Cement, as a fundamental material in modern construction, requires substantial energy and equipment support during its production process. Among these, air blowers, though representing a small proportion of the entire production line, play a vital role. Both vertical kiln calcination air supply and rotary kiln raw meal transportation homogenization rely on the support of air blowers.
Air blowers in the cement industry are primarily used in two core areas: vertical kiln calcination air supply and rotary kiln raw meal transportation homogenization. Vertical kilns for cement calcination offer characteristics such as low energy consumption, low startup capital, and high efficiency. Roots blowers, due to their structural features, provide excellent exhaust effects and good pressure adaptability, making them widely used in cement calcination air supply.
For cement vertical kilns, the required air pressure frequently changes due to variations in the material layer height inside the kiln - the higher the material layer, the greater the required air pressure and air volume. The hard exhaust characteristics of Roots blowers can effectively meet this requirement.
In rotary kiln production lines, Roots blowers are used for raw meal transportation and homogenization, creating fluidization for production to achieve raw meal homogenization. For such applications, blowers require relatively high pressure boost, generally ≥58.8 kPa, with a flow range of 5-160 m³/min.
Roots blowers, also known as rotary-type or positive displacement blowers, mainly consist of casing, shaft, gears, impellers, side covers, and bearings. Their advantages include compact structure, high wind pressure, and high efficiency, with airflow basically unaffected by pressure changes.
Centrifugal blowers generate centrifugal force through impeller rotation to increase gas pressure and transport gas. These blowers are typically suitable for applications requiring large air volume and not very high wind pressure, and they also have certain applications in the cement industry.
For application scenarios requiring higher pressure, cement plants choose specialized high-pressure blowers. These blowers can provide higher pressure output to meet special process requirements.
Screw blowers represent a new type of blower equipment that has emerged in recent years. They use a dry oil-free twin-screw main unit with no lubricating oil participating in the compression process, ensuring 100% oil-free compressed air.
Magnetic levitation blowers employ magnetic levitation bearing technology, enabling contactless operation without friction, which eliminates the need for lubrication systems. Air suspended blowers represent another advanced blower technology that uses air bearings instead of magnetic levitation, also offering oil-free operation and high efficiency. These advanced air blowers typically incorporate frequency conversion speed regulation and intelligent control, offering wide regulation ranges and adaptability to varying duty cycles and work conditions.
Air blowers serve as the core power source for the critical link pneumatic conveying in cement plants, and air blowers serve as their core power source. In pneumatic conveying systems, the selection of blowers directly affects conveying efficiency and energy consumption.
According to the design requirements of pneumatic conveying systems, air volume calculation is usually determined by the air-ash ratio. Taking a conveying system with an equivalent distance of 70m as an example, the air-ash ratio is generally set at 17 (meaning 1kg of air conveys 17kg of material). Based on this calculation, a system with a conveying capacity of 1000kg/min requires an air volume of approximately 59 m³/min. Considering system air leakage and other factors, the blower air volume should be selected at around 64.9 m³/min.
System wind pressure (pressure loss) calculation needs to consider multiple factors: pressure loss in the air pipe section (including straight sections, reducers, elbows, valves, branch pipes, etc.), resistance loss of low-pressure continuous pneumatic conveying pumps (divided into nozzle part and mixing diffusion section resistance loss), total resistance loss of ash conveying pipes, and resistance loss of dust collectors.
Selecting appropriate air blowers is crucial for the economic efficiency of cement production. In recent years, rising electricity prices have further increased the proportion of electricity costs in cement plant expenses. For major electricity consumers, reducing electricity costs has become increasingly urgent.
Air volume selection: The air volume blown into the kiln represents the oxygen supply for fuel combustion, which needs precise calculation based on production scale and process requirements.
Wind pressure determination: The incoming kiln wind pressure is used to overcome kiln resistance; greater kiln resistance requires greater wind pressure. Appropriate selection should be made based on the height of the material layer inside the kiln and system resistance.
Motor power: The usual solution for low pressure in Roots blowers is to replace them with larger motors, but this may reduce flow rate. Generally, increasing speed is necessary to boost pressure.
Many vertical kiln cement plants have adopted frequency converters for technological transformation of Roots blowers and have achieved significant economic results. Frequency conversion control has changed the traditional production method of regulating wind pressure or air volume by adjusting outlet (inlet) valve openings. This not only reduces labor intensity and improves regulation timeliness but also enhances product qualification rates and significantly decreases unit energy consumption.
As critical equipment in cement production, air blowers require regular maintenance to ensure normal operation. Common problems with Roots blowers include insufficient pressure and reduced flow rate.
To address low pressure issues, the usual solution is to replace with a larger motor, but this may affect flow rate. Another method is to increase pressure by raising the speed, but this requires comprehensive consideration of equipment capacity.
Changing the pressure required by the system can also be achieved by adjusting the outlet size of Roots blowers - larger outlet sizes reduce pressure, while smaller ones increase it. Installing pressure relief valves on blowers can accurately maintain safety and stability.
Machine vertical kilns generally commonly use blower types including Roots blowers, screw blowers, and centrifugal blowers. Among these, Roots blowers are the most widely used due to their good pressure adaptability and hard exhaust characteristics.
Calculate the required air volume using the air-ash ratio. Based on the conveying equivalent distance, set the air-ash ratio at U=17 (air calculated at 1Kg/m3, standard conditions), meaning 1kg of air conveys 17kg of material at 70m equivalent distance. The required air volume is Q1=W/U, then consider a coefficient of 1.1 to obtain the blower air volume Q2=1.1×Q1.
The usual solution for low pressure in roots blowers is to replace them with larger motors, but this may reduce flow rate. Therefore, increasing speed is generally necessary. Alternatively, changing the pressure required by the system, simply put, means adjusting the outlet size of roots blowers - larger outlets reduce pressure, smaller outlets increase it.
Many vertical kiln cement plants have adopted frequency converters for technological transformation of roots blowers. This changes the traditional production method of regulating wind pressure or air volume by adjusting outlet (inlet) valve openings, which can significantly reduce energy consumption.
System pressure loss consists of multiple parts: Pressure loss in the air pipe section; resistance loss of low-pressure continuous pneumatic conveying pumps; resistance loss of ash conveying pipes; resistance loss of dust collectors. Finally, plus them together and multiply by a safety factor.
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