Fluidized Bed Combustion Technology Research Articles

Numerical investigation of mixing and heat transfer of mixed biomass and silica sand particles in a bubbling fluidized bed combustor

Using fluidized bed combustion technology, biomass is being promoted for electricity production. However, a lack of biomass in a particular location or season poses a problem, leading to low thermal efficiency when using a single biomass. Thus, mixed biomass is considered a potential solution. This study uses CFD-DEM simulation to investigate the effects of various biomass types, loadings, and blending ratios on hydrodynamics and heat transfer in a bubbling fluidized bed. Coarse bagasse size provides the most efficient mixing behavior for a single biomass mixture. A blending ratio of 1:3 wood chip to coarse bagasse with 5% biomass loading, using 1 mm silica sand, is the appropriate condition. The primary factor for mixing is the difference in biomass sizes, while different biomass loadings have no significant influence. Smaller sand particles enhance the mixing and heat transfer. These findings provide useful guidelines for efficient biomass conditions in fluidized bed combustors.

Utilizing Sewage Sludge Slag, a By-Product of the Circulating Fluidized Bed Combustion Process, to Efficiently Remove Copper from Aquatic Environment

Currently, one of the greatest threats to the aquatic environment is industrial wastewater containing heavy metals and other toxic substances. Hence, it seems necessary to search for ecological and cheap technologies for removing metals from wastewater. In this research, slag was used as waste obtained in the circulating fluidized bed combustion technology (CFBC), which is considered to be a modern, clean, and very effective method of incineration of municipal sewage sludge. The physicochemical properties of the waste material were characterized using selected analytical techniques. Next, the processes of adsorption of Cu(II) ions on slag in aqueous solutions were investigated. The results showed a high metal removal efficiency of 98.8% at pH 1.8 and slag dosage 5 g/L. Numerous studies have demonstrated that high process efficiency at a level of at least 90% is attainable. Based on the Langmuir equation, the maximum adsorption capacity was calculated to be 70.3 mg/g. Kinetic analysis revealed that the process fits better into the pseudo-second-order reaction model and the Freundlich isotherm. The intraparticle diffusion model was considered as a rate-controlling step for Cu(II) adsorption. In summary, the slag waste produced in the CFBC technology seems to be a highly effective adsorbent for potential use in adsorption processes to remove heavy metals from the aquatic environment. This solution is in line with the current European ‘zero waste’ strategy and the assumptions of a sustainable development economy.

Utilization of coal gangue power generation industry by-product CFA in cement: Workability, rheological behavior and microstructure of blended cement paste

Circulating fluidized bed fly ash (CFA), by-product of coal gangue power generation industry based on circulating fluidized bed combustion technology, differs from ordinary fly ash (OFA) in its physical and chemical properties. This paper aims to investigate the influences of CFA with three particle sizes on the workability and rheological properties of cement paste. The results show that untreated raw CFA (RCFA) can significantly degrade many properties of fresh cement paste. Directly using CFA as a mineral admixture in cement-based materials is not suitable in terms of workability. However, CFA through grinding methods can significantly mitigate the detrimental effect of CFA on the flowability of cement paste. When 15% ultrafine CFA (UCFA) was added, the cement paste exhibited relatively favorable workability and rheological properties. The rheological behavior of cement paste containing CFA with three particle sizes follow the shear thinning, which is in line with the modified Bingham model. Furthermore, the reasons for the impact of CFA on the microscopic level of cement workability are analyzed and discussed. The addition of CFA reduces the amount of free solution in the cement paste, leading to the formation of a flocculated structure and an increase in the thixotropic loop area. Based on the analysis of TOC, BET and TEM, it was determined that numerous polycarboxylate superplasticizer (PCE) molecules are adsorbed onto the rough and porous surface structure of CFA particles, hence the destructive ability of PCE to the flocculation structure caused by cement hydration is weakened. Therefore, the mechanism that CFA affecting the working performance of cement paste can be determined as: the adsorption of free water and PCE molecules.

