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Isolating and identifying the conformational forms of molecules are imperative processes to investigate the chemical reaction pathways of individual conformers. Herein, we explored the conformational structures of tetrahydropyran in the neutral (S0) and cationic (D0) states by varying the supersonic expansion conditions using one-photon vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. The constructed 2D potential energy surfaces associated with conformational interconversion between the chair and boat forms in the S0 and D0 states revealed that the ionic transitions observed in the MATI spectra correspond to the most stable chair conformer. Accordingly, based on the 0-0 band in the VUV-MATI spectrum supported by the VUV photoionization efficiency curve, the adiabatic ionization energy for the conversion of the chair conformer to a cationic state was determined to be 74 687 ± 4 cm-1 (9.2600 ± 0.0005 eV). Definitive vibrational assignment of the measured MATI spectra using Franck-Condon fitting revealed the cationic structure of the twisted chair conformer. The geometrical change upon ionization promoted the vibrational modes associated with ring inversion and deformation motions in the cationic state. This behavior, which was attributed to the effect of electron removal from the highest occupied molecular orbital (HOMO) consisting of the nonbonding orbital of the oxygen atom, reveals the role of electrons in the HOMO.

Ring conformations of 3,4-dihydro-2H-pyran (34DHP) have attracted considerable interest owing to their structural similarity to cyclohexene, an important molecule in stereochemistry. In this study, we investigated the conformational interconversion of 34DHP in both the neutral (S0) and the cationic (D0) ground states. High-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy was utilized to obtain information regarding the adiabatic ionic transition between the S0 and the D0 states. Based on the 0–0 band in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the adiabatic ionization energy of 34DHP was accurately determined to be 8.3355 ± 0.0005 eV (67 230 ± 4 cm−1). To identify the conformer corresponding to this measured value, two-dimensional potential energy surfaces (2D PESs) associated with conformational interconversion in the S0 and the D0 states were constructed at the B3LYP/aug-cc-pVTZ level. It was revealed that in the S0 state, the twisted conformers undergo interconversion through the asymmetric bent conformation on the pseudorotational pathway, whereas in the D0 state, the half-bent conformers directly undergo interconversion via the planar conformation at the saddle point of 2D PES. The change in the conformational interconversion pathway upon ionization is attributed to electron removal from the highest occupied molecular orbital, which consists of a π orbital in the 2C–3C double bond interacting with a nonbonding orbital in the oxygen atom of 34DHP. Then, vibrational assignment of the observed spectrum could be achieved through Franck–Condon fitting for ionic transitions between the neutral twisted and the cationic half-bent conformers. The strong promotion of the ring bending and the 1O–2C–3C asymmetric stretching modes in the adiabatic ionic transitions confirmed the determined cationic structure of 34DHP.

This study investigates the possibility of achieving 65 % efficiency in a gas turbine combined cycle. Several options to realize it were compared. A sensitivity analysis was performed for the latest H-class gas turbine in a simple cycle to quickly and easily predict the performance variation due to changes in each design parameter. When each design parameter was improved by the same percentage, the combined cycle efficiency was maximized by the improvement in turbine efficiency. The degree of increase in the combined cycle power was the largest when improving the turbine inlet temperature (TIT). To realize the turbine industry’s goal of 65 % efficiency in the combined cycle, the efficiency of the compressor and the turbine should be improved by 2 %, the TIT should be increased by 100 °C, and the pressure ratio should be increased from 23 to 32 in comparison to current H-class gas turbines. The possibility of improving the cycle performance was also investigated through modifications of the gas turbine cycle, such as reheating, inter-cooling, and recuperation. When reheating and recuperation were adopted simultaneously, a cycle efficiency of 65 % was possible with an increase of 1 % in both the compressor and turbine efficiencies, which is a moderate and practical improvement.

Alkylpyrazines, which are well-known as aromatic substances and traditional medicines, are interesting molecular systems, and their methyl conformations result in unique structural and dynamical properties. We explored the conformational preference of the methyl group and the highest occupied molecular orbitals (HOMOs) of 2-methylpyrazine and its cation by utilizing high-resolution one-photon vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy and natural bond orbital analysis to understand the relevant molecular activities. The measured VUV-MATI spectrum of 2-methylpyrazine revealed its adiabatic ionization energy and the vibrational frequencies of its cation. From the 0-0 band in the MATI spectrum under the zero-field limit, the accurate adiabatic ionization energy was determined as 9.0439 ± 0.0006 eV (72 944 ± 5 cm-1), which is lower than that of pyrazine. The peaks observed in the spectrum were unambiguously assigned based on vibrational frequencies and Franck-Condon factors from quantum chemical calculations for individual totally symmetric transitions between the S0 and D0 states using the simple one-photon dipole selection rules. The most convincing molecular structure of the 2-methylpyrazine cation was determined by Franck-Condon fit spectral simulations. Upon removal of an electron from the non-bonding orbital (HOMO) on the para nitrogen atoms, a significant structural change takes place along the vibrational motion associated with ring distortion by contraction of the N-N distance, resulting in prominent overtones and combination bands. In addition, the methyl substitution of pyrazine lowered the adiabatic ionization energy and the methyl group preferred the anti-configuration with respect to the pyrazine moiety in the D0 state, resulting in a frozen internal rotation regardless of ionization.

