KR100979027B1 - Process for steam cracking heavy hydrocarbon feedstocks - Google Patents

Abstract

A process for feeding or cracking heavy hydrocarbon feedstock containing non-volatile hydrocarbons comprising: heating the heavy hydrocarbon feedstock, mixing the heavy hydrocarbon feedstock with a fluid and/or a primary dilution steam stream to form a mixture, flashing the mixture to form a vapor phase and a liquid phase, and varying the amount of the fluid and/or the primary dilution steam stream mixed with the heavy hydrocarbon feedstock in accordance with at least one selected operating parameter of the process, such as the temperature of the flash stream before entering the flash drum.

Description

Pyrolysis of heavy hydrocarbon feedstocks {PROCESS FOR STEAM CRACKING HEAVY HYDROCARBON FEEDSTOCKS}

The present invention relates to a method of cracking hydrocarbons containing relatively nonvolatile hydrocarbons and other contaminants.

Steam cracking has long been used to crack various hydrocarbon feedstocks into olefins. Conventional steam pyrolysis processes utilize a pyrolysis furnace having two main zones, a convection zone and a radiation zone. The hydrocarbon feedstock typically enters the convection zone of the furnace as a liquid (except for the light feedstock entering the vapor), where it is indirect contact with the hot flue gas from the radiation zone or with water vapor. It is heated and vaporized by direct contact. The vaporized feedstock and water vapor mixture is then introduced into the radiation zone, where pyrolysis takes place. The resulting product, including olefins, exits the pyrolysis furnace for further downstream treatment (eg quenching).

Conventional steam pyrolysis systems have been effective in cracking high quality feedstocks containing high fractions of light volatile hydrocarbons such as gas oil and naphtha. However, from an economical point of view of steam pyrolysis, it is often desirable, but not limited, to pyrolyze cheaper heavy feedstocks such as crude oil and atmospheric residues. Crude oils and atmospheric residues contain high molecular weight nonvolatile components with boiling points in excess of 1100 ° F. (590 ° C.). The nonvolatile components of these feedstocks are deposited as coke in the convection zone of conventional pyrolysis. Only very small amounts of non-volatile components can be tolerated downstream of the convection zone, where the harder components are completely vaporized. In addition, some naphtha is contaminated with heavy crude oil containing nonvolatile components during transport. Conventional pyrolysis does not have the adaptability to treat naphtha contaminated with residual oil, crude oil, or non-volatile components of gas oils or hydrocarbons contaminated with many residual oils or crude oils.

To address this coke formation problem, U.S. Patent No. 3,617,493, incorporated herein by reference, discloses the use of an external vaporizing drum for crude oil feed, and also provides a primary flash and 450 to 450 to remove naphtha as steam. The use of a secondary flash to remove steam having a boiling point of 1100 ° F. (230-600 ° C.) is disclosed. The steam is cracked into olefins in a pyrolysis furnace, and the separated liquid from the two flash tanks is removed and stripped with water vapor and then used as fuel.

US Pat. No. 3,718,709, incorporated herein by reference, discloses a method for minimizing coke deposition. This patent describes preheating the heavy feedstock internally or externally by pyrolysis to vaporize about 50% of the heavy feedstock with superheated water vapor and remove any remaining separated liquid. Light volatile hydrocarbon containing vaporized hydrocarbons are mainly added to the cracking process.

U. S. Patent No. 5,190, 634, incorporated herein by reference, discloses a method of inhibiting coke formation in a furnace by preheating the feedstock in the presence of a low critical amount of hydrogen in the convection zone. The presence of hydrogen in the convection zone inhibits coke formation by inhibiting the polymerization of hydrocarbons.

US Pat. No. 5,580,443, which is incorporated herein by reference, discloses a method of preheating the feedstock first and then recovering it from the preheater in the convection section of the pyrolysis furnace. This preheated feedstock is then mixed with a predetermined amount of water vapor (distilled water vapor) and then introduced into a gas-liquid separator to separate the required proportion of nonvolatile components and remove them from the separator as liquid. The vapor separated from the gas-liquid separator is returned to the pyrolysis furnace for heating and cracking.

