Coal-burning Power Plants Research Articles

Notes on the occurrence of phosphate mineral relics and spheres (phosphospheres) in coal and biomass fly ash

The occurrence of phosphorus minerals in coal is common, and its study is mainly related with the metallurgical coke making.Large amounts of phosphorus are emitted from coal and biomass combustion units and less direct methods, such as carbon black, are used for tracking stationary combustion sources of phosphorus.During the study of fly ash from coal burning power plants in the state of Jharkand, India, using XRD, SEM/EDS, XRF, ICP-MS and leaching tests, it was found that P-bearing spheres have unique visual characteristics. Therefore, this study is thought to represent the first time that P-spheres in coal fly ash are described and herein named as “phosphospheres”. To complement their characterization and how they form other fly ash types such as Quercus suber cork and chicken litter fly ashes were also studied using SEM.Under the SEM the phosphospheres are brighter than the associated aluminosilicate spheres, they may show a spongy (or “punctuated”) structure, have a high P-peak in the EDS profile, and their cross-sections typically show a “pomegranate” texture resulting from immiscible silicate and phosphate melts and the segregation of the P when the glassy matrix is still in a fluid stage. Therefore, with these unique characteristics, phosphospheres are easily recognized, and may be used as a direct method for phosphorus tracking.

Characteristics of ferrospheres in fly ashes derived from Bokaro and Jharia (Jharkand, India) coals

Coal burning power plants in the state of Jharkand, India, are facing the problem of fly ash landfilling and their economic and environmental impact. However, fly ash may be used in civil engineering constructions, including as geoliners for municipal wastes landfilling, however in this case the groundwater contamination should be taken in consideration.In this work a combination of analytical techniques is used to study the nature, composition and potential environmental impact of Fe-bearing morphotypes (ferrospheres) in fly ash from thermal power plants fed with coals from Bokaro and Jharia coalfields (Jharkand, India).The results show that the feed coals are sulfur-poor and ash-rich, dominated by quartz, clays and minor portions of Fe-bearing carbonates, such as siderite. Pyrite was not identified. Although iron is present in the fly ashes in significant proportions (from 2.7wt.% to 4.5wt.%), equivalent to an Fe2O3 content ranging from 3.5wt.% to 5.8wt.%, mineral phases such as magnetite and hematite are only present in minor proportions, or below detection limits of the XRD analyses. Iron in the ferrospheres occurs as massive or dendritic crystals, or as finely dispersed crystals trapped inside a glassy aluminosilicate matrix resulting from the release of iron oxide plumes into the aluminosilicate melt. In addition to these phases, iron also occurs as a component of the glass that makes up most of the fly ash materials. Finally, the contaminant potential of groundwater by the fly ash iron is negligible.

PROMISING BUSINESS DIRECTION IS THE MARKETABLE PRODUCT OF ASH AND SLAG

The article considers the problem of processing ash and slag (ZS) from coal burning power plants in commercial products. There is a review of uses ZS, the overview is presented in a condensed form. The main attention is paid to the organization processing industry ZS abroad and in Russia. It is shown that processing ZS – promising business direction, which can be a source of investments for technical re-equipment of thermal power plants; financial source of coverage of environmental charges; to increase the profitability of multi-stage products of this example and of electricity and heat. It is noted that Russia needs a national coordinating structure designed to solve effectively turning this example into marketable products. Domestic and international experience show that the most acceptable is the system of dry fly ash of selection.

Application of eco-efficiency in a coal-burning power plant benefitting both the environment and citizens: Design of a ‘city water heating’ system

In this work, the concept ‘city water heating’ is introduced. It consists in bringing a significant amount of residual thermal energy (waste heat) from a power plant to a city by means of heating the potable water supplied to this city. For this purpose (i) a great amount of the city water has to be supplied through a single aqueduct, (ii) the aqueduct has to pass near the power station, and (iii) the water supplied to the city has to be colder than the cooling circuit water in the power plant.The hot water generated in the power plant cooling circuit (which is usually dissipated in the cooling tower) is conducted through a pipe to a place near the aqueduct and, by means of a heat exchanger, part of the cooling water heat is then transferred to the colder potable water supplied to the city. This has the great advantage of using the existing city water network itself to transport the heat to the houses.Based on data from a coal power plant located in Asturias (Northern Spain), two city water heating systems of different sizes are described and analysed. The following advantages were found: (i) energy saving and cost reduction for inhabitants, (ii) reduction in global warming and (iii) CO2 emissions reduction.

