Method and apparatus for nitrogen purging and deoxygenation

Abstract

The application discloses a method and device for nitrogen purging and deoxidizing. The deoxidizing membrane is used as a separation medium. The water to be treated flows through one side of the membrane, and nitrogen is introduced into the other side for purging. The dissolved oxygen is removed by penetrating the membrane holes under the driving of the partial pressure difference, and the water molecules are blocked. The nitrogen passes through a uniform distribution device before purging the deoxidizing membrane. A plurality of inert solid particles are distributed in the uniform distribution device. The application has the advantages of simple and reliable structure and low cost. The nitrogen is uniformly distributed through the solid particles, the "short circuit" and "dead zone" are eliminated, the membrane utilization efficiency is improved, and the service life of the assembly is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of gas purification technology, and in particular relates to a method for nitrogen purging and deoxygenation, as well as an apparatus for nitrogen purging and deoxygenation using this method. Background Technology

[0002] In some water-using applications, such as boiler feedwater, it is necessary to remove oxygen from the water beforehand. Dissolved oxygen in boiler feedwater is a key factor causing corrosion in boiler systems, not only reducing boiler efficiency and shortening equipment lifespan but also potentially leading to safety accidents. Therefore, effective removal of dissolved oxygen is crucial. Currently, commonly used deoxygenation methods mainly include:

[0003] 1. Thermal deoxygenation: This method involves heating water to its boiling point (approximately 104°C), causing dissolved oxygen to escape. This method is technically mature and operates stably, reducing dissolved oxygen levels to below 7 µg / L. However, it suffers from high energy consumption, large equipment size, sensitivity to load fluctuations, and energy loss.

[0004] 2. Chemical deoxygenation: This method involves adding chemical reducing agents (such as sodium sulfite or hydrazine) to react with dissolved oxygen. It is simple to operate and low in cost, but carries the risk of secondary pollution, especially since hydrazine is toxic. Therefore, it is suitable for situations with low water quality requirements or as an auxiliary method.

[0005] 3. Vacuum deoxygenation: This method uses a vacuum system to reduce pressure, causing dissolved oxygen to escape. It is a physical deoxygenation method that does not introduce chemical substances, resulting in high effluent purity. However, it requires high equipment investment, strict sealing requirements, and significant energy consumption.

[0006] 4. Catalytic deoxygenation: This method accelerates the reaction between the reducing agent and oxygen using a catalyst (such as palladium or platinum). While this method is thorough and fast, the catalysts are expensive, have limited lifespan, and require complex operation and maintenance.

[0007] Compared to traditional methods, membrane deoxygenation (membrane degassing) technology exhibits significant advantages. This technology uses a bihydrophobic polytetrafluoroethylene (PTFE) membrane as the separation medium. The water to be treated flows through one side of the membrane, while a vacuum is applied to the other side or an inert gas (such as nitrogen) is introduced. Dissolved oxygen is removed through the membrane pores under the drive of the partial pressure difference, while water molecules are blocked, achieving highly efficient gas-liquid separation. Membrane deoxygenation has the following advantages:

[0008] (1) Significant energy saving: It can operate at room temperature or low temperature without heating, and its energy consumption is far lower than that of thermal deoxygenation.

[0009] (2) High deoxygenation efficiency: The dissolved oxygen in the effluent can be stably controlled below 7ppb, meeting the high standard of corrosion prevention requirements;

[0010] (3) Environmentally friendly: Pure physical separation, no chemical additives, eliminating secondary pollution;

[0011] (4) Flexible operation: quick start-up, adaptable to load fluctuations, compact structure, and easy installation.

[0012] Chinese patent CN109179728A discloses a deoxygenated membrane system for expanding demineralized water capacity in gas-fired power plants. The deoxygenated membrane security filter is connected via pipelines to several sets of deoxygenated membrane modules. Each deoxygenated membrane module is connected via pipelines to a steam-water separator, which is connected via pipelines to a vacuum pump. The deoxygenated membrane modules are also connected via pipelines to an air filter, which is connected via pipelines to a nitrogen generator. This invention enables a process system that replaces traditional deaerators and ensures no chemical residues in the effluent, achieving high deoxygenation through vacuuming and high-purity nitrogen purging.

[0013] One of the drawbacks of the above-mentioned membrane deoxygenation method is that this method usually relies on a high driving pressure. Therefore, the pressure of nitrogen inside the deoxygenation device is unbalanced, and the pressure difference is large at different places. This leads to uneven oxygen permeation of the membrane at different places, which affects the deoxygenation effect. Summary of the Invention

[0014] The purpose of this invention is to overcome the shortcomings of the prior art and provide a nitrogen purging deoxygenation method.

[0015] Another object of the present invention is to provide a nitrogen purging deoxygenation apparatus.

[0016] The technical solution adopted in this invention is as follows: a nitrogen purging deoxygenation method, which uses a deoxygenation membrane as a separation medium. The water to be treated flows through one side of the membrane, and nitrogen is introduced into the other side for purging. Dissolved oxygen is removed through the membrane pores under the drive of partial pressure difference, while water molecules are blocked. The feature is that the nitrogen passes through a uniform distribution device before purging the deoxygenation membrane. The uniform distribution device contains a number of inert solid particles.

