Low-emission sequential flow ethylene device and driving method thereof

Abstract

The invention belongs to the field of ethylene production, and particularly discloses a low-emission sequential process ethylene device and a starting method thereof. According to the starting method, natural gas, hydrogen, ethylene and propylene are introduced after system precooling is completed, the natural gas, the ethylene, the propylene and the hydrogen are used for breaking through the whole process from a cracking gas compressor to a cold box, a demethanizing tower, a deethanizing tower and a C2 reactor, and after a cracking furnace is fed, an ethylene rectifying tower can be switched to after hydrogenation of the reactor is qualified; the whole driving process is short in time, no torch is discharged, and economical, environment-friendly and low-emission driving is truly achieved.

Description

Technical Field

[0001] The invention belongs to the field of ethylene production, and in particular relates to a low-emission sequential process ethylene device and a start-up method thereof. Background Art

[0002] The typical startup method for a sequential process ethylene plant is to first start the propylene and ethylene refrigeration compressors, then start the cracking gas compressor for nitrogen operation. Nitrogen, propylene, and ethylene refrigerants are used to pre-cool the cold box, demethanizer, and other cryogenic systems. Simultaneously, ethylene and propylene are introduced to the ethylene and propylene distillation columns for full reflux operation. After completion, the cracking furnace is loaded and started. The entire startup process takes approximately 5-6 days.

[0003] The traditional startup method typically includes the following steps: 1. The day before the start-up, the cracked gas compressor is started for nitrogen operation, and the propylene and ethylene refrigeration compressors are operated with solid gas. 2. The cold box nitrogen pre-cooling process is established, and the pre-cooled nitrogen is returned to the cracked gas compressor via the low-pressure methane pipeline at the cold box outlet. 3. The propylene and ethylene refrigerant heat exchangers are commissioned, and the cold box temperature is lowered to the operating value according to the pre-cooling curve. 4. After the propylene refrigeration compressor has been adjusted and stabilized, vapor-phase ethylene is introduced into the ethylene distillation tower for full reflux operation. 5. Liquid-phase propylene and vapor-phase ethylene are added to the deethanizer to establish full reflux operation. 6. The cold box temperature is lowered to normal, and the system is checked for leaks. 7. The C2 reactor is preheated and gas replacement is completed, ready for commissioning. 8. Both cracking furnaces are fed simultaneously, and a section of nitrogen replenishment is slowly closed based on the cracked gas compressor suction pressure. The flare valve at the cracked gas compressor outlet is opened, and the system is replaced. 9. Introduce the cracked gas into the cold box system and raise the system pressure to normal. The low-pressure methane and hydrogen at the cold box outlet are discharged through the flare valve, which controls the pressure and discharges the flare to displace the nitrogen in the system. 10. After the liquid level in each cold box separator tank accumulates, begin feeding the demethanizer. Once the bottom liquid level is sufficient, start the bottom discharge pump to feed the deethanizer. 11. Adjust the deethanizer to maintain a stable pressure. Discharge the top material to the flare. After the reflux stabilizes, gradually lower the top temperature. 12. After the top temperature of the deethanizer drops to normal, feed the C2 reactor, with the material flared from the reactor outlet. 13. Commission the methanation reactor. After the reaction is satisfactory, hydrogen is discharged to the external pipeline network. After the pressure stabilizes, hydrogen is introduced into the C2 reactor. 14. Load the third and fourth cracking furnaces. 15. After the acetylene output of the C2 reactor indicates satisfactory reaction, it is fed to the ethylene distillation column. 16. Adjust the ethylene distillation column to produce satisfactory ethylene product. 17. After the deethanizer kettle liquid level stabilizes, feed the depropanizer. Control the flow of the C3 reactor into and out of the flare, and start the system. 18. Adjust the propylene distillation tower to produce qualified propylene products.

[0004] The traditional startup method uses nitrogen as a medium before charging. After the refrigeration compressor is put into operation, the temperature of low-temperature equipment such as the low-temperature heat exchanger and demethanizer in the cold box system is reduced to the operating temperature. This prevents material leakage caused by rapid temperature drop during the startup and charging process. Problems with instruments, equipment, and processes can be discovered through pre-startup. However, this startup method has the following disadvantages:

[0005] 1. After the cracking furnace is started up, a large amount of raw cracking gas is needed to replace the nitrogen in the cracking gas compressor system, cold box and demethanizer system. It takes about 16 to 24 hours from feeding to qualified products. Based on the minimum feed rate of 200t / h of naphtha raw material for start-up, 1,000 to 1,500 tons of materials still need to be discharged and burned in the flare after removing the recycled materials, resulting in waste of start-up materials.

[0006] 2. During nitrogen pre-cooling, the cold box and demethanizer are not connected to the deethanizer and C2 reactor of the subsequent system. There is still a switching and adjustment process after the formal feeding and start-up. If the switching cannot be smooth, the refrigeration compressor system will fluctuate or even stop, which will extend the product qualification time.

