Energy-saving system and energy-saving method for ethylene quenching system

Abstract

The invention provides an energy-saving system and an energy-saving method for an ethylene quenching system, and by adopting the energy-saving system and the energy-saving method provided by the invention, the heat utilization rate of the quenching water system can be improved. The energy-saving system comprises a quenching water tower used for quenching and washing pyrolysis gas by using quenching water; the process water stripping tower is used for stripping and deoiling the process water through steam; the quenching water user is used for using the quenching water output by the tower kettle of the quenching water tower and obtaining first cooled quenching water with reduced temperature; the heat pump unit is used for absorbing the heat of the tower top steam of the process water stripping tower and absorbing part of the heat of the first cooling and quenching water, and enabling the hot water to be heated to absorb the heat; the heat user is used for introducing the hot water to be heated into the heat pump unit and receiving the heated hot water; and the heat pump unit is used for inputting the second cooling quenching water into the upper part of the quenching water tower and inputting the steam condensate into a tower kettle of the quenching water tower.

Description

Technical Field

[0001] The invention belongs to energy-saving and consumption-reducing technology for a quenching system of an ethylene device, and specifically relates to an energy-saving system and an energy-saving method for an ethylene quenching system. Background Art

[0002] The main user of the quenching system of the ethylene unit is to recover the heat in the cracking gas. The quenching oil tower is used to recover the high-temperature heat between 105℃→210℃ of the cracking gas, and the quenching water tower is used to recover the low-temperature heat between 35℃→105℃ of the cracking gas. The heat recovered by the quenching water tower is of low quality and can only produce low-temperature hot water of about 80℃ for some low-temperature heat sinks inside the ethylene unit. The heat of about 80℃→60℃ can be used by the system, while the heat of about 60℃→35℃ cannot be used and can only be cooled by circulating water or air cooler, resulting in the waste of low-temperature heat and increasing the consumption of cooling utilities of the unit. Only about 40-50% of the low-temperature heat of the cracking gas can be used in the quenching water system, and the remaining 50-60% of the heat is wasted.

[0003] The heat entering the quenching water tower is mainly composed of two parts. The largest part, about 90%, comes from the heat released when the cracking gas is reduced from 105℃ to 35℃ and the heat released by the condensation of the dilution steam in the cracking gas. The other part, about 10%, comes from the process water stripping tower of the quenching unit. The main function of the stripping tower is to continue to steam strip the process water obtained after the initial condensation and oil removal of part of the quenching water from the quenching water tower, and strip out the VOC and part of the light oil in the quenching water. The process water after stripping is used to dilute the steam generating unit to produce dilution steam. The gas phase at the top of the stripping tower contains a small amount of oil substances. Considering that the oil contained in the steam is consistent with the oil in the quenching water tower, the heat of the stripping steam can be partially utilized after returning to the tower. Therefore, almost all ethylene units currently return this part of the stripped steam directly to the quenching water tower. The steam temperature at the top of the stripping tower is about 110℃. After returning to the tower directly, it is downgraded to 80℃ quench water heat, and only 40-50% can be utilized. The rest still needs to be taken away by circulating water or air cooling. This process design has a low heat recovery rate and also increases the consumption of cooling utilities. Summary of the invention

[0004] In view of this, the present invention provides an energy-saving system and energy-saving method for an ethylene quenching system. The energy-saving system and energy-saving method of the present invention can improve the heat utilization rate of the quenching water system and utilize the difficult-to-use low-temperature heat in the quenching system.

[0005] To achieve the purpose, the present invention provides the following technical solutions:

[0006] The present invention provides an energy-saving system for an ethylene quenching system, the energy-saving system comprising:

[0007] A quench water tower, used to quench and wash the cracked gas with quench water and obtain the quenched cracked gas at the top of the tower;

[0008] A process water stripping tower, used to use steam to strip the process water to remove oil, and output overhead steam at the top of the tower;

[0009] A quenching water user, used to use the quenching water output from the kettle of the quenching water tower and obtain first cooling quenching water with a lowered temperature;

[0010] a heat pump unit, for absorbing heat from the tower top steam of the process water stripping tower and absorbing part of the heat from the first cooling quenching water, and allowing the hot water to be heated to absorb the heat, so as to obtain heated hot water obtained by heating the hot water to be heated, second cooling quenching water obtained by cooling the first cooling quenching water, and steam condensate obtained by condensing the tower top steam;

[0011] A heat user, used to pass the hot water to be heated into the heat pump unit and receive the heated hot water;

[0012] The heat pump unit is connected to the quenching water tower and is used to input the second cooling quenching water into the upper part of the quenching water tower and input the steam condensate into the kettle of the quenching water tower.

