JP2008504376A - A delayed coking process for producing free-flowing coke using low molecular weight aromatic additives. - Google Patents

Abstract

A delayed coking process for producing substantially free-flowing coke, preferably shot coke. A coker feedstock, such as a vacuum residue, is heated to a coking temperature in a heating zone and subsequently fed into the coking zone where volatile materials are collected overhead and coke is formed. A low molecular weight additive is added to the feedstock before it is heated in the heating zone and / or before it is fed into the coking zone.
[Selection figure] None

Description

  The present invention relates to a delayed coking process for producing substantially free-flowing coke, preferably free-flowing shot coke. A coker feedstock, such as a vacuum residue, is heated to a coking temperature in a heating zone and subsequently fed into the coking zone where volatile materials are collected overhead and coke is formed. To enhance the formation of free-flowing coke, a suitable low molecular weight aromatic additive is added to the feedstock before it is heated in the heating zone and / or sent to the coking zone.

  Delayed coking involves pyrolyzing petroleum residues (residues) to produce gases, liquid streams of various boiling ranges, and coke. Delayed coking of residual oil from heavy and heavy sour crudes primarily converts some of the residual oil into more valuable liquid and gas products as a means of disposal of these low value feedstocks Is done by. The resulting coke is generally regarded as a low-value by-product, but as a fuel (fuel grade coke) and as an electrode for aluminum production (anode grade coke), it has some value depending on its quality. There is a case.

  In the delayed coking process, the feedstock is rapidly heated in a combustion heater or a tubular furnace. The heated feedstock is then sent to a coking drum that is maintained at conditions where coking occurs, i.e., generally above 400 ° C and superatmospheric pressure. The heated residue feed in the coke ram also forms volatile components, which are removed from the overhead and sent to the fractionator, leaving the coke behind. When the cauldrum is full of coke, the heated feed is switched to another drum and the hydrocarbon vapor is removed from the coke drum by steam. The drum is then quenched with water and lowered to a temperature below 300 ° F. (149 ° C.), after which the water is drained. When the cooling and draining process is complete, the drum is opened and the coke is removed after drilling and / or cutting with a high speed water jet.

  Typically, a hole penetrating the center of the coke floor is drilled by a high pressure water jet from a nozzle located in the drilling tool. Subsequently, the coke is cut out from the drum by a nozzle oriented horizontally at the tip of the cutting tool. The coke removal process greatly increases the processing time and cost of the entire process. For this reason, it is desirable to enable the production of free-flowing coke that does not require the cost and time associated with conventional coke removal.

  Even though the cauldrum appears to be completely cooled, some areas of the drum are not fully cooled. This phenomenon, sometimes referred to as “hot drum”, may be the result of a combination of coke forms in the drum. The drum may contain a combination of two or more solid coke products, ie needle coke, sponge coke and shot coke. Non-agglomerated shot coke can cool faster than other forms of coke, such as large shot coke lumps or sponge coke, so that to avoid or minimize hot drums, it is substantially possible in a delayed coker. It is desirable to produce mainly free-flowing coke, preferably shot coke.

In one embodiment of the invention,
(A) heating the petroleum residual oil to a temperature in the first heating zone that is below the coking temperature, but where the residual oil becomes a pumpable liquid;
(B) feeding the heated residual oil into a second heating zone where it is heated to a coking temperature;
(C) feeding the heated residual oil from the second heating zone to a coking zone where volatile products are collected in overhead to form a coke product; and (d) the residual oil; Introducing at least one low molecular weight aromatic additive effective in forming a substantially free-flowing coke, the additive at a point upstream of the second heating zone, the second heating A delayed coking method is provided that includes introducing into the residual oil at a point between or both of the zone and the coking zone.

  In one preferred embodiment, the coking zone is in a delayed coke ram and a substantially free flowing shot coke product is formed.

