Side-flashing

Hand Culverin with Bent Stock and two Culverins with Side Flash Pans ... 

Side-flashing can also occur below the ground to buried metal pipes or wires and care must be taken in the design and positioning of the grounding electrodes. Typical values of impulse breakdown in soil are 2 to 5kV/cm, which leads to side-flashes of several meters. In air the value is 9kV/cm and brick and concrete has a slightly lower breakdown strength. 

The grounding wires should radiate away from the structure, be strip conductors and should not be bonded to the structure. The overhead wires should be far enough from the structure to eliminate side-flashing which was described earlier and the protective angles from the wires must cover the building structure. 

Electrical Effects. No lightning strike to a structure has attracted more attention in the last decades than the so-called side-flash. It has been examined repeatedly and its dangers are illustrated in the technical literature. Its prevention must be provided in order to stop incidents in which a protected building has been struck and a person in such a building injured. 

An illustration of the principles of the conditions leading to the risk of a side-flash are shown in a simple example in Figure 12. 

Side-Flash or Flashover — Lightning first hits a tree or other object, but instead of going to ground flashes over to a nearby object or person. 

Incubation of Anacystis nidulans in liquid nutrient medium devoid of calcium and sodium results in a rapid loss of oxygen-evolving capacity. Addition of sub-millimolar amounts of either calcium or sodium effects full restoration of oxygen evolution. Other cations, mono-, di-, or trivalent, have little or no effect. Both the depletion process and restoration by either calcium or sodium are light-dependent. Partial reactions have isolated the site of this cation requirement at or very near the reaction center, on the oxidizing side. Flash yield decline in depleting cells indicates a decrease in the number of functional reaction centers. 

In a 500 ml. three-necked flask, equipped with a thermometer, a sealed Hershberg stirrer and a reflux condenser, place 32-5 g. of phosphoric oxide and add 115-5 g. (67-5 ml.) of 85 per cent, orthophosphoric acid (1). When the stirred mixture has cooled to room temperature, introduce 166 g. of potassium iodide and 22-5 g. of redistilled 1 4-butanediol (b.p. 228-230° or 133-135°/18 mm.). Heat the mixture with stirring at 100-120° for 4 hours. Cool the stirred mixture to room temperature and add 75 ml. of water and 125 ml. of ether. Separate the ethereal layer, decolourise it by shaking with 25 ml. of 10 per cent, sodium thiosulphate solution, wash with 100 ml. of cold, saturated sodium chloride solution, and dry with anhydrous magnesium sulphate. Remove the ether by flash distillation (Section 11,13 compare Fig. II, 13, 4) on a steam bath and distil the residue from a Claisen flask with fractionating side arm under diminished pressure. Collect the 1 4-diiodobutane at 110°/6 mm. the yield is 65 g. 

A report on the continuous flash pyrolysis of biomass at atmospheric pressure to produce Hquids iadicates that pyrolysis temperatures must be optimized to maximize Hquid yields (36). It has been found that a sharp maximum ia the Hquid yields vs temperature curves exist and that the yields drop off sharply on both sides of this maximum. Pure ceUulose has been found to have an optimum temperature for Hquids at 500°C, while the wheat straw and wood species tested have optimum temperatures at 600°C and 500°C, respectively. Organic Hquid yields were of the order of 65 wt % of the dry biomass fed, but contained relatively large quantities of organic acids. 

A simplified flow diagram of a modern H2SO4 alkylation unit is shown in Eigure 1. Excess isobutane is suppHed as recycle to the reactor section to suppress polymerization and other undesirable side reactions. The isobutane is suppHed both by fractionation and by the return of flashed reactor effluent from the refrigeration cycle. 

Several descriptions have been pubUshed of the continuous tar stills used in the CIS (9—11). These appear to be of the single-pass, atmospheric-pressure type, but are noteworthy in three respects the stills do not employ heat exchange and they incorporate a column having a bubble-cap fractionating section and a baffled enrichment section instead of the simple baffled-pitch flash chamber used in other designs. Both this column and the fractionation column, from which light oil and water overhead distillates, carboHc and naphthalene oil side streams, and a wash oil-base product are taken, are equipped with reboilers. 

FIG. 13-36 Graphical solution for a column with a partially flashed feed, a liquid side-stream and a total condenser. 

As shown in Fig. 13-92, methods of providing column reflux include (a) conventional top-tray reflux, (b) pump-back reflux from side-cut strippers, and (c) pump-around reflux. The latter two methods essentially function as intercondenser schemes that reduce the top-tray-refliix requirement. As shown in Fig. 13-93 for the example being considered, the internal-reflux flow rate decreases rapidly from the top tray to the feed-flash zone for case a. The other two cases, particularly case c, result in better balancing of the column-refliix traffic. Because of this and the opportunity provided to recover energy at a moderate- to high-temperature level, pump-around reflirx is the most commonly used technique. However, not indicated in Fig. 13-93 is the fact that in cases h and c the smaller quantity of reflux present in the upper portion of the column increases the tray requirements. Furthermore, the pump-around circuits, which extend over three trays each, are believed to be equivalent for mass-transfer purposes to only one tray each. Bepresentative tray requirements for the three cases are included in Fig. 13-92. In case c heat-transfer rates associated with the two pump-around circuits account for approximately 40 percent of the total heat removed in the overhead condenser and from the two pump-around circuits combined. 

A vapor poeket on the exchanger s low-pressure side can create a cushion that may greatly diminish the pressure transient s intensity. A transient analysis may not be required if sufficient low-pressure side vapor exists (although tube rupture should still be considered as a viable relief scenario). However, if the low-pressure fluid is liquid from a separator that has a small amount of vapor from flashing across a level control valve, the vapor pocket may collapse after the pressure has exceeded the fluid s bubble point. The bubble point will be at the separator pressure. Transient analysis will prediet a gradually inereasing pressure until the pressure reaches the bubble point. Then, the pressure will increase rapidly. For this ease, a transient analysis should be considered. 

Material stored at or below its atmospheric pressure boiling point has no superheat. Therefore there will be no initial flash of liquid to vapor in case of a leak. Vaporization will be controlled by the evaporation rate from the pool formed by the leak. This rate can be minimized by the design of the containment dike, for example, by minimizing the surface area of the liquid spilled into the dike area, or by using insulating concrete dike sides and floors. Because the spilled material is cold, vaporization from the pool will be further reduced. 

A visible cloud of vapor, 1 m deep, spread for 150 m and was ignited by a car that had stopped on a nearby road 25 minutes after the leak started. The road had been closed by the police, but the driver approached from a side road. The fire flashed back to the sphere, which was surrounded by flames. There was no explosion. The sphere was fitted with water sprays. But the system was designed to deliver only haif the quantity of water normally reeommended (0.2 U.S. gal/ft- min. or 8 L/m min.), and the supply was inadequate. When the fire brigade started to use its hoses, the supply to the spheres ran dry. The firemen seemed to have used most of the available w ater for cooling neighboring spheres to stop the fire from spreading, in the belief that the relief valve would pro-teet the vessel on fire. 

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