CN108793244B - Method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination - Google Patents
Method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination Download PDFInfo
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Abstract
The invention discloses a method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination, which comprises the following steps: calcining the filter-pressed metatitanic acid in a first-stage rotary kiln in sequence for dehydration, calcining in a second-stage rotary kiln for desulfurization, crystal form conversion and grain growth to obtain a kiln falling product, grinding and mixing the kiln falling product to obtain titanium dioxide, wherein a heat source for calcining in the second-stage rotary kiln is high-temperature gas generated by calcining natural gas, a heat source for calcining in the first-stage rotary kiln is kiln tail gas generated by calcining in the second-stage rotary kiln, and the kiln tail gas generated by calcining in the first-stage rotary kiln is sequentially subjected to a dust collection chamber and a bag dust collector to recover kiln tail dust. The invention improves the quality of titanium dioxide, improves the calcination recovery rate of the rotary kiln, has the recovery rate up to 99.8 percent, reduces the energy consumption of natural gas by 30 to 45 percent, and saves the using amount of the natural gas.
Description
Technical Field
The invention relates to the field of titanium dioxide production and waste gas treatment, in particular to a method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination.
Background
At present, most of titanium dioxide factories in China adopt a sulfuric acid method for production, and calcination is one of three most key processes for determining the quality of titanium dioxide. In the prior art, a single-section rotary kiln is adopted to complete three process stages of drying (dehydration and desulfurization), crystal conversion and particle growth of metatitanic acid and treat calcination tail gas, and the following problems exist: 1. the single-section rotary kiln metatitanic acid calcining process is a fine control system, the larger the kiln tail metatitanic acid feeding amount is, the larger the kiln tail material volume is, the smaller the kiln tail exhaust space is, the larger the water vapor generated by dehydration is, the lower the kiln tail temperature is, and the poorer the quality of the calcined titanium dioxide is. In order to ensure the temperature of the kiln tail, the feeding amount of the metatitanic acid at the kiln head is limited. 2. The metatitanic acid material viscosity is big after the filter pressing, can only get bigger piece (particle size 5 ~ 15cm) with it breakage, just can pass through screw conveyor to the rotary kiln smoothly. Because the size of the materials entering the rotary kiln is different, the calcination effect in the rotary kiln is different, so the difference of the particle size of the calcined falling product is larger, and finally the quality index fluctuation of the titanium dioxide is larger. 3. Because the feeding is uneven, the weight and the speed of the material advancing in the kiln are inconsistent, and the heat exchange with high-temperature gas is also unbalanced, which shows that the temperature of a kiln head medium always fluctuates along with the rotation of the rotary kiln, the temperature difference is as high as more than ten ℃, and the fluctuation of the product quality is large. 4. The temperature of the kiln tail gas is as high as 350-450 ℃, and the heat of the kiln tail gas, which accounts for 45-55% of the heat supply in the calcining process, is wasted. Because the temperature of the tail gas of the kiln is too high, a cloth bag is not suitable for dust collection, a large amount of clear water and alkaline water can only be used for spraying, cooling, desulfurizing and capturing titanium dioxide dust in the tail gas, and because the return flow of the sprayed and recovered titanium dioxide can influence the product quality, the titanium dioxide can only be used for neutralizing waste water, the recovery rate is low.
The calcination of the metatitanic acid rotary kiln is subject to multiple limitations of product quality, tail gas treatment, fuel energy consumption and the like, so that the capacity of the rotary kiln is greatly limited. How to solve the contradiction between the rotary kiln yield and the product quality, tail gas treatment and fuel energy consumption, so that the rotary kiln yield is increased, the product quality is improved, the tail gas treatment effect is better, the fuel energy consumption is lower, the recovery rate is high, and the method becomes one of the important subjects in the fields of titanium dioxide production and waste gas treatment.
