A heating device for a vinyl chloride mixed gas preheater

Abstract

This utility model relates to the field of chemical production technology, specifically a heating device for a vinyl chloride mixed gas preheater, comprising a heptane storage tank, a first heat exchanger, and a second heat exchanger. The outlet of the heptane storage tank is connected to the tube-side inlet of the first heat exchanger via a transfer pump. The shell-side inlet of the second heat exchanger is connected to the tube-side outlet of the first heat exchanger via a liquid inlet pipe. The shell-side outlet of the second heat exchanger is connected to the inlet of the heptane storage tank via a heptane outlet pipe. A third heat exchanger is also included. A steam outlet pipe is connected to the shell-side outlet of the first heat exchanger, and this steam outlet pipe is connected to the shell-side inlet of the third heat exchanger. A mixed gas inlet pipe and an intermediate connecting pipe are respectively connected to the inlet and outlet of the tube-side of the third heat exchanger. The low-temperature steam after heat exchange with heptane in the first heat exchanger is not directly discharged but is transported to the third heat exchanger to preheat the mixed gas, fully transferring the residual heat of the low-temperature steam to the mixed gas to be preheated, thus raising the temperature of the mixed gas in advance. This reduces the heat loss of the low-temperature steam and lowers the heat exchange load of the high-temperature heptane in the subsequent second heat exchanger.

Description

Technical Field

[0001] This utility model relates to the field of chemical production technology, specifically to a preheater heating device for vinyl chloride mixed gas, which is particularly suitable for the preheating process of acetylene and hydrogen chloride mixed gas in the calcium carbide method of vinyl chloride production. Background Technology

[0002] In the calcium carbide-based vinyl chloride production process, acetylene and hydrogen chloride must be mixed in a specific ratio and then cryogenically dehydrated. Afterward, they must be preheated to the required process temperature (usually ≥85℃) before entering the converter for catalytic reaction. The preheating effect directly affects the converter's reaction efficiency, catalyst lifespan, and the stability of subsequent systems; therefore, the preheating process is one of the key steps in the production process. In traditional processes, hot water is commonly used as the heating medium in the preheater, achieving temperature rise through heat exchange between the hot water and the mixed gas. However, when the preheater experiences internal leakage, the hot water reacts with the hydrogen chloride in the mixed gas to produce hydrochloric acid. This acidic mixed gas, upon entering the converter, not only easily causes catalyst agglomeration within the converter tubes, reducing the gas flow and conversion efficiency, but also severely corrodes the carbon steel equipment in the subsequent conversion system, leading to equipment damage, interrupting continuous production, and increasing maintenance costs and safety risks.

[0003] To address the aforementioned technical problem of hot water leakage, existing technologies have developed improved solutions using heptane as the heat transfer medium. For example, Chinese Patent Publication No. CN223345997U discloses a preheater for heating with heptane in the calcium carbide-based vinyl chloride production process. This preheater includes a heptane heater, a heptane storage tank, and a heptane circulation pump. The heptane heater, via the circulation pump, delivers heated heptane through a heptane inlet pipe to the shell side of the preheater, where it exchanges heat with the mixed gas in the tube side. The heptane then flows back to the heptane storage tank through a heptane outlet pipe, achieving circulation. Simultaneously, this solution uses a DCS controller to interlock and control the inlet regulating valve on the heptane inlet pipe, the outlet thermometer on the heptane outlet pipe, and the heptane heater, achieving automatic temperature regulation. This patent, by replacing hot water with heptane as the heat transfer medium, avoids the risk of reaction between the heat transfer medium and hydrogen chloride in the event of internal leakage, thus improving process safety and equipment lifespan.

[0004] However, the existing heptane heating schemes represented by CN 223345997U still have the following shortcomings that need to be improved in practical applications: 1. Low energy efficiency: In this patent, heptane needs to be heated to the target temperature by a heptane heater (usually using steam as a heat source). The low-temperature steam (which still contains a certain amount of heat) generated after the steam exchanges heat with heptane is not recovered and is directly discharged or condensed and discharged, resulting in energy waste and increasing the overall production energy consumption.

[0005] 2. Insufficient stability of the heptane circulation system: This patent does not include heptane filtration and impurity monitoring components. During long-term circulation, heptane is prone to mixing with impurities such as pipe welding slag and dust. These impurities can clog the heat exchange tubes of the preheater, reduce heat exchange efficiency, and even cause poor heptane circulation, affecting the preheating effect.

