Ryo Yoshiie

Influence of ash composition on heavy metal emissions in ash melting process

Two kinds of fly ash, discharged in the combustion of either refused derived fuel (RDF) or car shredder dust (SD), were examined for the emission of heavy metals in melting process under oxidizing and reducing conditions. The residual fractions of heavy metal in slag were experimentally estimated. As a result, it was confirmed that several volatile heavy metals were readily emitted during melting process. The type of atmosphere provided for the melting process was found to affect the emission of some volatile metals in RDF ash, but not in SD ash. The emission of volatile heavy metals in RDF ash under oxidizing conditions was lower than under any other conditions in this study. The emission behavior of iron and heavy metals in RDF ash under reducing conditions was similar to that in SD ash. These facts indicated that phosphorous in RDF ash had the property of fixing the volatile metals in the slag only under oxidizing conditions. Then the mixture of SD ash with phosphorous oxide powder was also tested in a melting process, and the result was consistent with the above inference of the effect of phosphorous.

Coal gasification with a subcritical steam in the presence of a CO2 sorbent: products and conversion under transient heating

Pulverized Taiheiyo coal (Japanese subbituminous coal) was gasified with steam in the presence of CO2 sorbent (Ca(OH)2) under relatively high pressure (approximately 20 MPa; subcritical condition) using a tubing-bomb microreactor (TB reactor). The transient characteristics in the conversion of coal and the formation of gaseous products during the gasification were investigated. During initial heating period, 40–50 wt.% of the coal initially loaded was rapidly converted to gas or tar. In the presence of Ca(OH)2, the yield of gaseous products was apparently increased owing to the catalytic effects of Ca(OH)2 on coal gasification. No CO2 was observed in the produced gas at any soaking time in the gasification with Ca(OH)2, suggesting that CO2 sorption by Ca(OH)2 took place effectively under high-pressure conditions. A rigid agglomeration of char and CO2 sorbent was observed at relatively high temperature, which is attributed to the formation of melts of the CO2 sorbent.

Use of Soft Plasma Ionization Source at Evacuated Air Atmospheres in Time-of-Flight Mass Spectrometry to Suppress Fragmentation of Volatile Organic Compounds

ABSTRACT This study describes a measuring system for mass spectrometry, consisting of a glow discharge ionization source for soft plasma ionization and a time-of-flight mass spectrometer, to detect toxic volatile organic compounds rapidly and easily. It is the most important to determine how the complicated fragmentation of such compounds can be suppressed to occur so as to recognize the mass spectra of the volatile organic compounds as their fingerprints. The novelty of this work is that the optimal discharge condition for the soft plasma ionization–time-of-flight mass spectrometer system could be selected, so that the parent mass peak of analyte molecules could be observed both with high sensitivity and with little or no fragmentation of them. Use of air gas at a pressure of 1000 Pa provided the most favorable result for these criteria, whereas, in a previous report, the soft plasma ionization source operating with argon at a pressure of 346 Pa had yielded additional mass peaks of the fragmented species. The reason for this would be explained by the fact that energetic electrons in the plasma, which principally cause the fragmentation of the volatile organic compounds, have lower number density at higher gas pressures, through de-accelerated collisions with the plasma gas.

Contribution of Volatile Interactions During Co-Gasification of Biomass with Coal

Abstract: Thermo-gravimetric behavior during steam co-gasification of Japanese cedar and coal was investigated. The difference between co-gasification behavior and the average gasification behavior of cedar and coal indicates two synergetic peaks. The first peak occurred between 300 °C and 550 °C while the second peak was observed above 800 °C. The first peak coincides with volatile release and therefore associated with volatile interactions while the second peak is linked with catalytic effect of alkali and alkaline earth metal (AAEM). Acid washed cellulose and Na rich lignin chemicals were used as artificial biomass components. In reference to Japanese cedar, mixture of cellulose and lignin i.e. simulated biomass , was also investigated. Co-gasification of cellulose with coal and co-gasification of lignin with coal, demonstrates contribution of volatile interactions and AAEM catalysis respectively. Morphology of partially gasified blends, shows hastened pore development and physical cracking on coal particles. Brunauer−Emmett−Teller (BET) surface area of the charred blend was lower than the average surface area for charred biomass and coal.

