Negative pressure pneumatic conveying system
"Negative pressure pneumatic conveying system" refers to the negative pressure of the system generated by roots blower, in which the powder particle material is evenly mixed with air at the receiver and pumped to the storage unit by pipeline. It is mainly used in coal-fired power plant ash removal system, also known as negative pressure pneumatic ash removal system. It is the introduction of foreign technology, domestic ash handling system designers have fully mastered the system design technology. The negative pressure generated by the negative pressure pneumatic conveying will transport the powder and granular materials uniformly mixed with air in the bin pump to the pneumatic conveying system of the sealing pump device through the pipeline. When conveying, the pressure of the whole pipeline is lower than the local air pressure. Pressure suction pneumatic conveying is a more reliable and mature whole air conveying mode, which has been applied earlier in practice. According to the working pressure, it can be divided into two types: low vacuum (vacuum degree less than 1000 mm water column) and high vacuum (vacuum degree greater than 1000 mm water column). Mainly used in coal-fired power plant ash conveying system, also known as negative pressure pneumatic ash removal system
The investment of "negative pressure pneumatic conveying system" is relatively low. It can receive materials at multiple points and requires a small clearance in the lower part of the ash hopper. The ash and slag treatment system is suitable for thermal power units below 300 MW. Leakage of equipment and piping can only occur in vacuum. Therefore, the environment is relatively clean. The disadvantage is that the negative pressure value is limited and the conveying distance is short. The limit geometric distance of general transportation is 200m, and the actual project is designed as ≤ 150m; the maximum output of a single system is usually 40t / h (fly ash).
1、 How it works
The fluidized bin of negative pressure suction pneumatic conveying makes full fluidization of fly ash particles by air, so that the fly ash can pass through the negative pressure suction and positive pressure conveying pipeline smoothly. The inside of the ash suction fluidized bin is composed of two porous thin steel plates, and the air permeable layer is sandwiched between the upper and lower porous plates.
Generally, roots vacuum pump is used as the power source for negative pressure pneumatic conveying. The pipeline and tank silo are pumped to a certain vacuum state, which makes the air inlet form two-phase flow of material powder and gas under the action of atmospheric pressure, and then it is sent to the cyclone separator through the conveying pipeline. Under the action of centrifugal force and gravity, the two-phase flow separates most of the material from the gas in the cyclone separator. A small amount of material and gas enter the dust collector, and the powder is separated from the gas by the filter bag, and the gas is discharged into the atmosphere. The porous plates in the whole fluidized bin are arranged at a certain gradient (4% - 10%). The fly ash is pumped by the separator into the combined pump, and then into the fluidization by the combined pump, and is fed to the air permeable layer at the feed inlet of the upper shell through the feeding equipment. The air enters into the lower shell from the fluidized bin and passes through the air permeable layer along the fluidized bin to fluidize the fly ash. The positive pressure generated by entering the air compressor or roots blower in the conveying machinery or entering the positive pressure conveying equipment will transport the materials to the bulk material warehouse (warehouse) through the feeding pipeline. Clean air is discharged from the upper part of the separator through the exhaust pipe and discharged into the atmosphere from the exhaust port of Roots blower (vacuum pump).
2、 Main features
1. The air tightness is reliable, the dust in the pipeline will not leak into the environment, which improves the environmental protection performance; the flexible configuration of the transmission pipeline makes the production process more reasonable.
2. Low requirements for equipment manufacturing and maintenance, strong operability of workers; less moving parts, convenient maintenance and easy automation
3. The pressure (vacuum degree) used is small and the safety is high. Inert pneumatic conveying can be used for materials with unstable chemical substances.
4. The transportation volume of material medium is large, the transportation distance is long, the transportation route is not restricted by the terrain, the bulk material transportation efficiency is high, and the packaging, loading and unloading and transportation costs are reduced.
5. Continuous transportation, no accumulation in the pipeline; multiple process operation can be realized simultaneously in the transportation process.
Materials can be collected from multiple points and can be sent to multiple points from one point;
7. Centrifugal fan, roots blower as gas source, long service life;
8. It has strong adaptability for conveying materials, and can stably transport powdery and granular materials. It can prevent the transported materials from getting damp, dirty and mixed with other impurities, so as to ensure the conveying quality.
3、 System price
Since the price of the whole set of negative pressure dilute phase pneumatic conveying system is difficult to estimate, if the construction cost is included, and the design cost of pneumatic conveying system does not charge the environmental protection cost of customers, we can only give the price of pneumatic conveying equipment.
The price of pneumatic conveying equipment is about several thousand yuan per set, and the most expensive one is 20000 yuan. The price of pneumatic conveying equipment is affected by many factors, such as brand, category, specification, market, etc. Before choosing to buy, it is necessary to understand and compare many aspects. Air slide conveyor uses compressed air as the conveying medium to transport pulverized coal to a certain particle size along the pipeline. It is suitable for filling, unloading, stacking and bulk transportation of grain processing, beer, brewing and other industries. Pneumatic conveying equipment can carry out horizontal, inclined and vertical transportation, and can also form a space conveying line, which is generally fixed. The conveyor has large conveying capacity and long conveying distance. It can complete a number of process operations at the same time in the conveying process, so it is widely used. It can be transported by one unit or multiple units, or by horizontal or inclined transportation system with other transportation equipment to meet the needs of different layout forms of operation lines.
Conclusion: pneumatic conveying is a kind of technology integrated system that uses air (or gas) flow as conveying power to transport bulk solid materials in pipelines. It mainly includes dilute phase and low-pressure pneumatic conveying. The air in the conveying system is inhaled by roots vacuum pump (negative pressure fan) installed at the end of the conveying system. The negative pressure air flow below atmospheric pressure is formed in the conveying pipeline. The materials and atmosphere enter the pipeline together from the starting nozzle. As the air flow is transported to the end separator, the material particles are separated from the air flow by gravity or centrifugal force The gas is removed by centrifugal fan or roots vacuum pump (negative pressure fan) and pumped into the atmosphere.
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