[0006] 3. Inadequate safety protection mechanism: This patent only controls process parameters through temperature interlocking and does not include a real-time detection component for heptane leakage. If an internal leak occurs in the preheater, causing heptane to enter the mixed gas system, it cannot be detected in time and a shutdown protection mechanism cannot be triggered. This could result in heptane entering subsequent processes with the mixed gas, causing new safety hazards and product quality risks. At the same time, the lack of linkage protection design for failures of key components (such as circulating pumps and heat exchangers) results in weak system fault tolerance.

[0007] Therefore, there is an urgent need for a vinyl chloride mixed gas preheater heating device that can further improve energy utilization, enhance system stability and safety protection capabilities, in order to solve the above-mentioned technical shortcomings of the existing heptane heating scheme. Utility Model Content

[0008] The purpose of this invention is to provide a heating device for a vinyl chloride mixed gas preheater, which solves the problems mentioned in the prior art in the background section.

[0009] To achieve the above objectives, this utility model provides the following technical solution: It includes a heptane storage tank, a first heat exchanger, and a second heat exchanger. The outlet of the heptane storage tank is connected to the tube-side inlet of the first heat exchanger via a delivery pump. The shell-side inlet of the second heat exchanger is connected to the tube-side outlet of the first heat exchanger via a liquid inlet pipe. The shell-side outlet of the second heat exchanger is connected to the inlet of the heptane storage tank via a heptane outlet pipe. It also includes a third heat exchanger. A steam outlet pipe is connected to the shell-side outlet of the first heat exchanger, and the steam outlet pipe is connected to the shell-side inlet of the third heat exchanger. A mixed gas inlet pipe and an intermediate connecting pipe are respectively connected to the inlet and outlet of the tube-side of the third heat exchanger, and the intermediate connecting pipe is connected to the tube-side inlet of the second heat exchanger.

[0010] Furthermore, the outlet of the tube side of the second heat exchanger is connected to a mixed gas outlet pipe, and a thermometer and a low-concentration heptane sensor are connected to the mixed gas outlet pipe.

[0011] Furthermore, the heptane storage tank and the delivery pump are connected by a delivery pipe, and the delivery pipe is equipped with a filter and a differential pressure transmitter located between the heptane storage tank and the delivery pump.

[0012] Furthermore, a steam inlet pipe is connected to the shell-side inlet of the first heat exchanger.

[0013] Furthermore, the heptane storage tank is equipped with a level gauge.

[0014] Furthermore, a flow meter is installed on the inlet pipe.

[0015] Furthermore, the delivery pump is connected to the inlet of the first heat exchanger tube side via a heptane inlet pipe, which is equipped with a regulating valve.

[0016] Furthermore, the shell-side outlet of the third heat exchanger is connected to a steam condensate discharge pipe.

[0017] This utility model addresses the problems of low energy utilization efficiency, insufficient stability of the circulation system, and imperfect safety protection mechanism in the preheater used for heating with heptane in the calcium carbide method of vinyl chloride production, as disclosed in CN 223345997U. Through targeted structural design and control logic optimization, it achieves multi-dimensional technical improvements, with the following specific beneficial effects: 1. Addressing the issue of wasted heat caused by the direct discharge of low-temperature steam generated after steam heating heptane in scheme CN223345997 U, this invention addresses the problem of wasteful heat due to the direct discharge of low-temperature steam (80-100℃) after heat exchange with heptane in the first heat exchanger. Instead of being directly discharged, the low-temperature steam is transported to the third heat exchanger for preliminary heating of the mixed gas, fully transferring the residual heat of the low-temperature steam to the mixed gas to be preheated, thus raising the temperature of the mixed gas to 50-70℃ in advance. This design not only reduces the heat loss of the low-temperature steam but also reduces the heat exchange load of the high-temperature heptane in the subsequent second heat exchanger. Compared to scheme CN223345997U, it reduces overall steam energy consumption, improves energy utilization efficiency, and meets the energy-saving requirements of chemical production.

