A system and method for recovering low-pressure steam produced as a byproduct in the production process of ethylene glycol

Abstract

The present invention belongs to the technical field of steam utilization, and relates to a system and method for recycling low-pressure steam produced as a byproduct in the production process of ethylene glycol, including: S1, establishing a low-pressure steam recycling system; S2, setting process parameters; S3, recycling low-pressure steam: adjusting the flow rates of two low-pressure steams in the low-pressure steam recycling system according to the set process parameters, and then passing the low-pressure steam into the low-pressure steam recycling system to complete the recycling and secondary utilization of the low-pressure steam. The present invention realizes the dual recycling and utilization of the waste and heat of the discharged low-pressure steam by constructing a low-pressure steam recycling system, effectively reduces the steam venting rate, realizes the secondary utilization of the low-pressure steam, and achieves the purpose of energy saving, emission reduction and consumption reduction.

Description

Technical Field

[0001] The invention belongs to the technical field of steam utilization, and relates to a system and method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol. Background Art

[0002] Ethylene glycol is an important chemical raw material. In the production process of ethylene glycol from synthesis gas, the carbonylation reaction of the dimethyl oxalate DMO synthesis process is a strong continuous exothermic process. The synthesis reactor of the carbonylation reaction generally adopts a tube-type fixed bed reactor, and the catalyst is loaded in the tube. The shell-side medium is the drum feed water; the boiler feed water enters the drum through the pipe network, and then enters the shell side of the tube-type fixed bed reactor through the drum feed water pump for forced circulation. The heat generated by the carbonylation reaction is removed by heating the drum feed water in the shell side. In this process, low-pressure steam with a pressure of 0.06MPaG to 0.1MPaG will be produced as a by-product. Since the low-pressure steam has a low pressure and low utilization value, there are two ways to deal with these low-pressure steam in actual production:

[0003] (1) The first treatment method: the low-pressure steam from the steam drum is directly discharged on site through the external exhaust pipe, which not only wastes resources but also causes thermal pollution to the environment;

[0004] (2) The second treatment method: The low-pressure steam coming out of the steam drum first enters the cooler for cooling to obtain condensate, which is then transported to the condensate pipeline network for reuse as cooling water; however, this treatment method still cannot effectively utilize the heat of the low-pressure steam.

[0005] In summary, the existing low-pressure steam processing methods cannot recycle the heat of the low-pressure steam, resulting in serious energy waste. Summary of the invention

[0006] In view of the technical problem that the heat of low-pressure steam cannot be recovered and utilized in existing low-pressure steam treatment, resulting in serious energy waste, the present invention provides a system and method for recovering low-pressure steam produced as a by-product in the production process of ethylene glycol.

[0007] The present invention constructs a low-pressure steam recovery and utilization system to divide the by-product low-pressure steam into two paths. The low-pressure steam in the first path is pressurized to form low-pressure steam, and the low-pressure steam in the second path is subjected to heat exchange and heat recovery to form condensate which is returned to the steam drum, thereby realizing the dual recovery and utilization of the discharged low-pressure steam waste and heat, effectively reducing the steam venting rate, realizing the secondary utilization of the low-pressure steam, and achieving the purpose of energy saving, emission reduction and consumption reduction.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for recovering low-pressure steam produced as a byproduct in the production of ethylene glycol comprises the following steps:

[0010] S1. Establish a low-pressure steam recovery and utilization system

[0011] The low-pressure steam produced as a byproduct of the steam drum in the ethylene glycol production system is divided into two paths. The first path of low-pressure steam is pressurized to form low-pressure steam, and the second path of low-pressure steam is heat-exchanged to recover heat and then forms condensate to return to the steam drum, thus completing the construction of a low-pressure steam recovery and utilization system; the pressure of the low-pressure steam is 0.06MPaG to 0.1MPaG;

[0012] S2. Set process parameters

[0013] The flow rates of the two low-pressure steam lines are set according to the needs of low-pressure steam grade users, the pressure of the low-pressure steam produced as a byproduct of the steam drum, and the discharge volume;

[0014] S3, low pressure steam recovery and utilization

[0015] According to the process parameters set in step S2, the flow rates and boosting parameters of the two low-pressure steam in the low-pressure steam recovery system are adjusted, and then the low-pressure steam is introduced into the low-pressure steam recovery and utilization system of step S1 to complete the recovery and secondary utilization of the low-pressure steam.

