The sealed roots blower belongs to the pressurization blower, and the pressurization of natural gas is easy to cause explosion. MVR steam compressor, made of 2205 two-way stainless steel, is generally used for water vapor transmission. There are three important changes to the sealed roots blower when conveying special gas.
1. The air outlet of the fan is connected to the casing through a pipe. The purpose of this is to prevent the air outlet pressure from being too high, resulting in gas leakage. The gas leakage can be effectively controlled through the return pipe.
2. Unless otherwise required by the customer, mechanical seal will be used, and labyrinth seal will be generally used, which is different from common nitrile rubber and skeleton oil seal, and the purpose is also to prevent gas leakage.
3. The over-current material is anti-corrosion coating, generally nickel plated. When Teflon coating is used, explosion-proof motor shall be selected as far as possible, and the transmission pipeline shall be safe.
Features of sealed roots blower:
Stable operation. The head of Roots blower adopts a special sealing structure, which is widely used to transport flammable and explosive gases such as biogas, hydrogen, carbon dioxide, etc. The motor adopts explosion-proof frequency conversion motor, making the Roots blower safer in operation!
Classification of sealing forms of Roots blower:
1： Labyrinth seal.
It is a non-contact dynamic seal that uses a channel composed of fluid passing through a series of throttling gaps and expansion chambers to make the working medium produce throttling effect and limit leakage. Labyrinth seal is widely used for wall plate shaft seal of Roots blower. The sealing mechanism can be simply explained as that the fluid passes through many zigzag channels and generates great resistance through multiple throttling, making it difficult for the fluid to leak, so as to achieve the purpose of sealing. This kind of seal is generally applicable to the occasion of conveying air. It is restricted when conveying toxic, flammable and explosive gases. This form is generally used for wall panel sealing of standard roots blower.
2： Packing seal.
It is a kind of sealing form in which the leakage channel is filled with packing to avoid leakage. The packing seal is simple in structure, easy to disassemble and widely used. In the packing seal structure of Roots blower, packing, shaped polytetrafluoroethylene packing and skeleton oil seal group packing are commonly used. As this seal is a contact type seal, it is easy to cause wear of the shaft (contact part with the oil seal lip or PTFE packing). Because of its simple structure, convenient disassembly and assembly, low cost, good sealing effect, and low requirements for working environment and maintenance, it has been widely used in fertilizer plants and other industries.
3： Ring expansion seal.
Place several elastic rings with notches into the sealing groove. Due to the elasticity of the ring itself, the outer circle is close to the shell, and there is no relative rotation between the outer diameter of the ring and the shell. Gas can only leak downstream through the gap between the ring and the ring groove. During operation, the ring is close to the ring groove and near the downstream end face of the ring groove under the effect of the gas pressure difference on both sides. The high pressure gas entering the gap fills the rear gap space, further strengthening the seal between the ring and the inner hole of the seal seat, and the rest of the leakage channels are the cuts of the ring. Due to the small gap of the incision, the slices are installed incorrectly during installation. After several ring seals, they rarely go out. If the sealing gas sealing device is installed, the sealing effect is good. Because this kind of seal is a contact type seal, it has a sealing effect, but it needs to be lubricated with fat when it is used. The newly developed rings made of special materials can be made without grease.
4： Mechanical seal.
Also called face seal, it is a device to limit the leakage of working fluid along the rotating shaft. It usually consists of static ring (static ring), rotating ring (dynamic ring), elastic or magnetic elements, rotating ring drive parts and sealing rings. When working, the sealing function is realized by using the two fitting surfaces and seals of the rotating ring and the static ring rotating relative to each other. Whether the mechanical seal can work normally depends on whether a stable and reliable lubricating film can be established on the surfaces of both ends to derive the friction heat in time. Mechanical seals are widely used in rotating machinery such as machinery industry and petrochemical industry due to their reliable operation, small leakage, long service life, automatic compensation for end face wear, no need for regular maintenance, small power loss, and no shaft wear.
How to select the type of sealed Roots blower?
The parameters are the same as those of ordinary roots blowers. In addition to the normal parameters, we need to pay attention to that the selection of roots blowers for gas transmission should be larger. Because the actual flow value is generally less than the theoretical flow value.
The reasons are as follows:
1. Internal and external leakage loss of Roots blower
Under the effect of the inlet and exhaust pressure difference, part of the gas in the exhaust chamber returns to the inlet chamber through the rotor gap. Or the gas leaks out from the exhaust chamber of the blower through the shaft end clearance, or leaks into the vacuum pump from the atmosphere.
2. Internal leakage caused by heating
The compressed and heated gas leaks into the air inlet cavity, heating the gas from the air inlet to a certain extent, increasing its specific volume and decreasing its mass flow.
3. Heat transfer of Roots blower components
Under the effect of compression heat, the temperature of the impeller and casing will rise, and the gas from the air inlet will also rise and expand when it comes in contact with them.
4. Loss of gas pressure
There is a certain pressure loss when the gas flows. These losses will be converted into heat that will be absorbed by the gas, causing the gas to rise in temperature and expansion, leading to a rise in pressure, thus increasing the leakage,
At a certain speed, the flow rate slightly decreases with the increase of pressure rise (or pressure ratio), because the leakage flow rate increases with the increase of pressure rise;
Under the condition of a certain pressure rise, the flow increases with the increase of speed. The flow curves at different speeds are roughly parallel to each other, because the theoretical flow is proportional to the speed, while the leakage flow has little relationship with the speed.
Therefore, we should select a larger size when selecting the sealed roots blower, so that the flow in use can reach the theoretical flow value!
The above is what should be paid attention to in the selection of sealed roots blower. I hope it can help you!
