Patent Application
20230101524
The present invention relates to the field of refining and more particularly to a method for production of anode grade coke in comparison to fuel grade pet coke directly from crude oils by employing a processing methodology different than a Delayed Coker Unit (DCU).
Crude oil is a complex mixture of thousands of chemical species, most of which are hydrocarbons, i.e., they are made of carbon and hydrogen. Some chemical species in crude oil contain other elements (referred to as “hetero elements”), such as sulfur, nitrogen, or metals such as vanadium or nickel. Crude oils from different locations on the earth have vastly different composition; the types and relative amounts of compounds they contain can vary greatly. For example, “heavy” crude oils contain a relatively higher amount of large hydrocarbon molecules whereas “light” crude oil contains a relatively higher amount of small hydrocarbon molecules. “Sweet” crude oil contains little sulfur (typically less than about 0.5 weight percent) whereas “sour” crude oil contains a higher amount of sulfur (typically 1-2 weight percent or more).
Petroleum residues are the remaining fraction left after the distillation of crude oil in Atmospheric Distillation Unit (ADU) and Vacuum Distillation Unit (VDU). Residue fraction obtained from the bottom of ADU which is also called Reduced Crude Oil (RCO) is further fractionated in a VDU. Residue fraction obtained from VDU is a heavy asphaltene containing fraction with high sulfur, high metals, high nitrogen and this feed stock is called Vacuum Residue (VR) which is processed in a thermal cracking unit of a refinery. This thermal cracking process commonly used to treat petroleum residue is termed as Delayed coking. In this process, the petroleum residue is heated and subjected to thermal cracking to produce valuable lower-boiling petroleum distillate products, and a solid carbonaceous residue known as coke. Coke with a high sulfur and/or metal content is generally subject to combustion as a fuel. “Fuel grade coke” is generally not suitable for other purposes.
Petroleum coke (also referred to as pet coke and referred to herein simply as coke) is a high carbon product produced as a result of thermal cracking of heavy residue feed stock in DCU. The marketability of coke depends on the amount of impurities such as sulfur, metals, nitrogen etc, and its crystalline structure. Coke with a relatively high sulfur content is referred to as fuel grade coke and is sold as fuel for coal-burning boilers, typically for power generation. Sulfur content in fuel grade coke is in the range of 6-8 wt %. Anode grade coke is a type of coke obtained from a DCU which has a relatively low impurity content and better crystalline structure than fuel grade coke and is used to make electrodes for production of aluminum.
U.S. Ser. No. 10/351,778 B2 describes methods and systems for producing anode grade coke from crude oil having a high sulfur content. Crude oil was subjected to atmospheric distillation and the residue generated thereof further divided into different parts. One part is subjected to hydrotreatment while another is subjected to solvent deasphalting. Synthetic stream generated by blending of hydrotreated resid stream and one or more streams from SDA were used for production of anode grade coke. The configuration proposed in this prior art is complex and may not be cost effective as hydrotreatment of residue is expected to have a very high hydrogen requirement.
WO 2012/162008A1 describes different embodiments of process for delayed coking of whole crude oil stream. The fresh whole crude feed stream is mixed with bottom stream of coker fractionator and heated to temperature of 480° C. to 530° C. in the Coker furnace. Thereafter, the outlet stream from coker furnace is routed to the coke drums for coking. The coke drum effluent vapors are subjected to flash separation from which a light product gas stream and heavy boiling stream is separated. This heavy boiling stream is routed to the main fractionator with heavy gas oil recycle.
U.S. Pat. No. 6,332,975 B1 describes a method of deasphalting a residue stream into resin and asphaltene fractions and producing anode grade coke by coking the resin fraction generated thereof after hydrotreatment. It describes hydrotreating of (1) a minor portion of the residue feedstock wherein the hydrotreated residue is fed to the delayed coker with the resin-containing stream, (2) the resin-containing stream wherein the hydrotreated resin-containing stream is fed to the delayed coker, or (3) a major portion of the residue feedstock wherein the hydrotreated residue is fed to the solvent deasphalting unit.
There is a requirement for developing alternative, improved methods for production of anode-grade coke. This invention discusses the production of improved quality anode grade coke using crude oils. This invention also discusses mixing of aromatic rich stream with crude oil overcoming the operational issue envisaged due to processing of paraffin containing crude feed along with improvement in coke quality.
It is a primary objective of the present invention to provide a method for production of coke with low impurity content directly from crude oils.
It is the further objective of the present invention to provide a method for production of anode grade coke in a Delayed Coker Unit (DCU).
It is the further objective of the present invention to provide a method to overcome the operational constraints of a DCU operation due to processing of crude oil.
It is further objective of the present invention to provide lower coke yield with an enhanced quality coke meeting anode grade coke specification.
It is the further objective of the present invention to maximize the recovery of lighter boiling fractions while producing Anode grade coke.
The present invention discloses a method for production of anode grade coke directly from crude oils in a DCU. In one of the aspects the present invention, provides a method for production of anode grade coke in a DCU, the method comprising:
In one of the aspects the present invention, provides a method for production of anode grade coke in a DCU, the method comprising:
In another aspect of the present invention, the hydrocarbon feedstock (1; 32) is selected from the group consisting of different crude oils, sour crude oil, sweet crude oils, opportunity crudes and heavier streams generated thereof.
In another aspect of the present invention, the coke drums (12, 13; 43, 44) are operated at an overhead temperature of 430-460° C., and a pressure of 1-5 Kg/cm2 (g), and the temperature of heated effluent stream (9; 40) from furnace (8;39) is in the range of 480-510° C.
