CFD Modelling for The Energy Industry: Beyond Explosions

At ESR Technology, we have many years’ experience of undertaking CFD explosion and flammable/toxic gas dispersion assessments for a range of offshore installations from simple unmanned wellhead towers to multi-jacket processing complexes.

There are however a number of less commonly undertaken CFD-based analyses which can be critical to operations often requiring specialist analysis. Typically, such studies are more bespoke and tailored to address very platform specific design or operational challenges. Moreover, the questions tackled through these studies tend not to be limited to the oil and gas sector but rather are often shared with other offshore sectors such as the wind energy industry amongst others.

Here we share the nature of some of these alternative studies, highlighting recent ESR projects and examples.

CFD Toxic/Thermal Exhaust Gas Dispersion – Exhausts sometimes found on oil and gas platforms or wind farm substation platforms include those from Emergency Diesel Generators (EDGs), Fire Water Pumps (FWPs), and gas turbines amongst others. Two considerations affecting exhaust tip location selection are the avoidance of toxic plumes reaching personnel areas and ensuring buoyant discharges do not adversely interact with the helideck. In one study, a client indicated exhaust fumes were being detected within a living quarters and commissioned a CFD exhaust dispersion analysis to assist in the relocation of existing exhausts to reduce NOx ingress concentrations. In a separate study from a design project, through a series of sensitivity studies ESR were able to advise on the optimal length of an exhaust pipe to limit thermal plumes reaching the platform helideck.

Warm Air Discharge Modelling – Regular features of offshore installations are cooling systems such as fin-fan coolers or other sources of warm air discharges such as transformers. It is often the case that the cooler units are located on a weather deck or equivalent to allow the warm air to dissipate. However, one often overlooked consideration is the potential for the buoyant air plumes to interact with the helideck airspace and the potential for breaches of CAP 437 guidelines on temperature rise (2°C). In one study, ESR assessed a design proposal for a new compression module including fin-fan coolers that was to be located adjacent to the helideck. The results demonstrated the potential for significant temperature rise in the helideck airspace leading to recommendations for the relocation of the cooler units.

Wind Chill Analysis – One of the reasons that the North Sea is popular for wind energy is the reliable frequency of relatively high wind speeds. However, when combined with relatively low ambient temperatures, this can mean that offshore personnel have a greater likelihood of significant wind chill exposure. CFD ventilation analysis can be used to predict the Wind Chill Index (WCI) in different platform areas to identify locations of high potential exposure. In one example project, the zones with the highest frequency of wind chill exposure were determined with the results then coupled with manning location data to indicate the worker groups at greatest risk. Where appropriate, recommendations were then made regarding the use of wind walling to reduce exposure or modifications to operational procedures to help minimise personnel exposure.

Stagnant Area Analysis – EI 15 hazardous area classification defines stagnant areas as zones with air velocities of <0.5 m/s. The presence of stagnant areas is relevant for flammable gas cloud build-up but also when identifying potential locations for air intakes or exhausts. In a recent project ESR assessed the potential for stagnant areas around a set of turbines and identified zones with higher frequency of stagnation in the vicinity of the proposed air intake locations, thereby resulting in recommendations that the intakes be relocated to regions of lower predicted stagnation frequency.

Helideck Wind-Driven Turbulence Assessment – As wind farm development projects grow in both quantity and scale, it is increasingly common to find helidecks located on substation platforms, a fairly common occurrence on most oil and gas platforms. One component of helideck availability is limitations on vertical turbulence within the helideck airspace. CAP 437 recommends the use of CFD-based ventilation analysis for helidecks so as to identify wind conditions that may yield excessive turbulence. ESR have undertaken a number of such studies in which the platform and helideck design are assessed, and helideck unavailability predicted. This has led to recommendations on the adequacy of the airgap beneath the helideck. In some cases, this wind driven turbulence assessment may be combined with thermal plumes from exhausts to determine total helideck unavailability.

CFD Vent/Flare Dispersion Analysis – Considerations about the location and height of a vent/flare tip include the potential for unignited or ignited discharges reaching manned areas. ESR have undertaken numerous worst-case loading assessments to model vent/flare releases and to predict flammable and toxic gas concentrations at personnel areas and SCEs. A recent example of such a study included a series of sensitivity studies examining the variation in gas concentrations in manned locations when discharges occurred from different flare tip elevations.

So, if you have novel and challenging situations where our CFD experience and modelling expertise may help we would be very pleased to discuss how we could assist.

For more information please contact Terry Atkinson (This email address is being protected from spambots. You need JavaScript enabled to view it.).