RU2162007C2 - Method of scrubbing aluminum electrolysis gas - Google Patents

Abstract

FIELD: dust separation; cleaning gases in non-ferrous metallurgy. SUBSTANCE: gas in subjected to scrubbing followed by delivery of gas to drip pan and then to smoke stack; part of solution is circulated in cold sprinkling loop and heat of gas delivered for scrubbing is recovered through heating part of solution directed for processing. EFFECT: enhanced efficiency of scrubbing; possibility of using heat of gases being scrubbed. 4 cl, 4 ex

Description

 The invention relates to the field of dust collection and purification of gases in non-ferrous metallurgy, in particular in the production of aluminum.

 Aluminum electrolysis gas contains hydrogen fluoride, sulfur dioxide, dust and tar. Two main methods of gas purification of aluminum electrolysis are known / 1, p. 396 - 399 /. The first is a two-stage cleaning method in the following variants: an electrostatic precipitator and a high-speed hollow scrubber or a high-speed hollow scrubber and a floating nozzle scrubber. Scrubbers irrigate a solution of soda. The second is dry sorption gas purification.

Aluminum electrolysis gas enters the purification with a temperature of up to 200 ^o C, however, both methods of purification do not involve the use of gas heat, which is dissipated into the environment. The non-use of gas heat is a disadvantage of the known methods for purifying aluminum electrolysis gas.

 The second disadvantage of the known methods of purification of aluminum electrolysis gases is the low degree of dust cleaning - 90 - 95% and resin - up to 60%. The degree of purification increases with increasing energy costs for its implementation / 2, p. 64 /, that is, with an increase in the resistance of the treatment devices, but at the same time, the vacuum in the electrolysis gas collection system decreases and the number of so-called lantern gases increases, which are not cleaned at all.

According to the claimed method of purification of aluminum electrolysis gas, the first drawback is eliminated by the fact that the heat of the gas is utilized by heating the spent solution. For this, part of the solution circulates in the cold irrigation circuit, i.e. do not allow its contact with hot gas entering for cleaning. Due to this, heating of the spent solution to 70 - 75 ^o C, sufficient for its processing, is achieved, and the consumption of steam intended for heating the spent solution is minimized.

 In addition, the temperature of the solution in the cold irrigation circuit decreases, which increases the degree of gas purification.

 Additional direct contact of the gas with the spent solution also increases the degree of gas purification. The use of a disintegrator in the proposed method of gas purification also eliminates the second drawback and compensates for the increase in system resistance caused by the passage of gas through the heater due to the additional pressure created by the disintegrator.

 We take as a prototype a two-stage method for purifying gas from an aluminum electrolyzer, consisting of an electrostatic precipitator and a high-speed hollow scrubber, as the most common in industry.

Salient features of the prototype:
- gas electrolysis of aluminum is cleaned in an electrostatic precipitator under vacuum created by a smoke exhauster,
- the gas supplied by the exhaust fan is directed to the lower part of the high-speed hollow scrubber irrigated with the solution from the solution circulation system,
- fresh soda solution is introduced into the solution circulation system,
- after a high-speed hollow scrubber, gas passes the droplet eliminator and is discharged into the atmosphere through the chimney, the liquid from the droplet eliminator is sent to the solution circulation system.

- part of it is pumped out of the solution circulation system as a spent solution for processing,
- excess heat from the gas purification circuit is dispersed into the environment as natural losses of pipelines and apparatuses.

The essential features of the claimed invention:
- gas electrolysis of aluminum is cleaned in an electrostatic precipitator under vacuum created by a smoke exhauster,
- the gas is cooled by the spent solution and purified in a disintegrator, feeding the solution into it from the circulation circuit of the heat irrigation,
- part of the solution circulates in the cold irrigation circuit,
- the gas supplied by the disintegrator is directed to the lower part of the high-speed hollow scrubber irrigated with a solution from the cold irrigation circulation circuit,
- fresh soda solution is introduced into the gas pipeline in front of the chimney droplet eliminator,
- gas from the gas pipeline after the high-speed hollow scrubber passes the droplet eliminator and is discharged into the atmosphere through the chimney, the soda solution from the droplet eliminator is sent to the cold irrigation circulation circuit,
- excess heat from the gas purification circuit is dissipated in the atmosphere by means of an air-cooling apparatus.

 The main cleaning essential feature of the claimed invention: "part of the solution circulates in the cold irrigation circuit."

Additional distinctive essential features of the claimed invention:
- the gas is cooled by the spent solution and purified in a disintegrator,
- fresh soda solution is introduced into the gas pipeline in front of the chimney droplet eliminator,
- excess heat from the gas purification circuit is dissipated in the atmosphere by means of an air-cooling apparatus.

