A device for treating low-boiling-point VOCs using liquid nitrogen deep condensation freezing method

Abstract

The present invention discloses a device for treating low-boiling-point VOCs using a liquid nitrogen deep condensation freezing method. The device comprises a precooler for precooling exhaust gas; a primary cooler for further initial condensation of the exhaust gas; a cryogenic cooler for deep condensation of the exhaust gas; and first and second freezers for freezing and thawing the exhaust gas. By utilizing the cryogenic properties of liquid nitrogen, the exhaust gas is deep condensed and then further cooled to a temperature below the condensation temperature of one or more VOC components. This allows for freezing of the exhaust gas, further reducing the VOC content in the exhaust gas, achieving a more thorough treatment, and improving the recovery rate.

Description

Technical Field

[0001] The present invention belongs to the field of environmental management, and in particular relates to a device for treating low-boiling-point VOCs by using a liquid nitrogen deep condensation freezing method. Background Art

[0002] Liquid nitrogen condensation has been widely used to treat VOCs. Liquid nitrogen is often used to prepare an intermediate refrigerant, which is then used to condense the exhaust gas. The deep low temperature characteristics of liquid nitrogen are not fully utilized, which can easily lead to problems such as high liquid nitrogen consumption, complex systems, and insufficient treatment of VOCs in the exhaust gas after treatment, making subsequent treatment difficult. Summary of the Invention

[0003] In response to the above-mentioned problems, the present invention provides a device for treating low-boiling-point VOCs using a liquid nitrogen deep condensation freezing method. This device fully utilizes the deep low-temperature characteristics of liquid nitrogen to minimize the content of VOCs in the treated tail gas and achieve a high recovery rate of the solvent, thereby solving technical problems in traditional processes such as high liquid nitrogen consumption, complex systems, and incomplete treatment of VOCs in the treated tail gas.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A device for treating low-boiling-point VOCs using a liquid nitrogen deep condensation freezing method comprises a tail gas feed main pipe, a liquid nitrogen feed main pipe, a precooler, a primary cooler, a cryogenic cooler, a first freezer, and a second freezer connected by pipelines;

[0006] The tail gas feed main pipe is divided into two routes: a first pipe and a second pipe. The first pipe is connected to the tail gas inlet of the precooler, the tail gas outlet of the precooler is connected to the tail gas inlet of the primary cooler, the tail gas outlet of the primary cooler is connected to the tail gas inlet of the cryogenic refrigerator, and the tail gas outlet of the cryogenic refrigerator is connected to the tail gas inlets of the first freezer and the second freezer respectively; the tail gas outlets of the first freezer and the second freezer are connected to the primary cooler for discharging the tail gas after the freezing treatment;

[0007] The liquid nitrogen feed main pipe is connected to the liquid nitrogen inlets of the first freezer and the second freezer respectively, the cryogenic refrigerator is connected to the liquid nitrogen outlets of the first freezer and the second freezer respectively, the low-temperature nitrogen pipeline of the cryogenic refrigerator is connected to the precooler, and the low-temperature nitrogen after heat exchange is discharged from the precooler.

[0008] Furthermore, the second pipeline is connected to the tail gas inlet of the first freezer and the second freezer respectively, and is used to thaw the first freezer or the second freezer to be thawed. The tail gas outlets of the first freezer and the second freezer are respectively connected to the first pipeline to output untreated tail gas for thawing.

[0009] Furthermore, the precooler, primary cooler, cryogenic cooler, first freezer and second freezer are all connected to the condensate tank pipeline, the condensate and the thawed liquid both enter the condensate tank, and the condensate tank is connected to a condensate pump.

[0010] Furthermore, switch valves are provided on the corresponding pipelines of the first freezer and the second freezer, and the opening and closing of the switch valves are automatically controlled by a DCS or PLC system.

[0011] Furthermore, the precooler, primary cooler, cryogenic freezer, first freezer and second freezer all adopt a shell-and-tube heat exchanger structure, with tail gas passing through the shell side and liquid nitrogen or cryogenic nitrogen passing through the tube side.

[0012] Furthermore, the first freezer and the second freezer perform freezing and thawing processes alternately. When one of the freezers is saturated, the deeply condensed exhaust gas is switched to the other freezer, and the saturated freezer enters the thawing process, thereby achieving alternating use.

