Process and apparatus for recovering liquid NO2 by condensation from a mixture containing NO2

Abstract

The application discloses a method and equipment for condensing and recovering liquid NO2 from mixed gas containing NO2, which comprises a skid-mounted box body and a gas filter, a gas compressor, a cooler, a buffer tank, a first-stage cryogenic device, a second-stage cryogenic device and a product collecting tank which are sequentially connected in the skid-mounted box body. The method provided by the application is simple in process steps and easy to realize, can pressurize and condense liquid NO2 from mixed gas containing NO2, is suitable for all mixed gas containing any concentration of NO2 after drying, is especially suitable for low partial pressure NO2 mixed gas, and the concentration of the prepared liquid NO2 is high. The equipment provided by the application is simple in structure, is concentrated in a relatively independent skid-mounted box body, is good in integrity, is strong in mobility, can be flexibly moved to be suitable for different application scenes, and is wide in application range.

Description

Technical Field

[0001] This invention belongs to the field of liquid NO2 recovery technology, specifically relating to a method and equipment for condensing and recovering liquid NO2 from a NO2-containing gas mixture. Background Technology

[0002] Almost all combustion processes are accompanied by NO. x The generation of NO, of which NO is caused by coal combustion. x It accounts for more than 70% of nitrogen oxide emissions in my country. Large amounts of NO... x Besides causing photochemical pollution and acid rain, NO can also cause diseases affecting human respiratory and skin organs. Therefore, NO is a serious concern. x Pollutant control is extremely important. Currently, SCR technology using NH3 is the mainstream denitrification technology in large-scale emission control processes, capable of removing NO3-. x It is reduced to N2, but problems such as ammonia escape still exist. From the perspective of a circular economy, NO in flue gas... x NO is an important resource that can be concentrated through adsorption and capture, and further utilized for resource recovery in flue gas. x The dual purpose of purification and recycling.

[0003] The invention patent, published under publication number "CN109794137A" and entitled "A Method and System for Adsorption, Purification, Enrichment, and Recovery of Nitrogen Oxides in Flue Gas," discloses a method and system for adsorption, purification, enrichment, and recovery of nitrogen oxides in flue gas. The method, while ensuring that no acid condensation or condensation occurs during flue gas transportation and that the NOx component content is not lost, first desulfurizes, cools, dehydrates, and then cools again the flue gas; then, sulfur-free, water-free, and room-temperature flue gas is passed into an adsorber to adsorb NO. x The adsorption process involves adsorption and removal; after adsorption saturation, the adsorbent is regenerated by heating and negative pressure to obtain a mixed desorbed gas containing high concentrations of NO2 and NO; finally, the desorbed gas is liquefied, separated, and concentrated using distillation to obtain high-purity liquid NO2 and gaseous NO products. This method overcomes the limitations of existing methods for removing NO from flue gas. x The shortcomings of non-destructive enrichment and recovery in the efficient removal of NO from flue gas x This method simultaneously produces high-value-added NO and NO2 products, but the steps are cumbersome, the system is complex, and it is not well-suited for treating low-partial-pressure NO2 gas. Therefore, there is an urgent need for a method and equipment capable of liquefying and recovering liquid NO2 products from NO2-containing gases, especially low-partial-pressure NO2 gases, which could achieve the treatment of NO in flue gas. x It can not only purify and remove NO2, but also achieve resource recovery of NO2. Summary of the Invention

[0004] To address the aforementioned shortcomings, one objective of this invention is to provide a method for condensing and recovering liquid NO2 from a NO2-containing gas mixture, thereby achieving the goal of recovering NO from flue gas. x It can not only purify and remove NO2, but also realize the resource recycling of NO2, forming a new approach that is both efficient and environmentally friendly.

[0005] The second objective of this invention is to provide a device for condensing and recovering liquid NO2 from a NO2-containing gas mixture, which has a simple overall structure and is flexible.

