Sulfuric Acid Dew Point Research Articles

Electrochemical Behavior and Passive Film Properties of Hastelloy C22 Alloy, Laser-Cladding C22 Coating, and Ti–6Al–4V Alloy in Sulfuric Acid Dew-Point Corrosion Environment

The electrochemical behavior and passive film properties of Hastelloy C22 alloy, laser-cladding C22 coating, and Ti–6Al–4V alloy in sulfuric acid dew-point corrosion environment were investigated through a combination of electrochemical measurements and surface analyses. The C22 alloy and laser-cladding C22 coating exhibited similar passivation and repassivation behavior without pitting corrosion, resulting from a similar passive film with a bilayer structure consisting of a Cr2O3-dominated compact inner layer and a porous outer layer containing oxides of Mo and hydroxides of Ni and Cr. The slightly poorer corrosion resistance and higher sensitivity to localized corrosion exhibited by the C22 coating were attributed to the microscale heterogeneity of the passive film resulting from the element segregation in the microstructure introduced by the laser-cladding process. The corrosion of the TC4 alloy performed as the preference dissolution of the β phase. Compared to the C22 alloy and C22 coating, the TC4 alloy exhibited more stable passivation behavior but poorer corrosion resistance, which is attributed to a compact but less protective single-layer passive film consisting of oxides of Ti and Al. An increase in temperature degrades passive film stability and accelerates the charge transfer process.

Effect of Cr on Corrosion Behavior of Laser Cladding Ni-Cr-Mo Alloy Coatings in Sulfuric Acid Dew Point Corrosion Environment

Ni-Cr-Mo alloy coatings with different content of Cr element were produced on carbon structural steel by laser cladding. Coatings exhibited similar phase composition containing γ-Ni solid solution and similar microstructure composed of primary grains and eutectics with segregated Mo. Corrosion behavior of coatings in a sulfuric acid dew point corrosion environment were investigated through the combination of immersion test, electrochemical measurements, and surface analysis. Coatings exhibited similar passive behavior and passive film with a bilayer structure consisting of a compact inner layer and a porous outer layer. An increase in Cr resulted in a more protective passive film with thicker and more compacting inner layer. However, the corrosion resistance was firstly degraded as the content of Cr increased from 18 wt.% to 22 wt.%, and then improved as the content of Cr increased from 22 wt.% to 26 wt.%. This phenomenon was attributed to the competition effect between the increase in Cr and relative decrease in Ni.

Electrochemical Behavior and Passive Film Properties of Hastelloy C22 Alloy, Laser Cladding C22 Coating, and Ti–6al–4v Alloy in Sulfuric Acid Dew Point Corrosion Environment

Electrochemical Behavior and Passive Film Properties of Hastelloy C22 Alloy, Laser Cladding C22 Coating, and Ti–6al–4v Alloy in Sulfuric Acid Dew Point Corrosion Environment

Failure analysis of gas-gas heater tubes for a flue gas desulfurization system

This paper presents the failure analysis of a gas-gas heater (GGH) tube in a coal-fired flue gas desulfurization (FGD) system. The GGH was operated at a temperature below those of the hydrochloric acid dew point as well as sulfuric acid dew point. Leaks were detected in the U-bend of the failed GGH tube. Corrosion products and ashes were attached on the surface of the tube, and uniform and localized corrosion were present throughout the surface. Corrosion products were mainly shown in reddish brown, orange and black color which were identified as hematite (Fe2O3), magnetite (Fe3O4), ferric sulfate (Fe2(SO4)3), ferrous sulfate heptahydrate (FeSO4·7H2O) and ferrous carbonate (FeCO3). In addition, S and Cl were observed in the corrosion products. This is a clear evidence that both sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occurred simultaneously. Further, when Cu and Cr are alloyed together, Cu segregates Cr into the grain boundary, forming a Cr depletion region, and localized corrosion occurs in this area. In the case of the fin-tube joint corrosion, the galvanic corrosion occurred at the filler metal because the filler metal acts as an anode with a middle potential.

Corrosion Behavior of a Ni–Cr–Mo Alloy Coating Fabricated by Laser Cladding in a Simulated Sulfuric Acid Dew Point Corrosion Environment

For this study, aimed at proposing a potential direction to prevent sulfuric acid dew point corrosion, a Ni–Cr–Mo alloy Hastelloy C22 coating was fabricated by coaxial laser cladding technology. The phase composition, microstructure, and corrosion behavior in a simulated sulfuric acid dew point corrosion environment were investigated and compared with a Hastelloy C22 alloy, a titanium alloy TC4, and 09CrCuSb steel (ND). The results showed that the phase composition of the C22 coating is essentially similar to that of the C22 alloy, consisting of a γ-Ni solid solution and Ni6Mo6C1.06. The finer microstructure of the C22 coating mainly contains eutectic and dentrite, presenting a typical solidification feature of laser cladding. The corrosion resistance of the C22 coating is very close to that of the C22 alloy, and outclasses that of TC4 and ND. The corrosion behavior of the C22 coating is intergranular corrosion resulting from the segregation of molybdenum, chromium containing corrosion products, and smaller anode micro-batteries.

