The fate of trace elements and bulk minerals in pulverized coal combustion in a power station

The behaviour of 15 trace elements (As, Ba, Cr, Cu, Mn, Mo, Nb, Ni, Pb, Rb, Sr, V, Y, Zn and Zr) and 10 major and minor elements (Al, Ca, Fe, K, Mg, Na, P, S, Si and Ti) in coal during combustion in a power station has been studied. Synchronized sampling of pulverized coal, bottom ash and fly ash was undertaken over a limited time period. Fly ash morphology was studied by SEM and the mineral composition was studied by EDX and XRD. Major, minor and trace elements were determined by XRF and AAS. Differences between the composition of the ashes of pulverized coal, bottom ashes and fly ashes have been observed. As, Cu, Mo, Pb and Zn were concentrated in the fly ash. The relationship between the composition of the fly ashes and their particle size was studied. Enrichment factors were calculated for each element in different size fractions. As the particle sizes of fly ash decrease, the concentrations of As, Cu, Mo, Pb and Zn increase. From the different composition of bottom ashes and fly ashes (and relying on the results of the characterization of the feed coal carried out in previous work), it can be assumed that pyrite and carbonates make a greater contribution to the furnace bottom ashes. Quartz carries through into the fly ash. This mineral is almost absent in the finest fractions, reflecting the absence of small quartz particles in the feed coal.     

Behavior of heavy metals in air pollution control devices of 2,400 kg/h municipal solid waste incinerator

We analyzed the behavior of heavy metals, such as Cd, Cr, Cu, Ni, Pb, Zn, and Hg, in air pollution control devices of a municipal solid waste incinerator. For this study, a municipal solid waste incinerator with a burning capacity of 2,400 kg/h was selected. A semi-dry reactor (SDR), fabric filter, and wet scrubber were installed to serve as air pollution control devices. Flue gas was sampled upstream and downstream of each air pollution control device to determine the heavy metal concentrations therein. Ash was collected from the furnace, boiler, SDR, and fabric filter to determine the heavy metal concentration in the ash produced by each device. Each heavy metal was found to have a different fate in the incinerator and air pollution control devices. Cd and Pb were mostly present in the fabric filter ash, whereas Cr, Cu, and Ni were most prevalent in the bottom ash of the furnace and boiler, and Zn was present in the bottom and fabric filter ash at a ratio of 7: 3. However, only a few percent of Hg was identified in the ash from the furnace, boiler, SDR, and fabric filter; the majority of Hg passed through the fabric filter and existed in an oxidized form. The wet scrubber exhibited high control efficiency for oxidized mercury, and the injection of commercial activated carbon at a rate of 0.2 g/Sm³ resulted in 93.2% mercury removal efficiency.     

煤灰基本特征及其微量元素的分布规律

对兖州矿区煤灰的化学成分、微量元素分布及灰的岩石学特征等方面进行了研究，并对灰产率与微量元素含量分布之间的关系进行了研究，同时对影响煤灰化学成分的因素方面进行了初步探讨。通过对兖州矿煤灰的采样分析可知,研究区煤灰由结晶物质、玻璃状物质和末燃尽有机质组成，其化学成分主要为SiO2,Al2O3,Fe2O3和CaO及少量的O3,P2O5,Na2O和TiO2,煤燃烧过程中微量元素发生了再分布，多数微量元素在煤灰中富集。同时它们在飞灰中富集的浓度明显高于底灰，即随着煤灰粒度的变小，它们在其中富集的浓度越高，其含量与煤灰的粒度成反比。微量元素Th,V,Zn,Cu,Pb与灰产率之间成正相关关系，而Cl与灰产率成负相关关系。     

Trace element behaviour in the Sasol-Lurgi MK IV FBDB gasifier. Part 2 - The semi-volatile elements: Cu, Mo, Ni and Zn

