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Corrosion failures due to condensing flue gases containing H2O, SO3, NOx and HCl still occur more often than might be expected. The corrosion failures can be of several…
Corrosion failures due to condensing flue gases containing H2O, SO3, NOx and HCl still occur more often than might be expected. The corrosion failures can be of several types: general corrosion, pitting attack and stress corrosion cracking (SCC). The chemistry of condensing gases is discussed, and some examples of corrosion in large‐scale installations are presented, including blast stoves for steel production, heat recovery steam generators, and waste incineration boilers. The use of thermal insulation inside boiler casings can result in nitrate SCC when the flue gas contains high concentrations of NOx. Nitric acid from flue gas can react with carbon steel and insulation material forming ammonium nitrate and calcium nitrate. Both materials have hygroscopic properties and are very corrosive, even above the water dewpoint of the gases.
Describes the development and application of an aerosol model for regional air quality simulations. The aerosol model MADE is based on a modal concept and describes the…
Describes the development and application of an aerosol model for regional air quality simulations. The aerosol model MADE is based on a modal concept and describes the chemical composition and the size distribution of atmospheric particulate matter. Primary as well as secondary aerosol components are considered in the model, which is fully integrated into the photochemical transport model EURAD. The model system has been applied to a European domain with different resolutions, using a one‐way nesting procedure. Simulations show the potential importance of secondary organics of anthropogenic and biogenic origin for the tropospheric particle loading. In addition it is shown that a reduction in precursor emissions for the inorganic ion fraction of PM (sulphate, nitrate and ammonium) does not necessarily lead to an equivalent reduction in PM2.5 mass concentrations, as for example a reduction in sulphate aerosol caused by reduced SO2 emissions might be compensated by enhanced formation of nitrate aerosols in certain regions.
Research over the last 20 years has had a major focus on the ecology of east coast estuaries, including the interaction between coastal seawater and saltmarshes. It is not…
Research over the last 20 years has had a major focus on the ecology of east coast estuaries, including the interaction between coastal seawater and saltmarshes. It is not possible to separate intertidal coastal saltmarshes from the rest of the coastal marine environment as they are involved in a truly interactive system. The significance of this system is attracting increasing attention as the effect of elevated nutrient concentrations on the ecology of the coastal zone has become apparent. It is only when we understand how the various chemical and biological processes influence the flux of nutrients through the estuarine interface between land and sea that any sensible management strategy can be developed.
A corrosion inhibitor may be defined as a material which, when added in small amounts to a corrosive product or environment affecting a metal, effectively decreases its corrosion rate or perhaps prevents it altogether.
The purpose of this paper is to investigate the influence of two decomposition processes, namely, composting and vermicomposting, on the chemical composition of the…
The purpose of this paper is to investigate the influence of two decomposition processes, namely, composting and vermicomposting, on the chemical composition of the finished products of a mixture of: cotton residues; soil and cotton residues; farmyard; soil.
Composting experiments were done over six months to prepare four different mixtures as follows: cotton residues+soil (C); cotton residues+soil+earthworms (C+E); cotton residues+soil+farmyard manure (C+F); and cotton residues+soil+farmyard manure+earthworms (C+F+E). Electrical conductivity, pH, nitrate-N, ammonium-N, ash, total phosphorus, total nitrogen, total organic carbon, carbon: nitrogen ratio, total potassium and trace elements (Mn, Fe, Cu and Zn) were determined on monthly-based samples.
Significant differences (p < 0.05) in organic carbon, nitrate-N, nitrogen, phosphorus, and potassium content were recorded in vermicompost compared to compost. In general, results indicated that vermicompost had a significant effect compared to compost and a positive effect on the chemical properties of the finished products.
This research work was carried out by four researchers from two institutions concerned with agricultural production and environmental aspects related to soil productivity. The paper emphasizes on production of organic fertilizers with good quality and monitoring of composting process for better management practices of agricultural wastes in Sudan.
