Boiler Corrosion Research Articles

Optimization of air distribution and coal blending in pulverized coal boilers for high-temperature corrosion prevention based on POD reduced-order modeling

High-temperature corrosion in coal-fired boilers poses a significant threat to safe operation. However, there is currently a lack of effective online monitoring and optimization methods for high-temperature corrosion. Therefore, this study proposes a novel approach to rapidly predict the distribution of chemical species and evaluate high-temperature corrosion degrees, along with optimizing operating conditions to prevent high-temperature corrosion. Firstly, a total of 564 Computational Fluid Dynamics (CFD) simulations are performed on a 330 MW tangentially fired boiler, covering various operating conditions, including coal blending, air distribution, boiler load, etc., to obtain a database of O2, CO, and H2S distributions within the boiler. Then a method based on Proper Orthogonal Decomposition (POD) and Support Vector Regression (SVR) is used to process the database to realize real-time prediction of boiler chemical species distribution, which is next utilized as inputs of a high-temperature corrosion evaluation to obtain in-situ corrosion degree distribution. Finally, Particle Swarm Optimization (PSO) is used to optimize coal blending and air distribution schemes, effectively reducing severe corrosion ratio from 36.34 % to 10.04 % in a typical case by improving the atmosphere near the water walls. This study thus provides a new perspective for online boiler diagnostics and digital twin construction, particularly by achieving online monitoring of high-temperature corrosion and optimizing operating conditions to prevent corrosion.

New Problems of Boiler Corrosion after Coupling Combustion of Coal and Biomass and Anti-Corrosion Technologies

New Problems of Boiler Corrosion after Coupling Combustion of Coal and Biomass and Anti-Corrosion Technologies

Micro analysis of the structure of the boiler pipe after experiencing the heating process and without heating

Piping is a tool that functions to drain fluid from one place to another. The problem at Factory X is the failure of the boiler pipe. Pipe failures that occur are known by indications of leaks in the boiler. The initial process of a failure in an ordinary pipe is characterized by corrosion. The problem of corrosion in boilers is usually caused by feed water or feed water which still contains high oxygen levels. The purpose of the research is to determine the microstructure of the boiler pipe after experiencing the combustion process in the combustion chamber. This research method is an analysis of the chemical composition of boiler pipe material, Visual / Macro and Micro Testing. From the results of the inspection, observation, it can be concluded, the cause of pipe damage on the outside of the fire side caused by erosion corrosion is classified as very severe because it is beyond the optimum thickness of the pipe. Specimen A which is a material that has not received heat treatment has a microstructure, where the condition of the fearlite area is greater than specimen B with heat treatment.

Experience in the Fabrication of Tube Grade 7CrMoVTiB10-10 with Inconel 625 Weld Overlay for Use in Steam Superheaters Exposed to Highly Corrosive Environments

Problems with corrosion in boilers and their parts can be solved by the application of different nickel alloys like 622, 625 or 686 by a variety of welding processes. This solution is used mostly in Waste-to-Energy plants or biomass stations burning waste wood, but it can also be found in the recovery boilers used in the paper industry. The most common material grades include low alloyed boiler steels like 16Mo3, 13CrMo4-5 and 10CrMo9-10. When there is a need to increase steam temperature and pressure more complicated alloys to become a natural choice. This paper focuses on the fabrication experience of welding of 7CrMoVTiB10-10 base tube with Inconel 625 weld overlay and presents a welding solution of matching filler metal used for root pass and S Ni 6625 filler metal for a fill-up and the cap performing a full strength weld without the need of overlay peeling and manual tie-in overlay. This method of welding saves a lot of time during execution in the workshop and on-site during installation and assures much better quality in the end. All examinations were performed to allow welding procedure qualification according to ASME and EN standards.

Enhancing the Fuel Efficiency of Cogeneration Plants by Fuel Oil Afterburning in Exhaust Gas before Boilers

