RU2457072C1 - Method of producing zinc powder and plant to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to materials intended for production of powder used in fabrication of paintwork materials, galvanic cells and in chemical industry. Zinc boiling 500-600 mm-high bed is used to evaporate zinc In furnace blowing in, nitrogen is fed at 500-600°C for 5-10 minutes at intervals of one hour In steady-state conditions, that is, at temperature of 1200-1450°C and rarefaction of 50-100 Pa, nitrogen is fed into zinc evaporation zone for 5-10 minutes in every 3-4 h. For zinc transfer into refrigerator, channel arranged 400-500 mm above boiling bed is used. Zinc powder is transferred into cyclone and bag filter by vacuum fan. Zinc loading and melting crucible is located at furnace center. Note here that melt overflow openings are made in lining at the level of its bottom.

EFFECT: fine high-purity zinc powder, lower production costs.

11 cl, 1 dwg, 1 tbl

Description

The invention relates to the metallurgical industry, in particular to the production of zinc powder, which can be used to obtain anti-corrosion paints and varnishes, for the manufacture of galvanic cells, in the chemical industry as a reducing agent.

A known method of producing zinc dust (pigment powder) by the method of rapid condensation of zinc vapor in an inert medium (carbon dioxide or nitrogen). To obtain zinc vapor, muffle furnaces are used, similar to those used to produce zinc oxide. Instead of an oxidizing chamber, these furnaces are equipped with steel sheet capacitors. Zinc vapor is transported to the capacitors by an inert gas supplied to the muffle. During the condensation of zinc vapor, particles of 10-20 microns in size are formed, which fall to the bottom of the capacitor and are collected by the screw. The content of zinc metal in such powders usually does not exceed 94-95%, the main part of the impurities is zinc oxide (E.F. Belenky, I.V. Riskin, Chemistry and technology of pigments, publishing house “Chemistry”, Leningrad Branch, 1974 g., s. 535-536).

The disadvantages of this method are:

- complex and laborious technology for producing zinc powder associated with the use of muffles;

- low quality zinc powder in terms of dispersion and purity of zinc;

- complex hardware design;

- limited scope of zinc powder due to poor quality.

A known method of producing finely dispersed zinc powder for the paint and varnish industry, including the evaporation of zinc, characterized by a low content of impurities, at a boiling point in nitrogen, as an inert medium, the transportation of zinc vapor, their rapid cooling (s. 1470 - 1570K to 520 - 670K) and powder collection (Non-ferrous metal powders edited by S.S. Nabokov, Moscow: Metallurgy, 1997, pp. 431-439).

This method differs from the previously described in that zinc is used for evaporation with a low content of impurities, therefore, all the disadvantages given previously for the known method are also characteristic of this method. A known method of producing fine zinc powder for anticorrosion paints and installation for implementing the method adopted by us as a prototype, evaporation of zinc in a protective nitrogen atmosphere, transportation of zinc vapor with nitrogen to a refrigeration unit, then zinc powder is sent to the installation where intermetallic compounds are separated in a magnetic field, then the powder is precipitated in a cyclone and the control collection of dusty powder is carried out in bag filters (RF patent No. 2393064, bull. 18, 06/27/2010).

This known invention has the following disadvantages:

- imperfect design of the furnace, which does not allow to separate the vapors of zinc from impurities, originally contained in zinc;

- a very large nitrogen consumption for transporting zinc vapor and zinc powder, given that zinc powder has a significant specific gravity;

- the possibility of clogging the refrigeration unit with zinc powder.

The objectives of the proposed method for producing zinc powder are as follows:

- to ensure the purification of zinc vapor from impurities at the stage of its evaporation;

- apply the design of the furnace, which allows you to continuously load zinc in the form of a melt in the zone of its evaporation and thereby ensure continuous operation of the process of evaporation of zinc;

- carry out rapid cooling of zinc vapor in the refrigeration unit and prevent it from clogging with zinc powder;

- sharply reduce nitrogen consumption;

- to provide zinc powder having a dispersion of not more than 0.5-5 microns and an impurity content of not more than 0.05%.

