Tight-cone conveying

Is it a dense phase or a compact phase? It’s a huge difference! ! In the case of a dense phase: gas-solid transport can generally be divided into two forms, namely dense-phase transport and dilute-phase transport, with dilute-phase transport also being known as pneumatic transport. There are two flow patterns in dense-phase transport: viscous-sliding flow and pneumatic flow. When the solid particles are relatively large and the relative velocity between the gas flow and these particles is not sufficient to fluidize them, the particles move downward slowly; the particles in the central area have a higher flow velocity, while those on the periphery have a lower flow velocity. This type of flow is known as viscous-sliding flow. If the relative velocity between the solid particles and the gas is high enough to fluidize the particles, then the gas-solid mixture exhibits fluid-like properties and can flow in any direction. This type of flow is called pneumatic flow. Compared to viscous-sliding flow, the velocity of gas-entrained flow is higher.

For a long period in the last century, our country relied on people carrying and transporting materials such as sand, gravel, and coal by hand, creating a spectacular continuous conveyor system that made significant contributions to the recovery and development of our nation’s economy. As the pace of industrialization in our country accelerates, this mode of transportation has gradually disappeared, existing only in some special circumstances. 　　The development of conveying technology in China’s cement industry is a reflection of the progress in continuous conveying technology within the country’s industrial sector. At present, it is an era in which mechanical continuous conveying technology and dilute-phase conveying play a dominant role. However, in today’s era focused on energy conservation and emission reduction, few people in the cement industry advocate for low conveying air velocities and high-concentration pneumatic conveying technologies. This technology is the dense-phase conveying technology that will be briefly introduced in this article. 1. Dense-phase conveying technology is one of the conveying technologies with great application prospects in China. Continuous conveyors can be classified into two main categories: mechanical and fluid-based types. Mechanical conveyors, depending on their application, generally include belt conveyors, gantry elevators, chain conveyors, vibrating conveyors, and screw conveyors, while fluid-based conveyors fall into categories such as pneumatic conveying, hydraulic conveying, pump-driven conveying, and containerized pipeline conveying. In various industrial sectors, conveyors or conveying systems play an important role akin to arteries. Over the past few decades, continuous conveying technologies and devices have seen various improvements and developments, including enhancements to their structure to enable flexible layout of the conveyance lines, efforts to prevent dust from being generated, leaks from occurring, or foreign substances from mixing in from an environmental and hygiene perspective, as well as improvements aimed at increasing reliability and the automation of the systems. The conveyor technologies and equipment with application potential in our country include: (1) belt conveyors with sealed cross-sections ； (2) Free and flexible 3D continuous conveying technology and equipment ； (3) Clean and hygienic hopper-type continuous conveyor ； (4) High-reliability and highly automated conveyor belts ； (5) Dense phase conveying technology ； (6) A comprehensive technology that combines mechanical continuous conveying technology with fluid-based continuous conveying technology. 　　Compact phase conveying technology – Advances in pneumatic conveying technologies featuring low conveying air speeds and high concentrations have enabled this previously energy-intensive method to achieve a level of performance comparable to that of mechanical continuous conveying systems. This technology can be widely applied in food raw materials, cement, chemical raw materials, pharmaceutical raw materials, coal powder and fly ash in the energy industry, as well as in various powder-related processes in the petrochemical industry. This is because dense-phase conveying technology can meet the higher requirements of today’s users regarding the prevention of crushing, sticking, agglomeration during conveying, as well as the prevention of foreign matter from entering and dust formation. 2. Current status of the application of dense-phase conveying technology and equipment in the cement industry Powder conveying is a topic that is both ancient and emerging. With the continuous advancement in research on pneumatic conveying theory and equipment, pneumatic conveying systems are also being updated generation after generation. Since its inception, a variety of conveying devices have emerged. Therefore, pneumatic conveying has been widely used, especially for transporting powder and granular materials using pneumatic conveying devices. A considerable number of cement plants in our country suffer from numerous failures in their conveying equipment, which prevents the main units (kilns and grinders) from operating stably over the long term; as a result, the systems cannot achieve full production capacity, leading to huge losses. The research and development of transition facilities between various plants has become an urgent task in China’s dry-process cement production. To improve the utilization rate of equipment and meet the needs of applications that require continuous feeding, as well as to address the industry’s growing demands for increased production while reducing consumption, China has developed dense-phase conveying systems that are now used in industrial production: large-capacity senders and tubular low-resistance fluidization devices, QSB dense-phase pneumatic conveying pumps, and XL-type flow-stabilizing silo pumps, among others. 