RU2246523C1 - Method of intensifying thermal cracking of heavy hydrocarbons and installation for implementation thereof - Google Patents

Abstract

FIELD: petroleum processing.

SUBSTANCE: petroleum products are heated in tubular furnace and decomposition products are additionally held in external reaction chamber. Heating of reaction mixture in tubular furnace is accomplished at temperature and pressure corresponding to inhibition parameters of petroleum product decomposition reaction assuring, after dropping pressure at the outlet of furnace, transfer of the reaction mixture into accessible overheating state followed by transferring molecules of the most temperature-resistant petroleum product components into non-associated state during decomposition proceeding in reaction chamber. Cracking installation comprises heating furnace and external reaction chamber communicating over throttle reactor in the form of hydraulic resistance device allowing drop of pressure at the outlet of furnace and feeding cracking process-intensifying homogenous additives into reaction zone of external reaction chamber.

EFFECT: increased yield of desired volatile fractions from heavy petroleum products.

2 cl, 2 dwg

Description

Invention

relates to the field of destructive processing of oil and oil products and can be used to organize the process of thermal and catalytic cracking of heavy residual raw materials.

There is a method of deepening the cracking of oil and heavy oil products by heating in a tube furnace (Mukhina TN, Barabanov NL, Babash S.E. et al. Pyrolysis of hydrocarbon feedstocks. M .: Chemistry, 1987). The disadvantages of this method are: the combination of the heating process and the thermal decomposition of petroleum products in a tubular furnace, which eliminates mutual adjustment and optimization, the limited rate of heat supply through the walls of the coil of the tubular furnace due to intense coke deposition on the pipe walls.

The closest in technical essence to the proposed method is to deepen the process of thermal cracking of heavy petroleum products in an external reaction chamber, selected as a prototype (Smidovich E.V. Technology of oil and gas processing. M .: Chemistry, 1968. P.64).

In this method, a remote reaction chamber installed after the tubular furnace provides additional withstanding the thermal decomposition products coming from the tubular furnace at high temperature due to the heat accumulated in it. At the same time, the share of the external reaction chamber accounts for 20-30% of the total gasoline formation.

The disadvantage of the prototype is the incomplete thermal decomposition of petroleum products, as well as the occurrence of undesirable secondary reactions in the process of thermal decomposition, in particular, intense coke formation in the pipes of the heating furnace, due to the fact that the pressure at the end of the coil of the heating furnace is practically at the pressure level in the external reaction chamber.

The objective of the proposed invention is to develop an effective method of deepening the thermal and catalytic cracking of heavy petroleum products using a tubular heating furnace and a device for its implementation, providing the elimination of these disadvantages inherent in the prototype.

The problem is solved by a method in which the reaction mixture is heated in a tube furnace at a temperature and pressure corresponding to the braking parameters of the decomposition of petroleum products, which, after depressurizing the outlet of the furnace, ensure that the reaction mixture is transferred to an achievable state of overheating, with subsequent transition to the unassociated state of the molecules heat-resistant components of petroleum products during their decomposition in a remote reaction chamber, while between the heating furnace and the remote a throttle reactor is installed in the reaction chamber in the form of hydraulic resistance, which provides pressure relief at the outlet of the heating furnace and the supply of homogeneous additives to the reaction zone of the external reaction chamber to intensify the process of deepening thermal cracking of heavy petroleum products.

A device for deepening thermal cracking of heavy petroleum products containing a tubular heating furnace and an external reaction chamber (Smidovich E.V. Thermal processing of oil and gas. M: Chemistry, 1966, p.64).

To implement the proposed method, a device is proposed in which a throttle reactor is additionally installed between the tubular heating furnace and the external reaction chamber.

The proposed invention (figure 1) contains a heating furnace 1 with a tubular heater (coil) 2 connected in series with an external reaction chamber 3, between which a throttle reactor 4 is installed.

The implementation of the proposed method and the operation of the device for its implementation are as follows (figure 1).

