Search

The basic properties of coal influence various procedures of power generation, such as the design of power generation plants, estimation of the current condition of boilers, and total efficiency of power plants. The elemental composition is a needed factor in evaluating the process of chemical conversion and predicting the flow of flue gas and the quality of air in coal combustion. In the past, several relationships have been established using ultimate and proximate analyses. This study aims to predict the elemental compositions of 104 thermal coals used for coal-fired power plants in South Korea using an artificial neural network (ANN) that uses proximate analysis values as input parameters. The ANN-based model was optimized with six activation functions and four hidden layers after evaluating various performance indices, including

The need to reduce global carbon dioxide (CO2) emissions is driving the conversion of coal-fired power plants to use methane, which can reduce CO2 emissions by >40%. However, conducting gas firing in coal boilers changes the heat transfer profile; therefore, preliminary evaluations using computational fluid dynamics are required prior to conversion. Here, methane was used as a heat input source in the simulation of an existing coal boiler, and combustion, nitrogen oxides (NOx) emission characteristics, and heat transfer profile changes inside the boiler were analyzed. Furthermore, changes in the burner zone stoichiometric ratio (BZSR) were simulated to restore the decreased heat absorption of the furnace waterwall, revealing that air distribution could change the heat absorption of the waterwall and tube bundles. However, this change was smaller than that caused by conversion from coal to methane. Therefore, to implement gas firing in coal boilers, alternatives such as output derating, using an attemperator, or modifying heat transfer surfaces are necessary. Despite these limitations, a 70% reduction in NOx emissions was achieved at a BZSR of 0.76, compared with coal. As the BZSR contributes significantly to NOx emissions, conducting gas firing in existing coal boilers could significantly reduce NOx and CO2 emissions.

Recently, ashless pretreatment of lignocellulosic biomass prior to pyrolysis has been used for removing mineral matters to prevent slagging and fouling. The purpose of this study is to fundamentally investigate the pyrolysis characteristics of ashless treated kenaf with torrefaction. The related kinetic parameters and thermal behaviors were examined using non-isothermal thermogravimetric experiments. Thermal degradation experiments were conducted at temperatures ranging from 300 to 900 K at six different heating rates in a N2 environment. Ashless treatment resulted in a slight increase in hemicellulose and cellulose contents with decreasing lignin, whereas torrefaction of ashless kenaf led the hemicellulose to be decomposed more into cellulose and lignin compared to only ashless treatment. The decrease in the devolatilization index (Di) for ashless kenaf (AK) reached approximately 20%, whereas the Di for torrefied ashless kenaf (TAK) increased nearly three times the raw kenaf (RK) value. The distributed activation energy model was used to analyze the kinetics and thermal parameters for pyrolysis. The activation energies of RK, AK, and TAK were estimated as 180.51, 195.32, and 187.15 kJ mol−1, respectively. Thermodynamic parameters (ΔH, ΔG, ΔS) and reaction mechanisms were also compared and evaluated. The results indicated that torrefaction can improve the thermal degradation process of AK and can provide useful information for the development and optimization of thermochemical conversion systems using pretreated kenaf as feedstock.

Torrefaction is an appealing pretreatment method for improving the fuel properties of kenaf biomass before its utilization in thermochemical processes. This study evaluated and compared the impact of torrefaction on thermal behavior and kinetics during pyrolysis and gasification. Thermogravimetric analysis experiments were conducted at temperatures of 300-1173 K at several heating rates under N2 and CO2 atmospheres. The raw and torrefied kenaf (RK and TK) during CO2 gasification in the low-temperature region ( 900 K), thus improving conversion efficiencies. The activation energy for TK in a CO2 atmosphere depending on the conversion was calculated using the distributed activation energy method. The activation of RK during CO2 gasification was higher than that of N2. However, TK during CO2 gasification exhibited a lower activation energy compared to that of N2, indicating its potential as a better feedstock during the CO2 gasification process and the ability to save energy.

