CN101352645A - Flue gas catalytic oxidation denitrification process and its catalyst - Google Patents

Abstract

The invention discloses a flue gas catalytic oxidation denitrification process, which adopts a catalyst with TiO ₂ or ZrO ₂ -TiO ₂ as a carrier and Co as an active component, and utilizes the oxygen contained in the flue gas itself to oxidize nitric oxide into easily soluble After the nitrogen dioxide in the water is absorbed by the lye, the nitrogen oxides are removed. The process of the invention has high denitrification efficiency and low cost. After controlling the content of nitrogen dioxide in flue gas after oxidation, nitrite in denitrification by-products can be selectively recovered to realize resource utilization of products.

Description

Flue gas catalytic oxidation denitrification process and its catalyst

technical field

The invention relates to the technical field of air pollution control, in particular to a flue gas catalytic oxidation denitrification process and a catalyst thereof, which are suitable for coal-fired and oil-fired boilers and industrial furnaces.

Background technique

Gas-phase oxidation-absorption denitrification technology uses gas-phase oxidation to oxidize the less soluble NO in flue gas NO _x into NO ₂ , N ₂ O ₅ , etc., and then use alkaline, oxidizing or reducing absorption liquid to oxidize them absorb. The method can not only realize denitrification and purification of waste gas, but also realize resource utilization of nitrogen oxides. The difference between various gas-phase oxidation-absorption denitrification technologies lies in the different gas-phase oxidation methods. Gas-phase oxidation methods can be divided into direct oxidation of gas-phase chemical agents, gas-phase photocatalytic oxidation, and gas-phase catalytic oxidation. Compared with SCR technology, gas phase oxidation-absorption denitrification technology has lower investment and operating costs, the absorption liquid can be used as resources, and the denitrification efficiency is higher, which is suitable for boilers of various sizes.

Chinese invention patents with publication numbers CN1768902A, CN1923341A and CN101053747A respectively disclose a boiler flue gas ozone oxidation denitrification method, a coal-fired boiler flue gas ozone oxidation simultaneous desulfurization and denitrification device and its method, and a wet ammonia flue gas cleaning method for simultaneous desulfurization and denitrification. The process and its system use ozone, hydrogen peroxide or methanol as the oxidizing agent to oxidize the nitric oxide in the flue gas into high-priced nitrogen oxides such as nitrogen dioxide, dinitrogen trioxide and dinitrogen pentoxide, which are easily soluble in water, but Owing to the consumption of chemical oxidants such as ozone, hydrogen peroxide and methanol is large, and the price is relatively expensive, which affects the economy of the method.

The flue gas of coal-fired boilers generally contains 3-8% O ₂ . Under normal conditions, the reaction rate of O ₂ and NO to form NO ₂ is very slow, so the content of NO ₂ in the flue gas only accounts for about 10% of the total NO _x . The gas-phase catalytic method uses a catalyst to accelerate the reaction of _O2 and NO, so that the proportion of _NO2 increases to facilitate liquid-phase absorption. The method does not need to add external oxidants, avoids the transportation and storage of strong oxidants, and improves the economy and safety of the denitrification system.

The Chinese invention patent with the publication number CN101028596A discloses a method for preparing a nitrogen oxide oxidation catalyst. The catalyst uses a co-precipitation method to prepare a manganese-based nano-powder oxide catalyst, which is characterized in that it has a large specific surface area and can catalyze The oxidation conversion rate is high. When the catalytic reaction temperature is 200°C, the catalytic conversion efficiency is about 70%. When the temperature rises to 400°C, the ratio of NO ₂ /(NO+NO ₂ ) in the exhaust gas can be as high as 92%. Although this method has obtained a high NO conversion rate, due to the presence of a relatively high concentration of SO ₂ in the flue gas of the coal-fired boiler, the activity of the catalyst in the presence of a high concentration of SO ₂ will determine whether the process can be used The key to denitrification of coal-fired flue gas. In addition, the _NO2 content in the flue gas determines the efficiency of nitrogen oxide absorption and the absorbed products, so the ratio of _NO2 in the flue gas after oxidation is also another key factor determining the feasibility of the process.

