MXPA06012976A - Delayed coking process for producing free-flowing coke using polymeric additives. - Google Patents

Abstract

A delayed coking process for making substantially free-flowing coke, preferably shot coke. A coker feedstock, such as a vacuum residuum, is heated in a heating zone to coking temperatures then conducted to a coking zone wherein volatiles are collected overhead and coke is formed. At least one polymeric additive is added to the feedstock prior to it being heated in the heating zone, prior to its being conducted to the coking zone, or both.

Description

DELAYED COQUIFICATION PROCESS TO PRODUCE FREE FLOW COKE USING POLYMER ADDITIVES FIELD OF THE INVENTION The present invention relates to a delayed coking process for making substantially free flow coke, preferably free-flowing coke. A coking raw material such as a vacuum residue is heated in a heating zone to coking temperatures then it is conducted to a coking zone where the volatile components are collected up and the coke is formed. A suitable polymeric additive is added to the raw material before being heated in the heating zone, before being conducted to the coking zone, or both, to improve the formation of the free-flowing coke.

DESCRIPTION OF THE RELATED ART Delayed coking comprises the thermal decomposition of petroleum residues (residues) to produce gas, liquid streams of different boiling scales, and coke. Delayed coking of petroleum residues, from heavy crude oils and very sulphurous (high sulfur content) is mainly carried out by means of the disposal of these low-value feed lots by converting part of the petroleum residues to gaseous products and most valuable liquids. Although it is generally thought that the resulting coke is a low-value by-product, it may have some value, depending on its degree, as a fuel (fuel-grade coke), for electrodes to make aluminum (anode-grade coke), etc. . In the delayed coking process, the raw material is quickly heated in a heated heater or tubular furnace. The heated raw material is then passed to a coking drum which is maintained under conditions under which coking takes place, generally at temperatures above 400 ° C under pressures above atmospheric. The waste feed heated in the coker drum also forms volatile components that are removed at the top and passed to a fractionator, leaving behind the coke. When the coker drum is filled with coke, the heated feed is changed to another drum and the hydrocarbon vapors are purged from the coker drum with steam. Then the drum is rapidly cooled with water to lower the temperature to less than 149 ° C (300 ° F) after which the water is emptied. When the cooling and draining steps are completed, the drum is opened and the coke is removed after drilling and / or cutting using high-speed water jets. Typically a hole is made through the center of the coke bed using high pressure water jets from the nozzles located in a drilling tool. The nozzles oriented horizontally on the head of a cutting tool then cut the coke from the drum. The step of removing the coke considerably increases the time and cost of the total process. Therefore, it is desirable to be able to produce a free-flowing coke, in a coker drum, that does not require the costs and time associated with conventional coke removal. Although it may appear that the coker drum is completely cold, some areas of the drum do not completely cool. This phenomenon, sometimes called "hot drum", may be the result of a combination of coke morphologies present in the drum, which may contain a combination of more than one type of solid coke product, ie needle coke , coke sponge and coke shot. Since the non-agglomerated coke shot may cool more rapidly than other cokes of different morphology, such as coke sponge or large shot coke masses, it is desirable to predominantly produce substantially free-flowing coke, preferably coke shot, in a delayed coker, in order to avoid or minimize the phenomenon of hot drums.

