Method and system for improving the operating cycle of a gas phase cracking furnace

Abstract

A method for improving the operating cycle of a gas-phase cracking furnace comprises: (1) mixing steam with air to obtain a de-coking gas; (2) preheating the de-coking gas obtained in step (1) to obtain a preheated de-coking gas; (3) incorporating the preheated de-coking gas obtained in step (2) into cracking raw materials, and then sending it to the radiation section of the cracking furnace for cracking reaction and de-coking reaction to obtain a mixed gas containing cracking gas, CO and CO2; (4) sequentially cooling, alkali washing and hydrogenation of the mixed gas obtained in step (3) to obtain a de-impurity mixed gas containing methane and cracking gas. A system for improving the operating cycle of a gas-phase cracking furnace is also provided. The method and system can remove coke generated during the cracking process as it is produced, avoid or reduce coke accumulation, and improve the operating cycle.

Description

Technical Field

[0001] The present invention belongs to the technical field of petrochemical industry, and in particular relates to a method and a system for improving the operating cycle of a gas phase cracking furnace. Background Art

[0002] The operating cycle of a gas-phase cracking furnace is a key indicator of the operational and operational performance of an ethylene plant. This cycle varies depending on the feedstock. Currently, domestic ethylene plants are using lighter feedstocks, with the use of cracking feedstocks such as ethane and propane. Due to the high carbon-to-hydrogen ratio of gas-phase feedstocks, high ethylene yields, and low ethane and propane prices, more and more ethylene plants are adopting gas-phase cracking to produce ethylene.

[0003] The operation cycle of ethylene produced by cracking gaseous raw materials is generally long, but there are also large differences due to the different quality of raw materials. The domestic operation cycle of gas-phase cracking furnaces has been explored and tested. Recently, ceramic furnace tubes with better effects have been used to effectively extend the operation cycle of gas-phase cracking furnaces, but their cost is relatively high.

[0004] During the cracking reaction, the material of the radiant section furnace tubes can promote coking. However, the inner surface finish of the radiant section tubes cannot be perfectly smooth, which can lead to coke deposition. The coking reaction mechanism is primarily the dehydrogenation of hydrocarbon feedstock and the polymerization of small aromatic hydrocarbons to form larger aromatic compounds. These compounds adhere to the inner surfaces of the tubes, depositing and forming coke. The parent molecules of the coke may be present in the feedstock or synthesized during the thermal cracking process. Therefore, feedstocks containing large amounts of aromatics or heavy compounds are more prone to coke formation. Ethylene production mostly uses hydrogen-rich feedstocks. As the cracking reaction proceeds, the hydrogen-rich feedstock is gradually separated to produce hydrogen, while the hydrogen content of the remaining fraction decreases. This hydrogen depletion phenomenon manifests itself as the formation of aromatic hydrocarbon molecules with increasing molecular weight. These molecules adhere to the inner surfaces of the radiant tubes and downstream heat recovery equipment, forming coke. Ultimately, at high cracking severity, nearly all of the hydrogen in the feedstock is consumed, leaving a coke-like residue with little or no hydrogen. Therefore, it is necessary to maximize olefin yield and minimize coking through cracking with the most selective cracking possible. This process requires a combination of short residence time, high temperature, low pressure drop and optimal dilution steam ratio. The USC cracking furnace system has the following characteristics: maximizing the production of ethylene and other valuable by-products and minimizing undesirable products. As the cracking depth increases, due to the continuous increase in the temperature in the furnace tube, the parent molecules of the coking products become more and more abundant and the thermodynamic activity becomes higher and higher. For example, a certain ethylene plant is designed to produce 1 million tons of ethylene annually, based on 8,000 operating hours per year. At the entrance of each group of radiation furnace tubes, there is a venturi tube. The design of the venturi can make the fluid reach the critical flow state, thereby ensuring that the material flow entering each group of radiation furnace tubes is uniform. When the ratio of the downstream pressure to the upstream pressure of the venturi throat (measured in absolute pressure ratio) is greater than 0.9, it is impossible to ensure that the material is evenly distributed to each group of radiation furnace tubes, and then a decoking operation is required. Generally, decoking is required once every 45 days, and the operating cycle is short. Summary of the Invention

[0005] The first object of the present invention is to provide a method for improving the operating cycle of a gas phase cracking furnace, which can remove coke generated during the cracking process as it is produced, thereby avoiding or reducing coke accumulation and improving the operating cycle;

[0006] The second object of the present invention is to provide a system for improving the operating cycle of a gas phase cracking furnace, which can remove the coke generated during the cracking process as it is produced, avoid or reduce coke accumulation, and improve the operating cycle.

[0007] In order to achieve the first object of the present invention, the following technical solutions are adopted:

[0008] A method for increasing the operating cycle of a gas phase cracking furnace comprises the following steps:

[0009] (1) Mixing steam with air to obtain de-coking gas;

[0010] (2) preheating the decoking gas obtained in step (1) to obtain preheated decoking gas;

[0011] (3) the preheated decoking gas obtained in step (2) is added to the cracking feedstock and then sent to the radiant section of the cracking furnace for cracking reaction and decoking reaction to obtain a mixed gas containing cracked gas, CO and CO2;

[0012] (4) The mixed gas obtained in step (3) is sequentially subjected to cooling, alkali washing and hydrogenation reaction to obtain a decontaminated mixed gas containing methane and cracked gas.