[0016] It is further defined that in step S2, the discharge volume of low-pressure steam is 60 t / h and the temperature is 110°C to 120°C; the pressure of the low-pressure steam grade required by users is 0.15 MPaG to 0.22 MPaG and the temperature is 130°C to 140°C.

[0017] It is further defined that in step S2, the flow ratio of the first low-pressure steam and the second low-pressure steam is (1.5-2.5):1.

[0018] Further defined, the specific process of step S3 is:

[0019] The second low-pressure steam exchanges heat with the heat exchange equipment in the low-pressure steam recovery system. The heat of the low-pressure steam is absorbed to form gas-liquid condensate for gas-liquid separation. The separated condensate is all recycled to the input end of the steam drum.

[0020] The separated steam enters the booster equipment together with the first low-pressure steam for compression. The pressure and temperature of the low-pressure steam are increased to form low-pressure steam which is transported to low-pressure steam grade users.

[0021] It is further defined that the low-pressure steam also includes the following process: the low-pressure steam also enters the heating equipment to recover the heat energy of the low-pressure steam, and then the low-pressure steam forms gas-liquid condensate, which is all sent to the condensate pipeline network for reuse.

[0022] It is further defined that in step S1, the low-pressure steam also includes the following processing methods:

[0023] The separated steam enters the air cooling device together with the first low-pressure steam for cooling, and the formed condensate returns to the input end of the steam drum;

[0024] The separated steam is compressed with the first low-pressure steam and the separated steam is cooled together with the first low-pressure steam. Either of the two treatment methods is selected.

[0025] A system for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol, which realizes the method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol. The system for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol comprises a steam drum, a low-pressure steam compressor, a low-pressure steam pipeline network, a condensate pipeline network, a heater, a synthetic cycle gas preheater and a low-pressure steam condensate separator; the output end of the steam drum is connected to the condensate pipeline network via the low-pressure steam compressor and the heater in sequence; the low-pressure steam pipeline network is connected to the low-pressure steam compressor; the output end of the steam drum is also connected to the input end of the steam drum and the low-pressure steam compressor via the synthetic cycle gas preheater and the low-pressure steam condensate separator.

[0026] It is further defined that the heater includes a synthetic cycle gas heater and a nitric acid reduction system heater connected in parallel; one end before parallel connection is connected to a low-pressure steam compressor, and one end after parallel connection is connected to a condensate pipe network.

[0027] It is further defined that a fourth gate valve is arranged between the low-pressure steam pipeline and the low-pressure steam compressor; a first gate valve is arranged between the output end of the steam drum and the low-pressure steam compressor; the low-pressure steam condensate separator is connected to the pipeline between the first gate valve and the low-pressure steam compressor; a fifth gate valve is arranged between the output end of the steam drum and the synthetic cycle gas preheater; and the fifth gate valve is arranged in parallel with the first gate valve.

[0028] It is further defined that the system for recovering and utilizing the low-pressure steam produced as a by-product in the ethylene glycol production process also includes a low-pressure steam air cooler, a low-pressure steam condensate buffer tank, a second gate valve and a third gate valve; one end of the low-pressure steam air cooler is connected to the first gate valve, the low-pressure steam condensate separator tank and the third gate valve respectively after the second gate valve, and the third gate valve is also connected to the low-pressure steam compressor; the other end of the low-pressure steam air cooler is connected to the input end of the steam drum via the low-pressure steam condensate buffer tank.

[0029] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0030] 1. The present invention constructs a low-pressure steam recovery and utilization system to divide the low-pressure steam produced as a by-product of the steam drum in the ethylene glycol production system into two paths. The low-pressure steam in the first path is pressurized and heated to form low-pressure steam, and the low-pressure steam in the second path is subjected to heat exchange to recover heat to form condensate and return to the steam drum, thereby realizing the dual recovery and utilization of the discharge of the low-pressure steam and the heat, effectively reducing the steam venting rate, realizing the secondary utilization of the low-pressure steam, and achieving the purpose of energy saving, emission reduction and consumption reduction.

