CN112408421B

CN112408421B - Method for preparing high-purity ammonium sulfite by using ammonia desulfurization wastewater

Info

Publication number: CN112408421B
Application number: CN202010260266.5A
Authority: CN
Inventors: 李小龙; 杨本涛; 魏进超; 崔泽星
Original assignee: Zhongye Changtian International Engineering Co Ltd
Current assignee: Zhongye Changtian International Engineering Co Ltd
Priority date: 2020-04-03
Filing date: 2020-04-03
Publication date: 2022-04-08
Anticipated expiration: 2040-04-03
Also published as: CN112408421A

Abstract

The invention discloses a method for preparing high-purity ammonium sulfite by using ammonia desulfurization wastewaterThe method sequentially separates insoluble impurities such as suspended matters, precipitates and the like in the wastewater, and then realizes the separation of soluble impurities such as F by adding soluble ferrous salt^‑、Cl^‑、NO₃ ^‑、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And the like, and simultaneously, the steps of heat treatment, washing absorption, crystallization drying and the like are added to generate and further improve the purity of the ammonium sulfite product, the process flow is simple, the resource recovery and utilization rate is high, the method enables the purity of the ammonium sulfite obtained by recycling the ammonia desulphurization wastewater to reach more than 99 percent, and the method has great benefit on the application of the ammonium sulfite. The method also greatly reduces the discharge of the ammonia desulphurization wastewater, realizes the secondary innovative utilization of waste resources with low cost, reduces the environmental pollution and improves the social and economic benefits.

Description

Method for preparing high-purity ammonium sulfite by using ammonia desulfurization wastewater

Technical Field

The invention relates to a production method of ammonium sulfite, in particular to a method for preparing high-purity ammonium sulfite by using ammonia desulphurization wastewater, and belongs to the technical field of chemical product preparation.

Background

In the existing flue gas desulfurization technology, ammonia desulfurization is used as one of high-efficiency wet desulfurization processes and is widely applied. The working principle of the method is that ammonia or ammonia water is used as a desulfurization absorbent and is in contact mixing with flue gas entering a desulfurization tower, sulfur dioxide in the flue gas reacts with the ammonia or ammonia water to generate ammonium sulfite, a small number of processes generate ammonium bisulfite, and then chemical fertilizer ammonium sulfite is generated in a drying separation or neutralization crystallization mode, so that the recycling of sulfur resources in the flue gas is realized, and the main reaction equation is as follows:

(1)2NH₃+SO₂+H₂O→(NH₄)₂SO₃

(2)(NH₄)₂SO₃+SO₂+H₂O→2NH₄HSO₃

(3)NH₄HSO₃+NH₃→(NH₄)₂SO₃

ammonium sulfite is one of the most common byproducts in the ammonia desulphurization technology, is an important chemical product, can be directly used as a fertilizer, and can also be further oxidized to generate ammonium sulfate for use.

In the industrial ammonium sulfite standard (HG/T2784-2012) in China, the requirements of qualified industrial-grade solid ammonium sulfite products are that the mass fraction of ammonium sulfite is not less than 85%, the mass fraction of ammonium bisulfite or ammonium bicarbonate is not more than 1%, and the mass fraction of ammonium sulfate is not more than 7%. The requirements of industrial grade solid ammonium sulfite first-grade products are that the mass fraction of ammonium sulfite is not less than 90%, the mass fraction of ammonium bisulfite or ammonium bicarbonate is not higher than 0.5%, and the mass fraction of ammonium sulfate is not higher than 5%. Generally, because impurities such as dust and the like in industrial flue gas are difficult to completely remove and substances such as hydrogen chloride, hydrogen fluoride, ammonium chloride and the like are contained, the purity requirement is difficult to achieve by adopting the traditional ammonia desulphurization by-product ammonium sulfite technology.

In the prior art, the technology for recovering ammonium sulfite by ammonia desulfurization mainly comprises the steps of reacting ammonia or ammonia water with sulfur dioxide in flue gas to generate ammonium sulfite or ammonium bisulfite solution, drying and separating to obtain solid powdery ammonium sulfite, or adding ammonium bicarbonate and ammonium bisulfite to neutralize and react to generate ammonium sulfite, and recrystallizing and drying to obtain solid ammonium sulfite. Although a great deal of research is carried out on the recovery of ammonium sulfite by ammonia desulfurization, the method still has more limitations.

