What is the oxygen excess coefficient for the air used in large-scale roasting in the production of acid from smelting flue gas?
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What is the oxygen excess coefficient of the air used for roasting in large furnaces in the production of acid from smelting flue gas? A high air excess coefficient leads to a decrease in gas concentration; what other effects does it have besides carrying away a large amount of heat?
The excess air coefficient for roasting is set at 1.25 (1.1–1.25); it cannot be set too high, as various factors such as negative pressure leaks at the feeding and discharging ports must be taken into account. A value of 1.1–1.15 is sufficient during operation. Generally, the ratio of air (by volume) to material (by weight) is 1.8:1 for wet materials, while it is close to 2:1 for dry materials. This ratio also depends on the sulfur content. Excessively high values can lead to: 1. an increase in soluble sulfur in the semi-finished products, resulting in greater sulfur loss; 2. most importantly, it prevents proper fluidization during roasting, which may cause bubbling phenomena; 3. disruption of the uniform stability of the boiling layer, making operation very difficult; 4. an increase in dust emissions, thereby increasing the load on subsequent equipment; 5. it may also cause positive pressure in the system.