Search Results (17)

Oxy-fuel combustion is a promising way to avoid process-based CO₂ emissions. In this paper, the operational range of a new semi-industrial oxy-fuel combustion chamber for pulverized biomass is analyzed. This approach is used to gain a deeper understanding of the combustion setup and to examine the differences between air and oxy-fuel combustion on an industrial scale. Both analyzed parameters—flame spread and temperature distribution—have a significant influence on heat transfer in commercial boilers. The stability of various operating conditions is assessed by monitoring the CO content in the flue gas via a gas analyzer unit. For stable operation using walnut shells as fuel in an air atmosphere, an overall air-to-fuel ratio of 1.57–1.75 and a local air-to-fuel ratio of 0.75–0.95 provide the most stable conditions. A high swirl number of $0.9$ is found to be critical for stability, as the increased fuel momentum entering the combustion chamber promotes a fuel jet-dominated swirl flame. For the corresponding oxy-fuel combustion with the same volume flows and three different oxygen concentrations between 27% and 33%, stable combustion behavior is also observed. Using a camera setup to analyze flame shape and spread, it is observed that the flame formed with an oxygen content of 33% most closely resembles the flame shape achieved under air combustion conditions. However, the combustion temperatures most closely match those of the air operating condition when the oxygen content is 27%. Overall, it is shown that the approach for corresponding oxy-fuel conditions features similar flame shapes to oxy-fuel combustion with flue gas recirculation in a semi-industrial combustion chamber. Full article

China has abundant biomass and renewable energy resources suitable for producing green methanol via biomass thermochemical conversion. Given China’s increasing demand for sustainable fuel alternatives and the urgency to reduce carbon emissions, optimizing biomass utilization through gasification is critical. Research has highlighted the potential of integrating biomass gasification with water electrolysis to enhance efficiency in green methanol production, leveraging China’s vast biomass reserves to establish a cleaner energy pathway. Four main biomass gasification technologies—fixed-bed, fluidized-bed, pressurized fluidized-bed, and entrained-flow—have been investigated. Fixed-bed and bubbling fluidized-bed gasification face low gas yield and scaling issues; whereas, circulating fluidized-bed gasification (CFB) offers better gas yield, carbon efficiency, and scalability, though it exhibits high tar and methane in syngas. Pressurized fluidized-bed gasification improves gasification intensity, reaction rate, and equipment footprint, yet stable feedstock delivery under pressure remains challenging. Entrained-flow gasification achieves high carbon conversion and low tar but requires finely crushed biomass, restricted by biomass’ low combustion temperature and fibrous nature. Current industrially promising routes include oxygen-enriched and steam-based CFB gasification with tar cracking, which reduces tar but requires significant energy and investment; oxygen-enriched combustion to produce CO₂ for methanol synthesis, though oxygen in flue gas can poison catalysts; and a new high oxygen equivalence ratio CFB gasification technology proposed here, which lowers tar formation and effectively removes oxygen from syngas, thereby enabling efficient green methanol production. Overcoming feedstock challenges, optimizing operating conditions, and controlling tar and catalyst poisoning remain key hurdles for large-scale commercialization. Full article

