Fluidized Bed Boiler Research Articles

Machine Learning Aided Numerical and Experimental Investigation of Hydrodynamic Performance in the Circulating Fluidized Bed Boiler

Abstract This study attempts to illustrate the benefits of integrating the concepts of machine learning algorithms with the field of thermo-fluidic applications. The current work is aimed at identifying effective or significant hydrodynamic input parameters, which are capable of deriving full benefit of fluidization that could yield a better circulating fluidized bed (CFB) furnace design using the Apriori algorithm. For this, historical datasets from the literature are collected and pretreated based on the design under observation. Association analysis performed by this Apriori algorithm measures the comparative strength of parameters under consideration. Also, this algorithm is capable of identifying the right combinations of parameters that can produce maximum fluidization performance. The end results suggested by this Apriori algorithm are validated using the computational fluid dynamics package. For this, the transient behavior of a scaled-down (1:20) reactor model of a real-time industrial CFB boiler is simulated using ansys fluent 18.0. In specific, the effects of fluidizing velocities, inventory heights of the bed, and particle sizes recommended by the Apriori algorithm are investigated. Here, the effects are assessed in terms of volume fraction distribution and axial velocity profile distribution profiles. From the results of simulations, it was clearly found that 2 m/s inlet velocity produced good circulating fluidized bed patterns on a bed inventory height of 0.5 m for a mean particle size of 200 µm. The results obtained from the simulations are once again validated visually against snapshots obtained during real-time laboratory fluidization experimental runs. Among all the cases of comparisons, the best agreement is demonstrated by Apriori algorithm compared to the numerical and the experimentally obtained results. Also, it is found that the manual time taken to identify the right combinations of parameters is drastically reduced by this method compared to conventional optimization algorithm and trial error methods.

Improved method for calculating CO2 emission from industrial solid wastes combustion system based on fossil and biogenic carbon fraction

Waste-to-Energy (WtE) technology is the most effective solution for managing non-recyclable wastes through mass burning and energy recovery. Owing to the significant volumes of plastics in China’s industrial solid wastes (ISW), a large amount of greenhouse gases (GHG) is generated during the incineration process. Therefore, monitoring GHG emissions from WtE facilities is essential. Owing to the lack of suitable accounting models and characterized fossil carbon fraction (FCF) data, current studies use default values provided by the Intergovernmental Panel on Climate Change’s (IPCC), which increases calculation inaccuracies. Therefore, this study established an improved method to accurately account for carbon emissions during solid waste incineration by firstly using radiocarbon dating by accelerator mass spectrometry (AMS) technique to determine the FCF of the solid waste components in China. Monte Carlo analysis was employed to perform the sensitivity analysis, and the results indicated that there was a significant deviation between the measured value and IPCC’s default values of FCF, 3.2, 32.48, 93.39, 93.76, 90.49, and 93.8 % for paper, cotton, synthetic textiles, artificial rubber, artificial leather, and plastics, respectively. By replacing coal with ISW in a 2 × 110 t/h circulating fluidized bed boilers, 9.251 × 104 t CO2-eq emissions were reduced, and the carbon emission factor reached 0.56 t CO2-eq/t waste. This study complements the research gap fossil carbon data of wastes in the IPCC guidelines and provides a more accurate and effective way to calculate carbon emissions during ISW incineration treatment.

Removal of multiple pollutants in air pollution control devices of a coal-fired boiler installed with a flue gas condensation scrubber

This work was conducted through field tests on a coal-fired circulating fluidized bed boiler with a condensation scrubber (CS) for flue gas waste heat recovery installed behind the wet flue gas desulfurization (WFGD) scrubber. Levels of multiple pollutants were investigated along various flue gas devices of the boiler, with the CS being the main focus. The CS demonstrated an excellent effect in removing filterable particulate matter (FPM), reducing it from 10.63–14.00 mg/Nm3 to less than 1 mg/Nm3, providing an alternative solution for ultra-low emission. The CS had the ability to remove SO2, reducing it from 211.8–272.0 mg/Nm3 to 11.1–13.0 mg/Nm3, which could be an aid to the WFGD scrubber. The CS showed an effect on SO3 removal, reducing it from 17.49–17.53 mg/Nm3 to 1.07–1.13 mg/Nm3, which might address the discharge of sulphate aerosols. The CS exhibited an effect in removing condensable particulate matter (CPM), reducing it from 29.68–38.48 mg/Nm3 to 12.18–22.80 mg/Nm3, providing a potential solution for CPM emission control. In addition, the escape of fine desulfurization slurry droplets from the WFGD scrubber could also be mitigated by the CS with the reduction efficiency of 88.30–90.51%. Overall, the synergistic removal of multiple pollutants including FPM, SO2, SO3, and CPM by the CS was verified in this case study. Considering its original function of waste heat recovery, the adoption of the CS is a promising measure for energy conservation and environmental protection.

