A titanium dioxide calcining kiln tail gas treatment process and device system

Abstract

The present invention relates to the technical field of tail gas treatment, and specifically to a treatment process and device system for tail gas from a titanium dioxide calcining kiln. The treatment process involves sequentially passing the tail gas emitted by the kiln through a metal bag filter dust collector for dust removal, and a medium-temperature SCR reactor for denitrification treatment. At the same time, part of the gas discharged from the metal bag filter dust collector is mixed with the air discharged from the cooling kiln as primary air and transported to the titanium dioxide calcining kiln for mixed combustion with natural gas. This not only effectively saves energy, improves the resource recovery rate of heat, and reduces costs, but also the primary air, as low-oxygen air, achieves passive nitrogen reduction at the source, and cooperates with the medium-temperature SCR reactor at the rear end of the titanium dioxide calcining kiln to achieve stable nitrogen oxides and reach higher emission standards. At the same time, under the action of the metal bag filter dust collector, the particulate matter content of the tail gas also reaches higher emission standards. This process can achieve energy saving, reduce costs, meet emission standards, and achieve unexpected technical effects.

Description

Technical Field

[0001] The present invention relates to the technical field of tail gas treatment, and in particular to the field of ultra-low emission reduction technology for tail gas from a sulfated titanium dioxide production process. The invention discloses in more detail a treatment process and device system for tail gas from a titanium dioxide calcining kiln. Background Art

[0002] Titanium dioxide (TiO2), also known as titanium dioxide, is a white pigment widely used in coatings, plastics, papermaking, inks, cosmetics, and other industries due to its excellent hiding power, lightfastness, weather resistance, and chemical stability. Titanium dioxide is one of the whitest pigments in the world, providing high brightness and wide-area hiding power.

[0003] The production process for titanium dioxide is complex, involving multiple chemical and physical steps, including raw material processing, flotation, pickling, washing and neutralization, calcination, and crushing and grading. Calcination, a crucial step in the titanium dioxide production process, primarily takes place in a titanium dioxide calcination kiln. Here, natural gas is typically burned in a burner with combustion air to generate the necessary heat. Under a strictly controlled high temperature of 800°C to 1000°C, the pickled titanium material is heated to its decomposition temperature, transforming it into high-quality titanium dioxide.

[0004] Precise control of the calcination process is crucial for improving the whiteness, purity, and stability of the product. Furthermore, environmental protection and safety during calcination are crucial aspects of titanium dioxide production that cannot be ignored. By continuously optimizing the process, we can improve resource utilization efficiency during the titanium dioxide calcination process, reduce environmental pollution, and achieve efficient and sustainable development of the titanium dioxide industry.

[0005] At present, titanium dioxide calcining kilns face some challenges during operation:

[0006] First, as environmental regulations continue to tighten, restrictions on particulate matter and nitrogen oxide emissions are becoming increasingly stringent. Existing calcining kilns emit high concentrations of particulate matter and nitrogen oxides in the exhaust gas, making it difficult for traditional cyclone dust collectors and gravity settling chambers to meet strict environmental emission standards. This undoubtedly poses a more severe challenge to the environmental protection work of back-end exhaust gas purification.

[0007] Secondly, during the titanium dioxide calcination process, to ensure safe operation of the calcination kiln, combustion air exceeding theoretical requirements is usually introduced to ensure sufficient combustion of the natural gas and avoid the production of harmful substances such as carbon monoxide. This is because harmful substances such as carbon monoxide are not only harmful to the environment and human health, but can also form explosive mixtures in the kiln, increasing safety risks.

[0008] Heating excess combustion air requires more natural gas consumption, increasing operating costs; excess air also increases the flue gas volume, resulting in an increase in the shaft power of the system fan, and the emission of high-temperature flue gas increases exhaust heat loss, reducing the calorific value utilization efficiency of the fuel, resulting in an increase in the overall energy consumption of the system, further increasing operating costs.

[0009] In the prior art, some manufacturers mix the hot air discharged from the cooling kiln with air at room temperature and use it as combustion-supporting air for natural gas. For example, the Chinese utility model patent CN211316929U discloses an improved device for the air system of a rotary kiln in titanium dioxide production. The gas discharged from the dust removal chamber is connected to the inlet of the tertiary fan, and the outlet of the tertiary fan is connected to the mixing chamber. The cooling drum is simultaneously connected to the inlet of the primary fan and the inlet of the secondary fan. The air entering the cooling drum is preheated by the material and then passed into the burner through the primary fan and the secondary fan A, thereby increasing the temperature of the air participating in the combustion. Although this reduces fuel consumption to a certain extent and achieves partial energy-saving effects, the cooling air volume of the cooling drum is limited and cannot meet the natural gas combustion requirements. In addition, the wind speed of the cooling drum should not be too fast, which limits the ventilation volume, so the energy-saving effect is limited.

[0010] Another example is Chinese invention patent application CN106247791A, which describes a titanium dioxide workshop rotary kiln and method with exhaust heat recovery. The kiln utilizes external air to cool the material discharged from the combustion chamber. A secondary fan A draws the exhaust air from the kiln into the primary air duct. The exhaust gas from the rotary kiln enters a dust suppression chamber, which then enters a cyclone separator. The cyclone separator's gas outlet communicates with the bag filter's inlet, which in turn communicates with the tertiary fan's inlet. The tertiary fan's outlet communicates with the tertiary air duct via a manual butterfly valve A. The tertiary and secondary air ducts are connected via a gate valve. An electric valve B is installed between the secondary air duct and the outlet of secondary fan A, and an electric valve A is installed between the primary air duct and the outlet of secondary fan A. This achieves exhaust heat recovery in the titanium dioxide workshop rotary kiln, allowing for partial exhaust gas recovery and reuse. However, this technology requires exhaust gas to pass through multiple devices, including a dust suppression chamber, cyclone separator, and bag filter, resulting in a rapid drop in exhaust temperature and a low amount of recycled exhaust gas. It also fails to optimize the ratio of supporting gas usage at the natural gas combustion nozzle, resulting in low exhaust heat recovery efficiency. Furthermore, this technology does not address the nitrogen oxides produced during natural gas combustion, requiring significant optimization and adjustment to meet higher environmental standards.