Chinese patent CN 100486676C provides a method for ammonia desulphurization of flue gas and by-production of ammonium sulfite, wherein the flue gas is dedusted and cooled by a cyclone separator and a heat exchanger, and then ammonia water, (NH) is treated in a drying tower₄)₂SO₃The solution is atomized and contacted with the flue gas to be desulfurized, dried and separated, and then the flue gas enters a spray absorption tower and sprayed (NH)₄)₂SO₃Contacting the solution to remove residual SO₂And NH₃Removed to a lower concentration and reacted (NH)₄)₂SO₃And of the solution itself (NH)₄)₂SO₃Drying into solid powder, and recovering to obtain byproduct (NH)₄)₂SO₃The method has the advantages of simple process, high efficiency, no impurity removal process, low purity of the produced ammonium sulfite and general quality.

Chinese patent CN102658015B discloses a method for flue gas ammonia desulphurization and by-production of high-purity solid ammonium sulfite, which mainly introduces flue gas containing high-concentration sulfur dioxide gas into a cyclone separator for dust removal and then carries out cooling; and then the flue gas is absorbed by a first-stage absorption tower, a second-stage absorption tower and a third-stage absorption tower respectively to generate a high-concentration ammonium bisulfite solution, and solid ammonium sulfite is obtained by adding quantitative ammonium bicarbonate for neutralization, cooling crystallization and centrifugal separation. The invention can purify SO₂And other harmful acid gases, and effectively improves the utilization rate of the ammonia absorbent, but the method does not separate and remove impurities from soluble substances in the solution, and the components of a product obtained by cooling and crystallizing are not easy to control, so that the purity of the ammonium sulfite product is lower.

Therefore, the problems prevalent in the prior art are: when the ammonium sulfite is produced, the soluble substances in the solution are not comprehensively separated and purified in the whole process flow, so that the product components obtained by drying or cooling and crystallizing are not easy to control, and the purity of the produced product is low. In general, the application value of the existing process is limited and needs to be improved.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide the method for preparing the high-purity ammonium sulfite by utilizing the ammonia desulphurization wastewater, which has simple process flow and high resource recycling rate, and not only ensures that the purity of the ammonium sulfite obtained by recycling the ammonia desulphurization wastewater can reach more than 99 percent, but also has great benefit on the application of the ammonium sulfite; meanwhile, the emission of ammonia desulphurization wastewater is greatly reduced, secondary innovative utilization of waste resources is realized at low cost, environmental pollution is reduced, and social and economic benefits are improved.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for preparing high-purity ammonium sulfite by using ammonia desulphurization wastewater comprises the following steps:

1) primary impurity removal: separating ammonia process desulfurization wastewater obtained after treating flue gas by adopting an ammonia process desulfurization process to obtain primary impurity removal mixed liquor and solid insoluble substances.

2) Secondary impurity removal: adding soluble ferrous salt into the primary impurity-removed mixed solution obtained in the step 1), stirring, dissolving, reacting, and separating to obtain secondary impurity-removed filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate and a mixed salt solution.

3) And (3) heat treatment: carrying out pyrolysis treatment on the secondary impurity-removed filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate obtained in the step 2), and carrying out pyrolysis treatment on NH obtained by pyrolysis₃And SO₂And washing and absorbing the gas by using a washing liquid to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite.

4) Chemical sedimentation: adding enough liquid ammonia into the mixed solution containing the ammonium sulfite and the ammonium bisulfite obtained in the step 3) for reaction, so that the ammonium sulfite generated by the reaction is supersaturated and crystallized to obtain ammonium sulfite crystals.

Preferably, the method further comprises: step 5) drying: drying the ammonium sulfite crystals obtained in the step 4) to obtain a pure solid ammonium sulfite product, and returning the condensed water obtained by drying to the step 3) to be used as a washing liquid for recycling absorption.

Preferably, the soluble ferrous salt is selected from one or more of ferrous chloride, ferrous sulfate, anhydrous ferrous sulfate and ferrous nitrate. Preferably an anhydrous ferrous sulfate salt.

Preferably, the temperature of the heat treatment in the step 3) is 400-1000 ℃, preferably 500-900 ℃, and more preferably 600-800 ℃. The heat treatment time is 0.3-5 h, preferably 0.5-4 h, and more preferably 1-3 h.

Preferably, the washing solution is selected from one or more of distilled water, deionized water and pure water; preferably deionized water.