Mercury oxidation in catalysts used for selective reduction of NOx (SCR) in oxy-fuel combustion

Emissions of mercury (Hg) and their control are a well-known problem for conventional coal combustion power plants but they still represent a challenge for relatively new technologies such as the oxy-combustion. In oxy-fuel combustion systems it is important that Hg be in its oxidized form (Hg2+) because in the form of elemental mercury (Hg0), it can damage the CO2 compression units. In conventional air combustion some catalysts used in selective catalytic reduction (SCR) of NOx could also co-benefit Hg oxidation. This study evaluates the oxidation of Hg in the presence of several SCR catalysts under an oxy-combustion atmosphere focusing on the main differences with conventional air coal combustion. In the experimental conditions of this study, a higher mercury oxidation was observed in the CO2-enriched atmosphere due to the fact that in this atmosphere the conversion of NOx was lower, which resulted in a higher concentration of NO and NO2 free to homogeneously oxidize mercury. In oxy-combustion conditions the high amount of CO2 and H2O present may block the active sites for mercury adsorption. Moreover, the differences between the active sites of catalysts based on V/W/TiO2 and Fe/Zeolite with/without Mn as doping agent were eclipsed by the effect of the flue gas composition.

Efficiency of stepwise magnetic-chemical site assessment for fly ash derived heavy metal pollution

Previous works revealed a close relationship between magnetic susceptibility (MS) and heavy metal (HM) contents originating from industrial sources. However, despite general statements on the usefulness of magnetic mapping, the benefit of this procedure for geochemistry was not quantified yet. We present a study on fly ash pollution in soil around a coal-burning power plant complex and simulate a stepwise approach of magnetic pre-screening and subsequent targeted sampling for chemical analysis. The aim of this study is not to discuss correlations between MS and HM, but to show that a combined stepwise magnetic-chemical approach is the most efficient way for outlining HM contamination. In order to provide quantitative evidence, we explored map similarities of spatial HM distributions based on magnetochemical data and chemical data only. We determined 3-D triangular planes defined by categorized HM values at the sampling coordinates and calculated the average dihedral angle of the normal vectors as a similarity result. The study shows that the ‘Targeted’ HM map (selection of 30 sites based magnetic pre-screening) has a higher similarity with the ‘True’ Pollution HM map (85 sites) than HM maps resulting from site selections (30 sites) without using magnetic pre-screening information.

Assessing Douglas-Fir Seedling Establishment Using Two Modified Forestry Reclamation Approaches in the Pacific Northwest

The Forestry Reclamation Approach uses uncompacted, mounded spoils to reforest mined-land and has been successful in hardwood forests in the Appalachian region. A surface coalmine reclamation site in the Pacific Northwest was used to compare the site’s standard reclamation approach (Reference) with a modified version of the Forestry Reclamation Approach (FRA) along with a modified FRA treatment that also incorporated an amendment of bottom ash from the coal burning power plant on-site (FRA + Ash). Survival and growth were followed for three growing seasons in bareroot and container Douglas-fir seedlings. Soil characteristics and understory cover were also assessed. Considerable variation in microsite characteristics was observed in the study area. Container seedlings did not improve survival compared to bareroot seedlings. In the soil reclamation treatments, seedling survival was significantly higher in FRA + Ash treatments compared to FRA and Reference treatments at the end of the second growing season. Survival declined in each year of the study, but the order of treatment effectiveness did not change. Relativized growth increment was significantly higher in the FRA treatment compared to both the Reference and FRA + Ash treatments during the third growing season. Understory cover was established after three years, but varied substantially across the study area.

Use of coal ash as geopolymer binder and coarse aggregate in pervious concrete

Fly ash (FA) and bottom ash (BA) are wastes from coal combustion power plant. Due to its coarse and porous particle, BA is usually disposed of at landfill sites. While, as-received FA can be used as pozzolanic material and source material to produce geopolymer binder. This study focused on the use of FA as geopolymer binder and BA as coarse aggregate to produce pervious concrete. The effect of NaOH concentration, partial replacement of FA with ordinary Portland cement (OPC), and curing temperature on the properties of pervious geopolymer concrete (PGC) were investigated. The results showed that the strengths of PGC increased with both NaOH concentration and level of OPC replacement. The curing at elevated temperature (90°C) was a significant factor for the strength development. The PGCs containing BA had the thermal conductivity of 0.30–0.33W/mK, density of 1466–1502kg/m3, and compressive strength of 5.7–8.6MPa and are suited for use as an environment friendly concrete.

