Fly ash pneumatic conveying
Fly ash pneumatic conveying
Fly ash pneumatic conveying is the mainstream technology for fly ash transportation in the industrial field, widely used in scenarios such as power plant fly ash collection, raw material transportation in building materials plants, and collaborative disposal in cement plants. Its core working principle is to use the kinetic energy of the airflow and the pressure difference inside and outside the pipeline to construct a gas-solid two-phase flow system in a closed pipeline, so that fly ash particles can be directionally transported with the airflow. Finally, the material and air are separated through a gas-solid separation device, achieving the goal of dust-free and high-efficiency material transportation. Compared with mechanical conveying, this technology has no direct contact between mechanical transmission components and materials throughout the entire process, fundamentally solving problems such as fly ash dust, material crushing, and equipment wear.
Fly ash itself has the physical characteristics of small particles, light texture, and good fluidity, which makes it easily entrained or pushed by air flow, making it an ideal material for pneumatic conveying technology. The essence of pneumatic conveying is to use the energy of the airflow to overcome the frictional and gravitational resistance of fly ash moving in the pipeline, so that the material can maintain a stable flow state in the pipeline until it is conveyed to the designated end point.
?1、 Core workflow (general qualitative description)
The complete process of pneumatic conveying of fly ash does not require complex mechanical linkage. It is mainly completed through four key links, which cooperate with each other to form a continuous and closed conveying loop:
Flow generation gas supply:The air source system is the power source for the entire conveying process. Compressed air is input into the conveying pipeline through equipment such as Roots blowers and air compressors, or a vacuum environment is formed inside the pipeline through a vacuum pump, thereby establishing a stable pressure difference between the inside and outside of the pipeline, or forming an airflow with sufficient kinetic energy inside the pipeline, providing a power foundation for material conveying.
Uniform feeding:Fly ash is usually stored in equipment such as ash silos and silos. The feeding device is used to smoothly and evenly feed the fly ash from the silo into the conveying pipeline, avoiding material accumulation or sudden influx that may cause pipeline blockage. The feeding process will achieve preliminary mixing of materials and airflow according to different conveying processes, laying the foundation for stable conveying in the future.
Pipeline transportation:When fly ash enters the conveying pipeline, it will fully merge with high-speed or high-pressure airflow to form gas-solid two-phase flow. According to the differences in airflow velocity, pressure, and conveying process, fly ash will exhibit two main flow states in pipelines - suspended flow or group flow. In a suspended flow, fly ash particles are completely entrained by the airflow and evenly dispersed in the pipeline as they move with the airflow; In the group flow, fly ash aggregates into material plugs or clusters, which move forward alternately under the push of airflow, and finally complete directional transportation along the pipeline from the starting point to the end point.
Gas solid separation:When the mixture of fly ash and airflow reaches the end of transportation, the material needs to be separated from the air to complete unloading. The mixture first enters separation equipment such as cyclone separators and bag filters, where fly ash particles are intercepted and collected due to their own gravity or filtration, and fall into the final material bin; After separation, the air will be purified to remove residual fine dust, and then discharged or returned to the air source system for recycling, which not only avoids air pollution but also achieves reasonable disposal of the airflow.
2、 The working characteristics of the three mainstream process forms
According to the different pressure states, airflow velocities, and material flow patterns inside the pipeline, fly ash pneumatic conveying is mainly divided into three mainstream processes: negative pressure conveying, positive pressure conveying, and dense phase conveying. The working logic of each of the three processes has its own focus and is adapted to different industrial scenarios:
Negative pressure conveying (suction type):This process creates a vacuum negative pressure environment inside the conveying pipeline through a vacuum pump. By utilizing the pressure difference between the atmospheric pressure outside the pipeline and the internal negative pressure, fly ash is "sucked" into the pipeline and then transported to the final separation device along with the airflow. The core of its work is "differential pressure suction", and the entire conveying system is in a negative pressure state. Even if there is a small leak in the pipeline, external air will flow inward, and there will be no fly ash dust leakage. Negative pressure conveying is particularly suitable for scenarios such as multi-point material collection and single point unloading, such as centralized transportation of fly ash from multiple ash hoppers in a power plant to a single ash silo.