Effect of ring baffle on erosion in circulating fluidized bed boiler

Effect of ring baffle on erosion in circulating fluidized bed boiler

Numerical and experimental investigation of co-combustion of chicken manure and lignite blends in a CFBB with novel compact combustion chamber

Increasing worldwide demand for chicken and chicken products has led to increased production of chicken manure. Therefore, chicken manure has an important application potential in the energy industry. This study aims to dispose of chicken manure, which is harmful to soil and groundwater, for thermal energy purposes and to reduce the emissions of lignite coal. For this purpose, it concerns the design and manufacture of a Circulating Fluidized Bed Boiler (CFBB) with a novel combustion chamber for burning chicken manure (CM) and lignite (L) fuels and their mixtures. The combustion behaviors and contaminating emissions of the mentioned fuels in such a CFBB are investigated experimentally and numerically. Emissions of major gaseous pollutants, including CO, SO2 and NO, and the temperature distribution throughout the combustion chamber are measured during the tests. Experimental results show that increasing the amount of CM in the mixture increases CO and reduces SO2. For this condition, NO emission either increases or decreases. According to the numerical results, the temperature of the combustion chamber decreases with the increase of the CM fraction. In the CFBB, the CO emission decreases in the CM fraction up to 25 %, while it increases in the CM fraction above 25 %. For increasing CM fraction, NO emission decreases in the cyclone while it increases in the evaporator. In the experimental and numerical results, the CO2 emission for the L, CM and CM fractions are observed to be equivalent to each other. In conclusion, this study clearly shows that in situ burning of chicken manure or lignite and chicken manure mixtures reduces lignite emissions and meets the heat requirement and disposal of waste in chicken processing plants.

Techno-economic and environmental evaluation of a supercritical CO2 coal-fired circulating fluidized bed boiler power generation

Replacing the steam cycle with the supercritical CO2 (S–CO2) cycle applied in coal-fired power generation is a demonstrated approach to greatly improving efficiency and flexibility. This promotes carbon reduction through efficient use of fossil fuels and improving utilization rate of renewable energy by deep peak shaving. Unlike most studies focusing on conceptual design and efficiency-based investigation, the techno-economic and environmental performance evaluations of the S–CO2 power generation are still rare and undiscovered. In this paper, techno-economic and environmental investigation of a 600 MW S–CO2 coal-fired circulating fluidized bed (CFB) boiler power plant is firstly considered. During this process, a series of economic cost and environmental assessment models and methods integrated with process simulation were proposed. The results showed that there exits an optimum turbine inlet temperature of 635 °C from the techno-economic perspective. The total cost of the S–CO2 power plant increases by ∼10 % and the cost of electricity (COE) decreases by 4.6 % compared to the same-capacity steam plants. The life cycle assessment (LCA) environmental impact potential of the S–CO2 power is far less compared to steam power plants. Its environmental impact is greatest on a global scale and relatively low on a regional scale, such as a country or region.

Combustion of chicken manure and Turkish lignite mixtures in a circulating fluidized bed

Burning chicken manure (CM) with lignites may be a promising method to ensure waste management. In this study, a circulating fluidized bed boiler (CFBB) system was designed, manufactured, and tested for the disposal of CM in poultry farming. Combustion and co-combustion tests of CM and Kale Lignite (L) were carried out in the CFBB to determine the effect of excess air ratio and CM share in the fuel mixture on combustion efficiency and flue gas emissions. As the CM share in the mixture increased, the combustion efficiency increased from 86 % to 95 %. It was observed that while CO emissions increased, SO2 and NOx emissions decreased with respect to CM share. CO emissions ranged from 726 to 2241 mg/Nm3 for 100%L and between 838 and 2450 mg/Nm3 for 100%CM. The NOx emissions changed between 177.5 and 240 mg/Nm3 for 100%CM; however, it was 276.3 mg/Nm3 for 100%L. While SO2 emissions (average) for 100%L were around 5200 mg/Nm3, as the CM share in the fuel mixture increased, emissions decreased, and when they became zero for 100%CM. CO emissions decreased as the excess air ratio increased. SO2 and NOx emissions increased as the excess air ratio increased in almost all fuel mixtures. This combustion system was proposed for waste disposal, emission reduction, and usage of domestic sources. Photovoltaic panels can support this system and meet farms' operational energy requirements away from the grid. Combustion efficiency can be increased by operating the system at oxy-firing mode instead of air-firing.