[0013] In the method of the present invention, preferably, in step (1), the steam includes dilution steam and / or medium-pressure steam; preferably, the dilution steam is 0.65-0.85 MPa steam; and the medium-pressure steam is 1.1-1.5 MPa steam;

[0014] Preferably, in step (1), the mixing ratio of steam to air is (1-25):100 by mass.

[0015] In the method of the present invention, preferably, in step (3), the reaction temperature in the radiation section is 800-900° C.; and / or

[0016] In step (3), the mixing ratio of the cracking raw material to the preheated decoking gas obtained in step (2) is (1-25):100 by mass ratio; and / or

[0017] In step (3), the cracking raw material is propane and the cracking gas is ethylene.

[0018] The method of the present invention preferably further comprises step (5), wherein the decontaminated mixed gas obtained in step (4) is tested and analyzed, and the amount of steam and air introduced in step (1) is adjusted according to the test and analysis results.

[0019] To achieve the second object, the present invention also provides a system for improving the operating cycle of a gas-phase cracking furnace, comprising a feeding unit, a preheating unit, a distribution reaction unit, and an analysis feedback unit connected in sequence;

[0020] The feeding unit includes a steam feeding pipeline and an air feeding pipeline arranged in parallel, for feeding steam and air respectively, and outputting decoking gas containing steam and air;

[0021] The preheating unit includes a preheating device; the preheating device is connected to the outlet pipeline of the feeding unit, and is used to preheat the decoking gas from the feeding unit to obtain preheated decoking gas;

[0022] The distribution reaction unit includes a venturi subunit and a cracking furnace connected to each other; the cracking furnace includes a radiant section; the feed end of the venturi subunit is connected to the cracking raw material feed pipeline, and the discharge end is connected to the radiant section, and the outlet pipeline of the preheating unit is connected to the discharge end of the venturi subunit, for respectively feeding the cracking raw material and the preheated decoking gas from the preheating unit into the radiant section for cracking reaction and decoking reaction, and outputting a mixed gas containing cracked gas, CO and CO2;

[0023] The analysis feedback unit includes a first quencher, a second quencher, an alkali scrubber and a hydrogenation reactor connected in sequence; the first quencher is connected to the outlet pipeline of the distribution reaction unit, and the first quencher and the second quencher are used to sequentially quench and cool the mixed gas from the distribution reaction unit and output the cooled mixed gas; the alkali scrubber is used to perform alkali washing on the cooled mixed gas from the second quencher to remove CO2 therefrom and output a primary impurity-removed mixed gas; the hydrogenation reactor is used to perform a hydrogenation reaction on the primary impurity-removed mixed gas from the alkali scrubber to remove CO therefrom and output a secondary impurity-removed mixed gas containing methane and cracking gas.

[0024] In the system of the present invention, preferably, in the feeding unit, a steam feeding valve is provided on the steam feeding pipeline, and an air feeding valve is provided on the air feeding pipeline; a flow display control instrument is provided on the outlet pipeline of the feeding unit, and the flow display control instrument is over-relaxedly connected to the steam feeding valve and the air feeding valve respectively;

[0025] In the system of the present invention, preferably, the steam feed line comprises a dilution steam feed line and / or an intermediate-pressure steam feed line, for feeding dilution steam and / or intermediate-pressure steam respectively.

[0026] In the system of the present invention, preferably, a first temperature control device is provided on the outlet pipeline of the preheating unit, and the first temperature control device is over-relaxedly connected to the preheating device for over-relaxing the preheating device to control the temperature of the preheated decoking gas output by the preheating unit.

[0027] In the system of the present invention, preferably, in the preheating unit, the preheating device includes any one or more parallel combinations of an electric heating device, a super steam heat exchanger and a cracking furnace.

[0028] In the system of the present invention, preferably, in the preheating unit, the preheating device is an electric heating device, and the first temperature control device is over-connected to the electric heating device for over-controlling the heating condition of the electric heating device; and / or

[0029] In the preheating unit, the preheating device is a cracking furnace, the cracking furnace includes a convection section, and the cracking furnace preheats the decoking gas from the feeding unit through its convection section; preferably, a first valve is provided on the outlet pipeline of the convection section of the cracking furnace, and the first temperature control device is connected to the convection section of the cracking furnace via the first valve for over-relaxation control of the opening of the first valve; and / or

[0030] In the preheating unit, the preheating device is a super steam heat exchanger, a second valve is provided on the heat medium outlet pipeline of the super steam heat exchanger, and the first temperature control device is connected to the super steam heat exchanger through the second valve for over-relaxation control of the opening of the second valve.

[0031] In the method of the present invention, preferably, a third valve is provided on the outlet pipeline of the preheating unit;

[0032] In the distribution reaction unit, a second temperature control device is provided on the feed pipeline of the radiation section, and the second temperature control device is over-relaxedly connected to the third valve for over-relaxing the opening of the third valve.

[0033] In the method of the present invention, preferably, the system comprises a plurality of the distribution reaction units, and the plurality of the distribution reaction units are arranged in parallel.

[0034] In the method of the present invention, preferably, in the distribution reaction unit, the cracking raw material is propane and the cracking gas is ethylene.

[0035] In the method of the present invention, preferably, in the analysis feedback unit, a first online analyzer is provided on the outlet material pipeline of the first quench cooler for analyzing and displaying the content of CO and CO2 in the material therein; and / or

[0036] A second online analyzer is provided on the outlet material pipeline of the second quench cooler for analyzing and displaying the pH value of the material therein and the content of CO2 in the material therein; and / or

[0037] A third online analyzer is provided on the outlet material pipeline of the alkali washing tower for analyzing and displaying the CO content in the material therein.

