FI119843B - Method for thermal cracking of residual hydrocarbon oil - Google Patents

Description

This invention relates to a process for thermal cracking of residual hydrocarbon oil. More specifically, this method relates to a process for thermal cracking of residual hydrocarbon oil, wherein the thermal cracking is combined with the gasification treatment of an asphaltene-rich base product obtained from said thermal cracking.

Tail hydrocarbon oils can be obtained as a base product from the distillation of crude oil at normal pressure ("normal pressure" or "long" residue) or under reduced pressure ("vacuum" or "short" residue).

The conversion of residual hydrocarbon oils by thermal cracking has long been known. In principle, thermal-cracking is an endothermic, non-catalytic process in which the larger hydrocarbon molecules of the residual oil fractions are cut into smaller molecules. The energy required to break larger molecules into smaller ones is supplied by heating the residual hydrocarbon oil feed to a sufficiently high temperature. However, a commonly recognized problem in thermal cracking operations is the formation of coke, especially under more severe cracking conditions. There are several ways known in the art to reduce the formation of this coke. For example, if the conversion of heavy hydrocarbons, i.e. hydrocarbons having a boiling point of 520 ° C and higher (520 ° C + hydrocarbons), is kept low enough, the formation of coke can be largely prevented. Depending on the feed type and the severity of the 1 heat cracking, said conversion level (hereinafter referred to as the 520 ° C + -30 version, i.e. the percentage by weight of hydrocarbons in the feed having a boiling point of 520 ° C and higher and converted to lower boiling components) 30% by weight. Another way to substantially prevent the formation of coke is to remove the asphalt 35 from the residual hydrocarbon oil before heat cracking, in which case more than 30% by weight or higher 520 ° C + conversions j 2 are achievable. The disadvantage, however, is that the asphaltenes to be removed can no longer participate in the production of distillates without further processing, separate from the asphalted oil.

5 The structure of an oven absorption vessel is known in the art of thermal cracking. The furnace undergoes heating of the residual hydrocarbon feed and a significant portion of the hydrocarbon feed is already cracked to lower boiling components. The heated oil is then fed to a soaking vessel or "reaction chamber". In these 10 impregnation vessels, the cracking reactions continue. Because cracking in the furnace is relatively cheap and easy, the usual goal is to convert as much high boiling material in the furnace as possible and use a solvent to further increase the conversion. However, the conversion level achieved in the furnace is limited by the formation of coke. In a conventional furnace soaking vessel structure where about 30% by weight of the final 520 ° C conversion can be achieved, about half of the final conversion (i.e., about 15% by weight) occurs in the oven and the other half in the soaking vessel. If the conversion in the furnace were higher, indicating that the cracking conditions were more severe, coke would be rapidly formed and precipitated in the furnace interior, thereby causing a rapid reduction in the heating efficiency of the furnace and hence a reduction in final conversion.

On the other hand, the formation of coke and the subsequent precipitation of coke on the metal parts of the impregnation vessel is also a commonly recognized problem in conventional thermal cracking processes. Therefore, the 520 ° C + conversion in the absorption vessel also has a maximum value. It will be appreciated that too rapid formation of 30 coke in the impregnation vessel also adversely affects the run time of the process after each cleaning of the equipment.

In addition, since heat is not usually introduced into the impregnation vessel, the temperature of the heated and partially modified oil 35 drops by about 15 to 30 ° C during passage through the impregnation vessel. This decrease in temperature is mainly due to the endothermic nature of the cracking reactions, formation of light distillates, and heat loss to the environment through the walls of the impregnation vessel. As a result of this decrease in temperature in the absorption vessel, the cracking reactions in the direction of the oil flow are reduced. Thus, the cracking efficiency in the impregnation vessel is not at an ideal level.

EP-A-0 328 216 discloses a process for thermal cracking of residual hydrocarbon oils, which is carried out without a furnace and wherein the residual hydrocarbon oil feed 10 is fed directly to the impregnation vessel together with hot synthesis gas. This synthesis gas is derived from the gasification of a heavy asphaltene-containing heavy hydrocarbon oil from the cracker residue of a thermal cracker. Thus, heating of the residual hydrocarbon oil feed is effected by direct heat exchange with hot synthesis gas. Although this method works well and provides a very high level of one-level between heat cracking and gasification, it cannot easily be applied to an existing refinery with thermal cracking and gasification capacity, as this would require major changes to both refinery adjustments and especially thermal cracking equipment. Such an application would therefore be very costly, calling into question its economic viability.

