KR920010280B1 - Process for improving product yields from delayed cooking - Google Patents

Abstract

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Description

Method of increasing product yield by delayed coking

1 is a schematic work flow diagram illustrating a conventional conventional delayed coking process.

2 is a schematic work flow diagram showing a preferred embodiment of the method according to the invention.

* Explanation of symbols for the main parts of the drawings

18: steam generator 30: coke oven

32: drum 60: feedstock surge tank

The present invention relates to a process for increasing the yield of a product in a delayed coking process, in particular in a delayed coking process.

Delayed coking has been practiced for many years, which pyrolyzes heavy hydrocarbons to produce gases, liquids of varying boiling ranges, and coke.

Coking of the residues from heavy crudes with high sulfur loadings is mainly done as a method of converting some of the residues into more useful liquid and gaseous products to treat residues with lower useful value. The coke produced is generally treated as a by-product of low useful value.

In the production of delayed coke for fuels, and also in the production of delayed coke for anodes or aluminum, it is desirable to minimize the yield of coke and maximize the yield of liquid because the liquid product is of higher value than the coke. It is also preferred to produce coke with a volatile content of 15% by weight or less, preferably in the range of 6 to 12% by weight.

In most refineries, the use of heavy crude oil with a high content of metals and sulfur is increasing, and the importance of delayed coking is also highly recognized. As coke ovens produce gases and liquids that are present in a form that sulfur can be removed relatively easily, there is a greater interest in minimizing air pollution to treat residual oil in delayed coke ovens.

In the basic delayed coking process to date, new feedstock is introduced into the bottom of the coke oven sorter and into the bottom of the classifier containing the recycle material, and then the new feedstock is heated in the coke oven to the coking temperature. . The heated feedstock is then sent to a coke drum maintained at the temperature and pressure of the coking conditions, where the feedstock decomposes to produce coke and volatile components. Volatile components are recovered as coke in steam and returned to the classifier. Heavy gas oil from the fractionator is added to the flash zone of the fractionator to condense the heaviest components from the coke oven steam. This can be done by conventional methods such as heat exchange, but in commercial conditions it is desirable to contact the inlet steam with heavy gas oil in the coke oven fractionator. Typical heavy recycle materials consist of condensed coke drum vapor and unflashed heavy gas oil. When the coke drum is filled with coke, the feedstock is switched to another drum to feed and the drum is cooled and then emptied in the usual manner.

The Delayed Coking Act, titled “Delayed Coking,” published by Kasch et al. On January 2, 1956, The Oil and Gas Journal, pp. 89-90. Described in the paper.

Coal tar pitch delayed coking is described using recycle material in US Pat. No. 3,563,884 to Bloomer et al. United States Patent No. 3,379,638 to Bloomer et al. Describes a delayed coking process of coal extracts using a separate surge tank to feed the feedstock to the coke oven.

Ozaki et al., U.S. Patent No. 4,036,736, describes a method for producing soft synthetic coal having a volatile content of 20% by weight or more, wherein diluent gas is added to a coke oven drum to maintain a reduced partial pressure of cracked hydrocarbons. Or under atmospheric pressure.

The initial delayed coking process was the "The Coking of Hydrocarbon Oils", written by Armistead, PP.103-111, March 16, 1946, "The Oil and Gas Journal." Intervened in

US Pat. No. 4,216,074, on the other hand, describes a binary coking process of coal liquefaction products, wherein the liquid condensed with the coke vapor and the unflashed heavy gas oil are used as recycled liquid to the locks.

In addition, US Pat. No. 4,177,133 describes a coking method for combining heavy material from a coke drum vapor as a recycled material into a fresh coke feedstock and then sending it to a coke drum.

US Patent Nos. 2,380,713, 3,116,231, and 3,472,761 describe modifications of the basic delayed coking technique. U.S. Patent Application No. 464,181 (filed Feb. 9, 1983; U.S. Patent No. 4,455,219) discloses that a hydrocarbon diluent having a boiling point lower than the boiling point of the heavy recycle material is usually combined with a new feedstock in a delayed coking process. A delayed coking technique is described that replaces a portion of.

