Radiation furnace tube

The invention provides a radiation furnace tube which comprises at least one group of 2: 1:...: 1: 1 type furnace tubes. Each group of 2: 1:...: 1: 1 type furnace tubes comprises first-pass tubes, a second-pass tube, a third-pass tube... and an Nth-pass tube, N is an even number, the number of the first-pass tubes is two, and the number of the second-pass tube, the number of the third-pass tube...and the number of the Nth-pass tube is one. The two first-pass tubes are communicated with the second-pass tube through a two-in-one back-bending elbow, and the second-pass tube, the third-pass tube... and the Nth-pass tube are sequentially communicated in an S shape through an upper 180-degree back-bending elbow or a lower 180-degree back-bending elbow. As the two first-pass tubes are small-diameter furnace tubes, the purpose of rapid heat absorption and temperature rise of a medium can be achieved by utilizing the characteristic of large specific surface area of the first-pass tubes. Due tothe fact that the second,