A critical issue concerning the gas turbine is that its power decreases considerably with increasing ambient temperature. Recently, it was proposed to maximize the power output of gas turbines in hot seasons through the simultaneous cooling of inlet air and hot parts cooling air, using an absorption chiller. This study serves to expand this concept and applies simultaneous cooling to combined cycle power plants using an H-class engine, the latest gas turbine model. Two methods for coolant pre-cooling were comparatively investigated and the best option was selected. The proposed dual cooling was compared with other conventional cooling schemes and their combinations. These include simple inlet air cooling using a mechanical chiller or an absorption chiller, and the combination of each of these schemes with independent cooling of the coolant by ambient air. The maximum degrees of coolant pre-cooling and inlet air cooling using the largest capacity commercial absorption chiller were predicted to be 45 K and 11 K, respectively, and the power boost of the combined cycle plant was estimated to be 8.2%, which was larger than that obtained with any other scheme. An economic analysis confirmed the feasibility of the dual cooling scheme.

The turbine inlet temperature (TIT) has a significant effect on the performance of gas turbines, and enhanced cooling methods are being applied to the latest gas turbines to increase this temperature. The coolant pre-cooling (CPC) is also used to improve the cooling performance. In this study, coolant inter-cooling (CIC) is proposed to reduce the coolant temperature and improve the gas turbine performance further. The air required for turbine cooling is extracted from the middle of the compressor, cooled, and pressurized by a separate compressor. This decreases both the coolant temperature and the power needed to compress it. The effect of CIC on the performance of a combined cycle power plant was analyzed in comparison with the conventional CPC method using an H-class gas turbine. A heat recovery system was considered to collect the heat wasted in the coolant cooling process and generates additional steam in the bottoming cycle. Various locations of the water source for the heat recovery were compared, and the optimal ones were selected. The proposed method enables higher power output and efficiency in a combined cycle power plant than the CPC method.

The major cause of the performance degradation of industrial gas turbines is compressor fouling due to airborne contaminants. Performance diagnostics is required to evaluate degradation precisely. In general, the measured performance in the fully opened inlet guide vane (IGV) condition is regarded as full-load performance and used for diagnostics. A new diagnostic method is proposed in this study. A scheme to determine whether the measured performance is at full-load operation is suggested. If operation is not at full-load, a virtual gas turbine state corresponding to the measured data is modeled using adaptive modeling. Then, the virtual full-load performance and the corrected performance are predicted using a reference firing temperature. This calculation methodology is applied to almost two-years of data of a 150 MW class gas turbine. The analysis revealed that the maximum reduction of power output and efficiency are 14.8 MW and 0.8 percentage points compared with the rated performance. In addition, it was shown that if the measured performance is used directly, the maximum deviation in the predicted power degradation was as much as 4.9 MW (2.8%) compared with the rated performance. This paper demonstrates the necessity of a model-based analysis for enhancing the accuracy of performance diagnostics.

Effusion and transpiration cooling can be an attractive method of air cooling for the next generation high-efficient gas turbine which has a very hot gas temperature over 1,600°C (TRIT). For higher effectiveness of air cooling for a gas turbine vane and blade, the air-cooled flow through effusion-holes and porous metal surface should not penetrate into the mainstream flow but still remain within the thermal boundary layer. The present visualization study examines flow behavior of microscale effusion and transpiration cooling on semi-cylinder. The secondary flow issued from the effusion-holes and porous metal surface is visualized by a smoke-tube method which consists of oil droplet generator, diode pumped solid state (DPSS) laser and highspeed imaging. The flow visualization of microscale effusion and transpiration cooling on semi-cylinder is characterized with various blowing ratios. It is found that the transpiration cooling consumes less coolant air than effusion cooling and has better cooling effectiveness based on the same flow rate of coolant air. Visual criteria can be provided to maintain the effusion and transpiration cooling on semi-cylinder for gas turbine cooling application. [This work was supported by the National Research Council of Science and Technology (NST) grant funded by the Ministry of Science and ICT, Korea (Grant No. KIMM-NK219B).]