The Chinese patent with publication number CN103183380A discloses a feeding method and equipment of a titanium dioxide calcining rotary kiln. The method is that the metatitanic acid material entering a flash evaporation dryer contacts with high-temperature flue gas from tail gas of a rotary kiln, under the high-speed rotation action of a rotating blade at the bottom, the material is crushed, dispersed, dried, subjected to dispersed steaming and drying, and then the material with the water content of 10-15% enters the rotary kiln. According to the scheme, the barrel of the flash evaporation dryer is subjected to anti-corrosion treatment by lining carbon steel with rubber and then lining two layers of corundum-mullite refractory bricks. The material of the used rotating blade is hastelloy. The tail gas of the rotary kiln in the scheme contains SO3、SO2And the like, so that the safety standards of corrosion prevention, leakage prevention and the like for equipment systems in large-scale production are high, the requirements on the material of the equipment are strict, and the maintenance requirements on the equipment are also high. In addition, the flash evaporation dryer reduces the water content of the metatitanic acid material to 10-15% in a short time, the temperature of the tail gas of the rotary kiln is as high as 350-450 ℃, and the temperature exceeds the temperature of the bound water which is separated from the metatitanic acid, so that not only free water but also part of the bound water are removed in the actual production, and the dehydrated metatitanic acid is easy to harden into blocks. Then the titanium white powder is crushed and dispersed by high-speed rotating blades, and the generated smaller-caking-shaped metatitanic acid enters a rotary kiln, so that the titanium white powder is easy to sinter and harden.
The chinese patent publication No. CN104567443B discloses a method for recycling heat of tail gas from a rotary calcining kiln. The device comprises a calcining rotary kiln, a cold air pipe, a fan and a heat exchanger; the rotary calcining kiln is provided with a tail gas outlet and a gas inlet; through the tail gas heat recovery device of the rotary calcining kiln, heat in tail gas of the rotary calcining kiln is heated through the heat exchanger, and the gravity type heat pipe is heated; then the cold air entering the calcining rotary kiln is heated through a gravity type heat pipe; therefore, the heat in the tail gas of the rotary calcining kiln can be recycled, and the effects of energy conservation and emission reduction are achieved. The scheme adopts a heat exchange principle, can only recycle partial heat of the tail gas of the rotary kiln, and has low utilization rate. In addition, the temperature of the waste gas is high, the moisture content is large, acid mist, sulfur oxide, titanium dioxide dust, water vapor, non-condensable gas and the like exist during the calcination of metatitanic acid in the production of titanium dioxide, the performance requirement of the material of the used heat exchanger is high, high-temperature acid resistant materials are needed, and meanwhile, the metatitanic acid calcination tail gas contains part of titanium dioxide dust and water vapor, so that the phenomenon that condensed water is generated due to the local water vapor saturation is hardly avoided in the heat exchange process, the condensed water is adhered to the titanium dioxide dust, the pipeline is easily blocked, and the system cannot operate is caused. Meanwhile, the cleaning and maintenance work of the equipment is also difficult.
In view of the problems that the calcination yield and quality of the rotary kiln cannot be considered at the same time, the heat of the calcination tail gas is greatly wasted, the tail gas treatment difficulty is high and the like due to the defects of the existing metatitanic acid calcination process and the tail gas treatment, the treatment of the calcination tail gas is necessary in the improvement of the metatitanic acid rotary kiln calcination process flow.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
The invention also aims to provide a method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination, which improves the quality of titanium dioxide, improves the rotary kiln calcination recovery rate, achieves the recovery rate as high as 99.8%, reduces the natural gas energy consumption by 30-45%, and saves the consumption of natural gas.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing titanium dioxide by dual stage rotary kiln calcination of metatitanic acid, comprising the steps of: calcining the filter-pressed metatitanic acid in a first-stage rotary kiln in sequence for dehydration, calcining in a second-stage rotary kiln for desulfurization, crystal form conversion and grain growth to obtain a kiln falling product, grinding and mixing the kiln falling product to obtain titanium dioxide, wherein a heat source for calcining in the second-stage rotary kiln is high-temperature gas generated by calcining natural gas, a heat source for calcining in the first-stage rotary kiln is kiln tail gas generated by calcining in the second-stage rotary kiln, and the kiln tail gas generated by calcining in the first-stage rotary kiln is sequentially subjected to a dust collection chamber and a bag dust collector to recover kiln tail dust.
Preferably, the filter pressing is carried out by adopting a diaphragm filter press, the feeding pressure is controlled to be 0.8-1.0 mpa, and the pressing pressure is controlled to be 1.2-1.4 mpa.
