阅读说明：本技术 一种阻止硫酸法钛白废酸多效浓缩一效结垢的方法 (Method for preventing multi-effect concentration and one-effect scaling of titanium dioxide waste acid produced by sulfuric acid process ) 是由 潘向雷 宋代磊 杨颖辉 吕小军 高鬲 李达 徐梦 于 2019-09-06 设计创作，主要内容包括：本发明公开了一种阻止硫酸法钛白废酸多效浓缩一效结垢的方法,将钛白生产车间产生的20~30%(包括转窑尾气预浓缩)的废酸,无需预处理直接进入预热器、一效加热器加热后在103~106℃,真空度为48~52KPa,将浓缩后成品酸或二效溢流进熟化槽的浓酸,依据进一效浓缩酸量比例加注到一效浓缩系统,酸含量稳定在38%以上的条件下达到动态平衡,废酸中FeSO4.7H<Sub>2</Sub>O、CaSO4.2H<Sub>2</Sub>O瞬间脱水；随溶解度降低Fe、Ca等离子硫酸盐的溶出物,可视为自生晶种结合同相盐类,生成固相沉淀物,避免Fe、Ca等离子溶出硫酸盐,着床于温度梯度的低端和高端界面,形成以硫酸钙为主的层垢和Fe盐的桥堵。(The invention discloses a method for preventing multi-effect concentration and one-effect scaling of titanium white waste acid produced in a titanium white production workshop by a sulfuric acid process, which comprises the steps of directly feeding 20 ~ 30% (including rotary kiln tail gas preconcentration) waste acid generated in a titanium white production workshop into a preheater and a one-effect heater without pretreatment, heating the waste acid, and then leading the waste acid to enter a ageing tank at 103 ~ 106 ℃ and under the vacuum degree of 48 ~ 52KPa, adding concentrated finished acid or secondary effect overflow into a one-effect concentration system according to the amount proportion of the primary effect concentrated acid, achieving dynamic balance under the condition that the acid content is stabilized to be more than 38%, instantly dehydrating FeSO4.7H 2 O and CaSO4.2H 2 O in the waste acid, reducing dissolved matters of Fe, Ca and other ionic sulfates along with the solubility, and considering that autogenous crystal seeds are combined with same-phase salts to generate solid-phase precipitates, avoiding the Fe, Ca and other ionic dissolved sulfates from depositing on the low-end and high-end interfaces of a temperature gradient, and forming layer scale mainly taking calcium sulfate and bridge blocking of Fe salt.)

1. A method for preventing multi-effect concentration and one-effect scaling of titanium dioxide waste acid produced by a sulfuric acid process is characterized by comprising the following steps:

(1) directly introducing titanium white waste acid with the concentration of 20 ~ 30% into a first-effect concentration system, adding concentrated sulfuric acid to keep the acid concentration in the first-effect concentration system at 38 ~ 42%, wherein the temperature of the first-effect concentration system is 103 ~ 106 ℃, the vacuum degree is 48 ~ 52kpa, and the first-effect concentration overflows into a second-effect concentration system after being in stable boiling;

(2) The double-effect concentration system is kept at the vacuum degree of 88 ~ 92kpa, the temperature is 76 ~ 78 ℃, the concentration of concentrated sulfuric acid is 53 ~ 55%, the concentrated sulfuric acid enters a slaking tank for cooling and crystallization, solid-liquid separation is carried out to remove impurities, and the concentrated finished acid can be continuously concentrated or recycled.

2. The method as claimed in claim 1, wherein the ratio of iron to titanium in the titanium liquor in the titanium white production process is 0.26 ~ 0.42.42.

3. The method according to claim 1, characterized in that the titanium dioxide spent acid has a concentration of 22-25%.

4. The method as claimed in claim 1, wherein the concentrated finished acid is added to the primary concentration system or the sulfuric acid is obtained by using secondary concentration overflow without separation from the viewpoint of energy saving.

5. The method of claim 1, wherein the concentration of sulfuric acid in the single effect concentration system is 38%, the temperature is 103 ℃, and the vacuum is 48 kpa.

6. The method of claim 1, wherein the temperature of the double effect concentration system is 76.5 ℃ and the vacuum degree is 88 kpa.

Technical Field

The invention relates to the technical field of waste acid treatment in titanium dioxide production by a sulfuric acid method, in particular to a method for preventing multiple-effect concentration and one-effect scaling of titanium dioxide waste acid by the sulfuric acid method.

