The kinetics of the reductive decomposition of calcium sulfate with carbon monoxide

The kinetics for the reductive decomposition of calcium sulfate in the presence of carbon monoxide were investigated using thermogravimetric equipment under various conditions of temperature (1050-1200°C) and gas composition (0-7% carbon monoxide, 0-10% sulfur dioxide, and 10-50% carbon dioxide). Pellets reacted at selected conditions were withdrawn from the reaction system at various stages of the reaction and analyzed by X-ray powder diffraction, scanning electron microscopy with electron microprobe, and BET surface area analysis;In contrast to previous views of the reaction, the reductive decomposition of calcium sulfate was found to involve two separate reactions: (1) the reduction of calcium sulfate to calcium oxide and (2) the sulfidation of calcium oxide to calcium sulfide. When the reducing potential, P[subscript]co/P[subscript]co[subscript]2, was lower than 0.25, sulfidation did not appear to occur until the sulfate was almost completely converted to the oxide. The reduction of sulfate was found to take place simultaneously throughout a pellet, indicating negligible resistance to intra-pellet diffusion. On the other hand, sulfidation of the oxide seemed to follow a shrinking unreacted-core model;The kinetics for calcium sulfate reduction were notable for an initial induction period. The extremely slow rate of reaction during this period appeared to be controlled by the rate of nucleation of the calcium oxide reaction product;A mathematical model based on the Erofeev equation was developed to represent both the nucleation kinetics and the intrinsic gas-solid reaction kinetics. The rate of reduction was found to be first order with respect to carbon monoxide concentration and to have an activation energy of 479 kJ/mole. These parameters were compared with the results obtained by the application of the well-known grain model when the induction period was neglected;For the sulfidation of the oxide, a shrinking unreacted-core model of chemical reaction control was used to analyze the experimental data. The reaction was found to be first order with respect to carbon monoxide concentration, with an activation energy of 174 kJ/mole

Experimental Study of Bridge Scour in Cohesive Soil

The bridge scour depths in cohesive soil have been predicted using the scour equations developed for cohesionless soils due to scarce of studies about cohesive soil. The scour depths predicted by the conventional methods will result in significant errors. For the cost effective design of bridge scour in cohesive soil, the Scour Rate In COhesvie Soil (SRICOS) for the singular circular pier in deep water condition was released in 1999, and has been developed for complex pier and contraction scour. The present study is the part of SRICOS-EFA method to predict the history of contraction scour, and local scours, such as abutment scour and pier scour. The main objective is to develop the prediction methods for the maximum and the uniform contraction scour depth, the maximum pier scour depth and the maximum abutment using flume test results. The equations are basically composed with the difference between the local Froude number and the critical Froude number. Because the scour happens when the shear stress is bigger than the critical shear stress, which is the maximum shear stress the channel bed material can resist from the erosion, and continues until the shear stress becomes equal to the critical shear stress. All results obtained from flume tests for pier scour have been conducted in Texas A&M University from 1997 to 2002 are collected and reanalyzed in this study. Since the original pier scour equation did not include soil properties. The effect of water depth effect, pier spacing, pier shape and flow attack angle for the rectangular pier are studied and correction factors with respect to the circular pier in deep water condition were newly developed in present study. For the abutment scour, a series of flume tests in large scale was performed in the present study. Two types of channel - rectangular channel, and compound channel - were used. The effect of abutment length, shape and alignment of abutment were studied and the correction factors were developed. The patterns of velocity and of scour were compared, and it was found that the maximum local scour occurred where the maximum turbulence was measured. For the contraction scour, the results obtained from a series of flume tests performed in 2002 and a series of flume tests for the abutment scour in the present study are analyzed. The methodologies to predict the maximum contraction scour and the uniform contraction scour in the compound channel was developed. Although all prediction methods developed in the present study are for the cohesive soils, those methods may be applicable to the cohesionless soils because the critical shear stress is included in the methods. All prediction methods were verified by the comparison with the databases obtained from flume test results and field data