In another embodiment,
(A) Contacting the vacuum residue with at least one effective amount of a low molecular weight aromatic additive at a temperature of 70 ° C. to 370 ° C. for a time sufficient to uniformly disperse the additive in the raw material. The step of causing;
(B) heating the contacted vacuum residue to a temperature effective for coking of the raw material;
(C) the heat-treated residual oil at a pressure of 15-80 psig (103.42-551.58 kPa) and a time effective to form a hot coke bed, at least a portion of which is free flowing; A delayed coking method is provided that includes charging the coking zone; and (d) quenching at least a portion of the hot coke bed with water.

  In another embodiment, the low molecular weight additive is selected from monocyclic and bicyclic aromatic systems having 1 to 4 alkyl substituents. In this case, the alkyl substituent is one containing 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. Monocyclic or polycyclic can be homonuclear or heteronuclear. The homonuclear aromatic ring means an aromatic ring containing only carbon and hydrogen, and the heteronuclear aromatic ring means an aromatic ring containing nitrogen, oxygen and sulfur in addition to carbon and hydrogen.

  In another embodiment, a substantially free flowing shot coke product is formed and removed from the coking zone. The caulking zone is preferably a delayed coke ram. The additive can be charged and bound to the raw material either before the raw material is introduced into the heating zone, which is a coker oven, or between the coker oven and the coca ram. It is also within the scope of the present invention to introduce the additive into the raw material at both positions. The same one or more additives can be added independently at each location, or different one or more additives can be added at each location.

  The terms “bond” and “contact” are used in their broadest sense. That is, in some cases, physical and / or chemical changes in the additive and / or raw material can occur. In other words, the present invention is not limited to the case where the additives and / or raw materials are not subject to chemical and / or physical changes following or in the process of contact and / or bonding. An “effective amount” of additive is that amount of additive that, when brought into contact with the raw material, results in forming shot coke in the coking zone, preferably forming substantially free-flowing coke. Effective amounts are generally in the range of 10 to 5,000 ppm (based on the total weight of the raw material), which will vary depending on such things as the type of additive used and its chemical and physical form. Will. The effective amount is generally less in the case of additive species in physical and chemical forms that provide good dispersion in the raw material than in the case of additive species that are more difficult to disperse. Will. Therefore, an additive that is at least partially soluble in the organic material, more preferably in the residue feedstock, is most preferred.

  Dispersing the additive uniformly in the residue feed is desirable to avoid extraneous portions of coke morphogenesis. That is, in the coke drum, a situation in which the coke is substantially free-flowing in some places and the coke is substantially non-free-flowing in other areas is not preferable. The dispersion of the additive is carried out in any suitable manner, preferably by introducing the additive side stream into the feedstock at the required location. Addition of the additive can be performed by solubilizing the additive in the residual oil raw material. Before the additive is mixed, the additive can be easily solubilized in the residual oil raw material by reducing the viscosity of the residual oil by heating, solvent addition, or the like. High energy mixing or static mixer equipment can be used to aid in dispersion of the additive, and is particularly useful for additives with relatively low solubility in the feed stream.

  Preferably, all coke formed by the process of the present invention, or substantially all coke, is substantially free-flowing coke, more preferably substantially free-flowing shot coke. It is also preferred that at least a portion of the volatile species present in the coca ram is separated and removed from the process during and after coke formation, preferably from the overhead of the coke ram.

Petroleum vacuum residue (residual oil) feedstock is suitable for delayed coking. Such petroleum residues are often obtained after removing the distillate from the crude feedstock under reduced pressure and have the properties of components of large molecular size and molecular weight, generally (a ) Asphaltenes and other high molecular weight aromatic structures that can slow the rate of hydrotreating / hydrocracking and cause catalyst deactivation; and (b) naturally contained in crude oil or crude oil And (c) when burning petroleum residue, the metal pollutant resulting from the pre-treatment of the metal and having a tendency to deactivate the hydrotreating / hydrocracking catalyst and prevent catalyst regeneration And relatively high concentrations of sulfur and nitrogen compounds that generate undesired amounts of SO ₂ , SO ₃ and NO _X. Nitrogen compounds present in the residual oil also tend to deactivate the catalytic cracking catalyst.