[0038] In the method of the present invention, preferably, in the analysis feedback unit, an online analysis controller is provided on the outlet material pipeline of the hydrogenation reactor, and the online analysis controller is over-relaxedly connected to the flow display control instrument to analyze and display the CO content in the material in the outlet material pipeline of the hydrogenation reactor, and over-relax-control the steam feed valve and the air feed valve.

[0039] The present invention also provides a method for increasing the operating cycle of a gas phase cracking furnace by utilizing the above system.

[0040] The beneficial effects of the present invention are:

[0041] The method and system for improving the operation cycle of a gas-phase cracking furnace of the present invention are as follows: steam and air are mixed and then incorporated into cracking raw materials, which are then fed into the radiation section of the cracking furnace for cracking reaction and coke-clearing reaction. On the one hand, the amount of propane introduced as the cracking raw material can be adjusted to reduce the amount of propane introduced, thereby slowing down the coking reaction, delaying the rate of coke formation, and reducing the amount of coke formed. On the other hand, steam and air (coke-clearing gas) can undergo an oxidation-reduction reaction (coke-clearing reaction) with the coke to generate CO and CO2, thereby avoiding the cracking furnace from burning due to the absolute pressure ratio reaching a critical value. After the reaction products (a mixed gas containing cracking gas, CO, and CO2) are analyzed and tested, the amount of steam and air introduced is adjusted based on the feedback of the analysis and test results, thereby effectively improving the operation cycle of the cracking furnace. Moreover, by cooling, alkali washing, and hydrogenating the reaction products, the influence of CO and CO2 in the reaction products on the subsequent system can be avoided, thereby achieving the purpose of long-term stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural schematic diagram of a system for improving the operating cycle of a gas phase cracking furnace according to one embodiment of the present invention. DETAILED DESCRIPTION

[0043] The technical solutions and effects of the present invention are further described below with reference to specific embodiments / examples and accompanying drawings. The following embodiments / examples are intended only to illustrate the present invention and are not intended to be limited to the following embodiments or examples. Simple modifications to the present invention that utilize the concepts of the present invention fall within the scope of protection claimed herein.

[0044] The present invention provides a method for improving the operating cycle of a gas phase cracking furnace, comprising the following steps:

[0045] (1) Mixing steam with air to obtain de-coking gas;

[0046] (2) preheating the decoking gas obtained in step (1) to obtain preheated decoking gas;

[0047] (3) the preheated decoking gas obtained in step (2) is added to the cracking feedstock and then sent to the radiant section of the cracking furnace for cracking reaction and decoking reaction to obtain a mixed gas containing cracked gas, CO and CO2;

[0048] (4) The mixed gas obtained in step (3) is sequentially subjected to cooling, alkali washing and hydrogenation reaction to obtain a decontaminated mixed gas containing methane and cracked gas.

[0049] The method for improving the operation cycle of a gas-phase cracking furnace of the present invention comprises the following steps: mixing steam with air and then incorporating the mixture into cracking raw materials, which are then fed into the radiation section of the cracking furnace for cracking reaction and coke-clearing reaction. On the one hand, the amount of propane introduced into the cracking raw materials can be adjusted to reduce the amount of propane introduced, thereby slowing down the coking reaction, delaying the rate of coke formation, and reducing the amount of coke formed. On the other hand, steam and air (coke-clearing gas) can undergo an oxidation-reduction reaction (coke-clearing reaction) with the coke to generate CO and CO2, thereby avoiding the cracking furnace absolute pressure ratio from reaching a critical value and causing coking. Furthermore, by cooling, alkali washing, and hydrogenating the reaction products, the influence of CO and CO2 in the reaction products on the subsequent system can be avoided, thereby achieving the purpose of long-term stable operation.

[0050] In one embodiment, in step (3), the cracking feedstock is propane.

[0051] In the present invention, the cracking reaction in step (2) is the cracking of the cracking raw material (propane) to produce cracking gas including acetylene, ethylene, propylene, methane, H2 and CO.

[0052] In the present invention, the decoking reaction in step (2) is a reaction between the preheated decoking gas (air, steam) and C, CO, and CO2, that is, O2 in the air reacts with C to produce CO and CO2; H2O in the steam reacts with CO to produce CO2 and hydrogen; and H2O in the steam reacts with CO2 to produce carbonic acid.

[0053] In the present invention, in step (4), the alkali washing is to remove CO2 by reacting alkali with CO2; the hydrogenation reaction is to hydrogenate acetylene in the cracked gas with H2 to produce ethylene.

[0054] Those skilled in the art will appreciate that in step (2), preheating can be performed using an electric heating device, a super steam heat exchanger (22), or a cracking furnace. When preheating is performed using a cracking furnace, the decoking gas obtained in step (1) is preheated by passing it through the convection section of the cracking furnace. In one embodiment, the preheating temperature is 500-600°C, such as 520°C, 540°C, 560°C, and 580°C.

[0055] In one embodiment, in step (1), the steam includes dilution steam and / or medium-pressure steam; preferably, the dilution steam is 0.65-0.85 MPa steam, such as 0.7 MPa, 0.75 MPa and 0.8 MPa; and the medium-pressure steam is 1.1-1.5 MPa steam, such as 1.2 MPa, 1.3 MPa and 1.4 MPa.