[0011] Therefore, optimizing the combustion process, saving energy and reducing costs have become necessary ways to improve the operating efficiency and economy of titanium dioxide calcining kilns. Summary of the Invention

[0012] The purpose of the present invention is to provide a titanium dioxide calcining kiln tail gas treatment process and its device system to address the problems that the tail gas generated during the operation of the existing titanium dioxide calcining kiln is difficult to meet more stringent environmental emission standards, excessive combustion air leads to increased energy consumption, and production cost energy consumption and environmental emission indicators are difficult to control.

[0013] In short, the present invention mixes part of the gas discharged from the metal filter bag dust collector with the exhaust air from the cooling kiln in proportion as the primary air and transports it to the titanium dioxide calcining kiln for combustion with natural gas. This not only recovers the waste heat of the flue gas and increases the temperature of the primary air, saving natural gas and reducing operating costs, but also reduces the oxygen concentration in the primary air mixture after the gas discharged from the metal filter bag dust collector is mixed with the cooling kiln exhaust gas, lowers the maximum temperature in the flame area, and suppresses the thermal NO x Combined with the medium-temperature SCR reactor process at the rear end of the titanium dioxide calcining kiln, FGR flue gas recirculation achieves both source and end-of-pipe nitrogen oxide emission reduction, providing a highly effective approach to reducing nitrogen oxide emissions from the sulfuric acid process titanium dioxide production. Furthermore, the titanium dioxide calcining kiln exhaust is purified by a high-temperature metal bag filter, providing a process measure for ultra-low particulate matter emissions from the sulfuric acid process titanium dioxide production.

[0014] In order to achieve the above object, the technical solution specifically adopted by the present invention is:

[0015] A process for treating tail gas from a titanium dioxide calcining kiln comprises the following steps:

[0016] The tail gas discharged from the titanium dioxide calcining kiln is transported to the metal filter bag dust collector for dust removal;

[0017] Part of the gas discharged from the metal filter bag dust collector is mixed with the exhaust air from the cooling kiln as primary air, which is then transported to the burner of the titanium dioxide calcining kiln and burned with natural gas. The primary air transport volume formed by the mixture of part of the gas discharged from the metal filter bag dust collector and the exhaust air from the cooling kiln is the amount of air required to consume the natural gas. The volume flow rate of the gas transported from the cooling kiln to the titanium dioxide calcining kiln is 82-88: the volume flow rate of the gas extracted from the metal filter bag dust collector to the titanium dioxide calcining kiln after dust removal is 12-18. The temperature of the gas discharged from the metal filter bag dust collector is 310°C to 350°C.

[0018] The residual gas discharged from the metal bag filter is transported to the medium-temperature SCR reactor for denitrification treatment;

[0019] The gas discharged from the medium-temperature SCR reactor is purified and then discharged.

[0020] The exhaust gas treatment process for a titanium dioxide calcining kiln proposed in the present invention involves sequentially passing the exhaust gas emitted by the kiln through a metal bag filter dust collector for dust removal and a medium-temperature SCR reactor for denitrification. The exhaust gas from the medium-temperature SCR reactor is then purified to meet standards before being discharged. During this process, a portion of the gas discharged from the metal bag filter is mixed with the exhaust air from the cooling kiln as primary air and transported to the titanium dioxide calcining kiln burner for mixed combustion with natural gas. On the one hand, the temperature of the gas discharged from the metal bag filter is relatively high. Combustion as primary air mixed with natural gas can effectively increase the temperature of the combustion-supporting air, saving natural gas usage to a certain extent and fully recovering the waste heat from the flue gas, achieving energy-saving effects. On the other hand, by controlling the ratio of the volume flow of the air from the cooling kiln and the air discharged from the metal bag filter dust collector in the hot combustion air, the volume of the air from the cooling kiln meets the baseline oxygen content of natural gas combustion, and the volume of the gas discharged from the metal bag filter dust collector meets the excess oxygen content of natural gas combustion. The exhaust gas from the kiln tail is purified by the metal bag filter dust collector and the oxygen content of the gas discharged is lower than that of conventional air. The excess oxygen content is adjusted to form a local reducing atmosphere, which will produce NO x Reduction, thereby inhibiting NO x The generation of NO in flue gas x Passive nitrogen reduction can be achieved at the source, and denitrification treatment can be carried out in conjunction with the back-end medium-temperature SCR reactor to ensure that after the exhaust gas is purified, particulate matter and nitrogen oxides can stably meet higher standards for air environmental protection emissions.

[0021] Compared with the existing tail gas recycling technology in the prior art, the tail gas treatment process provided by the present invention realizes the dual synergy of source nitrogen reduction and waste heat recovery and utilization, can achieve high efficiency and energy saving, reduce costs, and meet higher requirements for atmospheric environmental protection emissions.

