Coal Feed Research Articles

Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash.

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3×107 - 3.4×108 and 6.8×106 - 2.2×108 particles/mg, with the average particle sizes of 111nm and 87nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.

Differentiation of Rare Earth Elements in Coal Combustion Products from the Handan Power Plant, Hebei Province, China

As a potential source of REY (rare earth elements and yttrium), coal and its products have attracted much attention. In this paper, we aimed to study the enrichment and differentiation of rare earth elements in fly ash with different particle sizes and promote the full recovery and utilization of rare earth elements in fly ash. Our objective was to focus on the REY concentration in feed coal and its combustion products from the Handan Power Plant. We particularly focused on the distribution of REY in relation to different particle sizes, as well as on the state of occurrence (affinity), by applying stepwise chemical extraction and performing examinations using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that the REY content is affected by the mineral composition of coal ash, and REY is more easily enriched in slag and fine ash than coarse ash. In general, the REY content decreased with the decrease in particle size in coarse ash, whereas the REY content increased with the decrease in particle size in fine ash. It was found that the concentration distribution of REY in solid combustion products is as follows: light REY (LREY) > medium REY (MREY) > heavy REY (HREY). This indicates that the enrichment of REY in solid coal products decreases with the increase in atomic number. The results also show that the occurrence state of REY in raw coal and coal ash undergoes no obvious change (residue state > organic/sulfide-bound state > iron–manganese-oxide-bound state > carbonate-bound state > exchangeable state).

Partitioning and Migration of Trace Elements during Coal Combustion in Two Coal-Fired Power Plants in Hefei City, Anhui Province, Eastern China

Coal-fired thermal power plants that meet the huge energy demand of China largely contribute to carbon emissions, environmental pollution, and human health issues. To investigate the impact of coal-fired power plants on the environment in the most developed region of eastern China, samples of feed coal, limestone, slag, fly ash, and flue gas desulfurization (FGD) gypsum were collected from two coal-fired power plants in Hefei City, Anhui Province, China. The concentrations of trace elements in these samples were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results show that the feed coal was slightly rich in V, Cr, Se, In, Sb, Pb, and Ga compared to common Chinese coal. Most trace elements were concentrated in fly ash, especially in the fine particles. Only Sc, Cr, Rb, and Ba were enriched in slag. The smaller the particle size of the fly ash, the higher the fraction of volatile trace elements. The elemental concentrations of old fly ash, which was precipitated in the well of the flue gas pipeline, did not show noticeable differences from fresh fly ash. In addition, the short-time storage of fly ash did not influence the trace elements. To understand the possibility of recovering rare earth elements from coal combustion by-products, the outlook coefficients (Coutl) of coal combustion by-products for the Wanneng (WN) and Tianyuan (TY) power plants were calculated, and they were found to be promising for rare earth elements plus yttrium (REY) recovery. However, as per the evaluation diagram of cut-off grade and Coutl values, all feed coal and its by-products from these two coal-fired power plants are projected to be ‘unpromising’. Therefore, the coal combustion by-products from the WN and TY coal-fired power plants were not candidates for REY recovery.

Напрямки удосконалення технологій конверсії вугілля в синтетичні рідкі палива

Modern technologies for producing synthetic liquid fuels from coal include pyrolysis, hydrogenation, gasification, followed by synthesis of the final products by the Fischer-Tropsch process or via methanol. In pyrolysis, liquid fuels are obtained as by-products and their yield is usually no more than a few percent. A negative feature of hydrogenation is the formation of a significant amount (up to 40 %) of small, unreactive residue, the efficient use of which poses a significant scientific and technical challenge. The gas produced by coal gasification always contains more carbon monoxide CO than hydrogen, which is due to the need to ensure the heat balance of the process. At the same time, to be used in chemical syntheses, the hydrogen content in the gas should be several times higher than CO. To ensure the required Н2:СО ratio, part of the carbon contained in the feed coal is oxidised to carbon dioxide in an exothermic process. This improves the ratio in the resulting synthesis gas, but leads to irrational consumption of some carbon, reduces gas yield and ultimately increases the consumption factor of raw materials for the final product and worsens the technical and economic performance of the production. Therefore, obtaining additional hydrogen to improve the composition of synthesis gas is relevant. Until recently, however, the main way to produce hydrogen in industry was through the conversion of natural gas methane, which is unacceptable in today’s environment. The production of hydrogen from coke oven gas, where its content is about 60 % (by volume), by short-cycle adsorption is also unpromising, due to the several-fold decrease in coke production in Ukraine and, consequently, the almost complete absence of free coke oven gas resources. Therefore, it is important to introduce other industrial methods of hydrogen production. Keywords coal, synthetic liquid fuels, gasification, Fischer-Tropsch synthesis, hydrogen. Corresponding author: V.V. Shulga, e-mail: ko@ukhin.org.ua

