Cracking process

Abstract

The application relates to the field of cracking, and discloses a high-electrification-rate cracking method, which comprises the following steps: a gasification stage, in which raw materials and steam are preheated and mixed to generate cracking materials; a cracking stage, in which combustion-supporting agents are electrically heated, fuel gas is combusted, and the cracking materials output from the gasification stage are cracked into final products; and a quenching stage, in which the final products generated in the cracking stage are cooled. By using an electric heater and optimizing a process flow, the fuel gas consumption is maximally reduced, and the carbon dioxide emission is reduced without changing the existing process flow.

Description

Technical Field

[0001] This invention relates to the field of pyrolysis, and more specifically to a pyrolysis method. Background Technology

[0002] Given that some of the current electricity is already obtained from low-carbon or even zero-carbon emission sources such as wind, solar, geothermal, and nuclear power, as the proportion of green electricity increases in the future, increasing the proportion of electricity utilization in the equipment, that is, the electrification rate of the equipment, is an important measure and way to reduce the carbon emissions of the equipment.

[0003] In ethylene plants, cracking furnaces conventionally use fuel gas combustion to generate heat, providing a heat source for the cracking reaction. The cracking reaction has a large heat absorption capacity and high fuel gas consumption, contributing over 80% to the plant's carbon emissions. Therefore, increasing the electrification rate of the cracking furnace can effectively reduce carbon emissions at the source. In traditional steam cracking methods ( Figure 1 As shown in the figure, the fuel gas is mixed with the air preheated by hot water and burned to generate heat, which provides a heat source for the pyrolysis reaction in the radiation stage. The remaining flue gas is heat-exchanged through various modules in the convection stage to recover excess heat and is finally discharged into the atmosphere. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a pyrolysis method that minimizes fuel gas consumption and reduces carbon dioxide emissions by using an electric heater and optimizing the process flow without changing the existing process.

[0005] To achieve the above objectives, the present invention provides a pyrolysis method, comprising:

[0006] In the gasification stage, the feedstock and steam are preheated and mixed to generate the product to be cracked; the feedstock includes at least hydrotreated tail oil, diesel, naphtha, light hydrocarbons, LPG, propane, ethane, etc.

[0007] In the pyrolysis stage, the combustion aid is electrically heated to burn fuel gas, thereby pyrolyzing the pyrolysis product output from the gasification stage into the final product.

[0008] The rapid cooling stage cools the final products produced in the pyrolysis stage.

[0009] Preferably, the high-temperature flue gas generated in the pyrolysis stage is used to preheat the materials to be pyrolyzed in the gasification stage. Utilizing the high-temperature flue gas generated in the pyrolysis stage recovers waste heat, fully utilizes thermal energy, and achieves energy savings, reduces costs, and simplifies the process flow.

[0010] Preferably, the gasification stage includes:

[0011] Heating stage D: heating and outputting the raw material;

[0012] Heating stage E, heating the product of heating stage D and part of the steam to obtain a preliminary gasification product;

[0013] Heating stage F, heating part of the steam to obtain preheated steam;

[0014] and,

[0015] Heating stage G, heating the preliminary gasification product and the preheated steam to obtain a final gasification product;

[0016] Preferably, the heating stages are arranged in order of increasing temperature, and the temperature in heating stage D is 50-200℃, the temperature in heating stage E is 200-300℃, the temperature in heating stage F is 250-500℃, and the temperature in heating stage G is 350-650℃;

[0017] Further preferably, the flow rate of the steam in the preliminary gasification product is 1-4wt% of the raw material. The first injection of steam is generally about 1-4% of the raw material, which serves to reduce the viscosity and prevent coking. By arranging multiple heating stages, the heat energy in the high-temperature flue gas can be utilized in stages, and the heating can be performed gradually. When arranging the specific device, this method is advantageous for directly arranging the pipeline for conveying the cracking product at the discharge outlet of the high-temperature flue gas, and the temperature can be utilized in stages by countercurrent flow of the conveying of the cracking product and the discharge of the high-temperature flue gas, thereby simplifying the arrangement of the device.