[0031] 2. The present invention sets the flow rates of the two low-pressure steam paths according to the needs of low-pressure steam grade users, the pressure of the low-pressure steam produced as a by-product of the steam drum, and the discharge volume; and in actual processing, the flow rates of the two low-pressure steam paths are adjusted according to the set parameters. Preferably, the flow rate ratio of the first low-pressure steam path to the second low-pressure steam path is (1.5-2.5):1, which not only realizes the maximum recovery and utilization of the low-pressure steam, but also ensures the stability of the system pressure operation.

[0032] 3. In the present invention, a variety of processing methods are implemented for the low-pressure steam after pressurization and temperature increase, specifically heating, heat exchange and direct output, so as to recover the heat of the steam to the maximum extent and improve the utilization rate of heat.

[0033] 4. The low-pressure steam recovery and utilization system of the present invention, by setting a steam drum and a low-pressure steam compressor, pressurizes and heats the low-pressure steam and then transports it to the low-pressure steam network for direct secondary utilization; or enters the heater to fully utilize the heat and then enters the condensate network for utilization. It can be seen that the present invention can recover the low-pressure steam produced as a by-product in the production process of ethylene glycol and realize secondary utilization, thereby achieving the purpose of energy saving, emission reduction and consumption reduction.

[0034] 5. In the low-pressure steam recovery and utilization system of the present invention, the heater includes a synthetic cycle gas heater and a nitric acid reduction system heater connected in parallel, and the low-pressure steam generated in the production of ethylene glycol is pressurized and heated and reused in the intermediate process of ethylene glycol production to achieve heat recovery, with good recovery and utilization effect, which can effectively reduce the steam venting rate, reduce the energy consumption required for ethylene glycol production, and save costs. By setting a synthetic cycle gas preheater, the heat of the low-pressure steam is firstly recovered and utilized; and then the low-pressure steam after cooling is sent to the pressurization or air cooling treatment, so as to further improve the utilization rate of heat.

[0035] 6. A low-pressure steam air cooler is also provided in the low-pressure steam recovery and utilization system of the present invention. The steam condensate formed after the by-product low-pressure steam is air-cooled is then returned to the steam drum by gravity, which not only realizes the utilization of low-pressure steam, but also the low-pressure steam air cooler serves as a backup to ensure the stability of the system. In addition, a low-pressure steam condensate buffer tank is also provided to start the buffering effect on the formed steam condensate. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a system for recovering and utilizing byproduct low-pressure steam provided in Example 1;

[0037] Figure 2 A schematic diagram of a byproduct low-pressure steam recovery and utilization system provided in Example 2;

[0038] in:

[0039] E101-synthesis cycle gas preheater; E102-synthesis cycle gas heater; E103-nitric acid reduction system heater; E104-low-pressure steam air cooler; V101-steam drum; V102-low-pressure steam condensate separator tank; V103-low-pressure steam condensate buffer tank; C101-low-pressure steam compressor; Z001-first gate valve; Z002-second gate valve; Z003-third gate valve; Z004-fourth gate valve; Z005-fifth gate valve. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0041] Example 1

[0042] See also Figure 1 This embodiment provides a system for recycling low-pressure steam produced as a byproduct in the production process of ethylene glycol, including a steam drum V101, a low-pressure steam compressor C101, a low-pressure steam pipe network, a condensate pipe network and a heater. The output end of the steam drum V101 is connected to the condensate pipe network through the low-pressure steam compressor C101 and the heater; the low-pressure steam pipe network is connected to the low-pressure steam compressor C101.

[0043] In this embodiment, the low-pressure steam network is a steam network with a pressure of 0.15-0.22 MPaG; the condensate network is a condensate network with a pressure of 0.15-0.22 MPaG. When in use, according to actual needs, the low-pressure steam is pressurized to the pressure required by the secondary steam through the low-pressure steam compressor C101.

[0044] Preferably, the low-pressure steam pipeline network is a steam pipeline network with a pressure within 0.2 MPaG; and the condensate pipeline network is a condensate pipeline network with a pressure within 0.2 MPaG.

