CN101306308A - Method for synchronously treating the combined pollution exhaust gas containing nitric oxide and sulfur dioxide - Google Patents

Abstract

The invention relates to a method for simultaneous treatment of mixed pollutant exhaust gas containing NOx and SO2. Absorption liquid of ferrous salt, ethylenediaminetetraacetic acid disodium and a desulphurization agent and waste gas containing SO2 and NO are introduced into a conventional reactor to carry out the reaction, thereby realizing the simultaneous absorption of NO and SO2. The absorption liquid after the reaction can be introduced in a liquid-solid reactor which takes activated carbon as a catalyst for regeneration. The method is a low-cost wet desulphurization and denitrification technique with market competitiveness.

Description

A method for simultaneously treating mixed pollutant exhaust gas containing NOx and SO2

technical field

The invention relates to a method for simultaneously treating mixed pollutant waste gas containing _NOx and _SO2 , in particular to a simultaneous removal method for NO 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 NO _X are the two most harmful polluting gases with the largest emissions, 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 NO _X (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 NO _X 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 only accounts for a small amount, and more than 90% of NO _X in flue gas is also NO. Due to the poor reaction ability of NO and insoluble in water, 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 patents USP: 4,221,768, Swedish Patent 8404840-4, USP: 4,101,238, and US: 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 a waste of valuable resources .

Japanese patents P1659565j (1976), P181759c (1976), P63100918, and A2 (1988) proposed simultaneous removal of NO _X and _SO The method used for the oxidant, such as chloric acid, potassium permanganate, hydrogen peroxide, ozone, etc., liquid The phase oxidation of NO _X and so on has not been popularized due to reasons such as high cost. The yellow phosphorus method proposed by the Berkeley Laboratory of the University of California, USA (see the literature Nature, 1990, 343(11): 151-153), can simultaneously remove _NOx and SO ₂ in the 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.

In the early 1970s, it was proposed to use Fe(II)-EDTA (EDTA stands for disodium ethylenediaminetetraacetic acid) to remove NO from exhaust gas. The reaction formula of Fe(II)-EDTA and NO is as follows:

In the next thirty years, many scholars have conducted systematic research on this reaction, but there is still no industrial report, mainly because Fe(II)-EDTA is easily oxidized to Fe(III)- EDTA (see references: Bull.of theChem.Soc.of Jpn., 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. People propose to regenerate Fe(II) with biocatalytic reduction (see references: UnitedStates 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 this method is only in the exploratory stage at present. There are still many problems to be solved for large-scale application in the process of waste gas treatment.

Contents of the invention

The purpose of the present invention is to propose a method for simultaneously treating waste gas containing mixed pollutants _NOx and _SO2 .

The technical problem that the present invention needs to solve is to provide a kind of Fe(II)-EDTA solution to remove NO and _SO in the waste gas The method makes NO and _SO The absorption is carried out simultaneously, to overcome the above-mentioned defective that prior art exists, 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:

Use the absorption liquid containing Fe(II)-EDTA and desulfurizer to absorb NO and SO ₂ at the same time, and Fe(III)-EDTA generated by oxidation of Fe(II)-EDTA uses activated carbon as a catalyst to catalytically reduce and regenerate Fe(II) -EDTA, the basic principle of Fe(II)-EDTA catalytic regeneration is as follows:

Because acidic groups such as carbonyl, carboxyl, and phenolic groups on activated carbon can promote the dissociation of Fe(III)-EDTA into Fe(III) and EDTA (reaction (2)):

Fe(III) has a strong oxidation ability, the π-electron structure of activated carbon not only has the ability to transfer electrons, but also can become the center of reduction of Fe(III) ions, and the sulfite produced by dissolving _SO2 in the absorption solution acts as a reducing agent , Fe(III) is reduced to regenerate Fe(II) (reaction (3)), and sulfite is oxidized to sulfate.

