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How can I detemine the gas velocity in a plug flow reactor . I know the gas flow in tons,The length of the reactor,the Pipe ID,Gas inlet pressure, the pressure drop in reactor,The gas outlet pressure,
I jsut want a rough calculation to satisfy the operator level.
Regards
AFD
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Gas Velocity
Started by Guest_Guest_afdmello_*, Jul 22 2003 01:39 AM
6 replies to this topic
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#2
Guest_karthik_*
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Posted 22 July 2003 - 04:26 AM
Follow the steps:
1) Let the given gas flow in tons = m Ton/hr
2) Find the gas density at required temparature and pressure from any Hand Book(Perry) and let that value be = d Kg/m3
3) Volumetric flow rate q = m / d m3/hr;
Now velocity = Volumetric flow rate / Area
Area of the reactor = 3.14 * (ID of Pipe) * Length of the reactor
Thus we can calculate the velocity of the gas in PFR
1) Let the given gas flow in tons = m Ton/hr
2) Find the gas density at required temparature and pressure from any Hand Book(Perry) and let that value be = d Kg/m3
3) Volumetric flow rate q = m / d m3/hr;
Now velocity = Volumetric flow rate / Area
Area of the reactor = 3.14 * (ID of Pipe) * Length of the reactor
Thus we can calculate the velocity of the gas in PFR
#3
Guest_Guest_afdmello_*
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Posted 23 July 2003 - 02:40 AM
if the PFR is fed by a reciprocating comp can i take the suction flow indicated on the compressore nameplate as the volumetric flow
or should I use the formula PM/RT to find the density of the gas at discharge pressure conditions
AFD
or should I use the formula PM/RT to find the density of the gas at discharge pressure conditions
AFD
#4
Guest_karthik_*
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Posted 23 July 2003 - 04:03 AM
Yes, since the PFR is fed by compressor, naturally speaking you can very well take the volumetric flow rate discharged from the compressor.
#5
Diederik Zwart
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Posted 23 July 2003 - 10:22 AM
AFD,
You shouldn't use the nameplate suction capacity of the compressor as volumetric flow. The volume the compressor takes in at suction gets compressed, so discharge volumetric flow is less than suction flow. If you know the compression ratio of the compressor then discharge volumetric flow is:
Vdis = (Psuc/Pdis)*Vsuc (P in absolute units, not in gauge).
As Karthik stated discharge volume flow divided by cross-sectional area of the reactor gives the required velocity. However there was a mistake in the cross-sectional area calculation:
Area = (3.14/4) * (pipe ID)^2 * (number of pipes in the reactor)
Diederik Zwart
You shouldn't use the nameplate suction capacity of the compressor as volumetric flow. The volume the compressor takes in at suction gets compressed, so discharge volumetric flow is less than suction flow. If you know the compression ratio of the compressor then discharge volumetric flow is:
Vdis = (Psuc/Pdis)*Vsuc (P in absolute units, not in gauge).
As Karthik stated discharge volume flow divided by cross-sectional area of the reactor gives the required velocity. However there was a mistake in the cross-sectional area calculation:
Area = (3.14/4) * (pipe ID)^2 * (number of pipes in the reactor)
Diederik Zwart
#6
Guest_Guest_afdmello_*
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Posted 23 July 2003 - 05:11 PM
if it is a two stage compressor then second stage disch/first stage suction is R -correct?Istill get a answer much smaller than that written in the manual.
I tried ur method as well Zwart.
The DCS shows the flow in tons/hr.
AFD
I tried ur method as well Zwart.
The DCS shows the flow in tons/hr.
AFD
#7
Guest_Dave_*
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Posted 23 July 2003 - 06:43 PM
If you know the reaction chemistry details (rate constant etc), perhaps you could use the design equation for an ideal PFR to check your answer? You ought to know the conversion etc.
The ideal assumption may not be completely accurate, but should give an answer of the right magnitude (I would have thought), so you can see if your answer by other means is right.
Perhaps you could do a tracer test? This could give you the mean residence time, or perhaps use a flowmeter? You can get sonic flowmeters that don't require you to break the pipe for installation.
Dave.
The ideal assumption may not be completely accurate, but should give an answer of the right magnitude (I would have thought), so you can see if your answer by other means is right.
Perhaps you could do a tracer test? This could give you the mean residence time, or perhaps use a flowmeter? You can get sonic flowmeters that don't require you to break the pipe for installation.
Dave.
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