Kees van Wingerden

The influence of water sprays on gas explosions. Part 2: mitigation

Abstract Two papers have been prepared, reporting on experimental investigations into the influence of water sprays on gas explosions. The water sprays that were used in these experiments were produced by nozzles that are very commonly used on offshore facilities. The experiments addressed the influence of turbulence generated by these systems on the course of gas explosions and the mitigating effect that water sprays may have on gas explosions under certain circumstances. The first paper reports on the influence of turbulence produced by water spray, investigated in a 1.5 m3 rectangular box. The present paper reports on mitigation of gas explosions by water-spray systems. For mitigation of gas explosions to be possible using water spray produced by nozzles which are commonly used offshore, droplets need to be broken up. Analysis of experiments performed in a 50 m3 representation of an offshore module showed that a minimum rate of flame acceleration is necessary to cause the droplets to break-up. This rate of flame acceleration is dependent on the droplet size. The larger the droplets are, the easier it will be to cause droplet break-up and hence mitigate gas explosions.

The influence of water sprays on gas explosions. Part 1: water-spray-generated turbulence

Abstract Two papers have been prepared, reporting on experimental investigations into the influence of water sprays on gas explosions. The water sprays that were used in these experiments were produced by nozzles that are very commonly used on offshore facilities. The experiments addressed the influence of turbulence generated by these systems on the course of gas explosions and the mitigating effect that water sprays may have on gas explosions under certain circumstances. The second paper reports on mitigation of gas explosions by water-spray systems. The present paper reports on the influence of turbulence produced by water sprays, investigated in a 1.5 m3 rectangular box. The flame speeds found in the presence of turbulence due to various types of nozzles were approximately 1.4 to 2.3 times the flame speeds without water sprays. The properties of the turbulence appear to be related to the dimensions of the chamber in which the experiments were performed and not to the dimensions of the droplets.

Mitigation of gas explosions using water deluge

The degree of congestion in petro‐chemical installations has a strong impact on the strength of possible gas explosions. Model predictions and recent full‐scale explosion tests showed that there are situations where the consequences of such gas explosions are unacceptably high. These consequences make it necessary to consider several measures including very expensive ones such as control room relocation or strengthening of control rooms. When the costs are too high other mitigation methods may also have to be assessed. One of these methods is mitigation of gas explosions using water spray systems. Such systems are already in use for this purpose offshore, water curtain systems may be applicable onshore.

Ignition of dust clouds by brush discharges in oxygen enriched atmospheres

Abstract Brush discharge ignitions of sulphur dust in oxygen-enriched atmospheres have been established. From a total of approximately 300 trials, brush discharges were able to start explosions of sulphur dust in three trials. In these trials the atmospheres contained 55 vol%, 60 vol% and 70 vol% oxygen, respectively. The work is motivated by the fact that no brush discharge ignition of dust–air mixtures has been observed in laboratory trials, despite an equivalent energy of the discharge above the minimum ignition energy of some dusts. By adding oxygen to the atmosphere in which the brush discharge is generated, the dust–air mixture will be more prone to ignition. If the critical oxygen concentration to establish ignition of very sensitive dusts such as sulphur is considerably higher than the oxygen concentration in air, it may be stated that a brush discharge cannot ignite dust–air mixtures at atmospheric conditions. High-speed video recordings show that all three ignitions occurred at the top edge of an evolving dust cloud. The research is still ongoing.

A study on the effect of trees on gas explosions

The downstream as well as the upstream oil and gas industry has for a number of years been aware of the potential for flame acceleration and overpressure generation due to obstacles in gas clouds caused by leaks of flammable substances. To a large extent the obstacles were mainly considered to be equipment, piping, structure etc. typically found in many installations. For land based installations there may however also be a potential for flame acceleration in regions of vegetation, like trees and bushes. This is likely to have been the case for the Buncefield explosion, which led to the work described in the present paper. The study contains both a numerical and an experimental part and was performed in the period 2006–2008 (Bakke and Brewerton, 2008; Van Wingerden and Wilkins, 2008)

Prediction of pressure and flame effects in the direct surroundings of installations protected by dust explosion venting

Abstract When applying dust explosion venting as a measure to protect installations one should always bear in mind the secondary effects of application of venting, viz blast waves and flames emerging from the vent. These two effects pose hazards to the direct surroundings of explosion vents and these hazards should be considered during the design phase of the equipment. This paper will give an overview of the data and methods that are available to predict flame and blast effects associated with vented dust explosions.

Course and strength of accidental explosions on offshore installations

Abstract To be able to limit the consequences of gas explosions, one has to predict gas explosion loads. Once these loads are known, structural measures to limit damage to the offshire rig can be taken. Prediction of the loads due to gas explosions is only possible on the basis of a good understanding of the processes governing this phenomenon. The aim of this paper is to describe the current understanding of gas explosion development in complex geometries. Important parameters of influence will be presented using experimental results. The principles of mitigation methods will be explained and methods for predicting gas explosion loads will be reviewed. Work performed at Christian Michelsen Research will be used as examples.

Complex explosion development in mines: Case study—2010 upper big branch mine explosion

On April 5th, 2010, a methane explosion occurred within the Upper Big Branch mine south of Charleston, WV. Twenty‐nine men lost their lives as a result of a flammable concentration of methane that built up in the enclosed space and ignited, resulting in a methane explosion that transitioned into a coal dust explosion. This study used the FLACS computational fluid dynamics solver to conduct a detailed explosion analysis to evaluate the complex overpressure development throughout the mine as a result of the flammable cloud ignition. As a result of the accident investigation, unique explosion patterns were found in the mine where certain “blast indicators” within the mine shafts were deformed in such a manner that was inconsistent with the likely flow of the expanding blast wave. The FLACS analysis will analyze the explosion dynamics and shed light on the damage observations made after the blast.

A full‐scale experimental and modeling investigation of dust explosions in a roller mill

Combustion of biomass is becoming an increasingly important energy source. This is especially true for wood pellets, as several power companies have decided to use this fuel instead of coal. In this process, the wood pellets are ground in big mills and, from there, pneumatically transported to the burners in the boiler where they are consumed. The grinding of biomass and coal represents an explosion hazard, which can potentially result in considerable damage to the power plant upon propagation of the explosion from the mill into other parts of the installation.

Flame Inhibition by Potassium-Containing Compounds

ABSTRACT A kinetic model of inhibition by the potassium-containing compound potassium bicarbonate is suggested. The model is based on the previous work concerning kinetic studies of suppression of secondary flashes, inhibition by alkali metals, and the emission of sulfates and chlorides during biomass combustion. The kinetic model includes reactions with the following gas-phase potassium-containing species: K, KO, KO2, KO3, KH, KOH, K2O, K2O2, (KOH)2, K2CO3, KHCO3, and KCO3. Flame equilibrium calculations demonstrate that the main potassium-containing species in the combustion products are K and KOH. The main inhibition reactions, which comprise the radical termination inhibition cycle are KOH + H=K + H2O and K + OH + M=KOH + M with the overall termination effect: H + OH=H2O. Numerically predicted burning velocities for stoichiometric methane/air flames with added KHCO3 demonstrate reasonable agreement with available experimental data. A strong saturation effect is observed for potassium compounds: approximately 0.1% volume fraction of KHCO3 is required to decrease burning velocity by a factor of 2; however, an additional 0.6% volume fraction is required to reach a burning velocity of 5 cm/s. Analysis of the calculation results indicates that addition of the potassium compound quickly reduces the radical super-equilibrium down to equilibrium levels, so that further addition of the potassium compound has little effect on the flame radicals.