Coking process

Coking processes can also be used to produce various types of coke. Depending upon feedstock properties, coker unit design, and operating conditions, the petroleum coke can be (Speight, 1980)  

The physical and chemical properties of fuel coke, anode coke, and needle coke vary substantially, and determine the end use of the material that can be burned as fuel, calcined for use in the aluminum, chemical, or steel industries, or gasified to produce steam, electricity, or gas feedstocks for the petrochemicals industry. Petroleum coke can be successfully employed for the production of synthesis gas via gasification route. Since the main objective in a coking-based refinery is to maximize liquid product yield, any value added by selling the fuel grade coke is a bonus for the refiners (Jacob, 1971 Dymond, 1991). 

There are three main coking processes in use (Rana et al., 2007)  

Delayed or retarded coking, which can produce shot coke (a type of fuel coke), sponge coke (used to produce anode coke or as a fuel coke), or needle coke. This process accounts for the majority of the coke produced in the world today. 

Fluid-coking, which produces fluid coke typically used as fuel coke. 

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All modern refineries have conversion units, designed to transform black effluent streams into lighter products gas, gasoline, diesel fuel. Among these conversion units, coking processes take place by pyrolysis and push the cracking reaction so far that the residue from the operation is very heavy it is called coke . 

There are few coking units in the world, and the majority of them is found in the United States, such that coke production is marginal. Different coking processes have been described, but only two have survived (see Chapter 10) ... 

The coking process produces electrode quality coke from vacuum residues of good quality (low metal and sulfur contents) or coke for fuel in the case of heavy crude or vacuum residue conversion having high impurity levels. 

Table 10.12 contains some general data on coking processes and the resulting products. 

Approximately 50—55% of the product from a coal-tar refinery is pitch and another 30% is creosote. The remaining 15—20% is the chemical oil, about half of which is naphthalene. Creosote is used as a feedstock for production of carbon black and as a wood preservative. Because of modifications to modem coking processes, tar acids such as phenol and cresyUc acids are contained in coal tar in lower quantity than in the past. To achieve economies of scale, these tar acids are removed from cmde coal tar with a caustic wash and sent to a central processing plant where materials from a number of refiners are combined for recovery. 

Fluid coking (Fig. 4) is a continuous process that uses the fluidized soflds technique to convert atmospheric and vacuum residua to more valuable products (12,13). The residuum is converted to coke and overhead products by being sprayed into a fluidized bed of hot, fine coke particles, which permits the coking reactions to be conducted at higher temperatures and shorter contact times than they can be in delayed coking. Moreover, these conditions result in decreased yields of coke greater quantities of more valuable Hquid product are recovered in the fluid coking process. 

Several laboratory tests (3,6) are used to determine the desirabiHty of a coal or blend of coals for making coke. These are empirical and are carried out under conditions that approach the coking process. The three properties that have been studied are swelling, plasticity, and agglomeration. 

Coke ovens are major sources of fugitive air emissions. The coking process... 

Products from coking processes vary considerably with feed type and process conditions. These products are hydrocarbon gases, cracked naphtha, middle distillates, and coke. The gas and liquid products are characterized by a high percentage of unsaturation. Hydrotreatment is usually required to saturate olefinic compounds and to desulfurize products from coking units. 

There are two major commercial thermal cracking processes, delayed coking and fluid coking. Flexicoking is a fluid coking process in which the coke is gasified with air and steam. The resulting gas mixture partially provides process heat. 

In the fluid coking process, part of the coke produced is used to provide the process heat. Cracking reactions occur inside the heater and the fluidized-bed reactor. The fluid coke is partially formed in the heater. Hot coke slurry from the heater is recycled to the fluid reactor to provide the heat required for the cracking reactions. Fluid coke is formed by spraying the hot feed on the already-formed coke particles. Reactor temperature is about 520°C, and the conversion into coke is immediate, with... 

Coking (processing of coal to produce coke, a material used in iron and steel production)... 

Aromatic amines can be determined by measuring the difference of their UVV absorption spectra, taken at identical concentrations but different pH of the solution. Also, standard mixtures and samples of the amines isolated from coke processing products were tested LOD 0.1-1 ppm. The procedure is potentially useful for waste waters and industrial effluents, where techniques such as GC and nonaqueous titrations may prove difficult to apply333. A determination of certain metabolites symptomatic of pancreatitis... 

Propylene, another source of toxic releases from refineries, is produced as a light end during cracking and coking processes. It is volatile as well as soluble in water, which increases its potential for release to both air and water during processing. 

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