[0013] Furthermore, in order to reduce the consumption of liquid nitrogen, the device is provided with a cold recovery process, that is, the exhaust gas that has finally been frozen, the low-temperature nitrogen discharged from the freezer, and the lower-temperature nitrogen discharged from the condenser are all used as cold sources to pre-cool and condense the exhaust gas.

[0014] Furthermore, the exhaust gas that has been frozen enters the primary cooler to condense the exhaust gas; the low-temperature nitrogen discharged from the first freezer and the second freezer enters the cryogenic cooler to deeply condense the exhaust gas; the lower-temperature nitrogen discharged from the cryogenic cooler enters the precooler to pre-condense the exhaust gas.

[0015] Furthermore, thermometers are connected to the tail gas outlet and nitrogen outlet of the first and second freezers, as well as the tail gas outlet of the cryogenic refrigerator; flow meters are provided on the liquid nitrogen inlets of the first and second freezers and the nitrogen inlet pipeline of the cryogenic refrigerator.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] (1) By utilizing the low temperature characteristics of liquid nitrogen, the tail gas is deeply condensed and then the tail gas temperature is further reduced so that the operating temperature is lower than the condensation temperature of one or more components of VOCs, thereby achieving freezing treatment of the tail gas, thereby further reducing the VOCs content in the tail gas, making the treatment more thorough, and improving the recovery rate.

[0018] (2) Liquid nitrogen is used directly to deeply condense and freeze VOCs without the need for additional intermediate refrigerants or auxiliary cooling sources.

[0019] (3) For the deep freezing process, a thawing and cooling process of the freezer is set up, and freezing and thawing are switched between each other, eliminating the extension of the production period caused by the extra time required for thawing in the traditional process of single equipment operation.

[0020] (4) In order to reduce the consumption of liquid nitrogen, a cold recovery process is set up, that is, the exhaust gas that has finally been refrigerated, the low-temperature nitrogen discharged from the freezer, and the lower-temperature nitrogen discharged from the condenser can all be used as cold sources to pre-cool and condense the exhaust gas, thereby reducing the consumption of liquid nitrogen and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the device and process flow of the present invention;

[0022] In the figure: A, precooler; B, primary cooler; C, deep freezer; D1, first freezer; D2, second freezer; E, tail gas feed main pipe; F, fan; G, liquid nitrogen feed main pipe; H, flow meter; T, thermometer; (1-21): first pipeline - twenty-first pipeline. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. It is obvious that the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, a device for treating low-boiling-point VOCs by using a liquid nitrogen deep condensation freezing method includes an exhaust gas feed main pipe E, a liquid nitrogen feed main pipe G, a precooler A, a primary cooler B, a deep cooler C, a first freezer D1, and a second freezer D2 connected by pipelines;

[0025] The tail gas feed main E is divided into two routes: a first pipeline 1 and a second pipeline 2. The first pipeline 1 is connected to the tail gas inlet of the precooler A. The precooler A is the main equipment for precooling the tail gas. The tail gas outlet of the precooler A is connected to the tail gas inlet of the primary cooler B. The tail gas outlet of the primary cooler B is connected to the tail gas inlet of the cryogenic refrigerator C. The tail gas outlet of the cryogenic refrigerator C is connected to the tail gas inlets of the first freezer D1 and the second freezer D2 respectively; the tail gas outlets of the first freezer D1 and the second freezer D2 are connected to the primary cooler B, and the primary cooler B is connected to a fan F. After the tail gas has been frozen, it is discharged by the fan F or enters the lower-level processing equipment after heat exchange in the primary cooler B; in this embodiment, the fan F is arranged on the exhaust pipe of the primary cooler B, and can also be set at other suitable positions according to the actual situation of the tail gas.

[0026] The liquid nitrogen feed main G is connected to the liquid nitrogen inlets of the first freezer D1 and the second freezer D2 respectively, the cryogenic refrigerator C is connected to the liquid nitrogen outlets of the first freezer D1 and the second freezer D2 respectively, and the low-temperature nitrogen pipeline of the cryogenic refrigerator C is connected to the precooler A, and is discharged after heat exchange with the exhaust gas in the precooler A.