[0013] Preferably, the heat pump unit comprises a first heat pump and a second heat pump; the first heat pump is a first-type absorption heat pump, and the second heat pump is a second-type absorption heat pump;

[0014] The first heat pump is used to use the tower top steam of the process water stripping tower as a driving heat source, absorb the heat in the first cooling and quenching water and make part of the hot water to be heated absorb heat, so as to obtain the heated hot water, the third cooling and quenching water obtained by cooling the first cooling and quenching water, and the steam condensate obtained by condensing the tower top steam;

[0015] The second heat pump is used to use the third cooling and quenching water as a driving heat source, absorb heat in the third cooling and quenching water and make part of the hot water to be heated absorb heat, so as to obtain the heated hot water and the second cooling and quenching water obtained by cooling the third cooling and quenching water.

[0016] Further, the first heat pump includes a first regenerator, a first condenser, a first evaporator and a first absorber;

[0017] The first regenerator comprises a first driving heat source channel for inputting the tower top steam of the process water stripping tower; preferably, the first regenerator also comprises a second driving heat source channel for inputting a second driving heat source, preferably the second driving heat source is steam with a temperature of 120-150°C and a pressure of <0.4MpaG (e.g., S4 steam); the outlet of the first driving heat source channel is connected to the tower kettle of the quenching water tower;

[0018] The heat exchange tube inlet in the first evaporator is connected to the quench water user and is used to introduce part of the first cooling quench water from the quench water user;

[0019] The heat exchange tube inlet in the first absorber is connected to the hot water outlet to be heated of the heat user; the heat exchange tube outlet in the first absorber is connected to the heat exchange tube inlet in the first condenser, and the heat exchange tube outlet in the first condenser is connected to the heated hot water inlet of the heat user.

[0020] Further, the shell side outlet of the first condenser and the shell side inlet of the first evaporator are connected via a steam condensate pipeline, the shell side outlet of the first regenerator and the shell side inlet of the first absorber are connected via a refrigerant solution pipeline, and the steam condensate pipeline and the refrigerant solution pipeline are connected via a steam condensate branch pipe;

[0021] Preferably, a condensate pump is provided on the steam condensate branch pipe.

[0022] Further, the second heat pump includes a second regenerator, a second condenser, a second evaporator and a second absorber;

[0023] The inlet of the driving heat source channel of the second regenerator is connected to the outlet of the heat exchange tube in the first evaporator; the outlet of the driving heat source channel of the second regenerator is connected to the inlet of the heat exchange tube in the second evaporator, and the outlet of the heat exchange tube in the second evaporator is connected to the upper part of the quenching water tower;

[0024] The heat exchange tube inlet in the second absorber is connected to the hot water outlet to be heated of the heat user; the heat exchange tube outlet in the second absorber is connected to the hot water inlet after heating of the heat user.

[0025] Furthermore, the heated hot water inlet of the heat user is connected to a hot water inlet pipeline, and the heat exchange tube outlet in the first condenser and the heat exchange tube outlet of the second absorber are both connected to the hot water inlet pipeline.

[0026] Furthermore, a quenching water outlet for outputting the first temperature-reducing quenching water by the quenching water user is respectively connected to the middle of the quenching water tower and the heat pump unit.

[0027] The present invention also provides an energy-saving method for an ethylene quenching system, the energy-saving method comprising the following steps:

[0028] The cracked gas is passed into a quenching water tower for quenching and washing with quenching water, and the quenched cracked gas is obtained at the top of the tower;

[0029] The quenching water in the tower kettle of the quenching water tower is sent to the quenching water user for use, so as to obtain the first cooling quenching water with a lowered temperature;

[0030] The process water is sent to a process water stripping tower for stripping and oil removal with steam, and overhead steam is obtained at the top of the tower;

[0031] The top steam of the process water stripping tower and part of the first cooling quench water are sent to the heat pump unit to recover heat, and the hot water to be heated output by the heat user is sent to the heat pump unit to absorb heat, so that the hot water to be heated is heated to obtain heated hot water, the first cooling quench water is cooled to obtain second cooling quench water, and the top steam is condensed to obtain steam condensate;

[0032] The heated hot water is sent to the heat user for use, and the hot water to be heated is generated;

[0033] The second cooling quenching water is sent into the upper part of the quenching water tower, and the steam condensate is sent into the bottom of the quenching water tower;

[0034] Preferably, part of the first cooling quenching water is sent to the middle part of the quenching water tower;

[0035] Preferably, the energy-saving method is implemented by using the energy-saving system described in any one of claims 1-7.

