JPH0689335B2 - Day-decoding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a delayed coking method, and more particularly to a method for improving a production yield in a delayed coking operation.

Delayed coking has been in place for many years. This process broadly involves the pyrolysis of heavy liquid hydrocarbons to produce gases, liquid streams of varying boiling ranges and coke.

Coking of resids from heavy sour (sulfur-rich) crudes is performed primarily as a means of treating low value resids by converting some of the resids into more valuable liquid and gas products. It The coke obtained is generally processed as a low value by-product.

When producing fuel grade delayed coke, and to some extent anode or aluminum grade delayed coke, liquids are more valuable than coke, thus minimizing coke yield and maximizing liquid recovery. Is desirable. It is also desirable to produce coke having a volatile content of about 15 weight percent, preferably 6 to 12 weight percent. The increasing use of heavy crude oils with high metal and sulfur content in many refineries has increased the importance of delayed coking operations to refiners. There is growing interest in minimizing air pollution, which is yet another incentive for treating residual oil in delayed coking equipment. This is because the delayed coking equipment produces gases and liquids containing sulfur in a form that is relatively easy to remove.

[Conventional technology and problems]

In the basic delayed coking process practiced today, the feedstock is fed to the bottom of the coking rectification column and the bottom of the rectification column containing heavy recycle and feedstock is heated to the coking temperature in a coking oven. Be heated. Subsequently, the heated feedstock oil reaches the coke drum maintained at the temperature and pressure of the coking conditions. There the feedstock is cracked or cracked into coke and volatile components. Volatile components are recovered as coking vapor and returned to the rectification column. Heavy gas oil from the rectification column is added to the flash zone of the rectification column to condense the heaviest components from the coking vapor. The heaviest fraction of coke drum vapor could be condensed by other techniques such as heat exchange. However, in commercial-scale operation, it is common to contact the incoming steam with heavy gas oil in a coking rectification column.
Conventional heavy recycles consist of condensed coke drum steam and unflashed heavy gas oil. When the coke drum is filled with coke, the raw material is switched to another drum,
The filled drum is then cooled and emptied by conventional means.

The method of delayed coking is described in "Delayed Coki" by Kash et al.
ng "(The Oil and Gas Journal; January 2, 1956, 89-90)
Page). A delayed coking process for coal tar pitch exemplifying the use of heavy recycle is shown in U.S. Pat. No. 3,563,884.

A delayed coking process for coal extracts using a separate surge tank for feedstock to a coking furnace is shown in US Pat. No. 3,379,638.

A method for producing soft synthetic coal having a volatile matter content of 20 weight percent or more is described in US Pat. No. 4,036,736.
In this method diluent gas is added to the coking drum to maintain a reduced cracked hydrocarbon partial pressure.
Alternatively, the method is carried out under subatmospheric pressure.

The description of the early delayed coking method was written by Armistead in "T
he Coking of Hydrocarbon Oils "(The Oid and Gas J
ournal, March 16, 1946, pp. 103-111).

U.S. Pat. No. 4,216,074 describes a dual coking process for coal liquefaction products. According to this, the condensed liquid and unflashed heavy gas oil from the coke vapor stream are:
Used as a recirculating liquid to the coking oven.

U.S. Pat.No. 4,177,133 describes a coking process in which heavier material from a coke drum vapor line is mixed with fresh coking feedstock fed as a recycle and subsequently passed through a coke drum. .

There are many more references, such as U.S. Pat.
No. 380,713, No. 3,116,231 and No. 3,472,761 which disclose variations and modifications of the basic delayed coking method.

U.S. Pat.No. 4,455,219 describes a delayed coking process in which a diluent hydrocarbon having a boiling range lower than that of the heavy recycle is used in the delayed coking process. It is replaced as part of the heavy recycle normally mixed with the feed.