Preferably, the water content of the metatitanic acid after filter pressing is 45-55%, the water content of the metatitanic acid after the calcination and dehydration in a first-stage rotary kiln is 0, and the particle size is less than or equal to 1 cm.
Preferably, the temperature of kiln tail gas generated by the calcination of the first-stage rotary kiln is controlled to be 130-180 ℃, and the temperature of kiln tail gas generated by the calcination of the second-stage rotary kiln is controlled to be 350-450 ℃.
Preferably, the heat source for the secondary rotary kiln calcination is natural gas.
Preferably, the materials are evenly fed by a belt electronic scale before the calcination and desulfurization of the second-stage rotary kiln, and the feeding amount range of the belt electronic scale is within +/-0.3 t/h.
Preferably, the kiln head medium temperature of the second-stage rotary kiln is 800-950 ℃, and the fluctuation range of the kiln head medium temperature is within +/-3 ℃.
Preferably, kiln tail gas generated by calcination in the first-stage rotary kiln is discharged after being sequentially subjected to clean water spraying, alkaline water spraying and electric defogging treatment after kiln tail dust is recycled by the dust collection chamber and the cloth bag dust collector.
Preferably, the calcination recovery rate of the double-stage rotary kiln is more than or equal to 99.8 percent.
Preferably, the L value of the prepared titanium dioxide is more than or equal to 98.4, the decoloring force is more than or equal to 103%, and the dispersity is more than or equal to 80%.
The invention at least comprises the following beneficial effects:
according to the invention, through the arrangement of the double-section rotary kiln, the temperature of the metatitanic acid during dehydration is effectively controlled, so that the metatitanic acid is uniformly dehydrated, high-temperature caking is avoided, the dehydrated metatitanic acid has uniform granularity and uniform dehydration degree, and accurate feeding of a belt electronic scale is facilitated; meanwhile, the temperature of the kiln head and the kiln tail of the first-stage rotary kiln and the second-stage rotary kiln is effectively controlled, compared with a single-stage rotary kiln process in the prior art, the feeding amount of the partial taijic acid is increased, the feeding amount of the partial taijic acid is 1.65-2.25 times that of the prior art, part of titanium dioxide dust carried in the kiln tail gas of the first-stage rotary kiln is effectively recovered, the calcination recovery rate of the rotary kiln is improved, and the recovery rate is as high as 99.8%. The whiteness, namely the L value, of the titanium dioxide prepared by the method is more than or equal to 98.4, the decolorization force is more than or equal to 103%, and the dispersibility is more than or equal to 80%.
According to the invention, kiln tail gas generated by calcining the two-section rotary kiln is used as a heat source for calcining the one-section rotary kiln, compared with the prior art that natural gas is used as the heat source in the whole process of the single-section rotary kiln, the energy consumption of the natural gas is reduced by 30-45%, the using amount of the natural gas is saved, the kiln tail gas generated by calcining the two-section rotary kiln is fully utilized, and the green sustainable development concept is met.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
Detailed Description
The present invention is further described in detail below with reference to the drawings and examples so that those skilled in the art can practice the invention with reference to the description.
As shown in figure 1, the invention provides a method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination, which comprises the following steps: calcining the filter-pressed metatitanic acid in a first-stage rotary kiln in sequence for dehydration, calcining in a second-stage rotary kiln for desulfurization, crystal form conversion and grain growth to obtain a kiln falling product, grinding and mixing the kiln falling product to obtain titanium dioxide, wherein a heat source for calcining in the second-stage rotary kiln is high-temperature gas generated by calcining natural gas, a heat source for calcining in the first-stage rotary kiln is kiln tail gas generated by calcining in the second-stage rotary kiln, and the kiln tail gas generated by calcining in the first-stage rotary kiln is sequentially subjected to a dust collection chamber and a bag dust collector to recover kiln tail dust.
< example 1>
A method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination specifically comprises the following steps:
(1) and (3) metatitanic acid press filtration: and (3) carrying out pressure filtration on the metatitanic acid subjected to salt treatment by using a diaphragm filter press, wherein the feeding pressure is 0.83mpa, the pressing pressure is 1.20mpa, the pressure is maintained for 10 minutes, and the water content of the metatitanic acid subjected to pressure filtration is 53%.