Cogeneration or combined heat and power (CHP) has found wide application in various industries because it very effectively meets the growing demand for electricity, steam, hot water, and also has a number of operational, environmental, economic advantages over traditional electrical and thermal systems. Experimental and theoretical investigations of the afterburning of fuel oil in the combustion engine exhaust gas at the boiler inlet were carried out in order to enhance the efficiency of cogeneration power plants; this was achieved by increasing the boiler steam capacity, resulting in reduced production of waste heat and exhaust emissions. The afterburning of fuel oil in the exhaust gas of diesel engines is possible due to a high the excess air ratio (three to four). Based on the experimental data of the low-temperature corrosion of the gas boiler condensing heat exchange surfaces, the admissible values of corrosion rate and the lowest exhaust gas temperature which provide deep exhaust gas heat utilization and high efficiency of the exhaust gas boiler were obtained. The use of WFE and afterburning fuel oil provides an increase in efficiency and power of the CPPs based on diesel engines of up to 5% due to a decrease in the exhaust gas temperature at the outlet of the EGB from 150 °C to 90 °C and waste heat, accordingly. The application of efficient environmentally friendly exhaust gas boilers with low-temperature condensing surfaces can be considered a new and prosperous trend in diesel engine exhaust gas heat utilization through the afterburning of fuel oil and in CPPs as a whole.

Creep rupture of a Ni-Fe based model alloy under simulated fireside corrosion in coal-fired boilers

The influence of fireside corrosion on creep rupture of a Ni-Fe based model alloy was investigated by comparing the rupture life, fractography and microstructure of specimens in fireside corrosion and air. Results showed that the rupture life at 140 MPa in fireside corrosion is only 40% of that in air. The internal sulfidation along grain boundaries promoted the initiation of intergranular cracks, and was responsible for the premature rupture. The surface collapse in fireside corrosion was attributed to the outward propagation of internal cracks, while surface cracks in air originated from the formation of recrystallized grains in the surface layer.

Alkaline gases emission estimation and paraconsistent logic techniques application to label bagasse combustion conditions

When some renewable energy sources are used, such as biomass solid waste, it is necessary to measure and control pollutant emissions. Since raw sugarcane comes from a wide variety of supply sources, it is necessary to monitor the behavior of the biomass residues during the burning process to control flame stability, emissions, and combustion efficiency. The variation in the combustion temperature of biomass affects the combustion efficiency and also the emission of alkaline metals, such as potassium (K) and sodium (Na), which can cause corrosion in boilers. The objective of the present work is to estimate the content of alkali gases in the flames during the burning of solid biomass residues, specifically sugarcane bagasse in this case. The flame emission spectroscopy (FES) spectrometry technique is used and flame emission spectra is captured during the combustion of bagasse in a pilot furnace. The flame temperature is calculated using the two-color method together with the inverse Levenberg-Marquard method. Models and correlations from literature are used to obtain a database of emission content of sodium and potassium. Using paraconsistent logic techniques, a predictor algorithm is implemented and bagasse samples were labeled to identify similar physical combustion conditions. The results of the emission of sodium and potassium estimated for groups labeled using the algorithm of paraconsistent logic are compared and show good agreement between them. A good and reasonable agreement was found in the estimation of the emission content of potassium and sodium.

Accumulating and communicating research: Development of a Massive Open Online Course on ash

Based on 30 years of research on ash and deposit formation, corrosion and trace element transformations in utility boilers fired with solid fuels covering the entire range from coal via biomass to waste fuels, a Massive Open Online Course (MOOC) on this was launched ultimo July 2020.The basic idea behind the Ash MOOC, is to present recent data on fuel characterization, ash formations, slagging, fouling, and corrosion, in a course that can be readily provided for students and industry people.The Ash MOOC consists of a number of modules covering: 1) course introduction, 2) fuel and ash chemistry and characterization, 3) release of critical ash-forming elements, 4) formation of fly ash and aerosols, 5) transport and adhesion of ash particles, 6) deposit build-up, consolidation and shedding, 7) high-temperature Cl-corrosion, 8) use of additives to minimize deposit formation and high-temperature corrosion, and, last but certainly not least, 9) Danish case-studies on ash and deposit formation.This paper provide a brief introduction to how the idea of an Ash MOOC was born, what it takes to make such a MOOC, how to direct such knowledge toward a very wide range of receiving audience, and, some sorts about future development of this.