Syngas-based annex concepts for chemical energy storage and improving flexibility of pulverized coal combustion power plants

The increasing supply of fluctuating power from renewable sources not only in Germany requires improved capability for part load operation of conventional power plants in combination with electricity storage solutions to ensure the security of electricity supply.Different operational concepts are introduced to link a base load lignite-fired power plant with a small sized coal gasification and synthesis unit (annex unit). The annex unit comprises coal gasification, water electrolysis (optional), gas treatment and subsequent synthesis of storable fuels or chemicals (SNG, methanol). This unit is a power sink and chemical energy storage in times of renewable excess electricity, which reduces the overall net power output to the grid and lifetime-consuming start-ups and shutdowns of the power plant. In addition, the annex unit can also provide peak load in line with the actual demand. The concepts are modeled and evaluated regarding efficiency, CO2 emissions and the ability to reduce the minimal load of the total plant.The study was performed for an annex unit with 500MW(th) gasifier linked to a 2264MW(th) power plant. As a result, the annex concept with an additional 150MW(el) electrolysis unit can reduce the power output to the grid from 50% minimal load to 33–34% during “electricity storage” and can increase the power output to the grid from 100% nominal load to 152–154% during “peak load generation”. The improved flexibility of the annex concepts is accompanied by a reduction of the total efficiency (power plant and annex with re-combustion of the produced fuel) and a subsequent rise of the specific CO2 emissions. Thermal efficiencies of annex concepts without electrolysis result in 63.1% for SNG and 55.5% for methanol.The capital expenditure of an annex unit (without electrolysis) is 21% lower than for an equally sized stand-alone unit because of taking advantage of the shared infrastructure of the coupled power plant.Despite the growing share of green power there will be a significant demand for base load. The introduced annex concepts can contribute to flexibility and economics of existing conventional coal-fired power plants.

Use of fly ash in production of light-weight building bricks

Fly ash is one of the coal combustion products (CCPs) of coal burning power plants and it contains substantial amounts of potentially harmful constituents to the environment. It is known that nearly 600 million tons of fly ash is produced in the world per-annum. In Turkey, the annual production of fly ash is, on average, 13 million tons and only a small amount of this is utilized. This study examines the production of light-weight, high thermal insulating bricks made out of the fly ash and lime. Cylindrical brick samples were produced through steam curing of Seyitömer thermal power plant fly ash and lime mixtures in an autoclave in order to determine the optimum conditions for mechanically sound bricks. Subsequently, at the optimum conditions determined, real-size bricks were produced and subjected to standard tests. The findings of this paper suggest that fly ash/lime bricks can be an alternative product to aerated cellular concrete.

Effect of Strontium on the Catalytic Activity and Physicochemical Properties of Ru/Mn Catalysts for CO<sub>2</sub> Methanation Reaction

The recycling technology by the catalytic conversion offers a very promising technique for reducing greenhouse CO2 gas from flue gases of coal burning power plant by converting the carbon dioxide gas to methane. The methane produced from the reaction can be used as other fuel to run turbine for electricity generation. Therefore, the strontia based catalysts was prepared by impregnated with RuMn/Al2O3 catalyst and then calcined at 1000°C for 5 hour. Strontia catalyst is an effective material because of its highly basic properties which could enhance carbon dioxide adsorption and chemisorption on the catalyst surface but not been widely explored. The result obtained revealed that the addition of Sr to RuMn/Al2O3 as based catalyst had increased the catalytic activity and found to be more active for promoting the CO2 methanation reaction. Under reducing pretreatment at 300°C, the activity of CO2 conversion increased about 30.98% which is from 50.45% over RuMn-65/Al2O3 catalyst to 73.10% over RuMnSr-65/Al2O3 catalyst with 40% of methane yielded at reaction temperature of 210°C. The Sr addition did not modify the crystalline structure of the catalyst but gave higher surface area, smaller particle size and high metal dispersion as well as increased the degree of reduction and CO chemisorption.

