Boiler Flue Gas Research Articles

Experimental investigation of a liquid desiccant cooling system driven by flue gas waste heat of a biomass boiler

This paper presents the preliminary experimental results of a liquid desiccant cooling system driven by the flue gas waste heat of a biomass boiler. The desiccant cooling system is mainly composed of a regenerator, a dehumidifier and an evaporative cooler. The flue gas waste heat is applied to the regenerator to regenerate the desiccant solution. The environmentally friendly liquid desiccant potassium formate (HCOOK) solution is used in the dehumidifier for air dehumidification due to its less corrosion, lower cost, lower density and lower viscosity. A cross-flow heat and mass exchanger for indirect evaporative cooling is adopted in the evaporative cooler to ensure that product air meets the indoor air quality and thermal comfort standard. The desiccant cooling system operated in Autumn days in Nottingham was found to be able to decrease the air temperature by 4°C and reach a cooling capacity of up to 2381 W. Moreover, the dehumidifier is able to reduce the relative humidity of the humid air by 13%. The biomass boiler's flue gas waste heat extracted and supplied to the regenerator was found to be 554 W, which is insufficient to regenerate the dilute liquid desiccant solution under current experimental conditions. To obtain sufficient heat to regenerate the liquid desiccant, the existing first-of-its-kind concentric helical coil heat exchanger extracting the waste heat of the boiler needs to be redesigned, and, in particular, the concentric helical coils of the heat exchanger need to be placed inside the chimney to enhance the waste heat extraction.

Modelling of particles deposition in an environment relevant to solid fuel boilers

The paper reports on investigation of some issues in computational modelling of deposition of solid particles on oblique walls washed by a diluted gas-particle turbulent flow. The models and approaches considered are relevant to predicting the dynamics of deposit formation (the growth rate and the shape of the deposit) on tubes and bounding walls of superheaters, heat exchangers and other equipment in which the boiler flue gas is used or processed. This application, involving relatively large particles (over 8 microns) imposes some specific constraints, but also eliminates the need to consider phenomena relevant only to smaller (sub-micron and nano-) particles. Nevertheless, a practically useful model should account for a variety of phenomena. The paper focuses on analysing the performance of a model for deposit growth and effects of temperature on deposit formation for different particle sizes while using Single Particle Tracking (SPT) for modelling the particle dispersion in the fluid flow. Specifically, the particle-sticking probability approach controlled by temperature has been evaluated for three particle sizes in the test case of deposit formation on a cylindrical probe in cross flow, compared with prior simulation results of Zhou et al. (Fuel, 86, 1519–1533, 2007).

Simulation of carbon dioxide recovery from flue gases in aqueous 2-amino-2-methyl-1-propanol solutions

The modeling and simulation of the absorption of dilute CO 2 into falling film of aqueous solutions of a sterically hindered amine, 2-amino-2-methyl-1-propanol (AMP), was carried out using COMSOL Multiphysics Version 3.3. The operating cases were divided in gas turbine cases (CO 2 3 mol%) and boiler cases (CO 2 8.5 mol%). The key operating parameters for the studied cases are CO 2 partial pressure, operating temperature and amine concentration in the aqueous solution. The simulation focused on: (1) CO 2 loading in aqueous AMP solution; (2) contact time to reach equilibrium; (3) pH of rich AMP aqueous solution; and (4) total required interfacial area/circulated AMP aqueous solution. The modeling was validated by comparison with experimental results for CO 2 loading available in the literature, with deviations below 4%. High operating pressure, low operating temperature, and low AMP aqueous concentration increase CO 2 loading. The compression need for gas turbine flue gas was found to be higher than for boiler flue gas. The pH of rich AMP aqueous solution at maximum CO 2 loading was 8. The needed contact time to reach equilibrium decreases with temperature increases. The results were utilized to estimate the lower bound to the size of structured packed columns to absorb CO 2 from flue gases.

