A disproportionation stripping overhead vapor phase waste heat cascade recovery device

Abstract

The utility model discloses a kind of disproportionation stripping column overhead gas phase waste heat cascade recovery devices, comprising: disproportionation stripping column, column overhead gas / charge heat exchanger and column overhead gas / empty dry gas heat exchanger;Disproportionation stripping column's gas phase export connects the shell side entrance of column overhead gas / charge heat exchanger;The shell side export of column overhead gas / charge heat exchanger connects the shell side entrance of column overhead gas / empty dry gas heat exchanger;Still including air cooler, reflux tank and cooling system;The shell side export of column overhead gas / empty dry gas heat exchanger is connected at the entrance of air cooler;The outlet of air cooler connects the entrance of reflux tank;The gas phase export of reflux tank connects the entrance of cooling system;The outlet of cooling system connects the entrance of dry gas separation tank;The gas phase export of dry gas separation tank connects the tube side entrance of the column overhead gas / empty dry gas heat exchanger. Realize high-temperature gas phase and low-temperature gas phase's countercurrent heat exchange, to reduce air cooler load, eliminate low-temperature gas phase steam heating demand, make system comprehensive energy consumption drop.

Description

Technical Field

[0001] This utility model relates to the field of waste heat recovery technology, and in particular to a cascade recovery device for waste heat from the top gas phase of a disproportionation stripping tower. Background Technology

[0002] In the production process of aromatics disproportionation units, the treatment of the gas phase at the top of the stripping tower presents a significant energy utilization efficiency problem. Existing technology involves sequentially cooling the high-temperature gas phase generated at the top of the disproportionation stripping tower through a feed heat exchanger and an air cooler before finally entering a reflux tank for gas-liquid separation. Simultaneously, the low-temperature gas phase generated at the cooling unit outlet needs to be heated by a steam heater before being integrated into the fuel gas pipeline system. This approach results in the ineffective coordinated utilization of two independent energy flows.

[0003] Specifically, existing technologies suffer from two interconnected energy loss stages. On the one hand, the low-temperature gas phase temperature at the cooling unit outlet is typically in the range of 4-10°C. The cold energy it carries is not effectively utilized; instead, 1.0 MPa steam is required to heat the gas phase to above 35°C to meet the temperature requirements of the fuel gas pipeline, resulting in additional steam consumption. On the other hand, the high-temperature gas phase at the top of the stripping tower, with an initial temperature of 100-110°C, is only treated by a simple cooling method of "feed heat exchange + air cooler," failing to fully recover high-quality heat energy, leading to high energy consumption in the air cooler. This separate treatment mode results in a double waste of the heat energy from the high-temperature gas phase and the cold energy from the low-temperature gas phase.

[0004] For example, the Chinese patent document "A Method for Recovering Waste Heat from Stripping Tower Side Stream Gas to Replace Steam" (publication number CN105233520B) employs a combined heat and power technology to externally transport the stripping tower side stream gas from an acidic water stripping unit to other heat-using units. This gas is used to heat the materials in these units or as a heat source for reboilers, saving energy in the heat-using units while reducing cooling costs for the unit itself. This solution can be used for the design of new units and the upgrading of existing units. The required investment mainly includes pipelines and heat exchange equipment.

[0005] However, the main drawback of existing technologies lies in the failure to establish a coordinated energy exchange mechanism between the high-temperature and low-temperature gas phases. Although some units have recovered waste heat, the direct heat exchange between the two temperature gradient gas streams has not been resolved, making it impossible to achieve cascaded energy utilization. This results in persistently high overall system energy consumption, specifically manifested in the continuous operation of the steam heater and the high-load operation of the air cooler. Simultaneously, the liquid aromatic components carried in the low-temperature gas phase are not effectively recovered, affecting the stability of downstream unit operation. These shortcomings collectively constrain the overall energy efficiency level of the aromatic disproportionation unit. Utility Model Content

