CN110270240B

CN110270240B - Dilution steam mixer

Info

Publication number: CN110270240B
Application number: CN201910490513.8A
Authority: CN
Inventors: 周海燕; 和成刚; 张文明; 徐志刚
Original assignee: Changzhou Ruikai Chemical Equipment Co ltd
Current assignee: Changzhou Ruikai Chemical Equipment Co ltd
Priority date: 2019-06-06
Filing date: 2019-06-06
Publication date: 2024-05-24
Anticipated expiration: 2039-06-06
Also published as: CN110270240A

Abstract

The invention relates to a dilution steam mixer, which comprises an inner cylinder and an outer cylinder; the inner cylinder forms a straight cylinder section and an expanded cylinder section with an integrated structure along the axis direction, and the free end of the straight cylinder section extends outwards to the outside of the outer cylinder and forms a raw material inlet; the inner cylinder and the outer cylinder are fixedly connected through a straight cylinder section; the radius of the cross section of the free end of the expansion section is gradually enlarged, and a tiny gap is formed between the terminal port of the free end and the inner wall of the outer cylinder; the circumferential wall of the expansion section is provided with an upper steam through hole and a lower steam through hole which are staggered in angle; and a steam inlet is arranged on the wall of the outer barrel corresponding to the inner barrel expansion section. The invention has simple structure and convenient operation, can effectively control the steam dilution ratio, and can fully and uniformly mix the dilution steam and the gas-phase pyrolysis raw material in limited time and space.

Description

Dilution steam mixer

Technical Field

The invention belongs to the technical field of mixer equipment, and particularly relates to a mixer for mixing dilution steam and gas-phase pyrolysis raw materials in a process of preparing pyrolysis gas by hydrocarbon pyrolysis.

Background

An ethylene cracking furnace, namely a process for preparing cracking gas by cracking hydrocarbons. In the chemical balance, the primary reaction of hydrocarbon cracking is a reaction with increased volume, and the reduction of the reaction pressure is favorable for the hydrocarbon to go on in the direction of generating lower olefins such as ethylene and the like, so that the yield of target products is improved; the secondary reaction is a reaction with reduced gas volume, and the pressure is reduced, so that the secondary reaction can be restrained, and coking is reduced. Although the pressure cannot change the reaction rate constant in dynamics, it can affect the reaction rate by the change of the reactant concentration, and since the number of reaction stages of the primary reaction is smaller than that of the secondary reaction, the reduction of the pressure can increase the relative rate of the primary reaction to the secondary reaction.

From the above two aspects, it can be seen that the pressure reduction is advantageous for the primary reaction, and the progress of the secondary reaction can be suppressed, both thermodynamically and kinetically.

Because the hydrocarbon cracking reaction is carried out at high temperature, the safety is a problem by adopting a direct decompression method, the cracking furnace is not easy to seal at high temperature, and once air leaks into the high temperature furnace tube, explosion can occur; secondly, the subsequent cracking gas compression is unfavorable, so that the energy load is increased and the energy consumption is increased, therefore, an indirect decompression method is adopted in industry, namely, a diluent is added to reduce the hydrocarbon partial pressure in the furnace tube, and water vapor is generally adopted as the diluent in industry.

Steam dilution ratio is the ratio of dilution steam to the mass flow of the cracking feedstock. The dilution ratio is increased, so that the hydrocarbon partial pressure can be reduced, the stream speed of the furnace tube is improved, the film temperature drop is reduced, and the residence time is relatively shortened. However, too large a dilution ratio can have some adverse effects, such as decreasing the capacity of the plant, increasing steam and fuel consumption, so that the proper dilution ratio must be controlled. The dilution ratio varies with the cracking feedstock, and the principle is that dilution steam is used as little as possible under the condition of preventing coking, and the dilution ratio is properly increased only when the feedstock is easy to coke.

The advantages of steam as a diluent are mainly manifested in the following aspects:

① Stabilizing the cracking temperature. The steam has larger heat capacity, and can play a role in stabilizing the temperature when the operation heat supply is unstable, and can also protect the furnace tube from overheating.

② Protecting the furnace tube. When steam exists, the high-temperature steam has oxidizing property, so that the corrosion of sulfur contained in the cracking raw material to the furnace tube can be inhibited, and even if the sulfur content is up to 2% (mass fraction), the corrosion threat to the furnace tube is insufficient.