The present invention aims to improve the final 520 ° C + conversion of oven-soaked container designs to at least 35% by weight. In addition, the present invention aims to provide a thermal cracking process that can be applied relatively easily and at a relatively low cost to an existing refinery with at least thermal cracking capacity and optionally a cavity; residential capacity. More particularly, the present invention aims to reduce coke formation and precipitation in both the furnace and the soaking vessel while simultaneously improving the cracking efficiency in the soaking vessel, thereby increasing both 520 ° C + conversion and running time, which is obviously economically advantageous.

4

All of the above objectives have been achieved by the present invention, which relates to a process for thermal cracking of residual hydrocarbon oil which achieves a final 520 QC + conversion of at least 35% by weight, i.e. at least 35% by weight of hydrocarbons present in residual hydrocarbon having a boiling point 520 ° C or higher, converting to lower boiling components, said method comprising the steps of: (a) heating the charcoal oil feed furnace 10 to 400-510 ° C for a time sufficient to achieve 30-45% of the final 520 QC + conversion; {b) feeding the partially modified hot hydrocarbon oil and hot hydrogen gas formed in step (a) into a suction vessel, said hydrogen gas having a temperature sufficiently high to maintain the temperature of the hydrocarbon oil in the absorbent vessel by direct heat exchange from 420 to 650 ° C * up to 100% from the c + conversion, and (c) hydrogen retains its gas and cracked residue si-20 from a gas fraction recovery vessel.

Suitable residual hydrocarbon feeds which may be used in step (a) are heavy hydrocarbon feeds containing at least 25% by weight of 520 ° C + hydrocarbons, preferably more than 37.5% by weight of 520 ° C + hydrocarbons, and more preferably more than 75% by weight. % 520 ° C + hydrocarbons. Feeds containing more than 90% by weight of 520 ° C + hydrocarbons are most preferably used. Thus, suitable inputs are normal pressure residues and vacuum residues. If desired, the residual hydrocarbon oil may be blended with a heavy oil such as a hydrocarbon oil fraction, a catalytic cracker or a heavy hydrocarbon oil obtained by the extraction of the residual hydrocarbon oil. In step (a) \ 35 of the process of this invention, the residual hydrocarbon is heated in an oven at a temperature of 400-510 ° C for a sufficient time to achieve 30-45% of the final 5,520 ° C + conversion. In any event, the combination of oven temperature and dwell time should be such that 30-45% of the final 520 ° C + conversion occurs in this oven. Since, in conventional thermal cracking processes containing an oven and a subsequent soaking vessel, approximately 50% of the final conversion occurs in the oven, this indicates that the oven uses relatively mild heat-cracking conditions, such as those commonly used in visbreaking methods. The result of using relatively mild conditions in the furnace is that this furnace has less coking, thus allowing longer operating times. It is understandable that this is very attractive economically.

15 To compensate for the relatively low conversion of the float, the conversion absorbing stage must be higher than normal, i.e., greater than 50% of the final 52 0 ° 0 + conversion. In the process of the present invention, this is achieved by feeding hot hydrogen-containing gas to the impregnation vessel.

In this way, the aforementioned temperature drop in the impregnation vessel in the direction of the oil flow is avoided, and thus the thermal cracking reactions can proceed throughout the impregnation vessel at the same rate. The hot hydrogen-containing gas may be introduced into the impregnation vessel at one or more locations on its interior and / or on the basis of the impregnation vessel. In the event that the heated hydrocarbon oil feed from the furnace is fed from the bottom of the impregnation vessel, the hot gas is preferably fed from one or more locations within the impregnation vessel to ensure effective heating. On the other hand, if said oil supply arrives at the top of the impregnation vessel, the hot gas may suitably be supplied from the bottom of the impregnation vessel, since in this mode the convulsive gas and oil flow move from the opposite direction through the impregnation vessel.

