RU2345122C1 - Pyrolysis furnace for unsaturated hydrocarbon production - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention can be used for production of ethylene and other unsaturated hydrocarbons. Pyrolysis gas flow is delivered through supply mains 1 to inlet fittings of two inlet T-bands 2. Pyrolysis gas flow passed through four outlet fittings of two inlet T-bands 2, is delivered to convergent-divergent taper 3 where downstream takes turbulent character. Turbulent pyrolysis gas flow delivered to four small-diameter pipes 4, effects their walls with vibrations transmitted to all pipes of coiler, thus reducing potential carbon deposition on pipe walls. Extension of small-diameter pipes 4 resulted from temperature expansion and high-temperature pipe creep effects, is compensated due to possible vertical reposition of bundle of two pipes integrated with holder 9 and fixing mechanism 10.

EFFECT: avoiding of causes of carburising and sequential overheat of pipeline sections within small-diameter pipe taper to mean diameter pipes.

1 dwg

Description

The invention relates to the field of creating plants for the production of ethylene and other unsaturated hydrocarbons and can be used in the refining and chemical industries.

Known devices, patents of the Russian Federation No. 2021326, 394410, 305783, 386222, 1778144 and others, in which there are coils for pyrolysis furnaces. However, in all the aforementioned devices, the problem of carburizing the metal and subsequent coking on the walls of the reaction pipes and fittings of the pyrolysis furnace is relevant, which leads to an increase in the hydraulic resistance of the pipe system of the coil, a decrease in the efficiency and productivity of the pyrolysis furnace, and also causes a reduction in the working campaign of the coil pyrolysis furnaces due to excessive overheating of reaction tubes (above 1070 ° C) due to a decrease in heat removal from the walls of the pipe system of the coil .

In addition, during heating and cooling, the coil elements expand and contract differently - because of the temperature difference, the inlet sections of the coil expand less than the outlet. The coil hangs freely in a vertical position on the suspensions, while the lower bundle of pipes of the coil has the ability to move freely in the vertical and horizontal directions during operation due to the creep phenomenon (creep) of the pipe metal at high temperature and the pipes can come into contact with each other. When the pipes come into contact, the heat exchange process worsens, which also leads to overheating of the pipes and their premature wear and destruction. This fact also reduces the duration of the working campaign of the furnace or may lead to an emergency during its operation.

Known gasoline pyrolysis furnace designed by V.A. Butovsky, adopted as a prototype, (article "Modernization of pyrolysis furnaces by Butovsky's design for EP-300 ethylene production plants" JSSN0132-4535 "Issues of Materials Science", 2005, No. 2 (42), pp. . 120-125), containing a refractory casing, four vertically arranged sections of the same type, consisting of pipes of small, medium and large diameters, located in the combustion chamber. At the entrance, each section with its inlet pipes of two inlet tees is connected to the supply line of the pyrogas stream, and two pairs of outlet pipes of each of these two tees are connected in pairs with two vertical pipes of small diameter. At the exit, four pipes of small diameter are connected in pairs with the inlet pipes of two outlet tees. The two outlet pipes of these tees are connected to the inlet pipes of the transitional tee of medium diameter pipes, and the only outlet pipe of this tee is connected to the single inlet pipe of the inlet tee of medium diameter pipes. Two outlet pipes of this tee are connected at the inlet to two vertical pipes of medium diameter. At the outlet, the vertical pipes of medium diameter are connected to two inlet nozzles of the outlet tee, the outlet nozzle of which is connected to a large diameter pipe.

One of the drawbacks of V.A.Butovsky’s furnace design is overheating of the pipe system in the places of transition of small diameter pipes to pipes of medium diameter due to the large hydraulic resistance in these places, which led to carburization and coking of these sections of the pipe system and premature failure of radiant pipes .

The second disadvantage of the known design is that the lower bundle of small diameter pipes suspended in a free state, with a change in temperature, was able to move freely due to thermal expansion-contraction and creep of the metal. This circumstance led to uncontrolled contact of the pipes with each other in the transverse and longitudinal directions and created conditions for the pipes to overheat at the point of contact and to premature failure.

The technical result of the present invention is to eliminate the causes leading to increased coking and subsequent overheating of sections of the pipe system at the transition points of pipes of small diameter to pipes of medium diameter, as well as overheating in the lower part of the bundle of pipes of small diameter of the coil due to uncontrolled bending and their subsequent contact with each other .

The technical result is achieved due to the fact that in the pyrolysis furnace for the production of unsaturated hydrocarbons containing four vertically arranged similar sections of pipe systems located in the combustion chamber, at the input, each section is connected to the pyro-gas flow supply line by an inlet pipe and two inlet tees, and two outlet pipes of these two tees are connected in pairs with four pipes of small diameter, then the output ends of four pipes of small diameter are paired with two input pipes by sleeves of two outlet tees of pipes of small diameter, and the outlet pipes of these tees are connected to two pipes of medium diameter, at the output both pipes of medium diameter are connected to two inlet pipes of the outlet tee of pipes of medium diameter, and the outlet of this tee is connected to a pipe of large diameter, according to the invention at the entrance between the four outlet pipes of the two inlet tees and four pipes of small diameter, confuser-diffuser transitions are installed, and in the lower part of each section of the coil two cages are installed, each of which has two sockets, spaced at a fixed distance from each other, while in the nests of each cage are freely installed pairwise freely suspended pipe of small diameter and another pipe of the same diameter, rigidly connected to the locking mechanism, which allows this vertical movement system.