Movement behavior of char particles in a bubbling fluidized bed at high temperature – The influence of particle shape

The movement of fuel particles has a strong effect on the spatial distribution in fluidized bed boilers, not only due to the resulting fuel mixing patterns but also to the impact on fuel conversion rate (through varied bed-fuel mass and heat transfer fuel). Thus, understanding the movement of char particles becomes critical in order to control the temperature and combustion characteristics of fluidized bed boilers. Further, the preferred orientations exhibited by non-spherical fuel particles are known to influence their motion. In this study, we developed (including experimental validation) a CFD-DEM framework to investigate the movement behavior (both translational and rotational) of a single char particle under combustion conditions (i.e. high temperature) in a fluidized bed. The work studies how the char movement is influenced by the fluidization velocity and the char particle shape: spherical (as typically adopted in modeling studies) vs. non-spherical. For non-spherical char particles, the impact of applying different degrees of particle homogeneity (glue index) in the modeling was also studied. The metrics applied to evaluate the char particle movement behavior were spatial distribution and linear and rotational velocity of the particle.The results show that the movement of spherical char particles is generally more vigorous than that of non-spherical ones. An increase in fluidization velocity yields a higher probability of populating the splash zone instead of the bed surface, due to the enhanced bubble flow. Increased fluidization velocity yields also higher rotational velocity (especially for non-spherical particles, for which the orientation angle distribution becomes eventually evenly distributed).

Digital twin of biomass/coal co-firing circulating fluidized bed boiler by using computational fluid dynamics simulation

Combining biomass fuel with coal in circulating fluidized bed (CFB) boilers is attractive as the increasing of energy demand. The characteristics of biomass/coal co-firing in the industrial boiler are then investigated using computational fluid dynamics (CFD). In this study, fuels of interest are coal, wood chips, and bark. The fuel proportions were set for investigating their effects on the combustion using a simplex centroid mixture design. CFD simulations consist of a standard k-epsilon viscosity flow model, Euler multiphase fluid flow model, and a simplified biomass-char combustion reaction model. The predictive responses of the model are bed temperature, heat flux, and carbon dioxide (CO2) and carbon monoxide (CO) mass flows. The simulation results showed that the operation with coal gave the highest temperature and heat flux, followed by wood chips and bark. On the other hand, the operation with biomass releases fewer gas emissions, CO2 and CO, than those of the operation with coal. The type and proportion of boiler fuel can be easily determined using two methods: predictive equation and ternary contour plot graph, which can be likened to the digital twin of biomass/coal co-firing boiler.

Influence of recycled sand from biomass combustion on the mechanical, hydration and porous properties of mortar mixtures

The objective of this study is to valorise sands from biomass combustion from fluidised bed boilers into mortar formulations and to evaluate their effects on hydration properties, porosities and mechanical strengths. The properties of recycled sand from biomass combustion (RSBC) were compared to the boiler sand (BS) used in the combustion process in order to assess the effects of combustion. RSBC was then incorporated into mortar formulations as a volume replacement for the boiler sand (BS) from the biomass plant. Five formulations (0, 25, 50, 75 and 100% RSBC) were compared by examining their workability and strength properties (ranging from 7 to 180 days). Although a decrease in workability was observed, the substitution of sand with RSBC resulted in better mechanical properties. The accessible porosity, capillary absorption and hydration properties of three formulations (0, 50 and 100% RSBC) were also analysed. An improvement in these properties is observed when RSBC is incorporated with promising results for the valorisation of 100% RSBC.

Use of biomass bottom ash as granular substitute in mortar

An experimental investigation was undertaken on the effect of biomass bottom ash (BBA) as a sand substitution in a mortar design. The objective is to characterise the physico-chemical properties of BBA and to establish a reusable proportion in cementitious composites. The aim is to provide a new way to treat these industrial waste and to reduce the consumption of non-renewable natural aggregates. First, biomass bottom ash from fluidized bed boiler are characterised by physico-chemical and mineralogical analysis. Then, they are compared to the properties of boiler sand use in the combustion process. Finally, boiler sand was substituted by BBA into mortar with a rate of 0–100% of the sand volume. The results show that incorporation of BBA does not significantly influence the hydration kinetics of the cementitious matrix. However, an enhancement of the amount of heat hydration was observed. Furthermore, the BBA substitution leads to decrease the mortar workability. In the hardened state, BBA incorporation shows an increase of mechanical properties. This finding was confirmed by a decrease of the mortar porosity. The results of this study show that there is no contraindication to the use of BBA as an aggregate for the formulation of cementitious materials.

