Widely used methods for calculating thermal radiation impacts of flares and/or flame jets rely on point source, multiple point source, integral, or solid flame representations of the flame surface. The flame jet length and flame centerline geometry are established by calculating the curvilinear distance to the lower flammable limits without combustion. Some computational fluid dynamics models have attempted to include combustion reactions modeling, but such methods are still not practical for most design and risk applications.
In general, current methods generate adequate thermal radiation estimates in the far field because at distances far away from the flame, the flame will appear as a point source. In the near field, the flame geometry becomes more important. As more air is entrained into the flame, the flow momentum influence on flame geometry is reduced and the influence of buoyancy due to combustion on flame geometry dominates. This is especially important for horizontal releases and/or releases with light materials such as hydrogen.
Several types of models are commonly used to assess the thermal radiation hazards of flame jets and flares. These models are generally divided into three categories: (a) point source or line source models, (b) solid flame models, and (c) computational fluid dynamics (CFD) models. A line source model is made up of multiple point sources. A solid flame model represents the flame and flame surfaces using and idealized geometry to obtain incident thermal radiation levels at locations of interest.
The most practical flame jet and flare models are multiple point source models. They rely on jet dispersion to first establish the flame jet length and curvilinear path and then integrate the multiple point source energy release rates along the entire flame jet path.
A detailed multiple point source model for the calculation of thermal radiation from flame jets and flares using SuperChems® Expert is described in detail. While the fraction of flame jet combustion energy available for radiation is based on Shore's method or can be based on measured data, detailed combustion equilibrium calculations are also integrated to yield combustion species identities, compositions, flame temperature, as well as conversion and destruction efficiencies.
User tools are also provided by SuperChems® Expert for the assessment of thermal radiation on nearby structures as well as the calculation of gas purge rates, and visualization of noise and thermal radiation contours with options for sound power level weighting and combustion spectrum efficiency selection. Thermal radiation and/or noise contours from one or more sources/flares can be combined and displayed on site maps.
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