In response to current issues faced by coal-fired power plants, such as high fuel costs, weakly stable combustion performance at low loads, and insufficient peak-shaving capabilities, an integrated operational scheme is proposed based on the natural endowments of renewable energy surrounding the power plant, which utilizes photovoltaic power generation distributed in plants to produce hydrogen and oxygen via electrolysis of water, then to achieve hydrogen and oxygen co-firing in coal-fired boilers. By constructing a full-size numerical model for a tangentially coal-fired boiler, the calculation accuracy of temperature field, species concentration, and carbon content in fly ash is verified under pure pulverized coal combustion conditions, which could provide a benchmark for optimization of hydrogen and oxygen blending. Based on the typical application scenario of a 20 MW photovoltaic power generation to hydrogen and oxygen production in the plant, the effects of three mixing methods of hydrogen and oxygen on combustion efficiency, burnout characteristics and NO_x formation in the furnace are systematically studied. The results show that, a co-combustion mode which utilizes an independent hydrogen nozzle in conjunction with primary air mixing with oxygen can improve the combustion performance significantly. The carbon content in fly ash at the furnace outlet reduces to 0.97%, and the combustion efficiency is notably enhanced compared with that under pure coal combustion condition. At the same time, the reduction effect of reactive species generated by hydrogen combustion on NO_x leads to a decrease in NO_x emission mass concentration in the flue gas to 294.0 mg/m³, which is decreased by about 25% compared with that under baseline condition of pure coal combustion. This model achieves dual-benefit of coal substitution and combustion optimization through hydrogen and oxygen production from renewable energy, which not only reduces coal consumption but also expands the lower limit of stable combustion load for coal-fired boilers. It provides a technically feasible implementation reference path for the decarbonized retrofitting and flexibility improvement of coal-fired units.

Under the “dual-carbon” target, ammonia as a zero carbon fuel is expected to become a substitute for fossil fuels. Focusing on the problems of slow combustion speed, high ignition energy, and significant ignition delay in ammonia combustion, the effects of initial temperature, pressure, and oxygen volume fraction on ammonia combustion characteristics are studied via Chemkin simulation, based on the different ammonia combustion chemical reaction kinetics mechanisms of Shrestha, Mei, Mei-2021, Stagni, CEU-NH₃, Gotama, and Glarborg. The results show that, as the initial temperature increases, the propagation speed of ammonia laminar flame increases, and the ignition delay time decreases, which is beneficial for ammonia ignition and combustion. The increase in pressure reduces the propagation speed of laminar flames, but significantly shortens the ignition delay time. The increase in pressure is beneficial for ignition but not conducive to flame propagation. As the volume fraction of O2 increases, the laminar flame propagation speed increases and the peak shifts towards lean combustion. Sensitivity analysis reveals that the branching ratios of H+O₂=O+OH, H₂+NO=NNH+OH, and NH₂+NO=H₂O+N₂ have a positive promoting effect on flame propagation, while that of NH₂+O=HNO+H inhibits flame propagation. The reactions H+O₂(+M)=HO₂(+M), NH₃=H+NH₂, HNO=H+NO, and NH₂+HO₂=NH₃+O₂ exhibit high sensitivity at high pressures. The sensitivity coefficients of the reactions between HNO and N_iH_i is relatively high during lean burn combustion. H₂NO is an important intermediate component that affects the ignition delay time at high pressures and low temperatures. By optimizing the conditions of ammonia combustion and regulating key reaction pathways and reaction kinetics, the characteristics of ammonia combustion can be improved.

The effect of co-firing hydrogen/ammonia on nitrogen oxides emissions from boilers is investigated. The reaction kinetics file is modified based on coal quality analysis and experimental results. A psr reactor network based on CFD simulation results is constructed according to the fluid dynamics (CFD) simulation results. Combing with the chemical reaction kinetics analysis method, the NO_x emissions after burning hydrogen/ ammonia at four positions of primary air, peripheral air, secondary air and post secondary air in five schemes are analyzed. The results show that, for the researched boiler, when the hydrogen co-firing position is located in the secondary air scheme, and the hydrogen mixing ratio is 20%, the NO emission reduces by 32.4%, and the emission concentration of unburned carbon does not change much compared to the pure coal condition. When the ammonia co-firing position is located behind the secondary air, the NO emission mass concentration is slightly higher than that under the pure coal condition, and the emission mass concentration of unburned carbon reduces significantly. The above two schemes are recommended for co-firing hydrogen/ammonia in the coal-fired boiler, with nitrogen oxide emissions as the evaluation index. This method and conclusion provides a theoretical basis for the engineering implementation of hydrogen/ammonia co-firing technology.

