What is dilute phase pneumatic conveying, what is dilute phase pneumatic conveying, and what are its

Dilute phase pneumatic conveying is a general term for a continuous gap-free conveying method in which the pressure in the entire pipeline system is greater than the local air pressure. The gas pressure is lower, and the main characteristics of positive pressure dilute phase conveying are large conveying capacity, long conveying distance and stable operation.

The acceleration at the beginning of the system is about 10 m s2, and at the end it can reach a high speed of about 1300 m min, so the air velocity is high. The pressure at the beginning of the conveying pipeline is generally less than 1kg C, while the end is basically close to the atmospheric pressure. The power of dilute phase transmission is generally air or nitrogen, and the power supply is generally provided by centrifugal fans or roots vacuum pumps.

In the dilute phase, the material is suspended in the pipeline, and the conveying distance can reach hundreds of meters.

The dilute phase conveying is simple until the pneumatic conveying process, the ash gas ratio is less than 10, that is, the ash concentration is relatively low. Dilute phase conveying is generally used in low-pressure conveying systems, such as Yili mechanical material seal pump pneumatic ash conveying system, jet pump pneumatic conveying system, etc. This conveying system generally has a conveying distance of no more than 200 meters and an operating pressure of less than 1 kg.

The solid content is less than 1-10kg m3, the operating gas speed is high (about 18 30m s), and the conveying distance is basically within 300m. For the material seal pump of mature equipment, the conveying operation is simple, there are no mechanical rotating parts, the conveying pressure is low, and there is no maintenance and maintenance-free!

On the basis of dense phase pneumatic conveying, the wind speed is continuously increased, which is transformed into dilute phase pneumatic conveying. It is characterized by the increase of wind speed, because the pressure drop of friction orange increases with the increase of wind speed, which promotes the pressure drop of the material layer. In the vertical conveying pipe, the airflow resistance and the gravity of the material particles are on the same straight line, and the two only act on the material in the direction of the conveying flow.

However, the movement of the particle group in the actual vertical conveying pipe is more complex, and it will also be affected by the vertical directional force, therefore, the material will form an irregular interlaced serpentine movement, so that the movement state of the material in the conveyor pipe forms a uniformly distributed steady flow. In the horizontal conveying pipe, the higher the conveying air velocity, the closer the material is to uniform distribution. However, depending on the conditions, the flow state will change significantly when the conveying airflow is insufficient.

At the beginning of the conveying pipe, it is roughly evenly conveyed according to the bottom flow of the pipe, and the material is connected to the bottom of the pipe, and the distribution is dense, but there is no stagnation, and the material is irregularly rolled and collided on one side, and the other side is conveyed. The closer to the sparse flow is in the back section, the material is in a dense and uneven flow state in the horizontal tube, and some particles slide at the bottom of the tube, but there is no stagnation. Eventually, a pulsating flow or stagnant flow is formed, and the longer the horizontal tube, the more pronounced this phenomenon becomes.

Also known as airflow transportation, it is a specific application of fluidization technology to use the energy of airflow to transport granular materials along the airflow direction in a closed pipeline. The structure of the pneumatic conveying device is simple, easy to operate, can be used for horizontal, vertical or inclined direction of conveying, and can also be used in the conveying process at the same time to carry out physical operations or some chemical operations such as material heating, cooling, drying and air flow classification. Compared with mechanical conveying, this method consumes more energy, the particles are susceptible to breakage, and the equipment is also susceptible to abrasion.

Materials with high water content, adhesion or easy to generate static electricity during high-speed movement are not suitable for pneumatic conveying.

The main characteristics of pneumatic conveying are large conveying capacity, long conveying distance, and high conveying speed; It is possible to load in one place and then discharge in several places. According to the density of particles in the conveying pipeline, pneumatic conveying is divided into: dilute pneumatic conveying phase conveying:

The solid content is less than 1-10kg m3, the operating gas speed is high (about 18 30m s), and the conveying distance is basically within 300m. For the material seal pump of mature equipment, the conveying operation is simple, there are no mechanical rotating parts, the conveying pressure is low, there is no maintenance, and it is maintenance-free! Dense phase conveying:

The solid content is 10-30kg m3 or the solid-gas ratio is greater than 25. The operating air velocity is low and the pressure is higher than the air pressure. Now mature equipment bin pump, the conveying distance reaches more than 500m, suitable for long-distance transportation, but this equipment has more valves, pneumatic and electric equipment.

The conveying pressure is high, and all pipes need to be made of wear-resistant materials. Intermittent inflatable tank type dense phase conveying.