[0006] To address the problem of uncoordinated energy utilization between the high-temperature gas phase at the top of the stripping tower and the low-temperature gas phase at the outlet of the cooling unit in an aromatics disproportionation unit, which leads to high air cooler load, large steam heating consumption, and a significant increase in overall system energy consumption, this solution involves installing a tower top gas / vent dry gas heat exchanger. The gas phase outlet of the disproportionation stripping tower is connected to its shell-side inlet via the tower top gas / feed heat exchanger, and the gas phase outlet of the dry gas separator is connected to its tube-side inlet. This achieves countercurrent heat exchange between the high-temperature and low-temperature gas phases, thereby reducing the air cooler load, eliminating the need for steam heating in the low-temperature gas phase, and lowering the overall system energy consumption.

[0007] The second objective of this invention is to solve the problem of operational interruption caused by leakage in the newly added heat exchanger, and to achieve online disconnection of the heat exchanger through tube-side bypass channels and shell-side bypass channels.

[0008] The third objective of this invention is to solve the problem of venting dry gas temperature control by controlling the dry gas outlet temperature through a bypass channel control valve.

[0009] The fourth objective of this invention is to address the problem of liquid aromatics entrained in the gas phase at the outlet of the cooling unit affecting downstream stability. This is achieved by using a distributor in the liquid separator tank inlet and a double-layer defoaming screen to improve the recovery rate of liquid aromatics.

[0010] The fifth objective of this invention is to address the issues of system pressure fluctuations and overpressure safety risks, and to ensure the operational stability of the device under low-temperature conditions of 4-10°C through a pressure control system and a safety protection system.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A cascade recovery device for waste heat from the overhead gas phase of a disproportionation stripping tower includes: a disproportionation stripping tower, an overhead gas / feed heat exchanger, and an overhead gas / vent dry gas heat exchanger. The vapor outlet of the disproportionation stripping tower is connected to the shell inlet of the overhead gas / feed heat exchanger. The shell-side outlet of the overhead gas / feed heat exchanger is connected to the shell-side inlet of the overhead gas / vent dry gas heat exchanger. It also includes air coolers, reflux tanks, and cooling systems; The shell-side outlet of the top gas / vent dry gas heat exchanger is connected to the inlet of the air cooler. The outlet of the air cooler is connected to the inlet of the reflux tank; The vapor outlet of the reflux tank is connected to the inlet of the cooling system; The outlet of the cooling system is connected to the inlet of the dry gas separator; The gas phase outlet of the dry gas separator is connected to the tube-side inlet of the overhead gas / vent dry gas heat exchanger.

[0012] This design establishes a tiered energy exchange path between the high-temperature and low-temperature gas phases. The 100-110°C high-temperature gas phase generated by the disproportionation stripping tower first enters the shell side of the overhead gas / feed heat exchanger for preliminary cooling, and then flows into the shell side of the overhead gas / vent dry gas heat exchanger. Simultaneously, the gas phase from the reflux tank is cooled to 4-10°C by a cooling system to recover liquid aromatics before entering a dry gas separator for further separation of any remaining small amount of liquid aromatics. Its gas phase output is connected to the tube-side inlet of the overhead gas / vent dry gas heat exchanger. This design allows the high-temperature gas phase and the 4-10°C low-temperature dry gas to form a counter-current heat exchange within the heat exchanger. The high-temperature gas phase is pre-cooled to 45-55°C before entering the air cooler, while the low-temperature dry gas is heated to above 35°C. Compared to the high load on the air cooler and steam heating consumption caused by the independent processing of the two gas streams in traditional processes, this structure directly reduces the air cooler's power consumption by 30-50% and eliminates the need for steam heating through synergistic energy utilization. The precise setting of the connection relationship solves the problem of double energy waste pointed out in the background technology. The air cooler outlet is connected to the reflux tank to ensure the gas-liquid separation effect, and the cooling system outlet is connected to the dry gas separator to achieve further recovery of aromatics, forming a closed-loop energy exchange chain.

