FI85598C - FOERFARANDE OCH ANORDNING FOER TERMISK KRACKNING AV KOLVAETEOLJOR OCH FOER ANDRA VAETSKE / -GASREAKTIONER. - Google Patents

Description

85598

METHOD AND APPARATUS FOR THERMAL CRACKING OF HYDROCARBON OILS AND OTHER LIQUID / GAS REACTIONS

The invention relates to a process for the thermal cracking of hydrocarbons and other liquid / gas processes, in which the liquid feed is heated to the cracking temperature and passed to a substantially horizontal soaking cracker, where due to the larger flow cross-section the flow rate is reduced , and wherein the gas is removed at the beginning of the reaction vessel. The invention also relates to a soaking cracker implementing the method.

The method is also suitable for other liquid / gas processes in which the presence of a gas phase is not technically necessary, but occurs under the conditions of a reaction vessel.

The purpose of thermal cracking of hydrocarbons is to break down heavy oil fractions into lighter ones and increase the number of these more valuable light fractions. There are two main methods. In a simpler method, the oil feed is passed through a cracking furnace to a distiller. In the oven, the oil temperature rises to 450 ° -480 ° C, which breaks down some of the heavy fractions. The residence time at the process temperature is 1-4 25 minutes.

The second method uses a lower temperature (410 ° -450 ° C) and a longer residence time. This is done * so that, after the furnace, the hot oil feed is passed to a reaction vessel with a residence time of 10-30 minutes.

The reaction vessel of the latter method is usually formed by a cylindrical pressure vessel, to which one end is fed: a feed from the cracking furnace and a liquid / -35 gas mixture is removed from the other end to the next process step. The flow direction in the reaction vessel has been either top-down or bottom-up, which is more common today.

There are two main types of thermal cracking of hydrocarbons; 40 silicon reactions. The second is the desired cracking reaction, 2,85598 in which long chain hydrocarbon molecules are cleaved smaller, causing a decrease in viscosity. Another type of reaction is unwanted polycondensation, in which the molecules coalesce to form pitch, coke, and hydrogen, causing the growth of asphaltenes that degrade the quality of the cracked heavy fuel oil. Condensation reactions increase with increasing temperature, so efforts have been made to use lower reaction temperatures and correspondingly longer residence times. This is an essential advantage of the latter method over mere oven cracking. Other advantages of the method are lower energy consumption and slower clogging of the cracking furnace tubes, which allows longer operating cycles.

The residence time in the reaction vessel is an important quantity for thermal cracking. The desired cracking reactions do not have time to occur if the residence time is too short. If the residence time is too long, undesired reactions form harmful compounds which cause difficulties in the continued use of heavy fuel oil. The aim is thus to have a control time that is as controlled and even as possible, because then a homogeneous end product is obtained.

The main problem in the latter reaction vessel process is the presence of the gas phase. The cracking reactions produce light components which are in gaseous form in the reaction vessel.

· * · *: In one study, both the residence time and ....: the density of the gas phase in the reaction vessel was found to be about 60% by density measurements (Lauri Rantalainen, "Thermal cracking-j 30 unit 2 flow dynamics mapping with a radioactive tracer" 1979, TKK Espoo) The fraction of light fractions / proportion of the final products is usually in the range of 3 to 7% by weight, which leads to a similar estimate of the proportion of the gas phase, which poses two problems: first, the effective volume is less than half the theoretical value. the residence time is correspondingly half of the theoretical value.Second, the velocity of the gas phase is higher than the velocity of the liquid phase.This results in a strong mixing phenomenon.Therefore, the residence time of the liquid phase is not nearly uniform according to the plug flow, but the residence time distribution is quite wide. that part of the liquid passes very rapidly through the reaction vessel with the moving gas bubbles and part of the liquid mixes and stays longer in the reaction vessel. This, of course, has implications for both desired and especially undesired reactions. Since the actual residence time is less than half of the theoretical value, the process temperature must be raised accordingly to reach the same conversion value. This weakens e.g. the heat economy of the process and coking is accelerated.

By controlling the pressure in the reaction vessel, the amount of the gas phase can be affected to some extent, but in no way eliminates this problem.

Attempts have been made to solve the problems caused by the gas phase with the residence time of the liquid phase by means of various arrangements in the reaction vessels in which the flow takes place from the bottom up. U.S. Pat. No. 4,247,387 discloses torn intermediate bases inside the reaction vessel, which form a number of mixing points in the reactor, thus preventing backflow and aiming to provide a uniform residence time. The solution does not eliminate the loss of reaction volume caused by the gas phase. Solution 25 causes maintenance work to clean the baffles and a certain risk of the entire reactor coking due to fault operations.

