Fluidized Bed Coal Combustion Research Articles

The influence of selected mineral ingredients on the technological properties of sealing slurries

Sealing slurries used to modify the subsoil should meet a number of requirements, including: rheological properties, setting time, appropriate mechanical strength and durability. The study determined the technological properties of sealing slurries prepared with ordinary Portland cement and blended binders containing appropriately selected mineral additives. The tests used granulated blast furnace slag, silica fly ash and ash obtained in the fluidized bed combustion of coal. The assessment of the technological properties of fresh slurries included the selection of an appropriate rheological model and the assessment of the rheological properties of the sealing slurry, such as: plastic viscosity, apparent viscosity and yield point. The research determined the factors causing improvement of the technological properties of fresh slurry. The use of supplementary cementitious materials, also in systems with fluidizing admixtures, allowed for a significant modification of the rheology of the tested sealing slurries. The obtained results indicate their beneficial effect on the functional properties of slurries, enabling their use as binder components replacing Portland cement, while limiting or even eliminating the addition of superplasticizers.

Desulfurization Characteristics of Carbide Slag during Circulating Fluidized Bed Coal Combustion

At low loads, the desulfurization efficiency of circulating fluidized bed (CFB) boilers tends to decrease due to the deviation of low bed temperature from the optimal temperature required for limestone desulfurization. However, carbide slag, a waste product rich in Ca(OH)2 and possessing a low decomposition temperature, can be an economically viable alternative to limestone. In this study, the desulfurization characteristics during coal combustion with carbide slag addition were studied both in a fixed-bed reactor and a 30 kW CFB reactor. The effect of different reaction conditions on the desulfurization performance was evaluated. Results showed that the addition of carbide slag decreased SO2 emission effectively. A higher oxygen content prompted the improvement of the desulfurization efficiency. The carbide slag showed the highest desulfurization efficiency at about 800 °C. The desulfurization performance deteriorated when the temperature was beyond 800 °C. To explain this phenomenon, the micromorphology of carbide slag raw particle, calcined particle, and sulfated particle was observed by scanning electron microscopy. More holes formed on the surface of the particles after calcination. Besides, the outer surface of the holes formed more crystal grains with the increasing temperature. CaSO4 products covered the outer surface of the crystal grains after desulfurization. The crystal grain gaps on the surface of carbide slag were easily blocked at high temperatures, which resulted in the low desulfurization efficiency.

Hydration characteristics of cement with high volume circulating fluidized bed fly ash

Circulating fluidized bed fly ash (CFBFA) is a large industrial solid waste generated by clean circulating fluidized bed coal combustion technology. The coarse and porous particle structure and high content of f-CaO and II-CaSO4 are the main obstacles to the wide application of CFBFA as a supplementary cementitious material. In this study, the core–shell structure of f-CaO and II-CaSO4 were destroyed, and the pozzolanic activity of CFBFA was enhanced by ultrafine grinding. Physical activation can accelerate the mutual excitation of CFBFA and cement, promote the formation of ettringite (AFt) in the early stage of hydration, improve the microstructure, and the later strength of cement with 50 wt% UCFBFA can reach the level of pure cement. The hydration mechanisms of cements with pulverized fuel ash (PFA), CFBFA and ultrafine CFBFA (UCFBFA) were also comparatively analyzed and discussed. This study proves that ultra-fine grinding can effectively improve the reactivity of CFBFA, which provides ideas for the future research on the stability improvement of CFBFA-based cement and the large-scale resource application of CFBFA.

Role of CO2 in enhancing geopolymer properties formulated with fluidized bed combustion ash

Fluidized bed combustion coal ash was used together with conventional coal ash and alkaline materials to synthesize geopolymer cement. The production process was performed in a carbon dioxide-rich environment to integrate carbon dioxide into the cement. The presence of carbon dioxide was found to enhance the formation of crystalline carbonates during the hydration reaction yielding an enhanced geopolymer matrix with improved binding characteristics. The non-crystalline (metastable) carbonates formed undergo crystallization processes that complement the hydration reactions, and yield carbonate with beneficial binding effects. Experimental optimization was designed and implemented to select the desired formulation of raw materials for achieving high levels of carbon capture and engineering properties. The optimized formulation produced a geopolymer cement with 7.4 wt% CO2 content, which produced concrete materials with a flow table of 68 cm, an initial set time of 34 min, and 28-day compressive strength reaching 28.2 MPa with acceptable residual compressive strength.