Dynamic Limit Based Model Predictive Control of a Flash Drying Unit

A model predictive controller was implemented at the flash drying unit of the Anglo American Platinum Polokwane smelter. The controller uses a mix of standard model predictive control technology and dynamic control limits (based on the rate of change of the hot gas generator average bed temperature) to improve temperature stability across the unit. The improved temperature control resulted in the ability to process 1.80% more concentrate through the unit without the need to increase coal feed, as well as reducing the number of coal feeder trips that result from high temperature events.

Computational Investigation on the Impact of Coal Feed Size in a Tangentially Fired Gasifier

ABSTRACT Using a validated comprehensive model, the effect of coal particle size on two-phase flow inside a tangentially fired, Mitsubishi Heavy Industry entrained-flow coal gasifier is investigated. It is observed that the length of the central recirculation zone (CRZ) formed in the gasifier flow increases with an increase in the mean size of the injected coal particles. The CRZ lengths are 5.6, 4.5 & 2.1 m, respectively, for the cases with particle size distributions (PSDs) having mass mean diameters of 80, 40 & 20 µm. The generic swirl number, , captures this impact of particle size on the CRZ length, whereas the conventional swirl number, , is unable to do so. The value of does not vary significantly over most of the gasifier’s constant diameter zone in each case simulated in the present work, thereby underlining the utility of this swirl number to characterize similarity in swirl dynamics. Further, the analysis of the impact of coal particle size on char conversion yields that the PSD with finer particles leads to higher conversion due to the better combustibility of finer particles.

Cadmium concentrations in coals and fly ashes from coal fired thermoelectric power plants in Bulgaria

The goal of the present study is to present new data regarding concentration and distribution of Cd in feed coals and fly ashes from seven Bulgarian coal fired thermoelectric power plans (TPPs). The study was performed on feed coals and fly ashes collected from Maritza East 2, Maritza East 3, Maritza 3, Republika, Bobov Dol, Varna and Russe TPPs. Bulk fly ash from Maritza East 2 and Maritza East 3 TPPs were obtained and fly ashes from each row of electrostatic precipitators (ESPs) of Maritza 3, Republika, Bobov Dol, Varna and Russe TPPs were also collected. Feed coals from bunkers were sampled at each TPPs. The Cd was determined by using ICP-MS. The present investigation shows that the concentration of Cd in studied coal and fly ashes from almost all TPPs is around the average or lower than Cd content in comparison with Clark values. The exceptions are the fly ashes from the 2-nd and 3-rd row of ESPs from Maritza 3 TPP, where up to 2.5 times higher Cd content was registered. This study shows that Cd concentration in fly ashes gradually increases from the 1st to 3rd and 5th-row of ESP from almost all sampled thermoelectric power plants, whence the conclusion that Cd content increases significantly and is mainly concentrated in the finest fly ash particles.

