Lime rotary kiln tail gas treatment method

Abstract

The invention belongs to the technical field of tail gas treatment, and particularly relates to a lime rotary kiln tail gas treatment method which comprises the following steps: 1, tail gas collection: collecting tail gas generated by a lime rotary kiln; secondly, particulate matter separation is conducted, solid particulate matter in the tail gas is removed, and the tail gas is separated into the solid particulate matter and gas; 3, gas chemical conversion: converting the gas into stable or harmless gas substances, liquid substances and solid substances through chemical reaction; 4, energy recycling, wherein heat energy carried by residual tail gas obtained after gas chemical conversion is recycled through a heat exchanger; and 5, solid particle treatment: separating solid particles generated in the step 2 and the step 3 to separate out limestone, dust and coal ash. Tail gas can be divided into stable or harmless solid, liquid and gas which are made of different materials, emission of harmful gas in the atmosphere is reduced, and recycling of recycled materials obtained after tail gas treatment is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of exhaust gas treatment technology, specifically relating to a method for treating exhaust gas from a lime rotary kiln. Background Technology

[0002] Lime rotary kilns are a common type of industrial equipment, widely used in cement production, metallurgy, and chemical production. However, the operation of lime rotary kilns generates a large amount of exhaust gas, which contains harmful gases such as sulfur dioxide, nitrogen oxides, and carbon monoxide, as well as solid particulate matter such as limestone dust and coal ash. The emission of these harmful gases and solid particulate matter poses a serious threat to the environment and human health. Therefore, there is an urgent need for an efficient treatment method to purify the exhaust gas from lime rotary kilns.

[0003] Currently, there are some exhaust gas treatment technologies, such as electrostatic precipitators, chemical absorption, and gas catalytic conversion. However, because the solids separated after treatment are mixed together, they cannot be well reused, resulting in high costs and waste of resources.

[0004] Therefore, it is necessary to develop a new method for treating the exhaust gas of lime rotary kilns in order to purify the exhaust gas, reduce environmental pollution, and achieve resource recycling. Summary of the Invention

[0005] The purpose of this invention is to provide a method for treating the tail gas of a lime rotary kiln, which can separate the tail gas into solids, liquids and gases of different materials, which are stable or harmless, thereby reducing the emission of harmful gases in the atmosphere and facilitating the reuse of the recovered materials after tail gas treatment.

[0006] The specific technical solution adopted by this invention is as follows:

[0007] A method for treating tail gas from a lime rotary kiln includes the following steps:

[0008] Step 1: Tail gas collection, collecting the tail gas generated by the lime rotary kiln;

[0009] Step 2: Particulate matter separation, removing solid particulate matter from the exhaust gas, separating the exhaust gas into solid particulate matter and gas;

[0010] Step 3: Gas chemical conversion, which involves converting gases into stable or harmless gaseous, liquid, and solid substances through chemical reactions;

[0011] Step 4: Energy recovery, which involves recovering the heat energy carried by the remaining exhaust gas after the gas chemical conversion through a heat exchanger.

[0012] Step 5: Solid particle treatment. The solid particles generated in Step 2 and Step 3 are separated to obtain limestone, dust and coal ash.

[0013] Furthermore, step three includes the following steps:

[0014] Step 1: Hydrogen sulfide gas conversion, where hydrogen sulfide in the exhaust gas reacts with oxygen to produce sulfur dioxide and water;

[0015] Step 2: Nitrogen oxide conversion, where nitrogen oxides in the exhaust gas react with a reducing agent to produce nitrogen and water;

[0016] Step 3: Conversion of other harmful gases. Other harmful gases in the exhaust gas are converted into harmless substances using chemical reactions and catalytic conversion methods.

[0017] Further, step 1 includes the following steps:

[0018] Step 101: Add iron oxide into the exhaust gas at a temperature range of 400-600℃ and a pressure of 1-5kPa to carry out a chemical reaction, producing sulfur dioxide and water;

[0019] Step 102: Separate sulfur dioxide and water using a condenser to obtain liquid and gaseous products;

[0020] Step 103: Oxidize sulfur dioxide to convert it into sulfuric acid.

