Waste heat utilization device of closed spray dryer

The utility model discloses a waste heat utilization device of a closed spray dryer. Middle box, end plates are welded at the upper and lower ends of the middle box body; a plurality of through steelpipes are connected between the end plates; an upper box body is installed at the upper end of the middle box body, a lower box body is installed at the lower end of the middle box body, the two endsof the steel pipe communicate with the upper box body and the lower box body correspondingly, a first air inlet connecting pipe is fixedly installed on the lower side of the middle box body, and a first exhaust connecting pipe is fixedly installed on the upper side of the middle box body. High-temperature waste gas generated by the drying tower firstly flows into the middle box body to heat the steel pipe and then flows into the condenser to be cooled and separated, separated nitrogen is conveyed to the upper box body and preheated when flowing downwards from the steel pipe, and therefore waste heat of tail gas is util