Much progress has been made in the field of corrosion technology in the last few years and many new corrosion‐resisting materials have been developed, including improved types of plastics and metals such as zirconium, titanium and tantalum. Plastics are finding extensive use as lining materials for chemical plant operating at moderate temperatures, but the poor thermal conductivity of most plastics makes them unsuitable for the transfer of heat. The recently developed metals and their alloys are extremely expensive to produce and fabricate and, so far, their use has been confined to certain specialised applications, although full‐scale production of zirconium is being carried out in America, mainly because of the low capacity of the metal for absorbing thermal neutrons. At the moment, however, these metals, because of their high cost, cannot compete commercially on a large scale with the older well‐established corrosion‐resisting alloys such as the high‐silicon iron alloys. The excellent corrosion resistance of the high‐silicon iron alloys, even at high temperatures, and their high thermal conductivity have established them as almost standard alloys for acid concentration and cooling plant construction. The following article outlines their composition and properties.
Generally, of all the properties, corrosion resistance can be a prime consideration in determining whether a given alloy or metal is adequate for a proposed use. With the increasing ability to fabricate many alloys and metals into fibre material of extremely small diameter, a better knowledge of their chemical properties as related to their unique size becomes more essential since many of the potential applications involve exposure to corrosive environments. This article reviews the corrosion resistance of Brunsmet MF‐A1 stainless steel fibres produced by the Brunswick Corp., Chicago, Illinois.
Tantalum has a resistance to aqueous corrosion that may be compared closely with that of glass. The principal use of the metal is in the construction of chemical plant…
Tantalum has a resistance to aqueous corrosion that may be compared closely with that of glass. The principal use of the metal is in the construction of chemical plant where its excellent corrosion‐resistant properties have assured a place for it in special applications, particularly where corrosion resistance needs to be combined with a high degree of heat transfer. This sphere of application is expanding rapidly.
Waste Heat Recovery Boilers (WHRB's) enhance the thermal efficiency of gas turbine power generating plants by capturing the heat from the exhaust gas and utilising it to…
Waste Heat Recovery Boilers (WHRB's) enhance the thermal efficiency of gas turbine power generating plants by capturing the heat from the exhaust gas and utilising it to raise steam for increased electricity production or district heating. Under normal conditions the exhaust gas from the turbine is cooled from around 550°C to 80°C. Care is taken that condensation will not occur in the cooler parts of the boiler. Nevertheless, during normal operation, dry ammonium nitrate deposits can be formed in the WHRB. These deposits will become wet when the unit is started or shut down, when the temperature falls below the dew point. The deposits may also “sweat” (i.e. absorb atmospheric moisture and become liquid) during extended plant outage periods. In consequence, Intergranular Corrosion Attack (IGA) and Stress Assisted Intergranular Corrosion Attack (SA‐IGA) (in general called stress corrosion cracking) can occur in carbon steel construction materials. The sensitivity to IGA of a total of 86 steels, of known compositions, was tested. The steels were subjected to aerated ammonium nitrate solutions of 90°C with concentrations ranging between 2 and 35 per cent. After an exposure of 65 hours, cross sections of the steels were studied. If IGA occurred, the steel was considered sensitive to ammonium nitrate at that (critical) percentage. During the investigation it was observed that alloying elements in several types of steel influenced its resistance to IGA in ammonium nitrate. Elements such as molybdenum, manganese and chromium had a positive effect on the resistance to nitrate induced IGA, SA‐IGA and stress corrosion cracking, whereas carbon and copper were detrimental. The microstructure of the steel also appeared to be important. In many specimens taken from in‐service failures, strings of carbide precipitates were found to be present at grain boundaries. The precipitates were identified to be ternary carbides. It seems, therefore, that the presence of carbides at grain boundaries increases the susceptibility of a steel to intergranular corrosion.
The use of rubber compounds as corrosion‐resistant linings has been recognised and practised for many years. Today, metal pipes, tanks and vessels of all descriptions are lined with natural or synthetic rubbers and rubber‐like plastics, to prevent contamination and provide resistance to chemical attack or abrasion. A concise account of vessel lining with sheet neoprene, the conditions necessary and method of operation, are given in the following article. A subsequent article (page 77) describes neoprene's application by spray and brush.