GASES VACUUM DEDUSTING AND COOLING

Introduction. As a rule, to improve product quality, some additional production lines and equipment should be installed. The ladle degassing vacuum plant serves to extract the metal melts’ unnecessary components and to add the required ones. Therefore, the enterprise can produce steels that can not be manufactured without vacuum technology use. The vacuum evacuation process is associated with dedusting and cooling of the exiting process gases. Requirements for the molten steel ladle degassing plant’s dust control equipment are different from the requirements for equipment operating under normal conditions that is due to changes in amount, density and chemical composition of the process gases. Definitely, both choice and design of dust capturing equipment do affect the reliability and economic performance indexes of the entire ladle degassing system. Analysis of recent research and publications. The multichannel dust collector (buran) with dusty gas flow vertical rotation axis includes a hopper and a system of serially linked closed-loop curved channels connected thereto with a curved slot [1]. Aggregates of solid particles are removed from the dusty gas which is further filtered through layers of fine dust in each channel. Dust entrainment with the treated gas follows the relation [1]

Introduction.As a rule, to improve product quality, some additional production lines and equipment should be installed.The ladle degassing vacuum plant serves to extract the metal melts' unnecessary components and to add the required ones.Therefore, the enterprise can produce steels that can not be manufactured without vacuum technology use.The vacuum evacuation process is associated with dedusting and cooling of the exiting process gases.Requirements for the molten steel ladle degassing plant's dust control equipment are different from the requirements for equipment operating under normal conditions that is due to changes in amount, density and chemical composition of the process gases.Definitely, both choice and design of dust capturing equipment do affect the reliability and economic performance indexes of the entire ladle degassing system.
Analysis of recent research and publications.The multichannel dust collector (buran) with dusty gas flow vertical rotation axis includes a hopper and a system of serially linked closed-loop curved channels connected thereto with a curved slot [1].Aggregates of solid particles are removed from the dusty gas which is further filtered through layers of fine dust in each channel.Dust entrainment with the treated gas follows the relation where С init and С fin -inlet and outlet gas' dust burden; n -system's channels (closed loops) number.
The atmospheric emission comparable to the filter air dedusting is achieved at n>10.The validity of relation ( 1) is confirmed by the results accumulated over long-term operation of various burans at different enterprises under conditions close to normal ones [2].
The Aim of the Research is to analyze the possibilities to reduce environmental dust pollution by replacing cyclone with a buran equipped with four closed loops boiling steel ladle degassing system.Main Body.The vacuum chamber internal pressure decreases from the atmospheric value reaching 0,5 mbar during ladle degassing of 120 tons of molten steel [3].
That stepping-down is implemented through consecutive actuation of three different groups of vacuum rotary pumps.An assembly of fourteen parallel-connected vacuum pumps GV-400 (total capacity of 5600 Nm 3 /h) initially reduces the pressure from atmospheric to 100 mbar.Further actuated is an assembly of three pumps HV-14000 (total capacity of 42000 Nm 3 /h) with pressure dropping up to 10 mbar.The working vacuum of about 0,5 mbar is registered upon actuation of the third assembly of pumps HV-30000 (total capacity of 120000 Nm 3 /h).The pressure is temporarily increased when argon and nitrogen entering into the molten steel (Fig. 1).The vacuum chamber and the boiling steel ladle are the main sources of vacuum plant process gases' dust pollution.The process gases removed from vacuum chamber contain argon, carbon dioxide, air, liquid and solid refractory particles and particles of powder additives to steel [4].Submicron particles (less than 0,2 microns) make about 45 % thereof, with particles of 5 microns size reaching 95 % of the total post-dispersion weight.Volatile components released from the steel (alkaline metals, calcium, magnesium, manganese, etc.) are replaced in respective oxides with aluminium, silicium, carbon.Reduced metals interacting with the gas flow are forming the smallest nitride oxides, i.e. metal vapor condensation nuclei.Steel droplets taken out of the ladle by gases do harden when cooled.Thus, in the vacuum chamber and the gas duct formed are the heterogeneous systems with different physical and chemical properties, adversely affecting the vacuum rotary pumps and the environment.
Initially to decrease the vacuum rotary pumps and the environment dust burden we used a cylinder cyclone (d=1600 m) further replaced with a parallel-positioned vertical buran, n=4 (Fig. 2).The gas duct (d=1000 mm, initial section horizontally-positioned) connects the vacuum chamber to cyclone; the same diameter have the gas ducts at the cyclone output and the HV-30000 pumps manifold, the HV-14000 pumps manifold gas duct diameter is 700 mm, and the GV-400 gas duct diameter is 600 mm.The buran connecting ducts are ∅ 500 mm near the vacuum chamber and after the cyclone with gas ducts ∅ 1000 mm.The buran's designed productivity makes 10 4 Nm 3 /h.
Degasing the first 1080 tons of steel (9 test melts) resulted in accumulating such dust amounts: 18 kg at the cyclone inlet' gas duct, 10 kg at the cyclone, 10,4 kg at the manifold of ø 1000 mm, 3,3 kg at the protection grilles of HV-30000 pumps, 2 kg at the protection grilles of HV-14000 pumps.The horizontal section of gas duct ø 1000 mm together with the cyclone extracted from process gases up to 70 % of overall dust weight accumulated at the gas duct.At the issue of degasing 1800 tons of steel the 36 kg of process gas dust are extracted at the gas duct and 25 kg are collected by the cyclone.The buran collected 7 kg of dust upon degasing 120 tons of steel and 67 kg of dust have been discharged from the plant having degased 1680 tons of steel (Fig. 3).The buran provided degassing of 1800 tons liquid steel without revision and dust removal of rotary pumps HV-30000 grilles; the cyclone productivity was 3 times below [5].Bright glow of magnesium oxidized in air does evidence its significant amounts at the discharged dust.There arises the Ranque intense thermal effect at the channels system with gas swirling flow central regions' peripheral heating and cooling as shown in Fig. 4, a. Straightening the output swirling flow at the outlet and the circulation in closed hot dusty gas circuits do create an intense forevacuum effect increasing the rotary pumps station productivity (Fig. 4, b).

