Fluidized Bed Combustion Ash Research Articles

Use of slurry fluorogypsum (FG) with controlled pH-adjustment in FG-based blends

This study investigates the mechanical and durability properties of blends made of fluorogypsum (FG) with the pH adjusted by using controlled amounts of circulating fluidized bed combustion ash (CFBCA) and denoted as C-FG, class C fly ash (FA), and type II Portland cement (PC). A series of pH tests was conducted on samples of C-FG to develop an analytical relationship between acidity and CFBCA content, which can be used to determine the optimal amount of CFBCA needed to obtain a specified pH value. Two compositions of C-FG-based blends were investigated in detail to identify the effects of CFBCA content on compressive strength, modulus of elasticity, Poisson’s ratio, relative volumetric expansion, unit weight, and setting times. The obtained properties were compared with those of FG-based blends having the same composition and made using FG with the pH adjusted by using uncontrolled amounts of CFBCA (U-FG). Results suggest that the amount of CFBCA can have significant effects on the properties of C-FG-based blends, depending on the composition. In addition, C-FG-based blends generally achieve a higher compressive strength and initial stiffness than the corresponding U-FG-based blends.

Utilization of circulating fluidized bed combustion ash in producing controlled low-strength materials with cement or sodium carbonate as activator

The present study investigates the fresh and hardened properties of controlled low-strength materials (CLSM) utilizing circulating fluidized bed combustion (CFBC) ashes, activated with cement or sodium carbonate. Engineering properties such as flowability, settlement, setting behavior, compressive strength, and hydration characteristics were evaluated. The results provided new insights, demonstrating that CFBC ashes can be effectively utilized in producing CLSM with suitable material design as the CLSM could achieve the required performances specified in the ACI 299R-13. The CLSM mixtures showed a self-destruction characteristic due to the formation of ettringite, while it showed stable strength development in a dry condition.

Circulating fluidized bed combustion ash as controlled low-strength material (CLSM) by alkaline activation

The present study is aimed at providing a useful means of treating and utilizing the CFBC ash as controlled low-strength material (CLSM). The CLSM in this study was produced by activating a mixture of CFBC fly ash, bottom ash and blast furnace slag with sodium hydroxide (NaOH) solution. The characteristics of the CLSM were evaluated by the main factors such as flow, bleeding and compressive strength as stated in ACI 229, along with initial setting time and XRD patterns. The CLSM showed delayed strength development due to the reactivity of calcium sulfate in CFBC fly ash and bottom ash. This effect is evidenced by the XRD pattern of the CLSM at 7 and 56d which showed the consumption of gypsum asa source of calcium sulfate, to produce the reaction product ettringite.

Evaluation of Two-Atmosphere Thermogravimetric Analysis for Determining the Unburned Carbon Content in Fly Ash

Abstract The unburned carbon (UC) content of fly ash impacts the performance (e.g., air entrainment, rheology) of concrete mixtures. The loss on ignition (LOI) test is commonly used to estimate the UC content; however, this may be inaccurate, as the weight change upon igniting fly ash is also due to calcination of carbonates, desorption of bound water, and oxidation of sulfur and iron minerals. In this study, a two-atmosphere thermogravimetric analysis (2A-TGA) coupled with mass spectrometry (MS) was performed to evaluate the chemical reactions that occur upon heating of fly ash and to measure the true UC content. 2A-TGA was performed under two distinct atmospheres: (i) in non-oxidizing helium gas, to measure weight loss due to decomposition of carbonates and loss of bound water and (ii) in oxidizing air, to measure weight loss due to conversion of UC to carbon dioxide (CO2). The method was applied to five class F fly ashes with LOI in the range 1.89 % to 7.66 %, a class C fly ash (LOI = 3.86 %), and a fluidized bed combustion (FBC) ash (LOI = 8.10 %). The results were also compared with the total carbon (TC) of each fly ash measured using infrared (IR) spectroscopy via a commercial Laboratory Equipment Corporation (LECO) carbon analyzer. The results show that there is no one-to-one relationship between the LOI and the TC or UC contents of fly ash. LOI overestimated TC by up to 2.5 times and overestimated UC by up to 6.4 times.

