Coking and Thermal Processes

Nowadays more refineries are seeking lighter and higher quality products out of the heavy residues. Coking and other thermal processes convert heavy feedstocks, usually from distillation processes, to more desirable and valuable products that are suitable feeds for other refinery units. Such units include coking and visbreaking. 

The other thermal cracking process is visbreaking. This is a milder thermal process and is mainly used to reduce the viscosities and pour points of vacuum residues to 

Carbon source Needle Electrodes Synthetic graphite 

Fuel use Sponge Space heating in Europe/Japan Industrial boilers 

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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. 

Thermal Cracking. Heavy petroleum fractions such as resid are thermally cracked in delayed cokers or flexicokers (44,56,57). The main products from the process are petroleum coke and off-gas which contain light olefins and butylenes. This stream also contains a considerable amount of butane. Process conditions for the flexicoker are more severe than for the delayed coker, about 550°C versus 450°C. Both are operated at low pressures, around 300—600 kPa (43—87 psi). Flexicokers produce much more linear butenes, particularly 2-butene, than delayed cokers and about half the amount of isobutylene (Table 7). This is attributed to high severity of operation for the flexicoker (43). 

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. 

Before the advent of the catalytic cracking process, thermal cracking was the primary process available to convert low-value feedstocks into lighter products. Refiners still use thermal processes, such as delayed coking and visibreaking, for cracking of residual hydrocarbons. 

FLUID COKING A noncatalytic, thermal process for converting bitumen and coal liquids to lighter hydrocarbon fluids and gases. Developed by the Exxon Research Engineering Company and used commercially since 1954. See also FLEXICOKING. 

English Method,—It has already been pointed out that from thermal chemical reasons, the coke through which the steam is passing in the manufacture of water gas should be at about 1000° C. in order to obtain good results, and that as a result of the reaction between the coke and steam, the temperature of the former falls, necessitating the addition of heat to the coke mass, in order to keep up the efficiency of the process. 

Coke a gray to black solid carbonaceous material produced from petroleum during thermal processing characterized by having a high carbon content (95%+ by weight), a honeycomb appearance, and is insoluble in organic solvents. 

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