Preparation of Sulfuric Acid Vapor for Simulation of Sulfuric Acid Dew Point Corrosion by Inert Gas Carrying Method

Preparation of Sulfuric Acid Vapor for Simulation of Sulfuric Acid Dew Point Corrosion by Inert Gas Carrying Method

Catalytic Role of Process Dust in SO2-to-SO3 Conversion in Flash Smelting Heat Recovery Boilers

The aim of this work is to examine the catalytic role of copper smelter, copper converter, and nickel smelter process dusts in SO2-to-SO3 conversion at 750°C. To clarify the role of specific oxides in greater detail, synthetic dusts containing varying concentrations of either CuO or Fe3O4 were also studied. All studied dusts catalyzed SO3 conversion. Among the industrial flue dusts, the highest concentration of SO3 formed in the presence of copper smelter dust. Comparing individual oxides, CuO had a greater impact on the SO3 formation. Such catalytic effects of smelter dusts may lead to SO3 concentrations in the process gas so high that sulfuric acid dew point corrosion may occur.

The Effect of Flue Gas Environment on the Corrosion Behavior of the Sulfuric Acid Dew-Point Corrosion Resistant Steel

In order to compare the corrosion resistance of conventional low carbon steel, Cu containing low carbon steel for sulfuric acid dew-point corrosion inhibition, and stainless 409L, immersion tests were carried out in 50 wt.% sulfuric acid. The effects of HCl concentraion on the corrosion behavior in a fixed sulfuric acid concentration (16.9 vol.%) was also investigated by immersion test. In addition to immersion test, field test in a thermal plant was carried out for 10 months. As a result, it was confirmed that Cu-containing dew-point corrosion resistent steel has the highest corrosion resistance compared with other materials. To verify superior corrosion resistence of dew-point corrosion resistant steel, surface morpology after various test was observed by SEM. It was found that surface corroded product of the dew-point corrosion resistant steel was much denser and thicker compared with the other steel.

The Effect of Deposit Temperature on the Catalytic SO2-to-SO3 Conversion in a Copper Flash Smelting Heat Recovery Boiler

The aim of the work was to study the catalytic role of copper flash smelter deposit in the SO2-to-SO3 conversion. In addition, the effect of process gas temperature at 548 K to 1173 K (275 °C to 900 °C) on the amount of SO3 formed was addressed both in the absence and presence of genuine copper flash smelter deposit. The SO3 conversion rate changed as a function of process gas temperature, peaking at 1023 K (750 °C). A dramatic increase in the SO2-to-SO3 conversion was observed when process dust was present, clearly indicating that process dust catalyzes the SO2-to-SO3 conversion. Based on these results, the catalytic ability of the deposit may lead to sulfuric acid dew point corrosion.

The Methods Used to Provide the Reliability of Gas Bleeding Ducts for EPP Boilers

Erosion and corrosion damage of the elements of electric equipment is one of the main reasons for the normal operation disturbance and sometimes lockup of the thermal power equipment. The metal loss in the elements of power plants due to the erosion and corrosion wear over their entire service life exceeds 8 % of the original mass that results in the efficiency reduction. In addition, erosion and corrosion process products cause the blockage of water-steam circuit which negatively affects a reliable operation of the power equipment. The purpose of this research was to study the influence of the temperature of dew point on the reliability control. The domestic literature describes some relationships used for the definition of sulfuric acid dew point that were obtained using the dust firing technique. This method allows for the computation of temperature differences and the method showed that that temperature of sulfuric acid dew point exceeds that of the dew point of pure vapors (t р = 45–54 °С). To meet a condition of the prevention of condensate formation it is necessary to increase the temperature of the internal surface of gas bleeding circuit t s and decrease the humidity of furnace gases and thus decrease the temperature of their dew point t р. The technological areas of the disposal of furnace gases with no water steam condensation include the heat transfer to the water in the additional heating surface; additional heat transfer to the blow air through an increase in the temperature difference due to a decrease in the temperature of entering air, and the additional heat transfer to the feed water in available heating surfaces.

