# Experimental and Numerical Study for Gas Release and Dispersion on Offshore Platforms

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## Abstract

**:**

## 1. Introduction

## 2. Offshore Platform Gas Release and Dispersion Experiments

#### 2.1. Experimental Details

#### 2.1.1. Gas Leakage Module

#### 2.1.2. Data Acquisition Module

#### 2.1.3. Other Experimental Details

#### 2.2. Experimental Results and Discussions

#### 2.2.1. Constant Leakage Rates

#### 2.2.2. Time-Varying Leakage Rate

## 3. Model Verification

#### 3.1. The Modeling Concept

_{i}represents the velocity component in i-direction; Г

_{ϕ}represents the dispersion coefficient of the general variable φ; S

_{φ}represents the source term.

_{v}represents volume porosity; k represents the turbulent kinetic energy; β

_{j}represents area porosity in the j-direction; ε represents the turbulent kinetic energy dissipation rate; P

_{k}and P

_{ε}represent the production of turbulent kinetic energy and the production of dissipation, respectively; σ

_{k}and σ

_{ε}represent the Prandtl–Schmidt number of k and ε; C

_{2ε}is a constant.

_{ij}represents the stress tensor; δ

_{ij}represents the Kronecker delta function, δ

_{ij}= 1 if i = j, δ

_{ij}=0 if i ≠ j.

_{eff}in the above equations represents the effective viscosity, which is defined as follows:

_{μ}is a constant.

#### 3.2. Geometric Model and Mesh Generation of an Offshore Platform

#### 3.3. Basis of Validation of Numerical Calculation Results

_{m}represents the experimental data of concentration and C

_{p}represents the model prediction data of concentration.

#### 3.4. Model Validation against Scenarios with Constant Leakage Rates

- (1)
- The difference in the geometry of the detector. The detectors are imaginary in the numerical simulation. Some hypothetical detectors are set so that no extra geometry is involved. In the experiment, the gas detector exists objectively which may affect the dispersion behavior of the released gas.
- (2)
- The difference in the sampling dimension of the gas detector. In the experiment, the appearance of the sampling chamber is a plane rather than a point, and thus it actually captures the released gas within an area. In the numerical simulation, the gas concentration is associated with an exact coordinate.
- (3)
- The difference in the boundary conditions. The leakage rate is so low that the performance of the anti-interference is poor. There may be disturbances that affect the intensity of the air turbulence in the experiment. Similar conditions will not occur in the numerical simulation.
- (4)
- The inherent error of the experimental instrument and the numerical calculation. There are inherent errors in the experimental instruments, including the gas detector and the leakage rate regulator. FLACS uses the Reynolds Averaged Navier–Stokes (RANS) equations and a k-ε model for turbulence. Some reasonable simplifications are made and some empirical parameters are employed, which inevitably lead to errors.

#### 3.5. Model Validation against Scenarios with a Time-Varying Leakage Rate

## 4. Model Application

## 5. Summary and Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 3.**Some devices of the gas leakage module. (

**a**) The gas cylinder with pressure reducing valve. (

**b**) The leakage rate regulator, pressure gauge, and temperature gauge.

**Figure 6.**The variation in gas concentration of monitor #1 against different constant leakage rates.

**Figure 7.**The variation in gas concentration of different monitors when the leakage rate is 8.1 L/min.

**Figure 12.**Comparison between the experimental results and the simulation results against constant leakage rates.

**Figure 13.**Comparison between the experimental results and the simulation results against the time-varying leakage rate.

Length (cm) | Width (cm) | Height (cm) | |
---|---|---|---|

The whole experimental offshore platform | 255 | 210 | 308 |

The main deck | 255 | 210 | / |

The middle deck | 255 | 210 | 046 |

The lower deck | 255 | 210 | 046 |

Item | Value or Value Range | Item | Value or Value Range |
---|---|---|---|

Molecular weight | 44.10 | Critical pressure (MPa) | 4.25 |

Relative density | 1.56 | Minimus ignition energy (mJ) | 0.26 |

Viscosity (kg/m·s) | 1.01 × 10^{−5} | Flashpoint (°C) | −104 |

Saturated vapor pressure (kPa) | 53.32 (−55.6 °C) | Autoignition temperature (°C) | 450 |

Critical Temperature (°C) | 96.8 | Explosion limit (%) | 2.1~9.5 |

Grid Size (m) | 0.15 | 0.12 | 0.10 | 0.075 |
---|---|---|---|---|

Computation time (s) | 6259.29 | 8217.88 | 9872.21 | 18,834.57 |

Max. FLAM (m^{3}) | 0.289 | 0.248 | 0.237 | 0.234 |

SPM | MRB | MRSE | FAC2 | MG | VG |
---|---|---|---|---|---|

Acceptance criteria | −0.4 < MRB < 0.4 | MRSE < 2.3 | 0.5 ≤ FAC2 | 0.67 < MG < 1.5 | VG < 3.3 |

SPM | 4.4 L/min | 6.2 L/min | 8.1 L/min |
---|---|---|---|

−0.4 < MRB < 0.4 | 0.0129 | −0.0897 | −0.0877 |

MRSE < 2.3 | 0.0025 | 0.0081 | 0.0077 |

0.5 ≤ FAC2 ≤ 2 | 0.9885 | 1.0940 | 1.0920 |

0.67 < MG < 1.5 | 1.014 | 0.9145 | 0.9160 |

VG < 3.3 | 1.0026 | 1.0082 | 1.0078 |

SPM | Max. Concentration | Min. Concentration |
---|---|---|

−0.4 < MRB < 0.4 | −0.0797 | 0.1724 |

MRSE < 2.3 | 0.00635 | 0.02972 |

0.5 ≤ FAC2 | 1.083 | 0.841 |

0.67 < MG < 1.5 | 0.923 | 1.189 |

VG < 3.3 | 1.0064 | 1.0303 |

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## Share and Cite

**MDPI and ACS Style**

Xiao, F.; Li, Y.; Zhang, J.; Dong, H.; Yang, D.; Chen, G.
Experimental and Numerical Study for Gas Release and Dispersion on Offshore Platforms. *Processes* **2023**, *11*, 3437.
https://doi.org/10.3390/pr11123437

**AMA Style**

Xiao F, Li Y, Zhang J, Dong H, Yang D, Chen G.
Experimental and Numerical Study for Gas Release and Dispersion on Offshore Platforms. *Processes*. 2023; 11(12):3437.
https://doi.org/10.3390/pr11123437

**Chicago/Turabian Style**

Xiao, Fengpu, Yanan Li, Jun Zhang, Hai Dong, Dongdong Yang, and Guoming Chen.
2023. "Experimental and Numerical Study for Gas Release and Dispersion on Offshore Platforms" *Processes* 11, no. 12: 3437.
https://doi.org/10.3390/pr11123437