Device and method for utilizing reaction heat of high-pressure low-density polyethylene

Abstract

The application provides a device and method for utilizing reaction heat of high-pressure low-density polyethylene, which comprises a tubular reactor, a high-pressure separator, a soft product separator and a low-pressure separator connected in sequence; the tubular reactor comprises at least four reaction sections connected in series, and an independent jacketed heat exchanger is arranged outside the front half section and the rear half section of each reaction section, and a peroxide initiator injection port is arranged in front of each reaction section; a pulse valve and a post-cooler are arranged in sequence on the pipeline between the tubular reactor and the high-pressure separator, the post-cooler comprises two-stage jacketed heat exchangers arranged in sequence; two-stage soft product heat exchangers are arranged in sequence on the pipeline between the high-pressure separator and the soft product separator; and a circulating gas heat exchanger and a circulating gas cooler are arranged in sequence on the gas phase discharge pipeline of the soft product separator. According to the temperature difference at different positions in the reaction process, multiple independent temperature adjusting water systems are designed to realize full utilization of the reaction heat.

Description

Technical Field

[0001] This invention belongs to the field of oily wastewater treatment, specifically relating to an apparatus and method for utilizing the reaction heat of high-pressure low-density polyethylene. Background Technology

[0002] Low-density polyethylene (LDPE) is a thermoplastic resin obtained by free radical polymerization of polymer-grade ethylene as the monomer and peroxide as the initiator. Its density is 0.91–0.93 g / cm³. 3 It is the lightest variety of polyethylene resin. It possesses good flexibility, extensibility, electrical insulation, transparency, ease of processing, and some air permeability. It exhibits good chemical stability, is resistant to alkalis and common organic solvents, and has a wide range of applications, including extrusion coating, blown film, wire and cable sheathing, injection molding, and blow molding.

[0003] Because the free radicals generated by the initiator have a short lifespan, ethylene is highly compressed by increasing the reaction pressure (110–350 MPa), increasing its density to 0.5 g / cm³. 3 It is similar to an incompressible liquid. In order to shorten the intermolecular distance of ethylene, increase the probability of collision between free radicals or active growth chains and ethylene molecules, a free radical polymerization reaction is carried out to produce low-density polyethylene. Therefore, low-density polyethylene is also known as high-pressure low-density polyethylene.

[0004] Depending on the reactor type, processes can be divided into two types: high-pressure tubular reactors and high-pressure batch reactors. Each process has its own characteristics: tubular reactors have a simple structure, are easy to manufacture and maintain, and can withstand higher pressures; batch reactors have a complex structure, are relatively difficult to maintain and install, and their volume is usually smaller due to limited heat removal capacity.

[0005] Generally, large-scale plants mostly use the tubular process, while plants that produce high-value-added products such as EVA with special grades and high vinyl acetate content use the batch process.

[0006] The polyethylene reaction is exothermic, and the heat of reaction must be removed promptly during production. For tubular reactors, a shell-and-tube heat exchanger is installed outside the reaction tubes, and the heat of reaction is removed via circulating temperature-regulating water. In the current process, the temperature parameters of the temperature-regulating water are too low, and the high-temperature heat of reaction is not effectively recovered and utilized.

[0007] Against this backdrop, there is a need for an apparatus and method for utilizing the reaction heat of high-pressure low-density polyethylene. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an apparatus and method for utilizing the reaction heat of high-pressure low-density polyethylene. This method achieves full utilization of the reaction heat through systematic optimization of the temperature and pressure of the temperature-regulating water system.

[0009] To achieve the above objectives, the first aspect of the present invention provides an apparatus for utilizing the reaction heat of high-pressure low-density polyethylene, the apparatus comprising an ethylene feed line, a tubular reactor, a high-pressure separator and a soft product separator connected in sequence, and a low-pressure separator;

[0010] The tubular reactor includes at least four reaction sections connected in series. Each reaction section has its own independent shell-and-tube heat exchanger installed on the outside of the front and rear halves. Each reaction section is equipped with a peroxide initiator injection port.

[0011] A pulse valve and a reaction product aftercooler are sequentially installed on the pipeline between the tubular reactor and the high-pressure separator. The reaction product aftercooler includes a primary shell-and-tube heat exchanger and a secondary shell-and-tube heat exchanger arranged sequentially.

[0012] The high-pressure separator is equipped with a high-separation gas phase discharge pipeline and a high-separation liquid phase discharge pipeline. The high-separation gas phase discharge pipeline is connected to the soft product separator, on which a soft product primary heat exchanger and a soft product secondary heat exchanger are installed in sequence. The high-separation liquid phase discharge pipeline enters the low-pressure separator, on which a pressure reducing valve is installed.

[0013] The soft product separator is equipped with a soft gas phase discharge pipeline and a soft liquid phase discharge pipeline. A high-pressure circulating gas heat exchanger and a high-pressure circulating gas cooler are installed sequentially on the soft gas phase discharge pipeline.

[0014] The low-pressure separator is equipped with a low-volume gas phase discharge pipeline and a high-pressure low-density polyethylene discharge pipeline.

[0015] A second aspect of the present invention provides a method for utilizing the heat of reaction of high-pressure low-density polyethylene in the above-described apparatus, the method comprising the following steps:

[0016] Segmented reaction heat removal: After pressurizing and heating the ethylene gas, it is sent into a tubular reactor to carry out segmented polymerization reaction with peroxide initiators injected in at least four stages. The heat of reaction in each reaction stage is removed by circulating temperature-controlled water to obtain the primary polymerization product.