[0056] In one embodiment, step (1) further includes adjusting the amount of steam and air introduced by controlling the total flow rate of the mixed materials.

[0057] In one embodiment, in step (1), the mixing ratio of steam to air is (1-25):100 by mass, such as 5:100, 10:100, 15:100 and 20:100.

[0058] In one embodiment, in step (3), the reaction temperature in the radiation zone is 800-900°C, such as 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C and 890°C.

[0059] In one embodiment, the feed pressure ratio of the radiation section 32 is 0.6-0.95, such as 0.65, 0.7, 0.75, 0.8, 0.85, or 0.9, in terms of absolute pressure ratio.

[0060] In one embodiment, step (3) further comprises adjusting the amount of preheated decoking gas obtained in step (2) by controlling the temperature of the material after incorporation. When the temperature of the material after incorporation is high (800-900°C higher than the reaction temperature in the radiation section), the amount of preheated decoking gas obtained in step (2) is reduced; otherwise, the amount of preheated decoking gas is increased.

[0061] In one embodiment, in step (3), the mixing ratio of the cracking feedstock to the preheated decoking gas obtained in step (2) is (1-25):100 by mass, such as 5:100, 10:100, 15:100 and 20:100.

[0062] In one embodiment, in step (3), the obtained mixed gas is cooled to 35±10°C, such as 25°C, 30°C, 35°C, 40°C, or 45°C; and / or alkali washed to a pH of 6-8, such as 6.5, 7, or 7.5.

[0063] In one embodiment, in step (3), the reaction conditions of the hydrogenation reaction include: a reaction temperature of 60-70°C, such as 65°C; and / or a reaction pressure of 32-38 MPaG, such as 34 MPaG and 36 MPaG.

[0064] In one embodiment, the method further comprises step (5), detecting and analyzing the impurity-free mixed gas obtained in step (4), and adjusting the amount of steam and air introduced in step (1) according to the detection and analysis results.

[0065] The present invention provides a system for improving the operating cycle of a gas phase cracking furnace, such as Figure 1 As shown, the system includes a feeding unit, a preheating unit, a distribution reaction unit and an analysis feedback unit connected in sequence;

[0066] The feeding unit includes a steam feeding pipeline and an air feeding pipeline 11 arranged in parallel, for feeding steam and air respectively, and outputting decoking gas containing steam and air;

[0067] The preheating unit includes a preheating device; the preheating device is connected to the outlet pipeline of the feeding unit, and is used to preheat the decoking gas from the feeding unit to obtain preheated decoking gas;

[0068] The distribution reaction unit includes a venturi subunit 31 and a cracking furnace connected to each other; the cracking furnace includes a radiant section 32; the feed end of the venturi subunit 31 is connected to the cracking raw material feed pipeline, and the discharge end is connected to the radiant section 32; the outlet pipeline of the preheating unit is connected to the discharge end of the venturi subunit 31, and is used to feed the cracking raw material and the preheated decoking gas from the preheating unit to the radiant section 32 for cracking reaction and decoking reaction respectively, and output a mixed gas containing cracked gas, CO and CO2;

[0069] The analysis feedback unit includes a first quencher 41, a second quencher 42, an alkali scrubber 43 and a hydrogenation reactor 44 connected in sequence; the first quencher 41 is connected to the outlet pipeline of the distribution reaction unit, and the first quencher 41 and the second quencher 42 are used to sequentially quench the mixed gas from the distribution reaction unit to 35±10°C, such as 25°C, 30°C, 35°C, 40°C, and 45°C, and output the cooled mixed gas; the alkali scrubber 43 is used to perform alkali scrubbing on the cooled mixed gas from the second quencher 42 to a pH of 6-8 to remove CO2 therefrom, and output a primary impurity-removed mixed gas; the hydrogenation reactor 44 is used to perform a hydrogenation reaction on the primary impurity-removed mixed gas from the alkali scrubber 43 to remove CO therefrom, and output a secondary impurity-removed mixed gas (i.e., impurity-removed mixed gas) containing methane and cracking gas.

[0070] The system for improving the operating cycle of a gas-phase cracking furnace of the present invention performs cracking reaction and coke-clearing reaction by mixing steam and air and then incorporating the mixture into cracking raw materials and feeding the mixture into the radiation section of the cracking furnace. On the one hand, the amount of propane introduced into the cracking raw materials can be adjusted to reduce the amount of propane introduced, thereby slowing down the coking reaction, delaying the rate of coke formation, and reducing the amount of coke formation. On the other hand, steam and air (coke-clearing gas) can undergo an oxidation-reduction reaction (coke-clearing reaction) with the coke to generate CO and CO2, thereby avoiding the cracking furnace absolute pressure ratio reaching a critical value and causing coking. Furthermore, by cooling, alkali washing, and hydrogenating the reaction products, the influence of CO and CO2 in the reaction products on the subsequent system can be avoided, thereby achieving the purpose of long-term stable operation.

[0071] In one embodiment, in the feeding unit, a steam feed valve is provided on the steam feed pipeline, and an air feed valve is provided on the air feed pipeline 11; a flow display control instrument 14 is provided on the outlet pipeline of the feeding unit, and the flow display control instrument 14 is respectively connected to the steam feed valve and the air feed valve for over-relaxation control, and is used to over-relax the opening of the steam feed valve and the air feed valve, thereby controlling the feeding conditions of steam and air, including feed flow and feed rate, etc.