(2) Calcining in a first-stage rotary kiln: crushing the filter-pressed metatitanic acid by a crusher, feeding the crushed metatitanic acid into a first-stage rotary kiln through a feeding screw to calcine and dehydrate, wherein a heat source for calcining the first-stage rotary kiln is kiln tail gas generated by calcining a second-stage rotary kiln, the kiln head temperature of the first-stage rotary kiln is 360 ℃, and the kiln tail temperature is 140 ℃. The length of a section of rotary kiln was 28m and the diameter was 2.6 m. The feeding amount (calculated by titanium dioxide) of metatitanic acid in the first-stage rotary kiln is 4.7t/h, which is 1.68 times of the feeding amount (2.8 t/h) of a single-stage rotary kiln (with the diameter of 2.8m and the length of 55m) in the prior art, the water content of the metatitanic acid after dehydration is 0, and the particle size is less than or equal to 1 cm.
(3) And (3) calcining in a second-stage rotary kiln: storing the dehydrated metatitanic acid in a storage bin, conveying the metatitanic acid to a feeding bin of a second-stage rotary kiln by a screw, then uniformly feeding the metatitanic acid into the second-stage rotary kiln by a belt electronic scale, wherein the feeding amount (calculated by titanium dioxide) is 4.7 +/-0.2 t/h, and feeding the metatitanic acid into the second-stage rotary kiln by a feeding screw to perform calcination desulfurization, crystal transformation and grain growth to generate a kiln falling product. The length of the second stage rotary kiln is 55m, and the diameter is 2.8 m. The heat source for the two-stage rotary kiln is natural gas, and CO is generated during the combustion of the natural gas2High-temperature gas such as water vapor and the like carries a large amount of heat to flow in the second-stage rotary kiln, and the high-temperature gas is called kiln head medium, and the temperature of the kiln head medium is controlled to be 850 +/-2 ℃. The unit consumption of natural gas is 155m3T, compared with the prior art that when a single-section rotary kiln is used for calcination (the unit consumption of natural gas is 230 m)3The drop in/t) was 32.6%.
(4) Grinding, mixing powder and packaging: and cooling the product falling into the kiln, grinding by a Raymond mill, mixing powder and packaging to obtain the titanium dioxide, wherein the L value of the titanium dioxide is 98.6, the decoloring force is 105 percent and the dispersibility is 84 percent.
The combustion tail gas treatment in the process of preparing the titanium dioxide comprises the following steps: kiln tail gas generated by calcining the first section of rotary kiln sequentially passes through a dust collecting chamber and a cloth bag dust collector to recover kiln tail dustThe recovery rate of calcination in a double-section rotary kiln (a first-section rotary kiln and a second-section rotary kiln) is 99.8 percent, the temperature of tail gas after dust collection by a cloth bag is reduced to 120 ℃, the tail gas is sprayed by clean water for the first time, the temperature is reduced to 42 ℃, and then is sprayed by alkaline water for the second time, and the tail gas is electrically demisted and discharged after reaching the standard. The tail gas emission standard of the rotary kiln is as follows: SO (SO)2≤550mg/m3(ii) a Sulfuric acid mist is less than or equal to 45mg/m3(ii) a Dust is less than or equal to 200mg/m3。
< example 2>
A method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination specifically comprises the following steps:
(1) and (3) metatitanic acid press filtration: and (3) carrying out pressure filtration on the metatitanic acid subjected to salt treatment by using a diaphragm filter press, wherein the feeding pressure is 0.83mpa, the pressing pressure is 1.23mpa, the pressure is maintained for 10 minutes, and the water content of the metatitanic acid subjected to pressure filtration is 52%.
(2) Calcining in a first-stage rotary kiln: crushing the filter-pressed metatitanic acid by a crusher, feeding the crushed metatitanic acid into a first-stage rotary kiln through a feeding screw to calcine and dehydrate, wherein a heat source for calcining the first-stage rotary kiln is kiln tail gas generated by calcining a second-stage rotary kiln, the kiln head temperature of the first-stage rotary kiln is 380 ℃, and the kiln tail temperature of the first-stage rotary kiln is 150 ℃. The length of a section of rotary kiln was 28m and the diameter was 2.6 m. The feeding amount (calculated by titanium dioxide) of metatitanic acid in the first-stage rotary kiln is 5.1t/h, which is 1.82 times of the feeding amount (2.8 t/h) of a single-stage rotary kiln (with the diameter of 2.8m and the length of 55m) in the prior art, the water content of the metatitanic acid after dehydration is 0, and the particle size is less than or equal to 1 cm.
