Semi-dry solid-phase liquid-membrane denitration method for low-temperature furnace flue gas

Abstract

The invention discloses a low-temperature furnace flue gas semi-dry method solid-phase liquid membrane denitration method, which adopts a solid-phase liquid membrane absorbent to carry out absorption treatment on nitrogen oxides NOx in low-temperature furnace flue gas, the solid-phase liquid membrane absorbent comprises activated carbon particles AC and a liquid membrane adsorbed and loaded by the activated carbon particles AC, a solvent of the liquid membrane is water, and the water is a water-soluble liquid membrane. The liquid film contains an absorption auxiliary agent with the mass fraction of 0.5-2% and NaOH with the mass fraction of 3-7%, and the absorption auxiliary agent is prepared from sodium sulfite, ethylenediamine tetraacetic acid disodium salt EDTA-2Na and tetrabutylammonium bromide. In the absorption process of the absorbent, the liquid film not only serves as a solvent and a reactant, but also can convert a reduction product from NO to NO2 <-> by changing a reaction path, so that the absorption efficiency is remarkably improved.

Description

Technical Field

[0001] This invention relates to a semi-dry solid-liquid film denitrification method for flue gas from low-temperature furnaces. Background Technology

[0002] Currently, nitrogen oxides (NOx) in industrial furnace flue gas are being studied. x The emission control has introduced stricter requirements, requiring NO to be... x Emissions are controlled at 50 mg / m³ 3 The following is a summary of the previous points. While traditional selective catalytic reduction (SCR) denitrification methods are widely used in ultra-low denitrification of flue gas from coal-fired power plants, they are less suitable for industrial cryogenic furnaces due to their low flue gas emission temperature, high humidity, and high NO content. x The large fluctuations in concentration make it difficult to effectively apply SCR denitrification technology and meet the denitrification requirements of low-temperature furnaces.

[0003] The flue gas characteristics of low-temperature furnaces are complex, and its NO... x The emissions are mainly NO, which is difficult to reduce. In addition, the flue gas temperature in low-temperature furnaces is usually low, generally between 40-120°C, and the humidity is close to saturation (100%RH). The flue gas may also contain high concentrations of CO2 and other components. These characteristics make traditional denitrification technologies face many challenges in the treatment of flue gas from low-temperature furnaces.

[0004] Currently, denitrification methods for low-temperature furnaces are mainly divided into two categories: low-NOx combustion technology and flue gas tail-end emission reduction and denitrification technology. Low-NOx combustion technology suppresses NOx by optimizing the combustion process. x While nitrogen oxides are produced, their denitrification efficiency is relatively low and they are difficult to meet ultra-low emission requirements. Flue gas tail-end emission reduction and denitrification technologies include dry, wet, and semi-dry denitrification methods. Dry denitrification technologies, such as SCR, require high reaction temperatures and have poor adaptability to low-temperature flue gas; wet denitrification technologies suffer from problems such as absorbents being easily carried out by flue gas, causing secondary pollution, and large absorbent usage and low efficiency. Semi-dry denitrification technology combines the advantages of dry and wet methods, possessing high denitrification efficiency and good pollution control, but traditional semi-dry denitrification technologies still have shortcomings in absorbent selection and usage methods, requiring further optimization and improvement. For example, Chinese invention patent CN115814573A discloses a comprehensive treatment system for producing mineral-derived nitrohumic acid and nitrofulvic acid, which includes the treatment of nitrogen oxides. Nitrogen oxides undergo a composite treatment process involving physical adsorption through multiple channels of silica gel, molecular sieves, activated carbon, etc., and chemical absorption through absorbents made of sodium hydroxide or sodium peroxide solution, slaked lime, and calcium carbonate. The process is complex, the absorption cost is high, and the absorption efficiency of each treatment step is low.