In Finnish patent 65275, the design of the reaction vessel 30, which opens upwards in a conical manner, seeks to create the same flow rate for the gas phase and the liquid phase, taking into account the increase in bubble size caused by the pressure drop. However, due to the nature of the mixing phenomenon, the gas phase flow rate is higher than the liquid phase rate, so the situation does not improve significantly.

Finnish patent 65274 discloses three different methods for equalizing the residence time. One embodiment is to place a helical coil filling a reaction vessel in a reactor 4,85598. In the other two methods, the aim is to bring the liquid / gas mixture into tangential rotation by means of nozzles or by feeding tangentially to the reactor. The gas phase tends to separate from the liquid phase and causes 5 mixing phenomena along the entire reaction vessel despite these arrangements.

None of the known solutions described above seeks to separate the gas phase from the liquid phase.

10

Finnish patent application 843423 describes three different reactor solutions, all of which have the main objective of separating the gas phase from the liquid phase. This is achieved by flow deflectors located inside the reactor vessel. In this way, dead areas are formed into which the gas collected is discharged through several gas connections. The weakness of all these solutions is that the steady flow that is important for this process is deliberately disrupted. Complex structures must also be placed in the reactor, which poses a risk of entrapment and increases maintenance costs. Multiple degassing connections cause the construction of an equal number of surface adjustments, which increases costs.

It is an object of the invention to provide an improvement on the methods currently known. The characteristic features of the method according to the invention are set out in the appended claim 1 and the characteristic features of the soaking cracker according to the invention in claim 6. The method according to the invention; allows the gas phase to be rapidly separated from the liquid phase 30 with as little disturbance as possible in the reactor. This results in a high effective volume and a longer average residence time for the liquid flow, as well as a more even residence time distribution due to less mixing. There is also no need to place any additional structures in the reactor vessel.

Other features and advantages of the invention will be explained in more detail in connection with the embodiment shown below. The basics of the invention 5 85598 and a soaking cracker according to the invention are illustrated by the following figures.

Figures 1 and 2 show prior art cracking methods

Figure 3 shows the results of a residence time measurement

Figure 4 Gas bubble velocity pattern in horizontal liquid / gas phase flow

Figure 5 shows a schematic process diagram of a preferred embodiment of the method according to the invention

Figures 6a and 6b show the reaction vessel shown in Figure 5 in more detail

In a known simpler method, Fig. 1, cracking 15 is carried out by passing an oil supply via pipeline 1 to the piping 3 of the cracking furnace 2, where the cracking mainly takes place and the reaction continues in the next pipeline 4 along which the hydrocarbons are passed to the next process step 5. This is normally distilled. for example, 20 for gas and gasoline fractions 6, light fuel oil 7 and heavy fuel oil 8. The residence times are of the order of 1-4 minutes and the temperature of the order of 450 ®-480 ° C, depending on the process temperature.

In another more advanced cracking method according to the prior art, Fig. 2, the oil supply is led via a pipeline 1 to the piping 3 of a cracking furnace 2, where the temperature is raised to a cracking temperature (410-450 ° C) and led via a pipeline 4 .. .. to a reaction vessel 9 with a residence time 9. classes 10-30 *! 30 minutes. The hydrocarbons can be passed from the reaction vessel to the distillation process as in Figure 1. No heat is introduced into the reaction vessel "and since the reactions are mainly endothermic, the temperature ·. *. · Drops by 10-20 degrees. At lower temperatures, the process equipment becomes dirty more slowly, so longer operating cycles.

The reaction vessel may also be slightly skewed. Most preferably, the gas phase layer extends the entire length of the reaction vessel.

“·: 35 6 85598

Figure 3 shows the results of the aforementioned tracer experiment in a vertical reaction chamber. Curve 11 shows the theoretical residence time distribution and duration. Curve 10 shows that in practice the average residence time is about 5 to 40 percent of the theoretical value and is quite wide.

By using the lying reaction vessel according to the invention, it is possible to quickly separate the gas phase and the liquid phase from each other and thus substantially prevent the mixing phenomenon along the entire path of the reactor 10. When the hydrocarbon feed is introduced into the reaction vessel, it already contains the gas phase due to the reactions of the cracking furnace. Due to their lightness, the gas bubbles tend to rise immediately to the top of the reaction vessel. The gaseous reaction products generated in the reaction vessel also rise immediately to the top of the reaction vessel, from where they can be removed in a controlled manner by means of surface measurement and adjustment.

As previously shown by the research results, the gas phase flow rate is higher than the liquid phase rate.

