Delayed coke

Delayed Coking", is a semi-continuous process, developed at the end of the 1930 s. The reaction is conducted at 450-500°C under relatively low pressure, four atmospheres, maximum. 

Influence of the type of process fluid coking", compared to delayed coking" makes a harder coke that contains less volatile matter and forms finer grains. 

Product properties Delayed coking Fluid coking... 

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. 

Butylene yield Gas oil Residue Delayed coking Elexicoking Steam cracking of naphtha... 

Composition and properties Delayed coke Fluid coke... 

The delayed coking feed stream of residual oils from various upstream processes is first introduced to a fractionating tower where residual lighter materials are drawn off and the heavy ends are condensed. The heavy ends are removed and heated in a furnace to about 900 to 1,000 F and then fed to an insulated vessel called a coke drum where the coke is formed. When the coke drum is filled with product, the feed is switched to an empty parallel drum. Hot vapors from the coke drums, containing cracked lighter hydrocarbon products, hydrogen sulfide, and ammonia, are fed back to the fractionator where they can be treated in the sour gas treatment system or drawn off as intermediate products. 

Residuum Conversion This includes fluid coking, delayed coking, visbreaking, and residuum hydroprocessing. 

Products obtained as side streams are vacuum gas oil (VGO), lube oil base stocks, and asphalt. Asphalt may be used for paving roads or may be charged to a delayed coking unit. 

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. 

Crude Oil Processing and Production of Hydrocarbon Intermediates 57 Delayed Coking... 

In delayed coking, the reactor system consists of a short contact-time heater coupled to a large drum in which the preheated feed soaks on a hatch basis. Coke gradually forms in the drum. A delayed coking unit has at least a pair of drums. When the coke reaches a predetermined level in one drum, flow is diverted to the other so that the process is continuous. 

Coke produced from delayed coking is described as delayed sponge, shot, or needle coke depending on its physical structure. Shot coke is the most common when running the unit under severe conditions with sour crude residues. Needle coke is produced from selected aromatic feedstocks. Sponge coke is more porous and has a high surface area. The properties and markets for petroleum cokes have been reviewed by Dymond. Table 3-4 shows the types of petroleum cokes and their uses. ... 

Figure 3-3. Flow diagram of a delayed coking unit (1) coker fractionator, (2) coker heater, (3) coke drum, (4) vapor recovery column.

The feed to a catalytic reformer is normally a heavy naphtha fraction produced from atmospheric distillation units. Naphtha from other sources such as those produced from cracking and delayed coking may also be used. Before using naphtha as feed for a catalytic reforming unit, it must be hydrotreated to saturate the olefins and to hydrodesulfurize... 

Products from catalytic cracking units are also more stable due to a lower olefin content in the liquid products. This reflects a higher hydrogen transfer activity, which leads to more saturated hydrocarbons than in thermally cracked products from delayed coking units, for example. 

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. 

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