The Control Method for Wavelength-Based CCT of Natural Light Using Warm/Cool White LED

Reproducing circadian patterns of natural light through lighting requires technology that can control correlated color temperature (CCT) and short wavelength ratio (SWR) simultaneously. This study proposes a method for controlling wavelength-based CCT of natural light using LED light sources. First, the spectral power distribution (SPD) of each channel of the test lighting (two-channel LED lighting with warm white and cool white) is identified through actual measurement. Next, CCT and SWR are calculated based on the additive mixing of SPD using the mixing ratio from the measured SPD. Finally, the regression equations for mixing ratio-CCT and mixing ratio-SWR are derived through regression analysis. These equations are then utilized to implement a wavelength-based CCT control algorithm. For performance and evaluation purposes, natural light reproduction experiments were conducted, achieving a mean error of 94.5K for CCT and 1.5% for SWR

Fade Lighting Control Method for Visual Comfort and Energy Saving

This study proposes a fade lighting control method to ensure the visual comfort of indoor occupants through gradual illuminance control while saving energy. The illuminance sensor measures the indoor illuminance and calculates the required illuminance for achieving a reference illuminance of 500 Lux. The control illuminance for each lighting is derived based on the required illuminance, and it is confirmed to fall within the threshold range of 20%. The illuminance values and time intervals for fade lighting control are calculated, ensuring that the amount of illuminance adjustment is divided by the size of the threshold range or less. In the performance evaluation, the proposed method (experimental group) was compared with the influence-based control method (control group). The result shows that this fade lighting control method minimizes the visual discomfort of occupants caused by sudden changes in lighting, and the same energy-saving of 11-42% is achieved as the control group

Recent Advances In FTIR Photoacoustic Spectroscopy

Advances in FTIR photoacoustic (PA) spectroscopy have significantly extended the scope and utility of the PA technique in the areas of: microparticle spectroscopy, compositional determinations via factor analysis, coal surface oxidation measurements, spectroscopy of highly opaque samples, and PA detector technology. A method is reported for measuring FTIR spectra of single particles in the tens of Am size range which uses a tungsten needle to pick up particles and hold them in the sample chamber of the PA detector. The tungsten needle is initially mounted on a micromanipulator and particle pick-up is performed under a microscope. The needle and sample are then transferred directly to the PA detector sample holder which positions the particle in the IR beam. No sample alignment or thinning are necessary. Compositional determinations of kaolinite and quartz in coal have been performed using the Perkin-Elmer CIRCOM factor analysis program. The IR spectra were collected by DRIFTS and PA methods using synthesized samples of known compositions for the learning set and unknown test samples. The PA spectra yielded slightly better correlations. Coal surface oxidation was studied using a calibrated UV irradiation of coal to generate carbonyl species, thereby gauging the freshness of coal surfaces by how much carbonyl is formed by the UV exposure. FT-IR-PA difference spectra are used to measure the increase in carbonyl. UV generated carbonyl is found to increase with surface freshness. This method avoids the need of a fresh coal standard which is difficult to reproduce. The method\u27s probe depth is based on the decay length of UV rather than IR photons in coal resulting in an increase in surface specificity. The linearity of FT-IR-PA spectra as a function of absorbance has traditionally not been maintained at the peaks of strong bands in opaque samples. This leads to peak truncation and reduced spectral contrast. A method to extend linearity using the magnitude and phase information of the PA signal is reported based on the Rosencwaig-Gersho Theory of PA signal generations. Spectra of polymer slabs demonstrate the utility of this approach for enhancing spectral contrast. Developments are reported in PA detector technology which increase the scope of applications that commercial PA detectors can be used for. The new MTEC Photoacoustics Model 200 PA detector operates in diffuse reflectance, photoacoustic, and transmission measuring modes and handles both macro- and microsamples. The Model 200 has a simplified purging system and electronics designed for both fast scan and step scan FT-IR instruments. Spectra from a variety of applications are presented to demonstrate the Model 200 performance