7 replies to this topic

[ashetty]

I`m currently involved in a gas sweetening / Sulphur recovery revamp project.

Please refer attached sketch. On the hand drawn portion on the top right hand corner, the blue part is existing set up and the red parts are the new additions.
The required inlet pressure at the SRU units is 12.35 Psig.

Due to additional gas from new facilities (Red) the back-pressure at the existing Gas treating units outlet has increased. This means that the current operating pressure of stripper/reflux separator is less than my calculated pressure and therefore the operating pressure of reflux drums and stripper has to be slightly increased as shown in the Schematic .Im now trying to report the means to achieve that.

At my calculated minimum operating Pressure of 13.4 Psig for reflux seperator, the pressure at the top of column would be 14.2 Psig. This is based on pressure drop of 0.59 Psig for the overheads condenser plus line losses. This implies that to achieve the SRU B/L pressure of 12.35 Psig (at increased flow), the Column overhead pressure would be maintained at 14.2 Psig. In order to do that the following measures would have to be in place

● Operator would input set point of 12.67 Psig for PIC-123. At this set point, the reflux drum K82-D-243 would be operating at 13.4 Psig
● 13.4 Psig is the dewpoint pressure of the acid gas from the reflux seperator, at the condensing temperature of the overhead stream, i.e the condensing temperature of the overhead product is fixed by the operating pressure of the drum. The operator would have to input this value (Dew-point temperature) as the setpoint of TIC-123 .As temperature in the condenser in controlled by the cooing medium (air), TIC-123 would maintain the setpoint by varying the speed of the fan. This is not a problem from the design point of view as the new set-point for the TIC is higher than the current one,and the condenser duty would be lower than it is at present.

This is where my understanding of the situation ends as the control scheme is a bit complicated and my experience in this regard a little limited.
I know that steam flow to reboilers would increase…but how, and what other actions would I have to take to operate this system under new conditions and will it effect any other parameters
BTW this is amine treating, and amine has a degrades at temperatures above 260 F…but our basic engineering team says that it would be OK to operate the column at this new pressure as the bottoms temperature would be around 260.

Best regards.

Attached Files

•  Schematic.pdf   504KB   132 downloads

[Erwin APRIANDI]

Dear ashetty, so what is the real question?

I've done 3 project for sweetening, gas enrichment, and sulphur recovery so I know a bit regarding to gas sweetening.

to have the operation of amine stripping column you should know what kind of amine that you are using. MDEA, DEA, Mixture of MDEA and DEA or you can get the chemical data for your solvent from your solvent supplier.

the normal operating range of amine reboiler is at 220 - 260 deg F but you can increase up to higher level, depend on the type of amine

[Ingegnè]

Hi all,
a question regarding sweetening gas:
In my case I need to sweeten gas from oilfield (70% CH4, 10% C2H8, ...) containing 30000 ppm of H2S and 20000 ppm of CO2, both to 4 ppm in the outlet. the gas flowrate is 210000 SMC/d = 7.5 MMSCFD at 140°F and 20 barg.
For this scope, a preliminary calculation results in 15 m3/hr of DEA.
In order to design packed tower and pumps what liquid flowrate should I consider? DEA is dissoved in water, isn't it? at what percentage? if it is around 15-25%, it results in a total liquid flowrate 4 times higher. Am I right?

Thnks

[Pronab]

If it is MDEA, then degradiation temperature is more than 150 Deg.C. We operate our reboiler temperature 129 ~ 131 Deg C, found no degradiation
problem.
Like Erwin I am also cofused What is the question!
Regards.

[ashetty]

Hello Apriandi/Pronab,

Operating pressure of the mentioned column needs to be increased due to changed conditions downstream.

My question is how does the operator increase the column pressure?

1>Changing the set-point for PIC-123
2>calculating and inputing new setpoint for TIC-123

Apart from these, the operator would also have to increase in Reboiler steam flow in order to raise the column pressure.How does he do this? By simply inputing a new (calculated) value for the Reboiler FIC? How would it affect other parameters?I was having trouble understanding the reboiler flow control scheme shown in the sketch.

Another concern was that the Diglycol amine might degrade at the new temperature...but that is no longer a concern.

Thanks

[Pronab]

Q1: Increase PIC-123 SET pressure gradually to desire set point. ( Remember not to exced flare set pressure).
Q2: TIC-123 is Reflux temperature, no need to calculate, just increase or decrease to desire point.

TIC -234 will adjust reboiler steam flow.There is no connection with TIC-123 to control reboiler steam flow.
You should do this gradually. If it is in the commossioning stage, put steam flow valve on manual and increase steam flow to
get desire top temperature.
As per your sketch, reboier steam flow is taken from sour fedd gas , amine flow and top temperature, which is a little bit complex.
I am not sure you are using any MVC system? If it is , initialy you should try manually, then one by one put CAS and then MVC(if it is there).
Is it MDEA or DGA in your amine system?
By the way where is the plant location.

Regards.

[ashetty]

Hello Pronab,

Q1: Increase PIC-123 SET pressure gradually to desire set point. ( Remember not to exced flare set pressure).
Yes.To be changed from present value to calculated value of 12.67 as shown in the sketch.Increase in pressue (old vs new)is not significant, so flare set pressure would not be exceeded, but thank you for your input.

Q2: TIC-123 is Reflux temperature, no need to calculate, just increase or decrease to desire point.
Though this can/will be done at site, i need to inform operator of the new set point for the TIC-123.No issues, it can be done with a simulator.

"TIC -234 will adjust reboiler steam flow.There is no connection with TIC-123 to control reboiler steam flow."
Yes i know.

You should do this gradually. If it is in the commossioning stage, put steam flow valve on manual and increase steam flow to
get desire top temperature.As per your sketch, reboier steam flow is taken from sour fedd gas , amine flow and top temperature, which is a little bit complex.
Good/useful suggestion.This is what i was looking for.Though i know the plant engineers would probabely know how to do this, i still need to give our inputs to the client.

Is it MDEA or DGA in your amine system?
DGA,as shown in sketch and previous post.

By the way where is the plant location.
Saudi Arabia.

Best Regards

[Pronab]

Ashetty

Can you update your progress.
I am keen to know how it is running.

Regards.