Patent Description:
The present application relates to the field of needle coke production, and particularly to a system and method for producing needle coke with improved stability.

The production of needle coke is typically carried out by delayed coking process, but the formation of needle coke follows the liquid phase carbonization theory and a temperature-changing operation is adopted in the production process, which is different from the conventional delayed coking process.

<CIT> discloses a method for producing needle coke by temperature-changing operation, in which the temperature in a coke tower is controlled and maintained at <NUM>-<NUM> by controlling the outlet temperature of a coking furnace. In a first reaction stage, the temperature in the coke tower is <NUM>-<NUM>, and intermediate phase liquid crystal is formed in the system; in a second reaction stage, the temperature in the coke tower is raised to <NUM>-<NUM>, and the intermediate phase liquid crystal begins to solidify; and in a third reaction stage, the temperature in the coke tower is raised to <NUM>-<NUM> and the intermediate phase liquid crystal is fully solidified to form needle coke.

<CIT> discloses a method for producing needle coke by temperature- and pressure-changing operation, in which the outlet temperature of a coking furnace is controlled within a range of <NUM>-<NUM>, and the pressure of a coke tower is controlled within a range of <NUM>-<NUM> MPa. In a first reaction stage, the outlet temperature of the furnace is raised from a low temperature to <NUM>, and the pressure of the coke tower is kept at <NUM> MPa; in a second reaction stage, the outlet temperature of the furnace is continuously raised, the pressure of the coke tower is gradually reduced to <NUM>. 5MPa and then kept constant, and needle coke is formed.

<CIT> discloses a system for producing needle coke.

Due to the temperature- and pressure-changing characteristics of the production process of needle coke, the industrial production of needle coke is very difficult, and the device operation is unstable. In the initial reaction stage, a feedstock is fed to the coke tower at a lower temperature, a mild reaction occurs, a relatively lower amount of oil gas is produced, and liquid amount in the coke tower is continuously increased; as the reaction progresses, the temperature of the furnace is gradually raised, the temperature in the coke tower is gradually increased to the coking temperature, violent thermal cracking and thermal polycondensation reactions occur, and a large amount of oil gas is discharged to a fractionation system; at the end of the reaction, the materials in the coke tower are substantially solidified to form needle coke, and the amount of oil gas generated is reduced. In the whole reaction period, the fluctuation in the amount of oil gas discharged at the top of the coke tower is large, the adjustment range of the pressure control system at the top of the coke tower is wide, and the pressure control system cannot be always maintained in a proper operation range; moreover, the throughput of the fractionation unit fluctuates greatly, and consequently the separation effect is poor, and the operation stability is affected.

Directing to the defects of the prior arts, the present application provides a novel system and method for producing needle coke, by which the stability of the needle coke production process can be improved, and, in the whole reaction period, the coking fractionation unit shows a small fluctuation in the throughput and a high separation precision, and it is easy to control the pressure of the coke tower, so that the operation stability of the whole system is greatly improved.

In an aspect, the present application provides a system for producing needle coke, comprising:.

In another aspect, the present application provides a method for producing needle coke using the system of the present application, comprising the steps of:.

wherein the pressure at the top of the pressure stabilization tower is adjusted by the pressure controller at the top of the pressure stabilization tower, so that the pressure at the top of the coke tower is maintained at a set value.

Compared with prior arts, the system and method for producing needle coke have the following advantages:.

The present application will be further described hereinafter in detail with reference to specific embodiments thereof and the accompanying drawings. It should be noted that the specific embodiments of the present application are provided for illustration purpose only, and are not intended to be limiting in any manner.

Any specific numerical value, including the endpoints of a numerical range, described in the context of the present application is not restricted to the exact value thereof, but should be interpreted to further encompass all values close to said exact value, for example all values within ±<NUM>% of said exact value. Moreover, regarding any numerical range described herein, arbitrary combinations can be made between the endpoints of the range, between each endpoint and any specific value within the range, or between any two specific values within the range, to provide one or more new numerical range(s), where said new numerical range(s) should also be deemed to have been specifically described in the present application.

Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art; and if the terms are defined herein and their definitions are different from the ordinary understanding in the art, the definition provided herein shall prevail.

In the context of the present application, the term "coke tower" refers to a reaction equipment for producing needle coke from a hydrocarbon-containing feedstock via a coking reaction, which may be in any form commonly used in the art, to which there is no particular limitation in the present application.