순환유동층 석탄재의 활용 기술과 광산 채움재 관련 규격 동향

순환유동층(CFBC) 보일러 방식의 석탄화력발전소에서 발생하는 석탄재는 유리 석회와 무수석고의 함량이 풍부하고 자경성을 가지는 것을 특징으로 하는 물질로서 유용하게 활용해야 할 자원 중 하나이다. 최근 CFBC 석탄재를 포함하여 석탄화력발전소 부산물을 활용한 광산 채움 기술 및 광해 관리에 대한 관심이 점차 증가하고 있는 가운데, CFBC 석탄재를 광산 채움 분야에 적용하기 위해서는 기술에 대한 검토와 함께 관련 규격에 대해 향후 충분히 논의를 거쳐야 할 여지가 있다. 이를 위해, 본 논문에서는 CFBC 석탄재의 유효 활용 기술에 대한 연구동향을 소개하고, 광산 채움 분야의 활용을 위해 국외의 규격 동향을 고찰한 후 연구방향 및 시사점에 대해 정리하였다. Circulating fluidized bed combustion (CFBC) ash is one of useful mineralogical resources having abundant content of free lime and anhydrite, and has a self-cementitious property. Recently, considerable interest has been gained regarding the utilization of CFBC ash, along with its use in mine backfill and reclamation. Prior to adopt the use of CFBC ash in the mine backfill technology, discussion on the technology and related specification is prerequisite in the future. This paper presents a review on studies in the emerging technology of CFBC ash utilization, and provides useful information with regard to the specifications for mine backfills utilizing CFBC ash.

Stabilization/solidification of hot dip galvanizing ash using different binders

This study focuses on solidification of hot dip-galvanizing ash with a high content of zinc and soluble substances. The main purpose of this paper is to immobilize these pollutants into a matrix and allow a safer way for landfill disposal of that waste. Three different binders (Portland cement, fly ash and coal fluidized-bed combustion ash) were used for the waste solidification. Effectiveness of the process was evaluated using leaching test according to EN 12457-4 and by using the variance analysis and the categorical multifactorial test. In the leaching test, four parameters were observed: pH, zinc concentration in leachate, and concentration of chlorides and dissolved substances in leachate. The acquired data was then processed using statistical software to find an optimal solidifying ratio of the addition of binder, water, and waste to the mixture, with the aim to fulfil the requirement for landfill disposal set by the Council Decision 2003/33/EC. The influence on the main observed parameters (relative amount of water and a binder) on the effectiveness of the used method and their influence of measured parameters was also studied.

Study of Ettringite by Hydration of Yeelimite Clinker

This article describes the results of experimental works, dealing with long-term observing of ettringite stability (Ca6Al2(SO4)3(OH)12·26H2O). Thermodynamic stability of this mineral is important in terms of potential use of fluidized bed combustion (FBC) ash as an additive to Portland cement. Within the experimental work it was carried out observing of the ettringite formation by hydration of yeelimitu (Ca4Al6(SO4)·O12) in laboratory conditions. For the preparation of yeelimite it was proposed a three-component raw material mixture, consisting of a high percent limestone and gypsum and corundum. This mixture was subsequently placed in platinum crucibles and burnt in superkanthal kiln at 1200 °C. Formed clinker was mixed in chosen ratio with water and it was prepared a set of testing samples. These samples were exposed in the laboratory environment for up to 180 days. The hydration of the clinker was carried out using X-ray diffraction analysis (XRD) by determining the mineralogical composition.

Alkali Activation–Granulation of Hazardous Fluidized Bed Combustion Fly Ashes

The increasing amount of fluidized bed combustion (FBC) ash is putting pressure on researchers to invent novel methods for utilizing the ash. The low reactivity and heavy metal content constrict the use of FBC ash in the same way as coal ash from pulverized combustion. Four FBC fly ashes from different power plants were granulated with sodium silicate solution in order to produce artificial aggregates. All aggregates matched the definition for lightweight aggregate according to the EN 13055-1 standard. The strongest aggregates were produced from fly ashes that had the highest X-ray amorphous material content and the highest amount of selectively soluble SiO2 and Al2O3. However, the same leaching problem (leaching of the anionic species) as with coal fly ashes was observed with the FBC fly ashes. The simultaneous high shear granulation and alkali activation of FBC ashes showed that artificial aggregates with satisfactory physical properties, such as density and strength, can be obtained even from low-reactive fly ashes that contain heavy metals.