Gasification is a coal conversion process that could be considered to be more amenable with regards to environmental impact factors when compared to combustion, as it provides minimum direct emission to the atmosphere due to the opportunity to apply a series of gas cleaning processes. Emissions could be in the form of the well known trace elements labelled as toxic present in feed coal. Due to the minimal literature available on coal gasification when compared to coal combustion, a large amount of inference to coal combustion has been applied in discussing the partitioning behaviour of trace elements during coal utilization. Conducting mass balance calculations of trace elements around gasification processes have proven to be a challenging task. This is due to the limitation of the analytical techniques employed to quantify at the parts per million levels at which trace elements exist. The other challenge is analyzing for trace elements in all the different stream phases that occur after gasification. The availability of thermodynamic equilibrium packages i.e. Fact-Sage to perform high temperature calculations, at the same time handling all phases of material involved has simplified the challenges. Results obtained from such calculations have also proved to be close to reality, but have not been related to the fixed-bed counter-current gasification reactor operating on lump coal.The focus of this paper is to discuss more recent environmentally-focused research developments by Sasol, where trace element simulation and validation of model predictions have been undertaken for the gasification process. Fact-Sage thermodynamic equilibrium modelling was used to simulate the semi-volatile trace elements (Cu, Mo, Ni and Zn) gas phase and ash phase partitioning and speciation behaviour occurring in a fixed-bed pressurized gasifier. A Sasol-Lurgi Mark IV FBDB gasifier was mined via turn-out sampling in order to determine the trace element changes through the gasifier, results being used to validate the modelled results.The semi-volatile elements: Cu, Mo, Ni and Zn all showed limited (5% in the case of Zn) de-volatilization behaviour in the drying and pyrolysis zone of the fixed-bed gasifier. Predictions revealed that within the reduction zone of the fixed-bed gasifier that they are all highly volatile, producing gaseous species with an increase in temperature, varying in the order: Zn > Mo > Cu > Ni, which is contrary to what was found from the experimental results. This could imply that thermodynamic equilibrium conditions do not necessarily prevail in a fixed-bed gasifier operating on lump coal, since in reality mass and heat transfer limitations across coarse coal particles apply and the reactions are therefore more kinetically limited. Over-balances of Ni and Mo partitioning to the solid ash fraction, was found for the measured results. This anomaly was found to not be caused by erosion of the gasifier internals, but rather possibly be ascribed to accumulation and contamination caused by likely condensation and vaporisation of these species during the gasifier sampling campaign, as well as by the particle size reduction processes utilized prior to elemental analyses. Leaching tests conducted on the bottom ash collected from the gasifier have shown that the trace elements studied are firmly bound into the ash matrix and therefore would not be released during later disposal. The relative enrichment in trace element content observed for Ni and Mo within the gasifier should be further investigated.     

Trace elements (Mn,Cr, Pb,Se, Zn,Cd and Hg) in emissions from a pulverized coal boiler

The concentrations of seven trace elements (Mn, Cr, Pb, Se, Zn, Cd, Hg) in raw coal, bottom ash and fly ash were measured quantitatively in a 220 tons/h pulverized coal boiler. Factors affecting distribution of trace elements were investigated, including fly ash diameter, furnace temperature, oxygen concentration and trace elements' characteristics. Modified enrichment factors show more directly element enrichment in combustion products. The studied elements may be classified into three groups according to their emission features: Group 1: Hg, which is very volatile. Group 2: Pb, Zn, Cd, which are partially volatile. Group 3: Mn, which is hardly volatile. Se may be located between groups 1 and 2. Cr has properties of both Groups 1 and 3. The smaller the diameter of fly ash, the higher is the relative enrichment of trace elements (except Mn). Fly ash shows different adsorption mechanisms of trace elements and the volatilization of trace elements rises with furnace temperature. Relative enrichments of trace elements (except Mn and Cr) in fly ash are larger than that in bottom ash. Low oxygen concentration will not always improve the volatilization of trace elements. Pb forms chloride more easily than Cd during coal combustion.     

