Heavy materials

The complexity of petroleum products raises the question of sample validity is the sample representative of the total flow The problem becomes that much more difficult when dealing with samples of heavy materials or samples coming from separations. The diverse chemical families in a petroleum cut can have very different physical characteristics and the homogeneous nature of the cut is often due to the delicate equilibrium between its components. The equilibrium can be upset by extraction or by addition of certain materials as in the case of the precipitation of asphaltenes by light paraffins. 

For olefins, the limits are greater by about 30%. At ambient temperatures, heavy materials have a vapor pressure too low to cause an explosive mixture with air. 

With respect to fuels utilized as heating fuels for industrial furnaces, or as motor fuels for large diesel engines such as those in ships or power generation sets, the characteristics of primary importance are viscosity, sulfur content and the content of extremely heavy materials (asphaltenes) whose combustion can cause high emissions of particulates which are incompatible with antipollution legislation. 

The mixed oxidation products are fed to a stiU where the pelargonic and other low boiling acids are removed as overhead while the heavy material, esters and dimer acids, are removed as residue. The side-stream contains predominately azelaic acid along with minor amounts of other dibasic acids and palmitic and stearic acids. The side-stream is then washed with hot water that dissolves the azelaic acid, and separation can then be made from the water-insoluble acids, palmitic and stearic acids. Water is removed from the aqueous solution by evaporators or through crystallization (44,45). 

Introduction A jig is a mechanical device used for separating materials of different specific gravities by the pulsation of a stream of liquid flowing through abed of materials. The liquid pulsates, or jigs up and down, causing the heavy material to work down to the bottom or the bed and the lighter material to rise to the top. Each product is then drawn off separately. 

Air separation Jig separation Pneumatic separation (stoners) Used to separate light (organic) materials from heavy (inorganic) materials in solid waste Used to separate light and heavy materials in solid waste hy means of density separation Used to separate light and heavy materials in solid waste Zig-zag-air, vihrating-air, rotary-air, and air-knife classifiers used with processed wastes shaldng-tahle ... 

In light ends fractionation it is usually just as important to remove light material from the heavier cut as it is to keep heavy material out of the lighter cut sidestreams are seldom withdrawn. The desired purity (expressed as per cent of impurity) of the overhead and bottoms is determined by product specifications or by the requirements of subsequent processing units. To meet these purity requirements, higher reflux ratios and greater numbers of plates between cuts are required than in crude distillation units. 

In two stage units, it is often economical to distill more gas oil in the vacuum stage and less in the atmospheric stage than the maximum attainable. Gas formed in the atmospheric tower bottoms piping at high temperatures tends to overload the vacuum system and thereby to reduce the capacity of the vacuum tower. The volume of crude vaporized at the flash zone is approximately equal to the total volume of distillate products. Of course, the vapor at this point contains some undesirable heavy material and the liquid still contains some valuable distillate products. The concentration of heavy ends in the vapor is reduced by contact with liquid on the trays as the vapor passes up the tower. This liquid reflux is induced by removing heat farther up in the tower. 

Grit The heavy material present in wastewater, such as sand coffee grounds, eggshells, gravel and cinders. 

The usual feed is a virgin gas oil that is, the part of crude oil boiling between about 60 °F. and 1050°F. Sometimes material below 600°F will be included into the cat feed but more often, it is put into diesel fuel or home heating oil. The heavy material above 1050°F is not normally used as cat feed because it often contains metallic compounds that contaminate the catalyst. Even if metals are not present, there are sometimes tarry materials that end up on the catalyst. This deposit increases the load on the regenerator, and, hence, the 1050 °F+ material is less desirable than lower boiling feeds. 

The cracked products pass out through two stages of cyclones which collect entrained catalyst and return it to the dense bed. Velocities at the outlet of the dense bed are normally 2.0-3.0 ft./sec. Upon leaving the cyclones, the vapors go to the primary fractionator which separates the heavy products from the gasoline and lighter components. The light products go on to the light ends recovery unit. The heavy material is separated and either recycled to the reactor or withdrawn from the system. 

Mdien dscous liquids are handled in centrifugal pumps, the brake horsepower is increased, the head is reduced, and the capacity is reduced as compared to the performance with water. The corrections may be negligible for viscosities in the same order of magnitude as water, but become significant above 10 centistokes (10 centipoise for SpGr = 1.0) for heavy materials. While the calculation m.ethods are accepta oly good, for exact performance charts test must be run using the pump in the service. 

From Figure 8-58 at n = 18 trays theoretical, and A = 0.001235 read Eaj, except that in this low region some values cannot be read accurately. When A is considerably less than 1.0, use Eaj = A, (very litde light material recovered), and when Aj is quite a bit larger than 1.0, use Eai = 1.0 (heavy material mosdy recovered). 

Feed/catalyst injection. A well-designed injection system provides a rapid and uniform vaporization of the liquid feed. This will lower delta coke by minimizing non-catalytic coke deposition as well as reducing the deposits of heavy material on the catalyst. 

A Develop the equations describing an inverted batch distillation column. This system has a large reflux drum into which the feed is charged. This material is fed to the top of the distillation column (which acts like a stripper). Vapor is generated in a reboiler in the base. Heavy material is withdrawn from the bottom of the column. 

The effluent stream leaving the reactor is cooled and then treated with caustic (sodium hydroxide) and water to remove the catalyst. The cleaned up stream then contains about 35% unreacted benzene, 50% EB,.15% polyethylbenzene (PEB), and a small amount of miscellaneous heavy materials. 

As closure progresses and dismantling of the facility advances, the workforce will be required to handle increasingly heavy materials and equipment. This equipment will include all possibly agent-contaminated machinery, metal ducts, and piping, as well as bulk materials such as concrete. Consequently, some risks to workers may be encountered more frequently during the dismantling and demolition associated with facility closure ... 

Thus, a soft and heavy material has low vibrational frequencies, and low characteristic temperatures, so they are fully activated even at low temperatures for instance, lead has a characteristic temperature of 88 K. However, a brittle and light material would have a higher characteristic temperature and be fully activated only when the temperature is very high for instance, diamond has a characteristic temperature of 1860 K. Figure 4.17 is a plot of Cu/Cumax and temperature in an S-shaped curve, so that C = 0 when r/0 is close to zero, and C rises to the full value of R/2 for each degree of freedom when T/ goes to infinity. The value of C is 50% activated when T/ = 0.335, and 92% activated when T/ = 1. 

Generally, the heavy materials removed in the process included both resins and asphalts, but by operating in two or more stages, these materials can be segregated. This may often be desirable, as both products then may be obtained in a relatively pure state and thus they become of greater commercial importance. Deresining of heavy distillate fractions also is possible, and the process may be operated for the separation of special resin fractions (38), which may be of value in the manufacture of specialty products. 

A steam stripping section located at the bottom of the tower frees the carbon of adsorbed material, which is drawn off directly above or passes on up the tower as reflux. However, traces of heavy material remain on the surface of the carbon and these are removed by continuously withdrawing a fraction of the circulating carbon and passing it to a high-temperature steam stripping section. 

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