[0027] The second pipeline 2 is connected to the exhaust gas inlet of the first freezer D1 and the second freezer D2 respectively, and is used to defrost the first freezer D1 or the second freezer D2 that is in a thawing state. The exhaust gas outlets of the first freezer D1 and the second freezer D2 are respectively connected to the first pipeline 1 to output untreated exhaust gas for thawing.

[0028] In the present invention, the first freezer D1 and the second freezer D2 perform freezing and thawing processes alternately. When one of the freezers is saturated, the deeply condensed exhaust gas is switched to the other freezer, and the saturated freezer enters the thawing process, thereby achieving alternating use.

[0029] The precooler A, primary cooler B, cryogenic cooler C, first freezer D1, and second freezer D2 are all connected to the condensate tank V. Condensate and thawed liquid from each level of equipment enter the condensate tank V, which is connected to a condensate pump P. The condensate is pumped out regularly based on the liquid level in the condensate tank V.

[0030] In order to reduce the consumption of liquid nitrogen, the device of the present invention is provided with a cold recovery process, that is, the exhaust gas that has finally been frozen, the low-temperature nitrogen discharged from the freezer, and the relatively low-temperature nitrogen discharged from the condenser are all used as cold sources to pre-cool and condense the exhaust gas. Specifically, the exhaust gas that has been frozen, since it still has a certain amount of cold capacity, enters the primary cooler B to condense the exhaust gas; the low-temperature nitrogen discharged from the first freezer D1 and the second freezer D2 enters the deep freezer C to deeply condense the exhaust gas; the relatively low-temperature nitrogen discharged from the deep freezer C enters the pre-cooler A to pre-condense the exhaust gas.

[0031] The various heat exchange devices of the present invention, such as the precooler A, primary cooler B, cryogenic cooler C, first freezer D1 and second freezer D2, all adopt a shell-and-tube heat exchanger structure, with tail gas passing through the shell side and liquid nitrogen or low-temperature nitrogen passing through the tube side.

[0032] In the present invention, the specific process flow of tail gas and liquid nitrogen is as follows:

[0033] After the tail gas enters from the tail gas feed main E, it is divided into two routes: the first pipeline 1 and the second pipeline 2. The tail gas to be treated enters the precooler A pipe inlet through the first pipeline 1, and after pre-condensation, it enters the pipe inlet of the primary cooler B from the precooler A pipe outlet through the third pipeline 3 for further condensation. After that, it is discharged from the pipe outlet of the primary cooler B through the fourth pipeline 4 to enter the pipe inlet of the deep cooler C for deep condensation. After the precooled tail gas passes through the primary cooler B and the deep cooler C, most of the VOCs are condensed. After that, the exhaust gas that has undergone deep condensation is discharged from the pipe outlet of the deep freezer C, and then enters the first freezer D1 through the fifth pipeline 5-sixth pipeline 6 or enters the second freezer D2 through the fifth pipeline 5-seventh pipeline 7 (because the two freezers perform freezing and thawing processes alternately, when one freezer is performing the thawing process, the other freezer is performing the freezing process, and then they are performed alternately without delaying the construction period). The exhaust gas entering the first freezer D1 or the second freezer D2, after the freezing or thawing process, contains some cold energy, and direct discharge will cause a waste of cold energy. At this time, the exhaust gas enters the primary cooler B through the eighth pipeline 8-ninth pipeline 9, and the pre-condensed exhaust gas is preliminarily condensed again. After the secondary utilization of the cold energy in the exhaust gas, the exhaust gas is discharged by the fan F or enters the lower-level processing equipment.

[0034] At the same time as the exhaust gas enters the treatment device, liquid nitrogen also enters the treatment device. Liquid nitrogen is fed from the liquid nitrogen feed main G through the eleventh pipeline 11-the twelfth pipeline 12 or the thirteenth pipeline 13, respectively, into the first freezer D1 and the second freezer D2 for freezing the deep-condensed exhaust gas. When the first freezer D1 or the second freezer D2 reaches saturation, the other freezer switches to continue the freezing process, while the saturated freezer enters the thawing process. After heat exchange in the first freezer D1 or the second freezer D2, the liquid nitrogen is converted into low-temperature nitrogen gas. It enters the cryogenic unit C through the fourteenth pipeline 14 or the fifteenth pipeline 15, respectively, serving as a cooling source for the deep condensation of the exhaust gas in cryogenic unit C. The low-temperature nitrogen gas outlet of condenser C enters the precooler A through the sixteenth pipeline 16, serving as a cooling source for the pre-condensation of the exhaust gas in precooler A. The low-temperature nitrogen gas after heat exchange is discharged through the seventeenth pipeline 17.