[0045] In this embodiment, the heater includes a synthetic cycle gas heater E102 and a nitric acid reduction system heater E103 connected in parallel; one end before parallel connection is connected to the low-pressure steam compressor C101, and one end after parallel connection is connected to the condensate pipe network.

[0046] The synthesis circulating gas heater E102 and the nitric acid reduction system heater E103 are both heating devices in the ethylene glycol production system. The low-pressure steam generated in the dimethyl oxalate (DMO) synthesis step of ethylene glycol production is pressurized and heated and reused in the intermediate process of ethylene glycol production, realizing heat recycling, which can effectively reduce the steam venting rate, reduce the energy consumption required for ethylene glycol production, and save costs.

[0047] This embodiment provides a system for recovering and utilizing by-product low-pressure steam in the ethylene glycol production process, which also includes a synthetic cycle gas preheater E101; the output end of the steam drum V101 is connected to the input end of the steam drum V101 and the low-pressure steam compressor C101 respectively after passing through the synthetic cycle gas preheater E101.

[0048] In this embodiment, the system for recovering and utilizing the low-pressure steam produced as a by-product in the production process of ethylene glycol also includes a low-pressure steam condensate separator V102; the synthetic cycle gas preheater E101 is connected to the input end of the steam drum V101 and the low-pressure steam compressor C101 respectively after passing through the low-pressure steam condensate separator V102.

[0049] In this embodiment, a first gate valve Z001 is provided between the output end of the steam drum V101 and the low-pressure steam compressor C101; the low-pressure steam condensate separator V102 is connected to the pipeline between the first gate valve Z001 and the low-pressure steam compressor C101.

[0050] In this embodiment, a fifth gate valve Z005 is provided between the output end of the steam drum V101 and the synthesis cycle gas preheater E101; the fifth gate valve Z005 is provided in parallel with the first gate valve Z001.

[0051] In this embodiment, the synthetic cycle gas preheater E101 is a preheating device in the ethylene glycol production system. The low-pressure steam generated in the dimethyl oxalate DMO synthesis step of ethylene glycol production is pressurized and reused in the intermediate process of ethylene glycol production, thereby realizing heat recycling, effectively reducing the steam venting rate, reducing the energy consumption required for ethylene glycol production, and saving costs.

[0052] In this embodiment, the system for recovering and utilizing the by-product low-pressure steam in the ethylene glycol production process also includes a fourth gate valve Z004 arranged between the low-pressure steam network and the low-pressure steam compressor C101, and the fourth gate valve Z004 is used to control the opening and closing of the 0.2MpaG steam entering the low-pressure steam network.

[0053] Specifically, the by-product low-pressure steam is discharged from the output end (steam outlet end) of the drum V101; one end of the low-pressure steam compressor C101 is the steam inlet end, and the other end of the low-pressure steam compressor C101 is the steam outlet end, and the output end (steam outlet end) of the drum V101 is divided into two branches; the first branch is connected to one end (i.e., the steam inlet end) of the synthesis cycle gas preheater E101 through the fifth gate valve Z005, and the second branch is connected to the steam outlet end at the top of the low-pressure steam condensate separator V102 and the steam inlet end of the low-pressure steam compressor C101 after passing through the first gate valve Z001; the other end (i.e., the liquid outlet end) of the synthesis cycle gas preheater E101 is connected to the liquid inlet end of the low-pressure steam condensate separator V102, and the liquid outlet end at the bottom of the low-pressure steam condensate separator V102 is connected to the input end (i.e., the liquid inlet end) of the drum V101. The steam outlet end of the low-pressure steam compressor C101 is divided into three branches. The first branch is connected to the steam inlet end of the synthetic cycle gas heater E102, and the liquid outlet end of the synthetic cycle gas heater E102 is connected to the condensate pipeline network (0.2Mpa condensate pipeline network); the second branch is connected to the steam inlet end of the nitric acid reduction system heater E103, and the liquid outlet end of the nitric acid reduction system heater E103 is connected to the condensate pipeline network (0.2Mpa condensate pipeline network); the third branch is connected to the low-pressure steam pipeline network (0.2MpaG steam pipeline network).

[0054] The working process of the system for recovering and utilizing the by-product low-pressure steam in the ethylene glycol production process provided in this embodiment is as follows:

[0055] Open the first gate valve Z001 and the fifth gate valve Z005 so that the low-pressure steam coming out of the output end (steam outlet end) of the steam drum V101 is divided into two parts and processed through two paths.