The inventors have recognized that in using flash to separate the heavy liquid hydrocarbon fraction from the lighter fraction which can be treated in the pyrolysis furnace, it is important to separate most of the nonvolatile components in the liquid phase. Otherwise, heavy coke-forming nonvolatile components in the vapor will be transported into the furnace causing coke formation problems.

The inventors also note that in using flash to separate non-volatile components from the lighter fraction of the hydrocarbon feedstock, which can be treated in a pyrolysis furnace without causing coke formation problems, the use of vapor to liquid leaving the flash I found it important to carefully control the rain. Otherwise, valuable lighter fractions in the hydrocarbon feedstock may be lost in the liquid hydrocarbon bottom product, or the heavy coke-forming component may be vaporized and transported into the furnace as overhead product into the coke. May cause formation problems.

Controlling the vapor-to-liquid ratio leaving the flash has proved difficult because many variables are involved. The ratio of vapor to liquid is a function of the hydrocarbon partial pressure in the flash and also a function of the temperature of the stream entering the flash. The temperature of the stream entering the flash will change as the furnace load changes. If the furnace is full, the temperature is higher; if the furnace is partially loaded, the temperature is lower. The temperature of the stream entering the flash also depends on the flue temperature in the furnace heating the feedstock. The flue temperature again depends on the degree of coke formation in the furnace. If the furnace is clean or very lightly formed, the flue temperature is lower than when the coke was severely formed. Flue gas temperature is also a function of the combustion control that is done at the burners in the furnace. If the furnace is operated with a slight excess of oxygen during flue gas, the flue temperature of the middle to upper zones of the convection zone will be lower than if the furnace is operated with higher levels of excess oxygen during flue gas. Given all these variables, it is difficult to constantly adjust the ratio of vapor to liquid exiting the flash.

The present invention provides a process that is advantageously controlled to optimize the decomposition of volatile hydrocarbons contained in the heavy hydrocarbon feedstock and to eliminate or avoid coke deposition problems. The present invention provides a method of maintaining a relatively constant ratio of vapor to liquid exiting the flash by keeping the temperature of the stream entering the flash relatively constant. More specifically, the temperature of the flash stream is kept constant by automatically adjusting the amount of fluid stream mixed with the heavy hydrocarbon feedstock prior to flashing. The fluid is optionally water.

The present invention also provides a method of maintaining a relatively constant hydrocarbon partial pressure in a flash stream. By regulating the flash pressure and the ratio of fluid and steam to hydrocarbon feedstock, a constant hydrocarbon partial pressure is maintained.

Summary of the Invention

The present invention heats heavy hydrocarbons, mixes the heavy hydrocarbons with a fluid to form a mixture, and then flashes the mixture to form a vapor phase and a liquid phase, and mixes the heavy hydrocarbons according to one or more selected process operating parameters. A method of heating a heavy hydrocarbon feedstock is provided, the method comprising varying the amount of fluid being fed and feeding the vapor phase to the furnace. The fluid can be a liquid hydrocarbon or water.

According to one embodiment, the one or more operating variables may be the temperature of the heated heavy hydrocarbon prior to flashing. One or more operating parameters may also be one or more of flash pressure, temperature of the flash stream, flow rate of the flash stream, and excess oxygen in the flue gas.

In a preferred embodiment, the heavy hydrocarbons are mixed with the first dilution steam stream before flashing. In addition, the second dilution steam can be superheated in the furnace and then mixed with the heavy hydrocarbons.

The invention also

(a) preheating the heavy hydrocarbon feedstock to form a preheated heavy hydrocarbon feedstock;

(b) mixing the preheated heavy hydrocarbon feedstock with water to produce a water-heavy hydrocarbon mixture;

(c) injecting the first dilution steam into the water-heavy hydrocarbon mixture to form a mixture stream;

(d) heating the mixture stream in a row of heat exchange tubes by indirect heat transfer with hot flue gas to form a hot mixture stream;

(e) controlling the temperature of the hot mixture stream and the ratio of water vapor to hydrocarbon by varying the flow rate of water and the flow rate of the first dilution steam;

(f) flashing the hot mixture stream in a flash drum to form a vapor phase and a liquid phase, and then separating the vapor phase from the liquid phase;

(g) feeding the vapor phase into the convection zone of the furnace and further heating by hot flue gas from the radiant zone of the furnace to form a heated vapor phase;

(h) feeding the heated vapor phase to a radiant zone tube of the furnace such that the hydrocarbons in the vapor are pyrolyzed by radiant heat to form a product,

There is also provided a method of cracking heavy hydrocarbon feedstock in a furnace comprising a radiant zone burner that provides radiant heat and hot flue gas, and a convection zone consisting of multiple banks of heat exchange tubes.