Combining biomass co-firing with oxy-fuel combustion is a promising Bioenergy with Carbon Capture and Storage (BECCS) technology. It has the potential to achieve a large-scale reduction in carbon emissions from traditional power plants, making it a powerful tool for addressing global climate change. However, mercury in the fuel can be released into the flue gas during combustion, posing a significant threat to the environment and human health. More importantly, mercury can also cause the fracture of metal equipment via amalgamation, which is a major risk for the system. Therefore, compared to conventional coal-fired power plants, the requirements for the mercury concentration in BECCS systems are much stricter. This article reviews the latest progress in mercury control under oxy-fuel biomass co-firing conditions, clarifies the impact of biomass co-firing on mercury species transformation, reveals the influence mechanisms of various flue gas components on elemental mercury oxidation under oxy-fuel combustion conditions, evaluates the advantages and disadvantages of various mercury removal methods, and finally provides an outlook for mercury control in BECCS systems. Research shows that after biomass co-firing, the concentrations of chlorine and alkali metals in the flue gas increase, which is beneficial for homogeneous and heterogeneous mercury oxidation. The changes in the particulate matter content could affect the transformation of gaseous mercury to particulate mercury. The high concentrations of CO₂ and H₂O in oxy-fuel flue gas inhibit mercury oxidation, while the effects of NO_x and SO₂ are dual-sided. Higher concentrations of fly ash in oxy-fuel flue gas are conducive to the removal of Hg⁰. Additionally, under oxy-fuel conditions, CO₂ and metal ions such as Fe²⁺ can inhibit the re-emission of mercury in WFGD systems. The development of efficient adsorbents and catalysts is the key to achieving deep mercury removal. Fully utilizing the advantages of chlorine, alkali metals, and CO₂ in oxy-fuel biomass co-firing flue gas will be the future focus of deep mercury removal from BECCS systems. Full article

In recent years supercritical CO₂ power plants have seen a growing interest in a wide range of applications (e.g., nuclear, waste heat recovery, solar concentrating plants). The Allam Cycle, also known as the Allam-Fetvedt or NET Power cycle, seems to be one of the most interesting direct-fired sCO₂ cycles. It is a semi-closed loop, high-pressure, low-pressure ratio, recuperated, direct-fired with oxy-combustion, trans-critical Brayton cycle. Numerical simulations play a key role in the study of this novel cycle. For this reason, the aim of this review is to offer the reader a wide array of modeling solutions, emphasizing the ones most frequently employed and endeavoring to provide guidance on which choices seem to be deemed most appropriate. Furthermore, the review also focuses on the system’s performance and on the opportunities related to the integration of the Allam cycle with a series of processes, e.g., cold energy storage, LNG regasification, biomass or coal gasification, and ammonia production. Full article

In the coming carbon-neutral era, industrial gas turbines (GT) will continue to play an important role as energy conversion equipment with high thermal efficiency and as stabilizers of the electric power grid. Because of the transition to a clean fuel, such as hydrogen or ammonia, the main modifications will lie with the combustor. It can be expected that small and medium-sized gas turbines will burn fewer inferior fuels, and the scope of cogeneration activities they are used for will be expanded. Industrial gas turbine cycles including CCGT appropriate for the carbon-neutral era are surveyed from the viewpoint of thermodynamics. The use of clean fuels and carbon capture and storage (CCS) will inevitably increase the unit cost of power generation. Therefore, the first objective is to present thermodynamic cycles that fulfil these requirements, as well as their verification tests. One conclusion is that it is necessary to realize the oxy-fuel cycle as a method to utilize carbon-heavy fuels and biomass and not generate NO_x from hydrogen combustion at high temperatures. The second objective of the authors is to show the required morphology of the cooling structures in airfoils, which enable industrial gas turbines with a higher efficiency. In order to achieve this, a survey of the historical development of the existing cooling methods is presented first. CastCool^® and wafer and diffusion bonding blades are discussed as turbine cooling technologies applicable to future GTs. Based on these, new designs already under development are shown. Most of the impetus comes from the development of aviation airfoils, which can be more readily applied to industrial gas turbines because the operation will become more similar. Double-wall cooling (DWC) blades can be considered for these future industrial gas turbines. It will be possible in the near future to fabricate the DWC structures desired by turbine cooling designers using additive manufacturing (AM). Another conclusion is that additively manufactured DWC is the best cooling technique for these future gas turbines. However, at present, research in this field and the data generated are scattered, and it is not yet possible for heat transfer designers to fabricate cooling structures with the desired accuracy. Full article

In this paper, the co-combustion behavior of the walnut shell, biochar, and coal, and the respective binary and ternary blends were investigated by thermogravimetric analysis (TGA) in the oxy-fuel atmosphere (21% O₂/79% CO₂). The combustion reactivity of coal was similar to biochar but lower than that of the walnut shell. The presence of the walnut shell improved the combustion performance of coal and biochar. The interaction between only biochar and coal was inhibited in the binary blends. The presence of the walnut shell in the ternary blend covered up the inhibition between biochar and coal. The average activation energy of each sample was obtained using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) kinetic models. The results of this study provide a reference for the rational utilization of biomass and biochar and the practical improvement of the thermal conversion efficiency of coal. Full article