Selenium concentrations in coals and fly ashes from coal fired thermoelectric power plants in Bulgaria

The study present new data regarding concentration and distribution of Se in feed coals and fly ashes from seven Bulgarian coal fired thermoelectric power plant (TPPs). The investigation was performed on feed coals and fly ashes from the following TPPs – Maritza East 2, Maritza East 3, Maritza 3, Republika, Bobov Dol, Varna and Russe. Bulk fly ash from Maritza East 2 and Maritza East 3 TPPs and fly ash samples from each row of electrostatic precipitators (ESPs) from Republika, Bobov Dol, Varna and Russe TPPs were collected. Feed coals were also sampled from each TPPs. In order to determine Se concentration more precisely the samples were pre-treated before applying ICP-MS. As a result of the conducted research, the following regularities were established. Elevated amount of Se has been found in the lignite burned in Maritza East 2 and 3 TPPs, while in the bituminous coal burned in Varna and Russe TPPs Se is within the average and below average Se content. The low content of Se in fly ashes from almost all TPPs was observed, except Maritsa 3 TPP, where Se is from 4 to 7 times higher than Clarke value. It was found that the highest concentration of Se is in the finest fly ash fraction.

The Discrepancy between Coal Ash from Muffle, Circulating Fluidized Bed (CFB), and Pulverized Coal (PC) Furnaces, with a Focus on the Recovery of Iron and Rare Earth Elements

Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash.

Process optimization and thermodynamic analysis of autothermal coal chemical looping gasification industrial demonstration system

Chemical looping gasification (CLG) is an innovative clean coal conversion technology with industrial application prospects. The technical reliability of coal CLG (CCLG) in an autothermal state remains to be investigated. To clarify the process characteristics of an autothermal CCLG process, a CCLG autothermal operation system was established based on a CLG industrial demonstration unit. Process modeling of the CCLG reactor system and economizer, air preheater, and other heat exchange units was performed, to ensure autothermal operation of the global CCLG process. The optimal operating parameters of the system were established, the optimal heat exchange network was designed, and the source and distribution of thermodynamic irreversibility were clarified. The results showed that the optimal coal feed flow rate, air feed temperature and flue gas circulation temperature were 437.07 kg/h, 550 °C and 450 °C, respectively. The fuel reactor (FR) flue gas circulation was not conducive to system autothermal, resulting in weakened gasification performance. The optimal heat exchange plan allowed the system to operate without an external heat source. The thermodynamic irreversibility mainly originated from the redox process. The system heat efficiency was 81.63 %, the product exergy efficiency was 78.06 %, the total exergy efficiency was 41.10 %, and the total exergy destruction rate was 55.40 %. Additionally, the FR flue gas circulation caused high exergy loss, resulting in reduced system thermodynamic efficiency.

A New Approach for Failure Modes, Effects, and Criticality Analysis Using ExJ-PSI Model—A Case Study on Boiler System

Failure Modes, Effects, and Criticality Analysis are widely used to assess the failure modes of a system, along with their causes and effects. Several Multi-Criteria Decision-Making approaches have been developed to overcome the limitations of the traditional FMECA. In these approaches, several multiple criteria are considered to determine the criticality values and assign criticality ranks. In these developed approaches, only one expert can involve in criticality analysis. By incorporating several experts from design, manufacturing, and maintenance domains in the criticality analysis accuracy of the results can be improved. This paper proposes a new integrated Expert Judgment-based Preference Section Index (ExJ-PSI) model that combines MCDM approaches and integrates expert opinions. The proposed model is applied to a boiler system used in the textile industry. The results are compared with those obtained from the conventional FMECA and normalized median method. In the present study, the opinions of seven experts from various domains and organizations are discussed. To normalize the collected data, one scale is developed by considering four expert criteria, such as the experience of the expert, the number of boilers he is handling, the number of employees under his supervision, and the proficiency in the field. The proposed model is more effective and flexible in handling and analyzing data of complex configured systems consisting of many subsystems, components, and failure modes. The analysis reveals that the feed water pump, feed water pump motor, supply water temperature sensor, return water temperature sensor, header, and coal feed motor are some of the most critical components of the boiler system.

