Influence of Physical Characteristics and Ingredients on the Minimum Burning Pressure of Ammonium Nitrate Emulsions

Abstract

It has been well established that sustained combustion in ammonium nitrate water-based emulsions (AWEs) can only occur if the ambient pressure is held above some threshold value, usually referred to as the minimum burning pressure (MBP). For the commercial explosives industry, a good knowledge of the MBP for particular AWE formulations is essential to estimate safe operating pressures for the associated manufacturing and handling processes. In these processes, AWE products are most often pumped in closed systems and at elevated temperature. While previous studies have established that the MBP can depend critically on major ingredients, its dependence on physical characteristics such as temperature and viscosity had never been investigated. Moreover, the consequences of alterations in measurement methodologies on the resulting measured MBP values had not been studied.In the present work, MBP measurements were performed for a number of AWE systems representative of those found in the commercial explosives industry. The effect of the presence or absence of certain ingredients on the MBP will be discussed. In particular, the influence of glass or polymeric microspheres and testing geometry on the combustion behaviour of some AWEs will be evidenced. Experimental results showing the effect of other physical factors such as initial product viscosity and temperature on the measured MBP values are also presented.

Initiation and propagation of combustion waves with competitive reactions and water evaporation

“…Conservation equations for AN in its basic dissolved state, water in liquid and vapour form, and fuel, together with an energy equation, then comprise a highly nonlinear set of ODEs containing numerous (and often uncertain) parametric representations of the physical and chemical processes involved. More detailed results will be published elsewhere, but the influence of pressure on the time to ignition is demonstrated in figure 2, based on our computations, which shows clearly the existence of a practical cut-off (for the kinetics assumed) at around 3 atm (0.3 MPa) in accordance with the phenomenon of an MBP, which has been observed in experiments and industrial practice [1][2][3]. The zero-dimensional results shown in figure 2 clearly illustrate the important effects of ambient pressure on the dissociation of AN, and hence any subsequent fuel combustion.…”

“…The research described here was motivated by the ignition and subsequent burning behaviour of ammonium nitrate (AN)-based emulsion mixtures, of which experimental and observational results reveal aspects of behaviour that are not fully understood [1][2][3]. The emulsions usually consist of a water-AN solution and a hydrocarbon fuel, with, in most cases, other additives.…”

2D chaotic flow in competitive exothermic-endothermic reactions

“…However in many practical situations it is not adequate to lump the chemistry into a single reaction model, and it is necessary to retain at least two reactions in the lumped model, either both exothermic or one exothermic and one endothermic. Practical examples are dominated by solid state pyrolysis processes, but liquid cases are exemplified by behaviour of emulsion explosives [Manelis et al, 2003;Sinditskii et al, 2005;Turcotte et al, 2010]. The one-dimensional systems with an exothermic and endothermic reaction without mixing has been studied by Sharples et al [2012].…”

Numerical Study on Thermal Safety of Emulsion Matrix in Emulsifier

“…S. K. Chan and R. Turcotte et al. established a testing system to study the thermal safety of emulsion matrix under different ambient pressure and proposed the minimum burning pressure concept and analyzed the key influencing factors. In addition, some scholars have studied the thermal safety of emulsion matrix in the screw pump.…”