspicious calculations that don't make sense - even your own. We can't help you if your pride won't allow you. Show us your calculations and logical steps and we can help you. In order to expedite a quick response and show off your calculation ability, I recommend that you use an Excel spread sheet format and upload it here so that we can clearly see what you have done.

http://www.cheresour...?showtopic=3621
Post #8

You can use these prepared calculation sheets that I have uploaded on this forum for you and other students to use as caluclation formats. See the examples I have given you to get an idea of how engineering calculations are presented for review and checking.

Await your reply.