. Thermal and forevacuum effects of the vertical buran, n= 4: inlet (1), outlet (2) (а); cyclone (1), buran (2) (b)
Average decrease of the transit technological gas flow temperature at the storm plant (n=4) makes 2-folds.Replacing the cyclone with a vertical storm plant we increased the vacuum rotary pumps station productivity for 40 % having 1/3-reduced (from 37 to 25 minutes) the time of ladle degassing the 120 tons of molted steel.
The vacuum rotary pumps GV-400 are parallel-installed in two rows on the first floor of the pumps station (Fig. 2).They are actuated the first and reduce the pressure at vacuum chamber from atmospheric value to 100 mbar, further providing pressure of 0,5 mbar via forepumps (HV-1400 and HV-30000), compressing the process gas.Pumps GV-400 do emit process gases into atmosphere.The pump GV-400 No. 5 is preceded with a horizontal buran, allowing to connect the hopper with systems of four and six curved channels with closed loops (Fig. 5).The neighboring pump No. 7 has been studied to compare its results with these of the pump No. 5.
The burans bearing n=4 and n=6 gave practically equal indexes of fine-dispersion dust emission into atmosphere when non-stationary (initial) and stationary (final) conditions of liquid steel degassing.At the first case emission dustiness index at the pump's No. 7 inlet was 1,4 g/m 3 and 0,7 g/m 3 at the pump No. 5, and respective ciphers for the second case were 0,15 and 0,07 g/m 3 .The buran's dust suppression coefficient η=0,5 is maintained at 10-folds variations of gas consumption and dust content at process gas.
The horizontal buran (n=4) cooled the process gas under stationary conditions from 50 to 17 °С (Fig. 6, a) and 5 time augmented the GV-400 rotary vacuum pump productivity (Fig. 6, b).Results.Replacing the cyclone with a vertical buran (n=4) we 5-times decreased the dust atmospheric emission, increasing the vacuum rotary pumps station productivity for 40 %, the capital and operational expenses reduced, concurrently the time of ladle degassing the 120 tons of boiling steel is 1/3-shortened.The technological gases cooling and dedusting resulting from research of closed-loops buran allows to install and efficient operation of bag filter at the plant's outlet.