CN1120034C - Method for removing sulphur oxide and nitrogen oxide from smoke - Google Patents

Abstract

The present invention discloses a method for simultaneously eliminating SO2 and NOx in flue gas. The method uses O2 in flue gas as an oxidizing agent, uses a cobaltous complex compound as a main catalyst, and uses the negative ions of iodine (or other halogen, such as bromine, etc.) as a cocatalyst. NO is catalyzed, oxidated and recycled in a liquid phase, and meanwhile, SO2 is eliminated and recycled. The method can simultaneously catalyze, oxidate and absorb NO and can simplify technical processes, SO2 concentration in outlet gas can reach 0% at least, and the method solves the problems of poor sulfur resistance and poor water resistance of NO oxidation catalysts.

Description

A method for simultaneously removing SO2 and NOx from flue gas

technical field

The invention relates to a method for removing _SO2 and _NOx in gas, in particular to a method for removing _NOx and _SO2 in flue gas of a power plant.

Background technique

The pollution of acid rain and its harm have become one of the environmental problems concerned by countries all over the world. SO ₂ and NOx are two polluting gases with the largest amount of emissions and the most harmful effects, and they are also the main substances that form acid rain. In countries where coal is the main energy source, SO ₂ (1000-4000ppm) and _NOx (300-800ppm) produced by coal combustion are the main source of industrial waste gas pollution (acid rain hazard).

NO _x is a general term for nitrogen oxides, including N ₂ O, NO, N ₂ O ₃ , NO ₂ , N ₂ O ₅ and so on. The danger of NOx is not only that it is an acid rain gas, but also that NO, like chlorofluorocarbons, can significantly destroy the ozone layer. NO and N ₂ O are also greenhouse gases, and NO can react with hydrocarbons in sunlight to cause photochemical pollution.

More than 95% of NO _x in the atmosphere is NO, NO ₂ is only a small amount, and more than 90% of NO _x in flue gas is also NO. Due to the poor reaction ability of NO, its removal is technically quite difficult. After years of research, various denitrification methods have been developed. At present, the catalytic reduction method is widely used in industry. Such as the methods disclosed in US Patent 4,221,768, Swedish Patent 8404840-4, US Patent 4,101,238, and US Patent 4,048,112, but the reaction of this method needs to consume a large amount of reducing agent, and the nitrogen in the flue gas cannot be recycled, resulting in precious resources waste;

Most of the desulfurization methods that have been used in industry are wet methods. The main defect of this method is that it cannot remove _NOx in the flue gas at the same time. Therefore, it will be of great significance to improve the existing desulfurization methods and realize simultaneous desulfurization and denitrification. .

Japanese patents P1659565j (1976), P181759c (1976), P63100918, A2 (1988) proposed simultaneous removal of _NOx and _SO The method adopted adopts oxidant, such as chloric acid, potassium permanganate, hydrogen peroxide, ozone, etc. , liquid-phase oxidation of _NOx , etc. have not been popularized due to high cost and other reasons. The yellow phosphorus method proposed by SG Chang in the United States in the late 1980s can simultaneously remove NO _x and SO ₂ in flue gas, but it is a completely discarded method. This method consumes a large amount of phosphorus resources, and its toxicity is high, and the operation requirements are relatively high.

Contents of the invention

The purpose of the present invention is to propose a method for simultaneous removal of sulfur and nitrate in flue gas by NO liquid-phase catalytic oxidation reaction, so that the oxidation and absorption of NO can be carried out simultaneously, and _SO2 and _NOx in flue gas can be removed and recovered at the same time , to achieve rational utilization of resources.

Design of the present invention is such:

Using _O2 in flue gas as oxidant, cobalt complex as main catalyst, iodine, bromine and other halogen anions as co-catalyst, realize catalytic oxidation and recovery of NO in liquid phase, and remove and recover SO at the same time ₂ .

Cobalt complexes (such as Co(NH ₃ ) ₆ ²⁺ , etc.) can form peroxides (Formula 1) with oxygen. This peroxide has a strong oxidation ability and can oxidize NO into water-soluble NO ₂ (Formula 2, 3), NO ₂ dissolves in water and forms a salt with ammonia (Formula 4);

Co(NH ₃ ) ₆ ²⁺ itself is also oxidized to Co(NH ₃ ) ₆ ³⁺ in the process of catalytic oxidation of NO. Co(NH ₃ ) ₆ ³⁺ does not have the ability to carry oxygen, but it can undergo photochemical reactions, such as in Under the catalysis of 370nm ultraviolet light, I ^- is oxidized to I ₂ , which itself is reduced to Co(NH ₃ ) ₆ ²⁺ (Formula 5);

_I2 was reduced to I ⁻ using _SO2 present in the flue gas (Eq. 6).