[0021] Furthermore, step 2 includes the following steps:

[0022] Step 201: At a temperature range of 200 to 500°C and a pressure of 2 to 3 kPa, nitrogen oxides in the exhaust gas are brought into contact with ammonia, and through the action of a catalyst, nitrogen oxides are reduced to gaseous products composed of nitrogen and water.

[0023] Step 202: Separate the gaseous products through a condenser to obtain water and nitrogen;

[0024] Step 203: Filter out solid particles in the water to obtain pure water.

[0025] Furthermore, step 3 includes the following steps:

[0026] Step 301: Carbon monoxide conversion. The remaining tail gas after hydrogen sulfide gas conversion and nitrogen oxide conversion is oxidized to convert carbon monoxide in the tail gas into carbon dioxide.

[0027] Step 302: Particulate matter separation, using a liquid medium to separate particulate matter from the exhaust gas.

[0028] Furthermore, step five includes the following steps:

[0029] Step A: Magnetic separation, utilizing the magnetic differences between coal ash and limestone / dust to separate the coal ash, limestone, and dust in the mixed particles;

[0030] Step B: Electrostatic separation, utilizing the difference in electrostatic properties between limestone and dust to separate the limestone and dust.

[0031] Further, step A includes the following steps:

[0032] Step A1: Granulation process, which involves crushing and uniformly mixing solid particles to form mixed particles;

[0033] Step A2: Coal ash adsorption. The mixed particles are placed in a magnetic separator, where the coal ash is adsorbed by the magnetic poles of the separator to form a coal ash deposition layer, and the mixture of limestone and dust is discharged.

[0034] Step A3: Coal ash recovery. The coal ash is recovered by cleaning the coal ash deposit layer on the magnetic separator.

[0035] Further, step B includes the following steps:

[0036] Step B1: Wet the mixture of limestone and dust by adding water;

[0037] Step B2: Charge the wetted mixture using an electrostatic generator;

[0038] Step B3: Separate the charged limestone and dust using the positive and negative plates of the electrostatic separation device;

[0039] Step B4: Turn off the electric field and collect the particles on the positive and negative plates respectively;

[0040] Step B5: Dry and dehumidify the separated limestone particles and dust particles.

[0041] The technical effects achieved by this invention are as follows:

[0042] The present invention discloses a method for treating the tail gas of a lime rotary kiln, which can effectively reduce the emission of harmful gases in the atmosphere and reduce environmental pollution by treating the tail gas of the lime rotary kiln. After the tail gas is treated, it can be separated into solids, liquids and gases of different materials, which are stable or harmless, making it convenient to reuse the recovered materials after the tail gas treatment. Attached Figure Description

[0043] Figure 1 This is a flowchart of the steps of the present invention. Detailed Implementation

[0044] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0045] like Figure 1 As shown, a method for treating tail gas from a lime rotary kiln includes the following steps:

[0046] Step 1: Tail gas collection, collecting the tail gas generated by the lime rotary kiln;

[0047] Step 2: Particulate matter separation. The exhaust gas is passed through an electrostatic precipitator to remove particulate matter, separating the exhaust gas into solid particulate matter and gas.

[0048] Step 3: Gas chemical conversion, which involves converting gases into relatively stable or harmless gaseous, liquid, and solid substances through chemical reactions;

[0049] Specifically, step three includes the following steps:

[0050] Step 1: Hydrogen sulfide gas conversion, the hydrogen sulfide (H2S) in the tail gas reacts with oxygen (O2) to produce sulfur dioxide (SO2) and water (H2O), the reaction equation is 2H2S+O2→2SO2+2H2O;

[0051] Specifically, step 1 includes the following steps:

[0052] Step 101: Add iron oxide into the exhaust gas at a temperature range of 400-600℃ and a pressure of 1-5kPa to carry out a chemical reaction, producing sulfur dioxide and water;

[0053] Step 102: Separate sulfur dioxide and water using a condenser to obtain liquid and gaseous products;

[0054] Step 103: Oxidize sulfur dioxide to convert it into sulfuric acid.

[0055] Step 2: Nitrogen oxide conversion, the nitrogen oxides (NOx) in the exhaust gas are reacted with a reducing agent (such as ammonia) to produce nitrogen gas (N2) and water (H2O). The reaction equation is 4NO + 4NH3 + O2 → 4N2 + 6H2O.