1 is a schematic flow chart of a process according to the invention for steam pyrolysis, in particular in convection zones.

Unless stated otherwise, percentages, parts, ratios, etc., are all based on weight. Unless stated otherwise, reference to a compound or component includes the compound or component itself, and those compounds or components (eg, mixtures of compounds) mixed with other compounds or components.

In addition, amounts, concentrations, or other values or variables are provided listing the desired and smaller desired values, which are larger or less desirable values, whether or not these ranges are disclosed separately. It is to be understood that it specifically discloses all ranges formed from any pair of.

In the present invention, non-volatile components can also be determined as follows: The boiling point distribution of the hydrocarbon feed is measured by Gas Chromatograph Distillation (GCD) or other suitable method according to ASTM D-6352-98. Non-volatile components are fractions of hydrocarbons having a nominal boiling point higher than 1100 ° F. (590 ° C.) as measured by ASTM D-6352-98. The present invention works very well when using nonvolatile components having a nominal boiling point higher than 1400 ° F. (760 ° C.).

The present invention relates to a process for heating and steam pyrolysis of heavy hydrocarbon feedstocks. The method heats heavy hydrocarbons, mixes the heavy hydrocarbons with a fluid to form a mixture, flashes the mixture to form a vapor phase and a liquid phase, and mixes the heavy hydrocarbons according to one or more selected process operating parameters. Varying the amount of fluid.

The feedstock described includes large amounts, ie about 5-50% of heavy nonvolatile components. Such feedstocks include, but are not limited to, steam pyrolyzed gas oils and residues, gas oils, heating oils, jet fuels, diesel, kerosene, gasoline, coker naphtha, steam pyrolyzed naphtha, catalytically naphtha, Hydrocrackate, reformate, extractant reformate, Fischer-Tropsch liquid, Fischer-Tropsch gas, natural gasoline, distillate, virgin naphtha , Crude oil, atmospheric pipestill bottom products, vacuum pipe steel streams including bottom products, wide-boiling naphtha to gas oil condensates, heavy process hydrocarbon streams from refineries, vacuum gas oil, heavy gas oil, crude oil One or more of naphtha, atmospheric residue, heavy residue, C4 / residue mixture and naphtha residue mixture contaminated with.

Heavy hydrocarbon feedstocks have a nominal final boiling point of at least 600 ° F. (315 ° C.). Preferred feedstocks are low sulfur waxy residues, atmospheric residues, and naphtha contaminated with crude oil. Most preferred are residues containing 60 to 80% of ingredients having a boiling point of less than 1100 ° F. (590 ° C.), such as low sulfur content waxy residues.

The heavy hydrocarbon feedstock is first preheated in the upper convection zone 3. The heavy hydrocarbon feedstock can be heated in any form known to those skilled in the art. However, it is preferable to heat the feedstock in the upper convection zone 3 of the furnace 1 by indirect contact with the hot flue gas from the furnace's radiation zone. As a non-limiting example, this can be achieved by passing the feedstock through a row of heat exchange tubes 2 located in the upper convection zone 3 of the furnace 1. The preheated feedstock has a temperature of 300 to 500 ° F. (150 to 260 ° C.). Preferably, the temperature of the preheated feed is about 325 to 450 ° F. (160 to 230 ° C.), more preferably 340 to 425 ° F. (170 to 220 ° C.).

The preheated heavy hydrocarbon feedstock is mixed with the fluid. The fluid may be liquid hydrocarbons, water, water vapor or mixtures thereof. Preferred fluid is water. The temperature of the fluid may be below or equal to or above the temperature of the preheated feedstock.

