7 replies to this topic

[Padmakar Katre]

Dear All Che Members,
I have a query related to the gas purification/treatment to obtain the valuable products. I have 4 gas inlet streams coming at different terminal conditions. My aim is to extract the valuable products like LPG (Propane and Butane) and Naphtha (C5+ material) and off-gas (Fuel Gas). The gas streams have components like H2, H2S, CO, CO2, NH3 and N2 with HC like C1 to C5 and some portion of heavies (modeled as Pseudo Components). Here my concern is I am not able to start with any particular process/operation like amine sweetening or should I separate the Gas-Liquid and then to route Gas for amine sweetening and the liquid to heavies recovery (C3 onwards). While performing simulations with Hysys I encountered as usual issue with Amine Package i.e. its compatibility with pseudo components. The second option which I studied is I have multistage compression system and subsequent refrigeration to condense the material at 26 Kg/cm2g and -40 Deg C. But the separation is just like most of Lighters still in Liquid phase and heavies in vapor phase (Substantial amount of each component in the mixture or significant lighters in gas). The liquid stream I routed to a distillation column with a partial condenser for Fuel Gas, LPG and Naphtha recovery but the LPG product I found with so much of lighters like CO2, NH3, C1 and C2. Whereas the fuel gas from my condenser has high content of C3 (Actual recovery of C3 in LPG is 53 % of the original feed on weight basis). Actually I am in fix how to treat this gas. Any comment, information related to the thread will be highly appreciated.
I am attaching the Gas Streams’ Data for your kind observation.

Attached Files

•  Gas Streams Analysis.xls   12.79KB   90 downloads

[joerd]

The typical configuration is to first separate the condensables (typically C4+), then stabilize the condensate to its RVP spec. The combined gases are sweetened, so you don't have to deal with H2S in the rest of your plant, then dried if necessary, then recover C3+.
As a first approach, don't model the amine unit in Hysys. Just use a component splitter to take out H2S and CO2 to spec. You may tweak the split ratios to model hydrocarbon pickup, and get a better estimate of flash gas and acid gas compositions. Also, saturate the amine unit product streams with water.

[Zauberberg]

Hello Padmakar,

It's difficult to answer your question without knowing some basic inputs, i.e. inlet conditions, desired products and their specifications, field changes over time etc. It looks like conceptual process design of a gas plant.

Depending on the items listed above, you should develop the overall configuration and select the optimum technology for each section of the plant (sweetening, dehydration, conditioning, LPG/NGL recovery, condensate stabilization/fractionation). There are some basic approaches, but you will have to do a lot of leg work till the final decision can be made.

I am attaching a simple flow scheme that shows basic approach/plant layout. In 99% cases you will end up with a flow scheme as presented in the attachment. Some elements/order of unit operations may vary depending on site specific issues.

Best regards,

Attached Files

•  Gas Plant.pdf   58.06KB   167 downloads

[JoeWong]

Padmakar,
I have problem in opening the XLS file...

You have mentioned that H2, H2S, CO, CO2, NH3, N2, heavy HC like C1 to C5, C6+ may be present.
It is hard to provide any advice without knowing the feed composition and product spec. I would think all components are common and easily managed by scheme as shown by Zauberberg except CO and NH3. May consider catalytic conversion of CO and acid absorption of NH3 if the quantity is significant.

[Padmakar Katre]

The typical configuration is to first separate the condensables (typically C4+), then stabilize the condensate to its RVP spec. The combined gases are sweetened, so you don't have to deal with H2S in the rest of your plant, then dried if necessary, then recover C3+.
As a first approach, don't model the amine unit in Hysys. Just use a component splitter to take out H2S and CO2 to spec. You may tweak the split ratios to model hydrocarbon pickup, and get a better estimate of flash gas and acid gas compositions. Also, saturate the amine unit product streams with water.

Thanks dear Joerd,
But it won't give me an accuracy in simulation results if I will use component splitter and start modeling my system. Anyways thanks for your reply.

Hello Padmakar,

It's difficult to answer your question without knowing some basic inputs, i.e. inlet conditions, desired products and their specifications, field changes over time etc. It looks like conceptual process design of a gas plant.

Depending on the items listed above, you should develop the overall configuration and select the optimum technology for each section of the plant (sweetening, dehydration, conditioning, LPG/NGL recovery, condensate stabilization/fractionation). There are some basic approaches, but you will have to do a lot of leg work till the final decision can be made.