(3) And (3) calcining in a second-stage rotary kiln: storing the dehydrated metatitanic acid in a storage bin, conveying the metatitanic acid to a feeding bin of a second-stage rotary kiln by a screw, then uniformly feeding the metatitanic acid into the second-stage rotary kiln by a belt electronic scale, wherein the feeding amount (calculated by titanium dioxide) is 5.1 +/-0.2 t/h, and feeding the metatitanic acid into the second-stage rotary kiln by a feeding screw to perform calcination desulfurization, crystal transformation and grain growth to generate a kiln falling product. The length of the second stage rotary kiln is 55m, and the diameter is 2.8 m. The heat source for the two-stage rotary kiln is natural gas, and CO is generated during the combustion of the natural gas2High-temperature gas such as water vapor and the like carries a large amount of heat to flow in the two-section rotary kiln, and the high-temperature gas is called kiln head medium, and the temperature of the kiln head medium is controlled to be 870 +/-2 ℃. The unit consumption of natural gas is 150m3T, compared with the single-stage return in the prior artWhen the kiln is used for calcination (the unit consumption of natural gas is 230 m)3The/t) decreased by 34.8%.
(4) Grinding, mixing powder and packaging: and cooling the kiln falling product, grinding by a Raymond mill, mixing powder and packaging to obtain the titanium dioxide, wherein the L value of the titanium dioxide is 98.5, the decoloring force is 104 percent and the dispersibility is 83 percent.
The combustion tail gas treatment in the process of preparing the titanium dioxide comprises the following steps: kiln tail gas generated by calcination of the first-stage rotary kiln sequentially passes through the dust collecting chamber and the cloth bag dust collector to recover kiln tail dust, the recovery rate of calcination of the double-stage rotary kiln (the first-stage rotary kiln and the second-stage rotary kiln) is 99.8%, the temperature of tail gas after dust collection of the cloth bag is reduced to 140 ℃, the tail gas is sprayed by clean water for the first time, the temperature is reduced to 44 ℃, and the tail gas is sprayed by alkaline water for the second time, electrically demisted and discharged after reaching the standard. The tail gas emission standard of the rotary kiln is as follows: SO (SO)2≤550mg/m3(ii) a Sulfuric acid mist is less than or equal to 45mg/m3(ii) a Dust is less than or equal to 200mg/m3。
< example 3>
A method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination specifically comprises the following steps:
(1) and (3) metatitanic acid press filtration: and (3) carrying out pressure filtration on the metatitanic acid subjected to salt treatment by using a diaphragm filter press, wherein the feeding pressure is 0.88mpa, the pressing pressure is 1.25mpa, the pressure is maintained for 10 minutes, and the water content of the metatitanic acid subjected to pressure filtration is 50%.
(2) Calcining in a first-stage rotary kiln: crushing the filter-pressed metatitanic acid by a crusher, feeding the crushed metatitanic acid into a first-stage rotary kiln through a feeding screw to calcine and dehydrate, wherein a heat source for calcining the first-stage rotary kiln is from kiln tail gas generated by calcining a second-stage rotary kiln, the kiln head temperature of the first-stage rotary kiln is 400 ℃, and the kiln tail temperature is 160 ℃. The length of a section of rotary kiln was 28m and the diameter was 2.6 m. The feeding amount (calculated by titanium dioxide) of metatitanic acid in the first-stage rotary kiln is 5.5t/h, which is 1.96 times of the feeding amount (2.8 t/h) of a single-stage rotary kiln (with the diameter of 2.8m and the length of 55m) in the prior art, the water content of the metatitanic acid after dehydration is 0, and the particle size is less than or equal to 1 cm.