Background

Titanium dioxide is widely applied to various industries and has large demand. At present, the titanium dioxide is mainly produced by a sulfuric acid method, a chlorination method and a hydrochloric acid method, 90% of titanium dioxide in China is produced by the sulfuric acid method, waste acid is generated in the production process of the titanium dioxide, 6-7 tons of waste acid is discharged when 1 ton of titanium dioxide is produced, the waste acid contains about 20% of salts such as sulfuric acid, ferrous sulfate, calcium sulfate and the like, insoluble titanium dioxide, soluble titanium and the like, a large amount of impurities limit the long-period stable operation of the titanium dioxide waste acid concentration process, and a recovery concentration device is complex in treatment process and high in difficulty. The treatment of waste acid is related to the yield of titanium dioxide sulfuric acid consumption, so that the economic benefit is influenced, and simultaneously, a large amount of titanium gypsum generated by neutralizing the waste acid is related to the environmental protection problem, so that the survival and development of the titanium dioxide industry of the sulfuric acid process are influenced.

The main treatment method for treating waste acid at present comprises the following steps: (1) transport to open sea for discharge, but is prohibited due to environmental requirements; (2) the method is used for steel plants to wash steel plates, produce gypsum by lime neutralization and produce ammonium sulfate by ammonia water neutralization, but the utilization rate is very low; (3) concentrating and recycling waste acid; (4) the comprehensive utilization is carried out by qualified operators.

The waste acid concentration is the most resource-saving and environment-friendly treatment scheme, the existing treatment method is that the two are carried out synchronously, namely, the concentration of sulfuric acid is improved by concentration and salt slag is precipitated, at present, two methods are adopted for deslagging, (1) 98% concentrated sulfuric acid and 20% waste acid are directly mixed into 60% acid, a large amount of salt is separated out, the method needs to consume a large amount of concentrated sulfuric acid, (2) a multi-effect evaporation concentration method is adopted, waste acid (the concentration is 20 ~ 30%, the concentration of insoluble TiO ₂ is lower than 0.2 g/l) generated in the production process of titanium white by a sulfuric acid method is pumped to a storage tank for standby before concentration, a storage tank feeding pump is used for metering and then sent to a waste acid concentration device through a preheater and then to a one-effect negative pressure evaporation system, saturated steam is used for heating, flash evaporation and concentration, secondary steam generated in the one-effect concentration process of the waste acid is used as a heat source of a two-effect preheater, secondary steam condensate is collected through a liquid seal tank, circulating liquid of a one-effect evaporator enters a two-effect negative pressure evaporation system through overflow, and is evaporated and concentrated to overflow to a finished product acid after being qualified, the finished product acid is cooled and crystallized in a.

The concentration of about 20-30% in the traditional process is preheated and then enters a first effect, the waste acid is concentrated to 31-33%, the temperature is 108 ℃, the vacuum degree is 39 ~ 43kPa, in the second stage, the mass fraction of the waste acid is concentrated from 31-33% to 51 ~ 53%, the temperature is 86 ℃, and the vacuum degree is 85 ~ 88 kPa.

Although the problem of scaling and blocking can be solved by using single-effect concentration, the mass fraction of waste acid is concentrated by 55-65%, the steam quantity in a concentration unit is large, and the comprehensive cost is high, so that the single-effect concentration cannot be accepted by every titanium dioxide production enterprise.

Disclosure of Invention

In order to solve the problems, the invention provides a method for preventing scaling of one-effect in the multi-effect concentration process of titanium white waste acid by a sulfuric acid method, wherein in the process of waste acid concentration, a large amount of metal salt is separated out in the one-effect concentration process by accurately controlling process parameters, so that continuous production can be realized, scaling on the inner wall of a pipeline and a system can be avoided, and long-period start-up of a waste acid concentration device can be realized.

The invention is realized by the following technical scheme:

A method for preventing multi-effect concentration and one-effect scaling of titanium dioxide waste acid produced by a sulfuric acid process comprises the following steps:

(1) Directly adding titanium white waste acid with the concentration of 20 ~ 30% into a first-effect concentration system, adding concentrated sulfuric acid to keep the concentration in the first-effect concentration system at 38 ~ 42%, wherein the temperature of a first-effect evaporator is 103 ~ 106 ℃, the vacuum degree is 52 ~ 48kpa, and sulfuric acid overflows into a second-effect concentration system after the first-effect concentration;

(2) the double-effect concentration system is kept at the vacuum degree of 88 ~ 92kpa, the temperature is 78 ~ 76 ℃, the concentration of concentrated sulfuric acid is 53 ~ 55%, impurities are removed through plate-and-frame filter pressing, and the concentrated finished acid can be continuously concentrated or reused for titanium dioxide production.