Design of Online Detection System of Boiler Water Quality Based on STM32

Industrial boilers have strict requirements for water quality. It is necessary to adjust water treatment measures and regular blowdown according to the monitoring of phosphate and soluble silica content in boiler water to avoid boiler scaling, corrosion, and deterioration of steam quality, and prevent major accidents. The traditional boiler water quality detection technology has a strong lag and long detection time, which cannot meet real-time online detection. Aiming at the requirement of detection of phosphate radical and soluble silica content in boiler water quality, a portable and low-cost online detection system of boiler water quality based on STM32 was studied. The pump valve flow path is constructed with a syringe pump equipped with a syringe and a distribution valve, LED and silicon photocell are used for the light source and detector of the system respectively, and the photoelectric detection part is composed of a designed Z-shaped flow cell, which reduces the experimental cost; Design a data acquisition circuit based on STM32 microcontroller and a 16-bit high-precision analogy-to-digital converter, as well as a constant-current drive circuit for driving LED light sources, to improve the stability and high precision of the automatic measuring instrument. The system test results show that the boiler water quality online detection system based on STM32 can accurately detect the phosphate and soluble silica concentrations in boiler water quality.

Corrosion of Iron Covered with Iron Oxide Film by Chlorine and Hydrogen Chloride Gases: A Molecular Dynamics Simulation Study Using the ReaxFF

Flue gas produced by biomass fuel combustion contains various chlorine-containing substances and is an important factor causing biomass boiler corrosion. The corrosion processes of chlorine, hydrogen chloride and water on iron covered with an intact/damaged oxide film were investigated under the high temperature of 1300 K through reactive molecular dynamics simulation. The results show that the diffusion processes of oxygen and chlorine are similar and can be divided into three stages: rapid diffusion, continuous diffusion, and no oxide film (stable). Oxygen diffusion in Fe2O3 into a pure iron layer is the main cause of gas corrosion in iron/iron oxide systems. A complete oxide film can hinder iron corrosion by chlorine and hydrogen chloride. Damage in an oxide film significantly affects oxygen and chlorine diffusion and iron corrosion. However, such influence is gradually reduced. The integrity of a protective film is the key to alleviating corrosion. Water facilitates the dissociation of chlorine and hydrogen chloride, and it reacts with iron at high temperatures to enhance corrosion. This study improves the understanding of the iron oxide/iron corrosion from chlorine-containing gases from a microscopic perspective and is of great significance to metal corrosion protection and biomass combustion technologies.

Analysis of Boiler Corrosion in Thermal Power Plant

Analysis of Boiler Corrosion in Thermal Power Plant

High Temperature Corrosion Stability of Ceramic Materials for Magnetohydrodynamic Generators

Abstract Corrosion by alkali metals and their compounds poses a significant challenge to the long-term material stability and service life for both metal alloys and ceramics at high operating temperatures. Chemical reactivity between alkali metals and materials underlie numerous industry challenges ranging from fireside corrosion in biomass-fired boilers to reaction with silica-based refractory ceramics in glass furnaces. The problem is particularly significant in magnetohydrodynamic (MHD) generators, where potassium or cesium compounds are introduced to improve the electrical conductivity of the working fluid. Thus, resistance to attack by alkali metal vapor is an important consideration in the selection and fabrication of ceramic electrodes and insulators for MHD generators. We evaluated several refractory ceramics to assess phase stability and known reactions with potassium and its compounds at high temperatures (T > 1,200 °C). Refractory ceramics were tested for potassium vapor corrosion using a modified ASTM standard test method with in situ monitoring of gas composition. Unlike other materials, the magnesia (MgO) and ceria (CeO2) samples did not exhibit corrosion, and no phase or mass changes were observed. This indicates that CeO2 and MgO could exhibit long lifetimes as plasma facing components in MHD generators. Ultimately, this development provides valuable data in evaluating critical materials performance issues that can attest to the viability of high temperature direct fired MHD generator applications.

A review on protection of boiler tube steels with thermal spray coatings from hot corrosion

The conventional steels and their alloys are not able to withstand high temperature corrosion in boilers of thermal power plants. The problem of hot corrosion has become more severe issue due to increasing operating temperatures of boilers. In recent past, many researchers have tried to reduce hot corrosion of boiler steels by surface coatings. Different thermal spray coating techniques have been developed to spray different types of coatings on boiler steels. These coating techniques have been proved to enhance corrosion resistance of boiler steels and to increase their performance at high operating temperatures, which subsequently have increased their life span. The advancements and developments in thermal spraying techniques have resulted in development of surface coatings with highly excellent corrosion resistance properties. This paper reviews the performance, developments and applications of thermal spray coatings for high temperature corrosion resistance.

