Modeling Phase Distribution in a Condensed Gas Treatment Manifold

Overview

A natural gas processing facility reported persistent operational issues in its separation train: despite having three separators operating in parallel, liquids consistently accumulated in the last unit, causing level control instabilities and episodic slugging. These symptoms suggested a systemic imbalance in how the inlet manifold delivered gas, water, and condensate to each separator.

HCS was engaged to provide a fast, high-value diagnostic using conceptual CFD modeling—an approach designed to reveal governing physical mechanisms and evaluate practical remediation options without requiring detailed field campaigns or disruptive interventions.

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The Challenge

Operational records showed that the last separator systematically received the majority of the liquid, but the underlying mechanism was unclear.

The facility needed:

• A technical explanation for the uneven phase distribution
• A quantitative indicator to compare alternatives
• A set of feasible design adjustments to mitigate the imbalance

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Our Approach

HCS developed a conceptual multiphase CFD model of the 46-m inlet manifold and its three outlet branches, using OpenFOAM’s Euler–Euler formulation.

Why Conceptual Modeling?

Conceptual CFD focuses on capturing dominant physics rather than replicating equipment in full detail. It is ideal when:

• The goal is diagnostic rather than certification
• Field data for calibration is limited
• Multiple remediation strategies must be compared quickly
• Clients need directionally reliable insights to guide engineering decisions

This approach allowed us to evaluate the mechanism of phase segregation and compare design options in a short time.

Key Technical Elements

• Three-phase Euler–Euler model (gas, water, condensate)
• RANS turbulence model (k-ε)
• Representative droplet sizes for dispersed phases
• Realistic operating pressures and flowrates
• Transient solution to reach steady-state behavior

The simulation reproduced the uneven liquid distribution observed on site.

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Figure 1: Detail view of the computational mesh

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What We Found

Stratification Drives the Imbalance

The flow lacked sufficient mixing capacity along the manifold:

• Gas concentrated near the top
• Liquids accumulated at the bottom, increasing toward the manifold end

Since each separator extracted flow from the upper region, the first branches captured mostly gas, while liquid migrated toward the last outlet, producing:

• ±80% imbalance between first and last outlet
• Persistent liquid overload in the last separator
• Potential for transient oscillations

Sensitivity tests confirmed that this behavior is robust to droplet size assumptions.

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Evaluated Remediation Options

We assessed a few engineering alternatives under identical operating conditions. In particular, some of those were:

A. Lateral Takeoff

Changing the branch connection from the top to the side of the manifold.

Effect:

• Imbalance reduced from ±80% → ±40%
• Conceptually simple, but not so easy to implement on site due to piping constratints.

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Figure 2: Geometry of alternative with Lateral Takeoff

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B. Static Mixer Upstream of First Outlet

Installation of a compact, commercial static mixer.

Effect:

• Imbalance reduced to ±45%
• Quick to install; moderate improvement
• Additional mixers could further equalize distribution

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Figure 3: Geometry of alternative with Static Mixer

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Outcomes and Client Value

Through conceptual CFD, HCS delivered:

1. A physics-based explanation

The root cause of the imbalance is inherent flow stratification driven by geometry and operating conditions.

2. Actionable engineering guidance

Alternatives to improve the performance of the system were identified and validated.

Alternative	Residual Imbalance	Notes
Lateral takeoff	±40%	Simple, but difficult to implement
Static mixer	±45%	Low-impact, modular option

3. Decision-ready insight

Even without a detailed calibration dataset, the conceptual model provided directionally accurate evidence to support engineering decisions and prioritize modifications.

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Why This Matters

This project demonstrates the core value proposition of HCS:

• Targeted modelling study to support decsion making
• High-impact diagnostics at low modeling cost
• Rapid turnaround to support engineering schedules

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Interested in applying a similar approach to your case?

HCS supports international clients in diagnosing flow distribution issues, optimizing fluid systems, and evaluating future alternatives.

We help teams make confident decisions through robust, physics-based modeling aligned with your schedule and budget.