Fluid coking unit

Fig. 27. A Flexicoking unit combining fluid coking and gasification using three-bed fluidized beds.

The H-Coal process could operate in one of two modes, depending on the desired product slate. In the "syn-cmde" mode, a fluid-bed coking unit was employed to maximize recovery of distillate from the Hquefaction product (Fig. 7a). When operated in the fuel oil mode (Fig. 7b), no coker was used and the primary product was a coal-derived low sulfur fuel oil. Total hydrogen demand on the process was also reduced in the latter mode of operation. 

Reflux overhead vapor recompression, staged crude pre-heat, mechanical vacuum pumps Fluid coking to gasification, turbine power recovery train at the FCC, hydraulic turbine power recovery, membrane hydrogen purification, unit to hydrocracker recycle loop Improved catalysts (reforming), and hydraulic turbine power recovery Process management and integration... 

Fluid coking and fluid catalytic cracking (FCC) are mechanically similar The products of fluid coking and delayed coking are the same (i.e., coke and distillate products), but the equipment is physically different. Alkylation of the three- and four-carbon molecule products from these units is commonly performed to convert them to branched chain gasoline, which increases the octane rating. As can be seen from Figure 1.1 in Chapter One, the feed to fluid catalytic crackers is a gas-oil distillate. For delayed cokers and fluid cokers, the feed is residium. 

Fluid-bed coking is a continuous version that delays coking. Here the cokes are formed on fludized coke particles that are circulated between the coking unit where the endothermic pyrolysis reaction takes place and the regenerator in which the coke particles are reheated by partly burning off. 

The flexicoking process is an adaptation of the fluid coking process that uses the same reactor as a fluid coker but has an integrated gasification unit available for coke gasification to produce, in addition to the typical fluid coking slate of products, a low-BTU gas. 

In a fluid bed petroleum coking unit, pitch is injected through nozzles submerged in the bed unless the mixing is good both locally near the nozzles, and in the bed as a whole, the coke already in the bed is agglomerated by the pitch and defluidization occurs. 

In high-temperature (700"F plus) hydrocarbon service, the smooth surface tends to reduce the buildup of coke. Other fouling deposits also adhere more readily to a roughened carbon-steel surface. A fluid catalytic unit slurry oil-to-fresh-feed pumparound exchanger is one service where replacing carbon-steel tubes with stainless steel has improved the overall heat-transfer coefficient. 

Most refinery PM eomes from two sources - delayed coking units and the regenerators of fluid catalytic cracking (FCC) units. FCC regenerators also emit ammonia, which combines with SOx and NOx in the air to form ammonium sulfates and nitrates. According to the South Coast Air Quality Management District (AQMD) in Southern California, 1 ton of ammonia can generate 6 tons of PM 10 - airborne particulates with partiele diameters less than 10 microns. PM2.5 stands for airborne particulates with diameters less than 2.5 microns. 

In fluid coking, the feed is pumped through a furnace where it is heated, at 1110-1200°F (599-649°C), and then it proceeds to a reactor where it is thermally cracked, at 900-1050°F (482-566°C). Products other than coke are quenched overhead in a scrubber where entrained coke is removed. The lighter fractions go overhead to be treated elsewhere, while a heavy fraction with entrained coke fines is recycled to the reactor. Coke from the reactor circulates back to the heater, and it then passes again through the reactor until it finally leaves the process unit. 

Other than high-pressure jetting, there is little to offer for the process side of these units. The auxiliary systems associated with these units, especially fluid coking, offer applications for cleaning services. Emulsions of caustic and diesel fuel were used to clean a fractionator tower, and caustic foam was used to clear the air-cooled exchangers. 

Methyl- and dimethylnaphthalenes are contained in coke-oven tar and in certain petroleum fractions in significant amounts. A typical high temperature coke-oven coal tar, for example, contains ca 3 wt % of combined methyl- and dimethylnaphthalenes (6). In the United States, separation of individual isomers is seldom attempted instead a methylnaphtha1 ene-rich fraction is produced for commercial purposes. Such mixtures are used for solvents for pesticides, sulfur, and various aromatic compounds. They also can be used as low freezing, stable heat-transfer fluids. Mixtures that are rich in monomethyinaphthalene content have been used as dye carriers (qv) for color intensification in the dyeing of synthetic fibers, eg, polyester. They also are used as the feedstock to make naphthalene in dealkylation processes. PhthaUc anhydride also can be made from m ethyl n aph th al en e mixtures by an oxidation process that is similar to that used for naphthalene. 

Refinery Production. Refinery propylene is formed as a by-product of fluid catalytic cracking of gas oils and, to a far lesser extent, of thermal processes, eg, coking. The total amount of propylene produced depends on the mix of these processes and the specific refinery product slate. For example, in the United States, refiners have maximized gasoline production. This results in a higher level of propylene production than in Europe, where proportionally more heating oil is produced. 

The most dominant catalytic process in the United States is the fluid catalytic cracking process. In this process, partially vaporized medium-cut petroleum fractions called gas oils are brought in contact with a hot, moving, freshly regenerated catalyst stream for a short period of time at process conditions noted above. Spent catalyst moves continuously into a regenerator where deposited coke on the catalyst is burnt off. The hot, freshly regenerated catalyst moves back to the reactor to contact the hot gas oil (see Catalysts, regeneration). 

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