Flow heat transfer and NO_x emission characteristic of W-shaped radiant tubes with flue gas circulation

In order to solve the large wall temperature difference and high NO_x emission of W-shaped radiant tubes, this article introduces a kind of W-shaped radiant tube with flue gas circulation. A mathematical model of the radiant tube is established and the radiant tube is studied by the method of numerical calculation. On the basis of the model's reliability, the velocity field, temperature field and NO_x emission are compared between the radiant tube and a conventional W-shaped radiant tube. The average gas velocity of the new radiant tube is three times that of the conventional radiant tube, and 57.6% flue gas is involved in recombustion in the new radiant tube. The maximum combustion temperature of the new radiant tube is 2260 K, which is 192 K lower than that of the conventional radiant tube. The wall temperature difference of the new radiant tube is 166 K,which is 76 K lower than that of the conventional radiant tube. The NO_x emission of the new radiant tube is 9.9×10^-5, but the NO_x emission of the conventional radiant tube is 7.98×10^-4, nearly seven times higher.