[0006] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0007] A method for condensing and recovering liquid NO2 from a NO2-containing gas mixture, comprising the following steps:

[0008] S1: The NO2-containing mixed gas, after being dehydrated and dried, is compressed to obtain high-pressure gas; preferably, the boiling points of the remaining gas components in the NO2-containing mixed gas are all lower than the boiling point of NO2, 21.4℃; the NO2-containing mixed gas is filtered before compression to remove particulate impurities from the gas and prevent them from clogging the equipment pipeline.

[0009] S2: The high-pressure gas obtained after compression is cooled down to room temperature and then stored in a buffer tank;

[0010] S3: The high-pressure gas in the buffer tank flows sequentially through the first-stage cryogenic reactor and the second-stage cryogenic reactor after pressure regulation. The two independently operating cryogenic cold traps provide cooling capacity to the two-stage cryogenic reactors respectively. The NO2 in the high-pressure gas condenses into liquid NO2 on the wall of the second-stage cryogenic reactor.

[0011] S4: Collect the liquid NO2 to obtain a liquid NO2 product. Detect the flow rate and residual NO2 concentration of the gas discharged from the secondary cryogenic reactor. The recovery rate of NO2 recovered from condensation can be calculated based on the flow rate and NO2 concentration of the NO2-containing mixed gas, the flow rate and NO2 concentration of the residual gas after condensation, and the flow rate and NO2 concentration of the liquid NO2.

[0012] As a preferred embodiment of the present invention, in step S3, the water in the first-stage cryogenic reactor needs to be drained periodically, that is, a very small amount of residual water is drained periodically through the drain valve at the bottom of the first-stage cryogenic reactor to ensure the purity of the NO2 liquid as much as possible.

[0013] An apparatus for implementing the above-described method of condensing and recovering liquid NO2 from a NO2-containing gas mixture includes a skid-mounted housing and a gas filter, a gas compressor, a cooler, a buffer tank, a primary cryogenic cooler, a secondary cryogenic cooler, and a product collection tank disposed within the skid-mounted housing, wherein the gas filter, gas compressor, cooler, buffer tank, primary cryogenic cooler, secondary cryogenic cooler, and product collection tank are connected in sequence.

[0014] As a preferred embodiment of the present invention, the nitrogen protection pressure of the gas compressor is 0.05 to 0.2 MPa to prevent a small amount of leakage of the working gas during the compression process.

[0015] As a preferred embodiment of the present invention, the top of the secondary cryogenic reactor is provided with an outlet, which is connected to a flue gas analyzer. The flue gas analyzer can measure and record the concentration of NO2 in the condensed gas in real time, so as to monitor the operation effect of the skid-mounted equipment and calculate the recovery rate.

[0016] In a preferred embodiment of the present invention, multiple sets of temperature detection components are provided on both the primary and secondary cryogenic reactors. The purpose of these components is to measure the temperatures of the gas inside the tube, the outer wall of the tube, and the refrigerant outside the tube, respectively, in order to calculate the local heat transfer coefficients of each cryogenic reactor. Preferably, the number of temperature detection components on the secondary cryogenic reactor is greater than the number on the primary cryogenic reactor, preferably 1.5-3 times, to more accurately obtain the temperature at various locations within the cryogenic reactor.

[0017] The temperature detection assembly includes an internal tube detection thermocouple, an external tube wall detection thermocouple, and an external tube refrigerant detection thermocouple. The internal tube detection thermocouple measures the temperature of the gas inside the condenser tube, the external tube wall detection thermocouple measures the temperature of the outer wall surface of the condenser tube, and the external tube refrigerant detection thermocouple measures the temperature of the refrigerant flowing outside the condenser tube and inside the cryogenic chamber.

[0018] The beneficial effects of this invention are as follows: The method provided by this invention has simple process steps and is easy to implement. It can obtain liquid NO2 from a NO2-containing gas mixture by pressurization and condensation. It is applicable to all dried NO2-containing gas mixtures of any concentration, especially suitable for low partial pressure NO2 gas mixtures, and the obtained liquid NO2 has a high concentration. The equipment provided by this invention has a simple structure, is concentrated in a relatively independent skid-mounted housing, has good integration, strong mobility, and can be flexibly moved to suit different application scenarios, thus having a wide range of applications.

