CN101773770A - Method for removing waste gas pollutants of NOX and SO2 simultaneously - Google Patents

Abstract

The present invention relates to a method for simultaneously treating _NOx and _SO2 exhaust gas pollutants, in particular to a method for simultaneously removing NO and _SO2 from power plant flue gas, using an absorbing liquid composed of Fe(II)-NTA and a desulfurizer Simultaneously absorbing NO and SO ₂ , Fe(II)-NTA transfers NO from the gas phase to the liquid phase, and then reduces it to harmless nitrogen in the aqueous solution under the catalysis of activated carbon. Fe(Ⅱ)-NTA is regenerated under lower reduction, and the sulfite produced by dissolving SO ₂ in the absorption solution is used as a reducing agent, which realizes the recycling of NO absorbent, and also realizes NO absorption and reduction, SO ₂ absorption and oxidation at the same time The cost of nitrogen oxides and sulfur dioxide treatment has been greatly reduced.

Description

A method for simultaneously removing NOx and SO2 exhaust gas pollutants

technical field

The invention relates to a method for simultaneously treating NO _x and SO ₂ exhaust gas pollutants, in particular to a simultaneous removal method for NO and SO ₂ in power plant flue gas.

Background technique

my country is a country where coal is the main energy source. The emission of coal-fired power generation will cause great pollution to the environment, which has become a major factor restricting the sustainable development of the power industry. The SO ₂ (1000-4000ppm) and NOx (300-800ppm) produced by coal combustion are the main source of industrial waste gas pollution (acid rain hazard). Nitrogen oxides can also form photochemical pollution, produce the greenhouse effect, destroy the ozone layer, and have toxic effects on the human body. In 2004, the amount of NO emitted was 16 million tons. If effective pollution control measures are not taken, the emission of nitrogen oxides in China will reach about 29 million tons in 2020, and the emission of SO ₂ will reach more than 43.5 million tons. In recent years, the concentration of nitrogen oxides in the air of some super-large cities in my country has exceeded the standard, and the environmental capacity of nitrogen oxides is basically in a saturated state, and some places even produce photochemical smog. With the strengthening of SO ₂ emission control in China and the increase in the number of automobiles, the contribution of NO _x to acid rain will gradually catch up with or exceed that of SO ₂ . 0.15:1 developed to 0.20:1 in 2004, the control of SO ₂ and NO emissions is imminent.

NO _x is a general term for nitrogen oxides, including N ₂ O, NO, N ₂ O ₃ , NO ₂ , N ₂ O ₅ , etc. More than 95% of NO _x in the atmosphere is NO, and NO ₂ only accounts for a small amount. More than 90% of the _NOx in the flue gas is also NO. Due to the low chemical reactivity of low concentration 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.

Among the existing flue gas desulfurization devices in various countries in the world, the wet desulfurization process accounts for about 85%. Since the widely used mature desulfurization method is the wet method, improving the existing wet desulfurization process so that desulfurization and denitrification can be carried out simultaneously has strong economic competitiveness and is also a research and development hotspot of simultaneous desulfurization and denitrification technology. The solubility of NO in aqueous solution is very low, so there are only two ways to remove NO by wet method, one is to complex with the complex salt in the solution to remove NO from the exhaust gas; the other is to use liquid phase oxidant for oxidation , to oxidize NO to NO ₂ which is easily soluble in water.

Japanese patents P1659565j (1976), P181759c (1976), P63100918, and A2 (1988) proposed simultaneous removal of NO _X and _SO The method adopts chloric acid, potassium permanganate, hydrogen peroxide, ozone, etc. as oxidants, and NO liquid phase oxidation into NO ₂ , which is easily soluble in water, but it has not been popularized due to high cost and other reasons. The yellow phosphorus method (see literature Nature, 1990, 343 (11): 151-153) proposed by the Berkeley laboratory of the University of California, USA can simultaneously remove _NOx and SO ₂ in the flue gas. This method consumes a large amount of phosphorus resources, And its toxicity is big, and operation requirement is higher.