In the present invention, there is essentially no condensed material from the gas of the unflashed coke oven and the vapor of the coke drum as a feedstock for the coke oven. This is commonly practiced and can be achieved by removing the in-flash coke oven heavy gas oil and condensed material and removing them in the process. A hydrocarbon diluent having a boiling point lower than that of the conventional coke oven recycle material and having a lower coke forming component than the coke oven recycle material is combined with a fresh feedstock in an amount sufficient to effectively prevent the formation of coke in the coke oven tube. The amount of diluent required will depend on feedstock properties, furnace temperature, furnace design and other factors.

Generally, coke oven feedstock is fed to the bottom of the coke oven sorter, where it is combined with the unflashed coke oven heavy gas oil and condensate from the coke oven steam. The aforementioned U.S. Patent Application No. 464,181 describes a method for minimizing the amount of heavy recycled materials combined with new feedstocks. In this regard, the present invention seeks to completely remove heavy recycle material from the coke oven feedstock.

It is an object of the present invention to increase the yield of the product from the delayed coking process and also to eliminate the increase in gas oil and condensed coke oven in the unflashed coke oven in the feedstock fed to the coke oven. It is also an object of the present invention to replace, as part of the coke oven feedstock, a heavy recycle material with a relatively high coke forming component with a hydrocarbon diluent, which is a low boiling distillate with a low coke forming component.

A conventional delay coke and method is illustrated in FIG. However, in the conventional method, the new coke oven feedstock supplied through the line 10 is preheated using the heat exchanger 12 and then supplied to the lower portion of the coke oven sorter 14. Then, the gas oil in the coke oven from the draw pan 16 is pumped to the heat exchanger 12 and the steam generator 18. A portion of the gas oil in the coke oven from the steam generator 18 is then recovered as product via line 20 and the other part is sent via line 12 to the steam outlet of the coke drum 32 and another part. In the flash zone of the classifier 14 via line 22 which is returned to the spray nozzle 24 and the remainder is returned to the classifier via line 23 as internal reflux. In most coke oven sorters, however, a series of baffles called "shed decks" are used instead of spray nozzles to contact gas oil and inlet steam. Trays or other utensils may also be used for this purpose. Heavy gas oil applied to the shed deck or tray serves as spray oil here. The coke drum steam coming out of line 26 enters the flash zone of the fractionator 14 below the spray nozzle 24, with heavier components contained in the incoming steam being discharged from the spray nozzle 24. It condenses in contact with gas oil. The condensed material falls to the bottom of the flash zone, where they combine with the incoming new feedstock. Coke oven gas from the spray nozzle 24 and not vaporized in the flash zone is also combined with fresh feedstock at the bottom of the flash zone.

Combined fresh feedstock, condensed vapor and unflashed heavy gas oil are withdrawn via line 28 and pumped to coke oven 30 where they are heated to coking temperature and then sent to one of the coke drums 32. . Typically, one coke drum is filled while the other coke drum is cooled and emptied. When the drum to be filled is filled with coke, the heated feedstock is supplied to the empty drum. The steam from one drum 32 is sent to the fractionator 14 via steam line 26. A small amount of coke oven gas exiting line 21 is combined with steam exiting drum 32 to quench these vapors and also prevent coke from adhering to line 26.

Lighter material exiting line 26 rises up through sorter 14 and gas and naphtha exit through line 34. Naphtha, on the other hand, is cooled in receiver 36 and recovered via line 38. Part of the naphtha can also be refluxed back through line 40. The coke oven gas is then recovered as product via line 42. Distillate as intermediate product is recovered via line 44, steam sprinkled in stripper 46 and then through distillate product line 48.

In the design and operation of delayed coke furnaces, the coke furnace is the most important part of the apparatus, but the coke furnace must be able to raise the feedstock to the coking temperature without forming coke on the furnace tube. If the coke is coked, the operation must be stopped and the inside of the furnace clean. In some cases, steam is spouted into the tube with coke to increase turbulence and delay turbulence. However, it is desirable to minimize the vapor ejection because it is not effective and may adversely affect the quality of the coke. However, if the coke oven feed pump fails, the degree of vapor ejection should be such that the coke oven tube can be maintained in a steady state. The fully designed coke furnace can be operated for months without interrupting the operation to clean the tube.

