Nowadays, scientists have applied gas dispersion modelling in its assessment of the hazards and risks posed by toxic and flammable substances produced in chemical processes. Gas dispersion models have been established to analyze the influence of gas density, wind speed, atmospheric stability and other factors on gas diffusion, and predict the concentration change of gas concentration at different times after diffusion. At Alfa Chemistry, different dispersion models are used to realize the dynamic prediction, and the crucial parameters in the gas dispersion process are analyzed and calculated.
Figure 1. Dispersion modelling. (Witlox, H.; et al. 2011)
Release Types
- Chemical liquid pool/spill evaporation into gas.
- Chemical release from a continuous pressure source.
- Chemical release from instantaneous pressure vessel/pressure system failure.
Our Modeling Process
- Stream definition
We establish a stream by grouping equipment whose operating conditions are close enough together that a single modeling run will be representative for all of the selected equipment. A stream includes the following parameters:
1. Temperature
2. Pressure
3. Composition (Fractions of each component chemical)
- Dispersion modeling
We apply Gaussian dispersion models in which computational fluid dynamics are used. A series of dispersion models run for each stream, and the number and types of models will generally follow the risk analysis studies with modifications to suit the problem of gas detection mapping.
- Considering wind directions
Our teams also take wind directions into consideration by weighting the probability of different release directions based on wind direction probability.
- Plot release scenarios
We plot the dimensions of a release scenario on a plan view drawing of the facility, in which each individual release direction can be viewed with no overlaps.
Our Services
Alfa Chemistry provides high-quality gas dispersion modelling for you. Our experts are capable of performing various advanced modelling software for accurate gas dispersion simulation. Our gas dispersion modelling services include the following:
We select the model depending on the density of the gas/vapor, and employ both empirical models and computational fluid dynamic models for dispersion studies.
We also choose Gaussian dispersion modeling, in which factors like changes in density and thermodynamic properties of the fluid are investigated during modeling multiple scenarios.
In case of large gas release, the evolution of gas vapor cloud will be influenced by the characteristics of pool that forms from spill. We consider that buoyancy may take over the dispersion phenomenon since the obstacles and heat transfer mechanism may dilute the vapor faster.
Our dispersion modeling can be used to predict gas flow rate. At Alfa Chemistry, infrared cameras detect gas to a minimum detectable concentration. Gas flow rate is estimated based on the size of the cloud observed from thermograms. The amount of gas released depends of the upstream pressures and sizes.
We apply an advanced computational fluid dynamics (CFD) software that simulates ventilation and dispersion in complex geometries by solving the 3D Reynolds-Averaged Navier Stokes (RANS) equations. It includes a level of automation: all domain sizing, meshing, numerical setup and solution monitoring is handled automatically.
We design an integral model for instantaneous, steady continuous or time dependent releases of gas or aerosol. It can model multi-components based upon the assumption of either an ideal solution or complete immiscibility in the liquid phase (or a combination of these).
Our experts also establish specific interacting mixture models for hydrogen fluoride and ammonia. Our thermodynamic module considers heat of vaporisation and (in the case of ammonia and hydrogen fluoride) heat of solution. The basic model is derived in terms of a set of coupled differential equations.
Our Advantages
- We are also capable of modeling dispersion of releases in enclosed or semi-enclosed spaces.
- At Alfa Chemistry, simulations usually complete in just a few minutes even for highly complex geometries.
Gas dispersion modelling provides an effective way to optimize the chemical process. Our gas dispersion modelling services remarkably reduce the cost, promote further experiments, and enhance the understanding of chemical process for customers worldwide. Our personalized and all-around services will satisfy your innovative study demands. If you are interested in our services, please don't hesitate to contact us. We are glad to cooperate with you and witness your success!
Reference
- Witlox, H.; et al. Modelling of discharge and atmospheric dispersion for carbon dioxide releases including sensitivity analysis for wide range of scenarios. Energy Procedia, 2011, 4: 2253-2260.