Using Fe(II)-EDTA (EDTA stands for disodium ethylenediaminetetraacetic acid) to remove NO from exhaust gas has the advantage of high removal efficiency, but because Fe(II)-EDTA is easily oxidized to Fe(III)-EDTA( See references: Bull.of the Chem.Soc.ofJpn., 1968, 41:2234-2239.Ind.Eng.Chem.Res., 1987, 26:1468-1472.Inorg.Chem., 1990,29:1705 -1711.Ind.Eng.Chem.Res., 1993,32:2580-2594.), and Fe(Ⅲ)-EDTA cannot complex NO, so that the absorption efficiency drops rapidly. It has been proposed to regenerate Fe(II) by bioreduction (see references: United States Patent US5891408.Biotechnol.Prog., 2003, 19:1323-1328.J Chem Technol Biotechnol, 2004,79:835-841.Biotechnology and Bio engineering, 2005, 90: 433-441.Environ Sci Technol, 2005, 39: 2616-2623.J of Chem Technol and Biotechnol, 2006, 81: 306-311.), but the method is still in the exploratory stage, and Many problems need to be solved.

Nitrilotriacetic acid/nitrotriacetic acid/nitrotriacetic acid (NTA, English name: Nitrilotriacetic acid, molecular formula: N(CH ₂ COOH) ₃ , molecular weight: 191.14) and ferrous iron complex Fe(Ⅱ)-NTA It can complex with NO and remove NO pollution from exhaust gas (Ind.Eng.Chem.Res., 1990, 29:10-14). Compared with EDTA, nitrilotriacetic acid is cheap and has small molecular weight, which is economically There are advantages. However, like Fe(II)-EDTA, Fe(II)-NTA will also be oxidized to Fe(III)-NTA, and Fe(III)-NTA cannot complex NO, which reduces the removal efficiency of NO.

Contents of the invention

The purpose of the present invention is to propose a method for simultaneously removing NO and _SO2 exhaust gas pollutants.

The technical problem to be solved in the present invention is to _provide a kind of Fe(II)-NTA solution to remove NO and SO in the waste gas The method makes NO and _SO The absorption is carried out simultaneously, and NO is reduced to harmless nitrogen, In order to overcome the above-mentioned defects in the existing technology, reduce the treatment cost of wet desulfurization and denitrification, and improve the market competitiveness of wet desulfurization and denitrification technology.

Design of the present invention is such:

Absorption liquid containing Fe(II)-NTA and desulfurizer absorbs NO and SO ₂ at the same time, Fe(II)-NTA transfers NO from gas phase to liquid phase, and then reduces it to harmless NO in aqueous solution under the catalysis of activated carbon Nitrogen, Fe(Ⅲ)-NTA generated by oxidation at the same time is reduced and regenerated to Fe(Ⅱ)-NTA under the catalysis of activated carbon, and the sulfite produced by dissolving _SO2 in the absorption solution is the reducing agent. The basic principle of the whole process is as follows:

Fe(II)-NTA reacts with NO as shown in formula (1), transferring NO from the gas phase to the liquid phase:

The π-electron structure of activated carbon has the ability to transfer electrons, which can become the center of redox reaction, and the sulfite produced by dissolving _SO2 in the absorption solution can be used as a reducing agent to reduce NO in aqueous solution under the catalysis of activated carbon For harmless N ₂ :

Fe(II)-NTA will be oxidized to Fe(III)-NTA by the residual oxygen in the exhaust gas, thus losing the ability to complex and absorb NO. However, activated carbon can promote the dissociation of Fe(Ⅲ)-NTA into Fe(Ⅲ) and NTA (reaction (3)):

Fe(Ⅲ) has a strong oxidation ability, and the sulfite in the absorption solution can be used as a reducing agent to reduce Fe(Ⅲ) to Fe(Ⅱ) (reaction (4)):

Fe(II) combines with NTA in the solution to form Fe(II)-NTA (reaction (5)), so that the absorbent can be regenerated, and the ability of the absorbent to remove NO can be maintained for a long time.

Fe(Ⅱ)+NTA→Fe(Ⅱ)-NTA (5)

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

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

(1) Waste gas pollutant treatment: In a conventional reactor, ferrous salt, nitrilotriacetic acid (NTA) and a desulfurizer are dissolved in an aqueous solution as an absorption liquid, and waste gas containing NO and SO ₂ is introduced to realize Simultaneous NO and _SO2 absorption.

Described desulfurizer is ammonium sulfate, divalent metal oxide, hydroxide compound or carbonate etc., can be calcium oxide (lime), magnesium oxide, Mg(OH) ₂ or calcium carbonate (limestone) etc.

The concentration range of NO in the exhaust gas is: 100-1000ppm; the concentration range of _SO2 is 500-5000ppm.

