Titanium dioxide calcining kiln tail gas treatment process and device system

Abstract

The invention relates to the technical field of tail gas treatment, in particular to a titanium dioxide calcining kiln tail gas treatment process and device system.The titanium dioxide calcining kiln tail gas treatment process comprises the steps that tail gas discharged by a kiln is sequentially subjected to dust removal through a metal filter bag dust remover and subjected to denitration treatment through a medium-temperature SCR reactor; part of gas exhausted by the metal filter bag dust collector and air exhausted by the cooling kiln are mixed to serve as primary air to be conveyed into the titanium dioxide calcining kiln to be mixed with natural gas for combustion, energy is effectively saved, the resource recovery rate of heat is improved, cost is reduced, the primary air serves as low-oxygen air, passive nitrogen reduction is achieved at the source, and the environment is protected. According to the present invention, the tail gas purification device is matched with the medium temperature SCR reactor at the rear end of the titanium dioxide calcining kiln, such that the nitrogen oxide stably achieves the high emission standard, and the particulate matter content of the tail gas achieves the high emission standard under the action of the metal filter bag dust collector, such that the energy saving, the cost reducing and the standard emission can be achieved so as to achieve the unexpected technical effect.

Description

Technical Field

[0001] The present invention relates to the technical field of tail gas treatment, specifically to the field of ultra-low emission reduction process for the tail gas of titanium dioxide sulfate production process, and more specifically discloses a treatment process and device system for the tail gas of a titanium dioxide calcination kiln. Background Art

[0002] Titanium dioxide, with the chemical name titanium dioxide (TiO2), is a white pigment that is widely used in industries such as coatings, plastics, paper, inks, and cosmetics due to its excellent hiding power, light resistance, weather resistance, and chemical stability. Titanium dioxide is one of the whitest pigments in the world and can provide high brightness and large-area hiding effects.

[0003] The preparation process of titanium dioxide is relatively complex, involving multiple chemical and physical processes, mainly including raw material treatment, flotation treatment, pickling treatment, water washing and neutralization treatment, calcination treatment, and crushing and classification treatment, etc. Among them, the calcination process plays a crucial role in the production process of titanium dioxide, and this process is mainly carried out in a titanium dioxide calcination kiln. In this link, natural gas is usually burned with combustion-supporting air in a burner to generate the necessary heat. In a strictly controlled high-temperature environment of 800°C to 1000°C, the pickled titanium material is heated to the decomposition temperature and then converted into high-quality titanium dioxide.

[0004] Precise control of the calcination treatment is crucial for improving the whiteness, purity, and stability of the product. In addition, environmental protection and safety in the calcination treatment are also important aspects that cannot be ignored in the titanium dioxide production process. By continuously optimizing the process, the resource utilization efficiency of the titanium dioxide calcination process can be improved, environmental pollution can be reduced, and the efficient and sustainable development of the titanium dioxide industry can be achieved.

[0005] Currently, the titanium dioxide calcination kiln faces some challenges during operation: Firstly, with the continuous tightening of environmental protection regulations, the emission limits for particulate matter and nitrogen oxides are becoming increasingly strict. The concentrations of particulate matter and nitrogen oxides in the tail gas emitted by existing calcination kilns are relatively high, making it difficult for traditional cyclone dust collectors and gravity settling chambers to meet the strict environmental protection emission standards, undoubtedly posing a more severe challenge to the environmental protection work of the backend tail gas purification.

[0006] Secondly, during the calcination process of titanium dioxide, in order to ensure the safe operation of the calcination kiln, combustion-supporting air exceeding the theoretical demand is usually introduced to ensure the full combustion of natural gas and avoid the generation of harmful substances such as carbon monoxide. Because harmful substances such as carbon monoxide are not only harmful to the environment and human health but may also form explosive mixtures in the kiln, increasing the safety risk.

[0007] Heating excess combustion-supporting air consumes more natural gas, increasing the operating cost; the excess air also increases the flue gas volume, resulting in an increase in the shaft power of the system ventilator, and the emission of a large amount of high-temperature flue gas increases the heat loss of exhaust gas, reducing the calorific value utilization efficiency of the fuel, leading to an increase in the overall energy consumption of the system and further increasing the operating cost.

[0008] In the prior art, some manufacturers mix the hot air discharged from the cooling kiln with normal-temperature air as the combustion-supporting air for natural gas. For example, the improved device for the rotary kiln air system in titanium dioxide production disclosed in the Chinese Utility Model Patent CN211316929U connects the gas discharged from the dust removal chamber to the inlet of the tertiary fan, the outlet of the tertiary fan communicates with the mixing chamber, the cooling drum is connected to the inlets of both the primary fan and the secondary fan A at the same time. After the air introduced into the cooling drum is preheated by the material, it is then introduced into the burner through the primary fan and the secondary fan A, increasing the temperature of the air participating in combustion. Although it somewhat reduces the fuel consumption and achieves partial energy-saving effects, the cooling air volume of the cooling drum is limited and cannot meet the natural gas combustion demand, and the wind speed of the cooling drum should not be too fast, restricting the ventilation volume, so the energy-saving effect is limited.

