Pure nitrogen backflow expansion double-tower nitrogen making equipment

The utility model discloses a pure nitrogen backflow expansion double-tower nitrogen making device, which relates to the technical field of industrial nitrogen making and comprises an air filter, an air compressor, a pre-cooling unit, a moisture device, a molecular sieve adsorber, a turbo expander, a main heat exchanger, a subcooler, a high-pressure nitrogen tower, a main condensation evaporator I, a low-pressure nitrogen tower and a main condensation evaporator II. The molecular sieve adsorber is communicated with the main heat exchanger through a first pipeline, the first pipeline is communicated with a bearing gas and sealing gas inlet of the turbo expander through a second pipeline, the high-pressure nitrogen tower is connected with an input port of the turbo expander through a third pipeline, and the second pipeline is communicated with the third pipeline through a fourth pipeline. And valves are respectively arranged on the second pipeline and the fourth pipeline. According to the technical scheme, pure