In the context of the present application, the term "coking fractionation tower" refers to an equipment for separating the oil gas generated during coking reaction by fractional distillation, which may be in any form commonly used in the art, to which there is no particular limitation in the present application.

In the context of the present application, the term "light oil" refers to a component with a relatively lower boiling point obtained from the top of the coking fractionation tower, and the term "heavy oil" refers to a component with a relatively higher boiling point obtained from the bottom of the coking fractionation tower, and the cut point between the light oil and the heavy oil can be selected according to the actual need. Typically, the <NUM>% distillate temperature of the "light oil" is about <NUM>-<NUM>, preferably about <NUM>-<NUM>, and the <NUM>% distillate temperature of the "heavy oil" is controlled to be higher than the <NUM>% distillate temperature of the "light oil" by about <NUM> or more.

In the context of the present application, in addition to those matters explicitly stated, any matter or matters not mentioned are considered to be the same as those known in the art without any change. Moreover, any of the embodiments described herein can be freely combined with another one or more embodiments described herein, and the technical solutions or ideas thus obtained are considered as part of the original disclosure or original description of the present application, and should not be considered to be a new matter that has not been disclosed or anticipated herein, unless it is clear to those skilled in the art that such a combination is obviously unreasonable.

In a first aspect, the present application provides a system for producing needle coke, comprising:.

In the system of the present application, because the oil gas outlet at the top of the coke tower is in communication with the oil gas inlet of the pressure stabilization tower, and no pressure controller is provided in the coke tower or on the oil gas pipeline connecting the coke tower to the pressure stabilization tower, the pressure at the top of the coke tower and the pressure at the top of the pressure stabilization tower are closely interrelated, so that the pressure at the top of the coke tower can be controlled through adjusting the pressure at the top of the pressure stabilization tower.

According to the present application, the pressure stabilization tower may be any equipment suitable for receiving the oil gas from the coke tower and separating it into an overhead light fraction and a bottom oil, including, but not limited to, trayed columns, packed columns, and the like, that are commonly used in the field of distillation, to which there is no particular limitation in the present application.

According to the present application, the pressure controller provided at the top of the pressure stabilization tower is a general equipment commonly used in the coking field, to which there is no particular limitation in the present application, as long as it can effectively regulate the pressure at the top of the pressure stabilization tower. In a preferred embodiment, the pressure controller at the top of the pressure stabilization tower may regulate the pressure at the top of the pressure stabilization tower by adjusting the flow rate of the light fraction discharged at the top of the pressure stabilization tower, for example, by adjusting the opening of a valve on the light fraction discharge pipeline, and in turn maintain the pressure at the top of the coke tower at a set value.

In a preferred embodiment, at least two coke towers are provided, and there are always at least one coke tower that is in a reaction stage and at least one coke tower that is in a decoking stage.

According to the present application, the buffer tank may be any equipment suitable for receiving the bottom oil from the pressure stabilization tower and providing a buffering action, such as a conventional oil tank, to which there is no particular limitation in the present application.

In a preferred embodiment, the system further comprises a furnace for heating the hydrocarbon-containing feedstock to be fed to the coke tower.

In a preferred embodiment, the system further comprises a hydrogenation reactor for hydrotreating a hydrocarbon-containing initial feedstock to obtain the hydrocarbon-containing feedstock to be fed to the coke tower.

In a second aspect, the present application provides a method for producing needle coke using the system of the present application, comprising the steps of:.

In a preferred embodiment, prior to step (<NUM>), the method further comprises a step (<NUM>) of hydrotreating a hydrocarbon-containing initial feedstock to obtain the hydrocarbon-containing feedstock used in step (<NUM>).

According to the present application, the hydrocarbon-containing initial feedstock can be any feedstock that is suitable for the production of needle coke after hydrotreatment, to which there is no particular limitation in the present application. For example, the hydrocarbon-containing initial feedstock may be selected from the group consisting of catalytic cracking slurry oils, catalytic cracking decant oils, ethylene tars, thermal cracking residues, coal tars, coal tar pitches, and any combination thereof, preferably catalytic cracking slurry oils.

In a further preferred embodiment, prior to the hydrotreatment step (<NUM>), the method further comprises a step of subjecting the hydrocarbon-containing initial feedstock to a solid removal treatment. The solid removal treatment may be carried out by any suitable means, which may, for example, be selected from the group consisting of filtration, centrifugal sedimentation, vacuum distillation, solvent extraction and any combination thereof.