Mixing of the fluid with the preheated heavy hydrocarbon feedstock may be effected either inside or outside the pyrolysis furnace 1, but preferably outside the furnace. Mixing can be carried out using any mixing device known in the art. However, it is preferred to use the first ejector 4 of the double sparger assembly 9 for mixing. The first ejector 4 preferably comprises a perforated inner conduit 31 surrounded by the outer conduit 32 such that an annular flow space 33 is formed between the inner and outer conduits. Preferably, the preheated heavy hydrocarbon feedstock flows into the annular flow space, the fluid flows through the inner conduit and is injected into the feedstock through an opening in the inner conduit, preferably through a small circular hole. The first ejector 4 is provided to avoid or reduce hammering caused by sudden vaporization of the fluid when the fluid is introduced into the preheated heavy hydrocarbon feedstock.

The present invention uses steam streams in various parts of the process. The first dilution steam stream 17 is mixed with the preheated heavy hydrocarbon feedstock as described in detail below. In a preferred embodiment, the second dilution steam stream 18 is treated in the convection zone and then mixed with the heavy hydrocarbon fluid-first dilution steam mixture before flashing. The second dilution steam 18 is optionally divided into a bypass steam 21 and a flash steam 19.

In a preferred embodiment according to the present invention, in addition to the fluid mixed with the preheated heavy feedstock, the first dilution steam 17 is also mixed with the feedstock. The first dilution steam stream can preferably be injected into the second jet 8. It is preferable to inject the first dilution steam stream into the heavy hydrocarbon-fluid mixture before the resulting stream mixture enters the convection zone in (11) for further heating by radiation zone flue gas. Even more preferably, the first dilution steam is injected directly into the second jet 8, and the first dilution vapor is injected into the hydrocarbon feedstock-fluid mixture through a small circular flow distribution hole 34 as it passes through the jet. Be sure to

The first dilution steam may have a temperature that is higher, lower, or approximately the same as that of the heavy hydrocarbon feedstock-fluid mixture, but is preferably higher than the temperature of the mixture, thereby partially vaporizing the feedstock / fluid mixture. Do it. Preferably, the first dilution steam is superheated before injection into the second jet 8.

By exiting the second blower 8, the mixture of the fluid, the preheated heavy hydrocarbon feedstock, and the first dilution steam stream is heated again in the pyrolysis furnace 1 before flashing. Heating can be achieved by way of non-limiting example, by heating the feedstock mixture through a row of heat exchange tubes 6 located in the convection zone of the furnace and heating by hot flue gas from the furnace's radiation zone. This heated mixture exits the convection zone as a mixture stream 12 to be subsequently mixed with additional steam streams.

Optionally, the second dilution steam stream 18 skips the flash steam stream 19, which is mixed with the heavy hydrocarbon mixture 12 before the flash, and the flash of the heavy hydrocarbon mixture, and instead replaces the vapor phase from the flash with the furnace. It can be further divided into a bypass steam stream 21 which is mixed with these vapor phases before pyrolysis in the radiation zone. The present invention can work well when the second dilution steam 18 is all used as the flash steam 19 without the bypass steam 21. Alternatively, the present invention can be operated even when the second dilution steam 18 is directed only to the bypass stream 21 without the flash stream 19. In a preferred embodiment according to the invention, the ratio of the flash steam stream 19 to the bypass steam stream 21 should preferably be between 1:20 and 20: 1, most preferably between 1: 2 and 2: 1. Flash steam 19 is mixed with heavy hydrocarbon mixture stream 12 to form flash stream 20 before being flashed in flash drum 5. Preferably, the second dilution steam stream is superheated in the superheater portion 16 of the convection zone of the furnace before it is split and mixed with the heavy hydrocarbon mixture. The addition of flash steam stream 19 to the heavy hydrocarbon mixture stream 12 allows almost all of the volatile components of the mixture to vaporize before the flash stream 20 enters the flash drum 5.

Flash to separate the mixture of fluid, feedstock and first dilution steam stream (flash stream 20) into two phases, a vapor phase comprising predominantly volatile hydrocarbons and a liquid phase comprising predominantly nonvolatile hydrocarbons. It is introduced into the drum 5. The vapor phase is preferably removed from the flash drum as an overhead vapor stream 13. The vapor phase is preferably fed back to the lower convection zone 23 of the furnace for optional heating and also through the crossover pipe to the radiation zone for pyrolysis for decomposition. The separated liquid phase is removed from flash drum 5 as bottoms stream 27.