[0007] 3. Problems with instruments, equipment, and process operations cannot be fully exposed during nitrogen pre-cooling, and problems may occur after the formal loading and start-up. Summary of the Invention

[0008] In response to the above-mentioned problems existing in the prior art, the present invention proposes a low-emission sequential process ethylene plant and its start-up method. After the system is pre-cooled, natural gas, hydrogen, ethylene and propylene are introduced. Natural gas, ethylene, propylene and hydrogen are used to open up the entire process from the cracked gas compressor to the cold box, demethanizer, deethanizer and C2 reactor.

[0009] Specifically, one aspect of the present invention provides an ethylene plant, comprising:

[0010] Quenching water tower system, including quenching water tower;

[0011] Cracking gas compressor system, including cracking gas compressor and alkali washing tower;

[0012] Cold box systems, including cold boxes;

[0013] Demethanizer system, including demethanizer and demethanizer kettle pump;

[0014] a deethanizer system, including a deethanizer;

[0015] A carbon-2 reactor system, comprising a carbon-2 reactor;

[0016] An ethylene distillation tower system, comprising an ethylene distillation tower;

[0017] An ethylene refrigeration compressor system, comprising an ethylene refrigeration compressor and an ethylene refrigerant heat exchanger;

[0018] A propylene refrigeration compressor system, comprising a propylene refrigeration compressor and a propylene refrigerant heat exchanger;

[0019] a depropanizer system, including a depropanizer;

[0020] A C3 reactor system, comprising a C3 reactor; and

[0021] A propylene distillation tower system, comprising a propylene distillation tower;

[0022] The ethylene plant further comprises:

[0023] a pipeline connecting the outlet of the cracked gas compressor and the inlet of the cold box;

[0024] a pipeline connecting the outlet of the cold box and the inlet of the cracked gas compressor;

[0025] a pipeline connecting the tail gas outlet of the ethylene distillation tower and the kettle pump of the demethanizer;

[0026] a pipeline connecting the inlet of the C2 reactor and the inlet of the cracked gas compressor;

[0027] a pipeline connecting the top of the depropanizer and the inlet of the cracked gas compressor;

[0028] a pipeline connecting the outlet of the C2 reactor and the inlet of the cracked gas compressor;

[0029] A pipeline connecting the outlet of the C2 reactor and the ethylene distillation tower.

[0030] In one or more embodiments, the demethanizer kettle pump is a vertical multistage pump.

[0031] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the quench water tower and the cracked gas compressor.

[0032] In one or more embodiments, the ethylene plant further comprises a pipeline connecting the cold box and the demethanizer.

[0033] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the demethanizer and the deethanizer.

[0034] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the deethanizer and the C2 reactor.

[0035] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the ethylene distillation column and the propylene refrigeration compressor.

[0036] In one or more embodiments, the ethylene plant further comprises a pipeline connecting the propylene refrigeration compressor and the ethylene refrigeration compressor.

[0037] In one or more embodiments, the ethylene plant further comprises a pipeline connecting the ethylene refrigeration compressor to the cold box.

[0038] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the depropanizer and the C3 reactor.

[0039] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the C3 reactor and the propylene distillation column.

[0040] In one or more embodiments, the ethylene unit further comprises a pipeline connecting the deethanizer and the depropanizer.

[0041] In one or more embodiments, the ethylene plant further comprises valves disposed on each pipeline.

[0042] In one or more embodiments, the cold box includes a knockout drum.

[0043] Another aspect of the present invention provides a method for starting up an ethylene plant according to any of the embodiments herein, the method comprising the steps of:

[0044] S1: starting the cracked gas compressor to operate with nitrogen, and making the propylene refrigeration compressor and the ethylene refrigeration compressor operate with gas;

[0045] S2: returning the pre-cooled nitrogen from the outlet of the cold box to the cracked gas compressor via a pipeline;

[0046] S3: Put the propylene refrigerant heat exchanger and the ethylene refrigerant heat exchanger into use, and reduce the temperature of the cold box to an operating value according to a pre-cooling curve.