Gas turbines are most widely used for power generation and operate under various conditions and loads. Gas turbine control is important to cope with various situations, and the turbine inlet temperature (TIT) is the most important parameter because it is directly related to the power output and life cycle of the turbine. Thus, precise prediction and control of the TIT are important in terms of the stable operation and life cycle management of gas turbines. This paper proposes a new method to predict non-measured parameters such as the air flow and TIT using Kalman filter techniques. The Kalman filter is widely used for estimating the instantaneous state of a system and can estimate non-measured parameters. The Kalman filter algorithm was implemented in a gas turbine analysis program using MATLAB. The reliability of the new method was verified through various case studies using virtual data and real operating data. The results were compared with those of a model-based gas turbine diagnostics program. The computing time of the Kalman filter and model-based diagnostics program were also compared to confirm the capability of the new method. The results indicate that the new method is more suitable for diagnostics and monitoring applications than the model-based analysis program. Finally, two case studies were performed to confirm the feasibility of the new method using two virtual datasets. The results confirm that the Kalman filter can predict the non-measured parameters precisely.

The conformational structures of heterocyclic compounds are of considerable interest to chemists and biochemists as they are often the constituents of natural products. Among saturated four-membered heterocycles, the conformational structure of oxetane is known to be slightly puckered in equilibrium because of a low interconversion barrier in its ring-puckering potential, unlike cyclobutane and thietane. We measured the one-photon vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) and two-photon IR+VUV-MATI spectra of oxetane for the first time to determine the ring-puckering potential of the oxetane cation and hence its conformational structure in the D0 (ground) state. Remarkably, negative anharmonicity and large amplitudes were observed for the ring-puckering vibrational mode progression in the low-frequency region of the observed MATI spectra. We were able to successfully analyze the progression in the MATI spectra through the Franck–Condon simulations, using modeled potential energy functions for the ring-puckering modes in the S0 and D0 states. Considering that the interconversion barrier and puckered angle for the ring-puckering potential on the S0 state were found to be 15.5 cm−1 and 14°, respectively, the cationic structure is expected to be planar with C2v symmetry. Our results revealed that the removal of an electron from the nonbonding orbitals on the oxygen atom in oxetane induced the straightening of the puckered ring in the cation owing to an increase in ring strain. Consequently, we conclude that this change in the conformational structure upon ionization generated the ring-puckering vibrational mode progression in the MATI spectra.

We predicted the available maximum power output of Integrated gasification combined cycle (IGCC) plants under the operating limitations of a gas turbine. The power block of the IGCC using an F-class gas turbine was modeled, and its interactions of mass and energy with other components such as a gasifier and an air separation unit were considered. Variation in the gas turbine power output with nitrogen dilution was simulated, and the operating conditions under which the power should be limited below an allowable maximum were determined. The maximum net power output of the IGCC plant under the restrictions of syngas turbine power (232 MW) and blade temperature were estimated in a wide range in terms of ambient temperature and integration degree, and the optimal integration degree for each ambient temperature is suggested. At relatively high temperatures over 19°C, zero integration degree (air for the air separation unit is supplied solely from the ambient) provides the highest net power output and efficiency. As ambient temperature decreases, a higher integration degree provides higher net power. The optimal net IGCC power output varies from 260 MW to 347 MW (33%) in the ambient temperature range of 40°C to -10°C, while the optimal net efficiency varies by about one percentage point.

The ionization energy and cationic structure of cyanopyrazine have been determined for the first time by pulsed-field threshold ionization mass spectrometry. The ionization energy was accurately measured to be 80,305 ± 6 cm −1 (9.9566 ± 0.0007 eV) from the 0-0 band position in the mass-analyzed threshold ionization (MATI) spectrum obtained for the direct S 0 → D 0 transition using a vacuum ultraviolet laser pulse generated by four-wave mixing in Kr. The highest occupied molecular orbital (HOMO) and singly occupied molecular orbital (SOMO) calculations indicated the extent of conjugation of nonbonding orbitals on nitrogen atoms with the π orbital in cyanopyrazine, and clarified the effect of substitution of H with CN in pyrazine on the ionization energy of cyanopyrazine. The observed MATI spectrum was interpreted using the Franck–Condon factors and vibrational frequencies calculated through adjustment of the geometrical parameters of the cyanopyrazine cation in the ground electronic state at the B3LYP/cc-pVTZ level. From rigorous analyses, it has been concluded that upon ionization, the cyanopyrazine cation in the D 0 state should retain a planar structure with C s symmetry, similar to the ground state molecule.

