Method for removing acid from flue gas of waste incineration power plant based on caustic soda white mud

Abstract

This invention relates to a method for deacidification of flue gas from waste incineration power plants based on alkali-based white mud. The method involves mixing alkali-based white mud and wet deacidification waste liquid to form a slurry, which is then sieved to remove large particles, yielding a deacidification agent slurry. The alkali-based white mud in the slurry has a solid content of 15-25%. The alkali-based white mud has a pH of 10-12 and, by mass percentage (dry basis), comprises 70-90% CaO, 5-20% MgO, 1-3% SiO2, and 1-5% Al2O3. The deacidifying agent slurry is prepared by adding 0.5-1% Fe2O3, 0.3-2% Na2O, 0.5-3% chloride, and 0.5-5% SO3 to a spray drying tower in a semi-dry flue gas deacidification system. After atomization, it is sprayed into the flue to react with acidic gases in the flue gas of the waste incineration power plant to remove HCl and SO2. This method can achieve a HCl removal rate of up to 90% and a SO2 removal rate of up to 80%. It is a low-cost and effective method of "treating waste with waste".

Description

Technical Field

[0001] This invention relates to the field of air pollutant treatment technology, specifically to a method for deacidification of flue gas from waste incineration power plants based on alkali-making white mud. Background Technology

[0002] Because waste-to-energy incineration can effectively alleviate the current predicament, and with the increasing amount of municipal solid waste each year, more and more places are building waste-to-energy incineration plants. However, waste-to-energy incineration plants produce harmful acidic gases such as HCl and SO2 during operation. To ensure that the flue gas emission indicators of waste-to-energy incineration plants meet national standards (GB18485-2014 Standard for Pollution Control of Municipal Solid Waste Incineration) or local standards, the flue gas needs to be deacidified. Flue gas deacidification includes dry deacidification, semi-dry deacidification, and wet deacidification. Currently, all three methods commonly use quicklime as a deacidifying agent. However, quicklime has problems such as ecological damage, environmental pollution, and high costs in the mining, burning, and digestion processes.

[0003] Existing flue gas desulfurization technologies, in descending order of HCl and SO2 removal rates, are wet desulfurization, semi-dry desulfurization, and dry desulfurization. However, wet desulfurization generates a large amount of desulfurization waste liquid, which, if directly discharged, causes secondary pollution and generally requires treatment before reuse. Under the current development context of low-carbon emissions and "waste-to-waste" initiatives, reducing carbon emissions while meeting flue gas purification requirements and achieving a shift from resource-intensive pollution control to "waste-to-waste" treatment is the mainstream development direction. Therefore, finding a desulfurization agent that can utilize the waste liquid from wet desulfurization and replace quicklime has become an urgent problem for waste-to-energy incineration plants. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method for deacidification of flue gas from waste incineration power plants based on alkali-making white mud. The purpose is to discover that using a mixture of alkali-making white mud and wet deacidification waste liquid as a deacidification agent can replace the existing deacidification agent quicklime, thereby solving the technical problem that the cost of using quicklime as a deacidification agent is high.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for desulfurization of flue gas from a waste incineration power plant based on alkali-making sludge is provided, comprising the following steps:

[0006] The alkali-making white mud and alkaline wet deacidification waste liquid are mixed and stirred into a slurry, and large particles are removed by sieving to obtain a deacidifying agent slurry. The solid content of the alkali-making white mud in the deacidifying agent slurry is 15-25%.

[0007] The alkali-making white mud has a pH of 10-12 and, by mass percentage (dry basis), comprises 70-90% calcium-containing compounds, 5-20% MgO, 1-3% SiO2, 1-5% Al2O3, 0.5-1% Fe2O3, 0.3-2% Na2O, 0.5-3% chloride, and 0.5-5% sulfur-containing compounds (based on SO3 content); the calcium-containing compounds include calcium carbonate and calcium hydroxide, based on CaO content.

[0008] The obtained deacidifying agent slurry is added to the spray drying tower in the semi-dry flue gas deacidification system. After atomization, it is sprayed into the flue and reacts with the acidic gases in the flue gas of the waste incineration power plant to remove HCl and SO2.

[0009] Preferably, in the method for desulfurization of flue gas from a waste incineration power plant based on alkali-making sludge, the alkali-making sludge, by mass percentage, comprises 80-90% calcium-containing compounds on a dry basis, and its solid content is 25-40%.

[0010] Preferably, in the method for desulfurization of flue gas from a waste incineration power plant based on alkali-making sludge, the alkali-making sludge has an average particle size ≤40μm, wherein the proportion of particles with a particle size ≤45μm is greater than or equal to 90%.

[0011] Preferably, in the method for desulfurization of flue gas from waste incineration power plants based on alkali-making white mud, the alkali-making white mud has an average particle size ≤35μm, wherein the proportion of particles with a particle size ≤45μm is greater than or equal to 92%.

[0012] Preferably, in the method for deacidification of flue gas from waste incineration power plants based on alkali-making sludge, the wet deacidification waste liquid has a pH of 8-10 and its components include sodium hydroxide and carbonates.

[0013] Preferably, the method for deacidification of flue gas from waste incineration power plants based on alkali-making white mud involves mixing wet deacidification waste liquid at 10-20% of the mass of alkali-making white mud to prepare a slurry.

[0014] Preferably, in the method for deacidification of flue gas from a waste-to-energy plant based on alkali-making sludge, the deacidifying agent slurry is kept in a suspended state before entering the spray drying tower, and the flow rate into the spray drying tower is 2-5 m³ / h. 3 / h.

[0015] Preferably, in the method for deacidification of flue gas from a waste-to-energy plant based on alkali-making sludge, the flue gas temperature of the waste-to-energy plant is 160–230°C.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0017] The present invention provides a method for deacidification of flue gas from waste incineration power plants, which uses a mixture of alkali-making white mud and wet deacidification wastewater as a deacidification agent. The carbonates and NaOH in the deacidification wastewater can react with the free Ca in the white mud slurry. 2+ This process generates calcium carbonate and calcium hydroxide, increasing the amount of HCl and SO2 effectively removed from flue gas in the deacidification slurry, while simultaneously reducing free Ca in the white mud. 2+ With SO3 2- and SO4 2- The reaction converts the wastewater into calcium sulfate and calcium sulfite, preventing the formation of excessive calcium sulfate and calcium sulfite that could encapsulate the effective deacidification components. Furthermore, the residual NaOH in the deacidification wastewater can directly react with HCl and SO2 in the flue gas, further enhancing the deacidification effect. Additionally, the low content of SiO2 and other components in the alkali-making white mud can, to some extent, reduce the average particle size and impurity content of the white mud, thereby increasing its specific surface area. This allows the effective components of the white mud to fully react with HCl and SO2 in the flue gas, achieving the purpose of flue gas deacidification. Attached Figure Description

[0018] Figure 1 This is a SEM image of the alkali-making white mud from Example 1;

[0019] Figure 2 This is a SEM image of the alkali-making sludge and deacidification wastewater combined in Example 1. Detailed Implementation

[0020] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0021] White mud from alkali production is a waste residue discharged during the ammonia-soda process. It is a paste-like substance and alkaline. Although it can be used for flue gas deacidification, the solid particles in the white mud are relatively large, with uneven particle size distribution and high impurity content. Direct use results in poor deacidification and easily causes scaling and clogging. For example, the white mud contains calcium-containing compounds such as CaCO3, Ca(OH)2, and CaSO4, as well as free Ca... 2+ SO3 2- and SO4 2- SO3 2- and SO4 2- Able to react with free Ca 2+The formation of calcium sulfite and calcium sulfate can coat the effective deacidifying substances in the alkali-making white mud, hindering the removal of acidic gases from the flue gas. Furthermore, the proportions of various components in the alkali-making white mud vary significantly between different alkali plants. For example, some alkali-making white mud contains large amounts of chlorides, making it highly hygroscopic and deliquescent, thus limiting its industrial application. Therefore, the composition and proportions of the various components in the alkali-making white mud have a significant impact on the deacidification effect of power plant flue gas.

[0022] This invention studies the effect of different component proportions of alkali-making sludge on the deacidification effect. It finds that, by mass percentage, alkali-making sludge comprising 70-90% calcium-containing compounds (calculated as CaO), 5-20% MgO, 1-3% SiO2, 1-5% Al2O3, 0.5-1% Fe2O3, 0.3-2% Na2O, 0.5-3% chloride, and 0.5-5% sulfur-containing compounds (calculated as SO3) on a dry basis can be used in combination with the waste liquid from wet deacidification as a flue gas deacidification agent. The CaO content represents the content of calcium-containing compounds such as CaCO3, Ca(OH)2, and CaSO4, while the SO3 content represents SO3. 2- and SO4 2- The content of sulfur-containing compounds, etc.

[0023] The alkali-making sludge has a solid concentration of 25-40% and a pH of 10-12; the waste liquid from the wet deacidification process has a pH of 8-10 and its components include sodium hydroxide and carbonates; the two are compounded to prepare a deacidification agent slurry, the solid concentration of which is 15-25%, which is good for deacidification of power plant flue gas; preferably, the alkali-making sludge with a dry basis including 80-90% CaO is used for semi-dry deacidification, and the deacidification agent slurry compounded with the two can achieve a 90% removal rate of HCl and an 80% removal rate of SO2 in the flue gas of the waste incineration power plant.

[0024] Based on this, the present invention provides a method for desulfurization of flue gas from a waste incineration power plant based on alkali-making white mud, which includes the following steps:

[0025] Alkali-making sludge and alkaline wet deacidification waste liquid are compounded as deacidifying agents, mixed and stirred into a slurry, and large particles are removed by passing through a 325-mesh sieve to obtain a deacidifying agent slurry. The solid phase content of alkali-making sludge in the deacidifying agent slurry is 15-25%.

[0026] The alkali-making white mud has a pH of 10-12 and a solid content of 25-40%. By mass percentage, the dry white mud comprises 70-90% CaO, 5-20% MgO, 1-3% SiO2, 1-5% Al2O3, 0.5-1% Fe2O3, 0.3-2% Na2O, 0.5-3% chloride, and 0.5-5% SO3. The wet deacidification wastewater has a pH of 8-10 and comprises sodium hydroxide and carbonates. Preferably, the dry white mud comprises 80-90% CaO.

[0027] The obtained deacidifying agent slurry is added to the spray drying tower in the semi-dry flue gas deacidification system. After atomization, it is sprayed into the flue and reacts with the acidic gases in the waste incineration flue gas to remove HCl and SO2.

[0028] CaCO3 and Ca(OH)2 (based on CaO content) in alkali-making sludge are the main effective components for purifying HCl and SO2 in power plant flue gas, while SO4 in its slurry components... 2- (Based on SO3 content) can react with Ca 2+ Calcium sulfate is generated, which encapsulates the effective deacidification components, thereby reducing the purification effect of alkali-making white mud on flue gas. In this invention, alkali-making white mud and wet deacidification waste liquid are combined to prepare a deacidification agent slurry. The carbonates and NaOH in the wet deacidification waste liquid can react with the free Ca in the white mud slurry. 2+ The process generates calcium carbonate and calcium hydroxide, increasing the amount of HCl and SO2 effectively removed from the flue gas in the deacidification slurry. Calcium carbonate can adsorb acidic gases in the flue gas, facilitating the full contact and reaction between the deacidifying agent and the acidic gases to remove HCl and SO2. Simultaneously, it reduces the amount of free Ca in the white mud. 2+ It is converted into calcium sulfate and calcium sulfite, avoiding the formation of excessive calcium sulfate and calcium sulfite that would encapsulate the effective deacidification components, thus synergistically enhancing the deacidification effect of flue gas.

[0029] In addition, the content of SiO2 and other components in the alkali-making white mud is relatively low, which can reduce the average particle size and impurity particle content of the alkali-making white mud to a certain extent. The chloride content is less than 5%, and the hygroscopic and deliquescent properties are poor, so the alkali-making white mud can be used in industry.

[0030] In particular, adding 15-20% of wet deacidification waste liquid to the alkali-making white mud for compounding can effectively prevent the presence of calcium in the alkali-making white mud. 2+ The effective components that can remove acidic gases by converting to calcium sulfate and encapsulating it in white mud can also increase the amount of effective deacidification substances in the slurry. Furthermore, the residual alkali in the deacidification waste liquid can directly react with acidic gases in the flue gas, further enhancing the deacidification effect.

[0031] In some embodiments, the alkali-making sludge preferably has an average particle size ≤40μm, wherein the proportion of particles with a particle size ≤45μm is greater than or equal to 90%; more preferably, the average particle size of the alkali-making sludge is ≤35μm, wherein the proportion of particles with a particle size ≤45μm is greater than or equal to 92%. The small particle size of the alkali-making sludge is beneficial for two reasons: first, it facilitates the preparation of a deacidifying agent slurry with solid particle suspension, allowing the alkali-making sludge to interact with the waste liquid, which is conducive to the generation of more effective deacidifying substances such as calcium carbonate and calcium hydroxide; second, it has a large specific surface area and a fast particle dissociation rate, which is conducive to increasing the overall diffusion area of ​​the deacidification reaction, promoting the full reaction between the effective deacidifying components in the alkali-making sludge and the acidic gases in the flue gas, thereby improving the flue gas deacidification effect.

[0032] In some embodiments, a deacidifying agent slurry is prepared by mixing 10-20% of wet deacidification waste liquid according to the mass of alkali-making white mud.

[0033] In some embodiments, the deacidifying agent slurry is kept in a suspended state before entering the spray drying tower, and the flow rate into the spray drying tower is 2-5 m³ / h. 3 / h.

[0034] In some embodiments, the temperature of the waste incineration flue gas is 160-230°C. Under such high temperature, the water in the deacidifying agent slurry evaporates, and the calcium chloride, magnesium chloride, calcium sulfite, and other substances generated after reacting with the acidic gases in the flue gas are dried and the solid products are captured in the form of fly ash to avoid secondary pollution.

[0035] The following are examples.

[0036] Example 1

[0037] The alkali-making white mud used in this embodiment is waste residue discharged during the ammonia-soda process for alkali production. The solid content of the alkali-making white mud is 25-30%, and its dry basis electron microscopy scanning is as follows: Figure 1 As shown in Table 1, the dry basis composition of the alkali-making white mud was determined by XRF, and its particle size distribution is shown in Table 2.

[0038] Table 1. Dry composition of alkali-making white mud

[0039] Element CaO MgO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Na2O]]> <![CDATA[Cl - ]]> <![CDATA[SO3]]> other content 79.73％ 6.11％ 2.25％ 0.69％ 2.91％ 1.44％ 2.69％ 3.78％ 0.4％

[0040] Table 2. Particle size distribution of alkali-making white mud

[0041]

[0042]

[0043] The average particle size of the above-mentioned alkali-making mud is <40μm, of which the content of particles with a particle size ≤45μm is 95%.

[0044] The waste liquid generated from the wet deacidification process of the waste incineration power plant has a pH of 9.8 and its components include sodium hydroxide and carbonates.

[0045] The above-mentioned alkali-making white mud and wet deacidification waste liquid are combined as a deacidification agent. The specific flue gas deacidification method includes the following steps:

[0046] Alkali-making sludge and wet deacidification waste liquid are compounded, with the amount of wet deacidification waste liquid added being 20% ​​of the mass of alkali-making sludge. This mixture is then prepared into a deacidification slurry with a sludge solid concentration of 20-25%. The slurry is passed through a 325-mesh sieve to remove large particulate impurities, yielding a deacidifying agent slurry. Its dry basis electron microscopy scanning is as follows: Figure 2 As shown.

[0047] The deacidifying agent slurry is transported into a storage tank and stirred to keep the solid particles in the slurry suspended. Then, it is pumped into the spray drying tower of the semi-dry flue gas deacidification system. After being sprayed into the flue, the slurry is atomized to remove acidic gases such as HCl and SO2 from the flue gas.

[0048] The operational status of the semi-dry flue gas desulfurization process at the waste-to-energy incineration plant is as follows:

[0049] The designed waste processing capacity is 900 t / d. The temperature of the flue gas from the waste incinerator entering the spray drying tower is 160-230℃, where it undergoes a deacidification reaction. The flow rate of the deacidification agent slurry entering the spray drying tower is 4 m³ / s. 3 / h, after atomization, it fully reacts with HCl and SO2 in the flue gas to generate substances such as calcium chloride, magnesium chloride, and calcium sulfite. At the same time, the high temperature of the flue gas causes the water in the deacidifying agent slurry to evaporate, and the dried solid products are captured in the form of fly ash to avoid secondary pollution.

[0050] The acid removal efficiency of the above spray drying tower was measured as follows:

[0051] With an HCl removal efficiency of 90% and a SO2 removal efficiency of 80%, the HCl and SO2 emissions from the chimney outlet meet the emission standards and do not exceed the environmental impact assessment limits for the waste incineration power plant.

[0052] Comparative Example 1

[0053] Using the same alkali-making white mud as in Example 1 as the deacidifying agent, wherein the content of particles with a diameter ≤45μm is 80%, water is added at 10% of the mass of the alkali-making white mud to prepare a slurry. The solid phase concentration of the white mud in the slurry is 15-20%. The same deacidification method as in Example 1 is used to remove acidic gases from the flue gas. The deacidification efficiency results of the spray drying tower are as follows:

[0054] The efficiency of HCl removal is 70-80%, and the efficiency of SO2 removal is 30-40%, which is difficult to meet the standards. Even if the emission standards are met, there is still pressure. For example, the operating pressure of the wet system is relatively high, and more NaOH is needed for flue gas purification, which will lead to an increase in the consumption of environmental protection materials.

[0055] Comparative Example 2

[0056] Using the same wet deacidification waste liquid as in Example 1 as the deacidifying agent, wet deacidification was used to remove acidic gases from the flue gas. The deacidification efficiency results are as follows:

[0057] The efficiency of HCl removal is about 40-50%, and the efficiency of SO2 removal is 20-30%. It cannot guarantee that both HCl and SO2 at the chimney outlet will meet the emission standards, and it cannot play the role of a fallback in wet acid removal systems.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for acid removal from flue gas in a waste-to-energy plant based on alkali-making sludge, characterized in that, Includes the following steps: The alkali-making white mud and alkaline wet deacidification waste liquid are mixed and stirred into a slurry, and large particles are removed by sieving to obtain a deacidifying agent slurry. The solid content of the alkali-making white mud in the deacidifying agent slurry is 15-25%. The wet deacidification waste liquid has a pH of 8-10 and its components include sodium hydroxide and carbonates. The alkali-making white mud has a pH of 10-12 and an average particle size of ≤40μm, of which the proportion of particles with a particle size of ≤45μm is greater than or equal to 90%. On a dry basis, it comprises 70-90% calcium-containing compounds, 5-20% MgO, 1-3% SiO2, 1-5% Al2O3, 0.5-1% Fe2O3, 0.3-2% Na2O, 0.5-3% chloride, and 0.5-5% sulfur-containing compounds by mass percentage. The calcium-containing compounds include calcium carbonate and calcium hydroxide, based on CaO content. The obtained deacidifying agent slurry is added to the spray drying tower in the semi-dry flue gas deacidification system. After atomization, it is sprayed into the flue and reacts with the acidic gases in the flue gas of the waste incineration power plant to remove HCl and SO2.

2. The method for desulfurization of flue gas from waste incineration power plants based on alkali-making white mud as described in claim 1, characterized in that, The alkali-making white mud, on a dry basis, comprises 80-90% calcium-containing compounds, and its solid content is 25-40%.

3. The method for desulfurization of flue gas from waste incineration power plants based on alkali-making white mud as described in claim 2, characterized in that, The alkali-making white mud has an average particle size of ≤35μm, of which the proportion of particles with a particle size of ≤45μm is greater than or equal to 92%.

4. The method for desulfurization of flue gas from waste incineration power plants based on alkali-making white mud as described in claim 3, characterized in that, The slurry is prepared by mixing 10-20% of the mass of the alkali-making white mud with wet deacidification waste liquid.

5. The method for desulfurization of flue gas from a waste-to-energy plant based on alkali-making sludge as described in claim 4, characterized in that, The deacidifying agent slurry is kept in a suspended state before entering the spray drying tower, and the flow rate into the spray drying tower is 2~5 m³ / h.

6. The method for desulfurization of flue gas from a waste-to-energy plant based on alkali-making sludge as described in claim 5, characterized in that, The flue gas temperature of the waste incineration power plant is 160-230℃.

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