[0047] S4: After the propylene refrigeration compressor is stabilized, the gaseous ethylene is introduced into the ethylene distillation tower to perform full reflux operation of the ethylene distillation tower;

[0048] S5: introducing liquid propylene and gaseous ethylene into the deethanizer to perform full reflux operation of the deethanizer;

[0049] S6: After the total reflux of the ethylene distillation tower is stabilized, the tail gas of the ethylene distillation tower is sent to the kettle pump of the demethanizer;

[0050] S7: After the temperature of the cold box drops to a normal value and the system leakage check is completed, natural gas is introduced from the quenching water tower, and a section of the cracked gas compressor is shut down to replenish nitrogen;

[0051] S8: The alkali washing tower is connected to the cracked gas compression system, so that the alkali liquid in the alkali washing tower and the acid gas contained in the cracked gas compressed by the cracked gas compressor undergo a neutralization reaction;

[0052] S9: After the pressure balance among the various systems of the ethylene unit is stabilized, the natural gas is returned to the cracked gas compressor through a pipeline connecting the inlet of the C2 reactor and the inlet of the cracked gas compressor to establish a natural gas circulation loop;

[0053] S10: returning the C3 to the cracked gas compressor through a pipeline connecting the top of the depropanizer and the inlet of the cracked gas compressor;

[0054] S11: Introducing hydrogen to maintain the pressure of the cold box at 3.1-3.3 MPaG;

[0055] S12: preheating the C2 reactor and completing gas replacement to prepare it for use;

[0056] S13: After the liquid levels of the separation tanks of the cold box are stable, the demethanizer is fed; after the liquid level of the bottom of the demethanizer is stable, the deethanizer is fed;

[0057] S14: Pressurizing the C2 reactor and putting it into operation, maintaining the top temperature of the deethanizer at -15 to -20°C, and allowing the circulating material to begin returning to the cracked gas compressor from the outlet of the C2 reactor;

[0058] S15: feeding the first cracking furnace and the second cracking furnace, and slowly stopping the natural gas supply according to the suction pressure of the cracking gas compressor;

[0059] S16: sending the start-up hydrogen into the C2 reactor;

[0060] S17: feeding materials into the third cracking furnace and the fourth cracking furnace;

[0061] S18: After the acetylene output from the C2 reactor indicates that the reaction is qualified, the product from the C2 reactor is fed into the ethylene distillation tower, and the pipeline between the outlet of the C2 reactor and the inlet of the cracked gas compressor is closed.

[0062] S19: After the self-produced hydrogen of the ethylene unit passes the methanation reactor and is qualified, the supply of start-up hydrogen to the C2 hydrogenation reactor is stopped;

[0063] S20: After the liquid level in the bottom of the deethanizer is stabilized, feed the depropanizer and slowly close the pipeline connected to the inlet of the cracked gas compressor returning from the top of the depropanizer to start the C3 reactor.

[0064] In one or more embodiments, in step S1, the cracked gas compressor is started two days before feeding to perform nitrogen operation.

[0065] In one or more embodiments, in step S4, stabilization of the propylene refrigeration compressor means that the speed of the propylene refrigeration compressor reaches the rated speed, the suction pressure of the propylene refrigeration compressor reaches the design value, and the propylene refrigeration compressor can start to provide propylene refrigerant that meets the requirements.

[0066] In one or more embodiments, after the nitrogen content in the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit is qualified, the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit are introduced into the fuel gas system in advance and the flare emission is stopped.

[0067] In one or more embodiments, after the nitrogen content in the low-pressure methane, high-pressure methane, and hydrogen produced by the ethylene unit is qualified and the pressure of the fuel gas system is stable, the addition of supplementary fuel gas from outside the boundary is reduced or stopped.

[0068] In one or more embodiments, after the ethylene distillation column is supplemented with ethylene, the ethylene is introduced into the fuel gas system.

[0069] In one or more embodiments, in step S19, after the self-produced hydrogen in the ethylene unit passes through the methanation reactor and is qualified, the self-produced hydrogen is provided and incorporated into the hydrogen pipeline network.

[0070] In one or more embodiments, in step S19, the self-produced hydrogen comprises carbon monoxide.

[0071] In one or more embodiments, the method further comprises:

[0072] S21: adjusting the reaction conditions of the propylene distillation tower to produce a qualified propylene product.

[0073] The low-emission sequential process ethylene plant and its start-up method of the present invention are as follows: natural gas, hydrogen, ethylene and propylene are introduced after the system is pre-cooled; the natural gas, ethylene, propylene and hydrogen are used to connect the entire process from the cracking gas compressor to the cold box, demethanizer, deethanizer and C2 reactor; after the cracking furnace is charged, it only needs to wait for the reactor to pass the hydrogenation test before it can be switched to the ethylene distillation tower; the entire start-up process is short and flare-free, thus achieving truly economical, environmentally friendly and low-emission start-up. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a flowchart of the traditional driving method.

[0075] Figure 2 Schematic diagram of the flare emission point for traditional start-up methods.

[0076] Figure 3 It is a schematic flow chart of the low-emission driving method of the present invention.

[0077] Description of reference numerals:

[0078] 1 is the quenching water tower system; 2 is the cracking gas compressor system; 3 is the cold box system; 4 is the demethanizer system; 5 is the deethanizer system; 6 is the C2 reactor system; 7 is the ethylene distillation tower system; 8 is the ethylene refrigeration compressor system; 9 is the propylene refrigeration compressor system; 10 is the depropanizer system; 11 is the C3 reactor system; 12 is the propylene distillation tower system; 13 is the methanation reactor system. DETAILED DESCRIPTION

[0079] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used herein. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0080] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0081] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0082] Throughout this document, all features, such as values, amounts, amounts, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0083] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0084] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all substitutes, modifications and equivalents of the methods and materials described herein are within the scope defined by the present invention.