It is desirable to maintain a certain constant ratio of vapor to liquid in the flash drum 5. However, this ratio is difficult to measure and adjust. As an alternative, the temperature of the mixture stream 12 before the flash drum 5 is used as an indirect variable for measuring, adjusting and maintaining a constant vapor to liquid ratio in the flash drum 5. Ideally, when the mixture stream temperature is higher, more volatile hydrocarbons will vaporize and become available as vapor phases for cracking. However, if the mixture stream temperature is too high, more heavy hydrocarbons are present in the vapor phase and carried convection into the tube, eventually forming coke in the tube. If the mixture stream 12 temperature is too low and the vapor to liquid ratio in the flash drum 5 is low, more volatile hydrocarbons will remain in the liquid phase and will not be used for decomposition.

The mixture stream temperature is limited by conditions that maximize recovery / vaporization of volatile components in the feedstock while avoiding coke formation in the furnace tube or coke formation in the pipes and vessels 13 that transport the mixture from the flash drum to the furnace. Receive. Monitor the pressure drop across the pipe and vessel 13 and crossover pipe 24 that transport the mixture to the lower convection zone, and the temperature rise across the lower convection zone 23 to detect the onset of coke formation problems. can do. For example, if the crossover pressure and process inlet pressure into the lower convection zone 23 increase rapidly due to coke formation, the temperatures of the flash drum 5 and the mixture stream 12 must be reduced. If coke is formed in the lower convection zone, the temperature of the flue gas to the superheater 16 increases, requiring more superheater water 26.

The choice of temperature of the mixture stream 12 is also determined by the composition of the feedstock material. When the feedstock contains a greater amount of light hydrocarbons, the temperature of the mixture stream 12 can be set lower. Accordingly, the amount of fluid used in the first ejector 4 is increased and / or the amount of the first dilution water vapor used in the second ejector 8 is reduced, which amounts to the mixture stream 12. This is because it directly affects the temperature of). When the feedstock contains higher amounts of nonvolatile hydrocarbons, the temperature of the mixture stream 12 must be set higher. As a result, the amount of fluid used in the first blower 4 is reduced while the amount of the first dilution steam used in the second blower 8 is increased. By carefully selecting the mixture stream temperature, the present invention can be applied to a wide variety of feedstock materials.

Typically, the temperature of the mixture stream 12 is 600 to 950 ° F. (315 to 510 ° C.), preferably 700 to 920 ° F. (370 to 490 ° C.), more preferably 750 to 900 ° F. (400 to 480 ° C.) Most preferably, it is set and adjusted to 810-890 [deg.] F (430-475 [deg.] C). These values change as the volatile components are concentrated in the feedstock as discussed above.

The temperature of the mixture stream 12 is regulated by a control system 7 comprising at least a temperature sensor and any known control device (eg, using a computer). Preferably the temperature sensor is a thermocouple. The control system 7 is in communication with the fluid valve 14 and the first dilution steam valve 15 to regulate the amount of fluid and the first dilution steam entering the two ejectors.

In order to maintain a constant temperature for the mixture stream 12 mixed with the flash stream 19 and entering the flash drum, to achieve a constant vapor to liquid ratio in the flash drum 5, there is also a substantial temperature change and flash steam. In order to avoid the change in the liquid to liquid ratio, the present invention operates as follows: Once the temperature of the mixture stream 12 before the flash drum 5 is set, the control system 7 controls the fluid valves 14 and the second on both ejectors. 1 Adjust the dilution steam valve 15 automatically. When the control system 7 detects a temperature drop in the mixture stream, this causes the fluid valve 14 to reduce fluid injection into the first ejector 4. As the temperature of the mixture stream begins to rise, the fluid valve opens wider to increase the fluid injected into the first ejector 4. In a preferred embodiment, the latent heat of fluid vaporization controls the mixture stream temperature.

When the first dilution steam stream 17 is injected into the second jet 8, the second jet 8 is also controlled by using the temperature control system 7 to adjust the first dilution steam valve 15. The amount of the first dilution steam stream injected into can be adjusted. This further reduces the sudden change in temperature change in the flash 5. When the control system 7 detects a temperature drop in the mixture stream 12, the first dilution steam valve 15 is first dilute steam into the second jet 8 while further closing the valve 14. Instruction to increase the injection of the stream. As the temperature begins to rise, the first dilution steam valve is automatically closed further, opening the valve 14 more widely to reduce the first dilution steam stream injected into the second blower 8.

