Vinyl chloride mixed gas purifying and preheating device

Abstract

The utility model discloses a chloroethylene mixed gas purifying and preheating device which comprises a mixer, a cooler, a demister, a heat exchanger, a preheater, a steam preheater, an A-group converter, a B-group converter, a condensate tank and the like which are connected in sequence, a forced circulation pump arranged in the cooler increases the circulation volume of cooling water, reduces the temperature difference between the gas phase and the water phase of the graphite cooler, effectively controls the water content of the mixer, reduces the bed resistance of the converter and prolongs the service life of a catalyst; the steam preheater is arranged, so that the converter system is in a virtuous cycle by increasing the temperature of mixed gas and improving the conversion rate of the converter, the purity of crude VC is improved, the tail gas emptying amount is reduced, and safe and stable operation of a production device is ensured.

Description

Technical Field

[0001] The utility model belongs to the technical field of vinyl chloride production, and in particular relates to a vinyl chloride mixed gas purification and preheating device. Background Art

[0002] When producing vinyl chloride using the acetylene method, the raw gases acetylene and hydrogen chloride are mixed, pretreated, heated, and then fed into the converter. A low-mercury catalyst is used as the catalyst for the reaction. The reaction temperature in the converter usually needs to be between 110-160°C. Before the mixed gas from the preheater enters the converter, the mixed gas temperature drops rapidly due to changes in the cross-sectional area of ​​the pipeline and equipment. The temperature of the mixed gas will drop to around 83°C before entering the converter tubes. On the other hand, due to actual on-site installation reasons, the preheater is far away from the hot water tank, resulting in greater pipeline resistance and large heat loss in the middle. The preheater outlet temperature, as the starting temperature for the vinyl chloride synthesis reaction, significantly influences the subsequent synthesis reaction in the converter. A high preheater outlet manifold temperature results in a high starting temperature for the synthesis reaction, allowing the mixed gas to react rapidly upon entering the converter. A low preheater outlet temperature also results in a low starting temperature for the synthesis reaction, slowing the reaction upon entering the converter, increasing the converter bed resistance and subsequently reducing the conversion rate. A low-temperature mixed gas, upon contact with the catalyst, deviates significantly from the ideal reaction rate, requiring hot water and self-reaction heat to heat the mixed gas to the ideal reaction temperature. This results in inefficient use of the catalyst at the top of the converter tubes, uneven load distribution, and sub-economic operation of the converter. Low reaction temperatures result in low conversion rates, while higher temperatures increase them. However, excessively high temperatures can cause HgCl2 to sublime, destroying the catalyst's crystalline surface, causing acetylene gas to form resinous polymers that deposit on the catalyst surface, deactivating the catalyst. Therefore, appropriately increasing the preheater outlet manifold temperature can positively impact conversion rates.

[0003] Meanwhile, the mixed gas temperature at the cooler's outlet is controlled between -18°C and -13°C. However, the temperature at the cooler's water inlet is significantly lower than -18°C. This causes condensed acid to crystallize on the tube walls, forming ice. This ice layer thickens as it descends the tubes, forming a cone-shaped pattern from top to bottom. Over time, the cooler tubes fill with ice, gradually increasing system resistance and decreasing feed gas flow. Based on current production conditions, system resistance rises by approximately 3 kPa every eight hours, and feed gas flow begins to decrease. To reduce system resistance, the cooler's water inlet regulating valve is closed, allowing the mixed gas to defrost itself. During this defrosting process, the mixed gas remains uncooled and dehydrated, leading to agglomeration of the mercuric chloride catalyst, increased converter system resistance, and frequent corrosion and leaks in the converter tubes. Utility Model Content

[0004] The purpose of the utility model is to solve the problems of ice formation in the cooler tubes during the cooling and dehydration of the raw gas in the existing conversion system, which increases the system resistance and the frequent thawing of ice leads to high water content in the raw gas. The initial reaction temperature of the raw gas is low, and the reaction of the mixed gas is slow after entering the converter, which increases the bed resistance of the converter and reduces the conversion rate. The catalyst at the upper end of the converter tubes cannot be effectively utilized, and the load is unevenly distributed, resulting in the converter not being in an economical operation state.

