Many production occasions need to arrange a pneumatic conveying system, but for manufacturers, they often encounter such a problem: "This kind of pneumatic conveying can be divided into dilute phase pneumatic conveying and dense phase pneumatic conveying. Which one should I choose?"
Before doing this multiple choice question, we must first understand the nature of pneumatic transport
Pneumatic conveying, also known as air conveying, uses the energy of air flow to transport granular materials in a closed pipeline along the direction of air flow, and is a specific application of fluidization technology. The pneumatic conveying device has the advantages of simple structure and convenient operation. Can be used for horizontal, vertical or inclined conveying. During the conveying process, physical operations or some chemical operations can also be performed, such as material heating, cooling, drying, air classification, etc. But compared to mechanical conveying, the energy consumption is greater, the particles are more easily destroyed, and the equipment is more prone to wear. In addition, materials with high moisture content, adhesion or high-speed movement that are prone to static electricity are not suitable for pneumatic conveying.
Pneumatic conveying is divided into two types: dilute-phase pneumatic conveying and dense-phase pneumatic conveying, which are mainly different from dense-phase pneumatic conveying of particles in pipeline transportation. However, in order to make the right choice, we must first understand the strengths and weaknesses of both processes and then consider them in conjunction with our own process specification.
Dilute Phase Pneumatic Conveying
Diluted phase pneumatic conveying generally means that the solid phase content is less than 100kg/m3 or the solid-gas ratio (the mass flow ratio of the solid phase conveying volume and the corresponding air consumption) is 0.1 to 25, and the material is suspended in the pipeline. During the conveying process, it can be used for conveying in horizontal, vertical or inclined directions. Physical and practical operations such as heating, quenching, drying and air grading can also be done together with other mechanical equipment or some chemical operations.
The conveying forms of dilute phase pneumatic conveying are divided into pressure (positive pressure) type, suction (negative pressure) type and mixed type. The main features of positive pressure conveying are large conveying capacity, long conveying distance and stable operation. The main feature of suction conveying is that it can be conveyed from low position (or bulk), multiple points to high position and single point. Pressure pull-in can meet special conveying requirements.
From an investment perspective, due to the relative simplicity of the dilute phase system, the initial investment cost is very economical and easy to maintain compared to the dense phase (dense phase).
In the process of dilute phase conveying, the loss of conveying materials may be caused, because the high speed leads to the generation of dust and broken materials, and the energy efficiency is relatively low. The shorter the conveying distance, the smaller the conveying capacity, the more obvious. In addition, the dilute phase used to grind the product can cause wear on conveyor lines and piping bends.
Dense Phase Pneumatic Conveying
Dense phase pneumatic conveying generally refers to the conveying process with solid phase content greater than 100kg/m3 or solid-gas ratio greater than 25. The operating gas velocity is lower, that is, a higher gas pressure is used to form the gas supply system. There are several different ways of dense phase pneumatic conveying, such as conveying tank conveying and rotary feed conveying.
The pneumatic conveying of the conveying tank is maintained by filling the conveying tank with the necessary working pressure, and selecting the conveying exhaust valve and the air knife to convey the material (the material is in a plunger state in the pipeline). The conveying has the characteristics of low wind speed, high solid gas and high conveying pressure. The gas is usually delivered with air or nitrogen, and the power is generally provided by a compressor. Its specific feature is that the conveying speed is low, which has little effect on the quality of materials and products. The dense phase pneumatic conveying of the rotary feeder adopts the dilute phase positive pressure conveying method, and the power is provided by the compressor. The system has high pressure, small flow, and large conveying capacity, which basically has no adverse effect on the material.
Dense-phase pneumatic conveying has large conveying capacity and can carry out long-distance pressing, and low-speed conveying can reduce material and system wear. Abrasive products are more suitable for dense phase pneumatic conveying due to their slower speeds. When properly designed, dense phase pneumatic conveying is generally more energy efficient than dilute phase.
Dense phase pneumatic conveying can only be used when the air supply pressure is high or the conveying distance is short. In addition, in large-diameter, long-distance, large-dense-phase (dense-phase) systems, special pipe racks and additional steel structures may need to be installed to compensate for pipe forces, increasing installation and maintenance costs.
Generally speaking, the choice of conveying method should be considered in combination with conveying distance, pressure availability, characteristics of conveyed material and its own economic conditions. It can be summed up as follows:
1. Almost any material can be conveyed in dilute phase, but materials with larger friction such as abrasive products are more suitable for dense phase conveying;
2. The longer the conveying distance, the more inclined to dilute phase pneumatic conveying;
3. The dilute phase pneumatic conveying system wears out quickly, and the parts need to be replaced; although the initial cost of the dense phase pneumatic conveying system is higher, it is more convenient to maintain.