Background and Objectives: Internet addiction is an increasing problem in Korea. The previous studies in this area have targeted adolescents and young adults. This study was conducted to examine the risk of internet addiction in Korean adults and the effect of internet addiction on circadian rhythm. Materials and Methods: For this study, 508 subjects were chosen through population proportional sampling to represent the adult population in Korea, 325 of whom were included based on the Alcohol Use Disorder Identification Test-Korea (Audit-K), Zung's Self-Rating Depression Scale (SDS), drug use in the past year, and suicide attempts. In these subjects, sociodemographic factors including age, gender, and residential area were analyzed, and Young's Internet Addiction Scale (IAS), Morningness-Eveningness Questionnaire (MEQ), and an online survey examining sleep onset time on weekdays and weekends, wake-up time, and caffeinated drink intake were executed. Results: Of the 325 subjects, 136 (41.8%) belonged to a high-risk internet addiction group (), and 189 (58.2%) belonged to a normal group (IAS ) in the high-risk group (p = 0.024), who also showed a high proportion of caffeinated drink intake (p

The simultaneous use of gas turbine reheating and recuperation is favorable for improving the efficiency of the gas turbine combined cycle (GTCC). However, less power output is obtained from the combined cycle with both reheating and recuperation than with only reheating. Three cases of coolant cooling were analyzed to compensate for the power deficit and improve the efficiency: coolant inter-cooling, coolant pre-cooling, and conventional inter-cooling. The cycle with gas turbine reheating, recuperation, and coolant inter-cooling (RCRHCC-CIC) was predicted to be the most efficient among the three cases and showed higher efficiency than the conventional simple-cycle GTCC. In addition, scenarios of both the cycle improvement and required enhancements of the design parameters of components were investigated to achieve 67% cycle efficiency. RCRHCC-CIC achieved 67% efficiency with less enhancement of the component parameters in comparison to the simple-cycle GTCC, including 2% points less compressor efficiency and a more than 10% smaller flow path diameter. In conclusion, RCRHCC-CIC could be a possible option to reach the next level of GTCC efficiency goals.

In this study, an in-house program to predict steady state operation of micro gas turbines is constructed using MATLAB. The program consists of two parts: design and off-design simulations. The program is fully modular in its structure, and performance of each component (compressor, combustor, turbine, recuperative heat exchanger and pipe elements) is calculated in a separate calculation module using mass and energy balances as well as models for off-design characteristics. The off-design modules of compressor and turbine use performance maps, which are program inputs. The off-design operation of a micro gas turbine under development was predicted by the program. The prediction results were compared with those by commercial software, and the validity of the in-house program was confirmed. 1. 서 론 최근, 세계적으로 중앙 집중식 발전에서 분산발전으로 관심이 증가되고 있다. 그 이유는 분산발전을 통해 전력손실을 줄이고, 중앙 집중식 발전의 단점인 블랙아웃의 위험성을 줄일 수 있기 때문이다. 풍력, 태양열, 연료전지 등 다양한 분산 발전 시스템 중에서 빠른 응답성과 운전신뢰성, 유지 보수성이 좋은 마이크로 가스터빈이 주목을 받고 있다

One-photon vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy was used to characterize the essential conformations of tetrahydrofuran (THF) and thus determine the stereochemistry of the furanose ring constituting the backbones of DNA and RNA. Since the VUV-MATI spectrum of THF exactly corresponds to the vibrational spectrum of the gas-phase THF cation, the above cation was detected using time-of-flight mass spectrometry featuring the delayed pulsed-field ionization of the target in high Rydberg states by scanning the wavelength of the VUV pulse across the region of the vibrational spectrum. The position of the 0-0 band in the recorded VUV-MATI spectrum was extrapolated to the zero-field limit, allowing the adiabatic ionization energy of THF to be accurately estimated to be 9.4256 ± 0.0004 eV. The above ionization was assigned to a transition between C2-symmetric neutral (S0) and cationic (D0) ground states. The potential energy surfaces associated with molecular pseudorotation in the above states were constructed at the B3LYP/aug-cc-pVDZ level, being in good agreement with experimental observations. The twisted (C2-symmetric) and bent (CS-symmetric) conformers of the S0 state were predicted to be separated by a small interconversion barrier, whereas the D0 state exclusively existed in the C2 conformation. Based on the above, the peaks in the MATI spectrum were successfully assigned based on the Franck-Condon factors and vibrational frequencies calculated by varying the geometrical parameters of the C2 conformation, which determines the precise molecular structure of the THF cation.

