Influence of expanded bends on wear and particle degradation in pneumatic conveying system pipeline

Pneumatic conveying systems are used to convey a wide range of materials. Research during the last two decades has helped the designers to design reliable and energy efficient systems for a range of conveying applications. Erosion of plant components; especially the pipe bends, while conveying hard and abrasive materials has been one of the major operational problems, Most users have either lived with the problem or have employed expensive bend materials to decelerate the erosion rate and prolong the life of the bends. Velocity of conveying gas is probably the most important operating variable influencing the rate of erosion. It has been found that doubling the velocity can increase the erosion rate by about six times, It is, therefore, important that the systems are designed with lowest possible velocity of conveying, In a conventional conveying system, some materials can only be conveyed in dilute phase suspension flow for which high conveying velocity is used. It is a common practice to step the pipeline to a larger bore part way along the length to reduce the conveying velocity, which would otherwise increase from the beginning to the end of the conveying line due to the air expansion effect. A comprehensive test programme was undertaken to study the bend erosion in a pneumatic conveying pilot plant with modified test pipeline. Tapered divergent sections were placed on the upstream of the flow into a bend and tapered convergent sections were placed on the downstream of the flow from a bend. The bends used were also of a larger bore to match with the expanded section of the pipeline. The results were compared with the bend erosion in a pipeline loop of constant bore. The effect of reduced velocity of impact on the bends on the degradation of the product and its influence on the conveying line pressure drop is also discussed.