Fluidized Bed Boiler Research Articles

CO2 capture in pilot-scale unit using solid adsorbent in biomass fluidised bed boiler flue gas

The search for methods to capture carbon dioxide (CO2) emissions from solid fuel combustion processes has led to the development and subsequent testing of alternative innovative CO2 capture technologies. Vacuum Pressure Swing Adsorption (VPSA) method is a promising technology for efficient CO2 capture using solid sorbents. This article introduces CO2 capture using the VPSA technology, providing description of the selected VPSA method and the construction of a pilot-scale unit for VPSA CO2 capture. The main goal of this article is to present experimental results, including a description of the pilot-scale unit used for the VPSA adsorption tests using zeolite 13X, an industrially proven sorbent for CO2 capture. The measured adsorption values were compared with theoretical isotherms, allowing the assessment of VPSA method efficiency and accuracy in practical conditions. Results indicated discrepancies between the experimental unit and the theoretical adsorption models, attributed to non-ideal conditions, non-optimised processes, incomplete drying of the sorbent, and temperature variations affecting the adsorption efficiency. The conclusion confirms the VPSA lab unit’s ability to adsorb CO2 using solid sorbents, suggesting that further research and additional tests with new alternative sorbents is needed.

Study on the mechanism of thermal inertia action in circulating fluidized bed boiler

Study on the mechanism of thermal inertia action in circulating fluidized bed boiler

Dynamic modeling and transient simulation of circulating fluidized bed boilers during variable loads

Dynamic modeling and transient simulation of circulating fluidized bed boilers during variable loads

Validation and transients of a circulating fluidized bed boiler: Load-peaking and response mechanisms

Validation and transients of a circulating fluidized bed boiler: Load-peaking and response mechanisms

Research on expansion characteristics of circulating fluidized bed boiler bottom slag as concrete fine aggregate

Research on expansion characteristics of circulating fluidized bed boiler bottom slag as concrete fine aggregate

The Method for Assessing the Causes of Damage to a Bearing in a Rotary Air Preheater

This article presents a method for identifying the cause of damage to a rotary air preheater on one of the fluidized bed boilers operating in a power plant. The bearing in question operates under harsh conditions with the exhaust gas temperature reaching 287 °C and causing its casing to heat up intensively. It is therefore important to ensure that the bearing is constantly cooled by water, which lowers the operating temperature and thus extends its service life. Unfortunately, after a short period of operation, the upper double-row spherical roller bearing was damaged, and the tests presented in the assessment method helped to determine the cause of damage to its casing.

Effect of Impact Energy on High Temperature Erosion-Corrosion Behavior of Ni-xFe Alloys in Fluidized Silica Sand

