Papers by Author: Christophe Rapin

Abstract: Increase of the energy recovery efficiency facilities is one of the challenges fixed recently by UE to Municipal Solid Waste Incineration (MSWI) operators. To achieve this target, one option consists in optimizing the water/steam cycle to increase electrical efficiency. Nevertheless, higher steam temperature into heat exchanger tube is expected to increase the risks of fireside corrosion, particularly on superheater tubes, along with important loss of materials, frequent shutdowns for repairs and high operational costs. In this study, fireside corrosion test had been performed using an innovative laboratory-scale corrosion pilot. Effect of increase in metal temperature from 400°C to 450°C on corrosion performances of SA192 carbon steel tube and AISI 316L stainless steel had been examined. Mechanisms and corrosion rates are discussed with regards to lifetime reported for both materials after 1 year in service in the same plant.

Abstract: The determination of the corrosion processes of metallic materials in glass melts is of great interest for glass makers. Our attention has been specifically focussed on Cr-bearing alloys that form Cr2O3 layers when they are immersed in a silicate melt and offer a good resistance to melt corrosion. The comprehension of the corrosion processes has been extensively studied in the last 10 years using stationary electrochemical techniques. Results relative to the thermodynamic state were described. Complex impedance spectroscopy offers the possibility to determine the reaction kinetics in terms of limiting processes. Three chromium rods were directly immersed in molten glass at T=1050°C, maintained respectively in the active, passive and transpassive state and studied using electrochemical techniques. The results that are reported in this paper show a good agreement between complex impedance spectroscopy data, scanning electron microphotographies of the glass/metal interface and previous results obtained using stationary electrochemical techniques.

Abstract: This paper presents the corrosion of potassic glasses by SO2 gas at high-temperature. The corrosion phenomenon of potassic glass is well-known for medieval stained-glass windows under natural conditions of weathering [1]. Nevertheless the corrosion is also possible without humidity at high temperature in presence of polluting gas such as SO2 gas in the furnace. All source of SO2 gas can thermodynamically involve the main formation of K2SO4 and other alkaline salts such as Na2SO4. This corrosion manifests itself by the presence of “white flakes” in the bulk glass and this defect leads to discard of the piece for a crystal-maker like Daum. Alkali sulphate formation was determined by using scanning electron microscopy and presents a very particular morphology. This study allowed underlining on, one hand the influence of the temperature and on the other hand the role of gas concentration on the formation of the potassium sulphate. Thermal analysis technique (TGA) was carried out in order to understand the corrosion chemical kinetic of potassic glasses by SO2 gas.

Abstract: Most of equipments used in glass industry are superalloys containing up to 30 wt% chromium. The ability of these alloys to resist against silicate melt corrosion is directly linked to the formation of a chromia (Cr2O3) layer at the alloy/melt interface which can be protective under particular conditions. These conditions have been previously identified and are the temperature, melt composition and redox conditions. The aim of the present study is to establish the relationship between the protective (or non protective) behaviour of the chromia layer with the solubility of chromia in silicate melts under given conditions. The combination between results from the electrochemical study of pure chromium corrosion and total Cr solubility in Na2O-xSiO2 melts clearly indicates that both parameters are linked: the lower the total Cr solubility, the better the Cr is corrosion resistant.

Abstract: The efficiency of Waste-to-Energy (W-t-E) boilers is affected by fireside corrosion of the heat exchangers that involve unexpected shutdown of facilities for repairs and limit the increase of steam conditions used to produce electricity. The parameters governing fireside corrosion are various and mechanisms are very complex, nevertheless, they are relatively well documented in the literature. In this paper, a laboratory-scale corrosion pilot, which reproduces MSWI boilers conditions, is described. The specificity of our approach includes simultaneous simulation of the temperature gradient at flue-gas/tube interface, the velocity of flue-gas and ashes. Corrosion rates obtained on Tu37C carbon steel at a metal temperature equal to 400°C and a flue gas temperatures of 650°C and 850°C (1100 ppm HCl, 110 ppm SO2 and synthetic ashes free of heavy metals) are respectively around 1.6 2m/hour and 5.6 2m/hour. Preferential metal loss, attributed to erosion-corrosion phenomena, is also observed at low flue-gas temperature (T=650°C) on the face exposed at 90° to the flue-gas. The analysis of corrosion scales demonstrates the reproducibility of results and the reliability of corrosion mechanisms determined from experiments, with degradation observed similar to superheater tubes from EfW facilities. Thus, the corrosion pilot developed can be used as an accurate simulator of the environment encountered in MSWI.