[0056] The first part of the low-pressure steam enters the synthesis cycle gas preheater E101 through the fifth gate valve Z005, and enters the shell side of the synthesis cycle gas preheater E101 to recover the heat energy of the low-pressure steam, and then the formed gas-liquid condensate flows by gravity to the low-pressure steam condensate separator V102 for separation, and the separated condensate flows out from the bottom of the low-pressure steam condensate separator V102 and is all recycled to the input end of the steam drum V101; the separated steam flows out from the top of the low-pressure steam condensate separator V102; the second part of the low-pressure steam passes through the first gate valve Z001 and is mixed with the steam flowing out from the top of the low-pressure steam condensate separator V102, and then enters the low-pressure steam compressor C101 together for pressurization and temperature increase to obtain 0.2MPaG low-pressure steam. Afterwards, the 0.2MPaG low-pressure steam is divided into three routes: the first route goes to the shell side of the synthesis circulating gas heater E102 to recover heat energy, and then the formed gas-liquid condensate is sent to the condensate network for reuse; the second route goes to the shell side of the nitric acid reduction system heater E103 to recover heat energy, and then the formed gas-liquid condensate is sent to the condensate network for reuse; the third route all enters the low-pressure steam network for reuse, and outputs 0.2MPaG low-pressure steam to the outside through the low-pressure steam network. The 0.2MPaG low-pressure steam can be supplied to the ethylene glycol production system, and can also be transported to other devices that require this level of low-pressure steam, thereby realizing heat recovery and utilization of low-pressure steam, avoiding waste of resources, and reducing the consumption of heat energy in ethylene glycol production, saving costs.

[0057] Example 2

[0058] See also Figure 2 On the basis of Example 1, the system for recovering and utilizing the by-product low-pressure steam in the ethylene glycol production process provided in this embodiment further includes a low-pressure steam air cooler E104; one end of the low-pressure steam air cooler E104 is respectively connected to the first gate valve Z001, the low-pressure steam condensate separator V102 and the low-pressure steam compressor C101; the other end of the low-pressure steam air cooler E104 is connected to the input end of the steam drum V101.

[0059] In this embodiment, the system for recovering and utilizing the by-product low-pressure steam in the ethylene glycol production process further includes a low-pressure steam condensate buffer tank V103 disposed between the low-pressure steam air cooler E104 and the input end of the steam drum V101.

[0060] In this embodiment, the system for recovering and utilizing the low-pressure steam produced as a by-product in the production process of ethylene glycol also includes a second gate valve Z002 and a third gate valve Z003; the low-pressure steam air cooler E104 is connected to the low-pressure steam compressor C101 via the second gate valve Z002 and the third gate valve Z003 in sequence; the second gate valve Z002 is also connected to the low-pressure steam condensate buffer tank V103 and the first gate valve Z001 and the third gate valve Z003.

[0061] The sealed steam pipeline network is a 0.5MpaG steam pipeline network; the low-pressure steam pipeline network is a 0.2MpaG steam pipeline network; and the condensate pipeline network is a 0.2MpaG condensate pipeline network.

[0062] In this embodiment, the low-pressure steam air cooler E104 is used as a backup solution. When the low-pressure steam compressor C101 fails and shuts down, or the amount of 0.2MpaG steam obtained is large and needs to be balanced with the 0.2MPaG grade steam network, the third gate valve Z003 is closed and the second gate valve Z002 is opened to switch to the low-pressure steam air cooler E104 for processing.

[0063] The working process of the system for recovering and utilizing the by-product low-pressure steam in the ethylene glycol production process provided in this embodiment is as follows:

[0064] Part of the low-pressure steam passes through the first gate valve Z001 and is mixed with the steam flowing out from the top of the low-pressure steam condensate separator V102. It is then sent to the low-pressure steam air cooler E104 through the second gate valve Z002. The by-produced low-pressure steam is air-cooled to form steam condensate. The steam condensate all flows by gravity to the low-pressure steam condensate buffer tank V103, and then all flows by gravity to the input end of the steam drum V101 for reuse.