An internally circulating fluidized-bed boiler is composed of a combustion chamber and a heat recovery cell. The heat exchange tubes are exposed to complex erosive and corrosive conditions due to impact of sand particles under high-temperature corrosion in chlorine containing atmospheres, which results in the severe degradation of the materials. In general, protective coatings are applied on the heat exchange tubes to improve an erosion-corrosion (E-C) resistance. In our previous study, high-temperature E-C resistance of Ni-xFe alloys (x = 0, 10, and 30 wt.%) was found to increase with increasing Fe content because of a formation of the Fe-rich oxide scale, which is harder than a Ni oxide scale. However, factors affecting an E-C behavior such as the impact energy of sand particles and the salt concentration have yet to be sufficiently evaluated. In this study, the effect of the impact energy of silica sand on the high-temperature erosion-corrosion of Ni-xFe alloys was investigated.Pure Ni, Ni-10Fe and Ni-30Fe (wt%) alloys were prepared by Ar arc melting. Samples with a thickness of approximately 1mm were cut from the homogenized ingots and polished down to a 1200 grit using SiC papers. Figure 1 shows the schematic of the E-C test rig. The sample holder with affixed samples was inserted into the quartz tube containing silica sand (average particle size 500μm). The silica sand was heated to 700°C, and fluidized by compressed air preheated to 400°C at a flow rate of 25 L/min. The impact angle of the sand to the surface was set to be 45°, and the sample temperature was maintained at 360-380°C by water cooling of the sample holder. The salt vapor of KCl-40 mol.%NaCl-20 mol.%CaCl2 was continuously supplied from the bottom of quartz tube into sand by a compressed air. The impact energy of sand particles was set at 540 J/m2 and 1150 J/m2, which were calculated by a fluidized bed analysis. The high-temperature E-C test was stopped every 25 h or 50 h to change the silica sand and salt crucible , and continued for up to 100 h. After the E-C tests, the samples were analyzed by XRD, FE-SEM, EDS, and STEM. The STEM samples were prepared by using FIB.Figure 2 shows the relationship between the impact energy of silica sand and the mass change of each sample after 50 h of E-C test. The mass change at 0 J/m2 was defined as the mass change after the embedded corrosion test for 50 h in silica sand with 0.01 wt.% of KCl-40 mol.%NaCl-20 mol.%CaCl2 salts. The slope of the graph decreased with increasing Fe content, suggesting that the effect of impact energy on the E-C resistance became less pronounced for the alloy with higher Fe content. Regardless of the impact energy, no oxide scale formation was observed on the pure Ni after the E-C test, which indicates that mass loss might be caused by the erosion of the metal substrate. In Ni-10Fe, a thin (Fe, Ni) spinel was remained on outermost surface of the oxide scale and NiO containing several percent of Fe was remained beneath the spinel layer after the test at 540 J/m2, but no oxide scale was remained after the test at 1150 J/m2, which indicates that the mode of high temperature E-C might have changed from erosion of the oxide scale to that of the metal substrate as impact energy increased. In Ni-30Fe, Fe3O4 and (Fe, Ni) spinel was remained on most of the alloy surface after the test at 540 J/m2, suggesting that the E-C is predominated by erosion of oxide scale. However, some scratches due to the impact of sand particles were observed after the test at 1150 J/m2, and EDS analysis confirmed that the signals from oxygen was very weak on the scratched area, which indicates that not only the erosion of oxide scale but also the erosion of alloy substrate could occur in Ni-30Fe. These results suggest that the influence of impact energy depends on the type of oxide scale formed, and the dependence of the erosion rate constant on impact energy could be smaller for the Fe-rich oxide scale. Figure 1

A Multi-Objective Optimization Framework That Incorporates Interpretable CatBoost and Modified Slime Mould Algorithm to Resolve Boiler Combustion Optimization Problem.

The combustion optimization problem of the circulation fluidized bed boiler is regarded as a difficult multi-objective optimization problem that requires simultaneously improving the boiler thermal efficiency and reducing the NOx emissions concentration. In order to solve the above-mentioned problem, a new multi-objective optimization framework that incorporates an interpretable CatBoost model and modified slime mould algorithm is proposed. Firstly, the interpretable CatBoost model combined with TreeSHAP is applied to model the boiler thermal efficiency and NOx emissions concentration. Simultaneously, data correlation analysis is conducted based on the established models. Finally, a kind of modified slime mould algorithm is proposed and used to optimize the adjustable operation parameters of one 330 MW circulation fluidized bed boiler. The experimental results show that the proposed framework can effectively improve the boiler thermal efficiency and reduce the NOx emissions concentration, where the average optimization ratio for thermal efficiency reaches +0.68%, the average optimization ratio for NOx emission concentration reaches -37.55%, and the average optimization time is 6.40 s. In addition, the superiority of the proposed method is demonstrated by ten benchmark testing functions and two constrained optimization problems. Therefore, the proposed framework is an effective artificial intelligence approach for the modeling and optimization of complex systems.

Three-dimensional numerical simulation of coal and papermaking trash co-combustion in a circulating fluidized bed

Circulating fluidized bed (CFB) combustion is a important method of waste treatment with the benefits of harmlessness, recycling, and energy recovery. Using the existing co-firing CFB boiler to dispose of waste can reduce investment in boilers and environmental protection equipment. However, there is currently limited research available on the co-combustion of coal and waste (especially for papermaking trash), and the mechanism of pollutant emissions during unit operation remains unclear. In this work, the co-combustion of coal and papermaking trash in a three-dimensional industrial-scale CFB are investigated by using the Dense Discrete Phase Model (DDPM) method. Both homogeneous reactions (such as fuel particle pyrolysis, combustion, and surface reaction) and non-homogeneous reactions (such as gas combustion and pollutant generation) are considered. The co-combustion characteristics are comprehensively analyzed in terms of gas distribution, chemical reaction rates, and bed temperature under various operating conditions, including fuel mixing ratio, secondary air arrangement, and excess air coefficient. The results are obtained by comparing the distribution profile along the height. By reducing the mixing ratio of papermaking trash, the excess air coefficient, and adjusting the secondary air arrangement in the lower region, an expanding, reducing atmosphere is observed in the vicinity of the fuel feeding point. This, in turn, leads to an increase in CO concentration and a decrease in NO emissions, which is attributable to the interplay of gas distribution, chemical reaction rates, and bed temperature. A reduction in NO gas emissions was achieved by adjusting the secondary air arrangement and the excess air coefficient. Overall, this work provides valuable insights into the co-combustion characteristics of coal and papermaking trash in an industrial-scale circulating fluidized bed boilers.

