Boiler Corrosion Research Articles

98/03135 Effect of coal chlorine on the fireside corrosion of boiler furnace wall and superheater/reheater tubing

98/03135 Effect of coal chlorine on the fireside corrosion of boiler furnace wall and superheater/reheater tubing

98/02242 Corrosion in ultra supercritical boilers for straw combustion

98/02242 Corrosion in ultra supercritical boilers for straw combustion

98/02245 Effect of coal chlorine on the fireside corrosion of boiler furnace wall and superheater/reheater tubing

98/02245 Effect of coal chlorine on the fireside corrosion of boiler furnace wall and superheater/reheater tubing

Decentralized biomass combustion: state of the art and future development

The present amount of biomass used for heat, and to a smaller extent electricity production, is already considerable in several European countries but the potential unused in Europe is even higher. Combustion is the most mature conversion technology utilized for biomass. The systems addressed in this paper are plants with a nominal boiler capacity greater 0.5 MW th. The main combustion technologies used for these systems are underfeed stoker furnaces, moving grate firings (over-bed stoker fired units), bubbling and circulating fluidized beds. The most important biomass fuels are sawdust, wood chips, bark, straw, cereals and grass. The essential differences between them are their different combustion behaviour as well as the different concentrations of combustion relevant elements (such as N, S, Cl, K) they contain, influencing the necessary combustion, process control and flue gas cleaning technology. Important points that are now under development focus on possibilities of NO x reduction by primary measures, as well as on higher plant efficiencies by efficient biomass drying by well adjusting the excess oxygen level in the flue gas to the requirements for a complete combustion and by recovering energy from the flue gas. Furthermore, possibilities of influencing the material fluxes of ash forming elements by primary measures aiming at a sustainable ash utilization and an efficient dust precipitation are in progress. Problems still unsolved that need comprehensive R&D in the near future are reactions taking place in the hot flue gas, causing depositions and corrosion in furnaces and boilers (especially when K-, S- and Cl-rich biomass fuels such as straw, cereals and grass are used). Research on possibilities to prevent or control them (by material selection or appropriate technologies) are of great importance. Furthermore, the ash melting behaviour and its influencing variables have to be treated as urgent. Staged combustion systems, hot fly ash precipitation as well as specially designed boilers could represent solutions for these ash and aerosol related problems. Combined heat and power (CHP) production, already realized in plants with a nominal boiler capacity greater 10 MW th based on steam turbines, is also of growing importance for small-scale applications. Moreover, the lower limit for CHP plants is a nominal boiler capacity of about 5 MW th at the moment, due to the lower electric efficiencies achievable and to the economy of scale. Interesting technologies which are right now under development are sterling engines, a newly developed steam engine (screw-type motor) and organic rankine cycles (ORC) with hydrocarbons as working fluids operating at low temperature and pressure levels (in comparison with conventional steam processes). The basic requirements for the selection of an appropriate CHP process are a high electric efficiency to investment costs ratio and a well tested technology to ensure a continuous and undisturbed operation of the plant.

Synthesis and Crystal Structure of Maricite and Sodium Iron(III) Hydroxyphosphate

Maricite and sodium iron hydroxyphosphate (SIHP) are recently discovered iron(II) and iron(III) compounds that play a major role in phosphate “hideout” and corrosion in high-pressure boilers. This paper reports a novel method for synthesizing maricite by thermally decomposing the complex of aqueous iron(III) nitrilotriacetic acid at 200 °C and methods for the hydrothermal synthesis of SIHP from Fe3O4 or FePO4. The crystal structure of maricite is identical to the impure natural mineral (Le Page Y.; Donnay G. Can. Mineral. 1977, 15, 518−521). The X-ray diffraction pattern of SIHP is consistent with an orthorhombic unit cell containing 8 units of formula Na3Fe(PO4)2·(Na2(1-x)H2xO), with x = 0.226 ± 0.025. This is similar, but not identical, to the formula Na4Fe(OH)(PO4)2·1/3NaOH proposed by Ziemniak and Opalka (Proc. Sixth Int. Symp. on Environmental Degradation of Materials in Nuclear Power SystemsWater Reactors; Gold, R. E., Simonen, E. P., Eds.; Mater., Metals, Minerals Soc., 1993; pp 929−935.). The main structural feature is a chain of iron(III) ions linked by bridging oxygens and phosphate bridges. The iron phosphate chains are held together by sodium ions in the ratio 3Na/Fe/2(PO4). Charge balance with the O2- bridge between each iron ion is maintained by Na+ and H+ ions located in a relatively open cage in the phosphate lattice. The structure is significant in that it explains the variable stoichiometry observed in powder diffraction patterns, and it identifies the stoichiometry of H and O, which cannot be determined from solubility studies.