A commercial CFD package coupled with user-defined functions was used to observe coal particle combustion and tracking, particle capturing and deposition, and other related phenomena. A modified Watt-Fereday model for deposition employing experimental coefficients derived from the ash fusion test was used to predict ash viscosity, which showed that the samples had a nonadditive behavior due to the eutectic phenomenon. The furnace results showed that when the Bayan coal, containing a large amount of volatile matters, was injected at the top burner, the slagging propensity increased compared to when it was injected in the bottom burner. In addition, the specific blending ratio of 25 % Flame and 75 % Bayan coal, which had a lower melting temperature compared to the individual coals. This study suggests that sub-bituminous coal should be injected in the bottom burner, and the specific blending ratio that yields a low-temperature eutectic mixture should be avoided.

Using biomass to produce energy is becoming a more desirable approach to environmentally sustainable energy production. However, there are currently several obstacles to efficient exploitation of this fuel source. In this study, the effects of torrefaction and ash reduction on the grindability of pitch pine sawdust (PSD) and its blends with coal were investigated. The particle size distributions after grinding, Hardgrove grindability index (HGI), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) results of the fuels treated by the different methods were compared. The results indicated that ash reduction improved the grindability of raw PSD better than torrefaction, whereas torrefaction improved the grindability of ash-reduced PSD. Biomass particles produced by ash reduction generated high electrostatic forces and were relatively small. The SEM and BET results showed that the particles pretreated by ash reduction and torrefaction lost their characteristic fibrous structure and had a higher pore volume and surface area after grinding. The particle size distributions of the coal- PSD blends were between those of coal and biomass. Both the 10 wt.% raw and ash-reduced PSD-coal blends exhibited similar grinding behaviors to pure coal after torrefaction. Therefore, ash reduction and torrefaction improved the grindability of single biomass fuels and coal-PSD blends.

The main purpose of this study was to examine the effect of particle size on blending methods for pulverized coals, using a thermo-gravimetric analyzer (TGA) and an entrained drop tube reactor (EDT...

Biomass resources, which are carbon-neutral and sustainable, may help to address climate change and reduce greenhouse gas emissions. This study was performed to examine the effects of wood pellet (WP) particle size, environmental conditions (stoichiometric ratio; SR), and blending ratio on the combustion characteristics of single fuels and blends using a thermogravimetric analyzer and drop tube furnace (DTF). The results indicate that WP demonstrated a higher mass reduction in the devolatilization region and a faster reaction rate compared with coal. Blends tested in the analyzer showed the expected profiles for devolatilization and char oxidation without the presence of non-additive effects. However, the DTF results showed that simultaneous reactive and non-reactive phenomena occurred with increasing biomass-blending ratios. When WP fuel containing fine particles ( 600 μm) showed that unburned carbon (UBC) increased owing to slower reactivity. WP fuel containing particles of 400 μm or less in size demonstrated superior UBC performance, indicating that biomass-coal blends were significantly affected by blending ratio, particle size, and the surrounding environment.

The off-peak period of the grid load (i.e., deep peak load) prevents a power generation boiler from operating at full load. To achieve stable combustion of 550-MW tangentially fired pulverized coal boiler and ultra-low pollutant emissions (nitrogen oxides and unburned carbon) under half-load conditions, different operating parameters have been analyzed and optimized. In this study, under half-load conditions, the numerical method was used to simulate the flow field characteristics, combustion stability, and pollutant emissions of the boiler under various operating conditions. The operating conditions included various burner group arrangements, close-coupled overfire air (CCOFA)/separated overfire air (SOFA) distributions, and excess air ratios. The simulation prediction results showed that the middle burner group (BCDE) arrangement has a good flow field distribution. Compared with the upper burner group (CDEF) arrangement, this reduces NOX by approximately 62 ppm and also maintains a higher pulverized coal burnout rate than the lower burner group (ABCD) arrangement. Considering the stability of the combustion and lowest emissions, the ratio of CCOFA of 5% and SOFA of 15% were preferred as the operating conditions for the air-staging distribution. The high excess air caused an increase in NOX while the combustion temperature significantly reduced in the furnace, made the furnace exit gas temperature (FEGT) too low, and affected the steam temperature. In addition, the simulation results of the optimized scheme were in good agreement with the field test results.