[0009] Another example is the rotary kiln and method for titanium dioxide workshop with waste gas heat recovery function disclosed in the Chinese Invention Patent Application CN106247791A, which cools the material discharged from the combustion chamber by using external air in the cooling kiln, and the secondary fan A pumps the air discharged from the cooling kiln into the primary air duct; the gas discharged from the rotary kiln enters the dust settling chamber, the gas discharged from the dust settling chamber enters the cyclone separator, the gas outlet of the cyclone separator communicates with the inlet of the bag filter, the outlet of the bag filter communicates with the inlet of the tertiary fan, and the outlet of the tertiary fan communicates with the tertiary air duct through the manual butterfly valve A; the tertiary air duct and the secondary air duct are connected through a slide valve; an electric valve B is arranged between the secondary air duct and the outlet of the secondary fan A, and an electric valve A is arranged between the primary air duct and the outlet of the secondary fan A. In this way, the rotary kiln for the titanium dioxide workshop with the waste gas heat recovery function is realized, and partial waste gas recovery and reuse are achieved. However, the waste gas of this technology needs to pass through multiple devices such as a dust settling chamber, a cyclone separator, and a bag filter, resulting in a rapid decrease in the waste gas temperature, and the recycled waste gas volume is relatively low. It also does not solve the optimization of the proportion of the combustion-supporting gas consumption at the natural gas combustion nozzle, so the waste gas heat recovery efficiency is not high. In addition, this technology does not solve the nitrogen oxides generated during the natural gas combustion process either. When facing higher environmental protection requirements, a large amount of optimization and adjustment are still needed.

[0010] Therefore, optimizing the combustion process, saving energy, and reducing costs have become the necessary ways to improve the operating efficiency and economy of the titanium dioxide calcination kiln. Summary of the Invention

[0011] The object of the present invention is to provide a treatment process and device system for the tail gas of a titanium dioxide calcination kiln, aiming at the problems existing in the operation of the existing titanium dioxide calcination kiln, such as the tail gas being difficult to meet more stringent environmental protection emission standards, the excessive combustion-supporting air resulting in increased energy consumption, and the production cost energy consumption and environmental protection emission indexes being difficult to control.

[0012] Briefly, in the present invention, a part of the gas discharged from the metal filter bag dust collector is mixed with the air discharged from the cooling kiln in proportion as the primary air and conveyed into the titanium dioxide calcination kiln to be mixed with natural gas for combustion. This not only recovers the waste heat of the flue gas, raises the temperature of the primary air, saves natural gas, and reduces the operating cost, but also reduces the oxygen concentration in the primary air mixture after the part of the gas discharged from the metal filter bag dust collector is mixed with the cooling waste gas of the cooling kiln, reduces the maximum temperature in the flame area, and inhibits the formation of thermal NO x . Cooperating with the medium-temperature SCR reactor process at the rear end of the titanium dioxide calcination kiln, nitrogen oxides are treated and reduced at the source and end through FGR flue gas recirculation, providing an efficient way for nitrogen oxide reduction in the sulfuric acid process for titanium dioxide production. At the same time, the tail gas of the titanium dioxide calcination kiln is purified by a high-temperature metal filter bag dust collector, providing a process measure for the ultra-low emission of particulate matter in the tail gas of the sulfuric acid process for titanium dioxide production.

[0013] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows: A treatment process for the tail gas of a titanium dioxide calcination kiln, comprising the following steps: Convey the tail gas discharged from the titanium dioxide calcination kiln into a metal filter bag dust collector for dust removal treatment; Mix a part of the gas discharged from the metal filter bag dust collector with the air discharged from the cooling kiln as the primary air and convey it into the burner of the titanium dioxide calcination kiln to be mixed with natural gas for combustion; the conveying amount of the primary air formed after the part of the gas discharged from the metal filter bag dust collector is mixed with the air discharged from the cooling kiln is the amount of air required for consuming natural gas; the volume flow rate of the gas conveyed from the cooling kiln to the titanium dioxide calcination kiln: the volume flow rate of the gas extracted from the titanium dioxide calcination kiln after the metal filter bag dust collector removes dust is 82 - 88:12 - 18; the temperature of the gas discharged from the metal filter bag dust collector is 310°C - 350°C; Convey the remaining gas discharged from the metal filter bag dust collector into a medium-temperature SCR reactor for denitrification treatment; The gas discharged from the medium-temperature SCR reactor is discharged after purification.

[0014] The titanium dioxide calcination kiln tail gas treatment process proposed by the present invention involves passing the tail gas discharged from the kiln through a metal filter bag dust collector for dust removal and a medium-temperature SCR reactor for denitrification treatment, and then discharging the gas discharged from the medium-temperature SCR reactor after purification to meet the standards. During this process, a part of the gas discharged from the metal filter bag dust collector is mixed with the air discharged from the cooling kiln and used as primary air to be transported to the burner of the titanium dioxide calcination kiln and mixed with natural gas for combustion. On the one hand, a part of the gas discharged from the metal filter bag dust collector has a relatively high temperature. As primary air mixed with natural gas for combustion, it can effectively increase the temperature of the combustion-supporting air, save the consumption of natural gas to a certain extent, fully recover the waste heat of the flue gas, and achieve the effect of energy conservation. On the other hand, by controlling the proportion of the volume flow of the air from the cooling kiln and the air discharged from the metal filter bag dust collector in the combustion-supporting air of the natural gas, the volume of the gas from the cooling kiln meets the reference oxygen content for natural gas combustion, and the volume of the gas discharged from the metal filter bag dust collector meets the excess oxygen content for natural gas combustion. A part of the gas discharged from the kiln tail waste gas after being purified by the metal filter bag dust collector has a lower oxygen content than conventional air. By adjusting the content of the excess oxygen, a local reducing atmosphere is formed, and the generated NO x is reduced, thereby inhibiting the generation of NO x , reducing NO in the flue gas x , and passive nitrogen reduction can be achieved at the source. Cooperating with the denitrification treatment of the medium-temperature SCR reactor at the back end can ensure that after the tail gas is purified, particulate matter and nitrogen oxides can stably meet the requirements of higher-standard air environmental protection emission standards.