Through such a process, the catalytic oxidation and absorption of NO is realized, and the catalyst and co-catalyst can be regenerated and recycled. The overall reaction is shown in (Equation 7). Since Co(NH ₃ ) ₆ ²⁺ is formed by the reaction of divalent cobalt ions in the solution with excess ammonia water, the remaining ammonia in the absorption solution will react with SO ₂ (Formula 8) to generate ammonium sulfate, which can be removed simultaneously SO ₂ .

(2)

2NO ₂ (l)+H ₂ O+2NH ₃ →NH ₄ (NO ₂ )+NH ₄ (NO ₃ ) (4)

The overall response is:

The technical scheme that realizes the object of the present invention:

Said method of the present invention comprises the following steps successively:

(1) Catalytic oxidation reaction: pass the solution containing ammonia water (NH ₃ ·H ₂ O) and divalent cobalt complex ions, halogen simple substance or halogen monovalent anion salt and flue gas containing NO and SO ₂ into a conventional reactor Or in the separation tower, ammonia water and divalent cobalt complex ions first react to form a cobalt complex ---- Co(NH ₃ ) ₆ ²⁺ , and then the complex oxidizes NO in the flue gas into water-soluble NO ₂ , NO ₂ dissolves in water and ammonia to form nitrite and ammonium nitrate salts, SO ₂ in the flue gas dissolves in the solution and is oxidized to form ammonium sulfate, so that the NO and SO ₂ in the flue gas can be removed .

The pH of the solution is 8-13, preferably 9-11, the operating temperature is 30-80°C, the optimum value is 40-60°C, and the concentration of ammonia in the solution is 1-20% by weight, preferably 8-12%, The concentration range of NO in flue gas is 200-1000ppm; the concentration range of _SO2 is 1000-2500ppm, and the concentration of _O2 is 2-8%.

The divalent cobalt complex ion concentration of the main catalyst is 0.005-0.2molL ^-1 , preferably 0.01-0.1molL ^{-1 , the co-catalyst concentration is 0.001-0.03molL -1 ,} preferably 0.005-0.03molL ^-1 , the molar concentration of the main catalyst and co-catalyst The ratio is 2-10, preferably 3-8.

Said main catalyst divalent cobalt complex ion can be selected from water-soluble inorganic cobalt salt, commonly used is a kind of in cobalt nitrate, cobalt acetate or cobalt chloride; Preferred is cobalt nitrate;

Said halogen simple substance or monovalent anion salt can be selected from one of bromine, chlorine and iodine compounds or one of Br ₂ and I ₂ , preferably iodine:

(2) Regeneration of the reaction solution: the solution after the reaction in step (1) is placed in a glass circulation tank, irradiated with an ultraviolet lamp with a wavelength of 4 to 12W and a wavelength of 250 to 365nm to regenerate the main catalyst in the absorption liquid, and the solution The ammonium sulfite and ammonium salt in the solution can be separated by conventional methods, such as freezing and crystallization, and then supplemented with ammonia, the solution can be used again.

The invention adopts the liquid-phase composite catalyst, which can not only realize the catalytic oxidation and absorption of NO at the same time, simplify the process flow, and the minimum concentration of _SO2 in the outlet gas can reach 0%, but also solve the problem of sulfur resistance and water resistance of the traditional NO oxidation solid catalyst Poor puzzle.

Detailed ways.

The present invention will be further elaborated below in conjunction with embodiment.

Example 1

The experiment was carried out in a bubbling reactor with a diameter of 2 cm and a height of 90 cm. The amount of liquid added to the reactor was 200 ml, wherein: the main catalyst was cobalt nitrate with a concentration of 0.04M; the cocatalyst was iodine with a concentration of 0.01M and an ammonia concentration of 10 %, the pH value is 11;

The gas flow rate is 200ml/minute, and the temperature is 50°C;

The composition of the gas inlet is NO: 480ppm, SO ₂ : 1500ppm, O ₂ : 5.2%, and the rest is nitrogen.

The gas outlet concentration is analyzed online by an infrared spectrometer, with automatic sampling every two minutes. Within 180 minutes, the gas outlet concentration is NO: 30ppm, SO ₂ : 0%.