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0021] Figure 2 This is a schematic diagram of the temperature detection components of the first-stage cryogenic reactor in this invention.

[0022] Figure 3 yes Figure 2 A schematic diagram of the medium temperature detection component.

[0023] Figure 4 This is a schematic diagram of the temperature detection components of the secondary cryogenic reactor in this invention. Detailed Implementation

[0024] Example: See Figure 1 This embodiment provides a method and apparatus for condensing and recovering liquid NO2 from a NO2-containing gas mixture.

[0025] The equipment for condensing and recovering liquid NO2 from a NO2-containing gas mixture includes a skid-mounted enclosure, a gas filter, a gas compressor, a cooler, a buffer tank, a primary cryostat, a secondary cryostat, and a product collection tank.

[0026] The skid-mounted enclosure includes a rectangular frame and side panels that cover the rectangular frame. The rectangular frame and side panels are preferably made of stainless steel.

[0027] The locations of the gas filter, gas compressor, cooler, buffer tank, primary cryogenic reactor, secondary cryogenic reactor, and product collection tank within the skid-mounted enclosure are not limited. During actual installation, they are positioned according to the size and shape of the aforementioned components within the skid-mounted enclosure to fully and rationally utilize the space. Corresponding to the installation locations of each component, gas inlets, condensed gas outlets, NO2 liquid outlets, circulating water inlets, circulating water outlets, and nitrogen inlets are pre-reserved on the side plates.

[0028] The gas compressor is preferably a three-stage reciprocating compressor, driven by a three-phase motor, which drives the piston to achieve gas compression in a three-stage linkage. The gas compressor is equipped with two-stage cooling, both of which are tubular water-cooled heat exchangers. The heat generated by the gas compressor and the heat at the water-cooled heat exchanger are exchanged through circulating water. The nitrogen protection pressure of the gas compressor is 0.05-0.2 MPa to prevent a small amount of leakage of the working gas during the compression process.

[0029] The cooler is preferably a shell-and-tube water-cooled heat exchanger, using circulating water as the refrigerant.

[0030] The buffer tank can temporarily buffer and store high-pressure gas, enabling continuous and stable operation of the downstream condensation process. Preferably, the buffer tank is equipped with a safety valve and a pressure gauge, and a drain valve at the bottom. The outlet of the buffer tank is equipped with an electric valve and a pressure regulating valve, which can reduce the high pressure of the compressed gas to the required pressure for downstream condensation.

[0031] Preferably, a high-pressure flow meter is provided between the buffer tank and the first-stage cryogenic reactor, through which the gas flow rate from the buffer tank to the first-stage cryogenic reactor and the second-stage cryogenic reactor can be controlled.

[0032] Both the primary and secondary cryogenic reactors are preferably tubular cryogenic reactors. The refrigerant in the primary cryogenic reactor is supplied by a primary cold trap, and is preferably an ethylene glycol solution. The refrigerant in the secondary cryogenic reactor is supplied by a secondary cold trap, and is preferably an ethanol solution. Furthermore, the refrigerant temperature in the secondary cryogenic reactor is lower than that in the primary cryogenic reactor. The refrigerants in both the primary and secondary cryogenic reactors are controlled by corresponding cryogenic flow meters.

[0033] A drain valve is installed at the bottom of the first-stage cryogenic reactor to drain water periodically, thus ensuring the purity of the NO2 liquid as much as possible.

[0034] A back pressure valve and a safety valve are installed at the top of the secondary cryocooler. The back pressure valve controls the pressure inside the two cryocoolers, and the safety valve serves as a safety guarantee.

[0035] See Figure 2 and Figure 4 Multiple sets of temperature detection components 3 are sequentially arranged from top to bottom on both the primary cryogenic reactor 1 and the secondary cryogenic reactor 2. The number of temperature detection components 3 on the secondary cryogenic reactor 2 is greater than the number of temperature detection components 3 on the primary cryogenic reactor 1, preferably 1.5-3 times. In this embodiment, five sets of temperature detection components 3 are provided on the primary cryogenic reactor 1, while ten sets of temperature detection components 3 are provided on the secondary cryogenic reactor 2.

