Journal of The Energy Institute最新文献

The potential increase in nitrogen oxide emissions in the coal/ammonia co-firing can hinder the large-scale utilization of ammonia to reduce carbon emissions. In this work, a fluidized bed simulation model was established to investigate the NO_x and N₂O behaviors in the process of coal/ammonia co-firing. The effects of several variables on nitrogen oxides emission characteristics were studied, including the ammonia ratio, temperature, excess air ratio, and air/ammonia distribution strategies. The findings indicate that NO_x and N₂O concentrations rise and then decline with the NH₃ co-firing ratio (CR-NH₃) increased, peaking at 10 % and 5 % CR-NH₃. The formation of N₂O is insensitive to the addition of ammonia, while NO_x emissions vary dramatically with different ammonia ratios. Higher temperatures enhance the formation of NO_x but inhibit the generation of N₂O within 750 °C–950 °C. As the temperature rises, the primary decomposition path of N₂O shifts from N₂O→N₂H₂→NNH→N₂ to N₂O→NO₂→NO→N₂. The generations of NO_x and N₂O are both enhanced due to the weakness of the reduced atmosphere with the excess air ratio increased. When the primary air ratio is raised, N₂O gradually takes over as the main source of nitrogen oxides instead of NO_x. The specific primary air ratio in the fluidized bed should be considered in the priority treatment of NO_x or N₂O in the process of lowering nitrogen oxides emissions. Ammonia distribution strategies have opposite effects on NO_x and N₂O emissions. With more NH₃ introduced as a secondary fuel, the dilute phase area can change from the main source of NO to the consumption area of NO. The present findings can help control the emissions of nitrogen oxides during coal/ammonia co-combustion in coal-fired circulating fluidized bed power plants.

Biomass is considered a renewable green coal, and its clean and efficient utilization is of great significance for energy conservation and carbon reduction. One of the most critical aspects of biomass gasification is the selection of an appropriate catalyst. In this study, we synthesized a catalyst with 10 % Pr_1-xCe_xCoO₃ supported on dolomite using the sol-gel method. We conducted graded internal circulation gasification experiments to produce hydrogen-rich syngas. The effects of element substitution in PrCoO₃, temperature, catalyst composition, and steam injection rate on the products were investigated. The optimal gasification conditions were determined through response surface regression analysis. The data indicate that this catalyst can improve gasification efficiency, with Pr_0.4Ce_0.6CoO₃/Dol showing the best catalytic performance. It effectively reduces the required gasification temperature and steam amount, decreases CO₂ production, and increases CO and H₂ yields. The catalyst accelerates the cleavage and ring-opening reactions of hydrocarbons, leading to terminal chain hydroxylation, followed by the dehydration-condensation of methyl groups into ethers. As the temperature rises, the rate of carboxyl group removal gradually exceeds the rate of carboxyl group formation via the oxidation of hydroxyl and ether chains, resulting in an initial increase and then a decrease in the number of carboxyl groups. Under optimal gasification conditions, CO₂ production is reduced by one-fourth compared to using a dolomite catalyst.

As the greenhouse effect intensifies, ammonia is garnering increasing attention as a carbon-free fuel. In the transport sector, ammonia-diesel dual-fuel (ADDF) engines are regarded as an effective means of reducing carbon emissions. The objective of this study is to investigate the combustion and emission optimization of an ADDF engine under high load conditions. To this end, an experimental optimization study of different start of diesel injection timing (SODI) and exhaust gas recirculation (EGR) rates was conducted at a load of 18 bar and an ammonia energy ratio of 80 %. The mechanism of heat capacity, dilution, and chemical effects of EGR was also revealed by numerical simulation based on the separated variables method. It was demonstrated that advancing SODI is effective in enhancing combustion efficiency. However, this approach is limited by the upper limit of in-cylinder pressure and results in higher nitrogen oxides (NO_x) emissions, which can be mitigated by the EGR. The heat capacity effect of EGR increases the specific heat capacity and decreases the average temperature. The suppression of the combustion process leads to a reduction in thermal and fuel NO_x, but an increase in nitrous oxide (N₂O) emissions. The dilution effect of EGR results in insufficient oxygen, which decreases the heat release rate and combustion efficiency. Additionally, the NO_x and N₂O are significantly reduced. The chemical effect of EGR affects reactive groups and unburned components that accelerate heat release rate and increase accumulated heat release, resulting in significantly higher NO_x. The comprehensive effect of EGR results in a decrease in N₂O emissions and a significant reduction in thermal and fuel NO_x. The EGR and further optimization of SODI enabled the ADDF engine to achieve a gross indicated thermal efficiency of 48.5 % with a load of 18 bar and an ammonia energy ratio of 80 %. In addition, NO emissions were reduced by 32.8 percent and greenhouse gas emissions by 63.3 percent.