In recent years, global warming and climate change associated with emissions of CO₂ from fossil fuel-fired power systems are a big worry for authorities in many countries worldwide. The utilization of biomass as an alternative, carbon-neutral fuel can reduce emissions of CO₂ and other greenhouse gases. Furthermore, the coupling of oxy-combustion of biomass with CO₂ capture is an option for carbon-negative power generation technology. In this study, emissions of NO_x, SO₂, and CO from the air- and oxy-combustion of three energy crops (Miscanthus giganteus, Sida hermaphrodita, and Salix viminalis) are presented and compared with emissions from other biomass fuels and reference coal. Combustion tests in air and O₂/CO₂ mixtures were conducted in a 12-kW bench-scale CFB combustor at 850 °C. Measurements of flue gas compositions were taken using an FTIR spectrometer. In all tested atmospheres, emissions of SO₂, N₂O, and CO for biomass were lower than those for the reference coal. The oxidation of volatile nitrogen compounds was behind high emissions of NO_x from biomass burned in air and O₂/CO₂ mixtures. The lowest concentrations of NO were found in the 21% O₂/70% CO₂ mixture. Combustion in mixtures containing more oxygen (30% and 40% O₂) led to a decrease in emissions of N₂O and CO and an increase in emissions of NO and SO₂. Full article

Nowadays oxy-fuel combustion of coal and biomass is the most promising option for the reduction of CO₂ emissions from power plants. In this paper, emissions of NO_x (NO, NO₂, N₂O and their precursors, such as NH₃ and HCN), SO₂ and CO during conventional and oxy-fuel combustion of three kinds of biomass (agro, woody and energy crop) and a reference coal are presented and discussed. Combustion tests were conducted at 850 °C in the laboratory-scale circulating fluidized bed (CFB) reactor in air and O₂/CO₂ atmospheres. A FTIR spectrometer was used to measure instantaneous concentrations of all pollutants in the flue gas. Emissions of SO₂, N₂O and CO for the combustion of biomass in all atmospheres were lower than those for the combustion of reference coal. It was found that oxidation of nitrogen species released with volatile matter was responsible for high emissions of NO_x during combustion of biomass fuels in air and mixtures of O₂ and CO₂. The lowest NO emissions for tested fuels were detected in oxy-21 atmosphere (21% O₂/70% CO₂). Oxy-combustion of biomass in O₂/CO₂ mixtures at 30% and 40% O₂ caused a decrease in emissions of N₂O and CO while NO and SO₂ emissions increased. The results of this study show that the tested biomass fuels are ideal renewable energy resources both in conventional and oxy-fuel conditions with a minor potential for environmental pollution. Full article

For coal semi-char as a by-produced of low-temperature pyrolysis, combustion for power generation is one of the effective utilization methods to realize its clean and efficient utilization. However, the coal semi-char combustion process has a difficult ignition, unstable combustion and low burnout rate. The co-firing of the semi-char with biomass under oxy-fuel conditions can improve the combustion behavior and reduce fossil CO₂ emissions. In this paper, the combustion behavior of Shenhua coal semi-char (SHC) co-firing with straw (ST) in O₂/CO₂ mixture is investigated using thermogravimetric analysis. The results show that each curve lays between those of the individual fuels and presents three peaks (i.e., three stages). The thermogravimetric curves of SHC co-firing with ST can be divided into three stages: the volatile combustion of ST, the co-combustion of SHC and ST fixed-carbons and the SHC fixed-carbon combustion and the decomposition of the difficult pyrolytic material of ST. Blending ST into the SHC can significantly decrease the ignition temperature and improve the comprehensive combustion behavior of blended samples. In increasing the proportion of ST from 25 to 100%, the change of the blended ignition temperature is slight, but the burnout temperature decreases greatly. Kinetic parameters of combustion are calculated by using the Coats–Redfern integral method. Compared to that of stage I and stage III, the activation energy of stage II is significantly lower. As increasing blending ratio from 25% to 100%, the activation energy increases at stage I and decreases at stage III. Furthermore, the O₂ concentration obviously affects stage III of 50% SHC + 50% ST, and the thermogravimetric curves at this stage are obviously shifted to the lower temperature zone as the O₂ concentration increases. The activation energy of 50% SHC + 50% ST increases as the oxygen concentration increases. Besides, the activation energy shows that the combustion characteristics cannot be determined only by the activation energy obtained by the Coats–Redfern method. These findings can provide useful information for semi-char co-firing with biomass. Full article

