Titanium dioxide kiln calcining tail gas recycling method and device system thereof

Abstract

The invention relates to the technical field of tail gas treatment, and particularly discloses a titanium dioxide kiln calcining tail gas recycling method and device system.The method comprises the steps that tail gas discharged by a kiln is subjected to gravity settling and cyclone separation and then sequentially passes through a metal filter bag dust remover to be subjected to dust removal, and most dust is removed and recycled; and the medium-temperature SCR reactor carries out denitration treatment, and then the discharged gas is conveyed to the Venturi mixing heater. The medium-temperature SCR denitration device and the Venturi mixing heater are matched and cooperated, nitric oxide is purified and removed, meanwhile, waste heat of the tail gas of the calcining kiln is recycled, and waste heat recycling is achieved. By means of the method, it can be guaranteed that after tail gas is purified, particulate matter and nitric oxide stably meet the requirement of the higher-specification air environment-friendly emission standard, and popularization is convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of tail gas treatment, and in particular to a method for recycling tail gas from calcining a titanium dioxide furnace, and a device system thereof. Background Art

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

[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 combined with combustion air in a burner to generate the necessary heat. Under a strictly controlled high temperature of 800°C to 1000°C, the acidic 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 product whiteness and purity, as well as ensuring stable production line operation. Furthermore, environmental protection and safety management during the calcination process are crucial aspects of titanium dioxide production that cannot be ignored. Continuous process optimization 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: First, the concentrations of particulate matter and nitrogen oxides in the exhaust gas emitted by existing calcining kilns are relatively high. Traditional cyclone dust collectors and gravity settling chambers are difficult to meet higher environmental emission requirements, which undoubtedly poses a more severe challenge to the environmental protection work of back-end exhaust gas purification.

[0006] Secondly, titanium dioxide is obtained by high-temperature calcination of metatitanic acid. The exhaust temperature after high-temperature calcination is as high as 350°C to 380°C. The high-temperature exhaust gas discharged from the calcination kiln is usually sent to a settling chamber to settle the dust. The settled exhaust gas is then cooled by circulating water spray absorption. The cooled gas then enters a scrubbing tower for further cooling and defoaming. Finally, the defoamed gas enters an electrostatic precipitator, where the SO3 acid mist in the exhaust gas is removed under the action of the electric field. It is then further treated in an alkaline scrubbing tower before being discharged. However, the use of circulating water spray for cooling prevents the heat and SO3 acid mist in the exhaust gas from being effectively recycled, resulting in high titanium dioxide production costs and being unfavorable for energy conservation and emission reduction.

[0007] 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

[0008] The purpose of the present invention is to provide a method and device system for recycling titanium dioxide furnace calcination tail gas, in view of the problems in the existing titanium dioxide calcination tail gas treatment method, such as high concentrations of particulate matter and nitrogen oxides, low tail gas waste heat recovery efficiency, and difficult cost control.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: A method for recycling tail gas from calcining a titanium dioxide furnace comprises the following steps: The exhaust gas from the titanium dioxide calcining kiln is transported to the metal filter bag dust collector for dust removal after gravity sedimentation and cyclone separation; The 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 transported to a venturi mixing heater, wherein the venturi mixing heater is used to concentrate the dilute sulfuric acid by utilizing the waste heat of the gas discharged from the medium-temperature SCR reactor; The gas discharged from the Venturi mixing heater is cooled, washed with alkali for desulfurization and then discharged.

[0010] The method for recycling exhaust gas from the calcination of titanium dioxide furnaces proposed in the present invention includes subjecting the exhaust gas emitted from the furnace to gravity settling and cyclone separation, followed by dust removal through a metal bag filter, denitrification treatment in a medium-temperature SCR reactor, and heat recovery by a Venturi mixing heater. A Venturi mixing heater is used to recover waste heat from the denitrified exhaust gas using dilute sulfuric acid produced in the titanium dioxide production process, thereby concentrating the dilute sulfuric acid and recovering the waste heat. The medium-temperature SCR operates at a temperature of 280–400°C and can efficiently remove nitrogen oxides from the exhaust gas. The exhaust gas after the reaction has a high heat content, and direct pre-concentration of dilute sulfuric acid is performed. This results in a high utilization rate of the exhaust heat, reduced steam or electricity consumed by the dilute sulfuric acid concentration, high system integration, and significant improvement in overall efficiency.

