Patent Application
20140175187
The present invention relates to a delayed coking process used in petroleum refineries wherein heavy hydrocarbon petroleum residue is thermally cracked to obtain liquid and gaseous product streams and leaving behind solid, carbonaceous petroleum coke. Particularly, the invention relates to a hardware and method for supplying additives into the delayed coker unit.
In the recent years, there has been a constant increase in the tendency of petroleum refiners to implement delayed coking process as part of their overall operation of processing of the crudes, because of the advantages it is known to provide. Further, with the crude sources becoming heavier or with the more refiners switching to processing “opportunity crudes” (also referred in the industry as challenging crudes), it is anticipated that more interest will be shown in delayed coking processes. In Delayed Coker Unit (DCU), a heavy hydrocarbon feedstock is fed to a furnace, which heats the feedstock to the desired coking temperature and is designed and controlled to prevent premature coking in the heater tubes. The hot feedstock is then passed from the heater to one or more coker drums where the hot material is held for an extended period of time at desired pressure, until coking reaction completes. Vapors from the drums are fed to a fractionator where gas, naphtha, and gas oils are separated out. The heavier hydrocarbons obtained in the fractionator are recycled through the furnace as per the requirement. After the coke reaches a predetermined level in one drum, the feed flow is diverted to another coker drum to maintain continuous operation. The coked drum (i.e. coker drum having coke upto the predetermined level) is steamed to strip out entrapped hydrocarbons, cooled by water injection and decoked by mechanical or hydraulic methods.
Recently in prior art, a number of inventions have come up in the area of delayed coking process, that suggest addition of some external additive(s)/chemicals to the coker feedstock in order to meet various objectives like reduction of coke yield, improving the quantity as well as quality of liquid and gaseous products and improving the quality of coke produced. By way of example, U.S. Pat. No. 4,378,288 describes a method for increasing the distillate yield in delayed coking process by adding a free radical inhibitor to the coker feed material. U.S. Pat. No. 4,642,175 describes a process for upgrading the heavy hydrocarbon feedstock by reducing the coking tendency by contacting with free radical removing catalyst. U.S. Pat. No. 4,756,819 tries to prevent the coke formation in thermal treatment of heavy hydrocarbon residues by use of a metallic salt in the form of suspension of solid particles, in solution or as emulsion. U.S. Pat. No. 5,006,223 describes a method of increasing the thermal conversion of hydrocarbons without any substantial increase in gaseous products formed, by the addition of certain free radical initiators.
In the aforesaid documents, the additives are added to the feedstock at a stage before the feedstock is fed to the coker drum. Residence time of the additive in the process is increased by incorporation of the additives in the feedstock before the same is fed to the coker drum. This may lead to reduction in activity of the additive. Moreover, the presence of additives in the furnace tubes may lead to increase in the possibility of coke deposition on the metal surface.
Reference may be made to U.S. Patent Publication No. 2009/0209799 that describes a process in which the hydrocarbons are cracked or coked by adding an additive into the vapors emerging from the coker drum or coking vessel. Particularly, the document describes methods for injecting the additives into the vapor phase at an upper portion of the coker drum. It is felt that since the coking reactions predominantly take place in the liquid pool such a procedure may not be providing the best results. Thus, there exits a need to improvise the delayed coking process used in petroleum refineries for one or more of the following objectives (a) reduction of coke yield, (b) improving the quality and quantity of liquid and gaseous products or (c) improving the quality of coke produced, including coke morphology.
The present invention describes a delayed coking process useful in petroleum refineries wherein heavy hydrocarbon petroleum residue is thermally cracked to obtain liquid and gaseous product streams and leaving behind solid, carbonaceous petroleum coke, said process comprising adding one or more external additive(s)/chemicals to the coker feedstock maintained in a delayed coker drum at the vapor liquid interphase.