 The inventive method is illustrated in the drawing, which shows a scheme for gas purification of aluminum electrolysis. The diagram shows: 1 - a smoke exhaust, 2 - a waste solution heater, 3 - a disintegrator, 4 - a high-speed hollow scrubber, 5 - a chimney, 6 - a circulation tank, 7 - a circulation pump for a warm irrigation circuit, 8 - a circulation pump for a cold irrigation circuit, 9 - pump pumping the spent solution, 10 - air cooling apparatus.

 A - gas for cleaning, B - fresh solution, C - waste solution.

Example 1. Aluminum electrolysis gas in an amount of 45000 nm ³ / h is cleaned in an electrostatic precipitator (not shown in the diagram) and enters a smoke exhauster 1, which is supplied by its waste solution heater 2. Heater 2 is a dual riser with a solution collector. In the upper part of the riser, 8 - 10 m ³ / h of the spent solution supplied by pump 7 from the circulation circuit of warm irrigation is sprayed through nozzles. The gas passes first from the bottom up along one part of the riser, then from top to bottom along the other part and the spent solution is heated to 70 - 75 ^o C. In this case, 1 - 1.5 m ³ / h of water is evaporated. The heated spent solution is collected in a collection tank 2, from which 6 - 7 m ³ / h of the solution is pumped out by pump 9 for processing, and 1 - 1.5 m ³ / h of excess, through the overflow of the heater collector 2, enters the suction manifold of pump 7.

Gas from the heater 2 with a temperature of 70 - 75 ^o C enters the disintegrator 3 of a known design / 2, p. 158 - 161 /. Here, pump 7 serves 40-50 m ³ / h of solution from the circulation circuit of warm irrigation. After gas purification, the solution from the disintegrator 3 is poured into the suction manifold of the pump 7. 7 to 8 m ³ / h of solution from the circulation tank 6 of the cold irrigation circuit enter the same collector. Disintegrator 3 increases the gas pressure by 280 - 300 mm water column. and feeds it at a temperature of 45-50 ^° C to the bottom of the high-speed hollow scrubber 4. Into the upper part of the scrubber 4, through the nozzles 8, 90-100 m ³ / h of a solution with a temperature of 20-25 ^° C are fed from the circulation tank 6.

Gas with a temperature of 25 - 30 ^o C from a high-speed hollow scrubber 4 is sent to a droplet eliminator built into the chimney 5, and the atmosphere is emitted through it. The solution from the scrubber 4 and the droplet eliminator of the chimney 5 is discharged into the circulation tank 6. Here, 8-10 m ³ / h of fresh soda solution is supplied.

 Excess heat from the gas purification circuit is removed due to natural losses by pipelines and apparatuses into the environment.

 The degree of purification of aluminum electrolysis gas is 99.2% for hydrogen fluoride and sulfur dioxide, 99.1% for dust and 97.2% for resin.

 Example 2. An electrostatic precipitator is excluded from the aluminum electrolysis gas purification scheme. Further cleaning is carried out as described in example 1.

Example 3. The purification of aluminum electrolysis gas is carried out as described in examples 1 or 2. 8 - 10 m ³ / h of fresh soda solution instead of a circulation tank 6 is fed through nozzles to the gas duct after a high-speed hollow scrubber 4 in front of the chimney droplet separator 5, thereby achieving fine tertiary treatment gas. The degree of purification of aluminum electrolysis gas is 99.3% for hydrogen fluoride and sulfur dioxide, 99.2% for dust and 98% for resin.

Example 4. The purification of aluminum electrolysis gas is carried out as described in examples 1, 2 or 3. The excess heat of the cold irrigation circuit is removed by pumping the solution with pump 8 through an air cooler 10 of known design, by supplying the solution to a high-speed hollow scrubber 4. The temperature of the solution decreases to 10 - 20 ^o C, which increases the degree of gas purification to 99.4% for hydrogen fluoride and sulfur dioxide, 99.3% for dust and 98.4% for resin.

Sources of information
1. Gordon G.M., Peysakhov I.L. "Dust collection and cleaning of gases in non-ferrous metallurgy", M., "Metallurgy", 1977.

 2. Uzhov V. N. and others. "Purification of gases by wet filters", M., "Chemistry", 1972.4

Claims (4)

 1. The method of purification of aluminum electrolysis gas by wet cleaning with the subsequent supply of gas to a droplet eliminator and then to a chimney, characterized in that part of the solution is circulated in the cold irrigation circuit, and the heat coming to the gas treatment is utilized by heating part of the solution sent for processing.  2. The method according to claim 1, characterized in that the gas after cooling with the spent solution is purified in a disintegrator.  3. The method according to p. 1 or 2, characterized in that the fresh soda solution is introduced into the gas pipe in front of the chimney droplet eliminator.  4. The method according to any one of the preceding paragraphs, characterized in that the excess heat from the gas purification circuit is dissipated in the atmosphere by means of an air cooling apparatus.