ethane compression from 21 to 120 bar
ethane compression from 21 to 120 bar
(OP)
Is it possible to compress ethane from 21 bar to 120 bar in one compression stage??
More overall, in your thoughts it is better to transport ethane in gas phase or dense phase? which one is more practical and common?
What are the operating pressure and temperature??
Thank you for your time :)
More overall, in your thoughts it is better to transport ethane in gas phase or dense phase? which one is more practical and common?
What are the operating pressure and temperature??
Thank you for your time :)





RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
Your suction temperature should stay below a certain limit so that you don't get a too high discharge.
At the same time you should have also sufficient margin to dew point before entering the compressor. It depends from the gas composition: is it a pure Ethane, does it contain some heavy hydrocarbons etc. ?
Assuming pure Ethane, dew point temperature at 20 bar suction pressure should be around -10 deg C or so. With an inlet gas temperature to compressor of 10-15 deg C, it maybe doable with one compression (thermodynamic) stage depending on poly-tropic efficiency of the compressor.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
2) supposing you have to design a pipeline at about ambient temperature (to avoid expensive insulation) and assuming fluid temperature of 15 C (about 288 K) the density of pure ethane at 120 Bar.a and 288 K would be about 422 Kg/M3 (values calculated with PRODE PROPERTIES, extended Peng Robinson model),
that value (422) looks not too different from the density of a liquid phase
3) by solving a single polytropic stage for pure ethane, polytropic efficiency 0.75 and pin 20 Bar.a Tin 270 K, Pout 120 Bar.a the calculated temperature (again with PRODE PROPERTIES and Peng Robinson extended) is about 400 K which makes the single stage design difficult, however there are other equipments as for example screws which perhaps could do the work but you should consult an expert in this field to see if it's a practicable solutiion.
RE: ethane compression from 21 to 120 bar
3) by solving a single polytropic stage for pure ethane, polytropic efficiency 0.75 and pin 20 Bar.a Tin 270 K, Pout 120 Bar.a the calculated temperature (again with PRODE PROPERTIES and Peng Robinson extended) is about 400 K which makes the single stage design difficult, however there are other equipments as for example screws which perhaps could do the work but you should consult an expert in this field to see if it's a practicable solutiion.
Unquoted
Assuming 75 % poly efficiency as you did and an inlet temperature of 15 deg C, a discharge temperature of 165-170 deg C is still descent for a centrifugal and therefore a single stage will possible without too much issues.
We need to know if the gas composition contains pure ethane and what is the flow involved.
RE: ethane compression from 21 to 120 bar
Thank you for your time.
Dear rotaryworld :)
The gas contains about 99% methane and the flow rate is about 400000 tons per year.
RE: ethane compression from 21 to 120 bar
Is it Methane or Ethane ??
RE: ethane compression from 21 to 120 bar
Independent events are seldomly independent.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
The problem is not your 99% but the remaining 1%.
Heavy hydrocarbon may shift the dew point line.
Assuming (lot of assumptions here) we stay with the pure ethane dew point curve, it should be feasible with a small centrifugal.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
out of curiosity, how have you calculated those values ?
for pure ethane,
single polytropic stage with polytropic eff. 75%
tin 15 C pin 20 Bar.a
pout 120 bar.a
I get a tout of about 149 C
(about 50 C less)
RE: ethane compression from 21 to 120 bar
(Pin 20 Bar.a tin 15 C , Pout 120 Bar.a)
RE: ethane compression from 21 to 120 bar
quoted
As for the 1% other, its a nonevent, that 1% won't do anything, even if it were C8.
Unquoted
not agree..
running 1% with and without heavy hydrocarbon here
http://www2.questconsult.com/cgi-bin/jrm_dewbub
6 = Isopentane, C5H12 0.3%
7 = n-Pentane, C5H12 0.3%
8 = n-Hexane, C6H14 0.3%
Calculating dew point temperature at 2000.0 kPa absolute.
The dew point temperature is 284.3 degrees Kelvin.
6 = Isopentane, C5H12 0.0%
7 = n-Pentane, C5H12 0.0%
8 = n-Hexane, C6H14 0.0%
Calculating dew point temperature at 2000.0 kPa absolute.
The dew point temperature is 265.9 degrees Kelvin.
enough delta to compromise single stage option
I don't want to try in the commercial software, I know it be the same outcome
RE: ethane compression from 21 to 120 bar
C2 0.99
C1 0.0095
C3 0.0005
shows little difference at 20 Bar.a from bubble (-8.895) to dew (-7.408 C) lines
in this case the impact of light components (C1, C3) is limited.
Of course if you add small fractions of heavy components as C7 and above thinks would be different.
However in some cases it could be acceptable to have a very limited amount of liquid
entering the compressor providing it doesn't generate mechanical problems
(one should ask the manufacturer for a specific simulation),
we have had a compressor working with very small liquid fractions without problems.
from process simulation point of view,
you can solve polytropic stages with any amount of liquid
(polytropic stage with phase equilibria),
I have used this option (available in PRODE) to model screw compressors,
you can even solve a pump (liquid in, liquid out) as polytropic stage.
RE: ethane compression from 21 to 120 bar
But something posted above seems to mean that 1% will not matter "Anyhow". We know now that this is not true.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
I woonder why there is that large difference in results, about 12% (203-150)/(150+273) or 50 C in calculated temperatures,
where 150 C has been calculated with Peng Robinson and Huntigton method,
are you using the simplified GPSA equation ?
Tout = Tin*(Pout / Pin)**(k-1)/k
that may give those values.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
since you do not explain how you calculate that temperature I can only presume that you utilize some custom procedure and that result should, in my opinion, be validated,
actually 50 C difference can have a large impact on selection,
in these cases I prefer as first step use a standard procedure (rigorous polytropic stage with 75-80% efficiency) and then ask the manufacturer to include all the specific operating parameters (which may show large differences in different compressors)
RE: ethane compression from 21 to 120 bar
In real life, I'd guess that the screw compressor discharge temperature will be exactly 180 F. Trust me on that one.
When you use the GPA equation, which K do you use, there are 10 million different K's.
RE: ethane compression from 21 to 120 bar
in the last post temperature has been reduced to 82 C (180 F),
I would call this a big change.
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
RE: ethane compression from 21 to 120 bar
>Now I really do not understand anything to this discussion.
I think dcasto likes to create a bit of confusion
but don't care for that,
the correct answer was given in previous posts.
RE: ethane compression from 21 to 120 bar