[0036] See Figure 3 The temperature detection assembly 3 includes an internal tube detection thermocouple 31, an external tube wall detection thermocouple 32, and an external refrigerant detection thermocouple 33. The first-stage cryogenic unit 1 includes a cryogenic unit shell 11 and condenser tubes 12 disposed within the cryogenic unit shell 11.

[0037] The in-tube thermocouple 31 passes through the cryogenic shell 11 and is inserted into the condenser tube 12 to measure the temperature of the gas inside the condenser tube 12. To avoid the influence of the in-tube thermocouple 31 on the flow resistance of the gas inside the condenser tube 12, the diameter of the condenser tube 12 with the in-tube thermocouple 31 is appropriately increased. The outer wall thermocouple 32 passes through the cryogenic shell 11 and contacts the outer wall of the condenser tube 12 to measure the temperature of the outer wall surface of the condenser tube 12. Preferably, the outer wall thermocouple 32 has an arc-shaped recess at one end near the condenser tube 12 that matches the shape of the condenser tube 12, increasing the contact area and improving the fit. The outer refrigerant thermocouple 33 extends into the cryogenic shell 11 to measure the temperature of the refrigerant flowing outside the condenser tube 12 and inside the cryogenic shell 11.

[0038] The product collection tank can store the liquid NO2 condensed by the secondary cryogenic reactor. An electric valve is provided below the product collection tank, which can be opened periodically to send the liquid NO2 to the outside of the skid-mounted housing.

[0039] The top of the secondary cryogenic reactor is equipped with an outlet connected to a flue gas analyzer. This analyzer measures and records the concentration of NO2 in the condensed gas in real time, enabling monitoring of the equipment's operational performance and calculation of the recovery rate. The flue gas analyzer is connected to an industrial control computer, which allows for the control of the entire equipment and the acquisition and recording of all data.

[0040] The operating method of the device for condensing and recovering liquid NO2 from a NO2-containing gas mixture is as follows:

[0041] (1) The mixed gas containing NO2 is dried by removing water and filtered through the gas filter;

[0042] (2) The NO2-containing mixed gas obtained in step (1) is compressed to 2.2-2.8 MPa, preferably 2.5 MPa, by the gas compressor.

[0043] (3) The compressed gas mixture is cooled to room temperature by the cooler and then stored in the buffer tank.

[0044] (4) The high-pressure gas in the buffer tank then flows through the series-connected primary cryostat and secondary cryostat at a set pressure under the control of the pressure stabilizing valve and the electric valve; during the condensation process, water can be discharged periodically through the drain valve below the primary cryostat to ensure the purity of the NO2 liquid product as much as possible.

[0045] The NO2 in the high-pressure gas condenses into liquid NO2 on the wall of the secondary cryogenic reactor and flows into the product collection tank. When the liquid in the product collection tank reaches a certain level, it is then transported to the outside of the skid-mounted housing through the liquid outlet via a valve.

[0046] The remaining uncondensed gas is discharged to the outside of the skid-mounted enclosure via a valve. A portion of the condensed exhaust gas (flow rate of approximately 1 L / min) enters a flue gas analyzer for NO2 residual concentration detection.

[0047] The recovery rate of NO2 recovered by condensation can be calculated based on the flow rate and NO2 concentration of the NO2-containing mixed gas, the flow rate and NO2 concentration of the remaining gas after condensation, and the flow rate and NO2 concentration of liquid NO2. The method for calculating the recovery rate of NO2 recovered by condensation is as follows:

[0048] The inlet gas flow rate and NO2 concentration are Q in and C in The remaining gas flow rate and NO2 concentration after condensation are Q, respectively. out and C out The bottom liquid flow rate (NO2 liquid flow rate calculated as gas flow rate under standard conditions) and NO2 concentration are Q, respectively. B and C B Ignoring the effect of other impurities dissolving in NO2 liquid, i.e., C B =100%. The formula for calculating the NO2 recovery rate is:

[0049]

[0050] The average condensation heat transfer coefficient of the primary and secondary cryogenic units is calculated as follows:

[0051] First, calculate the heat flux density, which is obtained from the enthalpy rise of the refrigerant (energy conservation) and the surface area of ​​the vertical pipe.