[0072] In one embodiment, the steam feed line includes a dilution steam feed line 12 and / or a medium-pressure steam feed line 13 for feeding dilution steam and / or medium-pressure steam, respectively.

[0073] In one embodiment, the dilution steam is preferably 0.65-0.85 MPa, such as 0.7 MPa, 0.75 MPa and 0.8 MPa; the medium-pressure steam is 1.1-1.5 MPa, such as 1.2 MPa, 1.3 MPa and 1.4 MPa.

[0074] In one embodiment, a first temperature control device 24 is provided on the outlet pipeline of the preheating unit, and the first temperature control device 24 is over-relaxedly connected to the preheating device for over-relaxing the preheating device to control its preheating of the decoking gas from the feeding unit, thereby controlling the temperature of the preheated decoking gas output by the preheating unit.

[0075] In one embodiment, in the preheating unit, the preheating device includes any one or more parallel combinations of an electric heating device 21, a super steam heat exchanger 22, and a cracking furnace;

[0076] Preferably, in the preheating unit, the preheating device is an electric heating device 21, and the first temperature control device 24 is over-connected to the electric heating device 21 for over-controlling the heating condition of the electric heating device 21; and / or

[0077] In the preheating unit, the preheating device is a cracking furnace, and the cracking furnace includes a convection section. The cracking furnace preheats the clean coke gas from the feeding unit through its convection section; the convection section is provided with a convection section outlet pipeline for outputting the preheated clean coke gas (i.e., the preheated clean coke gas), and preferably, a first valve is provided on the convection section outlet pipeline of the cracking furnace, and the first temperature control device 24 is connected to the convection section of the cracking furnace via the first valve through over-relaxation control, so as to control the opening of the first valve to control the temperature of the preheated clean coke gas output from the preheating unit; and / or

[0078] In the preheating unit, the preheating device is a super steam heat exchanger 22, and a second valve is provided on the heat medium outlet pipeline of the super steam heat exchanger 22. The first temperature control device 24 is connected to the super steam heat exchanger 22 through the second valve over-relaxation, which is used to over-relax the opening of the second valve, thereby controlling the temperature of the preheated decoking gas output by the preheating unit.

[0079] Those skilled in the art understand that when the heat medium is steam, the heating condition is generally controlled by a steam outlet pipeline and a valve.

[0080] In one embodiment, a third valve is provided on the outlet pipeline of the preheating unit;

[0081] In the distribution reaction unit, a first pressure control device 33 is provided on the feed pipeline of the radiation section 32. The first pressure control device 33 is connected to the third valve for over-relaxation control, and is used to over-control the opening of the third valve, and over-control the amount of preheating and decoking gas from the preheating unit according to the pressure of the material in the feed pipeline of the radiation section 32.

[0082] In one embodiment, the pressure ratio of the material in the feed line of the radiation section 32 is 0.6-0.95 in terms of absolute pressure ratio, such as 0.65, 0.7, 0.75, 0.8, 0.85, or 0.9.

[0083] In one embodiment, the system includes a plurality of the distribution reaction units, and the plurality of the distribution reaction units are arranged in parallel.

[0084] In one embodiment, in the distribution reaction unit, the cracking feedstock is propane and the cracking gas is ethylene.

[0085] In one embodiment, in the analysis and feedback unit, a first online analyzer 45 is provided on the outlet material pipeline of the first quench cooler 41 for analyzing and displaying the content of CO and CO2 in the material therein, so that when the content of CO and CO2 in the material therein is large, such as the CO content is greater than 200 ppm and the CO2 content is greater than 500 ppm, the CO and CO2 content in the cracked gas components is controlled by the flow rate and the opening of the third valve. When the CO and CO2 content in the material therein increases at a high rate, such as greater than 5%, the opening of the third valve is reduced or closed to stop or reduce the injection amount of the preheating and decoking gas, or the production of CO and CO2 by-products is slowed down by adjusting the proportion of air; and / or

[0086] A second online analyzer 46 is provided on the outlet material pipeline of the second quench cooler 42 for analyzing and displaying the pH value of the material therein and the content of CO2 in the material therein; and / or

[0087] The outlet material pipeline of the alkali washing tower 43 is provided with a third online analyzer 47 for analyzing and displaying the CO content in the material therein.

[0088] In one embodiment, in the analysis feedback unit, an online analysis controller 48 is provided on the outlet material pipeline of the hydrogenation reactor 44, and the online analysis controller 48 is over-relaxedly connected to the flow display control instrument 14, for analyzing and displaying the CO content in the material in the outlet material pipeline of the hydrogenation reactor 44, and over-relaxing the opening of the steam feed valve and the air feed valve to control the feeding conditions of steam and air.

[0089] Those skilled in the art understand that, since the by-product gases CO and CO2 have different effects on the pH of the quench water, the alkali scrubber 43, and the hydrogenation reactor 44 (carbon dihydrogenation reactor), a high CO2 content will affect the pH of the quench water in the first quencher 41 and the second quencher 42. The more acidic gas, the faster the pH decreases. Therefore, it is necessary to adjust the injection amount of the alkaline neutralizer in a timely manner. When the CO2 content at the inlet of the alkali scrubber 43 increases, it will affect the regulation of the alkali scrubber 43. The increase in CO2 content will increase the amount of new alkali added to the alkali scrubber 43 and increase the difficulty of treating the oxidation of spent alkali. If the carbon monoxide content at the inlet of the hydrogenation reactor 44 changes too much, it will cause the selectivity of the hydrogenation reactor 44 to decrease, and in severe cases, it will cause leakage. Therefore, the first online analyzer 45, the second online analyzer 46, the third online analyzer 47, and the online analysis controller 48 are set up to analyze and feedback the CO and CO2 content in the corresponding materials, and adjust the steam and air feed amounts according to the feedback structure control.

