Bottom Ash Particle Size Research Articles

Chemical characteristics of bottom ash from biomedical waste incinerators in Ghana.

Biomedical waste (BMW) incineration is the most used alternative disposal method in developing countries, such as Ghana. The improper disposal of incinerator-generated bottom ash (BA) is a significant concern due to the hazardous nature of waste. A study was conducted at Tema Hospital (TGH) and Asuogyaman Hospital (VRAH) incinerator sites. The BA samples were sent to the Council for Scientific and Industrial Research, Institute of Industrial Research, Ghana. The BA samples were weighed with fisher analytical balance, ground, and sieved with standard grade meshes of 120, 100, and 80 to determine the BA particle size distribution. The chemical composition and heavy metals were analysed using X-ray fluorescence spectrometry (XRF) and atomic absorption spectroscopy (AAS) techniques. The results indicated the chemical composition of the analysed BA samples was CaCO3 (49.90%), CaO (27.96%) and MgCO3 (6.02%) for TGH and CaCO3 (48.30%), CaO (27.07%), and SiO2 (6.10%) for VRAH, respectively. The mean concentration (M) (kg m-3) and standard deviation (SD) for TGH in the BA were 7.082 ± 0.478 (Ti), 4.657 ± 0.127 (Zn) and 4.271 ± 1.263 (Fe), while that of VRAH consisted of 10.469 ± 1.588 (Ti), 7.896 ± 2.154 (Fe) and 4.389 ± 0.371 (Zn). Therefore, the heavy metals' mean concentration at the BA is above the WHO permissible limits of soil, i.e., 0.056kgm-3 (Ti), 0.085kgm-3 (Pb), 0.100kgm-3 (Cr) and 0.036kgm-3 (Cu). Furthermore, the heavy metal mean concentrations of TGH and VRAH present in the BA analysed samples were ranked in descending order: Ti > Zn > Fe and Ti > Fe > Zn, respectively. It is therefore recommended that BA must be properly disposed of because of the hazardous nature of heavy metals present in the analysed samples, which are able to cause environmental and public health issues.

Investigation of Strength and Microstructural Characteristics of Blended Cement-Admixed Clay with Bottom Ash

This research presents an experimental study of the strength and microstructural characteristics of cement-bottom ash-admixed Bangkok clay, paying special attention to the efficiency of adding up the bottom ash (BA) of different finesses as a cementitious material and the role played by BA in enhancing the strength of the mixture. The obtained results were discussed with cemented clay mixed with other industrial ashes (i.e., fly ash and risk husk ash). The pozzolanic reaction and packing effect of BA on strength development were also discussed with tests of mixtures with insoluble material. The experimental study was performed through unconfined compression (UC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) tests. The obtained results demonstrate that the BA could be advantageously supplemented as cementitious material into the cement-admixed clay mixture to improve the strength characteristic. The finer particle size of BA could be beneficial for achieving a high strength due to the pozzolanic reaction and packing effects. By adding up a BA content of larger than 15% when the base cement content is not less than 20%, the strength of the mixture increased efficiently with the increasing BA content. Compared with fly ash of a similar grain size, the higher efficiency of BA is obtained when a BA content of greater than 15% is considered. Finally, the microstructure and changes in elemental composition/distribution were analyzed by TGA and SEM tests to explain the mechanism to improve the strength of cement–BA-admixed clay.

Physicochemical properties of bottom ash obtained from an industrial CFB gasifier

To investigate the reasons of high carbon content in bottom ash (BA) and guide the suitable utilization of residual carbon, the physicochemical properties of BA which was obtained from an industrial circulating fluidized bed coal gasifier were primarily studied via Raman spectrometer, N2 adsorption test and thermogravimetric analysis and compared with raw coal (RC) and fly ash (FA). BA has the lowest combustion reactivity than RC and FA, which is attribute to high degree of carbon deactivation, limited specific surface area, low catalysis elements contents and high ash content. In this study, the carbon content of BA first increases and then decreases with increasing BA particle size and the peak value appears at about 2 mm. The degree of carbon deactivation increases and specific surface area decreases with increasing BA particle size. Furthermore, it was found that some BA particles were covered with compact shell, which probably hindered the adequate conversion of inside carbon. The formation of shell was presumably owing to the re-attachment of volatile matter to the char matrix and the migration of coal ash, based on the results of Ramen spectra and SEM.

