CN112742190B - Complexing denitration process capable of recycling - Google Patents

Abstract

The invention provides a complexing denitration process capable of recycling, which is characterized in that a compounding agent, an auxiliary agent, a nano reagent and a dispersing agent are added into a complexing agent mainly containing Fe (II) EDTA, the NO complexing ability of a denitration agent is improved, the oxidation resistance of the denitration agent is improved, the absorption capacity and the use stability of the complexing denitration agent are further improved, then Fe (III) in the invalid complexing denitration agent is precipitated and separated, and then a regenerating agent with reducibility is added to reduce Fe (II) EDTA (NO) into Fe (II) EDTA and N ₂ Then the by-product ferrous sulfate heptahydrate in the process of producing titanium dioxide by using sulfuric acid method is used for supplementing Fe ²⁺ The regeneration method of (1) regenerates the spent complexing denitration agent. Meanwhile, the auxiliary agent and the nano reagent added in the preparation process of the complex denitrifying agent can play a role in catalyzing the regeneration reaction and accelerate the regeneration reaction.

Description

A complex denitration process that can be recycled and regenerated

technical field

The invention belongs to the technical field of flue gas denitration, and in particular relates to a complex denitration process capable of cyclic regeneration.

Background technique

As one of the main air pollutants, the emission of nitrogen oxides (NO _X ) has caused great harm to human beings and the environment. The emission sources of NO _X are mainly fuel combustion process and various industrial production processes, mainly including flue gas of coal-fired power plants, industrial boilers (kilns) and automobile exhaust. Among them, NO _X produced by coal combustion accounts for about 100% of China's total fixed source emissions. 70%.

Steel, cement, metallurgy, coking, coal chemical industry, industrial boilers and industrial kilns are the fields with the largest coal consumption except for the power industry. Under the circumstance that the prevention and control of air pollution in the thermal power industry has reached a certain level, non-electrical industries such as steel, metallurgy, and building materials have also quickly opened the prelude to upgrading and transformation. In April 2019, the Ministry of Ecology and Environment of China issued the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Iron and Steel Industry", which clearly pointed out that the sintering machine head flue gas and pellet roasting flue gas under the condition of the benchmark oxygen content of 16%, NO _X hours. Mean emission concentration < 50 mg/m ³ . The opinion points out that in principle, new (including relocation) steel projects across the country should achieve ultra-low emissions. By the end of 2020, significant progress will be made in the ultra-low emission transformation of iron and steel enterprises in key regions, and efforts will be made to complete the transformation of about 60% of production capacity; by the end of 2025, key regions The ultra-low emission transformation of iron and steel enterprises has basically been completed, and the country strives to complete the transformation of more than 80% of the production capacity.

Due to the inherent characteristics of low temperature, high humidity and high dust in sintering flue gas, the selective catalytic reduction and denitrification technology (SCR) and selective non-catalytic reduction flue gas denitrification technology (SNCR) that are widely used in the power industry are not suitable for Denitration treatment of sintering flue gas. As a low-temperature wet denitration technology, Fe(II)EDTA complex denitrification can be better grafted with wet desulphurization equipment, and finally achieve the standard emission of SO ₂ and NO _X in sintering flue gas. However, during the denitration process, O ₂ in the flue gas will oxidize Fe ²⁺ in the solution to Fe ³⁺ , and the addition of EDTA chelating agent will speed up the oxidation reaction, while Fe(II) EDTA is oxidized to form Fe (III) EDTA has no affinity for NO, which causes the complex denitrification agent to be easily oxidized, fail quickly and produce precipitation, which seriously restricts the industrial application of this technology.

Fan Fenglan et al. carried out the catalytic reduction regeneration of Fe(III)EDTA in saturated complex denitrification solution, and studied the catalytic performance of activated carbon-supported copper-based catalyst for Fe(II)EDTA wet removal of nitrogen oxides, which was prepared by the method of equal volume impregnation. The supported copper-based catalysts were compared, and the denitration effects of activated carbon, acid-base modified activated carbon, and activated carbon-supported Cu and Cu ₂ O were compared. The research shows that increasing the time and temperature of the regeneration process is beneficial to the regeneration and denitration efficiency of the denitrification solution. The activated carbon modified by alkali is helpful for the regeneration of the denitrification solution, and the wet denitration performance is obviously improved after the copper-based catalyst is loaded. The activated carbon-supported copper catalyst prepared by sodium borohydride alkaline solution reduction has stable Fe(II)EDTA complex denitration performance. (Chemical Engineering, Vol. 48, No. 5, 2020).

Liu Fu et al. carried out the research on the simultaneous desulfurization and denitrification of waste liquid by Fe regeneration of ammonia/Fe(II)EDTA method. The ammonia/Fe(II)EDTA method was used to simultaneously remove SO ₂ and NO _X in flue gas, and the waste was regenerated by iron scraps. Fe(III) in the liquid maintains the denitration efficiency. The experimental results show that the desulfurization efficiency of the ammonia/Fe(II)EDTA method can reach 100%, and the denitration efficiency can reach 68.3%. However, with the extension of the experiment time, the denitration efficiency gradually decreased. The denitration efficiency increased from 48.% to 57.1% after Fe(III)-removal by iron scrap regeneration. (Industrial Safety and Environmental Protection, Vol. 43, No. 5, 2017).