Preferably, the iron-titanium ratio of the titanium liquid in the titanium white production is 0.26 ~ 0.42.42.

The iron-titanium ratio is the ratio of the total iron content and the total TiO ₂ content in the titanium liquid, and the formula is as follows, the total Fe content (g/l) iron-titanium ratio = the total Fe content (g/l)/the total TiO ₂ content (g/l) iron-titanium ratio has certain influence on the particle size and the structure of metatitanic acid of a hydrolysate.

Preferably, the concentration of the titanium white waste acid is 22-25%.

preferably, the concentrated finished acid is added into the single-effect concentration system or the sulfuric acid obtained by using the double-effect concentration overflow without separation is used from the viewpoint of energy conservation.

preferably, the concentration of the sulfuric acid in the one-effect concentration system is 38%, the temperature is 103 ℃, and the vacuum degree is 52 kpa.

Preferably, the temperature of the double-effect concentration system is 76.5 ℃, and the vacuum degree is 91 kpa.

The invention mainly aims at waste acid generated in the production process of titanium dioxide by a sulfuric acid method, the inner wall of a pipeline is easy to scale in the concentration evaporation treatment process, in the general waste acid concentration treatment process, the concentration of sulfuric acid in a one-effect evaporator is 31%, the temperature is 108 ℃, and the vacuum degree is 39 ~ 43kpa, but a layer of thick scale can be formed on the inner wall of the pipeline due to slow precipitation of calcium salt, ferric salt and titanium salt in the waste acid, the thickness becomes thicker and thicker along with accumulation of time, so that the pipeline is blocked, the inner wall is blocked, the heat transfer effect of a heater is reduced, and the normal production is seriously influenced.

The invention does not need to remove most metal salts in the waste acid before concentration, but removes the metal salts in the concentration process, 20 ~ 30% (including rotary kiln tail gas preconcentration) waste acid generated in a titanium white production workshop can directly enter a preheater and a one-effect heater for heating without pretreatment, and reaches dynamic balance under the conditions of 103 ~ 106 ℃, 48 ~ 52KPa vacuum degree, 38% of acid content being stabilized above 38%, FeSO ₄ & 7H ₂ O, CaSO ₄ & 2H ₂ O in the waste acid is instantly dehydrated, Fe, Ca and the like ionic sulfate is precipitated in the form of solid particles as autogenous crystal seeds and is combined with same-phase salts to generate solid-phase precipitates along with the reduction of the solubility, thereby avoiding the sulfate dissolved out by Fe, Ca and the like from being attached to the low end and high end interfaces of a temperature gradient to form calcium sulfate-based scale and bridge plugging of Fe salt, adjusting the concentration, pressure and temperature range to a certain range, enabling the metal salts to be instantly dehydrated to be precipitated to form large amount of large particles, avoiding the slow precipitation of the metal salts, blocking the inner walls of pipelines and equipment, and entering a plate frame for further controlling the scale deposition and recovering the large particles by pressure filtration.

Advantageous effects

a method for preventing sulfate process titanium dioxide waste acid from multiple-effect concentration and one-effect scaling is characterized in that the vacuum of a one-effect evaporator is increased from 40KPa to 48 KPa; the acid content of the one-effect concentration evaporation system is increased to 38% -42%; meanwhile, in order to ensure that the acid content of the first-effect concentration system is stabilized to be more than 38%, a first-effect acid concentration auxiliary device is additionally designed, acid of a concentrated finished product or acid of secondary-effect overflow into the ageing tank is added into the first-effect concentration system according to the proportion of the amount of the first-effect concentrated acid, so that the large fluctuation of the acid content in the first-effect concentration process is reduced, and the dynamic balance of the first-effect acid concentration is realized; by improving the first-effect concentration evaporation state, the first-effect vacuum degree is improved, and the dynamic balance of first-effect steam, second-effect steam, concentrated acid amount and a vacuum system is established; in the continuous concentration process of the waste acid, the inner wall of the pipeline can not be scaled, and the shutdown descaling and maintenance are not needed, so that the economic loss is reduced, the concentrated sulfuric acid can be reused for titanium dioxide production, the process is simple and easy to implement, and the application prospect is wide. And the reduction of temperature in the process of one-effect concentration also reduces the consumption of energy.

Drawings

FIG. 1A diagram of a non-fouled pipe in example 1;

FIG. 2 is a schematic representation of a fouled pipe in comparative example 1;

FIG. 3 is a layer scale pattern for the scale formed in comparative example 1;

FIG. 4: the flow chart of the device adopted by the embodiment.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.