Fuel pretreatment methods have attracted attention due global warming concerns. However, these methods impact the combustion and emission behaviors of pretreated fuels, and variations in fuel characteristics influence the formation of NO x during combustion. We investigated the impact of different pretreatment methods (torrefaction and ashless process) on combustion and NOx emission characteristics. Two biomass fuels, i.e., woody ( pitch pine sawdust ( PSD)) and herbaceous (Kenaf), and their pretreated fuels were subject to combustion analysis. The fundamental properties and structural pore characteristics as well as unburned carbon (UBC) and NO x emissions following combustion tests, with both raw and pretreated biomasses, were investigated. The results show torrefaction of both fuels improves the fuel ratio (FR), whereas the ashless process reduces the FR. For both fuels, torrefaction increased the fuel-N by approximately 30%–50%, whereas the ashless process decreased fuel-N. In fixed conditions, the combustion index (S) indicates the ashless process provides greater reactivity for both fuels. Upon torrefaction, S is higher for the PSD samples but lower for the Kenaf samples. In entrained conditions, the UBC for both samples decreased after the ashless process, but increased following torrefaction of Kenaf, which corresponds to the fuel ratios. The ashless process resulted in lower NOx emissions, whereas torrefaction resulted in a different tendency due to variations in N-compounds and fuel volatility for each fuel. These results indicate that the combustion and NOx emissions from different pretreatments are closely linked to characteristics of devolatilization and pore distribution in a fuel.

Dynamical processes in various natural and social phenomena have been described by a series of events or event sequences showing non-Poissonian, bursty temporal patterns. Temporal correlations in such bursty time series can be understood not only by heterogeneous interevent times (IETs) but also by correlations between IETs. Modeling and simulating various dynamical processes requires us to generate event sequences with a heavy-tailed IET distribution and memory effects between IETs. For this, we propose a Farlie-Gumbel-Morgenstern copula-based algorithm for generating event sequences with correlated IETs when the IET distribution and the memory coefficient between two consecutive IETs are given. We successfully apply our algorithm to the cases with heavy-tailed IET distributions. We also compare our algorithm to the existing shuffling method to find that our algorithm outperforms the shuffling method for some cases. Our copula-based algorithm is expected to be used for more realistic modeling of various dynamical processes., 7 pages, 4 figures

Retrofitting of an aging 500 MW tangential coal-fired boiler with high pollutant emissions in South Korea was investigated to achieve low nitrogen oxide (NOX) emissions and high combustion efficiency. This study evaluated and analyzed the combustion and emission characteristics of five arrangements to optimize the position and direction of a separated overfire air (SOFA) installation using a computational fluid dynamics (CFD) simulation. The results show that the air injection of SOFA at the center of the boiler wall causes substantial obstruction of the rising airflow below, causing unstable combustion behavior in the boiler, and increasing the amount of unburned carbon (UBC). However, combining the wall injection with corner SOFA helps reduce the formation of NOX and has the effect of promoting the burnout of UBC. For the direction of the wall injection under combined conditions, a clockwise airflow helps to reduce the formation of NOX with increasing UBC. Otherwise, the counter-clockwise airflow weakens the flow rate of the ascending airflow, increasing the residence time of unburned particles, increasing the coal burnout rate, and increasing the furnace exit gas temperature (FEGT). Among the five SOFA arrangements studies, this study recommends Case 4, which has a clockwise wall SOFA (30%) with corner SOFA (70%). This case has the best performance in terms of combustibility, NOX emission, UBC, and FEGT. The proposed condition was verified through a field test, and the results indicate that NOX emissions decreased from 169 ppm to 57 ppm, the UBC content decreased from 3.64% to 0.7%, and the boiler efficiency increased by 2%.