[0017] High-pressure separation: After the primary polymerization product is depressurized by a pulse valve, it is sequentially fed into the reaction product cooler and the high-pressure separator for cooling and gas-liquid separation to obtain gaseous and liquid materials.

[0018] Soft product separation: After two-stage cooling, the gaseous material is sent to the soft product separator for gas-liquid separation. The resulting gaseous product is then sent to the subsequent separation section after heat exchange and cooling.

[0019] Low-pressure separation: After the liquid material is depressurized by a pressure reducing valve, it is sent to a low-pressure separator for flash separation to obtain gaseous products and high-pressure low-density polyethylene. The gaseous products are cooled and sent to subsequent separation sections.

[0020] The effects of this invention are:

[0021] (1) The device for utilizing the reaction heat of high pressure low density polyethylene provided by the present invention divides the tubular reactor into at least four reaction sections, and each front half and rear half is equipped with its own independent shell heat exchanger. At the same time, different types of heat exchangers are set at the process nodes of high pressure low density polyethylene reaction, so that the removal of reaction heat is more precise and flexible.

[0022] (2) The device for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention is equipped with multiple temperature-regulating water systems according to the temperature differences at different locations during the reaction process. It can promptly remove the reaction heat of polymerization and the feed heat of separation reaction at different stages, making the polymerization and separation reaction processes safer and more controllable. At the same time, it makes full use of the reaction heat of polymerization and the feed heat of separation reaction at different stages.

[0023] (3) The device for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention is equipped with a temperature-regulating water tank and preferably a temperature-regulating steam generator. The temperature of the temperature-regulating water can be changed by adjusting the steam generation pressure to adapt to the change in reaction temperature when producing different grades of polyethylene products.

[0024] (4) The temperature-regulating water system of the device for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention can be equipped with a temperature-regulating water cooler, which can directly output the withdrawn reaction heat to the required equipment.

[0025] (5) The method for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention optimizes the temperature-regulating water system. Through the systematic optimization of the temperature and pressure of the temperature-regulating water system, it is possible to use the reaction heat to generate high-quality steam of different grades. Moreover, the heat of the temperature-regulating water with the lowest temperature can be upgraded and utilized by an MVR heat pump unit, so that the recovery and utilization rate of the reaction heat exceeds 90%, realizing the full utilization of the reaction heat and reducing energy operation.

[0026] (6) The method for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention can preferably send deoxygenated water to multiple temperature-regulating water systems after being pressurized by a deoxygenated water pump to supplement the steam production water.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0028] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0029] Figure 1 This is a schematic flowchart of a specific embodiment of the apparatus for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention.

[0030] Figure 2 This is a schematic flowchart of another specific embodiment of the apparatus for utilizing the reaction heat of high-pressure low-density polyethylene provided by the present invention.

[0031] Explanation of reference numerals in the attached figures

[0032] 1—Tubular reactor, 2—High-pressure separator, 3—Soft product separator, 4—Low-pressure separator, 5—Pulse valve, 6—Reaction product aftercooler, 7—First-stage heat exchanger for soft product, 8—Second-stage heat exchanger for soft product, 9—Pressure reducing valve, 10—High-pressure circulating gas heat exchanger, 11—High-pressure circulating gas cooler, 12—Low-pressure circulating gas cooler, 13—First temperature-regulating water system, 14—Second temperature-regulating water system, 15—Third temperature-regulating water system, 16—Fourth temperature-regulating water system, 17—Deoxygenated water pump, 18—MVR heat pump unit;

[0033] 101—First section of tubular reactor and its shell-and-tube heat exchanger; 102—Second section of tubular reactor and its shell-and-tube heat exchanger; 103—Third section of tubular reactor and its shell-and-tube heat exchanger; 104—Fourth section of tubular reactor and its shell-and-tube heat exchanger; 105—First-stage shell-and-tube heat exchanger; 106—Second-stage shell-and-tube heat exchanger; 107—First temperature-regulating water tank; 108—First temperature-regulating water circulation pump; 109—First temperature-regulating water heat exchanger; 110—Second temperature-regulating water tank; 111—Second temperature-regulating water circulation pump; 112—Second temperature-regulating water heat exchanger; 113—Third steam generator; 114—Third temperature-regulating water cooler; 115—Third temperature-regulating water circulation pump; 116—Fourth temperature-regulating water tank; 117—Fourth temperature-regulating water circulation pump; 118—Fourth temperature-regulating water cooler.

[0034] 301—The first half of the first section of the tubular reactor and its shell-and-tube heat exchanger; 302—The second half of the first section of the tubular reactor and its shell-and-tube heat exchanger; 303—The first half of the second section of the tubular reactor and its shell-and-tube heat exchanger; 304—The second half of the second section of the tubular reactor and its shell-and-tube heat exchanger; 305—The first half of the third section of the tubular reactor and its shell-and-tube heat exchanger; 306—The second half of the third section of the tubular reactor and its shell-and-tube heat exchanger; 307—The first half of the fourth section of the tubular reactor and its shell-and-tube heat exchanger; 308—The second half of the fourth section of the tubular reactor and its shell-and-tube heat exchanger. Detailed Implementation

[0035] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0036] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to their relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] This invention provides a device for utilizing the reaction heat of high-pressure low-density polyethylene, such as... Figure 1 As shown, the device includes an ethylene feed line, a tubular reactor 1, a high-pressure separator 2 and a soft product separator 3 connected in sequence, and a low-pressure separator 4.