Low-CO2 Cements from Fluidized Bed Process Wastes and Other Industrial By-Products

ABSTRACTAccording to the findings of X-ray diffraction analysis, calcium looping (CaL) spent sorbent (as a main source of CaO), anodization mud (as a source of Al2O3 and additional sulfate), and fluidized bed combustion (FBC) fly and bottom ashes, separately or in mixture (as main sources of CaSO4 plus alumina and uncarbonated lime) can replace limestone, bauxite, and gypsum as components of calcium sulfoaluminate (CSA) clinker-generating raw mixes. All of the hydrated CSA cements obtained from the corresponding clinkers and investigated by means of differential thermal-thermogravimetric analysis displayed a similar behavior. It has been demonstrated that the well-recognized environmentally friendly character of CSA cement manufacture can be further improved not only by using industrial wastes instead of natural materials, but also by virtue of the reduced CO2 emission and increased energy saving associated with the limestone substitution with poorly carbonated sources of lime, such as CaL spent sorbent and FBC ashes.

순환유동층 애시를 자극제로 사용한 고로슬래그 미분말 기반 비소성 시멘트의 수화 및 단열 특성

As people have more interest in environment-friendly structures recently, many researchers are actively researching non-sintered cement in Korea and other countries. Non-sintered cement shows various characteristics of its reaction products and hardeners, depending on the kind of alkali activators. Thus, this study manufactures ground granulated blast furnace slag based non-sintered cement binder by using circulating fluidized bed combustion ash, which is a kind of industrial byproduct, as a stimulant, and investigated its hardening characteristics and hydration, depending on the rate of circulating fluidized bed combustion ash. Besides, this study investigated its insulation property according to the weight lightening of non-sintered cement. As a result, ettringite and C-S-H were mainly formed in the hydration, and it was possible to manufacture a non-sintered cement hardener over 50 MPa. Lastly, it was possible to manufacture a non-sintered cement hardener in a thermal conductivity level of 0.127 W/m·K when the compressive strength was 10 MPa for weight lightening.

Effects of high-temperature fly ash and fluidized bed combustion ash on the hydration of Portland cement

This work is aimed at the comparison of the effects of high-temperature fly ash and fluidized bed combustion ash on the hydration of Portland cement and compressive strength of resulting materials. Two samples of high-temperature fly ash (FA), one sample of fluidized bed combustion ash (FBCA) and one sample of fluidized filter ash (FFA) were selected for this work. The pastes were prepared with the same water-to-binder ratio (0.4). The replacement of cement was 10, 20, 40 and 60wt.%. The influence of ashes on the hydration of ordinary Portland cement (OPC) was measured by means of isoperibolic calorimeter. The compressive strength was determined after 1, 7 and 28days of curing. The hydration slows down with increasing amount of fly ash, due to lower reactivity of FA compared to OPC. For fluidized ash, the hydration is accelerated through free lime. When comparing calorimetric curves with mechanical properties, it was found out that for the pastes with the same OPC_replacement, the samples with the highest developed heat also achieved the highest strength after one day of hydration. After 28days of hydration some samples achieved even higher strength than OPC paste.

The Impact of One-, Two- and Three-component Hydraulic Road Binder on the Properties of the Hydraulically Bound Mixture

The paper presents the results of tests on road base used in the construction and maintenance of roads stabilised with hydraulic binders. Seven hydraulic binder mixes were prepared under laboratory conditions by mixing three basic components: Portland cement CEM I 32.5 R, fluidized bed combustion ash (PF) and cement kiln dust (CKD). The proportions of the binder components were established in accordance with the experimental design. The percentage share of the hydraulic road binder in the bound mix was 6%. Two types of natural aggregates were used for the base. The percentage shares of the individual components in the mix were designed using the Proctor method. For pastes, made from binders, basic mechanical properties were determined. To assess the effect of binders on the properties of the base stabilised with hydraulically bound mixtures tests were conducted to measure the following: compressive strength after 7, 14, 28 and 42 days of curing, freeze-thaw resistance. Experimental results demonstrate that it is possible to determine the optimal composition of hydraulic binders for the required strength class of the base course.