He Feiqiang et al. carried out research on Fe(II)EDTA complexing wet denitrification and its regeneration. Fe(III)EDTA was reduced by iron powder at room temperature under aerobic conditions, and the oxygen content, the initial mole of iron powder and Fe(III)EDTA were studied. The effect of Fe(III)EDTA ratio, initial concentration of Fe(III)EDTA and pH value on the reduction of Fe(III)EDTA by iron powder. It was found that the reduction of Fe(III)EDTA by iron powder under aerobic conditions can be divided into two stages: Fe(II)EDTA ) concentration increasing stage and Fe(II) concentration decreasing stage. In the stage of increasing Fe(II) concentration, the reduction rate of Fe(III)EDTA by iron powder decreases with the increase of oxygen content or pH value in the solution, and the concentration of Fe(II)EDTA produced by reduction increases with the initial Fe(III)EDTA. concentration or the initial molar ratio of iron powder to Fe(III)EDTA increased; in the second stage, due to the presence of oxygen, the concentration of Fe(II)EDTA decreased, and red-brown γ-FeOOH precipitated, and finally The kinetic models of Fe(III)EDTA reduction by iron powder in anaerobic and aerobic environments were deduced. The metal powder combined with Fe(II)EDTA was used to remove NO, and the effect of iron powder and zinc powder combined with Fe(II)EDTA to remove NO in a permeable reaction device was investigated. The results showed that in the permeable reaction device, the iron powder combined with Fe(II)EDTA absorbing solution could keep the NO removal rate above 90% within 90 minutes and the NO removal rate above 80% within 130 minutes. When zinc powder is used instead of iron powder, its absorption effect is significantly enhanced, and the NO removal rate can be as high as 90% for 15 hours, which can provide a more efficient denitration technology for industrial denitrification. (PhD dissertation of South China University of Technology, June 2017)

Yin Xiangnan et al. carried out an experimental study on the removal of NO from Fe(II)EDTA. The preparation of the complexing solution is only the mutual solubility of Fe ²⁺ and EDTA, and the molar ratio of Fe ²⁺ /EDTA is 3:2. In other treatments, the complex solution has problems such as low absorption capacity and fast failure (Industrial Safety and Environmental Protection, Vol. 43, No. 10, 2017).

To sum up, on the one hand, Fe(II)EDTA complex denitrification has little research on the optimization and improvement of the solution itself, and has not fundamentally solved the problem of low absorption capacity, slow mass transfer, easy oxidation and fast failure of Fe(II)EDTA solution. And other issues. On the other hand, the treatment of failed complex denitrification agents generally adopts the method of adding reducing agents or microorganisms to reduce Fe(III)EDTA and Fe(II)EDTA(NO) to form Fe(II)EDTA, but all reduction methods exist in the reduction of Fe(II)EDTA. The problems of large agent consumption, low efficiency and high operating cost seriously restrict the engineering application of complex denitrification.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a complex denitration process capable of cyclic regeneration. The complex denitration process in the present invention has high denitration efficiency, and the denitration agent can be recycled and regenerated, and the operation cost is low.

The invention provides a complex denitration process that can be recycled and regenerated, comprising the following steps:

A) contact the complex denitrification agent with low-temperature flue gas, and carry out denitration, until the complex denitrification agent fails;

The denitration agent includes disodium EDTA, divalent iron salt, formulation, auxiliary agent, nano-agent, dispersant and solvent;

The preparation is one or more of cysteine, linphrine, methylcyclopentenolone, ethylenediamine, triethanolamine, piperazine, hydroquinone and dibutylhydroxytoluene. ;

The auxiliary agent is one or more of sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium sulfite, sodium sulfide, ascorbic acid and carbohydrazide;

The nanometer reagent is one or more of nanometer titanium dioxide, nanometer nickel oxide, nanometer ferric oxide, nanometer ferric oxide, nanometer iron powder and nanometer silicon dioxide;

B) adjusting the pH value of the complex denitrification agent ineffective in the step A) to 8.5-9.0 to remove the precipitation;

C) adjusting the pH value of the filtrate obtained by removing the precipitation in the step B) to 5.5-6, adding a regenerant, and performing a reduction reaction to obtain a reduced denitration agent;

D) adding ferrous iron supplement to the denitrifying agent after reduction ^, so that the mole number of Fe ²⁺ in the denitrifying agent is equivalent to the mole number of EDTA ²⁺ to obtain a regenerated complex denitrifying agent;

The divalent iron supplement is FeSO ₄ 7H ₂ O, a by-product of producing titanium dioxide by a sulfuric acid method.

Preferably, the divalent iron salt is ferrous sulfate; the dispersing agent is sodium citrate, sodium pyrophosphate, trihexylhexyl phosphoric acid, sodium dodecylbenzenesulfonate, polyacrylamide and triton one or more of them.

Preferably, the concentration of the divalent iron salt is 25-50 mmol/L; the concentration of the disodium EDTA is 120-150% of the concentration of the divalent iron salt; the concentration of the formulation is divalent 30-50% of the concentration of the iron salt; the concentration of the auxiliary agent is 50-70% of the concentration of the divalent iron salt; the concentration of the nano-agent is 0.1-0.2% of the concentration of the divalent iron salt; The concentration is 1 to 5% of the concentration of ferrous salts.