[0085] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0086] In this article, the demethanizer kettle pump is located in the demethanizer kettle and is responsible for transporting materials from the demethanizer to the deethanizer. The demethanizer kettle pump is a cryogenic pump and requires pre-cooling before commissioning. The demethanizer kettle pump is the most critical pump in a sequential ethylene plant. This vertical multi-stage pump utilizes the condensate from the ethylene distillation tower tail gas returning to the demethanizer pipeline to pre-cool the demethanizer from the packing section below No. 6 to the kettle. After ten hours, the kettle temperature can drop from -1°C to -53°C. As the liquid phase of supplemental ethylene accumulates in the demethanizer kettle, pre-cooling of the pump is completed before start-up and feeding, ensuring the ethylene plant is ready for commissioning.

[0087] By implementing the low-emission startup method of the present invention, the demethanizer kettle pump can complete liquid phase precooling before feeding, allowing the ethylene unit to operate stably in advance. The demethanizer kettle pump connects the demethanizer to the deethanizer. Specifically,

[0088] 1. The demethanizer kettle pump is the most critical pump in a sequential process ethylene plant. This pump is a vertical multi-stage pump, and normal precooling requires more than ten hours to prepare it for use. Precooling the pump has always been a difficult problem during the previous startup process because the cold box nitrogen precooling method in the traditional startup method does not have enough cold capacity to complete the precooling of the demethanizer. At most, the pump can only be precooled in the gas phase with cold nitrogen. It is necessary to wait until the demethanizer accumulates liquid after the start-up of the feed. The liquid phase precooling can not be carried out, which not only delays the startup time but is also not conducive to the safe operation of the cold pump. 2. In the low-emission startup method of the present invention, the condensate gas from the ethylene distillation tower tail gas is returned to the demethanizer pipeline to precool the section below the packing of the demethanizer No. 6 to the kettle. After ten hours, the kettle temperature drops from -1°C to -53°C. As the liquid phase of the supplementary ethylene accumulates in the demethanizer kettle, the pump is precooled and ready for use before the start-up of the feed, saving time for a smooth startup.

[0089] In this article, the caustic scrubber absorbs acidic gases, such as H2S and CO2, from the cracked gas. The caustic solution in the caustic scrubber can be an aqueous NaOH solution. Alkaline scrubbing in the caustic scrubber prevents the acidic gases in the cracked gas from deactivating catalysts in subsequent systems.

[0090] In this article, the fuel gas system is connected to the outlet of the cold box system. Its function is to control the pressure of the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit to be stable and then send them to the cracking furnace for use as fuel.

[0091] In this paper, during the startup of the ethylene unit, as the cracking furnace load increases, the low-pressure methane, high-pressure methane, and hydrogen produced by the unit can be connected to the fuel gas system in advance after the nitrogen content analysis is qualified, the flare discharge is stopped, and the off-site fuel gas supplementation can be reduced or stopped, saving startup fuel costs.

[0092] In this article, after the ethylene distillation tower is replenished with ethylene, the fuel gas system is started to replenish ethylene, which can also be used as a backup adjustment means for fuel gas replenishment.

[0093] The startup method described in this paper introduces a pre-startup cycle of C3 (propylene), ensuring that the properties of the circulating material are more similar to those of the regular feed, reducing the impact of changes in material properties on the system. This design facilitates a smoother transition between natural gas circulation and cracked gas feed, significantly improving operational stability after the unit's startup.

[0094] This paper uses natural gas to replace nitrogen and then connects the systems in series. This design helps to achieve smoother switching between natural gas circulation and cracking gas feeding, significantly improving the operational stability of the device after startup.

[0095] In some preferred embodiments, the driving method of the present invention is as follows:

[0096] Two days before feeding, start the cracking gas compressor to operate on nitrogen, and the propylene refrigeration compressor and ethylene refrigeration compressor to operate on gas;

[0097] Open up the nitrogen pre-cooling process of the cold box, and the pre-cooled nitrogen returns to the cracked gas compressor through the low-pressure methane pipeline at the cold box outlet;

[0098] Put propylene and ethylene refrigerant heat exchangers into use and reduce the cold box temperature to the operating value according to the pre-cooling curve;

[0099] After the propylene refrigeration compressor is adjusted and stabilized, gaseous ethylene is introduced into the ethylene distillation tower and the tower is operated with full reflux;

[0100] The deethanizer is supplemented with liquid propylene and gaseous ethylene to establish full reflux operation of the deethanizer;