An apparatus for supplying additive(s) into a coker drum is disclosed. The apparatus comprises an inlet for supplying a hydrocarbon feed stream into the coker drum and a plurality of conduits arranged along the circumference of walls of the coker drum, each of the plurality of the conduits is provided with an injection nozzle to supply additives inside the coker drum. The apparatus further comprises an injection control system for controlling the operation of the plurality of injection nozzles such that 1) one or more of the injection nozzles placed within a first predetermined distance in a first direction above a vapour liquid interphase of the hydrocarbon feed stream are configured to supply the additives; and 2) supply of the additive discontinues from a particular injection nozzle when a distance in the first direction between the injection nozzle and the vapour liquid interphase is less than or equal to a second predetermined distance. The apparatus optionally includes a mechanical drive system for moving at least one of the plurality of conduits based on the level of the vapour liquid interphase of hydrocarbon feed stream in the coker drum. Further, the injection nozzles located at a distance greater than the first predetermined distance are controlled so as to supply steam. Also, the injection nozzles located at a distance less than the second predetermined distance are controlled so as to supply steam.
A method for supplying additive(s) into a coker drum is also disclosed. The method comprises supplying a hydrocarbon feed stream into coker drum and supplying additives through a plurality of conduits arranged along the circumference of walls of the coker drum, each of the plurality of the conduits being provided with an injection nozzle for supplying additives inside the coker drum. The method further includes controlling the operation of the plurality of injection nozzles, including the steps of configuring one or more of the injection nozzles placed within a first predetermined distance in a first direction above a vapour liquid interphase of the hydrocarbon feed stream to supply the additives and discontinuing the supply of the additive from a particular injection nozzle when a distance in the first direction between the injection nozzle and the vapour liquid interphase is less than or equal to a second predetermined distance. The method optionally includes the step of optionally moving at least one of the plurality of conduits based on the level of the vapour liquid interphase of hydrocarbon feed stream in the coker drum. The method further includes controlling the injection nozzles located at a distance greater than the first predetermined distance to supply steam. Further, the method includes controlling the injection nozzles located at a distance less than the second predetermined distance to supply steam. In the case where vertical movement of conduits are possible, the plurality of conduits may be placed such that their injection nozzles are at same elevation and the additive injection control system will be such that 1) plurality of conduits to be placed inside the coker drum such that the tips of injection nozzles are kept within a first predetermined distance from the bottom of the coker drum 2) all injection nozzles to start supplying additive when the supply of hydro carbon feed stream to the coker drum starts 3) all conduits to be moved vertically upwards in a way such that tips of injection nozzles to be placed within a first predetermined distance in the first direction above vapour liquid interphase of the hydrocarbon feed stream 4) additive supply to all injection nozzles to discontinue and steam flow to start as the level of vapour-liquid interphase reaches up to around 75% of coker drum height.
In yet another embodiment, an apparatus for supplying additive into a coker drum is disclosed. The apparatus includes an inlet for supplying hydrocarbon feed stream and a plurality of injection nozzles located at varying elevations into the walls of the coker drum. The apparatus further includes an injection control system configured to control the operation of the plurality of injection nozzles, such that 1) one or more of the injection nozzles placed within a first predetermined distance in a first direction along a vapour liquid interphase of the hydrocarbon feed stream are configured to supply the additives; 2) supply of the additive discontinues from a particular injection nozzle when a distance in the first direction between the injection nozzle and the vapour liquid interphase is less than or equal to a second predetermined distance; and 3) one or more of the injection nozzles placed after a third predetermined distance in a second direction along a vapour liquid interphase are configured to supply steam. Further, the nozzles that are not supplying additives at a particular time may be configured to supply steam. In other words, all the nozzles may be configured to supply steam other than the nozzle supplying the additives. In the most preferred embodiment, the switch over from the supply of the additive to steam may be a simultaneous operation.
The attached figures show various aspects of the process of the present invention. Numbering adopted in the drawings is unique to each figure given.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the present invention. Furthermore, the one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention.
The parts of the device have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process, method. Similarly, one or more elements in a system or apparatus proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
Accordingly, the present invention describes a delayed coking process useful in petroleum refineries wherein heavy hydrocarbon petroleum residue is thermally cracked to obtain liquid and gaseous product streams and leaving behind solid, carbonaceous petroleum coke, said process comprising adding one or more external additive(s)/chemicals to the coker feedstock maintained in a delayed coker drum at the vapor liquid interphase. In addition to the above, the present invention describes at least one novel hardware that facilitates implementation of the aforesaid method.