SUMMARY OF THE INVENTION In one embodiment, a delayed coking process is provided comprising: (a) heating an oil residue in a first heating zone, at a temperature below the coking temperatures, but at a temperature at which the waste is a liquid that can be pumped; (b) conveying the hot residue to a second heating zone where it is heated to coking temperatures; c) conveying the hot residue from the second heating zone to a coking zone where the vapor products are collected from above and a solid coke product is formed; (d) introducing into the waste at least one polymeric additive which is effective for the formation of substantially free-flowing coke, wherein the additive is introduced into the waste at a point upstream of the second heating zone, between the second heating zone and the coking zone, or both. In a preferred embodiment, the coking zone is in a delayed coker drum, and a substantially free flow coke product is formed. In another embodiment, a delayed coking process is provided which comprises: (a) contacting a vacuum residue with an effective amount of at least one polymeric additive at a temperature from 70 ° C to 370 ° C for a sufficient time to disperse the additive substantially uniformly to the feed; (b) heating the contacted vacuum residue to an effective temperature to coke the feed; (c) loading the hot treated waste to a coking zone at a pressure from 15 to 80 psig (103.42 a 551. 58 kPa) for an effective period of time to allow the hot coke bed to form, at least a portion of which is free flowing; and (d) rapidly cooling at least a portion of the hot coke bed with water. In another embodiment, the polymeric additive is selected from the group consisting of polyoxyethylene, polyoxypropylene, polyoxyethylene-polyoxypropylene copolymer, tetraalkoxylated ethylenediamine alcohol of polyoxyethylene alcohol, ethylenediamine tetraalkoxylated alcohol of polyoxypropylene alcohol, ethylenediamine tetraalkoxylated alcohol of polyoxypropylene-polyoxyethylene alcohols and mixtures thereof. The polymeric additive will preferably have a molecular weight range of 1,000 to 30,000, more preferably 1,000 to 10,000. The copolymers are preferably block copolymers. Illustrative examples of the polymers are given in Figures 1 and 2 thereof. In another embodiment, a substantially free flow coke product is formed and removed from the coking zone. The coking zone preferably is a delayed coke drum. The additive can be incorporated and combined with the feed either before introducing the feed into the heating zone, which is a coker oven, or it can be introduced into the feed between the coker oven and the coker drum. It is also within the scope of the present invention to introduce the additive to the feed in both locations. The same additive, or additives, can be added independently at each location or a different additive or additives can be added at each location. The use of the terms "combine" and "put in contact" are used in their broadest sense, that is, in some cases physical and / or chemical changes may occur in the additive and / or the feed in the additive, the feed, or both when the additive is present in the feed. In other words, the invention is not restricted to cases in which the additive and / or feed do not undergo chemical and / or physical change after, or in the course of, the contact and / or combination. An "effective amount" of additive is the amount of the additive (s) that when brought into contact with the feed results in the formation of free-flowing coke in the coking zones, preferably coke trip of substantially free flow. A typically effective amount ranges from 100 to 100,000 ppm (based on the total weight of the feed). Of course, the amount used will depend on the particular additive species used and its physical and chemical form. The effective amount will typically be lower for additive species with a physical and chemical form that leads to better dispersion in the feed than for the additive species that disperse with greater difficulty. Therefore, most preferred are additives that are at least partially soluble in organic compounds, more preferably in the waste feed. The uniform dispersion of the additive in the waste feed is desirable to avoid heterogeneous areas of coke morphology formation. That is, no locations are desired in the coker drum where the coke is substantially free flowing and other areas where the coke is not substantially free flow. The dispersion of the additive is effected by any suitable technique, preferably by introducing a lateral stream of the additive into the feed at the desired location. The additive can be added by solubilizing the additive in the waste feed. The reduction of the viscosity of the waste before mixing in the additive, for example, by heating, addition of solvent, etc., will facilitate the solubilization of the additive in the waste feed. Mixing with high energy level or the use of static mixing devices can be used to help the dispersion of the additive, especially useful for additives that have relatively high solubility in the feed stream. Preferably, all or substantially all of the coke formed in the process of the present invention is substantially free-flowing coke, most preferably coke, substantially free-flowing shot. It is also preferred that at least a portion of the volatile species present in the coker drum during and after the formation of the coke be separated and removed from the process, preferably above the coker drum.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 thereof is an optical micrograph showing the residue of the example thereof where no additive is used. Figure 2 thereof is an optical micrograph showing the residue of the example thereof where the polyoxyethylene-polyoxypropylene (Pluronic) additive is used.

Figure 3 thereof is an optical micrograph showing the residue of the example thereof where the ethylenediamine tetraacetic ester of the polyoxyethylene alcohol additive (Tetronic) is used. All the photomicrographs in these Figures used in the polarized optical light microscope, with a viewing area of 170 by 136 micrometers.