[0022] Furthermore, the cooling kiln is a device for cooling the calcined titanium dioxide. In the present invention, air at room temperature is transported into the cooling kiln for heat exchange, and the air discharged from the cooling kiln is heated air, thereby improving the utilization rate of thermal energy.

[0023] Furthermore, the titanium dioxide calcining kiln is a rotary kiln device.

[0024] Furthermore, the exhaust gas from the medium-temperature SCR reactor is purified before being discharged. Preferably, the exhaust gas from the medium-temperature SCR reactor is cooled by spraying with dilute sulfuric acid, washed with alkali, washed with acid, and then subjected to wet electrostatic demisting before being discharged. Denitrification is performed in the medium-temperature SCR reactor, followed by cooling by spraying with dilute sulfuric acid, washing with alkali, and washing with acid to fully remove the acidic components in the exhaust gas, and the exhaust gas is discharged after meeting environmental protection standards.

[0025] Furthermore, the calcining kiln consumes (210-240) m3 of natural gas per ton of product. 3:The air volume required for the calcining kiln to consume natural gas per ton of product is (1999.2-2284.8) m 3 .

[0026] The use of part of the gas discharged from the metal filter bag dust collector and the gas discharged from the cooling kiln as the primary combustion air of the calcining kiln burner increases the primary air temperature, which not only recovers the waste heat of the flue gas and increases the primary air temperature, but also saves natural gas and reduces operating costs. In addition, the mixture of part of the gas discharged from the metal filter bag dust collector and the cooling kiln exhaust gas reduces the oxygen concentration in the primary air mixture compared to using outdoor air as the combustion air, reduces the maximum temperature of the flame area, and suppresses thermal NO x formation.

[0027] Furthermore, the volume flow rate of gas transported from the cooling kiln to the titanium dioxide calcining kiln: the volume flow rate of gas extracted to the titanium dioxide calcining kiln after dust removal by the metal filter bag dust collector is 85:15.

[0028] Reasonable control of the ratio of the gas volume delivered by the cooling kiln in the primary air and the gas volume delivered after purification by the metal filter bag dust collector can better achieve stable compliance with nitrogen oxide standards.

[0029] Furthermore, during the calcination of titanium dioxide, high-temperature flue gas disturbances within the kiln in existing technologies are a key factor affecting the dynamic calcination of the titanium material. The purpose of this flue gas disturbance is to create a reasonable airflow and temperature distribution within the kiln, allowing the titanium material to be evenly and fully heated. Although existing flue gas disturbances facilitate the calcination of metatitanate materials, in actual operation, due to limitations in the kiln structure and combustion conditions, uneven combustion may still occur, resulting in insufficient heating of some metatitanate materials. This not only affects the quality of the titanium dioxide product, but also the decomposition efficiency of titanium dioxide, resulting in reduced resource utilization.

[0030] Furthermore, the invention further includes extracting a portion of the exhaust gas from the metal filter bag dust collector as secondary air and conveying it to the titanium dioxide calcining kiln. The invention conveys a portion of the exhaust gas from the metal filter bag dust collector as secondary air to the titanium dioxide calcining kiln. The return of the secondary air disturbs the furnace gas in the kiln, improving the sufficiency and uniformity of the titanium dioxide calcination, thereby enhancing product quality. This has significant economic benefits and achieves the goals of environmental protection, energy conservation, and high efficiency.

[0031] Furthermore, per ton of product, the ratio of the volume flow of natural gas combustion to the volume flow of secondary air delivered to the titanium dioxide calcining kiln is (210-240):(2000-2300). Properly controlling the delivery of secondary air not only improves the disturbance of the furnace gas in the kiln, enhancing the sufficiency and uniformity of titanium dioxide calcination, but also achieves better energy savings.

[0032] Preferably, per ton of product, the volume flow rate of the natural gas burned: the volume flow rate of the secondary air delivered to the titanium dioxide calcining kiln is 1:8.3-10.96.

[0033] Furthermore, part of the gas discharged from the metal filter bag dust collector is extracted as secondary air and transported to the smoke mixing chamber of the titanium dioxide calcining kiln, where it is evenly mixed with the high-temperature flue gas generated by the combustion of natural gas and then transported to the calcining chamber of the titanium dioxide calcining kiln.

[0034] Furthermore, the angle between the secondary air inlet tangent to the smoke mixing chamber of the titanium dioxide calcining kiln and the axial direction of the titanium dioxide calcining kiln is maintained at 40° to 45°. By properly adjusting the secondary air entry angle, the disturbance effect can be better optimized and the calcination quality of the titanium dioxide can be guaranteed. Preferably, the angle between the secondary air inlet tangent to the smoke mixing chamber of the titanium dioxide calcining kiln and the axial direction of the titanium dioxide calcining kiln is maintained at 42° to 45°.

[0035] Furthermore, the temperature of the exhaust gas discharged from the titanium dioxide calcining kiln is 340°C to 380°C; the temperature of the air discharged from the cooling kiln is 180°C to 200°C.

[0036] Another object of the present invention is to provide a device system for the above-mentioned titanium dioxide calcining kiln tail gas treatment process.

[0037] The device system used in the above-mentioned titanium dioxide calcining kiln tail gas treatment process includes a titanium dioxide calcining kiln, a metal filter bag dust collector and a medium-temperature SCR reactor connected in sequence, and the tail gas outlet of the medium-temperature SCR reactor is connected to the tail gas purification system through the tail gas discharge pipeline;

[0038] The exhaust port of the metal filter bag dust collector is connected to the smoke mixing box through the first bypass air pipe. The air exhaust port of the cooling kiln is connected to the smoke mixing box, and the smoke mixing box is connected to the natural gas burner.

