Influence of Rotational Speed on Thermal Performance of Tri-Sector Rotary Regenerative Air Preheater

Abstract

This paper provides a detailed analysis of how a rotary regenerative air preheater’s performance parameters such as effectiveness, fluid and metal temperature fields, and ammonium bisulfate (ABS) deposition area vary with rotor rotational speed. A tri-sector rotary regenerative air preheater for a 600MW unit was studied as an example by use of effectiveness–modified number of transfer units (ε-NTU0) method and a finite difference method. The findings of the research are as follows: (1) There is a nonlinear relationship between matrix temperature distribution and rotational angle, and the degree of nonlinearity, represented by unsteady heat transfer correction factor Π, increases with decreasing rotational speed and varies between sectors; (2) There exist two equilibrium positions around the intersection points of matrix temperature curves for different rotational speeds, one occurring in the heating period and the other in the cooling period; (3) The act of reducing the rotor speed has two effects on ABS deposition. On the one hand, the height range of possible ABS deposition area will expand as the matrix temperature within the first third of gas sector’s angle range further decreases with decreasing rotational speed. On the other hand, after the rotational speed falls below a certain level, the hot-end matrix temperature climbs above the ABS formation temperature during part of the heating period, resulting in gasification and decomposition of the condensed product. The combined effect is yet to be examined through further theoretical and empirical analyses. (4) The trends of average outlet temperatures of primary and secondary air depend on rotor rotation direction and angles of sectors. (5) The effectiveness values calculated by ε-NTU0 method are greater than those acquired by the finite difference method, especially at low rotor rotational speeds.