The present invention relates to a thermal cracking process, where heavy petroleum residue are thermally cracked and converted into liquid and gaseous product streams and leaving behind solid, carbonaceous petroleum coke. Referring to
The liquid hydrocarbon feedstock to be used in the process can be selected from heavy hydrocarbon feedstocks like vacuum residue, atmospheric residue, deasphalted oil, shale oil, coal tar, thermal pyrolytic tar, visbreaker streams, clarified oil, slop oil or blends of such hydrocarbons. The Conradson carbon residue content of the feedstock can be a minimum of 5 wt % and preferably may vary from 5 wt % to 27 wt %. Feedstock used in the process can have a minimum density of 0.9 g/cc. These hydrocarbon feedstocks may or may not be hydro-treated for removal of sulfur and metals before feeding into the process, depending on the requirement.
Coking reactions predominantly take place in the liquid pool formed inside the coker drum or coking vessel due to the supply of hydrocarbon feedstock into the drum. The method disclosed in the present invention includes the supply of the additive(s)/chemicals at the vapor-liquid interphase inside the coker drum or coking vessel, instead of supplying them along with feed or supplying the additive from the top to the vapors emerging from the coker drum or coking vessel. The vapor liquid interphase inside the coker drum is in a highly turbulent state with vigorous mixing of gas and liquid. The injection of additive(s)/chemicals into the vapor liquid interphase is having the following advantages:
The additive(s)/chemicals or mixture of additive(s)/chemicals supplied can be in gaseous, liquid, solid, emulsion state or a mixture of the same. The non limiting examples of additives to be used for the process include, cracking catalysts, free radical removing catalysts, hydrogen donors, fuel gas, free radical generators, asphaltene stabilizers and/or a combination of the same. There can be a carrier fluid supplied along with the additive(s)/chemicals which can be in gaseous, liquid, solid, emulsion state or a mixture of the same. The non limiting examples of the carrier fluid are hydrocarbon liquids of suitable boiling range including the feedstock, residue, lighter hydrocarbons, gas oil, solvents, water, steam, nitrogen, inert gases, fuel gas, carbon monoxide, carbon dioxide and/or the like.
In accordance with a first option, the hardware to facilitate supply of additive(s) into the coker drum is shown in
According to a preferred embodiment, the number of conduits in the coker drum (33) ranges from 2-12, depending on coker drum diameter, such that the conduits (36) are placed within a radial distance of 5-30 percent of the radius from the wall of the coker drum (33), and more preferably 20 percent. Preferably, the conduits (36) are placed at varying elevations. The supply of the additives generally begins through the injection nozzle of the conduit at the lowest elevation. However, a certain number of conduits (36) may also be placed at the same elevation depending upon the requirements. In an alternate embodiment, the conduits may be connected to a mechanical drive system (not shown) to enable vertical and rotatory movement of conduits. Preferably, at a particular instant, only one injection nozzle placed in vicinity above the vapour liquid interphase is configured to supply the additive. However, more than one injection nozzle placed in vicinity above the vapour liquid interphase may be configured to supply the additive simultaneously. The preferable predetermined distance, at which the supply of the additive discontinues from one injection nozzle and switches to another injection nozzle in the elevation, is less than 0.01 m. The conduits not being used to supply additives at a particular instant may be used to supply steam or any other chemical based on the requirements. The injection control system may comprise of a microcontroller or a processor or any suitable control means to control switching off the supply of the additive from the injection nozzle that go below the vapour liquid interphase and the supply steam through them. The passing of the steam in this manner helps to create more number of channels through the coke bed. The creation of the additional channels through the coke bed has the following advantages:
Guides (not shown) are provided at the inner surface of the coker drum to hold the conduits in their position. Metallurgy of the conduit, injection nozzle, guide plates etc. shall be suitable for the conditions prevailing in the coker drum. The additive(s)/chemicals or mixture of additive(s)/chemicals supplied can be in gaseous, liquid, solid, slurry, foam, emulsion state or a mixture of the same. There can be a carrier fluid supplied along with the additive(s)/chemicals(s) which can be in gaseous, liquid, solid, emulsion state or a mixture of the same. The additives may be added in isolation or along with a carrier fluid. The non-limiting examples of the carrier fluid are hydrocarbon liquids of suitable boiling range which may include the feedstock, gas oil, lighter hydrocarbons, residue, solvents, water, steam, nitrogen, inert gases, carbon monoxide, carbon dioxide and/or the like. In case of blockage Steam or Nitrogen or other hydrocarbon gases or liquids like water, naphtha, gasoil, fuel oil, purge oil etc. can be used to clean the injection nozzles.