[0015] Compared with the existing tail gas recycling technologies, the tail gas treatment process provided by the present invention realizes the dual synergy of nitrogen reduction at the source and waste heat recovery and utilization, can achieve high-efficiency energy conservation, reduce costs, and meet the higher requirements of atmospheric environmental protection emissions.

[0016] Further, the cooling kiln is a device for cooling the calcined titanium dioxide; in the present invention, by transporting normal-temperature air into the cooling kiln for heat exchange, the air discharged from the cooling kiln is heated air, improving the utilization rate of thermal energy.

[0017] Further, the titanium dioxide calcination kiln is a rotary kiln device.

[0018] Further, the gas discharged from the medium-temperature SCR reactor is discharged after purification. Preferably, the gas discharged from the medium-temperature SCR reactor is discharged after being cooled by spraying dilute sulfuric acid, alkali washing, acid washing, and wet electrostatic demisting. After denitrification in the medium-temperature SCR reactor, and then spraying dilute sulfuric acid for cooling, alkali washing, and acid washing to fully remove the acidic components in the tail gas and discharge it after meeting the environmental protection standards.

[0019] Further, calculated per ton of product, the natural gas flow rate consumed by the calcination kiln is (210 - 240) m 3: The air volume required for natural gas consumption in the calcination kiln per ton of product is (1999.2 - 2284.8) m 3 .

[0020] Part of the gas discharged from the metal bag filter and the gas discharged from the cooling kiln are mixed as the primary combustion-supporting air for the burner of the calcination kiln, which increases the temperature of the primary air. Not only is the waste heat of the flue gas recovered and the temperature of the primary air increased, but also natural gas is saved and the operating cost is reduced. Moreover, after the part of the gas discharged from the metal bag filter and the cooling waste gas of the cooling kiln are mixed, the oxygen concentration in the primary air mixture is reduced compared with using outdoor air as the combustion-supporting air, the maximum temperature in the flame area is reduced, and the formation of thermal NO x is inhibited.

[0021] Furthermore, the gas volume flow rate of the cooling kiln transported to the titanium dioxide calcination kiln: the gas volume flow rate of the gas extracted from the metal bag filter after dust removal and transported to the titanium dioxide calcination kiln is 85:15.

[0022] Reasonably controlling the ratio of the gas volume transported by the cooling kiln and the gas volume transported after purification by the metal bag filter in the primary air can better achieve stable compliance of nitrogen oxides.

[0023] In addition, during the calcination process of titanium dioxide, the high-temperature flue gas disturbance in the kiln in the prior art is the key factor affecting the dynamic calcination of titanium materials. The purpose of this flue gas disturbance is to form a reasonable gas flow and temperature distribution in the kiln so that the titanium materials can be heated evenly and sufficiently. Although the existing flue gas disturbance helps the calcination of metatitanic acid materials, in actual operation, due to the limitations of the kiln structure and combustion conditions, there may still be uneven combustion, resulting in some metatitanic acid materials not being heated sufficiently. This will not only affect the quality of titanium dioxide products, but also affect the decomposition efficiency of titanium dioxide, resulting in a reduction in resource utilization rate.

[0024] Furthermore, it also includes extracting another part of the gas discharged from the metal bag filter as the secondary air and transporting it into the titanium dioxide calcination kiln. In the present invention, part of the gas discharged from the metal bag filter is used as the secondary air and transported into the titanium dioxide calcination kiln. The backflow of the secondary air disturbs the furnace gas in the kiln, improves the calcination sufficiency and uniformity of titanium dioxide, thereby improving the product quality, having significant economic benefits, and achieving the production goals of environmental protection, energy conservation, and high efficiency.

[0025] Furthermore, calculated per ton of product, the volume flow rate ratio of natural gas combustion: the volume flow rate of the secondary air transported into the titanium dioxide calcination kiln is (210 - 240):(2000 - 2300). Reasonably controlling the transportation volume of the secondary air can not only better achieve the disturbance of the furnace gas in the kiln, improve the calcination sufficiency and uniformity of titanium dioxide, but also better achieve the energy-saving effect.

[0026] Preferably, based on per ton of product, the volume flow rate of natural gas combustion: the volume flow rate of secondary air transported into the titanium dioxide calcination kiln is 1: 8.3 - 10.96.

[0027] Furthermore, a part of the gas discharged from the metal bag filter is extracted as secondary air and transported into the mixing chamber of the titanium dioxide calcination kiln, where it is mixed evenly with the high-temperature flue gas generated by the combustion of natural gas, and then transported into the calcination chamber of the titanium dioxide calcination kiln.

[0028] Furthermore, the included angle between the tangential direction of the inlet of the secondary air transported into the mixing chamber of the titanium dioxide calcination kiln and the axis direction of the titanium dioxide calcination kiln is maintained at 40° - 45°. By reasonably adjusting the inlet angle of the secondary air, the disturbance effect can be better optimized to ensure the calcination quality of titanium dioxide. Preferably, the included angle between the tangential direction of the inlet of the secondary air transported into the mixing chamber of the titanium dioxide calcination kiln and the axial direction of the titanium dioxide calcination kiln is maintained at 42° - 45°.

