Content: 1) What is coking 2) Types of coking 3) Delayed coking 4) Process Description

What is coking? Coking is a well-known process in the refining industry, the objective of which is to upgrade heavy fractions and, more especially, the distillation residues by subjecting them to heat decomposition. The residual products of the refinery from the feed for coking. The liquid feed is converted into gas, naphtha, heating oil, gas oil and coke. Coking is done to get either gas oil or coke as the main product. The gas oil is used as the feed for catalytic cracking While the coke used as a fuel of in the production of carbon electrodes and chemicals.

Main types of coking processes. 1) Delayed coking – continuous thermal cracking process which generates coke and produces various distillates in fractionators from vacuum residue. Coke drum temperature remains around 415 C -450 C. 2) Fluid coking – continuous coking process where residue is sprayed on to fluidised bed of hot coke particles. Here cracking takes place at much higher temperature than delayed coking ( temperature up to 565 C) Both are physical processes that occur at pressures slightly higher than atmospheric and at temperatures greater that 900 F that thermally crack the feedstock into products such as naphtha and distillate, leaving behind petroleum coke.

Delayed coking A delayed coking is a type of coking whose process consists of heating a residual oil feed to its thermal cracking temperature in a furnace with multiple parallel passes. Delayed coking is one of the unit processes used in many oil refineries. This cracks the heavy, long, chain hydrocarbon molecules of the residual oil into Coker gas oil and petroleum coke. Delayed Coking is the most commonly used carbon rejection process that upgrades residues to a wide range of lighter hydrocarbon gas and distillates through thermal cracking.

Delayed coking The by-product of delayed coking process is petroleum coke. The goal for delayed coking operation is to maximize the yield of clean distillates and minimize the yield of coke. Three operating parameters govern the yield pattern and product quality of Delayed Coking are – 1) Temperature 2) Pressure 3) Recycle Ratio (RR)

Schema of Delayed Coking

In delayed coking, two or more large reactors, called coke drums, are used to hold, or delay, the heated feedstock while the cracking takes place. Residual oil from the vacuum distillation unit is pumped into the bottom of the of the distillation column called the main fractionator. The residual oil by having it contact the hot vapours in the bottom of the fractionator. From fractionator it is pumped along with the some injected steam into the fuel fired furnaces and heated to its thermal cracking temperature. The injection steam helps to minimize the deposition of coke with in the furnace tubes. The heated stream transferring to coking drum where the temperature and pressure are maintained at coking conditions so that stream decompose into coke and volatile components. Process description

The process is called delayed coking because in this process the coal is heated using a much more complex system, and it consists of multiple furnaces or coke drums. The Coker fractionating system separates the volatile components generated in the coking drum into various lighter hydrocarbon streams and components. After coking, the coke drum is full of coke and it is then removed using water jets. Like other secondary processing units, coking play an important role in the refinery economics depending on the type and cost of the crude oil run at a refinery. Decoking – process for the removal of coke from a coking reactor of a series of coking reactors, comprising the projection of water under pressure at the coke via a water-ejection device hanging from a flexible tube guided by a guide pulley movably mounted above the reactors for translation between each reactor of the series of reactors.

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