Simulation of Flow Orifice in a

depressurization line working in critical flow.

Autores:

Victor Kanehiro Arume de Souza – ESSS

Leonardo Aquino Costa – Petrobras / CENPES

Cristhian Alberto Celestino Cortez – Petrobras / CENPES

Kaku Saito – Petrobras / CENPES

PRESENTATION TOPICS

• Company Overview;

• Problem Description;

• Methodology;

• Goals;

• Conclusion and next steps.

Exploration

Research and

Development

Cenpes

Technological

Management

Supply Research

and Development

Gas, Energy and Sustainable

Development Research

and Development

Exploration and

Production

Basic Engineering Downstream, Gas and

Energy Basic

Engineering

Production

Research and

Development

Cenpes´ Organizational Structure

In Brazil, partnership with over 120 universities and research centers

Agreements and contracts Thematic networks 7 regional centers

Abroad, more than 70 institutions

Multiclient projects Cooperatives researches Strategic Alliances Technological Exchanges

CENPES Today

• Flow Orifice study in the fast and slow

depressurization lines of a reactor;

• Last defense systems in case of a

uncontrolled temperature rise in reactors;

• Maintain the right depressurization rate it’s

a security issue:

– Depressurization to slow > Bad temperature

control;

– Depressurization to fast > Reactor damage /

Compromised Flare System;

Problem Description

Problem Description

• Divergence between designs of the detailed

project and the concept project;

• Lack of standards for critical flows;

• Different bibliographies gives different sizes

of FO;

Problem Description

• Two methodologies used:

– Concept Project: Based on the methodologies of flow

measurements under critical flow, described by Nelson

Martins [1];

– Detailed Project: Based on the methodologies of valve

controls under critical flow;

Concept Fast Line

Detailed Fast Line

Concept Slow line

Detailed Slow line

Line Diameter 215,9 124,4

Orifice Diameter 99,94 85 56,5 48,25

β 0,46 0,39 0,45 0,39

Plate Thickness 99,94 44,45 56,5 25,4

• 2D axisymmetric simplification;

Real 3D geom

2D simplified geom

Geometry

Thickness

Flow Orifice

Upstream Downstream

• Hexahedral Mesh:

FO Region

Detailed

Mesh

• Pressure–Pressure bc’s:

Boundary Conditions

Fast Depressurization

Pinlet = 1,54e+07 Pa

Poutlet = 1,27e+05 Pa

Slow Depressurization

Pinlet = 1,52e+07 Pa

Poutlet = 4,81e+06 Pa

Wall

Axis

Inlet Outlet

cp

y = 1.9494x + 6111.6

6700.00

6800.00

6900.00

7000.00

7100.00

7200.00

7300.00

300.00 400.00 500.00 600.00

Temperatura [K]

cp

[J/k

g.K

]

Viscosidade

y = 2E-08x + 5E-061.10E-05

1.20E-05

1.30E-05

1.40E-05

1.50E-05

1.60E-05

1.70E-05

1.80E-05

300.00 400.00 500.00 600.00

Temperatura [K]

Vis

co

sid

ad

e [

Kg

/m.s

]

Boundary Conditions

• Fluid Properties:

– Temperature = 51 ºC

– Molecular Weight = 4,8 kg/mol

– Specific mass = ideal gas

– Viscosity and cp = process simulator

• Mach:

Results

Fast Depressurization

Detailed

Concept

• Pressure:

Results

Fast Depressurization

Detailed

Concept

• Mach:

Results

Slow Depressurization

Detailed

Concept

• Pressure:

Results

Slow Depressurization

Detailed

Concept

• Achieved Mass Flow:

Results

Fast Depressurization Line Slow Depressurization Line

Project Detailed Concept Detailed Concept

Theoretical Mass Flow (kg/s)

87,97 28,05

Mass Flow (kg/s) - CFD

65,41 89,86 20,85 28,78

Error % -25,65 2,15 -25,64 2,63

Each project step in the same range of error.

Conclusion and Comments

• Error between methodologies:

– CFD vs Concept = 2,5%

– CFD vs Detailed = 25%

• This work showed the validation of Nelson Martins [1]

for the project of Flow Orifices under critical flow;

• There’s still a supersonic flow at the outlet boundary at

the Fast Depressurization case:

– Another shock wave will happen at upstream;

– Raised the concern on the equipment after the FO

(vibration, erosion due high speeds, etc.)

18

Bibliography

[1] Martins, Nelson. Manual de medição de vazão: através de

placas de orifício, bocais e venturis. Rio de Janeiro;

Interciência; Petrobras, 1998.

[2] ANSYS Fluent (2010) Theory Guide. Versão 13, abril de

2009. Cannonsburg, USA.

[3] Ewan B.C.R. and Moodie K. 1986 “Structure and velocity

measurements in under-expanded jets” Combustion Science

and Technology 45 pp275-288.

[4] Miller, R.W. Flow Measurement Engineering Handbook;

McGraw-Hill Book Company