[0029] Furthermore, the tail gas temperature discharged from the titanium dioxide calcination kiln is 340°C - 380°C; the temperature of the air discharged from the cooling kiln is 180°C - 200°C.

[0030] Another object of the present invention is to provide a device system adopted by the above-mentioned treatment process for the tail gas of the titanium dioxide calcination kiln.

[0031] The device system adopted by the treatment process for the tail gas of the titanium dioxide calcination kiln as described above includes a titanium dioxide calcination kiln, a metal bag filter, and a medium-temperature SCR reactor connected in sequence. The tail gas discharge port of the medium-temperature SCR reactor is connected to the tail gas purification system through a tail gas discharge pipeline; The discharge port of the metal bag filter is connected to the mixing chamber through a first bypass gas pipeline. The air discharge port of the cooling kiln is connected to the mixing chamber, and the mixing chamber is connected to the burner of natural gas.

[0032] The device system for treating the tail gas of a titanium dioxide calcination kiln provided by the present invention includes a titanium dioxide calcination kiln, a metal filter bag dust collector, and a medium-temperature SCR reactor that are sequentially connected through pipelines. The tail gas discharge port of the medium-temperature SCR reactor is connected to a tail gas purification system through a tail gas discharge pipeline; the discharge port of the metal filter bag dust collector is connected to the smoke mixing box of the titanium dioxide calcination kiln through a first bypass gas pipeline, the air discharge port of the cooling kiln is connected to the smoke mixing box, and the smoke mixing box is connected to a natural gas burner. The tail gas discharged from the titanium dioxide calcination kiln first passes through the metal filter bag dust collector for dust removal, and the dust-removed gas is transported to the smoke mixing box through the first bypass gas pipeline. Another part of the gas passes through the medium-temperature SCR reactor for denitrification treatment, and then is purified and discharged through the tail gas purification system; normal-temperature air enters the cooling kiln for heating up, and the heated air enters the smoke mixing box through a pipeline and is mixed with part of the gas discharged from the metal filter bag dust collector as combustion-supporting air and is transported to the combustion burner of the calcination kiln to be mixed with natural gas and then burned. This treatment device has a simple structure, low energy consumption, and is convenient for popularization.

[0033] Further, a bag filter is provided between the air discharge port of the cooling kiln and the smoke mixing box for purifying the gas at the outlet of the cooling kiln.

[0034] Further, a primary air blower is connected to the pipeline between the smoke mixing box and the natural gas burner.

[0035] Further, the discharge port of the metal filter bag dust collector is connected to the smoke mixing chamber of the titanium dioxide calcination kiln through a second bypass gas pipeline for mixing part of the purified gas discharged from the metal filter bag dust collector with the high-temperature flue gas generated by the combustion burner of the titanium dioxide calcination kiln.

[0036] The second bypass circulates the waste gas discharged from the metal filter bag dust collector back to the smoke mixing chamber. Preferably, it enters the smoke mixing chamber in a tangential direction at an angle of 40° - 45°, so that the flame of the natural gas burner is fully turbulized, and the high-temperature flame laminar jet into the calcination kiln is avoided. The high-temperature flame burning at the natural gas burner is mixed with the recycled secondary air, increasing the total amount of hot gas in the calcination kiln. At the same time, the hot gas enters the furnace of the calcination kiln in a turbulent form and is fully mixed with the material, achieving the effect of complete heating and conversion.

[0037] 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 furnace of the calcination kiln is more uniform, and the contact between the hot air and the material is more sufficient, better completing the transformation from anatase to rutile during the titanium dioxide calcination process.

[0038] Further, a secondary air blower is connected to the second bypass gas pipeline.

[0039] A secondary fan is installed on the gas pipeline of the second bypass to increase the kinetic energy of the secondary air entering the mixed smoke chamber. When tangentially mixing with the high-temperature gas flow generated by the flame at the natural gas burner, it can better complete the turbulence effect of the high-temperature gas flow and obtain hot flue gas that advances spirally. Moreover, the hot flue gas has strong turbulence characteristics. When contacting the material, it can quickly complete the efficient mixing of the gas-solid two phases, making the calcination energy consumption of titanium dioxide lower and the conversion efficiency higher.

[0040] Furthermore, the tail gas purification system includes a dilute sulfuric acid spraying and cooling device and subsequent purification devices connected in sequence.