[0039] The device system for treating exhaust gas from a titanium dioxide calcining kiln provided by the present invention includes a titanium dioxide calcining kiln, a metal bag filter dust collector, and a medium-temperature SCR reactor, which are connected in sequence via pipelines. The exhaust outlet of the medium-temperature SCR reactor is connected to an exhaust gas purification system via an exhaust gas discharge pipeline. The exhaust outlet of the metal bag filter dust collector is connected to the smoke mixing box of the titanium dioxide calcining kiln via a first bypass air supply pipe. The air outlet of the cooling kiln is connected to the smoke mixing box, which is connected to a natural gas burner. The exhaust gas discharged from the titanium dioxide calcining kiln first passes through the metal bag filter dust collector for dust removal. The dust-removed gas is then transported to the smoke mixing box via the first bypass air supply pipe. Another portion of the gas passes through the medium-temperature SCR reactor for denitrification treatment, and then is purified and discharged through the exhaust gas purification system. Normal temperature air enters the cooling kiln for heating. The heated air enters the smoke mixing box through a pipeline and is mixed with part of the gas discharged from the metal bag filter dust collector as combustion-supporting air. It is then transported to the calcining kiln burner and mixed with natural gas for combustion. The treatment device has a simple structure, low energy consumption, and is easy to promote.

[0040] Furthermore, a bag dust collector is provided between the air outlet of the cooling kiln and the smoke mixing box to purify the gas at the outlet of the cooling kiln.

[0041] Furthermore, a primary fan is connected to the pipeline between the smoke mixing box and the natural gas burner.

[0042] Furthermore, the exhaust port of the metal bag filter dust collector is connected to the smoke mixing chamber of the titanium dioxide calcining kiln through a second bypass gas pipe, which is used to mix part of the purified gas discharged from the metal bag filter dust collector with the high-temperature flue gas generated by the burner of the titanium dioxide calcining kiln.

[0043] The second bypass recycles exhaust gas from the metal bag filter back into the smoke mixing chamber, preferably at a tangential angle of 40°-45°. This allows the natural gas burner flame to be fully disturbed, preventing the high-temperature flame from laminarly ejecting into the calciner. The high-temperature flame from the natural gas burner mixes with the circulating secondary air, increasing the total amount of heat in the calciner. Simultaneously, the hot gas enters the calciner furnace in a turbulent flow, fully mixing with the material and achieving complete heating and conversion.

[0044] Due to the effect of introducing secondary air through the second bypass, on the one hand, the total amount of hot air in the furnace increases, and on the other hand, the temperature field of the hot air in the calcining kiln furnace is more uniform, and the contact between the hot air and the material is more sufficient, which better completes the transformation of titanium dioxide from anatase to rutile during the calcination process.

[0045] Furthermore, the second bypass air supply pipe is connected to a secondary air fan.

[0046] A secondary fan is installed on the second bypass gas pipeline to increase the kinetic energy of the secondary air entering the smoke mixing chamber. When it mixes tangentially with the high-temperature airflow generated by the natural gas burner flame, it effectively turbulently produces hot flue gas that spirals forward. Furthermore, the hot flue gas has strong turbulent characteristics, which quickly and efficiently mixes the gas and solid phases when it comes into contact with the material, resulting in lower energy consumption and higher conversion efficiency for the titanium dioxide calcination.

[0047] Furthermore, the tail gas purification system includes a dilute sulfuric acid spray cooling device and a subsequent purification device connected in sequence.

[0048] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0049] 1. The exhaust gas treatment process for the titanium dioxide calcining kiln proposed in the present invention involves sequentially passing the exhaust gas discharged from the kiln through a metal filter bag dust collector for dust removal and a medium-temperature SCR reactor for denitrification, and then purifying the gas discharged from the medium-temperature SCR reactor until it meets the standards before being discharged. In this process, part of the gas discharged from the metal filter bag dust collector is mixed with the exhaust air from the cooling kiln as primary air and transported to the titanium dioxide calcining kiln burner for mixed combustion with natural gas. On the one hand, the temperature of part of the gas discharged from the metal filter bag dust collector is relatively high. Mixing it with natural gas as primary air can effectively increase the temperature of the combustion-supporting air, save the amount of natural gas to a certain extent, fully recover the waste heat of the flue gas, and achieve energy-saving effects. On the other hand, by controlling the ratio of the volume flow of the air from the cooling kiln and the air discharged from the metal bag filter dust collector in the hot combustion air, the volume of the air from the cooling kiln meets the baseline oxygen content of natural gas combustion, and the volume of the gas discharged from the metal bag filter dust collector meets the excess oxygen content of natural gas combustion. The exhaust gas from the kiln tail is purified by the metal bag filter dust collector and the oxygen content of the gas discharged is lower than that of conventional air. The excess oxygen content is adjusted to form a local reducing atmosphere, which will produce NO x Reduction, thereby inhibiting NO x The generation of NO in flue gas x Passive nitrogen reduction can be achieved at the source, and denitrification treatment can be carried out in conjunction with the back-end medium-temperature SCR reactor to ensure that after the exhaust gas is purified, particulate matter and nitrogen oxides can stably meet higher standards for air environmental protection emissions.