[0005] Therefore, developing a highly efficient, stable, economical, and easily industrialized denitrification technology suitable for flue gas from cryogenic furnaces is of paramount importance. Based on this background, this invention proposes a novel semi-dry solid-phase liquid film denitrification technology, aiming to address the shortcomings of existing technologies in denitrification of flue gas from cryogenic furnaces. It utilizes a strong alkali-loaded solid carbon material with higher absorption efficiency, eliminating the need for high temperatures and catalysts, thus providing an effective solution for ultra-low emissions from industrial cryogenic furnaces. Summary of the Invention

[0006] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces and kilns.

[0007] The design concept of this invention combines the excellent physical adsorption properties of porous solid materials with the advantages of liquid-phase absorbents in improving absorption efficiency. By loading the liquid absorbent onto the porous solid material, the volume of the absorbent can be significantly reduced. After the porous solid material adsorbs NO2 into its pores, it reacts with a nano-liquid film containing NaOH as the main absorbent component and added absorption aids, which is loaded in some of the pores. Both the porous solid material and the nano-liquid film loaded in its internal pores simultaneously improve the NO2 absorption efficiency.

[0008] The technical solution adopted in this invention is as follows: A semi-dry solid-liquid film denitrification method for low-temperature furnace flue gas, employing a solid-liquid film absorbent to remove nitrogen oxides (NOx) from the low-temperature furnace flue gas. x The absorption process is performed using a solid-liquid membrane absorbent comprising activated carbon particles AC and a liquid membrane on which they are adsorbed. The solvent of the liquid membrane is water, and the liquid membrane contains 0.5-2% by mass of an absorption aid and 3-7% by mass of NaOH. The absorption aid is composed of sodium sulfite, disodium ethylenediaminetetraacetate (EDTA-2Na), and tetrabutylammonium bromide (TBAB).

[0009] The solid-phase liquid film absorbent of this invention uses activated carbon particles (AC) as a carrier, further loading a liquid film containing an absorbent aid and NaOH. Activated carbon particles were chosen as the carrier due to their high specific surface area and high carbon tetrachloride adsorption value (CTC), characteristics that enable them to efficiently adsorb nitrogen oxides (NOx) from flue gas. x Among numerous activated carbon particles, those with a specific surface area greater than 1000 m² are further preferred. 2 With activated carbon particles of / g, the specific surface area reaches 1200 m². 2 / g, to ensure maximum adsorption capacity. Simultaneously, the carbon tetrachloride adsorption value (CTC) is also an important indicator for selecting activated carbon particles. Activated carbon particles with a CTC value greater than 80% are further preferred, with an optimal CTC value of 81.9%, to ensure the absorbent effectively removes NO. xHighly efficient adsorption. Furthermore, the particle size of the activated carbon is precisely controlled within 2.5 mm ± 0.3 mm. This particle size range not only ensures excellent adsorption performance but also takes into account mechanical strength, making the absorbent more stable and reliable in practical applications.

[0010] Furthermore, the liquid film contains 1% ± 0.2% by mass of an absorption aid and 5% ± 0.5% by mass of NaOH.

[0011] Furthermore, based on mass fraction, the content of each component of the absorbent is as follows: sodium sulfite 0.3-0.7%, EDTA-2Na 0.08-0.15%, and the remainder is tetrabutylammonium bromide (TBAB).

[0012] Furthermore, optimizing the liquid membrane composition is crucial for the performance of the absorbent. The main effective components of the liquid membrane consist of an absorbent aid and sodium hydroxide (NaOH), with the mass fraction of the absorbent aid set at 1% ± 0.2%. TBAB acts as a catalyst and complexing agent in the absorbent, significantly enhancing the absorption of NO2. - The gas-liquid mass transfer process between the absorber and the liquid film significantly improves absorption efficiency. Experimental verification shows that a mass fraction of 1% ± 0.2% for the absorbent additive ensures absorption efficiency while avoiding potential problems caused by excessively high absorbent additive concentrations, such as increased absorbent cost or decreased absorbent stability. Sodium hydroxide (NaOH) is the main absorbent component in the liquid film, and its mass fraction is preferably 5% ± 0.5%. NaOH reacts chemically with NO2 to produce nitrates (NO3). - ) and nitrite (NO2) - This reaction process ensures the absorbent operates efficiently under alkaline conditions, effectively inhibiting NO formation and reducing repeated pollution. The 5% NaOH mass fraction was determined based on multiple experiments and theoretical analyses; it maximizes the utilization of NaOH while ensuring efficient NO2 absorption by the absorbent, avoiding resource waste.