Preferably, the complex denitration agent is prepared according to the following steps:

1) under the condition of introducing protective gas, disodium EDTA, ferrous salt, formulation, auxiliary agent, nano-agent and dispersant are mixed in a solvent to obtain a mixed solution;

2) ultrasonically vibrating the mixed solution to obtain a complex denitration agent.

Preferably, the residence time of the denitration is 5-7s, the liquid-gas ratio is 3-5L/m ² , the superficial flow rate is 2-2.5m/s, and the denitration temperature is 45-50°C.

Preferably, in the step B), an alkaline substance is added to adjust the pH value of the deactivated complex denitrification agent;

The alkaline substance is one or more of Na ₂ CO ₃ , NaOH and ammonia water.

Preferably, in the step C), an acidic substance is added to adjust the pH of the filtrate to 5.5-6;

The acidic substance is one or more of sulfuric acid, phosphoric acid and citric acid.

Preferably, the regenerant is one or more of sodium sulfite, sodium metabisulfite, sodium sulfide, urea, ascorbic acid, carbohydrazide and hydrazine hydrate;

The molar ratio of the regenerant to EDTA ²⁺ is (0.5-1):1.

Preferably, the temperature of the reduction reaction in the step B) is 40-55°C; the time of the reduction reaction in the step B) is 10-15 min.

The present invention provides a complex denitration process capable of cyclic regeneration, comprising the following steps: A) contacting a complex denitration agent with low-temperature flue gas to carry out denitration until the complex denitration agent fails; the denitration agent comprises ethyl acetate Disodium diaminetetraacetate, divalent iron salt, formulations, auxiliary agents, nano-agents, dispersants and solvents; the formulations are cysteine, linphrine, methylcyclopentenolone, ethyl acetate One or more of diamine, triethanolamine, piperazine, hydroquinone and dibutylhydroxytoluene; the auxiliary agent is sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium sulfite, sodium sulfide, One or more of ascorbic acid and carbohydrazide; the nanometer reagent is one or more of nanometer titanium dioxide, nanometer nickel oxide, nanometer ferric oxide, nanometer ferric oxide, nanometer iron powder and nanometer silicon dioxide. several; B) adjusting the pH value of the complex denitrification agent ineffective in the step A) to 8.5～9.0 to remove the precipitation; C) adjusting the pH value of the filtrate obtained by removing the precipitation in the step B) to 5.5～9.0 6. Add a regenerant, carry out a reduction reaction, and obtain a reduced denitrification agent; D) add a ferrous supplement to the reduced denitration agent, so that the mole number of Fe ²⁺ in the denitration agent is the same as that of EDTA ²⁺ . The number of moles is equivalent to obtain a regenerated complex denitration agent; the divalent iron supplement is FeSO ₄ 7H ₂ O, a by-product of the production of titanium dioxide by the sulfuric acid method. In the present invention, compounding agent, auxiliary agent, nano-agent and dispersing agent are added to the complexing agent mainly composed of Fe(II)EDTA, so as to improve the ability of the denitrification agent to complex NO, the antioxidant capacity of the denitrification agent is improved, and further The absorption capacity and use stability of the complex denitrification agent are improved, and then the Fe(III) in the failed complex denitrification agent is precipitated and separated, and then a reducing regenerant is added to convert Fe(II)EDTA (NO ) reduction to generate Fe(II)EDTA and N ₂ , and then use the by-product ferrous sulfate heptahydrate in the production of titanium dioxide by the sulfuric acid method to supplement the regeneration method of Fe ²⁺ to regenerate the ineffective complex denitrification agent. At the same time, the auxiliaries and nano-reagents added in the preparation process of the complex denitration agent can catalyze the regeneration reaction and accelerate the regeneration reaction.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 is the flow chart of the complex denitration process that can recycle and regenerate according to the present invention;

Fig. 2 is the concentration variation curve of NO at the _flue gas outlet in the technique in the embodiment of the present invention 1;

Fig. 3 is the concentration variation curve of NO _X at the flue gas outlet in the process in the embodiment of the present invention 2;

Fig. 4 is the variation curve of the concentration of NO _X at the outlet of the flue gas in the process of Example 3 of the present invention.

Detailed ways

The invention provides a complex denitration process capable of cyclic regeneration, comprising the following steps:

A) contact the complex denitrification agent with low-temperature flue gas, and carry out denitration, until the complex denitrification agent fails;

The denitration agent includes disodium EDTA, divalent iron salt, formulation, auxiliary agent, nano-agent, dispersant and solvent;

The preparation is one or more of cysteine, linphrine, methylcyclopentenolone, ethylenediamine, triethanolamine, piperazine, hydroquinone and dibutylhydroxytoluene. ;

The auxiliary agent is one or more of sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium sulfite, sodium sulfide, ascorbic acid and carbohydrazide;

The nanometer reagent is one or more of nanometer titanium dioxide, nanometer nickel oxide, nanometer ferric oxide, nanometer ferric oxide, nanometer iron powder and nanometer silicon dioxide;

B) adjusting the pH value of the complex denitrification agent ineffective in the step A) to 8.5-9.0 to remove the precipitation;

C) adjusting the pH value of the filtrate obtained by removing the precipitation in the step B) to 5.5-6, adding a regenerant, and performing a reduction reaction to obtain a reduced denitration agent;

D) adding ferrous iron supplement to the denitrifying agent after reduction ^, so that the mole number of Fe ²⁺ in the denitrifying agent is equivalent to the mole number of EDTA ²⁺ to obtain a regenerated complex denitrifying agent;

The divalent iron supplement is FeSO ₄ 7H ₂ O, a by-product of producing titanium dioxide by a sulfuric acid method.