[0035] When the thawing process of the first freezer D1 or the second freezer D2 is carried out, the untreated exhaust gas is used as a heat source to thaw the already frozen saturated freezer. The untreated exhaust gas enters the first freezer D1 or the second freezer D2 through the second pipeline-2 eighteenth pipeline 18 or the nineteenth pipeline 19 to thaw the already frozen saturated freezer. The untreated exhaust gas that has been thawed and heat exchanged returns to the first pipeline 1 through the twentieth pipeline 20-twenty-first pipeline 21 to carry out the condensation and freezing process of the untreated exhaust gas.

[0036] Untreated exhaust gas is used as a heat source to defrost the freezer, eliminating the need for additional heat sources and saving energy. When additional heat is required for production, an auxiliary heater can be installed at a suitable location on the exhaust gas pipeline before it enters the freezer. This can use electric heating or other heat sources for defrosting.

[0037] In the present invention, thermometers T are connected to the tail gas outlet and nitrogen outlet of the first freezer D1 and the second freezer D2, as well as the tail gas outlet of the cryogenic refrigerator C; flow meters H are provided on the liquid nitrogen inlets of the first freezer D1 and the second freezer D2 and the nitrogen inlet pipeline of the cryogenic refrigerator C.

[0038] This technology utilizes a DCS or PLC control system. On-off valves are installed in the corresponding pipelines of the first and second freezers D1 and D2, as well as in the thawing process pipeline. All valves are automatically opened and switched by the DCS or PLC control system. The control process is simple: simply adjusting the amount of liquid nitrogen entering the first and second freezers D1 and D2 controls the outlet temperature of the freezer exhaust gas and the outlet temperature of the nitrogen gas. Adjusting the amount of low-temperature nitrogen entering cryogenic freezer C controls the outlet temperature of the cryogenic freezer C. Defrosting time is set based on the characteristics of the exhaust gas, ensuring safe production. The freezers are thawed periodically, with freezing and thawing times calculated based on the exhaust gas characteristics. Furthermore, temperature ranges are pre-set for each monitoring point based on the exhaust gas characteristics. If the system detects a temperature outside the pre-set range, it automatically adjusts the amount of liquid nitrogen entering flowmeter H to keep the temperature at each point within the normal range.

[0039] It should be noted that the first freezer and the second freezer mentioned in this application adopt a special cooler structure. The relevant technology has been disclosed in a Chinese patent (CN113483582 A A freezer suitable for VOCs tail gas treatment) and will not be described in detail here.

[0040] This application provides a freezer thawing and switching process for deep freezing processes. Although the examples of this patent utilize a process involving two identical freezers switching between them (i.e., one in use while the other thaws), the use of freezing and thawing devices for treating VOCs or recovering solvents falls within the scope of this patent.

[0041] Example description:

[0042] The technology of the present invention has a wide range of applications and strong adaptability, as shown below:

[0043] 1) Example 1: Methanol exhaust gas

[0044] Methanol waste gas, gas volume 600Nm 3 / h, average discharge temperature 20℃, discharge pressure: normal pressure.

[0045] Methanol concentration: 172.25g / Nm 3 The calculation and actual processing results of methanol recovery using this patented technology are as follows:

[0046] Table 1 Calculation of methanol waste gas treatment

[0047]

[0048] 2) Example 2, toluene waste gas

[0049] Toluene waste gas, gas volume 600Nm 3 / h, average discharge temperature 20℃, discharge pressure: normal pressure.

[0050] Toluene concentration: 110.5g / Nm 3 The calculation and actual processing results are as follows:

[0051] Table 2 Calculation of toluene waste gas treatment

[0052]

[0053] It should be noted that although the waste gas to be treated in the working conditions of the embodiment is a single VOCs component, it does not mean that it can only treat waste gas of a single VOCs component. In fact, this patented technology has technical advantages in working conditions that treat multiple VOCs components and is suitable for working conditions requiring high recovery rates and liquefied hydrocarbon recovery. This patented technology can be used in combination with other treatment technologies.