[0018] 2. Addressing the issue of the CN223345997U design lacking a heptane filter and impurity monitoring component, which easily leads to impurities clogging the heat exchange tubes, this invention adds a filter and a differential pressure transmitter to the heptane circulation path. The filter effectively intercepts impurities such as welding slag and dust mixed in with the heptane, preventing clogging of the heat exchange tubes of the second heat exchanger. The differential pressure transmitter monitors the pressure difference between the filter inlet and outlet in real time. When the pressure difference exceeds a set threshold, it immediately triggers the PLC controller to close the regulating valve and stop the delivery pump, reminding the operator to clean the filter screen. This design ensures the smoothness of the heptane circulation from both impurity interception and clogging warning perspectives, avoiding a decrease in heat exchange efficiency due to heat exchange tube clogging, and improving temperature stability compared to the CN 223345997U design.

[0019] 3. Addressing the issues of lacking heptane leak detection and critical component failure linkage protection in the CN223345997U solution, this invention installs a low-concentration heptane sensor at the mixed gas outlet pipe. When a heptane concentration ≥50ppm is detected (indicating preheater internal leakage), the PLC controller immediately triggers to stop the delivery pump, close the regulating valve, and simultaneously activate an audible and visual alarm. This prevents heptane from entering subsequent conversion processes with the mixed gas, eliminating safety hazards and product quality risks, and filling the gap in leak detection in the CN223345997U solution. In addition to the differential pressure transmitter and filter blockage linkage, the PLC controller also achieves full parameter monitoring through thermometers, flow meters, and level gauges. When the mixed gas outlet temperature deviates from the process range, the heptane flow rate fluctuates by more than ±5%, or the heptane storage tank level is abnormal, the valve opening is immediately adjusted or an alarm is triggered to prevent malfunctions such as circulating pump idling and heat exchanger dry burning. Compared to the CN223345997U solution, this improves system fault tolerance and reduces equipment maintenance costs.

[0020] 4. This utility model continues the core advantage of using heptane as a heat medium in the CN223345997U scheme to avoid reaction with hydrogen chloride in case of internal leakage. At the same time, through the closed-loop design of the heptane circulation path, it realizes the efficient recycling of heptane, and also takes into account process safety and operating economy, ensuring that the device can produce stably and continuously for a long time. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a system block diagram of the present invention.

[0022] In the diagram: 1. Heptane storage tank; 2. First heat exchanger; 3. Second heat exchanger; 4. Transfer pump; 5. Inlet pipe; 6. Third heat exchanger; 7. Steam outlet pipe; 8. Mixed gas inlet pipe; 9. Intermediate connecting pipe; 10. Mixed gas outlet pipe; 11. Thermometer; 12. Low concentration heptane sensor; 13. Transfer pipe; 14. Filter; 15. Differential pressure transmitter; 16. Steam inlet pipe; 17. Level gauge; 18. Flow meter; 19. Heptane inlet pipe; 20. Control valve; 21. Heptane outlet pipe; 22. Steam condensate discharge pipe. Detailed Implementation

[0023] To make the objectives, technical solutions, and beneficial effects of this utility model clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments. Figure 1-2As shown, the vinyl chloride mixed gas preheater heating device disclosed in this utility model is based on a three-stage heat exchange logic: heat exchange between steam and heptane, preheating of the mixed gas with low-temperature steam, and preheating of the mixed gas with high-temperature heptane. Combined with PLC automatic control and fault linkage protection, it achieves efficient and safe preheating of the vinyl chloride mixed gas. The device consists of a medium storage unit (heptane storage tank 1), a heat exchange unit (first heat exchanger 2, second heat exchanger 3, and third heat exchanger 6), a conveying unit (conveyor pump 4), a detection unit (thermometer 11, low-concentration heptane sensor 12, flow meter 18, etc.), a control unit (PLC and regulating valve 20), and a piping system. It is suitable for the mixed gas preheating process in vinyl chloride polymerization, effectively improving heat exchange efficiency, reducing energy consumption, and avoiding the risk of heptane leakage and equipment blockage. Specifically: The heptane storage tank 1 of the media storage unit is made of 304 stainless steel, which has good resistance to organic solvent corrosion, avoiding tank corrosion caused by long-term storage of heptane; it is a vertical tank with a volume of 5m³. 3 The tank has a nominal diameter of 1200mm and a total height of 3500mm. The bottom of the tank is sloped (1:50) for easy sewage discharge. The top of the tank is equipped with a breather valve (model GFQ-2, nominal diameter DN50, material 304 stainless steel) to balance the pressure inside the tank. A level gauge 17 is installed on the side of the tank. The UHZ-517 type magnetic float level gauge is selected, with a range of 0-5m, an accuracy of ±1mm, and a material of 304 stainless steel. It monitors the heptane level in real time and outputs a 4-20mA analog signal to the PLC.