Adding hydrated lime for regulating hydration and carbonation properties of circulating fluidized bed boiler fly ash

The combined utilization of circulating fluidized bed boiler fly ash (CFBFA) and carbon dioxide from flue gas presents an effective strategy for the integrated management of industrial by-products. This study investigated the ratio of cement-hydrated lime added to CFBFA cementitious materials with carbonation curing by fuel gas. The prepared CFBFA cementitious material can be used as artificial composite gravels instead of natural gravels as road base material. Experimental results show that the optimal cement-to-hydrated lime ratio was determined to be 1:2. Under this optimal ratio, the compressive strength of the composite gravels achieved a maximum value of 8.91 MPa after 28 days of curing and CO2 absorption rate reached 3 %. Under carbonation curing, CFBFA composite gravels primarily results in the formation of carbonation products, with calcite being the dominant component. The absorption capacity of CO2 is positively correlated with the mechanical strength of CFBFA composite gravels. The addition of hydrated lime resulted in a higher quantity of ettringite being produced, characterized by fine and elongated morphologies that effectively filled the pores and cracks. Life Cycle Assessment (LCA) also evaluated the environmental benefits of using CFBFA and flue gas carbonation curing, showing up to a 68.02 % reduction in global warming potential (GWP) and a 57.52 % reduction in cumulative energy demand (CED) compared to traditional cement construction materials. These findings provide valuable insights into the sustainable application of CFBFA in construction materials.

A Comprehensive Review of CO2 Mineral Sequestration Methods Using Coal Fly Ash for Carbon Capture, Utilisation, and Storage (CCUS) Technology

CO2 emissions from fossil fuel combustion are the main source of anthropogenic greenhouse gases (GHGs). A method of reducing CO2 emissions is CCUS (carbon capture, utilisation, and storage) technology. One part of CCUS technology involves mineral sequestration as its final stage, utilisation, which can be carried out using natural raw materials or waste. This is a particularly interesting option for power and CHP plants that use coal as their primary fuel. Combustion processes produce fly ash as a waste by-product, which has a high potential for CO2 sequestration. Calcium fly ash from lignite combustion and fly ash from fluidised bed boilers have particularly high potential due to their high CaO content. Fly ash can be used in the mineral sequestration of CO2 via direct and indirect carbonation. Both methods use CO2 and flue gases. Studies conducted so far have analysed the influence of factors such as temperature, pressure, and the liquid-to-solid (L/S) ratio on the carbonation process, which have shown different effects depending on the ash used and the form of the process. Due to the large differences found in the properties of fly ash, related primarily to the type of fuel and boiler used, the process of mineral CO2 sequestration requires much research into its feasibility on an industrial scale. However, the method is promising for industrial applications due to the possibility of reducing CO2 emissions and, at the same time, recovering waste.

Experimental Study of Agglomeration Formation during Co-Combustion of Coal and Palm Kernel Shell in Fluidized Bed

Abstract Co-combustion of biomass and coal in Indonesia power plants are a key element of the path towards achieving net-zero emissions. However, introducing biomass into a coal-boiler furnace may pose operational challenges. Therefore, this study aims to assess the potential of agglomeration when mixing biomass with a fluidized bed boiler. Complementation simulation tests were conducted by combining coal with various fractions of palm kernel shell (PKS) in a furnace capacity of 5kWth maintained at 850°C within an hour. The initial fuel was 100% coal, gradually increasing the biomass mixture by 5%, 10%, 15%, 20%, and 25%. The results indicated that de-fluidization occurred at 25% of the biomass mixture and to prevent agglomeration, the temperature of the bed was kept below 850°C. The agglomeration test of coal and PKS mixtures was successfully performed in a 5kW lab-scale facility, and the result will be useful for predicting agglomeration phenomena in power plants.