In the production of coke for fuel or anode, it is common to recycle the fresh coke with a volume of recycled material of about 0.05 to about 0.7 per feedstock volume. This recycle material improves the operability to the coke oven and provides a solvent effect to prevent the coke from adhering to the coke oven tube. As mentioned above, a typical heavy recycle material is a combination of condensed material from a coke drum steam line and unflashed coke oven heavy gas oil, although a small amount of boiling point below 750 ° F. may be present in its boiling range. Is generally about 750-950 ° F or more. As described above, the operation of the coke oven where condensed vapor and unflashed heavy gas oil is combined with fresh feedstock at the bottom of the coke oven essentially results in at least a minimum amount of intermediate circulation material combined with the new feedstock. This minimum amount is about 0.05 volume of recycle material per fresh feed volume.

In the case of low quality feedstocks such as resids having very low weights, it is necessary to bring the volume of recycled material to about 0.3 to 0.7 per volume of fresh feedstock in order to prevent coke formation in the coke oven. However, it is not desirable to make the above recycled material ratio higher because it not only affects the production capacity of the coke furnace, but more importantly, increases the yield of coke, measured as a percentage of new feedstock. to be. The increase in the coke yield shown by increasing the recycle ratio of heavy recycle material is the result of the formation of coke in the recycle material itself. This is undesirable because coke is a product of little value in the coking process.

U.S. Patent No. 4,453,219, above, describes an improved method for minimizing the amount of recycle of the distillation used, and adding a distillate to the new feed to act as a diluent necessary to prevent coking in the coke oven tube. . This method is shown in FIG. 1, where the distillate from line 48 is combined with fresh feedstock via line 50 before preheating. This method is particularly useful when the coke oven feedstock requires at least about 0.05 volume of recycled material per fresh feedstock volume for proper operation of the coke oven.

The present invention improves the conventional method in the manufacture of fuel or anode coke, by completely eliminating the use of heavy recycle material, the yield of coke is reduced and the yield of liquid fraction is increased, resulting in increased product yield. will be. As described above, the good products of the present invention contain the minimum possible amount of coke because other products resulting from the coking operation are more valuable than coke.

A preferred embodiment of the present invention is shown in FIG. 2, with the same reference numerals being used as in FIG. The main difference between the preferred embodiment of the present invention and the prior art lies in the complete exclusion of heavy recycle material from the feedstock even when a substantial amount of diluent is required for the operation.

The removal of this recycled material is such that the fresh coke oven feedstock is fed to the feedstock surge drum instead of to the bottom of the classifier 14 as carried out in the conventional method (see FIG. 1). Can be achieved. The new feedstock from surge drum 60 is sent directly to coke oven 30 without adding any heavy recycle material thereto. In order to prevent the coke from adhering to the coke oven tube, instead of the recirculating material which is generally used, a sufficient amount of coke distillate is used to effectively prevent the coke from adhering to the furnace tube before being sent to the coke oven. 50) is applied to the new feedstock.

In the embodiment of the invention illustrated in FIG. 2, heavy gas oil is added to the flash zone of the fractionator 14 to cool the heavy coke drum vapor and to clean the material entering the flash zone from the steam line 26. However, the cooled coke drum steam and the unflashed heavy gas oil from the bottom of the fractionator 14 are removed in-process via line 64, which does not affect the coke yield as in conventional methods. The material from the bottom of the fractionator 14 can be sent to a vacuum distillation unit where the distillable portion of the material can be recovered as overhead, subjected to hydrodesulfurization or other purification apparatus such as fluidized bed catalytic cracking unit. Can be used as feedstock.

In a preferred embodiment of the present invention, the heavy recycle material is replaced by distillate from the coke oven sorter. This good distillate recycle material has a lower boiling point range than the medium recycle material and combines distillate from distillate product line 48 with fresh feedstock entering line 10 via distillate recycle line 50. Most preferably taken.

The distillate recycle material or diluent according to the invention should be a hydrocarbon material having a boiling point range of 335 to 850 ° F, preferably 450 to 750 ° F, most preferably 510 to 650 ° F. Generally, diluents come from the coke oven sorter, but those from elsewhere may be used in special cases.