[0041] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows: 1. The tail gas treatment process of the titanium dioxide calcination kiln proposed by the present invention involves passing the tail gas discharged from the kiln through a metal filter bag dust collector for dust removal and a medium-temperature SCR reactor for denitrification treatment in sequence, and then discharging the gas discharged from the medium-temperature SCR reactor after purification up to the standard. During this process, a part of the gas discharged from the metal filter bag dust collector is mixed with the air discharged from the cooling kiln as the primary air and transported to the burner of the titanium dioxide calcination kiln for mixing and combustion with natural gas. On the one hand, a part of the gas discharged from the metal filter bag dust collector has a relatively high temperature. As the primary air for mixing and combustion with natural gas, it can effectively increase the temperature of the combustion-supporting air, save the consumption of natural gas to a certain extent, and fully recover the waste heat of the flue gas, achieving the effect of energy conservation. 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 filter bag dust collector in the combustion-supporting air of the natural gas combustion, the volume of the gas from the cooling kiln meets the reference oxygen content for natural gas combustion, and the volume of the gas discharged from the metal filter bag dust collector meets the excess oxygen content for natural gas combustion. A part of the gas discharged from the kiln tail waste gas after being purified by the metal filter bag dust collector has a lower oxygen content than conventional air. By adjusting the content of the excess oxygen, a local reducing atmosphere is formed, and the generated NO x is reduced, thereby inhibiting the generation of NO x , reducing NO in the flue gas x , and passive nitrogen reduction can be achieved at the source. Cooperating with the denitrification treatment of the subsequent medium-temperature SCR reactor can ensure that after the tail gas is purified, the particulate matter and nitrogen oxides can stably meet the requirements of higher-specification air environmental protection emission standards.

[0042] 2. The tail gas treatment process of the titanium dioxide calcination kiln of the present invention uses a part of the gas discharged from the metal filter bag dust collector and the cooling waste gas of the cooling kiln to mix and reduce the oxygen concentration in the primary air mixture, reduce the highest temperature in the flame area, and inhibit the thermal NO xFormation. The source reduction of nitrogen oxides is achieved through FGR flue gas recirculation, and the denitrification treatment of the end-of-pipe is carried out by a medium-temperature SCR reactor, providing an efficient way for nitrogen oxide emission reduction in the titanium sulfate white pigment production process. The tail gas of the titanium dioxide calcination kiln is purified by a high-temperature metal filter bag dust collector, providing a process measure for the ultra-low emission of particulate matter in the tail gas of the titanium sulfate white pigment production process.

[0043] 3. The tail gas treatment process of the titanium dioxide calcination kiln of the present invention can ensure that after the tail gas is purified, particulate matter and nitrogen oxides stably reach the ultra-low emission level, having greater advantages in atmospheric environmental protection. The tail gas treatment process provided by the present invention can achieve energy conservation and emission reduction and reduce carbon emissions.

[0044] 4. The device system for treating the tail gas of the titanium dioxide calcination kiln provided by the present invention includes a titanium dioxide calcination kiln, a metal filter bag dust collector, and a medium-temperature SCR reactor connected in sequence through pipelines. The tail gas discharge port of the medium-temperature SCR reactor is connected to the tail gas purification system through a tail gas discharge pipeline; the discharge port of the metal filter bag dust collector is connected to the smoke mixing box of the calcination kiln through a second bypass gas transmission pipe, and the exhaust gas discharge port of the cooling kiln is connected to the smoke mixing box through a first bypass pipeline, and the smoke mixing box is connected to the natural gas combustion chamber pipeline. The tail gas discharged from the titanium dioxide calcination kiln first passes through the metal filter bag dust collector for dust removal, and the dust-removed gas is transported to the smoke mixing box through the first bypass gas transmission pipe. Another part of the gas passes through the medium-temperature SCR reactor for denitrification treatment, and then passes through the tail gas purification system for purification and is discharged; normal-temperature air enters the cooling kiln for heating, and the heated air enters the smoke mixing box through a pipeline and is mixed with a part of the gas discharged from the metal filter bag dust collector as combustion-supporting air and is transported to the burner of the calcination kiln and mixed with natural gas for combustion. This treatment device has a simple structure, low energy consumption, and is convenient for popularization. Description of the Drawings

[0045] Figure 1 It is a schematic diagram of the tail gas treatment process of the titanium dioxide calcination kiln in Example 1.

[0046] Figure 2 It is a schematic diagram of the tail gas treatment process of the titanium dioxide calcination kiln in Example 2.

[0047] Reference Numerals: 1 - Titanium dioxide calcination kiln; 11 - Burner; 111 - Natural gas transmission pipe; 2 - Metal filter bag dust collector; 21 - First bypass gas transmission pipe; 22 - Second bypass gas transmission pipe; 221 - Secondary fan; 3 - Medium-temperature SCR reactor; 4 - Tail gas purification system; 5 - Cooling kiln; 51 - Smoke mixing box; 52 - Bag dust collector; 53 - Primary fan. Detailed Embodiments

[0048] The present invention will be described in detail below with reference to the accompanying drawings.

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0050] Embodiment 1 Currently, the titanium dioxide calcination kiln faces some challenges during operation: First of all, as environmental protection requirements continue to tighten, the emission limits for particulate matter and nitrogen oxides are becoming increasingly strict. The concentrations of particulate matter and nitrogen oxides in the tail gas discharged from the calcination kiln are relatively high, making it difficult for traditional cyclone dust collectors and gravity settling chambers to meet the strict environmental protection emission standards. This undoubtedly poses a more severe challenge to environmental protection work.

[0051] Secondly, during the calcination process of titanium dioxide, in order to ensure the safe operation of the calcination kiln, combustion-supporting air exceeding the theoretical demand is usually introduced. Introducing excessive combustion-supporting air can ensure the full combustion of natural gas and avoid the generation 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 excessive combustion-supporting air requires consuming more natural gas, increasing the operating cost; excessive air also increases the flue gas volume, resulting in an increase in the shaft power of the system ventilator, and the emission of high-temperature flue gas increases the heat loss of exhaust gas, leading to high energy consumption and further increasing the operating cost. In the prior art, some manufacturers mix the hot air discharged from the cooling kiln with normal-temperature air and use it as the combustion-supporting air for natural gas. Although there is 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.