  In one embodiment, the residue feedstock is from petroleum crude oil atmospheric and vacuum distillation residues, or heavy oil, visbroken residue, liquefied coal, shale oil, de-history equipment. Of atmospheric or vacuum distillation residues of a combination of these materials or combinations of these materials. Heavy bitumen produced at the top in atmospheric and vacuum distillations can also be used. Such feedstocks are generally high boiling hydrocarbon materials having a nominal initial boiling point of 538 ° C. or higher, an API specific gravity of 20 ° or lower, and a Conradson residual carbon concentration of 0 to 40% by weight.

  The residual oil feedstock is typically subjected to delayed coking. Generally, in delayed coking, residual fractions such as petroleum residue feedstock are pumped to a heater at a pressure of 50 to 550 psig (344.74 to 3792.12 kPa), where 480 ° C. Heated to a temperature of ~ 520 ° C. Subsequently, the residual oil feed is discharged through the inlet at the base of the drum into a coking zone, typically a vertically insulated thermal coke ram. The pressure in the drum is usually relatively low, for example 15-80 psig (103.42-551.58 kPa), so that volatile materials can be removed from the overhead. The typical operating temperature of the drum will be between 410 ° C and 475 ° C. The hot feedstock is pyrolyzed in the cauldrum for a period of time (“coking time”) to dissipate volatile materials, mainly consisting of hydrocarbon products. This volatile product rises continuously through the coke mass (bed) and is collected in overhead. Volatile products are sent to a coker fractionator for distilling and recovering coker gas, naphtha, light gas oil and heavy gas oil fractions. In one embodiment, a small portion of the heavy coker gas oil present in the product stream introduced into the coker fractionator can be captured and combined with fresh feed (coker feed components) for recycling. . This forms a charge for a coker heater or coker furnace. Delayed coking forms solid coke products in addition to volatile products.

  In general, there are three different types of delayed coker solid products with different values, appearances and properties. That is, needle coke, sponge coke and shot coke. Needle coke is the highest quality of these three variants. Needle coke has a high electrical conductivity (and a low coefficient of thermal expansion) when further heat-treated, and is used for electric arc steelmaking. It is relatively low in sulfur and metal and is often produced from several high quality coker feedstocks, including more aromatic feedstocks such as slurries and decant oils from catalytic crackers and pyrolysis tar Is done. Generally, it is not formed by delayed coking of the residual oil feedstock.

  Sponge coke, a lower quality coke, is most often formed in refineries. A low quality refinery coker feed with a significant amount of asphaltenes, heteroatoms and metals produces this low quality coke. If the sulfur and metal content is sufficiently low, sponge coke can be used to make electrodes for the aluminum industry. If the sulfur and metal content is very high, the coke can be used as fuel. The name “sponge coke” comes from its porous, sponge-like appearance. Conventional delayed coking processes will generally produce sponge coke using the preferred vacuum residue feedstock of the present invention. This sponge coke is produced as an agglomerate requiring extensive removal processes including drilling and water jet technology. As already mentioned, this greatly complicates the processing steps by increasing the cycle time.

  Shot coke is considered the lowest quality coke. The term “shot coke” comes from its shape resembling a BB size [1/16 inch to 3/8 inch (0.16 to 0.95 centimeter)] sphere. Shot coke, like other types of coke, tends to agglomerate to large agglomerates and sometimes to diameters greater than 1 foot, especially in mixtures with sponge coke. This has the potential to create problems in refinery equipment and processing processes. Shot coke is usually made from the lowest quality high resin-asphalten raw materials and is a good high sulfur fuel source, especially for applications in cement kilns and steelmaking. There is also a coke called “transition coke”. This refers to coke having an intermediate form between sponge coke and shot coke, or coke made of a mixture of shot coke bonded to sponge coke. For example, a coke that has an almost sponge-like physical appearance but has the appearance that small shot spheres are beginning to form as separate shapes.