Destruction and formation of PCDD/Fs in a fluidised bed combustor co-incinerating automotive shredder residue with refuse derived fuel and wastewater treatment sludge

During an eight day trial automotive shredder residue (ASR) was added to the usual waste feed of a Fluidized Bed Combustor (FBC) for waste-to-energy conversion; the input waste mix consisted of 25% ASR, 25% refuse-derived fuel (RDF) and 50% wastewater treatment (WWT) sludge. All inputs and outputs were sampled and the concentration of the 17 PCDD/Fs with TEF-values was determined in order to obtain “PCDD/F fingerprints”. The ASR contained approximately 9000ng PCDD/Fs/kgDW, six times more than the RDF and 10 times more than the WWT sludge. The fingerprint of ASR and RDF was dominated by HpCDD and OCDD, which accounted for 90% of the total PDDD/F content, whereas the WWT sludge contained relatively more HpCDFs and OCDF (together 70%). The flue gas cleaning residue (FGCR) and fly and boiler ash contained approximately 30,000 and 2500ng PCDD/Fs/kgDW, respectively. The fingerprints of these outputs were also dominated by HpCDFs and OCDF. The bottom ash contained only OCDD and OCDF, in total 8ng PCDD/Fs/kgDW. From the comparison of the bottom ash fingerprints with the fingerprints of the other output fractions and of the inputs, it could be concluded that the PCDD/Fs in the waste were destroyed and new PCDD/Fs were formed in the post combustion process by de novo synthesis. During the ASR-co-incineration, the PCDD/F congener concentrations in the fly and boiler ash, FGCR and flue gas were 1.25–10 times higher compared to the same output fractions generated during incineration of the usual waste mix (70% RDF and 30% WWT sludge). The concentration of the higher chlorinated PCDD/Fs increased most. As these congeners have the lowest TEF-factors, the total PCDD/F output, expressed in kg TEQ/year, of the FBC did not increase significantly when ASR was co-incinerated. Due to the relatively high copper levels in the ASR, the copper concentrations in the FBCs outputs increased. As copper catalysis the de novo syntheses, this could explain the increase in PCDD/F concentrations in these outputs.

EMISSION OF FINE PARTICULATES FROM OIL SHALE FIRED LARGE BOILERS

Emissions of fine particulates of grade PM2.5 and PM10 from different oil shale (OS) power plant (PP) boilers were studied. Pulverized (PF) and circulating fluidized-bed (CFB) boilers burning oil shale, biomass and retort gas were investigated. Particle emissions from OS boilers were found to be very fine. Over 90% of emitted particulate matter was in the size range of PM10 and 40-60% under the size of 2.5 μm. Distribution of fine particles by size was found to be depending on OS firing mode (PF or CFB). At CFB firing mode the share of the finest fraction PM2.5 was higher than that at PF firing mode. The distribution varied at the same type of different PF boilers, depending on the efficiency of boiler flue gas cleaning system and value of total suspended particulates’ emission (TSP).

New energy efficient processes and improvements for flue gas CO2 capture

Abstract The Kansai Electric Power Co., Inc. (KEPCO) has developed energy efficient chemical absorbents and economical processes which aim to reduce the cost of CO 2 capture, in collaboration with Mitsubishi Heavy Industries, Ltd. (MHI). Together the companies have been developing and critically testing high efficiency, economical absorbents according to the latest absorbent development procedures and process simulation for CO 2 capture processes. This work has been ongoing since 1991, using several Japan based R&D facilities and a pilot plant, used to verify improvements, located at Nanko Power Station in Osaka, Japan. Following significant testing of a range of absorbents in the mid 1990s, KS-1 TM , KS-2 and KS-3 were developed. Based on subsequent rigorous evaluation of the three solvents, KS-1 TM was selected for commercialization because of its overall technical and economical merits. During long-term pilot plant testing, the improved absorbents demonstrated superior performance in relation to the regeneration energy requirements leading to the following results: 2.94 MJlkg- CO 2 in combination with KS-1 TM ” and the Kansai Mitsubishi Carbon Dioxide Recovery (KM-CDR Process TM ) commercial process. In addition, practical, commercially applicable improved absorbent properties such as low corrosiveness and low solvent consumption were also confirmed. KEPCO and MHI continue development work in this area and the current status is summarized as follows: The highly successful R&D phase has led to the commercial deployment of CO 2 capture technology and seven (7) commercial CO 2 capture plants are currently under operation, with a maximum CO 2 capture capacity of 450 metric tons per day (tpd). These commercial plants are deployed in the chemical and fertilizer industry, where the operational performance is assisting in the improved development of R&D concepts. Two (2) further commercial plants are under construction, with commissioning expected in Q3 2010. For further cost reductions in relation to CO 2 capture, recent work has focused on developing new energy efficient chemical absorbents and processes. Following modifications to the Nanko CO 2 capture pilot plant a new “Energy Saving Process”, was developed, which leads to a greater than 10% steam consumption reduction over the MHI conventional process using KS-1 TM absorbent. Additionally the same reduced steam consumption was recorded for tests using the KS-1 TM absorbent. A thermal energy requirement of less than 2.5 MJ/kg- CO 2 in combination with KS-1 TM and the “New Energy Efficient Process” has been confirmed under the optimum operation condition of the CO 2 capture process. In addition to select new absorbents which feature the best profile and fit to the actual operating condition, KEPCO and MHI have intensively evaluated vapor-liquid equilibrium (VLE) and reaction kinetics for a range of newly developed absorbents and their performance is presented in this paper. The above data was obtained using the Nanko CO 2 capture pilot plant which operates under a natural gas fired boiler condition and we expect that the thermal energy requirement of coal fired boiler flue gas (with greater CO 2 concentration condition) will be further reduced. KEPCO and MHI are continuing pilot tests for the “Energy Saving Process”, leading to the application of this new process in commercial CO 2 capture plant design. This paper introduces and presents the current status of the KEPCO & MHI CO 2 capture technology and concepts for future energy reduction improvements. The paper will also include test results in relation to newly developed absorbents, and the “New Energy Efficient Process”, which have enhanced the performance and reduced the associated energy penalty of the CO 2 capture process. KEPCO and MHI are continuing the development of efficient absorbents and optimized processes, thus helping to facilitate the future wide scale deployment of CO 2 capture technology as an effective counter measure against global warming.