[0101] After the full reflux of the ethylene distillation tower is stable, the tail gas of the ethylene distillation tower is sent to the demethanizer to pre-cool the tower kettle pump;

[0102] After the cold box temperature is lowered to normal and the system leak inspection is completed, natural gas (mainly methane) is introduced from the quenching water tower, and the first stage of the cracking gas compressor is shut down and nitrogen is added;

[0103] The compressed acid gas absorption alkali washing tower completes the alkali solution replenishment and is cut into the system for use;

[0104] After the system pressure balance is stable, open the pipeline from the C2 reactor inlet back to the cracking gas compressor section to circulate the natural gas back to the cracking gas compressor to establish a natural gas circulation loop;

[0105] Open the pipeline from the top of the depropanizer tower back to the cracking gas compressor to return C3 to the cracking gas compressor;

[0106] As the content of natural gas, ethylene and propylene in the circulating gas increases and the nitrogen content decreases, the cold box pressure will drop. At this time, it is necessary to introduce start-up hydrogen to maintain the cold box pressure at 3.1-3.3 MPaG.

[0107] The preheating and gas replacement of the C2 reactor have been completed and it is ready for use;

[0108] To address the issue of limited off-site fuel gas replenishment during the startup of an ethylene plant as the cracking furnace load increases, the low-pressure methane, high-pressure methane, and hydrogen produced by the plant are pre-introduced into the fuel gas system after the nitrogen content in the gas is analyzed and found to be qualified, and flaring is stopped. The off-site fuel gas replenishment can be reduced or even stopped, saving startup fuel costs.

[0109] After the ethylene distillation tower is replenished with ethylene, the fuel gas system can be started to replenish ethylene and can also be used as a backup regulation means for fuel gas replenishment;

[0110] After the liquid level of each separation tank of the cold box is stable, feed the demethanizer. After the liquid level of the demethanizer kettle is stable, start the kettle external pump to feed the deethanizer.

[0111] The C2 reactor is pressurized and put into operation. The temperature at the top of the deethanizer is maintained at -15 to -20°C. The circulating material begins to return to the cracked gas compressor from the reactor outlet.

[0112] The two cracking furnaces are charged at the same time, and the natural gas supplement valve is slowly closed according to the suction pressure of the cracking gas compressor, so that the flow rate of the circulating return cracking gas compressor is increased;

[0113] The C2 reactor begins to be fed with hydrogen for operation;

[0114] The third and fourth cracking furnaces are charged;

[0115] After the acetylene at the outlet of the C2 reactor is confirmed to be qualified, it will be fed into the ethylene distillation tower, and the valve returning to the cracked gas compressor at the outlet will be closed.

[0116] The methanation reactor is qualified, the self-produced hydrogen is qualified and connected to the grid, and the start-up hydrogen is stopped;

[0117] After the liquid level in the deethanizer kettle stabilizes, the depropanizer is fed. The compressor for the cracked gas returning from the top of the tower is slowly shut down, and the C3 system is started with feeding.

[0118] The propylene distillation tower is adjusted to produce qualified propylene products.

[0119] The present invention will be described below by way of specific examples. It should be understood that these examples are illustrative only and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the examples are, unless otherwise stated, conventional methods, reagents, and materials in the art. The compounds in the examples can all be purchased from commercial sources.

[0120] The fuel gas in the examples and comparative examples is natural gas, the main component of which is methane.

[0121] Comparative Example 1

[0122] This comparative example adopts the traditional driving method, according to Figure 1 and Figure 2 The process shown is for the start-up of a 1.19 million ton / year sequential process ethylene plant, and includes the following steps:

[0123] (1) The day before feeding, the cracking gas compressor is started to operate with nitrogen, and the propylene refrigeration compressor and the ethylene refrigeration compressor are started to operate with gas;

[0124] (2) Opening up the nitrogen pre-cooling process of the cold box, and returning the pre-cooled nitrogen to the cracked gas compressor through the low-pressure methane pipeline at the cold box outlet;

[0125] (3) Put propylene and ethylene refrigerant heat exchangers into use and reduce the cold box temperature to the operating value according to the pre-cooling curve;

[0126] (4) After the propylene refrigeration compressor is adjusted and stabilized, gaseous ethylene is introduced into the ethylene distillation tower and the tower is operated with full reflux;

[0127] (5) The deethanizer is replenished with liquid propylene and gaseous ethylene to establish full reflux operation of the deethanizer;

[0128] (6) The cold box temperature is lowered to normal value and the system is checked for leaks;

[0129] (7) The C2 reactor is preheated and gas replacement is completed, ready for use;

[0130] (8) Two cracking furnaces are fed at the same time, and nitrogen is slowly closed according to the suction pressure of the cracking gas compressor to supplement, and the flare valve at the outlet of the cracking gas compressor is opened to replace the system;

[0131] (9) Introducing the cracked gas into the cold box system, the system pressure is increased to normal value, and the low-pressure methane and hydrogen at the cold box outlet are discharged by the flare valve control system to discharge the nitrogen in the flare replacement system;

[0132] (10) After the liquid in each level of the cold box liquid separation tank accumulates, the demethanizer starts to be fed. After the liquid level in the tower bottom is sufficient, the tower bottom outfeed pump is started to feed the deethanizer.

