Charge reduction on polypropylene granules and suppression of incendiary electrostatic discharges by using a novel AC electrostatic ionizer

As a method to prevent or mitigate electrostatic charge and/or discharges, we have developed a novel AC electrostatic ionizer. In this study, we evaluated experimentally the practical version of the novel AC electrostatic ionizer with a modeling test system and a pneumatic powder transport facility. In addition, electrostatic discharges generated inside a silo while loading polypropylene (PP, 3 mm) granules were observed visually with/without the novel AC ionizer. The specific charge was clearly decreased with the novel AC electrostatic ionizer. The specific charge obtained with the four arranged AC electrostatic ionizers used was approximately one eighth of that without the AC ionizer. The incendiary bulk surface discharges completely died out inside the silo by using the four arranged ionizers.     

Spawning migration and returning behavior of white-streaked grouper Epinephelus ongus determined by acoustic telemetry

White-streaked grouper (Epinephelus ongus) is an important fishery target that forms fish spawning aggregations (FSAs) at specific spawning grounds. The aims of the present study were to investigate migration behavior and returning behavior in terms of FSA using acoustic telemetry. Among the 30 specimens tracked, three types of movement pattern were observed: type 1, high site fidelity at the release area before the spawning period, migration to the spawning ground during the spawning period and return to the release area just after the spawning period (17 specimens); type 2, high site fidelity at the release area, disappearance from the area during the spawning period but was not detected at the spawning ground and return to the release area (8 specimens); and type 3, high site fidelity at the release area was observed before, during and after the spawning period (5 specimens). For the 17 specimens that were categorized into type 1, the dates of departure from their release area and the dates of return to the release area of males were, respectively, significantly earlier and later than those of females. The duration between the departure date and the return date (“duration away”) of males was significantly longer than that of females. The duration away tended to be positively related to the condition factor. All 25 specimens that were categorized as type 1 and type 2 showed returning behaviors to the release area.     

Control of electrostatic charge for powder by using feedback control-type ionizer system

As a method to prevent or mitigate cone discharges in a specific section such as a large silo, we have developed a new feedback control-type ionizer system. The feedback control-type system is composed mainly of an ionizer, an electrostatic field strength meter, and computer control equipment. In this study, we evaluated experimentally the practical version of the feedback control-type ionizer system through several tests in a pneumatic powder transport facility. The specific charges of the falling pellets in the silo were also measured for 10 s using a Faraday cage. Polypropylene (PP) pellets with a mean particle size of 3 mm were used in this experiment. The results of the experiment revealed that the feedback control-type ionizer system had the following characteristics: (1) it is possible to control the performance of the ionizer with a supply current; (2) the electrostatic field strength in the loading pipe from the charged powder is reduced and maintained at near zero by using the feedback control-type system; and (3) the performance of the feedback control-type system is superior to that of others, such as the conventional AC- or DC-type ionizers.     

Suppression of cone discharges in a powder silo using a grounded metal rod

While filling a large silo with coarse nonconductive powders, strong electrostatic sparks known as a cone discharge, which can become sufficiently energized to ignite a flammable dust cloud, often occur on the surface of a powder heap. In an attempt to mitigate or eliminate a cone discharge, a long metal rod with a pointed tip or a flat tip was vertically installed in the center of an experimental silo (1.5 m in diameter, 2 m in effective height) with the objective that the static charge might be released by the corona discharges or the surface potential of the powder heap reduced by the electric field reducing effect. The experimental results are summarized as follows:(1) No cone discharges were observed while the silo was being filled with polypropylene pellets when either a pointed tip or a flat-tip rod was installed so that its lower end was located 10 cm above or 30 cm below the heap surface level. A corona discharge that occurred on the pointed tip was shown to be effective to some extent in reducing the charge of the powder heap.(2) Brush discharges were observed near the metal rod and its support. However, we assume that the maximum energy was not high enough to ignite a dust cloud with minimum ignition energy greater than 3 mJ.     

Utilization of regenerated iron oxide for treatment of organotin compounds in seawater

We examined the removal and degradation efficiencies of regenerated amorphous iron oxide on tributyltin (TBT) and triphenyltin (TPT) in seawater. It was confirmed that following contact with iron oxide at 20 and 60?°C, the half-lives of TBT and TPT were shortened. These half-lives were from one-thousandth to one-tenth for natural environment conditions. Dibutyltin and benzene were identified as the reaction products from TBT and TPT, respectively, indicating that the degradation pathways were mainly dealkylation and dephenylation. These results indicate that the treatment method by natural energy will enable the economical and rapid reduction of organotin compounds (OTCs). For OTCs in seawater will be adsorbed on the iron oxide by the ebb and flow of the tide and solar energy will be heat source for degradation when iron oxide is prepared in coastal locations.