10 replies to this topic

[vista]

hi every1,

can anyboby tell me how can i calculate the reboiler duty for a gas treatment plant using MDEA?

I need the basic guidelines and formulae

i only have the parameters of reboiler operation with me right now

[latexman]

The basic equation for the reboiler is Q = UA(delta T)_LM. Use consistant units.

[ankur2061]

vista,

You might like to have a look at the following:

http://msdssearch.do...fromPage=GetDoc

http://articles.comp...g-amine?start=5

Regards,
Ankur.

[vista]

thanks to ankur and latexman

i m confused about heat transfer area (A)...we have fire tube reboiler totally immersed in a aqeous MDEA...so i want to know that heat transfer area will be of fire tube or the whole shell of the reboiler?

[Art Montemayor]

Vista:

You are having problems getting your query resolved because you haven't furnished any required and necessary basic data regarding your MDEA reboiler. Now you return with the additional, important detail that yours is a direct-fired reboiler. You totally omitted that very important detail in your original post where you should have given ALL of the basic data - including a sketch.

I have had many years of amine unit experience - in design, installation, operation, and modifications. I have a very good idea of what I believe you have in front of you. But I can't guess what it is that you specifically want (or need) to do: do you want to re-design the tube bundle? do you simply want to understand how to design it? do you need to replace the bundle?

Who designed and built your unit? how long has it operated? What is its capacity (rich MDEA circulation)? What is the MDEA concentration? What acid gases are you removing and what is the composition of the feed gas to the MDEA absorber? If this is an existing unit, then you should have a detailed P&ID and you should supply us with a copy. With this infomation and background we can start to answer your specific questions.

I know how the direct-fired tube bundle is designed and built. I've done it before. But I won't respond to a query that has no required basic data. Help us help you.

[vista]

Art Montemayor

thnax for your response;
well i m doing internship at gas processing facility comprising of sweetning unit using MDEA...here partial removal of CO2 and complete H2S removal is carried out..lean amine circulation is 85 USGPM..i only want to know how can i calculate the amount of heat transfered during an hour (reboiler duty)...what i need to know before calculating reboiler duty?...the design duty is 5.1 MMBTU/hr and flux rate 7500 BTU/hr/ft2 with fire tube area 680 ft2....i need to calculate the duty for the particular hour

[vista]

Art Montemayor

please find attached the schematic also...

Attached Files

•  reboiler.xlsx   14.6KB   254 downloads

[Art Montemayor]

Vista:

Refer to the attached Rev1 of your workbook and to the worksheet where I have depicted the PFD of your unit and made the comments on how to calculate the reboiler duty.
You can obtain MDEA data and calculation examples from such literature sources as:

• John Campbell's Gas Processing books;
• The GPSA Engineering Databook;
• Kohl & Reisenfeld's book, "Gas Purification".

You can also obtain a lot of useful MDEA acid gas removal information from the Bryan Research and Engineering website, http://www.bre.com/ where you can download a lot of useful and helpful MDEA process information for free – such as the example I am also attaching to this post.

Attached Files

•  Analysis of Various Flow Schemes for Sweetening with Amines.pdf   432.96KB   304 downloads
•  MDEA Reboiler Duty Calculation Rev1.xlsx   97.3KB   377 downloads

[vista]

Art Montemayer:

Thanks alot for your useful comments and guidance. that is really helpful. such type of detailed response is really appreciating...

one thing i would like to ask again is that, as you have mentioned in your attached workbook, that i can calculate the reboiler duty by fuel gas firing rate..now the issue is that we only have a pressure regulator installed in fuel gas line, this regulator is used to increase or decrease the pressure of the fuel gas as per requirement of reboiler temperature...can you please tell me how can i calculate the firing rate with this instrumentation....

you guidance at this querry will also be very helpful for me in better understanding of reboiler operation...

[Art Montemayor]

Vista:

If you have no direct reading flow meter on your fuel gas supply to the direct-fired reboiler, you obviously have a cheap, “low-capital investment” type of installation for your unit. That brings back a lot of memories for me because that was the case in many of my early engineering projects when I was your age. I would think you have a means of knowing the fuel gas being consumed in your unit because of the prices of fuel today and the drive to account for all flue gases put into the atmosphere. But if you can’t obtain the fuel gas firing rate, that’s OK. You still have another method:

In Kohl & Riesenfeld’s book, “Gas Purification”, 3^rd Edition, Chapter 2: “Ethanolamines for Hydrogen Sulfide and Carbon Dioxide Removal”, pages 74 & 75, you will find specific instructions on how to estimate the heat load in an amine reboiler.

“Sufficient heat must be supplied to:

• Provide sensible heat to raise the temperature of the feed rich solution to that of the lean solution leaving the reboiler;
• Provide heat of reaction to dissociate the amine acid-gas compounds; and,
• Evaporate the water that leaves the stripping section of the Stripper as steam with the acid gas.”

I think that is exactly what I wrote in my comments in the workbook – except that I am more specific and direct than Kohl or Riesenfeld: I furnished you with a PFD and identified the four (4) streams you must account for in the heat balance that I specify. That is why I went to the pains of drawing a PFD – so that you could see how the heat balance accounts for the reboiler duty.

Always remember the this basic advice given to me by mentor many, many years ago: “When in doubt, always generate a heat and mass balance”.

Kohl and Riesenfeld give the necessary data on heat of reaction for MDEA and furnish an academic discussion on “Reflux” use in the Stripper (which I have always criticized and found lacking in practical and hands-on engineering knowledge). I have never used Reflux in my acid gas units and found that it isn’t required in a properly designed unit.

[vista]

Art Montemayor:

thanks again...i will be back with my calculation results of heat balancing very soon...