[0038] The tubular reactor 1 includes at least four reaction sections connected in series. Each reaction section has its own independent shell-and-tube heat exchanger installed on the outside of the front and rear halves. Each reaction section is provided with a peroxide initiator injection port.

[0039] A pulse valve 5 and a reaction product aftercooler 6 are sequentially installed on the pipeline between the tubular reactor 1 and the high-pressure separator 2. The reaction product aftercooler 6 includes a primary shell-and-tube heat exchanger 105 and a secondary shell-and-tube heat exchanger 106 arranged sequentially.

[0040] The high-pressure separator 2 is equipped with a high-separation gas phase discharge pipeline and a high-separation liquid phase discharge pipeline. The high-separation gas phase discharge pipeline is connected to the soft product separator 3, and a soft product primary heat exchanger 7 and a soft product secondary heat exchanger 8 are installed on it in sequence. The high-separation liquid phase discharge pipeline enters the low-pressure separator 4, and a pressure reducing valve 9 is installed on it.

[0041] The soft product separator 3 is equipped with a soft gas phase discharge pipeline and a soft liquid phase discharge pipeline. A high-pressure circulating gas heat exchanger 10 and a high-pressure circulating gas cooler 11 are sequentially installed on the soft gas phase discharge pipeline.

[0042] The low-pressure separator 4 is equipped with a low-volume gas phase discharge pipeline and a high-pressure low-density polyethylene discharge pipeline.

[0043] According to the present invention, the device further includes a first temperature-regulating water system 13, a second temperature-regulating water system 14, a third temperature-regulating water system 15 and a fourth temperature-regulating water system 16;

[0044] The first temperature-regulating water system 13 and the second temperature-regulating water system 14 both include a hot water inlet pipeline, a temperature-regulating water tank, a temperature-regulating water circulation pump, an optional temperature-regulating water cooler, and a cold water outlet pipeline, which are connected in sequence.

[0045] The refrigerant inlets of the first half of the reaction section, excluding the final reaction section, the shell-and-tube heat exchanger, the first-stage shell-and-tube heat exchanger 105, and the first-stage heat exchanger 7 for soft products are all connected to the cold water outlet pipeline of the first temperature-regulating water system 13 through independent pipelines.

[0046] The refrigerant outlets of the first half of the reaction section, excluding the final reaction section, the first-stage shell-and-tube heat exchanger 105, and the first-stage heat exchanger 7 for soft products are all connected to the hot water feed pipeline of the first temperature-regulating water system 13 through independent pipelines.

[0047] The refrigerant inlets of the first and second halves of the final stage reaction section, the second half of the reaction section excluding the final stage reaction section, and the secondary heat exchanger 8 for soft products are all connected to the cold water outlet pipeline of the second temperature-regulating water system 14 through independent pipelines.

[0048] The refrigerant outlets of the shell-and-tube heat exchangers in the first and second halves of the final stage reaction section, the shell-and-tube heat exchangers in the second half of the reaction section excluding the final stage reaction section, and the refrigerant outlets of the secondary heat exchanger 8 for the soft product are all connected to the hot water feed pipeline of the second temperature-regulating water system 14 through independent pipelines.

[0049] The third temperature-regulating water system 15 includes a hot water inlet pipeline, an optional steam generator, a temperature-regulating water cooler, a temperature-regulating water circulation pump, and a cold water outlet pipeline connected in sequence.

[0050] The refrigerant inlet and refrigerant outlet of the secondary shell-and-tube heat exchanger 106 are respectively connected to the cold water outlet pipeline and the hot water inlet pipeline of the third temperature-regulating water system 15;

[0051] The fourth temperature-regulating water system 16 includes a hot water inlet pipeline, a temperature-regulating water tank, a temperature-regulating water circulation pump, a temperature-regulating water cooler, and a cold water outlet pipeline connected in sequence.

[0052] The refrigerant inlet and refrigerant outlet of the high-pressure circulating gas heat exchanger 10 are respectively connected to the cold water outlet pipeline and hot water inlet pipeline of the fourth temperature regulating water system 16.

[0053] According to the present invention, the device further includes a deoxygenated water pump 17 and an MVR heat pump unit 18;

[0054] The temperature regulating water tanks of the first temperature regulating water system 13, the second temperature regulating water system 14 and the fourth temperature regulating water system 16 are each equipped with their own independent deoxygenated water inlet and steam outlet.

[0055] The steam generator of the third temperature-regulating water system 15 is equipped with a deoxygenated water inlet and a steam outlet, and the steam outlet is connected to the third steam discharge pipeline.

[0056] The inlet of the deoxygenated water pump 17 is connected to the deoxygenated water feed pipeline, and the outlet is connected to the discharge pipeline of the deoxygenated water pump 17. The discharge pipeline of the deoxygenated water pump 17 is divided into four branches, which are respectively connected to the deoxygenated water inlets of the first temperature-regulating water system 13, the second temperature-regulating water system 14, the third temperature-regulating water system 15 and the fourth temperature-regulating water system 16.