(3) And (3) calcining in a second-stage rotary kiln: storing the dehydrated metatitanic acid in a storage bin, conveying the metatitanic acid to a feeding bin of a second-stage rotary kiln through a screw, and then uniformly feeding the metatitanic acid into the second-stage rotary kiln through a belt electronic scale with the feeding amount (calculated by titanium dioxide)) 5.5 +/-0.2 t/h, and then enters a two-section rotary kiln through a feeding screw to be calcined, desulfurized, subjected to crystal form conversion and subjected to grain growth to generate a kiln falling product. The length of the second stage rotary kiln is 55m, and the diameter is 2.8 m. The heat source for the two-stage rotary kiln is natural gas, and CO is generated during the combustion of the natural gas2High-temperature gas such as water vapor and the like carries a large amount of heat to flow in the second-stage rotary kiln, and the high-temperature gas is called kiln head medium, and the temperature of the kiln head medium is controlled to be 890 +/-2 ℃. The unit consumption of natural gas is 145m3T, compared with the prior art that when a single-section rotary kiln is used for calcination (the unit consumption of natural gas is 230 m)3The drop in/t) was 37%.
(4) Grinding, mixing powder and packaging: and cooling the kiln falling product, grinding by a Raymond mill, mixing powder and packaging to obtain the titanium dioxide, wherein the L value of the titanium dioxide is 98.5, the decoloring force is 104 percent and the dispersibility is 82 percent.
The combustion tail gas treatment in the process of preparing the titanium dioxide comprises the following steps: kiln tail gas generated by calcination of the first-stage rotary kiln sequentially passes through the dust collecting chamber and the cloth bag dust collector to recover kiln tail dust, the recovery rate of calcination of the double-stage rotary kiln (the first-stage rotary kiln and the second-stage rotary kiln) is 99.8%, the temperature of tail gas after dust collection of the cloth bag is reduced to 150 ℃, the tail gas is sprayed by clean water for the first time, the temperature is reduced to 46 ℃, and the tail gas is sprayed by secondary alkaline water, electrically demisted and discharged after reaching the standard. The tail gas emission standard of the rotary kiln is as follows: SO (SO)2≤550mg/m3(ii) a Sulfuric acid mist is less than or equal to 45mg/m3(ii) a Dust is less than or equal to 200mg/m3。
< example 4>
A method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination specifically comprises the following steps:
(1) and (3) metatitanic acid press filtration: and (3) carrying out pressure filtration on the metatitanic acid subjected to salt treatment by using a diaphragm filter press, wherein the feeding pressure is 0.9mpa, the pressing pressure is 1.30mpa, the pressure is maintained for 10 minutes, and the water content of the metatitanic acid subjected to pressure filtration is 48%.
(2) Calcining in a first-stage rotary kiln: crushing the filter-pressed metatitanic acid by a crusher, feeding the crushed metatitanic acid into a first-stage rotary kiln through a feeding screw to calcine and dehydrate, wherein a heat source for the first-stage rotary kiln is from kiln tail gas generated by the second-stage rotary kiln, the kiln head temperature of the first-stage rotary kiln is 420 ℃, and the kiln tail temperature is 170 ℃. The length of a section of rotary kiln was 28m and the diameter was 2.6 m. The feeding amount (calculated by titanium dioxide) of metatitanic acid in the first-stage rotary kiln is 6.0t/h, which is 2.14 times of the feeding amount (2.8 t/h) of a single-stage rotary kiln (with the diameter of 2.8m and the length of 55m) in the prior art, the water content of the metatitanic acid after dehydration is 0, and the particle size is less than or equal to 1 cm.
(3) And (3) calcining in a second-stage rotary kiln: storing the dehydrated metatitanic acid in a storage bin, conveying the metatitanic acid to a feeding bin of a second-stage rotary kiln by a screw, then uniformly feeding the metatitanic acid into the second-stage rotary kiln by a belt electronic scale, wherein the feeding amount (calculated by titanium dioxide) is 6.0 +/-0.3 t/h, and feeding the metatitanic acid into the second-stage rotary kiln by a feeding screw to perform calcination desulfurization, crystal transformation and grain growth to generate a kiln falling product. The length of the second stage rotary kiln is 55m, and the diameter is 2.8 m. The heat source for the two-stage rotary kiln is natural gas, and CO is generated during the combustion of the natural gas2High-temperature gas such as water vapor and the like carries a large amount of heat to flow in the second-stage rotary kiln, and the high-temperature gas is called kiln head medium, and the temperature of the kiln head medium is controlled to be 910 +/-3 ℃. The unit consumption of natural gas is 140m3T, compared with the prior art that when a single-section rotary kiln is used for calcination (the unit consumption of natural gas is 230 m)3The reduction in/t) was 39.1%.