97/03948 Environmental impact of Orimulsion combustion in large utility boilers

There is considerable worldwide interest in the practical use of Orimulsion as a replacement fuel in both oil and coal fired utility boilers. Practical experience of such applications has been gained in Canada, UK, Japan, Europe and USA. Fundamental work has demonstrated the different combustion characteristics of Orimulsion which has been termed the {open_quotes}fourth{close_quotes} fossil fuel to the fossil fuels normally used for power generation and how, in certain circumstances, these can be used to advantage in the application of Orimulsion in utility boiler combustion systems. Orimulsion is an emulsify ed fuel prepared from naturally occurring bitumen deposits located in the Orinoco Basin in Venezuela and comprises approximately 70% bitumen and 30% water. Compared to the heavier fuel oils the sulphur content of Orimulsion is medium to high, the ash content is high with high levels of Vanadium and Nickel. The ash content is enhanced by the addition of Magnesium compounds, to the commercial fuel, to mitigate against the potential in boiler corrosion effects arising form the Va, Na and S content in the fuel.

Mixed oxidant high temperature corrosion in gasifiers and power plants

Data from long term exposure tests in several gasification plants are now available and will be critically reviewed. Exposure times ranged from 2000 to 20,000 hours. All exposures were in syngas coolers of entrained slagging gasifiers, where the gas composition is not in equilibrium. Due to rapid cooling of the syngas, the high temperature (>1,000°C) equilibrium is frozen in. Exposure temperatures ranged from 250–550°C. Most samples were exposed in water or steam-cooled loops. Corrosion rates observed were variable, quite high for low alloy steels, but generally moderate to low for stainless steels. Scale spallation, possibly caused by aqueous corrosion during downtime was found to accelerate the corrosion of stainless steels significantly, but not that of low alloy steels. Introduction of low NOx burner systems, using overfire air, has resulted in accelerated corrosion in many supercritical boilers in the USA. The accelerated corrosion is most likely to be due to an increase in the CO and H2S content of the fluegas near the waterwall and the presence of FeS deposits.

Corrosion in ultra supercritical boilers for straw combustion

In order to reduce CO2 emission, ELSAM (the electric utility company of the western part of Denmark) is looking into the possibilities for using biomass—mainly straw—for combustion in high-efficiency power plants. In this connection ELSAM has investigated three ultra supercritical boiler concepts for combustion of straw only or together with coal: (1) pulverized fuel boilers (PF-boilers); (2) circulating fluidized bed boilers (CFB-boilers); and (3) vibrating grate boilers with 100% straw. These investigations have mainly been full-scale tests with straw fed into existing boilers. Corrosion tests have been performed in these boilers using temperature regulated probes and in-plant test tubes in existing superheaters. The corrosion has been determined by detailed measurements of wall thickness reduction and light optical microscopic measurements of the material degradation due to high temperature corrosion. Corrosion mechanisms have been evaluated using SEM/EDX together with thermodynamic considerations based on measurements of the chemical environment of the flue gas.