졸-겔법에 의해 출발물질로 aluminum isopropoxide를 사용하여, 메탄올용매 내에서 가수분해 시킨 후 해교제인 초산, 질산 또는 염산을 각각 첨가하여 해교 시켜 3종류의 alumina sol을 제조하였다. 또한 이 sol에 실란커플링제인(3-glycidyloxypropyl) trimethoxysilane을 첨가하여 코팅 용액을 제조한 후, 이용액을 polycarbonate 기재 위에 담금 코팅 후 열 경화시켜 코팅 도막을 형성하였다. 이 과정 중 해교제의 종류 변화가 코팅 도막의 물성에 미치는 영향을 연구하였다. 그 결과 해교제로서 강산인 염산이나 질산을 사용한 코팅 도막은 H나 2H의 연필경도와 5B의 부착력을 나타내어 우수한 물성을 나타내었다. 반면에 해교제로서 약산인 초산을 사용한 경우에는 HB의 연필경도와 3B의 부착력을 보여 좋지 못한 물성을 나타내었다.

Coal is an important energy source to increase consumption continuously. However, the ash residues from coal combustion have produced ash deposition that causes slagging and fouling in boilers. The goal of this study is to examine the characteristics of ash deposits (i.e., the effects of the ash fraction and particle size) in pulverized coal combustion. For this study, five coals (Suek, Macqurie, Berau, Lanna and Vitol) are used, which have similar chemical components in the ash but differences in the ash fraction. A Thermomechanical analysis technique (TMA) and Drop tube furnace (DTF) are used to analyze the tendencies in the ash fusibility and deposition with temperature, respectively. Moreover, the size and morphology of the fly ash are analyzed for physical changes by using a particle-sizedistribution analyzer and Scanning electron microscopy (SEM), respectively. In the TMA results, all coal types have a similar fusibility because of the similar chemical components in the ash. The order of the deposited mass is Suek, Macqurie, Berau, Vitol and Lanna in accordance with the ash fraction in the DTF. The ash fraction in coal is a major factor in the ash deposit according to these results. The size of the fly ash changed compared to that of the raw coal according to the results of a particle-size analysis and SEM owing to physical processes such as fragmentation, shedding and coalescence during coal burning. On this basis, a deposition model is developed with the ash fraction and particle size. The model results are in good agreement with the measurements. The results demonstrate that the particle size and ash fraction influence the deposit.

The addition of biomass to an existing coal-fired boiler has emerged as a prospective option for reducing CO2 emissions to mitigate the problems associated with excess global warming. However, the cost associated with retrofitting an injection system and the unstable combustion hinder the use of this option. Therefore, we propose the use of coal impregnated with glycerol as fuel that can be directly injected into an existing boiler. This is a two-in-one fuel that combines a low-rank coal (LRC) with bio-liquid matter extracted from biomass such as molasses or sugarcane juice. In this study, for the first time, we used glycerol, which is a low value co-product of biodiesel production, as the bio-liquid, because the use of molasses or sugar-cane juice raises food ethical issues. The aim of this study was to investigate the combustion behavior of coal impregnated with glycerol, using experimental and numerical methods. The results showed that the calorific value of coal impregnated with glycerol increased, and the combustibility at low and high temperatures was improved by impregnation of low-rank coal with up to 20% glycerol. We also confirmed that the combustion performance of coal impregnated with glycerol was unaffected and was identical to that of original coal. However, excess glycerol (more than 20%) led to oxygen deficiency near the burner and thermal expansion, which reduced the combustibility. The results of this study therefore suggest that less than 20% glycerol is the optimal condition for low-rank coal impregnated with glycerol.