[0024] The conveying unit consists of a conveying pump 4 and related piping accessories, wherein: Transfer pump 4 is an ISW80-160 horizontal centrifugal pump; flow rate 50m³ / h 3 / h, head 32m, rated speed 2900r / min, motor power 7.5kW (three-phase 380V AC); pump body and impeller are made of 316L stainless steel, which has better corrosion resistance than 304 and is suitable for heptane operation; the sealing method is John Crane MG1 mechanical seal, the sealing fluid is No. 32 turbine oil, and the leakage is ≤0.1mL / h. The relevant piping accessories include filter 14, differential pressure transmitter 15, heptane inlet pipe 19, and regulating valve 20. Filter 14 is a GL41W-16P type Y filter with a nominal diameter of DN80 and a rated pressure of 1.6MPa; The valve body is made of 304 stainless steel, and the filter screen is made of 316L stainless steel with a filtration accuracy of 100 mesh. This 100-mesh filter effectively intercepts residual welding slag and dust from the heptane, preventing clogging of the heat exchanger tubes (especially Φ25×2.5mm heat exchange tubes) and ensuring stable heat exchange efficiency. The differential pressure transmitter 15 is a Rosemount 3051CD model with a range of 0-0.1MPa and an accuracy of 0.075 class. The wetted parts are made of 316L stainless steel. It is used to detect the pressure difference between the inlet and outlet of filter 14 and outputs a 4-20mA signal to the PLC to determine the filter clogging status. The heptane inlet pipe 19 is made of 304 stainless steel, with a nominal diameter of DN80 and a wall thickness of 3.5mm. The regulating valve 20 is a ZJHP-16P type pneumatic diaphragm regulating valve with a nominal diameter of DN80, a rated pressure of 1.6MPa, a valve body of 304 stainless steel, and a valve core of 316L stainless steel. The actuator is a diaphragm type, with an input signal of 4-20mA and an opening adjustment range of 0-100%. The heptane flow is controlled by a PLC.

[0025] The first heat exchanger 2, the second heat exchanger 3, and the third heat exchanger 6 of the heat exchange unit are all shell-and-tube heat exchangers. The first heat exchanger 2 is a BEM600-2.5-40 type shell-and-tube heat exchanger; nominal diameter 600mm, tube-side pressure 2.5MPa, shell-side pressure 1.6MPa, heat exchange area 40㎡; its heat exchange tubes are Φ25×2.5mm (316L stainless steel), tube sheet and shell shell are (304 stainless steel), heptane flows in the tube side, and steam flows in the shell side; the auxiliary pipeline steam inlet pipe 16 is made of 304 stainless steel, DN100, wall thickness 4mm, and steam outlet pipe 7 is made of 304 stainless steel, DN80, wall thickness 3.5mm. The second heat exchanger 3 is a BEM500-2.0-30 type shell-and-tube heat exchanger with a nominal diameter of 500mm, a tube-side pressure of 2.0MPa, a shell-side pressure of 1.8MPa, and a heat exchange area of ​​30㎡. The heat exchange tubes are Φ20×2mm (316L stainless steel), and the tube sheet and shell are made of 304 stainless steel. The tube side carries a mixed gas, and the shell side carries high-temperature heptane. The auxiliary component, the liquid inlet pipe 5, is made of 304 stainless steel, DN80, with a wall thickness of 3.5mm. A flow meter 18 (EMF-HLD300 electromagnetic flow meter, DN80, range 0-60m) is installed on the liquid inlet pipe 5. 3 / h, accuracy grade 0.5, electrodes 316L stainless steel, lining PTFE). The third heat exchanger 6 is a BEM400-1.6-25 type shell-and-tube heat exchanger with a nominal diameter of 400mm, a tube-side pressure of 1.6MPa, a shell-side pressure of 1.2MPa, and a heat exchange area of ​​25㎡. Its heat exchange tubes are Φ19×2mm (316L stainless steel), and the tube sheet and shell are made of 304 stainless steel. The tube side carries mixed gas, and the shell side carries low-temperature steam. The auxiliary pipeline mixed gas inlet pipe 8 is made of 316L stainless steel, DN125, with a wall thickness of 5mm. The intermediate connecting pipe 9 is made of 316L stainless steel, DN125, with a wall thickness of 4.5mm. The shell-side outlet is connected to a steam condensate discharge pipe 22, which is equipped with a CS11H-16P type steam trap (DN25, 304 stainless steel). The steam condensate discharge pipe 22 can guide uncondensed low-temperature steam back to the subsequent condensation and recovery system, reducing steam waste and further reducing energy consumption.