The high performance of diethylhydroxylamine in comparison with hydrazine for the removal of dissolved oxygen from boilers of power plant

In boilers and hot water heating systems, hydrazine is used as one of the powerful reducing agents for eliminating oxygen. Due to the toxicity and carcinogenicity of this material, a suitable replacement named diethylhydroxylamine (DEHA) can be used. DEHA has low acute toxicity and animal tests do not show mutagenic activity. In this study, hydrazine and DEHA as deoxygenation materials were used in boilers of Tarasht power plant in Iran (Tehran). In different months (May to November), deoxygenation was examined by these two substances. The oxygen removal value of DEHA was equal to hydrazine and sometimes far better than it. The rate of deoxygenation reaction of DEHA was 40 ppb in most months of the year, but the number of peaks in hydrazine was greater (2 peaks with 50 ppb and 1 peak with 60 ppb). Hydrazine analysis is time-consuming, as well as pollutes the environment. On the other hand, DEHA of tests were completed sooner. Also, DEHA as an economical material with low toxicity can be a good alternative to hydrazine in boilers. This material can prevent boiler corrosion by oxygen removal.

Non-Destructive Diagnostic Methods for Fire-Side Corrosion Risk Assessment of Industrial Scale Boilers, Burning Low Quality Solid Biofuels—A Mini Review

The use of low-emission combustion technologies in power boilers has contributed to a significant increase in the rate of high-temperature corrosion in boilers and increased risk of failure. The use of low quality biomass and waste, caused by the current policies pressing on the decarbonization of the energy generation sector, might exacerbate this problem. Additionally, all of the effects of the valorization techniques on the inorganic fraction of the solid fuel have become an additional uncertainty. As a result, fast and reliable corrosion diagnostic techniques are slowly becoming a necessity to maintain the security of the energy supply for the power grid. Non-destructive testing methods (NDT) are helpful in detecting these threats. The most important NDT methods, which can be used to assess the degree of corrosion of boiler tubes, detection of the tubes’ surface roughness and the internal structural defects, have been presented in the paper. The idea of the use of optical techniques in the initial diagnosis of boiler evaporators’ surface conditions has also been presented.

Repercussions of clinical waste co-incineration in municipal solid waste incinerator during COVID-19 pandemic

During coronavirus disease 2019 pandemic, the exponential increase in clinical waste (CW) generation has caused immense burden to CW treatment facilities. Co-incineration of CW in municipal solid waste incinerator (MSWI) is an emergency treatment method. A material flow model was developed to estimate the change in feedstock characteristics and resulting acid gas emission under different CW co-incineration ratios. The ash contents and lower heating values of the feedstocks, as well as HCl concentrations in flue gas showed an upward trend. Subsequently, 72 incineration residue samples were collected from a MSWI performing co-incineration (CW ratio <10 wt%) in Wuhan city, China, followed by 20 incineration residues samples from waste that were not co-incineration. The results showed that the contents of major elements and non-volatile heavy metals in the air pollution control residues increased during co-incineration but were within the reported ranges, whereas those in the bottom ashes revealed no significant changes. The impact of CW co-incineration at a ratio <10 wt% on the distribution of elements in the incineration residues was not significant. However, increase in alkali metals and HCl in flue gas may cause potential boiler corrosion. These results provide valuable insights into pollution control in MSWI during pandemic.

Assessment of the Composition of Forest Waste in Terms of Its Further Use.

This paper presents the results of the analysis of the chemical composition and content of heavy metal contamination in forest logging residues, in order to assess the possibility for their further utilisation. The samples were divided into 9 groups, which included coniferous tree cones, wood, and other multi-species logging residues. The elementary composition, ash content, and calorific value were determined as energy use indicators for the samples. Additionally, the content of heavy and alkali metals, which may affect combustion processes and pollutant emissions, was tested. The high content of heavy metals may also disqualify these residues for other uses. The research shows that the test residues are suitable for energy use due to their high calorific value and low content of heavy metals. However, an increased ash content in some samples and the presence of alkali metals, causing high-temperature corrosion of boilers, may disqualify them as a potential fuel in the combustion process. The forest residues may be used in other thermal processes such as pyrolysis or gasification. A low content of heavy metals and a high content of organic matter permit the use of these residues for the production of adsorbents or composite materials.