Oxygen is usually contained in the exhaust gas, and the concentration of _O2 is 0-20%.

The operating pressure is normal pressure, the temperature range is: 10-90°C, and the optimum value is: 30-60°C.

The pH range of the solution is generally: 1-9, and the optimum value is: 3-7.

The concentration range of the ferrous salt is: 0.008-0.2 mol l ^-1 , preferably 0.04-0.08 mol l ^-1 .

The concentration range of NTA is: 0.01-0.4 mol l ^-1 , preferably 0.08-0.15 mol l ^-1 .

The concentration of the desulfurizing agent is 0-0.3 mol l ^-1 , preferably 0.005-0.3 mol l ^-1 . For example, the concentration range of calcium oxide is: 0.005～0.3mol l ^-1 , recommended is 0.01～0.1mol l ^-1 ; the concentration range of magnesium oxide is: 0.005～0.3mol l ^-1 , recommended is 0.01～0.1mol l ^-1 ; The concentration range of calcium carbonate is: 0.005～0.3mol l ^-1 , recommended is 0.01～0.1mol l ^-1 ; the concentration range of (NH ₄ ) ₂ SO ₄ is: 0.005～0.3mol l ^-1 , recommended is 0.03～ 0.2mol l ^-1 ;

Usually the gas-liquid ratio (volume flow ratio, M ³ ) is 10-300:1, and the recommended gas-liquid ratio is 200:1.

The ferrous salt can be selected from commonly used ferrous sulfate, ferrous chloride, ferrous nitrate, preferably ferrous sulfate.

The present invention has no special requirements on the reactor for the simultaneous absorption of _NOx and _SO2 , and the removal of _NOx and _SO2 can be carried out in common gas-liquid reactors such as packed towers, tray towers or bubble towers.

(2) Regeneration of reaction solution: the solution after the step (1) reaction is passed into the reactor with active carbon as catalyst for regeneration, and this reactor is a commonly used liquid-solid reactor, such as fixed bed, slurry bed, etc. Activated carbon can be commonly used coconut shell activated carbon, sawdust activated carbon, coal-based activated carbon, asphalt-based activated carbon, etc. The regeneration temperature is 20-90°C, the optimum temperature is 50-80°C, and the regeneration pH is 1-9. The optimum pH is 3-7. The reaction solution can continue to be used after regeneration.

The basic process of the inventive method implementation: the above-mentioned absorption liquid is introduced continuously by the top or the upper side of the gas-liquid reactor, and the waste gas containing NO _{and SO} is continuously sent into the gas-liquid reactor from the bottom or the lower side. The _NOx and _SO2 absorption reactions are carried out in the gas-liquid reactor, and the reacted gas is continuously output from the top or upper side of the reactor, while the absorption liquid flows out from the bottom or lower side of the reactor, and is introduced into the activated carbon containing In the liquid-solid reactor, it will continue to be used after catalytic regeneration.

The present invention uses Fe-NTA solution as absorbent, activated carbon as catalyst, and sulfite as reducing agent to regenerate NO absorption active component Fe(II)-NTA, so as to realize the recycling of NO absorbent, and also realize NO Absorption and reduction, _SO2 absorption and oxidation are carried out at the same time, which greatly reduces the cost of nitrogen oxides and sulfur dioxide treatment.

Description of drawings

Fig. 1 is a kind of flowchart of the present invention.

Symbol Description.

In the drawings: 1-reactor, 2-liquid-solid reactor, 3-absorption liquid, 4-exhaust gas containing NO _X and SO ₂ , 5-activated carbon, 6-circulation tank.

Detailed ways

The present invention will be further elaborated below in conjunction with embodiment, but content of the present invention can not be limited.

Example 1

The absorption experiment was carried out in a packed tower with a diameter of 2cm and a height of 100cm. The gas-liquid two-phase countercurrent flow, the superficial gas velocity of the tower was 0.1m/s, the liquid spray density was 7m ³ /m ² .hr, and the absorption liquid was 500ml.

In the absorption liquid: the concentration of ferrous sulfate is 0.02mol l ^-1 , the concentration of nitrilotriacetic acid is 0.03mol l ^-1 , and the pH value is 6;

The gas flow rate is 300ml min ^-1 and the temperature is 50°C;

The composition of the gas inlet is NO: 600ppm, SO ₂ : 1500ppm, O ₂ : 5.2%, and the rest is nitrogen.