Magnesite as a Sorbent in Fluid Combustion Conditions—Role of Magnesium in SO2 Sorption Process

This article presents the results of research on magnesites from the Polish deposits of Szklary, Wiry and Braszowice as SO2 sorbents under the conditions of fluidized bed combustion technology. In practice, magnesites are not used as SO2 sorbents, and the role of magnesium in the desulfurization process under the conditions of fluidized bed combustion technology is evaluated differently among researchers. The literature data question the participation of magnesium in the process of SO2 capture from flue gas and prove its high reactivity. Similarly, previous studies referred to the problem of the stability of magnesium-containing desulfurization products under high temperature conditions. This paper analyzes the SO2 binding process and determines the parameters of the sorbent responsible for the efficiency of magnesite sorption. It was shown that MgO, formed as a result of thermal dissociation of magnesite, actively participates in the SO2 binding reaction to form magnesium sulfate phases (MgSO4 and CaMg2(SO4)3) stable in the temperature conditions of fluidized bed boilers. The problem of differentiated reactivity of magnesium-containing sorbents should be associated with the porosity of the sorbents. If the secondary surface of the sorbent is developed based on micropores and smaller mesopores (below 0.1 µm), the sorbent will be characterized by low sorption activity. It was shown that the SO2 binding process is then limited only to the outer part of the sorbent grains. This results in the formation of a massive, SO2-impermeable desulfurization-product layer on the sorbent grain surface. In real conditions, where the reactions of CaCO3 thermal dissociation and SO2 sorption occur almost simultaneously, the inside of the sorbent grains may remain undissociated. The results of experimental research allowed us to trace the dynamics of the SO2 binding process in relation to real conditions prevailing in fluidized bed boilers.

Investigation of fouling and corrosion of low-temperature reheater in a CFBC boiler

A remarkable feature of circulating fluidized bed combustion technology is the adeptness to handle a wide variety of solid fuels and their mixtures with high availability and low emissions. The fuels mainly used in fluidized bed boilers are various types of coal, peat, refuse-derived fuels, wood and other biomass. Nonetheless, the properties and behavior of some solid fuel ashes present challenges in power production regardless of the combustion technology and may even limit the use of these fuels. Biomass-based fuels typically contain high contents of easily vaporizable alkalis and chlorine, as also oil shale does. Extensive vaporization of alkalis or chlorine from the fuel increases the risk for ash-related problems such as fouling, slagging and corrosion.Co-utilization of biomass and retort gas in oil shale-fired power stations is an additional process option that increases the fuel flexibility but at the same it also increases operational risks, especially fouling and corrosion.Operational experience from Foster Wheeler two circulating fluidized bed combustion units, which were commissioned in 2004 and 2005, have proven that the above-mentioned fouling or slagging issues have been avoided. Even with different fuel mixtures. This was one of the main reasons why 300MWel Auvere power plant was acquired with circulating fluidized bed combustion technology in 2011. The plant was due to be handed over to Eesti Energia by General Electric (former Alstom) in November 2015. It was delayed since emission limits were not achieved. Therefore, additional flue gas cleaning devices were needed to be installed. Meanwhile, the power plant continued operating at loads where emissions standards were met.The 300MWel Auvere power plant was finally commissioned in 2018. Since then, the circulating fluidized bed combustion boiler has been facing severe operational problems such as fouling and corrosion of the low-temperature reheater.The failures of low-temperature reheater tubes have been occurred as a result of operation conditions.Three different reasons for low-temperature reheater malfunctions have been determined: erosion, changes in metal structure and high temperature chlorine corrosion.

A Novel Process for the Containment of SO2 Emissions from Class C Fly Ash in the Fired Materials by Haüyne Formation.