CO₂ and CH₄ are converted to syngas by dry reforming of methane (DRM) reaction. This research investigated the effects of the Mg promoter on Al₂O₃-supported Ni catalysts and Mg calcination temperature on the DRM performance in a parallel plate dielectric barrier discharge reactor. The Mg promoter played a crucial role in the DRM performance, as increasing the Mg calcination temperature from 700 °C to 800 °C significantly improved the DRM performance and catalyst properties, including increased specific surface area, decreased total acidity, reduced crystallite and particle sizes, and more uniform dispersion of the Ni nanoparticles. Under these conditions, the H₂ and CO selectivity were 77.0 % and 70.7 %, the CH₄ and CO₂ conversion were 25.1 % and 20.6 %, and the energy efficiency was 8.4 %. In addition, the catalyst was associated with a lower coking rate (0.5 mg C/g_cat h), a relatively low carbon deposit of 1.5 %, and a carbon loss of 2.8 %, possibly because the weak acidity hindered the Boudouard reaction and CH₄ decomposition. However, increasing the Mg calcination temperature to 900 °C increased the total acidity and Ni particle size, decreasing H₂ and CO selectivities and increasing carbon deposits on the catalyst surface.

This study delves into the intriguing prospect of concurrently utilizing macadamia husk and nutshell for biomass gasification, aiming to generate sustainable energy. By scrutinizing their physicochemical properties such as thermal behaviors, char conversion kinetics, and syngas properties we unveiled an intriguing revelation. The fusion of these residues creates an apt feedstock for biomass batch-gasification in industrial settings. This resultant blend inherits distinctive traits from its constituent parts, profoundly influencing gasification reactivity and fostering heightened char conversion efficiency and stability. Spanning 2165 s, this process exhibited commendable control. Furthermore, the residue amalgamation consistently yields an average syngas flow rate of 0.00136 [mol (g minute)⁻¹], predominantly composed of CO at 0.00097 [mol (g minute)⁻¹], constituting over 71 % of the syngas. These findings underscore the potential of merging these residues to optimize the conversion process and bolster resource availability, thus propelling advancements in waste-free energy production and sustainable energy technologies.

The preparation of bio-oil from cotton stalks and agricultural residue films using co-pyrolysis technology can achieve resource recovery and energy conversion, which has important research value and significance. In this study, cotton stalks were subjected to different chemical pretreatments using NaOH, HCl, and H₂O solutions to understand their structural changes and pyrolysis characteristics. In addition, the lower H/C ratio of cotton stalks resulted in higher oxygen content in the pyrolysis oil, which limited its efficient and clean utilization. Therefore, the characteristics and pyrolysis kinetics of the pyrolysis products of pretreated cotton stalks and LDPE (low-density polyethylene) were studied. The results showed that the ash content of alkali pretreatment cotton stalks decreased by 1.24 %, and the dense structure of cotton stalks significantly relaxed. NaOH pretreatment effectively removed hemicellulose sugars and cracked them. During the co-pyrolysis process, when the ratio of NaOH-CS/LDPE was 50/50, the synergistic effect was more pronounced, and the oil yield increased by 2 % compared to the theoretical value. The oxygen content of CO and CO₂ in the pyrolysis gas was higher than the theoretical value, at 10.4 % and 14.1 % respectively. The synergistic effect of bio-oil on hydrocarbons was the most significant, reaching 18.9 %. More hydrogen and less oxygen migrated into the co-pyrolysis oil, resulting in an increase in hydrocarbons and a decrease in oxygen-containing compounds, and improving the quality of bio-oil. Results from electron paramagnetic resonance (EPR) indicated that adding LDPE might raise the quantity of stable free radicals. The evolution mechanism of functional groups of NaOH-CS and LDPE co-pyrolysis behavior was analyzed by Fourier in-situ infrared spectrometry (FTIR), and it was found that C–O–C, C=O, and O–H decreased due to dehydroxylation, decarboxylation, decarbonylation, and demethoxy reactions with the increase of temperature, indicating that there was a synergistic effect between NaOH-CS and LDPE co-pyrolysis. The pyrolysis kinetics of NaOH-CS, LDPE and their blends were determined by the model-free method. The introduction of LDPE can reduce the activation energy of NaOH -CS pyrolysis alone, and the 3D diffusion (D3) model is suitable for their blends.

This study investigates the impact of reactor geometry (varying external electrode length) of Dielectric Barrier Discharge (DBD) reactors on the decomposition of toluene, a model compound for biomass gasification tar, using different carrier gases and various power levels. Results reveal that toluene decomposition is higher at longer electrode lengths (30 mm) at all power levels tested. Specifically, the toluene decomposition in H₂ carrier gas at 30 mm electrode length increased from 67.2 % to 97.5 % with rising power from 5 to 40 W, while it ranged from 52 % to 97.4 % at 15 mm electrode length. The decomposition of toluene was found to be higher in N₂ carrier gas than in H₂ carrier gas at both discharge lengths. At 30 mm external electrode and with rising power from 5 to 40 W, toluene decomposition ranged from 90.5 % to 98.7 %. Similarly, when the electrode length was reduced from 30 to 15 mm for N₂ carrier gas, the decomposition of toluene ranged from 74 % to 97.9 %. Thus, the results indicate that the decomposition of toluene is affected by both the electrode length and the nature of the carrier gas. The effect of electrode length was significant at lower power levels, and the difference between the conversion at both electrode lengths nearly disappeared at higher power levels.