[0090] The present invention also provides a method for increasing the operating cycle of a gas phase cracking furnace by utilizing the above system.

[0091] In one embodiment, the method comprises the steps of:

[0092] (1) The feeding unit feeds steam and air through a steam feeding pipeline and an air feeding pipeline 11, respectively, and outputs a decoking gas containing steam and air;

[0093] (2) inputting the decoking gas obtained in step (1) into the preheating device in the preheating unit for preheating to obtain preheated decoking gas;

[0094] (3) the preheated decoking gas obtained in step (2) is added to the cracking feedstock at the outlet of the venturi subunit 31 in the distribution reaction unit, and then sent to the radiation section 32 of the cracking furnace for cracking reaction and decoking reaction to obtain a mixed gas containing cracked gas, CO and CO2;

[0095] (4) The mixed gas obtained in step (3) is sequentially introduced into the first quencher 41, the second quencher 42, the alkali washing tower 43 and the hydrogenation reactor 44 in the analysis feedback unit for cooling, alkali washing and hydrogenation reaction to obtain a decontaminated mixed gas containing methane and cracking gas.

[0096] In one embodiment, the method further comprises step (5), detecting and analyzing the impurity-free mixed gas obtained in step (4), and adjusting the amount of steam and air introduced in step (1) according to the detection and analysis results.

[0097] In one embodiment, in step (1), the flow display control instrument 14 is used to override the steam feed valve and / or the air feed valve, respectively, so as to regulate the feed amount of steam and / or air according to the flow rate of the material in the outlet pipeline of the feed unit.

[0098] In one embodiment, in step (1), dilution steam is fed through the dilution steam feed line 12 ; and / or medium-pressure steam is fed through the medium-pressure steam feed line 13 .

[0099] In one embodiment, in step (2), the first temperature control device 24 is used to override the preheating device, thereby controlling the temperature of the preheated decoking gas output by the preheating unit.

[0100] In one embodiment, in step (3), the first pressure control device 33 is used to override the third valve, thereby regulating the feed rate of the preheated decoking gas by the temperature of the material in the feed pipeline of the radiation section 32 in the cracking furnace.

[0101] In one embodiment, in step (4), the first online analyzer 45 is used to analyze and display the content of CO and CO2 in the material in the outlet material pipeline of the first quench cooler 41.

[0102] In one embodiment, in step (4), the second online analyzer 46 is used to analyze and display the CO 2 content in the material in the outlet material pipeline of the second quench cooler 42 .

[0103] In one embodiment, in step (4), a third online analyzer 47 is used to analyze and display the pH and CO content of the material in the outlet material pipeline of the alkali washing tower 43.

[0104] In one embodiment, in step (4), the online analysis controller 48 is used to analyze and display the CO content in the material in the outlet material pipeline of the hydrogenation reactor 44, and the steam feed valve and the air feed valve are over-controlled based on the analysis results.

[0105] Compared with the prior art (in the prior art, only propane, a cracking raw material, is introduced during cracking, and steam and air are not introduced, and the operating cycle is about 36 days), the method and system of the present invention, by mixing steam and air and incorporating the mixture into the cracking raw material and feeding it into the radiation section of the cracking furnace for cracking reaction and coke removal reaction, can, on the one hand, reduce the amount of propane introduced as the cracking raw material by adjustment, thereby slowing down the coking reaction, delaying the rate of coke formation, and reducing the amount of coke generated; on the other hand, steam and air (coke removal gas) can undergo an oxidation-reduction reaction (coke removal reaction) with the coke to generate CO and CO2, thereby avoiding the cracking furnace absolute pressure ratio reaching a critical value and causing coking; and by cooling, alkali washing and hydrogenating the reaction products, the influence of CO and CO2 in the reaction products on the subsequent system can be avoided, thereby achieving the purpose of long-term stable operation, and the operating cycle can be increased to more than 60 days.

[0106] The present application is further described below through specific examples.

[0107] Example 1 (S1)

[0108] Use Figure 1 The system shown performs a method for improving the operating cycle of a gas phase cracking furnace as follows:

[0109] (1) Steam and air are fed into the steam feed line and the air feed line 11 respectively, and decoking gas containing steam and air is output; wherein,

[0110] The steam is dilution steam; the dilution steam is 0.7 MPa steam; the mixing ratio of steam to air is 15:100 by mass;

[0111] (2) The decoking gas obtained in step (1) is input into the preheating device (electric heating device 21) for preheating to 550° C. to obtain preheated decoking gas;

[0112] (3) The preheated decoking gas obtained in step (2) is added to the cracking feedstock (propane) at the outlet of the venturi subunit 31 in the distribution reaction unit, and then sent to the radiation section 32 of the cracking furnace for cracking reaction and decoking reaction to obtain a mixed gas containing cracked gas (ethylene), CO and CO2; wherein,

[0113] The mixing ratio of the cracking raw material (propane) and the preheated decoking gas obtained in step (2) is 15:100 by mass; the feed pressure ratio of the radiation section is 0.8 by absolute pressure ratio; and the reaction temperature in the radiation section is 850° C.