Optimal design and performance of eco-friendly materials stabilized with inorganic binder based on fluidized bed coal combustion fly ash and regenerated brick powder

The development of green and eco-friendly road engineering materials has become essential to achieving carbon emission reduction and sustainable development. In this study, recycled brick powder (RBP) from construction waste and fluidized bed coal combustion fly ash (FBCF) are combined to replace the traditional lime-fly ash diatomic material in order to produce eco-friendly materials stabilized with inorganic binder (EFMSIB) for roads. The results showed that, when the ratio of EFMSIB is m(RBP):m(FBCF):m(Aggregate) equals 7%:13%:80%, its 7d and 28d unconfined compressive strength are 3.4 MPa and 8.72 MPa, respectively, 180d compression rebound modulus is 1440 MPa, 180d bending tensile strength is 1.51 MPa, 28d mass loss rate is 1.87%, and the residual compressive strength was 93.36%, and all the properties reached the optimal values. The composite material of FBCF and RBP can complete the pozzolanic reaction to form ettringite (AFt) relatively quickly at the early stage of hydration, which promotes the development of the early strength of hydration products, resulting in the compressive strength of NT4 increased by 1.8 times compared with the reference sample. With the growth of the curing age, the active SiO2 and Al2O3 in the material react with CaO to produce hydrated calcium silicate, which promotes the development of the strength of the system in the later stage, resulting in the compressive strength of NT4 increased by 1.6 times compared with the reference sample. The prepared EFMSIB material has a better self-consolidation effect on heavy metals, and the leachate heavy metal ion concentration of NT4 can reach the standard of class III surface water.

Material innovation and performance optimization of multi-solid waste-based composite grouting materials for semi-flexible pavements

With the increasing power generation capacity of circulating fluidized bed boilers and electrolytic aluminum production worldwide, the emissions of fluidized bed coal combustion fly ash (FBCF) and bayer red mud (BRM) have increased dramatically, resulting in extremely severe environmental issues as it is difficult to utilize these as resources. To address this issue, this study uses industrial solid wastes such as BRM, FBCF, and silica fume as mineral admixtures to develop a green and low-carbon early strength multi-solid waste composite grouting material (ESMSWCGM) for semi-flexible pavements (SFPs). According to the findings of this study, 18 % of the cement in the ESMSWCGM could be replaced with the three solid waste mineral admixtures. With the optimal ratio, the developed ESMSWCGM exhibits initial and 20-min flow-cone fluidities of 12 s and 14 s, respectively, and initial and final setting times of 66 min and 69 min, respectively. The compressive strengths at 3 h, 1 d, 7 d, and 28 d are 17.05 MPa, 22.95 MPa, 29.55 MPa, and 30.72 MPa, respectively, and the dry shrinkage rate at 28 d is 0.12 %. The performance of the SFP material obtained through grouting is excellent. When the grouting saturation is 95 %, the SFP has a dynamic stability of 28911, a rutting depth of 1.19 mm, and a splitting strength of 1.91 MPa.

Use of Fluidized Bed Combustion Fly Ash as a Partial Substitute for Cement in Underwater Concrete Mixes.

Despite limitations to coal combustion energy production, many countries face the still-unresolved problem of utilising the wastes from fluidised bed coal combustion. One direction of rational utilisation can be using these wastes in the building materials industry. The study aimed to analyse the possibility of using fluidised bed combustion fly ashes as a partial substitute for cement in the underwater concrete (UWC). Two groups of concrete mixes were tested, containing 20 to 50% of fluidised bed combustion fly ashes. Investigations of the rheological properties of the concrete mixes and the mechanical performance of the hardened concrete confirmed the possibility of replacing cement in UWC with fluidised bed combustion fly ash up to 30% of the cement mass. The higher content of the fly ashes significantly worsens the UWC strength as well as the consistency and wash-out loss of the concrete mixes, excluding its use in underwater concreting.