[0013] Preferably, the tube-side outlet of the tower top gas / vented dry gas heat exchanger is connected to the fuel gas pipeline network. Connecting the heat-exchanged dry gas to the fuel gas pipeline network solves the temperature threshold problem of low-temperature dry gas grid connection, avoids the energy consumption of additional steam heating to above 35°C required in traditional processes, and the direct grid connection design simplifies the process and reduces equipment investment costs.

[0014] Preferably, a bypass channel is provided between the tube-side inlet and tube-side outlet of the overhead gas / vented dry gas heat exchanger. The bypass pipe has the same diameter as the main pipeline and can be made of the same stainless steel, allowing some low-temperature dry gas to bypass the heat exchanger tubes. When it is necessary to adjust the outlet temperature or when the heat exchanger pressure drop is abnormal, the airflow can be diverted through this channel to ensure continuous and undisturbed system operation.

[0015] Preferably, a regulating valve is provided on the bypass channel of the pipe side, which can control the flow rate through the bypass channel. The regulating valve changes the cross-sectional area of ​​the channel by the displacement of the valve core. The axial movement of the valve core is controlled by an actuator. When the opening degree increases, the proportion of bypass flow increases, resulting in more low-temperature dry gas being output directly without heating, thereby achieving precise regulation of the outlet temperature.

[0016] Preferably, a shell-side bypass channel is provided between the shell-side inlet and shell-side outlet of the overhead gas / vented dry gas heat exchanger. When the heat exchanger tube bundle leaks, the shell-side and tube-side bypasses are opened, allowing the medium to completely bypass the heat exchanger, achieving pressurized online isolation. The system remains operational during maintenance, avoiding economic losses from unit shutdown.

[0017] Preferably, the dry gas separator has a separator inlet on the side, a separator outlet on the top, and a drain outlet at the bottom; it also includes an inlet distributor fixed inside the tank and connected to the separator inlet, which can disperse the fluid into a swirling flow; and it also includes a defoaming screen horizontally disposed at the top of the tank cavity, the defoaming screen being located directly below the separator outlet.

[0018] Furthermore, the dry gas separator is equipped with a double-layer defoaming screen structure, including a lower pre-filter defoaming screen and an upper fine filter defoaming screen.

[0019] Preferably, a liquid collection chamber is formed between the double-layer foam breaking mesh structure, and a drain port is connected to the bottom of the chamber.

[0020] The gas phase enters through the side inlet and forms a swirling flow through the distributor's guide vanes, while the liquid aromatics are thrown towards the tank wall under centrifugal force. The rising gas flow intercepts 90% of the droplets through the lower large-aperture defoaming screen, and then the remaining 5% is finely filtered through the upper small-aperture screen. The liquid that accumulates between the two screens is discharged through the bottom drain port. This combined structure significantly improves the recovery rate of liquid aromatics and solves the problem of downstream unit fluctuations caused by dry gas carrying liquid.

[0021] Preferably, the heat exchanger shell side is provided with a tube bundle, which is supported and baffled by a tube bundle baffle provided in the shell side.

[0022] Preferably, a pressure control system is also included, comprising a pressure regulating valve located at the tube-side outlet of the top gas / vent dry gas heat exchanger. The pressure regulating valve automatically adjusts its opening based on feedback from the top pressure monitoring instrument to maintain stable pipeline pressure, ensuring a smooth receipt of dry gas by the fuel gas system.

[0023] Preferably, a safety protection system is also included, comprising a safety valve connected via a flange to the top of the gas phase of the reflux tank. When the pressure in the reflux tank exceeds a set value, the valve core opens instantaneously to release the high-pressure gas phase. The flange connection facilitates quick disassembly and verification, solving the maintenance challenge of periodically inspecting pressure vessel safety accessories.