Thermal Inertia of 330 MW Circulating Fluidized Bed Boiler during Load Change

Thermal Inertia of 330 MW Circulating Fluidized Bed Boiler during Load Change

Comparison of Fully 3-D, Simplified 3-D and 2-D Numerical Simulations on a Circulating Fluidized Bed Boiler

Comparison of Fully 3-D, Simplified 3-D and 2-D Numerical Simulations on a Circulating Fluidized Bed Boiler

The Characteristics of Self-Hydration and Carbonation Reaction of Coal Ash from Circulating Fluidized-Bed Boiler by Absorption of CO2.

The by-products of the circulating fluidized-bed boiler combustion (CFBC) of coal exhibit self-hardening properties due to the calcium silicates generated by the reaction between SiO2 and CaO, and the ettringite generated by the reaction of gypsum and quicklime with activated alumina. These reactions exhibit tendencies similar to that of the hydration of ordinary Portland cement (OPC). In this study, the self-hydration and carbonation reaction mechanisms of CFBC by-products were analyzed. These CFBC by-products comprise a number of compounds, including Fe2O3, free CaO, and CaSO4, in large quantities. The hydration product calcium aluminate (and/or ferrite) of calcium aluminate ferrite and sulfate was confirmed through instrumental analysis. The CFBC by-products attain hardening properties because of the carbonation reaction between calcium aluminate ferrite and CO2. This can be identified as a self-hardening process because it does not require a supply of special ions from the outside. Through this study, it was confirmed that CFBC by-products generate CaCO3 through carbonation, thereby densifying the pores of the hardened body and contributing to the development of compressive strength.

Optimization of Circulating Fluidized Bed Boiler Combustion Key Control Parameters Based on Machine Learning

During the coal-fired circulating fluidized bed unit participation in the peak regulation process of the power grid, the thermal automatic control system assists the operator to adjust the mode focusing on pollutant control and ignoring the economy so that the unit’s operating performance maintains a huge potential for deep mining. The high-dimensional and coupling-related data characteristics of circulating fluidized bed boilers put forward more refined and demanding requirements for combustion optimization analysis and open-loop guidance operation. Therefore, this paper proposes a combustion optimization method that incorporates neighborhood rough set machine learning. This method first reduces the control parameters affecting multi-objective combustion optimization with the neighborhood rough set algorithm that fully considers the correlation of each variable combination and then establishes a multi-objective combustion optimization prediction model by combining the online calculation of boiler thermal efficiency. Finally, the NSGAII algorithm realizes the optimization of the control parameter setting value of the boiler combustion system. The results show that this method reduces the number of control commands involved in combustion optimization adjustment from 26 to 11. At the same time, based on the optimization results obtained by using traditional combustion optimization methods under high, medium, and medium-low load conditions, the boiler thermal efficiency increased by 0.07%, decreased by 0.02%, and increased by 0.55%, respectively, and the nitrogen oxide emission concentration decreased by 5.02 mg/Nm3, 7.77 mg/Nm3, and 7.03 mg/Nm3, respectively. The implementation of this method can help better account for the economy and pollutant discharge of the boiler combustion system during the variable working conditions, guide the operators to adjust the combustion more accurately, and effectively reduce the ineffective energy consumption in the adjustment process. The proposal and application of this method laid the foundation for the construction of smart power plants.

Structural and Thermal Examinations of Polyamide Modified with Fly Ash from Biomass Combustion.

This paper presents the results of examinations of the structure and crystallinity of polyamide (PA6) modified with fly ash from biomass combustion in a fluidized-bed boiler. Composites based on a PA6 matrix were examined. They contained 5, 10, and 15 wt% fly ash. Fourier-transform infrared with attenuated total reflectance spectroscopy (FTIR-ATR) was used to identify the characteristic functional groups present in the chemical structure of polyamide and composites based on its matrix. Structural analysis was performed using a differential scanning calorimeter (DSC) and microscopic examinations. Analysis of the values of thermal effects determined using the DSC technique allowed for the evaluation of the degree of crystallinity of the materials studied. Polyamide is usually considered to be a two-phase system consisting of crystalline and amorphous regions. The addition of the filler in the form of fly ash reduced the degree of crystallinity of the studied specimens. Based on the FTIR-ATR spectra and the recorded DSC curves, it was found that the α-phase was the dominant crystalline phase in the studied materials. Microscopic examinations were conducted to analyze the microstructure of the materials, providing information on the distribution and shape of the filler particles. Most of the particles ranged in size from a few to tens of micrometers. Furthermore, the use of scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) allowed for the analysis of the distribution of chemical elements in selected filler particles.