I am attaching a simple flow scheme that shows basic approach/plant layout. In 99% cases you will end up with a flow scheme as presented in the attachment. Some elements/order of unit operations may vary depending on site specific issues.

Best regards,

Dear Zauberberg,
As usual hitting the issue at the right place. I studied couple of configurations so far I involved in this project. In one configuration I got all products on spec like for LPG (Spec-1 weathering test i.e. at 1 atm pressure and 2 Deg C temp LPG should be 95 vol% in vapor phase which will govern my lighters in LPG mainly C2 and another spec is Vapor Pressure at 65 Deg C., Fuel Gas is also ok and I can route it to Amine Sweetening and Naphtha i.e. C5+. But my problem is with the LPG recovery is maximum of 65% of the total C3-C4s in feed. Which is the main cause to worry that economics should be justified. I coompressed all these stream to 26 Kg/cm2g pressure and cooled it to (-)40 Deg C temperature where I found 27% liquid phase (more than the actual potentail of condensables in my feed.) but when this is flashed I lost 10 % of my propane with the Gas routed to Amine Sweetening. The liquid from the flash drum is fractionated in a column with full reflux (only vapor product) and bottom I got LPG+Naphtha which I sent it to another column(partial condenser) where I took LPG as Distillate and Naphtha as bottom Product. Now these two columns have vapor product streams and I am finding major loss of propane in these two streams. I am still looking for changing parameters in order to recover that lost Propane as LPG component and hence increased LPG recovery. Still I am concerned about the economics as there are multiple equipments are needed with the results which are not so impressive. I am just contineously putting efforts to get the desired results and will definetly share once I will find the best/optimized solution.

Padmakar,
I have problem in opening the XLS file...

You have mentioned that H2, H2S, CO, CO2, NH3, N2, heavy HC like C1 to C5, C6+ may be present.
It is hard to provide any advice without knowing the feed composition and product spec. I would think all components are common and easily managed by scheme as shown by Zauberberg except CO and NH3. May consider catalytic conversion of CO and acid absorption of NH3 if the quantity is significant.

Dear Joe,
Thanks for an acknowledgement of my query. It's actual a MS Excel workbook. If still you have problem to download it please let me know I will mail you. Replying to your comment related to NH3 removal which I achieved just by putting the water scrubber as the first tower and the further compression of the feeds. But still I have a CO/H2/N2/H2S/CO2 as the major constituents of the fuel gas. Amine sweeten will remove H2S and to a certain extent CO2 but I am not sure about the CO removal in amine sweetening unit. H2 and N2 I will keep in Fuel Gas. Waiting for your comments.

[abhi_agrawa]

Padmakar,

To remove both CO2 and H2S, you can also think about using a Caustic Wash. to remove CO you will have to use some kind of Adsorbent bed for this you will have to talk to Adsorbent vendors like Sud-chemie, BASF etc.

About getting low recoveries in flashes, I'd say use distillation columns.

Hope this helps,
Abhishek

[Zauberberg]

For efficient LPG recovery, consider one of the cryogenic turboexpander processes developed by Ortloff/UOP: GSP, SCORE, OHR etc. This is the best way for recovering C2+ or C3+ components from gas, if the gas is available at sufficiently high pressure. Otherwise, you will probably need a source of external refrigeration, or compression of gas upstream of turboexpander.

By connecting condensate stabilization system with gas treating facilities, the majority of C3+ components will be stripped of from condensate and processed within the gas train - ending up in the LPG product eventually. That could boost up the economics.

http://www.ortloff.com/ngl/nglmain.htm
http://www.ortloff.c...l/nglpapers.htm

Edited by Zauberberg, 17 September 2009 - 06:24 AM.

[Padmakar Katre]

Dear,
I achieved solutions with so many trial and errors on conceptualization of this configuration. I washed these gas streams with water to remove almost 99.99% NH3 and then Ammonia free gas is Amine Washed for removal of Acid Gases. Post Amine-treated gas is compressed to a pressure of 40 kg/cm2g pressure and cooler to (-) 40 Deg C temperature and flashed in 3-phase separator to get the falshed gas which was routed to Fuel Gas Header and Light Liquids(HC Liquids) is sent to LPG,Naphtha recovery where I found 87% of C3-C4 components recovery as LPG and balanced naphtha and very less quantity of fuel gas (C2 minus) products. I am just studying the economics involved. Thanks to all for their valuable contribution.