In gas turbine combined heat and power systems, steam injection is a good way to cope with seasonal variations in electricity and heat demands. However, even though thermal energy demand decreases considerably in cooling seasons, the surplus exhaust heat cannot be fully utilized for steam injection in conventional operation because of a reduction in compressor surge margin. This study suggests a modified operation to increase power output without damaging the minimum allowable surge margin. This can be realized by extracting some of the compressor discharge air and supplying it to the turbine exhaust side. This paper shows that the modified operation allows for more steam to be injected in comparison to conventional steam-injected operation while maintaining the same compressor surge margin. The modified operation provides another merit of modulating the heat-to-power-generation ratio by controlling both the amount of air bypass and the steam injection rate. In particular, pure power generating operation, where generated steam is fully injected such that no heat output is available, is possible without decreasing the surge margin below a desired minimum value. The impact of the air bypass is demonstrated for a sample ambient temperature condition and the trend with ambient temperature variation is also illustrated.

This study investigated the economics of co-firing biogas and natural gas within a small gas turbine combined heat and power (CHP) plant. The thermodynamic performance of the CHP plant was calculated with varying gas mixing ratios, forming the basis for the economic analysis. A cost balance equation was used to calculate the costs of electricity and heat. The methodology was validated, and parametric analyses were used to investigate the influence of gas mixing ratio and heat sales ratio on the costs of electricity and heat. The cost of electricity generation from the CHP plant was compared to that of a central combined cycle power plant, and an economical gas mixing ratio range were suggested for various heat sales ratios. It was revealed that the effect of the heat sales ratio on the cost of electricity becomes greater as the proportion of natural gas is increased. It was also demonstrated that the economic return from the installation of CHP systems is substantially affected by the gas mixing ratio and heat sales ratio. Sensitivity analysis showed that influence of economic factors on the CHP plant is greater when a higher proportion of natural gas is used.

We evaluated the economic feasibility of small CHP (combined heat and power) and CC (combined cycle) systems using a 5 MW-class gas turbine fueled with biogas. The significance of this study is that we used practical hourly and seasonal variations of the CHP and CC performance based on detailed performance analysis. Using the investment and running costs of the entire facilities and the prices of electricity and heat, economic indices such as the annual gross margin, the net present value of the cash flow and the payback period were estimated. Two kinds of heat demand patterns were compared in the CHP system. Major findings are as follows. A strong dependence of the project economics on heat sales was observed. Both of the CHP cases showed an economic benefit over both the CC system and the gas turbine-only system. Another important finding is that the CHP system would be more beneficial than the CC system in terms of the total net present value after twenty years as long as the annual heat demand is over thirty percent of the annual electricity supply. The effect of increasing prices and costs was also simulated, and improvements in project economics were estimated.

The integration between a gas turbine and an air separation unit (ASU) is important in IGCC plants. The portion of ASU air extracted from the gas turbine and the degree of nitrogen supply from the ASU to the gas turbine side are important operating parameters. Their effect on the gas turbine performance and operability should be considered in a wide ambient temperature range. In this study, appropriate nitrogen dilution rate and turbine inlet temperature that satisfy the two limitations of turbine blade temperature and maximum allowable power output were predicted. The air integration was set at zero. The simulation showed that the power output increases and turbine blade temperature decreases as the nitrogen dilution increases. The maximum allowable power output can be obtained under medium and low ambient temperature ranges. Under a high ambient temperature range, the achievable power is less than the maximum power.

Overheating of turbine blades is one of the major concerns in using low calorific value fuels in gas turbines. In this work, we examined the deviation of operating conditions of a gas turbine fired with a low calorific value gas fuel, with a focus on the turbine blade temperatures. Several measures to suppress blade overheating were compared in terms of the power output and efficiency of the gas turbine combined cycle plant. Blade overheating can be prevented by decreasing the firing temperature without the need for hardware modifications, but the accompanying power reduction is considerable. As a remedy to this large reduction in power, modulation of the coolant supply to each blade row was simulated, and a much lower power penalty was observed. Moreover, pre-cooling of the coolant enhances the power output further by reducing the coolant supply. Pre-cooling recovers 80% of the available maximum augmentation of the combined cycle by simply switching the fuel from natural gas to low calorific value gas. Pre-cooling also provides higher overall combined cycle efficiency compared to under-firing.

In an IGCC (integrated gasification combined cycle) plant, the operating environment of the gas turbine (GT) deviates from the design conditions due to its integration with both the gasifier and the air separation unit (ASU). In particular, a trial to design the entire system with low GT–ASU integration would cause a decrease in the compressor surge margin and the turbine blade overheating. In this study, modification of the turbine and compressor to avoid a decrease in the surge margin and overheating was simulated, and the result was compared with the case without modification. The entire IGCC plant was modeled and the full off-design operation of the gas turbine was simulated. Under-firing and a decrease in dilution nitrogen can mitigate the two problems without component modification but inevitably cause a considerable performance penalty in the low integration degree regime. Both turbine modification (annulus area increase) and compressor modification (increase in the surge pressure ratio) enabled a continuous increase in power and efficiency with decreasing integration degree. In the very low integration degree regime, the power benefits of the two modifications were similar and considerable. A sensible power boost can be achieved if the turbine coolant modulation can be adopted instead of under-firing in modification strategies.