In order to improve the hydrophilic property of polymer films, coating solutions which showed a good hydrophilic property, were prepared by the sol-gel method. The coating solutions were prepared by adding different types of silane coupling agents (aminosilane, epoxysilane and acrylsilane) to a colloidal silica (15 nm diameter). The solutions prepared by adding aminosilane resulted in gels which could not be used as coating solutions. On the other hand, the coating solutions prepared by the addition of epoxysilane showed contact angles of 10~15o and good hydrophilic property at R=0.10~0.15 (R=silane coupling agent/colloidal silica weight ratio). In addition, the coating solutions prepared by the addition of acrylsilane at R=0.03~0.07, exhibited contact angles of 5~10o, which means better hydrophilic property than aminosilane or epoxysilane.

Temporal inhomogeneities observed in various natural and social phenomena have often been characterized in terms of scaling behaviors in the autocorrelation function with a decaying exponent $\gamma$, the interevent time distribution with a power-law exponent $\alpha$, and the burst size distributions. Here the interevent time is defined as a time interval between two consecutive events in the event sequence, and the burst size denotes the number of events in a bursty train detected for a given time window. In order to understand such temporal scaling behaviors implying a hierarchical temporal structure, we devise a hierarchical burst model by assuming that each observed event might be a consequence of the multi-level causal or decision-making process. By studying our model analytically and numerically, we confirm the scaling relation $\alpha+\gamma=2$, established for the uncorrelated interevent times, despite of the existence of correlations between interevent times. Such correlations between interevent times are supported by the stretched exponential burst size distributions, for which we provide an analytic argument. In addition, by imposing conditions for the ordering of events, we observe an additional feature of log-periodic behavior in the autocorrelation function. Our modeling approach for the hierarchical temporal structure can help us better understand the underlying mechanisms behind complex bursty dynamics showing temporal scaling behaviors., Comment: 8 pages, 5 figures

* Graduate School of Mechanical Engineering, Pusan Nat’l Univ. ** PLM team, Boiler RD Revised October 29, 2015 ; Accepted November 10, 2015)Key Words: Biomass Blending Ratio(바이오매스 혼합 비율), Particle Size(입자 크기), Unburned Carbon (미연분, UBC), Oxygen Deficiency(산소 결핍) 초록: 최근 바이오매스와 석탄의 혼소 기술이 화력 발전의 주요한 연소 기술 중 하나로 떠오르고 있다. 그러나 혼소는 실제 발전용 보일러 적용시 많은 검증들을 필요로 한다. 본 연구에서는 바이오매스 혼소시 연소 특성을 알아보기 위해 열중량 분석기(Thermogravimetric analyzer, TGA)와 하향분류층 반응기(Drop tube furnace, DTF)를 사용하였으며, TGA의 TG/DTG 분석을 통한 반응성과 DTF를 이용한 UBC를 측정하여 연소 특성을 분석하였다. 특히 석탄과 바이오매스 혼소율(Biomass blending ratio) 및 바이오매스 입자 크기 변화에 따른 특성을 분석하였다. 그 결과, 바이오매스의 혼소율이 증가함에 따라 산소 부족으로 인한 반응 특성이 나타났으며, 이는 바이오매스가 가진 초기의 빠른 연소 특성 때문이다. 또한, 본 연구 결과를 통해 바이오매스의 최적 혼소 조건(UBC 발생량 기준)은 5%로 나타났으며, 산소 부화 조건은 바이오매스 혼소시 발생하는 산소 부족 현상을 저감시켜 미연분 상승을 완화시켜줄 수 있다.Abstract: Co-firing of biomass with coal is a promising combustion technology in a coal-fired power plant. However, it still requires verifications to apply co-firing in an actual boiler. In this study, data from the Thermogravimetric analyzer(TGA) and Drop tube furnace(DTF) were used to obtain the combustion characteristics of biomass when co-firing with coal. The combustion characteristics were verified using experimental results including reactivity from the TGA and Unburned carbon(UBC) data from the DTF. The experiment also analyzed with the variation of the biomass blending ratio and biomass particle size. It was determined that increasing the biomass blending ratio resulted in incomplete chemical reactions due to insufficient oxygen levels because of the rapid initial combustion characteristics of the biomass. Thus, the optimum blending condition of the biomass based on the results of this study was found to be 5 while oxygen enrichment reduced the increase of UBC that occurred during combustion of blended biomass and coal.