ensures efficient heat transfer between hot gas and oil. In addition to its heat transfer medium function, hot gas also acts as a stripping agent for removing lighter fractions 6 from the cracked oil, thereby increasing the stability of the remaining liquid, which in turn results in reduced coke formation on the metal parts inside the absorbent vessel. In this way, longer operating times and a higher final conversion of 520 ° C + can be achieved. The use of hydrogen-containing gas as a stripping agent in the thermal cracking process of this invention also constitutes a separate aspect of this invention. The presence of hydrogen during thermal cracking is also considered to be favorable to the stability of the remaining liquid and thus to the suppression of coke formation. Namely, thermal cracking in the presence of hydrogen is known to reduce the formation of carbon products during thermal cracking of heavy hydrocarbon oils, and is advantageous in terms of the stability of the oils formed, as described, for example, in JP-A-62-96 589.

The hydrogen-containing gas used in step (b) may, in principle, be any gas which is stable at elevated temperatures and contains hydrogen. It can be, for example, pure hydrogen or hydrogen-enriched gas. Particularly in a refinery with hydrotreating units, the use of such gases may be advantageous. Hot synthesis gas can also be used as hot hydrogen containing gas. This is a very useful alternative, which 25 refinery has a gasification unit in which hot synthesis gas is produced by gasification or partial oxidation of heavy asphaltene-containing oil fractions. In addition, the synthesis gas from the gasification unit may also contain carbon black. Without wishing to be bound by any particular theory, the presence of carbon black in the impregnation vessel may be advantageous because it provides a surface for the precipitation of coke and coke precursors thereby preventing contamination of the metal moieties in the impregnation vessel and can act catalytically in the activation of hydrogen gas present in synthesis gas. thanks to metals. In this context, the presence of nickel (as nickel sulphide) is considered particularly important.

7

It is to be understood that, due to the above-mentioned beneficial effects, hydrogen may also be present in the thermal cracking reactions in step (a) of the process of the present invention, i.e. in the furnace.

In any event, the hydrogen-containing gas must be stable at the high temperatures necessary to maintain the temperature of the hydrocarbon oil in the suction vessel at a temperature between 420 and 650 ° C, preferably 450 to 600 ° C, by direct heat exchange. As mentioned hereinbefore, by supplying heat and hydrogen to the impregnation vessel in the form of hot hydrogen gas, the temperature drop in the impregnation vessel is at least significantly reduced and the formation of coke on the metal parts inside the impregnation vessel which are in direct contact with the hydrogen gas or more of the final conversion can be accomplished in the impregnation vessel without excessive coke formation. Since coke formation is significantly reduced also in the furnace due to milder cracking conditions, the overall result is less coke formation from the furnace and into the interior of the impregnation vessel and thus longer operating times can be achieved. In other words, by shifting the conversion to some extent and under certain conditions from the furnace to the impregnation vessel, the formation of coke is reduced and longer operating times are achieved.

The total pressure in the impregnation vessel may range from 200 kPa to 10 MFa (2 to 100 bar). However, for economic reasons, it is preferable to use total pressures between 200 kPa and 6.5 MPa (2 to 65 bar). At pressures greater than 6.5 MPa (65 bar), and in particular above 10 MPa (100 bar), the high pressure equipment required is so expensive that it becomes extremely difficult to carry out this process economically.

Once the thermal cracking has occurred, the gaseous fraction containing the hydrogen-containing gas and the cracked residue is recovered from the impregnation vessel in step (c). Said gaseous fraction can then be further separated in a separator into a light fraction containing methane, ethane, and hydrogen gas, one or more gaseous lower hydrocarbons, i.e., propane, butane and the like, and a bottom fraction. If desired, the hydrogen-containing gas 5 may then be separated from said light fraction by, for example, a process in which adsorption is achieved by pressure variation. The cracked residue may have different uses. For example, it may be partially or completely recycled and mixed with the furnace and / or the feed of the soaking vessel 10 to re-expose it to thermal cracking conditions. However, it is preferred that in the next step (d) the cracked residue is further separated into one or more asphaltene-poor fractions and an asphaltene-rich base fraction. This separation may conveniently be carried out by expansion vacuum distillation or vacuum distillation. In this embodiment, the bottom fraction obtained by fractional distillation of the gaseous fraction from the impregnation vessel may optionally be vacuum distilled together with said cracked residue.