[0036] Specifically, the process water is obtained by removing oil from part of the quenching water in the kettle of the quenching water tower.

[0037] In some embodiments, the temperature of the quenching water in the kettle of the quenching water tower is 80-85°C, the temperature of the first cooling quenching water is 50-60°C, and the temperature of the second cooling quenching water is ≤30°C.

[0038] The technical solution provided by the present invention has the following beneficial effects:

[0039] The energy-saving system of the ethylene quenching system proposed in the present invention can effectively improve the low-temperature heat utilization rate of the quenching water system, can recover the heat of the top steam of the process water stripping tower and the quenching water in the tower kettle of the quenching water tower, and at the same time can reduce the return tower temperature of the quenching water and the top steam of the process water stripping tower to a lower level. The lower quenching water return tower temperature can reduce the cracking gas temperature at the top of the quenching water tower to a lower level, thereby reducing the power consumption of the subsequent cracking gas compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Shown is a schematic diagram of an energy-saving system in one embodiment;

[0041] Figure 2 Shown Figure 1 Schematic diagram of the working principle of the first heat pump;

[0042] Figure 3 Shown Figure 1 Schematic diagram of the working principle of the second heat pump. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used.

[0045] The directional terms such as up, down, left, right, front, back, front, back, top, bottom, etc. mentioned or may be mentioned in this specification are defined relative to the structures shown in the drawings. They are relative concepts and may change accordingly according to different positions and different usage conditions. The terms "first", "second", "third", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0046] The present invention provides an energy-saving system for an ethylene quenching system, see Figure 1 The energy-saving system includes a quenching water tower, a process water stripping tower, a quenching water user, a heat pump unit and a heat user.

[0047] Among them, the quenching water tower is used to use quenching water to quench and wash the cracking gas in the ethylene device, and obtain the quenched cracking gas at the top of the tower.

[0048] The process water stripping tower is used to use steam to strip process water for oil removal, and output the overhead steam at the top of the tower. Specifically, the process water is obtained by preliminary oil removal of part of the quench water in the tower kettle of the quench water tower, wherein the preliminary oil removal is, for example, coalescing or filtering the part of the quench water to remove most of the heavy oil and light oil therein.

[0049] The quench water user is used to use the quench water output from the tower bottom of the quench water tower, and the temperature of the used quench water is reduced, thereby obtaining the first cooled quench water with reduced temperature. Among them, the quench water user is, for example, a propylene distillation tower reboiler, a raw material preheater, etc.

[0050] The heat pump unit is used to absorb the heat of the top steam of the process water stripping tower and absorb part of the heat of the first cooling and quenching water, and make the hot water to be heated absorb heat, thereby obtaining heated hot water obtained by heating the hot water to be heated, second cooling and quenching water obtained by cooling the first cooling and quenching water, and steam condensate obtained by condensing the top steam.

[0051] The heat user is used to pass the hot water to be heated to the heat pump unit and receive the heated hot water obtained in the heat pump unit. The heat user is specifically, for example, a deethanizer reboiler, a depropanizer reboiler, etc.

[0052] The heat pump unit is connected to the quenching water tower and is used to input the second cooling quenching water into the upper part of the quenching water tower and to input the steam condensate obtained by condensing the top steam of the process water stripping tower into the tower kettle of the quenching water tower.

[0053] Through the ingenious design of the energy-saving system of the present invention, the heat of the top steam of the process water stripping tower and part of the first cooling quench water can be further utilized, and the return temperature of the quench water and the return temperature of the top steam of the process water stripping tower can be further reduced.

[0054] In some preferred embodiments, the heat pump unit includes a first heat pump 1 and a second heat pump 2, wherein the first heat pump 1 is a first type absorption heat pump, and the second heat pump 2 is a second type absorption heat pump. The first type absorption heat pump and the second type absorption heat pump are well known to those skilled in the art, and will not be described in detail.

[0055] In the present invention, the first heat pump 1 is used to absorb the heat in the first cooling and quenching water and make part of the hot water to be heated absorb the heat, so as to obtain the heated hot water, the third cooling and quenching water obtained by cooling the first cooling and quenching water, and the steam condensate obtained by condensing the top steam. The second heat pump 2 is used to absorb the heat in the third cooling and quenching water and make part of the hot water to be heated absorb the heat, so as to obtain the heated hot water and the second cooling and quenching water obtained by cooling the third cooling and quenching water. The second cooling and quenching water is sent to the upper part of the quenching water tower (for example, to the top), the steam condensate obtained by condensing the top steam of the process water stripping tower is sent to the kettle of the quenching water tower, and the heated hot water is reused to the heat user. The temperature of the third cooling and quenching water is, for example, 40-50°C. The temperature of the second cooling and quenching water is, for example, ≤30°C.

