From the emergence of pneumatic air slide transportation to its wide application, it has undergone a research transition from the dilute phase to the dense phase, which has promoted the continuous development of pneumatic air slide transportation.
As far as today’s research on pneumatic air slide conveying of powder is concerned, most of them still focus on short-distance dense-phase pneumatic conveying, mainly to solve the problem of short-range pneumatic conveying within or between factories. The long-distance pneumatic conveying system, such as the pneumatic conveying system for ash removal in power plants, is often realized by multi-stage relay or system series connection due to technical limitations.
However, in the case of limited site conditions or difficult land acquisition, it is still difficult to realize long-distance pneumatic air slide transportation. Therefore, research and development of new technologies for long-distance pneumatic air slide transportation is urgently needed.
The key factor affecting the long-distance pneumatic air slide conveying of powder is stability. Stability is the smoothness of the conveying process. Unstable conveying may cause blockage and make the conveying impossible.
Air slide conveying stability
Controlling the gas velocity in the pipe and making it stable within a certain range is the task that must be completed to ensure energy savings in transportation. The use of a reducing tube can effectively reduce the gas velocity within a certain range, thereby reducing the problems caused by the high delivery gas velocity.
The superficial gas velocity of long-distance pneumatic air slide transportation increases continuously along the pipeline, and the flow pattern of gas-solid two-phase flow also changes accordingly.
When the conveying gas velocity drops beyond the boundary of dense-phase steady-state conveying, unstable dune flow is formed, which is characterized by increased pressure fluctuations. Continuing to reduce the conveying gas velocity, the material will accumulate along the pipeline until the pipeline is blocked. Therefore, it is of great significance to study the stability of pneumatic Air Slide conveying so that the air slide conveying system can maintain a stable state for realizing long-distance pneumatic air slide conveying.
Double casing pneumatic air slide conveying system
The double-casing pneumatic air slide conveying system was originally designed to solve the clogging problem of long-distance transportation of fly ash in the power industry. security and reliability. A small tube with openings is arranged in the conveying pipeline, and the distance between the openings is related to the conveying material. When the powder accumulation in the conveying pipe is too high, the airflow will preferentially flow from the small pipe, and be ejected from the next hole at a higher airspeed, scouring the leeward side of the accumulated powder and reducing the height and length of the powder accumulation, so as to ensure the normal transportation of powder.
Double casing pneumatic air slide conveying system: The model calculation shows that the pressure loss flowing through the double casing is greater than that of the ordinary single pipe. The structural characteristics of the double casing only solve the problem of transportation stability, but to a certain extent Increased energy consumption.
Inner bypass pipe pneumatic air slide conveying system: low wear, anti-clogging, high ash-gas ratio, and low operating cost.
The fluidity of air slide delivery
The powder can be transported because it has the characteristics of flow to a certain extent, and the reason why the pipeline is blocked is caused by the deposition caused by poor fluidity. Therefore, the powder has good fluidity. It is very important for stable transportation. Fluidization is to contact the solid particle layer with the gas or liquid passing through it, so as to transform into a state similar to a fluid and meet the process requirements that are conducive to the flow of particle materials.
Fluidized silo pump
The fluidized silo pump is a feeding device designed by the principle of fluidization, which is conducive to the long-distance air slide transportation of powder.
The bottom of the fluidized silo pump is an air chamber, which is separated from the main body of the silo pump by a fluidized plate. The discharge port is located in the upper center of the fluidized plate, and the silo pump body acts as a mixing chamber. When the silo pump is working, the compressed gas from the lower chamber passes through the fluidizing plate to make the conveyed powder in a fluidized state. The conveyed powder and air are fully mixed before entering the conveying pipeline, thus eliminating the gas-solid two-phase flow into the pipeline. In addition, the fully mixed fluidized state makes the powder more evenly distributed in the conveying gas, reduces the possibility of deposition and blockage, and is conducive to long-distance powder transportation.
Three warehouse pump system
The three-way ball valve is used to realize zero-pressure differential feeding of the three bins of the bin pump, which not only reduces the valve wear during feeding but also reduces the downtime so that the system can maintain stable delivery for a long time. The three-silo pump system can realize continuous and stable transportation under the condition of changing material, gas, and gas pressure, which is beneficial to long-distance air slide transportation.
When the pneumatic air slide conveying system realizes long-distance conveying, the energy of the air will be continuously consumed, and the pressure in the pipeline will gradually decrease with the increase of conveying length. In order to solve this problem, a booster air supply device can be added to a specific length section to make up for the pressure loss caused by system friction, and to dredge the pipeline sections with more serious accumulation, so that the conveying sections can maintain a relatively stable state. It provides a pressure and stability guarantee for long-distance air slide transportation.
The demand for long-distance transportation is increasing, so unique research on long-distance pneumatic air slide transportation is required.
To solve the long-distance pneumatic air slide transportation of powder, it is necessary to comprehensively consider the energy consumption and stability of the transportation process, not only to meet the pressure requirements of the vehicle but also to ensure that the transportation is not blocked.
Whether it is to reduce the energy consumption of the conveying process or to ensure the smooth and unblocked conveying process, the gas-solid two-phase flow mechanism in the pipeline and the friction characteristics in the pipeline should be deeply studied.