Tutorial : Line Sizing Analysis with ASPEN HYSYS

Example problem: line sizing using ASPEN HYSYS (*)

Natural gas with following composition
C1   : 95%
C2   : 2.5%
C3   : 0.3%
N2   : 1.6%
CO2 : 0.6%
Mass flowrate : 95000 kg/h ; Operating Pressure : 900 kPag ; Operating Temperature : 45oC
The Oil and Gas Design criteria for vapor piping service is as follow:
𝞓P / L  = 1.5 bar/km
𝞺v²        = 15000 Pa
Calculate the minimum required piping diameter for this service.
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(*) ASPEN HYSYS is not a specialize software for the line sizing calculation. However, to get a rough picture and learn the philosophy of line sizing calculation, HYSYS could be used. Please note that pressure drop calculation is based on HYSYS default pressure drop calculation for pipe sizing analysis option in equipment sizing. Typically, an EPC company will develop their own line sizing spreadsheet that include well-known pressure drop calculation method e.g. Darcy formula for single phase flow. More detail about pipe sizing criteria, please refer to this article.

Solution:

The natural gas steam properties could be checked using Peng-Robinson fluid package in ASPEN HYSYS.

Then, click on the MATERIAL STEAM → go to ATTACHMENT tab → ANALYSIS → create PIPE SIZING Analysis → choose PRESSURE DROP calculation type

Here, we have to specify the Inside Diameter (ID) of the piping system. As mention above, ID could be calculated based on the pipe NPS and pipe schedule. Selected schedule will depend on the pipe class specification defined by EPC company as agreed with the Oil and Gas company.

For now, let's assume that we use Standard (STD) schedule for the pipe. 
We will check if the pipe with 12, 14, and 16 NPS will adequate for this natural gas service.

Inside diameter calculation (please browse for pipe NPS table, this could be easily found in any search engine)

Pipe NPS (inch)	12	14	16
DN (mm)	300	350	400
OD (mm)	323.9	355.9	406.4
wall thickness (mm)	9.53	9.53	9.53
ID (mm) (**)	304.84	336.84	387.34

**) ID = OD - 2*wall thickness

Enter calculated ID at the Pipe Sizing window and check the result in PERFORMANCE tab

Figure 4 - Pipe Sizing analysis in ASPEN HYSYS V10

Figure 5 - Performance Tab of  Pipe Sizing Analysis

Result recapitulation shown in the table below

Discussions:

• For NPS 12 pipe, segment pressure drop is above the criteria 1.5 bar/km and momentum ( 𝞺v² ) criteria is > 15000 Pa. Hence, a 12 NPS pipe will be undersized for this Natural Gas service 
• For NPS 14 pipe, the momentum ( 𝞺v² )  is below 15000 Pa but the segment pressure drop is above 1.5 bar/km. Therefore 14 NPS pipe will not adequate for this service.
• For NPS 16 pipe, both momentum ( 𝞺v² ) and pressure drop criteria is below the limit. Hence, we could choose 16 NPS as our pipe size for this natural gas service. Furthermore, to confirm this diameter selection, a hydraulic calculation shall be performed to ensure that the selected diameter is already suitable for the process. Hydraulic calculation will be discussed in another article.

Latest update : 17 July 2020