Trace element behaviour in the Sasol-Lurgi fixed-bed dry-bottom gasifier. Part 3 - The non-volatile elements: Ba, Co, Cr, Mn, and V

Coal contains most of the naturally occurring chemical elements in (at least) trace amounts, with specific elements and their concentrations dependent on the rank of the coal and its geological origins. The focus of this paper is to discuss more recent environmentally-focused research developments by Sasol, where trace element simulation and validation of model predictions have been undertaken for the gasification process operating on low-rank bituminous Highveld coal. A Sasol-Lurgi fixed-bed dry-bottom (FBDB) gasifier was mined via turn-out sampling in order to determine the trace element changes through the gasifier, results being used for comparison with Fact-Sage modelled data for the non-volatile trace elements Ba, Co, Cr, Mn and V.Considering the experimental error, good agreement between measured results and model predictions in terms of ash phase partitioning behaviour was obtained for Ba, Co, Mn and V. On the contrary, rather poor agreement between model predicted and measured results were obtained for Cr partitioning to the solid ash fraction, which yielded a large overbalance (outside of experimental error) in the case of the measured results. This anomaly was found to not be caused by erosion of the gasifier internals, but rather possibly be ascribed to accumulation and contamination caused by likely condensation and vaporisation of this species during the gasifier sampling campaign, as well as by the particle size reduction processes utilized prior to elemental analyses. When considering the predicted speciation behaviour of the elements studied, the model output in some cases needs to be treated with some caution when validating findings with standard text book data for the elements studied, but was found to correctly model the elemental ash phase partitioning behaviour during fixed-bed gasification. Leaching tests have been conducted on the bottom ash collected from the gasifier and results have shown that the trace elements studied are firmly bound into the ash matrix and therefore would not be released during later disposal. The relative enrichment in trace element content observed for Cr within the gasifier should be further investigated.     

Prediction of trace element volatility during co-combustion processes

The behaviour of some selected trace metals (Hg, Cd, As, Pb, Sb, Cr, Co, Cu, Mn, Ni and V) during co-combustion processes of bio-waste materials (sewage sludge, waste wood, refused derived fuel) and coal has been predicted by thermodynamic equilibrium calculations using the HSC-Chemistry 4.0 software. The influence of temperature, flue gas composition, trace element concentration and minor fly ash components on equilibrium composition was evaluated. For most of the elements, an increase in the HCl concentration favours the formation of gaseous species while increasing concentration of SO₂ in the gas composition enhances the formation of condensed species. Trace element interactions with minor fly ash components were predicted. From results obtained in this study it may be concluded that, from a thermodynamical point of view, the addition of a secondary fuel in combustion processes does not produce an increase in trace element emissions to the environment. Generally, trace elements are captured in ashes avoiding that these elements reach the stack.     

ICP-MS法测定注射用双黄连(冻干)无机阳离子的含量

注射用双黄连(冻干)样品经微波消解后,利用电感耦合等离子体质谱(ICP-MS)测定其中B、Al、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、As、Cd、Ba、Hg等15种微量元素的含量。结果表明,方法回收率为81.6%～96.3%,检出限为0.001～1.53 ng/g,方法快捷、准确、灵敏度高,可以用于注射用双黄连(冻干)的微量元素的测定,同时也进一步完善了注射用双黄连(冻干)无机元素分析,为其质量控制提供了参考依据。     

Thermodynamic equilibrium study of trace element transformation during underground coal gasification

In order to provide theoretical basis for gas cleaning and pollution control thermodynamic equilibrium calculations were performed to predict the partitioning of trace element species under special conditions for underground coal gasification, including both oxygen-steam gasification and air blown gasification under elevated pressures. The trace elements studied include As, Se, Pb, Ni, Cd, Cr, Sb. The results indicate, in the condition of large-section UCG process with oxygen-steam injection, all the elements studied present in the gas phase during gasification stage. Ni and Cr are hardly volatile and tend to condense below 1000 °C. Most of them will be enriched in bottom ash. As, Pb, Cd, Sb totally or partially occur in gas phase in underground gas cleaning system. In cold cleaning system, they exist in condensed phases and tend to be enriched in fly ash, which is beneficial to trace element removal. Se presents in gas phase in the form of H₂Se(g) even in ground cold gas cleaning system. The presence of potassium makes arsenic less volatile due to the formation of K₃AsO₄ and selenium is not affected. Also the amount of gaseous antimony chloride is reduced because of prior formation of alkali metal chloride. Pressure shows a remarkable effect on equilibrium partitioning of As, Se, Sb. With rising pressure, increasing quantities of hydrides of these trace elements are generated due to the enhancement of the reducing atmosphere. At the same time, the condensation points of all the trace elements sharply increase with pressure. It is found that for underground air blown gasification, the gaseous species of trace element sulfide can be easily formed, and the trace elements have lower condensation points than those for oxygen-steam gasification.     