Effect of coal chlorine on the fireside corrosion of boiler furnace wall and superheater/reheater tubing

EPRI studies have identified boiler tube failures as the principal cause of loss of power plant availability worldwide. A significant proportion of the failures in the furnace wall and pendant/platen superheater and reheater stages are the result, either directly or indirectly, of excessive metal loss by fireside corrosion. Despite fundamental differences in the corrosion mechanisms active on furnace walls (gaseous) and superheater/reheater stages (molten salt), much of the worsening fireside corrosion problems experienced in both sections on UK plant in the 1960s and 1970s was attributed to fuel chemistry, in particular the coal chlorine content. This paper explores the more recent history of fireside corrosion in CEGB and PowerGen Stations as extracted from a literature survey undertaken as the inaugeral exercise in a jointly sponsored EPRI/PowerGen project into the role of combustion parameters and fuel chemistry on fireside corrosion. The current view of the impact of coal chlorine on the wastage mechanisms concerned in each boiler stage is also detailed.

Fuel ash corrosion of boiler and superheater tubes

The scientific pursuit of the determination of mechanisms of corrosion of metals and alloys operating at high temperatures in thermal power generating environments has resulted in volumes of reported data, yet little achievement has been made so far. In reviewing the literature, it has been attempted here to indicate the diversified nature of the problems and the characteristics of various parameters such as mineralogical constituents of the fuel, fuel ash and various products of combustion (e.g. sulphurous oxides, sulphates, pyrosulphates, sulphides, etc.) in monitoring the rate of reactions, and hence corrosion, of component materials. Rapid and intensive corrosion attack due to conjoint action of gaseous, chemical and liquid phases under normal boiler operating conditions have been expressed to offer a really challenging situation for further studies.

Monitoring Corrosion in Boiler Systems with Colorimetric Tests for Ferrous and Total Iron

Because of the low oxygen conditions that prevail in industrial boiler systems, active corrosion releases soluble corrosion products that contain iron in the ferrous, Fe(II), oxidation state. Active corrosion can be detected throughout boiler systems by colorimetric determination of ferrous iron. Ferrous iron measurements are particularly useful for detecting corrosion in once-through components such as feedwater (FW) systems. The same approach is equally valuable for detecting internal boiler corrosion when accurate information on cycles of concentration is available. Ferrous iron testing also can differentiate the dispersion of iron oxide particulates in the FW from corrosion of the boiler internals. Corrosion mechanisms that generate ferrous iron species are discussed as well as the interpretation of data obtained by total iron testing.

95/01674 Preventing corrosion in steam boilers

95/01674 Preventing corrosion in steam boilers

Rational use of caustic magnesite dust in the production of refractories

Additionally conducted investigations showed the necessity of elimination of delivery to firing of fine dust from electrostatic precipitators contaminated with low-melting compounds of sulfur and fluorine and circulating in the kiln ⇆ electrostatic precipitators closed cycle, which makes it possible to reduce the unproductive load on the dust removal equipment and discharge of dust into the atmosphere and to eliminate the crust on waste-heat boiler tube surfaces and corrosion of metal and reinforced concrete structures.

Low temperature corrosion in domestic refuse boilers monitored with cooled corrosion probes and test heat exchangers

AbstractCorrosion properties of materials for utilizing of flue gas energy by cooling the gas below the acid dew point have been studied with cooled corrosion probes. The U‐tube corrosion probe is found to be a reliable method where tests can be done in the actual plant environment. Results from one domestic refuse boiler plant with severe low temperature corrosion problems are reported and the results described indicating a minimum temperature of 75°C to avoid corrosion.Another set of results is reported with flue gas cleaning and cooling in an experimental heat exchanger. Unalloyed steel is found to show the same level of corrosion in both raw uncleaned and cleaned flue gas. AISI 316 and 254 SMO stainless steels have shown high corrosion rates in the raw gas but a satisfactory resistance in the cleaned gas.

