Types of Discharge

An electrostatic dust ignition can occur when the discharge releases sufficient thermal energy within a sufficiently short period of time and small volume to ignite the suspended dust. Electrostatic ignition is complicated by the fact that there are a number of distinct ESD mechanisms important in electrostatic hazards and hazard abatement (Glor, 1988). 

Capacitive Discharges. Capacitive discharges are responsible for at least 90% of all dust and vapor ignitions of ESD origin. The 

Capacitive discharges are characterized by the electrostatic energy Ue converted to thermal energy in the spark. While somewhat difficult to measure accurately, the energy released in a capacitive spark is commonly estimated using the following relationship. 

C0bject is the capacitance and V the voltage between the two metal conductors. The capacitance of typical chargeable components depends on their size, shape, and distance from a grounded surface. For purposes of electrostatic hazard assessment, it is usually convenient to rely upon measured data like that in Table 6. 

In ordinary practice, the rather conservative value of 100 volts is recommended for Vminto provide a margin of safety (Gibson, 1979). 

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All three types of discharge involve the formation of ions as part of the process. For various reasons, most of the ions are positive. The ions can be examined by mass spectrometry. If small amounts of a sample substance are introduced into a corona or plasma or arc, ions are formed by the electrons present in the discharge or by collision with ions of the discharge gas. 

Solids Discharge The type of discharge mechanism utilized is dependent upon the necessity of sealing the atmosphere inside the fluidized-bea reactor and the subsequent treatment of the sohds. The simplest solids discharge is an overflow weir. This can be used only when the escape of fluidizing gas does not present any hazards due to... 

Electrostatic Discharges An electrostatic discharge takes place when a gas or vapor-air mixture is stressed, electrically, to its breakdown value. Depending upon the specific circumstances, the breakdown appears as one of four types of discharges, which vary greatly in origin, appearance, duration, and incendivity. 

The quality of the effluent discharge must be regularly checked. Depending on the quantity and type of discharge, this may require an in-house laboratory and analysis room. 

Table 3.2 presents an industry summary for the nonferrous metals industry indicating the number of subcategories and the number and type of dischargers. Table 3.3 presents best practicable technology (BPT) limitations that have been promulgated and reported in the Federal Register.3-5... 

The fluid from reliefs, sometimes two-phase flow, must first go to a knockout system, where the liquids and vapors are separated. Liquids are subsequently collected and the vapors may or may not be vented. If the vapors are nontoxic and nonflammable, they may be vented unless some regulation prohibits this type of discharge. 

This gives the relationship between the attractive force between two particles and the maximum surface field intensity. There is a limit to the magnitude that some type of discharge or emission. From data such as those of Earhart (El) one would conclude that Sma% cannot exceed some 100 to 200 V/micron before the particle would discharge... 

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