Fe(II) is combined with EDTA in the solution to form Fe(II)-EDTA (reaction (4)), 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)+EDTA→Fe(II)-EDTA (4)

The method of the present invention is realized by simultaneous desulfurization and denitrification reactions: in a conventional reactor, ferrous salt, ethylenediaminetetraacetic acid disodium (EDTA) and a desulfurizer are dissolved in an aqueous solution as an absorption liquid, and the NO And SO ₂ waste gas is introduced to realize simultaneous NO and SO ₂ absorption.

Described desulfurizer is 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 waste gas is: 100-1000ppm; the concentration range of _SO2 is 500-3000ppm.

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: 4-7.

The concentration range of the ferrous salt is: 0.005-0.1 mol l ^-1 , preferably 0.02-0.06 mol l ^-1 .

The concentration range of EDTA is: 0.01-0.2 mol l ^-1 , preferably 0.04-0.15 mol l ^-1 .

The concentration of the desulfurizing agent is 0-0.3 mol l ^-1 . Preferably it is 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 .

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.

The reaction solution in the method of the present invention can be regenerated: the above-mentioned reacted solution is passed into a reactor that uses activated carbon as a catalyst for regeneration. The reactor is a commonly used liquid-solid reactor, such as a fixed bed, a slurry bed, etc., the active The carbon can be commonly used coconut shell activated carbon, sawdust activated carbon, coal-based activated carbon, etc. The regeneration temperature is 20-90°C, the optimum temperature is 50-80°C, the regeneration pH is 1-9, and the optimum pH is 3-90°C. 7. The reaction solution can continue to be used after regeneration.

In other words, the method of the present invention can be carried out continuously like this: the above-mentioned absorption liquid is introduced from the top or upper side of the reactor, and the waste gas containing NO _X and _SO is introduced from the bottom or the lower side of the reactor to continue the reaction, after the reaction The gas continuously flows out 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 liquid-solid reactor containing activated carbon, and continues to be used after activation and regeneration.

The present invention uses Fe-EDTA solution as absorbent, activated carbon as catalyst, and sulfite as reducing agent to regenerate the NO absorption active component Fe(II)-EDTA, so as to realize the recycling of NO absorbent and realize NO and SO ₂ removal at the same time, so that the cost of simultaneous treatment of nitrogen oxides and sulfur dioxide is greatly reduced.

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 can not limit the scope of the present invention.

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 5m ³ /m ² .hr, and the absorption liquid was 500ml.

Wherein: ferrous sulfate concentration is 0.02mol l ^-1 , EDTA concentration is 0.04mol l ^-1 , pH value is 6,

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 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 80°C, the liquid flows from bottom to top in the regeneration tower at a rate of 25ml 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 an infrared spectrometer, and it is automatically sampled every two minutes. When the operation is stable, the gas outlet concentration is NO: 30ppm, SO ₂ : 150ppm. 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 reaches a steady state, the gas outlet concentration is NO: 30ppm, SO ₂ : 40ppm.

Example 3

The reactor and operating conditions are the same as in Example 1, but there is still 0.03 mol l ^-1 of magnesium oxide in the absorption liquid. When the operation reaches a stable state, the gas outlet concentration is NO: 30ppm, 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: 30ppm, SO ₂ : 40ppm.

Claims (9)

1. A method for simultaneously removing SO in exhaust gas with Fe-EDTA 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, disodium edetate and desulfurizer; wherein, the concentration range of ferrous salt is 0.005-0.1mol l ^-1 ; edetate The concentration range of disodium is 0.01～0.2mol l ^-1 ; the concentration of desulfurizer is 0～0.3mol l ^-1 ; The desulfurizing agent is divalent metal oxide, hydroxide compound or carbonate. 2. The method according to claim 1, characterized in that the temperature range is 30-60° C.; the gas-liquid volume flow rate ^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 500-3000ppm; 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 4-7. 5. The method according to claim 1, characterized in that the concentration of the iron salt is 0.02-0.06 mol l ^-1 ; the concentration of the disodium edetate is 0.04-0.15 mol l ^-1 ; 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; 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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