For the long-distance transport of flue gas, is it better to place the transfer fan near or far?
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This post was last edited by yggswl on 2021-7-6 10:41. For long-distance smoke transportation, is it better to place the delivery fan nearby or at a distance? When a induced draft fan is used for long-distance transportation, is it transported under negative pressure or positive pressure? What is the difference, and what are the advantages and disadvantages of each? Among them, the boiler outlet is at a slightly positive pressure, while the inlet of (the desulfurization and denitrification systems for other components) is at a slightly negative pressure. The flue gas volume of the boiler is approximately 40,000 Nm3/h, and the exhaust gas temperature at the boiler outlet is about 180°C. Are the fan design models the same for Plan 1 and Plan 2? Please see the figure, thank you!
I think Option 1 is relatively better, as boiler flue gas outlets usually have a waste heat recovery system, and Option 1 helps to reduce dust deposition on the surface of that recovery system.
Judging from the schematic diagram and the flue gas volume, it should be a three-pass fire-tube boiler of about 15 tons, of the WNS type for fuel oil and gas. The boiler is not large, so generally Plan 2 is adopted; in simple terms, the exhaust fan is located next to the chimney.
This post was last edited by yggswl on 2021-7-6 10:25. Is the optimal flow rate design the same for positive pressure conveying and negative pressure conveying? Does positive pressure conveying result in high conveying pressure losses? At the same time, could Option 1 result in poor control of the boiler’s outlet pressure? For example, with the same pressure of 6000 Pa and a flue gas flow volume of 40,000 Nm3, which is more reasonable: for the fan to operate under negative pressure or under positive pressure?
Why is it simply said that the exhaust fan is adjacent to the chimney? Are there any sayings?
I suggest that you first explain why a 400-meter flue is needed; this relates to the processing procedures and is directly connected to the placement of the exhaust fans. Secondly, you need to determine whether 180 degrees Celsius applies to the emissions or to the smoke outlet of the boiler; this is related to whether your 400-meter smoke duct is properly designed, as there is an issue of heat loss and condensation within it.
Party A does not want to install a desulfurization and denitrification system for the boiler; instead, it prefers to integrate this process into the desulfurization and denitrification system of the coke oven, although the transmission distance is relatively long. The flue gas temperature at the boiler outlet is around 180°C.
If the desulfurization and denitrification systems for the furnace gas at the rear have already been installed, it is necessary to verify whether the flue gas after being integrated into these systems meets the design requirements. If not, it is not recommended to proceed in this way; instead, the owner should be persuaded to consider installing separate desulfurization and denitrification systems for this boiler. The reason is that the composition of the flue gas entering these systems changes, and the volume of gas to be treated increases, which can affect the efficiency of the desulfurization and denitrification processes, or even result in failure to meet the required standards. If desulfurization and denitration of coke oven gas at the rear section have not been implemented, or have been implemented but still meet the requirements regarding increases and parameter changes, it is recommended to use Option 2, with variable frequency control for the fans ； The reason is that, regardless of where the fan is placed, the flue gas transfer at the rear of the boiler should function in a negative pressure mode, that is, it should create a suction effect. The purpose of this is to make it easier to control the pressure in the furnace, while also ensuring that the flue gas is delivered to the equipment at the rear (chimney, air preheater, desulfurization and denitrification units, etc.). The fan should therefore be located near these rear-mounted equipment or facilities ； If a blower is used, it is difficult to control the boiler pressure (at a slight positive pressure). Here, blowers and exhaust fans are used differently, and their models also vary ； Proper anti-corrosion measures need to be taken on the inside of the additional 400 meters of flue, and the exhaust fan must also be designed to be resistant to high temperatures and corrosion.
Thank you! :handshake
It is difficult for this exhaust fan to meet both the furnace pressure requirements and the air intake pressure requirements of the desulfurization and denitrification systems. It is recommended to use two units, one for sending and one for receiving
Yes, the desulfurization and denitration of the coke oven gas are carried out under negative pressure, which indicates that there must be an exhaust fan at the rear.