燃煤电厂脱硫粉煤灰单颗粒研究及元素组成

研究电厂脱硫粉煤灰以粒径在3～45μm的颗粒为主,数量占80%以上,并多是表面光滑的球形微珠,主要的矿物成分是莫来石和石英,它的排放因子达到了2.45 kg/t。脱硫粉煤灰的元素组成选取了Mn、Zn、Cr、Cu、Pb、Ni、Cd七种元素,其中Mn在脱硫粉煤灰中的含量最高,但Mn元素的相对富集因子则小于Zn元素的相对富集因子,说明元素含量高其相对富集因子不一定大,还需要考虑电厂燃烧的煤种中的元素含量,从而来确定元素的富集行为。     

Volatility and chemistry of trace elements in a coal combustor

The volatility of 16 trace elements (TEs) (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Sn, Te, Tl, V, Zn) during coal combustion has been studied depending on the combustion conditions (reducing or oxidizing) and type of coal (high- or low-ash coal), together with their affinities for several active gaseous atoms: Cl, F, H, O, and S.

The elements can be divided into three groups according to their tendencies to appear either in the flue gases or in the fly ashes from a coal combustor:

Group 1: Hg and Tl, which are volatile and emitted almost totally in the vapor phase.

Group 2: As, Cd, Cu, Pb and Zn, which are vaporized at intermediate temperature and are emitted mostly in fly ashes.

Group 3: Co, Cr, Mn and V, which are hardly vaporized and so are equally distributed between bottom ashes and fly ashes. In addition, Sb, Sn, Se and Te may be located between Groups 1 and 2, and Ni between 2 and 3.

At 400 and 1200 K, the 16 TEs behave differently in competitive reactions with Cl, F, H, O and S in a coal combustor.     

Heavy metal content of bottom ashes from a fuel oil power plant and oil refinery in Cuba

Fly and bottom ashes from fuel oil power plants and oil refineries may contain hazardous trace elements, such as heavy metals, which have a negative impact on the environment with time due to potential leaching through acid rains and into groundwaters. This study provides levels of As, Cr, Cu, Hg, Mn, Ni, Pb, Ti, V and Zn of bottom ashes from a thermal power plant and an oil refinery placed in Cienfuegos Bay, Cuba. Trace elements were measured using X-ray fluorescence (XRF) with a SPECTOR X-LAB PRO 2000 system. High contents of Cr, Ni, Pb, Ti, V and Zn were found in the ashes, with values significantly higher than those reported in literature. According to Cuban regulations these ashes are classified as hazardous waste. For this reason we discuss some management alternatives.This study represents the first report of heavy metals in bottom ashes from power plants and oil refineries in Cuba.     

Volatile trace element behaviour in the Sasol fixed-bed dry-bottom (FBDB)™ gasifier treating coals of different rank

Trace element simulation and validation of model predictions for the elements Hg, As, Se, Cd and Pb have recently been undertaken for the Sasol^® FBDB™ gasification process operating on lump coal. The validation was conducted by interpolating the residual trace elements content remaining behind in the solid coal/char/ash fractions after sequential mining of a quenched commercial-scale gasifier operating on low rank grade C bituminous Highveld coal used for gasification in South Africa. This paper extends the research understanding by comparing the volatile trace element behaviour of these same elements, using the same gasification technology, but operating on North Dakota lignite. The focus will be on the behaviour of the volatile Class III trace elements: Hg, As, Se, Cd and Pb within the Sasol^® FBDB™ gasifier as function of coal rank. This study excludes the downstream gas cleaning partitioning and speciation behaviour of these elements.Findings indicate that although the feed concentration and mode of occurrence of these elements differ quite substantially between the two coal types studied, that the volatilization profiles of the elements are indeed quite similar; being within 0.1%-15% lower in the case of the lignite when compared to the bituminous coal. In both cases, Hg was found to be the most volatile and As the least; with the volatility order varying slightly for the metals Se, Cd and Pb for the two coal types. The differences observed in the trace element volatilization rate are supported by the temperature profile which was inferred from the reflectance of vitrinite (RoV) measurements of the dissected fuel bed material. The highly reactive lignite, is successfully gasified at a lower temperature than is the case for bituminous coal using the Sasol^® FBDB™ gasification process. Speciation predictions have earlier shown that: H₂ Se, CdS, PbS/Pb/PbCl, and AsH₃ species possibly exist in the gas phase. In reality, organically-associated trace elements will also be volatilized into the gas phase, but due to a lack of thermodynamic data for the lignite organo-metallic species at this stage only inorganic associations could be modelled.     