A conventional delayed coking method is shown in FIG. In that process, new caulking feedstock coming in from line 10 is preheated in heat exchanger 12, followed by coking rectification column.
Supply to the bottom of 14. Heavy coking gas oil from draw pan 16 is pumped out and passed through heat exchanger 12 and steam generator 18. Part of the heavy coking gas oil from the steam generator 18 is recovered as a product via line 20, and part of it is recovered on line.
Via 21 it leads to the steam outlet of the coke drum 32 which is used to cool the coke drum steam, part of it is returned via line 22 to the spray nozzle 24 in the flash zone of the rectification column 14 and the rest inside Return to the rectification column via line 23 as reflux. In many rectification towers, a "shed deck" is often used to bring the gas oil into contact with the incoming steam.
deck) ”is used instead of the spray nozzle. A tray or other means may be used for this purpose. Heavy gas oil added to the shed deck or tray acts as a spray oil. Line 26
The coke drum vapor from the effluent enters the flash zone of the rectification column below the spray nozzle where the heaviest component of the incoming vapor is condensed by contact with the heavy cokekin gas oil from the spray nozzle 24. The condensed substance is
It falls to the bottom of the flash zone where it mixes with the new incoming feedstock. Any heavy coking gas oil from the spray nozzle 24 that is not vaporized in the flash zone mixes with fresh feed oil at the bottom of the flash zone.

Fresh mixed feed oil, condensed steam and unflashed heavy gas oil are drawn in via line 28 and pumped to a coking oven 30 where it is heated to the coking temperature and subsequently passed through one of the coking drums 32. . Conventional 1
One coke drum is full, the other is cooled and emptied, and when the full drum is full of coke, the heated feed is switched to an empty drum. Steam from either drum 32 enters the rectification column 14 through steam line 26. A small amount of heavy coking gas oil from line 21 is added to a steam exiting drum 32 to cool the steam in line 26 and to prevent coke deposits.

Lighter material from line 26 rises in the rectification column and gas and naphtha exit line 34. Naphtha is condensed in a steam sump and is recovered via line 38. A portion of the naphtha can be perfused through line 40. Coking gas is recovered as a product from line 42. The intermediate coking distillate is removed via line 44, the vapor is recovered in stripper 46 and the distillate product is recovered from line 48.

In the design and operation of delayed coking equipment, the furnace is the most important part of the equipment. The furnace must be able to heat the feedstock to the coking temperature without forming coke on the furnace tube. If coke is deposited on the furnace tube, the operation must be stopped and the furnace cleaned. As a means of suppressing the deposition of coke, steam may be injected to increase the velocity in the furnace tube and cause turbulence. However, steam injection is not energy efficient and can adversely affect coke quality, so it is desirable to minimize it. Nevertheless, in the case of a failure of the furnace supply pump, a good caulking furnace can be used for steam injection into the furnace tube for months without interruption due to tube cleaning. It is important to keep You can design and function.

When producing fuel grade or anode grade coke, about 0.05 to about 0 for each volume of fresh coking feedstock.
It is conventional practice to recycle 7 parts of heavy recycled material. This recycled material improves the operation of the coking oven and also provides a solvent effect that helps prevent coke deposits in the furnace tubes. Conventional heavy recycle materials are, as noted above, a mixture of condensate obtained from the coke drum steam line and unflashed heavy coking gas oil. It may also contain small amounts of components with boiling points less than 399 ° C (750 ° F), but the boiling point of the mixture is usually about 399 ° C to 510 ° C (750 ° F to 950 ° F).
Range or higher. Condensed steam and unflashed heavy gas oil are mixed with new feedstock at the bottom of the coking rectification column. At least a minimal amount of material is produced. This minimum amount is about 0.05 parts recycle for each volume of fresh feed.

If the feedstock is of low quality, such as very low specific gravity residual oil, 0.3 to 0.7 parts of recycle for each volume of fresh feedstock is required to prevent coke formation in the furnace. Will be done. Increasing the recycle rate in this way affects the productivity of the coking unit and, more importantly, increases the yield of coke, measured as a percentage of new feedstock. Is not desirable. Higher coke yields due to higher recycle rates of heavy recycle materials used are the result of coke formation from the recycle material itself. This is undesirable because coke is at least the least valuable product from the coking operation.

The process described in U.S. Patent Application No. 464,181 uses light volatiles to minimize the heavy recycle materials used and to provide some of the diluent needed to prevent coke formation in the furnace tubes. It has been shown to be added to fresh feedstock. This process is shown in FIG. 1 where volatiles are drawn from line 48 and passed through line 50 where they are mixed with fresh feedstock before being preheated. This method recycles the recycled material to one part of new feedstock for proper furnace operation.
It is especially useful for feedstocks where 0.05 part is required.

[Means for solving problems]

According to this invention, the feedstock oil supplied to the coking furnace is
Unflushed heavy coking gas oil and free of condensate from coke drum vapors. The process is practiced by removing the unflashed heavy coking gas oil and condensate from the coke drum steam from the process rather than mixing them with fresh coking feedstock as is conventional.