[0018] Preferably, the steam in heating stage F is heated by electric heating; and in heating stages D, E and G, the high-temperature flue gas is used as a heat source. When the electric heating power for the combustion-supporting agent is increased to increase the electrification rate, the total heat of the high-temperature flue gas generated during the cracking stage is reduced, and therefore additional heat needs to be provided to part of the heating stages in the gasification stage.

[0019] Preferably, the quenching stage includes a waste heat recovery stage; and in the waste heat recovery stage, the heat of the final product is recovered. By recovering the waste heat in the quenching stage, the initial raw material can be heated to provide heat and save energy.

[0020] Preferably, in heating stage D, part of the raw material is preheated;

[0021] In the waste heat recovery stage, another part of the raw material is heated by recovering the waste heat of the final product;

[0022] In heating stage E, the product of heating stage D, the product of the waste heat recovery stage and part of the steam are heated together.

[0023] Preferably, the flow ratio of the amount of raw material in the heating stage D to the amount of raw material in the waste heat recovery stage is adjustable. When the power of the electric heater for combustion-supporting agent is further increased, the heat in the flue gas is further reduced, resulting in insufficient heat exchange in the gasification section. Therefore, a part of the raw material stream originally entering the heating stage D can be divided into the waste heat recovery stage to recover part of the heat.

[0024] The second aspect of the present application provides a cracking method, comprising:

[0025] a gasification stage for preheating raw material, steam and combustion-supporting agent, and mixing the preheated raw material with steam to generate a to-be-cracked material; the raw material at least includes hydrocracking tail oil, diesel, naphtha, light hydrocarbon, LPG, propane, ethane, etc.;

[0026] a cracking stage for burning fuel gas and cracking the to-be-cracked material into a final product;

[0027] a quenching stage for cooling the final product generated in the cracking stage.

[0028] Preferably, the high-temperature flue gas generated in the cracking stage is used to preheat the to-be-cracked material and the combustion-supporting agent in the gasification stage;

[0029] Preferably, the to-be-cracked material includes raw material and steam.

[0030] Preferably, the gasification stage includes:

[0031] a heating stage K for heating and outputting the combustion-supporting agent;

[0032] a heating stage D for heating and outputting the raw material;

[0033] a heating stage E for heating the product of the heating stage D together with part of the steam to obtain a preliminary gasification material;

[0034] a heating stage F for heating part of the steam to obtain preheated steam;

[0035] and,

[0036] a heating stage G for heating the preliminary gasification material together with the preheated steam to obtain a final gasification material. Considering the improvement of the thermal efficiency of the cracking stage, a part of the link for directly preheating the combustion-supporting agent is additionally arranged at the top of the gasification section, the heat of the whole is fully utilized, and carbon emission is reduced.

[0037] Preferably, the steam in the heating stage F is heated in an electric heating manner; in the heating stage K, the heating stage D, the heating stage E and the heating stage G, the high-temperature flue gas is used as a heat source;

[0038] Preferably, the heating stages K, D, E and G are arranged in order of temperature from low to high.

[0039] Preferably, the quenching stage comprises a waste heat recovery stage.

[0040] In the waste heat recovery stage, the raw material is heated by recovering waste heat of the final product.

[0041] In the heating stage D, the raw material is the one output by the waste heat recovery stage. In order to avoid the temperature drop in the heating stage K and thus fail to heat the combustion-supporting agent as expected, part of the heat of the raw material is provided by the waste heat recovery stage, and after the complete utilization of the heat of the waste heat recovery stage, the raw material is provided in the heating stage D, which is beneficial to further improve the utilization of temperature gradient and reasonably arrange the temperature matching.

[0042] Preferably, in the gasification stage, an air compressor is used to offset the resistance drop.