[0026] The detection unit is used for temperature and concentration monitoring, including a thermometer 11 and a low-concentration heptane sensor 12. The thermometer 11 is a WZP-230 platinum resistance thermometer with a range of 0-200℃ and accuracy class A (±0.15℃, 0-100℃ range). Its protective tube is made of 316L stainless steel, with an insertion depth of 150mm (inserted to half the inner diameter of the mixed gas outlet pipe 10). It outputs a 4-20mA signal to the PLC to monitor the temperature of the preheated mixed gas. The low-concentration heptane sensor 12 is an MS400-C8H18 electrochemical sensor with a detection range of 0-1000ppm, accuracy ±5% FS, and response time ≤3s. Its probe is made of 316L stainless steel and is installed in the straight section of the mixed gas outlet pipe 10 (≥5 times the pipe diameter from valves and elbows). It outputs a 4-20mA signal to the PLC to detect heptane leakage.

[0027] The control unit is a Siemens S7-1200 series CPU 1214C DC / DC / DC controller, featuring 14 digital inputs, 10 digital outputs, and 2 analog inputs / outputs; it also supports expansion with an SM1234 analog module (4 inputs / 2 outputs) to adapt to various sensor signals. A 10.1-inch touchscreen (Siemens KTP1000 Basic) displays various parameters in real time (heptane flow rate, mixed gas temperature, liquid level, differential pressure, etc.), and supports manual / automatic mode switching and fault alarm query.

[0028] The heating process of this device involves three flow paths, namely: The first path is the heptane circulation heating path (heptane storage tank 1 → filter 14 → transfer pump 4 → first heat exchanger 2 → second heat exchanger 3 → heptane storage tank 1). Room temperature heptane (20-30℃) in heptane storage tank 1 flows out through transfer pipe 13 (304 stainless steel, DN80), first passing through filter 14 to filter impurities. Differential pressure transmitter 15 monitors the pressure difference between the filter inlet and outlet in real time (normal pressure difference ≤0.02MPa). The purified heptane enters transfer pump 4, is pressurized to 1.8-2.0MPa, and then transported to regulating valve 20 through heptane inlet pipe 19. The PLC controller adjusts the opening of regulating valve 20 (usually 50-70%) based on signals from flow meter 18 and thermometer 11, controlling the heptane flow rate to stabilize at 40±2m³ / h. 3 / h. Heptane enters the tube side of the first heat exchanger 2, where it exchanges heat with 0.8-1.2 MPa saturated steam (via steam inlet pipe 16) flowing into the shell side. The heptane temperature rises to 120-140℃, while the steam condenses into low-temperature steam (containing a small amount of condensate) at 80-100℃, which is discharged from the steam outlet pipe 7. The high-temperature heptane flows out from the tube side outlet of the first heat exchanger 2, enters the shell side of the second heat exchanger 3 via the liquid inlet pipe 5 (flow rate monitored in real time by flow meter 18), and exchanges heat with the mixed gas in the tube side. The heptane temperature drops to 80-100℃. The cooled heptane flows back to the heptane storage tank 1 from the shell side outlet of the second heat exchanger 3 via the heptane outlet pipe 21 (304 stainless steel, DN80), completing the cycle.

[0029] The second path is the low-temperature steam preheating path (first heat exchanger 2 → third heat exchanger 6 → steam condensate discharge pipe 22). Low-temperature steam (80-100℃, pressure 0.1-0.3MPa) discharged from the shell side of the first heat exchanger 2 is transported to the shell side of the third heat exchanger 6 via steam outlet pipe 7. The low-temperature steam exchanges heat with the mixed gas in the tube side of the third heat exchanger 6, releasing heat and partially condensing into water. The uncondensed steam and condensate are discharged together from the steam condensate discharge pipe 22, where a steam trap automatically discharges the condensate (drainage temperature ≤70℃) to prevent water accumulation in the shell side from affecting heat exchange efficiency. The uncondensed steam, after being discharged with the condensate, is processed by the subsequent condensate recovery system.