Class C fly ash has been receiving increasing attention due to the gradual transition of thermal power plants all over the world to the fluidized bed combustion technology with sulfur dioxide emissions capture. This research investigates the utilization of class C fly ash in fired ceramic materials with simultaneous efficient and novel containment of sulfur dioxide emissions in the flue gas during firing. A number of experiments were conducted by addition of sodium water glass with different molar ratios of SiO2:Na2O, sodium carbonate, and different ratios of sodium carbonate to water glass to the class C fly ash to examine the optimal combination and quantity for the creation and formation of the mineral phase haüyne which resulted in reduction and containment of SO2 emissions. Results revealed that a 12% dose of sodium water glass with a low molar ratio of 1.7 (SiO2:Na2O) combined with class C fly ash was more effective in the formation of haüyne and the resulting decrease of SO2 in the flue gas was more substantial. The newly formed mineral phase haüyne was identified by an X-ray diffraction analysis and scanning electron microscopy with energy dispersive X-ray spectroscopy. Outcomes reveal a potential for utilization of class C fly ash in the fired materials by containment of sulfur dioxide into their structure.

Reduction of life cycle impacts of oil shale electricity caused by the shift to fluidized bed combustion technology

Reduction of life cycle impacts of oil shale electricity caused by the shift to fluidized bed combustion technology

Application of Fluidized Bed Furnance Bottom Ash in Civil Engineering – A Review

For several years there has been widespread and open discussion about climate problems and human responsibility for the generated waste. The number of regulations has led to a search for applications for by-products of combustion. Moreover, the forecasted economic crisis additionally motivates to use every possible material to reduce the cost of manufacturing activities. Efficient waste management is a key element for Polish companies in their efforts to reduce their negative impact on the environment. Fluid combustion of fuels in the Polish power and heat industry still belongs to relatively new technologies. Despite the application of the most technologically advanced processing methods, bottom ashes from fluidized bed boilers are still reluctantly used. The author sees possibilities of using bottom ashes in geotechnical works. The aim of this review is to present the existing source papers relating to the use of bottom ashes in construction processes. A particular area of interest is the use of said ashes in jet-grouting (JG). The paper briefly refers to fluidized bed combustion technology as a source of combustion byproducts. The author pay special attention to the characteristics defining the characteristics of the ashes. The reader's attention will then be drawn to jet-grouting technology. References can be found to the methodology of general cement-soil testing. Due to the nature of the use of JG, the focus is particularly on their strength, water-permeability and frost resistance properties. Due to the need to determine the internal structure of the cement-ground, attention was also paid to the possibility of using X-ray computed tomography for soil cement testing.

Prospects for the Low Pollutant Emission Control of Circulating Fluidized Bed Combustion Technology

With the pollutant emission standards becoming increasingly stringent and considering the pressure of carbon neutral by 2060, the low pollutant emission potential of circulating fluidized bed (CFB) combustion technology needs to be further exploited, thus to promote the market competitiveness of CFB boilers; this is critical for the clean and efficient utilization of coal as well as for the energy transformation in China. In this article, we summarize the pollutant emission characteristics of CFB combustion, and review the development of major technologies for CFB boiler emission control. Based on the energy development strategies and corresponding policies in China, development suggestions are proposed for reducing pollutant emission of the CFB combustion technology. The most significant approach is to push the limits of original pollutant emission for CFB combustion by re-specifying the fluidization state and through in-furnace combustion adjustment, while the boiler thermal efficiency should be ensured. For the long-term development of coal energy, the new-generation CFB combustion technology with ultra-low emission should be researched and developed while combining with technologies such as supercritical/ultra-supercritical, intelligent operation, carbon capture, utilization, and storage, and energy storage technologies. The existing CFB boilers with small or medium capacity should also be upgraded. Considering the fuel flexibility of CFB combustion, biomass power generation should be promoted to realize low-cost and high-efficiency consumption of low-heat value fuels, urban refuse, industrial wastes, etc. The peak load regulation capacity and low pollutant emission property of the CFB boilers should be promoted to improve operation flexibility and renewable energy consumption. Moreover, the desulphurization ash produced in CFB combustion should be comprehensively utilized, and the N2O emission problem is also significant. The pollutant emission standards and related policies need to be formulated from an overall perspective to guide the healthy development of the energy industry.

