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The ionization source based on glow discharge plasma using ambient air is driven by a pulsed direct-current voltage for soft plasma ionization (SPI). The novelty of this work is that molecular ions [M+13]+ related to the analyte species (M), which may be formed by numerous oxidation, can be dominantly detected as a base peak with little or no fragmentation of them in an air plasma at a pressure of several kPa. The unique ion [M+13]+ was assigned to the oxidation product, [M+O-3H]+, which was confirmed as a deuterated ion [M+O-3D]+ ([M+10]+) by using a deuterated solvent. The ionization reactions were suggested that the product ion [M+O-3H]+ may arise from hydride abstraction reaction of M with O2+•, dehydrogenation reaction of [M-H]+• and subsequently oxidation reaction of [M-3H]+ with O3. n-Alkane mixtures was also measured to evaluate the intermolecular interaction in this system. The limits of detection (LOD) were in the range of 0.126-1.68 ppmv and the relative standard deviation (RSD) for repeatability was approximately 10.0% at the lowest concentration. To our knowledge, this is the first report demonstrating that the spectrum pattern of saturated hydrocarbons could be directly determined without any complicated fragmentation.

The objective of this paper is to suggest a new method for controlling temporal response of the emission signal from a pulsed radio-frequency (RF) glow discharge plasma for optical emission spectrometry. It is a noticeable feature that the emission profile accompanies a transient stage in the pulsed operation, appearing as a pre-peak which sometimes becomes 10–20 times as large as the plateau-stage intensity. Therefore, it is worth studying how the spike-like transient signal can be modified to a smooth response following the square-wave timing signal by using any experimental procedure. For this purpose, a phenomenon regarding self-bias voltage in RF plasma was focused on. The self-bias voltage is induced near the RF-loaded electrode, and then, a bias current can be introduced through an electric circuit including the plasma body by connecting an external electric device with the glow discharge plasma source. The bias current could be also pulsated, while it was synchronized with the pulsed RF plasma. Larger pulses of the bias current could change the characteristics of the plasma for atomic emission spectrometry, extending the size of the RF plasma as well as enhancing the emission intensity, which enabled the plateau stage to become more prominent in the pulsed emission profile. Several experimental parameters, such as an amplitude of the bias current, duty ratios of both the RF power and the bias current, and a phase shift between them, were investigated to obtain a plateau-like transient response of the emission signal. It was found that the phase-shift angle should be regulated between timing pulses of the RF voltage and the bias current.

This study describes an ionization source for mass analysis, consisting of glow discharge plasma driven by a pulsed direct-current voltage for soft plasma ionization, to detect toxic volatile organic compounds (VOCs) rapidly and easily. The novelty of this work is that a molecular adduct ion, in which the parent molecule attaches with an NO + radical, [M + NO] + , can be dominantly detected as a base peak with little or no fragmentation of them in an ambient air plasma at a pressure of several kPa. Use of ambient air as the discharge plasma gas is suitable for practical applications. The higher pressure in an ambient air discharge provided a stable glow discharge plasma, contributing to the soft ionization of organic molecules. Typical mass spectra of VOCs toluene, benzene, o -xylene, chlorobenzene and n -hexane were observed as [M + NO] + adduct ion whose peaks were detected at m / z 122, 108, 136, 142 and 116, respectively. The NO generation was also confirmed by emission bands of NO γ-system. The ionization reactions were suggested, such that NO + radical formed in an ambient air discharge could attach with the analyte molecule.

Oxy-fuel coal combustion has drawn attention as a useful technique to achieve carbon dioxide capture and storage (CCS). It is the technique that enriches CO 2 in exhaust gas by flue gas recirculation with additional pure O 2 , which makes it easy to capture and liquidize CO 2 downstream. However, in the oxy-fuel combustion system, various impurities in the flue gas are brought back to the combustion zone with recirculated flue gas, and more have accumulated in a boiler compared with the air combustion system. NO X formations, in particular, can be affected by nitrogen contents in the raw coal and recirculated multiple NO X compounds, such as NO and N 2 O. Then, in this study, we experimentally estimated the effects of NO and N 2 O recirculation by a drop tube furnace equipment simulating oxy-fuel atmosphere for three coal samples with different nitrogen contents. As a result, contributions of recirculated NO X to NO X emissions were found to be very small in oxy-fuel coal combustion. Instead, nitrogen conversion ratios to NO and N 2 O were governed by the ratio of char-N to fuel-N.

