Method for preparing titanium dioxide by calcining metatitanic acid in double-section rotary kiln

Abstract

The invention discloses a method for preparing titanium dioxide by calcining metatitanic acid in a double-section rotary kiln. The method comprises the following steps: enabling metatitanic acid afterfilter pressing to successively perform dehydration in a first-section rotary kiln for calcining, and perform desulfuration, crystal type transform and grain growth in a second-section rotary kiln for calcining, to obtain a kiln falling product, and performing grinding and powder mixing on the kiln falling product, wherein a heat source of the second-section rotary kiln for calcining is from a high-temperature gas generated by calcining a natural gas, a heat source of the first-section rotary kiln for calcining is from a kiln tail gas generated by the calcining of the second-section rotary kiln, and the kiln tail gas generated by the calcining of the first-section rotary kiln successively passes through a dust collecting chamber and a bag dust collector for recovering kiln tail dust. Themethod is capable of improving the quality of the titanium dioxide, and improving a calcining recovery rate of the rotary kiln, wherein the recovery rate is up to 99.8%. The energy consumption of thenatural gas is reduced by 30-45%, and a usage amount of the natural gas is reduced.

Description

technical field [0001] The invention relates to the fields of titanium dioxide production and waste gas treatment, in particular to a method for preparing titanium dioxide by calcining metatitanic acid in a double-stage rotary kiln. Background technique [0002] At present, most domestic titanium dioxide factories adopt the sulfuric acid method for production, and calcination is one of the three most critical processes that determine the quality of titanium dioxide. In the prior art, a single-stage rotary kiln is used to complete the three process stages of drying (dehydration, desulfurization), crystal conversion, and particle growth of metatitanic acid and to process the calcination tail gas, and the following problems exist: 1. The process of calcining metatitanic acid in a single-stage rotary kiln It is a precise control system. The larger the amount of metatitanic acid feed at the kiln tail, the larger the volume of the kiln tail material, the smaller the exhaust space ...

AI Technical Summary

Problems solved by technology

In the prior art, a single-stage rotary kiln is used to complete the three process stages of drying (dehydration, desulfurization), crystal conversion, and particle growth of metatitanic acid and to process the calcination tail gas, and the following problems exist: 1. The process of calcining metatitanic acid in a single-stage rotary kiln It is a precise control system. The larger the amount of metatitanic acid feed at the kiln tail, the larger the volume of the kiln tail material, the smaller the exhaust space at the kiln tail, the greater the water vapor generated by dehydration, and the lower the temperature at the kiln tail. The worse the quality of titanium dioxide

In order to ensure the temperature of the kiln tail, the feeding amount of metatitanic acid at the kiln head is limited

2. The metatitanic acid material after pressing is highly viscous, so it can only be broken into larger pieces (particle size = 5-15cm) before it can be smoothly conveyed to the rotary kiln through the screw

Due to the inconsistent size of the materials entering the rotary kiln, the calcining effect in the rotary kiln is different, so the particle size of the calcined products falling into the kiln is quite different, and the final quality index of titanium dioxide fluctuates greatly.

3. Due to the uneven feeding, the weight and speed of the material moving in the kiln are inconsistent, and the heat exchange with the high-temperature gas is also uneven. The temperature of the kiln head medium always fluctuates with the rotation of the rotary kiln, and the temperature difference is as high as ten A few degrees Celsius, resulting in large fluctuations in product quality

4. The temperature of the kiln tail gas is as high as 350-450°C, and the heat of the kiln tail gas, which accounts for 45-55% of the heat supply in the calcination process, is wasted

This scheme adopts the principle of heat exchange, and can only recycle part of the heat of the exhaust gas of the rotary kiln, and its utilization rate is not high

In addition, during the calcination of metatitanic acid in the production of titanium dioxide, the temperature of the exhaust gas is high, the moisture content is high, there are acid mist and sulfur oxides, titanium dioxide dust, water vapor, non-condensable gas, etc., the performance of the heat exchanger used The requirements are relatively high, and the high-temperature acidic material must be resistant. At the same time, because the metatitanic acid calcination tail gas contains some titanium dioxide dust and water vapor, it is inevitable that local water vapor will be saturated and condensed water will stick to the titanium dioxide dust during the heat exchange process. Together, it is easy to block the pipes and cause the system to fail to operate

At the same time, the cleaning and maintenance work of the equipment is also more difficult.

[0006] In view of the current defects in the metatitanic acid calcination process and tail gas treatment, resulting in the inability to balance the calcination output and quality of the rotary kiln, a large waste of heat from the calcination tail gas, and the difficulty of tail gas treatment, etc., in the process of improving the metatitanic acid rotary kiln calcination process. The treatment of calcination tail gas is very necessary

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