DETAILED DESCRIPTION OF THE INVENTION The raw materials of the oil remains ("residue") are suitable for delayed coking. Such petroleum residues are frequently obtained after the removal of crude raw material distillates under vacuum and are characterized by being composed of components with a large molecular weight and size, which generally contain: (a) asphaltenes and other aromatic structures with high molecular weight that could inhibit the hydrotreating / hydrocracking rate and cause deactivation of the catalyst; (b) metal contaminants that naturally occur in the crude oil or that result from a crude treatment of the crude, whose contaminants could tend to deactivate the hydrotreating / hydrocracking catalysts and interfere with the regeneration of the catalyst; and (c) a relatively high content of sulfur and nitrogen components that give rise to objectionable amounts of S02, S03 and N0X in the combustion of the oil remnant. The nitrogen components present in the waste also tend to deactivate the catalytic cracking catalysts. In one embodiment, the raw materials of petroleum residues include, but are not limited to, residues from vacuum distillation and atmospheric distillation of petroleum crudes, or vacuum or atmospheric distillation of heavy oils, visco-reduced residues, liquid coal, shale oil, pitting of deasphalting units or combinations of these materials. Heavy tars can also be used that are finished under vacuum or at atmospheric conditions. Typically, such raw materials are high-boiling hydrocarbonaceous materials having a nominal initial boiling point of 538 ° C or higher, an API gravity of 20 ° or less, and a Conradson Carbon Residue content of 0 to 40 percent. in weigh. The waste feeds are typically subjected to delayed coking. Typically, in delayed coking, a waste fraction, such as a petroleum residue raw material, is pumped to a heater at a pressure of 50 to 550 psig (344.74 to 3792.12 kPa) where it is heated to a temperature of 480 ° C to 520 ° C. It is then discharged to a coking zone, typically a vertically oriented isolated coker drum, through an inlet in the base of the drum. The pressure in the drum is relatively low, such as 15 to 80 psig (103.42 to 551.58 kPa) to allow volatile products to be removed overhead. Typical operating temperatures of the drum will be between 410 ° C and 475 ° C. The hot raw material breaks down thermally during a period (the "coking time") in the coker drum, releasing the volatile products that are mainly composed of hydrocarbon products that continuously rise through the coke mass (bed) and they are collected from above. The volatile products are sent to a coke fractionator for the distillation and recovery of fractions of heavy gas oil, light gas oil, coking gas, naphtha. In one embodiment, a small portion of the coked heavy gas oil in the product stream introduced into the coker fractionator can be captured for recycling and combined with the fresh feed (coke feed component), thereby forming the feed of the coking oven or coker heater. In addition to volatile products, delayed coking also forms a solid coke product. There are generally three different types of solid retarded coke products that have different values, appearance and properties, ie, needle coke, sponge coke and coke shot. The coke of needle is the one that has the best quality of the three varieties. The needle coke, after the additional heat treatment, has high electrical conductivity (and a low coefficient of thermal expansion) and is used in the production of electric arc steel. It has a relatively low content of sulfur and metals and is often produced from some of the highest quality coking raw materials that include the most aromatic raw materials such as mud oils and decanting catalytic disintegrating stills and decomposition tars. thermal It is not typically formed by delayed coking of oil residue feeds. Sponge coke, a coke of inferior quality, is very often formed in refineries. Low quality refinery coking raw materials that have significant amounts of asphaltenes, heteroatoms and metals produce this lower quality coke. If the sulfur and metals content is low enough, the coke sponge can be used for the manufacture of electrodes for the aluminum industry. If the sulfur and metals content is very high, then the coke can be used as fuel. The name "coque sponge" is derived from its porous appearance similar to that of sponges. Conventional delayed coking processes, using the preferred vacuum waste stock material of the present invention, typically produce coke sponge, which is produced as an agglomerated mass that requires an extensive removal process that includes jetting and drilling water technology . As mentioned, this considerably complicates the process by increasing the cycle time. The coke shot is considered the coke of lower quality. The term "coke shot" is derived from its shape similar to that of BB balls sized [from .16 to .95 centimeters (from 1/16 of an inch to 3/8 of an inch)]. The coke shot, as well as other types of coke, has the tendency to agglomerate, especially when mixed with coke sponge in larger masses, sometimes greater than 30.48 centimeters in diameter. This can cause problems in the refinery equipment and processing. The coke shot is usually made from feeds with high content of resin-asphaltene of the lowest quality and is a good supply of fuel with high sulfur content, particularly for use in the manufacture of steel and cement kilns. There is another coke called transition coke and it refers to a coke that has a morphology between that of coke sponge and coke shot or that is composed of a mixture of coke shot linked to coke sponge. For example coke that has a physical appearance very similar to that of a sponge, but with evidence of small firing spheres that begin to form as discrete shapes. The substantially free flux coke can be produced in accordance with the present invention by treating the waste raw material with one or more polymeric additives. The additives are those that improve the production of coke shot during delayed coking. The oil waste feed is subjected to treatment with one or more additives, at effective temperatures, that is, they will promote the dispersion of the additives in the raw material. Such temperatures will typically range from 70 ° C to 500 ° C, preferably from 150 ° C to 370 ° C, more preferably from 185 ° C to 350 ° C. Non-limiting examples of the polymeric additives of the present invention include those selected from the group consisting of polyoxyethylene, polyoxypropylene, polyoxyethylene-polyoxypropylene copolymer, tetraalkoxylated alcohol of polyoxyethylene alcohol ethylenediamine, tetraalkoxylated alcohol of ethylenediamine of polyoxypropylene alcohol, ethylenediamine tetraalkoxylated alcohol of polyoxypropylene-polyoxyethylene alcohols and mixtures thereof. The polymeric additive will be used in an effective amount. That is, in at least that amount that will result in a desired degree of free-flowing coke. This amount will usually be from 300 to 500 ppm, preferably from 300 to 3000 wppm, and more preferably from 300 to 2000 wppm, based on the weight of the heavy oil feed. It is within the scope of this invention that a second type of additive