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:在灰库底部设置仓泵，粉煤灰靠重力落入仓泵，完成进料后关闭进料阀，向仓泵内通入高压压缩空气，使物料流态化。

Pipeline transportation:仓泵内形成高压，将粉煤灰以料栓形式推入输送管道，料栓之间由空气柱隔开，靠空气柱压力推动料栓低速向前移动，全程无悬浮流的高速摩擦。

终点卸料：物料到达灰库后，经卸料装置完成气固分离，粉煤灰落入灰库，压缩空气经消声处理后排放。

Project effect:低流速输送大幅降低管道与设备磨损，管道使用寿命显著延长；物料与空气比高，耗气量较稀相系统大幅减少，能耗明显降低；仓泵间歇式输送有效避免堵管问题，系统运行稳定性提升，减少因设备故障导致的停机损失，改造后达到环保与节能双重目标。

案例四：密相输送 —— 跨区域粉煤灰长距离转运

Industry scenario:电厂与建材厂相距较远，且需利用现有地下管廊铺设输送管道，要求长距离输送、低磨损，同时不破坏周边环境。
Process selection:密相气力输送（长距离、低流速）。

Implementation process:

系统布局：在电厂设置高压仓泵输送站，建材厂设置接收仓与气固分离系统，输送管道沿现有地下管廊铺设，减少地面施工。

输送过程：仓泵将粉煤灰压缩成料栓，通过高压气流推动料栓沿地下管道低速输送，管道转弯处采用大曲率弯管，降低物料滞留风险。

接收与处理：物料到达建材厂后，经分离器将粉煤灰与空气分离，粉煤灰送入原料仓，用于水泥生产，尾气经净化后排放。

Project effect:利用密相输送技术实现长距离稳定转运，地下管廊铺设管道避免地面占地与环境破坏；低速料栓输送几乎无管道磨损，系统长期运行维护成本低，为跨区域粉煤灰资源化利用提供了密闭、高效的解决方案。