MXPA00003393A - Unit for supplying a coke-deposit inhibitor solution in tube furnaces used for the pyrolysis of raw hydrocarbons - Google Patents

Abstract

The present invention pertains to the petro-chemical industry and can be used in ethylene and propylene production plants where coke deposition is prevented by supplying an inhibitor solution into the coil. The purpose of this treatment is to eliminate coil burnout in the region where the inhibitor solution is injected. To this end, a supply unit comprises a coil straight section with a line for supplying the raw material, an inhibitor pulveriser, a duct for supplying the inhibitor to the pulveriser as well as an additional duct surrounding the first one, wherein the above-mentioned elements are coaxially mounted. The supply unit further comprises a flow rectifier for reducing the strong turbulence downward in the flow direction, wherein said rectifier is arranged coaxially in the straight section of the coil in the area where the inhibitor solution is injected. After 11-month experiments, no failure has been recorded in the operation of the inhibitor supply unit while no coil burnout occurred in the mounting area of said supply unit.

Description

UNIT TO INJECT A SOLUTION. THAT INHIBITS THE DEPOSIT OF COKE, IN TUBULAR OVENS, FOR THE HYDROCARBONS PIROLYSIS Field of the Invention The present invention relates to the petrochemical industry and is intended for use in plants for the production of ethylene and propylene, by thermal decomposition (pyrolysis) of hydrocarbon feedstocks.

BACKGROUND OF THE INVENTION At present, the world production of ethylene and propylene is based on the pyrolysis of hydrocarbon fillers, in the presence of water vapor, in furnaces with tubular coils. As the fillers, ethane, mixtures of propane / butane, as well as naphtha and gas oil fractions are used. Usually a pyrolysis oven has two sections: convection and radiant. Passing through the coil of the convection section, the charge material is evaporated, mixed with water vapor and preheated to 550-650 ° C. In the subsequent radiant section, this mixture is heated to 750-950 ° C and fractionated, thus forming ethylene, propylene, butylene and various by-products. The main problem in this process is the formation and accumulation of coke deposits on the walls of the coil of the radiant section. In most furnaces, these coke deposits are removed by burning and separating them with water vapor and oxygen. In some of the tubular pyrolysis furnaces, the coke deposit is prevented by the introduction of an inhibitor compound into the process stream, which includes, for example, alkali metal compounds. In most cases, an inhibitor compound is injected in the form of an aqueous solution or suspension of such compounds into the flow of the hot filler material, by means of an injection unit inserted near the boundary between the convection sections and radiant of the coil. During the operation, the burning / drilling of the wall frequently occurs in the injection zone of the inhibitor solution. This burning is caused by the droplet collision of the inhibition solution on the metal walls, near the injection point, which produces multiple cycle temperature changes, which cause the thermal fatigue of the metal and the resulting failure of the furnace. European Patent EP 0617112 A2 discloses an injection unit for introducing a liquid solution which inhibits the coke inside the tubular reactor for the pyrolysis of hydrocarbons, which incorporate a straight section of the coil with the inlet pipe, to supply a loading material , an atomizer of the inhibitor, a tube for supplying the inhibitor to the atomizer and surrounding an additional tube 10 placed coaxially. In this unit, the last tube that surrounds the atomizer, serves as a protective wrapping of the walls of the shock coil by the liquid inhibition solution. This tube, by itself, is not protected from the droplets of the inhibition solution. The European Patent EP 0606998 Bl discloses a unit for introducing the solution that inhibits the coke inside a tubular furnace for the pyrolysis of hydrocarbons, which includes a straight section of a coil with an inlet pipe, to supply a material of loading, an injection nozzle 20 for atomizing the inhibitor and a tube for supplying the inhibitor to the injection nozzle, which is Parallel to the flow of the load gaseous stream, and can move along an axial direction. In the operating position, the nozzle moves within the gaseous stream, which extends for a distance of approximately 1-3 times the diameter of the straight section of the coil. US Patent No. 5435904 discloses a unit for introducing a solution that inhibits coke within a tubular furnace for the pyrolysis of hydrocarbons, which includes a straight section of a coil, with an inlet tube for supplying a coke material. load, an inhibitor atomizer, a tube for supplying an inhibitor to the atomizer and surrounding an additional tube placed coaxially. To disperse a liquid by means of this unit, a compressed gas is used, which is supplied to the atomizer through an annular passage, between the internal and additional tubes. U.S. Patent No. 4,708,787 describes a unit for dispersing a liquid through a gaseous stream. This unit includes a straight section of the tube, equipped with an inlet duct together with an insert in the form of a venturi tube, to supply a gas, a liquid atomizer and a tube to supply a liquid to the atomizer, which are placed coaxially within the straight operating tube, and the atomizer is concentrically placed inside the venturi throat. The patent of E.U.A. No. 3812029 discloses a unit for the injection of a liquid, with the ability to form coke in a preheated container at a high temperature. This unit includes an internal tube for supply an injected liquid that surrounds it and envelop it, which introduces the water. This inner tube and the wrapping end in a common nozzle, where the injected liquid and water are mixed before its introduction into the heated container. 15 The USSR Inventor Certificate, No. 1661189 Al, discloses a unit for purging the internal surface of a cylindrical branch tube by an air stream. This unit includes a tube to supply compressed air, placed concentrically with the branch tube, together with a The fixed annular nozzle on a tube forms this air stream in a configuration of a hollow cone.

