Ventilation of Gas Turbine Package Enclosures: Design Evaluation Procedure

Abstract

Gas turbine packages provide a major portion of mechanical drive and power supply for the offshore operating oil and gas platforms. These packages are typically installed in acoustic enclosures, which need to be ventilated for both removing the heat rejected from the engine and package components, and properly diluting explosive gasses in case of a leak. Considering importance of safety and reliability of gas turbine equipment operating in the offshore environment, and also near industrial and populated areas, authors of the paper emphasize the need for experimental validation of a CFD prediction practice for effective ventilation of the turbine package enclosures. In a properly designed acoustic enclosure, ventilation system has to prevent overheating of the electrical and engine control components, as well as, dilution of potential fuel leakages to eliminate stagnant zones that could cause an ignition within enclosure. Conversely, an excessive flow of the vent air may result in masking local fuel leakages, which might pass undetected through explosion protection devices. Therefore, the optimum enclosure ventilation design has to be based on proper vent flow distribution to ensure acceptable temperature distribution within the enclosure, proper flow distribution to ensure no stagnation area, combined with appropriate gas detection setting. In order to achieve an optimum enclosure design, rather complex flow and heat transfer phenomena have to be studied to select the optimal configuration of the vent system. Numerical analysis of the enclosures with commercially available CFD codes is usually based on a number of simplifying assumptions and approximations. Therefore, to satisfy critical safety requirements in the offshore environment, authors of the paper emphasize role of experimental validation of the CFD predictions. The presented paper provides details of the enclosure design validation using a CFD study based on an earlier experimental validation of the numerical predictions. A midsize gas turbine package model was selected to demonstrate this procedure. The main features from the actual engine package were included in the CFD model. Effectiveness of ventilation was studied for both cold and heated engine surfaces. CFD analyses were also carried out for local CO2 injection emulating natural gas leakage. Both scenarios with CO2 and natural gas (methane) leakages were considered reducing uncertainty of predictions due to the differences in the density and buoyancy between these gasses. Based on presented study certain improvements in design of the enclosure were recommended and described in the paper.