Preferably, step 1) is specifically: and introducing the wastewater after the industrial flue gas containing sulfur (or sulfur and nitrogen) is subjected to ammonia desulphurization into a sedimentation tank, and standing for 1-48 h (preferably 3-24 h, and more preferably 5-18 h). Taking supernatant as primary impurity removal mixed liquor, and introducing the primary impurity removal mixed liquor into a clean sedimentation tank for later use. Or filtering the wastewater after the industrial flue gas containing sulfur (or sulfur and nitrogen) is desulfurized by an ammonia method; the obtained liquid phase is a primary impurity removal mixed liquid and is introduced into a clean sedimentation tank for standby.

Preferably, step 2) is specifically: adding a proper amount of soluble ferrous salt (such as anhydrous ferrous sulfate) into a sedimentation tank containing the primary impurity removal mixed solution obtained in the step 1) for dissolving reaction, simultaneously fully stirring (mechanically stirring or manually stirring for 5-120 min, preferably stirring for 15-90 min, more preferably stirring for 30-60 min) uniformly, standing for 0.5-5 h (preferably standing for 1-3 h), and filtering to obtain secondary impurity removal filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate for later use.

Preferably, the adding amount of the soluble ferrous salt is such that the molar ratio of ferrous ions to ammonium ions in the primary impurity removal mixed solution is 1: 1.5-2.5, preferably 1: 1.6-2.2, and more preferably 1: 1.8-2.0.

Preferably, step 3) is specifically: and (3) carrying out heat treatment on the secondary impurity-removed filter residue containing ferrous ammonium sulfite and ferrous ammonium sulfate obtained in the step 2) in a pyrolysis furnace at the temperature of 400-1000 ℃ (preferably 500-900 ℃, more preferably 600-800 ℃) for 0.3-5 h (preferably 0.5-4 h, more preferably 1-3 h). And simultaneously, completely collecting tail gas generated by pyrolysis and introducing the tail gas into a neutralization tank. And then washing and absorbing tail gas generated by pyrolysis by using a washing liquid (such as deionized water) to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite.

Preferably, the step 4) is specifically: and 3) after the step 3) is finished, adding enough liquid ammonia into a neutralization tank containing the mixed solution containing ammonium sulfite and ammonium bisulfite to carry out reaction until no new precipitate is generated and the reaction is finished (for example, the reaction time is 0.5-3 h, preferably 0.8-2.5 h). Crystallizing and filtering to obtain ammonium sulfite crystals.

Preferably, the amount of the liquid ammonia added is such that the molar ratio of the liquid ammonia to the ammonium bisulfate in the mixed solution is 5-10: 1, preferably 5.5-9: 1, and more preferably 6-8: 1.

Preferably, the step 5) is specifically as follows: and (3) introducing the waste heat generated in the heat treatment process in the step 3) into a dryer to centrifugally dry the ammonium sulfite crystals obtained in the step 4) (the drying time is 0.1-2 h, preferably 0.3-1 h) to obtain a pure solid ammonium sulfite product. And meanwhile, returning condensed water obtained by centrifugal drying to be used as washing liquid in the step 3) for cyclic absorption and use.

In the prior art, the technology for recovering ammonium sulfite by ammonia desulphurization comprises the following steps: firstly, ammonia or ammonia water is mainly used for reacting with sulfur dioxide in flue gas to generate ammonium sulfite or ammonium bisulfite solution, and solid powdery ammonium sulfite is obtained through drying and separation; other impurities are not removed, so that some impurity substances can be obtained by drying at the same time, and the purity of the product is low. And secondly, adding ammonium bicarbonate and ammonium bisulfite to perform neutralization reaction to generate ammonium sulfite, and then recrystallizing and drying to obtain solid ammonium sulfite. The process flow does not separate and remove impurities from soluble substances in the solution, and the components of the product obtained by cooling, cooling and crystallizing are not easy to control, so that the purity of the produced product is low. In general, the application value of the existing process is limited and needs to be improved.

In the invention, the wastewater containing a large amount of impurities (insoluble impurities and soluble impurities) obtained by ammonia desulphurization is collected into a sedimentation tank in a centralized manner, the insoluble impurities in the wastewater are settled at the bottom of the sedimentation tank in a separation treatment (such as natural standing), and then an upper layer liquid (namely a primary impurity removal mixed liquid) is extracted and transferred to another clean sedimentation tank for next impurity removal (mainly removing the soluble impurities).