We report a systematic and comprehensive laboratory investigation of the ash deposition behavior of Moolarben (MO) coal, which has recently begun to be imported into Korea. Ash deposition experiments were conducted in a drop tube reactor, and a water-cooled ash deposit probe was inserted into the reactor to affix the ash. The tests were conducted using five types of single coals (two bituminous and three sub-bituminous, including MO coal) and blended coals (bituminous coal blended with sub-bituminous coal). Two indices represent ash deposition behavior: capture efficiency and energy-based growth rate. A thermomechanical analysis evaluated the melting behavior of the resulting ash deposits. The MO coal had the least ash deposition of the single coals due to its high melting temperature, indicated by high ash silica content. Indonesian sub-bituminous coals formed larger ash deposits and were sticky at low temperatures due to relatively high alkali content. However, blends with MO coal had greater ash deposition than blends with other bituminous coals. This non-additive behavior of MO coal blends is likely due to interactions between ash particles. Coals with higher silica content more effectively retain alkali species, resulting in lower melting temperatures and larger ash deposits. Therefore, we recommend that when blending in a boiler, silica-rich coals (SiO2>80%, SiO2/Al2O3> 5) should be blended with relatively low-alkali coals (Na2O+K2O

Cities consist of infrastructure that enables transportation, which can be considered as topology in abstract terms. Once cities are physically organized in terms of infrastructure, people interact with each other to form the values, which can be regarded as the meta-information of the cities. The topology and meta-information coevolve together as the cities are developed. In this study, we investigate the relationship between the topology and meta-information for a street network, which has aspects of both a complex network and planar graph. The degree of organization of a street structure determines the efficiency and productivity of the city in that they act as blood vessels to transport people, goods, and information. We analyze the topological aspect of a street network using centralities including the betweenness, closeness, straightness, and information. We classify the cities into several groups that share common meta-information based on the centrality, indicating that the topological factor of the street structure is closely related to meta-information through coevolution. We also obtain the coevolution in the planned cities using the regularity. Another footprint is the relation between the street segment length and the population, which shows the sublinear scaling., Comment: 12 pages, 5 figures

* Pusan Clean Coal Center, Dept. of Mechanical Engineering, Pusan Nat’l Univ.,** PLM team, Boiler RD Revised October 5, 2014 ; Accepted October 6, 2014)Key Words: Biomass(바이오매스), Activation Energy(활성화 에너지), Unburned Carbon(미연탄소), Blending Ratio(혼소율)초록: 본 연구에서는 발전소의 혼합연료로서 바이오매스인 호두껍질(Walnut Shell)에 대한 연소특성을 조사하기 위하여 열중량 분석기(TGA)와 분류층 반응기(DTR)를 이용하여 실험을 수행하였다. 바이오매스 WS는 기존 석탄과 비교하여 낮은 온도 영역에서 활발한 연소반응을 보였고, 활성화 에너지 또한 낮은 값을 가짐으로써 연소반응속도가 더욱 증가함을 확인할 수 있었다. 바이오매스 WS와 역청탄의 혼소에 있어서 고정층 분석에서는 혼소 영향이 선형적으로 나타나는 것을 확인할 수 있었다. 그렇지만 분류층 반응기에서는 바이오매스 혼소율을 5%증가 시에는 UBC가 감소하다가 이후에 다시 UBC가 증가하는 Non-additive 현상을 확인할 수 있었다. 이는 바이오매스의 급격한 연소로 주위에 산소 부족현상이 생겨 석탄의 연소가 지연되는 것을 보여준다. 이 현상을 해결하기 위하여 산소를 증가시켜주었을 때 더 높은 혼소율을 성취할 수 있음을 보여주었다.Abstract: Combustion characteristics for co-firing of biomass (Walnut Shell) as blending fuel in coal fired boiler have investigated using thermogravimetric analyser (TGA) and drop tube reactor (DTR). The results show that devolatilization and char combustion for WS occurs at lower temperature than those of existing coals and has lower activation energy value, which is resulting in higher reactivity. When the WS is blended with coal, TGA results show linear profiles depending on blending ratio for each fuel. However, DTR results exist the non-additive phenomena for blending of WS. As blending ratio of WS increase, the UBC decrease at BBR 5%, but the UBC rather increase from BBR 10% due to oxygen deficiency formed from rapid combustion of WS. This paper propose that fuel lean condition by oxygen rich lead to higher blending ratio of biomass by solving the oxygen deficiency condition.