The complex denitration process in the present invention includes a denitration section and a regeneration section, the denitration section performs denitration reaction in the denitration system, and the regeneration section regenerates the failed complex denitration agent in the regeneration system.

In the present invention, the denitration agent includes disodium EDTA, ferrous salt, formulation, auxiliary, nano-agent, dispersant and solvent;

The divalent iron salt is preferably ferrous sulfate, and the concentration of the divalent iron salt is preferably 25-50 mmol/L, more preferably 30-45 mmol/L, most preferably 35-40 mmol/L, specifically, in In the embodiment of the present invention, it may be 25 mmol/L or 40 mmol/L.

In the present invention, the concentration of the disodium ethylenediaminetetraacetate (EDTA-2Na) is preferably 120-150% of the concentration of the divalent iron salt, more preferably 130-140%, that is, the ethylenediamine The concentration of disodium tetraacetate is preferably 30-75 mmol/L, more preferably 30-60 mmol/L, and specifically, in the embodiment of the present invention, it may be 30 mmol/L or 52 mmol/L.

In the present invention, the formulation is mainly used to improve the ability of denitrification solution to complex NO and accelerate the reaction, including cysteine, linphrine, methylcyclopentenolone, ethylenediamine, triethanolamine , piperazine, one or more of hydroquinone and dibutylhydroxytoluene, specifically, in an embodiment of the present invention, the formulation can be a combination of the above-mentioned materials, such as cysteine+ Methylcyclopentenolone + dibutylhydroxytoluene, cysteine + piperazine, etc.

The concentration of the preparation is preferably 30-50% of the concentration of the divalent iron salt, more preferably 35-45%, that is, the concentration of the preparation is preferably 7.5-25 mmol/L, more preferably 10 ~20 mmol/L, most preferably 12 to 15 mmol/L, specifically, in the embodiment of the present invention, it may be 12.5 mmol/L or 12 mmol/L. More specifically, in one embodiment of the present invention, the formulation is 10mmol/L cysteine+2mmol/L piperazine, and in another embodiment of the present invention, the formulation is 5mmol/L Cysteine+5mmol/L methylcyclopentenolone+2.5mmol/L dibutylhydroxytoluene.

In the present invention, the auxiliary agent is mainly used to improve the antioxidant capacity of the denitrification solution, including one or more of sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium sulfite, sodium sulfide, ascorbic acid and carbohydrazide Specifically, in the embodiment of the present invention, it may be sodium carbonate + disodium hydrogen phosphate + sodium sulfite + carbohydrazide, or sodium dihydrogen phosphate + sodium sulfite + ascorbic acid.

The concentration of the auxiliary agent is preferably 50-70% of the concentration of the divalent iron salt, more preferably 55-65%, that is, the concentration of the auxiliary agent is preferably 12.5-35 mol/L, more preferably 12.5- 30mol/L, specifically, in an embodiment of the present invention, can be 12.5mol/L or 28mol/L, more specifically, in an embodiment of the present invention, the auxiliary agent is 4mmol/L sodium carbonate+ 4mmol/L disodium hydrogen phosphate+2.5mmol/L sodium sulfite+2mmol/L carbohydrazide, in another embodiment of the present invention, the auxiliary agent is 10mmol/L sodium dihydrogen phosphate+10mmol/L sodium sulfite+8mmol /L ascorbic acid.

In the present invention, the nano-reagent is mainly used for the anti-oxidation effect of the catalytic assistant, including nano-titanium dioxide, nano-nickel oxide, nano-iron tetroxide, nano-iron trioxide, nano-iron powder and nano-silicon dioxide. One or more, specifically, in the embodiment of the present invention, may be nickel oxide + triiron tetroxide, or nano-titanium dioxide + nano-silicon dioxide.

In the present invention, the concentration of the nano-reagent is preferably 0.1-0.2% of the concentration of the divalent iron salt, that is, the concentration of the nano-reagent is preferably 0.025-0.1 mmol/L, more preferably 0.03-0.08 mmol /L, most preferably 0.04-0.05mmol/L, specifically, in an embodiment of the present invention, it can be 0.04mmol/L or 0.05mmol/L, more specifically, in an embodiment of the present invention, the The nano-reagent is 0.02mmol/L nickel oxide+0.02mmol/L nano iron tetroxide, and in another embodiment of the present invention, the nano-reagent is 0.025mmol/L nano titanium dioxide+0.025mmol/L nano silicon dioxide .

In the present invention, the dispersing agent mainly enables the nanometer reagent to be well dispersed in the denitration solution, including sodium citrate, sodium pyrophosphate, trihexylhexylphosphoric acid, sodium dodecylbenzenesulfonate, polyacrylamide One or more of and triton, specifically, in the embodiment of the present invention, can be sodium pyrophosphate + polyacrylamide or sodium dodecylbenzenesulfonate.

