7 replies to this topic

[applepe]

hi guys.. so i have a problem. i was tasked to do a hydraulic calculation of a pipeline (130 km) that will deliver 35 mmsfd of gas from a gas processing facilities to a lng pre treatment plant. the gas has 500 psig pressure and the arrival pressure should be at 750 psig. so i will have to install a compressor. my client asked me to simulate two cases, one where i put the compressor near the source (upstream), and one where i put the compressor near the destination (downstream). the problem was, when i simulate the case 2 (compressor at downstream) with smaller size of pipe (smaller than 12"), the pressure i sent would be 0 psig before it reaches the destination so there would be nothing to compress (i used pipesim and pipesim said the inlet pressure was too low so it adjusted the flow that can be delivered with the remaining pressure). so i offer a new solution for the client, what if we put the compressor, between the source anad the destination somewhere in the middle. the problem is i have no idea know where to put the compressor that would be the most efficient (cost wise). where do you think would be the best place to put the compressor?

[breizh]

Hi apple,

Consider this link where you can find pointers: 

https://en.wikipedia...pressor_station

 

Edit: typical unit.

http://www.mcilvaine...transcanada.pdf

 

Breizh

[applepe]

hi breizh thank u so much, that helps a lot!!

Hi apple,

Consider this link where you can find pointers: 

https://en.wikipedia...pressor_station

Breizh

[katmar]

This is more of a selection problem than a design problem. For the pipe you basically have a choice of 12", 14", 16" or 18". You can't choose anything in-between these sizes as they are not available. Similarly, compressors come in discrete sizes so you need to look at a few scenarios and do some preliminary cost estimates.

Once you have done some basic calculations you will need to get quotes from piping contractors and compressor suppliers. As the piping gets larger it gets more expensive, but the pressure drop decreases and the compressors get cheaper to buy and to run. You would need to amortize the power cost over the life of the project and come to a total cost.

I don't believe you can come up with an analytical solution that will spit out an answer. Once you have set up these scenarios and costed them you will be able to identify the trends and then maybe refine your options.

It would be similar with trying to put the compressor somewhere between the start and end of the line. Try sizing something for exactly in the middle and once you have the pipe and compressor sizes you can identify whether it would be better to move it slightly towards the start or end. But remember that there may not be infrastructure at that point and it might be better to limit the choice to the start or end points where the necessary facilities exist.

[breizh]

Hi apple,

I tend to agree with Kamar's comments.

His last sentence is key: "But remember that there may not be infrastructure at that point, and it might be better to limit the choice to the start or end points where the necessary facilities exist"

Let me share my personal experience: 20 years ago, I was OPs manager in a latex plant (Merak) West Java. For safety and security reasons it's no possible to let a compressor(s) station without 24/7 supervision by operators. This means you need to consider localizing operators and guards at the station with all the infrastructure to welcome them. 

You will need to bring utilities, to create a control room and may be dorm for them to stay there.

This will be additional cost to your project. 

Probably installing the station at the start is the safer and cheaper option (higher density). You may need a second unit at the arrival .

Good luck

Breizh 

[shvet1]

This will be additional cost to your project. 

Negligible one related to cost of a 56"@130km pipeline and a 35mmscfd@500psi turbine+compressor I should note.

 

Gentlemen, do you really consider this topic is serious? Would options preferences of such an expensive and major industry project be being discussed on the anonym forums? I suppose this is a midterm exam or some kind of general task assigned by senior colleagues to teach the topicstarter the very basics of hydraulics and value engineering.

 

Note that the topipcstarter had ignored the primitive calculations before the task posting. I would move this topic to the student forum.

Edited by shvet1, 07 October 2024 - 11:55 PM.

[Pilesar]

When optimizing hydraulic design choices like this, you can remove all constraints to find the purely theoretical solution. Then you add the additional real-world constraints to get a real-world optimum. Constraints will be the line size based on discrete sizes commercially available. These will come with a maximum pressure constraint. The compressor choices are limited by discrete sizes offered. The compressor locations may be limited by some of the reasons already mentioned. Perform a case study with a matrix of the different parameters to find the cost-effective answer. You must leave sufficient margins for operational variables. Natural gas composition changes with time. The compressor chosen depends on suction pressure as much as it does on discharge pressure. The real-world design should not be on the edges of the constraints.. You know 0 psig is not enough suction so determine what pressure is minimum. Does it need to be 10 psig? 100 psig? 200 psig? What will be your maximum pressure? You may want to leave excess operating margin away from the maximum allowable pressure. The pressures you choose will be constraints. Pipelines seem simple, but the variables can make it complex. When I designed similar pipeline, it was obvious I had to have a compressor somewhere in the middle as well as at the beginning and end. The choice was made by looking at a map and finding a service station and convenience store near the pipeline path. There was road and electrical power there and land available for lease. So that location became a constraint in the model and that is where the compressor went.

[snickster]

Just off the top of my head I am thinking compressor located upstream at start of pipeline would be more efficient for the following basic reasons:

 

If pressure is boosted at start of pipeline then entire line will be filled with higher pressure.  Pressure drop in compressible gas lines and velocity is lower for higher pressure which minimizes pipe size.

 

Compressor would operate at lower compression ratio and higher suction pressure which will minimize compressor size.