[0011] More importantly, the residual ammonia in the flue gas after SCR denitrification can be absorbed by dilute sulfuric acid, and then separated through precipitation in the reaction tank to obtain ammonium sulfate, realizing the resource utilization of denitrification by-products and avoiding ammonia escape pollution. The escaped ammonia can also react with sulfur dioxide and sulfur trioxide in the exhaust gas, reducing the corrosiveness of the exhaust gas during the subsequent cooling and purification process. The medium-temperature SCR equipment can be equipped with a Venturi tube device adjacent to the dilute sulfuric acid pre-concentration device. The equipment is compact and easy to retrofit and upgrade existing production lines. By sharing the flue gas pipeline, medium-temperature SCR reactor, and Venturi tube equipment, the shared structure reduces the floor space and operation and maintenance complexity.

[0012] In addition, the method of the present invention pre-processes the tail gas discharged from the titanium dioxide calcining kiln by gravity sedimentation and cyclone separation, which can reduce the adhesion of the tail gas to a certain extent and avoid the subsequent clogging of the metal filter bag dust collector. The metal filter bag dust collector is then used for dust removal, which can effectively improve the recovery of particulate matter (titanium dioxide) in the tail gas, with a purification efficiency of up to 99.85%, which can meet the particle matter 10mg / m 3 Therefore, this method can ensure that after exhaust gas purification, particulate matter and nitrogen oxides can stably meet higher environmental emission requirements, making it easier to promote.

[0013] The medium-temperature SCR reactor and the dilute sulfuric acid concentration process with a Venturi tube structure work together to achieve the cascade utilization of high-temperature exhaust gas thermal energy, coordinated treatment of pollutants, and resource recycling. This can significantly reduce the operating costs of the exhaust treatment device while meeting the dual goals of energy conservation and emission reduction. It significantly improves the economic benefits of comprehensive exhaust gas treatment and is of great significance to the high-quality upgrade and development of titanium dioxide production lines.

[0014] Furthermore, the gas discharged from the Venturi mixing heater is cooled and subjected to alkaline washing and desulfurization treatment, specifically including: The gas discharged from the Venturi mixing heater is transported to the cooling tower for cooling treatment; The gas discharged from the cooling empty tower is transported to the first alkali washing tower to further purify the SO2 and SO3 in the flue gas; the gas discharged from the first alkali washing tower is transported to the wet electric demisting tower to remove the droplets and fine particles in the gas.

[0015] Furthermore, the method further includes transporting the gas discharged from the wet electric demisting tower to a second alkali washing tower to further remove sulfides in the gas.

[0016] Furthermore, the exhaust gas temperature discharged from the titanium dioxide calcining kiln is 340℃~400℃; the gas temperature discharged from the metal filter bag dust collector is 310℃~350℃; the gas temperature discharged from the medium-temperature SCR reactor is 290℃~310℃; and the gas temperature discharged from the Venturi mixing heater is 70℃~90℃.

[0017] Another object of the present invention is to provide a device system used in the above-mentioned method for recycling the tail gas from calcining the titanium dioxide furnace.

[0018] A method for recycling tail gas from calcining a titanium dioxide furnace adopts a device system comprising a gravity settling device, a cyclone separation device, a metal filter bag dust collector, a medium-temperature SCR reactor, a Venturi mixing heater and a deep purification system connected in sequence; The gravity sedimentation device is used to be connected to the tail of the titanium dioxide calcining kiln to receive the titanium dioxide calcining tail gas; The venturi mixing heater further comprises a sulfuric acid inlet, a sulfuric acid tank and a dilute sulfuric acid circulation pump. The sulfuric acid tank is used to receive and precipitate the pre-concentrated sulfuric acid.

[0019] Furthermore, the dilute sulfuric acid circulation pump is used for the circulation of dilute sulfuric acid in the Venturi mixing heater; one end of the dilute sulfuric acid circulation pump is connected to the sulfuric acid tank, and the other end is connected to the dilute sulfuric acid inlet, and is used to return the pre-concentrated sulfuric acid in the sulfuric acid tank to the Venturi mixing heater for further concentration.