Positive pressure conveying (pressure conveying type):Positive pressure conveying is powered by compressed air generated by air compressors and Roots blowers. The compressed air enters the pipeline from the starting point of conveying and directly pushes the fly ash towards the end point of conveying. The core of its work is "pressure feeding", which maintains a positive pressure state inside the pipeline at all times, with high power transmission efficiency, and can achieve long-distance material transportation. This process is suitable for scenarios where single point feeding and multi-point unloading are required, such as transferring fly ash from a single ash silo to multiple end users such as cement plants and mixing plants.
Dense phase transportation:Dense phase transportation belongs to the positive pressure transportation form with high pressure and low flow rate. A high-pressure airflow is formed in the pipeline through a high-pressure gas source, so that the fly ash particles no longer disperse and flow in a suspended state, but gather into continuous or intermittent material plugs. The material plugs are separated by an air column, and are pushed forward by the pressure of the air column. The core of its work is "material plug pushing". Due to the low airflow velocity, the friction loss between fly ash and the inner wall of the pipeline is greatly reduced, and the material is not easily broken. Dense phase conveying is suitable for high flow, long-distance, and high concentration fly ash conveying scenarios, especially for industrial production that requires high material integrity and equipment wear control.
3、 Advantages of adaptability between fly ash and pneumatic conveying technology
Fly ash, as a solid waste from thermal power plants, has physical properties that are highly compatible with the working principle of pneumatic conveying. This is also the core reason why this technology is widely used in fly ash transportation. On the one hand, fly ash particles are fine and have low density, which can be carried or pushed without excessive airflow energy. The transportation energy consumption is relatively low, and the material is not easily deposited in the pipeline; On the other hand, fly ash is prone to dust and moisture, and is prone to clumping. The pneumatic conveying process uses a closed pipeline, which can effectively prevent environmental pollution and material loss caused by fly ash leakage, as well as prevent external water vapor and impurities from entering the pipeline and contaminating the fly ash, ensuring the purity of the material.
At the same time, fly ash has good fluidity and can adapt to different flow states such as suspended flow and group flow. It can flexibly match various conveying processes such as negative pressure, positive pressure, and dense flow, meeting the process layout, conveying distance, and conveying volume requirements of different factories. Therefore, it has become a typical application material of pneumatic conveying technology in the field of industrial solid waste treatment.
Case 1: Negative pressure dilute phase conveying - centralized transfer from multiple dust removal points in power plants to ash storage
Industry scenario:The dust removal system at the tail of coal-fired power plant boilers requires the centralized transportation of fly ash from multiple dust collectors' ash hoppers to the ash silo in the plant area, requiring strict dust control and small renovation work. Process selection: Negative pressure dilute phase pneumatic conveying (multi-point feeding, single point unloading).
Implementation process:
Pick up end:Unloading valves and suction branch pipes are installed below the ash hoppers of each dust collector, and the branch pipes are collected into the main conveying pipeline. Each branch pipe is equipped with anti blocking and switching devices.
Power and transmission:At the end of the system, a vacuum unit is configured to create a stable negative pressure in the main pipeline. By utilizing the pressure difference inside and outside the pipeline, fly ash is sucked into the pipeline from each ash hopper, and the material moves in a suspended flow state with the airflow towards the ash silo.
Separation and emission:The gas-solid mixture enters the cyclone separator and bag filter at the top of the ash silo, and the fly ash is intercepted and falls into the ash silo. The purified exhaust gas meets the emission standards.
Project effect:The entire process operates under negative pressure, and even if there are minor leaks in the pipeline, there is no dust leakage, completely solving the problem of dust from multiple material collection points; There is no need for large-scale renovation of the original ash hopper, the equipment layout is flexible, and daily maintenance only needs to focus on the discharge valve and filtration device, greatly reducing labor costs.
Case 2: Positive pressure dilute phase transportation - coordinated disposal from power plant ash storage to surrounding cement plants
Industry scenario:The power plant needs to transfer the finished fly ash from the ash silo in the plant area to the adjacent cement plant as a cement production mixture. It is required to have single point feeding and multi-point unloading, and be able to adapt to the material needs of different production workshops in the cement plant.