Gaseous emissions from advanced CLC and oxyfuel fluidized bed combustion of coal and biomass in a complex geometry facility:A comprehensive model

Since the formation of gaseous pollutants during solid fuel combustion in circulating fluidized bed (CFB) units, especially under oxyfuel combustion and chemical looping combustion conditions, is an extremely complex process, the development of a simple predictive model of gas emissions is of practical significance. This paper introduces a novel approach based on fuzzy logic (FL), one of the main artificial intelligence (AI) methods, for the prediction of CO2, CO, NOx (i.e., NO + NO2), N2O, and SOx (i.e., SO2 + SO3) concentrations in flue gases from coal and biomass combustion in various operational sceneries. The simulations are carried out for different combustion environments, i.e., air-firing, oxyfuel, iG-CLC (in-situ gasification chemical looping combustion), and CLOU (chemical looping with oxygen uncoupling), under a wide range of operating parameters. A mixture of oxygen with CO2 was used for oxyfuel combustion. Three different oxygen carriers (OC) were examined in the study for iG-CLC and CLOU, i.e., ilmenite, copper oxide (60% wt.) with the support of carbonate waste from ore flotation, and copper oxide (60% wt.) with the support of ilmenite (20% wt.) and fly ash. The validation of the model was successfully performed on a complex geometry laboratory–scale 5 kWth Dual-Fluidized-Bed Chemical-Looping-Combustion of Solid-Fuels (DFB-CLC-SF) facility. The gaseous pollutant emissions predicted using the developed model were in good agreement with experimental results. The maximum relative error between measured and predicted by the model emissions was lower than 8%. The proposed method constitutes a quick and easy-to-run technique and a complementary tool compared to the experimental procedures and the programmed computing approach. The developed fuzzy logic-based model of gaseous emissions from advanced combustion (GasAdComb) of solid fuels can be easily applied by scientists and engineers to simulate and optimize coal and biomass combustion processes.

Distribution of As within Magnetic and Non-Magnetic Fractions of Fluidized-Bed Coal Combustion Ash

Separation of coal ash into magnetic and non-magnetic fractions facilitates their utilization when processed separately. Due to desulphurization additives added to coal during the fluidised-bed combustion, non-magnetic fractions often contain elevated CaO levels (while magnetic concentrates are typically rich in Fe2O3). Both CaO and Fe2O3 are known for their ability to bind As during the combustion, whose distribution is a crucial parameter in terms of proper utilization of these fractions. Therefore, the study deals with the As partitioning within magnetic and non-magnetic fractions of fluidized-bed coal combustion ashes. Two different (successive) procedures of dry magnetic separation were used to separate each ash into strongly magnetic, less magnetic, and a non-magnetic fraction. Due to their optimal utilization, the concentrations of As and other target elements in these fractions were evaluated and compared. Magnetic concentrates from the first separation step (in vibrofluidized state) contained 60–70% Fe2O3, magnetic concentrates separated manually out of the residues after the first separation contained 26–41% Fe2O3, and the non-magnetic residues contained 2.4–3.5% Fe2O3. Arsenic levels were the highest in the non-magnetic residues and gradually decreased with the increasing Fe2O3 content in the magnetic fractions. The dominant As association in the studied samples was to CaO (r = +0.909) and with SO3 (r = +0.906) whereas its joint occurrence with Fe2O3 was improbable (r = −0.834).

Hardening Slurries with Fluidized-Bed Combustion By-Products and Their Potential Significance in Terms of Circular Economy.

Hardening slurries (water-bentonite-binder mixtures) constitute a well-established material used broadly, i.a., for cut-off walls in civil and water engineering. Although they usually contain Portland cement, similar to common concrete, their properties differ greatly, mostly due to a much higher water content. This characteristic of hardening slurries creates unique opportunities for the utilization of significant quantities of industrial by-products that are deemed problematic in the concrete industry. This article investigates the effect of the addition of by-products of fluidized-bed combustion of hard, brown coal and municipal sewage sludge, as well as ground granulated blast furnace slag, on the properties of slurries. Unconfined compressive strength tests, as well as mercury porosimetry, scanning electron microscopy, and X-ray diffraction analyses were performed. The results suggest that it is possible to design hardening slurry mixes of desired properties, both in liquid and solid state, containing at least 100–300 kg/m3 of industrial waste. This includes cement-free slurries based entirely on industrial by-products as binders. In addition, the analyzed slurries exhibited good chemical resistance to landfill eluates, at the same time effectively immobilizing heavy metals. It was concluded that hardening slurry technology can ensure the safe deposition of significant amounts of waste that would be otherwise difficult to manage, thus contributing to the circular economy concept.