[0133] (11) Adjust the deethanizer to control the tower pressure to be stable, discharge the top material to the flare, and gradually reduce the top temperature after the reflux is stable;

[0134] (12) After the temperature at the top of the deethanizer tower drops to normal, the material is fed into the C2 reactor and the material is discharged from the reactor outlet to the flare;

[0135] (13) The methanation reactor is put into use. After the reaction is qualified, the hydrogen is sent to the pipeline network. After the pressure stabilizes, the carbon-2 reactor begins to be supplied with hydrogen;

[0136] (14) Loading of materials into the third and fourth cracking furnaces;

[0137] (15) After the acetylene at the outlet of the C2 reactor is qualified, it is cut into the ethylene distillation tower;

[0138] (16) Adjust the ethylene distillation tower to produce qualified ethylene products;

[0139] (17) After the liquid level in the deethanizer kettle stabilizes, feed the depropanizer, control the inflow and outflow of the C3 reactor discharge flare, and start the system feeding;

[0140] (18) Adjust the propylene distillation tower to produce qualified propylene products.

[0141] The material and utility consumption of the conventional start-up method of Comparative Example 1 are shown in Table 1. The economic benefits of the conventional start-up method of Comparative Example 1 are shown in Table 3.

[0142] Example 1

[0143] This embodiment adopts the low emission driving method of the present invention, according to Figure 3 The process shown is for the start-up of a 1.19 million ton / year sequential process ethylene plant, and includes the following steps:

[0144] (1) Two days before feeding, the cracking gas compressor is started to operate with nitrogen, and the propylene refrigeration compressor and the ethylene refrigeration compressor are operated with gas;

[0145] (2) Opening up the nitrogen pre-cooling process of the cold box, and returning the pre-cooled nitrogen to the cracked gas compressor through the low-pressure methane pipeline at the cold box outlet;

[0146] (3) Put propylene and ethylene refrigerant heat exchangers into use and reduce the cold box temperature to the operating value according to the pre-cooling curve;

[0147] (4) After the speed of the propylene refrigeration compressor reaches the rated speed, the suction pressure of the propylene refrigeration compressor reaches the design value, and the propylene refrigeration compressor can begin to provide propylene refrigerant that meets the requirements, gaseous ethylene is introduced into the ethylene distillation tower to perform full reflux operation;

[0148] (5) The deethanizer is replenished with liquid propylene and gaseous ethylene to establish full reflux operation of the deethanizer;

[0149] (6) After the full reflux of the ethylene distillation tower is stable, the tail gas of the ethylene distillation tower goes to the demethanizer to precool the tower kettle pump;

[0150] (7) After the cold box temperature is lowered to normal and the system leak check is completed, natural gas (mainly methane) is introduced from the quenching water tower, and the first stage of the cracking gas compressor is shut down and nitrogen is added;

[0151] (8) The alkali washing tower is connected to the cracking gas compression system, so that the alkali liquid in the alkali washing tower and the acid gas contained in the cracking gas compressed by the cracking gas compression system undergo a neutralization reaction;

[0152] (9) After the pressure balance between the various systems of the ethylene unit is stabilized, the natural gas is returned to the cracked gas compressor through a pipeline connecting the inlet of the C2 reactor and the inlet of the cracked gas compressor to establish a natural gas circulation loop;

[0153] (10) returning the C3 to the cracked gas compressor through a pipeline connecting the top of the depropanizer and the inlet of the cracked gas compressor;

[0154] (11) As the content of natural gas, ethylene and propylene in the circulating gas increases and the nitrogen content decreases, the cold box pressure will decrease. At this time, start-up hydrogen is introduced to maintain the cold box pressure at 3.1-3.3 MPaG;

[0155] (12) The carbon-2 reactor is preheated and gas replacement is completed, and is ready for use;

[0156] After the nitrogen content in the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit is analyzed and qualified, the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit will be fed into the fuel gas system in advance and the flare will be stopped;

[0157] When the nitrogen content in the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit is qualified and the pressure of the fuel gas system is stable, slowly stop adding fuel gas;

[0158] After the ethylene distillation tower is replenished with ethylene, the ethylene replenishment fuel gas system is started as a backup regulation means for fuel gas replenishment;

[0159] (13) After the liquid level of each separation tank of the cold box is stable, feed the demethanizer. After the liquid level of the demethanizer kettle is stable, start the kettle external pump to feed the deethanizer.

