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October 24, 2014
1 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Calculation of Maximum Flow of Natural Gas through a Pipeline
using Dynamic Simulation in Aspen HYSYS
Muhammad Waqas Manzoor
Process Engineer
Email: [email protected]
Synopsis:
A dynamic simulation in Aspen HYSYS was performed to assess the maximum gas carrying capacity of a NPS 6”
SCH 80 pipeline having length of 12 km. At upstream end, the pipeline is connected with a Natural Gas
Regulating Station and at downstream end the pipeline is connected with domestic consumer pipeline network.
The pressure required by domestic consumer is very less compared with the pipeline pressure i.e. about 4 inches
WC = 0.144 psig. Therefore, to calculate the maximum flow (or choke flow) through the pipeline, 0 psig has been
considered at downstream of the NPS 6” SCH 80 12 km long pipeline. The pipeline absolute roughness for
calculation of frictional pressure drop has been considered to be equal to 0.04572 millimeters, which is the same
as of carbon steel pipes.
Background Information:
The Natural Gas Regulating Station can supply gas at a pressure of 40 psig to 100 psig, using a pressure control
valve, as per the seasonal consumer demand. During winter season the pressure may be increased to 100 psig
and during summer season the pressure may be reduced to 50 psig because gas consumption during winter
season is higher as compared to that in summer season, and only by increasing the gas pressure at the
downstream of the Natural Gas Regulating Station, the gas flow rate can be increased. The pressure at the
upstream of the Natural Gas Regulating Station is about 395 psig. However, it depends on pressure setting at
downstream of Natural Gas Regulating Station. Higher the downstream pressure, higher would be gas flow rate
and lower would be the upstream pressure.
Natural Gas Regulating Station
Inlet Pressure = 400 to 500 psig
Outlet Pressure = 50 to 100 psig
6”Pipeline
12km
Domestic Consumer Network
Required 2 to 3 MMSCFD in 2014
Forecast for 2015 is 5 to 6 MMSCFD
6”O
ffta
ke
20
met
ers
16”Burried Mainline near
Natural Gas Regulating Station
October 24, 2014
2 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
HYSYS Simulation Results:
Following are the results of the Dynamic Simulation,
S. No. Pressure at U/S
of Regulating Station (psig)
Pressure at D/S of Regulating Station (psig)
Max. Flow rate across NPS 6” 12 km long pipeline at D/S of Regulating Station (MMSCFD)
1. 397.0 50 2.08
2. 396.4 60 2.46
3. 395.2 80 3.23
4. 394.6 90 3.62
5. 394.0 100 4.01
It may also be noted that the actual absolute roughness would also be higher than 0.0457 millimeters depending
on the aging of pipeline and therefore, the actual maximum flow rate would be less than the values calculated
in this simulation. Therefore, the said line would be unable to cater the natural gas demand if it increases beyond
4 MMSCFD in 2015, as per the forecast.
The application of Dynamic Simulation in this particular case holds significance because Steady State Simulation
cannot simulate pressure balancing and therefore, can never imitate actual process in which flow rate depends
on pressure differential only. Even the pipe model in Steady State Simulation was unable to calculate natural
gas flow rate after the total pressure drop had been specified across the 6” dia. 12 km long pipeline.
October 24, 2014
3 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Gas Composition
The average gas composition for last month at the Regulating Station is used in the HYSYS Simulation.
HYSYS Simulation Snapshots
All these simulation snapshots were taken after the variables had reached their maximum or minimum values.
Maximum Flow rate for 50 psig is 2.08 MMSCFD
October 24, 2014
4 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Maximum Flow rate for 60 psig is 2.46 MMSCFD
Maximum Flow rate for 80 psig is 3.23 MMSCFD
October 24, 2014
5 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Maximum Flow rate for 90 psig is 3.62 MMSCFD
Maximum Flow rate for 100 psig is 4.01 MMSCFD
October 24, 2014
6 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Steady State Simulation
The pipe model in Steady State Simulation was unable to calculate natural gas flow rate after the total
pressure drop had been specified across the 6” dia. 12 km long pipeline. Total Pressure Drop = 50 psig - 0 psig
= 50 psi
October 24, 2014
7 ---- Muhammad Waqas Manzoor ---- Process Engineer ---- [email protected] ----
Flow rate calculation using Different Pressure Drop Correlations
Below is the comparison between flow rate calculated using different pressure drop correlations in the Dynamic
Simulation of only the 6” pipe,