Treatment of waste from titanium dioxide production--sulfuric acid method (2)

After 20% of the waste acid is preheated in two stages, it enters the system before the forced circulation pump of a concentrating device. Together with the circulating acid, it enters a heater and evaporator, most of which continue to circulate, and some enter the second-stage evaporation device. The same situation, and then enter the three-stage concentrating device, after three-stage forced circulation pump, three-stage heater, evaporator, most of the circulation continues, part of which is 70% waste acid flow to the tank with agitated liquid, and then The pump enters the middle tank with the agitating filter through the cooler, and is pumped by the pump to press the pressure plate frame filter. The filtrate is the finished acid into the finished acid tank and sent out to the system. The filter residue is acid-containing FeS0 ₄ ·H ₂ 0 is sent away by the belt conveyor.
A period of evaporation is concentrated under pressure, and the secondary vapor pressure is about 0.1 MPa, which is used as a heating steam for a second preheater that concentrates 20% acid, and a heating steam for a second stage concentrated heater. The steam condensate is collected in a condensate storage tank and is discharged by a condensate pump pumped to a 20% acid first preheater and exchanged with 20% acid.
The two-stage concentration and the three-stage concentration are vacuum evaporation, and the secondary steam enters a direct condenser of a closed loop at the same time. The circulating water is cooled and exchanged by a plate heat exchanger with external cooling water, and the circulating water is partially discharged at a certain time. The non-condensable gas is discharged to the atmosphere by a water ring vacuum pump.
After a period of evaporated secondary steam is used as the secondary preheating and the heating steam of the second stage concentrated heater, the non-condensable gas enters the condenser along with the second stage concentrated secondary steam.
The cooling water of the air pressure condenser and the 70% acid cooler is made of circulating water, the inlet water temperature is 30 ° C, and the outlet water temperature is 35 ° C.
Several basic process parameters for three-stage concentration:
1MPa; The first section 20%-28%, the temperature of 115 ° C, the pressure (gauge pressure) 0. 1MPa;
The second stage is 28%-60%, the temperature is 80 ° C, the pressure (absolute pressure) is 0. 008MPa;
The first stage is 60%-70%, the temperature is 115 ° C, and the pressure (absolute pressure) is 0. 008 MPa.
The technical parameters of the three-stage concentration and one-stage concentration are shown in Table 3. [next]

