【China Alumina Network】 The alumina plant purchases alumina stored in a silo and pipes it to electrolysis cells in the electrolysis plant. There are three ways to transport alumina to the electrolytic cell: dilute phase transport, dense phase delivery, and ultra-dense phase delivery. That is to say, alumina uses air as its carrier and “runs” from the pipeline to the electrolytic cell under external force.
Dilute phase transport When dilute phase transport, the solid-to-gas ratio is very low, ie the mass ratio is generally 5 to 10. At present, some small aluminum plants in China still use this method to deliver alumina. The transmission system of this method is mainly composed of a pressure pump and a transmission pipeline. The transmission distance is about 400m. Compressed air of 0.6~0.8N/mm2 is used as the power source. The alumina pump is directly sent from the storage tank to the next system through the warehouse pump. In the high storage tanks, the airflow velocity is often greater than 30m/s.
Dilute phase energy consumption is high, the solid-gas ratio is very low, the pipeline wear is severe, and the alumina powdering is severe. It is extremely unfavorable to electrolysis production and will be gradually replaced by the transportation of dense phase and ultra dense phase. Dilute phase transport, also known as suspension transport.
The dense phase transportation method is a relatively new way of alumina transportation. It overcomes the shortcomings of dilute phase transport and still uses compressed air as a power source. The system consists of a pressure vessel, a control system, and a pipe network. High degree of automation, small air consumption, low alumina flow rate and small breakage.
In general, the dense phase transportation is also called fluidized transportation. The airflow velocity is less than 15m/s and the solid-gas ratio is greater than 20. At this time, the material (aluminum oxide) is no longer evenly distributed in the pipeline, but is in a dense state, but also Do not block the pipe. This method is still based on the kinetic energy of air.
In dense phase delivery, plug flow delivery has been widely used. The conveying system is mainly composed of a pressure vessel device, a control pipe network, a delivery pipe with an inner pipe and an adjustment member, a compressed air system with a dehumidification system, a unloading and dust removal system, various valves, a detection instrument, a PLC control device, and a process. Control software and other components.
The plug-flow dense phase transfer technology developed by China has already entered the international advanced level and has many new highlights: the pressure vessel material metering system, the new technology for quick ramming of pipeline materials, the wear-free exhaust technology of pressure vessels, and the pressure/time parameter control material Bit technology, new type of inner tube adjustment mechanism and corresponding supporting process control software and hardware systems, calculation software, etc. The alumina transportation capacity of a single set of equipment is greater than 36 t/h, and the power index is 0.0102 kWh/(t·m). The conveyor line has the characteristics of novel technology, advanced technology, high degree of automation, accurate measurement method, stable operation, large transmission capacity, small wear of alumina materials, low energy consumption, investment and environmental protection, etc. It has already been used in some large-scale new construction and expansion projects. The project was effectively applied.
Ultra-dense phase transport The ultra-dense phase transport is relative to the dense phase transport. This method uses low-pressure fans for air supply and pneumatic flow trough transport. It is only suitable for long-distance horizontal transport of alumina and should be powdery. The technology is characterized by: alumina in the flow channel in the fluidized forward movement, solid-gas ratio is greater than 100, the movement speed is low, the material is not easy to break, the system is fully sealed, the required air pressure is low, the amount of wind is small, the degree of automation Advanced, which is an advanced alumina powder delivery technology, is used by most electrolytic aluminum plants and is used in silos to transport cleaned and returned fluorine-containing alumina to each electrolyzer.
The ultra-dense phase transport does not require compressed air as the transmission power, only the lower pressure air is required to float the alumina, the solid-gas ratio is as high as 500, and the air pressure is only about 0.005 N/mm2, and the centrifugal fan can meet the requirements.
The main equipment of the ultra-dense phase conveying system is the air moving chute and the centrifugal fan. The former does not include the moving machinery parts, and the maintenance workload is small; the conveying speed is low, the fitting wear is small, the gas damages the material particles is small, and the conveying pressure is low. Ordinary fans are enough to realize automatic operation; there are few control elements and the control operation process is quite simple, but compared with the dense phase transmission, there are great restrictions in the configuration and the flexibility is poor. The ultra-dense phase delivery system is particularly suitable for the transport of fluorinated alumina back to the electrolyzers along the daily bins on both sides of the electrolysis plant.
Selection of Conveyor Modes Large-scale large-scale electrolytic aluminum plants currently use large pre-baking cells and are horizontally configured. The following alumina transport mode is a preferred method for low investment, high degree of automation, low maintenance, low energy consumption, and no pollution. From the storage warehouse or warehouse to the daily storehouse, it adopts the pipeline type dense phase transportation, and the daily consumption bin to the electrolytic cell adopts the ultra-dense phase transport of the air-moving chute. The advantages of the two transportation methods are concentrated. (Wang Zhutang)
