Energy-saving biogas purification method

The invention discloses an energy-saving biogas purification method. The method comprises the following steps: feeding a biogas raw material to be purified into a biogas direct-drive purification system for desulfurization and condensation dehydration; the dehydrated marsh gas enters a heat exchanger and is reheated to normal temperature by utilizing low-temperature flue gas from an absorption refrigerating unit, and the low-temperature flue gas is discharged after heat exchange by the heat exchanger or is discharged after being purified according to the flue gas discharge standard and reaching the standard; the reheated biogas is filtered to remove micron-sized fine particles and then is fed into a direct-drive biogas compressor, one part of the biogas is supplied to the direct-drive biogas compressor, and the rest of the biogas is pressurized by the direct-drive biogas compressor and then enters a membrane separation device to separate CH4 and CO2, so that high-purity CH4-concentration biogas is obtained; h