[0050] 2. The tail gas treatment process of the titanium dioxide calcining kiln of the present invention uses part of the gas discharged from the metal filter bag dust collector to mix with the cooling waste gas of the cooling kiln to reduce the oxygen concentration in the primary air mixture, reduce the maximum temperature of the flame area, and inhibit the thermal NO xThe formation of nitrogen oxides (NOx) is prevented by flue gas recirculation (FGR) and the end-of-pipe denitrification (DNT) treatment in a medium-temperature SCR reactor provides a highly effective approach to reducing NOx emissions from the sulfated titanium dioxide production process. The exhaust from the titanium dioxide calcining kiln is purified by a high-temperature metal bag filter, providing a process measure for ultra-low particulate matter emissions from the sulfated titanium dioxide production process.

[0051] 3. The exhaust gas treatment process for titanium dioxide calcining kilns of the present invention ensures that after exhaust gas purification, particulate matter and nitrogen oxides are consistently and ultra-lowly emitted, providing greater environmental benefits. The exhaust gas treatment process provided by the present invention can achieve energy conservation and emission reduction, reducing carbon emissions.

[0052] 4. The device system for treating exhaust gas from a titanium dioxide calcining kiln provided by the present invention comprises a titanium dioxide calcining kiln, a metal bag filter dust collector, and a medium-temperature SCR reactor connected in sequence by pipelines. The exhaust outlet of the medium-temperature SCR reactor is connected to an exhaust gas purification system via an exhaust gas discharge pipeline. The exhaust outlet of the metal bag filter dust collector is connected to the smoke mixing box of the calcining kiln via a second bypass gas pipeline. The exhaust outlet of the cooling kiln is connected to the smoke mixing box via a first bypass pipeline. The smoke mixing box is connected to a natural gas combustion chamber pipeline. The exhaust gas discharged from the titanium dioxide calcining kiln first passes through the metal bag filter dust collector for dust removal. The dust-removed gas is then transported to the smoke mixing box via the first bypass gas pipeline. Another portion of the gas passes through the medium-temperature SCR reactor for denitrification treatment. After that, it is purified and discharged through the exhaust gas purification system. Normal temperature air enters the cooling kiln for heating. The heated air enters the smoke mixing box through a pipeline and mixes with part of the gas discharged from the metal bag filter dust collector as combustion air. It is then transported to the calcining kiln burner and mixed with natural gas for combustion. The processing device has a simple structure, low energy consumption and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the tail gas treatment process of the titanium dioxide calcining kiln in Example 1.

[0054] Figure 2 Schematic diagram of the tail gas treatment process of the titanium dioxide calcining kiln in Example 2.

[0055] Reference numerals:

[0056] 1-titanium dioxide calcining kiln; 11-burner; 111-natural gas transmission pipe;

[0057] 2-metal filter bag dust collector; 21-first bypass air pipe; 22-second bypass air pipe; 221-secondary fan;

[0058] 3-Medium temperature SCR reactor;

[0059] 4- Exhaust gas purification system;

[0060] 5-Cooling kiln; 51-Smoke mixing box; 52-Bag dust collector; 53-Primary fan. DETAILED DESCRIPTION

[0061] The present invention will be described in detail below with reference to the accompanying drawings.

[0062] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0063] Example 1

[0064] At present, titanium dioxide calcining kilns face some challenges during operation:

[0065] First, as environmental protection requirements continue to tighten, restrictions on particulate matter and nitrogen oxide emissions are becoming increasingly stringent. The concentrations of particulate matter and nitrogen oxides in the exhaust gas emitted by calcining kilns are relatively high, making it difficult for traditional cyclone dust collectors and gravity settling chambers to meet strict environmental emission standards. This undoubtedly poses a more severe challenge to environmental protection work.

[0066] Secondly, during the calcination of titanium dioxide, in order to ensure the safe operation of the calcination kiln, combustion air exceeding the theoretical requirement is usually introduced. Introducing excess combustion air can ensure the complete combustion of natural gas and avoid the production of harmful substances such as carbon monoxide. These substances are not only harmful to the environment and human health, but may also form explosive mixtures in the kiln, increasing safety risks. At the same time, heating the excess combustion air requires more natural gas, increasing operating costs; the excess air also increases the flue gas volume, resulting in an increase in the shaft power of the system fan, and the emission of high-temperature flue gas increases exhaust heat loss, resulting in high energy consumption and further increasing operating costs. In the existing technology, some manufacturers mix the hot air discharged from the cooling kiln with room temperature air and use it as combustion air for natural gas. Although this has a certain energy-saving effect, the energy-saving effect is limited. Therefore, optimizing the combustion process, saving energy, and reducing costs have become necessary ways to improve the operating efficiency and economy of the calcination kiln.

[0067] like Figure 1 As shown, this embodiment provides a device system for treating tail gas from a titanium dioxide calcining kiln.

[0068] It includes a titanium dioxide calcining kiln 1, a metal filter bag dust collector 2 and a medium-temperature SCR reactor 3 which are sequentially connected through pipelines, and the tail gas outlet of the medium-temperature SCR reactor 3 is connected to the tail gas purification system 4 through the tail gas discharge pipeline;

[0069] The exhaust port of the metal filter bag dust collector 2 is connected to the smoke mixing box 51 through the first bypass air pipe 21. The air exhaust port of the cooling kiln 5 is connected to the smoke mixing box 51. The smoke mixing box 51 is connected to the natural gas burner 11, and the burner is connected to the natural gas delivery pipe 111.

[0070] A bag filter 52 is provided between the air outlet of the cooling kiln 5 and the smoke mixing box 51 to purify the gas at the cooling kiln outlet. The bag filter 52 removes dust from the hot air discharged from the cooling kiln 5 to better ensure efficient combustion.

[0071] A primary fan 53 is connected to the pipeline between the smoke mixing box 51 and the natural gas burner 11 .

