Abstract: The erosion caused by solid particles is a major problem in catalytic cracking units. The riser outlet is the most vulnerable region to this process because a change in direction of the biphasic flow of gas and catalyst particles occurs. In this work, different configurations for a riser outlet were studied aiming at minimizing erosion. Computational Fluid Dynamics (CFD) with Dense Discrete Phase Model (DDPM) approach was used to simulate the gas-solid flow in a riser. The k-ε turbulence model was used to model the turbulence. It was observed that an abrupt L outlet produced the same average erosion rate as a soft outlet, while an abrupt T outlet provided an average erosion rate two times larger than the abrupt L outlet. Additionally, new riser outlet geometry was proposed in order to minimize erosion on top of risers. However it was found that this geometry presented disadvantages when compared to the other outlet geometries studied.

• Publication Date: 27-Sep-2015
• DOI: 10.15224/978-1-63248-068-2-04
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Abstract: Gravel extraction refers to the actual process of removal of gravel from a place of occurrence. The increase in demand for gravel for construction purposes has placed immense pressure on the environment where these resources occur. Gravel extractors employ different methods of extraction along river channels and their flood plains. Using environmental impact assessment guidelines, a host of environmental aspects were identified along Labasa, Dreket i (Naua) and Tabia Rivers of Vanua Levu. These aspects include collapsing river banks, habitat destruction, and impact on water quality, flora, fauna and riparian vegetation. These aspects have a significant impact on environmental functionality of the valley. It is therefore, concluded that there is need for more environmental r eg ulat ion s and stringent monitoring system to be developed and implemented.

• Publication Date: 27-Sep-2015
• DOI: 10.15224/978-1-63248-068-2-05
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