[0013] Furthermore, the preparation process of the solid-phase liquid film absorbent is equally crucial. First, activated carbon particles are finely ground to ensure their particle size is strictly controlled within the range of 2.5 mm ± 0.3 mm, achieving uniform adsorption performance and mechanical strength. Then, the absorbent aid and NaOH are dissolved in water, and the mixture is placed in a water bath at 30-50°C for 20-60 minutes to prepare a uniform and stable impregnation solution. Next, the pretreated activated carbon particles are immersed in the prepared impregnation solution and kept at this temperature for 10-60 minutes, ensuring that the micropores inside the activated carbon particles are fully filled with the impregnation solution, forming a uniform absorbent film. Finally, absorbent paper is used to remove excess solution from the surface of the activated carbon particles, thus completing the preparation of the solid-phase liquid film absorbent. Each step of this preparation process is carefully designed and optimized to ensure the high performance and stability of the absorbent.

[0014] Furthermore, the solid-liquid film absorbent absorbs nitrogen oxides (NOx). x At that time, the flue gas temperature was 40-80°C and the relative humidity was 0-100%RH.

[0015] The solid-liquid film absorbent of the present invention exhibits excellent absorption efficiency and selectivity for NO2 under low temperature and high humidity conditions, while also possessing excellent regeneration performance and long-term stability, making it an ideal choice for efficient denitrification of flue gas from industrial low-temperature furnaces and kilns.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. The solid-liquid film absorbent of the present invention can achieve an absorption efficiency of over 99% for NO2 under low temperature and high humidity conditions, which is significantly better than traditional wet and dry denitrification technologies.

[0017] 2. The absorbent can be regenerated in situ to restore its absorption performance. The effective utilization rate of sodium hydroxide (NaOH) is close to 100%, which reduces the waste of absorbent and lowers operating costs.

[0018] 3. This technology is suitable for flue gas conditions with low temperature, high humidity, and high CO2 concentration, and can still maintain high absorption efficiency under high air velocity conditions, making it widely adaptable.

[0019] 4. Pilot-scale testing has demonstrated that this technology possesses excellent absorption and regeneration performance under actual working conditions, enabling it to operate stably for extended periods and demonstrating great promise for industrial application. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings, wherein: Figure 1 This is the absorption effect of the absorbent in Example 1 on simulated flue gas. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] In this embodiment of the invention, the specific surface area of ​​the activated carbon particles (AC) reaches 1200 m². 2 / g, its carbon tetrachloride adsorption value (CTC) is 81.9%.

[0023] Example 1: The preparation method of the solid-liquid film absorbent includes the following steps: S1: First, the activated carbon particles are pretreated by grinding them to a particle size range of 2.5mm ± 0.1mm to ensure uniform particle size. Next, accurately weigh 1g of absorbent and 5g of sodium hydroxide (NaOH), mix them, add purified water to 100g, shake thoroughly to mix evenly, and place in a 40°C water bath for 30 minutes to prepare the impregnation solution. The absorbent, by mass fraction, contains: sodium sulfite 0.5%, EDTA-2Na 0.1%, and the remainder is tetrabutylammonium bromide.

[0024] S2: Then, the pretreated activated carbon particles are immersed in the prepared impregnation solution and kept warm for 20 minutes to ensure that the micropores inside the carrier are filled with the impregnation solution to form an absorbent liquid film. After that, the carrier is removed and the excess solution on the surface is absorbed with absorbent paper to complete the preparation of the solid-liquid film absorbent.