Counter-flow packed bed gasification was carried out featuring a combination of downdraft and updraft operation modes. A column reactor of inside diameter 102 mm and 1000 mm height was used. Downdraft and updraft air supply were varied while the total air supply was maintained constant. Counter-flow gasification with downdraft air supply at 12 L/min and updraft air at 4 L/min offered optimal conditions, producing syngas with 4.28 MJ/m 3 N LHV and 5.84 g/m 3 N tar content. Under similar operating conditions, cold gas efficiency was about 77% while carbon conversion reached 88%. Increasing the updraft air flow resulted in reduced tar generation and increased carbon conversion, however, the syngas LHV and cold gas efficiency were affected adversely.

Some ash particles in solid fuels adhere on heat exchanger tube surfaces inside coal and/or biomass combustion boilers. The authors have already proposed a surface treatment on tubes, using a thermal spraying technique, to reduce ash deposition. Understanding reduction mechanisms of the ash deposition is necessary to evaluate effects of the surface treatment technique on the reduction of ash deposition. The reduction mechanisms of the ash deposition were elucidated due to physical and chemical aspects, measuring adhesion forces between the ash particles and some alloy specimens of the tube at high temperature under the simulated boiler conditions. As a result, the adhesion force increased with time and depended on both the ash types and the alloy specimens. The thermal spraying of Ni-alloy, in particular, could reduce the adhesion force. Moreover interface reactions between the ash particles and the alloy specimen played an effective role in increasing the adhesion force, alkali metal compounds in the ash samples also related to an increase of the adhesion force. Fe, which was one of the main alloy elements, diffused into the ash deposition layer beyond the interface. This observation result suggested that the interface reactions of the ash particles with the alloy caused an increase of the adhesion force.

Boron behavior during coal combustion was studied experimentally and theoretically. Seven types of coal with different boron concentrations were pyrolyzed or burned, using an electrically heated drop tube furnace. In order to understand the effect of coal type on the boron component of ash, chemical equilibrium calculations were made to determine which boron compounds contributed to forming the boron compounds found in the ash particles. Additionally, XAFS analyses were also carried out to evaluate the results obtained by the chemical equilibrium calculations. Some boron compounds in coal were volatilized, and others remained in the molten coal ash after combustion. Both the chemical equilibrium calculations of the boron compounds under the combustion condition and the boron analysis of the ash particles by the XAFS suggested that the boron compound contained in the ash was mainly B 2 O 3 . The boron compounds were concentrated in the molten slag during combustion. The enrichment of boron into the ash as particles was related to the amount of slag formed. The index, (Base/Acid ratio) × (Ash content), correlates well with the volatilization fraction of boron even in the actual power plants.

It is important to be aware of the particle size distribution and composition of ash in coal combustion for prediction and control of ash deposition behavior, which results in the degradation of boiler performance via fouling and slagging. To elucidate fragmentation and coalescence behavior of mineral particles in a pulverized coal combustion process, char particles during the combustion reaction were sampled and analyzed for their particle size distribution and composition using a drop tube furnace. CCSEM analysis was conducted to identify included and excluded minerals in sampled char particles. Three coal samples having different char structures and ash melting temperatures were tested to estimate the effect of the physical properties of ash on fragmentation and coalescence behaviors of mineral particles. With the progress of combustion, the number of included mineral particles decreased due to their separation from char particles, leading to the increase of the number of excluded mineral particles. The total number of particles decreased with the progress of combustion. Some of particles were agglomerated, and some of them were fused to each other. These behaviors were less obvious for coal which experienced network structure of char particles during its combustion process. On the other hand, minerals in coal characterized by low melting point ash were rounded off during the coal combustion process. Fractions of included mineral were higher at smaller particle sizes, and they decreased with the progress of combustion. Elemental compositions of fused particles in coal characterized by low melting point ash are attributed to that of aluminosilicate.

A time-of-flight mass spectrometry (TOFMS) with a newly laboratory-made sampling cone interface fitted to an atmospheric pressure chemical ionization (APCI) positive ion source was successfully applied to easy, rapid on-line measurements of nanoparticles and components generated during combustion. The mass spectra for smoke from a mosquito coil ranged up to m/z 1202, corresponding to 1.2 nm with the carboneous material density as graphite 2.2 g cm−3. Typical m/z peaks were assigned to such synthetic pyrethroids, as d-allethrin and d-tetramethrin, at m/z 303 and 332, respectively. A specific pattern with a peak-to-peak interval of 74 was recognized in the higher mass range. The interval of 74 was confirmed by measuring with a standard silica solution in a positive ion mode using a conventional APCI interface under the same APCI conditions. The mass spectrum of the silica solution had a pattern with peak interval of 44 which was assigned to SiO. These results indicate that the pattern with an interval of 74 in the mass spectrum of the mosquito coil smoke is sample-derived peak. We assumed that the interval of m/z 74 is assigned to identified as triacetylene (1,3,5-hexatriyne) that is generated during the combustion.