Valorization of MSWI Bottom Ash as a Function of Particle Size Distribution, Using Steam Washing

Treatments to reduce the leaching of contaminants (chloride, sulfate, heavy metals) into the environment from bottom ash (BA) are investigated, as a function of the ash’s particle size (s). The aim is to make BA suitable for reuse as secondary raw material, in accordance with the legal requirements. Such treatments must be economically feasible and, possibly, have to use by-products of the plant (in this case, steam in excess from the turbine). For the sake of completeness and comparison, carbonation is performed on those BA particle size classes that are not positively responsive to steam washing. BA is partitioned into four different particle size classes (s ≥ 4.75, 4.75 > s ≥ 2, 2 > s ≥ 1 and s < 1 mm, corresponding to 36, 24, 13 and 27 wt%, respectively). In the case of s ≥ 2 mm (60 wt%), steam washing is effective in reducing to under the legal limits the leaching of chlorides, sulfate and heavy metals (Zn, Cu, Cd, Pb). It has been observed that steam washing causes both removal and dissolution of thin dust adherent to the BA’s surface. BA with 2 > s ≥ 1 (~13 wt% of total BA) requires a combination of steam washing and carbonation to achieve a leaching below the legal limits. The finest BA fraction, s < 1 mm (~27 wt% of total BA), is treated by carbonation, which reduces heavy metals leaching by 85%, but it fails to sufficiently curb chlorides and sulfates.

Correlation of Holding Time and Bottom Ash Particle Size to Mechanical Properties of Polypropylene Composite

The impact of holding time and particle size of bottom ash on the mechanical properties of polypropylene composites has been investigated. The size of the used particle were 200-250, 250-300, and 300-350 mesh with the holding time variations were 0, 30, 60, and 90 minutes. The initial process of the bottom ash was cleaned with fresh and warm water, then drained and dried at a 120°C for 3 hours. In the making process of composites, the bottom ash was mixed into the polypropylene matrix by stirring at a speed of 20 rpm for 30 minutes. The results of this study showed that the highest composite strength values were obtained in composites with the particle size of 250-300 mesh. Tensile strength increased about 45% for composites without providing holding time (0 minutes), while the bending strength value increased significantly to 103% obtained on composites given a holding time of 30 minutes. The results of this study will be used as a basis for further research and hopes of getting better alternative engineering materials in the form of composites.

Mechanism of Cement Paste with Different Particle Sizes of Bottom Ash as Partial Replacement in Portland Cement

Manufacturing of Portland cement consists of high volume of natural aggregates which depleted rapidly in today construction field. New substitutable material such as bottom ash replace and target for comparable properties with hydraulic or pozzolanic properties as Portland cement. This study investigates the replacement of different sizes of bottom ash into Portland cement by reducing the content of Portland cement and examined the mechanism between bottom ash (BA) and Portland cement. A cement composite developed by 10% replacement with 1, 7, 14, and 28 days of curing and exhibited excellent mechanical strength on day 28 (34.23 MPa) with 63 mm BA. The porous structure of BA results in lower density as the fineness particles size contains high specific surface area and consume high quantity of water. The morphology, mineralogical, and ternary phase analysis showed that pozzolanic reaction of bottom ash does not alter but complements and integrates the cement hydration process which facilitate effectively the potential of bottom ash to act as construction material.

Removal of Mn(II) from the acid mine wastewaters using coal fired bottom ash

Acid mine wastewater (AMW), the wastewater from mining activities which has low pH about 3-5 and contains hazardous heavy metals such as Cu, Fe, Mn, Zn, Pb, etc. Those heavy metals pollution is of prime concern from the environmental view point. Among the heavy metals, Mn occupies the third position in the AMW from one the iron ore mining company in Aceh, Indonesia. In this study, the possibility use of bottom ash from coal fired boiler of steam power plants for the removal of Mn(II) in AMW has been investigated. Experimental has been conducted as follows. Activation of bottom ash was done both by physical and chemical treatments through heating at 270 °C and washing with NaOH activator 0.5 and 1 M. Adsorption test contains two parts observation; preliminary and primary experiments. Preliminary study is addressed to select the best condition of three independent variables i.e.: pH of AMW (3 & 7), bottom ash particle size (40, 60 & 100 mesh) and initial Mn(II) concentrations (100 & 600 mg/l). AMW used was synthetics wastewater. It was found that the best value for NaOH is 1 M, pH is 7, particle size is 100 meshes and initial Mn(II) concentration is 600 mg/l from the adsorption efficiency point of view. The maximum adsorption capacity (qe) is 63.7 mg/g with the efficiency of 85%.