[0065] In the present embodiment, in the dimethyl oxalate DMO synthesis process of the ethylene glycol production system, as the carbonylation reaction time proceeds, the activity of the catalyst gradually decreases, and the steam drum V101 needs to be pressurized. Therefore, in order to ensure that the steam condensate after air cooling of the low-pressure steam air cooler E104 can smoothly flow back to the input end (liquid inlet end) of the steam drum V101, a low-pressure steam sealing device and a liquid seal are respectively provided on the low-pressure steam condensate buffer tank V103 to maintain the back pressure of the ethylene glycol production system and ensure the stability of the system operation.

[0066] Preferably, the side of the low-pressure steam condensate buffer tank V103 is connected to a sealed steam network (0.5MPaG low-pressure steam network) to perform low-pressure sealing on the low-pressure steam condensate buffer tank V103, so that the steam condensate after air cooling by the low-pressure steam air cooler E104 can smoothly flow back to the input end of the drum V101. Preferably, a U-shaped bend pipeline is provided at the liquid outlet at the bottom of the low-pressure steam condensate buffer tank V103 to perform bottom liquid sealing. The sealed steam network and the U-shaped bend pipeline ensure the pressure balance and stable operation of the system.

[0067] Example 3

[0068] This embodiment provides a method for recovering low-pressure steam produced as a byproduct in the production process of ethylene glycol, which comprises the following steps:

[0069] S1. Establish a low-pressure steam recovery system

[0070] According to the operation process of the ethylene glycol production system, the low-pressure steam produced as a byproduct of the drum is divided into two paths. The first path of low-pressure steam is pressurized and heated to form low-pressure steam, and the second path of low-pressure steam is heat-exchanged and heat-recovered to form condensate and return to the drum, thus completing the construction of the low-pressure steam recovery system.

[0071] S2. Set process parameters

[0072] The flow rates of the two low-pressure steam lines are set according to the needs of low-pressure steam grade users, the pressure of the low-pressure steam produced as a byproduct of the steam drum, and the discharge volume;

[0073] S3, low pressure steam recovery and utilization

[0074] According to the process parameters set in step S2, the low-pressure steam enters the low-pressure steam recovery system of step S1 to complete the recovery and secondary utilization of the low-pressure steam.

[0075] In this embodiment, the discharge capacity of low-pressure steam is 60t / h, the temperature is 110℃~120℃, and the pressure is 0.06MPaG~0.1MPaG; the pressure of the low-pressure steam grade required by users is 0.15MPaG~0.22MPaG, and the temperature is 130℃~140℃.

[0076] In step S2, the flow ratio of the first low-pressure steam to the second low-pressure steam is (1.5-2.5): 1. Preferably, the flow ratio of the first low-pressure steam to the second low-pressure steam is 2:1.

[0077] The specific process of step S3 is: the second low-pressure steam exchanges heat with the heat exchange equipment in the low-pressure steam recovery system, and the heat of the low-pressure steam is absorbed to form a gas-liquid condensate for gas-liquid separation, and the separated condensate is all recycled to the input end of the steam drum V101; the separated steam enters the boosting equipment together with the first low-pressure steam for compression, and the pressure and temperature of the low-pressure steam are increased to form low-pressure steam and transported to the low-pressure steam grade users.

[0078] The low-pressure steam also includes the following processes: the low-pressure steam also enters the heating equipment to recover the heat energy of the low-pressure steam; then the low-pressure steam forms gas-liquid condensate, which is all sent to the condensate pipeline network for reuse.

[0079] Preferably, there are two heating devices, which will divide the pressurized low-pressure steam into three paths, two of which enter the heating equipment to recover the heat of the low-pressure steam and then form condensate for recycling; the last path of low-pressure steam directly enters the low-pressure steam pipeline network and is transported to low-pressure steam grade users for use.

[0080] In this embodiment, in step S1, the low-pressure steam also includes the following processing methods: the separated steam and the first low-pressure steam enter the air cooling device for cooling, and the formed condensate returns to the input end of the drum V101; the separated steam and the first low-pressure steam are compressed and the separated steam and the first low-pressure steam are cooled together, and one of the two processing methods is selected, that is, all are pressurized and heated together, or all are cooled together.