Comparison of DeNOx additives in SNCR fluidized bed boiler system

Due to decreasing BAT emission limits of NOx the owners of heating plant are looking for DeNOx solution, especially by solid fuel firing boilers. Fluidized-bed boil-ers combustion temperature is generally lower, and some primary precautions were sufficient. Nowadays lots of plants install secondary precautions (especially SNCR) into their boilers due to increasing periods of exceeding emission NOx limits. The article is about comparison of water solution of urea (41 % wt.), ammonium sulfate (33 % wt.) and am-monia (22 % wt.) and their utilization in SNCR technol-ogy. Laboratory determination specified exact content of functional substance and content of redox nitrogen. Also, significant content of heavy metals was not detected. Operational tests were realized in CFB coal-biomass boiler (steam parameters: 140 t·h-1, 525 °C, 12.5 MPa). Dosing of DeNOx additives were only during boiler per-formance higher than 92 %, for lower performance pri-mary precautions were sufficient. There was higher tem-perature through the combustion chamber during active SNCR dosing (877 °C, standard temperature 850 °C), alt-hough the amount of combustion air was increased. Com-plication connected with high emission of NH3 was not detected. Lower emission of CO was also detected. All three additives are suitable for application in SNCR technology. To reach emission limits were needed 3.7 l·h-1 of ammonia solution, 5.04 l·h-1 of urea solution and 5.74 l·h-1 of ammonium sulfate solution. After recal-culation it means 0.65 kg·h-1 (ammonia), 1.1 kg·h-1 (urea) and 0,38 kg·h-1 (ammonium sulfate) of redox nitrogen content.

Combustion Process of Coal–Açai Seed Mixtures in a Circulating Fluidized Bed Boiler

This study investigates the effects of the co-combustion of coal and açai seed in circulating fluidized bed (CFB) boilers, highlighting the increase in thermal efficiency and relevance of a less-polluting source of energy. Using the computer software 1.5D CeSFaMB™® v4.3.0, simulations of the co-combustion process of coal and biomass were carried out in a CFB boiler, obtaining results such as the temperature profile, boiler efficiency and emissions. The work acquired data regarding the equipment in real operational conditions, consisting of the fundamental geometric and operational parameters used in the simulation campaign. The thermal and chemical properties of the fuels were analyzed by carrying out proximate, ultimate, heating value, particle size and specific mass analyses. The model validation was achieved by simulating the boiler in its real operating conditions and comparing the obtained results with the real data; the obtained error was below 10%. Simulations with different fractions of açai seed for energy replacement (10% and 30%) were carried out. As a result, an increase in the average temperature of the bed was observed, highlighting the region immediately above the dense bed. An increase in boiler efficiency was verified from 56% to 85% with 10% açai and to 83% with 30% açai seed. Decreases in SO2 and CO emissions with the insertion of açai were obtained, showing that co-combustion is more complete, while CO2 emissions were increased due to the higher quantity of fuel inserted into the equipment. The fossil CO2 emissions were reduced.

High-volume utilization of circulating fluidized bed fly ash for the production of autoclaved aerated concrete: Performance optimization and hydration characteristics

Circulating fluidized bed fly ash (CFA) is a waste emitted from coal combustion process in circulating fluidized bed boilers. The high SO3 and f-CaO content severely limits its application in building materials. The purpose of this study is to explore the possibility of large-scale application of CFA in autoclaved aerated concrete (AAC). The preparation parameters of AAC were discussed and the performance was optimized. Moreover, the workability and environmental properties of AAC were explored. The results indicated that AAC was well adapted to high CFA content, although a high CFA content caused a higher water demand as well as a reduction in the silicon content. The introduction of quartz sand and blast furnace slag effectively addressed the problems of insufficient active silica and high specific gravity. When the CFA doping was 50 %, H4 sample showed the best mechanical properties (3.82 MPa and 641 kg/m3), which meet the requests of A3.5, B06 in the Chinese national standard GB/T 11968–2020. Moreover, the toxicity leaching results showed that H4 sample was green and harmless. During the performance optimization process, more well-crystallized tobermorite was produced, whose crystal form changed from acicular to slat. Massive C-S-H gels and better crystallinity of tobermorite were observed, where were bonded and intercalated with each other, thus enhancing the properties. The paper may provide guidance for high dosing of CFA in AAC.

Failure Analysis of Y-Anchors of Hot Cyclone Refractory of Circulating Fluidized Bed Boilers

Failure Analysis of Y-Anchors of Hot Cyclone Refractory of Circulating Fluidized Bed Boilers

Experimental Study on Preparation of Inorganic Fibers from Circulating Fluidized Bed Boilers Ash.

