Scale Formation, Corrosion Product Deposition, and Enhanced Water Degassing in Thermal Power Plant Heat Transfer Systems: Mechanisms, Kinetics, and a Novel Iron-Scrap Deaerator Modification

Abstract

The major factors contributing to reduced efficiency and early failure of thermal power plant (TPP) equipment are scaling and corrosion product deposits on heat transfer surfaces. A mechanistic, thermodynamic, and kinetic analysis of scaling and corrosion processes will be presented, as well as an experimental demonstration of a novel, iron scrap reactive device installed within the de-aerating tank to enhance removal of dissolved gases. Inverse solubility of CaCO 3 , CaSO 4 , MgCO 3 , Mg(OH) 2 , CaSiO 3 , and MgSiO 3 has been characterised from 20 to 350 degrees C by means of solubility product (Ksp) analysis. Utilising a quantitative fuel consumption model, it has been found that for every 1 mm of CaCO 3 scaling, there is a corresponding increase in natural gas consumption of 2.8%, an increase of 7.8% at 5 mm scaling. Electrochemical corrosion mechanisms due to O 2 and CO 2 will be studied in detail with a thermodynamic and kinetic perspective. The iron scrap device utilises 12 competing heterogeneous reactions to chemically absorb dissolved O 2 and CO 2 prior to thermal expulsion, lowering dissolved O 2 by 19-20% and CO 2 by 17-18% when compared to conventional thermal de-aeration, while reducing hydrazine consumption by approximately 20%. As such, the combined thermal and chemical de-aeration strategy results in an annual net savings of $185,000-$210,000 per 100 MW unit, yielding a payback period of less than one month.