Papers by Keyword: Gas Analysis

Abstract: The gas composition of boiler bottom room above the water-seal is very important to the steady operation of utility boilers in thermal power plant. As the water seal keeps air from entering the bottom room of the boiler, the gas there is comparatively enclosed. Coal particles fall down into the water from main burning area with high temperature. There is the possibility that carbon at high temperature react with water to produce combustible gases such as CO. When large quantities of slag fall down from the furnace into the water seal, the furnace pressure fluctuates widely and sharply, which leads to the flame out of the boiler quite often. The understanding of gas composition of the bottom room above water seal would help to find the reason of the pressure fluctuation. On the other hand, the gas composition above the water seal is the basic information that is deeded to research the whole burning process of coal particles and to maintain the steady operation state of boilers. Measurements were made to reveal the gas composition above the water seal. Temperature of gas just above the water seal was also measured. According to the measurement, CO concentration of high than 1000ppm was detected and the gas composition under normal state was analyzed.

Abstract: A piezoelectric sensor array is introduced for the analysis of gas in mine. This sensor array is made of three different gas-sensitive piezoelectric sensors to detect an explosive gas mixture of methane, butane and hexane. The gas analysis is very important to reliable warning of explosion risk in mine. Because of cross sensing to gas for each sensor of sensor array, we use BP neural network in the artificial neural networks to process the sensing signal to get the concentration of methane, butane and hexane in the combustible gas mixture. Experimental results show that the analysis error is less than 5% and meets the requirements of safety monitoring.

Abstract: Virtual arrays formed by operating temperature modulation of a commercial non selective chemoresistor have been utilized for gas identification. Here, we are reporting the details of a refined system which distinctly classifies methanol, ethanol, 1-butanol, acetone and hydrogen contaminations in a wide concentration range. A staircase voltage waveform of 5 plateaus is applied to the sensor’s microheater and gas recognition is achieved in 25 s. Sensor’s output is modeled by an “autoregressive moving average with exogenous variables” (ARMAX) model. The modeling parameters obtained for an unknown analyte are utilized as the components of its feature vectors which afford its classification in a feature space. Cross-validation in the 5 to 100 ppm concentration range for H2, and 200 to 2000 ppm for the other analytes examined, resulted in an overall classification success rate of 100%.

Abstract: We have recently disclosed a novel technique for gas analysis based on monitoring the free diffusion-physisorption of the analytes in a microfluidic channel. Equipped with a single general gas sensor, the prototype can recognize variety of gases and gas mixtures. Here, the structural details of the fabricated prototype are given. The performance of the prototype is demonstrated by presenting analysis results obtained for a number of pure and mixed gaseous analytes.

Abstract: Facultative Fe(III)-reducing bacterium Acidiphilium SJH was incubated in media with ferric iron under various conditions with respect to oxygen availability for the growing cells. The bacteria oxidized organic substratum to carbon dioxide using oxygen and ferric iron as terminal electron acceptors. Ferric iron reduction was observed in all incubation modes. The distribution of reducing equivalents from the oxidation of organic carbon for the reduction of both O2 and Fe(III) was evaluated from CO2 production rate and O2 consumption rate. In fully aerobic conditions approximately 10 % of CO2 produced was coupled with reduction of Fe(III) as terminal electron acceptor. Under aerobic conditions, the ratio of CO2 produced to O2 consumed remained unaffected in a broad concentration range of dissolved oxygen. In the course of oxygen limitation (microaerobic conditions) the molar CO2 to O2 ratio increased from approx. 1 to 2 and even much more with respect to oxygen transfer rate during incubation. On the other hand no bacterial growth and extremely slow iron reduction was observed in obligatory anaerobic conditions in a reactor purged with either pure or CO2-enriched nitrogen.

Abstract: Acetylene and ethylene are frequently used in vacuum carburizing in Japan. In this study the natural gas which is available from the lifeline is applied to vacuum carburizing. The gas composition inside the furnace was analyzed by the gas chromatography in order to examine the carbon infiltration mechanism. Unsaturated hydrocarbon gases (such as acetylene and ethylene) are generated from the natural gas. The effect of acetylene concentration in the furnace on the carbon infiltration rate was investigated. The carbon amount which infiltrates into the steel increases, as acetylene concentration in furnace increases. It is possible that carbon concentration of specimen surface increases to the cementite precipitation concentration in the short term, when natural gas flow rate increases in the initial carburizing stage. After that, carbon concentration of specimen surface does not decrease, even if the natural gas flow decreases, because carbon atoms which are consumed for diffusion to inside are sufficiently supplied. By using this method, inhibition of soot generation, reduction of process gas and shortening of the carburizing period are possible. The carbon concentration profile of the vacuum carburized specimen was compared with the simulation.

Abstract: In this paper, the effect of electric current on sintering of hydroxyapatite (HAp) in spark plasma sintering (SPS) process was investigated. The carbonate partially substituting hydroxyapatite was sintered up to 900 °C, and CO₂ evolved from HAp powder were measured in situ by using mass spectroscopy apparatus in the same time. The same gas analysis was performed in thermal analysis as comparison. In the thermal analysis, CO₂ gas was evolved at about 600 °C. On the other hand, in the SPS process, CO₂ gas was detected at lower temperature than that of thermal analysis. This result indicates that the surface of hydroxyapatite particles would be heated up locally in SPS process due to electric current.