Condensed phase corrosion of P91 and DSS 2205 steels at advanced oxygen‐fired pressurized fluidized bed combustion plants

AbstractTo achieve the targets of high energy efficiency and reduced CO2 emission, advanced oxygen‐fired pressurized fluidized bed combustion technology is being developed. The generated flue gas condensates are very corrosive, but very limited information is available to select appropriate alloys for the cost‐effective construction and long‐term safe operation of flue gas components. Thus, this study investigated the corrosion performance of P91 and DSS 2205 steels in the simulated condensates at 60°C–150°C. The dominant reactions on the two steels were considerable oxide formation and high chemical dissolution of the formed oxides instead of localized pitting. The increase in temperature leads to an exponential increase in the long‐term corrosion rates of the steels. Benefited from its high Cr and Mo contents, DSS 2205 steel exhibited much better corrosion resistance, and the formed surface scales consisted of inner Fe‐enriched and outer Cr‐enriched oxides in which Cr2O3 was transformed into Cr(OH)3 with the increase in temperature. The corrosion products on P91 steel consisted of inner Cr–Fr–Mo oxides and outer Fe‐enriched oxides, which were porous and unable to protect the steel.

Potential of solid residues from power plants as thermochemical energy storage materials

Due to large amounts of solid residue of oil shales produced every year by thermal processing, new ways of utilizing them are constantly investigated. As the main components of oil shale ash are calcium, magnesium and silica, the material has potential for different areas. In this paper, we investigated the possibility and potential of utilizing Estonian oil shale ash, rich in CaO, for thermochemical energy storage material. The investigated samples included the sources of main ash flow—bottom and electrostatic precipitator ash from two power plants utilizing circulating fluidized bed combustion technology. The ash from the economizer was also analysed as a comparison. The samples were characterized through elemental and chemical analysis and XRF and subjected to thermal analysis in either mixtures or pure environments of N2 and/or CO2.

Some chosen aspects of CFB boilers operation

Central Europe, particularly Poland, has been one of the areas of intensive development of fluidized bed combustion technology for over 25 years. This paper deals with a brief discussion on the results of industrial tests carried out by the authors and focused on the reduction of nitrogen oxide emission, solids deposition and unburned carbon content in the fly ashes. Some selected data has been presented and come remarks and counteractions to improve the operation of industrial large-scale circulating fluidized bed boilers are given.

Modeling and analysis of solar thermal and biomass hybrid power plants

Stand-alone renewable energy plants are usually unable to generate stable electrical power because of resource intermittency. Consequently, grid operators find it difficult to plan power supply. Employing electrical storage, thermal energy storage, and hybridization in stand-alone plants could provide some solutions. However, electrical and thermal storage have limitations at megawatt scales with major ones being not cost-effective and the increased solar field. Hybridization of multiple sources of renewable energy is a promising way to address intermittency issues.This paper presents thermodynamic modeling for sizing a steam Rankine cycle based solar–biomass hybrid power plant. Solar system uses parabolic trough technology, and biomass system uses fluidized bed combustion technology to generate steam for power generation. The biomass system plays a significant role in the hybrid operation during the solar intermittency periods. Also, the boiler in a stand-alone mode can generate power post sunshine hours to meet the power demand. Further, the paper presents a case study to emphasize parameters such as solar field area requirements, biomass requirements, system efficiency, intermittency aspects, capacity utilization factor, capex, and levelized cost of electricity for various scales of hybrid systems. The results suggest that hybridization could be a possible sustainable solution.

Modeling of transient operation of steam superheater in CFB boiler

Currently, a need to balance power grids and compensate the variable electricity demand caused by a large share of electricity produced from renewable energy sources is observed. In countries where the coal-fired power plants are the main energy sources, the operation in the flexible regime is required. The flexible operation is characterized by frequent load changes, work outside the nominal operating conditions, and the more frequently start-ups, shutdowns, and partial load changes. Circulating Fluidized Bed combustion technology gives boiler and plant operators greater flexibility in burning a wide range of coal and other fuels, keeping high efficiency and reduced pollution. The unit load changes are realized by changing the amount of produced steam and load of the boiler. Paper presents the results of numerical modeling of superheater operation in Circulating Fluidized Bed (CFB) boiler. The superheater is characterized by the complex shape of tube cross-section. During the superheater calculations, the temperature distribution of the material in complex cross-section need to be determined. To perform numerical analysis and calculate the superheater operation in the transient state, the mathematical model of superheater was created. The use parameters dependent on temperature and pressure allowed to develop a universal superheater model. To verify the numerical model, the temperature distributions at steady state were compared with the results obtained using CFD software, confirming good results accuracy. Finally, the numerical analysis of the transient operation of steam superheater was performed. The calculation was carried out for three different partial loads and for changing steam temperature at the superheater inlet. Steam and tubes material temperature changes during transient flexible boiler operation were presented. The developed model can be used to perform calculations in the full range of boiler load, both during steady and transient boiler operation. Equations describing the physical processes occurring inside the superheater makes the model universal for a given type of a boiler.