[0052] As Figure 1 shown, this embodiment provides a device system for treating the tail gas of a titanium dioxide calcination kiln.

[0053] It includes a titanium dioxide calcination kiln 1, a metal filter bag dust collector 2, and a medium-temperature SCR reactor 3 connected in sequence through pipelines. The tail gas discharge port of the medium-temperature SCR reactor 3 is connected to a tail gas purification system 4 through a tail gas discharge pipeline; The discharge port of the metal filter bag dust collector 2 is connected to a mixed smoke box 51 through a first bypass gas pipeline 21. The air discharge port of the cooling kiln 5 is connected to the mixed smoke box 51, and the mixed smoke box 51 is connected to a burner 11 for natural gas. The burner is connected to a natural gas delivery pipe 111.

[0054] A bag filter 52 is provided between the air outlet of the cooling kiln 5 and the mixed gas box 51 for purifying the gas discharged from the cooling kiln outlet. The bag filter 52 removes dust from the hot air discharged from the cooling kiln 5, better ensuring the high efficiency of combustion.

[0055] A primary air blower 53 is connected to the pipeline between the mixed gas box 51 and the natural gas burner 11.

[0056] The tail gas purification system 4 includes a dilute sulfuric acid spray cooling device and subsequent purification devices connected in sequence.

[0057] The subsequent purification devices include a cooling water tower, a primary alkali washing desulfurization tower, a wet demisting tower, a system main blower, a secondary alkali washing tower, and chimney emissions connected in sequence.

[0058] Using Figure 1 The process of treating the tail gas of the titanium dioxide calcination kiln using the shown treatment device system includes the following steps: A process for treating the tail gas of a titanium dioxide calcination kiln includes the following steps: The tail gas at a temperature of 350 °C discharged from the titanium dioxide calcination kiln 1 is transported to the metal bag filter 2 for dust removal treatment; Part of the gas at 320 °C discharged from the metal bag filter 2 is transported through the first bypass gas pipeline 21 to the mixed gas box 51, and the hot air at 180 °C discharged from the cooling kiln 5 is transported to the mixed gas box 51. After mixing with part of the gas at 320 °C discharged from the metal bag filter 2, it is used as the combustion-supporting air for natural gas, that is, the primary air, and is transported to the burner 11 to be mixed with natural gas for combustion; The remaining gas discharged from the metal bag filter 2 is transported to the medium-temperature SCR reactor 3 for denitrification treatment; 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.

[0059] Among them, calculated by ton of product, the flow rate of natural gas consumed by the calcination kiln is (210 - 240) m 3 : The amount of air required for the calcination kiln to consume natural gas per ton of product is (1999.2 - 2284.8) m 3 , and the transportation volume of the primary air formed by mixing part of the gas discharged from the metal bag filter with the air discharged from the cooling kiln is the amount of air required for consuming natural gas.

[0060] In some embodiments, the volume flow rate of the gas transported from the cooling kiln to the titanium dioxide calcination kiln: the volume flow rate of the gas extracted to the titanium dioxide calcination kiln after dust removal by the metal bag filter is 82 - 88:12 - 18. Preferably, the volume flow rate of the gas transported from the cooling kiln to the titanium dioxide calcination kiln: the volume flow rate of the gas extracted to the titanium dioxide calcination kiln after dust removal by the metal bag filter is 85:15.

[0061] Mixing a part of the gas discharged from the metal bag filter dust collector and the gas discharged from the cooling kiln as the excess combustion-supporting air for natural gas can effectively reduce the energy consumption of the calcination kiln for heating the combustion-supporting air additionally, reduce the operating cost, better improve the efficient utilization of resources, and ensure the up-to-standard discharge of nitrogen oxides in the tail gas at the back end.

[0062] Meanwhile, reasonably controlling the ratio of the gas volume conveyed by the cooling kiln in the primary air and the gas volume conveyed after purification by the metal bag filter dust collector can better achieve the stable up-to-standard discharge of nitrogen oxides.

[0063] In some embodiments, the temperature of the tail gas discharged from the titanium dioxide calcination kiln 1 is 340°C to 380°C; the temperature of the gas discharged from the metal bag filter dust collector 2 is 310°C to 350°C; the temperature of the air discharged from the cooling kiln 5 is 180°C - 200°C.

[0064] After calculation, the particulate matter content of the tail gas discharged in this embodiment and other embodiments is ≤10mg / Nm 3 , and the nitrogen oxides are ≤100mg / Nm 3 , meeting the higher-standard emission standards required by the country at present. Among them, in this embodiment, the initial concentration of nitrogen oxides in the tail gas discharged from the titanium dioxide calcination kiln 1 is 400mg / Nm 3 .

[0065] Specifically, for the source of the combustion-supporting air, there are two situations in the prior art.

[0066] In the first situation, according to the specification, normal-temperature air at 20°C is mixed with natural gas for combustion. In some comparative examples, the theoretical volume flow ratio of natural gas to normal-temperature air per unit time is 1:9.52. The rest is the same as the treatment process of this embodiment, and the original tail gas discharged from the titanium dioxide calcination kiln 1 is the same as that of this embodiment.

[0067] In the second situation, the air heated by the cooling kiln is used as the primary combustion-supporting air for combustion. In some comparative experimental examples, the volume flow ratio of natural gas to the 180°C air heated by the cooling kiln per unit time is 1:9.52. The rest is the same as the treatment process of this embodiment, and the original tail gas discharged from the titanium dioxide calcination kiln 1 is the same as that of this embodiment.

