A METHOD FOR ASSESSING THE CONSEQUENCES OF SMALL LEAKS IN ENCLOSURES

摘要

Recently there has been interest in the possible consequences of a small leak of natural gas from high-pressure plant located in a confined volume. This paper describes a method for assessing the explosion hazards produced by such leaks. The method may be used for natural gas fired plant in turbine halls, for example. Of particular interest in this context is a method for assessing the consequences of the largest leak that is not detected by a gas detection system of a specified sensitivity. The scenario that is analysed is a high-pressure release of natural gas into an enclosure. The natural gas mixes with the surrounding air and the gas concentration distribution in the enclosure increases towards a steady state determined by the leak mass flow rate, location and orientation, the volume and shape of the enclosure and the ventilation characteristics of the enclosure. If the enclosure has a gas detection system then it is possible that the leak could be detected and mitigating actions taken before the steady state conditions are reached. The flammable volume that is produced by such a small leak may never then reach the hypothetical steady state value that would be created if the leak had not been detected. In this work, the consequences of igniting the flammable volume that is produced by the leak, whether it is detected or not, are evaluated. The method that is used to assess the consequences includes mathematical models for the leak flow rate, the gas dispersion or accumulation and the pressure generation, should a flammable volume be ignited. The method has been applied to a number of gas dispersion experiments carried out in enclosed volumes and has been found to give reasonable agreement with the data for the flammable volumes that are produced by the leaks. As an illustration of its application, the methodology is applied to two enclosures with different ventilation systems. In both cases, the predicted consequences of a small leak are evaluated and discussed.