(4) Grinding, mixing powder and packaging: and cooling the product falling into the kiln, grinding by a Raymond mill, mixing powder and packaging to obtain the titanium dioxide, wherein the L value of the titanium dioxide is 98.4, the decoloring force is 103 percent and the dispersibility is 81 percent.
The combustion tail gas treatment in the process of preparing the titanium dioxide comprises the following steps: kiln tail gas generated by calcination of the first-stage rotary kiln sequentially passes through the dust collecting chamber and the cloth bag dust collector to recover kiln tail dust, the recovery rate of calcination of the double-stage rotary kiln (the first-stage rotary kiln and the second-stage rotary kiln) is 99.8%, the temperature of tail gas after dust collection of the cloth bag is reduced to 160 ℃, the tail gas is sprayed by clean water for the first time, the temperature is reduced to 48 ℃, and the tail gas is sprayed by secondary alkaline water, electrically demisted and discharged after reaching the standard. The tail gas emission standard of the rotary kiln is as follows: SO (SO)2≤550mg/m3(ii) a Sulfuric acid mist is less than or equal to 45mg/m3(ii) a Dust is less than or equal to 200mg/m3。
< example 5>
A method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination specifically comprises the following steps:
(1) and (3) metatitanic acid press filtration: and (3) carrying out pressure filtration on the metatitanic acid subjected to salt treatment by using a diaphragm filter press, wherein the feeding pressure is 0.92mpa, the pressing pressure is 1.35mpa, the pressure is maintained for 10 minutes, and the water content of the metatitanic acid subjected to pressure filtration is 46%.
(2) Calcining in a first-stage rotary kiln: crushing the filter-pressed metatitanic acid by a crusher, feeding the crushed metatitanic acid into a first-stage rotary kiln through a feeding screw for calcination and dehydration, wherein a heat source for calcination in the first-stage rotary kiln is kiln tail gas generated by calcination in a second-stage rotary kiln, the kiln head temperature of the first-stage rotary kiln is 440 ℃, and the kiln tail temperature is 180 ℃. The length of a section of rotary kiln was 28m and the diameter was 2.6 m. The feeding amount (calculated by titanium dioxide) of metatitanic acid in the first-stage rotary kiln is 6.3t/h, which is 2.25 times of the feeding amount (2.8 t/h) of a single-stage rotary kiln (with the diameter of 2.8m and the length of 55m) in the prior art, the water content of the metatitanic acid after dehydration is 0, and the particle size is less than or equal to 1 cm.
(3) And (3) calcining in a second-stage rotary kiln: storing the dehydrated metatitanic acid in a storage bin, conveying the metatitanic acid to a feeding bin of a second-stage rotary kiln by a screw, then uniformly feeding the metatitanic acid into the second-stage rotary kiln by a belt electronic scale, wherein the feeding amount (calculated by titanium dioxide) is 6.3 +/-0.3 t/h, and feeding the metatitanic acid into the second-stage rotary kiln by a feeding screw to perform calcination desulfurization, crystal transformation and grain growth to generate a kiln falling product. The length of the second stage rotary kiln is 55m, and the diameter is 2.8 m. The heat source for the two-stage rotary kiln is natural gas, and CO is generated during the combustion of the natural gas2High-temperature gas such as water vapor and the like carries a large amount of heat to flow in the second-stage rotary kiln, and the high-temperature gas is called kiln head medium, and the temperature of the kiln head medium is controlled to be 930 +/-3 ℃. The unit consumption of natural gas is 135m3T, compared with the prior art that when a single-section rotary kiln is used for calcination (the unit consumption of natural gas is 230 m)3The/t) decreased by 41.3%.
(4) Grinding, mixing powder and packaging: and cooling the kiln falling product, grinding by a Raymond mill, mixing powder and packaging to obtain the titanium dioxide, wherein the L value of the titanium dioxide is 98.5, the decoloring force is 103 percent and the dispersibility is 82 percent.