The concentration of the dispersing agent is preferably 1-5% of the concentration of the divalent iron salt, more preferably 2-4%, most preferably 3-4%, that is, the concentration of the dispersing agent is preferably 0.25-2.5 mmol/L, more preferably 0.5-2 mmol/L, most preferably 1-1.5 mmol/L, specifically, in the embodiments of the present invention, it can be 1 mmol/L, more specifically, in an implementation of the present invention In an example, it can be 1mmol/L sodium dodecylbenzenesulfonate, and in another embodiment of the present invention, it can be 0.5mmol/L sodium pyrophosphate+0.5mmol/L polyacrylamide

In the present invention, the solvent is preferably water, which may be distilled water or deionized water.

Based on the formula of the above-mentioned complex denitrification agent, those skilled in the art can add other functional additives according to the conventional knowledge in this field without affecting the absorption capacity and stability of the complex denitrification agent in this scheme to meet the requirements of each used in different working conditions.

The present invention preferably prepares the complex denitration agent according to the following preparation method:

A) under the condition of introducing protective gas, disodium EDTA, ferrous salt, formulation, auxiliary agent, nano-agent and dispersant are mixed in solvent to obtain mixed solution;

B) ultrasonically vibrating the mixed solution to obtain a complex denitration agent.

In the present invention, the types and amounts of the disodium EDTA, divalent iron salts, formulations, auxiliary agents, nano-agents and dispersants, and solvents are the same as the disodium EDTA described above. , ferrous salts, formulations, additives, nano-agents and dispersants, and the types and amounts of solvents are the same, and will not be repeated here.

In the present invention, the oxygen in the solvent is preferably removed first, and a method commonly used by those skilled in the art to remove oxygen in the solvent can be used, such as heating and boiling distilled water, and introducing a protective gas into it under sealing conditions to eliminate the dissolution. Oxygen and isolating the oxidation of air, and then adding raw materials such as disodium EDTA to mix.

In the present invention, the protective gas is preferably nitrogen, helium or argon, and the flow rate of the protective gas is preferably 0.5-3 L/min, more preferably 1-2 L/min.

After adding raw materials such as disodium ethylenediaminetetraacetate, the protective gas was continuously introduced for 60min, and the mixture was uniformly mixed to obtain a mixed solution.

In the present invention, preferably, the mixed solution is sealed and put into an ultrasonic cell disruptor for ultrasonic oscillation to obtain a complex denitrification agent.

The invention utilizes the cavitation effect generated in the liquid by the ultrasonic cell disruptor to process the solution, which can significantly improve the stability and dispersibility of the solution. ~20min, and then ultrasonic vibration, repeated 4 to 6 times.

After ultrasonic vibration, the pH value of the complex denitrification agent is adjusted to a value of 6.5-7.5 using acid or alkali, such as sulfuric acid, sodium hydroxide and the like.

In the present invention, the denitration reaction is a gas-liquid contact reaction, the residence time of the denitration reaction is preferably 5-7s, the liquid-gas ratio of the denitration reaction is preferably 3-5L/m ² , and the superficial flow rate is 2 ~2.5m/s, the denitration temperature is 45~50℃.

The complex denitrification agent in the present invention is an efficient and stable complex denitration agent, and the failure time is as long as 270min. After the complex denitration agent fails, the present invention transports the complex denitration agent to the regeneration system through a booster pump In the process, the regeneration of the complex denitration agent is carried out.

In the present invention, the regeneration system includes a modulation tank, a filter, a regeneration reactor, a supplementary Fe ²⁺ tank and a circulating pump that are communicated in sequence, and the "communication" can be direct communication or indirect communication.

The method firstly transports the denitrification liquid that has failed after the reaction to the conditioning tank through a booster pump, adjusts the pH to 8.5-9.0, and after standing for 15-20 minutes, filters and precipitates to remove the oxidized Fe ³⁺ in the denitrification liquid.

In the present invention, an alkaline substance is preferably added to the spent complex denitration agent, and its pH value is adjusted to 8.5-9.0. Through a large number of experimental studies in this application, it is found that within the pH range of 8.5-9.0, the Fe ³⁺ in the solution is just right It can be combined with (OH) ^-1 (at this time, the combination of Fe ³⁺ and (OH) ^-1 is just stronger than the complexation with EDTA ^2- ) to form Fe(OH) ₃ precipitation, while Fe ²⁺ can remain with EDTA 2-. The complexation of EDTA ^2- does not form a precipitate; and the filtration separation of Fe(OH) ₃ precipitate is easier in this pH range. In the present invention, the alkaline substance is preferably one or more of Na ₂ CO ₃ , NaOH and ammonia water.

The filtrate obtained by filtration is transported to the regeneration reactor, an acidic substance is added to the filtrate obtained by the filtration, and its pH is adjusted to 5.5 to 6, and then a regenerant is added to carry out a reduction reaction, and Fe(II)EDTA(NO) The reduction produces Fe(II)EDTA and N ₂ to obtain a reduced denitration agent.

In the present invention, the acidic substance is preferably one or more of sulfuric acid, phosphoric acid and citric acid. Through a large number of experimental studies in this application, this pH range can accelerate the regeneration and reduction reaction on the one hand, and ensure that in the subsequent steps The pH of the complexed denitration solution was maintained at 7-7.5 after Fe ²⁺ supplementation (the pH denitration reaction proceeded the fastest).

