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Increasing Raw Natural Gas Dew Point and Molar Flow Rates
2

Increasing Raw Natural Gas Dew Point and Molar Flow Rates

Increasing Raw Natural Gas Dew Point and Molar Flow Rates

(OP)
Hello, I'm new in natural gas processing and refining.

I have this problem in that I need to separate HC liquid from Raw Natural Gas fresh from the well (@ 200 degF). The gas composition has very low water composition and low heavy carbon composition, thus its dew point temperature is around 97 degF and it has 17 MMSCFD molar flow rates at 1000 psig. They expect the separated gas around 30 MMSCFD and the liquid hydrocarbon flow rate at 1200 bbl/day. (I run simulations in Hysys for the problems)

My Question:

- Is there any way to increase the dew point temperature? since I only have 1 source of well.
- How can I increase the molar flow rates, so I can reach the specified properties?
- Is there usually any initial processing for the raw gas before I perform the separating process?

- if it's possible, can someone share their learning source for the process engineering of natural gas? I was initially a drafter and learned much about separator mechanical and sizing referring to GPSA, API, ASME, and stuff but lacked processing capability.

- if it's possible, can someone also share some of your works that use Hysys simulation (flow chart is enough) for processing raw natural gas from well as an example? Because it's easier to understand if there is an example. Even though I can find it on the internet, I'm not sure if it's really done by a professional and applicable in the real process (because I believe it must be more complicated).
Replies continue below

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RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

You can't have 17MM and 30MM. which is it?
Standard cubic ft is usually referenced at 14.7 psig and 69°F (sometimes 0°C in EU.
Never at 1000 psig and 97°F
Confirm your SCFD.
What are the specified properties?

Usually you want to reduce dew point temperature to get the gas dry enough to put in gas transmission pipeline. That is often done with a glycol treater.

The gas and condensate is first separated in gas/oil/water seperators.
Both are metered separately at the well site.
Once separated, water is disposed to tanks, condensate is pumped into a liquid gathering pipeline that takes it to condensate tank storage. Maybe trucks pick it up instead of a pipeline.
Gas Gathering pipeline transports gas to the glycol treating and metering station where it is dried in a glycol tower. Once dry you probably need a compressor station to inject it into meters and then on to the gas transmission pipeline.

You cannot increase molar gas flow.




--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

(OP)
Thank you for the reply.

- The raw gas composition (by Hysys calculation) is 17 MMSCFD, but the client gave me the expected refined gas spec (after the separator) to be 30 MMSCFD. Thus I wonder if molar gas flow can be changed by physical process or not; like changing its Pressure, Velocity, Temperature, or something that affects mass flow rate? I've tried adding a cooler, compressor, and stuff but the molar gas flow is still the same.

- By the Hysys calculation from raw gas composition and its properties, the HC dew point is 97 deg F. Since the raw gas temp from the well is ~200 degF, thus it's in vapor form. I want to increase its dew point (if possible) before separating it in GAS / 3-phase separator so I can reduce the Duty of the cooler instrument (Air Cooler / Chiller). It's related to sizing and material cost.

I'm Attaching the raw gas composition, and its properties from well.

https://files.engineering.com/getfile.aspx?folder=...
https://files.engineering.com/getfile.aspx?folder=...
https://files.engineering.com/getfile.aspx?folder=...

Also Thanks for your brief explanation of gas processing

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

Molar flow is fixed. It is the "weight" or number, or volume, depending on which conversion factor you use, of all the molecules in a unit mole of gas, which is about 379 ft3 at std conditions for all gases.

1 mole of Natural gas CH4 has a mole weight of 1 Carbon atom (atomic number=12) + 4 hydrogen (1 each) = 16
1 mole of Oxygen O2 is 2x16=32

If you mixed them both at standard conditions, then you would have 2 moles x 379ft3/mole of mixed gas. = 758ft3

30MMSCF of natural gas = 30MM / 379 = 79,155.6 moles. That's never going to change.