The combustion tail gas treatment in the process of preparing the titanium dioxide comprises the following steps: kiln tail gas generated by calcination in the first-stage rotary kiln sequentially passes through a dust collecting chamber and a cloth bag dust collector to recover kiln tail dust, the recovery rate of calcination in the double-stage rotary kiln (the first-stage rotary kiln and the second-stage rotary kiln) is 99.8%, the temperature of tail gas after dust collection in a cloth bag is reduced to 170 ℃, the tail gas is sprayed with clean water once again, the temperature is reduced to 50 ℃, and the tail gas is subjected to secondary alkaline waterSpraying, electrically demisting, and discharging after reaching standards. The tail gas emission standard of the rotary kiln is as follows: SO (SO)2≤550mg/m3(ii) a Sulfuric acid mist is less than or equal to 45mg/m3(ii) a Dust is less than or equal to 200mg/m3。
While embodiments of the invention have been disclosed above, it is not limited to the applications listed in the description and the embodiments, which are fully applicable in all kinds of fields of application of the invention, and further modifications may readily be effected by those skilled in the art, so that the invention is not limited to the specific details without departing from the general concept defined by the claims and the scope of equivalents.
Claims (7)
1. The method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination is characterized by comprising the following steps: calcining the filtered metatitanic acid in a first-stage rotary kiln in sequence for dehydration, calcining in a second-stage rotary kiln for desulfurization, crystal form conversion and grain growth to obtain a kiln falling product, and grinding and mixing the kiln falling product to obtain titanium dioxide, wherein the heat source for calcining in the second-stage rotary kiln is high-temperature gas generated by calcining natural gas, the heat source for calcining in the first-stage rotary kiln is kiln tail gas generated by calcining in the second-stage rotary kiln, and the kiln tail gas generated by calcining in the first-stage rotary kiln is sequentially subjected to a dust collection chamber and a bag dust collector to recover kiln tail dust;
the temperature of kiln tail gas generated by calcining in the first-stage rotary kiln is controlled to be 130-180 ℃, and the temperature of kiln tail gas generated by calcining in the second-stage rotary kiln is controlled to be 350-450 ℃;
the kiln head medium temperature of the two-section rotary kiln is 800-950 ℃, and the fluctuation range of the kiln head medium temperature is within +/-3 ℃.
2. The method for preparing titanium dioxide through metatitanic acid double-section rotary kiln calcination as claimed in claim 1, wherein the pressure filtration is performed by using a diaphragm filter press, the feeding pressure is controlled to be 0.8-1.0 MPa, and the pressing pressure is controlled to be 1.2-1.4 MPa.
3. The method for preparing titanium dioxide through double-section rotary kiln calcination of metatitanic acid according to claim 1, wherein the water content of metatitanic acid after filter pressing is 45-55%, the water content of metatitanic acid after first-section rotary kiln calcination and dehydration is 0, and the particle size is less than or equal to 1 cm.
4. The method for preparing titanium dioxide through calcination in a metatitanic acid double-section rotary kiln as claimed in claim 1, wherein the materials are fed in a balanced manner by a belt electronic scale before calcination and desulfurization in the double-section rotary kiln, and the fluctuation range of the feeding amount of the belt electronic scale is within +/-0.3 t/h.
5. The method for preparing titanium dioxide through metatitanic acid double-section rotary kiln calcination as claimed in claim 1, wherein kiln tail gas generated by the first-section rotary kiln calcination is discharged after sequentially passing through a dust collection chamber and a cloth bag dust collector to recover kiln tail dust, and sequentially passing through clear water spraying, alkaline water spraying and electric defogging treatment.
6. The method for preparing titanium dioxide by metatitanic acid double-section rotary kiln calcination as claimed in claim 1, wherein the calcination recovery rate of the double-section rotary kiln is not less than 99.8%.
7. The method for preparing titanium dioxide through metatitanic acid double-section rotary kiln calcination as claimed in claim 1, wherein the L value of the prepared titanium dioxide is not less than 98.4, the decoloring capacity is not less than 103%, and the dispersibility is not less than 80%.
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