Fluidized Bed Boiler Research Articles

Numerical Simulation of Flow Characteristics in Circulating Fluidized Bed Boiler

Considering the different particle sizes in the circulating fluidized bed boiler furnace, the binary-component method is used to analyze the flow characteristics in the circulating fluidized bed boiler furnace. The particle dynamics principle is used to solve the gas-solid two-phase mass equation, momentum equation and turbulence equation using the two-fluid model. The model uses more mature boiler design drawings, reproduces the flow characteristics of particles in the furnace, obtains the shape of the lower bubbling bed and the fast upper bed, and analyses the gas phase velocity and particle distribution in the furnace under the design parameters.

Technique for reducing erosion in large-scale circulating fluidized bed units

This paper presents a methodology, implemented for a real industrial-scale circulating fluidized bed boiler, to mitigate the risk of heating surfaces exposed to an intensive particle erosion process. For this purpose, a machine learning algorithm was developed to support the boiler reliability management process. Having a tool that can help mitigate the risk of uncontrolled power unit failure without expensive and technically complex modernization is desired. A virtual procedure can be seen as a milestone towards the application of digital models to the diagnostic procedure of large power units, providing answers for many scenarios that cannot be normally studied during boiler operation. The predictive model developed in this work allows us to provide the requested feedback to the unit control systems regarding possible changes in boiler operating conditions and reduce the erosion effect. The functionality of the discussed methodology is investigated via application of the developed multiphase computational model.

A Study on the High Temperature Phase Change under Alkaline Conditions in the Bed Material of the Circulating Fluidized Bed Boiler

A Study on the High Temperature Phase Change under Alkaline Conditions in the Bed Material of the Circulating Fluidized Bed Boiler

Recovered Fly Ashes as an Anthropogenic Raw Material

Poland is a country where the commercial power industry mainly uses coal to produce energy. As a result of energy production processes, by-products of combustion are generated, primarily fly ashes. In Poland, these are mostly obtained from conventional coal combustion boilers. Fly ashes from coal combustion account for 1.2% of all industrial waste generated in Poland. In addition, fly ashes are produced by fluidized-bed boilers. These are classified as a mixture of fly ashes and solid calcium-based reaction waste from flue-gas desulphurization, and constitute almost 2% of Polish industrial waste. This paper describes the amounts of fly ashes generated in Poland and considers activities related to their recovery and disposal. The high recovery levels of fly ashes (about 90%) and fluidized ashes (about 98%) mean that these waste products can also be considered anthropogenic raw materials. The use of these materials in the cement industry is an example of industrial symbiosis. Such usage benefits not only the economy but also the environment and, therefore, society as a whole. To describe the use of recovered fly ashes in cement plants, the authors use the anthropogenicity index, which characterizes the level of technological advancement and the substitutability of primary raw materials for secondary raw materials.

Risk Evaluation of Pollutants Emission from Coal and Coal Waste Combustion Plants and Environmental Impact of Fly Ash Landfilling.

Emission factors (EFs) of gaseous pollutants, particulate matter, certain harmful trace elements, and polycyclic aromatic hydrocarbons (PAHs) from three thermal power plants (TPPs) and semi-industrial fluidized bed boiler (FBB) were compared. EFs of particulate matter, trace elements (except Cd and Pb), benzo[a]pyrene, and benzo[b]fluoranthene exceed the upper limits specified in the EMEP inventory guidebook for all combustion facilities. The comparison of trace elements and PAHs content in fly ashes (FAs) from lignite and coal waste combustion in TPPs and FBB, respectively, as well as the potential environmental impact of FAs disposal, was performed by employing a set of ecological indicators such as crustal enrichment factor, risk assessment code, risk indices for trace elements, and benzo[a]pyrene equivalent concentration for PAHs. Sequential analysis shows that the trace elements portion is the lowest for water-soluble and exchangeable fractions. The highest enrichment levels in FAs are noticed for As and Hg. Based on toxic trace elements content, FAs from TPPs represent a very high ecological risk, whereas fly ash from FBB poses a moderate ecological risk but has the highest benzo[a]pyrene equivalent concentration, indicating its increased carcinogenic potential. Lead isotope ratios for Serbian coals and FAs can contribute to a lead pollution global database.