[0020] Furthermore, the deep purification system includes a cooling empty tower, a first alkali washing tower and a wet electrostatic demisting tower connected in sequence; The cooling empty tower is connected to the exhaust port of the Venturi mixing heater; The cooling tower is connected to a water cooling tower.

[0021] Furthermore, the deep purification system also includes a second alkali washing tower, and the second alkali washing tower is connected to the wet electrostatic demisting tower through a fan.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: The proposed method for recycling exhaust gas from a titanium dioxide kiln calcination process involves subjecting the kiln exhaust gas to gravity settling and cyclonic separation, followed by a metal bag filter to remove and recover the majority of the dust. Denitrification is then carried out in a medium-temperature SCR reactor, after which the exhaust gas is transported to a Venturi mixing heater. The medium-temperature SCR denitrification device and the Venturi mixing heater work together to purify and remove nitrogen oxides while simultaneously recovering waste heat from the kiln exhaust, achieving waste heat recovery.

[0023] Experimental verification shows that the use of a Venturi mixing heater can utilize the dilute sulfuric acid produced in the titanium dioxide production process to recover the waste heat from the exhaust gas after denitrification, achieving the dual effects of dilute sulfuric acid concentration and waste heat recovery, and realizing the goal of energy conservation and emission reduction.

[0024] The process of the present invention pre-treats the exhaust gas discharged from the titanium dioxide calcining kiln by gravity sedimentation and cyclone separation, which can reduce the adhesion of the exhaust gas to a certain extent and avoid the blockage of the subsequent metal filter bag dust collector. The metal filter bag dust collector is then used for dust removal, which can effectively improve the recovery of particulate matter in the exhaust gas, with a purification efficiency of up to 99.85%, which can meet the requirements of particulate matter 10mg / m 3 The process of the present invention ensures that after exhaust gas purification, particulate matter and nitrogen oxides stably meet higher air environmental emission standards, reducing the investment demand for other air purification equipment, facilitating the upgrading of environmental protection technologies, and achieving greater environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a process flow chart of the method for recycling tail gas from calcining titanium dioxide furnace.

[0026] Figure 2 Schematic diagram of the titanium dioxide calcination tail gas treatment system provided in Example 1.

[0027] Figure numerals: 1-gravity sedimentation device; 2-cyclone separation device; 3-metal filter bag dust collector; 4-medium temperature SCR reactor; 5-Venturi mixing heater; 6-cooling empty tower; 61-cold water cooling tower; 7-first alkali washing tower; 8-wet electric demisting tower; 81-fan; 9-second alkali washing tower; 100-titanium dioxide calcining kiln. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings.

[0029] 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 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 intended to limit the present invention.

[0030] Example 1 A certain company uses the sulfuric acid process to produce titanium dioxide. The main production steps include concentrate decomposition, iron-titanium separation, hydrolysis, and calcination. During the titanium dioxide production process, metatitanic acid is converted into rutile titanium dioxide through calcination in a rotary kiln. The main characteristics of the exhaust gas from the titanium dioxide calcination process are: high exhaust temperature (approximately 350-400°C), high humidity, and high concentrations of sulfur dioxide, titanium dioxide dust particles, non-condensable gases, water vapor, acid mist, and other substances. This makes exhaust gas treatment difficult and requires extensive investment in exhaust gas treatment equipment for purification.

[0031] Current status of particulate matter treatment in calcination exhaust gas: After removing most coarse dust particles through inertial forces (cyclone separators) and gravity settling (sedimentation chambers), the exhaust gas first enters a Venturi scrubber. In the Venturi throat, the gas is accelerated, and the high-speed airflow quickly breaks up the water, effectively colliding it. When the gas-liquid mixture enters the venturi's expanded section, it decelerates, and the water droplets collide with the dust particles and gas again, cooling the mixture. Some SO₃ is converted into acid mist, while most dust is captured and moistened by the water droplets, agglomerated into large particles, which are then discharged into a recovery tank along with the water. Simultaneously, the exhaust gas temperature drops to around 70°C. The initially degassing gas then enters an electrostatic precipitator, where a high-voltage electrostatic field removes the acid mist and a small amount of dust. After being introduced to an alkaline scrubber via an induced draft fan (IDF) 81, the remaining acid mist is further removed, and the exhaust gas, meeting emission standards, is discharged into the chimney.