Contents of the invention

The invention provides a flue gas catalytic oxidation denitrification process and a catalyst used therein. The catalyst and the oxygen contained in the flue gas are used to oxidize NO to achieve high-efficiency denitrification and recovery of by-products.

A flue gas catalytic oxidation denitrification process, comprising:

(1) A catalyst is arranged in the flue with a temperature range of 150-400 °C, and the flue gas is oxidized by using 3-8% oxygen _O2 in the flue gas to oxidize the NO in the flue gas into NO which is easily soluble in water ₂ ;

(2) Absorb the oxidized flue gas with lye to remove nitrogen oxides in the flue gas.

The catalyst is a catalyst prepared by a sol-gel method, a hydrothermal method or an impregnation method with Co as an active component and TiO ₂ or ZrO ₂ -TiO ₂ as a carrier, and the main form of active component Co is Co ₂ O ₃ and CoO, wherein the molar ratio of Co to Ti is 0.01-0.1, and the molar ratio of Zr to Ti is 0-0.5. At the same time, the catalyst can also be doped with one of Mn, Fe, Cu, V, Cr, Ce or Several metal elements, the molar ratio of doped metal to Ti is 0-0.01.

After using the catalyst for catalytic oxidation, the _NO2 content in the flue gas can be strictly controlled at 40-60%, so as to ensure that the absorbed product is nitrite.

When the catalyst is arranged in the flue, the catalytic oxidation section can be installed either before the flue dust collector or after the dust collector.

The lye is a denitration liquid commonly used in the denitrification process, such as sodium hydroxide NaOH, calcium hydroxide Ca(OH) ₂ , potassium hydroxide KOH, calcium carbonate CaCO ₃ , calcium oxide CaO, sodium sulfite Na ₂ SO ₃ and other aqueous solutions. at least one.

Catalyst among the present invention mainly has following characteristics:

1) Cobalt is used as the active component of the catalyst, and its main forms are Co ₂ O ₃ and CoO, which can provide active sites for catalytic reactions, adsorb reactants NO and O ₂ , and react.

2) Ti, as the main carrier of the active components of the catalyst, mainly exists in the form of TiO ₂ , the existence of Ti also provides a certain adsorption for NO and O ₂ , increasing the possibility of reactant adsorption on the catalyst surface.

3) ZrO ₂ and TiO ₂ are combined as a carrier, and Zr can replace the position of Ti in the original crystal lattice to form ZrTiO ₄ . At this time, new acidity and alkalinity will be formed on the carrier. When SO ₂ invades the catalyst, these basic sites will attract SO ₂ to form the target site for invasion and effectively protect the active site of the active material. And because the addition of Zr changes the bond energy of the crystal, SO ₂ can only form a weaker, reversible sulfate on the surface of ZrTiO ₄ . In addition, _ZrO2 can interact with active materials to form metal solid solutions, which makes it difficult for _SO2 to react with active materials to generate metal sulfates and sulfites.

4) Other metal oxides doped in the catalyst, its main function is to increase the electron transfer in the catalytic reaction, and use it as a better oxygen storage to enhance the oxidation recovery performance of the catalyst.

The invention provides a low-cost, high-efficiency flue gas denitrification technology. Under the action of the catalyst, the oxygen O ₂ in the flue gas is used to oxidize NO to NO ₂ without adding other oxidants. NO ₂ dissolves in water to generate HNO ₃ and HNO ₂ , which can achieve more than 70% denitrification when combined with lye efficiency. At the same time, controlling the proportion of NO ₂ in the flue gas after oxidation can selectively recover the nitrite in the denitrification by-product. Compared with other denitrification methods, the method has high efficiency, low cost, and can realize resource utilization of products.

