Gas Compression in Dense Phase 2

[mamed]

I looking for the properties of the Equipment that we can use to pump a gas in dense phase. What do you name it? Pump or Compressor? Do you know any licensor in this issue?

 

[MortenA]

Since natural gas will be in the dense phase around 85-90 barg you will encouter this many times. Generally they are called compressors - because that what they are

 

[dcasto]

My favorite subject. I operated a 2 stage IR HHE reciprocating 2 stage compressor on a dense phase fluid. In PARALLEL we had a Sulzer 8 stage split case water pump pumping the same fluid.. Now that Sulzer pump internals were made with Al impellers and not stainless steel normally used. Big reason, to shed the heat from compression.

The pumps were way cheaper than the compressors.

 

[rotw]

What is meant by dense phase ?
Does this mean operating at Pressure and Temperature such that the fluid state condition is inside the Liquid - Vapour phase envelop ?

 

[zdas04]

Dense phase is a state of matter where the density is on the order of the density of a liquid, but the bulk modulus is on the order of a gas. The stuff can be pumped or compressed. If I plot a phase diagram with temperature on the x axis and pressure on the y axis, then if my starting point is closer to the vertical boundary then I want to pump (i.e., a small change in suction temp would put me into the liquid phase and bust a compressor). If my starting point is closer to the horizontal line (i.e. a small change in suction pressure would put me into the gas region) then I want to compress.

I've attached a phase diagram for CO2 (for example). For this very special fluid, the critical point is 87.76F and 1070 psia. If I was starting at 2000 psia and 200F then it wouldn't make any difference which to use and you would pick a pump because it is less expensive (and fewer lubrication problems, dense phase CO2 is the best cleaning agent on the planet and CO2 compressors often suffer from lubrication failures when they dip into the dense phase). If I was starting out below 1100 psia then I'd use a compressor because a small drop in suction pressure would drop me out of dense phase and damage may pump technologies.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[zdas04]

I don't know why the diagram didn't attach. Let's try again (oh I see, I didn't do the last step, sorry). Here it is now.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[dcasto]

I like to describe dense phase supercritical phase as "a fluid that has the molecular energy of a gas, but the physical properties (or as zdas describes as bulk properties) of a liquid." If you look at a pump or compressor be it a positive displacement or centrifugal, they don't care what phase enters them, just don't change phase in the middle of the operation. A piston compressor water pump will pump air, but the efficiency and rate will be horrible until you change the inlet and outlet check valves to match the fluids bulk properties.

 

[rotw]

Thanks Zdas and dcasto. It was very informative.

 

[mamed]

Thank you for replays.
About ethane the Critical temperature is 32.17°C and the Critical pressure is 48.72 bar.
The operating inlet pressure at the mentioned pump station would be ~60 bar which need to be pressurized to ~95bar. According to simulation results, the operating inlet density is 290-330 kg/m3 and it will be increased between ~1 and ~12 percents during pressurization. The temperature changes during normal operation is <20°C. Hence, in Normal operation we do not need to reduce the internal energy of the fluid.

Regarding dcasto's comment I conclude that a multistage pump with specially designed impellers is the best choice.
I will appreciate your comments

 

[dcasto]

As a matter of fact, my parallel compressors were on high purity ethylene at rates in the 75,000 pounds per hour. The only difference was the reciprocating unit went from 850 psig to 2400 psig and the centrifugal 850 to 1600 psig.

 

[dcasto]

As a matter of fact, my parallel compressors were on high purity ethylene at rates in the 75,000 pounds per hour. The only difference was the reciprocating unit went from 850 psig to 2400 psig and the centrifugal 850 to 1600 psig.

Oh, and we added a ebara cryodynamics pump at a different location. It was a seamless pump with a gas cooled electric motor.