Claims

1. A device for treating low-boiling-point VOCs using a liquid nitrogen deep condensation freezing method, characterized in that: It includes an exhaust gas feed main pipe (E), a liquid nitrogen feed main pipe (G), a precooler (A), a primary cooler (B), a cryogenic cooler (C), a first freezer (D1), and a second freezer (D2) connected by pipelines; The tail gas feed main pipe (E) is divided into two routes: a first pipeline (1) and a second pipeline (2). The first pipeline (1) is connected to the tail gas inlet of the precooler (A), the tail gas outlet of the precooler (A) is connected to the tail gas inlet of the primary cooler (B), the tail gas outlet of the primary cooler (B) is connected to the tail gas inlet of the deep cooler (C), and the tail gas outlet of the deep cooler (C) is respectively connected to the tail gas inlets of the first freezer (D1) and the second freezer (D2); the tail gas outlets of the first freezer (D1) and the second freezer (D2) are connected to the primary cooler (B), and the primary cooler (B) is connected to a fan (F). After the tail gas has been cooled and heated in the primary cooler (B), it is discharged by the fan (F); The liquid nitrogen feed main pipe (G) is connected to the liquid nitrogen inlets of the first freezer (D1) and the second freezer (D2), respectively. The cryogenic refrigerator (C) is connected to the liquid nitrogen outlets of the first freezer (D1) and the second freezer (D2), respectively. The low-temperature nitrogen pipeline of the cryogenic refrigerator (C) is connected to the precooler (A), and the low-temperature nitrogen after heat exchange is discharged from the precooler (A). The second pipeline (2) is connected to the tail gas inlet of the first freezer (D1) and the second freezer (D2) respectively, and is used to thaw the first freezer (D1) and the second freezer (D2) to be thawed. The tail gas outlets of the first freezer (D1) and the second freezer (D2) are connected to the first pipeline (1) respectively, and the untreated tail gas is led out for thawing. The first freezer (D1) and the second freezer (D2) perform freezing and thawing processes alternately. When one of the freezers is saturated, the deeply condensed exhaust gas is switched to the other freezer, and the saturated freezer enters the thawing process, achieving alternating use.

2. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: The precooler (A), primary cooler (B), deep cooler (C), first freezer (D1) and second freezer (D2) are all connected to the condensate tank (V) pipeline, and the condensate and thawing liquid both enter the condensate tank (V). The condensate tank (V) is connected to a condensate pump (P).

3. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: On-off valves are provided on the corresponding pipelines of the first freezer (D1) and the second freezer (D2), and the opening and closing of the on-off valves are automatically controlled by a DCS or PLC system.

4. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: The precooler (A), primary cooler (B), cryogenic cooler (C), first freezer (D1) and second freezer (D2) all adopt a shell-and-tube heat exchanger structure, with tail gas passing through the shell side and liquid nitrogen or low-temperature nitrogen passing through the tube side.

5. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: In order to reduce the consumption of liquid nitrogen, the device is provided with a cold recovery process, that is, the exhaust gas that has finally undergone freezing treatment, the low-temperature nitrogen discharged from the first freezer (D1) and the second freezer (D2), and the lower-temperature nitrogen discharged from the cryogenic refrigerator (C) are all used as cold sources to pre-cool and condense the exhaust gas.

6. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 5, characterized in that: The exhaust gas that has been frozen enters the primary cooler (B) to condense the exhaust gas; the low-temperature nitrogen discharged from the first freezer (D1) and the second freezer (D2) enters the cryogenic cooler (C) to deeply condense the exhaust gas; the lower-temperature nitrogen discharged from the cryogenic cooler (C) enters the precooler (A) to pre-condense the exhaust gas.

7. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: Thermometers (T) are connected to the tail gas outlet and nitrogen outlet of the first freezer (D1) and the second freezer (D2), as well as the tail gas outlet of the cryogenic refrigerator (C).

8. The device for treating low-boiling-point VOCs by using liquid nitrogen deep condensation freezing method according to claim 1, characterized in that: Flow meters (H) are provided on the liquid nitrogen inlet pipes of the first freezer and the second freezer and the nitrogen inlet of the cryogenic refrigerator (C).

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