What is the function of the uppermost hollow hole in the tube sheet of the convection section of a heating furnace?
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I’ve been looking at the construction drawings for a heating furnace recently; in the convective section, there is a row of holes in the top layer of the tube sheet, but no convective tubes pass through them； The tube sheets at both ends are symmetrically opened, and 304 sleeves are inserted into these openings with the outer ends of the tube sheets being sealed ； The heating furnace uses 1Cr18Ni9Ti tube sheets, while the tube plates are made of 15CrMo; there is an air preheating section above the convection zone ； I would like to ask an expert: what is the purpose of these openings in this row? This post was last edited by Yang Zhanhui on 2009-4-16 06:26.]
It is used when expanding capacity by adding furnace tubes; sealing the outer end of the tube sheet prevents air leakage and heat loss.
To facilitate future expansion of the facility and further improve the thermal efficiency of the furnace.
Agree with the opinion from the 2nd floor; it’s for capacity expansion and renovation
Agree with the opinion from the 2nd floor; it’s for capacity expansion and renovation
The convection chamber has 8 rows of furnace tubes, with four tubes in each row; thus the effective length is 2 meters * 4 tubes = 8 meters. There is only one row of hollow holes at the very top. If there is a margin for capacity expansion, how large is that margin? Also, since the furnace tubes below are connected by sharp elbows, adding more furnace tubes on top merely increases the length of the convection tubes. As the diameter of these convection tubes remains unchanged, it seems that this only enhances waste heat recovery without significantly increasing the furnace’s processing capacity. Could an expert please provide a detailed explanation? Thank you.
The heating furnace uses 1Cr18Ni9Ti furnace tubes, which indicates that the temperature in the radiation chamber is not very high; 25CR35NI and 35CR45NI are the furnace tubes used in high-temperature furnaces. To prevent the uppermost tube bank in the convection section from being corroded by acid, the flue gas temperature should be slightly above 100 degrees. The original poster mentioned reserving a pipe connection position at the top layer. If this is to allow for future expansion, then there should also be reserved pipe connection positions in the convection sections of the other modules, as the temperature decreases as one moves upward from the lower modules. The original poster noted that the material used in the top layer is 304; I assume this is not only for future expansion purposes but also related to the designed exhaust temperature of the furnace. If the designed exhaust temperature in that area is less than 100 degrees, then it is indeed necessary to use 304 material, as ordinary pipes would be corroded by acids. So, the original poster needs to consider this in conjunction with the process specifications – furnace designs always include heat distribution diagrams.
Generally, two rows of furnace tubes are reserved in the upper part of the convection zone for future use in expanding capacity or introducing additional process media. Sometimes, depending on the need to heat multiple types of media using convection, these two rows of empty tubes can also be placed in the middle area to accommodate the possibility of expanding capacity for both types of media. The standards specify that the minimum material required for the tubes in contact with flue gas is 304; therefore, the tubes on the tube sheet are made of 304, even though the temperature of the flue gas here may not be very high. Generally, carbon steel is sufficient for the material of the tube sheet, thanks to the insulation lining present. However, some engineering companies require that the material of the lowest tube sheet plate be 15CrMo, as the temperature is relatively high.