[0005] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0006] A vinyl chloride mixed gas purification and preheating device comprises a mixer, a cooler, a demister, a heat exchanger, a preheater, a steam preheater, a group A converter, a group B converter, and a condensate tank connected in sequence; the cooler is connected to a cooling water supply pipe and a cooling water return pipe, the forced circulation pump inlet pipe is connected to the cooling water return pipe, the forced circulation pump outlet pipe is connected to the cooling water supply pipe, and a cooling water regulating valve provided on the cooling water supply pipe is electrically connected to a mixed gas thermometer at an outlet of the cooler;

[0007] The upper part of the steam preheater is connected to a steam pipe provided with a steam regulating valve and a steam flowmeter, the top of the steam preheater is connected to a mixed gas outlet pipe, the mixed gas outlet pipe is provided with a hot mixed gas thermometer, and the hot mixed gas thermometer is electrically connected to the steam regulating valve; the lower part of the steam preheater is connected to a condensate pipe connected to the top of the condensate tank, the condensate tank is provided with a condenser and a condensate tank level gauge, the bottom of the condensate tank outlet pipe is connected to a condensate pump, and the condensate pump outlet pipeline is provided with a condensate regulating valve and electrically connected to the condensate tank level gauge.

[0008] Furthermore, the mixer is connected to an acetylene gas pipe and a hydrogen chloride pipe.

[0009] Furthermore, the cooler, heat exchanger and preheater are graphite shell and tube coolers, which can be set to multiple stages according to process requirements. The cooling medium of the cooler is -35°C calcium chloride brine, the cooling medium of the heat exchanger is -7°C calcium chloride brine, and the heat exchange medium of the preheater is 97°C hot water.

[0010] Furthermore, the condensate pump outlet pipe is connected to a 97°C hot water return pipe.

[0011] The beneficial effects of the utility model are as follows: the utility model provides a vinyl chloride mixed gas purification and preheating device, the forced circulation pump arranged in the cooler increases the cooling water circulation volume, reduces the temperature difference between the gas phase and the water phase of the graphite cooler, effectively controls the water content of the mixer, reduces the resistance of the converter bed, and extends the service life of the catalyst; the steam preheater arranged increases the conversion rate of the converter by increasing the temperature of the mixed gas, puts the converter system in a virtuous cycle, improves the purity of crude VC, reduces the exhaust gas discharge volume, and ensures the safe and stable operation of the production device. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural diagram of the present utility model.

[0013] In the figure: 1. Mixer; 2. Cooler; 21. Mixed gas temperature gauge at cooler outlet; 22. Cooling water regulating valve; 23. Forced circulation pump; 24. Cooling water supply pipe; 25. Cooling water return pipe; 26. Forced circulation pump inlet pipe; 27. Forced circulation pump outlet pipe; 3. Defogger; 4. Heat exchanger; 5. Preheater; 6. Steam preheater; 61. Hot mixed gas temperature gauge; 62. Steam regulating valve; 63. Steam flow meter; 64. Condensate pipe; 65. Condensate; 66. Condensate tank level gauge; 67. Condensate regulating valve; 68. Condensate pump; 7. Converter group A; 8. Converter group B; 9. Condensate tank. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to more clearly and accurately understand the technical solution of the present invention, the following is a detailed explanation by way of examples. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0015] Example

[0016] Reference Figure 1 As shown, a vinyl chloride mixed gas purification and preheating device includes a mixer 1, a cooler 2, a demister 3, a heat exchanger 4, a preheater 5, a steam preheater 6, a group A converter 7, a group B converter 8, and a condensate tank 9 connected in sequence; the cooler 2 is connected to a cooling water supply pipe 24 and a cooling water return pipe 25, a forced circulation pump inlet pipe 26 is connected to the cooling water return pipe 25, and a forced circulation pump outlet pipe 27 is connected to the cooling water supply pipe 24. A cooling water regulating valve 22 provided on the cooling water supply pipe 24 is electrically connected to a mixed gas temperature meter 21 at the outlet of the cooler;

[0017] The upper part of the steam preheater 6 is connected to a steam pipe provided with a steam regulating valve 62 and a steam flowmeter 63. The top of the steam preheater 6 is connected to a mixed gas outlet pipe, and the mixed gas outlet pipe is provided with a hot mixed gas thermometer 61. The hot mixed gas thermometer 61 is electrically connected to the steam regulating valve 62. The lower part of the steam preheater 6 is connected to a condensate pipe 64 connected to the top of the condensate tank 9. The condensate tank 9 is provided with a condenser 65 and a condensate tank level gauge 66. The bottom of the outlet pipe of the condensate tank 9 is connected to a condensate pump 68. The outlet pipeline of the condensate pump 68 is provided with a condensate regulating valve 67 and is electrically connected to the condensate tank level gauge 66.

[0018] Furthermore, the mixer 1 is connected to an acetylene gas pipe and a hydrogen chloride pipe.

[0019] Furthermore, the cooler 2, heat exchanger 4 and preheater 5 are graphite shell and tube coolers, which can be set to multiple stages according to process requirements. The cooling medium of the cooler is -35°C calcium chloride brine, the cooling medium of the heat exchanger is -7°C calcium chloride brine, and the heat exchange medium of the preheater is 97°C hot water.

[0020] Furthermore, the outlet pipe of the condensate pump 68 is connected to a 97°C hot water return pipe.

