Switching drums

To minimize the amount of hard physical labor required to switch drums every 12 hours, the vapor valves should be fitted with locally controlled air operators. Such a device is little more than an air gun permanently mounted to the stem of each valve. The speed of the valve movement is controlled with a y4-in. air valve. 

Control of wound-rotor motors, as discussed, can be effected by adjusting the external secondaiy (rotor) resistance either in steps or continuously by liquid rheostat (this method is seldom used). Commonly when secondaiy resistance is varied to adjust speed or torque or to control acceleration, multiple resistance steps are used. These steps may be switched manually (typically a drum switch) or electrically by contac tor. 

The exciter is an AC generator with a stator-mounted field. Direct cur rent for the exciter field is provided from an external source, typically u small variable voltage rectifier mounted at the motor starter. Exciter oui put is converted to DC through a three-phase, full-wave, silicon-diode bridge rectifier. Thyristors (silicon-controlled rectifiers) switch the cur rent to the motor field and the motor-starting, field-discharge resistors These semiconductor elements are mounted on heat sinks and assembled on a drum bolted to the rotor or shaft. 

The delayed coking feed stream of residual oils from various upstream processes is first introduced to a fractionating tower where residual lighter materials are drawn off and the heavy ends are condensed. The heavy ends are removed and heated in a furnace to about 900 to 1,000 F and then fed to an insulated vessel called a coke drum where the coke is formed. When the coke drum is filled with product, the feed is switched to an empty parallel drum. Hot vapors from the coke drums, containing cracked lighter hydrocarbon products, hydrogen sulfide, and ammonia, are fed back to the fractionator where they can be treated in the sour gas treatment system or drawn off as intermediate products. 

In the second case a 0.75 kW motor with a pre-set springloaded tension apparatus is installed. The stainless steel wire (6) is wound 4-5 times around a drum. When the motor is switched on, the wire tightens and the filter net (3) is drawn backwards and forwards over the front roller (4). 

Republic Container Co. (Nitro, West Va.), a company that supplies steel drums, switched from a solvent-based paint to a water-based paint, reducing their VOC emissions to 2.8 Ib/gal and saving over 10,000 in costs. 

The feed stock, usually topped or reduced crude oil, is heated in pipe coils (Figure 1) from about 900° to 950° F. The oil is then fed to one of two or more vertical, insulated coke drums. The coke drums are connected by valves so that they can be switched onstream for filling, then switched off-stream for coke removal. The temperature in the drum will ordinarily be 775° to 850° F. and the pressure 4 to 60 pounds per square inch gage. Hot, coke-still vapors from the coke drum pass to a fractionator where gas and gasoline, intermediate gas oil, and heavy gas oil are separated. More or less of the heavy gas oil is recycled. The ratio of recycled heavy gas oil to fresh feed is usually less than 1 but may go up to about 1.6 (5,15,28, 40). 

Compressors are also served by high-liquid-level trips in their upstream knockout drums. These high-liquid-level trips work in the same way as the low-level boiler trips discussed above, except that the mercuroid switch is activated by a rising, rather than a falling, liquid level so as to protect the compressor from a slug of liquid. 

The refinery operators were in the process of switching feed from the D drum to the C drum when a 45-degree elbow in the feed line ruptured. Investigators later determined that the 6-inch-diameter elbow was made of carbon steel instead of the 5-percent chrome alloy steel required by specifications. It seems that this section of piping was fabricated and installed in 1963. The mistake in piping fabrication was discovered 20 years later. The extent of the fire damage was such that the central unit was down for a period approaching a year and the adjacent units were each down for a few weeks. [21]... 

So what can we do in this case If column operation requires that we stick to this control structure, feedforward control will help to reduce the swings in distillate flowrate. However, better plantwide performance can be achieved if we can switch the control structure to one in which the vapor distillate is not used to control pressure. One possible alternative is shown in Fig. 6.27. Condenser cooling is used to control pressure, reflux flowrate controls reflux drum level (with P-only control), and the flowrate of the vapor distillate is ratioed to reflux flowrate. With this structure we allow the disturbances that the column energy... 

The multiple-unit large-volume in situ filtration system consists of 12 pump-filter units, an electromechanical cable, a current monitoring and switching box interfaced to an Apple II control computer, a drum winch, and a level wind (Figure 1). 

Switch from active drum to inactive drum and steam out—8 hr. 

Some of the drum tests stress the materials much more severely. Methods 1 and 2 particularly are grindability tests producing abrasion values of up to 70%. On the other hand, methods 3 and 4 are so gentle that the results hardly differentiate between samples of different quality. Method 5 differentiates well but the relative measures of quality of materials A, B, and rock salt are switched. 

In the delayed coker the feed enters the bottom of the fractionator, where it mixes with recycled liquid condensed from the coke drum effluent. It is then pumped through the coking heater to one of two coke drums through a switch valve. It is at 480-500°C. Cracking and polymerization take place in the coke drum in a nominal 24-h period. Coking is a batch operation carried out in two coke drums. Coking takes place in one drum in... 

Delayed coking is the only main process in a modern petroleum refinery that is a batch-continuous process. The flow through the tube oven is continuous. The feed stream is switched between two drums. One drum is filling with coke while the other drum is being steam-stripped, cooled, decoked and warmed up (see chapter 6). The overhead vapors from the coke drums flow to a rectification unit. The rectification tower has a reservoir in the bottom where the fresh feed is combined with condensed product vapors (recycle) to make up the feed to the coker heater. 

Delayed coking is a well developed commercial process (6), and operates on a semi-continuous basis. Feed, usually vacuum residue, mixed with steam, is continuously pumped through tubular heaters in which it is heated to its incipient coking temperature. At this temperature the feed is injected into an insulated drum where coking takes place. The vapors produced in the drum during coking are continuously removed and fractionated. The fractions usually include coker naphtha and light and heavy coker gas oils. As a drum fills up, feed is switched to another drum. Meanwhile, the full drum is steam stripped, cooled and the coke drilled out. Whereas feed is continuously supplied to the drum, the coke is recovered intermittently. 

The antifoam can be added either on a continuous basis or when the foam front reaches a specified level. A series of level detectors is normally present on each drum, as shown in Figure 5. When the foam level is observed at the first level detector, the antifoam injection is started. An immediate drop in the level will be observed. At this time, the operators should be preparing the next drum to begin receiving feed. The antifoam injection will continue for some time after the drum switch occurs as the coke is being quenched with steam and water. 

What happens if the coke drum gets too full of resid Add a radiation level detector to notify the microcomputer when the drum is full so it can switch resid to the other drum which it has determined to be empty. 

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