  By treating the residual feedstock with one or more low molecular weight aromatic additives, a substantially free-flowing shot coke can be produced according to the present invention. This additive is an additive that enhances the formation of shot coke during delayed coking. The residual oil feed is treated with one or more additives at an effective temperature, i.e., a temperature that promotes dispersion of the additive in the feed oil. Such a temperature is generally 70 ° C to 500 ° C, preferably 150 ° C to 370 ° C, more preferably 185 ° C to 350 ° C.

  The low molecular weight aromatic additives of the present invention are selected from monocyclic and bicyclic aromatic systems having 1 to 4 alkyl substituents. In this case, the alkyl substituent is one containing 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. Monocyclic or polycyclic can be homonuclear or heteronuclear. The homonuclear aromatic ring means an aromatic ring containing only carbon and hydrogen, and the heteronuclear aromatic ring means an aromatic ring containing nitrogen, oxygen and sulfur in addition to carbon and hydrogen.

  Non-limiting examples of low molecular weight aromatic additives include benzene, toluene, xylene, methylnaphthalene, dimethylnaphthate, indane, methylindane, pyridine, methylpyridine, quinoline and methylquinoline. Additives are used in effective amounts. That is, the amount that can result in the required amount of free-flowing coke. This amount will generally be from 10 to 30,000 wppm, preferably from 10 to 5000 wppm, more preferably from 10 to 50 wppm, based on the weight of the heavy oil feedstock.

  It is within the scope of the present invention to use a second type of additive in combination with a polymeric additive. This second type of additive will be a metal-containing additive that can be used in liquid or solid form, but liquid form is preferred. Non-limiting examples of metal-containing additives that can be used in practicing the present invention include metal hydroxides, naphthenates and / or carboxylates, metal acetylacetonates, Lewis acids, metal sulfides, metal acetates, There are metal carbonates, high surface area metal-containing solids, inorganic oxides, and oxide salts. Preferred metals for the hydroxide are alkali metals and alkaline earth metals, with potassium and sodium being more preferred. Basic salts are preferred.

  It is preferred to keep the fraction material with an atmospheric boiling point (AEBP) of 900 ° F. to 1040 ° F. (482.22 ° C. to 560 ° C.) below 10% by weight. This will push the coke form back to a coke form with a lower degree of bonding and a lower degree of self-support.

  The precise conditions for treating the residual oil feedstock with additives vary depending on the feedstock and additives. That is, the conditions for treating the raw material with the additive depend on the composition and characteristics of the raw material to be coked and the additive used. These conditions can be determined by conventional methods. For example, several trials are performed at different times and temperatures depending on the particular raw material containing the additive, followed by caulking in a bench scale reactor such as a Microcarbon Residue Test Unit (MCRTU). be able to. The resulting coke is then analyzed using an optical polarization microscope as referred to herein. Preferred coke forms (ie forms that will produce substantially free-flowing coke) are discrete fine domain cokes having an average size of 0.5 to 10 μm, preferably 1 to 5 μm. It is a fine structure and is somewhat similar to the mosaic pattern of FIGS. 2, 3 and 5 herein. A coke microstructure representing shot coke that is not free-flowing is shown in FIG. 1, but it is substantially unseparated or quite large, up to a size of 60 μm or more, typically 10-60 μm. It shows the fine structure of coke composed of fluidized domains.

  Traditional coke aids including anti-foaming agents can be used in the method of the present invention. Shot coke has been produced by conventional methods, but this shot coke is usually agglomerated to the extent that water jet technology is still required for its removal.

  In one embodiment of the present invention, the residual feedstock is first treated with a low molecular weight additive of the present invention that promotes the formation of a substantially free-flowing coke. By keeping the cauldrum at a relatively low pressure, much of the emitted volatile material can be collected overhead, thereby preventing unwanted agglomeration of the resulting shot coke. The mixed raw material ratio (“CFR”) is a volume ratio of the amount charged to the furnace (fresh raw material + recycled oil) with respect to the amount of fresh raw material for continuous delayed coker operation. Delayed coking operations typically use 5% to 25% by volume recycle (1.05 to 1.25 CFR). In some examples, zero recycle is used, and in special applications, there may be up to 200% recycle in some cases. To facilitate the formation of free flowing shot coke, the CFR should be low and preferably no recycling should be used.