The ash generated by Circulating Fluidized Bed (CFB) boilers is featured by its looseness and porosity, low content of glassy substances, and high contents of calcium (Ca) and sulfur (S), thus resulting in a low comprehensive utilization rate. Currently, the predominant treatment approach for CFB ash and slag is stacking, which may give rise to issues like environmental pollution. In this paper, CFB ash (with a CaO content of 7.64% and an SO3 content of 1.77%) was used as the main raw material. The high-temperature melting characteristics, viscosity-temperature characteristics, and initial crystallization temperature of samples with different acidity coefficients were investigated. The final drawing temperature range of the samples was determined, and mechanical property tests were conducted on the prepared inorganic fibers. The results show that the addition of dolomite powder has a significant reducing effect on the complete liquid phase temperature. The final drawing temperatures of the samples with different acidity coefficients range as follows: 1270-1318 °C; 1272-1351 °C; 1250-1372 °C; 1280-1380 °C; 1300-1382 °C; and 1310-1384 °C. The drawing temperature of this system is slightly lower than that of basalt fibers. Based on the test results of the mechanical properties of inorganic fibers, the Young's modulus of the inorganic fibers prepared through the experiment lies between 55 GPa and 74 GPa, which basically meets the performance requirements of inorganic fibers. Consequently, the method of preparing inorganic fibers by using CFB ash and dolomite powder is entirely feasible.

Research Progress on the Dynamic Characteristics of Circulating Fluidized Bed Boilers While Processing Rapid Variable Loads

Research Progress on the Dynamic Characteristics of Circulating Fluidized Bed Boilers While Processing Rapid Variable Loads

Zinc speciation in fly ash from MSWI using XAS - novel insights and implications

The chemical forms of zinc in fly ash from municipal solid waste incineration (MSWI) crucially affect ash management, influencing both material recovery options and the risk of unwanted leaching into ecosystems. The zinc speciation was investigated in fly ash samples sourced from full-scale MSWI plants, including four grate fired boilers (GB) and one fluidized bed boiler (FB). We applied X-ray Absorption Spectroscopy (XAS), and the spectra were analyzed against a unique library of over 30 relevant compounds, tailored to the nuances of zinc chemistry of fly ash. Nano-XANES and sequential leaching were employed as complementary analytical methods. Multiple chemical forms of zinc were found in the ash, whereof potassium zinc chloride salts (K2ZnCl4) emerged as the predominant form in GB fly ash representing 41–64 % of the zinc content, while less for FB fly ash (19 %). The mere exposure to humidity in the air during storage resulted in hydroxylation of the alkali zinc chlorides into Zn5(OH)8Cl2·H2O. Other forms of zinc in the ash were Zn4Si2O7(OH)2·H2O, ZnFe2O4, ZnAl2O4, surface adsorbed zinc, and Zn5(CO3)2(OH)6. Notably, the proportion of zinc in spinel forms (ZnFe2O4 and ZnAl2O4) increased threefold in FB ash compared to GB ash, representing ∼60 % and ∼10–20 % of the zinc, respectively.

Investigation on NO and N2O emissions characteristics in deep peak regulation circulating fluidized bed boilers

Abstract To adapt to the increasing proportion of new energy power generation capacity, coal power must transition from its traditional role as the primary power source to serving as a fundamental backup and system regulation energy source. The circulating fluidized bed technology is known for its wide range of load regulation capabilities; however, emissions of pollutants during load regulation can exhibit significant variability. This study utilized Aspen Plus software to develop a circulating fluidized bed combustion model based on a gas-solid fluid dynamics model, an equivalent coal pyrolysis model, and a multi-phase macroscopic combustion reaction dynamics model of pyrolysis products. This model was used to predict both the temperature distribution within the furnace chamber and the distribution of pollutant concentrations. Predictions of pollutant emissions from 100 % load to 30 % load of the circulating fluidized bed were explored under the original combustion condition and 5 % proportion of recirculated flue gas. Under the primary combustion condition, the emission concentration of NO x showed a decreasing and then increasing trend with decreasing load, while the concentration of nitrous oxide, in contrast to NO x , showed an increasing and then decreasing trend. The effect of recirculated flue gas on pollutant emissions was not significant at reduced loads. This study aims to provide technical support and theoretical guidance for the management of pollutant emissions from the deep peak regulation of actual circulating fluidized beds.