[0056] In the present invention, the first heat pump is a first type absorption heat pump, specifically a first type lithium bromide absorption heat pump. The composition and working principle of the first type lithium bromide absorption heat pump are prior art in the art and will not be described in detail.

[0057] Specifically, the first heat pump 1 includes a first regenerator 11, a first condenser 12, a first evaporator 13 and a first absorber 14, which belongs to the conventional structure of the first type of absorption heat pump. In the preferred embodiment of the present invention, the first heat pump 1 is optimized to set two driving heat source channels based on the original single driving heat source channel of the first type of absorption heat pump in the prior art. Specifically, the first regenerator 11 includes a first driving heat source channel for inputting the top steam of the process water stripping tower, that is, the process water stripping tower is used as the driving heat source. The first regenerator also includes a second driving heat source channel for inputting the second driving heat source, preferably the second driving heat source is a steam with a temperature of 120-150°C and a pressure lower than 0.4MpaG, such as S4 steam; the outlet of the first driving heat source channel is connected to the kettle of the quenching water tower. Preferably, two driving heat source channels are set, and the heat load of the first regenerator 11 can be adjusted by the second driving heat source, the load and temperature of the first heat pump 1 can be flexibly adjusted, and the hot water outlet temperature of the first condenser 12 can be flexibly adjusted. The heat exchange tube inlet in the first evaporator 13 is connected to the quench water user, and is used to pass part of the first cooling quench water from the quench water user. The heat exchange tube inlet in the first absorber 14 is connected to the hot water outlet to be heated up of the heat user; the heat exchange tube outlet in the first absorber 14 is connected to the heat exchange tube inlet in the first condenser 12, and the heat exchange tube outlet in the first condenser 12 is connected to the hot water inlet after heating up of the heat user.

[0058] For ease of understanding, the working principle of the first heat pump 1 is described below. Figure 2 The top steam and S4 steam of the process water stripping tower are respectively introduced into the first and second driving heat source channels of the first regenerator 11. In the first regenerator 11, the dilute lithium bromide solution (refrigerant) is heated by the top steam and S4 steam of the process water stripping tower to become a concentrated lithium bromide solution, and water vapor is generated at the same time; the top steam of the process water stripping tower is condensed into steam condensate, and the S4 steam is also condensed into condensate. The heated lithium bromide concentrated solution continues to enter the first absorber 14, absorbs the water vapor from the first evaporator 13, obtains the lithium bromide dilute solution, and releases heat at the same time, which is absorbed by the hot water to be heated from the heat user; the lithium bromide dilute solution is circulated to the first regenerator 11 through the lithium bromide solution pump, and the heated hot water to be heated continues to enter the first condenser 12, and heat exchanges with the water vapor from the first regenerator 11 to continue to heat up, and obtain heated hot water; the water vapor is condensed in the first condenser 12 to obtain steam condensate, which is sent to the first evaporator 13 to exchange heat with the first cooling quench water from the quench water user to be heated again and vaporized into water vapor, and the first cooling quench water is cooled and cooled to obtain the third cooling quench water, and the water vapor continues to enter the first absorber 14. Through the above process, the heat of the top steam of the process water stripping tower and the first cooling quench water is fully utilized.

[0059] In some preferred embodiments, the first heat pump 1 of the present invention is additionally provided with a steam condensate branch pipe 5 relative to the existing first type absorption heat pump, see Figure 2 . Specifically, the shell outlet of the first condenser 12 and the shell inlet of the first evaporator 13 are connected through the steam condensate pipeline 3, so that the steam condensate obtained by condensing water vapor in the first condenser 12 enters the first evaporator 13; the shell outlet of the first regenerator 11 and the shell inlet of the first absorber 14 are connected through the refrigerant solution pipeline 4, so that the refrigerant solution (i.e., lithium bromide solution) in the first regenerator 11 is evaporated and concentrated and then enters the first absorber 14. In the preferred embodiment of the present invention, on this basis, a steam condensate branch pipe 5 is set between the steam condensate pipeline 3 and the refrigerant solution pipeline 4 for communication. In this preferred embodiment, on the basis of the existing first-class absorption heat pump, a steam condensate branch pipe 5 is added, which can flexibly adjust the concentration of the lithium bromide concentrated solution, so that it is not limited by the heat load of the first evaporator 13, and can avoid the adjustment limitation brought by the coupling of the heat load of the first regenerator 11 and the first evaporator 13 through the concentration of the lithium bromide solution. Preferably, a condensate pump is provided on the steam condensate branch pipe 5.