[0072] The tail gas purification system 4 includes a dilute sulfuric acid spray cooling device and a subsequent purification device connected in sequence.

[0073] The subsequent purification equipment includes a cold water cooling tower, a first-level alkaline washing and desulfurization tower, a wet demisting tower, a system main fan, a second-level alkaline washing tower and chimney emissions connected in sequence.

[0074] use Figure 1 The process of treating the tail gas from the titanium dioxide calcining kiln in the treatment device system shown includes the following steps:

[0075] A process for treating tail gas from a titanium dioxide calcining kiln comprises the following steps:

[0076] The tail gas discharged from the titanium dioxide calcining kiln 1 with a temperature of 350°C is transported to the metal filter bag dust collector 2 for dust removal;

[0077] The 320°C gas discharged from the metal bag filter 2 is transported to the smoke mixing box 51 through the first bypass gas pipe 21. The 180°C hot air discharged from the cooling kiln 5 is transported to the smoke mixing box 51 and mixed with the 320°C gas discharged from the metal bag filter 2 as the combustion air of the natural gas, i.e., primary air. The mixed air is then transported to the burner 11 and burned together with the natural gas.

[0078] The residual gas discharged from the metal filter bag dust collector 2 is transported to the medium-temperature SCR reactor 3 for denitrification treatment;

[0079] The gas discharged from the medium-temperature SCR reactor 3 is transported to the tail gas purification system for waste heat recovery and desulfurization treatment.

[0080] Among them, the natural gas flow consumed by the calcining kiln is (210-240) m3 per ton of product. 3 :The air volume required for the calcining kiln to consume natural gas per ton of product is (1999.2-2284.8) m 3The primary air delivery volume formed by mixing part of the gas discharged from the metal filter bag dust collector with the exhaust air from the cooling kiln is the air volume required to consume natural gas.

[0081] In some embodiments, the volume flow rate of gas delivered from the cooling kiln to the titanium dioxide calcining kiln: the volume flow rate of gas extracted to the titanium dioxide calcining kiln after dust removal by the metal filter bag dust collector is 82-88:12-18. Preferably, the volume flow rate of gas delivered from the cooling kiln to the titanium dioxide calcining kiln: the volume flow rate of gas extracted to the titanium dioxide calcining kiln after dust removal by the metal filter bag dust collector is 85:15.

[0082] By mixing part of the gas discharged from the metal bag filter dust collector with the gas discharged from the cooling kiln as excess combustion air for natural gas, the energy consumption of the calcining kiln for additional heating of the combustion air can be effectively reduced, the operating costs can be reduced, the efficient utilization of resources can be better improved, and the emission of nitrogen oxides in the tail gas at the back end can be guaranteed to meet the emission standards.

[0083] At the same time, reasonable control of the ratio of the gas volume delivered by the cooling kiln in the primary air and the gas volume delivered after purification by the metal filter bag dust collector can better achieve stable compliance with nitrogen oxide standards.

[0084] In some embodiments, the exhaust gas temperature from the titanium dioxide calcining kiln 1 is 340°C to 380°C; the gas temperature from the metal bag filter 2 is 310°C to 350°C; and the air temperature from the cooling kiln 5 is 180°C to 200°C.

[0085] After calculation, the exhaust particulate matter content of this embodiment and other embodiments is ≤10mg / Nm 3 , nitrogen oxides ≤ 100mg / Nm 3 , reaching the current national requirements for higher emission standards. In this embodiment, the initial concentration of nitrogen oxides in the exhaust gas discharged from the titanium dioxide calcining kiln 1 is 400 mg / Nm 3 .

[0086] Specifically, as to the source of combustion-supporting air, there are two situations in the prior art.

[0087] In the first case, standard practice was to mix and combust natural gas with ambient air at 20°C. In some comparative examples, the theoretical volume flow ratio of natural gas to ambient air per unit time was 1:9.52. The remaining treatment process was consistent with that of this embodiment, and the raw exhaust gas emitted from the titanium dioxide calcining kiln 1 was the same as that of this embodiment.

[0088] In the second scenario, air heated by the cooling kiln was used as the primary combustion air. In some comparative experimental examples, the volume flow ratio per unit time of natural gas to 180°C air heated by the cooling kiln was 1:9.52. The remaining treatment process was consistent with that of this embodiment, and the raw exhaust gas discharged from the titanium dioxide calcining kiln 1 was the same as that of this embodiment.

[0089] The first and second cases can control the nitrogen oxide content of the exhaust gas to 270 mg / Nm 3 Within, nitrogen oxides ≤100mg / Nm 3 . Unable to achieve particle content ≤10mg / Nm 3 New national emission standards.

[0090] In this example, the combustion air is a mixture of 180°C air from the cooling kiln and 320°C air from the metal bag filter, with the ratio of 85:15 per ton of product. The volume flow rate per unit time of natural gas to the mixed combustion air is 1:15.

[0091] The exhaust gas particulate matter content is ≤10mg / Nm 3 , nitrogen oxides ≤ 100mg / Nm 3 , meeting the current national requirements for higher emission standards.

[0092] Cost calculation:

[0093] According to the specification, the temperature is calculated at 20℃. After the technical transformation, the cooling kiln is used to cool the heated air as the primary combustion air of the burner. The combustion air temperature is 180℃ and the combustion air volume Q=13500m 3 / h, natural gas calorific value Q dw y =8400Kcal / Nm 3 , gas price 3 yuan / Nm 3 .

[0094] E=0.24×1.0035×1.013×13500×(180-20)=526977.19Kca / h, saving 62.74Nm of natural gas 3 / h, gas saving per hour: 62.74×3=188.21 yuan / h.