Invited Review Paper in Commemoration of Over 50 Years of Oxidation of Metals: Current Aspects of Deposit-Induced Corrosion

Alloys and coatings used in high temperature applications are often subject to surface degradation influenced by the presence of deposits. Typical examples are fireside corrosion in coal-fired boilers and hot corrosion of blades and vanes in the hot sections of gas turbines. Depending on the source, deposit compositions may occur in a wide range from primarily sulfate to primarily oxide and various combinations of the two. There does not seem to be evidence of severe corrosion caused by gaseous Na2SO4. Generally, severe corrosion occurs when the deposits are liquid. However, significant corrosion has been observed in some cases with deposits, which are nominally solid. Corrosion is often caused by liquid deposits, in which negative oxide solubility gradients for alloy components are established across the deposits by rapid interface reactions. Hot corrosion can occur at temperatures near 700 °C by a variety of mechanisms if a phase which allows rapid transport is formed. This includes compounds such as Na2MoO4 (even in atmospheres without SO3), MSO4–Na2SO4 solutions or metastable nanostructured phases. Calling all corrosion in this temperature regime “Type II” can be misleading with regard to mechanism. There are similarities in the underlying mechanisms of some forms of hot corrosion in the 700 °C range and fireside corrosion in that they involve synergistic fluxing. The corrosive species responsible for fireside corrosion of ferrous alloys is a liquid (Na,K)2SO4–Fe2(SO4)3 solution and not alkali iron trisulfate. The propagation mechanism involves a synergistic dissolution process of protective Cr2O3 and Fe2O3. Terms such as “Type I,” “Type II” and “gas-phase-induced acidic fluxing” should be used with care in describing mechanisms of deposit-induced corrosion.

Alkali activated porous material with nano graphene oxide as adsorbent in wastewater treatment

Removal of contaminants, impurities and suspended solid matter are termed as water treatment. The possible water treatment methods are coagulation, filtration, ion exchange, aerobic and non aerobic methods. But all this involves high cost. Earlier filtration using granular sand was termed as the efficient way of water treatment. But due to the non-availability of sand this method is no more adopted. The most effective and easy means of treatment of water and waste water is adsorption method because it is an easy and convenient method. Though there are many adsorbents like activated carbon, clay minerals, zeolite, plant based and industrial based by products, the commonly used material is activated carbon which is again a costly investment. The next effective material is the zeolite. It has proved to perform well than the granular media and conventional activated carbon in removing heavy metals and ammonia. The advantage of using zeolite is that it adsorbs these contaminants in its pores and forms a strong bond which prevents leaching of these contaminants back to the ground water. The other advantages are the high specific surface area which facilities efficient adsorption, reduces the number of back-wash cycles, non-toxic and environmental friendly. Zeolites are hydrated aluminosilicates classified as natural and synthetic zeolites. The natural one is gluconites or green sand and the synthetic one is permutit which contains sodium in it. Inspite of many advantages in using zeolite the greatest disadvantage is that the treated water has Na+ ions which replaces the Ca2+ and Mg2+ ions. So when such waters are used sodium bicarbonate hydrolysis to sodium hydroxide which causes corrosion of boilers and also water having high turbidity cannot be effectively treated by this method. This research work will be focused on synthesizing alkali activated aerated concrete with graphene oxide which is porous and which can act as an efficient adsorbent in removing the contaminants from water and waste water respectively.

Investigation of the mechanism for fireside corrosion in coal-fired boilers in South Africa

Furnace wall tubes from 600 MW subcritical boilers at three coal-fired power stations were sampled and the fireside deposits examined to determine the mechanism of fireside corrosion. This involved an in-depth investigation into the morphology and composition of the fireside deposits and the conditions of the furnace that enable this type of attack. SEM-EDS analysis revealed high concentrations of oxygen, iron, and sulphur, QEMSCAN and XRD analyses identified the presence of Fe3O4, Fe2O3, FeS, and FeS2. Differential thermal analysis showed thermal activities at temperatures of 500-600°C, 900-1100°C, and 1100-1250°C, which are associated, respectively, with FeS2 oxidation to FeS and Fe2O3, at 475-525°C, formation of aluminosilicates at 925-1100°C, and melting of FeS around 1190°C. The absence of sodium and potassium eliminates the contribution of molten alkali sulphates to the corrosion. The consistent coexistence of iron sulphide and iron oxide is indicative of the substoichiometric conditions in the furnace, while the detection of pyrite suggests that the coal is not completely combusted, which points to a poor combustion process. These observations were affirmed by gas analysis at one of the stations, where very high levels of carbon monoxide were measured at the furnace wall (&gt; 14 000 ppm) and furnace exit (&gt; 3500 ppm). The high CO concentrations are indicative of limited combustion caused by limited O2. These reducing conditions promote the formation of FeS-rich deposit, which is the corrosive species responsible for degradation.