[0057] The steam outlets of the first temperature-regulating water system 13 and the second temperature-regulating water system 14 are respectively connected to their respective steam discharge pipelines.

[0058] The steam outlet of the fourth temperature-regulating water system 16 is connected in sequence to the MVR heat pump unit 18 and the fourth steam discharge pipeline. The fourth steam discharge pipeline and the third steam discharge pipeline are connected to the steam extraction pipeline.

[0059] In this invention, based on the temperature differences at different locations in the reaction process, four independent temperature-regulating water systems are designed to recover reaction heat and generate corresponding levels of steam. Moreover, the heat of the temperature-regulating water at the lowest temperature is upgraded and utilized by an MVR heat pump unit 18, so that the recovery and utilization rate of reaction heat exceeds 90%.

[0060] In this invention, the tubular reactor 1 is divided into at least four reaction sections, and each of the first and second halves is equipped with its own independent shell-and-tube heat exchanger. At the same time, different types of heat exchangers are set at the process nodes of the high-pressure low-density polyethylene reaction, so that the heat of reaction can be removed more accurately and flexibly.

[0061] In this invention, multiple temperature-regulating water systems are set up according to the temperature differences at different locations during the reaction process. These systems can promptly remove the heat of polymerization and the heat of feed from the separation reaction at different stages, making the polymerization and separation processes safer and more controllable. At the same time, they make full use of the heat of polymerization and the heat of feed from the separation reaction at different stages.

[0062] Preferably, a low-pressure circulating gas cooler 12 is installed on the low-segment gas phase discharge pipeline of the low-pressure separator 4;

[0063] A booster pump and a heater are installed sequentially on the ethylene feed pipeline.

[0064] The present invention also provides a method for utilizing the reaction heat of high-pressure low-density polyethylene in the above-described apparatus, the method comprising the following steps:

[0065] Segmented reaction heat removal: After pressurizing and heating the ethylene gas, it is sent into the tubular reactor 1 to carry out segmented polymerization reaction with peroxide initiators injected in at least four segments. The heat of reaction in each reaction segment is removed by circulating temperature-controlled water to obtain the primary polymerization product.

[0066] High-pressure separation: After the primary polymerization product is depressurized by pulse valve 5, it is sequentially sent to reaction product aftercooler 6 and high-pressure separator 2 for cooling and gas-liquid separation to obtain gaseous and liquid materials.

[0067] Soft product separation: After two-stage cooling, the gaseous material is sent to the soft product separator 3 for gas-liquid separation. The gaseous product is then sent to the subsequent separation section after heat exchange and cooling.

[0068] Low-pressure separation: After the liquid material is depressurized by the pressure reducing valve 9, it is sent to the low-pressure separator 4 for flash separation to obtain gaseous products and high-pressure low-density polyethylene. The gaseous products are cooled and sent to the subsequent separation section.

[0069] According to the present invention, the polymerization reaction heat generated in the first half of the reaction section other than the final reaction section in the segmented reaction heat removal step, the heat released by the primary polymerization product in the first-stage shell-and-tube heat exchanger 105 of the reaction product aftercooler 6 in the high-pressure separation step, and the heat released by the gaseous material in the first stage of the two-stage cooling in the soft product separation step are all removed by circulating water in the first temperature-regulating water system 13.

[0070] In the segmented reaction heat removal step, the polymerization heat generated in the latter half of the reaction section other than the final reaction section, the polymerization heat generated in the entire final reaction section, and the heat released by the gaseous material in the second stage of the two-stage cooling in the soft product separation step are all removed by circulating water in the second temperature-regulating water system 14.

[0071] The heat released by the primary polymerization product in the secondary shell-and-tube heat exchanger 106 of the reaction product aftercooler 6 during the high-pressure separation step is removed by circulating water in the third temperature-regulating water system 15.

[0072] The heat from the gaseous products during the soft product separation step is removed by circulating water in the fourth temperature-controlled water system 16.

[0073] Preferably, the heat removed by the circulating water in the first temperature-regulating water system 13 is used to generate first steam through its own temperature-regulating water tank and / or output through its own temperature-regulating water cooler.

[0074] The heat removed by the circulating water in the second temperature-regulating water system 14 is generated as second steam through its own temperature-regulating water tank and / or output through its own temperature-regulating water cooler.

[0075] The heat removed by the circulating water in the third temperature-regulating water system 15 is generated into third steam through its own steam generator and / or output through its own temperature-regulating water cooler.

[0076] The heat removed by the circulating water in the fourth temperature-regulating water system 16 is boosted to the pressure of the third steam by the fourth steam generated by its own temperature-regulating water tank and mixed with the third steam and / or output through its own temperature-regulating water cooler.

[0077] This invention optimizes the temperature-controlled water system. Through systematic optimization of the temperature and pressure of the temperature-controlled water system, it utilizes the heat of reaction to generate high-quality steam of different grades. Moreover, the heat of the temperature-controlled water with the lowest temperature is upgraded and utilized by an MVR heat pump unit 18, so that the heat of reaction recovery and utilization rate exceeds 90%, realizing the full utilization of the heat of reaction and reducing energy operation.

[0078] In this invention, the temperature-regulating water system of the device for utilizing the reaction heat of high-pressure low-density polyethylene provided by this invention can be equipped with a temperature-regulating water cooler, which can directly output the withdrawn reaction heat to the required equipment.