[0052]

[0053] In the above formula: c is the specific heat of the refrigerant (60% ethylene glycol solution or ethanol solution), and the unit is kJ / (kg·K); T represents the mass flow rate of the refrigerant, expressed in kg / s. out and T in These represent the temperatures of the refrigerant entering and exiting the condenser, respectively; D is the outer diameter of the vertical condenser tube, in meters; and L is the tube length of the condenser, in meters.

[0054] Then, the average temperature of the mixed gas is used. and average wall temperature Calculate the average condensation heat transfer coefficient:

[0055]

[0056] The calculation method for the local condensation heat transfer coefficient of the primary and secondary cryogenic units is as follows:

[0057] The local heat flow can be obtained by using the slope of the refrigerant temperature distribution in the phase change region:

[0058]

[0059] In the above formula: m cw Cp is the mass flow rate of the refrigerant, in kg / s; Cp is the specific heat of the refrigerant, in kJ / (kg·K); D i T represents the inner diameter of the condenser tube, in meters (m). cw t is the temperature of the refrigerant, in °C; z is the distance from the inlet, which in this device is the height, in meters.

[0060] The inner wall temperature is calculated using the measured outer wall temperature and the obtained heat flux density:

[0061]

[0062] In the above formula: T w,i (z) and T w,o (z) represent the temperatures of the inner and outer walls of the condenser, respectively, in °C; D o K represents the outer diameter of the condenser tube, in meters (m). sus is the thermal conductivity of stainless steel, taken as 20 W / m·K.

[0063] Then, the local heat transfer coefficient is calculated based on the heat flux density, wall temperature, and overall temperature.

[0064]

[0065] The device provided by this invention can pressurize and condense a NO2-containing gas mixture to obtain liquid NO2, and the resulting liquid NO2 has a high concentration. Then, parameters such as recovery rate, average condensation heat transfer coefficient, and local condensation heat transfer coefficient can be obtained using the above calculation method, which can be used to monitor the operating performance of the device.

[0066] Currently, the technology of this invention is applied to the 360m section of the Hebei Iron and Steel Group Handan Iron and Steel Group Handan Baosteel Plant. 2 The sintering workshop has been built to a capacity of 50,000 m². 3 This is a demonstration project for the purification and resource utilization of sintering flue gas. The average concentration of NO2 desorbed gas obtained from the regeneration of the denitrification tower is approximately 3.5%. Liquid NO2 with a purity greater than 99.99% was obtained through a skid-mounted NO2 resource utilization system, achieving an annual recovery of 70 tons of liquid NO2 as a byproduct, while simultaneously reducing annual NO2 emissions. x99 tons. During the trial period, the equipment operated stably. Testing showed that this invention is suitable for all dried NO2-containing gas mixtures, especially low-partial-pressure NO2 mixtures. Furthermore, it can be applied to NO2-containing flue gas from industries such as steel, glass, cement, and ceramics. x Treatment, using adsorption technology to treat NO x This invention can be used for capture and concentration, and can be further condensed and recovered from liquid NO2 products. It can also be applied to rocket launch sites and NO2 production enterprises to treat NO2-containing waste gas, liquefy and recover liquid NO2, and has a wide range of applications.

[0067] As described in the above embodiments of the present invention, other methods or devices obtained by using the same or similar methods are all within the protection scope of the present invention.