[0017] The inert solid particles are ceramic balls with a particle size between 0.5-5 mm.

[0018] The present invention also adopts the following technical solution: a nitrogen purging deoxygenation device, comprising a shell, a deoxygenation membrane provided inside the shell, and a nitrogen gas source provided outside the shell. The water to be treated flows through one side of the deoxygenation membrane, and nitrogen enters the shell and purges the other side of the deoxygenation membrane; characterized in that: the gas path inside the shell is equipped with a uniform distribution device, and a number of inert solid particles are distributed in the uniform distribution device.

[0019] The inert solid particles are ceramic balls with a particle size between 0.5-5 mm.

[0020] Furthermore, the deoxygenation membrane is arranged longitudinally, with the water to be treated flowing down one side of the membrane, and nitrogen entering the shell from the lower end of the shell; the uniform distribution device consists of several units distributed around the deoxygenation membrane.

[0021] The uniform distribution device using inert solid particles enables the uniform purging of each RO membrane. Its core lies in transforming potentially uneven nitrogen input into a highly uniform and stable output airflow with consistent cross-sectional pressure and velocity. It creates a microscopically uniform "isobaric surface" by forcibly dispersing, mixing, and reforming the airflow through a randomly packed internal particle bed, and utilizes the tank volume to buffer pressure fluctuations. In independent series configurations, this uniform gas source provides a perfect "fair starting point" for the subsequent distribution system, allowing the airflow to be naturally and evenly distributed to each branch. In integrated configurations, it directly ensures that the airflow uniformly covers the entire inlet cross-section of the membrane module, thus achieving consistent purging of each membrane filament or channel from a fundamental and automatic physical perspective, without relying on complex pipeline symmetry or manual adjustments.

[0022] The present invention has a simple and reliable structure and low cost; nitrogen gas is evenly distributed through solid particles, eliminating "short circuits" and "dead zones", which can improve membrane utilization efficiency and extend module life. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of this embodiment. Detailed Implementation

[0024] See the attached drawings. This embodiment includes a housing 1 made of stainless steel; a longitudinal deoxidation membrane 2 is arranged inside the housing; a water inlet 3 is located above the housing, through which the water to be treated flows into the housing and passes through the deoxidation membrane; a gas valve 4, a nitrogen inlet 5, and a gas passage 6 are located below the housing, through which nitrogen enters the housing.

[0025] Several uniformly distributed devices 7 are arranged radially around the periphery of the deoxidation membrane 2. Each uniformly distributed device is filled with several ceramic balls. The end closest to the deoxidation membrane is a purge port 72 for directly purging the deoxidation membrane, and the other end away from the center is a nitrogen inflow end with a porous baffle 71 to prevent the ceramic balls from escaping.

[0026] Nitrogen gas enters through nitrogen inlet 5 at the bottom, is distributed to each uniform distribution device 7 via gas path 6, and then evenly blows across the surface of the deoxygenation membrane 2 through the uniform distribution of ceramic balls. Water to be treated enters from the top of the assembly, and the deoxygenated feedwater exits from the bottom outlet of the assembly. After real-time monitoring by an online dissolved oxygen analyzer, the water is sent to the boiler once it meets the standards. The nitrogen outlet and water inlet / outlet procedures are the same as in existing technologies and will not be described in detail here.

[0027] In this embodiment, the effective length of the hollow fiber membrane is 0.3-0.5m, and the component diameter can be adjusted according to the gas volume processed. Laboratory-scale testing shows that compared to traditional designs, this device improves deoxygenation efficiency by 25-40%, reduces nitrogen consumption by 20-35%, significantly improves system operational stability, reduces pressure drop fluctuations by 60%, and can stably reduce dissolved oxygen in feedwater from approximately 8 mg / L at room temperature to below 7 μg / L, fully meeting the feedwater requirements of medium- and high-pressure boilers.

Claims

1. A nitrogen purging deoxygenation method, employing a deoxygenation membrane as the separation medium, wherein the water to be treated flows through one side of the membrane, and nitrogen is purged through the other side, dissolved oxygen is removed through the membrane pores under the drive of partial pressure difference, while water molecules are blocked; characterized in that: Before purging the deoxygenation membrane, nitrogen gas passes through a uniform distribution device containing several inert solid particles.

2. The method as described in claim 1, characterized in that: The inert solid particles are ceramic balls with a particle size between 0.5-5 mm.

3. A nitrogen purging deoxygenation device, comprising a housing, an oxygen deoxygenation membrane disposed within the housing, and a nitrogen gas source disposed outside the housing; water to be treated flows through one side of the oxygen deoxygenation membrane, and nitrogen gas enters the housing and purges the other side of the oxygen deoxygenation membrane; characterized in that: The gas path inside the casing is equipped with a uniform distribution device, which contains several inert solid particles.

4. The apparatus as described in claim 3, characterized in that: The inert solid particles are ceramic balls with a particle size between 0.5-5 mm.

5. The apparatus as described in claim 3 or 4, characterized in that: The deoxygenation membrane is arranged longitudinally, with the water to be treated flowing down one side of the membrane, and nitrogen entering the shell from the lower end of the shell; the uniform distribution device consists of several units distributed around the deoxygenation membrane.

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