A Comment on Metzger and Zaring: The Quicksilver Problem

I INTRODUCTION It is a pleasure to comment on the fine institutional studies in this issue by Gillian Metzger and David Zaring. (1) Professor Metzger explores the many ways in which financial regulation, as reflected in the regulatory functions of the Federal Reserve (the Fed), differs from mainstream administrative law, as represented by the Environmental Protection Agency (EPA). She describes the historical roots of the divergence, explains how it has persisted over time, and offers some intriguing thoughts about the possibilities for convergence in the future. Professor Zaring paints a fascinating portrait of the Federal Open Market Committee (FOMC), the entity within the Fed that determines national monetary policy. Drawing upon transcripts of FOMC meetings during the Alan Greenspan era, he concludes that internal custom provides a more important constraint on the Committee's behavior than formal administrative law does. A common theme of both the Metzger and Zaring studies is that financial regulators differ from ordinary administrative agencies on the familiar dimensions of accountability and transparency. Both the Fed and the FOMC are highly independent, effectively immune from presidential oversight, and largely free to ignore Congress because they are funded out of their own operations. They operate under vague statutory mandates that confer enormous discretion. There is no public participation in the Fed's oversight of banks or the FOMC's setting of monetary policy. As Professor Zaring notes, judicial review is almost completely absent. (2) Moreover, most of the critical functions performed by the Fed and the FOMC are shrouded in secrecy. Meetings of the Fed and the FOMC are closed to the public, the results of bank examinations are confidential, the monetary policy directives of the FOMC are not disclosed until they are no longer in effect, and the transcripts of these meetings remain under wraps for five years. What is missing from both studies is the identification of a key attribute of financial regulation that helps explain these departures from traditional administrative law. Financial regulation concerns activity that has very low exit costs. What is being regulated is money, money substitutes (like money market funds and short-term repurchase agreements), and other financial assets, such as bonds, stocks, and derivatives. Financial regulation is concerned with the ultimate in slippery stuff; financial instruments are like quicksilver that can wiggle out of your grasp at a moment's notice. (3) This attribute exerts a pervasive influence on the nature of financial regulation, rendering it difficult in many circumstances to adopt ordinary norms of administrative law. There seems to be no prospect of this changing in the foreseeable future, and therefore it is unlikely that a complete convergence between financial regulation and other forms of administrative law will occur. II EXIT COSTS AND THE NATURE OF REGULATION Ordinary administrative law developed in the context of activities that either had no exit option or very high exit costs. Railroads are the pioneering example, as they were the subject of the first major federal regulatory statute--the Interstate Commerce Act. (4) Railroads have large fixed costs and are literally nailed to the ground. The only way to exit from the industry is to go bankrupt. Other public utilities, like electric and gas distribution companies, share similar features. Professor Metzger takes EPA rulemaking as the paradigm of modern administrative law, which reflects the thinking of most administrative law scholars. (5) EPA regulations, no less than rate regulations by the Interstate Commerce Commission and public-service commission orders, target facilities that have high fixed costs and little ability to relocate in the short run, such as coal-burning power plants and automobile assembly and distribution facilities. …

Kicking the Oil Addiction

Kicking the Oil Addiction

Mercury Retention by Fly Ashes from Oxy-fuel Processes

The objective of this study is to determine the mechanism of mercury retention in fly ashes, the main solid waste from coal combustion power plants, and to evaluate the interactions between the type of mercury and fly ashes. The work was based on the results of mercury speciation in the gas and the solid fly ash before and after mercury retention. The identification of the mercury species in the gas was performed using previously validated methods, but the speciation of the mercury retained in the fly ashes was carried out using a mercury temperature-programmed desorption technique (HgTPD) still under development. The fly ashes were sampled from conventional coal combustion in air and oxy-combustion power plants. The main mercury species identified in the raw fly ashes and after they were subjected to an oxy-combustion atmosphere were mercury bound to organic matter and HgS, the ratio of these species depending on the characteristics of the ashes. The results obtained indicate that fly ashes are the route of mercury oxidation in an oxy-combustion atmosphere, although they hardly retain any mercury unless the unburned carbon content is high. HgTPD analysis shows that the main mechanism for mercury retention in the fly ashes is via the carbon matter.

Mineralizable carbon in biosolids/fly ash/sugar beet lime treated soil under field conditions

Fly ash (FA) from coal burning power plants is generally used for biosolids stabilization to reduce numbers of pathogens and availabilities of heavy metals contained in biosolids. The objective of this study was to determine the suitability of sugar beet lime (SBL) from sugar beet processing factories as fly ash substitute. Post-harvest soil samples were employed in a 180d incubation study for each of two year field experiments. A first order logistic model was used to estimate sizes of labile and delayed logistic C pools. All treatments with one exception significantly (P<0.05) reduced plant biomass compared to the mineral fertilization treatment in the first year under maximum water stress conditions. However, biosolids (7.5Mgha−1), biosolids+FA (7.5Mgha−1), and biosolids+SBL (7.5Mgha−1) significantly (P<0.05) raised plant biomass compared to the mineral fertilization in the second year under minimum water stress. Applications of biosolids together with either FA (7.5 and 15Mgha−1) or SBL (7.5 and 15Mgha−1) significantly (P<0.05) increased sizes of labile and delayed logistic pools in the first year, but they did not in the second year. The sizes of potentially mineralizable carbon pools were bigger in the second year probably due to increased accumulation of wheat root biomass originating from enhanced soil water regime. Carbon mineralization in soils treated with biosolid/fly ash/sugar beet lime at agronomic application rates depends also on plant biomass accumulation, which affects total root biomass and rhizodeposition. Sugar beet lime containing 70% CaO and 5% organic carbon seems to be a good biosolids stabilizing agent compared to fly ash in terms of plant biomass accumulation and mineralizable carbon.