In one of the preferred aspects, the heavier stream fraction having a boiling point >300° C. in step (ii) is mixed with an aromatic rich stream (6), routed through the bottom of pre-separator vessel.
In another aspect of the present invention, the aromatic rich stream (6) is selected from the group consisting of pyrolysis tar, aromatic tar, clarified light oil.
In another aspect of the present invention, the heavier stream fraction having a boiling point >300° C. obtained from step (ii) is mixed with a recycle stream (38), before routing to the furnace (39).
In another aspect of the present invention, the Coke drum effluent (47) in the main fractionator (49) is washed by an aromatic rich stream (48), to condense heavier molecules from coke drum product vapor effluent (47) and to produce recycle stream (38), and the aromatic rich stream (48) is selected from the group consisting of pyrolysis tar, aromatic tar, clarified light oil.
In one of the preferred aspects of the present invention, the sulfur and nitrogen content of coke produced are ≤3 wt and 0.1. %, respectively and coke meets anode grade coke quality.
In one of the aspects of the present invention, the method comprising:
In still another aspect of the present invention, the method comprising:
For promoting an understanding of the principles of the present disclosure, reference will now be made to the specific embodiments of the present invention further illustrated in the drawings and specific language will be used to describe the same. The foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated method, and such further applications of the principles of the present disclosure as illustrated herein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinarily skilled in the art to which this present disclosure belongs. The methods, and examples provided herein are illustrative only and not intended to be limiting.
Anode grade coke is a type of coke product obtained from a Delayed Coker Unit having a sponge like structure with relatively low levels of sulfur and impurities such as metals, Nitrogen etc.
Feed Stock:
Feed stocks in the present invention are selected from sour/sweet crude oils, opportunity crudes. Aromatic oils are selected from oils such as clarified light oils, aromatic tars, pyrolysis tars.
The main embodiment of the present invention provides a method for production of anode grade coke by processing crude oil in a Delayed Coker Unit (DCU), the method comprising:
In another embodiment of the present invention, the crude oil feed stream is separated in a ‘Pre-separator vessel’ to obtain lighter components (300° C.−) from the heavier molecules of crude oil containing 300° C.+ fraction.
In another preferred embodiment of the present invention provides a method to overcome the operational constraints of a DCU operation due to processing of crude oil. The heavy streams (300° C.+) are mixed with an aromatic rich stream such as pyrolysis tar, aromatic tar, Clarified Light Oil (CLO) etc. and routed to the Coker furnace and Coke drums subsequently.
In another embodiment of the present invention, hydrocarbon feed stock used in the process are different crude oils; sour and sweet, opportunity crudes and heavier streams generated thereof etc.
Process Conditions:
The process described herein have been carried out by maintaining the Furnace Coil Outlet Temperature in the range of 480-510° C. and the coke drum overhead temperature in the range of 430-460° C. The operating pressure maintained in the process is in the range of 1-5 Kg/cm2 (g).
A schematic process flow diagram of one of the aspect of the present invention is depicted in
Another schematic process flow diagram of the present invention as depicted
Processing of 300+ fraction of crude oil and mixing of aromatic rich stream enhances the coke quality in comparison to that obtained from Vacuum residue feed stock.
Example 1: Crude Blend A with property provided in Table-1 was subjected to thermal cracking as per process conditions provided in Table-2 in a lab scale thermal cracker unit to obtain Raw Petroleum Coke A (RPC A). RPC obtained from the experiment was subjected to calcination in a batch calcination unit at conditions provided in Table-3 to obtain Calcined Petroleum Coke A (CPC A). CPC properties are provided in Table-4.
Coke as described in Table 4 was subjected to XRD analysis for measurement of Crystallite Size (Lc). Lc value was observed to be 37 Å, indicating a good quality crystalline structure. It can be observed that all properties of crude derived CPC A fall in the range of anode grade coke.
Example 2: Crude A described in Table-1 was subjected to Atmospheric Distillation followed by Vacuum Distillation to generate Vacuum Residue (VR) which is a typical Coker feed stock (Table-5). VR was subjected to thermal cracking in a thermal cracker unit as per process conditions described in Table-6 to obtain Raw Petroleum Coke B (RPC B). RPC B thus obtained was subjected to calcination in a batch scale calcination unit as per conditions in Table-7 to generate Calcined Petroleum Coke B (CPC B). Property of coke thus obtained is provided in Table-8
CPC B as described in Example-2 was subjected to XRD analysis for measurement of Crystallite size (Lc). Lc was observed to be 34.7 Å which is lower than that of CPC A, indicating a lesser evolved crystalline structure. Also, metals such as Vanadium, Nickel and Sodium were concentrated in coke leading to poor quality of coke. Impurities such as sulphur and Nitrogen content were also found to be high in RPC & CPC B generated from VR.
Example 3: In another experiment, aromatic stream of Clarified Light Oil (CLO) having property as provided in Table-9 was mixed with crude oil feed stock in a ratio of 10:90 and processed in a laboratory scale thermal cracking unit as per process conditions mentioned in Table-10 to obtain Raw Petroleum Coke C (RPC C). RPC C generated thereof was subjected to calcination as per conditions provided in Table-11 to obtain Calcined Petroleum Coke C (CPC C). Calcined coke obtained had property provided in Table-12.
Calcined coke as described in Example-3 was subjected to XRD analysis for measurement of Crystallite size (Lc). Lc was observed to be ˜38 Å indicating an improvement in coke quality.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202121044025 | Sep 2021 | IN | national |
