Satish C. Koria

Study of free fall gas atomisation of liquid metals to produce powder

Abstract A free fall gas atomising unit was designed and constructed to produce metal powder. The effect of focal length, number, and diameter of nozzles and apex angle of atomisers is studied on size and size distribution of the powder, atomisation efficiency, and particle shape by disintegrating the molten stream at various plenum pressures, superheats, and free fall distances. Droplets were found to be solidified and built up around the nozzles and the liquid delivery tube whenever the atomiser was used beyond a particular value of the plenum pressure; this pressure is termed limiting plenum pressure. All the powder collectives produced under a wide range of conditions were found to obey log normal distribution function. The geometric standard deviation was shown to bear a constant value. The mass median size was correlated with the dynamic parameters characterising the atomising field and a correlation is proposed. The atomisation efficiency was correlated with the mass flowrate and velocity of gas.

Influence of post-combustion heat transfer efficiency on fuel reduction in COREX process

Abstract The influence of post-combustion, heat transfer efficiency, and the degree of metallisation is studied with regard to coal saving and export gas in the COREX process using a thermochemical model. An increase in post-combustion ratio decreases the coal rate and the amount of reduction gas, which influences the achievable degree of metallisation, when no additional reduction gas is added to the system. Further post-combustion with oxygen generates a higher temperature than that with air at all post-combustion ratios. A higher heat transfer rate is necessary to keep the temperature of the gas within the refractoriness limits of the lining material. It is asserted that the post-combustion ratio, the degree of metallisation, and the medium for post-combustion must be adjusted according to the refractoriness of the lining material of the melter–gasifier, the efficiency of heat transfer mechanisms from the post-combustion zone to the bath, the gas handling efficiency, and the thermal energy requirement of the surplus gas, when considering the use of post-combustion in the COREX process.

Studies on metal build upon atomisers during free fall gas atomisation of liquid metals

Abstract In free fall gas atomisation of liquid metals, the atomised droplets mainly move downward, while some of them fly in an upward direction. Under certain conditions the upward moving droplets will deposit on the surface of the gas nozzle and metal delivery tube of an atomiser, which may cause a hindrance to the flow of liquid metal and gas. The effect of atomisation parameters, such as gas pressure, focal length, apex angle and diameter of gas nozzle, on the metal buildup on the atomiser have been studied during the free fall gas atomisation of lead, zinc and aluminium. The plenum pressure of gas at which deposition of atomised droplets on the surface of the gas nozzle and metal delivery tube takes place has been termed as limiting plenum pressure, and the corresponding gas velocity at the impingement point as limiting gas velocity. It has been shown that the limiting plenum pressure is different for different metals in the same atomiser. The limiting plenum pressure has been found to increase with free fall distance or specific gravity of liquid metals, and with a decrease in apex angle of atomiser. A correlation is proposed to determine the limiting gas velocity for free fall gas atomisation of metals.