[0056] Specifically, step 2 includes the following steps:

[0057] Step 201: At a temperature range of 200–500℃ and a pressure of 2–3 kPa, nitrogen oxides in the exhaust gas are reacted with ammonia (NH3) as a reducing agent in a selective catalytic reduction (SCR) reactor. In the SCR reactor, nitrogen oxides are contacted with ammonia and reduced to gaseous products composed of nitrogen (N2) and water (H2O) by a catalyst (such as a vanadium-titanium catalyst).

[0058] Step 202: Separate the gaseous products through a condenser to obtain water and nitrogen.

[0059] Step 203: Remove solid particles from the water by filtration or sedimentation to obtain pure water;

[0060] Step 3: Conversion of other harmful gases. Other harmful gases in the exhaust gas are converted into harmless substances using chemical reactions and catalytic conversion methods.

[0061] Step 3 includes the following steps:

[0062] Step 301: Carbon monoxide conversion. The remaining tail gas after hydrogen sulfide gas conversion and nitrogen oxide conversion is oxidized to convert carbon monoxide in the tail gas into carbon dioxide (CO2). The reaction formula is 2CO + O2 → 2CO2.

[0063] Step 302: Particulate matter separation, using a liquid medium to separate particulate matter from the exhaust gas, the liquid medium can be water.

[0064] Step 4: Energy recovery, which involves recovering the heat energy carried by the remaining exhaust gas after the gas chemical conversion through a heat exchanger.

[0065] Step 5: Solid particle treatment, separating the solid particles generated in Step 2 and Step 3 to separate limestone, dust and coal ash;

[0066] Specifically, step five includes the following steps:

[0067] Step A: Magnetic separation, utilizing the magnetic differences between coal ash and limestone / dust to separate the coal ash, limestone, and dust in the mixed particles;

[0068] Specifically, step A includes the following steps:

[0069] Step A1: Granulation process, which involves crushing and uniformly mixing solid particles to form mixed particles;

[0070] Step A2: Coal ash adsorption. The mixed particles are placed in a magnetic separator, where the coal ash is adsorbed by the magnetic poles of the separator to form a coal ash deposition layer, and the mixture of limestone and dust is discharged.

[0071] Step A3: Coal ash recovery. The coal ash is recovered by cleaning the coal ash deposit layer on the magnetic separator.

[0072] Step B: Electrostatic separation, utilizing the difference in electrostatic properties between limestone and dust to separate the limestone and dust;

[0073] Specifically, step B includes the following steps:

[0074] Step B1: Wet the mixture of limestone and dust by adding water or other wetting agents. Wetting helps to increase the conductivity and electrostatic properties of the particle surface.

[0075] Step B2: Charge the wetted mixture using an electrostatic generator or other high-voltage power source. The charging method can be direct contact or through an electric field.

[0076] During the charging process, due to the differences in physical properties between limestone and dust, their electrostatic characteristics may also differ; typically, limestone may carry a stronger positive charge, while dust may carry a stronger negative charge.

[0077] Step B3: Separate the charged limestone and dust using the positive and negative plates of the electrostatic separation device;

[0078] Electrostatic separation devices typically consist of separation chambers with electrodes. In the charged separation chambers, electrostatic forces cause limestone and dust particles with opposite charges to be affected by different electric field forces. Under normal circumstances, particles with opposite charges are attracted to the corresponding electrode plates by the electric field force. In this way, limestone particles and dust particles are collected separately on different electrode plates in the separation chamber.

[0079] Step B4: Turn off the electric field. Limestone particles and dust particles will accumulate on the plates in the separation chamber. Collect the particles on the positive and negative plates respectively to complete the separation and collection of limestone particles and dust particles.

[0080] Step B5: Dry and dehumidify the separated limestone particles and dust particles to remove residual moisture and process the collected material.

[0081] In summary, this technical solution can effectively reduce the emission of harmful gases in the atmosphere and reduce environmental pollution by treating the tail gas of a lime rotary kiln. After the tail gas is treated, it can be separated into solids, liquids and gases of different materials that are stable or harmless, which facilitates the reuse of the recovered materials.