In the present invention, the regenerant mainly plays a reducing role, preferably one or more of sodium sulfite, sodium metabisulfite, sodium sulfide, urea, ascorbic acid, carbohydrazide and hydrazine hydrate, specifically, in the implementation of the present invention In the example, it can be the combination of sodium sulfite+urea, the combination of sodium sulfite+carbazide, the combination of sodium sulfide+hydrazine hydrate; more specifically, the regenerant can be the above-mentioned several combinations according to a certain molar ratio, for example, sodium sulfite : urea=4:1, sodium sulfite:carbohydrazide=1:1, sodium sulfide:hydrazine hydrate=1:2.

In the present invention, the molar ratio of the regenerant to EDTA ²⁺ is (0.5-1):1, preferably (0.6-0.9):1, more preferably (0.7-0.8):1; In the embodiment of the present invention, it may be 0.48:1 or 0.83:1.

After adding the regenerant, the solution is heated and heated to carry out a reduction reaction to obtain a reduced complex denitration agent.

In the present invention, the temperature of the reduction reaction is preferably 40-55°C, more preferably 45-50°C; the time of the reduction reaction is preferably 10-15 min.

After the reduction and regeneration is completed, the present invention transports the reduced complex denitrification agent to the Fe replenishment tank, and adds a divalent iron salt supplement, so that the mole number of Fe ²⁺ in the denitrification agent ^{is equivalent to the mole number of EDTA 2+ ,} Make up for the iron lost due to the precipitation of Fe ³⁺ .

In the present invention, the by-product FeSO ₄ 7H ₂ O produced in the production of titanium dioxide by the sulfuric acid method, in the production process of titanium dioxide by the sulfuric acid method, ilmenite reacts with sulfuric acid to obtain Ti(SO ₄ ) ₂ and TiOSO ₄ , FeSO ₄ and Fe ₂ (SO ₄ ) ₃ are produced at the same time, the reaction is as follows:

TiO ₂ +H ₂ SO ₄ →TiOS ₄ +H ₂ O

FeO ₂ +H ₂ SO ₄ →FeSO ₄ +H ₂ O

FeO ₂ +3H ₂ SO ₄ →Fe ₂ (SO ₄ ) ₃ +3H ₂ O

The mixture of TiOSO ₄ and FeSO ₄ generated by acid hydrolysis is leached and sedimented to remove about 20% of insoluble impurities. After removing impurities, the solution is added with scrap iron for reduction treatment, so that the Fe ³⁺ in the solution is in the form of Fe ²⁺ Exist, TiOSO ₄ exists in the form of Ti ₂ (SO ₄ ) ₃ . The purified and reduced titanium solution is concentrated and cooled in a vacuum to crystallize ferrous sulfate in the form of FeSO ₄ 7H ₂ O, dried by a centrifuge and taken out. Every 1t of titanium dioxide produced will produce 3 to 4t of ferrous sulfate. Due to the large output of ferrous sulfate, its treatment has always been a difficult problem for the titanium dioxide industry by the sulfuric acid method.

After the above process treatment, both Fe(III)EDTA and Fe(II)EDTA(NO) in the failed complex denitrification agent are treated, and the complex denitration solution restores the denitration performance, and is pumped into the denitrification tower through the circulating pump to continue denitration.

In the present invention, compounding agents, auxiliary agents, nano-agents and dispersing agents are added to the complexing agent mainly composed of Fe(II)EDTA, and the antioxidative ability of the denitrifying agent is improved while the ability of the denitrifying agent to complex NO is improved, and further The absorption capacity and use stability of the complex denitrification agent are improved, and then the Fe(III) in the failed complex denitration agent is precipitated and separated, and then a reducing regenerant is added to convert the Fe(II)EDTA (NO ) reduction to generate Fe(II)EDTA and N ₂ , and then use the by-product ferrous sulfate heptahydrate in the production of titanium dioxide by the sulfuric acid method to supplement the regeneration method of Fe ²⁺ to regenerate the ineffective complex denitrification agent. At the same time, the auxiliaries and nano-reagents added in the preparation process of the complex denitration agent can catalyze the regeneration reaction and accelerate the regeneration reaction.

In order to further illustrate the present invention, a complex denitration process capable of cyclic regeneration provided by the present invention will be described in detail below with reference to the examples, but it should not be construed as a limitation on the protection scope of the present invention.

Example 1

First prepare 1000L complex denitration solution: add 25mmol/L ferrous sulfate, 30mmol/L disodium EDTA, 12.5mmol/L formulation (5mmol/L cysteine+5mmol/L to 1000L distilled water successively) Methylcyclopentenolone+2.5mmol/L dibutylhydroxytoluene), 12.5mmol/L auxiliary (4mmol/L sodium carbonate+4mmol/L disodium hydrogen phosphate+2.5mmol/L sodium sulfite+2mmol/L carbon hydrazide), 0.05mmol/L nano reagent (0.025mmol/L nano titanium dioxide+0.025mmol/L nano silica), 1mmol/L dispersant (1mmol/L sodium dodecylbenzenesulfonate). After mixing evenly, the above solution was sealed and put into an ultrasonic cell disrupter for ultrasonic oscillation. The frequency of ultrasonic oscillation was 20KHz, and the oscillation was stopped for 20 min after every 30 min of oscillation, and then ultrasonic oscillation was performed. Repeat this for 6 times. The pH was adjusted to 7 with the denitrification solution.