[0024] Preferably, the cooling unit outlet pipe is equipped with a temperature detection interface. The interface monitors the temperature of the 4-10°C low-temperature dry gas in real time, providing a control signal source for the temperature control valve, forming a closed-loop temperature control to ensure the stability of the dry gas cooling temperature and guarantee the recovery effect of liquid aromatics.

[0025] Therefore, this utility model has the following beneficial effects.

[0026] By connecting the overhead gas / vented dry gas heat exchanger to the overhead gas / feed heat exchanger and the dry gas separator, direct countercurrent heat exchange between the 70-90°C high-temperature gas phase and the 4-10°C low-temperature dry gas is achieved, which reduces the load on the air cooler and eliminates the steam heating link, thus solving the problem of double energy waste.

[0027] The dry gas separator features a double-layer defoaming screen and a cyclone distributor to intercept and recover liquid aromatics in the dry gas, effectively improving the recovery rate and solving the fluctuation defects in downstream units caused by liquid carryover in the dry gas.

[0028] When the tube bundle leaks, the heat exchanger can be switched online through the tube-side and shell-side bypass channels. The dual bypass switching is used to maintain system operation and avoid production loss due to unit shutdown and maintenance.

[0029] The combination of safety protection system and pressure control system prevents pipeline pressure fluctuations while ensuring continuous and stable system operation. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the layout structure of this utility model.

[0031] Figure 2 This is a schematic diagram of the structure of the tower top gas / vent dry gas heat exchanger in this utility model.

[0032] Figure 3 This is a schematic diagram of the dry gas separator in this utility model.