[0160] (14) The C2 reactor is pressurized and put into operation, the temperature at the top of the deethanizer is maintained at -15 to -20°C, and the circulating material begins to return to the cracked gas compressor from the outlet of the C2 reactor;

[0161] (15) The two cracking furnaces are fed at the same time, and the natural gas valve is slowly closed according to the suction pressure of the cracking gas compressor to increase the flow rate of the circulating return cracking gas compressor;

[0162] (16) The C2 reactor begins to be fed with hydrogen;

[0163] (17) The third and fourth cracking furnaces are charged;

[0164] (18) After the acetylene output from the C2 reactor is online and indicates that the reaction is qualified, the product of the C2 reactor is fed into the ethylene distillation tower, and the pipeline between the outlet of the C2 reactor and the inlet of the cracked gas compressor is closed at the same time;

[0165] (19) After the self-produced hydrogen (including carbon monoxide) of the ethylene unit has passed the methanation reactor, the supply of start-up hydrogen to the C2 reactor is stopped, and the self-produced hydrogen is incorporated into the hydrogen pipeline network;

[0166] (20) After the liquid level in the deethanizer kettle stabilizes, the depropanizer is fed, the cracked gas compressor returning to the top of the tower is slowly shut down, and the C3 system is started;

[0167] (21) Adjust the reaction conditions of the propylene distillation tower to produce qualified propylene products.

[0168] The material and utility consumption of the low-emission start-up method of Example 1 is shown in Table 2. The economic benefits of the low-emission start-up method of Example 1 are shown in Table 3.

[0169] Table 1: Materials and utilities consumed by conventional startup methods for a sequential process ethylene plant

[0170]

[0171]

[0172] Table 2: Materials and Utilities Consumed for Low Emission Startup Methods of Sequential Process Ethylene Plants

[0173]

[0174]

[0175] Table 3: Economic benefits of low-emission startup methods for sequential process ethylene plants

[0176]

[0177] From the data in Table 1-2 we can see that:

[0178] 1. The low-emission start-up process increases the start-up time and utility material consumption due to the cycle of the natural gas pre-start-up process;

[0179] 2. Low-emission start-up: Through pre-start-up, the device only takes about 3 hours from feeding to qualified products, and the material from the outlet of the C2 reactor can still be returned to the inlet of the cracking gas compressor for circulation, so that the flare emissions are effectively controlled; the low-emission solution feeds 3,000 to 4,000 tons less naphtha than the traditional solution, avoiding at least 1,000 to 2,000 tons of material from being discharged into the flare, truly realizing emission-free start-up.

[0180] According to the data in Table 3, by implementing the low-emission start-up method, the economic benefits of each start-up of the ethylene plant are increased by approximately RMB 887.1-769.2 = RMB 1.179 million.

Claims

1. An ethylene plant, characterized in that: The ethylene unit comprises: Quenching water tower system, including quenching water tower; Cracking gas compressor system, including cracking gas compressor and alkali washing tower; Cold box systems, including cold boxes; Demethanizer system, including demethanizer and demethanizer kettle pump; a deethanizer system, including a deethanizer; A carbon-2 reactor system, comprising a carbon-2 reactor; An ethylene distillation tower system, comprising an ethylene distillation tower; An ethylene refrigeration compressor system, comprising an ethylene refrigeration compressor and an ethylene refrigerant heat exchanger; A propylene refrigeration compressor system, comprising a propylene refrigeration compressor and a propylene refrigerant heat exchanger; a depropanizer system, including a depropanizer; A C3 reactor system, comprising a C3 reactor; and A propylene distillation tower system, comprising a propylene distillation tower; The ethylene plant further comprises: a pipeline connecting the outlet of the cracked gas compressor and the inlet of the cold box; a pipeline connecting the outlet of the cold box and the inlet of the cracked gas compressor; a pipeline connecting the tail gas outlet of the ethylene distillation tower and the kettle pump of the demethanizer; a pipeline connecting the inlet of the C2 reactor and the inlet of the cracked gas compressor; a pipeline connecting the top of the depropanizer and the inlet of the cracked gas compressor; a pipeline connecting the outlet of the C2 reactor and the inlet of the cracked gas compressor; A pipeline connecting the outlet of the C2 reactor and the ethylene distillation tower.

2. The ethylene plant according to claim 1, wherein The ethylene plant has one or more of the following features: The demethanizer kettle pump is a vertical multi-stage pump; The ethylene device further comprises a pipeline connecting the quench water tower and the cracked gas compressor; The ethylene unit further comprises a pipeline connecting the cold box and the demethanizer; The ethylene unit further comprises a pipeline connecting the demethanizer and the deethanizer; The ethylene unit further comprises a pipeline connecting the deethanizer and the C2 reactor; The ethylene device further comprises a pipeline connecting the ethylene distillation tower and the propylene refrigeration compressor; The ethylene device further comprises a pipeline connecting the propylene refrigeration compressor and the ethylene refrigeration compressor; The ethylene device further comprises a pipeline connecting the ethylene refrigeration compressor and the cold box; The ethylene unit further comprises a pipeline connecting the depropanizer and the C3 reactor; The ethylene device further comprises a pipeline connecting the C3 reactor and the propylene distillation tower; The ethylene unit further comprises a pipeline connecting the deethanizer and the depropanizer; The ethylene device further comprises valves arranged on each pipeline; The cold box includes a knockout tank.