Production and characterization of geopolymers based on mixed compositions of metakaolin and coal ashes

Mixtures of coal ashes from pulverized coal combustion (PCC) or fluidized bed combustion (FBC) and metakaolin were used to synthetize geopolymers. Upon full characterization of the raw powders (chemical and mineralogical composition), geopolymerization tests were conducted using an alkali aqueous solution of NaOH/Na2SiO3 at different dilutions. The produced geopolymers were subjected to SEM analysis, as well as to leaching, thermal and mechanical tests. The final microstructure and the properties of the geopolymers indicate that FBC ash can be conveniently used as a partially reactive filler in combination with the metakaolin powder. The composite material has good thermal performance and compressive strength (∼30 MPa) suitable for the building sector.

Effect of circulating fluidized bed combustion ash on the properties of roller compacted concrete

Circulating fluidized bed combustion (CFBC) ash, which has such a high content of f-CaO and SO3, is a waste or by-product of petroleum coke combustion power stations. The purpose of this study is to investigate the effects of CFBC ash on the properties of roller compacted concrete (RCC). CFBC ash was used to replace fine aggregate with various dosages (5%, 10% and 15%) by weight. All mixtures were designed according to ACI 211.3R and prepared for testing. During casting, cylinders were vibrated and compacted with different pressures of 25g/cm2, 50g/cm2 and 75g/cm2, respectively. Test results show that CFBC ash can increase the water absorption and effectively reduce the initial surface absorption. Meanwhile, CFBC ash has a positive effect on compressive strength, splitting tensile strength, and sulphate attack resistance of hardened RCC. SEM revealed that the main hydration products of specimens containing CFBC ash are AFt (ettringite), C–S–H (hydrated calcium silicate) and portlandite. Based on the presented observations and results, RCC with the dosage of 5% CFBC ash as fine aggregate replacement and the roller compaction pressure of 75g/cm2 is recommended.

Effect of Clean Coal Combustion Products in Reducing Soluble Phosphorus in Soil I. Adsorption Study

The study examined the effectiveness of various coal combustion products (CCPs) [fly ash (FA), fluidized bed combustion ash (FBC), and flue gas desulfurization gypsum (FGD)] on phosphorus (P) adsorption in soils using batch sorption studies. The results indicated that P adsorption increased with increasing application rates of CCPs. The effect of CCPs in increasing P adsorption followed: FBC > FA > FGD. There was an inverse relationship between the CCP-induced increase in P adsorption and initial soil pH, demonstrating that acidic and neutral soils responded more effectively to CCP addition than alkaline soils. The increases in soil pH and calcium (Ca) concentration in the soil solution resulting from CCP application enhanced P retention through adsorption and precipitation reactions.

Verification of the Possibility of Solidification Product Made of Neutralization Sludge use in the Building Industry

This paper deals with hazardous waste solidification/stabilisation, specifically neutralization sludge that comes from active industrial sources and neutralization sludge that comes from old ecological sources. As solidification agents fluidized bed combustion ash, classic fly ash and ordinary Portland cement were used. According to the valid legislation and selected possible future use of solidification product a laboratory testing of proposed solidification/stabilisation recipes was performed. The results of leachability tests, unconfined compressive strength and ecotoxicological test showed that solidification product use as a technological and reclamation material on depots and setting pits is possible.

Development of synthetic aggregate using off-ASTM specification ashes

This paper presents a comprehensive laboratory evaluation for developing synthetic aggregate using off-ASTM specification ash produced through a fluidized bed combustion (FBC) process. To determine optimum mix design which produces strong and durable synthetic aggregate, different combinations of water to fly ash ratio, various combination of fly ash (FAf) to stockpiled material (FAsp) ratio, curing temperature, and calcium chloride content were applied. Then, to evaluate the performance of synthetic aggregate for construction application, basic characteristics of synthetic aggregate such as density, specific gravity, absorption, gradation, strength, abrasion resistance, and soundness were carried out.The results indicate that 100% RH and 40°C was determined to be the optimum curing conditions for both fly ash paste and FAf/FAsp mortar mixtures in terms of strength and minimal potential sulfate attack. The aggregate characterization results indicate that the produced synthetic aggregates met ASTM C 33/330 criteria for a concrete aggregate without inducing any soundness problems despite their relatively high water absorption. Therefore, the FBC ash and stockpiled ash can be used as primary resource materials for manufacturing synthetic light weight aggregate.