[0060] In some embodiments, the temperature of the heated hot water output by the first heat pump 1 can be adjusted between 80-110° C. The temperature of the heated hot water output by the second heat pump 2 can be adjusted between 70-80° C.

[0061] In the present invention, the second heat pump can directly adopt the conventional second type absorption heat pump in the art, specifically, for example, the second type lithium bromide absorption heat pump. The composition and working principle of the second type lithium bromide absorption heat pump are the prior art in the art, and will not be described in detail.

[0062] Specifically, the second heat pump 2 includes a second regenerator 23, a second condenser 21, a second evaporator 24 and a second absorber 22, which is a conventional structure of the second type absorption heat pump. In the present invention, the inlet of the driving heat source channel of the second regenerator 23 is connected to the outlet of the heat exchange tube in the first evaporator 13; the outlet of the driving heat source channel of the second regenerator 23 is connected to the inlet of the heat exchange tube in the second evaporator 24, and the outlet of the heat exchange tube in the second evaporator 24 is connected to the upper part of the quenching water tower. The inlet of the heat exchange tube in the second absorber 22 is connected to the outlet of the hot water to be heated of the heat user; the outlet of the heat exchange tube in the second absorber 22 is connected to the inlet of the heated hot water of the heat user. For ease of understanding, the working principle of the second heat pump is introduced as follows: the third cooling quenching water output from the first evaporator 13 of the first heat pump 1 is sent to the driving heat source channel of the second regenerator 23 as a driving heat source. In the second regenerator 23, the dilute lithium bromide solution is heated by the third cooling quenching water to become a concentrated lithium bromide solution and generate water vapor. At the same time, the third cooling quenching water is cooled. The cooled quenching water continues to enter the second evaporator 24 and is absorbed by the steam condensate obtained by condensing from the second condenser 21 (using circulating water to condense water vapor), so that the aforementioned quenching water continues to cool down to obtain the second cooling quenching water, and the steam condensate is heated and vaporized into water vapor. The water vapor enters the second absorber 22 and is absorbed by the lithium bromide concentrated solution from the second regenerator 23, releasing heat to obtain a dilute lithium bromide solution. The released heat is absorbed by the hot water to be heated from the heat user to obtain heated hot water. The aforementioned dilute lithium bromide solution is circulated to the second regenerator 23 again. Through the above process, the temperature of the second cooling quench water for returning to the upper part of the quench water tower can be reduced to a lower level, for example, between 20-30°C. The quench water is returned to the upper part of the quench water tower for spraying, and directly contacts with the cracked gas to cool it down. The temperature of the cracked gas at the top of the quench water tower can be reduced even further, which has the effect of reducing energy consumption for the operation of the compressor in the next process. This is something that the quench water tower of the ethylene plant in the prior art cannot do.

[0063] Furthermore, the heated hot water inlet of the heat user is connected to the hot water inlet pipeline 6, and the heat exchange tube outlet in the first condenser 12 and the heat exchange tube outlet of the second absorber 22 are both connected to the hot water inlet pipeline 6. That is, the heated hot water output by the first condenser 12 and the heated hot water output by the second absorber 22 are mixed and then enter the heat user. In this way, the temperature flexible adjustment function of the first heat pump 1 in the preferred embodiment can be fully utilized, which is beneficial to improve the availability of low-temperature heat in the second heat pump 2, and at the same time, it is beneficial to ensure the water supply temperature of hot water. Specifically, the heated hot water obtained by the first heat pump 1 and the second heat pump 2 are respectively combined and pressurized by the hot water circulation pump 7 before entering the heat user, thus forming a closed-loop hot water circulation system.

[0064] Furthermore, the quenching water outlet for outputting the first cooling quenching water by the quenching water user is respectively connected to the middle of the quenching water tower and the heat pump unit, that is, part of the first cooling quenching water circulates to the middle of the quenching water tower, and part is sent to the heat pump unit for heat recovery.

