A comprehensive understanding of the non-uniform characteristics and regulation mechanism of six external loops in a 600 MW supercritical CFB boiler

Abstract

As the carrier of material circulation, the uniformity of multi-parallel external loops directly affects the operation of large-scale circulating fluidized bed (CFB) boilers. Some non-uniform phenomena have been found, but the non-uniform characteristics and the absorptive capacity in full process of external loops under changeable operating parameters were seldom considered. To solve this, comprehensive cold/thermal field tests were conducted on the external loops of the first 600 MW supercritical CFB boiler. Operating characteristics of the loops and the fluidization uniformity of fluidized bed heat exchangers (FBHEs) under various cases were fully demonstrated. The influence of air-coal distribution on the operating non-uniformity of the external loops were analyzed, and the absorptive capacity to thermal deviations were quantified. The regulation mechanisms of cyclones and FBHEs were clarified, and the key reason of thermal deviations in FBHEs was also figured out. Eventually, a new coal feeding method to maintain heat balance in dense phase zone was proposed. The results of this paper fully reflected the operating characteristic of the full process in external loops and the response characteristics to air-coal adjustments, which could provide the most direct guidance for academic research as well as optimal design and operation of large-scale CFB boilers.