These tasks are solved as follows.

To clean zinc vapor from impurities, zinc is evaporated in the zone of the furnace, separated from the zones of heating and crucible of the furnace, at a temperature of 1200-1450 ° C in a nitrogen atmosphere and a vacuum of 50-100 Pa and a height of a fluidized zinc layer of 500-600 mm, while the height of the free space above the surface of the fluidized zinc layer and the lower level of the hog used to supply zinc vapor to the refrigeration unit, equal to 400-500 mm.

These conditions prevent the entrainment of zinc droplets along with the zinc vapor, and thereby the pollution of zinc vapor by impurities present in the zinc melt is prevented.

Impurities in the zinc melt in the form of metal oxides and intermetallic compounds, which have a significant molecular weight and have increased adsorption activity, as a result of boiling the melt belong to the walls of refractory brick masonry and are deposited on them in the form of a layer.

The design of the furnace for the evaporation of zinc has the following features:

- in the center of the furnace there is a crucible, separated from the zone of evaporation of zinc by a refractory brick masonry on a refractory mortar with a wall thickness of 120 mm, in the lower part of the masonry there are windows measuring: height - 100 mm, width - 70 mm. The windows are located at the bottom of the crucible of the furnace and serve to flow the molten zinc from the crucible into its evaporation zone. The heating and melting of the zinc ingots, which are loaded into the crucible of the furnace, is ensured by the heat from the fluidized bed of zinc in the evaporation zone and due to the heat transmitted by the zinc vapor through the masonry to the zinc ingots. This ensures a stable and continuous operation of the furnace for the evaporation of zinc. By changing the temperature regime in the zone of zinc evaporation, various properties of the zinc powder can be set.

Fast and efficient cooling of zinc vapor and the exclusion of clogging of the refrigeration unit is achieved as follows.

The transportation of zinc vapor from the zone of its evaporation to the refrigeration unit is carried out not by a stream of nitrogen, but due to the partial pressure of zinc vapor and vacuum in the furnace, equal to 50-100 Pa, created by an exhaust fan. This ensures a reduction in the heated gas mass entering the refrigeration unit, and, on the other hand, when transporting zinc vapors through a boron laid out of refractory brick on a refractory mortar and having a masonry wall thickness of 120 mm, heat is transferred to the walls of the boron masonry and further to the atmosphere. Zinc vapor enters the middle of a refrigeration unit installed vertically. Cooling elements are tubes installed vertically in the refrigeration unit and connected to a distribution pipe installed at the bottom of the unit through which the refrigerant (freon or ammonia) enters, and with the upper pipe through which the spent refrigerant enters the compressor again.

At the top of the refrigeration unit, atmospheric air is supplied due to the operation of the exhaust fan. The air stream cleans the refrigeration unit from the zinc powder formed in the annular space, which enters the exhaust fan.

A sharp decrease in nitrogen consumption is achieved by the fact that nitrogen is supplied periodically with an interval of 3-4 hours for 5-10 minutes to the zinc evaporation zone.

This provides a protective environment in the zone of evaporation of zinc.

The provision of powdered zinc having a dispersion of not more than 0.5-5 microns is achieved by the fact that the zinc vapor entering the refrigeration unit is rapidly diluted with a stream of atmospheric air and cooled in the unit, which prevents the transition of the gaseous phase of zinc into liquid and solid phases, the aggregation of zinc particles, since the aggregation of zinc particles occurs at the stage of formation of the liquid phase and the aggregates will be larger, the greater the concentration of zinc vapor and the longer the residence time in the liquid phase.

In our case, such conditions are absent.

Obtaining zinc powder containing not more than 0.05% of impurities is provided by special conditions for the evaporation of zinc, as noted above.

