Multi-stage single-component refrigerated natural gas liquefaction system

The utility model discloses a multi-stage single-component refrigerated natural gas liquefaction system. The temperature of purified natural gas is gradually reduced in six heat exchangers (evaporators) and a plate-fin heat exchanger (a natural gas subcooler) until the purified natural gas is liquefied; cold required in a liquefaction process is provided by a propane system, an ethylene system and a methane system; and the system is abundant in adjustment means, and can provide matched cold for the natural gas liquefaction process, so that flexibility of the method on operation and adaptability to raw materials are embodied. The multi-stage single-component refrigerated natural gas liquefaction system has the advantages that the energy consumption in the natural gas liquefaction process is low; refrigerant compressors are single-component compressors; the design is easy, purchasement is convenient, the compressors run stably, domestic equipment can be adopted, and accordingly the construction investment of a liquefaction plant is reduced effectively; and the selection range of the heat exchangers used in the liquefaction process is wide, and the heat exchangers can be of cold-tank structures or tube-and-shell structures or cold-tank and tube-and-shell combined structures.