[0033] In the diagram: 1. Disproportionation stripping tower; 2. Top gas / feed heat exchanger; 3. Top gas / vent dry gas heat exchanger; 31. Tube-side outlet; 32. Tube-side inlet; 33. Head baffle; 34. Shell-side inlet; 35. Shell-side outlet; 36. Tube bundle baffle; 37. Tube bundle; 38. Heat exchanger support; 4. Air cooler; 5. Reflux tank; 6. Cooling system; 7. Dry gas separator; 71. Separator inlet; 72. Separator outlet; 73. Pressure gauge interface; 74. Defoamer; 75. Level gauge; 76. Separator support; 77. Manhole; 78. Drain; 79. Inlet distributor; 8. Pressure control system; 9. Safety protection system; 10. Fuel gas pipeline. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1 like Figure 1 , 2As shown in Figure 3, this embodiment proposes a cascade recovery device for the waste heat of the top gas phase of a disproportionation stripping tower. The disproportionation stripping tower 1 serves as the initial equipment for aromatic hydrocarbon separation, and its top gas phase outlet is connected to the shell-side inlet of the top gas / feed heat exchanger 2 via a pipeline and flange. The heat exchanger adopts a shell-and-tube structure, with the medium flow channels in the shell side arranged as baffles, while the tube side is connected to the device's feed system to achieve initial heat recovery. The shell-side outlet of the heat exchanger is connected to the shell-side inlet 34 of the top gas / vent dry gas heat exchanger 3 via a seamless steel pipe. The latter serves as the core heat exchange equipment, and its tube bundle 37 is fixed by tube bundle baffles 36 to form a multi-pass flow channel. The end cap baffles 33 divide the tube side into independent circulation paths, ensuring that the medium flows completely through all heat exchange tubes from the tube side inlet to the outlet. The shell side is designed as a single-pass flow, with the medium flowing axially along the shell to flush the outer wall of the tube bundle 37. The shell-side outlet 35 of the heat exchanger is connected to the inlet of the air cooler 4 via a pipe and flange. The air cooler 4 consists of multiple finned tube bundles, and its outlet is connected to the cylindrical inlet of the reflux tank 5 via a short section. The reflux tank 5 serves as a gas-liquid separation container, and its gas phase outlet is vertically connected to the inlet of the cooling system 6 via a flange. The cooling system 6 uses a cooling unit based on the compressor refrigeration principle, and the cooler outlet is connected to the side inlet of the dry gas separator 7 via a cryogenic steel pipe. The internal structure of the separator includes an inlet distributor 79, which consists of radial guide vanes to create a swirling motion in the gas phase entering the tank. In this embodiment, the tube-side inlet 32 ​​of the heat exchanger is connected to the top outlet pipeline of the dry gas separator 7 via a pipe and flange, and the tube-side outlet 31 is connected to the fuel gas pipeline network via a pressure regulating valve. The tube bundles are made of stainless steel with an outer diameter of 25 mm. The shell-side inlet 34 is located at the top of the heat exchanger and connects to the shell-side outlet of the top gas / feed heat exchanger 2. The shell-side outlet 35 is located at the bottom and connects to the inlet of the air cooler 4. Longitudinal baffles inside the shell guide the gas phase to vertically scour the outer surface of the tube bundle, enhancing turbulence and improving heat transfer efficiency. The heat exchanger support 38 is fixed with a saddle-type bracket, and a PTFE sliding plate is installed between the bracket and the shell to absorb thermal expansion stress. This structure achieves stable counter-current heat transfer between the 70-90°C high-temperature gas phase and the 4-10°C low-temperature dry gas. The temperature difference of over 50°C between the tube and shell sides is compensated for by the large contact area, mitigating the low gas-to-gas heat transfer coefficient. The separator inlet 71 is located on the side of the tank and is connected to the cooling unit outlet pipeline via a flange. The swirl distributor installed at the inlet consists of eight radial guide vanes, forcing the gas phase to enter the tank tangentially, generating a rotating flow field. A double-layer defoaming screen 74 is horizontally installed in the upper part of the tank; the lower layer is a 3mm pore size stainless steel coarse filter, and the upper layer is a 1mm pore size fine filter. The spacing between the two screens forms a collection trough. The separator top outlet 72 is connected to the heat exchanger tube-side inlet 32 ​​via a bend in the pipe. A fine filter is installed directly below the outlet pipe to intercept residual droplets in the rising airflow. A drain port 78 is located at the bottom of the tank head to periodically discharge accumulated liquid aromatics. A magnetic level gauge 75 installed on the side of the tank displays the liquid level in real time, and a pressure gauge interface 73 is located at the top of the tank to monitor the separation pressure. The separator support 76 adopts a leg-type support, and the support height meets the installation space requirements of the drain valve. A manhole 77 is located in the middle of the tank for easy maintenance of the defoaming screen 74.This structure utilizes the principle of centrifugal sedimentation: during gas-phase swirling, liquid aromatics are thrown towards the tank wall by centrifugal force. A coarse filter intercepts large droplets, while a fine filter captures micron-sized droplets, achieving an aromatics recovery rate of over 95%. Specifically, the internal structure of the dry gas separator 7 achieves efficient aromatics recovery through a swirling distributor and a double-layer defoaming screen 74. The radial guide vanes of the inlet distributor 79 force the gas phase entering the tank to rotate tangentially, and the liquid aromatics, under centrifugal force, are thrown towards the tank wall and flow down the wall surface. The rising airflow first passes through the lower layer of large-aperture metal wire mesh, whose mesh size allows gas to pass through but intercepts droplets larger than 3mm in diameter. Uncaptured micron-sized droplets continue to rise and are intercepted a second time by the upper layer of small-aperture fine filter. The collection space formed by the spacing between the two meshes allows the condensed droplets to converge at the drain port 78 at the bottom of the tank. This physical separation process requires no external energy input and relies on fluid dynamics to achieve a high aromatics recovery rate. The pipe wall thickness of the three-pass pipe connecting the top gas phase outlet of the separator to the top gas / vent dry gas heat exchanger is the same as that of the main pipeline, ensuring resistance to cold brittleness when transporting low-temperature media at 4-10°C.