Equipment material. The heater is graphite . When heated by secondary steam, the outer casing is made of carbon steel lining rubber, and the heater is divided into two types: hole type and tube type.
The evaporator is made of glass fiber reinforced plastic lined with polyfluoroplastic (fluorinated ethylene propylene).
Forced circulation pump is an axial pump high silicon iron, silicon in an amount of 15%, the slurry pump, filter feed pump is a centrifugal pump high ferrosilicon.
The condenser is a glass fiber reinforced plastic.
Plate heat exchangers and vacuum pumps, steam condensate pumps are 254 stainless steel (Swedish standard).
The finished acid cooler is graphite and the outer casing is carbon steel.
The plate and frame filter press is polypropylene, and the filter cloth is polyvinyl fluoride. [next]
(2) domestic waste acid sulfate process titanium white powder handling domestic titanium dioxide industry should be said that the real beginning of the early 1960s, while developing sulfuric acid method titanium dioxide industry, we have realized the seriousness of the problem of spent acid. Domestic titanium dioxide production plants are small and scattered, so they are often solved according to local conditions.
1 Direct use. Directly mixed with calcium production, such as Zhuzhou Chemical Plant; used for steel pickling, such as Shanghai Titanium Dioxide Factory; production of manganese sulfate, such as Guangzhou Titanium Dioxide Factory.
2 processing use. The use of titanium dioxide waste acid processing is mainly to concentrate and purify the waste acid, and then used in other aspects. Nanjing Chemical Plant oils such as about 20% of the spent acid is concentrated to 40%, the cryogenic separation of ferrous sulfate for export phosphorus fertilizer production for many years, but the evaporation device is a jacket enamel 11:50, equipment behind a previously installed tube The graphite evaporator was not officially put into production due to the high content of metatitanic acid in the original waste acid.
3 other uses. The former Ministry of Chemical Industry Institute of paint has done a small test work utilizing waste acid synthetic rutile and titanium-rich material, the disadvantage of this method is still dilute spent acid to be treated.
4 The introduction of three sets of sulfuric acid titanium white waste acid treatment methods in the former Eastern Europe. The domestic introduction of titanium sulphate waste acid treatment method, the 404 plant is located in the desert hinterland, designed to neutralize the lime into the pond, and naturally evaporate. Shandong Yuxing also uses this method. Chongqing Dagang produces a waste acid concentrating device. Like the above-mentioned Finnish process, the problem is that the heat exchanger in the initial stage is fouled, easy to block, and the production is abnormal, often causing environmental hazards. To this end, the United States NL Commodities International, the first step in the United States, in 1988 applied for Chinese invention patents (priority day 87. 10. 26, CN 1042527A) "Sulphuric acid process for the production of titanium dioxide associated with the treatment of waste acid", the purpose is to Occupy the commanding heights of China's titanium dioxide waste acid treatment technology.
As mentioned above, China has done a lot of work in the comprehensive utilization of waste acid, and it has achieved results. However, no practical treatment has been found for the titanium dioxide waste acid in the large-scale titanium dioxide factory.
(3) Domestic related patents and latest technology US NL Commodity International applied for Chinese invention patents in 1988 (Priority Day 1987. 10. 26, CN 1042527A) "Process for Treatment of Dilute Acids Associated with Titanium Dioxide Production by Sulfuric Acid Process". In order to solve the problem of heat exchanger clogging in the vacuum evaporation concentration method, the inventive method of the patent uses a two-stage concentration three-time separation method to remove impurities in the acid. The first stage uses titanium dioxide calcination kiln exhaust gas to preconcentrate 20%-24% dilute sulfuric acid to 26%-29%, the first separation of the residue precipitated here, and then the separated filtrate is cooled and cooled to precipitate heptahydrate sulfuric acid. Ferrous iron, secondary separation, separation of solid phase material - ferrous sulfate heptahydrate, to obtain 30% -35% of dilute sulfuric acid; then, the obtained 30% -35% dilute sulfuric acid by vacuum evaporation concentration method The second stage is concentrated to a sulfuric acid concentration of 60% to 71%; finally, the subsequent precipitation in the acid is subjected to a third separation to obtain about 70% sulfuric acid.
The implementation of this patent has many process equipments and long process flow; the surface looks energy-saving. After two stages of concentration and separation of the lengthy process, the equipment investment and direct evaporation and enrichment costs are not reduced, but the increase is large, the operation cost and operation cost are also many.
To this end, Sichuan Longyan Group, based on its own and social development needs, based on a set of technological innovations summarized in the production of inorganic chemicals, especially wet inorganic chemicals (mineral chemicals), and effective experience in leading markets. A green production process in which spray concentrated iron is used to treat spent acid and used for phosphating production is proposed. In 2000, the "Study on the comprehensive utilization of sulfuric acid titanium dioxide waste and the research of improving product quality series" was launched. A total of 6 scientific research projects were completed, 4 invention patents were applied, and 2 provincial scientific and technological achievements were completed. After the laboratory test was completed In 2001, he invested more than 13 million yuan in industrial intermediate research experiments. It is worth mentioning that Chongqing Municipality, which has been in the market for one month to 500km, buys high-priced sulfuric acid waste white powder, in order to obtain and test the reliability of these patents and scientific and technological achievements. In 2003, a new 40,000 tons of sulfuric acid titanium dioxide waste acid recovery treatment was built. After one year of actual production, the device not only meets and exceeds the design capability and expected technical specifications, but also has lower investment and operating costs than the advanced equipment level in Europe; it has attracted the attention and favor of European sulfuric acid titanium dioxide producers. Even the desire to buy. As in the 1990s in Europe, the problem of waste acid will be solved fundamentally, and the sulfuric acid titanium dioxide will be re-energized to a stronger vitality.

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