COKING
Delayed coking is a type of coking process that consists of heating black oil to its thermal cracking temperature in furnace coils. As a result, heavy, long chain hydrocarbon molecules crack into gas oil and petroleum coke.
Coke produced by the delayed coking process has various commercial uses. It is most often used as a raw material for electrodes or fuel production.Green Anode Grade Petroleum Coke is used:
• As fuel for space heaters, large industrial steam generators, fluidized bed combustions,
Integrated gasification combined cycle units, and cement kilns;
• In silicon carbide foundries;
• For producing blast furnace coke;
Calcined Petroleum Coke is used:
• As anodes in the production of aluminum;
• In the production of titanium dioxide;
• As a carbon raiser in cast iron and steel making;
• For producing graphite electrodes and other graphite products used
in electrical equipment;
• In carbon structural materials;
As cracking takes place in the coke drum, gas oil and lighter components are generated
in vapor phase and separate from the liquid and solids. Gas oil and light components in the vapor phase, except for any liquid or solids, are directed to main fractionator where there are separated into desired boiling point fractions.
The solid coke is deposited and remains in the coke drum in a porous structure that allows flow through the pores. Depending upon the overall coke drum cycle being used, a coke drum may fill in 16 to 24 hours. After the first drum is full of the solidified coke, the hot mixture from the surface is switched to the second drum. While the second drum is filling, the filled first drum is steamed out to reduce the hydrocarbon of the petroleum coke, and then quenched with water to cool it. The top and bottom heads of the full coke drum are removed, and the solid petroleum coke is then cut from the coke drum with a high-pressure water nozzle, where it falls into a pit,pad, or sluiceway for reclamation to storage.
HEAVY OIL
RESIDUES
Petroleum coke is produced by coking liquid petroleum residues and pitches, during cracking and pyrolysis of petroleum distillation products, electrode pitch coke is produced
by coking of high-melting coal pitch. Petroleum and electrode pitch coke are the main raw materials for the electrodes production. Petroleum and electrode pitch coke have a very
low ash content compared to coal coke, usually, it is no higher than 0.3 % (up to 0.8% for petroleum coke).
Coking of black oil residues is a type of high-destruction thermal cracking of hydrocarbonsto produce petroleum coke and gas oil fractions. It is carried out at 420-560 °C and pressure up to 0.65 MPa. The process duration varies from tens of minutes to tens of hours. The raw materials for the process are heavy fractions of oil refining, residues of deasphaltization, thermal and catalytic cracking, pyrolysis of gasoline and gas oils.
The essence of the process is successive reactions of cracking, dehydrogenation, cyclization, aromatization, polycondensation, and compaction to form a solid coke cake. The released volatile products are rectified to separate the target fractions and stabilize them, and the residuum is returned to the process. The carbonized coke is regularly unloaded, dried and calcined.According to the instrumentation, there are: delayed coking in unheated coke drums (for obtaining high-carbon coke), heated residuums (for obtaining electrode and special types of coke), coking in a fluidized bed of powdered coke (referred to as thermoform-type cracking). When the last method is combined with coke gasification, native asphalts and bitumens can be involved in the process in addition to oil residues.
Petroleum coke (green coke or calcined coke) is a black porous solid residue, derived
as a result of the cracking or destructive distillation of petroleum or obtained from oils
of bituminous minerals. It is mainly used as a raw material for the electrodes production (calcined coke) or as a fuel (green coke).
According to BusinesStat estimates, petroleum coke sales in the world increased by 7.4%, from 126.5 to 135.9 million tons within the period from 2014 to 2018. By the end of 2018, there was a slight decline in sales due to a downturn in one of the pivotal markets — India.
The leaders in terms of sales volume of petroleum coke among the world’s countriesin recent years were the US, which accounted for an average of 17.5% of the aggregate measure, as well as China (16.7%) and India (16.2%). In 2018, the three largest consumer countries accounted for more than half of global petroleum coke sales in physical terms.
At the same time, the US share of global sales has been declining over the past five years, while the shares of China and India have been growing. It is noteworthy that the largest volume of petroleum coke sales per head of population in 2014-2018 was recorded in Greece with an average of 114.5 kg.
According to market experts, the largest growth in demand for petroleum coke is expected
in the segment of baked anodes required for aluminum production with an average annual growth of 5-7% in the coming years. Petroleum coke sales as fuel for thermal power plants and cement factories will grow by an average of 4-5% per year. In 2023, worldwide petroleum coke sales will reach 150 million tons. The sales will exceed the indicator values of 2018 by 10.2%. India will be leading in petroleum coke sales and will account for
an average of 18.2% of global sales in the next five years.
The world market volume of petroleum coke: 60 million tons per year in 2004, 100 million tons per year in 2010, 126.5 million tons per year in 2014, and in 135.9 million tons per year in 2018.
COKING
The flow diagram and description a delayed
coking unit (operating DCU NOVOUFIMSK OIL REFINERY):
1 – scrubber;
2 – tube kiln;
3 – coke drums;
4 – fractionating column;
5 – refrigerators;
6 – stripping column;
7 – condenser-refrigerator;
8 – gas separator;
The DCU operates the following way:
Fresh raw material (tar or cracked residue) is heated in the convection section of the furnace 2 to 370-390°C and enters the cascade trays of the fractionating column 4, flowing down which it contacts with the rising vapors coming from the working reaction chamber and having a temperature of 430-450°C. As a result of mass transfer, the heavy part of the vapor condenses and together with the raw material forms a secondary raw material with a temperature of 380-400°C in the lower part of the column. From the bottom of the fractionating column, secondary raw materials are pumped through the soaking section
of the heating furnace and at a temperature of 485-500°C are sent to the reaction chamber. Temperature of secondary raw materials at the reactor inlet is lower by 10-15°C, which
is due to heat loss in the transfer pipeline and switching valves.