[0036] The energy transfer of the waste heat recovery unit from the top gas phase of the disproportionation stripping tower 1 begins with the approximately 105°C gas phase at the top of the disproportionation stripping tower 1. After being cooled by the top gas / feed heat exchanger 2, it enters the shell side of the top gas / vent dry gas heat exchanger 3. Simultaneously, the gas phase from the top of the reflux tank 5 is cooled to 4-10°C in the cooling unit and then enters the separator. The cyclone distributor causes the liquid aromatics in the gas phase to be thrown towards the tank wall under centrifugal force. After being intercepted by the double-layer defoaming screen 74, they accumulate at the drain port 78. The purified low-temperature dry gas enters the tube side of the heat exchanger from the top of the tank. The two gas phases with a temperature difference of nearly 80°C form a countercurrent exchange in the heat exchanger: the high-temperature gas phase in the shell side transfers heat to the low-temperature dry gas in the tube side, and its own temperature drops to approximately 50°C before entering the air cooler 4; the low-temperature dry gas in the tube side absorbs heat and rises to above 35°C, meeting the temperature requirements of the fuel gas pipeline network. This heat exchange process enables tiered energy utilization, with the cooling load of the high-temperature gas phase being partially borne by the low-temperature dry gas cooling energy, directly reducing the power consumption of the air cooler 4. A flange installed at the top of the reflux tank 5 connects to the safety protection system 9, which includes a safety valve that instantly opens to release pressure in case of overpressure. The release port diameter matches the maximum gas phase flow rate. The top of the reflux tank 5 is connected to the cooling system 6, and the outlet of the cooling system 6 is connected to the separator.

[0037] A bypass channel is provided between the tube-side inlet 32 ​​and the outlet of the heat exchanger, using a steel pipe of the same diameter as the main pipeline. A regulating valve installed on the bypass channel changes the cross-sectional area of ​​the channel through axial displacement of the valve stem. When it is necessary to adjust the dry gas outlet temperature, the valve opening is changed to allow some low-temperature dry gas to directly bypass the heat exchanger, thus regulating the temperature. The shell-side bypass channel is arranged parallel to the side of the heat exchanger shell, working in conjunction with the tube-side bypass to achieve an emergency cut-off function: when the heat exchanger tube bundle leaks, opening the double bypass valves allows both media to completely bypass the heat exchanger, maintaining continuous system operation.

[0038] This solution further eliminates the problem of liquid carryover in dry gas in traditional processes. The combination of a cyclone distributor and a double-layer defoaming screen 74 within the separator improves the recovery efficiency of liquid aromatics and resolves downstream fluctuations caused by liquid carryover in dry gas. The entire unit achieves efficient energy transfer through the thermodynamic countercurrent mass transfer principle. The heat exchange between the high-temperature gas phase and the low-temperature dry gas follows the heat balance equation, i.e., heat Q equals the overall heat transfer coefficient U multiplied by the heat exchange area A multiplied by the logarithmic mean temperature difference ΔTm. The countercurrent arrangement maximizes the logarithmic mean temperature difference ΔTm, and the heat exchange area A is optimally distributed through the tube bundle baffles 36. The overall heat transfer coefficient U is maintained at a low level due to the gas-gas heat exchange characteristics but is compensated for by the large temperature difference. Compared to traditional processes, this structure eliminates the steam heating stage, while the recovered liquid aromatics increase economic benefits.

[0039] In this embodiment, the tube box of the top gas / vented dry gas heat exchanger 3 includes a head baffle 33. The head baffle 33 significantly increases the flow velocity of the fluid inside the tubes by dividing the flow channel into multiple tube passes. This increased flow velocity enhances the turbulence of the fluid, effectively disrupting the thermal boundary layer of the tube wall, thereby greatly enhancing the heat transfer efficiency. Simultaneously, the extended flow path also increases the effective heat transfer length of the fluid, making the heat exchange process more complete. The heat exchanger also includes a tube bundle disposed within the shell side, which is supported and deflected by tube bundle baffles disposed within the shell side.

