Describe the working mechanism of a dense phase pneumatic conveying system for ash transport.

A dense phase pneumatic conveying system transports ash using relatively low-velocity air and a high solids-to-air ratio. This contrasts with dilute phase systems, which use high-velocity air to suspend individual particles. In a dense phase system, the ash is moved in slugs or plugs through a conveying pipeline. The process begins with the ash being fed into a pressure vessel or hopper. Compressed air, typically supplied by an air compressor, is then introduced into the vessel. The air pressure forces the ash to form a dense plug within the pipeline. The air velocity is kept low, typically between 1 to 15 meters per second, to minimize particle attrition (wear and tear) and pipeline erosion. Auxiliary air injectors, strategically placed along the pipeline, may be used to help maintain the plug formation and prevent blockages. These injectors introduce small bursts of air to break up any compacted ash and ensure smooth flow. The dense ash plugs are conveyed through the pipeline to the destination, such as a storage silo or disposal area. At the discharge point, the air separates from the ash, and the ash is deposited. Dense phase systems are particularly suitable for transporting abrasive materials like ash because the low velocity reduces wear on the pipeline. They also minimize dust emissions because the ash is transported in a contained manner.