Calculation of the average temperature of coke oven chimneys

This problem may seem ordinary, but it actually involves profound fundamental theoretical knowledge. To resolve it thoroughly from a theoretical perspective, it is necessary to consider the coke oven itself as well as the flue and chimney as a whole, and to solve for the temperature field! Currently, there are many tools available for conducting calculations and research in this area within engineering design. Generally, the temperature at the entrance of the chimney is around 240 degrees, while the average temperature of the airflow inside the chimney is around 220 degrees! !

Currently, the total temperature of our flue gas is 320 degrees; I assume the temperature at the chimney inlet must be above 240 degrees. What is the average temperature of the exhaust gas at this time? This question is raised because of a doubt: when a waste heat recovery unit is installed, the average temperature inside the chimney generally does not exceed 180 degrees, resulting in a relatively low suction force. However, once the waste heat recovery unit loses power and the bypass valve opens promptly, a relatively higher suction force is required, which seems to be contradictory. To calculate the chimney draft before and after, the average temperature of the exhaust gas is required.

There are specific calculation formulas; please refer to Volume 1 of the Coking Design Manual, Anshan Coking and Refractory Research Institute

Under normal conditions, the temperature at the chimney inlet is around 240 degrees! !

When the thickness of the chimney wall is 0.5 m, the decrease in the temperature of the exhaust gas per meter of chimney height can be calculated using the following formula: △t = A/√D. Here, A is a coefficient; generally, A is taken as 0.6. D represents the average outer diameter of the chimney, with D = (d_top + d_bottom) ÷ 2 + 2 × 0.5

Could you provide the source of the empirical formula? Thank you!

The section on the calculation of chimney height is included in \"Coking Technology\" written by Su Yichun.

Currently, many coking plants are installing waste heat recovery and desulfurization systems, and they are all facing such problems! Once the fans in the waste heat recovery system stop working, the coke oven system loses its suction force. Everyone tries to use the suction power of the chimneys to maintain production, but since most of the waste heat is absorbed by the waste heat boilers, various methods are employed to keep the temperature of the chimneys at a certain level; however, these methods are still being tested out. The temperatures achieved range from 120 degrees, to 180 degrees, and even below 100 degrees, but none of these values have been determined through precise calculations. I think the question could be something like this: by considering only the resistance of the coke oven system, calculate the lowest temperature of the chimney as well as the minimum amount of heat required to maintain a sufficient suction in the chimney. The suction force of the chimney in the coking manual consists of three components: the total resistance of the coke oven system + chimney resistance + reserve suction force. It’s not about maintaining normal production; rather, it’s about ensuring that, even when the coke oven is operating at reduced capacity or is shut down, or when no furnace gas is used for combustion, the overall airflow within the coke oven can still maintain a minimum chimney temperature that allows normal operation.

Different turnover times correspond to different combustion temperatures and exhaust gas flows, so the chimneys also have different suction forces and temperatures. In addition to considering the normal operation of the coke oven, the temperature of the chimney must also take into account the issue of acid dew point corrosion; it is recommended that the temperature at the chimney outlet not drop below 160 degrees, regardless of the turnover time

Could you explain in detail the problem of dew point corrosion in chimneys?