In a preferred embodiment according to the invention, the control system 7 can be used to control both the amount of fluid injected into the two jets and the amount of the first dilution steam stream.

If the fluid is water, the controller varies the amount of water and the first dilution steam to maintain a constant mixture stream temperature 12 while maintaining a constant ratio of water to feedstock in the mixture 11. In order to further avoid sudden changes in flash temperature, the present invention also preferably utilizes an intermediate superheat reducer 25 in the superheat zone of the second dilution steam in the furnace. Thereby, the outlet temperature of the superheater 16 can be adjusted to a constant value regardless of furnace load change, coke formation degree change, and excess oxygen level change. Typically, this superheat reducer 25 has a temperature of the second dilution steam of 800-1100 ° F. (430-590 ° C.), preferably 850-1000 ° F. (450-540 ° C.), more preferably 850-950. F ° (450-510 ° C.), most preferably 875-925 ° F. (470-500 ° C.). The superheat reducer is preferably a control valve and a water atomizing nozzle. After partial preheating, the second dilution steam exits the convection zone and is subjected to a fine spray 26 of water which is rapidly vaporized to lower the temperature. The steam is then further heated in the convection zone. The amount of water added to the superheater controls the temperature of the water vapor mixed with the mixture stream 12.

It is desirable to adjust the amount of fluid and the first dilution steam stream injected into the heavy hydrocarbon feedstock of the two jets 4, 8 according to the desired temperature of the mixture stream 12 before the flash drum 5, but the same control. The mechanism can be applied to other variables at different locations. For example, the flash pressure, temperature and flow rate of the flash steam 19 can be varied to change the vapor to liquid ratio in the flash. Excess oxygen during flue gas can also be a control variable, albeit slowly.

In addition to maintaining a constant temperature of the mixture stream 12 entering the flash drum, it is also desirable to maintain a constant hydrocarbon partial pressure of the flash stream 20 to maintain a constant ratio of vapor to liquid in the flash. For example, by using a control valve 36 in the vapor phase line 13 to maintain a constant flash drum pressure, and also by adjusting the ratio of water vapor to hydrocarbon feedstock in the stream 20, to maintain a constant hydrocarbon partial pressure. Can be.

Typically, the hydrocarbon partial pressure of the flash stream of the present invention is set and adjusted to 4 to 25 psia (25 to 175 kPa), preferably 5 to 15 psia (35 to 100 kPa), most preferably 6 to 11 psia (40 to 75 kPa). .

The flash is performed in one or more flash drum containers. Preferably the flash is a one step process with or without reflux. The flash drum 5 is typically operated at a pressure of 40 to 200 psia (275 to 1400 kPa), the temperature of which is usually equal to or slightly lower than the temperature of the flash stream 20 before entering the flash drum 5. Typically, the pressure in the flash drum container is about 40-200 psia (275-1400 kPa) and the temperature is about 600-950 ° F. (315-510 ° C.). Preferably, the pressure in the flash drum container is about 85 to 155 psia (600 to 1100 kPa) and the temperature is about 700 to 920 ° F. (370 to 490 ° C.). More preferably, the pressure in the flash drum container is about 105 to 145 psia (700 to 1000 kPa) and the temperature is about 750 to 900 ° F. (400 to 480 ° C.). Most preferably, the pressure in the flash drum container is about 105 to 125 psia (700 to 760 kPa) and the temperature is about 810 to 890 ° F (430 to 480 ° C.). Depending on the temperature of the flash stream, usually 50 to 95%, preferably 60 to 90%, more preferably 65 to 85% and most preferably 70 to 85% of the mixture entering the flash drum 5 is the flash drum. Is vaporized to the top of.