[0095] Assuming 180℃, after the technical transformation, part of the exhaust gas purified by the dust collector replaces the original cooling kiln exhaust gas as secondary air. The secondary air temperature is 330℃, and the secondary air volume Q=13500m 3 / h, natural gas calorific value Q dw y =8400Kcal / Nm 3 , gas price 3 yuan / Nm 3 .

[0096] E = 0.24 × 1.424 × 1.0035 × 13500 × (330-180) = 694486.2 Kcal / h, saving 82.68 Nm of natural gas 3 / h, gas saving per hour: 82.68×3=248.03 yuan / h.

[0097] By adopting the process of the present invention, on the one hand, the temperature of part of the gas discharged from the metal filter bag dust collector is relatively high. When it is mixed with natural gas as primary air for combustion, the initial temperature of the combustion-supporting air can be effectively increased. In order to reach the high temperature of the calcining chamber in the titanium dioxide calcining kiln, the amount of natural gas used can be saved to a certain extent, and the waste heat of the flue gas can be fully recovered to achieve the effect of energy saving. On the other hand, the oxygen content of part of the gas discharged from the metal filter bag dust collector is lower than that of conventional air, belonging to low-oxygen air. By adjusting the content of excess oxygen, a local reducing atmosphere is formed to reduce the generated NO x Reduction, thereby inhibiting NO x The generation of NO in flue gas x This technology can passively reduce nitrogen at the source, and combined with a back-end medium-temperature SCR reactor for denitrification, ensures that after exhaust purification, particulate matter and nitrogen oxides consistently meet higher emission standards. The exhaust gas treatment process provided by this invention achieves unexpected technical benefits, including energy savings, cost reduction, and standard emissions.

[0098] Example 2

[0099] Furthermore, during the titanium dioxide calcination process, flue gas disturbance within the kiln is a key factor affecting the dynamic calcination of the titanium material. This configuration aims to create a reasonable airflow and temperature distribution within the kiln, ensuring uniform and sufficient heating of the titanium material. While flue gas disturbance in existing processes facilitates dynamic calcination, in practice, due to limitations in the kiln structure and combustion conditions, uneven flue gas flow may still occur, resulting in insufficient heating of some titanium material. This not only affects the quality of the titanium dioxide product but also the decomposition efficiency of the titanium dioxide, resulting in reduced resource utilization.

[0100] like Figure 2 As shown, the exhaust port of the metal bag filter dust collector 2 is connected to the smoke mixing chamber of the titanium dioxide calcining kiln 1 through the second bypass gas pipe 22, which is used to mix part of the purified gas discharged from the metal bag filter dust collector 2 with the high-temperature flue gas generated by the burner 11.

[0101] The second bypass air supply pipe 22 is connected to a secondary air blower 221 .

[0102] Calculated per ton of product, the volume flow rate of the natural gas burned: the volume flow rate of the secondary air transported to the titanium dioxide calcining kiln 1 is 1: 8.3 to 10.96.

[0103] The present invention uses a portion of the exhaust gas from the metal bag filter dust collector as secondary air to transport it to the titanium dioxide calcining kiln. The return of the secondary air disturbs the furnace gas in the kiln, improving the sufficiency and uniformity of the titanium dioxide calcination, thereby enhancing product quality. This method has significant economic benefits and achieves the goals of environmental protection, energy conservation, and high efficiency.

[0104] In some embodiments, the volume flow rate of natural gas combustion: the volume flow rate of secondary air delivered to the titanium dioxide calcining kiln 1 is (210-240): (2000-2300) per ton of product. Reasonable control of the secondary air delivery rate not only improves the disturbance of the furnace gas in the kiln, enhances the sufficiency and uniformity of titanium dioxide calcination, but also achieves better energy conservation.

[0105] In some embodiments, part of the gas discharged from the metal filter bag dust collector 2 is extracted as secondary air and transported to the smoke mixing chamber of the titanium dioxide calcining kiln 1 to be evenly mixed with the high-temperature flue gas generated by the combustion of natural gas, and then transported to the calcining chamber of the titanium dioxide calcining kiln 1.

[0106] In some embodiments, the angle between the inlet tangent direction of the secondary air delivered to the smoke mixing chamber of the titanium dioxide calcining kiln 1 and the axial direction of the titanium dioxide calcining kiln 1 is maintained at 40° to 45°, for example, 45° can be used. Those skilled in the art can adjust the corresponding inlet tangent direction and the angle value of the axis of the calcining kiln according to actual production conditions to achieve better control effect. By reasonably adjusting the entry angle of the secondary air, the disturbance effect can be better optimized and the calcination quality of titanium dioxide can be guaranteed. Preferably, the angle between the inlet tangent direction of the secondary air delivered to the smoke mixing chamber of the titanium dioxide calcining kiln 1 and the axial direction of the titanium dioxide calcining kiln 1 is maintained at 42° to 45°.

[0107] Compared to Example 1, Example 2 incorporates the addition of secondary air, improving titanium dioxide quality and calcination efficiency by 5-8%. Due to the optimized secondary air circulation and turbulent flow injection, the secondary air ratio is controlled within 45-50% of the total air intake. Experimental data demonstrates that the gradient injection of secondary air effectively improves oxygen distribution uniformity within the kiln, reducing the oxygen concentration in the material area from 4% in conventional processes to 1.5%.