[0032] 1.1 Analysis and calculation of the company's existing metatitanic acid calcining rotary kiln: Nitrogen oxides in calcination tail gas: At present, the company's calcination process uses natural gas for heating, and the natural gas energy consumption per ton of product is about 215 Nm 3 / ton, the designed production capacity of a single production line is 6.7 tons, and the natural gas consumption per hour is 1440.5 Nm 3 / h, combustion air volume required: 20100 Nm 3 / h, combustion air is directly from outdoor air, secondary air volume is 13400 Nm 3 / h, using cooling kiln to cool materials and exchange exhaust gas, the normal concentration of natural gas in the tail gas of calcination process is 120-140 mg / m 3 Since the company currently uses the heat exchange exhaust gas from the cooling kiln to cool the materials as secondary air, the emission indicators of nitrogen oxides in the calcination tail gas cannot stably meet the DB50 / 659-2016 "Industrial Furnace Air Pollutant Emission Standards" after conversion. There is a problem of excessive nitrogen oxide emissions, and additional purification equipment is needed to improve the purification effect.

[0033] Energy consumption issues of calcining rotary kiln: The calcining rotary kiln is a major energy consumer in titanium dioxide production, accounting for approximately 20% of total energy consumption. Furthermore, the exhaust gas temperature at the kiln outlet is relatively high, at approximately 350-400°C. Currently, companies use direct spray cooling followed by alkaline desulfurization, which results in significant waste of heat and water resources. According to GB 32051-2015, "Energy Consumption Limits per Unit of Titanium Dioxide Product," the permitted energy consumption per unit of titanium dioxide product is ≤1100kgce / t, and the advanced energy consumption per unit of titanium dioxide product is ≤950kgce / t. Therefore, waste heat recovery is essential. However, heat utilization is low, and alkaline desulfurization consumes large amounts of alkaline reagents, increasing titanium dioxide production costs.

[0034] In addition, since the emission of harmful gases such as titanium dioxide dust, acid mist, and sulfur oxides generated during the calcination process aggravates environmental pollution and damage, the treatment of titanium dioxide calcination tail gas has become an important stage in the titanium dioxide manufacturing process. GB32051-2015 "Titanium Dioxide Unit Product Energy Consumption Limit" entry value requirements, with the development of the environmental protection industry, the pollution control of the chemical industry has become more and more stringent. Based on this, the implementation of energy conservation and NO x Ultra-low emission transformation is very necessary.

[0035] Analysis of processing efficiency of existing technologies: The exhaust gas from the calcining kiln first passes through a cyclone dust collector, where inertia and gravity settling remove most large dust particles. It then enters a Venturi scrubber, where it is cooled by water spray. Water droplets collide with dust particles and gas, cooling the gas. Some sulfur trioxide is absorbed by the water and converted into sulfuric acid mist. Dust, moistened by the water, condenses into large particles and flows into the circulation tank. A circulating pump then pumps the waste gas to a recirculation tank for recovery, cooling the exhaust gas. The gas exiting the Venturi tube enters an empty tower, where water spray further absorbs acidic gases. It then passes through a desulfurization tower for desulfurization before entering an electrostatic precipitator. Acid mist and a very small amount of dust are removed by a high-voltage electrostatic field. Finally, it is fed to an alkaline scrubber via fan 81, where sulfuric acid mist and particulate matter are further removed, completing the purification process.

[0036] The particulate matter in the exhaust gas during the existing technology treatment process is 25 mg / m 3 , sulfur dioxide 30 mg / m 3 , nitrogen oxides 270mg / m 3 .

[0037] 1.2 Innovative solutions of the present invention: like Figure 1 and Figure 2 As shown, this embodiment provides a titanium dioxide furnace calcination tail gas treatment device system and a tail gas recycling treatment method.

[0038] The device system includes a gravity settling device 1, a cyclone separation device 2, a metal filter bag dust collector 3, a medium-temperature SCR reactor 4, a venturi mixing heater 5, a cooling empty tower 6, a first alkali washing tower 7, a wet electric demisting tower 8 and a second alkali washing tower 9, which are connected in sequence; The gravity sedimentation device 1 is used to be connected to the tail of the titanium dioxide calcining kiln 100 to receive the titanium dioxide calcining tail gas; The venturi mixing heater 5 further includes a dilute sulfuric acid input port and a sulfuric acid tank, wherein the sulfuric acid tank is used to receive and precipitate the pre-concentrated sulfuric acid.