[0068] In the first situation and the second situation, the nitrogen oxide content of the tail gas can be controlled within 270 mg / Nm 3 , and the nitrogen oxides are ≤100mg / Nm 3 . It cannot meet the new national emission standard of particulate matter content ≤10mg / Nm 3 .

[0069] In this embodiment, the 180°C air discharged from the cooling kiln and a part of the 320°C air discharged from the metal bag filter are mixed according to the volume ratio of 85:15 per ton of product as combustion-supporting air. The volume flow ratio of natural gas to the mixed combustion-supporting air per unit time is 1:15.

[0070] The particulate matter content of the exhausted tail gas ≤ 10 mg / Nm 3 , and the nitrogen oxides ≤ 100 mg / Nm 3 , meeting the current national requirements for higher-standard emission standards.

[0071] Cost calculation: Calculated at 20°C according to the specification, after the technological transformation, the cooling kiln is used to cool and heat the air as the primary combustion-supporting air of the burner. The temperature of the combustion-supporting air is 180°C, and the volume of the combustion-supporting air Q = 13500 m 3 / h, and the calorific value of natural gas Q dw y = 8400 Kcal / Nm 3 , and the unit price of the gas is 3 yuan / Nm 3 .

[0072] E = 0.24×1.0035×1.013×13500×(180 - 20) = 526977.19 Kca / h, saving 62.74 Nm of natural gas 3 / h, and the cost saved per hour for gas: 62.74×3 = 188.21 yuan / h.

[0073] Calculated at 180°C, after the technological transformation, a part of the purified waste gas from the dust collector is used to replace the original cooling waste gas of the cooling kiln as the secondary air. The temperature of the secondary air is 330°C, and the volume of the secondary air Q = 13500 m 3 / h, and the calorific value of natural gas Q dw y = 8400 Kcal / Nm 3 , and the unit price of the gas is 3 yuan / Nm 3 .

[0074] E = 0.24×1.424×1.0035×13500×(330 - 180) = 694486.2 Kcal / h, saving 82.68 Nm of natural gas 3 / h, and the cost saved per hour for gas: 82.68×3 = 248.03 yuan / h.

[0075] 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. It is used as primary air and mixed with natural gas for combustion, which can effectively increase the initial temperature of the combustion-supporting air. In order to reach the high temperature of the calcining chamber in the titanium dioxide calcining kiln, the amount of natural gas 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, and it belongs 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 Passive nitrogen reduction can be achieved at the source, and denitration treatment can be carried out in conjunction with the back-end medium-temperature SCR reactor, which can ensure that after the tail gas is purified, particulate matter and nitrogen oxides can stably meet higher emission standards. The tail gas treatment process provided by the present invention can achieve energy saving, reduce costs, meet emission standards, and achieve unexpected technical effects.

[0076] Example 2 In addition, during the calcination process of titanium dioxide, the flue gas disturbance in the kiln is a key factor affecting the dynamic calcination of titanium materials. The purpose of this configuration is to form a reasonable airflow and temperature distribution in the kiln so that the titanium material can be heated evenly and fully. Although the existing process flue gas disturbance is conducive to dynamic calcination, in actual operation, due to the limitations of the kiln structure and combustion conditions, there may still be uneven flue gas flow, resulting in some titanium materials not being fully heated. This will not only affect the quality of titanium dioxide products, but also affect the decomposition efficiency of titanium dioxide, resulting in reduced resource utilization.

[0077] 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 a 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.

[0078] The second bypass air supply pipe 22 is connected to a secondary air fan 221 .

[0079] Calculated by 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: 8.3-10.96.

[0080] Part of the gas discharged from the metal filter bag dust collector is transported as secondary air to the titanium dioxide calcining kiln. The present invention transports part of the gas discharged 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, improves the calcination sufficiency and uniformity of the titanium dioxide, thereby improving the product quality, having significant economic benefits, and achieving the production goals of environmental protection, energy saving, and high efficiency.

[0081] In some embodiments, based on per ton of product, the volume flow rate of natural gas combustion: the volume flow rate of secondary air transported into the titanium dioxide calcination kiln 1 is (210 - 240):(2000 - 2300). Reasonably controlling the delivery volume of secondary air can not only better achieve the disturbance of furnace gas in the kiln, improve the calcination adequacy and uniformity of titanium dioxide, but also better achieve the energy-saving effect.

[0082] In some embodiments, a part of the gas discharged from the metal bag filter 2 is extracted as secondary air and transported into the mixing chamber of the titanium dioxide calcination kiln 1. After being evenly mixed with the high-temperature flue gas generated by the combustion of natural gas, it is transported into the calcination chamber of the titanium dioxide calcination kiln 1.

[0083] In some embodiments, the included angle between the tangential direction of the inlet of the secondary air transported into the mixing chamber of the titanium dioxide calcination kiln 1 and the axial direction of the titanium dioxide calcination kiln 1 is maintained at 40° - 45°. For example, 45° can be adopted. Those skilled in the art can adjust the numerical value of the included angle between the corresponding inlet tangential direction and the axis of the calcination kiln according to the actual production situation to achieve a better control effect. By reasonably adjusting the inlet angle of the secondary air, the disturbance effect can be better optimized to ensure the calcination quality of titanium dioxide. Preferably, the included angle between the tangential direction of the inlet of the secondary air transported into the mixing chamber of the titanium dioxide calcination kiln 1 and the axial direction of the titanium dioxide calcination kiln 1 is maintained at 42° - 45°.

