Reverse pulse

Osteryoung J and Murphy M M 1991 Normal and reverse pulse voltammetry at small electrodes Microelectrodes Theory and Applications (Nate ASI Series E vol 197) ed M I Montenegro, M A Queiros and J L Daschbach (Dordrecht Kluwer)... 

The off-gas from each furnace is cooled in an evaporative gas cooler and cleaned in a reverse pulse baghouse before being either vented to atmosphere or used in manufacturing sulfuric acid. The baghouse dust from both the smelting and reduction furnaces is combined and recycled through the smelting furnace. 

FIG. 17-60 Reverse-pulse fahric filter (a) filter cylinders (h) wire retainers (c) collars (d) tube sheet (e) venturi nozzle (f) nozzle or orifice (g) solenoid valve (h) timer (/) air manifold (k) collector housing (/) inlet (m) hopper (n) airlock (o) iipperplenum, (Mikropul Division, US. Filter Coip.)... 

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally rein-... 

TABLE 17-7 Physical Properties of Selected Felts for Reverse-Pulse Filters... 

Reverse pulse The use of jets of high-pressure air to dislodge material from the exterior of a bag filter. 

Fabric-filter designs fall into three types, depending on the method of cleaning used (1) shaker-cleaned, (2) reverse-flow-cleaned, and (3) reverse-pulse-cleaned. 

In the reverse-pulse-cleaned filter, the bag forms a sleeve drawn over a cylindrical wire cage, which supports the fabric on the clean-gas side (i.e., inside) of the bag. The dust collects on the outside of the bag. 

As a result, there is a growing trend to off-line clean reverse-pulse filters by using bags with multiple compartments. These sections allow the outlet-gas plenum serving a particular section to be closed off from the clean-gas exhaust, thereby stopping the flow of inlet gas. On the dirty-side of the tube sheet, the isolated section is separated by partitions from the neighboring sections where filtration continues. Sections of the filter are cleaned in rotation as with shaker and reverse-flow filters. 

Reverse-pulse filters are typically operated at higher filtration velocities (i.e., air-to-cloth ratios) than shaker or reverse-flow designs. Filtration velocities may range from 3 to 15 feet per minute in reverse-pulse applications, depending on the dust being collected. However, the most the commonly used range is 4 to 5 feet per minute. 

As discussed in the preceding section, filter bags must be periodically cleaned to prevent excessive build-up of dust and to maintain an acceptable pressure drop across the filters. Two of the three designs discussed, reverse-flow and reverse-pulse, depend on an adequate supply of clean air or gas to provide this periodic cleaning. Two factors are critical in these systems the clean-gas supply and the proper cleaning frequency. 

In reverse-pulse applications, most plants rely on plant-air systems as the source for the high-velocity pulses required for cleaning. In many cases, however, the plant-air system is not sufficient for this purpose. Although the pulses required are short (i.e., 100 milliseconds or less), the number and frequency can deplete the supply. Therefore, care must be taken to ensure that both sufficient volume and pressure are available to achieve proper cleaning. 

A related technique, reverse-pulse voltammetry, has a pulse sequence that is a mirror image of that of normal-pulse voltammetry (5). hi this case, the initial potential is on the plateau of the wave (i.e., where reduction occurs), and a series of positive-going pulses of decreasing amplitude is applied. 

Redox switching, 126 Reference electrodes, 100, 105, 142 Reflectance spectroscopy, 44 Resistance, 22, 105 Resolution 50, 71 Reverse pulse polarography, 68 Reversible systems, 4, 31 Reticulated vitreous carbon, 114, 115 Riboflavin, 37... 

Sometimes besides direct pulses, reverse pulses are also applied (Tacussel PRG 5 polarograph), because by tracing out the polarogram using first positive-, then negative-going pulses, one may study the reversibility of reactions. 

Lopez-Fonseca et al. [11] discussed the theory of reverse pulse polarography and the technique was applied in the determination of penicillamine electrochemically coated on a dropping-mercury electrode. Using long drop times and short pulses, the drug can be determined at levels as low as 50 nM in the presence of Cu(II), and the technique compares well with normal-pulse and differential-pulse polarography. 

Fig. 15. SEM micrographs of Cu-Al deposits containing 5 a/o A1 that were prepared with different plating techniques at zavg = 0.70 mA in the 60.0 m/o AlCl3-EtMeImCl melt at room temperature (a) DC plating (b) superimposed-pulse current plating, ip = 1.254 mA, ton = 1 s, is = 0.509 mA, ts = 3 s, and (c) reverse-pulse current plating, ip = 1.254 mA, ton = 1 s, ir = 0.43 mA, tr = 0.5 s. The thickness of each deposit is approximately 5 pm based on a compact layer of pure copper. Reproduced from Zhu et al. [103]...

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally reinforced with a woven insert. The physical properties and air permeabilities of some typical woven and felt filter fabrics are presented in Tables 17-6 and 17-7. The air permeability of a filter fabric is defined as the flow rate of air in cubic feet per minute (at 70°F, 1 atm) that will pass through 1 ft2 of clean fabric under an applied differential pressure of Vt in water. The resistance coefficient KF of the clean fabric is defined by the equation in Table 17-6, which may be used to calculate the value of KF from the air permeability. If Ap, is taken as 0.5 in water, t as 0.0181 cP (the viscosity of air at 70°F and 1 atm), and Vj as the air permeability, then //, = 27.8/air permeability. 

Leith and First [J. Air Pollut. Control Assoc., 27, 534 (1977) 27, 754 (1977)] studied the collection efficiency of reverse-pulse filters and concluded that once the dust cake has been established, straight-through penetration by dust particles that pass through the filter without being stopped is negligible by comparison with penetration by dust... 

Unlike in CV, pairs of current measurements are made on each period of the square wave. These are at time forward late in the forward pulse, named /forward, and frevere in the reverse pulse, named Iteveix- Both tformad and Reverse are much greater than the time for fully charging the electrode capacitance, so that only the Faradaic current is recorded. With calculation of /net, the difference between /forward and /reverse, SWV presents three types of peak-shaped I-E relations. Figure 65 displays the SWV of a reversible one-electron reduction process. 

Tokoro R, Osteryoung J. 1982. [Study of the reduction mechanism of 1,2-dibromothane by reverse pulse polarography]. An Sim Bras Eletroquim Eletroanal 1 307-316. (Spanish)... 

The 1-methyl-2-, 3-, and 4-methoxycarbonylpyridinium ions have been investigated by pulse polarography and reverse pulse polarography. The 4-isomer was found to give a radical stable both in acetonitrile and methanol,... 

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