Effect of the sulfur compounds structure on the SO2 conversion and capture in a bubbling fluidized-bed combustor

SO2 is the main pollutant produced by fluidized bed boiler. Most studies only consider the effect of operating parameters on SO2, while the influence of sulfur structure in coal is ignored. Combustion experiments using pure char loaded with various sulfur structures in a bench-scale bubbling fluidized bed combustor was carried out in this paper to determine the influence of different sulfur structures on SO2 conversion. Effects of excess air, bed temperature and desulfurization efficiency were also investigated. The experimental results show that the order of SO2 conversion is ferrous sulfate > 1-Dodecanethiol > pyrite > diphenyl sulfide > diphenyl sulfoxide > dibenzothiophene. Most sulfur models showed an increase in SO2 conversion with increasing temperature. When the excess air increases, the oxygen content in the furnace is increased, which is beneficial to the conversion of sulfur model to SO2. The desulfurization efficiency of ferrous sulfate and pyrite is higher than that of organic sulfur.

Fouling monitoring in a circulating fluidized bed boiler using direct and indirect model-based analytics

Fouling is a phenomenon where material accumulates on the exterior of convective heat exchangers (HX) and other surfaces. In boilers fired by waste-derived or biomass fuels, these surfaces are cleaned frequently to maintain adequate heat transfer between the flue gas and fluid. However, excess cleaning of HX surfaces wastes money and resources, and the common practice of soot removal at fixed time intervals is not an optimal strategy. An adaptive timing method would be beneficial; however, real-time knowledge of HX condition is hard to obtain.In this paper, we present (1) a state estimation approach for fouling monitoring in a Circulating Fluidized Bed (CFB) boiler, fusing knowledge from a physical model with process measurement data, and (2) a novel condition monitoring scheme based on modal-vibrational sensing, with potential for a directly estimating the degree of fouling on heating surfaces. The results are demonstrated on a full-scale commercial CFB. Combining physical models, machine learning, and modal analysis in mutually supporting ways provides a solid basis for future sootblowing optimization efforts and improved fouling management.

Piecewise affine model identification and predictive control for ultra-supercritical circulating fluidized bed boiler unit

In this paper, fully considering the form of the nonlinear model after linearization at the steady-state point, an improved subspace identification method based on the steady-state points' deviations data was proposed to identify piecewise affine model. Besides, the construction of the excitation signal in practical applications is fully considered. The identification results demonstrate that the method has better adaptability to strong nonlinear systems. The identification normalized root mean square error of each working condition is almost all less than 10%. On this basis, a framework that is widely applicable to complex system control is established combining with the mixed logic dynamic model. The canonical form realization is performed to transfer the local models into the same state basis. Predictive control was carried out on the boiler-turbine system of the 660-MW ultra-supercritical circulating fluidized bed unit based on the above framework. The results indicate the effectiveness of the framework.

Eco-friendly zeolites for innovative purification of water from cationic dye and heavy metal ions.

Along with industrial development, coal consumption and the amount of waste fly ash increase, negatively impacting the environment. Fly ash contains silicon and aluminum oxides, and could serve as a substrate for the synthesis of zeolite. The novelty of this study was to assign a potential of fly ashes from lignite combustion in three energy blocks operating on circulating fluidized bed boilers to convert them into zeolites. The X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy; pore volume, size and specific surface area tests; thermal analysis; leaching test; and radioisotope activity analysis were applied to characterize the materials. Zeolites were synthesized using hydrothermal and fusion methods modified in the molar concentration of NaOH, the ratio of NaOH to raw material, drying and heating temperatures, and treatment time. Both, hydrothermal and fusion synthesis were found to result in the efficient formation of the zeolite Linde Type A, gismondine, and sodalite; with the largest specific surface area of zeolite developed after fusion synthesis (132 m2 g−1). The zeolite had surpassingly high efficiency of adsorption of cationic impurities from post-production wastewater, ranging from 85% to 97% and from 89% to 100%, when tested with methylene blue and lead ions, respectively. The costs of zeolite production were estimated to range from 3.82 to 6.36 $ per 1 kg, thus reducing the price of commercial zeolite by up to 99.5%. The new engineering method of zeolite is an attractive alternative to the storage of hazardous byproducts from coal-fired power plants. Eco-zeolite is also a technological innovation in the cleaning of post-production wastewater from harmful impurities, while water reuse in a closed circuit. Our studies provide tools for novel and integrated environmental management in line with the 'Cleaner Production' goal to reduce the production of waste, while improving use efficiency of energy, resources, and water.