In one embodiment, the flash drum 5 is operated to minimize the temperature of the liquid phase at the bottom of the vessel because too much heat can cause coke formation of the nonvolatile components in the liquid phase. The use of the second dilution steam stream 18 in the flash stream entering the flash drum lowers the vaporization temperature because it reduces the partial pressure of hydrocarbons (ie, the larger mole fraction in the vapor is water vapor) and thus lowers the required liquid phase temperature. . This may also help to cool a portion of the externally cooled flash drum bottom liquid 30 to the flash drum container to cool the newly separated liquid phase at the bottom of the flash drum 5. Stream 27 is transported from cooler 28 via pump 37 from the bottom of flash drum 5. The cooled stream 29 is divided into a recycle stream 30 and an outlet stream 22. The temperature of the stream to be recycled is ideally 500 to 600 ° F. (260 to 315 ° C.), preferably 505 to 575 ° F. (263 to 302 ° C.), more preferably 515 to 565 ° F. (268 to 296 ° C.), most Preferably it is 520-550 degreeF (270-288 degreeC). The amount of stream recycled should be about 80 to 250%, preferably 90 to 225%, more preferably 95 to 210%, most preferably 100 to 200% of the amount of freshly separated bottom liquid inside the flash drum. do.

In another aspect, the flash drum is also operated to minimize liquid retention / retention time in the flash drum. Preferably, the liquid phase exits the vessel via a small diameter “boot” or cylinder 35 at the bottom of the flash drum. Typically, the liquid phase residence time in the drum is less than 75 seconds, preferably less than 60 seconds, more preferably less than 30 seconds, most preferably less than 15 seconds. The shorter the liquid phase retention / retention time in the flash drum, the less coke is deposited at the bottom of the flash drum.

In the flash, the vapor phase 13 usually contains less than 400 ppm, preferably less than 100 ppm, more preferably less than 80 ppm and most preferably less than 50 ppm nonvolatile components. The vapor phase is very high in volatile hydrocarbons (such as 55 to 70%) and water vapor (such as 30 to 45%). The final boiling point of the vapor phase is usually below 1400 ° F. (760 ° C.), preferably below 1100 ° F. (600 ° C.), more preferably below 1050 ° F. (570 ° C.) and most preferably below 1000 ° F. (540 ° C.). Optionally, the vapor phase is continuously removed from the flash drum 5 via a overhead pipe that carries steam to a centrifuge 38, which removes trace amounts of entrained liquid. The steam then flows into the manifold which distributes the flow to the convection zone of the furnace.

The vapor phase stream 13, which is continuously removed from the flash drum, is preferably superheated to about 800 to 1200 ° F. (430 to 650 ° C.), for example by pyrolysis, by flue gas from the radiant zone from the lower convection section 23 to the furnace. . The steam is then introduced and decomposed into the radiation zone to the pyrolysis furnace.

The vapor phase stream 13 removed from the flash drum is optionally mixed with the bypass steam stream 21 before being introduced into the furnace lower convection zone 23.

Bypass steam stream 21 is a steam stream divided from second dilution steam 18. Preferably, the second dilution steam is first heated in the pyrolysis furnace 1 before being split and mixed with the vapor phase steam removed from the flash 5. In some applications, the bypass steam can be superheated again after being separated from the second dilution steam but before mixing with the vapor phase. The overheated steam 21 is mixed with the vapor phase stream 13 and then superheated so that all components except the heaviest of the mixtures in this section of the furnace are vaporized before entering the radiation zone. Increasing the temperature of the vapor phase in the lower convection zone 23 to 800-1200 ° F. (430-650 ° C.) assists in operation in the radiation zone since the radiant tube metal temperature can be reduced. This reduces the likelihood of coke formation in the radiation zone. The superheated steam is then decomposed in the radiation zone to the pyrolysis furnace.

From the foregoing description, those skilled in the art can readily identify the essential features of the present invention, and various changes and modifications can be made to the present invention without departing from the spirit and scope thereof. You can make it. For example, although preferred embodiments require the use of water to mix with the preheated feedstock in the ejector, other fluids such as naphtha may also be used.

The invention is illustrated by the following examples which are provided for purposes of illustration and are not to be considered as limiting the scope of the invention. Unless stated otherwise, percentages, parts, etc., are all based on weight.

Example 1

Industrial calculations were performed to simulate the treatment of atmospheric pipe steel bottom products (APS) and crude oil according to the present invention. The accompanying Table 1 summarizes the results of the simulation of tapping ATP bottoms product and tapes crude oil in a commercial size furnace with flash drums. Very light components in crude oil work like water vapor to reduce the partial pressure of heavy components. Thus, at a nominal 950 ° F. (510 ° C.) cut point, the flash drum can be operated at a temperature of 100 ° F. (38 ° C.) lower than the atmospheric residue.