According to the present application, the hydrotreating step (<NUM>) may be carried out using a hydrogenation reactor commonly used in the art, to which there is no particular limitation in the present application. For example, the hydrogenation reactor may be selected from the group consisting of fixed bed hydrogenation reactors, ebullated bed hydrogenation reactors, suspended bed hydrogenation reactors, moving bed hydrogenation reactors, and any combination thereof, preferably a fixed bed hydrogenation reactor.

According to the present application, the hydrotreating step (<NUM>) may be carried out using any hydrogenation catalyst commonly used in the art, to which there is no particular limitation in the present application. For example, the hydrogenation catalyst may be an existing heavy oil hydrotreating catalyst, of which the carrier is typically an inorganic oxide such as alumina, and the active component is an oxide of a metal of Group VIB and/or Group VIII, such as oxides of Mo, W, Co, Ni and the like. The hydrogenation catalyst may also be existing commercially available catalysts, such as the FZC series hydrogenation catalysts developed by Fushun Research Institute of Petroleum and Petrochemicals.

In a further preferred embodiment, the reaction conditions of the hydrotreating step (<NUM>) include: a reaction temperature of about <NUM>-<NUM>, preferably about <NUM>-<NUM>, a reaction pressure of about <NUM>-20MPa, preferably about <NUM>-10MPa, a hydrogen-to-oil volume ratio of about <NUM>-<NUM>, preferably about <NUM>-<NUM>, and a liquid hourly space velocity of about <NUM>-<NUM>-<NUM>, preferably about <NUM>-<NUM>-<NUM>.

In a preferred embodiment, the temperature of the heated hydrocarbon-containing feedstock of step (<NUM>) (i.e., the outlet temperature of the furnace) is from about <NUM> to about <NUM>, preferably from about <NUM> to about <NUM>, and the temperature raising rate of the hydrocarbon-containing feedstock (i.e., the heating rate of the furnace) is from about <NUM>/h to about <NUM>/h, preferably from about <NUM>/h to about <NUM>/h; the pressure at the top of the coke tower is about <NUM>-<NUM> MPa, preferably about <NUM>-<NUM> MPa, and the coke tower can be operated at constant pressure or variable pressure, and if operated at a variable pressure, the change rate of the pressure is about <NUM>-<NUM> MPa/h; the reaction period is about <NUM> to about <NUM>, preferably about <NUM> to about <NUM>.

In a preferred embodiment, the overhead light fraction of the pressure stabilization tower in step (<NUM>) comprises non-condensable gas and distillate oil, the <NUM>% distillate temperature of the distillate oil is controlled to be in a range of from about <NUM> to about <NUM>, preferably from about <NUM> to about <NUM>, and more preferably from about <NUM> to about <NUM>. The <NUM>% distillate temperature of the distillate oil in the overhead light fraction of the pressure stabilization tower may be a fixed value or fluctuate within a certain range.

In a preferred embodiment, the liquid level of the pressure stabilization tower in step (<NUM>) is controlled to be about <NUM>% to about <NUM>% of the total height of the tower.

In a preferred embodiment, the first stream of bottom oil in step (<NUM>) is returned to the middle of the pressure stabilization tower after being subjected to a temperature adjustment, e.g., heat exchanged with a heat exchange medium (typically a cooling medium). Preferably, the mass ratio of the first stream of bottom oil to the feed of the coke tower is from about <NUM> to about <NUM>, preferably from about <NUM> to about <NUM>; and/or the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is controlled to be about <NUM>-<NUM>, preferably about <NUM>-<NUM>.

In a preferred embodiment, the heat exchange medium may be cold oil, such as the hydrocarbon-containing initial feedstock, and the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is controlled by adjusting the flow rate of the heat exchange medium. For example, when a cooling medium is used, increasing the flow rate of the cooling medium can lower the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower, and conversely, decreasing the flow rate of the cooling medium can raise the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower.

In a preferred embodiment, the <NUM>% distillate temperature of the distillate oil in the overhead light fraction of the pressure stabilization tower is regulated by adjusting the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower. Specifically, when the <NUM>% distillate temperature of the distillate oil is increased to <NUM> or higher, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is lowered (for example, by increasing the flow rate of the cooling medium), so that the temperature of the evaporation section of the pressure stabilization tower is reduced, and in turn the <NUM>% distillate temperature of the distillate oil is reduced; when the <NUM>% distillate temperature of the distillate oil is reduced to <NUM> or lower, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is raised (for example, by reducing the flow of the cooling medium), so that the temperature of the evaporation section of the pressure stabilization tower is increased, and in turn the <NUM>% distillate temperature of the distillate oil is increased.