[0030] The third path is the preheating path for the vinyl chloride mixture (mixed gas inlet pipe 8 → third heat exchanger 6 → second heat exchanger 3 → mixed gas outlet pipe 10). Ambient temperature (20-30℃) vinyl chloride mixture (composition: vinyl chloride 95-97%, hydrogen chloride 2-4%, volume ratio, pressure 0.5-0.8MPa) enters the tube side of the third heat exchanger 6 from the mixed gas inlet pipe 8. The mixture exchanges heat with the low-temperature steam in the shell side, raising its temperature to 50-70℃ (completing "preliminary heating"), and then is transported to the tube side of the second heat exchanger 3 via the intermediate connecting pipe 9. In the tube side of the second heat exchanger 3, the mixture exchanges heat a second time with the high-temperature heptane (120-140℃) in the shell side, finally raising its temperature to 90-110℃ (the preheating temperature required by the process). The preheated mixed gas is discharged from the mixed gas outlet pipe 10 (316L stainless steel, DN125) and enters the subsequent vinyl chloride polymerization reaction process; the thermometer 11 monitors the outlet temperature in real time, and the low concentration heptane sensor 12 detects the heptane concentration in the mixed gas simultaneously (normal ≤30ppm).

[0031] When using this device: When the low-concentration heptane sensor 12 detects a heptane concentration ≥50ppm in the mixed gas outlet pipe 10 (a set threshold that can be adjusted via PLC), the sensor transmits a signal to the PLC controller. The PLC controller immediately outputs a stop signal, controlling the delivery pump 4 to stop running (motor power off); at the same time, it closes the regulating valve 20 (opening reduced to 0%), cutting off the heptane circulation path; it triggers the audible and visual alarm on the operation panel (LTE-1101 type, 220V AC, sound ≥85dB, red light flashing), and displays a heptane leakage fault on the touch screen, prompting the operator to check for potential leaks such as the sealing surface of the shell and tube side of the second heat exchanger 3 and the flange connection of the mixed gas outlet pipe 10.

[0032] When the differential pressure transmitter 15 detects a pressure difference ≥ 0.05 MPa (set threshold) between the inlet and outlet of filter 14, it determines that the filter is severely clogged. The transmitter transmits a signal to the PLC controller, which outputs a signal to close the regulating valve 20, cutting off the path of heptane into the first heat exchanger 2. At the same time, it stops the delivery pump 4 to prevent the pump from running dry due to insufficient suction pressure (≤ 0.2 MPa), which could damage the mechanical seal. The touch screen displays "filter clogged," and the red fault light on the operation panel illuminates. The operator needs to remove filter 14, replace it with a 316L stainless steel filter (100 mesh), clean it, and reinstall it. The system can only be restarted after the fault is reset.

[0033] When thermometer 11 detects that the outlet temperature of the mixed gas is <90℃, the PLC controls the opening of regulating valve 20 to increase the heptane flow rate and improve the heat exchange effect of the second heat exchanger 3. When the temperature is >110℃, the opening of regulating valve is reduced (reduced by 5-10% each time) to ensure that the temperature is stable at 90-110℃.

[0034] When flow meter 18 detects a deviation of 40m in heptane flow rate 3 When the flow rate is ±5% per hour, the PLC directly adjusts the opening of the regulating valve by 20 degrees to correct the flow deviation and avoid flow fluctuations affecting the heat exchange efficiency.

[0035] When the level gauge 17 detects that the liquid level in the heptane storage tank 1 is <1m (low liquid level threshold), the touch screen displays a low liquid level alarm and the yellow indicator light illuminates. The operator needs to add heptane to the tank through the heptane replenishment pipeline (DN50, 304 stainless steel). When the liquid level is >4.5m (high liquid level threshold), the orange indicator light illuminates, and replenishment is stopped to prevent heptane overflow.

[0036] The installation of all components of this device must comply with the "Code for Construction and Acceptance of Chemical Equipment Installation Engineering" (GB 50235-2010): The heptane storage tank 1 is installed on a concrete foundation (strength C30), with a foundation flatness error ≤5mm and a tank verticality error ≤1‰.