Analysis of MSWI Bottom Ash Reused as Alternative Material for Cement Production

The bottom ash sample was obtained from one of three stably running municipal solid waste incineration plants in Beijing. The major components of bottom ash, i.e. CaO, SiO2, Al2O3, Fe2O3, were similar to that of ordinary Portoland cement, suggesting that bottom ash had the potential for reuse as cement material. In this paper, the smaple was sieved into 8 fractions according to the particle size distirbution. The content of CaO and chloride in the bottom ash almost decreased with the increase of particle size of bottom ash, contrary to the SiO2 content variation in the bottom ash. The Al2O3 and Fe2O3 content were relatively stable in the bottom ash with different particle size. The chloride, which could cause serious corrosion in the cement kiln, in 8 portion of bottom ash were all higher than its allowable limit in raw material for cement production and clinker quality, the dosage of bottom ash used as alternative material for cement production must be stringently controled, and some proper treatment must be used to reduce the corrion caused by chloride. The heavy metals concentration in the bottom ash were relatively high, but met standard requirements for heavy metals concentration in raw meterial. The content of alkaline oxide (K2O, Na2O) and sulphur, also affected cement production, in bottom ash with differernt particle size were all relative high. The bottom ash had the potential to be recycled as alternative material for cement production, but proper treatment measures, such as by-pass system, must be taken to satisfy the cement production, clinker quality and environmental safety.

Effect of co-contaminated soil mixtures as fixed/fluidized bed media on pollutants emission under thermal treatment

Thermal treatment of soil polluted by lube oil and heavy metals (cadmium, chromium, copper, and lead) was carried out by using a laboratory-scale incinerator. The effect of co-contaminated soil mixtures as fixed/fluidized bed media was studied with different ratios of sand bed amount to soil feeding. Additionally, the effect of soil moisture content on incineration system was further investigated. The reduction in air input altered the mode of fluidized bed to fixed bed which resulted in an increase in organic pollutants such as benzene, toluene, ethylbenzene, xylene, and polycyclic aromatic hydrocarbons. The combustion efficiency of fixed bed mode was observed to be relatively high at a lower ratio of sand bed amount to soil feeding, whereas high combustion efficiency was found in fluidized bed mode at a higher ratio of sand bed amount to soil feeding. Much higher concentration of organic pollutants in both gas phase and bottom ash is found under a higher soil moisture content. In addition, the increase in moisture content has resulted in an increase in lead, cadmium, and chromium in fly ash while copper was decreased. An important consideration is that the partitioning of heavy metals was randomly distributed in particle sizes of bottom ash. The highest concentration of heavy metals was deposited on fine-sized particle. The distribution of heavy metals in medium-sized and coarse-sized particles to form eutectic species might be produced by the soil–sand aggregation.

Detoxification of ashes from a fluidized bed waste incinerator

This paper was to test and control the toxicity of bottom and fly ashes from a circulated fluidized bed (CFB) incinerator. Bottom and fly ashes were firstly subject to TCLP test. Even though leachates of most particle size of bottom ash were below regulatory limit, the leachates of finer bottom ash may exceed the regulatory limit. Therefore, finer bottom ash should be separated and treated before landfilled directly or used as cement replacement. Due to high amounts of leached heavy metals, thermal treatment of fly ash was carried out to remove heavy metals. The influence of temperature, residence time, metal chloride and gas velocity were studied. In all conditions, Cd can be well removed. Pb can be almost completely removed with MgCl2 addition at 1000°C in 1h. The removal of Zn and Cu was accelerated significantly by MgCl2 and higher temperature separately. At optimum conditions, more than 90% of Cu and 95% of Zn could be removed, while a maximum 20% of Cr was removed due to the existence or formation of CaCr2O4, MgCr2O4 and K2Cr2O4 in raw or treated fly ashes.