A thermodynamic study of the gaseous potassium chemistry in the convection sections of biomass fired boilers

AbstractThermodynamic calculations of the gaseous potassium species in boiler flue gases are presented. Results show that if the K(g)/Cl(g) molar ratio is still higher than 1 after the K2SO4(s) aerosol formation at high gas temperatures, the excess potassium is in the form of KOH(g). K(g)/Cl(g) molar ratios at the inlet of the convection section for biomass fired boilers were estimated from the chemical analysis of the fuels, with the assumption that all the fuel sulfur had reacted to K2SO4(s) aerosols before the inlet of the convection section. 0–100% conversion of fuel alkali to vaporized alkali was calculated. Generally, if the conversion was more than 60%, the calculated ratios for biomass fuels were higher than 1. Furthermore, due to the thermodynamic instability of K2CO3(g), it is likely that the formation of K2CO3(s) on the heat transfer surfaces follows a heterogeneous route where KOH(l,s) is transformed to K2CO3(s) at the surface, not in the gas phase. This leads to a possible formation of a basic salt melt on the heat transfer surfaces and thus alloying with Cr may be ineffective in improving the hot corrosion resistance of steels in these environments. Based on the literature data of oxide solubilities in basic alkali melts, it is suggested that alloying with Ni or Co will provide better protection in these applications.

Improvement in $\hbox{NO}_{\rm x}$ Removal Performance of the Pilot-Scale Boiler Emission Control System Using an Indirect Plasma–Chemical Process

NOx removal from the flue gas of a smoke tube boiler using an ozonizer for NO oxidation and a Na2SO3 aqueous solution scrubber (diameter: 0.6 m; height: 3.7 m) was investigated. In this paper, in order to determine the correlation NOx removal performance, the height of the packing material layer in the scrubber was varied from 2.1 to 0 m. The performance tests were carried out using both a compressed natural gas (CNG) and a heavy oil. The flue gas flow rates were in the range of 455-1440 Nm3/h under CNG firing and 675-1330 Nm3/h under heavy oil firing, and the boiler NOx emission concentrations were approximately 40 and 100 ppm, respectively. A total packing height of 0.75 m resulted in NOx removal efficiencies of 70% and 60% for CNG and heavy oil, respectively. Moreover, the Na2SO3 consumption rate at 0.75 m was 10%-20% less than that at 1.2 m, although the NOx removal efficiency was nearly the same. The correlation between the NOx removal performance and the gas retention time in the scrubber was obtained, providing the design information of the scrubber for industrial applications.

