ANS:B - purging

The phenomenon described, where a part of the outlet stream is rejected as waste to maintain the impurity level within acceptable limits, is termed as purging. In chemical processes, purging is a crucial operation to ensure the quality and purity of the product. It involves removing a portion of the process stream, often containing impurities or undesired components, to prevent their accumulation and maintain the desired specifications of the product. Purging is a process used in various industries, particularly in chemical and manufacturing processes, to remove impurities or undesired components from a system or a stream. It involves the intentional removal or disposal of a portion of the process stream to maintain the desired quality, purity, or operating conditions. There are several reasons why purging is employed:

1. Impurity Control: Purging helps to control the concentration of impurities or contaminants in a process stream. By removing a portion of the stream that contains high levels of impurities, the overall purity of the product or process can be maintained within acceptable limits.
2. Product Quality: Purging is often used to ensure the quality and consistency of the final product. By removing any undesirable components or by-products, the product can meet the required specifications and standards.
3. System Cleanliness: In systems where buildup of residues or fouling can occur, purging helps to keep the system clean and prevent blockages or damage to equipment. It removes accumulated debris, solids, or other materials that may interfere with the operation of the system.
4. Safety: Purging is sometimes employed for safety reasons, particularly in systems handling hazardous or reactive materials. By removing potentially dangerous substances or by-products, the risk of accidents or unexpected reactions can be minimized.

Purging can be achieved using various methods, depending on the specific requirements of the process. It may involve diverting a portion of the process stream to waste, flushing the system with clean fluids or gases, or employing specialized purification techniques such as filtration or distillation. Overall, purging plays a critical role in maintaining the efficiency, safety, and reliability of industrial processes by ensuring the quality and purity of products and systems.