Emission and Energy Characteristics of the Combination Use of Coal and Biomass in Circulating Fluidized Bed Boilers (CFBB) in Steam Power Plant

Currently there are still many power plants using fossil fuels, including oil, gas and coal to produce electricity. The problem recently received by many developing countries, including Indonesia, is environmental degradation due to CO, SO2 and NOx emissions. Co-burning of biomass with coal is in most countries one of the most economical technologies available today for significant pollutant reduction. This study tested the combined combustion of coal and biomass in a direct co-firing Circulating Fluidized Bed Boiler (CFBB) with two treatments, namely 5 wt% sawdust biomass and 95 wt% coal, 5 wt% woodchip biomass and 95 wt% coal. The results of the two tests were compared with the parameters when using 100 wt% coal. This study aims to (1) analyze the energy produced from burning a combination of coal and biomass, and (2) analyze the emission content, including SO2, CO, NOx. The mixture of coal and sawdust produces 82 MWh of gross electricity, higher than coal and woodchips and requires the smallest amount of fuel, namely 18.7 tons per hour. The 5 wt% woodchip emitted the lowest emissions compared to the other 2 cases, namely 71.5 mg/Nm3 SO2 and 222.4 mg/Nm3 for NOx. The lowest CO emission was issued by a 5 wt% woodchip mixture, namely 4.0 ppm.

Research on the effect of the flue gas recirculation on the combustion and operating economy of circulating fluidized bed boiler

To meet the requirements of the power grid’s deep peak shaving, a 300MW CFB boiler in a power plant transformed the flue gas recirculation. After the transformation, it is found that after putting into the flue gas recirculation, the main parameters of the boiler such as environmental protection emission value, the boiler operating bed temperature, and the inlet temperature of the separator had changed. To analyze the changes, this paper was carried out by related thermal state tests during the start-up or the normal operation of the boiler. The operating data of the boiler was collected before and after putting into the flue gas recirculation, and the influence of the gas recirculation on the main parameters and economic indicators of the boiler is quantitatively analyzed and discussed. The result shows that the technology of the flue gas recirculation can reduce the oxygen content in the dense phase area of the furnace and increases the reducing gas atmosphere to reduce the generation of NOX emission during the start-up or in the normal operation of the boiler. This provides a technical reference that optimizes the operation mode of the flue gas recirculation during the deep peak shaving in the CFB boiler.

Novel BECCS implementation integrating chemical looping combustion with oxygen uncoupling and a kraft pulp mill cogeneration plant

Bioenergy with CO2 capture and storage (BECCS) is a promising negative emission technology (NET). When using sustainably produced biomass as fuel, BECCS allows the production of power and heat with negative CO2 emissions. The main technical challenges hindering the deployment of BECCS technologies include energy penalties associated with the capture process. This work evaluates the performance of an advanced CO2 capture technology, chemical looping with oxygen uncoupling (CLOU), replacing a conventional fluidized bed boiler in the power boiler role in a large, modern integrated pulp and paper mill. Results from a MATLAB/Simulink reactor model were incorporated in a plant and integration model developed in a commercial process simulation software to quantify the performance of the CLOU-integrated cogeneration plant. The results show that in this specific application, the typically already low efficiency penalty of CLOU-based carbon capture and storage (CCS) systems could be eliminated entirely, and actually even a very small efficiency gain could be obtained. The highly efficient operation is possible due to the high moisture and hydrogen contents of the biomass and the separation of combustion products and excess air streams in the CLOU process; this provides an opportunity to recover a significant amount of heat by flue gas condensation at a higher temperature level than what is possible in a conventional boiler. Together with abundant low-temperature heat sinks available at the pulp and paper application allows freeing a considerable amount of low-pressure steam for expansion in the condensing turbine. The resulting increase in gross generator output proved enough to not only match, but very slightly exceed the approximately 18 MW parasitic load introduced by the CLOU system in comparison to the conventional boiler.