Prediction of the distribution of trace elements between the product streams of the Prenflo gasifier and comparison with reported data

The equilibrium distribution of the major, minor and trace elements in Pittsburgh No. 8 coal has been predicted for gasification under the conditions of the Prenflo gasifier using the FACT and MTDATA suites of predictive programs. The databases normally available with these programs have been supplemented with the MIRO-NPL oxide melt representation, a model of oxide melts from the field of geochemical modelling and representation of trace element solution in oxide melts based on the IMCC model. The results have been compared with observations at the Fürstenhausen Prenflo plant available in the literature. The gasifier is modelled as two regions: in the first the temperature is high (1400-2300 K) and the reacting mixture consists of the coal, carrier gas, added steam and oxygen. In the second region the equilibrium mixture from the first is quenched by addition of an equal amount of the cooled, dried product gas, then cooled in 10 K steps from 1073 to 473 K. The observed and predicted distributions of the elements are in general agreement. The elements may be grouped into those which are virtually immobile (Cr, Ni, Ba, Mn, V), somewhat mobile (Mo, Cu, Be), mobile (Sb, B) and almost totally mobilised (As, Cd, Pb, Tl, Sn, Zn) according to predictions, and this grouping is consistent with the experimental mobility as deduced from the relative abundances in slag, fly ash and filter cake. On cooling, arsenic is found to persist in the gas at 473 K at the highest fraction of the input level of any of the trace elements, which is consistent with observations.     

The fate of trace elements in fluidised bed combustion of sewage sludge and wood

Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highly volatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition). As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150 °C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag filter in the gas cleaning system in order to achieve good removal of toxic trace elements.     

西部煤中环境敏感性痕量元素的燃烧迁移行为

应用仪器中子活化( INAA)、电感耦合等离子体原子发射光谱( ICP- AES)和原子吸收光谱( AAS)对我国西北部五个电厂原煤、底灰和飞灰中环境敏感性痕量元素的含量进行了系统测定,通过不同电厂原煤与燃烧产物中痕量元素的含量变化特征,揭示了痕量元素在不同燃烧产物中的相对富集规律.以痕量元素在不同燃烧产物中的相对富集系数为评价标准,建立了燃烧产物中痕量元素的分配模型.结合痕量元素的原始赋存状态,总结了痕量元素燃烧的迁移富集机理和环境效应.     

Trace elements in Turkish biomass fuels: Ashes of wheat straw, olive bagasse and hazelnut shell

Ash contents of wheat straw, olive bagasse and hazelnut shells were 7.9%, 3.9%, 1.2%, respectively, which seemed to be within the average values of ash of biomass. The microstructure of ashes included smooth, polygonal, granular and molten drop structures. A large percentage of particles present in ashes are commonly ∼1-20 μm in size. SEM/EDS analyses performed on the major ash forming elements in different ashes indicated that Si, Ca, K and Mg and P were generally the most abundant species. Trace element levels in ash samples of various biomass types such as hazelnut shell, wheat straw, olive bagasse were analysed using ICP spectroscopy. The elements determined were some of those considered being of great environmental concern such as, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb. In all of the ashes studied Fe had the highest concentration among other trace elements, Mn was the second element that exhibited higher concentrations. The order of concentration of elements in the ashes from the highest to the lowest values was as follows: Fe > Mn > Zn > Cu > Ni > Cr > Pb > Co.     

