The quest for fast and sustainable speeds

Joel Makower Tuesday, January 7, - 2: How a Big Mac becomes sustainable.

This model suffers from a problem common to all simplified explosion models: In the BST model, the fuel reactivity, flame expansion, and obstacle The quest for fast and sustainable speeds parameters are used to select a flame speed from a limited matrix of possible values.

It provides for a continuous range of flame speeds that can then be used with the existing BST blast curves to calculate the characteristics of the vapor cloud explosion.

The QMEFS approach provides the user with a method for describing a VCE that is more detailed than the BST model, and establishes a more refined system for predicting the consequences of vapor cloud explosions. Text Download a PDF Any release of a flammable fluid in a petrochemical facility has the potential to generate a flammable vapor cloud that, if ignited, could produce a vapor cloud explosion VCE.

The concern for human injury or death is most often addressed in the form of a building siting study. Because people are somewhat less likely to be injured or killed by the effects of a VCE when outside, as compared to when inside a building, the siting study focuses on the potential VCE impacts to buildings within and around petrochemical facilities.

It then becomes the task of process safety professionals to estimate the potential for VCE events, and their resulting overpressure impacts on buildings. Prediction of the overpressures resulting from a VCE is typically done using one of two categories of models: Introduction Any release of a flammable fluid in a petrochemical facility has the potential to generate a flammable vapor cloud that, if ignited, could produce a vapor cloud explosion VCE.

CFD models calculate the overpressure field by solving the Navier-Stokes equations numerically and incorporating different sub-models to account for turbulence and combustion reactions.

Results are often strongly dependent on the location and strength of the ignition point, the location and composition of the flammable cloud throughout its volume, and the location and configuration of any obstacles or obstructions within the cloud. Given the number of combinations of ignition points and cloud geometries e.

Simplified models such as the Baker-Strehlow-Tang BST model or the TNO Multi-energy model use information taken from CFD studies to generate curves defining the relationship between explosion overpressure and distance from the explosion center. These curves can then be used in a more general manner to estimate the overpressure impacts generated by an exploding vapor cloud.

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However, both approaches require the user to estimate the strength of the explosion as a function of the reactivity of the flammable material and the degree of confinement or congestion present in the cloud. This information is then used to determine which strength curve in the case of the TNO model or flame speed in the case of the BST model is used to calculate the overpressure of the explosion as a function of distance from the center of the explosion.

The TNO Multi-energy model provides little guidance for selecting the explosion strength curve. Curves for strengths in the range of 1 to 10 are provided, and it is left to the user to determine how the reactivity of the flammable gas and the degree of confinement or congestion relate to one of these curves.

The BST model is based on a simple set of guidelines that result in a selection of a flame speed, which corresponds to an overpressure vs. Three parameters are used to determine the flame speed to be used: Reactivity is divided into three categories: According to the current BST model, materials having a laminar flame speed also known as fundamental burning velocity greater than 0.

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All other materials are considered to be medium reactivity. The effect of the confinement of the flammable cloud is taken into account by determining the number of dimensions in which the burning gas may expand. Finally, 1-D expansion is used for flames propagating in pipes. The effect of obstacles in the flammable cloud is characterized by the obstacle density, classified as low, medium, or high.The Quest for Personal Best: Individual Sports 6-Pack.

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Is it biting off more than it can chew? Exclusive: Inside McDonald's quest for sustainable beef. Joel Makower. Tuesday, January 7, - am McDonald’s sustainable beef journey began nearly five years ago, when it engaged a team from WWF.