A revolution of the global energy industry is without an alternative to solving the climate crisis. However, renewable energy sources typically show significant seasonal and daily fluctuations. This paper provides a system concept model of a decentralized power-to-green methanol plant consisting of a biomass heating plant with a thermal input of 20 MW_th. (oxyfuel or air mode), a CO₂ processing unit (DeOxo reactor or MEA absorption), an alkaline electrolyzer, a methanol synthesis unit, an air separation unit and a wind park. Applying oxyfuel combustion has the potential to directly utilize O₂ generated by the electrolyzer, which was analyzed by varying critical model parameters. A major objective was to determine whether applying oxyfuel combustion has a positive impact on the plant’s power-to-liquid (PtL) efficiency rate. For cases utilizing more than 70% of CO₂ generated by the combustion, the oxyfuel’s O₂ demand is fully covered by the electrolyzer, making oxyfuel a viable option for large scale applications. Conventional air combustion is recommended for small wind parks and scenarios using surplus electricity. Maximum PtL efficiencies of η_PtL,Oxy = 51.91% and η_PtL,Air = 54.21% can be realized. Additionally, a case study for one year of operation has been conducted yielding an annual output of about 17,000 t/a methanol and 100 GWh_th./a thermal energy for an input of 50,500 t/a woodchips and a wind park size of 36 MWp. Full article

The fluidized bed combustion (FBC) of biomass and solid recovered fuel (SRF) is globally emerging as a viable solution to achieve net-negative carbon emissions in the heat and power sector. Contrary to conventional fossil fuels, alternative fuels are highly heterogeneous, and usually contain increased amounts of alkaline metals and chlorine. Hence, experimental studies are mandatory in order to thoroughly characterize the combustion behavior and pollutant formation of non-conventional fuels in novel applications. This work gives an overview of experimental investigations on the oxy-fuel combustion of hard coal, wheat straw, and SRF with a limestone bed in a semi-industrial circulating fluidized bed (CFB) pilot plant. The CFB combustor was able to be operated under different fuel blending ratios and inlet O₂ concentrations, showing a stable hydrodynamic behavior over many hours of continuous operation. The boundary conditions introduced in this study are expected to prevail in carbon capture and storage (CCS) processes, such as the oxy-fuel combustion in the CFB calciner of a Calcium Looping (CaL) cycle for post-combustion CO₂ capture. Full article

Nowadays, despite a negative impact on the natural environment, coal combustion is still a significant energy source. One way to minimize the adverse side effects is sophisticated combustion technologies, such as, e.g., staged combustion, co-combustion with biomass, and oxy-combustion. Maintaining the combustion process at its optimal state, considering the emission of harmful substances, safe operation, and costs requires immediate information about the process. Flame image is a primary source of data which proper processing make keeping the combustion at desired conditions, possible. The paper presents a method combining flame image processing with a deep convolutional neural network (DCNN) that ensures high accuracy of identifying undesired combustion states. The method is based on the adaptive selection of the gamma correction coefficient (G) in the flame segmentation process. It uses the empirically determined relationship between the G coefficient and the average intensity of the R image component. The pre-trained VGG16 model for classification was used. It provided accuracy in detecting particular combustion states on the ranging from 82 to 98%. High accuracy and fast processing time make the proposed method possible to apply in the real systems. Full article