Description of drawings

Fig. 1 is a kind of implementation device schematic diagram of the inventive method;

Fig. 2 is a schematic diagram of another implementation device of the method of the present invention.

Detailed ways

As shown in Figure 1, the flue gas from the coal-fired boiler 1 passes through the NO catalytic oxidation reactor 3 and then enters the dust collector 2. Part of the NO in the flue gas is oxidized into NO ₂ and enters the absorption tower 4 for washing, so that SO ₂ and NO _x are The absorption liquid 6 is transported by the circulating pump 7, and the absorbed flue gas passes through the defogging plate 5 and then enters the chimney 8 to be discharged up to the standard. The absorption liquid is transported to the resource recovery system for separation and crystallization.

Fig. 2 is another arrangement scheme of the method of the present invention, which is basically the same as that shown in Fig. 1, except that the flue gas from the coal-fired boiler 1 first enters the dust collector 2 and then enters the catalytic oxidation reactor 3.

Example 1:

1) Preparation of catalyst CoO _x /TiO ₂ by sol-gel method

Using n-butyl titanate, ethanol, water, and acetic acid as raw materials, the volume ratio of each component is as follows, n-butyl titanate: ethanol: water: acetic acid = 1: 1.5: 0.5: 0.5, and the amount of cobalt nitrate added is Co : Ti (molar ratio) = 0.1, mixed, after the sol is transformed into a gel, dried, ground, and calcined at 500° C. to obtain a catalyst.

2) Denitrification process

The concentration of O ₂ in the treated flue gas is 3%, GHSV (gas space velocity per hour) = 30000h ^-1 , the catalytic reactor is installed upstream of the dust removal device, the reaction temperature is 300°C, and the ratio of NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the spray tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 90%, and the denitrification efficiency is 75%.

Example 2:

1) Preparation of catalyst CoO _x /TiO ₂ by impregnation method

Cobalt nitrate was added to commercial titanium dioxide slurry, stirred for 48 hours, dried at 100°C, calcined at 500°C for 2 hours, and ground to obtain a catalyst. The amount of cobalt added is Co:Ti (molar ratio)=0.05.

2) Denitrification process

The O ₂ concentration of the treated flue gas is 5%, GHSV (gas space velocity per hour) = 50000h ^-1 , the catalytic reactor is installed upstream of the dust removal device, the reaction temperature is 350°C, and the NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the packed tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 95%, and the denitrification efficiency is 80%.

Example 3:

1) Preparation of catalyst CoO _x /ZrO ₂ -TiO ₂ by sol-gel method

Using n-butyl titanate, ethanol, water, and acetic acid as raw materials, the volume ratio of each component is as follows, n-butyl titanate: ethanol: water: acetic acid = 1: 1.65: 0.05: 0.07, and the amount of cobalt nitrate added is Co : Ti=0.05, the addition of zirconium nitrate is Zr:Ti (molar ratio)=0.1, mixed, after the sol is converted into gel, dried, ground, and roasted at 600°C to obtain the catalyst.

2) Denitrification process

The O ₂ concentration of the treated flue gas is 8%, GHSV (gas space velocity per hour) = 40000h ^-1 , the catalytic reactor is installed downstream of the dust removal device, the reaction temperature is 200°C, and the NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the swirl plate tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 90%, and the denitrification efficiency is 85%.

Example 4:

1) Preparation of catalyst CoO _x /ZrO ₂ -TiO ₂ by sol-gel method

Using n-propyl titanate, propanol, water, and nitric acid as raw materials, the volume ratio of each component is as follows, n-propyl titanate: ethanol: water: acetic acid = 1: 1.85: 0.06: 0.02, and the amount of cobalt nitrate added is Co: Ti (molar ratio) = 0.08, the addition of zirconium nitrate is Zr: Ti (molar ratio) = 0.5, mixed, after the sol is converted into a gel, dried, ground, and roasted at 400-600 ° C to obtain catalyst.