  Generally, the additive is fed into the coking process in a continuous mode. If necessary, the additives can be dissolved in a suitable transport liquid or mixed into a slurry. The transport liquid is generally a solvent that is compatible with the residual oil, such that the additive can be substantially dissolved therein. Thereafter, the fluid mixture or slurry is pumped into the coking process at a flow rate that achieves the required concentration of the additive in the feed. The introduction point of the additive can be, for example, at the discharge side of the furnace raw material charging pump or into the coker transport line. It is also possible to provide a pair of mixing vessels that are operated to continuously introduce the additive into the coking process.

  The introduction flow rate of the additive can be adjusted according to the nature of the residual oil raw material to the coker. A feedstock that is at the limit of shot coke formation will require less additive than a feed that is far from that limit.

  For additives that are difficult to dissolve or disperse in the residual oil feed, the additive is fed into a mixing / slurry vessel and mixed with a slurry medium that is compatible with the feed. Non-limiting examples of suitable slurry media include coker heavy gas oil, water, and the like. In order to disperse the additive, energy may be supplied to the container by, for example, a mixer.

  In the case of an additive that can be easily decomposed or dispersed in the residual oil feedstock, the additive is fed into a mixing vessel and mixed with a fluid transport medium compatible with the feedstock. Non-limiting examples of suitable fluid transport media include heated residue (temperature 150 ° C. to 300 ° C.), coker heavy gas oil, light cycle oil, heavy reformed oil, and mixtures thereof. Catalytic cracked slurry oil (CSO) can also be used, but under certain conditions, may reduce the ability of the additive to produce a dense shot coke. In order to disperse the additive in the fluid transport medium, the container may be supplied with energy, for example by a mixer.

  The invention will be better understood by reference to the following non-limiting examples presented for purposes of illustration.

Example 1
In the first set of tests, two model polynuclear aromatic (PNA) compounds 1 (PTE) and 2 (PDI) are known and reported to form mesophases in the temperature range of 100 ° C. to 450 ° C. Was used to demonstrate that the intermediate phase intermediate of PNA is incorporated into the formation of anisotropic mesophase coke. The perylene PNA compound of this model is shown below.

  The crystalline compound PTE exhibits a liquid crystal or an intermediate phase at 140 ° C. to 315 ° C. PTE was heated in a micro-residual carbon (MCR) apparatus to 400 ° C. for 2 hours to obtain a coke residue (60.4%). A photomicrograph of the coke residue observed for the PTE residue by the crossed polarization microscope technique is shown in FIG. In FIG. 1, an anisotropic coke morphology of medium sized domains (10-25 μm), including isolated regions of mesophase spheres (1-6 μm), is observed, which is intermediate to the PNA intermediate phase The body is incorporated into the formation of anisotropic mesophase coke.

  The crystalline compound PDI exhibits a liquid crystal mesophase at 330 ° C. to 480 ° C. The PDI was heated in an MCR apparatus to 400 ° C. for 2 hours to obtain a coke residue (98.2%). The micrograph of the coke residue observed with a polarizing microscope for PDI is also shown in FIG. In FIG. 2, an anisotropic coke morphology including a thin anisotropic lath structure (thickness 0.5-1 μm) is observed, which is an intermediate phase of PNA intermediate phase. It is shown to be incorporated into the formation of coke.

Example 2
In this set of tests, untreated sweet vacuum residue, sweet VTB and toluene-added sweet VTB (460 ppm) were used. Addition sweet VTB was prepared by adding 20 mL of toluene to 10 g of residual oil followed by evaporation of toluene at 100 ° C. for 24 hours. GC analysis of the residue showed that the residual toluene “bound” or “occluded” in the residue was 460 wppm. This toluene occlusion residue was heated in an MCR apparatus to 400 ° C. for 2 hours to obtain a coke residue (24.4%). A photomicrograph of the coke residue of this test observed with a polarizing microscope is shown in FIG. FIG. 4 shows a photomicrograph of the coke residue observed with a polarizing microscope for the management trial without addition of toluene. Comparing FIGS. 3 and 4, a greatly enhanced anisotropic coke morphology is observed, indicating that the occluded toluene enhances the formation of anisotropic coke. Based on a first set of tests on model compounds and a second set of tests on sweet VTB, toluene changes the intermediate phase intermediate, which leads to a more rapid formation of anisotropic mesophase coke. I guess that.

