Recirculation load

X 0.0518-0.0418 VF, 0.0518-0.0113 where X = quantity of fresh air and = total air flow. Thus 75.3 percent of the air is recirculated. Load on the preheater is obtained from an enthalpy balance... 

The ilmenite flowsheet is shown in Figure 25.11 and was specifically designed to reduce recirculation loads of gangue during cleaning operations. 

Dust from the kiln is largely captured in a suspension preheater that which is not is removed by an electrostatic precipitator before the gas passes up the chimney. The flow of gas is aided by an exhaust fan. The dust is as far as possible returned to the system by mixing with the raw meal or with the fuel (insufflation), though the extent to which either is possible may be restricted by its content of alkali sulphates or chlorides, which if high could lead to an unduly high recirculating load, conducive to the formation of deposits or undesirably high concentrations in the clinker. 

Advantages claimed for the drum granulator over the disc are greater capacity, longer retention time for materials difficult to agglomerate or of poor flow properties, and less sensitivity to upsets in the system due to the damping effect of a large recirculated load. 

Atmospheric Leach and Precipitation Processes. Aluminum is completely precipitated at the pH used for ferrous iron oxidation. The precipitated aluminum reports to the residue recycle stream and is releached in the Induced Jarosite Precipitation stage. There is therefore the risk of a recirculating load building up in the circuit between the Induced Jarosite Precipitation and Secondary Neutralization circuits. However, the pH of the intervening Primary Neutralization step is sufficiently high to precipitate excess aluminum and provide a safe bleed from the process. 

When finer material is required, a ball mill is used in a closed circuit. The feed is ground and then classified to separate coarse from fine sohds. The coarse sohds, also called oversized particles, are returned back to the mill for further grinding. This is called the recirculation load and the circuit is considered a closed circuit. In a dry circuit, the classifier may be a set of vibrating screens. 

In a typical copper or zinc circuit, the recirculation load can be as high as 250-350% of the new feed. The mill and mill discharge pumps must then be sized for the combination of recirculation load and new feed. 

Soft high clay is present in certain copper ores. In a diluted form at weight concentration smaUer than 40%, it can be handled fairly weU. However, particular attention must be paid in mUling circuits when the concentration may approach 50%, as the viscosity affects flow and recirculation loads. 

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