[0021] The implementation process of this system:

[0022] The pretreated raw materials acetylene gas and hydrogen chloride gas enter the mixer 1 for mixing according to n(HCl):n(C2H2)=1.02~1.0:1, and the mixed gas after sufficient mixing enters the cooler 2. Usually, the cooler 2 is set to two stages, and the cooler is cooled by -35°C brine. The cooler 2 is connected to a cooling water supply pipe 24 and a cooling water return pipe 25. The forced circulation pump inlet pipe 26 is connected to the cooling water return pipe 25, and the forced circulation pump outlet pipe 27 is connected to the cooling water supply pipe 24. The cooling water regulating valve 22 provided on the cooling water supply pipe 24 automatically adjusts the -35°C brine supply water volume according to the display value (-15--17°C) of the mixed gas thermometer 21 out of the cooler, thereby reducing the temperature difference between the gas phase and the water phase in the cooler to prevent freezing. The forced circulation pump increases the cooling water circulation volume, effectively controls the water content in the mixer, and reduces the resistance of the converter bed.

[0023] After cooling and removing water, the mixed gas enters the demister 3. A large amount of acid mist is captured and filtered, then enters the heat exchanger 4 and preheater 5 for cascade preheating. It then enters the steam preheater 6. The steam regulating valve 62 automatically adjusts the steam flow rate based on the displayed value of the hot mixed gas thermometer 61 (100-111°C) to ensure that the mixed gas reaches the reaction temperature when entering the converter. Upon contact with the catalyst, the reaction begins, effectively utilizing the catalyst, improving the converter's conversion rate, and placing the converter system in a virtuous cycle. This improves the purity of crude VC, reduces the amount of tail gas venting, and ensures safe and stable operation of the production unit. The condensate from the preheating of the steam preheater 6 flows through the condensate pipe 64 into the condensate tank 9. The liquid level in the condensate tank 9 is pumped into the 97°C hot water return pipe by the condensate pump 68 and then recycled into the hot water tank for reuse.

[0024] Principle of raw gas freeze dehydration: As the temperature of the raw gas decreases, the water condensed in the hydrogen chloride reacts with the hydrogen chloride gas to form saturated hydrochloric acid. As the pressure increases and the temperature drops, the concentration of the generated hydrochloric acid gradually increases. At 40kPa and around -16°C, the hydrochloric acid concentration can reach around 40% (mass fraction). However, when the temperature drops below -18°C, the generated concentrated hydrochloric acid easily forms hydrate crystals and blocks the tubes of the graphite cooler. Therefore, the freeze dehydration temperature of the mixed gas is generally controlled above -18°C.

[0025] The above is only a preferred specific implementation method of the present invention, but the protection scope of the present invention is not limited to this. Any technician familiar with the technical field within the technical scope disclosed by the present invention can make equivalent replacements or changes based on the technical solution and utility model concept of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A chlorinated vinyl gas mixture purification and preheating device, characterized by: It includes a mixer, a cooler, a demister, a heat exchanger, a preheater, a steam preheater, a group A converter, a group B converter and a condensate tank connected in sequence; the cooler is connected to a cooling water supply pipe and a cooling water return pipe, the forced circulation pump inlet pipe is connected to the cooling water return pipe, the forced circulation pump outlet pipe is connected to the cooling water supply pipe, and the cooling water regulating valve provided on the cooling water supply pipe is electrically connected to the mixed gas thermometer at the outlet of the cooler; The upper part of the steam preheater is connected to a steam pipe provided with a steam regulating valve and a steam flowmeter, the top of the steam preheater is connected to a mixed gas outlet pipe, the mixed gas outlet pipe is provided with a hot mixed gas thermometer, and the hot mixed gas thermometer is electrically connected to the steam regulating valve; the lower part of the steam preheater is connected to a condensate pipe connected to the top of the condensate tank, the condensate tank is provided with a condenser and a condensate tank level gauge, the bottom of the condensate tank outlet pipe is connected to a condensate pump, and the condensate pump outlet pipeline is provided with a condensate regulating valve and electrically connected to the condensate tank level gauge.

2. The ethylene chloride mixed gas purification and preheating device according to claim 1, characterized in that: The mixer is connected with an acetylene gas pipe and a hydrogen chloride pipe.

3. The ethylene chloride mixed gas purification and preheating device according to claim 1, characterized in that: The cooler, heat exchanger and preheater are graphite shell and tube coolers, which can be set to multiple levels according to process requirements. The cooling medium of the cooler is -35°C calcium chloride brine, the cooling medium of the heat exchanger is -7°C calcium chloride brine, and the heat exchange medium of the preheater is 97°C hot water.

4. The ethylene chloride mixed gas purification and preheating device according to claim 1, characterized in that: The condensate pump outlet pipe is connected to the 97°C hot water return pipe.

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