Gas issues

Good gas distribution is necessary for the bed to operate properly, and this requites that the pressure drop over the distributor be sufficient to prevent maldistribution arising from pressure fluctuations in the bed. Because gas issues from the distributor at a high velocity, care must also be taken to minimize particle attrition. Many distributor designs are used in fluidized beds. The most common ones are perforated plates, plates with caps, and pipe distributors. 

Jet Penetration. At the high gas velocities used in commercial practice, there are jets of gas issuing from distributor holes. It is essential that jets not impinge on any internals, otherwise the internals may be quickly eroded. Figure 14 is a graphical correlation used to determine the jet penetration length as a function of gas velocity and gas density. Jets from horizontal and downflow holes are considerably shorter than those that are pointed upward. 

New materials also emerged. Nylon, developed brilliantly by W. H. Carothers and his team of research workers for Du Pont as a fibre in the mid-1930s, was first used as a moulding material in 1941. Also in 1941 a patent taken out by Kinetic Chemical Inc. described how R. J. Plunkett had first discovered polytetrafluoroethylene. This happened when, on one occasion, it was found that on opening the valve of a supposedly full cylinder of the gas tetrafluoroethylene no gas issued out. On subsequently cutting up the cylinder it was found that a white solid, polytetrafluoroethylene (PTFE), had been deposited on the inner walls of the cylinder. The process was developed by Du Pont and, in 1943, a pilot plant to produce their product Teflon came on stream. 

Gas, Natural. Any gas issuing from under the earth s crust thru openings or bored wells, may be called natural gas. The most important natural gas is that consisting of a mixture of hydrocarbons. Such gas is often found in and near coal or petroleum deposits in many... 

The classical view is that a turbulent flame is equivalent to a distorted and wrinkled laminar flame. The turbulent flame brush is thus supposed to be an integrated picture of a rapidly fluctuating surface, and instantaneous schlieren pictures seem to support this interpretation 50). Grumer, however, has shown that schlieren snapshots of turbulent hot gas issuing from a Bunsen burner look very much like the flame pictures (34) the implication is that one sees, not the instantaneous flame surface, but the boundary of the hot gas. 

Two types of trays are most common sieve trays and valve trays. A sieve tray is a simple perforated plate. Gas issues from the perforations to give a multiorifice effect liquid is prevented from descending the perforations or weeping by the upward motion of the gas. At low gas flow rates, the upward gas motion may be insufficient to prevent weeping. 

Light the gas issuing from the capillary jet and note the products of the freely burning hydrogen sulphide. The odor of sulphur dioxide is unmistakable. If a cold bottle is held over the flame, water condenses inside the bottle. Now thrust a piece of cold porcelain half way into the flame and note the deposit of sulphur. 

Langmuir expected to find a small volume of gas issuing from the heated wires in the glass bulbs. But what astonished him almost beyond belief was the tremendous quantities of gas... 

At low gas velocities, intermittent bubbling through the slots is obtained because of liquid surface-tension effects, and the pressure drop is a function of tjie surface tension and the slot dimensions. When the velocity increases sufficiently, the gas issues from the slots in a steady stream, and the effect of surface tension becomes unimportant. 

Description of Cottrell Precipitator, The principle of Cottrell method can be learned from Fig 243, p 722 of Ref 3, which is reproduced here as Fig E28, The dirty gas enters at pipe (3), connected at right angle to the vertical pipe (2), in which.a copper or lead-covered copper wire (1) is suspended axially. The pipe (2) is 3 to 12 inches in diam and from 5 to 15 feet long. Its lower part is attached to a dust-collecting box. A hi -tension direct current passes from the wire (1) to the surrounding pipe, as shown in Fig, Ttiis causes the particles of solids present in the dirty gas to be electrified by the silent discharge of wire and then to be attracted by the pipe, which has the opposite polarity. The gas issued from the top of the pipe is known as "clean gas because it is free of... 

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