2.1 Large-volume senders and tubular low-resistance fluidization devices In November 2007, the large-volume senders and tubular low-resistance fluidization devices developed by Hefei Cement Research and Design Institute were approved by an expert panel. The expert group believes that large-volume senders and tubular low-resistance fluidization devices improve the material-gas mixing ratio in dense-phase transportation, establish a mathematical model for long-distance, high-concentration gas-solid two-phase flow transportation, reduce gas consumption, and achieve low power consumption and minimal wear ； The transmitter is equipped with a modular weighing system that enables instantaneous and cumulative weighing of materials, and it features real-time monitoring as well as control of system parameters. The system is scientifically designed, has a rational structure, and exhibits a high degree of mechatronics integration. 　　The practical application of large-capacity senders and tubular low-resistance fluidization devices at Zhoukou Cement Co., Ltd., part of Henan Tianrui Group, over the past two years has shown that when transporting fly ash, with a pipeline length of 1268 m (equivalent distance of 1504 m), a transport rate of 56.8 t/h is achieved, and the power consumption is 4.3 kWh/t (3.6 kWh/t·km). The material-gas mixing ratio can reach up to 23.6, while the average flow velocity is 8.7 m/s. The system is easy to operate, and it achieves significant energy savings and reduced consumption. The technical and economic indicators of the system’s operation have reached international advanced levels. 　　Large-capacity senders and tubular low-resistance fluidization devices feature energy efficiency and environmental friendliness, flexible layout, and good adaptability. Their cost-performance ratio is superior to that of similar foreign products, making them suitable as substitutes for imported ones. It has broad prospects for application and promotion in industries such as building materials, chemicals, metallurgy, power, and port logistics. 2.2 QSB Dense Phase Pneumatic Conveying Pump The QSB type fully automatic dense phase pneumatic conveying pump is an upward-fed silo pump. It represents a new type of dense phase pneumatic conveying device that combines the principles of pressure difference, jet technology, and fluidization technology. It serves as the main equipment in positive pressure pneumatic conveying systems; it uses compressed air as power to transport powdered materials through pipelines to ash storage tanks or material bins. This silo pump features advanced technology, a novel design, stable performance, reliable operation, a high degree of automation, simple operation, minimal maintenance requirements, and low overall operating costs. 2.3 XL-type flow-stabilizing silo pump: The XL-type flow-stabilizing silo pump consists of a top silo (for storing material and providing buffering), two pressure chambers, an air compressor, and an electrical control system. It is a pneumatic conveying device capable of continuously transporting powdered materials, and can be used in the cement industry for applications such as the continuous supply of raw material at the end of the kiln, coal powder at the beginning of the kiln, and kiln ash. By achieving continuous conveying, the output of conveyance pipelines of the same diameter can be increased (50%–100%) ； It can reduce the standby time of the air compressor, improve its operational efficiency, and lower the electricity consumption per ton of cement transported. Power consumption reduction of 11%–35% ； This device can be used in both dilute-phase pneumatic conveying systems and dense-phase pneumatic conveying systems ； By reducing the start and end stages of transportation, it improves the average solid-gas ratio and system stability, while reducing gas consumption. 3 Prospects for the Application of Dense Phase Conveying Technology in the Cement Industry. The use of dense phase conveying technology in China’s cement industry is relatively limited; it is particularly not favored by specialized cement design institutes, which prefer to use reliable, though energy-intensive, dilute phase pneumatic conveying technologies as well as mechanical continuous conveying equipment. Based on the practical applications of large-capacity senders and tubular low-resistance fluidization devices, QSB dense-phase pneumatic conveying pumps, and XL-type flow-stabilizing silo pumps, it can be concluded that dense-phase conveying technology possesses the following characteristics that make it suitable for modern industrial production: (1) It enables the equipment to operate in a dust-free, noise-free environment, while also being explosion-proof and reliable ； 　　(2) Various sensors can be used to achieve fully automatic operation of the equipment and systems ； 　　(3) The multi-product, small-volume production system minimizes inventory on hand and stock buildup for sales. In other words, “produce the required amount using the necessary materials within the required time.” It is a production system that is flexible and can be adjusted promptly and flexibly. At this time, in the manufacturing sector, robots, precision machining equipment with automatic control, and computer-controlled systems composed of unmanned handling and conveying equipment along with necessary information enable the manufacturing sector to achieve high quality management as well as efficiency and rationalization. 　　(4) Maintain cleanliness to prevent the material from breaking or being contaminated with foreign substances during transportation ； 　　(5) Achieve further energy savings through higher efficiency, faster speed, and higher concentration ； 　　(6) It can prevent raw materials or cement from sticking together, agglomerating, or arching, and enables research and comprehensive application of supporting technologies such as material transportation, dust collection, grading, and metering ； 　　(7) It frees the owner from the hassle of wear and tear issues with mechanical conveyors. Low-energy dense-phase conveying technology has now reached a level where it can compete with mechanical continuous conveying. There are numerous bulk transportation processes in new dry-process cement production lines; in light of the responsibilities and tasks related to energy conservation and emission reduction, dense-phase conveying technology and equipment will inevitably be used more widely. Since the conveying system is the backbone of the cement production process, it is recommended that design firms in China’s cement industry thoroughly understand and grasp the entire system during the design phase, in order to achieve the most efficient continuous conveying technologies and equipment configurations, thereby ensuring lower energy consumption in cement production.