[0079] In this invention, the device for utilizing the reaction heat of high-pressure low-density polyethylene is equipped with a temperature-regulating water tank and a temperature-regulating steam generator. The temperature of the temperature-regulating water can be changed by adjusting the steam generation pressure to adapt to the changes in reaction temperature when producing different grades of polyethylene products.

[0080] According to the present invention, the method further includes the following steps:

[0081] Deoxygenated water replenishment: After pressurization, the deoxygenated water is sent to the first temperature-regulating water system 13, the second temperature-regulating water system 14, the third temperature-regulating water system 15 and the fourth temperature-regulating water system 16 respectively to replenish the water used for steam production.

[0082] In this invention, the deoxygenated water is pressurized by the deoxygenated water pump 17 and then sent to multiple temperature-regulating water systems to supplement the steam production water.

[0083] Preferably, the temperature of the ethylene gas fed into the tubular reactor 1 is 170-190°C and the pressure is 280-320 MPa.

[0084] The temperature of the primary polymerization product after pressure reduction by pulse valve 5 is 310-350℃, and the pressure is 25-35MPaA;

[0085] After being cooled by the reaction product cooler 6, the temperature of the primary polymerization product is 270-290℃.

[0086] After two stages of cooling, the temperature of the gaseous material is 180-200℃;

[0087] After heat exchange and cooling, the temperature of the gaseous products is 40-50℃.

[0088] Preferably, the temperature of the circulating temperature-regulating water entering the first temperature-regulating water system 13 is 190-200℃ and the pressure is 1.0-1.2MPaA, the temperature of the circulating temperature-regulating water leaving the first temperature-regulating water system 13 is 180-188℃ and the pressure is 2.7-2.9MPaA, and the pressure of the first steam is 1.0-1.2MPaA;

[0089] The temperature of the circulating temperature-regulating water entering the second temperature-regulating water system 14 is 175-185℃, and the pressure is 0.75-0.85MPaA. The temperature of the circulating temperature-regulating water leaving the second temperature-regulating water system 14 is 167-173℃, and the pressure is 2.1-2.3MPaA. The pressure of the second steam is 0.75-0.85MPaA.

[0090] The temperature of the circulating temperature-regulating water entering the third temperature-regulating water system 15 is 170-180℃ and the pressure is 3.5-3.7MPaA. The temperature of the circulating temperature-regulating water leaving the third temperature-regulating water system 15 is 162-167℃ and the pressure is 3.9-4.1MPaA. The pressure of the third steam is 0.55-0.65MPaA.

[0091] The temperature of the circulating temperature-regulating water entering the fourth temperature-regulating water system 16 is 125-135℃ and the pressure is 0.20-0.24MPaA. The temperature of the circulating temperature-regulating water leaving the fourth temperature-regulating water system 16 is 85-95℃ and the pressure is 1.1-1.3MPaA. The pressure of the fourth steam is 0.20-0.24MPaA.

[0092] The present invention will be described in more detail below through embodiments.

[0093] Example

[0094] A 250,000-ton / year high-pressure low-density polyethylene plant uses a tubular process for production. The heat of reaction is extracted using low-temperature temperature-controlled water. The original temperature-controlled water system has a low temperature, with the highest water temperature after heat exchange being about 120°C and the lowest being only about 60°C. The waste heat cannot be utilized and can only be discharged through air cooling and water cooling, resulting in energy waste.

[0095] like Figure 1 As shown, this embodiment modifies the above-mentioned device to provide a device for utilizing the reaction heat of high-pressure low-density polyethylene. The device includes an ethylene feed line, a tubular reactor 1, a high-pressure separator 2 and a soft product separator 3 connected in sequence, as well as a low-pressure separator 4.

[0096] The tubular reactor 1 includes four reaction sections connected in series. Each reaction section has its own independent shell-and-tube heat exchanger installed on the outside of the front and rear halves. Each reaction section is equipped with a peroxide initiator injection port.

[0097] A pulse valve 5 and a reaction product aftercooler 6 are sequentially installed on the pipeline between the tubular reactor 1 and the high-pressure separator 2. The reaction product aftercooler 6 includes a primary shell-and-tube heat exchanger 105 and a secondary shell-and-tube heat exchanger 106 arranged sequentially.

[0098] The high-pressure separator 2 is equipped with a high-separation gas phase discharge pipeline and a high-separation liquid phase discharge pipeline. The high-separation gas phase discharge pipeline is connected to the soft product separator 3, and a soft product primary heat exchanger 7 and a soft product secondary heat exchanger 8 are installed on it in sequence. The high-separation liquid phase discharge pipeline enters the low-pressure separator 4, and a pressure reducing valve 9 is installed on it.

[0099] The soft product separator 3 is equipped with a soft gas phase discharge pipeline and a soft liquid phase discharge pipeline. A high-pressure circulating gas heat exchanger 10 and a high-pressure circulating gas cooler 11 are sequentially installed on the soft gas phase discharge pipeline.

[0100] The low-pressure separator 4 is equipped with a low-splitting gas phase discharge pipeline and a high-pressure low-density polyethylene discharge pipeline.