Heavy oil products subject to in-depth thermal cracking enter the heating furnace 1, where, using a tube heater 2, the reaction mixture is heated at a temperature and pressure corresponding to the braking parameters of the thermal decomposition of the most heat-resistant components of heavy oil products and the evaporation of light fractions. Next, the heated reaction mixture with a predetermined temperature and pressure enters the throttle reactor 4. At the outlet of the reactor, pressure is released with a simultaneous increase in the speed of the reaction mixture and its transition to an achievable state of overheating, in which the molecules of the most heat-resistant components are in an unassociated (isolated from friend, as in gas systems) condition. The weakening of the van der Waals bonds, including the dipole – dipole interaction between the molecules, ensures the liberation of the vibrational, rotational, and translational degrees of freedom of the heavy oil molecules at the outlet of the throttle reactor and in the reaction chamber 3. Translation of large molecules into an unstable, overexcited compared to the associated state in the coil, causes an increase in their reactivity - an additional division into fragments and thereby provides an effective deepening of the thermal cracking of heavy oil products with a short residence time of components in the reaction zone, increases the yield of the final light target thermal decomposition products. The increase in the supply of thermal energy of the mixture in the coil as a result of reducing the proportion of gas fractions also contributes to the intensification of thermal decomposition of the mixture and provides the greatest yield of light fractions in comparison with the prototype. Then the reaction mixture enters the external reaction chamber 3, in which the thermal decomposition process and fixation of the final composition are also carried out.

Example. To test the possibility of deepening the cracking of heavy fractions of oil refining by the proposed method, the tests were carried out on a laboratory bench, shown in figure 2. The cracked residue obtained from the processing of fuel oil with a material balance was used as the initial product: hydrocarbon gas 3.7%, stabilization head 3.4%, cracked gasoline 19.1%, kerosene-gas oil fraction - 5.8%, cracking residue - 68%. The initial product with a volume of about 10 l is fed by extrusion from monzhus 1 into a tubular heat exchanger 2, which is heated by gas burners in chamber 3 to a temperature of 540 ° C (determination of the heating temperature is described below). The heated reaction mixture enters through the throttle reactor 4 and valve 5 into the receiver 6, where it is cooled to an equilibrium temperature, the value of which is established in the experiment (about 460 ° C). The presence in the pipeline of the hydraulic resistance created by the throttle provides an increase in the pressure necessary to transfer the reaction mixture to an achievable state of overheating in the reactor itself and in the external reaction chamber. As a throttle, a centrifugal two-component nozzle is used for spraying and twisting liquid fuel. The presence of two channels in such an injector makes it possible to introduce additional homogeneous components into the reaction mixture, for example, homogeneous additives to intensify the thermal decomposition process or hydrogen for hydrocracking. To remove incompletely reacted products at an unsteady mode of operation of the unit and to prevent pressure increase in the system, a bypass and safety valve 7 and 8 are installed. The temperature at the end of the heat exchanger is measured by a thermocouple method. The reduced pressure that is installed behind the throttle, inhibits the flow of undesirable secondary reactions in the process of thermal decomposition, possible in the prototype. Since the decomposition reaction proceeds mainly in the reactor and the external reaction chamber, coke formation on the walls of the heating pipe practically does not occur, and the lowered temperature in the external chamber reduces coke formation and coke deposition on the walls of this chamber.

As a result of the thermal decomposition tests of the cracked residue, an additional approximately 2% of hydrocarbon gas and 3% of cracked gasoline are obtained, calculated on 100% by weight of the initial fuel oil. Accordingly, the content of other fractions and, in particular, the coke residue is reduced. Thus, the tests performed show that reducing the time of the thermal decomposition process and intensifying it by transferring the reaction mixture to an achievable state of overheating with the help of a throttle device leads to a deepening of thermal cracking and an increase in the yield of target fuel oil products.

