Masaharu Nifuku

A study on the static electrification of powders during pneumatic transportation and the ignition of dust cloud

Abstract Large amounts of powders are being handled in industrial activities, and these are facing static electrification that might lead to dust explosion or fire. Therefore, it is important to know about the static electrification in detail in the powder handling processes to prevent the hazards. The authors investigated the static electrification characteristics such as the relation between the powder charge and dust concentration, transportation velocity, transportation distance, etc., using pneumatic transportation system. Also, the influences of spark duration time, ignition energy and feeding ratio of the ignition energy to initiate the dust explosion were investigated because there is a potential risk of dust explosion due to the static electrification. From the results of the experiments, the information on the static electrification and the ignition of the dust cloud was obtained. This would contribute to maintain safe operation of the powder handling, especially pneumatic transportation, by regulating the transport conditions.

Gas temperature of capacitance spark discharge in air

Capacitance spark discharge has been widely used for studying the ignition of flammable gas caused by electrostatic discharge. In the present study, the gas temperature of capacitance spark discharge is measured. The gas temperature is an important factor in understanding the electrostatic ignition process because it influences the reaction rate of ignition. Spark discharge is generated in air with a pulse duration shorter than 100ns. The discharge energy is set to 0.03–1mJ. The rotational and vibrational temperatures of the N2 molecule are measured using the emission spectrum of the N2 second positive system. The rotational and vibrational temperatures are estimated to be 500 and 5000K, respectively, which are independent of the discharge energy. This result indicates that most of the electron energy is consumed in the excitation of vibrational levels of molecules rather than the heating of the gas. The gas temperature after discharge is also measured by laser-induced fluorescence of OH radicals. It is s...

Some aspects in testing and assessment of metal dust explosions

Abstract The dust explosion committee of the Association of Powder Process Industry and Engineering, Japan recently established two testing standards for dust explosions. In the investigations for the standardization, many experimental data have been obtained for the dusts currently used in Japanese industries. Data for zirconium, tantalum and silicone dusts are presented to discuss the use of test methods, which have been accepted internationally. The test methods for dust explosions have to consider a variety of kinds and forms of dusts to be tested.

Recent development of standardization of testing methods for dust explosion in Japan

Abstract The Dust Explosion Committee of the Association of Powder Process Industry and Engineering (APPIE) of Japan has acted to establish the standard for the member of the Association. Two testing methods have been authorized by the Association. The methods are established to evaluate sensitivity and severity for dust explosion. The ignition sensitivity is evaluated by the minimum explosive dust cloud concentration. Tapping sieve equipment and a strictly-specified Hartmann-type explosion tube have been selected as the testing apparatus. The tapping sieve equipment is applied to measure the minimum explosive concentration by forming a dust cloud supplied from a sieve on the top of the explosion chamber. The Hartmann-type tube is used to investigate roughly whether the test powder is explosive or not. A lot of explosion tests had been carried out to standardize the equipment and evaluate the sensitivity. This APPIE standard is being revised. Along with the ISO standard for explosion severity, Research Institute of Industrial Safety, the Ministry of Labour published a Guide to Test Method for Explosion Pressure and Rate of Pressure Rise for Combustible Dusts in 1994. Based on this Guide, The APPIE Committee has made the draft for the member. These standards and drafts are aimed to be the Japanese Industrial Standard (JIS). No other similar standard exists in Japan. In the present paper, technical data and explosion statistics which are the background of the APPIE standard for the ignition sensitivity are to be described.

Incendiary characteristics of electrostatic discharge for dust and gas explosion

Abstract Paying attention to the ignition potentiality of static electricity, the relation between the discharge characteristics and the ignition of a dust cloud and the gas produced was studied, applying an electrical power supply of which the electrical circuit is adjustable. The effect of ignition characteristics on dust and gas explosions was investigated. The results of the study indicate that the probability of an explosion is influenced by the minimum ignition energy, spark duration time, feeding rate of ignition energy, circuit capacitance, ignition voltage, etc.

Evaluation of the explosibility of malt grain dust based on static electrification during pneumatic transportation

Abstract The possibility of dust explosions by static electricity in a malt grain silo was investigated. Two kinds of experimental equipment were applied. One was to supply electrostatic charge in order to investigate the charge build up characteristics. The other was to transport the malt grain pneumatically in order to investigate the frictional charge accumulation in the transportation system. The particle charge of the pulverized malt grain was in the order of 10 −14 C. The particle charge of the malt grain was in the order of 10 −9 C and the pipe charge in the transport system was also in the order of 10 −9 C. The charge accumulated on both the pulverized particle and the grain particle were small in view of the incendiary potentiality. However, attention must be paid when the particles are dumped into isolated space. There might be a charge accumulation that will lead to the ignition of the dust cloud.