[0040] Specifically, the tube bundle baffles 36 inside the top gas / vent dry gas heat exchanger 3 force the tube-side fluid to flow back and forth along a U-shaped path through the entire tube bundle. The longitudinal baffles on the shell side guide the gas phase to vertically scour the outer surface of the tube bundle. This design compensates for the low heat transfer coefficient of gas-to-gas heat exchange by extending the medium residence time and enhancing the turbulence intensity.

[0041] The bypass system relies on manual switching on-site. Valve operation is extremely infrequent, which reduces investment costs.

[0042] The pressure control system 8 uses a pressure control valve to form a control loop with the pressure detection device located at the top of the tower, thereby achieving precise pressure control.

[0043] The outlet temperature detection interface of the cooling unit is located at least 0.5 meters away from the inlet of the separator to ensure that the temperature detection avoids the fluid disturbance zone and accurately reflects the actual temperature state of the dry gas. The detection signal is transmitted to the control room via armored cable, providing operators with real-time data for adjusting the dry gas temperature.

[0044] Before commissioning, a pipeline airtightness test must be completed to maintain the top pressure within the normal operating range. When the high-temperature gas phase flows through the shell side of the top gas / feed heat exchanger 2, it undergoes its first heat exchange with the feed in the tube side, resulting in a decrease in gas phase temperature. This gas flow then enters the shell side inlet 34 of the top gas / vent dry gas heat exchanger 3. Operators fine-tune the flow distribution through the valve in the shell side bypass channel. Simultaneously, the cooling unit compressor is started, cooling the top gas phase of the reflux tank 5 to 4-10°C before introducing it into the dry gas separator 7. The cyclone distributor inside the tank causes the gas phase to rotate along the tank wall. Liquid aromatics are thrown towards the tank wall and accumulate under centrifugal force. During the upward flow, droplets are intercepted by the lower large-aperture defoaming screen 74 and then finely filtered through the upper small-aperture screen. The separated liquid aromatics are periodically discharged from the bottom drain port 78. The purified low-temperature dry gas flows out from the top of the tank and is transported via pipeline to the tube side inlet of the top gas / vent dry gas heat exchanger 3.

[0045] During the stable operation phase of the system, the 70-90°C high-temperature gas phase and the 4-10°C low-temperature dry gas form a countercurrent heat transfer within the heat exchanger. Operators read the dry gas temperature in real time through temperature detection and achieve precise control of the dry gas temperature by automatically adjusting the opening of the control valve in the bypass channel of the tube side through the automatic control system.

[0046] In the event of a sudden internal leak in the heat exchanger, operators should simultaneously open the tube-side and shell-side bypass valves according to the emergency procedures. First, rotate the tube-side bypass valve handwheel counterclockwise to the fully open position, then operate the shell-side bypass valve in the same direction, and finally close the valves at the tube-side and shell-side inlet / outlet of the heat exchanger. At this time, the high-temperature gas phase flows directly to the air cooler 4 through the shell-side bypass, and the low-temperature dry gas flows directly into the fuel gas pipeline network through the tube-side bypass, maintaining the system's operational status. Maintenance personnel can disassemble the heat exchanger head to inspect the tube bundle, replace damaged components, and then put it back into service.

[0047] When shutting down the unit, first turn off the cooling unit compressor, and then close the drain valve after the liquid level in the dry gas separator 7 drops to its lowest point. Next, sequentially cut off the gas phase output of the disproportionation stripping tower 1, stop the air-cooled fan, and finally close the fuel gas pipeline connection valve. Continuous operation of this system in a 3.16 million tons / year disproportionation unit shows that the dry gas temperature can be automatically controlled, and the separator discharges approximately 3.5 tons of liquid aromatics per week. Compared to before the modification, operators no longer need to monitor the steam heater temperature, reducing daily inspection time.

