Sulphur Trioxide Content Research Articles

Controlling aluminate phase hydration for sulfate resistance of Portland–limestone cements

Sulfate optimisation of the aluminate phase (C3A) in Portland–limestone cements (PLCs) is critical for improving their hydration performance. This study investigates the changes in the sulfate attack performance of an undersulfated interground PLC (14.6% limestone) through the addition of gypsum. Isothermal calorimetry is used to measure the early-age hydration kinetics to optimise the sulfur trioxide content of the PLC. Sulfate expansion and strength loss of the undersulfated and optimised PLC in combination with fly ash is measured in both sodium sulfate and magnesium sulfate solutions. Sulfate optimisation of the PLC reduced its expansion to a greater extent in magnesium sulfate and improved strength at later ages to a greater extent in sodium sulfate. Less physical deterioration was also observed for the optimised PLC samples. Fly-ash incorporation resulted in improved expansion and strength performance for certain mixtures. Optimised samples underwent less sulfate attack as indicated by their higher calcium hydroxide contents measured by thermogravimetric analysis at later ages. The improved sulfate attack performance can be attributed in part to the formation of carboaluminate hydrates as determined by X-ray diffraction in the optimised PLC. This research study highlights the importance of sulfate optimisation in achieving PLCs with greater sulfate attack resistance.

Statistical Analysis of Fly Ash Sampling Frequency

Abstract Fly ash is a byproduct of the combustion of pulverized coal, which has found an application as a supplementary cementitious material that offers several benefits such as improved workability, durability, and improved long-term strength to concrete. The requirements for sampling frequency of this material are laid out in ASTM C311, Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland-Cement Concrete. The article analyzes the composite sampling frequency and provides insight into how changing it would affect the ability to capture changes in fly ash properties. The analysis is based on data collected using the current composite sampling requirements during the calendar year of 2016 from four power plants located in the United States. Fly ash properties included in the analysis are the sum of silica, alumina, iron oxide content, sulfur trioxide content, loss on ignition (LOI), fineness, and the strength activity index at 7-days and 28-days. The statistical analysis shows that reducing the composite sampling frequency to monthly, instead of every 2,900 Mg (3,200 tons), would not affect the ability to properly identify the properties of fly ash. This conclusion is supported by the observation that the parameters show small variability throughout the year and that those dependent on plant operational changes (such as fineness and LOI) are monitored on site at an even higher frequency, daily or every 360 Mg (400 tons).

Influence of Cement Chemistry on the Performance of Cement Stabilized Tropical Lateritic Soil

Chemical composition affects overall performance of cement on other materials such as when used in concrete or for stabilization of lateritic soil. This research studied the influence of chemical composition of three Portland cement types represented as samples A, B and C on engineering performance when mixed with laterite under tropical environmental conditions.The Lateritic soil sample classified according to AASHTO as A-5(4) was collected from a typical tropical region. Performances of these cements were considered at different cement-laterite proportions, varying from 2-14%. Parameters determined include chemical and metallic contents of the cements as well as Maximum Dry Density (MDD), California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) of cement-laterite mixat a temperature range of 26-28°C. One-way Anova test was used to validate the significant variation in the chemical composition of cements and the unconfined compressive strength. Results indicate that the bearing capacity and unconfined compressive strength of laterite – cement mix depend on the quantity of lime (CaO) and silicon dioxide (SiO2) content in the cement; results also confirm the influence of Aluminium Oxide (Al2O3) and sulphur trioxide (SO3) content on the setting time of cement.

The influence of physico-chemical properties of fly ash and CKD on strength generation of high-volume fly ash concrete

This paper presents a laboratory study on the use of cement kiln dust (CKD) as an activator of fly ash when used in high volumes within concrete. Two separate batches of fly ash and CKD were tested to assess the effect of material variability on binder properties and compressive strength gain. Ternary blends of fly ash (55–65%), CEM 1 (30%) and CKD (5–15%) and quaternary blends that included moderate amounts (15–18·5%) of ground granulated blast-furnace slag (GGBS) were prepared. Physico-chemical properties of individual binder materials were compared and concrete compressive strength was measured at 2 d, 7 d and 28 d. Ternary blends of 60% fly ash, 30% cement and 10% CKD resulted in moderate early age and 28 d strength and addition of GGBS enhanced strength significantly due to increased ettringite formation. Particle fineness, water demand and loss on ignition content of fly ash, and calcium oxide and sulfur trioxide content of CKD were found to be the main physico-chemical factors that influence compressive strength gain.