③ And removing the coking. The iron and nickel in the furnace tube can catalyze the charcoal-forming reaction of hydrocarbon gas, the water vapor has oxidation effect on the iron and nickel, can inhibit the catalysis effect on the charcoal-forming reaction, and has certain removal effect on the generated charcoal.

Therefore, how to add dilution steam level in a limited furnace space is an important topic and direction of research.

Disclosure of Invention

The invention aims to provide a dilution steam mixer which has a simple structure and convenient operation, and can fully and uniformly mix dilution steam and gas-phase pyrolysis raw materials in a limited time and space.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

a dilution steam mixer comprises an inner cylinder and an outer cylinder; the inner cylinder forms a straight cylinder section and an expanded cylinder section with an integrated structure along the axis direction, and the free end of the straight cylinder section extends outwards to the outside of the outer cylinder and forms a raw material inlet; the inner cylinder and the outer cylinder are fixedly connected through a straight cylinder section;

the radius of the cross section of the free end of the expansion section is gradually enlarged, and a tiny gap is formed between the terminal port of the free end and the inner wall of the outer cylinder; the circumferential wall of the expansion section is provided with an upper steam through hole and a lower steam through hole which are staggered in angle;

and a steam inlet is arranged on the wall of the outer barrel corresponding to the inner barrel expansion section.

As a further improvement of the invention: the outer cylinder main body is of a straight cylinder structure, and the tail end of the outer cylinder main body is of a diameter-reducing structure. The cooperation of the straight cylinder structure and the tail end reducing structure can further strengthen the mixing disturbance of the pyrolysis gas and the diluted steam flow in the lower space of the outer cylinder, so that the pyrolysis gas and the diluted steam flow are promoted to be fully mixed in the lower space of the outer cylinder.

As a further improvement of the invention: the expansion section is in a round platform structure. The bottom angle alpha of the shaft section of the cone-shaped structure of the expansion section is 75-85 degrees. The design of the cylinder expansion structure can reduce the flow velocity of the gas, thereby being more beneficial to the suction and drainage of the gas; at the same time, the minimum resistance of the surface of the fluid and the minimum loss of the pressure drop of the fluid can be ensured.

As a further improvement of the invention: the central axis of the steam through hole is inclined towards the outlet end of the outer cylinder, so that the mixing speed is further increased.

As a further improvement of the invention: because the dilution steam is injected into the inner barrel expansion section area through the steam through holes, the jet flow penetrates into the cracking raw material gas flow, and when the large-scale macroscopic concentration distribution uniformity is to be achieved, the momentum of the dilution steam is required to be larger than the momentum of the cracking raw material gas flow. The high-speed jet flow causes a shearing layer, and the instability of the shearing layer can drive the surrounding fluid to move, so that the cracking raw material fluid is broken into a plurality of small micro-clusters, the area of molecular diffusion is increased, and the uniform mixing of the fluid is achieved. Thus, the dilution steam is formed into a jet, and the pore size of the steam through hole is high. For a certain amount of open area, the aperture is small, the flow speed is high, and although the turbulence degree of the dilution steam is large, the injection area of the dilution steam after injection is small, so that the flow of a boundary layer can not be completely driven; the aperture is large, the flow velocity is small, and high-speed jet fluid cannot be formed to drive the pyrolysis gas flow, so that the aperture of the steam through hole is controlled to be 10-20mm.

The working principle of the invention is as follows: after the pyrolysis raw material is turned out from the convection section of the pyrolysis furnace, the pyrolysis raw material enters the inner cylinder of the dilution steam mixer, and pyrolysis gas flows from top to bottom along the straight cylinder section of the inner cylinder; diluting steam enters an upper cavity formed by the outer cylinder and the inner cylinder through a steam inlet for buffering, and then enters a lower cavity formed by the outer cylinder and the inner cylinder through a steam through hole; the diluted steam and the pyrolysis gas are coarsely mixed in the expansion section of the inner cylinder, and then the pyrolysis gas and the diluted steam are further mixed in the lower space of the outer cylinder.

The invention has simple structure and convenient operation, can effectively control the steam dilution ratio, and can fully and uniformly mix the dilution steam and the gas-phase pyrolysis raw material in limited time and space.

Drawings

FIG. 1 is a front view block diagram of the present invention;

FIG. 2 is a schematic structural view of an inner cylinder according to the present invention;

FIG. 3 is an enlarged sectional view of the structure A-A shown in FIG. 2.

