Decoking

The cracked products leave as overhead materials, and coke deposits form on the inner surface of the dmm. To provide continuous operation, two dmms are used while one dmm is on-stream, the one off-stream is being cleaned, steamed, water-cooled, and decoked in the same time interval. The temperature in the coke dmm is in the range of 415—450°C with pressures in the range of 103—621 kPa (15—90 psi). Overhead products go to the fractionator, where naphtha and heating oil fractions are recovered. The nonvolatile material is combined with preheated fresh feed and returned to the furnace. The coke dmm is usually on stream for about 24 hours before becoming filled with porous coke, after which the coke is removed hydraulically. 

Both Mitsubishi and Mitsui TLEs differ drastically from other designs. Mitsubishi offers a TLE with an integral steam dmm and cyclone for vapor—hquid separation. The pyrolysis gas flows in the shell side, and is claimed to accomplish the decoking of the furnace and the transferline exchanger in one operation. The Mitsui quench cooler uses three concentric tubes as the tube element, and requires steam—air decoking to clean the TLE (58,59). 

Basic Yield Data. This is a good place to start asking questions. If the process uses a catalytic reaction, do the yields represent new catalyst or catalyst regenerated a number of times For a thermal reaction like an olefin plant steam cracker, questions might be asked about on-stream time between decokings. Therefore, how much contingency is there in the specified number of crackers required ... 

Coking Heater stack gas (CO, SO, NO, hydrocarbons and PM), vents and fugitive emissions (HCs) and decoking emissions (HCs and PM). 

Decoking is a routine daily occurrence accomplished by a high-pressure water jet. First the top and bottom heads of the coke drum are removed then a hole is drilled in the coke from top to hottom.. A rotating stem is lowered through the hole, spraying a jet high-pressure water sidewavs... 

Decoking the filled drum can be accomplished by a hydraulic system using several water jets under at least 3,000 pounds per square inch gauge. 

Some deactivation processes are reversible. Deactivation by physical adsorption occurs whenever there is a gas-phase impurity that is below its critical point. It can be reversed by eliminating the impurity from the feed stream. This form of deactivation is better modeled using a site-competition model that includes the impurities—e.g., any of Equations (10.18)-(10.21)— rather than using the effectiveness factor. Water may be included in the reaction mixture so that the water-gas shift reaction will minimize the formation of coke. Off-line decoking can be... 

Example 11.15 Coke formation is a major cause of catalyst deactivation. Decoking is accomplished by periodic oxidations in air. Consider a micro-porous catalyst that has its internal surface covered with a uniform layer of coke. Suppose that the decoking reaction is stopped short of completion. What is the distribution of residual coke under the following circumstances ... 

Solution For part (a), oxygen has access to the entire internal surface. We expect uniform combustion and a gradual reduction in coke thickness throughout the catalyst pellet. If a completely clean surface is required for catalytic activity, partial decoking will achieve very little. 

Determine the position of the reaction front in the diffusion-limited decoking of a spherical cracking catalyst. 

X. H. Ren, M. Bertmer, H. Kuhn, S. Stapf, D. E. Demco, B. Blumich, C. Kem, A. Jess 2002, ( H, 13C and 129Xe NMR study of changing pore size and tortuosity during deactivation and decoking of a naphtha reforming catalyst), NATO Sci. Ser. ITMath., Phys. Chem. 7b, 603. 

ASCOT [Asphalt coking technology] A process combining de-asphalting and decoking, offered by Foster-Wheeler, United States. 

This reaction is important in such processes as the decoking of catalysts, the manufacture of activated carbon for adsorption, and the gasification of carbonaceous materials for production of hydrogen or fuel gas. 

Deck area, of screens, 22 281-282 Decoction mashing, 3 578 Decoking, 10 609... 

In addition, some processes create considerable amounts of particulate matter and other emissions from catalyst regeneration or decoking processes. Volatile chemicals and hydrocarbons are also released from equipment leaks, storage tanks, and wastewaters. Other cleaning units, such as the installation of filters, electrostatic precipitators, and cyclones, can mitigate part of the problem. 

Particulate emissions from decoking can also be considerable. Coke-laden water from decoking operations in delayed cokers (hydrogen sulfide, ammonia, suspended solids) and coke dust (carbon particles and hydrocarbons) occur. 

Decoking removal of petrolenm coke from equipment snch as coking drums hydraulic decoking nses high-velocity water streams. 

Decoking means the removal of the coke from the drum or vessel where it was formed. Manual Decoking. Early atmospheric coke stills were manually decoked. Men went into the stills with hand tools, broke up the coke, and removed it manually. Because of the heat and the dirt, it was not a desirable job (85). 

Cable Decoking. With the advent of vertical coke drums, cable decoking came in as a vast improvement over manual decoking. A coiled steel cable, placed inside the coke drum, is supported on hooks. At the end of the coking cycle the bottom of the... 

Decoking by Drilling. For this method of decoking, a hydraulically controlled, rotating drill stem is mounted in a well below the coke drum. At the end of the cycle, the bottom from the coke drum is removed and a hole is drilled upward through the coke bed. The drill is then removed from the stem and knocker-bars are mounted in its place. The knocker-bars swing out from the drill stem when it is rotated, hit the coke, and break it loose from the drum. The coke falls out and is recovered (5,40). 

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