How to evaluate pozzolanic activity of sulfate-rich fly ash

The Frattini test and strength activity index (SAI) test have been commonly used methods to assess the pozzolanic activity of pozzolan by measuring its reaction extent, which would be affected by the sulfate content in pozzolan and the cement used. This study investigates the effect of sulfate content in sulfate-rich fly ash on the test results regarding pozzolanic activity by means of the Frattini test and SAI test; three fly ashes with different sulfate contents are used and their sulfate contents are further increased by adding calcined gypsums. There is significant correlation between the test results of the pozzolanic activity and the sulfur trioxide content of the cement–fly ash system, no matter whether the sulfates came from cement or fly ash. However, current methods may confound the test results regarding the pozzolanic activity of sulfate-rich fly ash. It is suggested that the sulfur trioxide content of the cement–fly ash system should be kept constant when the Frattini test and SAI test are selected to evaluate the pozzolanic activity of sulfate-rich fly ash or to compare with other fly ashes and pozzolans.

Methane Oxidation over a V2O5 Catalyst in the Liquid Phase

The selective oxidation of methane by V2O5 catalysts in oleum has been studied. The effects of the reaction temperature, the concentration of V2O5, and the residence time on the conversion of methane and the yield of methanol were investigated. We have found that methane was transformed to methyl bisulfate first, and the methyl bisulfate was then hydrolyzed to methanol. The process of the selective oxidation of methane was involved in electrophilic alternative mechanisms by V2O5 catalysts, and the sulfur trioxide in oleum was necessary for the reaction systems. The methane oxidation reaction was determined to be a first-order reaction, based on the pressure−time relationship. The maximum methanol yield of 45.5% and the methane conversion of 54.5% were obtained at a V2O5 concentration of 0.0175 mol, a reaction temperature of 453 K, a methane pressure of 4.0 MPa, a reaction time of 2 h, and the sulfur trioxide content in oleum is ∼50%.

Sulfuric Acid Corrosion in Oil-Fired Boilers—Studies on Sulfur Trioxide Formation

Abstract Experimental studies on economizer and air-heater corrosion resulting from the formation of sulfuric acid in residual-oil-fired boilers are described. Factors controlling the oxidation of sulfur dioxide to sulfur trioxide have been investigated in a small experimental boiler. The fuel used was a distillate oil to which synthetic compounds were added to simulate the sulfur and metallic components commonly found in residual oils. The sulfur trioxide content of the flue gases was determined indirectly by measuring the corrosion of and sulfate deposition on a steel specimen maintained at a controlled temperature. In an initially clean boiler, approximately equal quantities of sulfur trioxide formed in the flame, furnace, and convection sections, while less formed in the economizer-air heater section. Nickel, iron, sodium, and vanadium in the fuel each decreased the corrosion normally experienced by the test specimen, the magnitude of the effect increasing in the order given. Deposits of these metallic fuel-ash components in the boiler had a relatively small effect on the corrosion of the test specimen. Only the iron deposits indicated significant catalytic activity for the oxidation of sulfur dioxide to sulfur trioxide. Combinations of sodium and vanadium in the fuel were found to decrease corrosion in an initially clean furnace, but boiler deposits from certain combinations of these elements were found to increase corrosion substantially. This catalytic effect is predominant over extended periods of time.

The use of cements of different fineness in soil-cement mixtures

Summary A study of the literature has shown that increasing the fineness of the cement in mortar and concrete mixes results in an increase in their strength at early ages. This paper describes tests to determine whether a similar effect is obtained with mixtures of soil and cement, so that if possible a reduction could be made in the proportion of cement used in soil stabilization by using a cement of greater fineness than the commercial varieties now employed. That fraction of a sample of ordinary Portland cement that passed the B.S. No. 300 sieve was added to a silty clay and test specimens were prepared. The 7-day unconfined compressive strength obtained was found to be 140% of the strength obtained when the whole cement was used. Taking the compressive strength at 7 days as the criterion, this suggests that if 10% of ordinary Portland cement was normally required to stabilize this soil, 7% of the fine-grained cement should prove equally satisfactory. In further tests, a cement clinker was ground to three different degrees of fineness in a laboratory ball mill, the coarsest being equivalent to ordinary Portland cement. The 7-day compressive strength obtained when the finest cement (specific surface = 5,800 cm2/g) was added to the silty clay was 125% of the strength obtained when the coarsest cement (specific surface = 2,900 cm2/g) was used. The corresponding increase for mixtures of sand and cement was 120%. Chemical analysis showed that the removal of the coarse grains in an ordinary Portland cement increased the proportion of sulphur trioxide present. In a third series of experiments, the compressive strength of a cement-stabilized silty clay obtained with a cement of given fineness was found to increase when the proportion of gypsum added to the cement was increased to a certain optimum value, but the increase was not as large as that obtained in the previous experiments by sieving cement. It is believed that fineness, sulphur trioxide content and possibly also the particle-size distribution can affect the strength obtained with a given cement, and further experiments are needed to determine the combination of fineness and sulphur trioxide content required to obtain a cement of maximum strength from clinker processed in a given way.