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.

An inexact multiple-recourse hybrid-fuel management model with considering carbon reduction requirement for a biofuel-penetrated heating system

In China’s goal of reaching carbon neutrality by 2060, the blending-biofuel-based heating technique is being used to reduce CO2 and air-pollutant emissions in existing district heating systems in northern China. This brings a series of new system components, complex interactions, and multiple-polymorphic uncertainties to the heating systems, making it difficult for the heating-system manager to improve the traditional fuel management mode while considering the demands of society, economy, policy, environment, and system operation. To address this issue, this study proposes an inexact multi-recourse hybrid-fuel management model for a biofuel-penetrated district heating system (BDHS). The model minimizes the total heating cost by optimizing the biofuel blending ratio, coal and biofuel deficit-recourse pattern among different heating sources, and selecting the optimal CO2 reduction mode under uncertainties. An application of the model to a BDHS case in Dalian City shows that the 5% biofuel blending ratio is suitable for both main heating sources and that the 0 deficit of high-quality coal can be up to [2.48, 2.69] × 103 tonne with the “cold-degree” changing from “mild” to “cold”. The results also indicate that the proposed model can ensure biofuels and high-quality coal are not overused or misused, but instead consumed responsibly. Additionally, most of the CO2 produced in the pulverized coal boiler is traded, while most of the CO2 sourced from the circulating fluid bed boiler is treated by the chemical absorption equipment. Finally, the model reveals that a high system cost (up to [84.73, 96.83] × 106 CNY) and low CO2 emission (down to [66.13, 78.07] × 103 tonne) can be obtained at a high thermalization coefficient through the tradeoff analysis.

Failure of an ASTM A213 T12 steel tube of a circulating fluidized bed boiler

During a maintenance shutdown, a localized bulging was observed in a section of the outermost tube of the superheater, an ASTM A213 grade T12 (UNS K11562), Cr-0.5Mo ferritic steel. The objective of this work was to investigate the failure of the steel tube, part of a L-shape superheater of a CFB boiler. The investigation was performed through microstructural characterization, chemical analysis, thermodynamic calculations, hardness measurements, tensile and creep tests, measurements of the oxide scale thickness on selected regions of the failed tube for determination of the remaining life assessment. It was concluded that the failure was due to a conjunction of long time overheating and creep. A welding defect (root dropout) caused an alteration of the steam flow and, therefore, impaired the proper heat transfer between the tube and the steam. In addition, the uneven flow of the flue gas induced a heterogeneous heat distribution along the tube length, particularly in the area facing the flue gas, evidenced by the erosion marks. The high local temperature resulted in intense oxidation, decarburization and degradation of the microstructure. As a consequence, the steel strength was reduced, with consequent bulging and failure. These points were reinforced by the results of the RUL assessment, where the value was negative at the referred region, meaning the end of its operational life.

Hydrodynamic Analysis Inside a Circulating Fluidized Bed Boiler Based on Time Change Using CFD

The power generation industry has progressively improved the design of power plants to tackle global climate change. Coal-fired power plants will be cleaner and more efficient with the CFB (Circulating Fluidized Bed) technology in the boiler. CFB boilers have the advantage where the resulting carbon dioxide, SOx, and NOx emissions are significantly reduced. This makes research on CFB boilers widely carried out, especially those using CFD (Computational Fluid Dynamic). This study aims to determine the most appropriate turbulence model using CFD simulations on CFB boilers to analyze the hydrodynamic elements in the boiler against time changes, including the distribution of solid volume fractions, pressure, velocity, and wall shear stress. Three turbulence models were tested as part of the simulation: standard , RNG , and RSM, which were then compared to earlier research. The RNG model produces the closest result to the experimental data, with an error value of 6.24%. Solid volume fraction area is increasingly widespread with values ranging from 0.05 to 0.1 from the furnace’s bottom to a height of 15 m. The high-pressure area further expands at the bottom of the furnace to a height of 15 m, with values ​​ranging from 3 kPa to 10 kPa. The outlet line velocity has increased from 43 m/s to 50 m/s. The wall shear stress increases from 0.75 Pa to 1.1 Pa at the outlet wall.