The drawing shows the proposed design of the pipe system of the coil section of the pyrolysis furnace (the coil consists of 4 pairwise arranged mirror-symmetric sections).

The pipe system of the coil section contains two pyrogas flow supply lines (1) connected to the inlet pipes of two inlet tees (2), four outlet pipes of which are connected to four confuser-diffuser transitions (3), which in turn are connected to four pipes (⌀ 83 × 7 mm) of small diameter (4). At the exit, four pipes of small diameter (4) are connected in pairs with four inlet pipes of two outlet tees of pipes of small diameter (5). Two outlet pipes of these two tees (5) are connected to two pipes of medium (⌀104 × 9 mm) diameter (6). At the exit, two pipes of medium diameter are connected to two inlet pipes of the outlet tee of pipes of medium diameter (7), the output pipe of which is connected to a large diameter pipe (⌀134 × 9 mm) (8), and two cages (9) are installed in the lower part of the coil , each of which has two sockets, spaced at a fixed distance from each other, while in the nests of each cage, a freely suspended pair of small diameter pipe and another pipe of the same diameter are rigidly connected to the locking mechanism (10), providing the possibility of this system of vertical movement. The systems of small and medium pipes of the coil are suspended using rods (11) to the section holders located outside the zone of the furnace volume. The outlet tee of the furnace section (12) is connected with its two inlet pipes of large diameter by one of its two inlet pipes, one of which (13) is the outlet pipe of the symmetrically located section.

The pipe system operates as follows.

Pyrogas flow at a speed of about 50 m / s enters from the supply lines (1) to the inlet pipes of the two inlet tees (2), of which it flows through the four outlet pipes of the two inlet tees (2) to the confuser-diffuser junctions (3), where the output becomes turbulent. A turbulent pyrogas flow entering four pipes of small (⌀83 × 7 mm) diameter (4) affects their walls, causing vibrations that are transmitted to all pipes of the coil, reducing the likelihood of coke deposits on the pipe walls. By varying the feed rate of the pyrogas stream, it is possible to change the oscillation frequency of the pipes, choosing the most optimal one.

The pyrogas stream enters the coil at a temperature of 550-600 ° C, passing through it, is additionally subjected to heating due to the heat generated from the combustion of gas fuel in burners located along the entire furnace, which ensures a continuous increase in its temperature, which is at the outlet of the coil section reaches 850-870 ° C, providing the process of pyrolysis of hydrocarbon raw materials in the pipes of the coil, and the speed of the pyrogas stream increases to ~ 200 m / s.

In addition, during the operation of the pyrolysis furnace, especially when the temperature regime changes, each of the four pipes of small diameter (4) is subject to elongation due to thermal expansion and creep of the pipe metal at high temperature. This elongation is compensated for by the possible vertical movement of the beam from two pipes connected by a cage (9) and a fixing mechanism (10) into one single system.

If a thermal expansion of one of the pipes of this beam does not have the same magnitude, this difference is compensated by a rotation through a certain angle of the holder (9), which combines the two pipes. Moreover, since each pair of pipes is placed in the holders of the cage (9), located at a fixed distance from each other, the possibility of contact of the pipes with each other in the horizontal plane and, as a result, their overheating at the points of contact is excluded.

Due to the fact that in the design of the coil, zones with increased hydraulic resistance were eliminated at the junctions of pipes of small diameter to pipes of medium diameter where coke deposition took place, and also due to the removal of coke by vibration of the pipes of the coil, the coke deposition process in the pipes was significantly slowed down. The possibility of pipe contact with each other is eliminated and, as a result, their overheating at the contact points is prevented.

The technical and economic result of the invention in comparison with the prototype will be expressed in increasing the service life of the pipe system of the pyrolysis furnace, which will increase the reliability and durability of the entire pyrolysis furnace as a whole.

Claims (1)

A pyrolysis furnace for the production of unsaturated hydrocarbons containing four vertically arranged similar sections of pipe systems located in the combustion chamber, at the entrance, each section is connected to the pyro-gas flow supply line with an inlet pipe and two inlet tees, and two outlet pipes of these two tees are paired with four pipes of small diameter, then the output ends of four pipes of small diameter are paired with two inlet pipes of two outlet tees of pipes of small diameter, and the outlet pipes of these tees are connected to two pipes of medium diameter, at the output both pipes of the middle diameter are connected to two inlet pipes of the outlet tee of the pipes of medium diameter, and the outlet pipe of this tee is connected to a pipe of large diameter, characterized in that at the inlet between the four output pipes two inlet tees and four small-diameter pipes are equipped with confuser-diffuser transitions, and two clips are installed in the lower part of each coil section, each of which has two nezda spaced apart by a fixed distance, while in the nests of each cage freely mounted pairwise freely suspended small diameter pipe and another pipe of the same diameter, rigidly connected with a fixing mechanism to ensure the possibility of the vertical displacement system.