2) Denitrification process

The concentration of O ₂ in the treated flue gas is 4%, GHSV (gas space velocity per hour) = 30000h ^-1 , the catalytic reactor is installed downstream of the dust removal device, the reaction temperature is 160°C, and the ratio of NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the packed tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 85%, and the denitrification efficiency is 75%.

Example 5:

1) Preparation of catalyst CeO _x /CoO _x /TiO ₂ by hydrothermal method

Using n-butyl titanate as precursor and ethanol as solvent, Ce-doped CoO _x /TiO ₂ was prepared by hydrothermal method. The molar ratio of n-butyl titanate, ethanol and water was 1:1:10, and cobalt nitrate The addition amount is Co:Ti (molar ratio) = 0.1, the addition amount of cerium nitrate is Ce: Ti (molar ratio) = 0.005, the mixed solution is added to the autoclave, and a hydrothermal reaction occurs at 100-250°C for 6-36h , washed after the reaction to obtain nano-scale CeO _x /CoO _x /TiO ₂ catalyst.

2) Denitrification process

The concentration of O ₂ in flue gas is 5%, GHSV (gas space velocity per hour) = 30000h ^-1 , the catalytic reactor is installed upstream of the dust removal device, the reaction temperature is 400°C, and the ratio of NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the sieve plate tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 85%, and the denitrification efficiency is 75%.

Embodiment 6:

1) Preparation of catalyst CeO _x /MnO _x /CoO _x /ZrO ₂ -TiO ₂ by sol-gel method

With titanium isopropoxide, ethanol, water, acetic acid as raw materials, the volume ratio of each component is as follows, titanium isopropoxide: ethanol: water: acetic acid = 1: 1.65: 0.4: 0.5, the addition of zirconium nitrate is Zr: Ti (mol ratio)=0.5, the add-on of cobalt nitrate is Co:Ti (mol ratio)=0.05, the add-on of manganese acetate is Co:Ti (mol ratio)=0.005, the add-on of cerous nitrate is Ce:Ti( molar ratio) = 0.001, mixed, after the sol is transformed into a gel, dried, ground, and roasted at 200-600°C to obtain a catalyst.

2) Denitrification process

The concentration of O ₂ in the treated flue gas is 3%, GHSV (gas space velocity per hour) = 50000h ^-1 , the catalytic reactor is installed upstream of the dust removal device, the reaction temperature is 300°C, and the ratio of NO ₂ /(NO+NO ₂ ) at the reactor outlet The ratio is about 40%-60%. The oxidized flue gas enters the swirl plate tower, and the _SO2 and _NOx are removed together in the absorption tower. The desulfurization efficiency is 95%, and the denitrification efficiency is 90%.

Claims (4)

1. A flue gas catalytic oxidation denitrification process, comprising: (1) A catalyst is arranged in the flue with a temperature range of 150-400°C, and the oxygen in the flue gas is used to oxidize the flue gas; (2) Absorb the oxidized flue gas with lye to remove nitrogen oxides in the flue gas; The catalyst is a catalyst prepared by a sol-gel method, a hydrothermal method or an impregnation method, with Co as an active component and TiO ₂ or ZrO ₂ -TiO ₂ as a carrier. 2. The flue gas catalytic oxidation denitrification process as claimed in claim 1, characterized in that: the catalyst is doped with one or more metal elements in Mn, Fe, Cu, V, Cr, Ce, doped metal and The molar ratio of Ti is 0-0.01. 3. The flue gas catalytic oxidation denitrification process according to claim 1 or 2, characterized in that the molar ratio of the catalyst Co to Ti is 0.01-0.1, and the molar ratio of Zr to Ti is 0-0.5. 4. The flue gas catalytic oxidation denitrification process according to claim 1 or 2, characterized in that: the alkali solution is sodium hydroxide aqueous solution, calcium hydroxide aqueous solution, potassium hydroxide aqueous solution, calcium carbonate aqueous solution, calcium oxide aqueous solution , At least one of sodium sulfite aqueous solution.

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