Application of Plume-Cooling Technology To Solve a GTG Impingement Problem: A Case Study

Abstract

• Warming of air over the helipad, causing a sudden change in aircraft performance and possible loss of control • Direct exposure of workers to elevated air temperatures and dangerous concentrations of carbon dioxide (CO2) and carbon monoxide (CO) The level of risk for the preceding impacts depends on the type and power output of the engine. Gas-turbine engines are particularly prone to impingement problems because of their high exhaust temperatures (> 500°C) and large volumetric flow rates. The diameter of the exhaust uptake and its proximity to AOIs on the platform also play an important role in the probability and severity of impingement impacts. Thus, platform designs that have their gasturbine engines located centrally tend to put many areas of the platform at risk. Up to this point, the standard practice for reducing the risk associated with exhaust-plume impingement has been to locate the exhaust-duct exit as far away from sensitive areas as possible, or to extend the exhaust duct vertically upward until all the AOIs are below the duct exit (Fig. 1). Either of these two solutions, although effective, can result in long exhaust-duct runs with associated support structure, which adds weight to the platform. There is another solution to the plume-impingement problem, and that is the use of plume-cooling technology. Plume cooling has been used successfully on military ships for more than 40 years as a means of reducing the IR signature of the ship. A ship’s engine exhausts are the primary source of heat aboard, and thus any reduction in the temperature of visible metal or plume will reduce the detectibility of the ship in the IR band (Thompson et al. 1998). Another advantage of the use of plume cooling aboard a ship is that the temperature of mast-mounted sensors and communications equipment is lower in the event that the plume impinges upon them. An example of plume-cooling use on a military ship is the USS Makin Island (LHD-8), shown in Fig. 2. This ship class was originally powered by steam turbines, but the eighth ship was converted to gas-turbine propulsion, which greatly increased exhaust-gas temperatures, and thus required plume cooling to protect equipment on the ship’s two masts. At the time this paper was written, the authors were not aware of any plume coolers in service aboard existing offshore facilities. Currently, there are three new platform constructions that have plume coolers installed on their GTGs: Chevron Big Foot, ExxonMobil Hebron, and Statoil Gina Krog. An explanation for why plume coolers have not been used more frequently to solve impingement problems may be as simple as designers are not aware that the technology exists. Bringing the benefits of plume cooling to the attention of designers and operators is the primary purpose of this paper. Plume coolers are simple air/air ejectors that passively draw in cool, ambient air and mix it with the exhaust gases before they exit the device (Birk and Davis 1998). Fig. 3 illustrates schematically how a typical plume cooler functions. The technology is scalable to any size of exhaust. Development of the technology for use aboard military ships has resulted in a very compact and lightweight design that Copyright © 2016 Society of Petroleum Engineers