[0101] The device also includes a first temperature-regulating water system 13, a second temperature-regulating water system 14, a third temperature-regulating water system 15, and a fourth temperature-regulating water system 16;

[0102] The first temperature-regulating water system 13 and the second temperature-regulating water system 14 both include a hot water inlet pipeline, a temperature-regulating water tank, a temperature-regulating water circulation pump, and a cold water outlet pipeline connected in sequence.

[0103] The refrigerant inlets of the first half of the reaction section, excluding the final reaction section, the shell-and-tube heat exchanger, the first-stage shell-and-tube heat exchanger 105, and the first-stage heat exchanger 7 for soft products are all connected to the cold water outlet pipeline of the first temperature-regulating water system 13 through independent pipelines.

[0104] The refrigerant outlets of the first half of the reaction section, excluding the final reaction section, the first-stage shell-and-tube heat exchanger 105, and the first-stage heat exchanger 7 for soft products are all connected to the hot water feed pipeline of the first temperature-regulating water system 13 through independent pipelines.

[0105] The refrigerant inlets of the first and second halves of the final stage reaction section, the second half of the reaction section excluding the final stage reaction section, and the secondary heat exchanger 8 for soft products are all connected to the cold water outlet pipeline of the second temperature-regulating water system 14 through independent pipelines.

[0106] The refrigerant outlets of the shell-and-tube heat exchangers in the first and second halves of the final stage reaction section, the shell-and-tube heat exchangers in the second half of the reaction section excluding the final stage reaction section, and the refrigerant outlets of the secondary heat exchanger 8 for the soft product are all connected to the hot water feed pipeline of the second temperature-regulating water system 14 through independent pipelines.

[0107] The third temperature-regulating water system 15 includes a hot water inlet pipeline, a steam generator, a temperature-regulating water cooler, a temperature-regulating water circulation pump, and a cold water outlet pipeline connected in sequence.

[0108] The refrigerant inlet and refrigerant outlet of the secondary shell-and-tube heat exchanger 106 are respectively connected to the cold water outlet pipeline and the hot water inlet pipeline of the third temperature-regulating water system 15;

[0109] The fourth temperature-regulating water system 16 includes a hot water inlet pipeline, a temperature-regulating water tank, a temperature-regulating water circulation pump, a temperature-regulating water cooler, and a cold water outlet pipeline connected in sequence.

[0110] The refrigerant inlet and refrigerant outlet of the high-pressure circulating gas heat exchanger 10 are respectively connected to the cold water outlet pipeline and hot water inlet pipeline of the fourth temperature regulating water system 16.

[0111] The device also includes a deoxygenated water pump 17 and an MVR heat pump unit 18;

[0112] The temperature regulating water tanks of the first temperature regulating water system 13, the second temperature regulating water system 14 and the fourth temperature regulating water system 16 are each equipped with their own independent deoxygenated water inlet and steam outlet.

[0113] The steam generator of the third temperature-regulating water system 15 is equipped with a deoxygenated water inlet and a steam outlet, and the steam outlet is connected to the third steam discharge pipeline.

[0114] The inlet of the deoxygenated water pump 17 is connected to the deoxygenated water feed pipeline, and the outlet is connected to the discharge pipeline of the deoxygenated water pump 17. The discharge pipeline of the deoxygenated water pump 17 is divided into four branches, which are respectively connected to the deoxygenated water inlets of the first temperature-regulating water system 13, the second temperature-regulating water system 14, the third temperature-regulating water system 15 and the fourth temperature-regulating water system 16.

[0115] The steam outlets of the first temperature-regulating water system 13 and the second temperature-regulating water system 14 are respectively connected to their respective steam discharge pipelines.

[0116] The steam outlet of the fourth temperature-regulating water system 16 is connected in sequence to the MVR heat pump unit 18 and the fourth steam discharge pipeline. The fourth steam discharge pipeline and the third steam discharge pipeline are connected to the steam extraction pipeline.

[0117] A low-pressure circulating gas cooler 12 is installed on the low-segment gas phase discharge pipeline of the low-pressure separator 4.

[0118] A booster pump and a heater are installed sequentially on the ethylene feed pipeline.

[0119] Based on the temperature differences at different locations in the reaction process, this embodiment designs four independent temperature-regulating water systems to recover the heat of reaction.

[0120] The first temperature-regulating water system 13 recovers the waste heat at five locations with the highest temperature: the first half of the shell-and-tube heat exchangers in the first to third sections of the tubular reactor 1, the first-stage shell-and-tube heat exchanger 105 of the reaction product aftercooler 6, and the first-stage heat exchanger 7 of the soft product, generating approximately 27 t / h of steam at 1.1 MPaA. The second temperature-regulating water system 14 recovers the waste heat at six locations with the next lowest temperature: the second half of the shell-and-tube heat exchangers in the first to fourth sections of the tubular reactor 1, the first half of the shell-and-tube heat exchanger in reactor section 4, and the second-stage heat exchanger 8 of the soft product, generating approximately 0.8 MPaA of steam. The steam output is approximately 28 t / h; the third temperature-regulating water system 15 recovers the waste heat from the secondary shell-and-tube heat exchanger 106 of the aftercooler 6 of the reaction products, generating approximately 5 t / h of 0.6 MPaA steam; the fourth temperature-regulating water system 16 recovers the waste heat from the high-pressure circulating gas heat exchanger 10, generating approximately 7 t / h of 0.22 MPaA steam. Since the temperature of 0.22 MPaA steam is low and there are no users in the surrounding area, the MVR heat pump unit 18 is used to pressurize it to 0.6 MPaA and mix it with the steam generated at the same pressure by the third temperature-regulating water system 15. The MVR heat pump unit 18 increases the power consumption by 450 kW.