Corrosion Studies on a Model Rotary Air-Preheater★

Abstract Tests have been carried out on a model rotary air heater in an attempt to study, on a laboratory scale, corrosion phenomena under conditions similar to those experienced in industrial practice. The acid dew-point of the combustion gases used varied from 240 to 320 F and maximum corrosion occurred at surface temperatures within the range 215–240 F. The results confirm previous conclusions as to the influence of the acid dew-point and of the sulfur trioxide content of the gases on corrosion.

Corrosion Studies on a Model Rotary Air-preheater

Tests have been carried out on a model rotary air heater in an attempt to study, on a laboratory scale, corrosion phenomena under conditions similar to those experienced in industrial practice. The acid dew-point of the combustion gases used varied from 240 to 320 deg. F. and maximum corrosion occurred at surface temperatures within the range 215–240 deg. F. The results confirm previous conclusions as to the influence of the acid dew-point and of the sulphur trioxide content of the gases on corrosion.

The influence of zinc oxide smokes on the oxidation of sulphur dioxide in coal‐gas flames

AbstractThe effect of zinc oxide smoke additions on the dew‐point and sulphur trioxide content or an aerated coal‐gas flame containing sulphur dioxide has been studied. Measurements on filtered and unfiltered gases show that the presence of smoke tends, at first, to increase the amount of oxidation of dioxide to trioxide, but if sufficient smoke is present, the trioxide formed is absorbed and zinc sulphate is formed.

The influence of carbon smokes on the dew‐point and sulphur trioxide content of flame gases

AbstractDew‐point and chemical methods of analysis have been used to investigate the effect o carbon smokes on the sulphur trioxide content of flame gases. As the quantity of smoke increases from zero the conductivity‐temperature characteristics of condensed films of acid become complex owing to the deposition of electrically conducting carbon on the dew‐point element. Conductivity measurements indicate that deposited carbon and sulphuric acid films react at temperatures above about 140° c. Analytical determinations show that the sulphur trioxide content of the gases is decreased in the presence of carbon. Suggestions are made of the means whereby the sulphur trioxide content is lowered.

The influence of carbon smokes on the dew-point and sulphur trioxide content of flame gases

The influence of carbon smokes on the dew-point and sulphur trioxide content of flame gases

The influence of carbon smokes on the corrosion of metal surfaces exposed to flue gases containing sulphur trioxide

AbstractFurther work has been carried out to assess the effect of the presence of carbon smokes on the corrosion of a mild‐steel surface by flue gases containing sulphur trioxide. The results obtained have confirmed the view that a peak rate in corrosion obtains at temperatures of 20‐45°c. below the dew‐point of the gas and that the presence of carbon smokes can profoundly affect the extent of corrosion. As the smoke concentration is increased from zero there is an initial increase in corrosion but eventually the dew‐point of the gases and their corrosive properties are substantially reduced.Comparison of the behaviour of filtered and unfiltered smoke‐laden gases would indicate that carbon reduces the sulphur trioxide content of flue gases by a process of physical adsorption.

The influence of silica smokes on the dewpoint of combustion gases containing sulphur oxides

AbstractSilicon monoxide is released when various mixtures of silicates and carbon are heated above 1200°. On leading this into a coal gas flame containing sulphur oxides the initial high dewpoint due to the presence of sulphur trioxide is reduced. Similar results arc obtained when a silica smoke is produced by the disintegration and subsequent oxidation of alkyl silicates sprayed into the flame. The significance of dewpoint measurements in the presence of silica smokes is discussed and it is considered that there is a definite reduction in the sulphur trioxide content of the combustion gases. The mechanism whereby this is brought about is discussed.

The automatic estimation of sulphur trioxide in flue gas

AbstractExperimonts conducted during the development of an earlier instrument showed that the acidic sulphur oxides present in washed flue gas were not readily absorbed by hydrogen peroxide solutions, whereas sulphur dioxide was completely absorbed. These experiments have been extended, and by the use of a wetted sintered glass disc, complete absorption is effected. Distilled water absorbs sulphur trioxide completely; a trace of sulphur dioxide is absorbed, and is removed by scrubbing the solution with acid‐free Hue gas. Descriptions are given of devices used to ensure constancy of flow conditions in the instrument under all conditions of plant load, thus ensuring that the electrical conductivity of the absorbent is strictly proportional to the sulphur trioxide content of the flue gas.