Diluent hydrocarbons with boiling points lower than those of traditional heavy coking recycle materials and lower amounts of coke-forming components than heavy coking recycle materials will effectively form coke in the furnace tube. It is mixed with fresh oil in an amount sufficient to prevent it. The amount of diluent required will depend on feedstock quality, furnace temperature, furnace design and other factors.

Usually the coking feedstock is fed to the bottom of the coking rectification column where it is mixed with the unflashed heavy coking gas oil and condensed material from the coking vapor stream. The process described in the aforementioned U.S. Pat. No. 4,455,219 is directed to minimizing the amount of heavy recycle mixed with the novel feed. The present invention relates to the elimination of all heavy recycle from coking feedstocks.

The present invention is an improvement over the above prior art, in which heavy recycle materials are not used in producing fuel grade or anode grade coke. This will result in improved product yields and reduced coke yields,
The liquid yield is increased. As pointed out earlier, it is desirable to have as little coke as possible in the yield of product, as other products from the coking operation are more valuable than coke.

A preferred embodiment of this invention is shown in FIG. Where the first
Similar numbers are used for common items in the figure. The difference between the preferred embodiment of the present invention and the prior art is that even when a large amount of diluent is required to operate the furnace,
The elimination of all heavy recycled materials from the raw material.

To remove the heavy recycle material from the feedstock, fresh coking feedstock is sent to the feedstock surge drum instead of being sent to the bottom of the rectification column 14 as is done in the prior art method (Figure 1). There is a need. The fresh feed from the surge drum 60 is then passed directly through the coking oven 30 without the addition of heavy recycle. Instead of the heavy recycles normally used to prevent coke deposits in the furnace tube, the coking volatiles are provided in an amount sufficient to effectively prevent coke deposits in the furnace tube. Add to the new feedstock via line 50 before passing.

In the embodiment of the invention shown in FIG. 2, heavy gas oil is added to the flash zone of rectification column 14 to condense coke drum vapors and to scrub the material entering the flash zone from vapor line 26. . But the rectification tower
Condensed coke drum vapors from the bottom of 14 and unflashed heavy gas oil are removed from the process via line 64, but this does not affect overall coke recovery.
However, the prior art methods do have an effect. The material from the bottom of the rectification column 14 may be passed through a vacuum distillation apparatus, where the distillable portion is recovered as distillation column overhead vapor. Alternatively, the material may be hydrodesulfurized or used as a feed to another refining unit such as a fluid bed catalytic cracking unit.

In the most preferred embodiment of this invention, the heavy recycle material is replaced by distillation material from the coking rectification column.
The boiling range of this preferred distillation recycle material is lower than that of the heavy recycle material, and most preferably it is obtained from the distillation product line 48 and passed through the recycle line 50 to the line
At 10 new raw oil is mixed.

The distillation recycle or diluent of this invention may have a boiling range of about 168 ° C (335 ° F) to about 454 ° C (850 ° F), preferably about 232 ° C (450 ° F) to about 399 ° C (750 ° F). F), most preferably about 265 ° C (510 ° F) to about 343 ° C (650 ° F)
The hydrocarbonaceous substances of should be selected. Usually the diluent is from a coking rectification column, but in special cases diluents from other sources may be used.

The amount of diluent is the amount required for good furnace operation. The amount of this diluent is 0.7 per 1 volume of new feed oil for feed oil in which coke is very likely to be formed in the furnace tube.
You can add more. This amount also varies depending on the furnace design and the operating conditions of the furnace, and usually must be determined for each feedstock and each coking furnace. It is desirable that the amount of diluent be the minimum that can be operated without significant coke deposits in the furnace tube. Using more than the minimum amount that does not cause coke deposits in the furnace does not cause any particular difference, but it may affect operability and effect.

The feedstock used in the method of the present invention is suitably a conventional feedstock for delayed coking. Petroleum residual oil is the most common feedstock for heat grade or anode grade coke. Usually, the residual oil is a vacuum residual oil from a crude oil vacuum distillation apparatus, but an atmospheric residual oil from a crude oil atmospheric distillation apparatus may be used.
Coke may be produced from a feedstock oil other than petroleum residual oil. Such feedstocks include, but are not limited to, coal tar pitch, tar sand bitumen, pyrolysis tar, slurry oil or decant oil and shale oil from liquid bed cracking units. Mixtures of any of the above may also be used.