[0114] (4) The mixed gas obtained in step (3) is sequentially introduced into the first quencher 41, the second quencher 42, the alkali washing tower 43 and the hydrogenation reactor 44 in the analysis feedback unit for cooling to 35°C, alkali washing to a pH of 6-8, and hydrogenation reaction to obtain a decontaminated mixed gas containing methane and cracked gas (ethylene); wherein the hydrogenation reaction conditions include: reaction temperature of 65°C and reaction pressure of 35 MPaG.

[0115] Results: In the impurity-removed mixed gas obtained in step (4), the CO2 content is 0 and the CO content is 200 mg / L, which will not affect the subsequent system; the operating cycle of the system can reach 70 days.

[0116] Example 2 (S2)

[0117] Use Figure 1 The system shown performs a method for improving the operating cycle of a gas phase cracking furnace, which differs from Example 1 only in that:

[0118] In step (1), the steam is medium-pressure steam; the medium-pressure steam is 1.3 MPa steam; the mixing ratio of steam to air is 2:100 by mass ratio;

[0119] In step (2), the preheating device is a super steam heat exchanger 22, which is preheated to 500°C;

[0120] In step (3), the mixing ratio of the cracking feedstock (propane) and the preheated decoking gas obtained in step (2) is 1:100 by mass; the feed pressure ratio in the radiation section is 0.6 by absolute pressure ratio; and the reaction temperature in the radiation section is 800° C.

[0121] In step (4), the temperature is lowered to 25° C.; alkali washing is performed until the pH is 6-8; and the hydrogenation reaction conditions include: reaction temperature of 60° C. and reaction pressure of 32 MPaG.

[0122] Results: In the impurity-removed mixed gas obtained in step (4), the CO2 content is 0 and the CO content is 250 mg / L, which will not affect the subsequent system; the operating cycle can reach 61 days.

[0123] Example 3 (S3)

[0124] Use Figure 1 The system shown performs a method for improving the operating cycle of a gas phase cracking furnace, which differs from Example 1 only in that:

[0125] In step (1), the steam is dilution steam and medium-pressure steam; the dilution steam is 0.65 MPa steam; the medium-pressure steam is 1.2 MPa steam; the mixing ratio of steam to air is 25:100 by mass;

[0126] In step (2), preheating to 600°C;

[0127] In step (3), the mixing ratio of the cracking feedstock (propane) and the preheated decoking gas obtained in step (2) is 25:100 by mass; the feed pressure ratio in the radiation section is 0.95 by absolute pressure ratio; and the reaction temperature in the radiation section is 900° C.

[0128] In step (4), the temperature is lowered to 45° C.; alkali washing is performed until the pH is 6-8; and the hydrogenation reaction conditions include: a reaction temperature of 70° C. and a reaction pressure of 38 MPaG.

[0129] Results: In the impurity-removed mixed gas obtained in step (4), the CO2 content is 0 and the CO content is 220 mg / L, which will not affect the subsequent system; the operating cycle can reach 66 days.

[0130] Example 4 (S4)

[0131] Use Figure 1 The system shown performs a method for improving the operating cycle of a gas phase cracking furnace, which differs from Example 1 only in that:

[0132] The method further comprises step (5), wherein the impurity-removed mixed gas obtained in step (4) is tested and analyzed, and the amount of steam and air introduced in step (1) is adjusted according to the test and analysis results; wherein,

[0133] When the CO content in the impurity-removed mixed gas obtained in step (4) is greater than 200 ppm and the CO2 content is greater than 500 ppm, the CO and CO2 contents in the cracking gas components are controlled to be reduced to a CO content of no more than 200 ppm and a CO2 content of no more than 500 ppm by reducing the flow rate and reducing the opening of the third valve; when the CO and CO2 content increase rate is greater than 5%, the opening of the third valve is reduced or closed to reduce or stop the injection amount of the preheating and decoking gas.

[0134] Results: In the impurity-removed mixed gas obtained in step (4), the CO2 content is 0 and the CO content is 240 mg / L, which will not affect the subsequent system; the operating cycle can reach 80 days.

Claims

1. A method for increasing the operating cycle of a gas phase cracking furnace, characterized in that: The method comprises the following steps: (1) Mixing steam with air to obtain de-coking gas; (2) preheating the decoking gas obtained in step (1) to obtain preheated decoking gas; (3) the preheated decoking gas obtained in step (2) is added to the cracking feedstock and then sent to the radiant section of the cracking furnace for cracking reaction and decoking reaction to obtain a mixed gas containing cracked gas, CO and CO2; (4) subjecting the mixed gas obtained in step (3) to cooling, alkali washing and hydrogenation reaction in sequence to obtain a decontaminated mixed gas containing methane and cracked gas; wherein, In step (1), the steam includes dilution steam and / or medium-pressure steam; the dilution steam is 0.65-0.85 MPa steam; the medium-pressure steam is 1.1-1.5 MPa steam; In step (1), the mixing ratio of steam to air is (1-25):100 by mass ratio; In step (3), the reaction temperature in the radiation section is 800-900°C; In step (3), the mixing ratio of the cracking raw material to the preheated decoking gas obtained in step (2) is (1-25):100 in terms of mass ratio; In step (3), the cracking raw material is propane and the cracking gas is ethylene.

2. The method according to claim 1, characterized in that The method further comprises a step (5) of detecting and analyzing the impurity-removed mixed gas obtained in the step (4), and adjusting the amount of steam and air introduced in the step (1) according to the detection and analysis results.

