Rotary Kiln: Difference between revisions

The direct fire kiln is a single shell vessel with rings added inside to slow the catalyst/[[feedstock]] as it tumbles from the inlet (elevated part) towards outlet (lower part). The oxidation medium (air) can flow co-current or counter current to catalyst/[[feedstock]] movement depending on the reactor design. The oxygen concentration in the medium/[[feedstock]] will decrease in the same direction because of its consumption. Therefore, the zone in the vessel located near the inlet may function as a stripper of volatile components of coke. The kiln is fired by gas burners directly against the outer shell of the vessel. The temperature inside the kiln is controlled by adjusting the burner heat, varying concentration of oxygen in the oxidizing medium (air) and its flow.  

The indirect fire kiln, often referred to as calciners, comprises of a double-shell cylinder vessel. The inner shell is similar as that of the direct fire kiln and the outer shell is heated, using a heat shroud, which raises the temperature of the [[combustion]] gas or steam in the space between the shells. This means that indirect fired kilns process material in an inert environment as the catalyst/[[feedstock]] does not come into contact with the process gas<ref>[https://feeco.com/rotary-kiln-design-direct-fired-vs-indirect-fired/ Rotary Kiln Design: Direct Fired Vs. Indirect Fired]</ref>. However, in some cases, the inner cylinder shell is ebullated (fluidised by the continual injection of gas and liquid) allowing hot gases or steam to enter and contact the tumbled catalyst/[[feedstock]]. The catalyst/[[feedstock]] temperatures are controlled by monitoring the temperatures of the inlet and outlet gases<ref>[https://www.sciencedirect.com/science/article/pii/B9780444535566000069 Handbook of Spent Hydroprocessing Catalysts]</ref>.