Example 2

Table 2 summarizes the simulated performance of the flash of residue mixed with two concentrations of C4. At the desired flash temperature, pressure and water vapor rate, each% of C4 mixed with the residue increases the vaporized residue in the flash by about 1/4%. Thus, adding C4 to the feed vaporizes more hydrocarbons from the residue.                 

Claims (31)

Heating the heavy hydrocarbons, Mixing the heavy hydrocarbons with a fluid to form a mixture, Flashing the mixture to form a vapor phase and a liquid phase, Process operation selected from the group consisting of the temperature of the heavy hydrocarbon before the mixture is flashed, the pressure at which the mixture is flashed, the temperature at which the mixture is flashed, the flow rate of the mixture, the excess oxygen in the flue gas produced by the furnace and combinations thereof Varying the amount of fluid mixed with the heavy hydrocarbons in accordance with the parameters, and Feeding the vapor phase to a furnace Comprising, a heavy hydrocarbon feedstock heating method. The method of claim 1, Wherein the process operating parameter is the temperature of the heavy hydrocarbon before the mixture is flashed. The method of claim 1, Wherein said operating parameter is selected from the group consisting of the pressure at which the mixture is flashed, the temperature at which the mixture is flashed, the flow rate of the mixture and excess oxygen in the flue gas produced by the furnace. The method according to any one of claims 1 to 3, Prior to flashing the mixture, further comprising mixing the heavy hydrocarbon with a first dilution steam. The method according to any one of claims 1 to 3, Prior to mixing the heavy hydrocarbons with the fluid, the heavy hydrocarbons are heated in a convection zone to a pyrolysis furnace. The method according to any one of claims 1 to 3, A method of heating a heavy hydrocarbon feedstock, wherein the fluid comprises at least one of liquid hydrocarbons and water. delete The method according to any one of claims 1 to 3, Prior to flashing the mixture, a second dilution steam stream is superheated in a pyrolysis furnace and then mixed with the mixture. delete The method according to any one of claims 1 to 3, Heavy hydrocarbon feedstock heating, wherein the heavy hydrocarbon comprises one or more of vacuum gas oil, heavy gas oil, crude oil contaminated with naphtha, atmospheric residue, heavy residue, C4 / residue mixture, naphtha / residue mixture and crude oil Way. The method according to any one of claims 1 to 3, Wherein the nominal final boiling point of the heavy hydrocarbon is at least 315 ° C. (600 ° F.). The method according to any one of claims 1 to 3, And wherein the final boiling point of the vapor phase is below 760 ° C. (1400 ° F.). delete The method of claim 4, wherein The furnace comprises a convection zone consisting of a radiant zone burner for providing radiant heat and hot flue gas, and a heat exchange tube of several banks; The fluid is water; This method, Prior to flashing the mixture, heating the mixture to a controlled temperature by indirect heat transfer with hot flue gas in a row of heat exchange tubes, wherein both the regulated temperature and the ratio of water vapor to hydrocarbon are dependent upon the flow rate of water and 1 step controlled by varying the flow rate of the dilute steam, Performing a flashing step in a flash drum to form a vapor phase and a liquid phase, and separating the vapor phase from the liquid phase, Supplying the vapor phase to the convection zone of the furnace to be further heated by hot flue gas from the radiant zone of the furnace to form a heated vapor phase, and Feeding said heated vapor phase to a radiation zone tube of said furnace, wherein hydrocarbons in said vapor phase are pyrolyzed by radiant heat to form a product Further comprising a heavy hydrocarbon feedstock heating method. The method of claim 14, Wherein the first dilution steam is mixed with the water and the heavy hydrocarbon feedstock and then injected into the product mixture. delete delete The method of claim 14, 60-80% of the heavy hydrocarbon feedstock is boiled below 600 ° C. (1100 ° F.). delete The method of claim 14, Wherein the controlled temperature is between 315 ° C. and 510 ° C. (600 ° F. to 950 ° F.). delete delete delete delete delete delete delete delete delete delete delete

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