[0043] Through the above technical solutions, without changing the existing cracking furnace process with fuel gas as the heat source, green electricity heating equipment is introduced to optimize the process and improve the electrification rate of the cracking furnace. Meanwhile, the adaptability of the electrification equipment is considered to ensure the stable operation and high thermal efficiency of the device, minimize the consumption of fuel gas and reduce carbon emissions. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a flow chart of a traditional steam cracking method;

[0045] Figure 2 is a flow chart of a specific embodiment one of the cracking method of the present application;

[0046] Figure 3 is a flow chart of a specific embodiment two of the cracking method of the present application;

[0047] Figure 4 is a flow chart of a specific embodiment three of the cracking method of the present application;

[0048] Figure 5 is a flow chart of a specific embodiment four of the cracking method of the present application.

[0049] REFERENCE SIGNS

[0050] B, first mixer; C, second mixer; D, heating stage D; E, heating stage E; F, heating stage F; G, heating stage G; H, radiation stage; I, quench heat exchanger; J, waste heat recovery heat exchanger; K, combustion-supporting agent preheater; 1, raw material; 2, total dilution steam; 3, partial steam to F stage; 4, partial steam to first mixer; 5, raw material to first mixer; 6, preliminary mixture; 7, preliminary gasification; 8, post- superheated dilution steam; 9, final mixture; 10, final gasification; 11, end product; 12, end product after quench heat exchanger; 13, end product after waste heat recovery heat exchanger; 14, combustion-supporting agent; 15, preheated combustion-supporting agent; 16, fuel gas; 17, partial raw material to first mixer; 18, partial raw material to waste heat recovery heat exchanger; 19, partial raw material to heating stage D; 20, raw material out of waste heat recovery heat exchanger; 21, high-temperature heat exchange stream; 22, post-heat exchange stream. DETAILED DESCRIPTION

[0051] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0052] In the present application, the orientation words such as "upper" and "lower" generally refer to the orientation in the assembled and used state, unless otherwise specified. "Inner" and "outer" refer to the inner and outer relative to the outline of each component.

[0053] Glossary: Gasification stage refers to the part of the process in which the raw material 1 and steam are mixed after being preheated, and the material entering the gasification stage is prepared for the cracking stage. Cracking stage refers to the process stage in which high temperature is obtained by burning fuel gas and the material to be cracked is cracked. Quenching stage refers to the process stage in which the end product produced by the cracking stage is cooled.

[0054] The flow chart of the conventional steam cracking method is as follows Figure 1As shown, a pyrolysis furnace is provided, with a radiant coil at its bottom. The pyrolysis stage takes place within the radiant coil. The high-temperature flue gas generated after the combustion of fuel gas 16 moves upward along the height of the pyrolysis furnace, recovering heat from the high-temperature flue gas. Raw material 1 enters the heating stage D at the top of the pyrolysis furnace. After preliminary post-heating, it is output to the first mixer. Raw material 5 enters the first mixer B. Partial dilution steam 4, separated from the total dilution steam 2, enters the first mixer B. Preliminary mixture 6 is output from the first mixer B and enters the heating stage E. Preliminary gasified product 7 is output from the heating stage E to the second mixer C. Partial total dilution steam 2 is extracted and enters the heating stage F, after which superheated post-dilution steam 8 is output to the second mixer C. The final mixture 9 is output from the second mixer C to the heating stage G. Final gasified product 10 is output from the heating stage G to the radiant stage H. The combustion aid 14 is heated through a high-temperature heat exchange stream, and the preheated combustion aid 15 is output to the radiant stage H. Fuel gas 16 is introduced into the radiant stage H. In the radiation stage H, fuel gas 16 is burned, and the final gasified product 10 is cracked into final product 11. The final product is passed into quench heat exchanger I for preliminary cooling, and then into waste heat recovery heat exchanger J before being output. Specific Implementation Example 1:

[0056] like Figure 2 As shown, this invention provides a pyrolysis method with a high electrification rate, comprising: a gasification stage, preheating the pyrolysis material to be pyrolyzed, and outputting the preheated pyrolysis material; a pyrolysis stage, electrically heating the combustion-supporting agent 14 to burn fuel gas 16, thereby pyrolyzing the pyrolysis material output from the gasification stage into final products; and a quenching stage, cooling the final products produced in the pyrolysis stage. By adding electrification equipment to heat the combustion-supporting agent 14, heat is provided for the combustion of fuel gas 16 in the pyrolysis stage, reducing the heat provided by combustion, resulting in a higher initial combustion temperature, more complete combustion, and reduced fuel gas 16 consumption, thereby reducing total carbon emissions.

[0057] Specifically, in the pyrolysis stage, the fuel gas 16 is burned to generate high-temperature flue gas, which is then introduced into the gasification stage to preheat the material to be pyrolyzed. The material to be pyrolyzed includes raw material 1 and total dilution steam 2. The gasification stage includes heating stage D, heating stage E, heating stage F, and heating stage G. The gasification process for the material to be pyrolyzed is as follows: 1) After the raw material 1 enters heating stage D, it mixes with a portion of the steam and enters heating stage E to output preliminary gasified material; 2) After a portion of the steam enters heating stage F, it mixes with the preliminary gasified material and enters heating stage G to output final gasified material; 3) The final gasified material is introduced into the pyrolysis stage. It should be noted that heating stages D, E, F, and G are figurative concepts, corresponding to different heating stages.

[0058] To achieve temperature gradient utilization, preferably, the heating stages are arranged in ascending order of temperature: heating stage D, heating stage E, heating stage F, and heating stage G. As the high-temperature flue gas at the bottom of the pyrolysis furnace rises spatially, its temperature gradually decreases. Correspondingly, as the pipe carrying the material to be pyrolyzed passes through heating stages D, E, F, and G in sequence within the pyrolysis furnace, the temperature of the material gradually increases, thus achieving temperature gradient utilization.

[0059] More specifically, the steam flow rate in the preliminary gasification is 1-4 wt% of the raw material 1. The heating temperature in the heating stage D is relatively low, and a correspondingly smaller amount of steam is set for preliminary mixing with the raw material 1 to meet actual needs.

[0060] This solution can increase the electrification rate of the pyrolysis unit by 3-7%. Specific Implementation Example 2:

[0062] like Figure 3 As shown, this invention provides a pyrolysis method with a high electrification rate. Based on specific embodiment one, this embodiment increases the power of electrically heating the combustion aid 14, thereby reducing the total heat of the high-temperature flue gas in the pyrolysis furnace. This means that the high-temperature flue gas alone cannot provide sufficient heat during the gasification stage. Therefore, in the heating stage F, part of the steam is heated by electrified equipment, further increasing the electrification rate of the process while ensuring process perfection and stable operation of the equipment.

[0063] This solution can increase the electrification rate of the pyrolysis unit by 5-10%. Specific Implementation Example 3:

[0065] like Figure 4 As shown, this invention provides a pyrolysis method with a high electrification rate. Based on specific embodiment two, the power of the air electric heater is further increased, and the heat in the high-temperature flue gas is further reduced. At this time, the heat provided to the raw material 1 in heating stage D is insufficient. Therefore, in the waste heat recovery heat exchange stage, part of the raw material 1 is heated by waste heat recovery. The heated raw material 20 exiting the waste heat recovery heat exchanger and part of the raw material 17 output from heating stage D are input into the first mixer B together.

