Stream Degassing Research Articles

Rainfall-driven and hydrologically-controlled variations in cave CO2 sources and dynamics: Evidence from monitoring soil CO2, stream flow and cave CO2

Speleothems are used as a promising proxy for high-resolution paleoclimate reconstruction. Partial pressures of CO2 (pCO2) is one of the most important factors in the processes of speleothem formation in caves. The objective of our study was to monitor the CO2 variations in the overlying soil, the cave air and the stream, and distinguish its sources and processes based on stable carbon isotopes in the Xueyu Cave system from October 2014 to February 2017. Overlying soil CO2 was influenced by soil temperature and soil moisture. The cave air pCO2 and equilibrium pCO2 in the stream water during two years showed very similar seasonal variations, fluctuating with high values in wet seasons and low values in dry seasons. The average δ13Csoil air value was −19.3 ± 0.8‰ and δ13Ccave air value was −18.8 ± 0.4‰ in November; while the average δ13Csoil air value was −23.9 ± 1.4‰ and δ13Ccave air value was −23.3 ± 0.3‰ in June. Moreover, the contribution from soil during the transitional ventilation (in November) was calculated based on the two end-members model of stable carbon isotopes. On the contrary, in wet season, cave air CO2 were mainly controlled by soil CO2 inputs. The total amount of C from stream degassing was calculated, which was higher in June than in November. High-resolution monitoring of cave air CO2 and its sources reveals the highly sensitive nature of CO2 dynamics within cave environments, and highlights its sensitivity to hydrological conditions in the cave system.

Rate of Hydrogen Desorption in Mold Stream Degassing Process

The rate of hydrogen desorption in the mold stream degassing process was measured to investigate the effect of hydrogen partial pressure. Experiments were conducted on 10.5 mass% Cr steel, 100 ton scale ingots. The hydrogen desorption reaction was controlled by metal side mass transfer at the gas/metal interface in this experimental condition. And the value of the volumetric mass transfer coefficient was estimated to be approximately 5.18 s−1. As is the case with the hydrogen desorption reaction, the rate of nitrogen desorption was measured, and the nitrogen desorption reaction was controlled by metal side mass transfer. Some mass transfer models such as Film theory, Penetration theory, and Surface renewal theory were taken into account to explain the present results. The mass transfer mechanism of hydrogen and nitrogen desorption in this process is explained by the Penetration theory or Surface renewal theory.

Nozzle Pressure during Stream Degassing

Nozzle Pressure during Stream Degassing

Degassing Kinetics of Molten Metals in Vacuum

A brief review of the theoretical and experimental work on the kinetics of the vacuum degassing of liquid metals is given. This review is limited to the case usually encountered where the transport in the melt alone is rated determining, i.e., where desorption processes at the melt surface and the transport in the gas phase may be neglected. Different models describing the mass transfer from the interior of the melt to the interface are also discussed. The course of degassing of a melt pool without bubble formation, based on the mathematical treatments of Kraus (see Refs. 1 and 2) and Machlin (see Ref. 3) is described. In the model of Kraus—which may be applied, for instance, to ladle degassing—convection currents in the interior of the melt develop by density differences caused by the heat loss of the freely radiating melt surface. The calculations of Machlin refer to inductively stirred melts. Formulas for the mass transfer coefficients for these two cases are given. If layers of surface active elements or slags accumulate at a melt surface, the rate of degassing may be largely reduced. There is also an examination of how far the model of Kraus is applicable to degassing in electron-beam and vacuum-arc melting with consumable electrodes. Most technical degassing processes rely on the formation of bubbles, for only with them are the high rates required for economical degassing obtained. Also shown are the conditions under which bubble nuclei may exist and growth of the bubbles in a melt pool or in stream degassing is possible. Reference is made to the calculations of the gas pick-up of ascending CO bubbles in a steel melt made by Kraus (see Refs. 1 and 2), which also permit the calculation of the mass transfer coefficient if, in this case, a surplus of nuclei in the melt exists. If the gas content is too low for spontaneous bubble nucleation, the use of a neutral scavenging gas is advantageous. Computations of its purging effect have been made by Bradshaw and Richardson (see Ref. 4) as well as by Lange et al. (see Ref. 5). Stream degassing is not accessible to an exact mathematical treatment. However, an estimation of the degassing rates of droplets and experimental results show that the removal of hydrogen probably takes place mainly by diffusion from the external surfaces of metal droplets and bubbles, whereas nitrogen and oxygen removal depends more on the bubble formation in the metal stream and melt pool.

Effect of variations in vacuum deoxidation technique on nonmetallic inclusions

Studies of the distribution and composition of nonmetallic inclusions found in vacuum-deoxidized 8-ton 0.20% carbon steel ingots showed that: 1. Ladle-to-mold stream degassing, without strong deoxidants but with a slag-off prior to tap, produced fully-killed ingots averaging less than 0.0020% oxygen. 2. Large complex inclusions were found concentrated in the axial portion of the bottom one-third of the ingots. Practice variations had no effect on this distribution. 3. Calcium, as detected by micro-probe analysis, was the major constituent in the complex inclusions. This calcium was traced to entrained furnace slag. A slag-off prior to tap significantly improved the cleanliness of the steel. 4. A gradient addition of 0.05% aluminum added during stream degassing showed that only 50% of the oxygen was removed during free fall in vacuum. Numerous endogenous deoxidation products resulted from the aluminum addition. Coalescence of slag particles was inhibited. 5. A gradient addition of 0.05% silicon did not affect vacuum de-oxidation. Composition of the calcium-rich inclusions was not altered.

Physical considerations in the stream degassing of steel

Physical considerations in the stream degassing of steel

Vacuum degassing of low carbon unkilled steel during casting or during solidification into block form. II. Casting by stream degassing of unkilled soft steel.

Vacuum degassing of low carbon unkilled steel during casting or during solidification into block form. II. Casting by stream degassing of unkilled soft steel.