Use of co-combustion bottom ash to design an acoustic absorbing material for highway noise barriers

The present study aims to determine and evaluate the applicability of a new product consisting of coal bottom ash mixed with Portland cement in the application of highway noise barriers. In order to effectively recycle the bottom ash, the influence of the grain particle size of bottom ash, the thickness of the panel and the combination of different layers with various particle sizes have been studied, as well as some environmental properties including leachability (EN-12457-4, NEN-7345) and radioactivity tests. Based on the obtained results, the acoustic properties of the final composite material were similar or even better than those found in porous concrete used for the same application. According to this study, the material produced presented no environmental risk.

Effect of bottom ash particle size on strength development in composite geomaterial

This study investigated how the particle size of bottom ash affects the frictional resistance and pozzolanic reaction of bottom ash-added composite geomaterial. A composite geomaterial (CGM) consists of dredged soil, bottom ash, and cement. The frictional resistance and pozzolanic reaction were evaluated using bottom ash-added mixtures with three different particle sizes: the original bottom ash and two generated bottom ashes. These three bottom ashes had almost identical chemical components and differed only in particle size. Three kinds of mixtures were prepared with various bottom ash contents ranging from 0 to 100% by the weight of dry dredged soil. Several series of laboratory tests including unconfined compression tests, SEM analyses, and physical tests, were carried out on the mixtures at various curing times ranging from 7 to 120days. The results indicated that the unconfined compressive strength of CGM increased with an increase in bottom ash content and curing time due to the frictional resistance and pozzolanic reaction, which were induced by adding bottom ash to the mixture. During the early stages of curing time (less than 28days), the strength development was mainly governed by the hydration reaction and frictional resistance. However, for curing times greater than 28days, the pozzolanic reaction contributed to the strength development as a function of curing time. Experimental results indicated that smaller particles of bottom ash produced more strength development with increasing curing time from the pozzolanic reaction than larger particles of bottom ash.

Heavy metals distribution characteristics in different particle size of bottom ash after agglomeration/defluidization at various fluidization parameters

This study examined the effects of variations in alkali and alkaline earth metal content, bed material diameter, static bed height and gas velocity in a fluidized-bed combustion process to understand the distribution of heavy metals in bottom ash after agglomeration/defluidization. A smaller diameter bed material increased the relative abundance of small particle sizes in the bottom ash due to attrition and thermal impact at high temperature. The addition of Na led to an increase in the large particle abundance of the bottom ash, likely due to the formation of a eutectic with a low melting point, causing agglomeration. The addition of Ca inhibited the agglomeration/defluidization and increased the abundance of large particles in the bottom ash. In general, heavy metal concentrations increased when the bottom ash size was smaller than 0.59 mm and larger than 0.84 mm. Regarding the different fluidization parameters, the bottom ash had the lowest concentration of heavy metals at 1.5 Umf, an H/D of 2.1 and a bed material (silica) particle size of 0.645 mm. The concentrations of heavy metals in the bottom ash after Ca addition were higher than of those without Na or with Na only. Addition of Ca prolonged the operation time of fluidization and increased the feed quantity of heavy metal, helping the bed material adsorb more heavy metal. Therefore, the addition of Ca not only prolonged the fluidization time, reducing agglomeration/defluidization, but also resulted in a higher adsorption of heavy metals by the bed material, reducing their emission.

Adsorption of organic pollutants from coking and papermaking wastewaters by bottom ash

Bottom ash, a power plant waste, was used to remove the organic pollutants in coking wastewater and papermaking wastewater. Particular attention was paid on the effect of bottom ash particle size and dosage on the removal of chemical oxygen demand (COD). UV–vis spectra, fluorescence excitation-emission matrix (FEEM) spectra, Fourier transform infrared (FTIR) spectra, and scanning electron microscopic (SEM) photographs were investigated to characterize the wastewaters and bottom ash. The results show that the COD removal efficiencies increase with decreasing particle sizes of bottom ash, and the COD removal efficiency for coking wastewater is much higher than that for papermaking wastewater due to its high percentage of particle organic carbon (POC). Different trends of COD removal efficiency with bottom ash dosage are also observed for coking and papermaking wastewaters because of their various POC concentrations. Significant variations are observed in the FEEM spectra of wastewaters after treatment by bottom ash. New excitation-emission peaks are found in FEEM spectra, and the fluorescence intensities of the peaks decrease. A new transmittance band in the region of 1400–1420 cm −1 is observed in FTIR spectra of bottom ash after adsorption. The SEM photographs reveal that the surface of bottom ash particles varies evidently after adsorption.