In a preferred embodiment, the liquid level of the pressure stabilization tower is regulated by adjusting the discharge rate of the bottom oil from the pressure stabilization tower and/or the recycle rate of the first stream of bottom oil. Specifically, when the liquid level of the pressure stabilization tower is increased to <NUM>% or more of the total height of the tower, the discharge rate of the bottom oil from the pressure stabilization tower is raised, and/or the recycle rate of the first stream of bottom oil is lowered, so as to decrease the liquid level of the pressure stabilization tower; when the liquid level of the pressure stabilization tower is reduced to <NUM>% or less of the total height of the tower, the discharge rate of the bottom oil from the pressure stabilization tower is lowered, and/or the recycle rate of the first stream of bottom oil is raised, so as to increase the liquid level of the pressure stabilization tower.

In a further preferred embodiment, the temperature and flow rate at which the first stream of bottom oil is returned to the pressure stabilization tower are controlled to simultaneously regulate the <NUM>% distillate temperature of the distillate oil in the overhead light fraction and the liquid level of the pressure stabilization tower.

In a particularly preferred embodiment, when the liquid level of the pressure stabilization tower is increased to <NUM>% or more of the total height of the tower and the <NUM>% distillate temperature of the distillate oil is increased to <NUM> or higher, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is lowered and the discharge rate of bottom oil from the pressure stabilization tower is raised; when the liquid level at the bottom of the pressure stabilization tower is increased to <NUM>% or more of the total height of the tower and the <NUM>% distillate temperature of the distillate oil is decreased to <NUM> or lower, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower and the discharge rate of the bottom oil from the pressure stabilization tower are raised; when the liquid level at the bottom of the pressure stabilization tower is decreased to <NUM>% or less of the total height of the tower and the <NUM>% distillate temperature of the distillate oil is increased to <NUM> or higher, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower and the discharge rate of the bottom oil from the pressure stabilization tower are lowered; or when the liquid level at the bottom of the pressure stabilization tower is decreased to <NUM>% or less of the total height of the tower and the <NUM>% distillate temperature of the distillate oil is decreased to <NUM> or lower, the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower is raised, and the discharge rate of the bottom oil from the pressure stabilization tower is lowered.

In a preferred embodiment, the liquid level of the buffer tank is controlled at about <NUM>-<NUM>% of the total height of the tank in step (<NUM>).

In a preferred embodiment, the flow rate of the second stream of bottom oil in step (<NUM>) is controlled according to the liquid level of the buffer tank. Particularly, the flow rate of the second stream of bottom oil is lowered when the liquid level of the buffer tank is lower than <NUM>%, and the flow rate of the second stream of bottom oil is raised when the liquid level of the buffer tank is higher than <NUM>%.

In a preferred embodiment, the temperature at which the second stream of bottom oil enters the coking fractionation tower in step (<NUM>) is controlled to be from about <NUM> to about <NUM>, preferably from about <NUM> to about <NUM>.

In a further preferred embodiment, the temperature at which the second bottom oil enters the coking fractionation tower in step (<NUM>) can be regulated by heat exchange with the oil gas obtained in step (<NUM>), heating with a furnace, or a combination thereof.

In a preferred embodiment, the <NUM>% distillate temperature of the light oil separated by the coking fractionation tower in step (<NUM>) is controlled to be in a range of about <NUM> to about <NUM>, preferably in a range of about <NUM> to about <NUM>.

In a preferred embodiment, the light oil separated from the coking fractionation tower in step (<NUM>) may be partially recycled to the pressure stabilization tower to regulate the pressure at the top of the pressure stabilization tower and the pressure at the top of the coke tower to maintain them at the set value.

In a preferred embodiment, the heavy oil separated by the coking fractionation tower in step (<NUM>) has a <NUM>% distillate temperature that is at least about <NUM> higher than the <NUM>% distillate temperature of the light oil.

In a preferred embodiment, the heavy oil separated by the coking fractionator in step (<NUM>) may be directly recycled to the coke tower, or may be subjected to a solid removal treatment and then recycled to the coke tower, preferably the latter. The solid removal treatment may be carried out by any suitable means, which may, for example, be selected from the group consisting of filtration, centrifugal sedimentation or any combination thereof, preferably filtration.