[0025] The method for semi-dry chemical absorption denitrification of low-temperature furnace flue gas using the solid-liquid film absorbent prepared in Example 1 includes the following steps: Step 1: At the start of the absorption process, the prepared solid-liquid film absorbent is uniformly filled onto the wire mesh inside the glass reaction tube of the cage-type bed denitrification device, ensuring a flat absorbent bed. Subsequently, simulated flue gas is introduced into the denitrification device, controlling the flue gas temperature at 40°C, relative humidity at 100% RH, and NO2 concentration at 500 mg / m³. 3 The flow rate was 1.2 L / min. The experimental setup was started to allow NO2 in the flue gas to come into contact with the absorbent and undergo a chemical absorption reaction. The measured volumetric space velocity was 106000 h⁻¹. -1 NO levels before and after the reaction are monitored in real time using a flue gas analyzer. x The concentration of NO2 was recorded every 10 minutes, including the inlet and outlet concentrations, to calculate the absorption efficiency.

[0026] Step 2: Once the absorbent is saturated, its absorption efficiency drops significantly. At this point, the flue gas introduction is stopped, and the regeneration process begins. The absorbent bed is washed with clean water using a spray device to remove nitrates, resulting in a low-concentration nitrate aqueous solution. The spraying time is 30 minutes, and the spray flow rate is 1.2 L / min. After spraying, the absorbent bed is placed in a constant-temperature drying oven at 40°C for 2 hours to ensure complete drying. Finally, a strong alkaline solution (30% NaOH solution) is sprayed a second time to regenerate the absorbent and restore its adsorption performance. The spraying time is 20 minutes, and the spray flow rate is 1.2 L / min. After regeneration, the electric heater in the adsorption chamber is activated to heat the absorbent, accelerating the opening of the micropores within the activated carbon particles. The heating temperature is controlled at 40-60°C and maintained for 30 minutes to ensure the absorbent can continue to efficiently absorb NO2. After heating, the absorbent is sprayed with an aqueous solution containing 1% absorbent aid and 5% NaOH. After the liquid film is loaded, simulated flue gas is introduced again to repeat the absorption process and verify the activation effect of the absorbent.

[0027] Experimental results show that, under the experimental conditions, the novel absorbent achieves an initial NO2 absorption efficiency of over 99%, maintaining high efficiency for the first 60 minutes. During the 120-minute experimental period, the absorption efficiency of the novel absorbent for NO2 remains above 90%, demonstrating its excellent long-term absorption performance. Through multiple regeneration cycle tests, the novel absorbent maintains its high NO2 absorption performance after each regeneration. In 10 regeneration cycles, the absorbent consistently maintains high NO2 absorption efficiency for extended periods, exceeding 90%. Particularly in the first 5 regeneration cycles, its absorption efficiency reaches over 95% within 210 minutes. No NO is generated during this highly efficient absorption period, and the NO2 absorption effect meets the requirements for use in low-temperature furnaces.

[0028] Within a temperature range of 40-80°C, the novel absorbent achieved an absorption efficiency of over 90% for NO2, demonstrating its good stability under different temperature conditions. At 100% RH humidity, the novel absorbent exhibited the highest NO2 absorption efficiency and maintained good absorption performance under various humidity conditions. Under simulated high-air-velocity conditions (volume hourly space velocity of 106,000 h⁻¹), [further details on this point are needed for accurate translation]. -1 When the novel absorbent is used, it can still maintain high efficiency in absorbing NO2 in the initial stage, with an absorption efficiency of over 90%, demonstrating its good adaptability under high air velocity conditions.

[0029] The simulated flue gas contained 200 mg / m³ 3 NO2, 100 mg / m³ 3NO, 30% CO2, 5% O2, flue gas flow rate 1.2 L / min, flue gas temperature 80℃, water vapor content 100% RH, simulated flue gas passing through the solid-liquid film absorbent prepared in Example 1 has a volume hourly space velocity of 106000 h⁻¹. -1 At that time, the concentrations of NO2 and NO in the outlet flue gas were as follows: Figure 1 As shown, the absorbent's absorption effect on NO2 fully meets expectations. Under the current experimental conditions, the absorbent can maintain high-efficiency absorption of NO2 for 200 min, with an absorption efficiency of over 99%. At 240 min, the absorption efficiency is close to 90%. The absorbent also has a small absorption effect on NO. The absorption effect on NO2 can meet the denitrification requirements of most low-temperature furnaces.