[0081] Taking a 400,000 tons / year ethylene glycol production unit with 60 t / h of low-pressure steam as a by-product of the steam drum as an example, the method of this embodiment is used to recycle the low-pressure steam.

[0082] (1) Construct a low-pressure steam recovery system according to Example 2.

[0083] (2) The 60t / h low-pressure steam produced as a byproduct of the drum is divided into two routes. The first route is 40t / h of low-pressure steam that is pressurized by the low-pressure steam compressor C101 to form low-pressure steam; the second route is 20t / h of low-pressure steam that is sent to the shell side of the synthetic cycle gas preheater E101 for heat exchange and heat recovery.

[0084] After the heat of the second low-pressure steam is absorbed, a gas-liquid condensate is formed, which flows by gravity to the low-pressure steam condensate separator V102 for gas-liquid separation. The separated condensate is all recycled to the input end of the steam drum V101; the separated steam is sent to the low-pressure steam compressor C101 together with the first 40t / h low-pressure steam, and is compressed by the low-pressure steam compressor C101, and the pressure of the low-pressure steam is increased to form 0.2MPaG low-pressure steam.

[0085] (3) The 0.2MPaG low-pressure steam is divided into the following three routes: 11.6t / h low-pressure steam goes to the shell side of the synthesis circulating gas heater E102 for heat exchange and heat recovery to form gas-liquid condensate, which is all sent to the 0.2MPaG condensate network for reuse; 11.4t / h low-pressure steam goes to the shell side of the nitric acid reduction system heater E103 for heat exchange and heat recovery, and then forms gas-liquid condensate, which is all sent to the 0.2MPaG condensate network for reuse; the remaining low-pressure steam all enters the 0.2MPaG steam network and is output to the 0.2MPaG grade steam users in the ethylene glycol production system for secondary utilization.

[0086] The above technical scheme provided by the present invention is applicable to by-product steam (i.e., low-pressure steam) with a pressure of 0.06-0.1MpaG and a temperature of 110°C-120°C. The secondary low-pressure steam (preferably, the secondary low-pressure steam is 0.2MPaG) with a pressure of 0.15-0.22MPaG and a temperature of 130°C-140°C obtained by supercharging can effectively recycle the by-product low-pressure steam and realize secondary utilization, thereby achieving the purpose of energy saving, emission reduction and consumption reduction. At the same time, by adopting the above technical scheme, 60t / h low-pressure steam is recycled and utilized, and the annual production operation time is calculated as 7200h. The unit price of secondary low-pressure steam is about 12 yuan / t, which can save 5.184 million yuan in economic costs each year; at the same time, the present invention utilizes the heat of low-pressure steam, and it is calculated that the thermal energy utilization rate of low-pressure steam reaches 75%, which greatly reduces the cost of raw materials required to generate heat energy.

[0087] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for recovering low-pressure steam produced as a byproduct in the production of ethylene glycol, characterized in that: The following steps are involved: S1. Establish a low-pressure steam recovery and utilization system The low-pressure steam produced as a byproduct of the steam drum (V101) in the ethylene glycol production system is divided into two paths. The low-pressure steam in the first path is pressurized and heated to form low-pressure steam. The low-pressure steam in the second path is heat-exchanged and heat-recovered to form condensate and return to the steam drum (V101), thereby completing the construction of a low-pressure steam recovery and utilization system. The pressure of the low-pressure steam is 0.06MPaG to 0.1MPaG. S2. Set process parameters The flow rates of the two low-pressure steam lines are set according to the needs of low-pressure steam grade users, the pressure of the low-pressure steam produced as a byproduct of the steam drum, and the discharge volume; S3, low pressure steam recovery and utilization According to the process parameters set in step S2, the flow rates of the two low-pressure steam in the low-pressure steam recovery system are adjusted, and then the low-pressure steam is introduced into the low-pressure steam recovery and utilization system of step S1 to complete the recovery and secondary utilization of the low-pressure steam.

2. The method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol according to claim 1, characterized in that: In step S2, the discharge rate of low-pressure steam is 60 t / h and the temperature is 110°C to 120°C; the pressure of the low-pressure steam grade required by users is 0.15MPaG to 0.22MPaG and the temperature is 130°C to 140°C.