Combustion Characteristic Prediction of a Supercritical CO2 Circulating Fluidized Bed Boiler Based on Adaptive GWO-SVM.

The development of a new and efficient supercritical carbon dioxide (S-CO2) power cycle system is one of the important technical ways to break through the bottleneck of coal power development, improve the efficiency of power generation, and realize energy saving and emission reduction. In order to simplify the complicated workload and save the huge time cost of numerical simulations on combustion characteristics, it is of great significance to accurately make the combustion characteristic prediction according to the operating performance of the S-CO2 CFB boiler. This study proposed a combustion characteristic prediction model corresponding to the S-CO2 CFB boiler based on the adaptive gray wolf optimizer support vector machine (AGWO-SVM). The parameters of the gray wolf optimizer algorithm were processed adaptively first combined with the boiler characteristics, and then the adaptive gray wolf optimizer algorithm was integrated with the support vector machine to solve the imbalance of local and global search problems of particles being easy to gather in a certain position in the process of pattern recognition. The novel method effectively predicts the boiler in the scaling process from the aspect of boiler capacity, optimizes the combustion characteristic expression by numerical simulations, greatly saves time cost and applicability of enlarged design by altering complex numerical simulations, and lays the application foundation of the S-CO2 CFB boiler in the industrial field with acceptable operation accuracy.

Experimental Study on Denitration Transformation of CFB Boiler Burning Fujian Anthracite

Two 75 t/h medium-temperature separated circulating fluidized bed boilers burning Fujian anthracite were upgraded with low NOx combustion (LNC). By reducing the effective cross-sectional area of the air distributor (from 13.43 m2 to 11.38 m2), improving the secondary air rate (from 40% to 45%), adjusting the secondary air supply method (adding a layer of upper secondary air, raising the height of the lower secondary air nozzle (0.4 m), and increasing the secondary air speed (from 48 m/s to 54 m/s), the reform of low nitrogen combustion was carried out. The transformation achieved remarkable results, i.e., the original NOx emission concentration can be controlled between 140–160 mg/m3 after the transformation, and the lowest value is below 120 mg/m3.

Facility-Level Emissions and Synergistic Control of Energy-Related Air Pollutants and Carbon Dioxide in China.

Boilers involve ∼60% of primary energy consumption in China and emit more air pollutants and CO2 than any other infrastructures. Here, we established a nationwide, facility-level emission data set considering over 185,000 active boilers in China by fusing multiple data sources and jointly using various technical means. The emission uncertainties and spatial allocations were significantly improved. We found that coal-fired power plant boilers were not the most emission-intensive boilers with regard to SO2, NOx, PM, and mercury but emitted the highest CO2. However, biomass- and municipal waste-fired combustion, regarded as zero-carbon technologies, emitted a large fraction of SO2, NOx, and PM. Future biomass or municipal waste mixing in coal-fired power plant boilers can make full use of the advantages of zero-carbon fuel and the pollution control devices of coal-fired power plants. We identified small-size boilers, medium-size boilers using circulating fluidized bed boilers, and large-size boilers located in China's coal mine bases as the main high emitters. Future focuses on high-emitter control can substantially mitigate the emissions of SO2 by 66%, NOx by 49%, PM by 90%, mercury by 51%, and CO2 by 46% at the most. Our study sheds light on other countries wishing to reduce their energy-related emissions and thus the related impacts on humans, ecosystems, and climates.

A Study on the Performance Characteristics of a Circulating Fluidized Bed Boiler by the Mixing Ratio of Biomass Fuel

A Study on the Performance Characteristics of a Circulating Fluidized Bed Boiler by the Mixing Ratio of Biomass Fuel