![]() Dense phase also refers to the solids loading within the conveying line. In plug flow, coarse, permeable bulk solids like pellets or catalyst beads can be reliably conveyed, whereas with moving bed flow, fine and air-retentive bulk solids like cement or fine ash can be effectively conveyed. Only certain powders or bulk solids can be effectively conveyed in these two dense phase modes. Two modes of flow can result in dense phase, namely piston/plug flow and moving bed flow. This occurs when particles are conveyed in the gas stream at a velocity that is less than the saltation velocity. ![]() Typically, a dilute phase line conveys less than 15 lb (~7 kg) of solids per pound (~0.5 kg) of gas at a pressure of less than 15 psig (~1 barg).ĭense phase. Dilute phase also refers to the lean solids loading within the conveying line. Many bulk solids can be conveyed in dilute phase however, potential adverse effects such as pipeline wear or particle attrition could occur due to high conveying velocity. This type of system is often referred to as a stream flow system because particles are fully suspended in the gas stream. This occurs when particles are conveyed in the gas stream at a velocity that is greater than the saltation velocity. Choking velocity is similar to saltation, except it is in the vertical orientation.ĭilute phase. This is the gas velocity at which particles that are fully suspended within a horizontal conveying line begin to drop out of suspension and settle in a layer on the bottom of the pipeline. ![]() Numerous terms are used to describe gas/solids flow and pressure conditions within a pneumatic conveying system. A systems approach is vital when selecting a pneumatic transport system. Key components of the gas flow generator, solids hopper/feeder, pipeline/valves, and filter all play a role in effective operation of a pneumatic conveying system ( Figure 1). Compounding the difficulty of careful design is the fact that pneumatic conveying relies on a system instead of a single equipment component, like a pump. Poorly designed pneumatic conveying systems can be unreliable and inefficient, and may even be unsafe. Thus, users of the technology often rely on equipment suppliers, prior applications, and in some cases, trial-and-error. Though many advances have been made to pneumatic conveying systems, problems of insufficient capacity, plugging, line buildup, pipeline wear, particle attrition, and excessive energy consumption still plague many operations.įurthermore, the selection and design process for dilute or dense phase systems is not generally taught to engineers at universities. Pneumatic transport remains a popular conveying technology compared to mechanical systems ( e.g., screws, belts, and drags) because of the benefits of flexible arrangements, product containment, low maintenance, and ease of automation. Compare this to the selection of a pump for a liquid or gas, where proven design methods and best practices are ubiquitous, provided accurate definition of the fluid and the equipment requirements. Though the use of these systems to transfer bulk materials at all types of manufacturing facilities has been very common for over half a century, the selection and design process is not as well-known. You may have come across the terms dilute or dense phase pneumatic conveying in your powders or bulk solids handling applications. Use this methodology to select a dilute or dense phase mode of pneumatic transport. Step 3: Navigate the conveyor selection flowchart.Step 2: Determine material characteristics.
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