^^^^^^^^^^^^^^^ H ^ M ^^^^ l ^^^ aM The USSR Inventor Certificate, No. 633892 reveals a unit for the introduction of a deposit inhibitor. coke in a tubular furnace, for the pyrolysis of hydrocarbons. This unit includes tubes, internal and external, placed concentrically. The preferred preheated hydrocarbon charge material flows through the inner tube. A gaseous coke inhibitor is introduced into the charge flow, through a passage, between the inner and outer tubes.

SUMMARY OF THE INVENTION The invention solves the problem of eliminating the burning of the coil in the injection zone of the inhibition solution. To solve this problem, a unit for injecting a solution for inhibiting the coke deposit inside a tubular furnace, for the pyrolysis of hydrocarbons, which includes a straight section of a coil with an inlet pipe to supply a filler material, a Inhibitor atomizer, a tube for supplying an inhibitor to the atomizer and surrounding an additional tube placed coaxially, is provided with a vortex gate, to reduce turbulence, downstream of the injection point. The vortex gate is located concentrically within a straight section of a coil in the injection zone of the inhibition solution. The vortex gate is an aerodynamic grid that divides the flow into individual streams aligned parallel to the axis of the coil. Within a specific distance, related to the diameter of the coil in the straight section, current under the flow of the gate of the vortex, the turbulence decreases with the corresponding reduction in the regime of radial drag of the additions. This regime of radial entrainment of the droplets of the inhibition solution from the core of the flow stream to the wall layer of the coil decreases and the evaporation of the droplets is completed before they reach the wall. This prevents the risk of burning the coil wall. The preferred atomizer is a swirling element. The advantage of this swirl element is the axially symmetrical shape of the cone of the atomized liquid, which eliminates the alteration of the flow of the charge material at the outlet of the vortex gate. This preferred configuration of the invention also has the following characteristics: The vortex gate consists of radial plates and cylindrical rings, - "The radial plates are symmetrically joined to the additional tube;" The cylindrical rings are attached to the radial plates coaxially with the tube additional and form an internal passage, which expands in stages in the direction of flow of the loading material; "The gate of the vortex includes 3 to 5 cylindrical rings, whose widths increase in the direction of flow, progressively from 0.25 to 0.9 times the internal diameter of the coil in the straight section;" The distance from the edge upstream of the plate to the nearest point of connection of an input branch pipe to supply the load material, is not less than twice the internal diameter of the coil in its straight section.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further illustrated in the accompanying drawings. In Figure 1 is shown, the general view of the injection unit and in Figure 2 the sectional view of the vortex gate is shown.