Prediction and minimization of NOx emission in a circulating fluidized bed combustor: Improvement of bed quality by optimizing cyclone performance and coal particle size

• Improvement of cyclone performance contributes to reducing the NO x emission. • Reducing coal particle size can decrease the NO x emission. • NO x emission may be further reduced by reducing the height of the coal inlet. • Effects of cyclone efficiency and coal size on combustion efficiency are discussed. • A comprehensive CFB mathematical model is applied to further analyze the mechanism. The NO x emission of circulating fluidized bed (CFB) boilers can be evidently reduced via optimization of the cyclone performance and the coal particle size, which has been proved in industrial practices, while there are few reasonable interpretations for these phenomena so far. In this paper, a comprehensive 1-dimensional/1.5-dimensional CFB mathematical model was applied to investigate the effect of these two important factors on NO x emission. Simulation results on two commercial CFB boilers indicate that increasing the cyclone efficiency and reducing the coal particle size can significantly decrease the average size of bed materials and increase the solid suspension density in the freeboard zone; namely, the bed quality is improved. The local gas–solid flow behaviors inside the CFB furnace will be accordingly changed, such as the increasing volume fraction of bubble phase in dense bed, shortening of secondary air penetration depth, enrichment of particles in the downward-flow annulus or clusters, etc. Consequently, the reducing atmosphere will be formed or enhanced in local areas, leading to the effective inhibition of NO x formation. Meanwhile, the increase in the bed inventory of fine char particles also facilitates the reduction of NO x . Moreover, if appropriately reducing the height of the coal inlet or feeding fine coal particles from the solid recycle system, the NO x emission may be further reduced due to the adjustment of the volatiles release pattern. In addition, the reduction of coal particle size can contribute to the increase in fuel combustion efficiency, while the unburned carbon content in fly/bottom ash may increase or decrease with the improvement of cyclone efficiency. This study further analyzes the influence of gas–solid flow characteristics on the chemical reaction process and provides a new solution to the low-cost pollutant emission control for CFB boilers.

Speciation, bioaccessibility and human health risk assessment of chromium in solid wastes from an ultra-low emission coal-fired power plant, China

Chromium (Cr) in solid wastes from ultra-low emission (ULE) coal-fired power plants (CFPPs) could engender adverse effects on environment and human health. Hence, solid waste samples containing bottom ash, fly ash, gypsum and sludge were collected from a typical ULE CFPP in China to study the distribution, speciation, bioaccessibility and human health risk of Cr. The results showed that Cr was depleted in gypsum, whereas significantly enriched in bottom ash, fly ash and sludge comparing with feed coal. The ratios of Cr(VI) to total Cr in solid wastes were relatively low, but the increase of flow fractions in Cr chemical binding forms implied the deterioration of environmental stability. Based on the in vitro simulated digestion methods of solubility bioavailability research consortium (SBRC) and physiologically based extraction test (PBET), the bioaccessibility of Cr in the gastric and intestinal phases reached the highest values in either gypsum or sludge. After incorporating bioaccessibility in human health risk assessment, the carcinogenic risk (CR) within acceptable limits of Cr in solid wastes to adults and children was concluded, with the non-carcinogenic hazard quotient (HQ) was all within the safety threshold. The Monte Carlo model was applied to evaluate the uncertainty analysis of human health risk assessment at 5% and 95% confidence interval, and the fitting results were consistent with the calculation results of the carcinogenic and non-carcinogenic risk for adults and children. This study is expected to provide insights for the integration of bioaccessibility into the health risk assessment of Cr in solid wastes from ULE CFPPs, thus is conducive to the disposal of solid wastes and human health protection.

Modeling Study on Non‐Uniform Lateral Distribution in Large‐Scale Circulating Fluidized Bed Boilers

AbstractWith the development of the circulating fluidized bed (CFB) combustion technology, the cross‐sectional area of the boiler furnace increases gradually, making the lateral non‐uniform distribution in the furnace more prominent. To investigate the flow field inhomogeneity in the furnace, a two‐dimensional mass balance model was established in this work, and the lateral solid concentration deviation was adopted to evaluate the degree of the flow field inhomogeneity. Afterwards, the effect of four factors on the lateral non‐uniform distribution was examined. It turned out that the lateral profile of the primary air flow rate had a much greater influence than that of the coal feeding rate.