Figure 4 schematically shows how the horizontal velocity component of the liquid flow 24 and the vertical velocity component 25 of the gas bubble lead to the final velocity vector 26 of the gas bubble in magnitude and direction. Thus, even in the most unfavorable case, if the gas bubble detaches from the liquid phase at the bottom of the reaction vessel 25, it rises to the gas space of the reaction vessel by a horizontal distance smaller than the reaction ** '; the diameter of the container. The distance by which the gas bubbles interfere with the • · ____: liquid flow is well below the distance possible in vertically arranged reactors. From the point of view of dimensioning the reaction vessel 30, it is advantageous to use a large length / diameter ratio, the optimal values of which would be in the order of 15: 1 to 25: 1.

• · • · ·

It is advantageous to provide flow control into and out of the reaction vessel via either conical or elliptical end funnels. An additional advantage provided by gas phase separation is normally achieved in the next process distillation. Potential problems with this distillation are due to foaming. 7 85598 sa that the feed contains 50-60% gas In the distillation column, the gas phase tends to rise rapidly to the top of the distillation column, carrying heavy fractions with it, and thus the operation of the distillation column is severely disturbed.

5

Once the gas phase has been largely separated already in the reaction vessel, it can be passed to the distillation column on the bottoms above the liquid feed at an optimal location and thus substantially reduce the foaming problem. From the point of view of the cracking reaction, it has been found that on a 10 industrial scale a suitable temperature is between 410-470 ”and a pressure of 2-20 bar. The presence of a gas phase in the reaction conditions after the cracking furnace is not necessary for the desired reactions, but only causes problems.

In Fig. 5, the oil supply is led through a pipe 1 to the pipelines 3 of the cracking furnace 2, where its temperature is raised to between 410 and 470 ° C. From the furnace 2, the oil is led through a pipe 4 to a reaction vessel 14, which is generally horizontal, but can also be placed in an inclined position, the extreme positions 20 preferably varying between -5 ° and + 5 °. From the reaction vessel, the liquid phase is led out via line 23 and the gas phase via line 22. In the next process step, for example, gas + petrol 6, light fuel oil and heavy fuel oil 8 can be separated in the distillation column 5. The average residence time in the reaction zone is 5-100 minutes, depending on the dimensioning.

Figure 6a shows the reaction vessel 14 in a supine position without thermal insulation with a conical inlet section 12 and 30 in the actual reaction zone in which the liquid phase 19 and the gas phase 20 can be separated. The liquid phase is removed through the conical outlet section 15 and the gas phase at the conical or tubular outlet section. 16 through. The location of the gas phase outlet is not critical in the horizontal structure, but the optimal placement is at the beginning of the reaction vessel where most of the gas separates from the liquid phase.

A reliable surface measurement for the reaction vessel conditions can be constructed using radioactive measurement. using the

Claims (7)

8 85598 in favor of the reaction vessel's own volume, separate structures are avoided inside the reaction vessel. Figure 6b shows the reaction vessel 4 in cross section at the gas phase outlet section 16. 5 A process for the thermal cracking of hydrocarbons and other liquid / gas processes, wherein the liquid feed is heated through a substantially horizontal reaction vessel (14) where, due to a larger flow cross-sectional area, the flow rate decreases and a delay is achieved to achieve the desired additional reactions. and 15 in which the gas is removed at the beginning of the reaction vessel (14), characterized in that a gas phase layer (20) is arranged over the liquid phase (19) over a large length of the reaction vessel (14) and the liquid surface is substantially constant by removing gas as required. 20 A method according to claim 1, characterized in that the flow is directed to the reaction vessel (14) to expand evenly over the entire flow cross-section and the flow is removed as a uniformly converging flow. 25 Method according to Claim 1 or 2, characterized in that the degassing is controlled on the basis of surface measurement and adjustment. Process according to Claim 1, 2 or 3, characterized in that the liquid is heated to 410 to 470 ° C,. the pressure is between 2-20 bar and the average residence time 5-100 min. Process according to one of Claims 1 to 4, characterized in that the gas phase layer extends over substantially the entire length of the reaction vessel (14). A soaking cracker for carrying out the method according to claim 1, comprising a substantially horizontal tubular reaction vessel (14) for retaining liquid and degassing devices, characterized in that the reaction vessel (14) comprises inlet and outlet funnel ends (12, 15), and that the degassing devices comprise a surface-measuring sensor and transmitter (21), a control device (18) and a valve (17) connected to the degassing connection (16), adapted to keep the liquid surface at a constant height in the reaction vessel (14) and longitudinally a gas phase layer (20) at the top of the reaction vessel (14). Soaking cracker according to Claim 6, characterized in that the angle of expansion of the hopper (12) is less than 15 °. 15