Simulating sulfuric acid dew point corrosion of enamels with different contents of silica

Corrosion of three bulk enamels with different silica contents in sulfuric acid was studied. Catastrophic corrosion happened for enamel with 54.6wt% silica. Its weight loss reached 36.90mg/cm2 after seven-day corrosion. A porous leached layer with tremendous cracks formed at surface during corrosion, which favored acid invading and further corrosion. On the contrary, the durability of enamels with silica content over 60wt% was guaranteed by their highly connected silicate network and a developed dense gel layer that clogged corrosion pits. Their weight losses were less than 0.2mg/cm2 after seven-day corrosion.

Failure analysis on abnormal corrosion of economizer tubes in a waste heat boiler

Abstract Repeated shell side corrosion occurred on economizer tubes of a waste heat boiler. In order to find out the root cause of the corrosion, a series of characterization methods were conducted. First of all, the tubes were proved to be qualified A106 Gr.A steel in chemical compositions and metallographic structures. Then, both macroscopic and microscopic characteristics of the failed tube were observed thoroughly. After that, phase compositions of the deposits collected from failed tubes were analyzed. Content of sulfur and nitrogen of deposits was determined precisely as well. The results revealed that repeated failures were primarily owing to sulfuric acid dew point corrosion and the sulfur mainly came from waste liquid of methyl methacrylate (MMA). Finally, mechanisms of the failure were discussed in detail and practical countermeasures were put forward.

Prediction of sulfuric acid dew point temperature on heat transfer fin surface

Sulfuric acid dew point temperature is an important parameter denoting the dew point corrosion. The sulfuric acid dew point temperature is calculated by considering both the vapor–liquid equilibrium effect and multi-component diffusion effect. In addition, the local distribution of acid dew point temperature on fin surface is numerically predicted for the first time. The influences of fuel type (sulfur content, water content and ash content), wall temperature, excess air ratio, flue gas inlet velocity, fly ash particle (size and quantity) and heat transfer fin structure on the sulfuric acid dew point temperature are discussed. The results show that different types of fuels (which differ in gas composition and combustion temperature) have a great impact on the sulfuric acid dew point temperature. The sulfuric acid dew point temperature decreases with the reduction of excess air ratio, the increasing of wall temperature, and the condensation of sulfuric acid vapor on ash particle surface. The sulfuric acid vapor condensates more seriously on the tube windward than on the leeward. The novel types of heat transfer fins with high heat transfer performance can also reduce the local sulfuric acid dew point temperature, and the maximum reduction of sulfuric acid dew point is 4.1 K between the novel fin surface and the original H-type fin surface.

On the Failure Analysis of an Air Preheater in a Steam Power Plant

The air heater is a rotary regenerative heat exchanger which recovers heat from the outgoing hot gases of the boiler and transforms it to the incoming air needed for combustion process. This system is composed of large numbers of heat transfer elements made from corrosion-resistant material (Corten) or enamel coated in order to resist acid dew-point corrosion. In this study, a root cause failure analysis of heating elements was carried out. Visual inspection, chemical analysis, and microscopic examinations of the heating elements, enamel coating, and depositions were conducted. Sulfuric acid dew-point temperature (ADPT) was determined to be 138–142 °C based on the sulfur dioxide of the flue gases. Moreover, temperature distribution across the air heater matrix was simulated using Fluent software. The failures of the heating elements were mainly due to sulfuric acid dew-point corrosion and under-deposit pitting corrosion. The corrosion products were mainly iron sulfate, iron oxide, and iron sulfide. In the case of enamel-coated elements, the failure was attributed to the existence of a large number of cracks and big bubbles in the coating, allowing the penetration of corrosive elements into and beneath the surface of coating and thus the detachment of coating.

Development of Sulfuric and Hydrochloric Acid Dew-Point Corrosion-Resistant Steels : 2. Reliability Verification of New Corrosion-Resistant Steel by Field Test

Development of Sulfuric and Hydrochloric Acid Dew-Point Corrosion-Resistant Steels : 2. Reliability Verification of New Corrosion-Resistant Steel by Field Test

Development of Sulfuric and Hydrochloric Acid Dew-Point Corrosion-Resistant Steels: 1. Effect of Alloying Elements on the Corrosion Resistance of Low-Alloy Steels

Development of Sulfuric and Hydrochloric Acid Dew-Point Corrosion-Resistant Steels: 1. Effect of Alloying Elements on the Corrosion Resistance of Low-Alloy Steels