The prepared complex denitrification liquid is subjected to gas-liquid contact reaction with low-temperature flue gas. The gas flow rate is 500 m ³ /h, the NO _X concentration is 280-300 mg/m ³ , and the O ₂ concentration is 15-15.5%. The residence time of the gas-liquid contact reaction is 5s, the liquid-gas ratio was 3L/m ³ , the superficial flow rate was 2m/s, and the reaction temperature was 50°C. After the reaction, the complex denitrification solution that failed after the reaction was transported to the conditioning tank by a booster pump, and NaOH was added to adjust the pH to 8.5. After standing for 15 minutes, the precipitation was filtered to remove the oxidized Fe ³⁺ in the denitration solution. The filtrate after the filtration treatment was adjusted to pH 5.5 with sulfuric acid, and the regenerant sodium sulfite and carbohydrazide were added (the total concentration of the two was 25mmol/L, and the ratio was 1:1), heated to 45°C, and reacted for 10min under stirring conditions, The by-product FeSO ₄ 7H ₂ O (25mmol/L) produced in the production of titanium dioxide produced by the sulfuric acid method was added to the complex denitrification solution in the Fe ²⁺ replenishment tank, and the mixture was uniform. Both Fe(III)EDTA and Fe(II)EDTA(NO) are treated, and the complexed denitration solution restores the denitration performance, and is pumped into the denitration tower by the circulating pump to continue denitration.

Figure 2 shows that the NO _X concentration at the outlet stably maintained <50mg/m ³ within the 12h test time.

Example 2

First prepare 1000L complex denitration solution: add 40mmol/L ferrous sulfate, 52mmol/L disodium EDTA, 12mmol/L formulation (10mmol/L cysteine+2mmol/L piperine to 1000L distilled water successively) oxazine), 28mmol/L auxiliary (10mmol/L sodium dihydrogen phosphate+10mmol/L sodium sulfite+8mmol/L ascorbic acid), 0.04mmol/L nano reagent (0.02mmol/L nickel oxide+0.02mmol/L nano trioxide tetraoxide) iron), 1 mmol/L dispersant (0.5 mmol/L sodium pyrophosphate + 0.5 mmol/L polyacrylamide). After sealing the above solution, put it into an ultrasonic cell disruptor for ultrasonic vibration, the frequency of ultrasonic vibration is 20KHz, stop for 15 minutes after every 25 minutes of vibration, and then perform ultrasonic vibration, repeat this for 4 times, and adjust the prepared complex denitrification solution. pH was 6.5.

The prepared complex denitrification liquid is subjected to gas-liquid contact reaction with low-temperature flue gas. The gas flow rate is 500 m ³ /h, the NO _X concentration is 280-300 mg/m ³ , and the O ₂ concentration is 15-15.5%. The residence time of the gas-liquid contact reaction is 5s, the liquid-gas ratio was 3L/m ³ , the superficial flow rate was 2m/s, and the reaction temperature was 50°C. After the reaction, the complex denitrification solution that failed after the reaction was transported to the conditioning tank by a booster pump, and NaOH was added to adjust the pH to 8.5. After standing for 15 minutes, the precipitation was filtered to remove the oxidized Fe ³⁺ in the denitration solution. The filtrate after the filtration treatment was adjusted to pH 5.5 with sulfuric acid, and the regenerant sodium sulfite and carbohydrazide were added (the total concentration of the two was 25mmol/L, and the ratio was 1:1), heated to 45°C, and reacted under stirring conditions for 10min, The by-product FeSO ₄ 7H ₂ O (25mmol/L) produced in the production of titanium dioxide produced by the sulfuric acid method was added to the complex denitrification solution in the Fe ²⁺ replenishment tank, and the mixture was uniform. Both Fe(III)EDTA and Fe(II)EDTA(NO) are treated, and the complexed denitration solution restores the denitration performance, and is pumped into the denitration tower by the circulating pump to continue denitration.

Figure 3 shows that, after the optimization and improvement of the denitrification agent formula, the outlet NO _X concentration was stably maintained at <40mg/m ³ within the 12h test time.

Example 3

First prepare 1000L complex denitration solution: add 40mmol/L ferrous sulfate, 52mmol/L disodium EDTA, 12mmol/L formulation (10mmol/L cysteine+2mmol/L piperine to 1000L distilled water successively) oxazine), 28mmol/L auxiliary (10mmol/L sodium dihydrogen phosphate+10mmol/L sodium sulfite+8mmol/L ascorbic acid), 0.04mmol/L nano reagent (0.02mmol/L nickel oxide+0.02mmol/L nano trioxide tetraoxide) iron), 1 mmol/L dispersant (0.5 mmol/L sodium pyrophosphate + 0.5 mmol/L polyacrylamide). After sealing the above solution, put it into an ultrasonic cell disruptor for ultrasonic vibration, the frequency of ultrasonic vibration is 20KHz, stop for 15 minutes after every 25 minutes of vibration, and then perform ultrasonic vibration, repeat this for 4 times, and adjust the prepared complex denitrification solution. pH was 6.5.