The diameter and length of the supply conduit can be determined based on the flow rate of the additives or additives along with carrier fluid to be supplied into the coker drum, with the length being limited by the elevation of the coker drum. The material of construction of the supply conduit can be selected based on the operating conditions like temperature and pressure prevailing inside the coker drum. The carrier fluid and the additive material can have a different temperature than the hydrocarbon feedstock entering the coker drum.
Referring to
In accordance with a second option, the hardware to facilitate the supply of additive(s) into the coker drum is shown in
The rate of movement of the vertically movable additive supply conduit (46) with injection nozzle (47) at the end, is normally kept such as the tip of the conduit is above the vapor liquid interphase by an elevation of minimum by 0.01 m to 0.8 m, and preferably 0.5 m, which shall be determined based on the hydrocarbon feed rate into the coker drum (43), for supply of the additives into the vapor liquid interphase inside the drum (43). The additive supply conduit will be moved vertically in the upward direction with the increasing vapor-liquid interphase level inside the coker drum, keeping a minimum distance of 0.01 m to 0.8 m, and preferably 0.5 m between the vapor liquid interphase and the tip of the supply conduit. Additives supply can be continuous or as pulses.
In accordance with a third option, the hardware to facilitate the supply of additive(s) into the coker drum is shown in
As the supply of hydrocarbon feedstock starts in the coker drum, the additive supply is started through the injection nozzle placed at the lowest elevation inside the coker drum. As the vapor-liquid interphase level inside the drum increases and reaches near the location of a given injecting nozzle at a vertical elevation by less than 0.01 additive(s)/chemicals(s) flow to that particular nozzle is discontinued and switched over to the injection nozzle placed at the next higher elevation. Additives supply can be stopped and steam supply can be started when the liquid/coke level reaches the maximum limit or at any desirable level inside the coker drum. The timings of starting and stopping of additive supply to the various injection nozzles can be determined based on the hydrocarbon feed rate and liquid/coke filling rate inside the coker drum. There can be more than one injector nozzle located at a given elevation inside the coker drum. The nozzles may be placed at any radial location at a given elevation. The orientation of the injector nozzle can vary from 45 to 135 degrees to the vertical drum wall. Metallurgy of the injection nozzle shall be in accordance to process conditions and material coming into contact with it. The passing of the steam in such manner into the coker drum has several advantages as has been discussed before and are not being repeated again herein.
The additive(s)/chemicals or mixture of additive(s)/chemicals supplied can be in gaseous, liquid, solid, slurry, foam, emulsion state or a mixture of the same. There can be a carrier fluid supplied along with the additive(s)/chemicals(s) which can be in gaseous, liquid, solid, emulsion state or a mixture of the same. The additives may be added in isolation or along with a carrier fluid. The non limiting examples of the carrier fluid are hydrocarbon liquids of suitable boiling range which may include the feedstock, gas oil, lighter hydrocarbons, residue, solvents, water, steam, nitrogen, inert gases, fuel gas, carbon monoxide, carbon dioxide and/or the like. In case of blockage Steam or Nitrogen or other hydrocarbon gases or liquids like water, naphtha, gasoil, fuel oil, purge oil etc. can be used to clean the injection nozzle.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.
While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2945/MUM/2012 | Oct 2012 | IN | national |