The amount of diluent required is sufficient to facilitate the operation with coke. This amount is about 0.7 volume per volume of fresh feedstock, which is very likely to form coke on the tube with coke. In addition, this amount should generally be determined for feedstock and coke oven, according to the design and operating conditions of the coke oven. The preferred amount of diluent is the minimum amount that can be manipulated without coke formation on the tube with coke. The use of more than this minimum amount is not particularly bad, but can adversely affect the work capacity and efficiency.

Suitable feedstocks in the process of the present invention also include conventional delayed coking feedstocks. The most common feedstock for fuel grade or bipolar coke is petroleum residue heavy oil. These resid heavy oils are usually resid heavy oils from crude oil vacuum distillation units, but sometimes use resids from crude oil atmospheric distillation units. In some cases, feedstocks other than petroleum residue heavy oil are coked. Such feedstocks include, but are not limited to, coal tar pitch, tar sand bitumen, pyrolysis tar, slurry oils or decant oils from fluidized bed crackers, and shale oils, and mixtures thereof may also be used.

Coking operation conditions applicable to the method of the present invention are conditions for providing a coke product having a volatile content of 15% by weight or less, preferably 6-12% by weight. As described in the art, such conditions include a coke oven outlet temperature of about 875 to 950 ° F., preferably 925 to 930 ° F., and a vapor temperature of the coke drum outlet of 775 to 850 ° F., preferably about 835 ° F. , Drum pressure with coke from 5 to 75 psig, preferably about 15 to 20 psing. Maintaining the coke oven drum pressure below atmospheric pressure is undesirable for several reasons. The pressure of the coke oven drum is close to atmospheric pressure and the economic loss of the process is rapidly lowered, and operating below atmospheric pressure is very dangerous because there is a possibility of oxygen (air) leaking into the drum containing hydrocarbons at 900 ° F. In addition, as pointed out in Ozaki et al., If the pressure in the drum is at or below atmospheric pressure, a product closer to pitch than to coke is produced. For example, the example of Ozaki et al. Was conducted at drum pressure of atmospheric pressure or lower, where a soft pitch type product was formed with a content of volatile matter of 20% by weight or more. The coke product according to the process of the invention has a content of volatile components of 15% by weight, preferably 6 to 12% by weight.

In order to account for the possible coke yields when combined with conventional heavy recycle material and new coke, the contribution to the coke yield from several fractions of coke oven heavy gas oil was determined. The various boiling range fractions of gas oil in the coke oven were individually coke, and then the coke yield and the amount of each fraction were determined as a percentage.

The result is as follows:

TABLE 1

As shown in Table 1, the possible coke yields from gas oil in the coke oven are significant. It is also evident that most of the coke from heavy gas oil is produced in the portion with the highest boiling point range. Therefore, it is particularly important to remove the heaviest condensable material in the coke oven steam and to remove the heaviest material in the coke oven gas oil from the coke oven feedstock. By using a distillate of hydrocarbon material having a boiling point range of about 335 to about 850 ° F. instead of the commonly used recycle material, the coke yield, expressed as a percentage of fresh feedstock, is reduced, leading to an increase in the yield of more desirable liquid products. do.

Coke oven classifiers are not used to perform "clean" separations, while gas oils in coke ovens may contain small quantities of substances with boiling points as low as 550 ° F, while coke oven distillates have boiling points of 750 ° F. It can contain high amounts of materials, and in any case can contain materials with boiling points as high as 850 ° F. However, the amount of such high boilers in the coke oven distillate (such as from line 44 in FIG. 2) is very low and the gearing for the overall coke yield from these small amounts of high boilers is Not remarkable On the other hand, condensed coke drum vapor and unflashed coke oven gas oils have a relatively high boiling point of + 850 ° F. and if they are combined with new feedstock as in conventional methods, the gearing for the overall coke yield will be significant. .

The most important object of the present invention is a delayed coking process operated under the conditions of producing a delayed coke product for fuel or anode having a volatile content of about 15% by weight or less, the material coming from the bottom of the flash zone of the coke furnace sorter. Is completely removed from the coke oven feedstock. This purpose is usually a hydrocarbon diluent with a lower boiling range than conventional heavy recycle materials in a quantity sufficient to processly remove the material associated with the new feedstock as a recycle material and effectively prevent the coke from adhering to the coke tube. Can be achieved by substituting

In other words, the condensed coke drum steam falling to the bottom of the flash zone in the fractionator and the unflashed portion of the heavy gas oil applied to the flash zone are collected during the process rather than combined with a new feedstock as a recycle material, and low-boiling hydrocarbon distillation Replace with liquid.

