Hygroscopic Properties of Calcium Chloride and Its Role on Cold-End Corrosion in Biomass Combustion

Abstract

In biomass combustion, hygroscopic and deliquescent salts may cause cold-end corrosion and operational problems, such as deposit buildup and decrease in heat transfer. Calcium chloride is a deliquescent salt that can be found in the cold-end of boilers. In this study, the hygroscopic properties and corrosiveness of CaCl 2 in flue gas conditions were studied. The formation of hydrates and the deliquescent properties of CaCl 2 were studied with various techniques. The hydrate formation, deliquescence, and water absorption at various temperatures, humidities, and cooling rates were studied using thermogravimetric analysis. A stable flow of water vapor (5−35 vol %) was created with a membrane humidifier with a humidity sensor. Deliquescence and recrystallization of CaCl 2 were determined by a two-electrode chronoamperometric setup. The effect of mixtures containing CaCl 2 , CaCO 3 , and CaSO 4 on deliquescence was also studied. Furthermore, the corrosivity of CaCl 2 on mild steel was studied above and below the deliquescence temperature, and the corrosion products were analyzed by means of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). This work revealed that both deliquescence and recrystallization of CaCl 2 are of importance when assessing the corrosivity of the salt. When deliquescence occurred, the corrosion rate was substantial, and the corrosion rate was dependent on the ion concentration of the formed solution. Drying or crystallization of the salt solution occurred at 35−42 °C higher than the deliquescence temperature with 10−35 vol % H 2 O. Thus, large variations in the flue gas water vapor concentration will impact the wetting and drying of the salt. The observations presented in this paper give guidelines on how to prevent corrosion caused by deliquescent CaCl 2 .

Torrefaction as a Pretreatment Technology for Chlorine Elimination from Biomass: A Case Study Using Eucalyptus globulus Labill

“…Chlorine is usually present in biomass in low concentrations [84,85]. However, during combustion, hydrochloric acid is formed, which can lead to corrosion in the furnace [86][87][88]. Therefore, it is crucial to determine the torrefaction temperature that will eliminate that component.…”

Enhanced predictive corrosion modeling of crevice evolution at e‐coat defects under cyclic climate conditions

“…The TOW of the sheets during climate 1 and climate 2 is very different as the humidity of climate 2 is higher and the electrolyte during the salt spray phase contains CaCl 2 , which is highly hygroscopic. [ 22 ] Hence, the delamination width for a sheet inclination of 85° is higher at climate 2 despite the higher current density of the polarization data measured with 5 wt NaCl electrolyte (Figure 7).…”

Effect of Ca(OH)2 on the Release Characteristics of HCl during Sludge Combustion

“…As a hygroscopic salt, CaCl 2 may react differently with water to form hydrates. The specific reactions are as follows ( eqs 1 – 3 ) 44 …”