계획예방정비가 발전소 공기예열기의 성능에 미치는 영향

초록: 발전설비내공기예열기는보일러연소가스로부터열을회수하여유효열의손실을감소시킴으로서보일러의열효율을높이기위해설치된다. 본연구에서는계획예방정비가공기예열기의성능에미치는영향을고찰하였다. 공기예열기의성능지표들은공기예열기의계획예방정비전후의운전상태와성능변화모두를고려하여계산되었고, 공기예열기의중요한성능지표로는가스측온도효율, 공기누설률, 열회수율, 열관류율과열용량비들이다. 계획예방정비전후의공기예열기성능평가로부터공기예열기의모든성능지표가계획예방정비후향상되었다.Abstract: Air heater used in power plant helps increase the thermal efficiency of the boiler by recovering the heatfrom the boiler flue gas and thus preventing the loss of useful heat. This study investigates the effect of preventivemaintenance on the performance of the air heater in a power plant. Performance indexes for the air heater arecalculated to observe the changes in the performance and operation status of the air heater before and afterpreventive maintenance. The major performance indexes considered are temperature efficiency of the flue gas side,air leakage rate, heat recovery rate, heat transmission rate, and heat capacity ratio. The performance of the airheater is evaluated before and after preventive maintenance; our results show that all the abovementionedperformance indexes are improved after the maintenance.

S0801-1-3 火力発電所排ガス中の二酸化炭素分離・回収技術について(IGCC/CCS)

Carbon Capture Technology can contribute to Carbon Dioxide reduction and stable supply of Electric Power in the near future. This paper describes Carbon Capture Technology for Thermal Power Systems. Toshiba has adopted Post Combustion Capture (PCC) System that captures Carbon Dioxide from boiler flue gas. In September 2009, Toshiba completed the construction and commenced operation of PCC Pilot Plant at Mikawa Thermal Power Station, at Sigma Power Ariake in Ohmuta city, Fukuoka Japan. Toshiba is conducting test for research and development of Carbon Capture Technology at this Pilot Plant toward Commercial plant design. Progress and results of our research and development to date are introduced in this paper.

Energy, exergy and economic analysis of industrial boilers

In this paper, the useful concept of energy and exergy utilization is analyzed, and applied to the boiler system. Energy and exergy flows in a boiler have been shown in this paper. The energy and exergy efficiencies have been determined as well. In a boiler, the energy and exergy efficiencies are found to be 72.46% and 24.89%, respectively. A boiler energy and exergy efficiencies are compared with others work as well. It has been found that the combustion chamber is the major contributor for exergy destruction followed by heat exchanger of a boiler system. Furthermore, several energy saving measures such as use of variable speed drive in boiler's fan energy savings and heat recovery from flue gas are applied in reducing a boiler energy use. It has been found that the payback period is about 1 yr for heat recovery from a boiler flue gas. The payback period for using VSD with 19 kW motor found to be economically viable for energy savings in a boiler fan.

Multistage Fluidized Bed Reactor Performance Characterization for Adsorption of Carbon Dioxide

Carbon dioxide and its different compounds are generated as primary greenhouse gases from the flue gases of coal-fired thermal power plants, boilers, and other stationary combustion processes. This greenhouse gas causes global warming after being emitted to the environment. To deal with this problem, a new dry scrubbing process was tested in this study. A three-stage countercurrent fluidized bed adsorber was developed, designed, and fabricated. It was used as a removal apparatus and operated in a continuous regime for the two-phase system. The height of each stage was 0.30 m, and the inner diameter was 0.10 m. The paper presents the removal of CO2 from gas mixtures by chemical sorption on porous granular calcium oxide particles in the reactor at ambient temperature. The advantages of a multistage fluidized bed reactor for high mass transfer and high gas−solid contact can enhance the removal of the gas when using a dry method. The effects of the operating parameters such as sorbent, superficial gas velocity, and the Weir height on CO2 removal efficiency in the multistage fluidized bed were investigated. The results indicate that the removal efficiency of the carbon dioxide was around 71% at a high solid flow rate corresponding to lower gas velocity at room temperature. In comparison with wet scrubbers, this dry process appears to have lower cost, less complicated configuration, and simpler disposal of used sorbent. The results in this study assume importance from the perspective of use of a multistage fluidized bed adsorber for control of gaseous pollutants at high temperature.

