MDEA semi-lean cycle desulfurization device and method using low-temperature heat

The invention belongs to the field of petrochemical engineering, and provides an MDEA semi-lean cycle desulfurization device and method utilizing low-temperature heat. The device comprises an absorption tower, a flash tank, a semi-barren liquor/rich liquor heat exchanger, a barren liquor/rich liquor heat exchanger, a pre-desorption tower, a pre-desorption tower bottom reboiler, a pre-desorption tower top condenser, a secondary desorption tower, a secondary desorption tower bottom reboiler, a secondary desorption tower top condenser, a semi-barren liquor water cooler, a barren liquor water cooler, a semi-barren liquor circulating pump and a barren liquor circulating pump. The desorption tower is divided into the pre-desorption tower and the secondary desorption tower, one part of semi-barren liquor which is not completely purified and obtained by the pre-desorption tower is used for absorbing acid gas, the energy consumption in the desorption process is reduced, the treatment capacity of the secondary desorpti