Selection of return air fans for boilers

To the best of my knowledge, rotary vane blowers are generally chosen for return air fans

This post was last edited by pzhmotor on 2015-9-12 at 11:51. The working principles of the two are different: a Roots blower is a positive-displacement blower, and its principle is similar to that of a gear pump (I imagine it as an air pump). A centrifugal fan uses a high-speed rotating impeller to accelerate the gas, which is then decelerated and directed in a different direction, converting kinetic energy into potential energy. The following are my personal opinions for reference: When choosing a Roots blower, if there is excessive pressure at the outlet, the motor will experience overcurrent and trip. Generally, the exhaust valve at the fan outlet is adjusted to set the pressure and control the current. In my opinion, using a Roots blower as a return air fan is not very suitable for systems that control the amount of return air by adjusting the pressure of that air. Unless the electrical control system is further refined. The control of the return material amount is also somewhat controversial; the U-shaped returner is a type of small bubbling bed. Some sources state that the amount of return material is controlled by adjusting the height of the material leg (in what is known as establishing a balance), while other sources say it is controlled by air pressure. In practical applications, individuals prefer the former because it is relatively safer. As a return air fan, the centrifugal fan has the advantage of easy control over air volume. The downside is that it is difficult to achieve very high and stable wind pressure. It seems that the motor has a higher power rating than the Roots blower. If the outlet is too small, it will cause congestion, leading to vibration or heating of the outlet pipe (this phenomenon is particularly evident in gas compressors, and it is controlled within certain limits by adjusting the balance valve). Generally, small CFB boilers use the primary air fan duct as the return air fan, while larger CFB boilers mostly employ Roots fans. It is recommended to contact the manufacturer and consider replacing it with a Roots blower.

This post was last edited by han*chen on 2015-9-12 at 13:14. For the CFB units with capacities of 65, 75, 130, 220, and 480 t/h that I have worked with, rotary blowers were used as the return air fans, and I think this is a good choice. Both the outlet pipe of the rotary blower and the primary air duct are equipped with control valves for regulation; of course, frequency control can also be implemented.