is used in combination with the polymeric additive. This second type of additive will be an additive containing metals that can be used in liquid or solid form, with liquid form which is preferred. Non-limiting examples of metal-containing additives which can be used in the practice of the present invention include metal hydroxides, naphthenates and / or carboxylates, metal acetylacetonates, Lewis acids, a metal sulfide, metal acetate, metal carbonate, solids containing metal high surface area, inorganic oxides and oxide salts. The preferred metals of the hydroxides are the alkali and alkaline earth metals, more preferably potassium and sodium. Salts that are basic are preferred. If an additive containing metals is used in combination with the polymeric additive, the total amount of both additives will not exceed the maximum amount given for the polymeric additive, which is up to 500 wppm. It is preferred that the fraction of 482.22 ° C (900 ° F) at 560 ° C (1040 ° F) of the atmospheric equivalent boiling material (AEBP) is kept under 10% by weight, which will boost the coke morphology of new to a coke morphology of less linked and less self-support. The dehydration / coking / rapid interruption of the liquid mesophase initially formed results in the formation of liquid spheres that form coke firing. The slow dehydration of the mesophase allows the initially liquid mesophase to be released and the coke established and results in the formation of an extended coke sponge network. The intermediate dehydration rates produce transition coke which is a mixture of sponge cokes and firing with the coke shot embedded in the sponge coke. This latter situation can lead to coke eruptions, or "hot drums", when the coke drum of a delayed coker is cut / punched because the coke sponge forms a coke seal inlay shot and superheated steam. When the perforator hits such a seal, it is related to steam and coke shot BBs. It is highly desirable to be able to produce coke shot or sponge in a controlled manner and to avoid the formation of transition coke. The refinery can cut the coke sponge or drain the coke shot without the need to drill. In addition to the polymeric additive of the present invention, coking is allowed at a higher temperature because it reduces the thermal crosslinking reactions between the mesophase layers that allow the faster dehydration of coke and the formation of coke firing spheres. In addition to higher temperatures, operating the coke drum at lower pressures, eg 15 psi versus 45 psi (103.42 versus 310.26 kPa), allows the cracking products to escape and minimize their residence time as a liquid in the mesophase. Polyether additives are also effective in interrupting heavy oil mesophase formation and crosslinking because they decompose at a slower rate in the coke drum (typically at 425 ° C) than the rate of coke dehydration. The precise conditions in which the waste raw material is treated with the additive are fed and are dependent on the additive. That is to say, the conditions to which the feed is treated with the additive are dependent on the composition and properties of the feed that is coked and the additive used. These conditions can be determined conventionally. For example, various tests can be made with a particular feed containing an additive at different times and temperatures by coking in an experimental scale reactor such as a Microcarbon Residue Test Unit (MCRTU). The resulting coke is then analyzed by the use of a polarized transverse optical light microscope as set forth herein. The morphology of the preferred coke (i.e., that which will produce substantially free-flowing coke) is a coke microstructure of discrete microdomains having an average size of 0.5 to 10 μm, preferably 1 to 5 μm, somewhat similar to mosaic shown in Figures 2 and 3 thereof. The coke microstructure representing coke that is not coke free-flowing shot is shown in Figure 1 thereof, showing a coke microstructure that is substantially composed of non-discrete and substantially large flow domains of up to 60 μm or greater in size, usually 10 to 60 μm. Conventional coke processing aids, including an anti-foaming agent, can be employed in the process of the present invention. ough the coke shot has been produced by conventional methods, it usually agglomerates to such a degree that water jet technology is still necessary for its removal. In one embodiment of the present invention, the raw material of the waste is first treated with the polymeric additive of the present invention that promotes the formation of substantially free-flowing coke. By keeping the coker drum at relatively low pressures, many of the volatile products in development can be collected from above, which prevents undesirable agglomeration of the resulting coke shot. The combined feed ratio ("CFR") is the volumetric ratio of the furnace load (fresh feed plus oil for recycling) to fresh feed to the continuous delayed coker operation. Delayed coker operations normally employ recycled up to 200%. The CFRs must be low to assist in the formation of free-flowing shot coke and preferably, no recycling should be used. Normally, the additive or additives are conducted to the coking process in a continuous mode. If necessary, the additive can be dissolved or saturated in an appropriate transfer fluid, which will normally be the solvent that is compatible with the residue and in which the additive is substantially soluble. The fluid mixture or slurry is then pumped into the coking process at a rate to achieve the desired concentration of additives in the feed. The point of introduction of the additive may be, for example, in the discharge of the furnace feed loading pumps, or near the outlet of the coker transfer line. There may be a pair of mixing vessels operated in a manner so that there is continuous introduction of the additives in the coking process. The speed of introduction of the additive can be adjusted according to the nature of feeding the waste to the coker. The feeds that are in the threshold to produce coke firing may require less additive than those which are farther from the threshold. For additives that are difficult to dissolve or disperse in the waste feeds, the additive or additives are transferred into the mixing / slurry vessel and mixed with a slurry medium that is compatible with the feed. Non-limiting examples of suitable slurry media include heavy gas oil from the coker, etc. Energy may be provided within the container, for example, by a mixer to disperse the additive. For additives which can be dissolved or dispersed more easily in the feeds of the waste, the additive or additives are transferred into the mixing vessel and mixed with a fluid transfer medium that is compatible with the feed. Non-limiting examples of suitable fluid transfer media include hot residues (temperature between 150 ° C to 300 ° C), heavy gas oil of the coker, light cycle oil, heavy reformate and mixtures thereof. Catalytic slurry oil (CSO) can also be used, although under some conditions it can inhibit the ability of the additives to produce loose shot coke. The energy may be provided within the container, for example, by a mixer, to distribute the additive within the fluid transfer medium.