That's only the basic stuff. Not much process there except for glycol drying. If you have H2S, or other stuff in the stream, you may need to do more processing. Liquid extraction and further separation of the butane and Propane gas, and any other HC liquid condensates will happen at a central processing plant, which might be done at the field, or sometimes a couple hundred km into the gas transmission pipeline.

Natural gas coming from a well is usually assumed to be fully saturated (full of all the water it can possibly jold at the given formation temperature). There are formations that are dry, but that isn't normally the case. If you want more water, you will probably have to add steam into the flow stream and increase the stream temperature. I suspect your cooler isn't going to like that.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

Quote (Lowrentstuff)

I want to increase its dew point (if possible) before separating it in GAS / 3-phase separator so I can reduce the Duty of the cooler instrument (Air Cooler / Chiller).

No disrespect intended, but you clearly need to start with developing an understanding of the fundamental concepts involved here before jumping into process engineering and HYSYS modeling.

E.g. explain how increasing the dew point of your natural gas stream would decrease cooling duty.

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

I didn't want to know that. 😕

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

@Lowenstuff,

Its quite common that the process engineer cant get the reservoir people numbers to match based on the composition he gets from the reservoir engineer. One trap to avoid is if the reservoir people include any lift gas. Unlikely in this case but it happens. Also, check that their model and your model uses the same EOS.

One way to solve the dilemma is to "modify" the well stream in the HYSYS model. What I would do is to get the test separator pressure that the model is based on. In your case the conditions for the 30 MMSCFD flow (could be standard conditions e.g. 60ºF and 0 PSIG but it could also be something else. Then do a flash with the specified composition at this condition and the take the flash gas from the flash and add it to the well fluid until you get the gas flow the reservoir model predicts. I had set up a model with some adjusts etc to automate it.

Its very difficult to get the reservoir guys to see the problem. But try to explain your metodology and at least get a buy in.

I no longer work in O&G so i cant help you more here.

--- Best regards, Morten Andersen

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

(OP)
Thank you all @1503-44, @GBTorpenhow, @MortenA for your answer~

@GBTorpenhow, the initial problem is the client wants HC liquid product to be ~1300 bbl/day. since the raw natural gas is dry (I just know it's unusual, perhaps I'm going to ask the client to make sure again) I need to reduce its temperature from 200 deg F to ~15 deg F so I can achieve that production rate. But to reduce that much temperature I need a bigger Air-cooler, chiller, and/or heat exchanger. So I thought if it's possible to increase dew points then I need only to reduce the raw gas temperature from 200 deg F to let's say ~100 deg F, and by that, I perhaps only need a smaller air cooler and/or heat exchanger.

But later I found out that even if I get 1300 bbl/day of HC liquid from the 3-Phase separator, after the distillation/fractionation column, the Heavy Liquid production is still around 200 bbl/day because I suspect the raw gas composition has a small amount of Heavy HC mole composition at the first place.

and I thank you again for your concern, that's why I'm also asking for learning source material for whatever I'm lacking. Because I have no clue what I'm doing, to be honest. I'm just following the Hysys course that you need this and that and voila you get your product. But life must go on and I need to learn new things.

Alright sir @MortenA, I'm going to try your suggestion. Thank you~

and thank you so much again, all~

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates



I think there is not 200 bbls of C-n there.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

(OP)


oh yeah, you're right @1503-44. Above are the Hysys calculations if I follow the gas flow rate at 17 MMSCFD. Below are the calculation of the what-if scenario when the raw gas flows at 30 MMSCFD, and it barely reaches 200 bbl/days.



Unless the specs of the equipment output they give me are designed specs and not production specs, I guess can do nothing since the product contains low liquid flow of Heavier HC in the first place.

RE: Increasing Raw Natural Gas Dew Point and Molar Flow Rates

@Lowrenstuff,

That is actually also a possibility - they gave you the design capacity (based on gas flow) and a production profile to confirm how a process designed for 30 MMSCFD would operate with the expected lower flow.

--- Best regards, Morten Andersen

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