Comparison of leachable trace element levels in coal gasifier ash with levels in power plant ash

The levels of 14 trace elements in leachates from three types of ash of a common origin coal were compared. The study was conducted over a one year period at the Kosovo plant in Obilic, Yugoslavia comparing coal gasifier ash with fly ash and bottom ash from a coal-fired power plant using lignite from the Dobro Solo mine. Results obtained indicate that levels of Sb, As, Be, Cr, Cu, Pb, Mo, Ni and Zn in gasifier ash leachate were similar to those in fly ash leachate. Barium levels in gasifier ash leachate averaged 2.7 times that in fly ash and selenium levels averaged 0.33 times. The average ratio for the total set was 0.99. The set average, relative to bottom ash, was 2.1 with the nickel ratio (R_{Ni = 0.31}) differing significantly from the average. Metal oxides, CaO, MgO, Na₂O, K₂O and MgO, in the Kosovo gasifier ash were found at levels similar to those in Kosovo fly ash, and except for K₂O, were approximately twice those in bottom ash. Concentration levels of all components showed relatively small variations averaging 50% of their mean annual concentration over the test period.     

Trace element behaviour in the Sasol-Lurgi MK IV FBDB gasifier. Part 1 - The volatile elements: Hg, As, Se, Cd and Pb

Coal-fired power and heat production are the largest single source of Hg in the atmosphere, and in March 2005, the US-EPA ruled regarding Hg reduction from coal utilization in the USA. Appropriate Hg pollution control of technology, as well as reductions in the uses of Hg and coal-containing Hg can readily reduce the releases of Hg from coal utilities. Integrated multi-pollutant (SOx, NOx, particulate matter and Hg) control technologies may be a cost-effective approach. Prior to considering mitigation technologies, it is necessary to understand the quantity of mercury in the feed coal, its mode of occurrence (i.e. mineral or organic associations), its partitioning behaviour during the process, and the volume and species in which it is being emitted via stacks. These factors have all been investigated up to the point of release for the Sasol gasification and steam-raising plants, including other trace elements.The focus of this paper is to discuss the more recent environmental research developments by Sasol, where trace element simulation and validation of model predictions have been undertaken for the Sasol-Lurgi gasification process operating on lump coal. Fact-Sage thermodynamic equilibrium modeling was used to simulate the trace elements: Hg, As, Se, Cd and Pb gas phase and ash phase partitioning and speciation behaviour occurring in a fixed-bed pressurised gasifier. A Sasol-Lurgi Mark IV (MK IV) fixed-bed dry bottom (FBDB) gasifier was mined via turn-out sampling in order to determine the trace element changes through the gasifier, findings being used to validate the modeled results. This paper will focus on the behaviour of the volatile Class I trace elements: Hg, As, Se, Cd and Pb within the Sasol-Lurgi MK IV FBDB gasifier as function of coal quality. This study excludes the downstream gas cleaning partitioning and speciation behaviour of these elements, which will form the basis of a future paper.Good agreement between model-predictions and measurements have been attained in this study, with the exception of As. Hg, Cd, Pb, As and Se were all found to be highly volatile, partitioning into the gas phase. Hg was found to be the most volatile element during fixed-bed gasification and is present in the gas phase in the form of elemental Hg (g). As, Se, Cd and Pb have lower volatilities when compared to Hg, and they vary in an order: Hg > Se > Cd > Pb > As. Speciation predictions showed that: Hg, AsH₃, H₂Se, PbSe, Cd, CdS, and PbS/Pb/PbCl, species could potentially exist in the raw gas phase.     

Analysis of fly ash heavy metal content and disposal in three thermal power plants in India

The study investigates the heavy metal content of fly ash and bottom ash from three major power plants in North India, using flame atomic absorption spectrometry. It also studies the prevalent disposal methods used at these sites. The ashes were analysed for the presence of Cr, Mn, Pb, Zn, Cu, Ni and Co and detectable levels of all were found in both fly ash and bottom ash. The concentrations of Cr and Zn were highest while Co concentration was less. The wet disposal method is used in two of the power plants (site 1 and site 3). Neither of the sites uses ash pond lining in the construction of the ash ponds, hence leaching of the heavy metals is possible. Site 2 has adopted 100% dry disposal system which allows better utilization but incurs additional costs. Better management practices, increased utilization and proper disposal practices need to be undertaken to minimize the adverse environmental impact.