In a third aspect (not according to the presently claimed invention), the present application provides a method for improving the stability of a needle coke production process, comprising the steps of:.

In a preferred embodiment, the step i) is carried out according to the method for producing needle coke according to the second aspect of the present application, the specific operation of which is omitted herein.

In a preferred embodiment, the step ii) is carried out by regulating the discharge rate of the light fraction from the top of the pressure stabilization tower, for example by adjusting the opening of a valve on the light fraction discharge pipeline.

In a preferred embodiment, the step iii) is carried out in the following manner: when the <NUM>% distillate temperature of the distillate oil is increased to <NUM> or higher, lowering the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower (for example, by increasing the flow rate of a cooling medium), thereby reducing the <NUM>% distillate temperature of the distillate oil; when the <NUM>% distillate temperature of the distillate oil is decreased to <NUM> or lower, raising the temperature at which the first stream of bottom oil is returned to the pressure stabilization tower (for example, by reducing the flow rate of the cooling medium), thereby increasing the <NUM>% distillate temperature of the distillate oil.

In a preferred embodiment, the step iv) is carried out in the following manner: when the liquid level of the pressure stabilization tower is increased to <NUM>% or more of the total height of the tower, raising the discharge rate of the bottom oil from the pressure stabilization tower and/or lowering the recycle rate of the first stream of bottom oil, thereby reducing the liquid level of the pressure stabilization tower; when the liquid level of the pressure stabilization tower is decreased to <NUM>% or less of the total height of the tower, lowering the discharge rate of the bottom oil from the pressure stabilization tower and/or raising the recycle rate of the first stream of bottom oil, thereby increasing the liquid level of the pressure stabilization tower.

As shown in <FIG>, in a preferred embodiment, the system for producing needle coke of the present application comprises a hydrogenation reactor <NUM>, a furnace <NUM>, coke towers 6A/B, a pressure stabilization tower <NUM>, a buffer tank <NUM>, a coking fractionation tower <NUM>, a filter <NUM>, a heat exchanger <NUM>, and a furnace <NUM>. Coke towers 6A/B are provided with a feedstock inlet and an oil gas outlet; the pressure stabilization tower <NUM> is provided with an oil gas inlet, an overhead light fraction outlet, a bottom oil outlet and a cycle oil inlet, and a pressure controller <NUM> is provided at the top of the pressure stabilization tower (for example, on an overhead light fraction discharge pipeline <NUM>) for regulating the pressure at the top thereof; the buffer tank <NUM> is provided with an inlet, a first bottom oil outlet and a second bottom oil outlet; and the coking fractionation tower <NUM> is provided with an inlet, a light oil outlet and a heavy oil outlet. The oil gas outlet of the coke towers 6A/B is in communication with the oil gas inlet of the pressure stabilization tower <NUM> through a pipeline <NUM>, and no pressure controller for adjusting the pressure at the top of the coke towers 6A/B is provided in the coke tower or on the oil gas pipeline <NUM> connecting the coke tower to the pressure stabilization tower. The bottom oil outlet of the pressure stabilization tower is in communication with the inlet of the buffer tank <NUM> through a pipeline <NUM>, the first bottom oil outlet of the buffer tank <NUM> is in communication with the cycle oil inlet of the pressure stabilization tower <NUM> through a pipeline <NUM>, a temperature adjuster (such as a heat exchanger <NUM>) is provided on the pipeline <NUM>, and the second bottom oil outlet of the buffer tank is in communication with the inlet of the coking fractionation tower <NUM> through pipelines <NUM> and <NUM>, and the heavy oil outlet of the coking fractionation tower <NUM> is in communication with the feedstock inlet of the coke towers 6A/B through pipelines <NUM>, <NUM> and <NUM>.