[0039] In some embodiments, the Venturi mixing heater 5 also includes a dilute sulfuric acid circulation system, which is a dilute sulfuric acid circulation pump; one end of the dilute sulfuric acid circulation pump is connected to the sulfuric acid tank, and the other end is connected to the dilute sulfuric acid inlet, which is used to return the pre-concentrated sulfuric acid in the sulfuric acid tank to the Venturi mixing heater 5 for further concentration.

[0040] In some embodiments, the cooling tower 6 is connected to a cold water cooling tower 61 .

[0041] In some embodiments, the second alkali washing tower 9 is connected to the wet electrostatic demisting tower 8 via a fan 81 .

[0042] Specific processing methods: The following steps are involved: The exhaust gas discharged from the titanium dioxide calcining kiln 100 is transported to the metal filter bag dust collector 3 for dust removal after gravity sedimentation and cyclone separation; The gas discharged from the metal bag filter 3 is transported to the medium-temperature SCR reactor 4 for denitrification treatment; The gas discharged from the medium-temperature SCR reactor 4 is transported to the venturi mixing heater 5, which is used to pre-concentrate the dilute sulfuric acid by utilizing the waste heat of the gas discharged from the medium-temperature SCR reactor 4; The gas discharged from the venturi mixing heater 5 is transported to the cooling empty tower 6 for cooling treatment; The gas discharged from the cooling empty tower 6 is transported to the first alkali washing tower 7 to further purify the SO2 and SO3 in the flue gas; The gas discharged from the first alkali washing tower 7 is transported to the wet electric demisting tower 8 to remove the mist droplets and fine particles in the gas.

[0043] The gas discharged from the wet electric mist removal tower 8 is transported to the second alkali washing tower 9 to further remove sulfides in the gas.

[0044] First, the exhaust gas undergoes pretreatment via gravity settling and cyclone separation to reduce its viscosity and prevent subsequent clogging of the metal bag filter 3. The exhaust gas is then transported to the metal bag filter 3 for dust removal, recycling the tiny titanium dioxide dust particles in the exhaust gas. It then passes through the medium-temperature SCR reactor 4, where a highly efficient and rapid catalytic reaction purifies and removes nitrogen oxides. By adjusting the amount of ammonia used in the SCR catalytic reaction, nitrogen oxide emissions can be met. Excess ammonia is further purified and removed when the exhaust gas enters the Venturi scrubber. The exhaust gas removed by the medium-temperature SCR is accelerated in the Venturi's constricting section. Upon reaching the Venturi throat, the flow rate is maximized and the pressure is minimized. Dilute sulfuric acid is drawn in using local negative pressure, and the liquid sulfuric acid is blown to the expanding section by the high-speed exhaust gas flow. The dilute sulfuric acid is fully dispersed into droplets, allowing the high-temperature flue gas and the dilute sulfuric acid droplets to fully contact, effectively exchanging heat. At the same time, when the gas-liquid mixture forms turbulence in the venturi expansion section, the dilute sulfuric acid droplets collide with the residual dust particles and high-temperature exhaust gas again to exchange heat, and the residual SO3 is also absorbed by the dilute sulfuric acid. The residual dust is also captured by the droplets, moistened and aggregated into large particles, and enters the reaction pool below the venturi to complete the recovery.

[0045] Furthermore, the exhaust gas temperature discharged from the titanium dioxide calcining kiln 100 is 340℃~400℃; the gas temperature discharged from the metal filter bag dust collector 3 is 310℃~350℃; the gas temperature discharged from the medium-temperature SCR reactor 4 is 290℃~310℃; the gas temperature discharged from the Venturi mixing heater 5 is 70℃~90℃.

[0046] This embodiment uses 316L stainless steel metal filter bags to improve the recovery of titanium dioxide particulate matter in exhaust gas, with a purification efficiency of 99.85%, meeting the requirements of particulate matter 10mg / m 3 emission requirements.

