12 replies to this topic

[Dmitry]

Hello,

 

We have Amine tratment unit to remove CO2 and H2S from natural gas with 5,89 % mole fr. of CO2 and 0,15 % mole of H2S in ilet gas. We are using 50% weight of MDEA in lean amine solution.

  

Components      Content

                         wt %   mol %

H2S                 0,293   0,158

Helium              0,001   0,006

Hydrogen          0,007   0,066

CO2                 14,107 5,893

Nitrogen            0,371   0,243

Methane            79,238 90,803

Ethane               3,394   2,075

Propane             0,882   0,368

Iso-butane         0,262   0,083

Н -butane          0,214   0,068

Iso-pentane        0,134   0,034

Н- pentane        0,073   0,019

psC6                0,136   0,030

psC7                0,339   0,065

psC8                0,364   0,063

psC9                0,138   0,021

С10+               0,048   0,007

Total:               100,00 100,00

Standard density, kg/m3        0,766

Molar weight, g/mole 18,38

Relative density (against air) 0,636

 

Pressure in Absorber is 6 MPag.

Gas flow rate is 30 MMSCFD.

Lean amine flow rate is 50 m3/hr

Current lean amine temperature is +40 deg. C.

Inlet gas temperature is + 32 deg. C.

 

I know that lean amine temperature should be always higher at 5-10 deg. C. than gas temperature to avoid condensation of hydrocarbon in absorber, so it could start foaming, amine loses and so on... However we measured real HC dew point og gas upstream absorber and recieved it +15 deg. C.

 

My question is could we reduce gas temperatur from +40 to + 25 deg.C? We will keep 10 deg. C above HC dew point so no liquid should be in absorber. 

 

Many thanks,

Dmitry

Edited by Dmitry, 18 February 2015 - 12:37 AM.

[Zauberberg]

I'd suggest a good reading on the subject, pages 1-5 from the document: http://www.bre.com/p...ulesofthumb.pdf

 

If the absorber works fine with the current setup, don't try to fix it.

[Dmitry]

Thanks, we want to make a study with reducing gas temparature and removing of H2S and CO2. Now it's work fine but we want to increased gas flow from 30 MMSCFD to 60 MMSCFD, while design is 40 MMSCFD. So what do you think?

 

Dmitry

[Zauberberg]

I think that much more information would have to be provided in order to assess this subject. Everything is possible - the true question is at what price it comes.

 

We don't know the design case for your absorber, neither the design conditions for amine solution. If the absorber diameter is set based on the gas flow, I'm afraid there is no way you can put 100% more gas through it. If there is a good margin to increase vapor/gas throughput, then you would have to see if amine circulation rate or concentration can be increased, and if the entire regeneration section can handle the new set of conditions. I seriously doubt this can be achieved.

 

There is a whole array of unit benchmarking activities that need to be undertaken before one can give a more precise answer.

[PingPong]

However we measured real HC dew point og gas upstream absorber and recieved it +15 deg. C.

What really matters is not the hydrocarbon dewpoint of the gas upstream the absorber, but the hydrocarbon dewpoint of the sweet gas (free of CO₂ and H₂S) leaving the absorber at the top.

The lean amine has to be warmer than that sweet gas hydrocarbon dew dewpoint.

 

In fact: at any point in the absorber the amine has to be warmer than the hydrocarbon dewpoint of the gas at that same point.

Edited by PingPong, 18 February 2015 - 05:45 AM.

[RockDock]

How do you know your hydrocarbon dew point? Is it modeled or sampled? Do you have any BTEX?

[shan]

It seems to me that your lean amine temperature (+40 deg C) is higher than your inlet gas temperature (+ 32 deg C).  Isn't it?

[Bobby Strain]

If it's working, keep fixing it until it no longer works!

 

Bobby

[Dmitry]

How do you know your hydrocarbon dew point? Is it modeled or sampled? Do you have any BTEX?

Hello,

 

We have HC dew point measurement device, which I connected to the gas process line upstream Amine unit

 

Regards,

Dmitry

[Dmitry]

It seems to me that your lean amine temperature (+40 deg C) is higher than your inlet gas temperature (+ 32 deg C).  Isn't it?

Yes, this is normal operating range of temperatures. We always keep 5...8 deg. C. difference.

 

Regards,

Dmitry

[Dmitry]

If it's working, keep fixing it until it no longer works!

 

Bobby

 

Thanks, but I explained that we want to increase gas production from 30 MMSCFD to 60 MMSCFD, while design is 40 MMSCFD.  We already has 50 MMSCFD  with well CO2/H2S recovery, after we optimized lean amine flow and temperature. 

So adjusting amine flow rate, gas/amine temperature we try to optimize CO2/H2S recovery.

Only one way is to make a study with reducing gas temparature and removing of H2S and CO2 and next parameters.

 

Dmitry 

[RockDock]

A HC dew point of 15 C seems very low to me with a gas like yours.I would expect it to be around 25 C. I recommend taking a sample of the gas to send to the lab to be sure.

 

What is your sweet gas composition right now?

 

Decreasing the temperature will decrease the CO2 being reacted with the MDEA, increasing your CO2 in the sweet gas. Do you have room for the CO2 to increase?

[Bobby Strain]

Once you have achieved the maximum rate by adjusting parameters, add a bit of MEA to your amine solution. Or, call BASF and pay them for activator.

 

Bobby