To tackle the challenges associated with the poor combustion performance of ammonia fuels and the high NO_x emissions in exhaust gases, experimental research on enhancing ammonia combustion through the use of a swirling burner combined with a gliding arc plasma generator was carried out. The effects of various combustion enhancement methods, including methane-assisted combustion, plasma-assisted combustion, and plasma-coupled methane-assisted combustion, on the combustion characteristics of NH₃ swirling flames and the generation of NO were investigated. The experimental results indicated that, compared with the methane-assisted combustion, both plasma-coupled methane-assisted combustion and plasma-assisted combustion significantly enhanced the stability of ammonia combustion. This improvement was evidenced by a substantial expansion of the stable combustion limit range of the NH₃ swirling flame, enabling normal combustion within an NH₃/Air equivalence ratio range of 0~5.0. In comparison to single methane-assisted or plasma-assisted combustion, plasma-coupled methane-assisted combustion (with a plasma power of 0.8 kW and a methane flow rate of 1 L/min) significantly enhanced the active species H_α and OH generated by the discharge, thereby strengthening the chemical effects in plasma-assisted combustion. Under these conditions, the NO emission mass concentration in the exhaust gases rapidly decreased from over 7 000 mg/m³ to approximately 100 mg/m³ as the NH₃/Air equivalence ratio was increased from 0.6 to 0.8. Furthermore, the gas temperature under these conditions was only slightly lower than that observed in pure plasma-assisted combustion, where the flame temperature of ammonia combustion could reach up to approximately 2 030 K.

A simulation study on a 300 MW tangentially-fired boiler with 20% ammonia doping at 60% load was carried out to analyze the combustion process of ammonia doping in pulverized coal boiler, and to seek for the best coal-ammonia co-combustion scheme to ensure the optimal combustion efficiency and the lowest pollutant emission. By adjusting the position of ammonia burners and the ratio of the separated over fire air, the temperature field of the flue gas in the furnace, the molar fraction distribution of the combustion components, as well as the combustion characteristics and the NO_x emission level at the furnace outlet were systematically analyzed using numerical simulation. The comprehensive analysis shows that, the best coal-ammonia co-combustion solution is to place the ammonia burner on top layer (tertiary air) and the CD layer (secondary air) when the ratio of the separated over fire air is 33.5%. This scheme ensures the combustion efficiency and stability while controlling the NO_x emission level comparable to that of the pure coal-fired condition, which provides a new way of thinking for large-scale coal-fired power plants to realize clean and efficient combustion.

A 660 MW opposed firing boiler is designed with staggered lower over fire air (OFA) burner arrangement, in response to the problems of high NO_x emission and low burn-out efficiency at the furnace outlet caused by the use of upper burners on the front wall, numerical simulation is performed to study the effects of the coal mill combinations, as well as the lower OFA ratios, injection angles, heights of the burners on front wall on the combustion and NO_x emission characteristics under full load conditions. The results show that, the NO_x emission mass concentration decreased by 29.49 mg/m³ and the carbon content in fly ash decreased by 0.16% after the upper burner of the front wall was deactivated. The combined operation mode of BCDEF burners should be selected in actual operation. When keeping the lower OFA ratio unchanged, the NO_x emission mass concentration increased after the lower OFA ratio on the front wall was increased from 10.2% to 14.2%. When the air rate exceeded 13.2%, insufficient overfire air at the lower part of the back wall led to a decrease in burnout efficiency. The lower OFA rate on the front wall should be controlled within 12.2%~13.2% during actual operation. The NO_x emission mass concentration reduced by 18.13 mg/m³ and the carbon content in fly ash increased by 0.38 percentage point after the lower OFA was changed from 15° injection to horizontal injection. When the lower OFA burners on the front wall were moved up to the height of the lower OFA burners on the rear wall, the NO_x emission mass concentration decreased by 41.78 mg/m³, and the carbon content in fly ash increased by 0.68 percentage point. Compared to the opposed firing boilers with conventional lower OFA burners, the one with staggered layout of lower OFA burners has relatively weak deep air staged combustion effect, but with high burnout rate and better adjustability.