Evaluation of synthetic aggregates using off-ASTM specification ashes as road base course materials

In recent years, there has been renewed interest in synthetic aggregate for flexible or rigid base manufactured with coal combustion by-products because of a scarcity of dependable sources of aggregate and high transportation cost. This creates the need for alternative cost-effective sources for material that are available locally. Although successful use of hydrated ponded Class C fly ash as road-base material has been reported, the utilization of off-ASTM specification ash such as fluidized bed combustion (FBC) ash as flexible or rigid base material is still challenging due to inherent ash properties (high sulfate and carbon contents, angular shape, and free lime). Therefore, this research was performed to identify and develop the potential of FBC ash as both a synthetic aggregate and a stabilizer in flexible base construction.To assess the performance characteristics of FBC aggregate in a base-course mix design, the laboratory tests including the determination of optimum moisture content, unconfined compressive strength, evaluation of the moisture susceptibility using the tube suction test, and 3-dimensional swelling test of the fabricated specimens were carried out.The results have shown that a usable aggregate using FBC fly ash can be manufactured with virtually no potential for sulfate attack in base course application. Furthermore, FBC fly ash as a stabilizer from either naturally stockpiled or manufactured fly ash aggregate blends could be effectively used in flexible base construction without sacrificing its ability to develop high early strength and without causing sulfate swelling due to ettringite formation.

Suppression of phosphate release from coastal sediments using granulated coal ash

In order to evaluate suppression of phosphate release from sea bottom sediments using granulated coal ash (GCA), a byproduct from coal thermal electric power stations, field experiments were carried out at oyster culture sites where the sediments are rich in organic matter. Two types of GCA with the diameter of <40 mm were applied on separate bottom sediment plots of 50 m × 75 m with ca. 20 cm depth each. The first GCA type is composed of pulverized coal combustion ash (ExpA) and another consists of pressurized fluidized bed combustion ash (ExpB). Sediment pH was increased up to ca. 8.5 in both experimental plots due to hydrolysis of CaO. Phosphate concentration in the interstitial water of the sediment was significantly decreased in ExpA due to adsorption onto the GCA. A numerical model to quantify chemical and biological processes in the sediment was applied to estimate how phosphorus cycle was changed due to the application of GCA. The model output showed that release rate of phosphate from the sediment at ExpB was suppressed to the level of about 1 order lower (400 μmol m−3 d−1) than that in the control site (4800 μmol m−3 d−1), whereas decomposition of detrital phosphorus in the experimental site was estimated to have been enhanced 4.8 times compared to the control site. Considering both laboratory and simulated field experiments carried out previously, it was proven in the present study that GCA can effectively adsorb phosphate from interstitial water in organically enriched sediments and suppress the release of phosphate from the sediments to the upper water column in the field experiments.

Evaluation of the co-application of fly ash and sewage sludge on soil biological and biochemical quality

Disposal of sewage sludge (SS) and fly ash (FA) is a multifaceted problem, which can affect environmental quality. FA has the potential to stabilize SS by reducing metal availability and making the SS suitable for application in the agricultural sector. An experiment was performed to evaluate soil biological quality changes with the combined amendment of SS and FA (fluidized bed combustion ash (FBCA) and lignite fly ash (LFA)). SS was amended with 0, 10, 30, 50 and 100%, (w/w) of FA, and then the FA–SS mixtures were incubated with red soil at 1:1 (v/v). Soil quality parameters such as pH, electrical conductivity, N, soil enzyme activities such as dehydrogenase (DHA), urease (URE), and catalase (CAT), and microbial biomass carbon (MBC) were evaluated at 20, 30, and 60 days of incubation. pH and EC increased with FA–SS dose; however, N decreased. DHA and URE were found to be increased with 10% LFA amendment; thereafter it decreased. However, URE increased up to 30% of FBCA. CAT and MBC increased with both FA amendments, even up to addition of 50% FA. Bioavailable Zn, Cu, and Co contents were decreased by the addition of FA. Principal component analysis showed that pH is the most influential factor. MBC appears to be a sensitive soil indicator for the effects that result from the addition of FA–SS. Phytotoxicity studies with Zea mays showed optimum performance at 30% FA. Addition of 10–30% FBCA or LFA to SS has a positive advantage on soil biological quality.