CN113753922A - Method for purifying waste incineration flue gas and comprehensively utilizing fly ash - Google Patents

Abstract

The invention relates to a method for purifying flue gas and comprehensively utilizing fly ash, which comprises the steps of purifying flue gas, collecting fly ash, treating fly ash, separating and carrying out a first double decomposition reaction. The method of the invention uses the sodium-based process to replace the calcium-based process to treat the waste incineration flue gas, thereby improving the treatment effect, reducing the raw material cost of the whole process flow, reducing the amount of residual waste after treatment and realizing the resource utilization of the waste incineration fly ash.

Description

Method for purifying waste incineration flue gas and comprehensively utilizing fly ash

Technical Field

The invention belongs to the comprehensive technical field of environmental protection and chemical engineering, and relates to a method for treating flue gas generated after incineration of domestic garbage or dangerous waste and performing harmless and recycling treatment on fly ash generated after treatment.

Background

With the progress of urbanization, it is urgent to properly treat wastes such as domestic garbage in various cities. Among the current major waste disposal methods, incineration is gradually replacing landfill and becoming the leading method of waste disposal because of its advantages of good reduction effect, saving project area, high disposal speed, and being accompanied by power generation. However, a large amount of acid gas, particulate matters and other harmful components generated by the waste incineration enter the flue gas, and the flue gas is required to be properly treated to reach the emission standard.

Solid particles settled in the flue gas purification process and captured by devices such as a dust remover and the like are called fly ash, the fly ash has fine particles and high specific surface area, and is very easy to enrich and carry toxic and harmful substances such as heavy metal, dioxin and the like, and the waste incineration fly ash is definitely listed in national hazardous waste records in China. The waste incineration fly ash has complex components and great treatment difficulty.

The most commonly used waste incineration flue gas purification process in China at present is a semidry lime slurry spraying deacidification process, and the aim of removing acid gas is fulfilled by spraying lime slurry (namely calcium hydroxide slurry) into flue gas to react with the acid gas. Although the lime slurry is low in cost, the reaction efficiency of the lime slurry and the acid gas is low, and the flue gas can be discharged up to the standard only by increasing the amount of the lime slurry sprayed. The problems brought by the increase of the sprayed amount of the lime slurry are that: besides the fly ash generated by normal removal of acid gas, a large amount of unreacted calcium hydroxide is left, so that the total amount of the generated fly ash is large and is difficult to dispose, and the toxic and harmful fly ash also has the problems of secondary pollution and high harmless disposal cost.

The current methods for treating fly ash mainly include the following methods: firstly, the solidification and stabilization are carried out for landfill, the method has low cost, but occupies a large amount of land resources, and the treated product has instability, still belongs to dangerous waste and has high possibility of generating secondary pollution; secondly, the fly ash is cooperatively treated by the cement kiln, so that the total amount of hazardous waste is reduced, but the fly ash is difficult to effectively remove a large amount of chloride ions in the fly ash, so that the fly ash is difficult to enter the cement kiln for cooperative treatment, the fly ash is not suitable for long-distance transportation, and a waste incineration device and a cement plant need to be jointly constructed, so that the application range and the application scene of the method are limited; thirdly, high-temperature sintering is adopted, the method is beneficial to reducing waste, but the energy consumption is high, and the treatment difficulty of flue gas generated by sintering is high; fourthly, plasma melting, the method can effectively remove harmful substances, but has extremely high energy consumption and the problem of difficult treatment of smoke pollution.

Chinese patent CN104324590B provides a comprehensive absorption deacidification system for hazardous waste incineration flue gas, which uses sodium bicarbonate powder to carry out quenching and pre-deacidification on flue gas, although the sodium bicarbonate reactivity is stronger than calcium hydroxide, the deacidification effect is good, the sodium bicarbonate cost is high, in addition, the fly ash after flue gas deacidification is harmful substance, and the patent does not relate to how to treat fly ash.

Chinese patent publication CN110368801A proposes a treatment device and a treatment method for flue gas desulfurization byproducts by a sodium-based dry method or a semi-dry method. The process utilizes sodium bicarbonate to desulfurize coke oven flue gas and then converts sodium sulfate/sodium sulfite into gypsum using lime slurry and oxygen supply. However, this method is only suitable for the treatment of coke oven flue gas with simple components, but is not suitable for the treatment of domestic waste incineration flue gas and fly ash with more complex components and related toxic substances.

Disclosure of Invention

Problems to be solved by the invention

The existing waste incineration flue gas and fly ash treatment process route has the defects of large fly ash amount generated by the process, incomplete treatment of toxic and harmful substances, secondary pollution possibility after fly ash treatment, lack of flexibility of the process route, high comprehensive treatment cost and the like.

Means for solving the problems

In order to solve one or more problems in the prior art, the present disclosure provides a method for flue gas purification and fly ash comprehensive utilization, comprising the steps of:

flue gas purification: spraying sodium bicarbonate powder into the flue gas to enable the sodium bicarbonate to react with the acidic gas in the flue gas;

a fly ash collecting step: collecting fly ash generated in the flue gas purification step;

fly ash treatment: conveying the fly ash collected in the fly ash collecting step to a dissolving device, adding water, stirring, settling, filtering, collecting filter residues, and preparing clear liquid obtained by filtering into refined salt water;

a separation step: separating out sodium sulfate and sodium chloride from the refined brine in a cooling or concentrating mode, and separating the separated sodium sulfate and sodium chloride from the rest mother liquor;

a first metathesis reaction step: and (3) reacting the sodium chloride obtained in the separation step with ammonium bicarbonate to obtain ammonium chloride and sodium bicarbonate.

In the method for flue gas purification and fly ash comprehensive utilization provided by the further embodiment of the present disclosure, in the separation step, potassium sulfate and potassium chloride are further separated from the refined brine by cooling, and the separated potassium sulfate and potassium chloride are separated from the remaining mother liquor.

In a further embodiment of the present disclosure, a method for flue gas purification and fly ash integrated utilization is provided, which further comprises a second metathesis reaction step after the separation step: reacting the sodium sulfate obtained in the separation step with ammonium bicarbonate to obtain ammonium sulfate and sodium bicarbonate;

wherein the order of the first metathesis reaction step and the second metathesis reaction step may be interchanged.

In the method for purifying the flue gas and comprehensively utilizing the fly ash, provided by the further embodiment of the disclosure, the flue gas is generated by burning domestic garbage or dangerous waste.

In the method for flue gas purification and fly ash comprehensive utilization provided by the further embodiment of the present disclosure, a pretreatment step is added between the fly ash treatment step and the separation step, and in the pretreatment step, sulfuric acid or hydrochloric acid is added into the refined brine to react with carbonate ions in the refined brine.

In a further embodiment of the present disclosure, in the method for flue gas purification and fly ash integrated utilization, the sodium bicarbonate obtained in the first double decomposition reaction step and/or the sodium bicarbonate obtained in the second double decomposition reaction step are recycled to the flue gas purification step for reacting with the acid gas in the flue gas.

In a method for flue gas purification and fly ash integrated utilization provided in a further embodiment of the present disclosure, in the first metathesis reaction step:

dissolving the sodium chloride obtained in the separation step into a mother solution containing chloride ions, ammonium ions, bicarbonate ions and sodium ions, then reducing the temperature of the solution, separating the precipitated ammonium chloride, adding ammonium bicarbonate into the solution obtained after the ammonium chloride is separated, carrying out double decomposition reaction on the sodium chloride and the ammonium bicarbonate, separating the precipitated sodium bicarbonate, and circulating the solution remaining after the sodium bicarbonate is separated to the beginning of the first double decomposition reaction step for dissolving the sodium chloride obtained in the separation step.

In a method for flue gas purification and fly ash integrated utilization provided in a further embodiment of the present disclosure, in the second metathesis reaction step:

and dissolving ammonium bicarbonate and the sodium sulfate obtained in the separation step into mother liquor containing sulfate ions, ammonium ions, bicarbonate ions and sodium ions, stirring, cooling, separating the separated sodium bicarbonate, heating and concentrating the solution remaining after the separation of the sodium bicarbonate to separate out ammonium sulfate, and circulating the solution remaining after the separation of the ammonium sulfate to the beginning of the second double decomposition reaction step for dissolving the ammonium bicarbonate and the sodium sulfate obtained in the separation step.

In the method for purifying flue gas and comprehensively utilizing the fly ash, the filter residue collected in the fly ash treatment step is passivated, organic and toxic components in the filter residue are chemically decomposed, and then the treated filter residue is used for preparing building materials.

In a method for flue gas purification and fly ash integrated utilization provided in a further embodiment of the present disclosure, in the separating step:

cooling the refined brine to be less than or equal to 40 ℃, separating out sodium sulfate, further cooling the mother liquor after separating out the sodium sulfate to be less than or equal to 20 ℃, separating out potassium sulfate and potassium chloride, concentrating the mother liquor after separating out the potassium sulfate and the potassium chloride, separating out sodium chloride, returning the mother liquor after separating out the sodium chloride to the beginning of the separation step, and mixing the mother liquor with the refined brine;

or concentrating the refined brine at a temperature higher than 40 ℃ to separate out sodium chloride, cooling the mother liquor after the sodium chloride is separated to be less than or equal to 40 ℃ to separate out sodium sulfate, further cooling the mother liquor after the sodium sulfate is separated to be less than or equal to 20 ℃, separating out potassium sulfate and potassium chloride, returning the mother liquor after the potassium sulfate and potassium chloride are separated to the beginning of the separation step, and mixing the mother liquor with the refined brine.

ADVANTAGEOUS EFFECTS OF INVENTION

The present disclosure achieves the following advantageous technical effects in one or more aspects:

1) the process based on sodium bicarbonate (sodium base) replaces the process based on slaked lime (calcium base) to treat the flue gas generated by burning the garbage, so that the treatment effect is improved;

2) realizes the recycling of the sodium bicarbonate, greatly reduces the raw material cost of the whole process flow, and enables the sodium-based treatment process to be widely used in the flue gas purification.

3) By comprehensively treating the components of the flue gas and the fly ash generated by the waste incineration, the amount of residual waste after treatment is greatly reduced, and a remarkable waste reduction effect is achieved.

4) The process disclosed by the invention fully recycles valuable components in the fly ash, changes waste into valuable and realizes resource utilization of the waste incineration fly ash.

5) The whole set of process achieves the synergistic effect in various aspects such as improving the comprehensive economic value, saving land for landfill, eliminating the hidden danger of secondary pollution and the like.

Drawings

FIG. 1 is a schematic illustration of an exemplary process flow of the flue gas cleaning and fly ash integrated utilization method of the present disclosure.

Detailed Description

In the present disclosure, "optional" or "optionally" means that the subsequently described step may or may not be performed, and the expression includes both cases where the subsequently described step is performed and cases where the subsequently described step is not performed.

The method for purifying the flue gas and comprehensively utilizing the fly ash has wide application range, can treat various types of combustion flue gas, but has particular advantages when being used for treating the flue gas and the fly ash generated by burning household garbage or dangerous solid wastes.

The main components of a typical waste incineration flue gas are as follows:

wherein the smoke particles contain heavy metals such as zinc, lead, copper, chromium, cadmium and the like or oxides thereof.

The flue gas may also contain harmful components such as dioxin, furan and the like.

The concrete process steps

Flue gas purification

In this step, sodium bicarbonate (i.e., baking soda) powder is sprayed into the waste incineration flue gas to react with the acidic gas in the flue gas. The composition of the garbage to be incinerated is changed to a certain extent, the components of the smoke fluctuate, and the amount of the sodium bicarbonate powder sprayed can be adjusted according to the content of the acid gas in the smoke. In general, the completeness of the acid gas reaction is facilitated by spraying the sodium bicarbonate in slight excess based on the theoretical amount of sodium bicarbonate required for the acid gas reaction. However, from the viewpoints of controlling raw material cost, reducing fly ash amount, avoiding increasing burden of subsequent treatment, etc., the excessive amount of sodium bicarbonate is not suitable. Preferably, the sodium bicarbonate powder can be sprayed in an amount of 105-150% of the theoretical amount of sodium bicarbonate required for the reaction of the acid gas, so that a better comprehensive treatment effect can be achieved.

The temperature of the flue gas entering the reactor is generally controlled to be 120-300 ℃. The reaction process has slight influence on the temperature of the flue gas, and the subsequent process which may be carried out and needs the flue gas to keep high temperature (such as denitration by an SCR method) can reduce or even does not need heating, thereby being beneficial to reducing energy consumption.

In addition, other substances can be added into the flue gas according to actual conditions, for example, active carbon is added to adsorb harmful components such as dioxin.

The main reaction process of the baking soda and the acid gas in the flue gas is as follows:

2SO₂+4NaHCO₃+O₂→2Na₂SO₄+4CO₂+2H₂O

HCl+NaHCO₃→NaCl+CO₂+H₂O

fly ash collection

And collecting the generated fly ash after the flue gas purification treatment. The specific method of collection is not limited, and various conventional devices such as an electric dust collector, a bag-type dust collector and the like can be used for collection.

Fly ash treatment

In this step, the collected fly ash is purified and separated. The fly ash is sent into a dissolving tank, water is added for stirring, water-insoluble substances are naturally settled or flocculating agents are added for settling, the flocculating agents can adopt agents commonly used for industrial sewage treatment, such as aluminum sulfate, alum, polymeric ferric sulfate, polymeric aluminum chloride, polyacrylamide and the like, but are not limited to the listed types, and the ordinary flocculating agents can be selected by a person skilled in the art according to experience.

And (3) performing mechanical separation after the sedimentation, wherein the mechanical separation can adopt conventional separation equipment, such as a plate and frame filter, a vacuum belt filter, membrane filtration, a centrifuge and the like. The filter residue can be washed as required during or after separation, so that the content of soluble salt in the filter residue is reduced as much as possible.

The filter residue contains some heavy metal components and harmful substances such as dioxin, etc., and stabilizer can be added for passivation treatment, and dioxin, etc. can be chemically decomposed (such as reduction treatment by adding calcium oxide, calcium hydroxide, etc.). The treated filter residue can be subjected to landfill treatment according to hazardous waste; or desalting the filter residue to reach the standard, and adding into cement production process or sending to cement plant for synergistic treatment; or passivating the filter residue, chemically decomposing organic toxic components, and using the treated filter residue for preparing building materials, such as baking-free bricks and other building materials by adding cement and the like. The fly ash is easy to transport after being processed into filter residues, and the flexibility of the waste incineration flue gas purification process in practical application is effectively enhanced.

The clear solution obtained by filtration is refined by filtration or the like, and insoluble substances or harmful components in the filtrate are further reduced to obtain refined brine. The refined brine mainly contains chloride ions, sulfate ions, sodium ions, potassium ions and the like, and also can contain some carbonate ions and the like, and basically does not contain heavy metal components, dioxin and other harmful components.

Pretreatment of

This step is an optional step. If necessary, the refined brine obtained after fly ash purification is subjected to a pretreatment. The skilled person can determine empirically whether or not to perform the pre-treatment. One exemplary way is to select the method of removal of the refined brine made from fly ash based on the nature of the ions, if it contains significant amounts of other ions besides chloride, sulfate, sodium, potassium ions, which may interfere with the subsequent process. For example, if the refined brine contains a significant amount of carbonate ions, it can be removed by adding an appropriate amount of hydrochloric or sulfuric acid.

Separation of

This step includes separation of chloride ions, sulfate ions, sodium ions, potassium ions, and the like contained in the purified brine. The basic principle of separation is: based on the characteristic that the solubility of sodium sulfate, potassium sulfate and potassium chloride changes obviously along with the temperature, part of the sodium sulfate, potassium sulfate and potassium chloride is crystallized and separated out mainly by a solution cooling mode; based on the characteristic that the solubility of sodium chloride does not obviously change along with the temperature, part of sodium chloride is crystallized and separated out mainly by a solution concentration mode.

According to the basic principle, sodium sulfate and sodium chloride are separated out from the refined brine in a cooling and concentrating combined mode, and potassium sulfate and potassium chloride can also be separated out from the refined brine when the potassium ion content is high and the recovery value is high. The cooling and concentrating processes can be continuously carried out or can be repeatedly carried out for a plurality of times. The order of cooling and concentration is not particularly limited as long as sodium sulfate, sodium chloride, and optionally potassium sulfate and potassium chloride can be separated from the refined brine. Preferably, the specific flow of the separation can be determined reasonably according to the content and proportion of various ions in the saline solution. Several preferred separation modes are exemplified below:

1) in the first case, the amount of chloride ions and sulfate ions in the refined brine is not much different

When the amount of chloride and sulfate ions (by weight) in the refined brine does not differ significantly (e.g., the amount of chloride does not exceed 110% of the amount of sulfate ions), an alternative separation means is:

by utilizing the characteristic that the solubility of the sodium sulfate changes obviously along with the temperature, a cooling crystallization mode is firstly adopted to crystallize and separate out part of the sodium sulfate, and preferably, the temperature for crystallizing and separating out the sodium sulfate is less than or equal to 40 ℃;

separating the separated sodium sulfate;

optionally, if the filtrate after the separation of sodium sulfate contains a large amount of potassium ions and has a recycling value, continuously cooling the mother liquor remaining after the separation of sodium sulfate, for example, to less than or equal to 20 ℃, separating out potassium sulfate and potassium chloride, and separating the separated potassium sulfate and potassium chloride;

heating and concentrating the residual liquid (mother liquid after separating sodium sulfate, or mother liquid after separating sodium sulfate, potassium sulfate and potassium chloride) to separate out sodium chloride crystal;

after separating the precipitated sodium chloride, the remaining mother liquor is returned to be mixed with refined brine. The residual mother liquor may also contain partial undissociated chloride ion, sulfate ion, sodium ion and potassium ion, but because the residual mother liquor is returned to be mixed with refined brine, the circulation can continuously carry out the production, and the separation effect is not affected.

And washing and purifying the separated sodium sulfate and sodium chloride crystals, and taking the sodium sulfate and sodium chloride crystals as raw materials to enter the next procedure, or drying the sodium sulfate and sodium chloride crystals to be used as products to be packaged and put in storage. The potassium sulfate and potassium chloride obtained by separation can be used as products after being washed and dried.

2) In the second case, the chloride ions in the refined brine are significantly more than the sulfate ions

When the amount of chloride ions in the refined brine is significantly greater (by weight) than the amount of sulfate ions (e.g., the amount of chloride ions exceeds 110% of the amount of sulfate ions), an alternative separation means is:

concentrating the refined brine at a high concentration temperature (e.g. higher than 40 ℃) to make sodium chloride supersaturated and precipitated;

separating the precipitated sodium chloride, cooling the filtrate after the sodium chloride is separated to be less than or equal to 40 ℃ so as to precipitate supersaturated sodium sulfate, and separating the precipitated sodium sulfate;

optionally, if the filtrate after the separation of the sodium sulfate contains a large amount of potassium ions and has a recycling value, further cooling the filtrate after the separation of the sodium sulfate to be less than or equal to 20 ℃, so that the potassium sulfate and the potassium chloride are supersaturated and separated out, and separating the separated potassium sulfate and the potassium chloride;

and returning the residual mother liquor (mother liquor after separating sodium sulfate or mother liquor after separating sodium sulfate, potassium sulfate and potassium chloride) to be mixed with the refined brine. The residual mother liquor may also contain partial undissociated chloride ion, sulfate ion, sodium ion and potassium ion, but because the residual mother liquor is returned to be mixed with refined brine, the circulation can continuously carry out the production, and the separation effect is not affected.

And washing and purifying the separated sodium sulfate and sodium chloride crystals, and taking the sodium sulfate and sodium chloride crystals as raw materials to enter the next procedure, or drying the sodium sulfate and sodium chloride crystals to be used as products to be packaged and put in storage. The potassium sulfate and potassium chloride obtained by separation can be used as products after being washed and dried.

The main ways of separating sodium chloride, sodium sulfate, potassium chloride and potassium sulfate from refined brine are listed above. It should be noted that the sequence of cooling to separate out the salts and concentrating to separate out the salts is not strictly limited, as long as the target product to be separated out is separated out, and those skilled in the art can flexibly select the salts according to the specific situation of the refined brine prepared from each batch of fly ash.

In addition, if the refined brine contains salts or soluble substances other than sodium chloride and sodium sulfate, and the content is large, which may interfere with the separation of sodium chloride or sodium sulfate, or which itself has a recycling value, an additional step may be added to separate such soluble salts.

Metathesis reactions

Although the sodium chloride and sodium sulfate obtained in the separation step can be sold as products, the double decomposition reaction step is preferably performed by using the sodium chloride and sodium sulfate obtained in the separation step from the viewpoints of realizing material recycling, improving economic benefits of a fly ash treatment process, and the like. The step comprises two main metathesis reactions, wherein one metathesis reaction or both metathesis reactions can be carried out according to actual conditions.

1) A first metathesis reaction: reaction of sodium chloride with ammonium bicarbonate

NaCl+NH₄HCO₃→NH₄Cl+NaHCO₃

Dissolving sodium chloride in mother liquid containing saturated ammonium chloride and sodium bicarbonate at temperature not higher than 60 deg.c, and lowering the temperature to not higher than 20 deg.c to separate out ammonium chloride crystal. The precipitated ammonium chloride is separated by filtration, centrifugation or the like.

And adding ammonium bicarbonate into the solution obtained after the ammonium chloride is separated, controlling the temperature to be less than or equal to 60 ℃, and carrying out double decomposition reaction on sodium chloride and ammonium bicarbonate to generate sodium bicarbonate and ammonium chloride, wherein the sodium bicarbonate is partially crystallized and separated out due to low solubility.

The precipitated sodium bicarbonate is separated, the remaining mother liquor still contains a part of chloride ions, ammonium ions, bicarbonate ions, sodium ions and the like (namely, the remaining mother liquor is dissolved with nearly saturated ammonium chloride and sodium bicarbonate), and the remaining mother liquor is circulated to the beginning of the step to dissolve sodium chloride.

The sodium bicarbonate can be sold as a product after being washed and dried, but is more preferably used as a front-end flue gas purification raw material and recycled in the flue gas purification step. Through this cycle, the amount of sodium bicarbonate raw material purchased for the purification of waste incineration flue gas can be significantly reduced, thereby greatly reducing the raw material cost of the process of the present disclosure. In addition, if the amount of sodium bicarbonate required in the flue gas purification step is large, a part of sodium chloride raw material can be purchased separately, and sodium bicarbonate can be prepared according to the step of the first double decomposition reaction so as to meet the requirement of the flue gas purification step. The first double decomposition reaction is used for preparing sodium bicarbonate with low-price sodium chloride, and the sodium bicarbonate is supplied to the flue gas purification step, so that the cost of the whole process disclosed by the invention can be obviously reduced.

The ammonium chloride obtained by crystallization and separation in the step can be sold as a product. The purity of the ammonium chloride obtained in the step can reach more than 92 percent, and the ammonium chloride can be used for agricultural purposes.

2) A second metathesis reaction: reaction of sodium sulfate with ammonium bicarbonate

Na₂SO₄+2NH₄HCO₃→(NH₄)₂SO₄+2NaHCO₃

Dissolving sodium sulfate and ammonium bicarbonate in a mother solution at a temperature of less than or equal to 60 ℃ and with dissolved ammonium sulfate, sodium bicarbonate and the like which are close to saturation in proportion, stirring and reacting, reducing the temperature of the solution to less than or equal to 20 ℃, and crystallizing and separating out the sodium bicarbonate due to low solubility.

Separating the separated sodium bicarbonate by centrifugation or filtration, heating and concentrating the separated liquid at a temperature of less than or equal to 60 ℃ during concentration, and reducing the temperature to less than or equal to 40 ℃ after the concentration is carried out until the ammonium sulfate is nearly saturated, so as to separate out the ammonium sulfate.

The precipitated ammonium sulfate is separated, the residual mother liquor still contains partial sulfate ions, ammonium ions, bicarbonate ions, sodium ions and other components (namely, the residual mother liquor is dissolved with nearly saturated ammonium sulfate and sodium bicarbonate), and the residual mother liquor is circulated to the beginning of the step for dissolving sodium sulfate and ammonium bicarbonate.

The sodium bicarbonate can be sold as a product after being washed and dried, but is more preferably used as a front-end flue gas purification raw material and recycled in the flue gas purification step. Through this cycle, the amount of sodium bicarbonate raw material purchased for the purification of waste incineration flue gas can be significantly reduced, thereby greatly reducing the raw material cost of the process of the present disclosure. In addition, if the amount of sodium bicarbonate required in the flue gas purification step is large, part of sodium sulfate raw material can be purchased additionally, and sodium bicarbonate can be prepared according to the step of the second double decomposition reaction so as to meet the requirement of the flue gas purification step. The cost of the overall process of the present disclosure can also be significantly reduced by preparing sodium bicarbonate from inexpensive sodium sulfate via a second metathesis reaction for delivery to the flue gas purification step.

The ammonium sulfate obtained by crystallization and separation in the step can be sold as a product.

The basic steps of the process of the present disclosure are described above. Through the process steps disclosed by the invention, toxic and harmful components such as dioxin, heavy metals and the like in the waste incineration flue gas are removed, insoluble residues can be used for preparing building materials, and various soluble components in the fly ash are separated and recovered or converted into usable products. Therefore, at least 90% of the total amount of the fly ash can be harmlessly utilized as resources, the total amount of waste is greatly reduced, and the economic value is created by producing various products.

The basic steps of the disclosed process are described above. Embodiments of the present disclosure will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present disclosure and should not be construed as limiting the scope of the present disclosure. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Example 1

The basic parameters of a batch of flue gas generated by a garbage incineration device in a certain place in Sichuan are shown in the table 1:

TABLE 1 main parameters of waste incineration flue gas

Referring to fig. 1, the process flow for treating the flue gas is as follows:

1) and (3) spraying sodium bicarbonate (sodium bicarbonate) into the flue gas, controlling the spraying amount to be 120% of the reaction equivalent of the sulfur dioxide and the hydrogen chloride, and reacting the sodium bicarbonate with the sulfur dioxide, the hydrogen chloride and the hydrogen fluoride in the flue gas to generate sodium sulfite, sodium chloride and sodium fluoride, wherein the sodium sulfite is further oxidized into sodium sulfate. In order to ensure that dioxin at a flue gas outlet does not exceed the standard, simultaneously spraying activated carbon into the flue gas, wherein the spraying amount of the activated carbon is controlled to be 0.5 kg/ton of garbage, and the dioxin at the flue gas outlet is less than or equal to 0.1TEQ ng/Nm³The temperature of the flue gas after the reaction is 240 ℃, and the flue gas basically keeps stable.

2) The flue gas after the reaction with the sodium bicarbonate passes through a bag-type dust collector to intercept the fly ash. The content of particulate matters in the gas phase of the flue gas after fly ash removal is less than 4mg/Nm³. After the purification reaction and the fly ash interception treatment, the sulfur dioxide content in the flue gas is reduced to 25.0mg/Nm³The hydrogen chloride content is reduced to 30.0mg/Nm³Fluoride content of less than 1mg/Nm³. About 483kg of fly ash collected per hour was measured.

3) Mixing the collected fly ash and normal temperature water in a dissolving tank, and adjusting the water consumption according to the content of sodium chloride in the fly ash to ensure that the content of the sodium chloride in the solution is more than or equal to 18 percent. After sufficient stirring, the sodium sulfate and sodium chloride were almost completely dissolved in the water to form a mixture of insoluble matter and salt solution. Adding flocculating agent polyacrylamide to accelerate the sedimentation and agglomeration of insoluble substances.

4) And (3) passing the mixed solution through a vacuum belt filter to perform solid-liquid separation. And (3) adding water for washing during filtering, and reducing the content of soluble salt in the filter residue to be lower than 1% of the total amount of the filter residue. And drying the separated filter residue, and sending the filter residue to a cement plant for cooperative treatment.

The filtrate is filtered by a mechanical filter, and the filtering precision is less than or equal to 15 mu m. The backwash liquid of the mechanical filter is returned to the dissolution tank. Refined brine is obtained after refining, and the content of the main components is as follows: 12% of chloride ions, 3.8% of sulfate ions, 9.5% of sodium ions and 2.2% of carbonate ions, and basically no insoluble substances and dioxin are contained. A small amount of hydrochloric acid is added to the refined brine to react with carbonate ions.

5) Heating refined salt water to 50 deg.C, and vacuum concentrating to increase sodium chloride concentration to 60%. The concentrated refined brine was sent to a sodium chloride crystallizer and crystallized at 50 ℃ under normal pressure. Separating the crystallized sodium chloride crystals from the mother liquor, continuously heating and concentrating a part of the mother liquor to separate out the sodium chloride, and sending the other part of the mother liquor (wherein the concentration of the sodium sulfate reaches 28%) to a sodium sulfate crystallizer.

6) Adding condensate generated during partial vacuum concentration of refined brine into a sodium sulfate crystallizer, controlling the sodium chloride concentration of the solution to be less than or equal to 25%, reducing the temperature of the solution to be less than 10 ℃, and cooling and crystallizing to obtain sodium sulfate. The crystals were separated and a portion of the remaining mother liquor was returned to the beginning of step 5), mixed with fresh purified brine and the other portion was further concentrated under vacuum to further precipitate sodium sulfate.

7) The sodium chloride crystallized from step 5) is sent to a sodium chloride metathesis reactor containing a mother liquor containing nearly saturated ammonium chloride, sodium bicarbonate, etc. The temperature was lowered from 50 ℃ to 20 ℃ to crystallize out ammonium chloride. The precipitated ammonium chloride was separated by centrifugation. The purity of the ammonium chloride obtained by separation is more than 92%.

8) And (3) adding ammonium bicarbonate into the solution remained after the ammonium chloride is separated in the step 7), controlling the temperature at 50 ℃, so that the sodium chloride and the ammonium bicarbonate are subjected to double decomposition reaction to generate sodium bicarbonate and ammonium chloride, and the sodium bicarbonate is partially crystallized and separated out due to low solubility.

Separating the precipitated sodium bicarbonate, wherein the residual mother liquor still contains partial chlorine ions, ammonium ions, bicarbonate ions, sodium ions and other components, and the residual mother liquor is circulated to the beginning of the step 7) for dissolving sodium chloride. And (3) washing and drying the sodium bicarbonate to be used as a front-end flue gas purification raw material, and circularly reacting the sodium bicarbonate with the flue gas in the step 1).

9) Adding the sodium sulfate and ammonium bicarbonate crystallized in the step 6) into a sodium sulfate double decomposition reactor in proportion, dissolving the sodium sulfate and ammonium bicarbonate into mother liquor containing ammonium sulfate, sodium bicarbonate and the like at 50 ℃, cooling the solution to 20 ℃ after stirring reaction, and crystallizing and separating out the sodium bicarbonate. And (3) washing and drying the sodium bicarbonate to be used as a front-end flue gas purification raw material, and circularly reacting the sodium bicarbonate with the flue gas in the step 1).

10) Separating the sodium bicarbonate separated out in the step 9) in a centrifugal mode, concentrating the separated liquid in vacuum at 50 ℃ to increase the content of ammonium sulfate in the system to be more than 50%, and then reducing the temperature of the solution to be lower than 40 ℃ to separate out the ammonium sulfate. Separating the precipitated ammonium sulfate, mixing the residual mother liquor with the concentrated condensate, and circulating to the beginning of step 9) for dissolving sodium sulfate and ammonium bicarbonate. And cleaning, drying and warehousing the ammonium sulfate obtained by crystallization and separation.

The processes of waste incineration and flue gas treatment are continuously carried out for 24 hours, and the original total amount of the collected fly ash intercepted by the bag-type dust remover is 11.5 t. After the collected fly ash was treated, about 800kg of residue was obtained, and 93% of the components of the total weight of the original fly ash were used comprehensively.

Comparative example 1

In comparative example 1, the flue gas parameters to be treated were the same as in example 1.

Slaked lime (calcium hydroxide) is added to water and mixed to make a 10% lime slurry. The lime slurry is atomized and sprayed into the flue gas, and the calcium hydroxide reacts with the acid gas to generate calcium sulfate and calcium chloride. In order to ensure the flue gas emission index, the dosage of the lime slurry is 300 percent of the reaction equivalent of the sulfur dioxide and the hydrogen chloride. In order to ensure that dioxin at a flue gas outlet does not exceed the standard, active carbon is sprayed into the flue gas, and the spraying amount of the active carbon is controlled to be 0.5 kg/ton of garbage.

The flue gas after the reaction with the calcium hydroxide passes through a bag-type dust collector to intercept fly ash. It was measured that about 720kg of fly ash was collected per hour.

A stabilizer is added to the collected fly ash for solidification treatment, and quick lime (calcium oxide) is added to treat dioxin. The solidified and chemically treated fly ash is disposed of in landfills as hazardous waste. According to the method, 17.3 tons of fly ash are produced every day, the direct cost of passivation treatment and landfill is 1200 yuan/ton, a landfill site is needed, and the risk of secondary pollution still exists in the fly ash.

Therefore, compared with the comparative example of the calcium-based method, the method for treating the waste incineration flue gas firstly reduces the total amount of the originally generated fly ash, and further, after the fly ash is treated, components accounting for more than 90% of the total amount of the fly ash can be harmlessly utilized as resources, the amount of the treated residues is extremely small, and materials such as baking soda and the like are recycled in the process, so that the process cost is greatly reduced.

Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims (10)

1. A method for purifying flue gas and comprehensively utilizing fly ash is characterized by comprising the following steps:

flue gas purification: spraying sodium bicarbonate powder into the flue gas to enable the sodium bicarbonate to react with the acidic gas in the flue gas;

a fly ash collecting step: collecting fly ash generated in the flue gas purification step;

fly ash treatment: conveying the fly ash collected in the fly ash collecting step to a dissolving device, adding water, stirring, settling, filtering, collecting filter residues, and preparing clear liquid obtained by filtering into refined salt water;

a separation step: separating out sodium sulfate and sodium chloride from the refined brine in a cooling or concentrating mode, and separating the separated sodium sulfate and sodium chloride from the rest mother liquor;

a first metathesis reaction step: and (3) reacting the sodium chloride obtained in the separation step with ammonium bicarbonate to obtain ammonium chloride and sodium bicarbonate.

2. The method for flue gas purification and fly ash comprehensive utilization according to claim 1, wherein in the separation step, potassium sulfate and potassium chloride are further separated from the refined brine by cooling, and the separated potassium sulfate and potassium chloride are separated from the remaining mother liquor.

3. The method for flue gas purification and fly ash integrated utilization according to claim 1, further comprising a second metathesis step after the separation step: reacting the sodium sulfate obtained in the separation step with ammonium bicarbonate to obtain ammonium sulfate and sodium bicarbonate;

wherein the order of the first metathesis reaction step and the second metathesis reaction step may be interchanged.

4. The method for flue gas purification and fly ash comprehensive utilization according to any one of claims 1 to 3, wherein the flue gas is flue gas generated by domestic waste incineration or hazardous waste incineration.

5. The method for flue gas purification and fly ash comprehensive utilization according to any one of claims 1 to 4, wherein a pretreatment step is added between the fly ash treatment step and the separation step, and sulfuric acid or hydrochloric acid is added to the refined brine in the pretreatment step to react with carbonate ions in the refined brine.

6. The method for flue gas purification and fly ash recycling according to any of claims 3 to 5, wherein the sodium bicarbonate obtained in the first metathesis reaction step and/or the sodium bicarbonate obtained in the second metathesis reaction step is recycled to the flue gas purification step for reacting with the acid gas in the flue gas.

7. The method for flue gas purification and fly ash integrated utilization according to any one of claims 1 to 6, wherein in the first metathesis reaction step:

dissolving the sodium chloride obtained in the separation step into a mother solution containing chloride ions, ammonium ions, bicarbonate ions and sodium ions, then reducing the temperature of the solution, separating the precipitated ammonium chloride, adding ammonium bicarbonate into the solution obtained after the ammonium chloride is separated, carrying out double decomposition reaction on the sodium chloride and the ammonium bicarbonate, separating the precipitated sodium bicarbonate, and circulating the solution remaining after the sodium bicarbonate is separated to the beginning of the first double decomposition reaction step for dissolving the sodium chloride obtained in the separation step.

8. The method for flue gas purification and fly ash integrated utilization according to claim 3, wherein in the second metathesis reaction step:

and dissolving ammonium bicarbonate and the sodium sulfate obtained in the separation step into mother liquor containing sulfate ions, ammonium ions, bicarbonate ions and sodium ions, stirring, cooling, separating the separated sodium bicarbonate, heating and concentrating the solution remaining after the separation of the sodium bicarbonate to separate out ammonium sulfate, and circulating the solution remaining after the separation of the ammonium sulfate to the beginning of the second double decomposition reaction step for dissolving the ammonium bicarbonate and the sodium sulfate obtained in the separation step.

9. The method for flue gas purification and fly ash comprehensive utilization according to claim 1, wherein the filter residue collected in the fly ash treatment step is passivated, organic toxic components in the filter residue are chemically decomposed, and then the treated filter residue is used for preparing building materials.

10. The method for flue gas purification and fly ash comprehensive utilization according to claim 2, wherein in the separating step:

cooling the refined brine to be less than or equal to 40 ℃, separating out sodium sulfate, further cooling the mother liquor after separating out the sodium sulfate to be less than or equal to 20 ℃, separating out potassium sulfate and potassium chloride, concentrating the mother liquor after separating out the potassium sulfate and the potassium chloride, separating out sodium chloride, returning the mother liquor after separating out the sodium chloride to the beginning of the separation step, and mixing the mother liquor with the refined brine;

or concentrating the refined brine at a temperature higher than 40 ℃ to separate out sodium chloride, cooling the mother liquor after the sodium chloride is separated to be less than or equal to 40 ℃ to separate out sodium sulfate, further cooling the mother liquor after the sodium sulfate is separated to be less than or equal to 20 ℃, separating out potassium sulfate and potassium chloride, returning the mother liquor after the potassium sulfate and potassium chloride are separated to the beginning of the separation step, and mixing the mother liquor with the refined brine.