Attrition of high ash Ekibastuz coal in a bench scale fluidized bed rig under O2/N2 and O2/CO2 environments

While fluidized bed coal combustion technology has advanced significantly, attrition and its impact on combustion remains a problem. Using a bench scale fluidized bed unit, we examined the experimental attrition data for batches of coal ash particles. Experiments were carried out in the presence of bed material (sand) by adding coal particle to the hot riser, which has a height of 500 mm and internal diameter of 25.4 mm. Combustion of coal particles with high ash content was carried out in both O2/N2 and O2/CO2 environments. Coal particles with sizes of 0.4–0.8 mm and 0.8–1.4 mm were prepared by sieving and examined in this work. Using this data, the effect of critical factors on attrition such as gas velocity, particle size, and combustion environments were analyzed. In addition, the composition of ash particles was analyzed by SEM/EDX and XRF. The sizes of ash particles were less than 0.2 mm after combustion. A higher attrition rate was determined at higher gas velocity, regardless of the combustion environment. The ash composition analysis showed high concentration of silicon and aluminum oxide in the ash, and this possibly was increased due to kaolinite decomposition.

Effect of Atmosphere and Additive on Enrichment Characteristics of Trace Elements during Fluidized Bed Coal Combustion

The enrichment characteristics of trace elements (Cr, Mn, Co, Ni, Cd, Pb, Hg, As, Se) were investigated under air and O2/CO2 atmosphere during fluidized bed coal combustion. Results showed that Co, Ni, Cd, Pb, Hg, As, Se were more volatile than Cr and Mn. The increase of temperature promoted Mn, Co, Ni, Cd and Pb to migration from bottom ash to fly ash, and contributed Hg, As and Se to vapor phase. Cr, Mn, Co, Cd, Se tended to decrease in bottom ash and increase in fly ash during oxy combustion, while 21%O2/79%CO2 atmosphere led to the emission of gaseous As and the enrichment of Ni, Pb in both bottom ash and fly ash. With the increase in O2 concentration, the relative enrichment of all the trace elements except As increased, suggesting that their volatility were inhibited. Adding limestone and mixture of limestone and kaolinite had an inhibiting effect on volatilization of trace elements (especially Mn, Cd, Pb, Hg, As, Se) and the inhibiting behavior was strengthened under the oxy atmosphere.

Behavior of Pb During Coal Combustion: An Overview

Despite the progress in understanding heavy metals behavior during coal combustion, mitigation of heavy metals emissions is still a tough challenge due to a complex character of this phenomenon. Several lists of potentially toxic elements have been presented; in most cases, Pb belongs to the elements with the greatest environmental and human-health concern. The review paper is focused upon the behavior of Pb during coal combustion. with particular attention paid to decreasing its emissions. It summarizes the dominant parameters affecting its redistribution among coal combustion streams. As gaseous emissions can quite easily pass through the particulate control device, attention was paid primarily to Pb distribution between condensed and volatilized phases. A crucial factor enhancing Pb volatility is the presence of organic or inorganic chlorides, which is discussed in detail, including their chlorination mechanisms and interactions with other fuel/flue gas species. Components decreasing Pb volatility and promoting the formation of condensed phases are also discussed (higher levels of moisture, Na, O2 etc.). Factors enhancing Pb volatility, as well as factors facilitating Pb retention, are discussed with the view of fluidized-bed combustion, pulverized-fuel combustion, or co-combustion of coal with wastes.

PG test of 250 TPH, 9.8 Mpa Circulating Fluidized Bed Combustion Coal Fired Boiler and 4 X 61.5 MW Condensing Steam Turbine.

