System and method for extracting helium from helium-poor natural gas and co-producing multiple products

The invention discloses a system and a method for extracting helium from helium-poor natural gas and co-producing multiple products. The system comprises a first-stage refrigeration device, a first-stage low-temperature separator, a pre-denitrification tower, a demethanizing tower, a second-stage refrigeration device, a helium extraction tower, a denitrification tower and the like. According to the system and the method disclosed by the invention, the nitrogen, the methane, the ethane and the propane are sequentially rectified and separated according to the boiling points of the components from low to high, the nitrogen and the methane are separated by utilizing the pre-denitrification tower, the concentration of helium in tower top gas can be concentrated by about 30 times, and meanwhile, the content of carbon dioxide in the tower top gas is controlled to be lower than 50ppm; and the separation of nitrogen and helium is realized by utilizing low-temperature rectification. Economical and effective recovery of