The installation for producing zinc powder is shown in Figure 1. Furnace lining. 2. The heating zone of the furnace. 3. The zone of evaporation of zinc. 4. Crucible furnace. 5. Masonry from heat-resistant brick on a refractory mortar. 6. Hog. 7. Windows in the masonry oven. 8. Hog to remove the combustion products of natural gas into the exhaust pipe. 9. Gas pipeline and gas burner. 10. Pipeline for introducing nitrogen into the zone of evaporation of zinc. 11. The lid of the furnace. 12. The cover of the crucible furnace. 13. The melt of zinc. 14. Refrigeration unit. 15. Pipeline for refrigerant supply. 16. The pipeline to remove the refrigerant. 17. Pipeline for supplying atmospheric air to the refrigeration unit. 18. Exhaust fan. 19. Pipeline for transporting zinc powder. 20. The cyclone. 21. The cyclone hopper. 22. Installation of bag filters. 23. Hopper for installing bag filters.

The set of features of the proposed technical solution of the method for producing zinc powder and the installation for implementing the method are different from the prototype and do not follow explicitly from the studied prior art, therefore, the authors believe that the method and installation are new and have an inventive step.

The method of producing zinc powder and the installation for implementing the method can improve working conditions to eliminate time-consuming operations, to ensure stable and continuous operation of the installation, to obtain high-quality zinc powder with low cost. The method of producing zinc powder is as follows. First, the furnace is put into operation. Natural gas is supplied to the gas pipeline system, gas burners are switched on (pos. 9). After reaching a temperature of 500-600 ° C in the zinc evaporation zone and 450-500 ° C in the furnace crucible, nitrogen is fed into the zinc evaporation zone for 5-10 minutes (item 10) to displace the air from the zinc evaporation zone. Zinc ingots containing at least 99.5% zinc metal are loaded into the crucible of the furnace (item 4). As the zinc ingots melt in the crucible of the furnace and the zinc melt flows into the zone of its evaporation (pos. 3) through the windows (pos. 7) in the masonry of the crucible of the furnace, the zinc ingots are constantly loaded into the crucible of the furnace until 11 tons of zinc are remelted. This will correspond to the height of the zinc melt layer in the evaporation zone of 500 mm. When the temperature in the evaporation zone reaches 800 ° С, the refrigeration unit (pos. 14) is turned on, the exhaust fan (pos. 18) is turned on. Set the desired temperature in the zone of evaporation of zinc in the range of 1200-1450 ° C. Hourly, 230-300 kg of zinc ingots are loaded into the crucible of the furnace (item 4), depending on the set temperature. At the beginning of the start-up of the furnace, the supply of nitrogen (10) to the evaporation zone is carried out every hour for 5-10 minutes. After 3-4 hours of stable operation of the system, nitrogen is fed into the evaporation zone for 5-10 minutes every 3-4 hours. Constantly check the vacuum in the system, which should be 50-100 Pa. The required vacuum in the system is regulated by the supply of atmospheric air (pos. 17) to the refrigeration unit. Every 3-4 hours, zinc powder is unloaded into the packaging container from the cyclone hopper (key 21), and unloading is carried out every 12 hours from the bag filter hopper (key 23). After establishing a predetermined regime for the production of zinc powder, work continues for a month. Then carry out a routine inspection of the entire installation according to special instructions. After conducting a routine inspection of the installation, it is put into operation as described above, and the time of continuous operation of the installation is determined until the next routine inspection.

When processing zinc ingots containing 0.5% impurities, the continuous operation period will be approximately one month, and when the content of impurities in zinc is 0.1%, the continuous operation period will be approximately five months.

Data technological parameters known (US Pat. RF. No. 2393064, bull. No. 18, 06/27/2010) and the proposed methods are presented in table 1.

Example.

The composition of zinc, wt.%:

Mass fraction of zinc - 99.5;

Mass fraction of impurities - 0.5.