[0084] Compared with Example 1, in Example 2, the process of adding secondary air improves the quality of titanium dioxide, and the calcination adequacy is increased by 5 - 8%. Due to the optimization of the secondary air circulation turbulent flow supplement, the proportion of secondary air is controlled within the range of 45 - 50% of the total air intake. Experimental data show that the gradient supplement of secondary air can effectively improve the uniformity of oxygen distribution in the kiln, reducing the oxygen concentration in the material area from 4% in the conventional process to 1.5%.

[0085] Unless otherwise specified, in the description of the specific embodiments of the present invention, the expression terms of the orientation or positional relationship indicated by "upper", "lower", "left", "right", "center", "inner", "outer", etc. are all based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the invention product / device / equipment is usually used and placed. These terms of orientation or positional relationship are only for the convenience of describing the solution of the present invention or simplifying the description in the specific embodiments, facilitating technicians to quickly understand the solution, rather than indicating or implying that a specific device / component / element must have a specific orientation or be constructed and operated in a specific positional relationship. Therefore, it cannot be understood as a limitation to the present invention.

[0086] In addition, when terms such as "horizontal", "vertical", "hanging", "parallel" appear, it does not mean that the corresponding device / component / element is required to be absolutely horizontal or vertical or hanging or parallel, but it can be slightly inclined or deviated. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and it does not mean that the structure must be completely horizontal, but it can be slightly inclined. Or, it can be simply understood that the corresponding device / component / element is arranged in directions such as "horizontal", "vertical", "hanging", "parallel", etc., 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%, more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still perform its function in the solution of the present invention.

[0087] In addition, when expressions such as "first", "second", "third", etc. appear in the terms, they are only 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.

[0088] In addition, in the description of the embodiments of the present invention, "several", "multiple", "a number of" represent at least 2. It can be any situation such as 2, 3, 4, 5, 6, 7, 8, 9, etc., and even can be a situation exceeding 9.

[0089] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / limited, when terms such as "set", "installed", "connected", "linked", "provided with", "laid", "arranged" appear, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be connection means commonly used in the art such as welding, riveting, bolting, threaded connection, etc. Such a connection can be a mechanical connection, an electrical connection or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components.

[0090] Nm 3 It represents standard cubic meters, which is a commonly used gas volume unit in engineering and science, indicating the volume of gas at standard temperature and pressure (Standard Temperature and Pressure, STP), and is used for the standardized calculation of the intake and exhaust gas volume in a calcining kiln.

[0091] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope 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 filter bag dust collector is mixed with the exhaust air from the cooling kiln as the primary air, which is transported to the burner of the titanium dioxide calcining kiln and mixed with natural gas for combustion; the primary air transport 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 the natural gas; the gas volume flow rate from the cooling kiln to the titanium dioxide calcining kiln: the gas volume flow rate extracted to the titanium dioxide calcining kiln after dust removal by the metal filter bag dust collector is 82-88:12-18; the gas temperature discharged from the metal filter bag dust collector is 310℃-350℃; The residual gas discharged from the metal bag filter is transported to the 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, characterized in that: The calcining kiln consumes 210 m3 of natural gas per ton of product. 3 -240 m 3 :The amount of air required for the calcining kiln to consume natural gas per ton of product is 1999.2 m 3 -2284.8 m 3 .

3. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 1, characterized in that: It also includes extracting a portion of the exhaust gas from the metal filter bag dust collector as secondary air and transporting it to the titanium dioxide calcining kiln.

4. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 3, characterized in that: Calculated per ton of product, the ratio of the volume flow rate of natural gas combustion: the volume flow rate of secondary air transported to the titanium dioxide calcining kiln is (210~240): (2000~2300).

5. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 4, characterized in that: Calculated per ton of product, the volume flow rate of natural gas combustion: the volume flow rate of secondary air transported to the titanium dioxide calcining kiln is 1:8.3~10.

96.

6. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 3, characterized in that: 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. After being evenly mixed with the high-temperature flue gas generated by the combustion of natural gas, it is transported to the calcining chamber of the titanium dioxide calcining kiln.

7. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 6, characterized in that: 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°.

8. The process for treating tail gas from a titanium dioxide calcining kiln according to claim 7, characterized in that: 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°.

9. The process for treating tail gas from a titanium dioxide calcining kiln according to any one of claims 1 to 8, characterized in that: The exhaust gas temperature from the titanium dioxide calcining kiln is 340℃~380℃; the air temperature from the cooling kiln is 180℃~200℃.

10. 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 9, 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, and the tail gas outlet of the medium-temperature SCR reactor is connected to the tail gas purification system through a tail gas emission pipeline; 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.

11. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 10 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.

12. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 10, characterized in that: A primary fan is connected to the pipeline between the smoke mixing box and the natural gas burner.

13. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 10, 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.

14. The device system used in the process for treating tail gas from a titanium dioxide calcining kiln according to claim 13, characterized in that: The second bypass air supply pipe is connected to a secondary fan.

15. The device system used in the calcining kiln tail gas treatment process according to any one of claims 11 to 14, characterized in that: The tail gas purification system comprises a dilute sulfuric acid spray cooling device and a subsequent purification device which are connected in sequence.

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