[0048] Comparative Example 1 Taking a disproportionation process with a capacity of 3.16 million tons / year as an example, the existing technology's processing methods are as follows: The disproportionated dry gas enters the fuel gas system at a flow rate of 12.88 t / h. During operation, it was found that the disproportionated dry gas had insufficient residence time in the refrigeration system, resulting in poor gas-liquid separation and the presence of a small amount of liquid droplets in the dry gas, which affected the stable operation of downstream units. In addition, the cooled dry gas needs to be heated by a steam heater before being connected to the fuel gas pipeline network, resulting in high steam consumption.

[0049] Comparing Example 1 with Comparative Example 1, in Comparative Example 1, the disproportionated dry gas had insufficient residence time in the refrigeration system, resulting in poor gas-liquid separation and the presence of small amounts of liquid droplets in the dry gas, affecting the stable operation of downstream equipment. Furthermore, the cooled dry gas needed to be heated by a steam heater before being connected to the fuel gas pipeline, leading to high steam consumption. In Example 1, 223 tons of benzene can be recovered annually from the gas phase, significantly reducing the liquid carryover in the disproportionated dry gas and bringing certain benefits. Through the synergistic utilization of low-temperature gas-phase cold energy and high-temperature gas-phase heat energy, 3945 tons of low-pressure steam are saved annually, resulting in a revenue of approximately 670,000 yuan. The air-cooling load is reduced by more than 30%, saving approximately 80,000 kWh of electricity annually, resulting in a revenue of approximately 80,000 yuan.

Claims

1. A device for cascade recovery of waste heat from the top gas phase of a disproportionation stripping tower, characterized in that... include: Disproportionation stripping tower; The top gas / feed heat exchanger has its shell-side inlet connected to the gas phase outlet of the disproportionation stripping tower; The shell-side inlet of the overhead gas / vent dry gas heat exchanger is connected to the shell-side outlet of the overhead gas / feed heat exchanger. The air cooler has its inlet connected to the shell-side outlet of the overhead gas / vented dry gas heat exchanger; The reflux tank has its inlet connected to the outlet of the air cooler; The cooling system has its inlet connected to the vapor phase outlet of the reflux tank; The dry gas separator has its inlet connected to the outlet of the cooling system and its gas phase outlet connected to the tube-side inlet of the overhead gas / vent dry gas heat exchanger. The dry gas separator is provided with a separator inlet on the side, a separator outlet on the top, and a drain outlet at the bottom; it also includes an inlet distributor fixed inside the tank and connected to the separator inlet, which can disperse the fluid into a swirling flow; it also includes a defoaming screen horizontally installed at the top of the tank cavity, the defoaming screen being located directly below the separator outlet.

2. The apparatus according to claim 1, characterized in that: The tube-side outlet of the top gas / vent dry gas heat exchanger is connected to the fuel gas pipeline network.

3. The apparatus according to claim 1, characterized in that: A tube-side bypass channel is provided between the tube-side inlet and tube-side outlet of the tower top gas / vent dry gas heat exchanger.

4. The apparatus according to claim 3, characterized in that: The bypass channel is equipped with a regulating valve, which can control the flow rate through the bypass channel.

5. The apparatus according to claim 1, characterized in that: A shell-side bypass channel is provided between the shell-side inlet and shell-side outlet of the top gas / vent dry gas heat exchanger.

6. The apparatus according to claim 1, characterized in that: The heat exchanger shell side is provided with a tube bundle, which is supported and deflected by tube bundle baffles provided in the shell side.

7. The apparatus according to any one of claims 1-5, characterized in that: It also includes a pressure control system, which includes a pressure regulating valve located at the tube-side outlet of the top gas / vent dry gas heat exchanger.

8. The apparatus according to any one of claims 1-5, characterized in that: It also includes a safety protection system, which includes a safety valve connected to the top of the gas phase of the reflux tank.

9. The apparatus according to any one of claims 1-5, characterized in that: The cooling system is a compression refrigeration system, and a temperature detection interface is provided on the outlet pipe of the cooling system.

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