The present invention will be better understood for reference to the following non-limiting examples that are presented for illustrative purposes.

EXAMPLES Tetronic and Pluronic polymers available from BASF Corporation were used to illustrate the present invention. These polymeric compounds were co-polymers of ethylene oxide and propylene oxide. The average molecular weight for each polymeric additive was 1500. The polymeric additive compounds shown below were used in this example. These polymeric compounds are co-polymers of ethylene oxide and propylene oxide and are commercially available. The additive on the left is a Tetronic copolymer and the other on the right is a Pluronic co-polymer available from BASF Corporation. The average molecular weight for each polymeric additive was 1500. Two grams of a Baton Rouge Refinery Vaccum Towe Bottoms were loaded into a Microcarbon Reactor Test Unit (MCR). The residue was heated to 400 ° C and maintained at 400 ° C for 2 hours and the residue analyzed gravimetrically. The residue was also tested with the addition of 3000 wppm of the two above polymeric additives. Polarized light optical examination of the residues was conducted. The following table shows the results, TABLE The microscopic results are shown in photomicrographs of Figures 1, 2 and 3 thereof which demonstrate the effect of the polymeric additives of the present invention. Figure 1 is the result of no additive and many bright spheres can be observed which indicates the presence of a substantial amount of anisotropic coke. Figure 2 represents the test made using the polyoxyethylene-polyoxypropylene (Pluronic) where it was observed that relatively few microspheres are presented compared to those of Figure 1, thus indicating the suppression of anisotropic coke. Figure 3 thereof represents the test made using ethylenediamine tetraalkoxylated alcohol of polyoxyethylene-polyoxypropylene alcohol (Tetronic) where it was observed that an isotropy phase occurs indicating that the formation of anisotropic coke has been substantially completely eliminated. In this way, the polymeric additives of the present invention suppress the made anisotropic coke and alter the morphology of the coke.