It is to add the particles to the pressure tank in batches, and then ventilate and blow them loose, and after the tank reaches a certain pressure sensitivity, open the opening valve, and blow the granules into the conveying pipe to bury Naming for transportation. Pulse conveying is to pass a stream of compressed air into the lower tank to blow the material loose; Another pulse compressed air stream with a frequency of 20 40min-1 is blown into the inlet of the conveying pipe, forming alternating small sections of material columns and small sections of air columns in the pipeline, which are pushed forward by air pressure. Negative pressure conveying:

The pressure in the pneumatic conveying pipeline is lower than the atmospheric pressure, and the material is self-priming, but it must be discharged under negative pressure, and the distance that can be conveyed is short; Advantages: small equipment investment and load. Cons:

The operating flow rate is high, the pipe is seriously worn, and the wear and tear is undetectable.

1.The conveying distance is long, and the conveying distance can reach more than 1000 meters with appropriate measures2Point-to-many conveying is possible.

3.The use of small diameter (50-120mm) conveying pipes is convenient for installation in the plant. 4.

The air consumption is small, the weight ratio of the material and the air can reach the conveying speed of 6-12 meters per second, the conveying pipeline is not easy to wear, and the material is not easy to break. 6.Because it is a low-speed dense phase conveying, the air consumption is small, and the amount of tail gas treatment is also small, so the dust removal is convenient and conducive to environmental protection.

7.In addition to the pneumatic valve, there are few movable mechanical devices in the whole machine, and the daily maintenance workload is small. On the basis of rapid fluidization, if the fluidized air volume is increased or the amount of bed material is reduced, the concentration of particles in the bed will become thinner, and the particles in the bed will be evenly distributed up and down, which is the dense phase pneumatic conveying.

It is characterized by the fact that the pressure drop per unit height of the material layer does not change with the change of the height of the material layer. The dense phase pneumatic conveying system is mainly divided into: basic conveying of the sending tank (or bin pump), fluidized conveying of the sending tank, pressurized conveying of the sending tank, full load conveying of the sending tank, and upward conveying of the sending tank.

The conveying system uses a higher gas pressure to squeeze the material under positive pressure, so that it flows in the pipeline and is sent to the corresponding equipment through the conveying pipeline. Therefore, it is often referred to as a high-pressure, low-speed system. It has a high feed-gas m (usually the feed-gas ratio m=20 100, the pressure p=0, and the velocity v=are classified as high-pressure low-speed systems).

The initial velocity of the system is approximately the start-up velocity, the pressure of the conveying line is generally the same, and the velocity at the end of the system is almost zero. The system uses an empty compressor unit as the power source, which is characterized by low conveying speed and less impact on material quality. At present, the use of high-pressure dense phase system has been very extensive, and different conveying methods can be selected for different conveying materials, so as to maximize the use performance, efficiency and economic advantages.

Its main components are electric control cabinets, sending tanks, boosters, discharge valves, exhaust dust collectors, air compressor units, separators, etc.

The principle of dense phase transportation: when dense phase transportation, the particles move collectively in the fluidized state of a small amount of loose gas, and do not rely on gas to accelerate it, and the movement of the solid is driven by the static pressure difference. In the high and low parallel riser catalytic cracking unit, the inclined tube is used for catalyst transportation, which relies on the static pressure difference.

The driving force of the catalyst flow is formed by the static pressure head of the material column in the inclined tube to overcome the flow resistance of the catalyst in the inclined tube and the fracturing side-difference between the two instruments. The material is added from the hopper to the transfer pump under the control of the feed valve. The air compressor produces a high-pressure gas.

The material is transported to the designated storage bin at a certain speed, and after the material and gas are separated, it is filtered by the bag filter and then exhausts the atmosphere or is connected to the dust removal air network. System features: This system is a dense phase pneumatic conveying system that uses air compressor as the air source to convey materials by pump.

The selection of pneumatic conveying system parameters, process design and equipment structure design of our company have undergone a large number of experiments and field applications, so as to ensure that the system has the characteristics of low flow rate, small wear, long distance and large conveying capacity, and can effectively prevent pipeline blockage.

When the velocity of the fluidized medium is high, the solid particles begin to be carried out. As the velocity of the fluidized medium increases, so does the entrainment of particles. This time the gap increases and the pressure drop decreases.

The solid particles form a suspended dilute phase in the fluid and are carried out of the fluidized bed together with the fluid, and this stage is called the airflow transport stage, also known as the dilute phase transport.

Dilute phase conveying is the traditional method of transporting alumina materials in China's aluminum plants, and most aluminum plants, especially small aluminum plants, still use this method to transport alumina. The system is mainly composed of pressure pump and conveying pipeline, and the conveying distance is generally about 400m. The dilute phase conveying system uses compressed air as the power source, and the alumina material is pressed directly from the silo to the high-level silo of the next system through the silo pump.