As a promising carbon-free fuel, ammonia is expected to be widely applied in internal combustion engines. However, the physical properties of ammonia are quite different from those of conventional fuels, which leads to different spray characteristics. In this paper, the ammonia spray under injection pressure as high as 80 MPa was visualized by the diffused back-illumination imaging method, and the liquid ammonia spray characteristics under different ambient pressures and ambient temperatures were analyzed. The liquid spray penetration length, cone angle and tip velocity calculated from the spray images provide a reference database for numerical simulation. The results show that the development characteristics of liquid ammonia spray are significantly different under flare flash boiling, transitional flash boiling and non-flash boiling conditions. Flash boiling (especially flare flash boiling) inhibits the initial liquid spray penetration. The spray tip velocity increases first and then gradually decreases under flash boiling conditions. Ammonia spray has obvious radial expansion at the initial stage of flare flash boiling and the spray contour under flare flash boiling conditions is noticeably distorted, forming an obvious dilute region. With the increase of ambient pressure, the intensity of flash boiling reduces, the dilute region gradually disappears, and the distortion of the spray contour gradually weakens. Under non-flash boiling conditions, ammonia spray presents a dense and regular shape; there is no spray acceleration but a sharp decrease in spray tip velocity at the initial stage, and then the spray penetrates forward at a similar velocity. The spray penetration velocity decreases significantly with the increase of ambient pressure. The increase in ambient temperature accelerates the vaporization of ammonia spray. The liquid spray penetration length decreases and maintains with only slight fluctuations during the injection process as the ambient temperature increases from 300 K to 600 K because the vaporization rate and penetration velocity reach a balance.

This paper investigates the combustion and thermoacoustic instability characteristics of ethanol/methane co-firing flames. Methane was introduced into the combustion chamber in three different mixing methods: the premixing method, single-tube injection, and dual-tube injection. The effects of mixing ratio, equivalence ratio, jet pipe diameter and position on combustion performance are also considered. The results show that under the premixed combustion mode, as the methane ratio increases, combustion instability shows a trend of first enhancement and then weakening, reaching a maximum pressure pulsation of 228.8 Pa at a 30 % mixing ratio. When methane is injected transversely into the combustion chamber using a single-tube or dual-tube, the inner diameter of the injection tube, injection height, and injection distance are essential factors affecting combustion instability, all of which will change the inhibitory effect of the transverse jet on instability. In addition, when the methane mixing ratio reaches 50 %, the co-firing flames will be in a relatively stable combustion state under all conditions. But at this time, the increase in flame temperature and the oxygen-deficient environment in the combustion chamber will cause simultaneous increases in CO and NOx emissions, which are not conducive to clean and efficient fuel combustion.

The oxy-fuel combustion contributes to carbon capture, while the recirculation of flue gas brings about high concentrations of SO₂ and H₂O, which can affect the transformation of minerals in high-alkali coal. The staged oxy-fuel combustion, as an effective method for NO_x reduction, can also change the ash deposition behavior of high-alkali coal. Two kinds of diluting agents, including pure CO₂ for O₂/CO₂ combustion and simulated “recycled flue gas” (CO₂, SO₂, and H₂O) for O₂/RFG combustion, were employed in the present work. The ash deposition and NO emission of high-alkali coal during the staged oxy-fuel combustion were simultaneously studied under O₂/CO₂ and O₂/RFG conditions. The conversion ratios of fuel-nitrogen to NO (C_NO) and ash deposition efficiencies (E_d) at different stoichiometric ratios in primary combustion zone (SR₁) and different oxygen concentrations were obtained. Afterwards, a series of tests were performed to further analyze the ash deposits. The experimental results show that as SR₁ increases from 0.6 to 1.2, C_NO jumps from 2.0 % to 23.5 % (O₂/CO₂ combustion) and from 1.9 % to 19.9 % (O₂/RFG combustion). The additions of SO₂ and H₂O can reduce the NO emission. With the rising SR₁, E_d under the O₂/CO₂ and O₂/RFG conditions decreases from 4.0 % to 2.6 % and from 4.8 % to 2.1 %, respectively. At high SR₁, the CaSO₄ amount declines and the iron contributes less to the ash deposition. In O₂/RFG combustion, the small sticky particles of sodium aluminosilicates on large particle surfaces reduce, and the large particles of calcium aluminosilicates shrink because some calcium produces CaSO₄. Moreover, the exposure of ferrous iron to H₂O helps its oxidization so iron is harder to cause severe adhesion. As O₂ concentration rises from 21 % to 40 %, C_NO shows an upward trend. Meanwhile, E_d under the O₂/CO₂ and O₂/RFG conditions increases from 2.6 % to 3.7 % and from 2.3 % to 2.7 %, respectively. The present work is expected to provide some conducive information for the clean utilization of high-alkali coal and secure operation of boiler, as well as large-scale CO₂ capture.