[0047] After treatment by the method of this embodiment, the particulate matter in the exhaust gas is ≤10 mg / Nm 3 , sulfur dioxide ≤ 10 mg / Nm 3 、Nitrogen oxides ≤100 mg / Nm 3 .

[0048] According to the initial concentration of nitrogen oxides 400mg / m 3 The long-term target emission value is 100mg / m 3 Therefore, the method of the present invention can well meet long-term emission targets without the need for additional large-scale purification equipment, and the waste heat of the tail gas is fully utilized, significantly reducing the production cost of titanium dioxide.

[0049] Therefore, the present invention adopts a Venturi mixing device and uses the dilute sulfuric acid produced in the titanium dioxide production process to recover the waste heat of the exhaust gas after denitrification, thereby concentrating the dilute sulfuric acid and recovering the waste heat. At the same time, the medium-temperature SCR is combined with the dilute sulfuric acid pre-concentration process to ensure that the emission of nitrogen oxides meets higher environmental protection requirements.

[0050] 1.3 Comparison of energy-saving benefits between this embodiment and the prior art: A graphite-lined Venturi tower is used to recover waste heat from the SCR reactor's flue gas outlet through spray cooling. The Venturi spray tower inlet temperature is 300°C, and the Venturi spray tower outlet flue gas temperature is set at 90°C. The dilute sulfuric acid concentration is 22%. This example uses the enthalpy drop of the flue gas generated in the calcination process as an estimate of the waste heat recovery heat. The natural gas energy consumption of a single calcination kiln per ton of product is approximately 215 Nm 3 / ton, the designed production capacity of a single production line is 6.7 tons, and the natural gas consumption per hour is 1440.5 Nm 3 / h, when the burner nozzle takes α=1.3, the calcining kiln flue gas volume Q=18565.6 Nm 3 / h, the flue gas density is 0.7kg / m 3 , secondary air volume Q=13500m 3 / h, secondary air temperature: 330℃.

[0051] The outlet temperature of the graphite venturi spray tower is 105℃, and the corresponding flue gas enthalpy is 977.29Kj / kg. Outlet flue gas enthalpy: 18565.6 Nm 3 / h×0.7kg / m 3×977.29Kj / kg×0.24Kj / Kcal=3048187.84Kcal / h.

[0052] The outlet temperature of the graphite venturi spray tower is 300℃, and the corresponding flue gas enthalpy is 3004.81Kj / kg. Inlet flue gas enthalpy: 18565.6 Nm 3 / h×0.7kg / m 3 ×3004.81Kcal / Nm 3 ×0.24Kj / Kcal=9372064.89Kcal / h.

[0053] Theoretically, the heat absorbed by dilute sulfuric acid spraying through a graphite venturi spray tower is: Q=9372064.89Kcal / h-3048187.84Kcal / h=6323877.05Kcal / h Taking into account the heat loss of the graphite venturi spray tower, sulfuric acid pool and pipeline, the actual heat absorbed by the dilute sulfuric acid spraying through the graphite venturi spray tower is calculated as 50%, which is: 6323877.05Kcal / h×0.5=3161938.53Kcal / h, Converted to gas, it is about 376.42 Nm 3 / h, gas price 3 yuan / Nm 3 , spraying dilute sulfuric acid through a graphite Venturi spray tower can save gas costs: 376.42 Nm 3 / h Nm 3 / h×3 yuan / Nm 3 =1129.3 yuan / h.

[0054] At the same time, the study found that changing the gas purification sequence of this embodiment and lacking a medium-temperature SCR made it difficult to reduce nitrogen oxide emissions to a lower standard.

[0055] 1.4 Conclusion The method for recycling exhaust gas from the calcination of titanium dioxide furnaces proposed in the present invention comprises subjecting the exhaust gas emitted from the furnace to gravity settling and cyclone separation, followed by dust removal through a metal bag filter 3 to remove and recover most of the dust, and denitrification treatment in a medium-temperature SCR reactor 4, after which the exhaust gas is transported to a venturi mixing heater 5. The medium-temperature SCR denitrification device and the venturi mixing heater 5 are used in coordination to purify and remove nitrogen oxides while recovering the waste heat from the calcination furnace exhaust, thereby achieving waste heat recovery and utilization. Experimental verification has shown that the use of the venturi mixing heater 5 can utilize the dilute sulfuric acid generated in the titanium dioxide production process to recover the waste heat from the denitrified exhaust gas, achieving the dual effects of dilute sulfuric acid concentration and waste heat recovery, thereby achieving the goal of energy conservation and emission reduction.

