Roots blower in the mine application

In the dehydration process of the mine, the disc filter or the cylinder filter were commonly used in the past. Although the types of pressure air sources used are different, they have some disadvantages. We believe that the roots blower as a filter of the pressure source, is its advantage.

I.the effect of roots blower on the dehydration of concentrate  can be seen from the following aspects:

1. Low energy consumption. Compared with water ring compressor, roots blower has better energy saving effect.
2. The water supply system was cancelled. Roots blower does not need water supply, which not only saves water consumption, but also fundamentally eliminates the possibility of water in the pressure wind, which is beneficial to dehydration.
3. Stable work and small maintenance work. Roots blower can run for a long time, except for changing the lubricating oil of the gear box once, other aspects are normal.
4. Reliable operation and easy operation. In the process of continuous operation, the production has never been affected by the failure of roots blower. Due to the simple operation, in addition to regular supplement of the appropriate amount of grease, there is almost no other maintenance workload. Therefore, the operator can quickly adapt to the use of roots blower process, and satisfied with the transformation.
5. Save fuel consumption. It is not difficult to see from the working principle and small maintenance workload of roots blower that the fuel consumption of roots blower is very small. Compared with the water-ring compressor, it can at least save oil for cleaning parts, and compared with the plunger compressor, it can save oil for cylinder lubrication.

FIG. 1 application of roots blower in mine

The performance of roots blower

The performance of roots blower is suitable for dewatering process of concentrate. The purpose of the pressure wind for the dewatering of concentrate is to blow and scrape the filter cake which has been dewatered by vacuum from the filter cloth. In order to keep the dried concentrate without adding water and prolong the flat life of the filter cloth, there are specific requirements for the pressure, air volume and gas composition of the air source. The performance of roots blower is as follows.
1. Air pressure: roots blower rotates synchronously by two rotors that do not directly contact with each other and pushes the gas in the cylinder volume to achieve the purpose of boosting pressure in the exhaust cavity. It is a volumetric rotary gas compressor, its pressure ratio is only 1.2-1.7. The commonly used roots blower pressure is generally 3500-5000mm water column, which is very close to the required value of concentrate dehydration.
2. Air volume: the air volume of roots blower is proportional to the product of effective working volume and speed. The total air consumption is proportional to the total area of the filter. Q= lambda · PI (2) • D2·Cn·L·n m/min (1)
Type:
Lambda – exhaust coefficient, lambda =0.6-0,9;
D — rotor diameter, m;
L — rotor length, m;
N — rotor speed, RPM;
Cn — area utilization coefficient.
In the process of production, the material of filter cloth should also be considered. When the filter cloth is compact, the air consumption is small; otherwise, the air consumption is large. By selecting the proper type of roots blower and changing the rotating speed, the air volume can be changed in a wide range to meet the requirements of concentrate dehydration.
3. The relationship between air pressure and air volume, because the pressure of the roots blower is small, between the rotor and there is a space between the rotor and cylinder block, make fan AP – Q curve is flat, as the chart, the existence of the gap in fact automatically adjust the pressure role, when the air volume increases pressure drop, the leakage is decreased at the same time, thus play a role of maintaining the pressure. This characteristic is of great importance to the dewatering of concentrate.

FIG. 2 performance curve of roots blower

The air pressure of concentrate dewatering is required to be stable. When the air volume increases suddenly (such as damaged filter layout), the air pressure cannot drop too much. When air volume suddenly drops, wind pressure cannot rise too high. This means that the wind pressure changes less when the air volume changes. It is not difficult to see from figure 2 that the pressure change caused by the change of air volume is relatively small in the area with the wind pressure of 0.1-0.2 kg force/cm 2, which happens to be the working range of the filter.

The choice of roots blower

Roots blower is used in cupola, forge furnace and other equipment. If directly according to the data selection manual, will inevitably produce too much noise, high wind pressure. The noise of roots blower is mainly aerodynamic noise caused by periodic constant volume compression, followed by internal clearance leakage, eddy current and mechanical movement noise. In order to prevent noise pollution and adjust the wind pressure, we think the two-step method is reasonable.

Installation mode and air pressure adjustment

Roots blower for concentrate dehydration, suitable for the overall installation, between the base and the base should be pad with 10-12 mm thick soft rubber plate, in order to absorb the noise caused by the vibration of the body.
The air storage box should be installed at the air outlet, and the safety valve should be installed at the top of the box to prevent the fan from operating under overpressure. The gas reeds can also maintain uniform exhaust and absorb aerodynamic noise.
Dust cover should be installed at the air inlet to prevent sundries from entering the fan and causing blade damage.
A section of connecting pipe with the same diameter as the exhaust outlet shall be installed between the air inlet and the exhaust outlet, and a gate valve shall be installed in the middle of the pipe to adjust the exhaust pressure.

FIG. 3 installation diagram of roots blower

Roots blower is undoubtedly successful in dewatering concentrate. It has simple structure, reliable work, stable operation, small maintenance workload, but also can save electricity and water. If it is used to replace water ring compressor, the effect of saving electricity and water is better in technology and economy.