Detailed Description

The present invention will be described in further detail below with reference to the drawings and examples for the purpose of enhancing the understanding of the present invention.

As shown in fig. 1: the embodiment relates to a dilution steam mixer for mixing dilution steam with a gas-phase pyrolysis feedstock, which comprises an inner barrel and an outer barrel.

As shown in fig. 1: the main body of the outer cylinder 1 is of a straight cylinder structure, the diameter of the main body is 270mm, the upper end port is used for being connected with the inner cylinder 2, the lower end port is of a diameter-reducing structure, the minimum diameter formed after diameter reduction is larger than or equal to the radius of the straight cylinder part of the outer cylinder, and the diameter-reducing structure enables downward airflow to be disturbed again, so that pyrolysis gas and dilution steam are further mixed in a strengthening mode. The steam inlet 11 is arranged on the wall of the outer cylinder 1 corresponding to the position of the inner cylinder expansion section 22.

As shown in fig. 2: the inner cylinder 2 forms a straight cylinder section 21 and an expanded cylinder section 22 which are integrally formed along the axial direction, namely from top to bottom, the diameter of the straight cylinder section 11 is 150mm, and the free end of the straight cylinder section 11 extends outwards to the outside of the outer cylinder to form a raw material inlet 211; the middle part of the straight section 21 of the inner cylinder is fixedly connected with the upper end port of the outer cylinder 1 through a flange or welding.

As shown in fig. 2: the radius of the free end of the expansion section 22 of the inner cylinder is gradually enlarged to form a circular truncated cone structure, so that the circular truncated cone structure is more beneficial to the suction and drainage of gas, but if the expansion angle of the expansion section is too large, the fluid resistance can be increased, and the pressure drop can be increased. The bottom angle alpha of the shaft section of the formed truncated cone structure is 80 degrees in the embodiment, so that the expansion angle of the expansion section is controlled, the minimum fluid resistance loss can be ensured, and the mixing effect is ensured.

As shown in fig. 1: before the pyrolysis raw material is mixed with the pyrolysis gas, the temperature is about 350 ℃, and the temperature difference can cause the axial thermal expansion of the inner cylinder, so that a tiny gap is formed between the free end port of the inner cylinder expansion section 22 and the inner wall of the outer cylinder 1; in addition, the dilution steam can sweep the gas at the lower part of the periphery through the tiny gaps, so that the liquid accumulation is avoided, and dead zones are generated.

As shown in fig. 2 and 3: the circumference wall of the inner cylinder expansion section 22 is provided with an upper steam through hole 221 and a lower steam through hole 221 which are staggered in angle, so that dilution steam is dispersed and relatively uniformly enters the inner cylinder expansion section area; in order to form the dilution steam into a high-flow jet, the aperture of the steam through hole 221 is controlled to be 10-20mm, and the aperture of the steam through hole 221 is 15mm in the embodiment. In order to promote the high-speed airflow to drive the cracking raw materials to flow downwards and accelerate the mixing speed, the central axis of the steam through hole 221 is inclined towards the outlet end of the outer cylinder.

The above description is only for the purpose of illustrating the technical solution of the present invention and not for the purpose of limiting the same, and other modifications and equivalents thereof by those skilled in the art should be included in the scope of the claims of the present invention without departing from the spirit and scope of the technical solution.

Claims

1. A dilution steam mixer, characterized by: comprises an inner cylinder and an outer cylinder;

The inner cylinder forms a straight cylinder section and an expanded cylinder section with an integrated structure along the axis direction, and the free end of the straight cylinder section extends outwards to the outside of the outer cylinder and forms a raw material inlet; the inner cylinder and the outer cylinder are fixedly connected through a straight cylinder section;

2. The dilution steam mixer of claim 1, wherein: the outer cylinder main body is of a straight cylinder structure, and the tail end of the outer cylinder main body is of a diameter-reducing structure.

3. The dilution steam mixer of claim 1, wherein: the expansion section is in a round platform structure.

4. A dilution steam mixer according to claim 3, wherein: the bottom angle alpha of the shaft section of the cone-shaped structure of the expansion section is 75-85 degrees.

5. The dilution steam mixer of claim 1, wherein: the central axis of the steam through hole is inclined towards the outlet end of the outer cylinder.

6. The dilution steam mixer of claim 1, wherein: the aperture of the steam through hole is 10-20mm.