This paper describes the outcome of the design of a 200 kW class micro gas turbine and the sensitivity of its performance (efficiency and power) to the variations in major design parameters. The reference design parameters were set up based on the best available component technologies. The resulting net electricity generation efficiency of the micro gas turbine package was found to be competitive to those of other systems in the market. The sensitivities of power and efficiency to the variations in compressor and turbine efficiencies, pressure ratio, turbine inlet temperature, recuperator effectiveness, secondary air ratio, pressure loss ratios of both the cold and hot sides of the recuperator were estimated. Based on the sensitivity data, a simplified method to predict the variation in system performance responding to the combinations of small changes in all design parameters were set up and validated. † 1. 서 론 최근 들어 분산발전(distributed generation)시스템에 대한 관심이 높아지면서 중대형 발전시스템에 사용되는 것들보다 소형이면서도 운전성능과 신뢰성이 우수한 전력 생산 장치에 대한 관심이 높아지고 있다. 마이크로 가스터빈(micro gas turbine, MGT)은 수백 kW 이내의 소형 가스터빈으로서 일반적인 가스터빈의 설계 특성이 대부분 반영되어 운전 신뢰성 (reliability)과 유지보수성(maintenability)이 좋기 때문에 분산발전시스템용으로 주목받고 있다.

Mass-analyzed threshold ionization (MATI) time-of-flight mass spectrometer using coherent vacuum ultraviolet (VUV) laser generated by four-wave difference frequency mixing (FWDFM) in Kr has been constructed and utilized to obtain the accurate ionization energy of acetone. From the MATI onsets measured from various applied pulsed fields, the ionization energy to the ionic ground state of acetone has been determined to be 9.7074 ± 0.0019 eV.

This study analyzed the influence of firing biogas on the performance and operation of a gas/steam turbine combined system. A reference gas/steam turbine combined system, designed with biogas fuel(57% volumetric methane) was set up and off-design simulation was made to investigate operating characteristics when a couple of operating schemes to mitigate turbine blade overheating were applied. Performance at base-load operation using each scheme was compared and part load operation using the variable inlet guide vane was analysed. Also, differences in operating characteristics and performance caused by changes in the methane content of biogas and ambient temperature were examined. †† 1. 서 론 화석연료가 고갈됨에 따라 대체에너지를 개발하려는 많은 시도들이 이어지고 있다. 또한 국제협약으로 인해 온실가스 감축의무가 발생함에 따라 온실가스를 저감할 수 있는 재생에너지 자원에 대한 관심이 증가하는 추세이다. 바이오 가스는 이러한 두 가지 측면을 만족시킬 수 있는 에너지 자원으써 이용가치가 높다. 기체 상태의 바이오연료는 크게 두 가지로 분류된다. 첫 번째는 고형폐기물을 가스화 반응시켜 나오는 바이오매스 합성가스이며 나머지는 음식물 쓰레기 같은 원료를 소화반응 시킬 때 나오는 바이오가스이다. 이와 같은 기체 상태의 바이오연료는 가스터빈의 대체 연료로 사용가능하며, 현재 이를 다룬 많은 연구들이 있다.

Effects of coolant pre-cooling and fuel pre-heating on the performance of a combined cycle using a F-class gas turbine were investigated. Coolant pre-cooling results in an increase of power output but a decrease in efficiency. Performance variation due to the fuel pre-heating depends on the location of the heat source for the pre-heating in the bottoming cycle (heat recovery steam generator). It was demonstrated that a careful selection of the heat source location would enhance efficiency with a minimal power penalty. The effect of combining the coolant pre-cooling and fuel pre-heating was also investigated. It was found that a favorable combination would yield power augmentation, while efficiency remains close to the reference value. † 1. 서 론 가스터빈은 복합발전의 주 기기로써 발전 분야에서 중요한 역할을 하고 있다. 가스터빈은 단독 운전 시 30% 중, 후반의 효율을 내고 증기터빈과 연계된 복합발전 시스템을 구성할 때에는 50% 중반 이상의 효율을 낼 수 있다. 최근에 출시된 최고성능 가스터빈들(예를 들어 H Class)의 경우 복합사이클에서 60% 이상의 효율을 목표로 하고 있다. (1) 하지만 현재까지 설치되어 있는 발전설비의 규모나 사용처에 따라 사용되는 가스터빈의 출력범위가 상이하고 복합발전의 효율도 차이를 보인다. 이에 따라 가스터빈의 효율 및 출력을 향상시키기 위한 많은 시도가 이루어지고 있다. 최근 많은 연구가 이루어지고 있는 가스터빈 입구냉각의 경우를 보면, Najjar 등