[0108] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or positional relationship, such as "upper", "lower", "left", "right", "center", "inside", and "outside", are based on the expressions of the orientation or positional relationship shown in the accompanying drawings, or are the orientation or positional relationship in which the invented product / device / apparatus is placed when it is conventionally used. These terms of orientation or positional relationship are merely for the purpose of facilitating the description of the scheme of the present invention or simplifying the description of the specific embodiments to facilitate the rapid understanding of the scheme by technicians, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship, and therefore should not be understood as limiting the present invention.

[0109] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simply understood that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", and "parallel", and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the solution of the present invention.

[0110] In addition, the expressions “first”, “second”, “third”, etc. in the terms are merely used to distinguish the description of the same or similar components, and should not be understood as emphasizing or implying the relative importance of specific components.

[0111] In addition, in the description of the embodiments of the present invention, "several," "plurality," and "a number" represent at least two. It can also be any number such as two, three, four, five, six, seven, eight, nine, or even more than nine.

[0112] Furthermore, in the description of the technical solution of the present invention, unless otherwise expressly specified, defined, or limited, the terms "disposed," "installed," "connected," "connected," "provided with," "laid," and "arranged" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections. They may be welded, riveted, bolted, threaded, or other commonly used connection methods in the art. Such connections may be mechanical, electrical, or communicative; they may be direct, indirect via an intermediate medium, or internally connected between two components.

[0113] Nm3 It stands for standard cubic meter and is a unit of gas volume commonly used in engineering and science. It represents the volume of a gas at standard temperature and pressure (STP) and is used for the standardized calculation of intake and exhaust volumes in calcining kilns.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for treating tail gas from a titanium dioxide calcining kiln, characterized in that: The following steps are involved: The tail gas discharged from the titanium dioxide calcining kiln is transported to the metal filter bag dust collector for dust removal; Part of the gas discharged from the metal bag filter dust collector is mixed with the exhaust air from the cooling kiln as primary air, which is then transported to the burner of the titanium dioxide calcining kiln and burned with natural gas. The primary air transport volume formed by mixing part of the gas discharged from the metal bag filter dust collector with the exhaust air from the cooling kiln is the air volume required to consume natural gas. The volume flow rate of the gas transported from the cooling kiln to the titanium dioxide calcining kiln is 82-88: the volume flow rate of the gas extracted from the metal bag filter dust collector to the titanium dioxide calcining kiln after dust removal is 12-18. The temperature of the gas discharged from the metal bag filter dust collector is 310℃-350℃. The calcining kiln consumes 210 m3 of natural gas per ton of product. 3 -240m 3 :The air volume required for the calcining kiln to consume natural gas per ton of product is 1999.2m 3 -2284.8m 3 ; The process also includes extracting part of the gas discharged from the metal filter bag dust collector as secondary air and transporting it to the smoke mixing chamber of the titanium dioxide calcining kiln to mix it evenly with the high-temperature flue gas generated by the combustion of natural gas, and then transporting it to the calcining chamber of the titanium dioxide calcining kiln; the angle between the inlet tangent direction of the secondary air transported to the smoke mixing chamber of the titanium dioxide calcining kiln and the axial direction of the titanium dioxide calcining kiln is maintained at 40° to 45°; and the remaining gas discharged from the metal filter bag dust collector is transported to a medium-temperature SCR reactor for denitrification treatment; The gas discharged from the medium-temperature SCR reactor is purified and then discharged.

2. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 1, wherein: The ratio of the volume flow of natural gas combustion to the volume flow of secondary air delivered to the titanium dioxide calcining kiln per ton of product is (210-240): （2000～2300）。 3. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 2, wherein: Calculated per ton of product, the volume flow rate of natural gas burned: the volume flow rate of secondary air transported to the titanium dioxide calcining kiln is 1:8.3~10.

96.

4. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 1, wherein: The angle between the inlet tangent direction of the secondary air transported to the smoke mixing chamber of the titanium dioxide calcining kiln and the axial direction of the titanium dioxide calcining kiln is maintained at 42° to 45°.

5. The process for treating tail gas from a titanium dioxide calcining kiln according to any one of claims 1 to 4, characterized in that: The exhaust gas temperature from the titanium dioxide calcining kiln is 340℃~380℃; the exhaust air temperature from the cooling kiln is 180℃~200℃.

6. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to any one of claims 1 to 5, characterized in that: It includes a titanium dioxide calcining kiln, a metal filter bag dust collector and a medium-temperature SCR reactor connected in sequence. The tail gas outlet of the device is connected to the tail gas purification system through the tail gas discharge pipeline; The exhaust port of the metal filter bag dust collector is connected to the smoke mixing box through the first bypass air pipe, and the air exhaust port of the cooling kiln is connected to the The smoke mixing box is connected to the natural gas burner.

7. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 6 is characterized in that: A bag dust collector is installed between the cooling kiln air outlet and the smoke mixing box to purify the cooling kiln outlet gas.

8. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 6 is characterized in that: A primary fan is connected to the pipeline between the smoke mixing box and the natural gas burner.

9. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 6 is characterized in that: The exhaust port of the metal filter bag dust collector is connected to the smoke mixing chamber of the titanium dioxide calcining kiln through the second bypass gas pipe, which is used to mix part of the purified gas discharged from the metal filter bag dust collector with the high-temperature flue gas generated by the burner of the titanium dioxide calcining kiln.

10. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 9 is characterized in that: The second bypass air supply pipe is connected to a secondary air fan.

11. The device system used in the calcining kiln tail gas treatment process according to any one of claims 7 to 10, characterized in that: The tail gas purification system includes a dilute sulfuric acid spray cooling device and a subsequent purification device connected in sequence.

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