Passive double-back-pressure low-vacuum heat supply system of direct air cooling unit

The utility model relates to a passive double-back-pressure low-vacuum heat supply system of a direct air cooling unit. The heat supply system comprises a first low-pressure cylinder, a second low-pressure cylinder, an air cooling island, a first steam exhaust device, a second steam exhaust device, a condenser, a heat supply network heater, a condensate pump and a first valve. The first low-pressure cylinder is communicated with the air cooling island and the first steam exhaust device; the second low-pressure cylinder is communicated with the air cooling island and the second steam exhaust device; the first steam exhaust device is communicated with the condensate pump; the condensate pump is communicated with the outside; the second steam exhaust device is communicated with the first steam exhaust device through a regulating valve; the first valve is arranged on an inlet pipeline of the heating network heater; the steam side of the condenser is communicated with a second low-pressurecylinder and a second ste