[0065] The present invention proposes an energy-saving system for an ethylene quenching system, which improves the low-temperature heat utilization rate of the quenching water system from two aspects. First, by changing the process flow of returning the steam from the top of the process water stripping tower to the quenching water tower in the traditional process flow to a high-temperature driving heat source as the first heat pump 1, the low-temperature heat in the quenching water is recovered. That is, the heat input of the quenching water tower is reduced, and the low-temperature heat is recovered. Secondly, by recycling the heat at a lower temperature of the quenching water in another stage of heat pump (the second heat pump 2), and at the same time reducing the return temperature of the quenching water to a lower temperature (for example, about 30°C), compared with the traditional ethylene device using circulating water cooling, which can be reduced to 35°C, in this scheme, the lower quenching water return tower temperature can reduce the cracking gas temperature at the top of the quenching water tower to a lower level, thereby reducing the power consumption of the subsequent cracking gas compressor. The scheme of the present invention can increase the heat temperature of the quenching water that cannot be used below 60°C through a primary heat pump, and then recover the heat and reduce the temperature through the primary heat pump, which can increase the traditional quenching water heat utilization rate from 40-50% to about 75%, and reduce the cooling utilities by about 50-60%, and also has the effect of reducing the power consumption of the subsequent cracking gas compressor.

[0066] The present invention also provides an energy-saving method for an ethylene quenching system, the energy-saving method comprising the following steps:

[0067] The cracked gas is passed into a quenching water tower for quenching and washing with quenching water, and the quenched cracked gas is obtained at the top of the tower;

[0068] The quenching water in the tower kettle of the quenching water tower is sent to the quenching water user for use, so as to obtain the first cooling quenching water with a lowered temperature;

[0069] The process water is sent to a process water stripping tower for stripping and oil removal with steam, and overhead steam is obtained at the top of the tower;

[0070] The tower top steam of the process water stripping tower and part of the first cooling quench water are sent to the heat pump unit to recover heat, and the hot water to be heated output by the heat user is sent to the heat pump unit to absorb heat, so that the heated hot water to be heated is heated to obtain heated hot water, the first cooling quench water is cooled to obtain the second cooling quench water, and the tower top steam is condensed to obtain steam condensate;

[0071] The heated hot water is sent to heat users for use, and hot water to be heated is generated;

[0072] The second cooling quench water is sent to the upper part of the quench water tower, and the steam condensate obtained by condensing the steam at the top of the process water stripping tower is sent to the bottom of the quench water tower.

[0073] The above energy-saving method can be implemented by using the above energy-saving system, and any part of the energy-saving method not described in detail can refer to the above description of the energy-saving system.

[0074] Furthermore, part of the first cooling and quenching water is sent to the middle of the quenching water tower for reflux, for example, the amount of the refluxed first cooling and quenching water is 40-60% of the total amount.

[0075] Specifically, the process water is obtained by removing oil from part of the quenching water in the bottom of the quenching water tower.

[0076] In some embodiments, the temperature of the quenching water in the kettle of the quenching water tower is 80-85°C, the temperature of the first cooling quenching water is 50-60°C, and the temperature of the second cooling quenching water is ≤30°C.

[0077] Through the energy-saving system and energy-saving process proposed by the present invention, first, the heat of the quenching water can be recovered, and the heat utilization rate of the quenching water system can be increased from less than 50% to more than 70%. Calculated by a set of one million tons of ethylene equipment, more than 20MW of low-temperature heat can be directly reused. After two three-stage heat recovery, the temperature of the quenching water can be reduced to 30°C or even lower. Compared with ordinary ethylene equipment, the gas phase temperature at the top of the quenching water tower can be reduced, thereby reducing the energy consumption of the ethylene cracking gas compressor. Secondly, the steam at the top of the process water stripping tower is input into the heat pump system, which reduces the heat input of the stripping steam in the original process flow, and can also reduce the heat input of the quenching water tower. The method of the present invention breaks through the lowest temperature (about 35°C) that the quenching water can be cooled to by using circulating water in the traditional ethylene process. The solution of the present invention can further reduce the cracking gas temperature by 3-5°C on this basis, and can save the power consumption of the downstream cracking gas compressor.

[0078] The energy-saving system and energy-saving method of the present invention are exemplarily described below through application examples:

[0079] Example 1

[0080] An ethylene plant uses light hydrocarbon raw materials (ethane, propane, butane, LPG) as raw materials to produce ethylene. The quench water temperature of the quench water tower is 80℃, and the circulation volume is 3000t / h. Before the transformation, the quench water from the tower bottom enters the quench water circulation pump to increase the pressure to 0.9MpaG, and the quench water enters a series of quench water users to supply low-temperature heat, and the quench water temperature of the quench water users is reduced to 55℃. After leaving the quench water users, 1600t / h of quench water returns to the middle of the quench water tower, and 1400t / h of quench water is cooled to 35℃ by circulating water, and then returns to the top of the quench water tower. During the cooling process of the quench water by circulating water, the heat taken away by the circulating water is 33MW, and the circulating water used is about 2500-3000t / h. 8t / h steam is used for stripping at the top of the process water stripping tower, and about 8t / h of oil-containing steam after stripping returns to the bottom of the quench water tower (i.e., the tower bottom). The 105℃ overhead steam from the process water stripping tower is directly fed into the kettle of the quenching water tower, inputting about 4MW of high-temperature heat into the quenching water tower.