In a preferred embodiment of the method for producing needle coke of the present application, as shown in <FIG>, a hydrocarbon-containing initial feedstock <NUM> having been subjected to a solid removal treatment is mixed with hydrogen gas <NUM> and then fed to a hydrogenation reactor <NUM>, where the mixture is contacted with a hydrogenation catalyst for reaction, and the resulting refined oil is fed via a pipeline <NUM> to a delayed coking furnace <NUM>, heated therein to a certain temperature, and fed via a pipeline <NUM> to the coke towers 6A/B. Coke produced in the coke towers 6A/B deposits on the bottom of the towers and the oil gas produced is passed to the pressure stabilization tower <NUM> through a pipeline <NUM>. Light fraction separated by the pressure stabilization tower <NUM> is discharged from the top of the tower through a pipeline <NUM>, and the bottom oil is sent to the buffer tank <NUM> through a pipeline <NUM>. The bottom oil in the buffer tank <NUM> is discharged in two streams, one stream is sent to the heat exchanger <NUM>, and after heat exchange therein, the stream is recycled to the pressure stabilization tower <NUM> through a pipeline <NUM>, and contacted with the coking oil gas from a pipeline <NUM> in the pressure stabilization tower to conduct mass transfer and heat transfer; the other stream is sent via a pipeline <NUM> to the furnace <NUM>, where it is heated to a certain temperature and then sent via a pipeline <NUM> to a coking fractionation tower <NUM>. The second stream of bottom oil is separated in the coking fractionation tower <NUM> to produce a light oil and a heavy oil, wherein the light oil is discharged through a pipeline <NUM>, and the heavy oil is sent to the filter <NUM> through a pipeline <NUM>, to remove solid particles such as coke breeze therein, and then mixed with the refined oil from the pipeline <NUM> through a pipeline <NUM>, and sent to the furnace <NUM>. The pressure at the top of the pressure stabilization tower is regulated by the pressure controller <NUM> at the top thereof, so that the pressure at the top of the coke tower is maintained at a set value.

The present application will be further illustrated with reference to the following examples, but the present application is not limited thereto.

The hydrocarbon-containing initial feedstock used in the following examples and comparative examples was a catalytic cracking slurry oil that had been subjected to a solid removal treatment, the properties of which are shown in Table <NUM>.

An experiment was carried out in accordance with the process flow shown in <FIG>, in which a catalytic cracking slurry oil had been subjected to a solid removal treatment was mixed with hydrogen and fed into a hydrogenation reactor. A hydrogenation catalyst with a trade name of FZC-<NUM> (commercially available, developed by Fushun Research Institute of Petroleum and Petrochemicals) was used, and the hydrogenation conditions included: a reaction temperature of <NUM>, a reaction pressure of 8MPa, a hydrogen-to-oil volume ratio of <NUM>, and a liquid hourly space velocity of <NUM>-<NUM>. The resulting hydrofined oil was sent to a delayed coking reaction unit (comprising a furnace and a coke tower), the outlet temperature of the furnace was <NUM>-<NUM>, the coke tower was operated at a variable pressure, the initial pressure at the top of the tower was <NUM> MPa, when the feeding time reached <NUM>% of the reaction period, the pressure at the top of the tower was reduced to <NUM> MPa at a rate of <NUM> MPa/h, and the reaction period was <NUM>; the coking oil gas generated by the reaction was sent to a pressure stabilization tower, a light fraction was discharged from the top of the pressure stabilization tower, in which the distillate oil had a <NUM>% distillate temperature of <NUM>, and a bottom oil was discharged from the bottom of the tower to a buffer tank. The bottom oil withdrawn from the buffer tank was split into two streams, the first stream was adjusted to a temperature of <NUM> and then recycled to the middle of the pressure stabilization tower, and the second stream was sent to a coking fractionation tower, and separated therein into a light oil and a heavy oil, wherein the light oil had a <NUM>% distillate temperature of <NUM>, the heavy oil had a <NUM>% distillation temperature of <NUM>, and the heavy oil was returned to the delayed coking reaction unit after being filtered for solid removal. The <NUM>% distillate temperature of the feed to the coking fractionation tower was plotted as a function of reaction time as shown in <FIG>. The load of the coking fractionation tower over the reaction period is shown in <FIG>.

An experiment was carried out as described in Example <NUM>, except that the coke tower was operated at a constant pressure of <NUM> MPa. The load of the coking fractionation tower over the reaction period is shown in <FIG>.