3. The method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol according to claim 2, characterized in that: In step S2, the flow ratio of the first low-pressure steam to the second low-pressure steam is (1.5-2.5):

1.

4. The method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol according to claim 1, characterized in that: The specific process of step S3 is: The second low-pressure steam exchanges heat with the heat exchange equipment in the low-pressure steam recovery system. The heat of the low-pressure steam is absorbed to form gas-liquid condensate for gas-liquid separation. The separated condensate is all recycled to the input end of the steam drum (V101); The separated steam enters the booster equipment together with the first low-pressure steam for compression. The pressure and temperature of the low-pressure steam are increased to form low-pressure steam which is transported to low-pressure steam grade users.

5. The method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol according to claim 4, characterized in that: The low pressure steam also The process includes: The low-pressure steam also enters the heating equipment to recover the heat energy of the low-pressure steam. Then, the low-pressure steam forms gas-liquid condensate, which is all sent to the condensate pipeline network for reuse.

6. The method for recovering and utilizing by-product low-pressure steam in the production process of ethylene glycol according to claim 4, characterized in that: In step S1, the low-pressure steam also includes the following processing methods: The separated steam enters the air cooling device together with the first low-pressure steam for cooling, and the formed condensate returns to the input end of the steam drum (V101); The separated steam is compressed with the first low-pressure steam and the separated steam is cooled together with the first low-pressure steam. Either of the two treatment methods is selected.

7. A system for recovering low-pressure steam produced as a byproduct in the production of ethylene glycol, which realizes the method for recovering low-pressure steam produced as a byproduct in the production of ethylene glycol according to claim 6, characterized in that: The system for recovering and utilizing by-product low-pressure steam in the ethylene glycol production process comprises a steam drum (V101), a low-pressure steam compressor (C101), a low-pressure steam pipe network, a condensate pipe network, a heater, a synthetic cycle gas preheater (E101) and a low-pressure steam condensate separator (V102); The output end of the steam drum (V101) is connected to the condensate pipe network via the low-pressure steam compressor (C101) and the heater in sequence; the low-pressure steam pipe network is connected to the low-pressure steam compressor (C101); The output end of the steam drum (V101) is also connected to the input end of the steam drum (V101) and the low-pressure steam compressor (C101) respectively after passing through the synthesis cycle gas preheater (E101) and the low-pressure steam condensate separator (V102).

8. The system for recovering and utilizing by-product low-pressure steam in the ethylene glycol production process according to claim 7, characterized in that: The heater comprises a synthetic cycle gas heater (E102) and a nitric acid reduction system heater (E103) connected in parallel; one end before the parallel connection is connected to a low-pressure steam compressor (C101), and one end after the parallel connection is connected to a condensate pipe network.

9. The system for recovering and utilizing by-product low-pressure steam in the ethylene glycol production process according to claim 8, characterized in that: A fourth gate valve (Z004) is arranged between the low-pressure steam pipeline network and the low-pressure steam compressor (C101); a first gate valve (Z001) is arranged between the output end of the steam drum (V101) and the low-pressure steam compressor (C101); the low-pressure steam condensate separator (V102) is connected to the pipeline between the first gate valve (Z001) and the low-pressure steam compressor (C101); a fifth gate valve (Z005) is arranged between the output end of the steam drum (V101) and the synthesis cycle gas preheater (E101); the fifth gate valve (Z005) is arranged in parallel with the first gate valve (Z001).

10. The system for recovering and utilizing by-product low-pressure steam in the ethylene glycol production process according to claim 9, characterized in that: The system for recovering and utilizing byproduct low-pressure steam in the ethylene glycol production process also includes a low-pressure steam air cooler (E104), a low-pressure steam condensate buffer tank (V103), a second gate valve (Z002) and a third gate valve (Z003); One end of the low-pressure steam air cooler (E104) is connected to the first gate valve (Z001), the low-pressure steam condensate separator tank (V102) and the third gate valve (Z003) respectively through the second gate valve (Z002), and the third gate valve (Z003) is also connected to the low-pressure steam compressor (C101); the other end of the low-pressure steam air cooler (E104) is connected to the input end of the steam drum (V101) through the low-pressure steam condensate buffer tank (V103).

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