Claims

1. A method for condensing and recovering liquid NO2 from a NO2-containing gas mixture, characterized in that, It includes the following steps: S1: The NO2-containing mixed gas, after being dehydrated and dried, is compressed to 2.2–2.8 MPa to obtain high-pressure gas; S2: Cool the high-pressure gas to room temperature and store it in a buffer tank; S3: The high-pressure gas in the buffer tank flows successively through a primary cryogenic reactor and a secondary cryogenic reactor. The refrigerant in the primary cryogenic reactor is provided by a primary cold trap and is an ethylene glycol solution. The refrigerant in the secondary cryogenic reactor is provided by a secondary cold trap and is an ethanol solution. The refrigerant temperature in the secondary cryogenic reactor is lower than that in the primary cryogenic reactor. The NO2 in the high-pressure gas condenses into liquid NO2 on the wall of the secondary cryogenic reactor. S4: Collect the liquid NO2 to obtain liquid NO2; The remaining uncondensed gas is discharged to the outside of the skid-mounted housing through a valve. The skid-mounted housing is equipped with a gas filter, a gas compressor, a cooler, a buffer tank, a primary cryogenic cooler, a secondary cryogenic cooler, and a product collection tank. The gas filter, gas compressor, cooler, buffer tank, primary cryogenic cooler, secondary cryogenic cooler, and product collection tank are connected in sequence. The top of the secondary cryogenic unit is provided with an air outlet, which is connected to a flue gas analyzer; A portion of the condensed exhaust gas enters a flue gas analyzer for NO2 residual concentration detection. The recovery rate of NO2 recovered by condensation is calculated based on the flow rate and concentration of the NO2-containing mixed gas, the flow rate and concentration of the remaining gas after condensation, and the flow rate and concentration of liquid NO2. The calculation method for the NO2 recovery rate by condensation is as follows: The inlet gas flow rate and NO2 concentration are Q in and C in The remaining gas flow rate and NO2 concentration after condensation are Q, respectively. out and C out The bottom liquid flow rate and NO2 concentration are Q, respectively. B and C B The flow rate of NO2 liquid is calculated based on the gas flow rate under standard conditions, neglecting the effect of other impurities dissolving in NO2 liquid, i.e., C B =100%; the formula for calculating NO2 recovery rate is: ； Both the primary cryocooler and the secondary cryocooler are equipped with multiple sets of temperature detection components, which are used to measure the temperature of the gas inside the tube, the outer wall of the tube, and the refrigerant outside the tube to calculate the local heat transfer coefficient of each of the two cryocoolers; the number of temperature detection components on the secondary cryocooler is 1.5-3 times the number of temperature detection components on the primary cryocooler. The temperature detection assembly includes an internal tube detection thermocouple, an external tube wall detection thermocouple, and an external tube refrigerant detection thermocouple; wherein the internal tube detection thermocouple is used to measure the temperature of the gas inside the condenser tube, the external tube wall detection thermocouple is used to measure the temperature of the outer wall surface of the condenser tube, and the external tube refrigerant detection thermocouple is used to measure the temperature of the refrigerant flowing outside the condenser tube and inside the cryogenic chamber.

2. The method for condensing and recovering liquid NO2 from a NO2-containing gas mixture according to claim 1, characterized in that, The boiling points of the remaining gas components in the NO2-containing mixture are all lower than the boiling point of NO2.

3. The method for condensing and recovering liquid NO2 from a NO2-containing gas mixture according to claim 1, characterized in that, The NO2-containing gas mixture is filtered before compression.

4. The method for condensing and recovering liquid NO2 from a NO2-containing gas mixture according to claim 1, characterized in that, In step S3, the water in the first-stage cryogenic reactor needs to be drained periodically.

5. The method for condensing and recovering liquid NO2 from a NO2-containing gas mixture according to claim 1, characterized in that, The flow rate and residual NO2 concentration of the gas discharged from the secondary cryogenic condenser are detected.

6. The method for condensing and recovering liquid NO2 from a NO2-containing gas mixture according to claim 5, characterized in that, The recovery rate of NO2 recovered by condensation is calculated based on the data of the flow rate and NO2 concentration of the NO2-containing mixed gas, the flow rate and NO2 concentration of the remaining gas after condensation, and the flow rate and NO2 concentration of liquid NO2.

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