[0121] After optimization and renovation, the total steam production of all stages increased by approximately 67t / h, and the heat pump unit increased its power consumption by 450kW.

[0122] The embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A device for utilizing the reaction heat of high-pressure low-density polyethylene, characterized in that, The device comprises an ethylene feeding pipeline, a tubular reactor, a high-pressure separator, a soft product separator and a low-pressure separator connected in sequence; The tubular reactor comprises at least four reaction sections connected in series, and each reaction section is provided with a jacketed heat exchanger independently arranged outside the front half and the rear half of the reaction section, and each reaction section is provided with a peroxide initiator injection port in front of the reaction section; A pulse valve and a reaction product after-cooler are arranged in sequence on the pipeline between the tubular reactor and the high-pressure separator, and the reaction product after-cooler comprises a first-stage jacketed heat exchanger and a second-stage jacketed heat exchanger arranged in sequence; The high-pressure separator is provided with a high-fraction gas phase discharge pipeline and a high-fraction liquid phase discharge pipeline, wherein the high-fraction gas phase discharge pipeline is connected with the soft product separator, and the soft product separator is provided with a soft product first-stage heat exchanger and a soft product second-stage heat exchanger arranged in sequence; The soft product separator is provided with a soft-fraction gas phase discharge pipeline and a soft-fraction liquid phase discharge pipeline, and the soft-fraction gas phase discharge pipeline is provided with a high-pressure circulating gas heat exchanger and a high-pressure circulating gas cooler arranged in sequence; The low-pressure separator is provided with a low-fraction gas phase discharge pipeline and a high-pressure low-density polyethylene discharge pipeline; The device further comprises a first temperature-adjusting water system, a second temperature-adjusting water system, a third temperature-adjusting water system and a fourth temperature-adjusting water system; The first temperature-adjusting water system and the second temperature-adjusting water system each comprise a hot water feeding pipeline, a temperature-adjusting water tank, a temperature-adjusting water circulating pump, an optional temperature-adjusting water cooler and a cold water discharge pipeline connected in sequence; The coolant inlets of the jacketed heat exchangers of the front half of the reaction sections except the last-stage reaction section, the first-stage jacketed heat exchanger and the soft product first-stage heat exchanger are connected to the cold water discharge pipeline of the first temperature-adjusting water system through independent pipelines; The coolant outlets of the jacketed heat exchangers of the front half of the reaction sections except the last-stage reaction section, the first-stage jacketed heat exchanger and the soft product first-stage heat exchanger are connected to the hot water feeding pipeline of the first temperature-adjusting water system through independent pipelines; The coolant inlets of the jacketed heat exchangers of the front half and the rear half of the last-stage reaction section, the jacketed heat exchangers of the rear half of the reaction sections except the last-stage reaction section and the soft product second-stage heat exchanger are connected to the cold water discharge pipeline of the second temperature-adjusting water system through independent pipelines; The coolant outlets of the jacketed heat exchangers of the front half and the rear half of the last-stage reaction section, the jacketed heat exchangers of the rear half of the reaction sections except the last-stage reaction section and the soft product second-stage heat exchanger are connected to the hot water feeding pipeline of the second temperature-adjusting water system through independent pipelines; The third temperature-adjusting water system comprises a hot water feeding pipeline, an optional steam generator, a temperature-adjusting water cooler, a temperature-adjusting water circulating pump and a cold water discharge pipeline connected in sequence; The coolant inlets and the coolant outlets of the second-stage jacketed heat exchanger are connected to the cold water discharge pipeline and the hot water feeding pipeline of the third temperature-adjusting water system, respectively; The fourth temperature-adjusting water system comprises a hot water feeding pipeline, a temperature-adjusting water tank, a temperature-adjusting water circulating pump, a temperature-adjusting water cooler and a cold water discharge pipeline connected in sequence; The coolant inlets and the coolant outlets of the high-pressure circulating gas heat exchanger are connected to the cold water discharge pipeline and the hot water feeding pipeline of the fourth temperature-adjusting water system, respectively.

2. The apparatus of claim 1, wherein, The device further comprises a deoxygenated water pump and an MVR heat pump unit. The temperature-adjusting water tanks of the first, second and fourth temperature-adjusting water systems are respectively provided with independent deoxygenated water inlets and steam outlets; The steam generator of the third temperature-adjusting water system is provided with a deoxygenated water inlet and a steam outlet, and the steam outlet is connected with a third steam discharge pipeline; The inlet of the deoxygenated water pump is connected with the deoxygenated water feeding pipeline, and the outlet is connected with a deoxygenated water discharge pipeline of the deoxygenated water pump, which is divided into four branches and connected with the deoxygenated water inlets of the first, second, third and fourth temperature-adjusting water systems respectively; The steam outlets of the first and second temperature-adjusting water systems are respectively connected with their own steam discharge pipelines; The steam outlet of the fourth temperature-adjusting water system is sequentially connected with an MVR heat pump unit and a fourth steam discharge pipeline, and the fourth steam discharge pipeline is connected with the third steam discharge pipeline to form a steam production pipeline.

