5 replies to this topic

[lee1706]

Hi, I have modeled methane gas separator process as attached file. (I want to upload HYSYS hsc. file, however there is note saying 'You're not permitted to upload this kind file' so only image file)

 

Current process is simple, Feed LNG is fed to tank and goes to vaporizer, then go to separator. Vapor from separaror goes to consumer and liquid such as ethane, propane etc. in the separator goes back to tank as recycle.

 

1. What I am wondering first is why mass flow rate increase as recycle iteration number is increased in the steady state.

 

2. Finally what I am trying to do is dynamic simulation after steady state setting.

Intended process is same as the attached file, however the different is that  feed stream valve is closed (meaning no feed stream) and LNG liquid flow to vaporizer will be made from initial holdup in the tank.

So the tank will have 2 outlet streans(Boil off gas and LNG liquid flow to vaporizer) and 1 inlet(heavy hydrocarbon such as ethane and propane etc).

After then I expected to see how LNG composition in the tank will vary as time goes.

As I am begainer to HYSYS, so not sure whether the mentioned process above can be solved through HYSYS.

Please anyone help me.

Thanks.

Edited by lee1706, 02 January 2018 - 11:10 PM.

[Bobby Strain]

This process is not one that would be used in actual operation. It appears to be an academic query. So, what is your objective?

 

Bobby

[lee1706]

Hi Bobby,

Thanks for the attention on this post.

The intended process is for the ship operation, not an onshore purpose.

As you know, LNG is potential fuel for the ship as an alternatvie to HFO.

The reson I don't need feed flow is that LNG will be loaded in port, and then ship start using LNG stored in the tank during sailing. That's whay I have mentioned that valve in feed flow will be closed as I do not need that flow.

 

The attached porcess in previous post is the actual used in the ship.

 

Several engine makers provide LNG duel fuel engine with some Methane Number limit, therefore separator is required. After separtor, vapor(mainly methane) goes to engine, and liquid heavy hydrocarbon such as ethane, propane need to go somewhere(fuel tnak or separate tank etc.)

In that point of view, I got curiosity about what will happen if heavy hydrocarbon from separator is returned to tank, as some manufacturer design fuel gas supply system in such a manner \.

 

Do you think that process cannot be solved in the HYSYS?

Hope your help.

Thanks.

Edited by lee1706, 21 December 2017 - 09:37 PM.

[Bobby Strain]

I have never seen such a system. I know that engines designed for methane fuel use injectors at about 300 bar. So your scheme looks strange to me. Maybe you can point me to a system such as yours offered by an engine manufacturer.

 

Bobby

[lee1706]

Hi Bobby,

I cannot say what company I am working for,, but I can say I have reviewed this kind of fuel gas supply system many times.

 

 I can elaborate my object as following,

As per ABS LNG Bunkering Advisory,

typical LNG composition commerically utilized has following average composition(molar percentage) ;

- Methane : 90.4%

- Ethane : 6.4%

- Propane : 1.8%

- Butane : 0.9%

- Nitrogen : 0.5%

 

So we can consider 2 cases as following,

Case #1 : all components are vaporized. then we can check methane number to see suitability for targeted engine.

Case #2 : majority of methane and nitrogen are vaporized and ethane, propane etc remain liquid(due to boiling point difference)

 

For the case #1, I have used Wartsila Methane Number Calculator. Then it turns out methane number is not met.

For the case #2, Methane Number is met, however we need separator to remove liquid ethane, and propane etc.

So what I wann check through HYSYS is whether we need separate tank or we can send those liquid back to fuel tank.

 

if there are something wrong in my explaination, or you do not understand, please let me know.

Also please advise me whether that system can be solved through HYSYS which is interesting point.

thanks.

Edited by lee1706, 22 December 2017 - 02:15 AM.

[Bobby Strain]

Well, I got an education on LNG fuel systems for ship engines like Wartsilla. For simulation, you can approximate composition changes if you are creative. As far as I know, HYSYS won't perform a direct calculation. If you can use LNG from the USA, it should always meet the required methane number. You must analyze operation for the actual LNG compositions that the ship will use. Looking at the average is useless. Good luck.

 

Bobby

Edited by Bobby Strain, 22 December 2017 - 11:58 AM.