Co-combustion of biomass-based fuels and fossil fuels in power plant boilers, utility boilers, and process furnaces is a widely acknowledged means of efficient heat and power production, offering higher power production than comparable systems with sole biomass combustion. This, in combination with CO₂ and other greenhouse gases abatement and low specific cost of system retrofit to co-combustion, counts among the tangible advantages of co-combustion application. Technical and operational issues regarding the accelerated fouling, slagging, and corrosion risk, as well as optimal combustion air distribution impact on produced greenhouse gases emissions and ash properties, belong to intensely researched topics nowadays in parallel with the combustion aggregates design optimization, the advanced feed pretreatment techniques, and the co-combustion life cycle assessment. This review addresses the said topics in a systematic manner, starting with feed availability, its pretreatment, fuel properties and combustor types, followed by operational issues, greenhouse gases, and other harmful emissions trends, as well as ash properties and utilization. The body of relevant literature sources is table-wise classified according to numerous criteria pertaining to individual paper sections, providing a concise and complex insight into the research methods, analyzed systems, and obtained results. Recent advances achieved in individual studies and the discovered synergies between co-combusted fuels types and their shares in blended fuel are summed up and discussed. Actual research challenges and prospects are briefly touched on as well. Full article

Solar thermochemical gasification is a promising solution for the clean production of low-emission synthetic fuels. It offers the possibility to upgrade various biomasses and waste feedstocks and further provides an efficient way to sustainably store solar energy into high-value and energy-intensive chemical fuels. In this work, a novel continuously-fed solar steam gasifier was studied using beechwood and solid recovered fuels (SRF) particles. Solar-only and hybrid solar/autothermal gasification experiments were performed at high temperatures to assess the performance of the reactor and its flexibility in converting various types of feedstocks. The hybrid operation was considered to increase the solar reactor temperature when the solar power input is not sufficient thanks to partial feedstock oxy-combustion. The hybrid solar process is thus a sustainable alternative option outperforming the conventional gasification processes for syngas production. Wood and waste particles solar conversion was successfully achieved, yielding high-quality syngas and suitable reactor performance, with Cold Gas Efficiencies (CGE) up to 1.04 and 1.13 respectively during the allothermal operation. The hybrid process allowed operating with a lower solar power input, but the H₂ and CO yields noticeably declined. SRF gasification experiments suffered furthermore from ash melting/agglomeration issues and injection instabilities that undermined the continuity of the process. This study demonstrated the solar reactor flexibility in converting both biomass and waste feedstocks into syngas performed in continuous feeding operation. The experimental outcomes showed the feasibility of operating the reactor in both allothermal (solar-only) and hybrid allothermal/autothermal (combined solar and oxy-combustion heating) for continuous syngas production with high yields and energy conversion efficiencies. Full article

In this paper, response surface methodology (RSM) designs and an artificial neural network (ANN) are used to obtain the optimal conditions for the oxy-combustion of a corn–rape blend. The ignition temperature (T_e) and burnout index (D_f) were selected as the responses to be optimised, while the CO₂/O₂ molar ratio, the total flow, and the proportion of rape in the blend were chosen as the influencing factors. For the RSM designs, complete, Box–Behnken, and central composite designs were performed to assess the experimental results. By applying the RSM, it was found that the principal effects of the three factors were statistically significant to compute both responses. Only the interactions of the factors on D_f were successfully described by the Box–Behnken model, while the complete design model was adequate to describe such interactions on both responses. The central composite design was found to be inadequate to describe the factor interactions. Nevertheless, the three methods predicted the optimal conditions properly, due to the cancellation of net positive and negative errors in the mathematical adjustment. The ANN presented the highest regression coefficient of all methods tested and needed only 20 experiments to reach the best predictions, compared with the 32 experiments needed by the best RSM method. Hence, the ANN was found to be the most efficient model, in terms of good prediction ability and a low resource requirement. Finally, the optimum point was found to be a CO₂/O₂ molar ratio of 3.3, a total flow of 108 mL/min, and 61% of rape in the biomass blend. Full article