Co-combustion of biomass and coal can significantly reduce the pollutants and carbon emissions. However, the pollutants emission, ash characteristics and their influence factors during co-combustion of coal and biomass are still obscure. A micro-fluidized bed reactor was used to investigate the co-combustion of rice husk (RH) and bituminous coal (SC). The effects of combustion temperature, atmosphere and blending ratio on the emission characteristics of NO, SO₂ and ash were studied. The results indicated that, with the increase of temperature, the mass concentration of NO emissions during co-combustion rose at first and then fell, while the SO₂ emissions mass concentration gradually increased. High temperature would promote the interaction of minerals in the ash, generating Na₂Al₂SiO₆ and lowering the melting point of the co-combustion ash. In oxygen-deficient atmosphere, NO and SO₂ emission mass concentrations increased with the O₂ volume fraction. In oxygen-enriched atmosphere, the NO emission mass concentration gradually decreased as the O₂ volume fraction increased, while the SO₂ emission mass concentration increased at first and then decreased. The influence of reaction atmosphere on the main composition and crystal structure of the co-combustion ash was relatively minor. NO and SO₂ emissions during co-combustion can be effectively reduced due to the addition of RH. As the RH blending ratio was increased, Ca₃Al₂O₆ in ash tended to form low-melting-point compounds with SiO₂, leading to a noticeable melting phenomenon.

The use of large-scale coal-fired power units mixed with refused derived fuel (RDF) can reduce carbon emissions and solve the problem of waste management. To verify the feasibility of co-firing RDF in coal-fired boilers, initial tests were conducted using a one-dimensional furnace to determine the maximum allowable proportion of RDF. Then, pilot-scale tests were carried out on a 4 MW boiler to study the effect of RDF co-firing on coal grinding, combustion, pollutant emissions, and slagging and fouling. The results showed that, when the co-firing ratio of RDF was less than 10% (mass ratio), the mass concentration of dioxins in the flue gas, and dioxins and heavy metals in the ash residue were all below the pollutant control standards. When 10% of RDF was co-grounded with coal in a medium speed mill, the fineness of R₉₀ increased to 27.2%. When the coal and RDF were mixed and co-fired, the flame temperature and NO_x formation concentration decreased, the slagging in the combustion air zone increased, while the horizontal flue fouling changes were relatively minor, and the combustible content in the bottom slag increased to about 15%. The research will provide reference for co-firing RDF in coal-fired boilers.

Circulating fluidized bed (CFB) boilers play a pivotal role in China’s power generation landscape. However, the intricate combustion system within the CFB boiler furnace exhibits strong coupling characteristics, characterized by multiple parameters, variables, nonlinearity, and time-varying dynamics, posing a significant challenge for precise system modeling and prediction. Machine learning (ML), with its robust nonlinear processing capabilities and predictive performance, holds immense promise in the domain of CFB technology. This paper delves into the application of ML techniques in this field, encompassing the prediction of minimum fluidization velocity, emissions forecasting, bed pressure forecasting, bed temperature/thermal efficiency prediction, particle circulation rate prediction, reduced-order models of computational fluid dynamics (CFD) flow fields, and boiler safety control system models. The paper critically evaluates the strengths and limitations of these technologies in various scenarios, providing an insightful perspective on the opportunities and challenges faced by CFB boilers in the era of big data. Emphasizing aspects like model interpretability, enhancing generalization capabilities, improving data quality and diversity, integrating models with conventional methods, and experimental validation are crucial areas worth attention for future advancements.

In the context of “carbon peak, carbon neutral”, how to utilize biomass fuel safely, efficiently and environmentally friendly has become a hot research issue in the industry. The research progress of biomass fuel fluidized bed combustion technology both domestically and internationally was summarized based on the extensive practical engineering experience in fluidized bed combustion, providing a comprehensive overview of progress in biomass fluidized bed combustion power generation technology from an engineering perspective. The analysis compares the characteristics and problems of biomass boilers, with particular emphasis on the research and application status of biomass utilization in circulating fluidized bed. In addition, the combustion characteristics of biomass fuels, NO_x pollutant emission control, chlorine corrosion, and ash deposition and slagging issues caused by alkali metals in fluidized bed combustion were discussed. The reaction mechanisms in each process were described, and the future development directions of related technical issues were forecasted.