The objective of this paper is study the various methods and procedures involved in performance guarantee of 250 TPH, 9.8 Mpa CFBC (Circulating fluidized bed combustion coal fired Boiler and 4 X 61.5 MW, 238 TPH, 8.83 MPA, 537 °C condensing turbine. Contractor has to demonstrate the guaranteed performance in accordance with relevant section of the Contract Document. The tests will be carried out as per ASME PTC 4.1 - 1991 code for 04 hours duration. The various values, parameters, conditions mentioned herein are in line with the contract specifications. In case of any clarification, the Purchase order shall be referred. This paper describes the procedure of performance test to be conducted for testing of 61.5 MW Steam turbine generator. Performance test will be conducted to establish the following agreed performance requirements. 1) Heat Rate 2) Auxiliary Power consumption

Alternative Micro-Milled Binders in Cold Recycling Technologies

Abstract In addition to bituminous binders (bituminous emulsion, foamed bitumen), hydraulic binders are applied in cold recycling technologies to increase the strength of a final structural layer as well as to increase its resistance to water and frost impacts. This paper deals with the use of energy by-products from fluidized bed coal combustion and mineral waste and their modification into reactive material with the potential of replacing commonly used hydraulic binders. The increase in the reactive potential takes place through a high-speed milling process where the mechanical-chemical activation of the material takes place. This process is associated with the refinement of the material, a higher proportion of micro and nanoparticles, an increased surface area, opening of particles, etc. The material treated exhibits binding properties, and it can be used as an active filler that allows for the partial or complete substitution of hydraulic binders. The experimental part is focused on the application of alternative binders to cold recycling mixtures and their assessment according to valid technical regulations, i.e., an assessment of their indirect tensile strength and water susceptibility as well as compressive strength and resistance to the effects of water and frost.

Fluidized bed combustion coal fly ash: comparative evaluation for potential use in alkali-activated binders

ABSTRACT The physical, chemical, mineralogical and toxicity attributes of two fluidized bed combustion (FBC) coal fly ashes were evaluated, and were compared against that of a conventional coal fly ash. The potential use of the FBC ash in alkali-activated binders was also evaluated. Alkali-activated mortars were prepared and tested for compressive strength at different ages. The alkali-activated binders were also evaluated using SEM, TGA and FTIR methods. This investigation accounted for: (i) the differences in the combustion temperatures of FBC versus conventional methods of coal combustion; (ii) capture of sulfur from combustion emissions in the FBC method, and its incorporation into fly ash as crystalline solids; and (iii) the type and particle size of the sorbent used in the FBC process for capture of sulfur from combustion emissions. FBC ashes were found to differ from the conventional coal fly ash in terms of chemical composition, crystalline phases and carbon content. The higher crystallinity and carbon content and the larger particle size of FBC ashes were noted to challenge their potential use in alkali-activated binders. Suggestions are made based on the experimental results towards effective use of FBC ashes in alkali-activated binders.Abbreviations: FBC: Fluidized Bed Combustion; SEM: Scanning Electron Microscope; TGA: Thermogravimetric Analysis; DTA: Differential Thermal Analysis; XRF: X-Ray Fluorescence; XRD: X-Ray Diffraction; LOI: Loss-On-Ignition; TDS: Total Dissolved Solids; EPA: Environmental Protection AgencyI; CP-OES: inductively couple plasma spectroscopy; DI: Deionized; CFB: Circulating Fluidized Bed; ASTM: American Society for Testing and Materials

Experimental investigation on the coal combustion in a pressurized fluidized bed

Pressurized oxy-coal combustion is considered as one of the most promising carbon capture technologies in terms of high carbon capture efficiency and low cost. However, practical operational experience with pressurized coal combustion in a fluidized bed, especially with continuous coal feeding, is still very limited. In this study, a pressurized fluidized bed combustion system was developed and a series of coal combustion experiments were carried out with continuous coal feeding under the pressures from 0.1 to 0.4 MPa. The effects of the combustion pressure and stoichiometric air coefficient on the fluidized bed combustion performances of a Chinese lignite in terms of the temperature distribution profile, apparent solid holdup, combustion efficiency, conversion ratio of carbon in coal to CO2 and ash composition were investigated. The experimental results show that an increase in pressure is beneficial to the improvement of combustion efficiency, and the positive effect of increasing stoichiometric air coefficient on the conversion ratio of carbon in coal to CO2 is more obvious with a lower combustion pressure. The bottom ash and fly ash have similar chemical compositions under different pressures. Based on the experimental data, a correlation as the functions of pressure and stoichiometric air coefficient is proposed to predict the conversion ratio of carbon in coal to CO2.