DESCRIPTION OF THE PREFERRED EMBODIMENT The injection unit comprises the straight section of a coil, with the flange 2, the input branch pipes 3, 4 and the insert assembly includes the rear flange 5, the supply tube 6 of the inhibitor, the additional tube 7, the swirling element 8 and the vortex gate, formed by the radial plates 9 and the cylindrical rings 10, 11, 12, 13. The insert assembly is centered within the straight section of the coil 1 by the flange 2 and by the projections of the radial plates 9. The cylindrical rings 10, 11, 12, 13 are joined to the radial plates 9 coaxially with the additional tube 7 and form the internal passage that expands in stages in the flow direction. The injection unit operates in the following manner. Through the branches 3 and 4 of the tube, the flow of the loading material coming from the convection section ___.... of the furnace (not shown in the drawings) enters the straight section of the coil 1 of the radiant section of the furnace. The aqueous solution of the coke deposit inhibitor is delivered under pressure from an external source (not shown in the drawings) to the swirling element 8, through the supply tube 6 of the inhibitor and is injected into the flow of the charging material. The cylindrical rings 10, 11, 12, 13 and the radial plates 9 together form the vortex gate, which divides the flow of the load material into individual streams aligned in parallel to the axis of the straight section of the coil. As a result of the influence of the vortex gate on the flow of the load material, its turbulence decreases downstream for a distance equivalent to 5-10 times the diameter of the coil in the straight section. In this zone, the regime of the radial drag of additives also decreases. As a consequence of this regime of the inhibition solution, the transfer of the droplets from the core of the flow of the filler material to the wall decreases and thus the evaporation of the droplets is complete before they reach the wall. The particles of the inhibitor formed after the evaporation of the droplets of solution do not cause damage to the walls of the coil in contact with them. The vortex gate includes four cylindrical rings 10, 11, 12 and 13. Its width increases in relation to the internal diameter of the coil in the straight section from 0.25 for the ring 10 to 0.9 for the ring 13. The widths of the rings have been developed experimental data. The number of the rings has been selected based on the effectiveness of the vortex gate that has less than 3 sharply decreasing rings, but the vortex gate that uses more than 5 rings under the operating conditions of the injectors is inconvenient, due to the restrictions generated in the cross section of the coil flow. Preferably, the distance from the upstream edge of the plate 9 to the narrowest point of the joint of the supply line 4 of the loading material is not less than twice the internal diameter of the coil. The effectiveness of the injection unit at that distance increases due to the additional decrease in the turbulence intensity of the flow at the injection site of the inhibitor.

Commercial Applicability The present invention can be applied in tubular furnaces for the pyrolysis of hydrocarbons, where the formation of coke is prevented by injecting an inhibition solution into the hot stream of the process. When making units based on this invention, it is necessary to use materials that are capable of prolonged operation (tens of thousands of hours) when exposed to temperatures of the order of 600 to 650 ° C, without the development of the thermal brittle state. Steels of stable austenite structure, incapable of structural changes under prolonged exposure to heat, should be used mainly, for example steels of type 18-8 or 18-12, stabilized by titanium or niobium. Twelve units, based on this invention, were manufactured. These injection units were tested under operating conditions in 6 commercial pyrolysis furnaces, and the results were excellent. For more than two years, in no case did any failure occur in the furnace coils in the region of the location of the furnace. unity .

Claims (5)

1. , i CLAIMS 1. A unit for injecting a solution that inhibits the deposit of coke in tubular furnaces, for the pyrolysis of hydrocarbons, which includes a straight section of a coil, with an inlet pipe to supply a charge material, an atomizer of the inhibitor, a tube for supplying an inhibitor to the atomizer and surrounding an additional tube, placed coaxially, where, for the reduction of the turbulence, the injection unit is provided with a vortex gate, located concentrically within a straight section of a coil in the injection zone of the inhibition solution.
2. 2. The injection unit of claim 1, wherein the atomizer is a swirling element.
3. 3. The injection unit of claim 1, wherein the vortex gate consists of radial plates, which are symmetrically joined to the additional tube, and of cylindrical rings, which are joined to the radial plates coaxially with the additional tube and form an internal passage , which expands in stages in the direction of flow of the loading material.
4. 4. The injection unit of claim 3, wherein the vortex gate includes 3 to 5 5 cylindrical rings and the width of the rings progressively increases in the direction of flow from 0.25 to 0.9 times the internal diameter of the coil in the straight section, from the first to the last ring correspondingly.
5. 5. The injection unit of claim 3, wherein the distance from the upstream edge of the plate to the nearest point of the nearest input branch pipe seal, to supply a loading material, is not less than double the internal diameter of the straight section 15 of the coil. Mi ^ i ____ ^ _ a _ ^ _______ ^ ___ «? _ M__i___I___l