The coking operating conditions applicable to the process of this invention are those which yield a coke product having a volatile content of less than 15 weight percent, preferably 6 to 12 weight percent. As is known in the art, such conditions are as follows. Temperature at caulking furnace outlet is approx.
468 ° C (875 ° F) to about 510 ° C (950 ° F), preferably
496 ° C (925 ° F) to 499 ° C (930 ° F). The steam temperature at the coke drum outlet is 412 ° C (775 ° F) to 454 ° C (850 ° C)
° F), preferably about 446 ° C (835 ° F). And the caulking drum pressure is 353 to 5295 g weight / cm ² in gauge pressure, (5 to 5
75 psig) preferably about 1059 to 1412 g weight / cm ² (15 to ²⁰ p
sig).

Lowering the caulking drum pressure below atmospheric pressure is unacceptable for several reasons. The economics of this method decrease rapidly as the coking drum pressure approaches atmospheric pressure. Also, operating the coking drum below atmospheric pressure is very dangerous as oxygen (air) may leak into the drum containing hydrocarbons at a temperature of 482 ° C (900 ° F). Similarly, as noted in U.S. Pat.No. 4,036,736, discussed above, lowering the coking drum pressure to atmospheric pressure or subatmospheric pressure yields a product that has pitch properties rather than coke. It For example, all of the examples in this US patent are demonstrated at or below atmospheric pressure to produce a soft pitch type product having a volatile content of greater than 20 weight percent. The volatile content of the coke products obtained from this invention is less than 15 weight percent, preferably 6 to 12 weight percent.

To show the expected coke yield from mixing a conventional heavy recycle oil with a new coking feedstock,
The influence of coke yield on various fractions of heavy coking gas oil was determined. Coke was obtained from several boiling range fractions of heavy coking gas oil, and the coke yield in weight percent and the amount of each fraction were measured. The results are shown below.

As shown in Table 1, the coke yield expected from the heavy coking gas oil is remarkable. It is also clear that the majority of coke obtained from heavy gas oil comes from the highest boiling fraction. It is also very important to remove the heaviest condensable substances in the coking steam and the heaviest substances in the heavy coking gas oil that is sent from the feedstock to the coking furnace. Boiling point of commonly used heavy recycle material is about 16
By replacing the distilled hydrocarbon material at 8 ° C (335 ° F) to about 454 ° C (850 ° F), the coke yield, expressed as a percentage of the new feedstock, is significantly reduced, resulting in a more desirable liquid product. The yield of is increased.

It is difficult to obtain a clear separation in a coking rectification column, and heavy coking gas oils may contain small amounts of substances with boiling points as low as 288 ° C (550 ° F), while coking volatiles have 389 ° C. It may contain small amounts of substances with boiling points as high as (750 ° F), and in some cases may contain small amounts of substances with boiling points as high as 454 ° C (850 ° F). However, the amount of this high boiling material in the coking volatiles (such as from line 44 in FIG. 2) is very low and the effect of this low high boiling material on the total coke yield is not significant. On the other hand,
Condensed coke drum vapors and unflashed heavy coking gas oils are relatively high in the substance at 454 ° C (850 ° F) and significantly affect the total coke yield when they are mixed with the new feedstock of the prior art process. Exert.

The essence of this invention is the elimination of all material from the flash zone bottom of the coking rectification column from the coking furnace feedstock during the delayed coking operation. The operation is carried out under conditions that produce a fuel grade or anode grade delayed coke product having a volatile content of less than 15 weight percent. This is an amount effective to remove coke deposits in the coking furnace tube from the process, which is normally a material that is mixed with the new feedstock as recycle material, and instead has a boiling point range that is less than conventional heavy recycles. Completed by using a lower hydrocarbon diluent than that of the cycle.

Another way to explain is that the condensed coke drum vapor that falls to the bottom of the flash zone of the rectification column and the unflashed portion of the heavy gas oil that is added to the flash zone are collected and mixed as a recycle with fresh feedstock. Volatiles of low boiling hydrocarbons are used instead.

