6 replies to this topic

[kybele39]

Hello All,

I have attached an oil mix heating curves data. I need to size a water bath heater. The oil mix also has 45%CO2 in it.

My questions are:


1.Should I separate the 3 phase via multi-separators system?
2. CO2 content may create corrosion in the process coil (carbonic acid corrosion and the oil mix is sweet). So suitable material I choose Carbon steel with 6mm corrosion allowance instead 316L SS for the process coil. Is the 316L used in the wells water bath heater's process coil?
3.Fuel gas also has 45%CO2. I am thinking to remove the CO2 in the gas before its fired. With this way I am not going to have corrosion issue in the fire tube during shutdowns.
4.The glycol bath will be warm during the shutdowns like around 100F. This may be slows the carbonic acid corrosion in the process coil during shutdowns.

I appreciate if you give your inputs in this matter. Thank you.

Attached Files

•  three phase oil mix.pdf   108.55KB   20 downloads

Edited by kybele39, 19 October 2010 - 01:24 PM.

[Zauberberg]

Kybele,

What actually do you want to heat, and what does the system look like? Uploading a sketch or PFD would be of great help.

[kybele39]

There are 3 oil wells. From the wells the oil mix feed to the indirect fired water bath to heat up to 160F. However, the mix has 45% CO2. Also the fuel gas that will be fired for the fire tube consists 45% CO2.

My questions were:

1. If I feed the mix into heater, the mix has 3 phases vapor.liquid and aqueous. Can I use the Dittus Boelter equation? If yes how? SHould I first calculate the oil mix's properties ) Cp, k, viscosity? Or is there an emprical formula for three phases to calculate the heat transfer coefficient?

2.Instead of doing item one, should I use a multiphase separator to separate the 3 phases, then I can heat the liquid part in one coil and the gas portion in another process coil.

3.Is the 45% mass CO2 in the oil mix corrosive when you heat it? So best material is CS or 316L SS? ( I am planning to use CS with ample Corrosion allowance on the tube wall, like a 6mm)

4.Is the 45% CO2 can be combusted in the burner without corrosion? and the heating value of the flue gas will be slightly lower due to CO2?

5.Finally the glycol bath temperature that I will use probably would be around 225F. During the shutdowns, the bath temperature want be less then 120F. Is this temperature may help to slow down the corrosion occurrence in the process coil and fire tube?

ABove is my questions and command to such crude oil heating process. Could you please give your inputs if I am in the right track or I need more information for the wellstream oil mixes.

Mixes phase data is in my previous post as a pdf file.

PS:I also ask the client for the full wellstream composition and boiling point temperature for each well's oil. I have already pour point temps inmy hand in order to assay calculation of the each wells oil.

Again I thank you very much for any response to my topic.

Kybele

[Zauberberg]

From your post, I have concluded that the wellstream is water-free. If that is the case, there are no corrosion concerns and you can use Carbon Steel. As long as there is no aqueous phase inside the system, CO2 corrosion will not occur. This also addresses your query with respect to the fuel gas system.

Relative phase flowrates are also not known, but from my experience it is better to handle all streams separately - as far as heat transfer is concerned. Having multiphase flow can always introduce pressure surges, some sort of hammering, and vibration. This increases project cost but increases unit reliability as well.

The part related to shutdown - you should be on the safe side without heating, but check if cooling the trapped gas will cause water to condense - does your gas stream contains water? Combining CO2 and water will promote corrosion, so you may need to think about corrosion protection during shutdown periods, e.g. in terms of purging the coil and preserve it with non-corrosive fluid.

[kybele39]

Zauberberg,

Actually I have 3 phases Vapor, Liquid and Aqueous.

Here is the data chart attached for you. I have water in the oil mix. And 45% (mass) CO2 on both oil and the fuel gas. Fuel gas will be fired in the burner. I thought to remove the CO2 before the inlet to the burner but the CO2 removing system is so large to use.

I am going to have a CO2 corrosion issiue somewhere down in the process I am sure. But 316 L is too exspensive to use in the design for a crude oil water bath heater aren't you agree on this?

So you are saying it is better to separate all phases and design a heater for each Hydrocarbon liquid and the Natural Gas?

Thanks for your great input.

K

Attached Files

•  Properties Chart.pdf   52.93KB   12 downloads

[Zauberberg]

Depending on the use (downstream processing) of each phase, you really may opt for 3-phase separation prior to heating. Knowing the purpose of heating, and downstream route of each phase of the wellstream, it would be easier to get the picture of your design task and come up with more reasonable suggestions. For example, if aqueous phase is simply disposed after the final separation (e.g. somewhere downstream of the bath heater), then it is better to separate it upstream of the heater - since the aqueous phase content is >21% weight, you can mitigate corrosion potential up to a great extent and at the same time reduce the size of heating equipment, by removing water from the production stream.

Metallurgy selection is not a matter of cost - if there are no other choices, especially if any sort of catastrophic failure may happen due to incorrect material selection philosophy. You need a material expert on this. I remember units/systems operating at >5 bara CO2 partial pressure being trouble free, when 316L was used as material of choice (columns and vessels were cladded with 316L, piping was made of solid 316L).

I don't see any issues with CO2 in the fuel gas, as long as it is free of liquid water.

[kybele39]

Zauberberg,

Thanks for your inputs.

With no separation, I did worked it out on Promax with the composition of the well stream. It is almost 13 MMbtu/hr two process coil and the heater skid is 13 ft by 44ft. pretty big for a water bath heater. And I used 316L on the coils.

What I hesitate the pressure drop requirements for such system is only 14.50 psi. And the stream's linear velocity in a pipe with this design is only 4.3ft/s to meet the requested pressure drop. So the velocity to me is pretty low.

Any way, again thanks a lot for your inputs.

kybele