[0056] The method of the present invention pre-processes the tail gas discharged from the titanium dioxide calcining kiln 100 by gravity sedimentation and cyclone separation, which can reduce the cohesiveness of the tail gas to a certain extent and avoid the subsequent clogging of the metal filter bag dust collector 3. The metal filter bag dust collector 3 is then used for dust removal, which can effectively improve the recovery of particulate matter in the tail gas, with a purification efficiency of up to 99.85%, which can meet the requirements of particulate matter 10mg / m 3 The method of the present invention ensures that after exhaust gas purification, particulate matter and nitrogen oxides stably meet higher air environmental emission standards, reducing the investment demand for other air purification equipment, facilitating the upgrading of environmental protection technologies, and achieving greater environmental benefits.

[0057] 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 method for recycling tail gas from calcining titanium dioxide furnace, characterized in that: The following steps are involved: The exhaust gas from the titanium dioxide calcining kiln is transported to the metal filter bag dust collector for dust removal after gravity sedimentation and cyclone separation; The 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 transported to a venturi mixing heater, wherein the venturi mixing heater is used to concentrate the dilute sulfuric acid by utilizing the waste heat of the gas discharged from the medium-temperature SCR reactor; The gas discharged from the Venturi mixing heater is cooled, washed with alkali for desulfurization and then discharged.

2. The method for recycling tail gas from calcining titanium dioxide furnace according to claim 1, characterized in that: The treatment of cooling and alkaline washing and desulfurization of the gas discharged from the Venturi mixing heater specifically includes: The gas discharged from the Venturi mixing heater is transported to the cooling tower for cooling treatment; The gas discharged from the cooling empty tower is transported to the first alkali washing tower to further purify the SO2 and SO3 in the flue gas; The gas discharged from the first alkali washing tower is transported to the wet electric demisting tower to remove droplets and fine particles in the gas.

3. The method for recycling tail gas from calcining titanium dioxide furnace according to claim 2, characterized in that: Also includes, The gas discharged from the wet electric mist removal tower is transported to the second alkali washing tower to further remove sulfides in the gas.

4. The method for recycling tail gas from calcining titanium dioxide furnace according to claim 1, characterized in that: The exhaust gas temperature from the titanium dioxide calcining kiln is 340℃~400℃; the exhaust gas temperature from the metal filter bag dust collector is 310℃~350℃; the exhaust gas temperature from the medium-temperature SCR reactor is 290℃~310℃; the exhaust gas temperature from the Venturi mixing heater is 70℃~90℃.

5. The device system used in the method for recycling tail gas from calcining of titanium dioxide furnace according to any one of claims 1 to 4, characterized in that: It includes a gravity settling device, a cyclone separation device, a metal filter bag dust collector, a medium-temperature SCR reactor, a Venturi mixing heater and a deep purification system connected in sequence; The gravity sedimentation device is used to be connected to the tail of the titanium dioxide calcining kiln to receive the titanium dioxide calcining tail gas; The venturi mixing heater further comprises a dilute sulfuric acid inlet, a sulfuric acid tank and a dilute sulfuric acid circulation pump. The sulfuric acid tank is used to receive and precipitate the pre-concentrated sulfuric acid.

6. The device system according to claim 5, characterized in that: The dilute sulfuric acid circulation pump is used for circulating the dilute sulfuric acid of the Venturi mixing heater; one end of the dilute sulfuric acid circulation pump is connected to the sulfuric acid pool, and the other end is connected to the dilute sulfuric acid inlet of the Venturi, and is used to return the pre-concentrated sulfuric acid in the sulfuric acid pool to the Venturi mixing heater for further concentration.

7. The device system according to claim 5, characterized in that: The deep purification system includes a cooling empty tower, a first alkali washing tower and a wet electrostatic demisting tower connected in sequence; The cooling empty tower is connected to the exhaust port of the Venturi mixing heater; The cooling tower is connected to a water cooling tower.

8. The device system according to claim 7, characterized in that: The deep purification system also includes a second alkali washing tower, which is connected to the wet electrostatic demisting tower through a fan.

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