Energy recovery from municipal solid waste incineration—A review

Heat recovery from the incineration of municipal solid waste (MSW) can make a useful contribution to the nation's energy needs. This paper reviews the literature on the field of energy recovery from MSW incineration. This review includes (1) An historical background on the MSW methods of disposal and the recent trends. (2) The potential role of waste as a fuel from the knowledge of its analysis, heating value and quantity. (3) The alternative methods of waste disposal including the thermal (mass incineration, refuse-derived fuel and pyrolysis), the mechanical and the biochemical processes. (4) Some economic considerations regarding MSW disposal costs. (5) The combustion characteristics of MSW and waste combustion plants. (6) Heat recovery from waste burning including the main types of waste heat boilers; the heat recovery rates; heat exchange boundary conditions; fouling, erosion and corrosion of waste heat boilers; control of waste incineration particulate emissions and finally the control of nitrogen oxides emissions. The intensive data given here is essential to the proper design and operation of any MSW-to-energy plant. The design needs to be undertaken with careful consideration of the experience that already exists in order to achieve success.

Chemistry of Iron and Its Corrosion Products in Boiler Systems

Abstract This paper reviews prominent investigations of magnetite formation and internal corrosion in boilers. This review includes publications that have been cited extensively in the past few years, as well as some important recent contributions to the subject. The classic proposals of Potter and Mann regarding magnetite formation in boilers are summarized and contrasted with some more recently suggested mechanisms. Following this, a brief description of the various pathways of internal boiler corrosion is presented.

Review on high temperature corrosion of PCF boilers in Poland

AbstractThe paper presents selected data on power industry in Poland. The information given comprises electric energy production, number of power plants, steam and fuel (coal) characteristics as well as chemical compositions of construction materials being currently in use for furnace wall and superheater tubing.Briefly discussed are also the results of investigations on fireside corrosion of pcf boilers. It has been found that the high temperature corrosion phenomena observed on furnace wall tubes in the vicinity of burners are related with local reducing conditions and chlorine content in coal whereas those encountered on superheater tubes are associated with fused ash deposits.Preventive measures to combat fireside corrosion and slagging planned for the nearest future are the application of bimetallic coextruded tubes and the dosage of additives in coal combustion.

Fireside corrosion in boilers of the Dutch electricity undertakings

AbstractIn 1990 the electricity in the Netherlands will be generated for more than 50% with coal as fuel. Fireside corrosion causes a minor, but from an economic point of view not negligible, contribution to unforseen plant unavailability. Measures are taken concerning materials, additives and coal blending. Around 1980 heavy oil had an essential (40%) part in the power generation: experiences with corrosion and additives from that period are summarized. Research has been carried out with new coextruded materials under severe corrosion conditions in order to improve the overall unit efficiency. Creep tests at elevated temperatures have been performed in connection to this. Furthermore research is going on concerning the effects of low NOx burning techniques (on the corrosion behaviour of waterwall tubes) and in the field of IGCC‐plants.

Effects of heat flux on corrosion of high pressure boilers

AbstractThe results of experiments on high pressure boiler rigs at Harwell and elsewhere are used to illustrate the processes which can give rise to increased corrosion rates under heat flux. The presence of a heat flux increases the metal surface temperature, and, where boiling occurs, can lead to the concentration of solutes present in the feedwater. In the absence of boiling, the increase in corrosion rate owing to the presence of a heat flux should be small and related to the known activation energy of the process. In the nucleate boiling region, the increased surface temperature and mass transport to the wall can lead to the production of thicker coherent oxide films in the presence of soluble corrosion products with reverse solubility curves. Where defects are present in the surface of the boiler tube, or porous structures develop, enhanced boiling can occur, and corrosive salt concentrations many orders of magnitude greater than in the feedwater can be developed within them. Similar concentrations ...

Selection of stainless steel tubes to minimize hot corrosion in utility boilers

Austenitic stainless steel tubes of AlSI 304, 316, 321, and 347 types are sometimes exposed to severe hot corrosion environments in superheaters and reheaters of utility boilers. Hot corrosion depends on the existence of V2O5 and Na2SO4 in the oil-fired boilers, and of Na2SO4 and K2SO4 in the coal-fired boilers. Among various kinds of ash corrosions, the alkali sulphateside corrosion has been