Acid Leaching of Rare Earth Elements from Coal and Coal Ash: Implications for Using Fluidized Bed Combustion To Assist in the Recovery of Critical Materials

High-temperature pretreatment of coal-based mineral matter in an oxidizing environment significantly enhances the leaching characteristics of rare earth elements (REEs). A research study has found that the temperatures used in fluidized bed combustion (FBC) of coal to produce electricity are near optimum for pretreating the associated mineral matter prior to leaching to maximize the recovery of critical materials. Tests were performed on representative samples collected from preparation plants treating West Kentucky No. 13, Illinois No. 6, and Fire Clay coal seam sources as well as fly ash and bed ash samples from two FBC power plants. Acid leaching tests using 1.2 M HCl at 75 °C were performed on both the coal and the FBC ash samples. Prior to leaching, the coal samples were pretreated at temperatures of 600, 750, and 900 °C in an oxidizing environment to study the effect on leaching characteristics. The results showed that pretreatment at 600 °C for 2 h resulted in a significant increase in REE recovery from a range of 20–40 to ∼80% for all coal sources. The leaching kinetics is characterized by a quick release of rare earth elements within the first few minutes of the process. For the West Kentucky No. 13 coal source, ∼75% of the REEs were leached in the first 15 min from the 1.4–1.8 specific gravity (SG) fraction that was calcined at 600 °C. Additionally, the leaching kinetics of the major contaminant, that is, Fe, was much lower than that of the REEs, which significantly benefits the efficiency of leaching and the downstream upgrading processes. REE leaching characteristics of the FBC ash samples were similar to those of the calcined coals. Mineralogy characterization showed that the degree of crystallinity for both the calcined coal and FBC samples was similar to the original associated mineral matter, which provided evidence for the advantage of using the FBC byproducts as REE feedstocks over pulverized coal boilers that utilize temperatures greater than 1200 °C. These findings were used to develop a conceptual flowsheet that incorporates FBC technology and its typical combustion environment to enhance the feasibility of recovering critical materials from coal-based sources.

Numerical and Experimental Study on Oxy-fuel Coal and Biomass Co-firing in a Bubbling Fluidized Bed

As one of the most promising approaches to reduce CO2 emissions from power plants, oxy-fuel fluidized bed combustion technology still has a lot of basic uncertainties requiring in-depth studies, especially in application for coal and biomass co-firing. This work focuses on results of coal co-firing with biomass under O2/CO2 combustion conditions in a 6 kWth bubbling fluidized bed combustor. With the same thermal input maintained, computational fluid dynamics (CFD) was adopted as a predictive tool to examine the effects of firing coal and co-firing biomass with coal under O2/CO2 atmospheres. Hydrodynamics, heat transfer, species concentration, and char gasification in a fluidized bed were investigated. In comparison to coal combustion, the hydrodynamic and temperature profiles of biomass co-firing are not affected much when maintaining the same thermal input. The temperature of biomass co-firing at the bottom of the dense-phase zone, which is mainly the char combustion area, is about 10 K lower than that o...