2 is a photomicrograph of coke residue observed by cross-polarized microscopy technique for the PTE residue of Example 1. The photomicrograph in this figure uses a cross-polarized light microscopy technique, and its field of view is 170 × 136 μm. 2 is a photomicrograph of coke residue observed by cross-polarization microscopy technique for the PDI residue of Example 1. The photomicrograph in this figure also uses the cross polarization optical microscope technique, and its field of view is 170 × 136 μm. It is the microscope picture observed by the cross polarization microscope technique of the coke residue obtained by processing the vacuum residue of Example 2 using toluene as an additive. The photomicrograph in this figure also uses the cross polarization optical microscope technique, and its field of view is 170 × 136 μm. It is the microscope picture observed by the cross polarization microscope technique of the coke residue obtained without processing the residual oil of Example 2 with toluene. The photomicrograph in this figure also uses the cross polarization optical microscope technique, and its field of view is 170 × 136 μm.

Claims (10)

(A) heating the petroleum residual oil to a temperature in the first heating zone that is below the coking temperature, but where the residual oil becomes a pumpable liquid;
(B) feeding the heated residual oil into a second heating zone where it is heated to a coking temperature;
(C) feeding the heated residual oil from the second heating zone to a coking zone where volatile products are collected in overhead to form a coke product; and (d) the residual oil; Introducing at least one low molecular weight aromatic additive effective in the formation of substantially free-flowing coke, said additive at a point upstream of said second heating zone, in said coking zone; Introduced into the residual oil at an upstream point or both, wherein the additive consists of a mono- or bicyclic homonuclear or heteronuclear aromatic ring having 1-4 alkyl substituents, said alkyl substituents Includes a process comprising 1 to 8 carbon atoms. (A) Contacting the vacuum residue with at least one effective amount of a low molecular weight aromatic additive at a temperature of 70 ° C. to 370 ° C. for a time sufficient to uniformly disperse the additive in the raw material. The additive comprises a monocyclic or bicyclic aromatic ring having 1 to 4 alkyl substituents, wherein the alkyl substituent comprises 1 to 8 carbon atoms;
(B) heating the treated residual oil to a temperature effective for coking of the raw material;
(C) charging the heat-treated residual oil at a pressure of 15-80 psig (103.42-551.58 kPa) into a coking zone for a coking time to form a hot coke bed; and (d) A delayed coking method comprising a step of quenching at least a part of a hot coke floor with water.   The delayed coking method according to claim 1, wherein the alkyl substituent contains 1 to 4 carbon atoms.   The delayed coking method according to claim 1, wherein the residual raw material oil is a vacuum residue.   The additive is one or more selected from the group consisting of toluene, benzene, xylene, methylnaphthalene, indane, methylindane, pyridine, methylpyridine, quinoline, and methylquinoline. The delayed coking method according to any one of the above.   6. The delayed coking method according to claim 1, wherein the generated coke is substantially shot coke.   7. The additive according to claim 1, wherein the additive is introduced into the vacuum residue at a point upstream of the first heating zone, a point upstream of the second heating zone, or both. Delayed coking method.   An effective amount of a second additive is also used, wherein the second additive is selected from the group consisting of metal naphthenates, metal acetylacetonates, Lewis acids, high surface area metal-containing materials, inorganic oxides and inorganic oxide salts. The delayed coking method according to claim 1, wherein the additive is a metal-containing additive.   9. The metal-containing additive, wherein the second additive is one or more Lewis acids selected from aluminum chloride, zinc chloride, iron chloride, titanium tetrachloride and boron trifluoride. The delayed coking method described in 1.   The delayed coking method according to claim 8 or 9, wherein the second additive is one or more selected from the group consisting of KOH and NaOH.

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