Ashes from bituminous coal burning in fluidized bed boilers as a potential source of rare earth elements

Ashes from bituminous coal burning in fluidized bed boilers as a potential source of rare earth elements

Performance analysis and techno economy of post overhaul circulating fluidized bed boiler PLTU

All countries in the world have a high dependence on energy. Predictions of energy demand continue to increase in all countries, so savings measures are needed. One of the saving measures in the power generation industry is an overhaul. An overhaul is a maintenance activity that must be carried out periodically to maintain the NPHR performance of the power plant as it was when the initial conditions were built. This study aims to (1) determine the performance of the power plant before and after overhaul, (2) determine how the PLTU performs at 50%, 75%, and 100% load, and (3) analyze the techno-economics of overhaul activities with a serious type inspection. The results of this study explain that the three treatments of the post-overhaul loading pattern have a good impact on the PLTU, namely in the form of a decrease in the NPHR after the overhaul work. The impact of the reduced post-overhaul NPHR value at this PLTU is that it can save fuel costs of 17.5 billion rupiah per year. The cost for this overhaul work is 14.9 billion rupiah so in 1 year it can save around 2.6 billion rupiah.

PCDD/Fs, PAHs and HCl emissions from co-combustion of lignite and chicken manure in a circulating fluidized bed boiler with compact refractory casting

Chicken manure (CM) should be used in energy production due to its high production potential for the waste-to-energy approach. Co-combustion of CM with lignites may be a good practice in terms of reducing its environmental impact and the need for fossil fuels. However, the level of organic pollutants originated from CM combustion is not clear. This study investigated the potential of CM to be combusted in a circulating fluidized bed boiler (CFBB) with a local lignite. Combustion and co-combustion tests of CM and Kale Lignite (L) were performed in the CFBB to measure PCDD/Fs, PAHs and HCl emissions. CM burned in the upper parts of the boiler due to its high volatile matter content and low density compared to coal. This caused the bed temperature to decrease with the increase in the amount of CM in the fuel mixture. It was also observed that the combustion efficiency increased as the share of CM in the fuel mixture increased. Total PCDD/F emissions increased with CM share in the fuel mixture. However, all are less than emission limit value (100 pg I-TEQ/m3). Co-combustion of CM with lignite at different ratios did not have a significant effect on HCl emissions. PAH emissions were found to increase with the increase of the CM share when the CM share was more than 50% by weight.

Oxidative Potential of Metal-Containing Nanoparticles in Coal Fly Ash Generated from Coal-Fired Power Plants in China.

The overwhelming magnitude of coal-fired power plants has caused an inevitable release of metal-containing nanoparticles (MNPs) into the atmosphere, which may be inhaled into the respiratory system and cause oxidative stress. In this study, MNPs and oxidative potential (OP) were analyzed in <1 μm fractions of 56 coal fly ashes collected from Chinese CFPPs. The particle number concentrations (PNCs) of Fe- and Ti-containing NPs, as the dominant MNPs in CFAs, were in the range of 1.5 × 109 to 9.4 × 1010 and 6.4 × 108 to 4.1 × 1010 particles/mg, with average particle sizes of 87 and 89 nm, respectively. Average OP values of <1 μm fractions were 1.4-2.2 nmol AA min-1 μg-1 for three simulated lung fluids, which were 2-3 orders of magnitude higher than those of urban atmospheric PM2.5. According to structural equation model analysis, metal concentrations in <1 μm fractions, PNCs of Fe-/Ti-containing NPs, and their corresponding dissolved Fe/Ti (including NPs with minute sizes) can regulate OP of <1 μm fractions in CFAs. Elevated PNCs of MNPs in CFAs can be produced by CFPPs burning low-rank coals and with a low combustion efficiency boiler (e.g., circulating fluidized-bed boiler). Once entering lung fluids, they likely release more dissolved metals or tiny corresponding NPs, thus generating greater OP. This study provides the first comprehensive investigation of OP generated by MNPs in CFAs.