Table 1 Energy consumption per 1 ton of zinc powder, kW Mass fraction of zinc metal in zinc powder,% The period of continuous operation of the furnace, days Productivity for evaporated zinc, kg / m ² . hour By a known method According to the proposed method By a known method According to the proposed method By a known method According to the proposed method By a known method According to the proposed method 850 768 99.94 99.95 not installed 35 78.3 83.0 870 770 99.95 99.94 not installed 34 75.1 83.1 840 760 98.96 99.96 not installed 35 76.8 83.0

Claims (11)

1. The method of producing zinc powder by evaporation of zinc in a nitrogen atmosphere at a temperature of 1200-1450 ° C and a vacuum of 50-100 Pa, cooling of zinc vapor in a refrigeration unit / transportation of zinc powder by an exhaust fan in a cyclone and in a bag filter, characterized in that for zinc vapors form a boiling layer of zinc 500-600 mm high; for transporting zinc to a refrigeration unit, a boron is used located at a height above the boiling layer of zinc equal to 400-500 mm at the initial moment of starting the furnace into the zinc evaporation zone, when temperatures of 500-600 ° C, nitrogen is supplied for 5-10 minutes with a periodicity of one hour, and at a steady state operating mode of the furnace nitrogen is supplied to the zinc evaporation zone for 5-10 minutes every 3-4 hours. 2. The method according to claim 1, characterized in that the refrigeration unit and the exhaust fan are turned on when the temperature of the zinc melt in the zone of its evaporation reaches 800-900 ° C. 3. The method according to claim 1, characterized in that the zinc vapor is transported through the pine forest due to their partial pressure and vacuum in the furnace-refrigeration unit-exhaust fan system in the middle part of the refrigeration unit mounted vertically. 4. The method according to claim 1, characterized in that refrigerant is supplied with refrigerant in the form of freon or ammonia through vertically installed tubes from the bottom up, top down into the annular space, and the formation of zinc powder from zinc vapor in the annular space is carried out at temperature 250-350 ° С. 5. Installation for producing zinc powder, containing a furnace for evaporating zinc, a refrigeration unit for cooling zinc vapor and the formation of zinc powder, an exhaust fan to create a vacuum in the furnace, refrigeration unit and transporting zinc vapor from the furnace to the refrigeration unit and zinc powder from the refrigeration unit into a cyclone and bag filters, characterized in that in the center of the furnace there is a crucible for loading and melting zinc, as well as the flow of zinc melt into the zone of zinc evaporation through windows formed in the treasure ke crucible furnace at the level of its bottom. 6. Installation according to claim 5, characterized in that the internal diameter of the crucible of the furnace is 250-300 mm, and the windows made in the masonry have dimensions: height - 100 mm, width - 70 mm. 7. The installation according to claim 5, characterized in that the width of the furnace heating zone is 200 mm, the width of the zinc evaporation zone is 755 mm, the masonry separating the furnace crucible, the evaporation zone and the furnace heating zone are made of refractory bricks with high thermal conductivity on the refractory solution and have a thickness of 120 mm. 8. The installation according to claim 5, characterized in that the masonry of the hog is made of refractory bricks with high thermal conductivity on the refractory mortar and has a thickness of 120 mm, and the hog has internal dimensions: height - 500 mm, width - 500 mm. 9. The installation according to claim 5, characterized in that the lid of the furnace and crucible are made of heat-resistant steel with a thickness of 20 mm and lined on both sides with heat-resistant concrete. 10. Installation according to claim 5, characterized in that the refrigeration unit is made up of tubes mounted vertically and has a refrigerant distribution system at the bottom — an input, at the top — an outlet of spent refrigerant to the compressor, and a pipe for atmospheric air is mounted in the upper part into the annulus of the refrigeration unit due to the operation of the exhaust fan. 11. Installation according to claim 5, characterized in that an exhaust fan is directly installed after the refrigeration unit.