Experimental study on mercury transformation and removal in coal-fired boiler flue gases

This paper reported mercury speciation and emissions from five coal-fired power stations in China. The standard Ontario Hydro Method (OHM) was used into the flue gas mercury sampling before and after fabric filter (FF)/electrostatic precipitator (ESP) locations in these coal-fired power stations, and then various mercury speciation such as Hg 0, Hg 2+ and Hg P in flue gas, was analyzed by using EPA method. The solid samples such as coal, bottom ash and ESP ash, were analyzed by DMA 80 based on EPA Method 7473. Through analysis the mercury speciation varied greatly when flue gas went through FF/ESP. Of the total mercury in flue gas, the concentration of Hg 2+ is in the range of 0.11–14.76 μg/N m 3 before FF/ESP and 0.02–21.20 μg/N m 3 after FF/ESP; the concentration of Hg 0 ranges in 1.18–33.63 μg/N m 3 before FF/ESP and 0.77–13.57 μg/N m 3 after FF/ESP, and that of Hg P is in the scope of 0–12.11 μg/N m 3 before FF/ESP and 0–0.54 μg/N m 3 after FF/ESP. The proportion of Hg 2+ ranges from 4.87%–50.93% before FF/ESP and 2.02%–75.55% after FF/ESP, while that of Hg 0 is between 13.81% – 94.79% before FF/ESP and 15.69%–98% after FF/ESP, with that of Hg P is in the range of 0%–45.13% before FF/ESP and 0%–11.03% after FF/ESP. The mercury in flue gas mainly existed in the forms of Hg 0 and Hg 2+. The concentrations of chlorine and sulfur in coal and flue gas influence the species of Hg that are formed in the flue gas entering air pollution control devices. The concentrations of chlorine, sulfur and mercury in coal and the compositions of fly ash had significant effects on mercury emissions.

A novel feature selection technique for number classification problem using PNN—A plausible scheme for boiler flue gas analysis

A number of industrial problems involve accruing data from sensor like devices for further analysis more specifically in applications such as boiler flue gas analysis, computer vision, etc. Several feature selection techniques have been utilized by researchers for data conditioning, such as sequential search technique, branch and bound technique, best individual selection technique, etc. This study reports on the plausible solution for ascertaining the composition of gases during complex boiler flue gas data analysis by taking a number classification problem as a model. For this purpose an indigenously developed arithmetic residue (AR) scheme has been devised as a feature selection technique. For the purpose of classification of data (number of classes of gases), a probabilistic neural network (PNN) has been implemented and its classification capability has been analyzed first for the data acquired from ORSAT analyzer and then for the data from KANE ® analyzer.

DOAS对烟气中SO2测量的四步校准方法

SO2 monitoring in the flue gas of a coal burning boiler is important for environmental protection. The nonlinearity of practical condition causes deviation from theoretical law. On the basis of the Lambert-Beer Law, a new four-step calibration method is introduced. This method includes cross section interpolation, weighting spectral region combination, acquiring the spectrum with new calibration devices, and least-square fitting. Compared with conventional methods, this new method is low cost, convenient, and accurate. In the proof test, SO2 samples with different concentrations are measured. The average errors are less than 1.5%, while the maximum deviation is less than 4.5%.

NO x removal from the flue gas of oil-fired boiler using a multistage plasma-catalyst hybrid system

The study on removal of NO x from the flue gas of oil-fired boiler has been carried out using non-thermal plasma cum catalyst hybrid reactor at 150 °C. Propylene (C 3H 6) was used as a reducing agent. A multistage plasma-catalyst hybrid reactor was newly designed and successfully operated to clean up the flue gas stream having a flow rate of 30 Nm 3/h. TiO 2 and Pd/ZrO 2 wash-coated on cordierite honeycomb were used as catalysts in the present study. Though the plasma-catalyst hybrid reactor with TiO 2 showed good activity on the removal of NO yet it removed only 50–60% of NO x because a significant portion of NO oxidized to NO 2. On the contrary, the plasma-catalyst hybrid reactor with Pd/ZrO 2 removed about 50% of inlet NO with a negligible amount of NO oxidation into NO 2. The plasma/dual-catalysts hybrid system (front two units of plasma-Pd/ZrO 2 + rear two units of plasma/TiO 2) proved to be very promising in NO x removal in the presence of C 3H 6. DeNO x efficiency of about 74% has been achieved at a space velocity of 3300/h at 150 °C.