The absorption liquid enters the packed tower from the top of the tower to absorb NO and SO ₂ , flows into the circulation tank through the bottom of the tower, and then enters the fixed bed reactor with a height of 50cm and a diameter of 2cm equipped with coconut shell activated carbon from the circulation tank for catalyst regeneration. The temperature is 70°C, the liquid flows from bottom to top in the regeneration tower at a speed of 35ml min ^-1 , and the absorption liquid leaving the regeneration tower directly enters the packed tower to absorb NO and SO ₂ . The gas outlet concentration is analyzed online by the infrared spectrometer, and the sample is automatically taken every two minutes. When the operation is stable, the gas outlet concentration is NO: 50ppm, SO ₂ : 160ppm. The flow chart of logistics is shown in Figure 1.

Example 2

The reactor and operating conditions are the same as in Example 1, but there is still 0.03 mol l ^-1 of calcium oxide in the absorption liquid. When the operation is stable, the gas outlet concentration is NO: 50ppm, SO ₂ : 40ppm.

Example 3

The reactor and operating conditions are the same as those in Example 1, but there is still 0.03 mol l ^-1 of magnesium oxide in the absorption liquid. When the operation is stable, the gas outlet concentration is NO: 50ppm, SO ₂ : 40ppm.

Example 4

The reactor and operating conditions are the same as in Example 1, but there is still 0.03 mol l ^-1 of limestone in the absorption liquid. When the operation is stable, the gas outlet concentration is NO: 50ppm, SO ₂ : 40ppm.

Example 5

The reactor and operating conditions are the same as in Example 1, but there is 0.03 mol l ^-1 (NH ₄ ) ₂ SO ₄ in the absorption liquid. When the operation reaches a steady state, the gas outlet concentration is NO: 50ppm, SO ₂ : 40ppm.

Claims (10)

1. A method for simultaneously removing SO in waste gas with Fe-NTA solution ₂ and NO method, it is characterized in that in conventional reactor, when normal pressure and 10～90 ℃, feed absorption liquid and contain SO ₂ and NO The waste gas is reacted, and the gas-liquid volume flow ratio ^M3 is 10～300:1; The absorption liquid is an aqueous solution of pH 1-9 containing ferrous salt, nitrilotriacetic acid and desulfurizer; wherein, the concentration range of ferrous salt is 0.008-0.2mol l ^-1 ; the concentration range of nitrilotriacetic acid is 0.01- 0.4mol l ^-1 ; the concentration of desulfurizer is 0~0.3mol l ^-1 ; The desulfurizing agent is ammonium sulfate, divalent metal oxide, hydroxide or carbonate. 2. The method according to claim 1, characterized in that the temperature range is 30-60°C, and the gas-liquid volume flow ratio ^M3 is 200:1. 3. The method according to claim 1, characterized in that the concentration range of NO in the waste gas is 100-1000ppm; the concentration range of _SO2 is 500-5000ppm; the concentration of oxygen contained in the waste gas is 0-20%. 4. The method according to claim 1, characterized in that the pH range of the absorption liquid is: 3-7. 5. The method according to claim 1, characterized in that the concentration of the iron salt is 0.04 to 0.08 mol l ^-1 ; the concentration of the nitrilotriacetic acid is 0.08 to 0.15 mol l ^-1 ; the The concentration of the desulfurizing agent is 0.005-0.3 mol l ^-1 . 6. The method according to claim 1, characterized in that said divalent metal oxide is calcium oxide, magnesium oxide or calcium carbonate; the concentration range of said calcium oxide is 0.005～0.3mol l ^-1 ; The concentration range of the magnesium oxide is 0.005-0.3 mol l ^-1 ; the concentration range of the calcium carbonate is 0.005-0.3 mol l ^-1 . 7. the method for claim 1 is characterized in that described ferrous salt is ferrous sulfate, ferrous chloride or ferrous nitrate. 8. The method according to claim 1, characterized in that the absorbed liquid after the reaction is passed into a liquid-solid reactor using activated carbon as a catalyst for regeneration at 20-90° C. and a pH of 1-9. 9. The method according to claim 1, characterized in that the activated carbon is commonly used coconut shell activated carbon, sawdust activated carbon or coal-based activated carbon, etc., the regeneration temperature is 50-80°C, and the pH is 3-7 . 10. The method as claimed in claims 1 and 8, characterized in that the absorption liquid flowing out from the conventional reactor is introduced into the liquid-solid reactor as claimed in claim 8.

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