Deposit Formation of the Low-Pressure Economizer in a Coal-Fired Thermal Power Plant

Abstract

A field study was conducted to investigate the deposit formation of the low-pressure economizer (LPE) in a 330 MW thermal power plant. The deposits on the LPE were inspected visually, and eight deposit samples were collected at the inlet and outlet of the LPE according to the site conditions. The samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and particle size analysis. The results showed that the thick deposits on the supporting tubes at the LPE inlet were mainly due to the ash particles that had absorbed the H 2 SO 4 condensate in the flue gas before the LPE inlet. NH 4 HSO 4 began to form on the heat-exchange tubes at the LPE inlet. Both the H 2 SO 4 condensation and NH 4 HSO 4 formation stimulated the deposit formation on the heat-exchange tubes at the LPE inlet. The plugging of the heat-exchange tubes at the LPE outlet was primarily induced by the condensation of much more H 2 SO 4 . H 2 SO 4 and NH 4 HSO 4 could also react with the fly ash to form sulfates. The LPE deposition mechanism was discussed, and the coupling model of the H 2 SO 4, NH 4 HSO 4, and fly ash behaviors during the deposit formation under different temperature conditions was proposed.