Continuous operation of commercial-scale plasma–chemical aftertreatment system of smoke tube boiler emission with oxidation reduction potential and pH control

NO x removal from an actual boiler flue gas is investigated using an indirect plasma and chemical hybrid system comprising a commercial ozonizer and an Na 2SO 3 chemical scrubber. A high NO x removal efficiency in the continuous operation of a commercial-scale apparatus is achieved by controlling pH and oxidation reduction potential (ORP) and injecting additional Na 2SO 3 and NaOH aqueous solutions into the scrubber sump when required. Ozone injection is demonstrated to be extremely effective for NO oxidation. The relation between the ORP and NO x removal efficiency, which is essential for the optimal operation of this system, is obtained.

A mathematical model to characterize effect of silica content in the boiler fly ash on erosion behaviour of boiler grade steel

Fly ash particles entrained in the flue gas of coal-fired boilers can cause serious erosion on the critical components along the flow path. Such erosion can significantly jeopardise operational life of the boiler. A first principle based theoretical model has been developed embodying the mechanisms of erosion involving cutting wear, plastic deformation wear and effect of temperature on erosion behaviour, to predict erosion rates of pertinent boiler grade steels. Various grades of steels commonly used in the fabrication of boiler components and published data pertaining to boiler fly ash has been used in modelling the phenomena. The model also provides a quantitative predictive framework to study the effect of percentage of silica content in the ash particles on the erosion potential. The erosion sensitivity of particle impact velocity, angle of impingement and variation of surface temperature of the substrate (steel) have also been studied as a function of silica content in the ash. The model has been implemented in a computer code to predict the erosion rates at room and elevated temperature for various grades of steels under different particle impact conditions. The model predictions have been found to be in good agreement with the published data. This investigation illustrated that any minor increase in silica level in the ash can considerably aggravate the erosion rates, signifying the fact that silica content in the ash plays a critical role in characterising erosion potential of fly ash.

06/01690 Adsorption separation of carbon dioxide from flue gas of natural gas-fired boiler by a novel nanoporous ‘molecular basket’ adsorbent: Xu, X. et al. Fuel Processing Technology, 2005, 86, (14–15), 1457–1472

06/01690 Adsorption separation of carbon dioxide from flue gas of natural gas-fired boiler by a novel nanoporous ‘molecular basket’ adsorbent: Xu, X. et al. Fuel Processing Technology, 2005, 86, (14–15), 1457–1472

Equilibrium modelling of single and binary adsorption of cadmium and nickel onto bagasse fly ash

Abstract The present study deals with the competitive adsorption of cadmium (Cd(II)) and nickel (Ni(II)) ions onto bagasse fly ash (BFA) from single component and binary systems. BFA is a waste material obtained from the flue gas of the bagasse-fired boilers of sugar mills. Equilibrium adsorption is affected by the initial pH (pH0) of the solution. The pH0 ≈ 6.0 is found to be the optimum for the individual removal of Cd(II) and Ni(II) ions by BFA. The pH of the system, however, increases during the initial sorption process for about 20 min and, thereafter, it remains constant. The equilibrium adsorption data were obtained at different initial concentrations (C0 = 10–100 mg/l), 5 h contact time, 30 °C temperature, BFA dosage of 10 mg/l at pH0 6. The single ion equilibrium adsorption data were fitted to the non-competitive Langmuir, Freundlich and Redlich–Peterson (R–P) isotherm models. The R–P and the Freundlich models represent the equilibrium data better than the Langmuir model in the studied initial metal concentration range (10–100 mg/l). The adsorption capacity of Ni(II) is higher than that for Cd(II) for the binary metal solutions and is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined action of Cd(II) and Ni(II) ions on BFA is generally found to be antagonistic. Equilibrium isotherms for the binary adsorption of Cd(II) and Ni(II) ions onto BFA have been analyzed by using non-modified Langmuir, modified Langmuir, extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) models. The competitive extended Freundlich model fits the binary adsorption equilibrium data satisfactorily and adequately. Desorption with various solvents showed that the hydrochloric acid is the best solvent; the maximum elution being about 65% for Cd(II) and about 42% for Ni(II). Since BFA is a waste material obtained at almost no cost, the spent BFA can be combusted to recover its energy value and the bottom ash can be blended with cementitious mixture for making building blocks.