Optical diagnostics on coal ignition and gas-phase combustion in co-firing ammonia with pulverized coal on a two-stage flat flame burner

Gradual substitution of coal with green ammonia is a practical approach for the coal power phasedown at a minimal cost of modification, but the ignition and gas-phase reaction during co-firing NH3 with coal remain largely unclear. In this work, we investigate the co-combustion behaviors of NH3 and a high-volatile coal on a two-stage flat flame burner. Remarkably, the post-flame oxygen mole fraction Xi,O2 of the inner stage can be manipulated to reproduce a proper reducing-to-oxidizing environment that coal particles experience in the practical combustor. We first reveal that, under certain values of Xi,O2 and NH3 co-firing energy ratios ENH3, the reaction intensity (manifested by OH-PLIF signals) in the NH3-coal flame is stronger than burning either pure coal or NH3. This synergetic effect originates from an NH3-combustion-induced enhancement of volatile release. We then propose a characteristic time scale τOH from the OH signals for the initiation of overall reactions in the system. In the case of Xi,O2=0, τOH monotonically increases with ENH3, while for Xi,O2=0.2, the trend transitions to a decreasing one. It can be interpreted by comparing τOH with the characteristic O2 diffusion time, coal particle heating time, and the coal pyrolysis time under different Xi,O2. Furthermore, the coal particle ignition in coal-NH3 flames can no longer be determined by visual images. Instead, we apply CH* chemiluminescence to identify the stages of coal particle ignition and volatile combustion in the NH3-coal flame. While NH3 addition has both positive (elevating temperatures & diluting coal particles) and negative (consuming O2) effects on coal ignition, the combined influence of ENH3 is marginal on coal ignition delay time. On the other hand, the volatile combustion time decreases linearly with ENH3, suggesting a pure effect of reduced coal feed rate.

Fine chemical speciation and environmental impact capacity of trace elements with different enrichment levels in coal

Enriched trace elements in coal are considered to have a high environmental impact, but the extent of the influence of the enrichment level is unclear. To study the chemical speciation and environmental behavior of trace elements in coal at different enrichment levels, representative coal samples from multiple provinces in China were collected, including bituminous coal I-L2 from Inner Mongolia with high concentrations of Be, Y, Zn, Tl, U, Er, and Yb, and 72-9 coal from Anhui enriched with Cu, Cd, Pb, V, and Zn. The chemical speciation of trace elements in coal was analyzed using a variety of techniques, including X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS), and sequential chemical extraction procedures. Cluster analysis was used for grouping the coal samples based on the enrichment coefficients of trace elements. Coal samples with similar genesis and in closer regions were more likely to be grouped. Metal carbonates and metal sulfate were observed in coals through XPS analysis. The main C species in coal were identified as phenolic C, carboxylic C, unsaturated C, and O-alkyl C/carbonyl C through NEXAFS. The amplitude variation of peaks for the fly ash was smaller than that for the feed coal, which showed that the structure of carbon became homogeneous after high-temperature combustion. It was difficult to identify the chemical speciation difference of trace elements with different enrichment degrees in coals through XPS and NEXAFS, but the results of the sequential chemical extraction could compensate. Several enriched trace elements in coal were relatively high in the chemical fractions (exchangeable, carbonates and monosulfides associated, or FeMn oxide bound) that were easy to extract and relatively low in the less insoluble chemical fractions (organic matter-bound, disulfides associated, or silicates associated), indicating that enriched trace elements in coal had higher environmental impact capacity.