[0030] Example 2 further investigated the effect of different concentrations of organic absorbents on absorption performance. The experimental procedures were the same as in Example 1, except that absorbent solutions containing 0.5%, 1.0%, and 1.5% absorbent were prepared respectively during the impregnation solution preparation stage. The experimental results showed that the absorbent prepared under the condition of 1.0% absorbent impregnation solution had the highest initial absorption efficiency for NO2, reaching over 99%, and maintained an absorption efficiency of over 90% within 120 minutes.

[0031] Example 3: Investigating the effect of different concentrations of sodium hydroxide (NaOH) on absorption performance. The experimental procedures were the same as in Example 1, but impregnation solutions containing 3%, 5%, and 7% NaOH were prepared respectively. The experimental results showed that the absorbent prepared under the 5% NaOH impregnation solution condition had the highest initial absorption efficiency for NO2, reaching over 99%, and maintained an absorption efficiency of over 90% within 120 minutes.

[0032] Through these experiments, we verified the high efficiency of the novel semi-dry solid-liquid film absorbent for NO2 absorption under low temperature and high humidity conditions, as well as its excellent regeneration performance and stability. These results indicate that this technology has broad application prospects in practical industrial applications, especially in treating NOx in low-temperature furnace flue gas.

Claims

1. A method for semi-dry solid-liquid film denitrification of flue gas from low-temperature furnaces and kilns, characterized in that, Using solid-liquid film absorbents to remove nitrogen oxides (NOx) from flue gas in low-temperature furnaces and kilns x The absorption process is performed using a solid-liquid membrane absorbent comprising activated carbon particles AC and a liquid membrane on which they are adsorbed. The solvent of the liquid membrane is water, and the liquid membrane contains 0.5-2% by mass of an absorption aid and 3-7% by mass of NaOH. The absorption aid is composed of sodium sulfite, disodium ethylenediaminetetraacetate (EDTA-2Na), and tetrabutylammonium bromide.

2. The method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces as described in claim 1, characterized in that, The liquid film contains 1% ± 0.2% by mass of an absorption aid and 5% ± 0.5% by mass of NaOH.

3. The method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces as described in claim 1, characterized in that, Based on mass fraction, the content of each component of the absorbent is as follows: sodium sulfite 0.3-0.7%, EDTA-2Na 0.08-0.15%, and the remainder is tetrabutylammonium bromide.

4. The method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces and kilns as described in claim 1, characterized in that, The specific surface area of ​​the activated carbon particles is greater than 1000 m². 2 / g, carbon tetrachloride adsorption value (CTC) is greater than 80%.

5. The method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces and kilns as described in claim 1, characterized in that, The preparation method of the solid-liquid film absorbent includes the following steps: S1: First, the activated carbon particles are pretreated by grinding them and then screened to ensure uniform particle size within a range of 2.5mm ± 0.3mm. S2: Dissolve the absorbent and NaOH in water to prepare an impregnation solution; then immerse the pretreated activated carbon particles in the prepared impregnation solution at 30-50℃ for 10-60 minutes to ensure that the micropores inside the activated carbon particle carrier are filled with the impregnation solution to form an absorbent film before removing them. S3: Use absorbent paper to remove excess solution from the surface of the activated carbon particle carrier, thus preparing the solid-liquid film absorbent.

6. The method for semi-dry solid-liquid film denitrification of flue gas in low-temperature furnaces and kilns as described in claim 1, characterized in that, The solid-liquid film absorbent absorbs nitrogen oxides (NOx). x At that time, the flue gas temperature was 40-80°C and the relative humidity was 0-100%RH.

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