Process selection:Positive pressure dilute phase pneumatic conveying (single point feeding, multi-point unloading).
Implementation process:
Feeding and Power:A rotating feeder is installed at the bottom of the power plant ash silo to evenly feed fly ash into the conveying pipeline. The Roots blower provides compressed air, forming a positive pressure airflow inside the pipeline.
Transportation and distribution:The airflow drives the fly ash to be transported in a suspended state along the pipeline. A material distribution valve is installed in the cement plant area to distribute the material to multiple unloading points such as the clinker grinding workshop and the mixed material warehouse.
Unloading and Closing:Each unloading point is equipped with a small separator and a level control device, allowing the fly ash to smoothly fall into the workshop material bin, and the exhaust gas to be discharged after simple filtration.
Project effect:Positive pressure conveying has high power transmission efficiency and can flexibly achieve multi-point unloading, meeting the synchronous material use requirements of multiple workshops in cement plants; The system has a simple structure, low equipment investment and operating costs, realizes the resource utilization of fly ash, and replaces traditional automobile transportation, reducing dust and traffic pressure on roads around the factory area.
Case 3: Dense/Dense Phase Transportation - Energy saving Renovation of Ash Transport System in Old Power Plants
Industry scenario:The original dilute phase conveying system of the old power plant had severe pipeline wear, high energy consumption, and easy blockage. It needs to be transformed into a long-distance, high flow conveying system, which requires reducing pipeline wear and energy consumption while adapting to the original plant space layout.
Process selection:Dense/dense phase pneumatic conveying (bin pump type, high pressure and low flow rate).
Implementation process:
Feeding process:A bin pump is installed at the bottom of the ash silo, and fly ash falls into the bin pump by gravity. After feeding is completed, the feed valve is closed and high-pressure compressed air is introduced into the bin pump to make the material fluidized.
Pipeline transportation:High pressure is formed inside the silo pump, pushing fly ash into the conveying pipeline in the form of material plugs. The material plugs are separated by air columns, and are driven forward at low speed by the pressure of the air columns, without high-speed friction of suspended flow throughout the entire process.
Terminal unloading:After the materials arrive at the ash silo, the gas-solid separation is completed by the unloading device, and the fly ash falls into the ash silo. The compressed air is discharged after noise reduction treatment.
Project effect:Low flow rate transportation significantly reduces pipeline and equipment wear, and significantly extends pipeline service life; The material to air ratio is high, and the gas consumption is significantly reduced compared to the dilute phase system, resulting in a significant decrease in energy consumption; The intermittent delivery of the warehouse pump effectively avoids pipe blockage problems, improves system stability, reduces downtime losses caused by equipment failures, and achieves dual goals of environmental protection and energy conservation after renovation.
Case 4: Dense phase transportation - long-distance transportation of cross regional fly ash
Industry scenario:The power plant is far away from the building materials factory and requires the use of existing underground pipe galleries to lay transmission pipelines, requiring long-distance transportation, low wear, and not damaging the surrounding environment.
Process selection:Dense phase pneumatic conveying (long-distance, low flow rate).
Implementation process:
System layout:Set up a high-pressure warehouse pump delivery station in the power plant, and a receiving warehouse and gas-solid separation system in the building materials factory. The delivery pipeline is laid along the existing underground pipe gallery to reduce ground construction.
Transportation process:The warehouse pump compresses fly ash into a material plug, which is driven by high-pressure airflow to transport the material plug at low speed along the underground pipeline. A large curvature bend is used at the turning point of the pipeline to reduce the risk of material retention.
Reception and processing:After the materials arrive at the building materials factory, the fly ash is separated from the air by a separator and sent to the raw material warehouse for cement production. The exhaust gas is purified and discharged.
Project effect:Utilizing dense phase transportation technology to achieve long-distance stable transportation, laying pipelines in underground pipe galleries to avoid ground occupation and environmental damage; Low speed material plug conveying has almost no pipeline wear, and the long-term operation and maintenance cost of the system is low, providing a closed and efficient solution for the cross regional utilization of fly ash resources.