Mathematical simulation of the ignition of coal particles in airflow

A numerical study of interrelated heat and mass transfer processes with consideration for the thermal reaction of the organic matter of fuel on the gas-phase ignition of coal particles with sizes from 50 to 500 μm in airflow was performed. Minimum air temperatures at which the ignition of volatile substances occurs in an oxidizing atmosphere were determined. The calculated values are lower than the level of maximum permissible temperatures in the individual sections of systems for the preparation of pulverized coal at coal-burning power plants.

Single and binary adsorption of Cd (II) and Zn (II) ions from aqueous solutions onto bottom ash

Bottom ash, a waste obtained from coal-burning power plant, was used as a low cost adsorbent for the removal of Cd (II) and Zn (II) ions from single and binary systems in batch experiments. The results of adsorption capacity showed that bottom ash could be considered as a potential adsorbent. The uptake of Zn (II) ion was greater than that of Cd (II) ion. For single adsorption, based on the correlation coefficient (R2) values, both Langmuir and Freundlich isotherms suitably described the adsorption equilibrium data in the initial metal ion concentration range of 10–50 mg/L. The multicomponent isotherms, including the extended Langmuir and IAST-Freundlich isotherms, were used to predict the binary adsorption of Cd (II) and Zn (II) ions. Furthermore, the appropriate multicomponent isotherm was investigated by minimizing the average relative error (ARE) function. It should be confirmed that the extended Langmuir isotherm fitted the binary adsorption equilibrium data satisfactorily.

Temperature programmed desorption as a tool for the identification of mercury fate in wet-desulphurization systems

In this study a thermal desorption procedure (HgTPD) was used to identify mercury species in samples of gypsum obtained from wet flue gas desulphurization plants (WFGD). Gypsum from industrial coal combustion power plants and gypsum from a laboratory device that simulates mercury retention in the WFGD process were studied. It was concluded that mercury sulphide (HgS) is the mercury species present in WFGD gypsums unless an additive is used. Mercury speciation in this kind of residue can contribute to a better understanding of the reaction and adsorption behaviour of mercury species in the WFGD process and provide a deeper knowledge of the environmental impact caused by the disposal or reuse of these Hg-containing residues.

Influence of Bottom Ash Replacements as Fine Aggregate on the Property of Cellular Concrete with Various Foam Contents

This research focuses on evaluating the feasibility of utilizing bottom ash from coal burning power plants as a fine aggregate in cellular concrete with various foam contents. Flows of all mixtures were controlled within 45 ± 5% and used foam content at 30%, 40%, 50%, 60%, and 70% by volume of mixture. Bottom ash from Mae Moh power plant in Thailand was used to replace river sand at the rates of 0%, 25%, 50%, 75%, and 100% by volume of sand. Compressive strength, water absorption, and density of cellular concretes were determined at the ages of 7, 14, and 28 days. Nonlinear regression technique was developed to construct the mathematical models for predicting the compressive strength, water absorption, and density of cellular concrete. The results revealed that the density of cellular concrete decreased while the water absorption increased with an increase in replacement level of bottom ash. From the experimental results, it can be concluded that bottom ash can be used as fine aggregate in the cellular concrete. In addition, the nonlinear regression models give very high degree of accuracy (R2&gt;0.99).

Prediction of NOx Emission from Coal Fired Power Plant Based on Real-Time Model Updates and Output Bias Update

In order to deal with the nonlinear varying behavior of NOx emissions for long term predictions, a real-time recursively updating model is indispensable. In this paper, new recursively updating models are proposed to predict NOx emissions. The proposed real-time models are equipped with an initial LSSVM model and subsequent updating methods to adapt the models with recent changes to process data. The updating methods include solo Least Squares Support Vector Machines (LSSVM) update, solo output bias update, and the combination of these two termed as the LSSVM-Scheme. These models are applied to NOx emission process data from a coal combustion power plant in Korea. Prediction results obtained from the proposed real-time LSSVM models are compared with their counterpart real-time PLS models, which reveal that real-time LSSVM models outperform their counterpart real-time PLS models. Among other models developed in this work, LSSVM-Scheme and solo output bias update based on LSSVM predicts NOx emissions robustly for a long passage of time with the highest accuracy.