Reduction of Ash Deposition in Pulverized Coal Fired Boilers

This study proposes reduction technology of ash deposition on the heat exchanger tube in pulverized coal fired (PCF) boilers. Thermal spraying technique is adopted to change the surface properties of tube to reduce the ash deposition. As a result, Ni alloy as a thermal spraying material played an effective role to reduce the deposition under both the ash deposition experiments and the actual coal combustion experiments. However, it is necessary to change ash types in order to evaluate that the thermal spraying technology is universally useful or not. If this technology will be applied to the commercialized PCF boilers, additionally, the effectiveness for the long-term will also be studied as well as the theoretical elucidation on the reduction of ash deposition must be discussed. In this study, therefore, four types of coal ash with different melting points were tested as samples for the ash deposition experiments. The long-term ash adhesion experiments were also carried out, using a precise tension tester at high temperature. As the theoretical approaches, the compositions of each ash particle depositing on the tube surface were analyzed by a computer-controlled scanning electron microscope (CCSEM) with electron dispersive spectroscopy (EDS) detector, thereby the interfacial reactions between the ash deposition layer and the heat exchanger tube were discussed. Those results obtained were also compared to the results obtained by the thermal equilibrium calculations.

Slagging Behavior of Upgraded Brown Coal and Bituminous Coal in 145 MW Practical Coal Combustion Boiler

The purpose of this study is to quantitatively evaluate behaviors of ash deposition during combustion of Upgraded Brown Coal (UBC) and bituminous coal in a 145 MW practical coal combustion boiler. A blended coal consisting 20 wt% of the UBC and 80 wt% of the bituminous coal was burned for the combustion tests. Before the actual ash deposition tests, the molten slag fractions of ash calculated by chemical equilibrium calculations under the combustion condition was adopted as one of the indices to estimate the tendency of ash deposition. The calculation results showed that the molten slag fraction for UBC ash reached approximately 90% at 1,523 K. However, that for the blended coal ash became about 50%. These calculation results mean that blending the UBC with a bituminous coal played a role in decreasing the molten slag fraction. Next, the ash deposition tests were conducted, using a practical pulverized coal combustion boiler. A water-cooled stainless-steel tube was inserted in locations at 1,523 K in the boiler to measure the amount of ash deposits. The results showed that the mass of deposited ash for the blended coal increased and shape of the deposited ash particles on the tube became large and spherical. This is because the molten slag fraction in ash for the blended coal at 1,523 K increased and the surface of deposited ash became sticky. However, the mass of the deposited ash for the blended coal did not greatly increase and no slagging problems occurred for 8 days of boiler operation under the present blending conditions. Therefore, appropriate blending of the UBC with a bituminous coal enables the UBC to be used with a low ash melting point without any ash deposition problems in a practical boiler.

Control of ash deposition on the surface of heat transfer tube

Ash deposition, called fouling, is one of major problems occurring in boiler that incinerates waste products as fuel. Ash deposition layer on heat transfer tube in a boiler causes not only heat transfer inhibition but also corrosion of the surface of heat transfer tube. Compared with pulverized coal combustion boiler, a concern of fouling becomes larger under waste incineration conditions due to their high contents of chlorine compounds. In this study, using ash samples derived from waste incineration processes, ash deposition experiments were carried out in vertical ash deposition furnace with a thermal spraying burner. Ash samples deposited on the tube surface were analyzed for elemental compositions and their distributions, using CCSEM equipped with EDX. A thermal spraying technique was applied to improve the surface properties of heat transfer tubes in boiler for reduction of ash deposition. Ni alloy as a thermal spraying material showed a positive effect to reduce ash deposition even under waste incineration conditions. In addition, to clarify the mechanism of ash deposition, thermal equilibrium analysis was also carried out.

Monitoring of heavy metals in particulates suspended in flue gas by LIBS

Objective in the present study is to quantify a concentration ratio of heavy metal to major element in particulates, such as fly ash suspended in flue gas. The concentration ratio is important information to estimate the enrichment factor, which shows the partitioning behavior of heavy metals in combustion process. Aluminum is not only a normalizing element for an enrichment factor but also an internal reference element for the spectroscopic analysis in this study. Calibration lines for relative line intensities of iron against its concentration ratio in particle samples, simulating fly ash, are presented in this paper. To generalize the calibration lines, plasma temperature decreasing after breakdown was also investigated via Boltzmann plots of iron lines.

Adiabatic Efficiency of Supersonic Faraday MHD Generator.

Objectives of the present experimental study are to investigate adiabatic efficiencies of a supersonic Faraday MHD (magnetohydrodynamics) generator with cesium seeded argon and at the same time to achieve high enthalpy extractions. MHD power generation experiments were carried out with a shock tube facility. The MHD channel has 35 pairs of electrodes and the width between its insulator walls is expanded along the flow direction. Total pressures were measured at the exit of the MHD channel and total pressure losses were evaluated. Furthermore, the adiabatic effciency was measured for the first time in the present experiments in which an enthalpy extraction ratio of about 10% was achieved. Comparison of these results with those for a disk generator indicates that a Faraday generator has higher adiabatic efficiencies at the same enthalpy extraction ratio. Influences of voltage drops on loading parameters and electrical efficiencies are also discussed.