3. The apparatus of claim 2, wherein, A low-pressure circulating gas cooler is arranged on the low-pressure gas phase discharge pipeline of the low-pressure separator; A booster pump and a heater are sequentially arranged on the ethylene feeding pipeline.

4. A method for utilizing reaction heat of high-pressure low-density polyethylene, characterized by, The method comprises the following steps: Segmented reaction heat removal: ethylene gas is pressurized and heated, and then is sent into a tubular reactor to sequentially react with peroxide initiators injected in at least four segments, and the reaction heat of each reaction segment is removed by circulating temperature-adjusting water to obtain a primary polymerization product; High-pressure separation: the primary polymerization product is sent into a reaction product post-cooler and a high-pressure separator in sequence after being depressurized by a pulse valve to be cooled and gas-liquid separated, thereby obtaining gas phase material and liquid phase material; Soft product separation: the gas phase material is sent into a soft product separator after being cooled in two stages to be gas-liquid separated, thereby obtaining gas phase product which is sent into a subsequent separation section after being sequentially heat exchanged and cooled; Low-pressure separation: the liquid phase material is sent into a low-pressure separator after being depressurized by a pressure reducing valve to be flash separated, thereby obtaining gas phase product and high-pressure low-density polyethylene, and the gas phase product is sent into a subsequent separation section after being cooled; The polymerization heat generated in the first half of the reaction segment except the last reaction segment in the segmented reaction heat removal step, the heat released by the primary polymerization product in the primary jacket heat exchanger of the reaction product post-cooler in the high-pressure separation step, and the heat released by the gas phase material in the first stage cooling of the two-stage cooling in the soft product separation step are all removed by the circulating water in the first temperature-adjusting water system; The polymerization heat generated in the second half of the reaction segment except the last reaction segment in the segmented reaction heat removal step, the polymerization heat generated in the whole last reaction segment, and the heat released by the gas phase material in the second stage cooling of the two-stage cooling in the soft product separation step are all removed by the circulating water in the second temperature-adjusting water system; The heat released by the primary polymerization product in the secondary jacket heat exchanger of the reaction product post-cooler in the high-pressure separation step is removed by the circulating water in the third temperature-adjusting water system; The heat of the gas phase product in the soft product separation step is removed by the circulating water in the fourth temperature-adjusting water system; The heat removed by the circulating water in the first temperature-adjusting water system is used to generate first steam in the temperature-adjusting water tank of the first temperature-adjusting water system and / or output by the temperature-adjusting water cooler of the first temperature-adjusting water system; The heat removed by the circulating water in the second temperature-adjusting water system is used to generate second steam in the temperature-adjusting water tank of the second temperature-adjusting water system and / or output by the temperature-adjusting water cooler of the second temperature-adjusting water system; The heat removed by the circulating water in the third temperature-adjusting water system is removed by the third steam generator and / or output by the temperature-adjusting water cooler; The heat removed by the circulating water in the fourth temperature-adjusting water system is removed by the fourth steam generated by the temperature-adjusting water tank and mixed with the third steam after being boosted to the pressure of the third steam and / or output by the temperature-adjusting water cooler.

5. The method of claim 4, wherein, The method further comprises the following steps: Deoxygenated water supplement: The deoxygenated water is boosted in pressure and then fed into the first, second, third and fourth temperature-adjusting water systems respectively to supplement the water for steam generation.

6. The method of claim 5, wherein, The temperature of the ethylene gas fed into the tubular reactor is 170-190℃, and the pressure is 280-320MPaA; The temperature of the primary polymerization product after pressure reduction by the pulse valve is 310-350℃, and the pressure is 25-35MPaA; The temperature of the primary polymerization product after cooling by the post-reactor cooler is 270-290℃; The temperature of the gas-phase material after two-stage cooling is 180-200℃; The temperature of the gas-phase product after heat exchange and cooling is 40-50℃.

7. The method of claim 6, wherein, The temperature of the circulating temperature-adjusting water entering the first temperature-adjusting water system is 190-200℃, and the pressure is 1.0-1.2MPaA; the temperature of the circulating temperature-adjusting water leaving the first temperature-adjusting water system is 180-188℃, and the pressure is 2.7-2.9MPaA; the pressure of the first steam is 1.0-1.2MPaA; The temperature of the circulating temperature-adjusting water entering the second temperature-adjusting water system is 175-185℃, and the pressure is 0.75-0.85MPaA; the temperature of the circulating temperature-adjusting water leaving the second temperature-adjusting water system is 167-173℃, and the pressure is 2.1-2.3MPaA; the pressure of the second steam is 0.75-0.85MPaA; The temperature of the circulating temperature-adjusting water entering the third temperature-adjusting water system is 170-180℃, and the pressure is 3.5-3.7MPaA; the temperature of the circulating temperature-adjusting water leaving the third temperature-adjusting water system is 162-167℃, and the pressure is 3.9-4.1MPaA; the pressure of the third steam is 0.55-0.65MPaA; The temperature of the circulating temperature-adjusting water entering the fourth temperature-adjusting water system is 125-135℃, and the pressure is 0.20-0.24MPaA; the temperature of the circulating temperature-adjusting water leaving the fourth temperature-adjusting water system is 85-95℃, and the pressure is 1.1-1.3MPaA; the pressure of the fourth steam is 0.20-0.24MPaA.

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