We investigated the influence of firing biogas on the performance and operating characteristics of gas turbines. Combined heat and power systems based on two different gas turbines (simple and recuperative cycle engines) in a similar power class were simulated. A full off-design analysis was performed to predict the variations in operations due to firing biogas instead of natural gas. A wide range of biogas compositions differing in CH4 content was simulated. Without consideration of operating restrictions on the compressor and turbine, using biogas was predicted to augment the power output in both engines. Power output increased as CH4 content decreased. The main reason is the increase in turbine power due to increased fuel flow. Gas turbine efficiency increased with decreasing CH4 content in the simple cycle engine, but decreased in the recuperative cycle engine. Net efficiency including the fuel compression power consumption decreased with decreasing CH4 content even in the simple cycle engine. The heat recovery also increased by firing biogas. However, the increased turbine flow was accompanied by a surge margin reduction of the compressor and overheating of the turbine blade. These two problems were more severe in simple cycle gas turbines and as the ambient temperature increased. The turbine blade temperature and the compressor surge margin could be recovered to the reference values by either under-firing or compressor air bleeding, which are effective for blade temperature control and surge margin control, respectively. However, satisfaction of both restrictions by a single modulation caused excessive power and efficiency losses. An optimal combination between under-firing and air bleeding would minimize the performance penalty.

Cooling of hot sections, especially the turbine nozzle and rotor blades, has a significant impact on gas turbine performance. In this study, the influence of precooling of the cooling air on the performance of gas turbines and their combined cycle plants was investigated. A state-of-the-art F-class gas turbine was selected, and its design performance was deliberately simulated using detailed component models including turbine blade cooling. Off-design analysis was used to simulate changes in the operating conditions and performance of the gas turbines due to precooling of the cooling air. Thermodynamic and aerodynamic models were used to simulate the performance of the cooled nozzle and rotor blade. In the combined cycle plant, the heat rejected from the cooling air was recovered at the bottoming steam cycle to optimize the overall plant performance. With a 200K decrease of all cooling air stream, an almost 1.78% power upgrade due to increase in main gas flow and a 0.70 percent point efficiency decrease due to the fuel flow increase to maintain design turbine inlet temperature were predicted.

A general-purpose performance prediction program, which can simulate various types of gas turbine such as simple, recuperative, and reheat cycle engines, has been developed. A stage-stacking method has been adopted for the compressor, and a stage-by-stage model including blade cooling has been used for the turbine. The combustor model has the capability of dealing with various types of gaseous fuels. The program has been validated through simulation of various commercial gas turbines. The simulated design performance has been in good agreement with reference data for all of the gas turbines. The average deviations of the predicted performance parameters (power output, thermal efficiency, and turbine exhaust temperature) were less than 0.5% in the design simulations. The accuracy of the simulation of off-design operation was also good. The maximum root mean square deviations of the predicted off-design performance parameters from the reference data were 0.22% and 0.44% for the two simple cycle engines, 0.22% for the recuperative cycle engine, and 0.21% for the reheat cycle engine. Both the design and off-design simulations confirmed that the component models and the program structure are quite reliable for the performance prediction of various types of gas turbine cycle over a wide range of operations.

This study analyzed the influence of firing biogas on the performance and operation of a gas turbine combined heat and power (CHP) system. A reference CHP system designed with natural gas fuel was set up and off-design simulation was made to investigate the impact of firing biogas in the system. Changes in critical operating parameters such as compressor surge margin and turbine blade temperature caused by firing biogas were examined, and a couple of operating schemes to mitigate their changes were simulated. Part load operation of the biogas-fired system was compared with that of natural-gas fired system, and it was found that as long as the two system produce the same electric power output, they exhibit nearly the same heat recovery.