SO3 Emissions and Removal by Ash in Coal-Fired Oxy-Fuel Combustion

The sulfur oxide (SOx) concentrations during oxy-fuel combustion are generally higher compared to conventional air firing. The higher SOx concentrations, particularly sulfur trioxide (SO3) in combination with high concentration of water in the recycled flue gas, increase the sulfuric acid dew point temperature in oxy-fuel fired systems, thereby increasing allowable flue gas temperatures and reducing the thermal efficiency of a power plant. This paper presents results of experiments carried out at a 20 kW once-through combustion rig of the Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart simulating different extents of oxy-fuel recycle gas cleaning by impurities injection to the oxidant gas of a once-through combustion reactor. Three Australian coals that have previously been tested under air and oxy-fuel conditions at the Aioi furnace of IHI in Japan were used in the experiments. The SOx emissions were measured, conversion ratios of sulfur dioxide (SO2) to SO3 were calculated, and results were compared with existing literature, finding good agreement. The experiments with different extents of recycle gas cleaning and therefore different SO2 levels in the system, revealed differences in the SO3 generation behavior: A coal-specific trend of increasing conversion ratios of SO2 to SO3 with increased flue gas SO2 levels was observed that could be related to the ash composition of the three different coals. The capture of SOx in a baghouse filter was also evaluated. Acid dew point temperatures (ADPs) for the flue gas were calculated for the various firing conditions. Acid dew point (ADP) temperatures increased by up to 50 °C when changing from air to oxy-firing with recycling of H2O and SO2. Considerable differences in the ADPs were found for different extents of oxy-fuel recycle gas treatment and were evaluated in respect to power plant efficiency implications.

Oxidation degradation of polyphenylene sulfide needle felt at different sulfuric acid dew point temperatures

Sulfuric acid dew point is an important parameter in coal-fired power plants as it affects many equipments, materials, and pipes, including filter bags. This article puts forward a new method to test the effect of different sulfuric acid dew points on the performance of polyphenylene sulfide (PPS) needle felt. Oxidation reaction mechanisms were predicted using Fourier transform infrared analysis. The results show that the degradation starts with S atoms in the PPS molecular chain; first, the thioether bond is broken, followed by sulfonation of benzene, and finally concluding with the carbonization of PPS. Furthermore, PPS thermal properties also show a decrease in the melting temperatures and thermal decomposition temperatures as well as an increase in the residual mass of the initial weight with increasing sulfuric acid dew point. Changes in the thermal properties of PPS further confirmed that different reaction mechanisms exist under different acid dew points.

Sulfur recirculation for increased electricity production in Waste-to-Energy plants

Sulfur recirculation is a new technology for reducing boiler corrosion and dioxin formation. It was demonstrated in full-scale tests at a Waste to Energy plant in Göteborg (Sweden) during nearly two months of operation. Sulfur was recirculated as sulfuric acid from the flue gas cleaning back to the boiler, thus creating a sulfur loop.The new technology was evaluated by extensive measurement campaigns during operation under normal conditions (reference case) and operation with sulfur recirculation. The chlorine content of both fly ash and boiler ash decreased and the sulfur content increased during the sulfur recirculation tests. The deposit growth and the particle concentration decreased with sulfur recirculation and the dioxin concentration (I-TEQ) of the flue gas was reduced by approximately 25%. Sulfuric acid dew point measurements showed that the sulfuric acid dosage did not lead to elevated SO3 concentrations, which may otherwise induce low temperature corrosion.In the sulfur recirculation corrosion probe exposures, the corrosion rate decreased for all tested materials (16Mo3, Sanicro 28 and Inconel 625) and material temperatures (450°C and 525°C) compared to the reference exposure. The corrosion rates were reduced by 60–90%. Sulfur recirculation prevented the formation of transition metal chlorides at the metal/oxide interface, formation of chromate and reduced the presence of zinc in the corrosion products. Furthermore, measured corrosion rates at 525°C with sulfur recirculation in operation were similar or lower compared to those measured at 450°C material temperature in reference conditions, which corresponds to normal operation at normal steam temperatures. This implies that sulfur recirculation allows for higher steam data and electricity production without increasing corrosion.

Sulfuric acid dew point corrosion in waste heat boiler tube for copper smelting furnace

This paper presents the sulfuric acid dew point corrosion found on waste heat boiler tube for a copper smelting furnace. Macroscopic and microscopic observation results for the failed boiler tubes are shown. Then the analyzed results by X-ray fluorescence, X-ray diffraction and EPMA on failed boiler tubes are demonstrated. Finally effective alloying elements for waste heat boiler tube material against sulfuric acid dew point corrosion are briefly described on the basis of the exposure test results for three kinds of steels in the radiation section of the waste heat boiler.