Process study and CO2 emission reduction analysis of coal liquefaction residue fluidized bed pyrolysis

The direct coal liquefaction process usually produces a liquefaction residue of about 30% of its coal feed. The effective utilization of the coal liquefaction residue (CLR), which contains about 80% organic matter, is of great significance for improving the oil yield of the direct liquefaction process and reducing the amount of pollution emitted from this oil-containing organic solid waste. In this study, the CLR fluidized bed pyrolysis process was studied through a fluidized bed reactor pyrolysis experiment and steady-state thermal analysis. The characteristics of CLR were first analyzed, and then the pyrolysis experiment was conducted in a fluidized bed reactor system. The experiment results show that the oil yield is 34.81% at 540°C for an ash-free feedstock using a fluidized bed pyrolysis reactor. Based on the pyrolysis experimental data and the Aspen Plus software platform, the fluidized bed pyrolysis reactor, fractionation column, coke burner, gasifier, and other equipment were modeled to compare four different process schemes. CLR pyrolysis is an endothermic reaction, and its heat is usually supplied by coke combustion, which produces significant CO2 emissions. Case studies of the pyrolysis process were performed in detail in order to reduce CO2 emissions. Thermal efficiency, carbon efficiency, solid waste discharge, and CO2 emissions of the different schemes were compared, and a flexible fluidized pyrolysis (FFP) process coupled with water electrolysis was proposed. The introduction of green hydrogen and green oxygen to the process can realize near-complete utilization of carbon and hydrogen elements in the CLR and produce high-quality liquid fuels and syngas (for further chemical synthesis), and this new process can achieve almost near-zero CO2 emission in the entire unit. This process principle can also be applied to the CO2 emission reduction of organic solid waste pyrolysis, catalytic fluid cracking, fluid coking, and so on.

Proposal for an Improvement of Hard Coal Enrichment Accuracy in Systems with Secondary Beneficiation

There are various ways to improve the accuracy of hard coal enrichment. This article discusses the possibility of improving the accuracy of beneficiation by using the same enrichment machines located in the processing plant, introducing only the multiple (secondary) enrichment of raw coal feed. Secondary enrichment is a technology that allows for an improvement of the accuracy of mineral separation. The main advantage of this solution compared to that currently used is the lack of the necessity of introducing the crushing process. Secondary enrichment without crushing is a simple solution, and at the same time beneficial from the point of view of obtaining a commercial product with specific quantitative and qualitative parameters. This article shows the effect of this type of enrichment on the improvement of the shape of partition curves in an example of systems with two-product jigs. On the basis of the results of simulation studies, it was shown that the use of secondary enrichment results in obtaining a higher yield of concentrate of a given quality and thus increasing production value. The article uses the method of digital modelling of coal processing operations and technological systems, which should be treated as one of the possible methods of creating new knowledge, in particular knowledge about the behavior of concentrator group systems under different production assumptions and with different raw coal characteristics.

Minimizing mission cost for production system with unreliable storage

Considerable research efforts have recently been devoted to the reliability analysis and optimization of production systems with product storage. The existing models, however, failed to address a crucial design factor of cost. This paper makes contributions by modeling the expected mission cost (EMC) of an imperfect production system with storage subject to failures during uploading and downloading processes. To perform a successful mission, the system must meet a certain demand during a specified mission time. The EMC modeled encompasses operation and standby cost of the production unit, downloading and uploading cost of the storage, cost of losses associated with the failure of the production unit and storage, as well as penalty cost associated with the mission failure. The optimal EMC problem is formulated and solved, which determines the scheduled storage uploading time to minimize the EMC. A detailed case study of a coal feeding system is conducted to demonstrate the proposed probabilistic evaluation method and influences of different model parameters on the mission success probability and EMC as well as on the optimization solutions. The advantage of using the production storage is also illustrated through a comparison to a dual-production unit system without storage.

Radiation exposure for the population living around the coal-fired power plant complexes in Vietnam.

A coal-fired power plant's operation can release radioactive nuclides and radon gas into the environment, affecting the surrounding ecosystem. In this work, the collective effective dose due to the inhalation and the consumption of food containing the deposited radionuclides from the atmospheric release of the plants were evaluated. The results show that the radioactivity concentration in coal and fly ash samples depends on the originof feed coal. The distribution of Th and U radionuclides in the 6a1 dust coal and bituminous coal is different. In general, the collective effective dose for different organs due to radiation exposure from the atmospheric release of two surveyed CFPP complexes are lower than the corresponding value published by UNSCEAR.