[0081] The above existing energy-saving process is transformed by adopting the scheme of the present invention (the energy-saving method and energy-saving system adopted hereinafter can refer to the attached Figure 1-3 , where details are not described in detail, please refer to the above description of the energy-saving method and energy-saving system of the present invention, and no further description will be given).

[0082] A first heat pump 1 and a second heat pump 2 are added, wherein the first heat pump 1 is a first-type lithium bromide absorption heat pump, and the second heat pump 2 is a second-type lithium bromide absorption heat pump.

[0083] 1400t / h of the first cooled quench water of 55℃ (the original process of this quench water is to enter the circulating water cooler, cool to 35℃ and then return to the tower) is sent to the first evaporator 13 of the first heat pump 1. The first regenerator 11 of the first heat pump 1 uses the top steam of the process water stripping tower and S4 steam as the driving heat source.

[0084] The first cooling quenching water is cooled to 50°C after passing through the first evaporator 13, i.e., the third cooling quenching water, and then flows through the second regenerator 23 and the second evaporator 24 of the second heat pump 2. After the quenching water is further cooled in the second heat pump 2, the temperature of the second cooling quenching water output in the second evaporator 24 is 30°C, and the second cooling quenching water of this temperature is returned to the top of the quenching water tower.

[0085] The low-temperature heat of the above-mentioned 55℃→30℃ quench water is 42MW, which is used by the heat pump unit. After passing through the first heat pump 1, the quench water outlet temperature (i.e., the temperature of the third cooling quench water) is 50℃, and the output hot water temperature (i.e., the hot water after heating) is 80℃. The first regenerator 11 in the first heat pump 1 uses 8t / h of steam from the top of the stripping tower as a high-temperature driving heat source, and at the same time adds 8t / h of S4 steam. The COP of the first heat pump 1 is between 1.5-2.5. The quench water passing through the first evaporator 13 of the first heat pump 1 is recovered in the second heat pump 2, and the quench water temperature out of the second heat pump 2 (i.e., the temperature of the second cooling quench water) is reduced to 30℃, and returns to the quench water tower, and the top cracking gas temperature is reduced from the original 38℃ to 35℃.

[0086] The hot water produced by the first heat pump 1 and the second heat pump 2 has a temperature of 80°C and a flow rate of 1000 t / h, and enters the heat users (specifically low-temperature heat users) to supply heat to such low-temperature heat users. The hot water (i.e. the hot water to be heated) leaving these heat users has a temperature of 55°C and returns to the first heat pump 1 and the second heat pump 2 of the heat pump unit.

[0087] After the transformation, the quench water system recovered a total of 32MW of heat, equivalent to 16t / h of low-pressure steam, saving 1,500t / h of circulating water flow. According to the settlement price of the enterprise's public works, low-pressure steam is 180 yuan / ton, circulating water is 0.2 yuan / ton, and the annual device operation time is 8,000h. After the transformation, the energy saving benefit is 44 million, the investment cost is 12 million, and the investment payback period is 3 months.

[0088] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. An energy-saving system for an ethylene quenching system, characterized in that: The energy-saving system comprises: A quench water tower, used to quench and wash the cracked gas with quench water and obtain the quenched cracked gas at the top of the tower; A process water stripping tower, used to use steam to strip the process water to remove oil, and output overhead steam at the top of the tower; A quenching water user, which is used to use the quenching water output from the kettle of the quenching water tower and obtain first cooling quenching water with a lowered temperature; a heat pump unit, for absorbing heat from the tower top steam of the process water stripping tower and absorbing part of the heat from the first cooling quenching water, and allowing the hot water to be heated to absorb the heat, so as to obtain heated hot water obtained by heating the hot water to be heated, second cooling quenching water obtained by cooling the first cooling quenching water, and steam condensate obtained by condensing the tower top steam; A heat user, used to pass the hot water to be heated into the heat pump unit and receive the heated hot water; The heat pump unit is connected to the quenching water tower and is used to input the second cooling quenching water into the upper part of the quenching water tower and input the steam condensate into the kettle of the quenching water tower.