In the invention, the "adding soluble ferrite" in the step 2) may be gradually added, that is, the soluble ferrite is added for multiple times (for example, 2 to 10 times, each time of addition needs to be added after the ferrite added for the previous time is dissolved, or the soluble ferrite is added in an equal or gradually decreasing manner after the same time interval (for example, the interval time is 1, 3, 5, 10, 20, 30, 60min, etc.).

In the invention, the term "adding an appropriate amount of soluble ferrous salt" in the step 2) means that the addition amount of the ferrous salt is slightly lower than the theoretical addition amount required for completely reacting all ammonium ions in the mixed solution, for example, less than 0.1-2% wt, preferably less than 0.2-1% wt, so as to avoid overhigh total iron in the filtrate after the reaction.

In the invention, the term "sufficient amount" in the "adding sufficient amount of liquid ammonia" in the step 4) refers to a theoretical addition amount of liquid ammonia required for reacting all ammonium bisulfite in the mixed solution to generate ammonium sulfite, which is obtained by conversion according to a stoichiometric ratio of the ammonium bisulfite and the liquid ammonia, and then the theoretical addition amount excess of liquid ammonia obtained by calculation of the amount of actually added liquid ammonia is a sufficient amount (or a proper amount), for example, the amount (by volume) is 1-20% excess, and preferably 3-10% excess.

In the invention, the primary impurity removal mixed liquor mainly contains SO₄ ^2-、SO₃ ^2-And NH₄ ⁺The plasma (mainly in the form of ammonium sulfite or ammonium sulfate) and other substances such as F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And plasma impurity ions. To further remove F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺Adding appropriate amount of soluble impurity ions (the addition amount can be determined according to SO in the mixed solution) into a settling pond containing the mixed solution for primarily removing impurities₄ ^2-、SO₃ ^2-And NH₄ ⁺Plasma content adjustment) of soluble ferrous salts (to add ferrous ions to the mixed liquid system), SO as to make the mixed liquid system SO₄ ^2-、SO₃ ^2-And NH₄ ⁺The plasma reacts with the ferrous ions which are supplemented into the plasma to generatePrecipitating ferrous ammonium sulfite or ferrous ammonium sulfate, and then precipitating SO₄ ^2-、SO₃ ^2-And NH₄ ⁺Plasma from containing F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And separating out the mixed solution of the soluble impurity ions, thereby realizing the purpose of removing impurities. The specific reaction mechanism is as follows:

2NH₄ ⁺+2SO₃ ^2-+Fe²⁺→(NH₄)₂Fe(SO₃)₂↓

2NH₄ ⁺+2SO₄ ^2-+Fe²⁺→(NH₄)₂Fe(SO₄)₂↓

in the invention, the secondary impurity-removed filter residue (mainly containing ferrous ammonium sulfite or ferrous ammonium sulfate) obtained by secondary impurity removal is pyrolyzed in a relatively closed heat treatment device in a heat treatment mode to obtain heat treatment tail gas (sulfur dioxide and ammonia gas), and the tail gas obtained by heat treatment is introduced into a neutralization tank to be fully washed and absorbed by washing liquid (such as deionized water or distilled water) to obtain mixed liquid containing sulfite ions and ammonium ions (in order to prevent the sulfite ions from being oxidized into sulfate ions, the neutralization tank is in an oxygen-free or low-oxygen environment); the pyrolysis process is as follows:

(NH₄)₂Fe(SO₃)₂—FeO+2NH₃+2SO₂+H₂O

2(NH₄)₂Fe(SO₄)₂—Fe₂O₃+2NH₃+N₂+4SO₂+5H₂O

the washing liquid (water) washing absorption process is as follows:

2NH₃+SO₂+H₂O→(NH₄)₂SO₃

NH₃+H₂O→NH₃·H₂O

(NH₄)₂SO₃+SO₂+H₂O→2NH₄HSO₃

in the invention, a proper amount of liquid ammonia or a little excess of liquid ammonia is continuously added into the obtained mixed solution containing sulfite ions and ammonium ions for reaction, so that the ammonium sulfite generated in the mixed solution is supersaturated and precipitated (the purity of the generated ammonium sulfite is high because the mixed solution system does not contain other impurities), and the reaction process is as follows:

NH₄HSO₃+NH₃→(NH₄)₂SO₃

2NH₄ ⁺+2SO₃ ^2-→(NH₄)₂SO₃

in the invention, through the processes of secondary impurity removal, heat treatment, washing absorption, chemical precipitation and the like, the primary mixed solution containing impurities (soluble impurities) and ions (SO) required by raw materials are firstly mixed₄ ^2-、SO₃ ^2-And NH₄ ⁺Etc.), then is thermally decomposed, washed and absorbed to obtain a mixed liquid (mainly containing HSO) without impurities₃ ^-、SO₃ ^2-And NH₄ ⁺Etc.), then obtaining a high-purity ammonium sulfite product through a chemical precipitation process. Namely, ferrous ions are added into the primary mixed liquid to ensure that SO in the primary mixed liquid₄ ^2-、SO₃ ^2-And NH₄ ⁺The plasma combines with ferrous ions to generate ammonium ferrous sulfite or ammonium ferrous sulfate, thereby achieving SO₄ ^2-、SO₃ ^2-And NH₄ ⁺Etc. with F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺Plasma impurity ion separation. Then S and N in the ammonium ferrous sulfite or ammonium ferrous sulfate are separated in the form of sulfur dioxide and ammonia gas by means of heat treatment, and then washing liquid (water) is further used for absorption (oxygen-free or oxygen-poor environment) to obtain the product only containing SO₃ ^2-And NH₄ ⁺Mixed liquid of (2). Through the steps, not only F is skillfully removed^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺Plasma impurity ions and removing SO₄ ^2-(avoid the subsequent reaction to generate ammonium sulfate and influence the purity of the generated ammonium sulfite). Finally, only HSO is contained by adding liquid ammonia₃ ^-、SO₃ ^2-And NH₄ ⁺Supersaturation precipitation of the generated ammonium sulfite in the mixed solution to obtain high-purity ammonium sulfite crystals.

In the invention, the waste heat generated in the heat treatment process is used for drying the ammonium sulfite crystals (more ammonium sulfite crystals can also be obtained by evaporating and crystallizing the filtrate filtered out of the ammonium sulfite crystals), and meanwhile, the condensed water obtained in the drying process is recycled to the heat treatment step and used as the scrubbing solution for circularly absorbing sulfur dioxide and ammonia gas. Thereby reducing energy consumption, reducing resource waste and waste discharge and maintaining the health of production environment.

In the invention, the ammonia desulphurization wastewater obtained after the flue gas is desulfurized by adopting the ammonia process mainly comprises the following ionic components: SO (SO)₄ ^2-、SO₃ ^2-、NH₄ ⁺、F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And insoluble matters such as suspended matters, precipitates and other impurities.

In the invention, the primary impurity removal aims to remove insoluble impurities such as suspended matters, precipitates and the like in the ammonia desulphurization wastewater. After preliminary impurity removal, the ionic components of the preliminary impurity removal mixed liquid are mainly as follows: SO (SO)₄ ^2-、SO₃ ^2-、NH₄ ⁺、F^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺Etc., the solid insoluble matter mainly includes insoluble matter such as suspended matter and precipitateAnd the like.

In the present invention, the secondary impurity removal is carried out for removing the solubility such as F in the solution^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And the like. Obtain the sediment and filter and obtain the secondary edulcoration filter residue through adding soluble ferrite reaction in mixing solution to preliminary edulcoration, it mainly includes ferrous ammonium sulfite and ferrous ammonium sulfate, and the ionic composition that includes in the mixed salt solution mainly is: f^-、Cl^-、NO₃ ^-、Fe³⁺、Cu²⁺、Hg²⁺、Pb²⁺、Na⁺、K⁺And the like.

In the present invention, the purpose of the heat treatment is to decompose ferrous ammonium sulfite and ferrous ammonium sulfate to produce SO₂And NH₃. After pyrolysis treatment and washing treatment of tail gas generated by pyrolysis, the mixed solution mainly comprises ammonium sulfite and ammonium bisulfite.

In the invention, the purpose of chemical precipitation is to generate ammonium sulfite after the liquid ammonia reacts with the ammonium bisulfite until the ammonium sulfite is supersaturated and crystallized to obtain ammonium sulfite crystals. And adding liquid ammonia into the mixed solution containing ammonium sulfite and ammonium bisulfite for reaction, and obtaining ammonium sulfite crystals with purity of over 99 percent after crystallization treatment.

In the present invention, the drying in step 5) is performed to dry and dehydrate the ammonium sulfite crystals to obtain solid ammonium sulfite. And drying the ammonium sulfite crystals to obtain a pure solid ammonium sulfite product, wherein the purity of the solid ammonium sulfite product can reach more than 99%.

Compared with the prior art, the invention has the following beneficial technical effects:

1: the method is characterized in that the soluble ferrous salt is utilized to react with ammonium sulfite and ammonium sulfate solution to generate precipitates of the ammonium ferrous sulfite and the ammonium ferrous sulfate so as to realize separation from soluble impurities, and sulfate ions can be further removed after tail gas generated by subsequent high-temperature decomposition is reabsorbed and washed and crystallized and centrifugally dried, so that a high-purity ammonium sulfite product can be obtained.

2: the waste heat of high-temperature decomposition can be utilized to dry the ammonium sulfite and evaporate the filtrate containing the ammonium sulfite, and simultaneously, the condensed water obtained by drying and evaporation can be utilized to wash and absorb the tail gas of high-temperature decomposition, thereby realizing the high-efficiency utilization of energy and the internal cyclic utilization of resources.

Drawings

FIG. 1 is a process flow diagram of the present invention.

FIG. 2 is a graph of the pyrolysis profile of an insoluble precipitate according to the present invention.

Detailed Description

The technical solution of the present invention is illustrated below, and the claimed scope of the present invention includes, but is not limited to, the following examples.

Preferably, the washing solution is selected from one or more of distilled water, deionized water and pure water. Preferably deionized water.

Preferably, step 2) is specifically: adding a proper amount of soluble ferrous salt (such as anhydrous ferrous sulfate) into a sedimentation tank containing the primary impurity removal mixed solution obtained in the step 1) for dissolving reaction, fully stirring (mechanically stirring or manually stirring for 5-120 min, preferably stirring for 15-90 min, more preferably stirring for 30-60 min) uniformly, standing for 0.5-5 h (preferably standing for 1-3 h), and filtering to obtain secondary impurity removal filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate for later use.

Example 1

Taking wastewater of an ammonia desulphurization process system for detection and experiment: wherein the wastewater contains total iron 0.15mg/L, total copper 0.12mg/L, total mercury 0.11mg/L, and fluorine (F)^-) Chlorine (Cl) in an amount of 115mg/L^-) Ammonia (NH) in an amount of 1201mg/L₄ ⁺) The content is 145022 mg/L; the initial SS (suspended matter) concentration was 307mg/L, pH-5.5.

1) Standing 100L of wastewater of the ammonia desulphurization process system in a sedimentation tank for 24h, and taking supernatant as primary impurity removal mixed liquor for later use.

2) Adding 61.2Kg of anhydrous ferrous sulfate into the supernatant (primary impurity removal mixed liquid) obtained in the step 1) in 4 batches in total, simultaneously mechanically stirring to dissolve and react, finally reacting for 60min until no new precipitate is generated, standing for 2h, filtering, and taking the obtained filter residue as secondary impurity removal filter residue for later use.

3) Pyrolyzing the filter residue (secondary impurity-removed filter residue) obtained in the step 2) at 700 ℃ for 2h, collecting and introducing all tail gas obtained by reaction into a neutralization tank, and washing and absorbing the tail gas by using deionized water to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite.

4) Adding enough liquid ammonia into the mixed solution containing the ammonium sulfite and the ammonium bisulfite obtained in the step 3) to react for 2 hours until no new precipitate is generated, and obtaining ammonium sulfite crystals.

5) And (3) filtering, collecting and drying the precipitate (ammonium sulfite crystals) obtained in the step 4) for 1h to obtain a dry solid (a solid ammonium sulfite product).

After the whole system was operated, the final dried solid was measured to be ammonium sulfite with a purity of 99.4% and the impurity component was mainly ammonium sulfate.

The wastewater is treated by the process, and the total iron content, the total copper content and the total mercury content in the filtrate obtained in the step 2) are respectively 0.16mg/L, 0.12mg/L and 0.11mg/L, and fluorine (F)^-) The content of chlorine (Cl) was 118mg/L^-) 1211mg/L of ammonia (NH)₄ ⁺) The content is 75.79 mg/L; the SS (suspended matter) concentration was 9 mg/L.

Example 2

1) Filtering 100L of wastewater of the ammonia desulphurization process system, and taking the obtained filtrate as a primary impurity removal mixed solution for later use.

2) Adding 72.5Kg of ferrous nitrate into the supernatant (primary impurity removal mixed liquid) obtained in the step 1) in 4 batches in total, simultaneously mechanically stirring to dissolve and react, finally reacting for 70min until no new precipitate is generated, standing for 2.5h, filtering, and taking the obtained filter residue as secondary impurity removal filter residue for later use.

3) Pyrolyzing the filter residue (secondary impurity-removed filter residue) obtained in the step 2) at 700 ℃ for 2.5h, collecting all tail gas obtained by reaction, introducing the tail gas into a neutralization tank, and washing and absorbing the tail gas by using deionized water to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite.

After the whole system is operated, the measured final dry solid is ammonium sulfite, the purity is 99.2%, and the impurity component is mainly ammonium sulfate.

The wastewater is treated by the process, and the total iron content, the total copper content and the total mercury content in the filtrate obtained in the step 2) are respectively 0.16mg/L, 0.12mg/L and 0.11mg/L, and fluorine (F)^-) 119mg/L of chlorine (Cl)^-) 1213mg/L of ammonia (NH)₄ ⁺) The content is 80.13 mg/L; the SS (suspended matter) concentration was 6 mg/L.

Example 3

2) Adding 51.1Kg of ferrous chloride salt into the supernatant (primary impurity removal mixed liquor) obtained in the step 1) in 4 batches in total, simultaneously mechanically stirring to dissolve and react, finally reacting for 60min until no new precipitate is generated, standing for 2.5h, filtering, and taking the obtained filter residue as secondary impurity removal filter residue for later use.

After the whole system is operated, the measured final dry solid is ammonium sulfite, the purity is 99.1%, and the impurity component is mainly ammonium sulfate.

The wastewater is treated by the process, and the total iron content, the total copper content and the total mercury content in the filtrate obtained in the step 2) are respectively 0.17mg/L, 0.12mg/L and 0.11mg/L, and fluorine (F)^-) A content of 117mg/L, chlorine (Cl)^-) 1209mg/L of ammonia (NH)₄ ⁺) The content is 129.61 mg/L; the SS (suspended matter) concentration was 7 mg/L.

Claims

1. A method for preparing high-purity ammonium sulfite by using ammonia desulphurization wastewater is characterized by comprising the following steps: the method comprises the following steps:

1) primary impurity removal: separating ammonia process desulfurization wastewater obtained after treating flue gas by adopting an ammonia process desulfurization process to obtain primary impurity-removed mixed liquor and solid insoluble substances;

2) secondary impurity removal: adding soluble ferrous salt into the primary impurity-removed mixed solution obtained in the step 1), stirring for dissolving reaction, and then performing separation treatment to obtain secondary impurity-removed filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate and a mixed salt solution;

3) and (3) heat treatment: carrying out pyrolysis treatment on the secondary impurity-removed filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate obtained in the step 2), and carrying out pyrolysis treatment on NH obtained after pyrolysis₃And SO₂Washing and absorbing the gas by using a washing liquid to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite;

2. The method of claim 1, wherein: the method further comprises the following steps: step 5) drying: drying the ammonium sulfite crystals obtained in the step 4) to obtain a pure solid ammonium sulfite product, and returning the condensed water obtained by drying to the step 3) to be used as a washing liquid for recycling absorption.

3. The method according to claim 1 or 2, characterized in that: the soluble ferrous salt is selected from one or more of ferrous chloride, ferrous sulfate, anhydrous ferrous sulfate and ferrous nitrate.

4. The method of claim 3, wherein: the soluble ferrous salt is anhydrous ferrous sulfate.

5. The method according to any one of claims 1, 2, 4, wherein: the heat treatment temperature is 400-1000 ℃; the heat treatment time is 0.3-5 h.

6. The method of claim 3, wherein: the heat treatment temperature is 400-1000 ℃; the heat treatment time is 0.3-5 h.

7. The method of claim 5, wherein: the heat treatment temperature is 500-900 ℃; the heat treatment time is 0.5-4 h.

8. The method of claim 6, wherein: the heat treatment temperature is 500-900 ℃; the heat treatment time is 0.5-4 h.

9. The method according to claim 7 or 8, characterized in that: the heat treatment temperature is 600-800 ℃; the heat treatment time is 1-3 h.

10. The method of any one of claims 1-2, 4, 6-8, wherein: the washing liquid is selected from one or more of distilled water, deionized water and pure water.

11. The method of claim 3, wherein: the washing liquid is selected from one or more of distilled water, deionized water and pure water.

12. The method of claim 5, wherein: the washing liquid is selected from one or more of distilled water, deionized water and pure water.

13. The method of claim 10, wherein: the washing liquid is deionized water.

14. The method according to claim 11 or 12, characterized in that: the washing liquid is deionized water.

15. The method of any one of claims 1-2, 4, 6-8, 11-13, wherein: the step 1) is specifically as follows: introducing wastewater obtained after sulfur-containing industrial flue gas is subjected to ammonia desulphurization into a sedimentation tank and standing for 1-48 h; taking the supernatant as a primary impurity removal mixed solution; or filtering the wastewater of sulfur-containing industrial flue gas subjected to ammonia desulphurization; the obtained liquid phase is a primary impurity-removed mixed liquid.

16. The method according to claim 15, characterized in that the sulfur-containing industrial flue gas is a sulfur and nitrogen-containing industrial flue gas; the standing treatment time is 3-24 h.

17. The method according to claim 15, characterized in that the sulfur-containing industrial flue gas is a sulfur and nitrogen-containing industrial flue gas; the standing treatment time is 5-18 h.

18. The method of claim 15, wherein: the step 2) is specifically as follows: adding a proper amount of soluble ferrous salt into a sedimentation tank containing the primary impurity removal mixed liquid obtained in the step 1) for dissolving reaction, simultaneously fully stirring uniformly, standing for 0.5-5 h, and filtering to obtain secondary impurity removal filter residues containing ammonium ferrous sulfite and ammonium ferrous sulfate for later use.

19. The method of claim 18, wherein: the adding amount of the soluble ferrous salt is such that the molar ratio of ferrous ions to ammonium ions in the primary impurity removal mixed solution is 1: 1.5-2.5.

20. The method of claim 18, wherein: the adding amount of the soluble ferrous salt is such that the molar ratio of ferrous ions to ammonium ions in the primary impurity removal mixed solution is 1: 1.6-2.2.

21. The method of claim 18, wherein: the adding amount of the soluble ferrous salt is such that the molar ratio of ferrous ions to ammonium ions in the primary impurity removal mixed solution is 1: 1.8-2.0.

22. The method of claim 18, wherein: the stirring is mechanical stirring or manual stirring for 5-120 min; the standing time is 1-3 h.

23. The method of claim 18, wherein: the stirring is mechanical stirring or manual stirring for 15-90 min.

24. The method of claim 18, wherein: the step 3) is specifically as follows: carrying out heat treatment on the secondary impurity-removed filter residue containing ammonium ferrous sulfite and ammonium ferrous sulfate obtained in the step 2) in a pyrolysis furnace, and simultaneously collecting all tail gas generated by pyrolysis and introducing the tail gas into a neutralization tank; and then washing and absorbing tail gas generated by pyrolysis by using a washing liquid to obtain a mixed solution containing ammonium sulfite and ammonium bisulfite.

25. The method of claim 24, wherein: the step 4) is specifically as follows: after the step 3) is finished, adding sufficient liquid ammonia into a neutralization tank containing mixed liquid containing ammonium sulfite and ammonium bisulfite for reaction until no new precipitate is generated and the reaction is finished; crystallizing to obtain ammonium sulfite crystals.

26. The method of claim 25, wherein: the adding amount of the liquid ammonia is such that the molar ratio of the liquid ammonia to the ammonium bisulfate in the mixed solution is 5-10: 1.

27. The method of claim 25, wherein: the adding amount of the liquid ammonia is such that the molar ratio of the liquid ammonia to the ammonium bisulfate in the mixed solution is 5.5-9: 1.

28. The method of claim 25, wherein: the adding amount of the liquid ammonia is such that the molar ratio of the liquid ammonia to the ammonium bisulfate in the mixed solution is 6-8: 1.

29. The method of claim 25, wherein: the step 5) is specifically as follows: introducing the waste heat generated in the heat treatment process in the step 3) into a dryer to centrifugally dry the ammonium sulfite crystals obtained in the step 4) to obtain a pure solid ammonium sulfite product; and meanwhile, returning condensed water obtained by centrifugal drying to be used as washing liquid in the step 3) for cyclic absorption and use.

30. The method of claim 29, wherein: the drying time is 0.1-2 h.

31. The method of claim 29, wherein: the drying time is 0.3-1 h.