This thesis is concerned with the combustion hazard posed when there are accidental releases of methane from plant, particularly within the petrochemical 'exploration and production' industry. At the present time, such explosion hazards are controlled using explosion suppression systems based around Halon 1301 deployment. However, due to its environmental impact, such methods are being reviewed with the objective being their replacement with environmentally friendly alternatives. During the course of this study, the effect of water in the form of vapour and 'fine' mists has been investigated to determine its effectiveness in the containment and control of a potential methane explosion. Laminar flame/water interaction has been studied in considerable detail, and to a lesser extent the interaction with turbulent burning mechanisms has been studied through a demonstration study based on the conclusions of the laminar flame studies the efficiency of water in various concentrations and states (vapour or liquid-droplets) has been appraised. The research studies have also necessitated fundamental studies of droplet formation via supersaturated vapours, within small-scale laboratory test facilities, and methods suitable for generating large-scale sprays deemed suitable for the replacement of Halon systems were then appraised and characterised so as safety systems of the future may be optimised. The laminar test programme illustrated that water is a competitive explosion suppressant capable of extinguishing a fully propagating flame. It was found that water vapour and 'fine' water droplets are most effective in the mitigation of methane-air flames during early flame formation when curvature effects are a predominant factor, with 'fine' water droplets being more effective than vapour at this time. Turbulent experiments demonstrated that water in the form of 'fine' droplets can be used to fully arrest a propagating stoichiometric methane-air explosion, at concentrations probably less than the molar water concentration associated with inerting methane air explosions. A system based on the 'flashing' concept was fully characterised to illustrate that sprays similar to those utilised in the laboratory combustion work can be produced in a full- scale release, leading to the conclusions that Halon based systems may in the near future be replaced by environmentally sound explosion suppression systems that utilise water.
展开▼