This study investigated the changes in performance and operating characteristics of an F-class gas turbine according to the change of working fluid from air to carbon dioxide. The revised gas turbine is the topping cycle of the semi-closed oxy-fuel combustion combined cycle. With the same turbine inlet temperature, the CO 2 gas turbine is expected to produce about 85% more power. The main contributor is the greater compressor mass flow and the added oxygen flow for the combustion. Compressor pressure ratio increases about 50%. However, the gas turbine efficiency reduces about 10 %. Modulation of inlet guide vane to reduce the compressor inlet mass flow, the major purpose of which is to reduce the compressor inlet Mach number, was also performed. †† 1. 서 론 최근 지구온난화와 관련하여 온실가스의 저감이 중요한 사회적인 이슈가 되고 있다. 그중 이산화탄소는 대표적인 온실가스로서 현재 대기 중으로 배출되는 이산화탄소를 줄이기 위한 연구가 활발히 진행이 되고 있다. 이산화탄소 배출량을 감소시키기 위한 기술을 통칭, 이산화탄소 포집 및 저장(Carbon capture and storage, CCS) 기술이라 하는데, 이는 크게 분류하면 연소 전처리(Pre-combustion), 연소 후처리(Post-combustion), 그리고 순산소 연소 기술(Oxy- fuel combustion)로 구분된다. 이중에서 순산소 연소기술은 공기 분리기(Air Separate Unit, ASU)를 통해서 대기 중의 산소성분 만을 분리하여 연소기에서 연료와 반응시킴으로 연소 후 가스성분이 이산화탄소와 수증기만으로 구성이 되기 때문에, 터빈 출구 가스 응축과정을 통하여 고 순도의 이산화탄소를 상대적으로 쉽게 분리, 포집할 수 있는 기술이다.최근 들어 순산소 연소를 사용하는 발전 시스템에 대한 연구가 활발히 진행되고 있다.

0.2–1.1 mol. % Dy was doped in BaTiO3 ceramics and the doping effect of Dy on the microstructure and the dielectric properties including permittivity and breakdown voltage was studied. The addition of Dy in the BaTiO3 ceramics was found to enhance the dielectric properties, which are attributed to an increase in tetragonality and a significant reduction in the average grain size due to the suppressed grain growth. The doped Dy plays an essential role in the formation of the core-shell structure in the BaTiO3 grains. The 0.8 mol. % Dy-doped BaTiO3 ceramics presented the highest dielectric constant and breakdown voltage due to the increased tetragonality, a remarkably reduced average grain size, and a well-developed core-shell structure in the grains.

MW-class gas turbines are suitable for distributed generation systems such as community energy systems(CES). Recently, biogas is acknowledged as an alternative energy source, and its use in gas turbines is expected to increase. Steam injection is an effective way to improve performance of gas turbines. This study intended to examine the influence of injecting steam and using biogas as the fuel on the operation and performance a gas turbine combined heat and power (CHP) system. A commercial gas turbine of 6 MW class was used for this study. The primary concern of this study is a comparative analysis of system performance in a wide biogas composition range. In addition, the effect of steam temperature and injected steam rate on gas turbine and CHP performance was investigated.

This study aims to provide a systematic overview of the relations between IGCC performance and major design and operating parameters such as integration degree, nitrogen dilution, and ambient temperature. A unique feature of this study is that allowable maximum values of both the gas turbine power ouput and the turbine blade temperature were considered. For this purpose, a simulation tool to predict operation and performance of a syngas turbine, which was modified from a base gas turbine model, was set up using off-design models. Then, an entire integrated gasification combined cycle using the syngas turbine was modeled. The power block (i.e. the combined cycle) was modeled in detail and mass and energy interactions of the power block with a gasifier block and an air separation unit were included. Variation in syngas turbine power output according to varying nitrogen dilution was simulated and operating conditions where gas turbine power needs to be suppressed to the allowable maximum value were found out. Maximum net IGCC power output under the limitations of gyngas turbine power and blade temperature was predicted for various integration degrees in a wide ambient temperature range. The influence of steam dilution on plant performance was also investigated.Copyright © 2014 by ASME

Gas turbines are widely used for cogeneration systems. In general, electricity and heat demands are not constant throughout the year. In cooling seasons, generally, heat demand decreases but electricity demand increases. In small gas turbine cogeneration systems, steam injection is a good way to respond to the demand variation. However, steam injection causes compressor discharge pressure to rise. This means a reduction in compressor surge margin, which is a critical operational parameter. Hence, even though thermal energy demand decreases considerably as is the case in cooling seasons, the surplus exhaust heat cannot be utilized for the steam injection in the conventional operation. In this study, a modified steam injected operation is suggested, which uprates electric power output without damaging a minimum allowable surge margin. This can be realized by extracting some of compressor discharge air and supplying it to the turbine exhaust side. The modified operation allows more steam to be injected into the combustor in comparison to the conventional steam injected operation while it guarantees the same compressor surge margin. The modified operation concept provides another merit of modulating the heat to power generation ratio by controlling both the amount of air bypass and the steam injection rate. In particular, pure power generating operation, where full amount of generated steam is injected and thus no heat output is available, is possible without decreasing the surge margin below a desired minimum value.Copyright © 2013 by ASME