Arrangement structure of tail flue of a double reheat boiler

The invention discloses a tail flue arrangement structure of a secondary reheating boiler. The tail flue is divided into a front flue, a middle flue and a rear flue from front to back, coal economizers, a first low-temperature reheater located in the front flue, a second low-temperature reheater located in the middle flue and a low-temperature superheater located in the rear flue are arranged in the tail flue, the coal economizers comprise an inlet header, a first-stage coal economizer, a second-stage coal economizer and an outlet header, wherein the inlet header, the first-stage coal economizer, the second-stage coal economizer and the outlet header are connected successively in series, the first-stage coal economizer comprises a first-stage coal economizer tube group and a second-stage economizer tube group which are connected in parallel, the first-stage coal economizer tube group is arranged at the lower part of the first low-temperature reheater, the second-stage coal economizer tube group is arranged at the lower part of the second low-temperature reheater, and the second-stage coal economizer acts as a third-stage coal economizer tube group arranged at the lower part of thelow-temperature superheater. According to the tail flue arrangement structure of the secondary reheating boiler, the series-parallel grading arrangement of the coal economizer tube groups is carried out based on the smoke temperature of the flue of each-stage coal economizer tube group, the heat absorption deviation among the coal economizer tube groups in flues at the tail part is eliminated, sothat the minimum under-enthalpy of the working medium in the coal economizers is expanded.