[0082] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A method for treating tail gas from a lime rotary kiln, characterized in that: Includes the following steps: Step 1: Tail gas collection, collecting the tail gas generated by the lime rotary kiln; Step 2: Particulate matter separation, removing solid particulate matter from the exhaust gas, separating the exhaust gas into solid particulate matter and gas; Step 3: Gas chemical conversion, which involves converting gases into stable or harmless gaseous, liquid, and solid substances through chemical reactions; Step 4: Energy recovery, which involves recovering the heat energy carried by the remaining exhaust gas after the gas chemical conversion through a heat exchanger. Step 5: Solid particle treatment. The solid particles generated in Step 2 and Step 3 are separated to obtain limestone, dust and coal ash.

2. The method for treating tail gas from a lime rotary kiln according to claim 1, characterized in that: Step three includes the following steps: Step 1: Hydrogen sulfide gas conversion, where hydrogen sulfide in the exhaust gas reacts with oxygen to produce sulfur dioxide and water; Step 2: Nitrogen oxide conversion, where nitrogen oxides in the exhaust gas react with a reducing agent to produce nitrogen and water; Step 3: Conversion of other harmful gases. Other harmful gases in the exhaust gas are converted into harmless substances using chemical reactions and catalytic conversion methods.

3. The method for treating tail gas from a lime rotary kiln according to claim 2, characterized in that: Step 1 includes the following steps: Step 101: Add iron oxide into the exhaust gas at a temperature range of 400-600℃ and a pressure of 1-5kPa to carry out a chemical reaction, producing sulfur dioxide and water; Step 102: Separate sulfur dioxide and water using a condenser to obtain liquid and gaseous products; Step 103: Oxidize sulfur dioxide to convert it into sulfuric acid.

4. The method for treating tail gas from a lime rotary kiln according to claim 2, characterized in that: Step 2 includes the following steps: Step 201: At a temperature range of 200 to 500°C and a pressure of 2 to 3 kPa, nitrogen oxides in the exhaust gas are brought into contact with ammonia, and through the action of a catalyst, nitrogen oxides are reduced to gaseous products composed of nitrogen and water. Step 202: Separate the gaseous products through a condenser to obtain water and nitrogen; Step 203: Filter out solid particles in the water to obtain pure water.

5. The method for treating tail gas from a lime rotary kiln according to claim 2, characterized in that: Step 3 includes the following steps: Step 301: Carbon monoxide conversion. The remaining tail gas after hydrogen sulfide gas conversion and nitrogen oxide conversion is oxidized to convert carbon monoxide in the tail gas into carbon dioxide. Step 302: Particulate matter separation, using a liquid medium to separate particulate matter from the exhaust gas.

6. The method for treating tail gas from a lime rotary kiln according to claim 1, characterized in that: Step five includes the following steps: Step A: Magnetic separation, utilizing the magnetic differences between coal ash and limestone / dust to separate the coal ash, limestone, and dust in the mixed particles; Step B: Electrostatic separation, utilizing the difference in electrostatic properties between limestone and dust to separate the limestone and dust.

7. The method for treating tail gas from a lime rotary kiln according to claim 6, characterized in that: Step A includes the following steps: Step A1: Granulation process, which involves crushing and uniformly mixing solid particles to form mixed particles; Step A2: Coal ash adsorption. The mixed particles are placed in a magnetic separator, where the coal ash is adsorbed by the magnetic poles of the separator to form a coal ash deposition layer, and the mixture of limestone and dust is discharged. Step A3: Coal ash recovery. The coal ash is recovered by cleaning the coal ash deposit layer on the magnetic separator.

8. The method for treating tail gas from a lime rotary kiln according to claim 6, characterized in that: Step B includes the following steps: Step B1: Wet the mixture of limestone and dust by adding water; Step B2: Charge the wetted mixture using an electrostatic generator; Step B3: Separate the charged limestone and dust using the positive and negative plates of the electrostatic separation device; Step B4: Turn off the electric field and collect the particles on the positive and negative plates respectively; Step B5: Dry and dehumidify the separated limestone particles and dust particles.

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