Examples This invention results in excellent product yields, which are shown in the following mimicry examples based on a successfully developed caulk design scheme. In this example, the same raw materials were used,
Two series of experiments were tried under the same conditions. However, the conventional heavy recycle material (20 parts by volume for each 100 parts by volume of feedstock) was used in one system as the recycle material, and the boiling range was used in another system.
Hydrocarbon distillate from 266 ° C (510 ° F) to 379 ° C (650 ° F) (20 parts by volume for each 100 parts by volume of feed oil) was used.

In both lines, Bachaq (559 ° C (1000 ° F))
uero) Vacuum distillation bottom oil (API degree, 4.3; Conradson carbon number, 23.5 weight percent; UOP characteristic coefficient K, 11.5; sulfur content, 3.5 weight percent), 1412 g weight / cm ² coke drum pressure and 446 ° C ( Coke was obtained at a coke drum top temperature of 835 ° F. The product distribution for the two lines is shown in the table below.

As can be seen in the above table, when volatile hydrocarbons with a boiling point range of 266 ° C (510 ° F) to 343 ° C (650 ° F) are used as the recycle instead of the conventional heavy coking recycle,
The yield decreased by 6% or more (34.66-32.53 / 32.53). Corresponding to this, about 5% with C ₅ + liquid (34.66-32.53 / 32.5
3) Yield increased. Different raw materials were used with the same or different coking conditions, but the coke yield was similarly reduced and the liquid yield was increased. The values shown here exclude substances that are normally used as recycled materials from the process.

[Brief description of drawings]

FIG. 1 showing the prior art is a schematic flow chart illustrating a conventional delayed coking method. FIG. 2 is a schematic flow chart illustrating a preferred embodiment of the method of the present invention. The foregoing description of the preferred embodiments of this invention has been attempted to illustrate rather than limit the invention, which is defined here by the appended claims.

Continuation of front page (56) References JP-A-58-194981 (JP, A) JP-A-60-35087 (JP, A)

Claims (9)

[Claims] 1. To perform delayed coking of a heavy hydrocarbon oil feedstock by a coking device equipped with a coking furnace, a coking drum and a coking rectification column to obtain a delayed coke, a cracked liquid and a gaseous hydrocarbon product. (A) a step of delay coking the heavy hydrocarbon oil in the coking drum under conditions such that a delayed coke having a volatile content of 15% by weight or less is produced, ) Introducing overhead vapor from the coking drum into the coking rectification column, (c) condensing the highest boiling fraction of the overhead vapor and removing this highest boiling fraction from the process, and (D) A hydrocarbon having a boiling point range lower than that of the highest boiling point fraction and serving as a diluent is added to the heavy hydrocarbon oil raw material, and the heavy carbonization is performed. Comprising heating a crude oil feedstock to a coking temperature in the coking oven, wherein the diluent hydrocarbon is added in an amount sufficient to effectively prevent coke deposition in the coking oven, Thereby, the yield of the delayed coke having a volatile matter content of less than 15% by weight is lower than the yield obtained when the highest boiling point fraction of the overhead vapor is mixed with the raw material, and the liquid yield is reduced. Delayed coking method characterized by high rate. 2. A process according to claim 1, wherein a delayed coke having a volatile content of 6 to 12% by weight is produced. 3. A patent in which the feedstock oil is first mixed with a diluent hydrocarbon and fed to a feedstock surge drum, followed by direct introduction into the caulking furnace without the addition of any other hydrocarbon substances. The method according to claim 1. 4. The boiling point range of the hydrocarbon of the diluent is about 23.
The method of claim 1 which is between 2 ° C (about 450 ° F) and about 399 ° C (about 750 ° F). 5. The boiling point range of the hydrocarbon of the diluent is about 26.
The process of claim 1 which is between 2 ° C (about 510 ° F) and about 343 ° C (about 650 ° F). 6. A process according to claim 1 wherein the diluent hydrocarbon is a side stream of product from the coking rectification column. 7. The raw material is selected from the group consisting of petroleum vacuum distillation residual oil, petroleum atmospheric residual oil, coal tar pitch, tar sand bitumen, slurry oil, decant oil, shale oil, pyrolysis tar and mixtures thereof. The method according to claim 6, which is provided. 8. The heavy gas oil from the coking rectification column comprises:
7. A process according to claim 6, wherein the process is returned to the flash zone of the rectification column and is contacted with the inflowing coking vapor to condense the highest boiling fraction of that vapor. 9. The method of claim 8 wherein the diluent hydrocarbon is only the material that has been mixed with the feedstock prior to feeding the feedstock to the coking oven.