3. A method for starting up an ethylene plant according to claim 1 or 2, characterized in that: The method comprises the following steps: S1: starting the cracked gas compressor to operate with nitrogen, and making the propylene refrigeration compressor and the ethylene refrigeration compressor operate with gas; S2: returning the pre-cooled nitrogen from the outlet of the cold box to the cracked gas compressor via a pipeline; S3: putting the propylene refrigerant heat exchanger and the ethylene refrigerant heat exchanger into use, and reducing the temperature of the cold box to an operating value according to a pre-cooling curve; S4: After the propylene refrigeration compressor is stabilized, the gaseous ethylene is introduced into the ethylene distillation tower to perform full reflux operation of the ethylene distillation tower; S5: introducing liquid propylene and gaseous ethylene into the deethanizer to perform full reflux operation of the deethanizer; S6: After the total reflux of the ethylene distillation tower is stabilized, the tail gas of the ethylene distillation tower is sent to the kettle pump of the demethanizer; S7: After the temperature of the cold box drops to a normal value and the system leakage check is completed, natural gas is introduced from the quenching water tower, and a section of the cracked gas compressor is shut down to replenish nitrogen; S8: causing the alkali liquid in the alkali washing tower to react with the acid gas contained in the cracked gas compressed by the cracked gas compressor to undergo a neutralization reaction; S9: After the pressure balance among the various systems of the ethylene unit is stabilized, the natural gas is returned to the cracked gas compressor through a pipeline connecting the inlet of the C2 reactor and the inlet of the cracked gas compressor to establish a natural gas circulation loop; S10: returning the C3 to the cracked gas compressor through a pipeline connecting the top of the depropanizer and the inlet of the cracked gas compressor; S11: Introducing hydrogen to maintain the pressure of the cold box at 3.1-3.3 MPaG; S12: preheating the C2 reactor and completing gas replacement to prepare it for use; S13: After the liquid levels of the separation tanks of the cold box are stable, the demethanizer is fed; after the liquid level of the bottom of the demethanizer is stable, the deethanizer is fed; S14: Pressurizing the C2 reactor and putting it into operation, maintaining the top temperature of the deethanizer at -15 to -20°C, and allowing the circulating material to begin returning to the cracked gas compressor from the outlet of the C2 reactor; S15: feeding the first cracking furnace and the second cracking furnace, and slowly stopping the natural gas supply according to the suction pressure of the cracking gas compressor; S16: sending the start-up hydrogen into the C2 reactor; S17: feeding materials into the third cracking furnace and the fourth cracking furnace; S18: After the acetylene output from the C2 reactor indicates that the reaction is qualified, the product from the C2 reactor is fed into the ethylene distillation tower, and the pipeline between the outlet of the C2 reactor and the inlet of the cracked gas compressor is closed. S19: After the self-produced hydrogen of the ethylene unit passes the methanation reactor and is qualified, stopping supplying the startup hydrogen to the C2 reactor; S20: After the liquid level in the bottom of the deethanizer is stabilized, feed the depropanizer and slowly close the pipeline connected to the inlet of the cracked gas compressor returning from the top of the depropanizer to start the C3 reactor.

4. The method according to claim 3, wherein In step S1, the cracked gas compressor is started two days before feeding to perform nitrogen operation.

5. The method according to claim 3, wherein In step S4, the propylene refrigeration compressor is stable, which means that the speed of the propylene refrigeration compressor reaches the rated speed, the suction pressure of the propylene refrigeration compressor reaches the design value, and the propylene refrigeration compressor can start to provide propylene refrigerant that meets the requirements.

6. The method according to claim 3, wherein After the nitrogen content in the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene device is qualified, the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene device are fed into the fuel gas system and the flare emission is stopped.

7. The method according to claim 3, wherein After the nitrogen content in the low-pressure methane, high-pressure methane and hydrogen produced by the ethylene unit is qualified and the pressure of the fuel gas system is stable, the addition of fuel gas is reduced or stopped.

8. The method according to claim 3, wherein After the ethylene distillation tower is replenished with ethylene, the ethylene is introduced into the fuel gas system.

9. The method according to claim 3, wherein In step S19, the self-produced hydrogen contains carbon monoxide.

10. The method according to claim 3, wherein The method further comprises: S21: adjusting the reaction conditions of the propylene distillation tower to produce a qualified propylene product.

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