Example 2

The experiment was carried out in a packed tower with a diameter of 2 cm and a height of 100 cm. The gas-liquid two-phase flow was countercurrent, the superficial gas velocity was 0.1 m/s, and the liquid spray density was 6 m ³ /m ² .hr.

Wherein: the main catalyst is cobalt nitrate, the concentration is 0.04M, the cocatalyst is bromine, the concentration is 0.01M, the ammonia concentration is 10%, and the pH value is 11;

The gas flow rate is 200ml/minute, and the temperature is 50°C;

The composition of the gas inlet is NO: 480ppm, SO ₂ : 1500ppm, O ₂ : 5.2%, and the rest is nitrogen.

The absorption liquid is recycled, and the gas outlet concentration is analyzed online by an infrared spectrometer. Automatic sampling is performed every two minutes. Within 180 minutes, the gas outlet concentration is NO: 15ppm, SO ₂ : 0%

Example 3

The reactor and _operating conditions are the same as in Example 2, and the glass circulation tank (500ml) of the absorbing liquid is irradiated with a _12W 365nm ultraviolet lamp to regenerate the main catalyst in the absorbing liquid. %, when the absorption solution of 0.04MCo(NH ₃ ) ₆ ²⁺ , 0.01MKI, and 10% ammonia water reaches a stable operation, the NO removal rate remains at 96%.

Example 4

Reactor and operating condition are the same as embodiment 3, take out the ammonium sulfate precipitate from the bottom of the glass circulation tank every 5 days, filter and crystallize, can obtain ammonium sulfate, replenish ammoniacal liquor in the glass circulation tank simultaneously, make to reach the concentration of 10%.

Comparative example 1

The reactor and operating conditions are the same as in Example 1, the absorbent is _H2O2 , and the concentration is 10%; the gas outlet concentration is analyzed online by _an infrared spectrometer, and automatic sampling is performed every two minutes. Within 180 minutes, the gas outlet concentration is NO: 240ppm, _SO2 : 300ppm.

Comparative example 2

The reactor and operating conditions are the same as in Example 1, the absorbent is Fe-EDTA, and the concentration is 0.01M; the gas outlet concentration is analyzed online by an infrared spectrometer, and automatic sampling is performed every two minutes. Within 180min, the gas outlet concentration is NO: 220ppm , SO ₂ : 250ppm.

Claims (7)

1. one kind removes SO in the flue gas simultaneously ₂And NO _xMethod, it is characterized in that in turn including the following steps:

(1) catalytic oxidation: will contain the solution of ammoniacal liquor and divalence cobalt complex ion, halogen simple substance or halogen monovalence anion salt and contain NO and SO ₂Flue gas react at the reactor or the knockout tower of routine;

The pH value of solution is 8～13, and operating temperature is 30～80 ℃, and the weight percent concentration of ammonia is 1～20% in the solution, O in the flue gas ₂Concentration be 2～8%;

Major catalyst divalence cobalt complex ion concentration is 0.01～0.1molL ^-1, co-catalyst halogen simple substance or halogen monovalence anion salt concentration are 0.005～0.03molL ^-1

(2) regeneration of reaction solution: with step (1) reacted solution wavelength is the ultra violet lamp of 250～365nm, and replenishes ammonia after removing ammonium salt in the solution with conventional method, and solution recycles.

2. the method for claim 1 is characterized in that, the pH value of solution is 9～11, and operating temperature is 40～60 ℃, and the weight percent concentration of ammonia is 8～12% in the solution.

3. the method for claim 1 is characterized in that, said major catalyst divalence cobalt complex ion is selected from the water-soluble inorganic cobalt salt; Co-catalyst halogen monovalence anion salt is selected from a kind of in bromine, chlorine or the iodine compound.

4. method as claimed in claim 2 is characterized in that, said major catalyst divalence cobalt complex ion is selected from the water-soluble inorganic cobalt salt; Co-catalyst halogen monovalence anion salt is selected from a kind of in bromine, chlorine or the iodine compound.

5. method as claimed in claim 3 is characterized in that, major catalyst divalence cobalt complex ion is selected from a kind of in cobalt nitrate, cobalt acetate or the cobalt chloride.

6. method as claimed in claim 4 is characterized in that, major catalyst divalence cobalt complex ion is selected from a kind of in cobalt nitrate, cobalt acetate or the cobalt chloride.

7. as claim 5 or 6 described methods, it is characterized in that major catalyst divalence cobalt complex ion is selected from cobalt nitrate.