Heat exchanger design and calculation
Thread Content
Background: The flue gas from the rotary kiln used for burning hazardous waste has an exit temperature of 1100°C; therefore, an air heat exchanger is needed to preheat air at a room temperature of 20°C to 200°C before feeding it into the rotary kiln, in order to reduce energy consumption. In other words, the flue gas temperature at the inlet of the heat exchanger is 1100°C, the temperature at the outlet is 200°C, and the heat exchange medium is air. The flue gas volume is 6400 m3/h. I’m not from a thermal engineering background, so I’m not familiar with the calculations related to heat exchangers. Could someone give some advice? What parameters are needed? Or at least recommend two design manuals so I can explore on my own? Thank you
Also, can domestic heat exchanger manufacturers handle such high inlet flue gas temperatures?
This is the most basic thing; it’s not difficult to design. However, it would be best if you provided the following parameters: 1. Air volume, or: flue gas composition 2. Is there a chimney for exhaust smoke? This relates to the pressure drop limit of the heat exchanger.
It is recommended to adopt a segmented design: a fire-tube boiler is used in the front section to generate steam, while a heat-pipe exchanger is used in the rear section to preheat the air before it enters the furnace. Send a parameter to create a plan
1. Just provide the flue gas composition and dust content； 2. Our company is capable of handling flue gas inlet temperatures of 1100°C; flue gas at this temperature provides a better preheating effect for the air ； 3. If necessary, you can contact me; Penguin ID: 1711819313.
Thanks for the reply from above. I did the calculations myself based on Qian Songwen’s design manual, and I have the following questions: 1. The thermal resistance of soot in flue gas that I found on Baidu is 0.000516. Is this reasonable? The fuel is diesel, and the material is soil. I think the composition of flue gas has little impact on the thermal resistance of dirt. 2. The design approach involved first determining the heat transfer coefficient for the tube side, and assuming a value of 15 for the heat transfer coefficient on the shell side. However, after a series of calculations, the actual heat transfer coefficient on the shell side was found to be 5.9, which is only 60% different from the assumed value. Is this reasonable? 3. The heat transfer coefficient in the shell side of the annular baffle is calculated using Kern’s formula, which requires the specific temperature as well as the fluid viscosity at the wall temperature. How is this wall temperature determined? Qian Songwen’s manual does not provide a method for determining the wall temperature. The design and verification methods are based on this document: http://wenku.baidu.com/searchword=%BB%BB%C8%C8%C6%F7%C9%E8%BC%C6%CA%B5%C0%FD&lm=0&od=0&fr=top_home&fr_ext=ceiling
One additional question: the Prandtl number is used to calculate the heat transfer coefficient. The value found differs significantly from the calculated value. For this Prandtl number, is it calculated during design or looked up directly from a table?
The kiln body section does not have a chimney. The entire system has only one chimney at the exhaust treatment end for venting smoke.
It is a common practice to install a chimney at the end of the exhaust gas treatment system for smoke emission. Generally, the pressure drop of such heat exchangers should not exceed 2 kPa; the lower, the better. However, as the pressure drop decreases, the area increases: this is a contradiction, it represents a challenge in design, and it is also the reason why many engineering projects fail due to arbitrary design decisions.