[0066] This solution can increase the electrification rate of the pyrolysis unit by 12-16%. Specific Implementation Example 4:

[0068] like Figure 5As shown, the application provides a high electrification rate cracking method, on the basis of scheme three, considering temperature matching and cracking furnace heat efficiency improvement, adding heating stage K in the gasification stage. In heating stage K, the combustion improver 14 originally heated by electricity is heated by high-temperature flue gas. At the same time, in order to avoid insufficient temperature in heating stage K, the temperature drop in heating stage D is reduced. First, the raw material 1 is heated in the waste heat recovery heat exchange stage, and then the raw material 1 is heated twice in the heating stage D after sufficient heat absorption.

[0069] In order to offset the resistance brought by the pipeline. As a preferred, an air compressor is arranged at the top of the cracking furnace.

[0070] The present scheme can improve the electrification rate of the cracking device by 12-30%.

[0071] The preferred embodiments of the application are described in detail above in combination with the drawings, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application. In order to avoid unnecessary repetition, various possible combinations are not described again. However, these simple modifications and combinations should also be regarded as disclosed content of the application, and all belong to the protection scope of the application.

Claims

1. A pyrolysis method, characterized in that, include: In the gasification stage, the raw materials and steam are preheated and mixed to generate the product to be pyrolyzed; In the pyrolysis stage, the combustion aid is electrically heated to burn fuel gas, thereby pyrolyzing the pyrolysis product generated in the gasification stage into the final product. The rapid cooling stage cools the final products generated in the pyrolysis stage. The gasification stage includes: Heating stage D: heating and outputting a portion of the raw material; In heating stage E, the product of heating stage D is heated together with a portion of the steam to obtain a preliminary vaporized product. In heating stage F, a portion of the steam is heated to obtain preheated steam. In addition, in the heating stage G, the preliminary vaporized product and the preheated steam are heated together to obtain the final vaporized product; In the heating stages D, E, and G, the high-temperature flue gas generated in the pyrolysis stage is used as the heat source. In heating stage F, part of the steam is heated by electrified equipment; The rapid cooling stage includes a waste heat recovery stage; in the waste heat recovery stage, the heat of the final product is recovered. In the waste heat recovery stage, the remaining raw materials are heated by recovering the waste heat of the final product. In the heating stage E, the product of the heating stage D, the raw materials produced in the waste heat recovery stage, and a portion of the steam are heated together.

2. In the pyrolysis method according to claim 1, the flow rate of the steam in the preliminary gasification is 1 to 4 wt% of the feedstock.

3. The pyrolysis method according to claim 1, characterized in that, The flow rate ratio of the raw material quantity in the heating stage D to the raw material quantity in the waste heat recovery stage is adjustable.

4. A pyrolysis method, characterized in that, include: In the gasification stage, the raw materials, steam and combustion aid are preheated, and the preheated raw materials are mixed with steam to generate the product to be pyrolyzed. During the pyrolysis stage, fuel gas is burned to pyrolyze the material to be pyrolyzed into the final product. The rapid cooling stage cools the final products generated in the pyrolysis stage. The gasification stage includes: In heating phase K, the combustion-supporting agent is heated and output; Heating stage D: heating and outputting the raw material; In heating stage E, the product of heating stage D is heated together with a portion of the steam to obtain a preliminary vaporized product. In heating stage F, a portion of the steam is heated to obtain preheated steam. In addition, in the heating stage G, the preliminary vaporized product and the preheated steam are heated together to obtain the final vaporized product; In heating stage F, part of the steam is heated by electrified equipment; The rapid cooling stage includes a waste heat recovery stage; In the waste heat recovery stage, the raw materials are heated by recovering the waste heat of the final product. In the heating stages K, D, E, and G, the high-temperature flue gas generated in the pyrolysis stage is used as the heat source. In the heating stage D, the raw material being heated is the raw material produced in the waste heat recovery stage.

5. The pyrolysis method according to claim 4, characterized in that, The heating stages are arranged from lowest to highest temperature provided by the high-temperature flue gas as heating stage K, heating stage D, heating stage E, and heating stage G.

6. The pyrolysis method according to claim 4, characterized in that, During the vaporization stage, the resistance drop is offset by an air compressor.

Images