Spiral outer half tube design reduces the wall thickness of the kettle and improves its pressure bearing capacity. The wall thickness of the kettle body and lower head is 37.5% and 50% thinner than the wall thickness designed according to the jacket, which is beneficial for improving heat transfer efficiency. It can both increase the heat transfer coefficient and reduce thermal resistance, and is also suitable for cooling processes; It can also increase the flow rate of the medium in the coil, and high-speed flowing medium can effectively prevent scaling on the inner surface of the jacket; Save energy consumption. The ratio of jacket volume to half tube volume is 8, reducing investment. Reduce the overall diameter of the kettle body, facilitate workshop layout, and save steel. The production process of the entire outer coil tube reactor is more complex than that of a regular jacket reactor, which slightly increases the labor cost of the reactor manufacturer.