Photocopy of typescript. / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

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In recent years there have been many reports of dust explosions associated with industries handling particulate materials. A study has been undertaken to investigate the influence of various transporting parameters of a pneumatic conveying system on the tribo-electrification of powders. These parameters include powder transportation velocity, powder flow rate, space charge field of the powder passing through the pipes, particle size, resistivity and relative humidity. The specific charge is a linear function of the transport air velocity. The specific charge reaches a saturation level as the powder flow rate increases and falls at high powder flow rates. The saturation specific charge of powder particles is determined by a self generated space charge field during normal pneumatic conveying. The tribo-charging can hence be controlled by controlling the space charge field. Hazardous conditions may arise when the charged powder enters a storage silo as explosible dust concentrations can result and, with the presence of an ignition source, a risk of fire and explosion exists. It is generally accepted that dispersed flammable dust clouds may be ignited by discharges from electrostatically charged conducting objects. These discharges can however be excluded if grounded conductive equipment is used. The question 'Can a flammable powder be ignited by the charge accumulated on the powder itself, even if the powder is handled in earthed conductive installation?' is investigated. The magnitude and incendivity of discharges from the surface of bulked powder and the dust cloud to probes is studied It is possible to obtain incendive discharges which are capable of igniting a propane/air mixture with a minimum ignition energy of 0.25 mJ. The experimental results from a laboratory scale rig show that the largest probability of ignition of propane/air/nitrogen are defined for moderate streaming currents and specific charge densities.

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Call number: LD2668 .T4 1979 B73 / Master of Science

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This thesis is concerned with the experimental determination of the fundamental flame characteristics in a dust-air mixture and the influence of turbulence on flame propagation. Experiments were carried out in a tube having a 0.19 meter inside diameter and a length of 0.93 meter, and 1.86 meter with both ends closed. A dispersion system was developed giving a good quality uniform dust suspension. A comparative method for the estimation of dust flame characteristics, based on well defined methane-air flame characteristics, was developed and employed to estimate the characteristics of a flame propagating in a cornstarch dust-air mixture. A systematic study of the influence of dispersion-induced turbulence on the dust flame propagation was carried out. The influence of obstacles on flame propagation also was investigated. Some mechanisms of flame propagation in a cornstarch dust-air mixture have been proposed and discussed. In the conclusion, general remarks concerning the dust flame characteristics and the influence of turbulence on flame propagation are made. The future direction of research is also indicated.

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