3. A system for improving the operating cycle of a gas phase cracking furnace, characterized in that: The system comprises a feeding unit, a preheating unit, a distribution reaction unit and an analysis feedback unit connected in sequence; The feeding unit comprises a steam feeding pipeline and an air feeding pipeline (11) arranged in parallel, for feeding steam and air respectively and outputting decoking gas containing steam and air; The preheating unit includes a preheating device; the preheating device is connected to the outlet pipeline of the feeding unit, and is used to preheat the decoking gas from the feeding unit to obtain preheated decoking gas; The distribution reaction unit comprises a venturi subunit (31) and a cracking furnace connected to each other; the cracking furnace comprises a radiant section (32); the feed end of the venturi subunit (31) is connected to a cracking raw material feed pipeline, and the discharge end is connected to the radiant section (32); the outlet pipeline of the preheating unit is connected to the discharge end of the venturi subunit (31), and is used to feed the cracking raw material and the preheated decoking gas from the preheating unit to the radiant section (32) for respectively performing cracking reaction and decoking reaction, and outputting a mixed gas containing cracked gas, CO and CO2; The analysis feedback unit includes a first quencher (41), a second quencher (42), an alkali scrubber (43) and a hydrogenation reactor (44) connected in sequence; the first quencher (41) is connected to the outlet pipeline of the distribution reaction unit, and the first quencher (41) and the second quencher (42) are used to sequentially quench and cool the mixed gas from the distribution reaction unit, and output the cooled mixed gas; the alkali scrubber (43) is used to perform alkali scrubbing on the cooled mixed gas from the second quencher (42) to remove CO2 therefrom, and output a primary impurity-removed mixed gas; the hydrogenation reactor (44) is used to perform a hydrogenation reaction on the primary impurity-removed mixed gas from the alkali scrubber (43) to remove CO therefrom, and output a secondary impurity-removed mixed gas containing methane and cracking gas.

4. The system according to claim 3, characterized in that In the feeding unit, In the feeding unit, a steam feeding valve is provided on the steam feeding pipeline, and an air feeding valve is provided on the air feeding pipeline (11); a flow display control instrument (14) is provided on the outlet pipeline of the feeding unit, and the flow display control instrument (14) is respectively connected to the steam feeding valve and the air feeding valve.

5. The system according to claim 4, characterized in that The steam feed line comprises a dilution steam feed line (12) and / or a medium-pressure steam feed line (13), which are used to feed dilution steam and / or medium-pressure steam respectively.

6. The system according to any one of claims 3 to 5, characterized in that A first temperature control device (24) is provided on the outlet pipeline of the preheating unit. The first temperature control device (24) is over-connected to the preheating device and is used for over-controlling the preheating device to control the temperature of the preheated decoking gas output by the preheating unit.

7. The system according to claim 6, characterized in that In the preheating unit, the preheating device comprises any one or more parallel combinations of an electric heating device (21), a super steam heat exchanger (22) and a cracking furnace.

8. The system according to claim 7, characterized in that In the preheating unit, the preheating device is an electric heating device (21), and the first temperature control device (24) is connected to the electric heating device (21) in an over-relaxation manner for over-controlling the heating condition of the electric heating device (21); and / or In the preheating unit, the preheating device is a cracking furnace, the cracking furnace includes a convection section, and the cracking furnace preheats the decoking gas from the feeding unit through its convection section; a first valve is provided on the outlet pipeline of the convection section of the cracking furnace, and the first temperature control device (24) is connected to the convection section of the cracking furnace through the first valve for over-relaxing the opening of the first valve; and / or In the preheating unit, the preheating device is a super steam heat exchanger (22), a second valve is provided on the heat medium outlet pipeline of the super steam heat exchanger (22), and the first temperature control device (24) is connected to the super steam heat exchanger (22) via the second valve for over-relaxation control of the opening of the second valve.

9. The system according to any one of claims 3-5 and 7-8, characterized in that A third valve is provided on the outlet pipeline of the preheating unit; In the distribution reaction unit, a first pressure control device (33) is provided on the feed pipeline of the radiation section (32), and the first pressure control device (33) is connected to the third valve for over-relaxation control of the opening of the third valve.

10. The system according to claim 9, characterized in that The system includes a plurality of the distribution reaction units, and the plurality of the distribution reaction units are arranged in parallel.

11. The system according to any one of claims 3-5, 7-8 and 10, characterized in that In the analysis feedback unit, a first online analyzer (45) is provided on the outlet material pipeline of the first quench cooler (41) for analyzing and displaying the content of CO and CO2 in the material therein; and / or A second online analyzer (46) is provided on the outlet material pipeline of the second quench cooler (42) for analyzing and displaying the pH value of the material therein and the content of CO2 in the material therein; and / or The outlet material pipeline of the alkali washing tower (43) is provided with a third online analyzer (47) for analyzing and displaying the CO content in the material therein.

12. The system according to claim 11, wherein: In the analysis feedback unit, an online analysis controller (48) is provided on the outlet material pipeline of the hydrogenation reactor (44), and the online analysis controller (48) is connected to the flow display control instrument (14) for analyzing and displaying the CO content in the material in the outlet material pipeline of the hydrogenation reactor (44), and for over-controlling the steam feed valve and the air feed valve.

13. A method for increasing the operating cycle of a gas phase cracking furnace using the system according to any one of claims 3 to 12.

Images