Heat Stress Assessment on an Offshore Platform using Computational Fluid Dynamics and Wet Bulb Globe Temperature Models
Kuochen Tsai, Shell International E&P
Paper #: SPE-174963-MS
Deep water oil discovery has played an increasingly critical role for the oil industry. With the increased water depth of new discoveries, oil temperature keeps hitting new highs as well and has huge impact for equipment and the work environment on the oil rig. A wet-bulb globe temperature (WGBT) model has been incorporated into computational fluid dynamics (CFD) software to assess heat stress for the safety of work environment on an offshore platform crowded with oil processing units. The model contains all critical elements needed to model WBGT, including conductive and convective heat transfer from the ambient air, the radiative heat from the hot processing unit surfaces, solar load and ambient atmosphere, and most importantly the cooling effect from perspiration evaporation. The feasibility of such a comprehensive model greatly enhances our understanding of the heat stress distribution and opened new opportunities for remedial actions.
The CFD model was constructed with geometry files directly imported from 3-D modeling software used for large offshore platform structures. The imported geometry was then extracted for necessary parts critical for the thermal modeling. Smaller features, such as deadleg pipes, nuts and bolts that won’t influence the results are removed to reduce computational costs. The parts were then grouped according to thermal boundary conditions to be applied, including temperature, heat transfer coefficients and emissivity. A wrapping mesh was applied to convert the CAD geometry into a meshable domain and mesh was generated with specified sizes that can eliminate small gaps and undesirable features ill-suited for CFD solutions. A WBGT model was incorporated into the CFD software (ANSYS FluentTM) using an iterative procedure from the work of LilJegren et al. (2008). The inclusion of the WBGT model greatly enhances the predictive capability of CFD models for assessing the heat stress for human operators due to its ease of use without explicitly modeling the human body surfaces and locations.
The modeled results show that it is necessary to insulate the processing unit surfaces for safe operation due to the proximity to high temperature surfaces from the impact of thermal radiation. Other remedial measures were also explored and although the results were disappointing, the method opens up new possibilities that allows the evaluation of safe work environment in the planning phase and enables more effective project control.
J. C. Liljegren, R. A. Carhart, P. Lawday, S. Tschopp and R. Sharp, “Modeling the wet bulb globe temperature using standard meterological measurements,” J. of Occupational and Environmental Hygiene, 5, pp. 645-655, 2008.
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