Mass, energy and exergy analysis of a biomass boiler: A portuguese representative case of the pulp and paper industry

This work deals with the mass, energy and exergy analyses of the energy conversion process in a 50 MWth thermal power plant, using residual forest biomass as fuel and integrating bubbling fluidized bed combustion technology. This is a representative case study of the energy production from eucalyptus residual biomass in the Portuguese pulp and paper industry. Analyses are made of the mass, energy and exergy flows, and how they change in the main components of the system, namely the combustion chamber, boiler, drum, superheater, economizer, and combustion air pre-heaters. Sankey and Grassmann diagrams highlight the mass, energy and exergy flows. Special emphasis is given to the energy and exergy efficiencies, which must be based on the useful produced superheated steam to include the influence of the biomass moisture content. The main goal is to find where and what potential exists for energy efficiency improvements. Results show that the main exergy destruction occurs in the combustion process, and that energy and exergy losses are minimal due to the system’s good thermal insulation. Results also show that the main potential for improvement is on the decrease of the residual biomass moisture content.

Research in the fluidized bed combustion in the Laboratory for thermal engineering and energy - Part B: Achievements in technology implementation

Paper gives a review of the most important results of extensive and wide-ranging research program on R&D of fluidized bed combustion technology in the Laboratory for Thermal Engineering and Energy of the VINCA Institute of Nuclear Sciences. Paper presents detailed overview of R&D activities from the beginning in the second half of the 1970's up to present days. These activities encompass applied research achievements in the field of characterization of limestones and bed agglomeration and sintering and modeling of overall processes during fluidized bed combustion, all of which have facilitated the R&D of the fluidized bed combustion technology. Attention is also given to steady-state combustion testing of a wide-range of fuels (coals, liquid fuels, biomass, waste solid and liquid materials, etc.) in our fluidized bed combustor and development of original methodology for testing the suitability of fuels for fluidized bed combustion, as well as specific achievements in the area of technology application in Serbia.

Effective adsorption of lead ions using fly ash obtained in the novel circulating fluidized bed combustion technology

Fly ash was examined for the separation efficiency of Pb2+ ions from water in batch experiments. Fly ash is industrial waste produced from the incineration of sewage sludge by the novel circulating fluidized bed combustion (CFBC) technology and was taken into the experiments. Physical and chemical properties of the material were characterized using several methods, such as fraction analysis, particle size distribution, bulk density, composition, morphology, surface and internal structure by elemental analysis, FT-IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, comprehensive thermal analysis, fly ash texture by BET adsorption isotherms, specific surface area, volume of pores, average pore diameter and pore volume distribution by the BJH method. The influence of pH values on zeta potential of the fly ash surface before and after the adsorption process was conducted. The calculated maximum adsorption capacity of Pb2+ by fly ash reached 51.98 mg/g. The kinetic analysis revealed that the adsorption process is better described by the pseudo-second order equation and it is well fitted to the Freundlich model. In conclusion, fly ash obtained in the CFBC technology is a promising low cost adsorbent for the highly effective recovery of Pb2+ from wastewater.

Co-Firing of Coal with Pine Needles in a 20kw Oxy-Fired Bubbling Fluidized Bed: Experimental Investigation

Oxy-fired fluidized bed combustion is one of promising technique which serves a dual purpose i.e. benefits of fluidized bed combustion and oxygen firing technology. India, being a diversified country has a vast resource of biomass which includes agricultural waste, organic matter, forest waste etc. Pine needles (PN) a forest biomass are abundantly available in the hills of North India and its proper utilization will strengthen the economy as well as reduces the pollution. Co-firing with oxy-fired fluidized bed has potential for negative CO2 emission level for power generation. Co-firing at low percentages of the thermal power (typically below 5-10 %) avoids the characteristic operating problems of biomass combustion. The present work extensively investigate the temperature profile, flue gas emission and the performance of co-firing coal with pine needles under air-fired and oxy-fired condition in a 20kW bubbling fluidized bed (BFB) combustor. Five different ratios of coal and pine needles are considered for this study are 100%/0%, 75%/25%, 50%/50%, 25%/75% and 0%/100%. Combustion is observed under control and stable for the blend when pine needle share is in-between 25% to 50%. Maximum combustion efficiency of 97.05 % could be achieved with 75%coal/25%PN under oxy-fired condition. The measured percentage of NOx and other gases are found in permissible limit.