[Yes]

Yields improved by the method of the present invention can be demonstrated through the following simulations induced by the highly developed coke oven design program. In this example, in one case a conventional heavy recycle material is used as the recycle material (20 parts per 100 parts of fresh feedstock), and in other cases a hydrocarbon distillate having a boiling point range of 510 to 650 ° F. is used as the recycle material. Consumption was carried out twice using the same feedstock and coking conditions, except as above. In both examples, 20 psig of 1000 ° F Bachaguero vacuum residue with 4.3 APT specific gravity, 23.5% Conradson carbon, 11.5 UOP characteristic factor “K” and 3.5 wt% sulfur content. Coke at coke drum pressure and a coke drum top temperature of 835 ° F. The product distribution in both examples is as follows:

As shown in the table above, a reduction in coke yield of more than 6% (34.66 vs. 32.53) is obtained when using hydrocarbon distillates having a boiling range of 510 to 650 ° F. instead of conventional heavy recycle materials. And, for a C ₅ -liquid, an increase (58.84 vs. 55.99) can be achieved that is nearly 5%. Since similar reductions in coke yields and increases in liquid yields are obtained with different feedstocks under the same or different conditions, the removal of materials usually used as recycled materials in the process is demonstrated.

The embodiments of the present invention are described as illustrative rather than limiting the present invention.

Claims (10)

In the process of improving product yield by delayed coking of a heavy petroleum feedstock in a coking furnace composed of a coking drum and a coking furnace classifier for removing delayed coke, liquid and gaseous hydrocarbon products ( a) delaying coking heavy oil in a coking drum under conditions of producing delayed coke with a volatile content of 15% by weight or less; (b) passing overhead steam from the coke oven drum to the coke oven fractionator; (c) condensing and removing the portion of the highest boiling point of the overhead vapor; (d) Before heating the heavy petroleum feedstock to the coking temperature in the coke oven, a sufficient amount of hydrocarbon diluent having a boiling point lower than that of the highest boiling point to effectively prevent coking in the coke oven. By applying the petroleum feedstock of the overhead, the yield of delayed coke having a volatile content of 15% by weight or less is higher than the yield obtained when the portion of the overhead vapor having the highest boiling point is combined with the feedstock. A process for increasing product yield by a delayed coking process characterized by low and high yield of liquid fractions. 2. The process of claim 1 wherein delayed coke with a volatile content of 6-12 wt% is produced. 2. The process according to claim 1, wherein the feedstock is initially fed with a hydrocarbon diluent, fed to the feedstock surge drum, and then sent directly to the coke oven without adding any other hydrocarbon material. Method of increasing product yield. The process of claim 1 wherein the hydrocarbon diluent has a boiling point range of 335 to 850 ° F. 5. The method of claim 4 wherein the boiling point range of the hydrocarbon diluent is from 450 to 750 ° F. 5. The process according to claim 4, wherein the boiling range of the hydrocarbon diluent is from 510 to 650 DEG F. to increase in product yield by delayed coking. 5. The process of claim 4 wherein the hydrocarbon diluent is product sidestream exiting the coke oven sorter. 8. The process of claim 7, wherein the phase feedstock is in a group consisting of vacuum distillation residues of petroleum, atmospheric distillation residues of petroleum, tar pitch, tar sand bitumen, slurry oil, decant oil, shale oil, pyrolysis tar and mixtures thereof. A method for increasing product yield by delayed coking, characterized in that the method is selected. 8. The delayed coke of claim 7, wherein the heavy gas oil exiting the coke oven fractionator is returned to the flash zone of the classifier to contact the incoming coke oven increments and then cool the portion having the highest boiling point therefrom. Method of increasing product yield by chemical method. 10. The method of claim 9 wherein the hydrocarbon diluent is the only substance missing from the feedstock before it is fed to the coke oven.

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