To establish the processing regime, the parameters of the achievable overheating of the reaction mixture should first be determined: temperature and pressure. For this purpose, the contact thermoanalytical method was previously proposed (Shlensky O.F., Rekus G.G. et al. Method for determining the kinetic parameters of materials, A.S. 1627952, application 4467221 dated July 29, 1988 Bull. No. 6, 15.02. 91). Data on the dependence of the temperature of the achievable overheating on pressure are given in the literature (E.D. Nikitin et al. Temperatures of the achievable overheating of some commercial oil products // Thermophysics of High Temperatures, 2001, v. 39, No. 1, pp. 97-100). The contact method of thermal analysis allows not only to determine the temperature of achievable overheating, for example, for oil from the Arlan field this temperature was 500 ° C, but also to establish the rates of thermal decomposition of oil products. According to the rate of thermal decomposition reactions, the necessary residence time of the reaction mixture in the reactor for its most complete decomposition and the dimensions of the reactor are determined (Shlensky OF, Rekus GG and others. Method for determining the rate of evaporation and gasification of liquid substances, A / C. No. 1827605 15.07.93 Bull. No. 26). The temperature dependence of the achievable superheat was established in the theory of thermodynamic similarity according to the data of the publication published by E. D. Nikitin et al. So, for example, to obtain the temperature of the achievable superheat of fuel oil at a pressure of 0.1 MPa at 500 ° C in a throttle reactor at the end of the heat exchange a pressure of about 7 MPa at a temperature of the reaction mixture of 540 ° C during the entire process of thermal decomposition. Additionally, tests were carried out to heat catalytic cracking gas oil on a contact thermoanalytic installation at a temperature as close as possible to an achievable superheat (500 ° C). The samples were tested in the form of thin layers (5–7 μm) of gas oil, which were applied to the surface of a preheated steel plate — they were galvanically coated with a gold film. Tests have shown that while reducing the decomposition time of thin layers of gas oil to 490 ° C from ten minutes to 5 seconds, the yield of coke residue decreases from 8% to 2%. This result confirms the effectiveness of the choice of gas oil processing conditions in the mode of achievable overheating of the initial product.

The choice of design of the throttle reactor to a large extent depends on the viscosity of the processed product. For products with a low viscosity, it can be in the form of a perforated plate with narrow channels, for products with a high viscosity - a simpler form of the unit of hydraulic resistance in the form of a diaphragm. A necessary requirement when choosing the pressure drop and temperature of the thermal decomposition reaction is the creation of conditions for the maximum possible achievable overheating of non-volatile components.

It should be noted other advantages of the proposed method, which can be implemented when installing a throttle reactor. The increase in pressure in the tube furnace, significantly exceeding the pressure in the external reaction chamber, leads to an increase in the temperature of the onset of thermal decomposition and boiling fractions of the reaction mixture, therefore, the equilibrium of the chemical reactions of thermal decomposition shifts to the high-temperature region. As a result, the process of exit of gaseous cracking products in a tube furnace slows down and the proportion of liquid fractions increases. The decrease in the proportion of gaseous components of the reaction mixture leads to an increase in the heat transfer coefficient through the coil walls and the amount of accumulated heat in the heated products, which allows to reduce the heating time of the mixture and thereby reduce coke deposition on the coil walls. An increased supply of thermal energy is consumed in the subsequent endothermic decomposition of petroleum products, providing a greater yield of light fractions.

One of the components of a more complete cracking of heavy oil products is the reduction of coke formation during the thermal decomposition reaction in the reactor itself. When molecules are transferred to an unassociated state near the temperature of achievable overheating, the “cell” effect is significantly weakened, which promotes the occurrence of recombination reactions, the formation of secondary products, as well as coke synthesis in the reaction mixture. Tests showed that practically no coke formation occurs behind the throttle reactor, which was also facilitated by the short residence time of the mixture in the reactor in the range of 0.01-0.001 s. Methods for calculating the reaction mixture heating modes are described in the publication Polyakov A.A., Shlensky O.F. // Chemistry of solid fuels, 1994, No. 1. S.83.

Due to the simplicity of the design, the developed method and device are applicable in catalytic cracking processes, in which case the hydraulic resistance unit is installed before the reaction mixture enters the contact zone with the catalyst.

An important advantage of the proposed method and device is multifunctionality - reduction of coke formation, hardening of cracked products after formation, simplicity and low cost of the structure, small overall dimensions, the possibility of replacing and repairing it without stopping the process in the furnace (when two reactors are installed in parallel), and the possibility of installation on already available technological equipment.

Claims (2)

1. A method of deepening the cracking of heavy oil products by heating them in a tubular furnace and additionally keeping the decomposition products in an external reaction chamber, characterized in that the heating of the reaction mixture in a tubular furnace is carried out at a temperature and pressure corresponding to the braking parameters of the decomposition of oil products, providing after pressure relief at the outlet of the furnace, the reaction mixture is transferred to an achievable state of overheating, with subsequent transfer to an unassociated state of molecules on and more heat-resistant components of oil products in the process of decomposition in a remote reaction chamber. 2. A device for implementing the method according to claim 1, comprising a tubular heating furnace and an external reaction chamber, characterized in that between the heating furnace and the external reaction chamber an additional reactor is installed.

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