Thermodynamic Analysis of Supercritical CO2 Power Cycle with Fluidized Bed Coal Combustion

Closed supercritical carbon dioxide (S-CO2) Brayton cycle is a promising alternative to steam Rankine cycle due to higher cycle efficiency at equivalent turbine inlet conditions, which has been explored to apply to nuclear, solar power, waste heat recovery, and coal-fired power plant. This study establishes 300MW S-CO2 power system based on modified recompression Brayton cycle integrated with coal-fired circulating fluidized bed (CFB) boiler. The influences of two stages split flow on system performance have been investigated in detail. In addition, thermodynamic analysis of critical operating parameters has been carried out, including terminal temperature difference, turbine inlet pressure/temperature, reheat stages, and parameters as well as compressor inlet pressure/temperature. The results show that rational distribution of split ratio to the recompressor (SR1) achieves maximal cycle efficiency where heat capacities of both sides in the low temperature recuperator (LTR) realize an excellent matching. The optimal SR1 decreases in the approximately linear proportion to high pressure turbine (HPT) inlet pressure due to gradually narrowing specific heat differences in the LTR. Secondary split ratio to the economizer of CFB boiler (SR2) can recover moderate flue gas heat caused by narrow temperature range and improve boiler efficiency. Smaller terminal temperature difference corresponds to higher efficiency and brings about larger cost and pressure drops of the recuperators, which probably decrease efficiency conversely. Single reheat improves cycle efficiency by 1.5% under the condition of 600°C/600°C/25Mpa while efficiency improvement for double reheat is less obvious compared to steam Rankine cycle largely due to much lower pressure ratio. Reheat pressure and main compressor (MC) inlet pressure have corresponding optimal values. HPT and low pressure turbine (LPT) inlet temperature both have positive influences on system performance.

Attapulgite suspension mitigates fine particulate matter (PM2.5) emission from coal combustion in fluidized bed

To reduce fine particulate matter emission from coal burning sources especially fossil fuel fired energy generation facility is critical to improve air quality. Attapulgite suspension was attempted to spray in a 6 kW fluidized bed facility and reduce fine particulate matter emission during coal combustion. The key parameters such as attapulgite mass, flowrate and spraying zone were investigated to determine the optimal and critical conditions that influence fine particulate matter emission. Exciting results indicate that both fine particle number and mass concentrations are largely decreased due to the physical/chemical absorption with the suitable mass ratio of 3 wt%. The spray of attapulgite suspension in both dense bed and dilute bed effectively mitigates fine particle emission based on the agglomeration and absorption. The most excellent result is achieved at a flowrate of 38 ml/min in dense bed with particle number reduction up to 93.5% in PM2.5 (fine particles is equal to/less than 2.5 μm), 93.6% in PM1.0 (fine particles is equal to/less than 1.0 μm) and 93.7% in PM0.1 (fine particles is equal to/less than 0.1 μm), respectively. The work highlights the potential of spraying attapulgite suspension as an effective process to reduce fine particle emission during coal combustion in fluidized bed system.

THERMODYNAMIC ANALYSIS OF A FLUIDIZED BED COAL COMBUSTOR STEAM PLANT IN TEXTILE INDUSTRY

T he examinations of first and second laws of thermodynamics are performed on a 6.5 MW power plant, established in Adana, Turkey. The equipment for the investigated plant can be aligned as a fluidized bed coal combustor (FBCC), a heat recovery steam generator (HRSG), an economizer (ECO), fans, pumps, a cyclone and a chimney. Whole parts of equipment are investigated separately and energetic and exergetic inspections are enforced for whole parts of the plant. The maximum exergy destruction rates in the plant are obtained for the FBCC, HRSG and ECO with 95%, 3% and 1% of the whole system, respectively. Higher excess air in the system induces heat losses, especially in the FBCC component by virtue of the rising in mass flow rate of the flue gas. This situation can be considered as one of the primary reasons of irreversibility. Additionally, higher excess air induces the decrement of combustion efficiency in FBCC. Therefore, this value and adverse effects on combustion efficiency can be decreased by reducing the flow rate of air.