Resolving ash-related problems such as fouling and slagging is crucial to the operation of a heat recovery steam generator (HRSG) in a power plant using heavy fuel oil (HFO). This paper presents numerical predictions of ash particle deposition using a model implemented with CFD code. The deposition model considers the force of gravity, elastic rebound, and adhesion forces acting at the moment of ash particle impact, which determine if the particle bounces off or stays on the surface and accumulates into a deposit. The 2D simulation results showed that ash deposition depends significantly on the particle size and velocity. The normal gravity force is a significant parameter that determines the position of deposition. The simulation results for ash deposition in an HFO-HRSG showed that ash deposits are highest (~34%) in the first and second rows, where the particles hit first, after which deposition decreases. However, ash deposits in the internal array increase again in the rear rows because rebounding particles decelerate and are deposited because of gravity, as confirmed by observations of actual deposit formation.

The purpose of this study was to investigate and compare the influence of torrefaction and an ashless process on the physical and chemical properties of pitch pine sawdust (PSD) and kenaf as types of woody and herbaceous biomass. The physicochemical properties of the materials pretreated by the ashless process with torrefaction including proximate and ultimate analysis, hydrophobicity, grindability, morphology, and structure were analyzed. The results showed that when ashless Kenaf was torrefied, the high heating rate and atomic ratios of O/C and H/C increased. The tendency of the torrefied, ashless Kenaf to absorb water decreased, and it became more hydrophobic (approximately 0% for the uptake rate of moisture). In addition, the grindability of the torrefied, ashless Kenaf was substantially improved compared to that of pretreated PSD. Brunauer&ndash, Emmett&ndash, Teller and scanning electron microscopy results showed that when Kenaf was pretreated, particles easily lost their fibrous structure and cracked as the number of macropores decreased. These results indicate that the herbaceous biomass of Kenaf, when pretreated with both torrefaction and the ashless process, exhibits improved physicochemical properties compared to the woody PSD.

For thermal power generation companies, the use of refined ash (defined as having a loss on ignition (LOI) of less than 6%) has not only made it suitable to produce lightweight aggregate, but has also introduced significant cost benefits through recycling. However, the ash having a high unburned carbon content (greater than 6%) cannot be recycled and still must be disposed of underground and by landfill. In this paper, an ash recycling and reburning technology was examined to improve ash usage in 500 MW pulverized coal (PC) boiler and simulation was performed to find the optimal conditions of ash supplying position and its amount that would not affect the boiler condition. Kinetic parameters for the reaction rate of ash were derived from a drop tube furnace (DTF) and adopted to accurately describe the characteristics of high LOI ash. In addition, the simulation results were then validated through real scale tests. Based on the simulation results, this paper suggest that the optimal supply condition for ash reburning is D burner sight window and 4 ton/h (with 0.01% of total air) in terms of combustion stability and burnout because the upper burner location has more sufficient oxidizer in the particle pathway as well as maximized mixing effect between coal and oxidizer. The real scale tests evidently represent that ash reburning can be method to make low LOI ash.