The prepared complex denitrification liquid is subjected to gas-liquid contact reaction with low-temperature flue gas. The gas flow rate is 500 m ³ /h, the NO _X concentration is 280-300 mg/m ³ , and the O ₂ concentration is 15-15.5%. The residence time of the gas-liquid contact reaction is 7s, the liquid-gas ratio was 5L/m ³ , the superficial flow rate was 2m/s, and the reaction temperature was 50°C. After the reaction, the complex denitrification solution that failed after the reaction was transported to the conditioning tank by the booster pump, and NaOH was added to adjust the pH to 9. After standing for 15 minutes, the precipitation was filtered to remove the oxidized Fe ³⁺ in the denitration solution. The filtrate after the filtration treatment was adjusted to pH 6 with sulfuric acid, and the regenerant sodium sulfide and hydrazine hydrate were added (the total concentration of the two was 25mmol/L, and the ratio was 1:2), heated to 50°C, and reacted for 10min under stirring conditions, The by-product FeSO ₄ 7H ₂ O (25mmol/L) produced in the production of titanium dioxide produced by the sulfuric acid method was added to the complex denitrification solution in the Fe ²⁺ replenishment tank, and the mixture was uniform. Both Fe(III)EDTA and Fe(II)EDTA(NO) are treated, and the complexed denitration solution restores the denitration performance, and is pumped into the denitration tower by the circulating pump to continue denitration.

Figure 4 shows that after the optimization and improvement of the denitrification agent formulation, gas-liquid reaction parameters and regeneration parameters, the outlet NO _X concentration was stably maintained at <25mg/m ³ within the 12h test time.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (9)

1. A complex denitration process that can be recycled and regenerated, comprising the following steps: A) contact the complex denitrification agent with low-temperature flue gas, and carry out denitration, until the complex denitrification agent fails; The denitration agent includes disodium EDTA, divalent iron salt, formulation, auxiliary agent, nano-agent, dispersant and solvent; The preparation is one or more of cysteine, linphrine, methylcyclopentenolone, ethylenediamine, triethanolamine, piperazine, hydroquinone and dibutylhydroxytoluene. ; The auxiliary agent is one or more of sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium sulfite, sodium sulfide, ascorbic acid and carbohydrazide; The nanometer reagent is one or more of nanometer titanium dioxide, nanometer nickel oxide, nanometer ferric oxide, nanometer ferric oxide, nanometer iron powder and nanometer silicon dioxide; B) Adjust the pH value of the complex denitrification agent that has failed in the step A) to 8.5-9.0, so that Fe ³⁺ combines with (OH) ^-1 to form Fe(OH) ₃ precipitation, while Fe ²⁺ remains with Complexation of EDTA ^2- , no precipitate is formed, and the precipitate is removed; C) adjusting the pH value of the filtrate obtained by removing the precipitation in the step B) to 5.5-6, adding a regenerant, and performing a reduction reaction to obtain a reduced denitration agent; D) adding a divalent iron supplement to the denitrifying agent after reduction, so that the mole number of Fe in the denitrifying agent ^{is equivalent to the mole number of EDTA 2+ to} obtain a regenerated complex denitrifying agent; The divalent iron supplement is FeSO ₄ 7H ₂ O, a by-product of producing titanium dioxide by a sulfuric acid method. 2. complex denitration technology according to claim 1, is characterized in that, described ferrous salt is ferrous sulfate; Described dispersant is sodium citrate, sodium pyrophosphate, trihexyl hexyl phosphoric acid, ten One or more of sodium dialkylbenzene sulfonate, polyacrylamide and triton. 3. complex denitration process according to claim 1, is characterized in that, the concentration of described divalent iron salt is 25～50mmol/L; The concentration of described disodium EDTA is divalent iron salt concentration The concentration of the preparation is 30-50% of the concentration of the divalent iron salt; the concentration of the auxiliary agent is 50-70% of the concentration of the divalent iron salt; the concentration of the nano-agent is two 0.1-0.2% of the concentration of the ferric salt; the concentration of the dispersant is 1-5% of the concentration of the ferrous salt. 4. The complex denitration process according to any one of claims 1 to 3, wherein the complex denitration agent is prepared according to the following steps: 1) under the condition of introducing protective gas, disodium EDTA, ferrous salt, formulation, auxiliary agent, nano-agent and dispersant are mixed in a solvent to obtain a mixed solution; 2) ultrasonically vibrating the mixed solution to obtain a complex denitration agent. 5 . The complex denitration process according to claim 4 , wherein the residence time of the denitration is 5 to 7 s, the liquid-gas ratio is 3 to 5 L/m ² , and the superficial flow rate is 2 to 2.5 m/s. 6 . , and the denitration temperature is 45-50°C. 6. complex denitration technology according to claim 1, is characterized in that, in described step B), add alkaline substance to adjust the pH value of described failure complex denitration agent; The alkaline substance is one or more of Na ₂ CO ₃ , NaOH and ammonia water. 7. The complex denitration process according to claim 1, characterized in that, in the step C), an acidic substance is added to adjust the pH value of the filtrate to 5.5-6; The acidic substance is one or more of sulfuric acid, phosphoric acid and citric acid. 8. complex denitration technology according to claim 1, is characterized in that, described regeneration agent is one or more in sodium sulfite, sodium metabisulfite, sodium sulfide, urea, ascorbic acid, carbohydrazide and hydrazine hydrate; The molar ratio of the regenerant to EDTA ²⁺ is (0.5-1):1. 9 . The complex denitration process according to claim 1 , wherein the temperature of the reduction reaction in the step B) is 40-55° C.; the time of the reduction reaction in the step B) is 10-15 min. 10 .

Images