[0037] The first heat exchanger 2, the second heat exchanger 3, and the third heat exchanger 6 are installed horizontally, with 5mm thick 304 stainless steel gaskets between the supports and the foundation. The horizontality error of the heat exchanger axis is ≤0.5‰.

[0038] When installing the transfer pump 4, the coaxiality error between the pump shaft and the motor shaft should be ≤0.1mm to reduce operating vibration (vibration value ≤6.3mm / s).

[0039] When connecting pipelines, the flange sealing surface is raised face (RF), and the gasket is an XB450 type oil-resistant asbestos rubber gasket (3mm thick); stainless steel pipelines need to be degreased with carbon tetrachloride before installation to remove oil stains inside the pipes.

[0040] When installing the sensor, the thermometer 11 should be inserted to a depth of 1 / 3 to 1 / 2 of the pipe's inner diameter. The probe of the low-concentration heptane sensor 12 should face the direction of the mixed gas flow. Avoid installing it near bends or valves (at a distance of ≥5 times the pipe diameter from the component).

[0041] Daily checks include the operating current (10-14A) and vibration level of transfer pump 4; weekly checks include checking for mechanical seal leakage; daily monitoring of parameters (temperature, flow rate, liquid level, differential pressure) via the touchscreen and data recording; monthly cleaning of filter 14; quarterly replacement of the mechanical seal fluid (No. 32 turbine oil) for transfer pump 4; and semi-annual citric acid descaling of the three heat exchangers (5-8% citric acid solution, 60-70℃, circulating cleaning for 2-3 hours). Quarterly calibration of thermometer 11 (standard constant temperature bath calibration, error ≤ ±0.5℃) and differential pressure transmitter 15 (standard pressure source calibration, accuracy ≤ 0.075 grade); semi-annual backup of the PLC controller program; and annual inspection of the PLC controller wiring terminals to prevent loosening that could cause signal abnormalities.

Claims

1. A heating device for a vinyl chloride mixed gas preheater, comprising a heptane storage tank (1), a first heat exchanger (2), and a second heat exchanger (3), wherein the outlet of the heptane storage tank (1) is connected to the tube-side inlet of the first heat exchanger (2) via a transfer pump (4), the shell-side inlet of the second heat exchanger (3) is connected to the tube-side outlet of the first heat exchanger (2) via a liquid inlet pipe (5), and the shell-side outlet of the second heat exchanger (3) is connected to the inlet of the heptane storage tank (1) via a heptane outlet pipe (21), characterized in that, It also includes a third heat exchanger (6); the shell-side outlet of the first heat exchanger (2) is connected to a steam outlet pipe (7), the steam outlet pipe (7) is connected to the shell-side inlet of the third heat exchanger (6), the inlet and outlet of the tube side of the third heat exchanger (6) are respectively connected to a mixed gas inlet pipe (8) and an intermediate connecting pipe (9), and the intermediate connecting pipe (9) is connected to the tube-side inlet of the second heat exchanger (3).

2. The heating device as described in claim 1, characterized in that, The tube side outlet of the second heat exchanger (3) is connected to a mixed gas outlet pipe (10), and a thermometer (11) and a low-concentration heptane sensor (12) are connected to the mixed gas outlet pipe (10).

3. The heating device as described in claim 1, characterized in that, The heptane storage tank (1) and the delivery pump (4) are connected by a delivery pipe (13), which is equipped with a filter (14) and a differential pressure transmitter (15) located between the heptane storage tank (1) and the delivery pump (4).

4. The heating device as described in claim 1, characterized in that, The first heat exchanger (2) has a steam inlet pipe (16) connected to the shell side inlet.

5. The heating device as described in claim 3, characterized in that, The heptane storage tank (1) is equipped with a level gauge (17).

6. The heating device as described in claim 1, characterized in that, A flow meter (18) is installed on the inlet pipe (5).

7. The heating device as described in claim 5, characterized in that, The delivery pump (4) is connected to the tube inlet of the first heat exchanger (2) via a heptane inlet pipe (19), and a regulating valve (20) is provided on the heptane inlet pipe (19).

8. The heating device as claimed in claim 1, characterized in that, The shell-side outlet of the third heat exchanger (6) is connected to a steam condensate discharge pipe (22).

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