2. The energy-saving system according to claim 1, characterized in that: The heat pump unit comprises a first heat pump and a second heat pump; the first heat pump is a first-type absorption heat pump, and the second heat pump is a second-type absorption heat pump; The first heat pump is used to use the tower top steam of the process water stripping tower as a driving heat source, absorb the heat in the first cooling and quenching water and make part of the hot water to be heated absorb heat, so as to obtain the heated hot water, the third cooling and quenching water obtained by cooling the first cooling and quenching water, and the steam condensate obtained by condensing the tower top steam; The second heat pump is used to use the third cooling and quenching water as a driving heat source, absorb heat in the third cooling and quenching water and make part of the hot water to be heated absorb heat, so as to obtain the heated hot water and the second cooling and quenching water obtained by cooling the third cooling and quenching water.

3. The energy-saving system according to claim 2, characterized in that: The first heat pump includes a first regenerator, a first condenser, a first evaporator and a first absorber; The first regenerator comprises a first driving heat source channel for inputting the top steam of the process water stripping tower; preferably, the first regenerator also comprises a second driving heat source channel for inputting a second driving heat source, preferably the second driving heat source is steam with a temperature of 120-150°C and a pressure of <0.4MpaG; The outlet of the first driving heat source channel is connected to the kettle of the quenching water tower; The heat exchange tube inlet in the first evaporator is connected to the quench water user for introducing part of the first cooling quench water from the quench water user; The heat exchange tube inlet in the first absorber is connected to the hot water outlet to be heated of the heat user; the heat exchange tube outlet in the first absorber is connected to the heat exchange tube inlet in the first condenser, and the heat exchange tube outlet in the first condenser is connected to the heated hot water inlet of the heat user.

4. The energy-saving system according to claim 3, characterized in that: The shell side outlet of the first condenser and the shell side inlet of the first evaporator are connected through a steam condensate pipeline, the shell side outlet of the first regenerator and the shell side inlet of the first absorber are connected through a refrigerant solution pipeline, and the steam condensate pipeline and the refrigerant solution pipeline are connected through a steam condensate branch pipe; Preferably, a condensate pump is provided on the steam condensate branch pipe.

5. The energy-saving system according to claim 3, characterized in that: The second heat pump includes a second regenerator, a second condenser, a second evaporator, and a second absorber; The inlet of the driving heat source channel of the second regenerator is connected to the outlet of the heat exchange tube in the first evaporator; the outlet of the driving heat source channel of the second regenerator is connected to the inlet of the heat exchange tube in the second evaporator, and the outlet of the heat exchange tube in the second evaporator is connected to the upper part of the quenching water tower; The heat exchange tube inlet in the second absorber is connected to the hot water outlet to be heated of the heat user; the heat exchange tube outlet in the second absorber is connected to the hot water inlet after heating of the heat user.

6. The energy-saving system according to claim 5, characterized in that: The heated hot water inlet of the heat user is connected to a hot water inlet pipeline, and the heat exchange tube outlet in the first condenser and the heat exchange tube outlet of the second absorber are both in communication with the hot water inlet pipeline.

7. The energy-saving system according to any one of claims 1 to 6, characterized in that: The quenching water outlet of the quenching water user for outputting the first temperature-lowering quenching water is respectively connected to the middle of the quenching water tower and the heat pump unit.

8. An energy-saving method for an ethylene quenching system, characterized in that: The energy-saving method comprises the following steps: The cracked gas is passed into a quenching water tower for quenching and washing with quenching water, and the quenched cracked gas is obtained at the top of the tower; The quenching water in the tower kettle of the quenching water tower is sent to the quenching water user for use, so as to obtain the first cooling quenching water with a lowered temperature; The process water is sent to a process water stripping tower for stripping and oil removal with steam, and overhead steam is obtained at the top of the tower; The top steam of the process water stripping tower and part of the first cooling quench water are sent to the heat pump unit to recover heat, and the hot water to be heated output by the heat user is sent to the heat pump unit to absorb heat, so that the hot water to be heated is heated to obtain heated hot water, the first cooling quench water is cooled to obtain second cooling quench water, and the top steam is condensed to obtain steam condensate; The heated hot water is sent to the heat user for use, and the hot water to be heated is generated; The second cooling quenching water is sent into the upper part of the quenching water tower, and the steam condensate is sent into the bottom of the quenching water tower; Preferably, part of the first cooling quenching water is sent to the middle part of the quenching water tower; Preferably, the energy-saving method is implemented by using the energy-saving system described in any one of claims 1-7.

9. The energy saving method according to claim 8, characterized in that: The process water is obtained by removing oil from part of the quenching water in the kettle of the quenching water tower.

10. The energy saving method according to claim 8, characterized in that: The temperature of the quenching water in the kettle of the quenching water tower is 80-85°C, the temperature of the first cooling quenching water is 50-60°C, and the temperature of the second cooling quenching water is ≤30°C.

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