Claims (10)

1. A delayed coking process, comprising: (a) heating an oil residue in a first heating zone, at a temperature below the coking temperatures, but at a temperature at which the waste is a liquid that can be pumped (b) conveying the hot residue to a second heating zone where it is heated to coking temperatures; c) conveying the hot waste from the second heating zone to a coking zone where the steam products are collected, collected from above and a coke product is formed; (d) introducing into the waste at least one polymeric additive which is effective for the formation of substantially free-flowing coke, wherein the polymeric additive is introduced into the waste at a point upstream of the second heating zone, between the second heating zone and the coking zone, or both.

2. A delayed coking process, comprising: (a) contacting a vacuum residue with an effective amount of at least one polymeric additive at a temperature from 70 ° C to 370 ° C for a time sufficient to disperse the agent uniformly within the feed, (b) heating the residue to an effective temperature to coke such feed; (c) charging and heating the residue under vacuum to a coking zone at a pressure of 15 to 80 psig (103.42 to 551.58 kPa) for a coking time that allows a hot coke bed to form, at least a portion which it is free flowing; and (d) quenching at least a portion of the hot coke bed with water.

3. The process of any previous claim, where the raw material of the waste is the vacuum residue.

4. The process of any preceding claim, wherein at least a portion of the additive is soluble in the raw material.

5. The process of any preceding claim, wherein the effective amount of the additive is from 300 to 5,000 wppm. The process of any preceding claim, wherein the polymeric additive is selected from polyoxyethylene, polyoxypropylene, polyoxyethylene-polyoxypropylene copolymer, tetra-alkoxylated alcohol of ethylenediamine of polyoxyethylene alcohol, tetra-alkoxylated alcohol of ethylenediamine of polyoxypropylene alcohol, tetra-alkoxylated alcohol of ethylenediamine of polyoxypropylene-polyoxyethylene alcohols and mixtures thereof. 7. The process of any preceding claim, wherein the molecular weight of the polymeric additive is from 1,000 to 30,000. 8. The process of any preceding claim, wherein the produced coke is substantially a coke shot. The process of any preceding claim, wherein an effective amount of a second additive is also used, which second additive is a metal-containing additive selected from one or more metallic naphthenate, metallic acetylacetonate, a Lewis acid, a material containing metal of high surface area, an inorganic oxide, and salts of inorganic oxides. 10. The process of any preceding claim, wherein the second additive is one or more of KOH; NaOH, carboxylates and acetylacetonates.