20 The asphaltene-rich base fraction can then be used in a number of ways. For example, it can be used in asphalt for road paving and roofing purposes, in emulsion fuels or in solid fuels through pelleting. However, in a preferred embodiment of the present invention, the asphaltene-rich base fraction is partially oxidized (gasified) in a further step (e) in the presence of oxygen and steam, generally high pressure steam, thereby producing hot synthesis gas. This synthesis gas, in turn, can be used in the refinery as pure combustion gas or as an aid to electricity and steam generation, hydrogen production and hydrocarbon synthesis processes. However, for the purposes of the present invention, it is preferred that j at least a portion of the hot synthesis gas produced in step (e) | the sludge is fed to the impregnation vessel according to step (b) of the method 35 of this invention.

9

Figure 1 illustrates an example of a refinery diagram that includes a preferred embodiment of the thermal cracking method of the present invention, i.e. the furnace impregnation vessel structure located in conjunction with the gasification unit.

The residual hydrocarbon oil feed (6) is fed to the furnace (2), where it is heated to 400-510 ° C and 30-45% of the final conversion occurs. The hot partially modified hydrocarbon oil (7) is removed from the furnace and fed to the impregnation vessel (3) together with the hot synthesis gas 10 (9) produced in the gasification unit (1) by partial oxidation of the asphaltene-containing fraction (19) with oxygen / vapor. being. The gaseous fraction (10) and the cracked residue (15) are recovered from the impregnation vessel (3). The gaseous fraction (10) is separated in a fractional distillation apparatus (4) into a light fraction (11) containing methane, ethane and synthesis gas, a light hydrocarbon fraction (12) and (13) and a bottom fraction (14). This bottom fraction (14) is fed to the vacuum distillation apparatus (5) together with the cracked residue (15), where separation into low 20 asphaltene fractions (16), (17) and (18) and a high asphaltene bottom fraction (19) occurs. Thereafter, a portion of the bottom fraction (19) is used to supply the gasification unit (1).

The present invention will be further described by the following Examples.

Example 1 and Comparative Example 1

Upon exposure to a Middle East quality short residue having the properties set forth in Table I for thermal cracking, a final weight conversion of 40% by weight at 520 ° C + can be achieved using the process of this invention as described in Figure 1 (Example 1). Under similar conditions, the conventional thermal cracking process yields a final 520 ° C + conversion of only 31% by weight (Comparative Example 1). The pressure in the impregnation vessel in Example 1 is 3 to about 1 MPa (10 bar). Other conditions under which both heat cracking processes take place, as well as conversion levels in the oven and in the soaking vessel and product stream yields are shown in Table II. The numbers in the "flow / unit" column refer to the numbers used in Figure 1.

From the results given in Table II, it can be concluded that, compared to the conventional oven impregnation vessel heat cracking process, the process of the present invention allows for a higher final 520 ° C conversion resulting in higher yields of useful product streams boiling below 520 DC and less 10 hydrocarbons.

Table I Feed Properties 350-520 ° C Fraction 5.0 wt% 520 ° C + Fraction (wt%) _ 95.0 Sulfur (wt%) __ 5.4

Conradson carbon number 20.3 wt%) C7-as £ aldenes (wt%) 10.2 viscosity at 2350 at 100 ° C (mm2 / s) __ density 70/4 0.998 11

Table II heat cracking tests flow / - example 1 ver. Example 1 unit feed 6 1000 1000 (t / d) feed gas 9 255 (t / d)

T gas (° C> 9,650 FOT (° C) 2,460,460 SOT (° C) __ 3__460 __432______ product streams (t / d) gas 11,288.6 25.2 0-165 ° C 12 74.4 54.0; 165 - 350 ° C 13 140.7 104.1 350 - 520 ° C 16, 17, 18 182.5 166.7 520 ° C + __ 19__568,8_ 650.0_520 ° C + conversion (wt%) in oven 15 (37 , 5%) 15 (48.4%) final 40 31

The abbreviations and expressions used in Table II have the following meaning: t / d: tonnes / day by weight: percentage by weight of feed gas: synthesis gas from the gasification unit

T gas: feed gas temperature FOT: furnace outlet temperature SOT: infiltration outlet temperature;

Product streams are shown in their boiling range! and the 520 ° C + conversion represents the final conversion (11 final ") and what portion of it has been achieved in the furnace. The percentage in the bones 12 indicates the percentage of the final 520 ° C + conversion achieved in the furnace.