The use of low-rank coal (physical and combustion characteristics are different from those of high-rank coal) is rapidly expanding both in Korea and globally owing to economic constraints; fully understanding the impact of low-rank coal on combustion and emission processes is thus imperative. Observations from several studies on low-rank coal are reviewed in this paper; these studies were conducted at Pusan clean coal center (PC3) with entrained flow reactors (laminar flow reactor and drop tube furnace). This study provides several contributions to the analysis of the combustion and emission characteristics of low-rank coal. Such contributions include the establishment of a simplified prediction model of burning coal and analysis of the effect of particle size and environmental conditions. A numerical model that incorporates the chemical percolation devolatilization sub-model is also developed, and the effect of volatile matter and in-furnace blending method is investigated. Results obtained from analyzing low rank-coal and the developed models provide insights into the application of low-rank coal in power plants.

본 연구에서는 다양한 석탄 연구에 적용되고 있는 층류 반응기(LFR)를 이용하여 열분해와 연소 분위기에서 탄종에 따른 화염형상을 분석하였고, 휘발분 함량이 다른 두 석탄의 타르와 수트의 발생률을 구하였으며 이를 촤입자의 표면 적 및 표면 형상 변화와 함께 비교하였다. 본 연구에서 사용된 층류 반응기는 화염형상을 가시적으로 분석하기에 뛰어 나므로 석탄이 반응할 때 생성되는 수트 클라우드를 측정하여 그 형상 변화를 근거로 탈휘발의 종료 지점을 가정하였다. 휘발분 함량이 많은 Berau 탄은 Glencore A.P. 탄보다 수트 클라우드의 폭과 길이가 증가하였고, 연소 분위기에서 는 촤와 수트의 산화반응에 의하여 열분해 때보다 화염과 수트 클라우드의 길이가 짧아지면서 더 밝은 빛을 내었다. 포집높이 50 mm까지에서는 휘발분 함량이 많은 Berau 탄의 타르와 수트 발생률이 Glencore A.P. 탄보다 작았다. 이 는 석탄 연료의 조성 중 Berau 탄내에 상대적으로 높은 산소 성분의 함량과 OH- 같은 라디칼들로 인해 타르가 산화 되기 때문이다. 반면에, 50 mm 이후부터는 Berau 탄이 Glencore A.P. 탄보다 더 많은 타르와 수트의 발생률이 나타나 며 탄종간에 수트 발생률의 역전현상이 일어나는데 이는 촤입자 내부의 휘발물질과 탈휘발 과정에서 생성된 화염 속 의 잔여 타르 및 light gas 성분이 반응하여 수트를 발생시켰기 때문이다. 이를 통해서 석탄 내의 휘발분의 함량과 산소농도는 수트클라우드의 길이와 폭에 명확한 영향을 주며, 수트 발생률에 매우 중요한 인자라는 것을 확인할 수 있었다. SEM과 B.E.T.의 결과로부터 탈휘발이 종료된 후에도 촤 입자 내부의 잔존 휘발물들이 분출되면서 타르와 수트가 발생함을 확인할 수 있었고, 각 탄의 휘발분 함량과 기공의 발달 차이를 통해서 100 mm 이후에 나타난 타르와 수트의 발생률 역전 현상을 설명할 수 있었다.

The influence of coal blending methods, such as out-furnace (external or premixed) blending and in-furnace (initially nonmixed) blending, with different excess oxygen (highest, medium, and lowest s...

Mission Equipment Package(MEP) system is a collection of avionic components that are integrated to perform the mission of the Korean Utility Helicopter(KUH). Built In Test(BIT) reduces the need for skilled personnel and special test equipment, and reduces maintenance down-time of system. The increasing complexity of avionics equipments has resulted in an increased need to provide BIT functions. This paper describe the development and verification for the KUH MEP system BIT.