A prior art method was employed to produce needle coke, in which no pressure stabilization tower or buffer tank was provided, and the oil gas generated by coking reaction was directly sent to a coking fractionation tower. The catalytic cracking slurry oil had been subjected to a solid removal treatment was mixed with hydrogen, and fed into a hydrogenation reactor. The hydrogenation catalyst with a trade name of FZC-<NUM> was used, and the hydrogenation conditions included: a reaction temperature of <NUM>, a reaction pressure of 8MPa, a hydrogen-to-oil volume ratio of <NUM>, and a liquid hourly space velocity of <NUM>-<NUM>; the resulting hydrofined oil was sent to a delayed coking reaction unit, the outlet temperature of the furnace was <NUM>-<NUM>, the coke tower was operated at a variable pressure, the initial pressure at the top of the tower was <NUM>. 0MPa, when the feeding time reached <NUM>% of the reaction period, the pressure at the top of the tower was reduced to <NUM> MPa at a rate of <NUM>. 4MPa/h, and the reaction period was <NUM>; the coking oil gas generated by the reaction was sent to a coking fractionation tower, and separated into a light oil and a heavy oil. The <NUM>% distillate temperature of the light oil fluctuated between <NUM> and <NUM>, the <NUM>% distillation temperature of the heavy oil was <NUM>-<NUM>, and the heavy oil was returned to the delayed coking reaction unit after being filtered for solid removal. The <NUM>% distillate temperature of the liquid in the feed to the coking fractionation tower was plotted as a function of reaction time as shown in <FIG>. The load of the coking fractionation tower over the reaction period was shown in <FIG>.

An experiment was carried out as described in Comparative Example <NUM>, except that the coke tower was operated at a constant pressure of <NUM> MPa. The load of the coking fractionation tower over the reaction period was shown in <FIG>.

As shown in <FIG>, in Example <NUM>, the fluctuation range of the <NUM>% distillate temperature of the liquid material fed to the coking fractionation tower is about <NUM>; in Comparative Example <NUM>, the fluctuation range of the <NUM>% distillate temperature of the liquid material fed to the coking fractionation tower is about <NUM>. The above comparison shows that the composition of the feed to the coking fractionation tower is relatively stable in Example <NUM>, whereas the fluctuation range is larger in Comparative Example <NUM>.

As shown in <FIG>, the feed rate of the coking fractionation tower changes as the reaction proceeds, i.e., the load of the coking fractionation tower changes continuously. As shown in <FIG>, the coking fractionation tower of Example <NUM> has a peak load that is <NUM> times the starting load. As shown in <FIG>, the coking fractionation tower of Example <NUM> has a peak load of <NUM> times the starting load. In contrast, as shown in <FIG>, the coking fractionation tower of Comparative Example <NUM> has a peak load of <NUM> times the starting load; as shown in <FIG>, the coking fractionation tower of Comparative Example <NUM> has a peak load of <NUM> times the starting load. The above comparison shows that the fluctuation in the load of the coking fractionation column of Comparative Examples <NUM>-<NUM> is significantly larger than that of Examples <NUM>-<NUM>.

The present application is illustrated in detail hereinabove with reference to preferred embodiments, but is not intended to be limited to those embodiments. Various modifications may be made following the inventive concept of the present application, and these modifications shall be within the scope of the present application.

Claim 1:
A system for producing needle coke, comprising:
a coke tower provided with a feedstock inlet and an oil gas outlet, where a hydrocarbon-containing feedstock is reacted to produce needle coke and oil gas;
a pressure stabilization tower provided with an oil gas inlet, an overhead light fraction outlet, a bottom oil outlet and a cycle oil inlet, where the oil gas from the coke tower is received and separated into an overhead light fraction and a bottom oil, and a pressure controller is provided at the top of the pressure stabilization tower for adjusting the pressure at the top thereof;
a buffer tank provided with an inlet, a first bottom oil outlet, and a second bottom oil outlet, for receiving the bottom oil from the pressure stabilization tower and providing a buffering action; and
a coking fractionation tower provided with an inlet, a light oil outlet and a heavy oil outlet, where the bottom oil from the buffer tank is received and separated into a light oil and a heavy oil;
wherein the oil gas outlet of the coke tower is in communication with the oil gas inlet of the pressure stabilization tower through a pipeline, and no pressure controller for adjusting the pressure at the top of the coke tower is provided in the coke tower or on the oil gas pipeline connecting the coke tower to the pressure stabilization tower,
the inlet of the buffer tank is in communication with the bottom oil outlet of the pressure stabilization tower, the first bottom oil outlet of the buffer tank is in communication with the cycle oil inlet of the pressure stabilization tower through a pipeline with a temperature adjuster provided thereon, and the second bottom oil outlet of the buffer tank is in communication with the inlet of the coking fractionation tower, and
optionally, the heavy oil outlet of the coking fractionation tower is in communication with the feedstock inlet of the coke tower.