The use of CFD to assess valve performance and operation in extreme conditions. BVAA Conference Tuesday 12 th May Alex Roff Engineering Director

Transcription

1 The use of CFD to assess valve performance and operation in extreme conditions BVAA Conference Tuesday 12 th May 2015 Alex Roff Engineering Director

2 Overview: Introduction. The use of CFD in the valve industry. CFD case study Joule Thomson effect in a valve. Industry simulation trends. Questions.

3 Introduction Simulation can be used in the valve industry to gain confidence and verify the performance of equipment. Representing operating conditions for valves and actuators can be challenging and in some cases an impossible task. Where test facilities are available, testing can be expensive. Gives you the ability to understand what is happening within the valve itself. Ability to find the limit of operation of the components, as opposed to just verifying test conditions. Gain confidence in a design before metal is cut. Demonstrate an increased understanding to customers and compliance to the relevant design codes.

4 Computational Fluid Dynamics Overview Computational Fluid Dynamics Uses in Valve Industry: Flow behaviour / Cv calculation Multi-phase flows Valve closure analysis Erosion / deposition analysis Extreme flow conditions

5 Choke Valve Thermal Assessment Problem Statement: 4 Subsea Choke 3 Stage Concentric Cage Trim ΔP across choke 100 bar Inlet Temp 5 C Mass Flow Rate 25kg/s What is the minimum temperature of the gas at the exit of the Choke Valve? Demonstrate that the downstream pipe remains within design temperature limits.

6 Choke Valve Thermal Assessment Input Parameters: Geometry Simplifications Expected Outputs Fluid Properties ANALYSIS PLAN Assumptions Customer Review and Approval

7 Choke Valve Thermal Assessment Geometry Simplification: Geometry Preparation Simplify Internal flow geometry. Split geometry into mesh regions. Extend inlet and outlets.

8 Choke Valve Thermal Assessment Meshing: Mesh: Inflation layers used next to the walls to resolve the boundary layers. Local refinements required (very different length-scales). Regions swept, where possible, to control element size. Split sizing in stream-wise & cross-flow directions. Reduce number of elements large mesh, memory issues, solve times.

9 Choke Valve Thermal Assessment Ideal Gas vs. Real Gas: Ideal gas law cannot be used to capture the Joule Thomson effect. Assumes the molecules have a negligible volume. Assumes there are no intermolecular forces between the molecules. Assumes all collision between the molecules are elastic. Real gases need to be represented using an alternative Equation of State.

10 Choke Valve Thermal Assessment Equation of State: Real gas effects modelled using the Peng-Robinson Equation of State. Model developed for hydrocarbon processes. Cubic equation; determines molar volume, given pressure & temperature. Predicts liquid and vapour properties & vapour-liquid equilibrium.

11 Choke Valve Thermal Assessment Equation of State Mixture: Peng-Robinson Equation of State used to calculate the properties each component. Real gas mixing rules implemented. Psuedo-critcial constants determined for the mixture. Also Considered: Specific Heat Capacity, Dynamic Viscosity, Thermal Conductivity.

12 Choke Valve Thermal Assessment Boundary Conditions: Choked flow conditions, means that conventional boundary conditions cannot be easily applied. Flow Conditions Specified outlet pressure. Specified inlet pressure & temperature. Initially solved using mass flow rate to determine initial conditions. Boundary condition then updated. Mass flow then an output of the analysis. Adiabatic wall boundary conditions.

13 Choke Valve Thermal Assessment Solve Process: Multiple convergence criteria monitored through out the solve process. Minimum fluid temperature and location determined. Analysis Solve time: 10 hours (750 iterations). Using in-house 48-core dedicated High Performance Computing Cluster. Solve time in excess of 7 days for desktop computer.

14 Choke Valve Thermal Assessment Results Mach Number: Mach Number for 100% open case. Maximum Mach number 1.1 Maximum Velocity 300m/s

15 Choke Valve Thermal Assessment Results Streamlines:

16 Choke Valve Thermal Assessment Results Absolute Pressure: Absolute Pressure for 100% open case.

17 Choke Valve Thermal Assessment Results Temperature: Temperature for 100% open case. Inlet Temperature 5 C Average Outlet Temperature -30 C Absolute Minimum Temperature -60 C

18 Choke Valve Thermal Assessment Model Verification: Best verification of the model is to compare test data vs. the predicted results. Results of Cv flow testing were compared against the CFD model (blind). Verifies model set-up/geometry. Verifies mesh quality. Best verification that was possible.

19 Choke Valve Thermal Assessment Model Verification: Comparison of calculated fluid properties with PVT data from 3 rd party review. Comparison of results with simple flash calculations performed by others. Rigorous review of final reports by end customer: International Oil Company (Confidential) EPC Contractor (Confidential) Flow Assurance DNV 3 rd Party Review

20 Choke Valve Thermal Assessment Further Work: Examination of the valve body temperatures. Inclusion of the external sea water domain. Determination of Icing and the subsequent effects. Transient analysis to determine the rate of ice build up.

21 Simulation Trends More demand from end users for both CFD and FEA reports. The general complexity of analysis requested is increasing. More rigour applied to the depth and detail of the analysis requirements. The use of simulation to mitigate risk, shorten development timescales and reduce costs. Will become a mandatory requirements for some safety critical valves (API 17G (WD6)).

22 Questions?

23 Contact Details: PDL Solutions (Europe) Ltd PDL Solutions (North America) LLC PDL Solutions (Asia) Pte. Ltd 1 Tanners Yard Westheimer Raffles Place Hexham Suite 1100 #32-01 UOB Plaza Northumberland Houston Singapore NE46 3NY TX United Kingdom United States of America T: T: T: E: solutions@pdl-group.com E: solutions@pdl-group.com E: pdl-group.com W: W: W: