A method for removing dioxins from kiln exhaust gas

Abstract

The invention discloses a method for removing dioxins from kiln exhaust gas, which relates to the technical field of exhaust gas treatment. Zinc-containing waste is recycled in a rotary kiln; the exhaust gas in the rotary kiln flows to: kiln head-high temperature section-medium temperature section-low temperature section-waste heat boiler-bag-desulfurization-chimney discharge; a dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes at least one of modified diatomaceous earth, sulfur or sulfide-containing compounds, ammonium-containing compounds and calcium-containing inorganic substances. The invention greatly reduces dioxins when they are discharged by adding a dioxin inhibitor into the kiln head.

Description

Technical Field

[0001] The invention relates to the technical field of waste gas treatment, and in particular to a method for removing dioxins from kiln waste gas. Background Art

[0002] During the roasting process of the rotary kiln, if the raw materials contain organic matter such as oil and plastic insulation, and the smelting process lasts for a long time in the temperature range of 250-500℃, chemical pollutants PCDD / PCDF (polychlorinated benzodioxins, polychlorinated benzofurans) may be produced. Since the raw materials may contain organic matter during the production of zinc-containing waste, the working temperature is greater than 1100℃, and dioxins will not be produced under normal working conditions. However, it is not ruled out that during the process of adding materials and heating, some organic matter is not completely burned to generate intermediate products and enter the flue gas. At the same time, in the process of flue gas decreasing from high temperature to low temperature, these organic intermediates stay at 250℃~500℃ for a sufficient time, and then they will synthesize and produce dioxins. Dioxins usually refer to 1,4-dioxadiene and its derivatives. This type of substance is highly toxic and harmful to the human body and the natural environment. Summary of the invention

[0003] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a method for removing dioxins from kiln exhaust gas.

[0004] The technical solution of the present invention is as follows:

[0005] A method for removing dioxins from kiln exhaust gas, wherein the temperature of the reaction zone of the zinc-containing waste in the rotary kiln is 1100-1200°C, and the temperature of the flue gas at the kiln tail is 550-650°C;

[0006] Rotary kiln exhaust gas flow direction:

[0007] Kiln head - high temperature section (1200℃) - medium temperature section (700-900℃) - low temperature section (600℃) - waste heat boiler (600-180℃) - bag - desulfurization - chimney emission; dioxins are mainly synthesized in the high temperature section and medium temperature section;

[0008] A dioxin inhibitor is sprayed into the kiln head; the dioxin inhibitor comprises at least one of modified diatomaceous earth, sulfur or sulfide-containing compounds, ammonium-containing compounds and calcium-containing inorganic substances.

[0009] Preferably, the particle size of the dioxin inhibitor is 200-400 mesh.

[0010] Preferably, the amount of the dioxin inhibitor added is 0.02-0.4 g / m 3 ·h.

[0011] Preferably, the sulfur-containing compound is CH4N2S, the ammonium-containing compound is CO(NH2)2 and / or (NH4)2HPO4, and the calcium-containing inorganic substance is CaO.

[0012] Preferably, the dioxin inhibitor comprises modified diatomaceous earth, S and CO(NH2)2, (NH4)2HPO4 and CH4N2S, CaO and CO(NH2)2.

[0013] Preferably, the preparation method of the modified diatomaceous earth is as follows:

[0014] The diatomaceous earth is dispersed in deionized water, and then an alkali solution and an acid solution are added in sequence, and the diatomaceous earth is activated at 600-800°C, and then ultrasonically treated in a sodium chloride solution at -10°C to 4°C, and after the treatment, the temperature is raised to 25-35°C for power treatment. After the power is turned on, the diatomaceous earth is filtered and the treated diatomaceous earth is irradiated.

[0015] Preferably, the alkali solution is sodium hydroxide, and the acid solution is citric acid.

[0016] Preferably, the ultrasonic power is 200-280w, and the power treatment is performed for 5-10min.

[0017] Preferably, the irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is below 800R.

[0018] The beneficial effect of the present invention is that the dioxin discharge is greatly reduced by adding a dioxin inhibitor at the kiln head.

[0019] The main inhibition principles of dioxin inhibitors can be summarized as follows:

[0020] (1) The inhibitor used in the present invention reduces the amount of dioxin generated by consuming the chlorine source (Cl2, HCl) or changing the form of the chlorine source. For example, SO2 can convert Cl2 into HCl with lower activity.

[0021] (2) The inhibitor used in the present invention reacts with the metal catalyst and deactivates the catalytic effect, thereby reducing the catalytic efficiency of the metal catalyst for dioxin formation. This mechanism is considered to be the main working principle of sulfur-containing or nitrogen-containing inhibitors. Sulfur-containing compounds can convert metal chlorides into sulfates (oxidation conditions) or sulfides (reduction conditions), deactivating metal catalysts; while nitrogen-containing compounds react with metal catalysts in a complex manner to form strongly bonded organic metal nitride complexes, resulting in irreversible deactivation of the catalytic site.

[0022] (3) The inhibitor used in the present invention can react with dioxin precursors to prevent the precursors from reacting to generate dioxins.

[0023] (4) The inhibitor used in the present invention can change the pH value of the fly ash surface. For example, nitrogen-containing compounds can reduce the number of acid catalytic sites on the fly ash surface, thereby inhibiting the formation of dioxins.

[0024] (5) Modified diatomaceous earth is added to the inhibitor of the present invention. While the inhibitor plays the above-mentioned role, it also has an adsorption effect on dioxins in the rotary kiln. During the adsorption, it can better contact with other substances for decomposition or inhibition. Moreover, the modified diatomaceous earth is immersed in alkaline solution and acid solution to corrode its surface or pores, making its pore structure richer. Then, it is rapidly activated at high temperature and treated at low temperature to make its pores looser. After the power is applied, the decomposed ions flow in the pores in an orderly manner after the electrolyte is energized, making it more difficult to empty and clean the pores of the diatomaceous earth. Finally, the irradiation treatment is combined to reduce its surface energy, making it easier for adsorbed substances to combine with it, thereby improving its adsorption or inhibition effect. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0026] The zinc-containing waste materials treated in the following examples are specifically: dust collected by the dust collection (removal) device during the electric furnace steelmaking process and wastewater treatment sludge. The specific components are as follows:

[0027] Table 1 Composition of zinc-containing waste

[0028] Zn Pb Cu Cd Fe As S Cl 22.13 0.88 0.010 0.12 19.08 0.001 0.5 1.13

[0029] The main fuel of the rotary kiln is coke powder, and the specific composition is shown in the table below.

[0030] Table 2 Coke powder composition (wt%)

[0031] raw material element S C Heat Coke powder content(%) 0.5 82.5 6400kcal / kg

[0032] The zinc-containing waste is prepared and then roasted at high temperature in a rotary kiln to produce zinc oxide. After the various raw materials are mixed evenly, they are fed into the rotary kiln through the kiln tail feeding port by a belt conveyor. The temperature of the rotary kiln reaction zone is 1100-1200℃, and the flue gas temperature at the kiln tail is 650℃. The valuable metal zinc in the material is reduced and enters the gas phase, where it is oxidized into oxides, namely secondary zinc oxide dust, which is then collected in the flue, waste heat boiler, and bag dust collector. The secondary zinc oxide dust is sent to the zinc leaching workshop. The tail gas is discharged after being treated by the desulfurization system.

[0033] Example 1

[0034] The flow of waste gas in the rotary kiln is: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 6 parts by weight of modified diatomaceous earth, 2 parts by weight of S and 3 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 3 parts by weight of CH4N2S, 3 parts by weight of CaO and 2.6 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 250 mesh. The addition amount of the dioxin inhibitor is 0.2g / m 3 ·h.

[0035] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 600-800°C, then ultrasonically treated in a sodium chloride solution at -10°C to 4°C, heated to 28°C after treatment for power-on treatment, filtered after power-on treatment, and the treated diatomite is irradiated. The alkali solution is sodium hydroxide, and the acid solution is citric acid. The ultrasonic power is 230w, and the power-on treatment is 5min. The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is 500R.

[0036] Example 2

[0037] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 3 parts by weight of modified diatomaceous earth, 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0038] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 600°C, then ultrasonically treated in a sodium chloride solution at -10°C, heated to 25°C after treatment for power-on treatment, filtered after power-on treatment, and the treated diatomite is irradiated. The alkali solution is sodium hydroxide, and the acid solution is citric acid. The ultrasonic power is 200w, and the power-on treatment is 5min. The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is 800R.

[0039] Example 3

[0040] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 4 parts by weight of modified diatomaceous earth, 2 parts by weight of S and 2 parts by weight of CO(NH2)2, 3 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 2 parts by weight of CaO and 1.5 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 350 mesh. The amount of the dioxin inhibitor added is 0.4g / m 3 ·h.

[0041] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 800°C, then ultrasonically treated in a sodium chloride solution at -5°C, heated to 30°C for power treatment after treatment, filtered after power-on, and the treated diatomite is irradiated. The alkali solution is sodium hydroxide, and the acid solution is citric acid. The ultrasonic power is 220w, and the power treatment is 7min. The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is 700R.

[0042] Example 4

[0043] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 6 parts by weight of modified diatomaceous earth, 2 parts by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1.5 parts by weight of CH4N2S, 2 parts by weight of CaO and 2 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 260 mesh. The amount of the dioxin inhibitor added is 0.1g / m 3 ·h.

[0044] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 700°C, then ultrasonically treated in a sodium chloride solution at -2°C, heated to 35°C for power treatment after treatment, filtered after power-on, and the treated diatomite is irradiated. The alkali solution is sodium hydroxide, and the acid solution is citric acid. The ultrasonic power is 270w, and the power treatment is 6min. The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is 600R.

[0045] Example 5

[0046] The flow direction of waste gas in the rotary kiln is: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 10 parts by weight of modified diatomaceous earth, 3 parts by weight of S and 8 parts by weight of CO(NH2)2, 5 parts by weight of (NH4)2HPO4 and 3 parts by weight of CH4N2S, 4 parts by weight of CaO and 9 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 400 mesh. The addition amount of the dioxin inhibitor is 0.4g / m 3 ·h.

[0047] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 800°C, then ultrasonically treated in a sodium chloride solution at 4°C, heated to 35°C for power treatment after treatment, filtered after power-on, and the treated diatomite is irradiated. The alkali solution is sodium hydroxide, and the acid solution is citric acid. The ultrasonic power is 280w, and the power treatment is 10min. The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dose is 700R.

[0048] Comparative Example 1 (without diatomaceous earth)

[0049] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0050] Comparative Example 2 (diatomaceous earth without modification)

[0051] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 3 parts by weight of diatomaceous earth, 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0052] Comparative Example 3 (modified diatomite impregnated with only alkali solution and acid solution)

[0053] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 3 parts by weight of modified diatomaceous earth, 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0054] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, and then alkali solution and acid solution are added in sequence for impregnation, wherein the alkali solution is sodium hydroxide and the acid solution is citric acid.

[0055] Comparative Example 4 (No power supply, irradiation modification)

[0056] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 3 parts by weight of modified diatomaceous earth, 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0057] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then added with alkali solution and acid solution in sequence, activated at 600°C, and then ultrasonically treated in a sodium chloride solution at -10°C, wherein the alkali solution is sodium hydroxide and the acid solution is citric acid. The ultrasonic power is 200w.

[0058] Comparative Example 5 (No Radiation Modification)

[0059] The flow of waste gas in the rotary kiln is as follows: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed into the kiln head, and the dioxin inhibitor includes 3 parts by weight of modified diatomaceous earth, 1 part by weight of S and 2 parts by weight of CO(NH2)2, 2 parts by weight of (NH4)2HPO4 and 1 part by weight of CH4N2S, 1 part by weight of CaO and 3 parts by weight of CO(NH2)2. The particle size of the dioxin inhibitor is 200 mesh. The amount of the dioxin inhibitor added accounts for 0.02g / m 3 ·h.

[0060] The preparation method of the modified diatomite is as follows: diatomite is dispersed in deionized water, then alkali solution and acid solution are added in sequence, activated at 600°C, then ultrasonically treated in a sodium chloride solution at -10°C, heated to 25°C after treatment, and filtrated after the end of the power-on. The alkali solution is sodium hydroxide, the acid solution is citric acid, the ultrasonic power is 200w, and the power-on treatment is 5min.

[0061] The fly ash treated in the above examples and comparative examples was tested for dioxins, and the inhibition rate was calculated. The results are shown in Table 3. Without adding dioxin inhibitor at the kiln head, the dioxin content m1 at the kiln tail was measured. After adding dioxin inhibitor, the dioxin content m2 at the kiln tail was measured. The inhibition rate (%) = (m1-m2) / m2.

[0062] Table 3 Dioxin inhibition rate of fly ash treatment in Examples and Comparative Examples

[0063]

[0064]

[0065] As can be seen from the table, the inhibition rate of dioxins in fly ash in the embodiments is lower than that in the comparative examples. The possible reasons are as follows: from the analysis of comparative examples 1 and 2, it can be seen that the addition of modified diatomaceous earth, while the inhibitor plays the above-mentioned role, also has an adsorption effect on dioxins in the rotary kiln, and better contacts with other substances for decomposition or inhibition during adsorption; from the analysis of comparative examples 3-5, it can be seen that the modified diatomaceous earth is immersed in alkali solution and acid solution to corrode its surface or pores, and the pore structure is richer. Furthermore, it is activated quickly at high temperature and treated at low temperature to make its pores looser. The ions decomposed after the electrolyte is energized flow in the pores in an orderly manner, making it more difficult to empty and clean the pores of the diatomaceous earth. Finally, the combined irradiation treatment reduces its surface energy, making it easier for adsorbed substances to combine in adsorption, thereby improving its adsorption or inhibition effect.

[0066] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for removing dioxins from kiln exhaust gas, wherein zinc-containing waste is recycled in a rotary kiln; characterized in that: The flow direction of waste gas in the rotary kiln is: kiln head - high temperature section - medium temperature section - low temperature section - waste heat boiler - bag - desulfurization - chimney discharge; dioxin inhibitor is sprayed at the kiln head, and the dioxin inhibitor includes at least one of modified diatomaceous earth, sulfur or sulfur-containing compounds, ammonium-containing compounds and calcium-containing inorganic substances; The preparation method of the modified diatomite is as follows: The diatomaceous earth is dispersed in deionized water, and then alkali solution and acid solution are added in sequence for immersion, and activated at 600-800°C, and then ultrasonically treated in a sodium chloride solution at -10°C to 4°C, and after treatment, the temperature is raised to 25-35°C for power treatment, and after the power is turned on, the diatomaceous earth is filtered and irradiated.

2. A method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The particle size of the dioxin inhibitor is 200-400 mesh.

3. The method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The amount of dioxin inhibitor added is 0.02-0.4 g / m 3 •h.

4. A method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The sulfur-containing compound is CH4N2S, the ammonium-containing compound is CO(NH2)2 and / or (NH4)2HPO4, and the calcium-containing inorganic substance is CaO.

5. The method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The dioxin inhibitor includes modified diatomaceous earth, S, (NH4)2HPO4, CH4N2S, CaO and CO(NH2)2.

6. The method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The alkaline solution is sodium hydroxide, and the acid solution is citric acid.

7. A method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The ultrasonic power is 200-280w, and the power treatment time is 5-10min.

8. The method for removing dioxins from kiln exhaust gas according to claim 1, characterized in that: The irradiation treatment uses a Co-60 gamma ray source, and the irradiation treatment dosage is below 800R.

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