Example 2 To a 100 ml mixing autoclave was added about 25 g of the same Middle East short residue used in Example 1. The filled autoclave was pressurized with synthetic gas to 5 MPa (50 bar). The reactor and its contents were then heated. was quickly maintained at 450 ° C (2 minutes starting at 350 ° C) and maintained at this temperature for 20 minutes, allowing the heat-cracking reactions to occur, then cooling the reactor rapidly to room temperature, depressurizing and decanting the autoclave and collecting the sample for analysis. The amount of coke was determined by extraction with tetrahydrofuran It was found that only 4.7% by weight of the total gas and liquid were coke, and the surfaces of the autoclave 20 and the mixing parts in contact with the synthesis gas remained free of coke.

Comparative Example 2

The procedure of Example 2 was repeated except that this time nitrogen was used to pressurize the filled autoclave to 5 MPa (50 bar) instead of synthesis gas.

It was found that coke accounted for 7.8% by weight of the total amount of gas and liquid recovered and that coke was formed on the surfaces of the autoclave and agitator parts in contact with nitrogen.

Comparison of the results from Example 2, which mimics the conditions of the absorbent vessel controlled by the method of this invention, with the results of Comparative Example 2, shows that in the presence of hot hydrogen gas, coke formation is significantly reduced and coke deposition on metal remains. which are in direct contact with the hot gas mentioned may even be completely avoided.

Example 3

About 25 g of the same Middle East quality short residue used in Example 1 was charged to a 5,100 ml volume autoclave with stirring. The filled autoclave was pressurized with pure hydrogen gas to 1 MPa (10 bar). The autoclave was run at constant pressure using a pressure valve in the autoclave outlet and a continuous supply of 10 gas through the liquid residue through a hollow mixer. The gas flow was kept constant at 200 Nl / kg-h.

The residue was then reheated to 340 ° C with stirring and held there for 15 minutes. It was then heated at 45 ° C / minute to the desired reaction temperature (450 ° C) and held there for 15 minutes to allow thermal cracking reactions to occur. The autoclave was then cooled to room temperature at 90 ° C / min. The autoclave was then depressurised and the liquid was collected and a sample was taken for analysis. The amount of coke was determined by extraction with tetrahydrofuran. It was found that only 3.5% by weight of the total amount of gas and liquid produced was coke. In addition, the inner surfaces of the autoclave and the blender parts in contact with the synthesis gas had remained coke free.

The results of this example show that under heat-cracking conditions, even in the presence of hydrogen, even as low as 1 MPa (10 bar), the formation of coke is significantly reduced while the coke precipitation of metal parts inside the impregnation vessel which are in direct contact with hydrogen is completely prevented. . j j £

Claims (5)

A process for thermal cracking of residual hydrocarbon oil which achieves a final conversion of at least 35% by weight of 5,520 ° C +, characterized in that this process comprises the steps of: (a) heating the residual hydrocarbon oil feed to a temperature of 400-510 ° C for a sufficient time To achieve 30 to 45% of the final 520 ° C + conversion, 10 (b) feeds the partially modified hot hydrocarbon oil and hot hydrogen gas into the impregnation vessel, said hydrogen gas having a sufficiently high temperature to maintain the temperature of the hydrocarbon oil in the impregnation stream from 420 ° C to 650 ° C, where the remainder of the final 520 ° C + conversion to 100% occurs in the impregnation vessel; and (c) recovering from the impregnation vessel a hydrogen fraction containing a gas containing hydrogen and a cracked residue. 2. The process of claim 1, further comprising the step of (d) further separating the cracked residue recovered in step (c) into one or more asphaltene-poor fractions and an asphaltene-rich base fraction. 3. A process according to claim 2, further comprising the step of (e) partially oxidizing the asphaltene-rich base fraction from step (d) in the presence of oxygen and vapor, thereby producing hot synthesis gas. A process according to claim 3, characterized in that at least part of the hot synthesis gas produced in step (e) is used as hot hydrogen-containing gas in step (b). Use of hydrogen-containing gas as a stripping agent in the process according to any one of claims 1-4. j