Pub Date : 2024-11-01DOI: 10.1016/j.joei.2024.101872
The increasing production of waste plastics poses significant environmental and health risks. Low-density polyethylene (LDPE), a major component of plastic waste, is a high-quality feedstock for pyrolysis due to its high carbon and hydrogen content. Traditional pyrolysis methods, such as thermal cracking and one-step catalytic pyrolysis, have limitations in yield and selectivity of valuable products like light olefins. This study introduces a two-stage catalytic pyrolysis (TSCP) process aimed at enhancing the production of light olefins from LDPE. In the first stage, LDPE undergoes pyrolysis with MCM-41 catalyst, yielding a substantial number of liquid products and a minor portion of light olefins. The second stage utilizes Mg-ZSM-5 catalyst to further crack the high-temperature volatile matter into light olefins. The optimal conditions identified were 450 °C in the first stage and 500 °C in the second stage, achieving a maximum light olefin yield of 45.80 wt% and a low reaction temperature, decreasing the energy consumption. Additionally, the MCM-41 catalyst demonstrates excellent regeneration performance, with only a slight decrease in liquid yield after nine cycles. The Mg-ZSM-5 catalyst maintains high stability, with light olefin yield remaining at 83.60 % of the initial yield after 48 h of operation.
{"title":"Boosting light olefin production from pyrolysis of low-density polyethylene: A two-stage catalytic process","authors":"","doi":"10.1016/j.joei.2024.101872","DOIUrl":"10.1016/j.joei.2024.101872","url":null,"abstract":"<div><div>The increasing production of waste plastics poses significant environmental and health risks. Low-density polyethylene (LDPE), a major component of plastic waste, is a high-quality feedstock for pyrolysis due to its high carbon and hydrogen content. Traditional pyrolysis methods, such as thermal cracking and one-step catalytic pyrolysis, have limitations in yield and selectivity of valuable products like light olefins. This study introduces a two-stage catalytic pyrolysis (TSCP) process aimed at enhancing the production of light olefins from LDPE. In the first stage, LDPE undergoes pyrolysis with MCM-41 catalyst, yielding a substantial number of liquid products and a minor portion of light olefins. The second stage utilizes Mg-ZSM-5 catalyst to further crack the high-temperature volatile matter into light olefins. The optimal conditions identified were 450 °C in the first stage and 500 °C in the second stage, achieving a maximum light olefin yield of 45.80 wt% and a low reaction temperature, decreasing the energy consumption. Additionally, the MCM-41 catalyst demonstrates excellent regeneration performance, with only a slight decrease in liquid yield after nine cycles. The Mg-ZSM-5 catalyst maintains high stability, with light olefin yield remaining at 83.60 % of the initial yield after 48 h of operation.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-31DOI: 10.1016/j.joei.2024.101873
The study of the combustion characteristics of NH₃/bio-syngas/air under NH₃ partial cracking and elevated initial temperatures can enhance its feasibility as a practical fuel. The effects of NH₃ cracking rates (ζ) and initial temperature (T0) on the laminar burning velocity (SL), instability, and NO emissions of NH₃/bio-syngas/air premixed flames under different equivalence ratios are investigated. The results indicate that increasing ζ and T0 enhances the SL of the premixed flame, with ζ having a more pronounced effect on combustion enhancement. Virtual gas analysis reveals that pre-cracking primarily strengthens combustion through chemical effect. An increase in ζ significantly shifts the peak SL towards the fuel-rich region, while at any T0, the peak SL consistently occurs around Φ = 1.1. Increasing ζ and T0 reduces the critical radius (rc) and the critical Peclet number (Pec) of the premixed fuel, with rc decreasing more rapidly when ζ is below 30 %. The dimensionless growth rate (∑) increases with the rise in ζ and T0, consistently remaining positive, indicating an unstable state. Additionally, ∑ varies more significantly with T0 when T0 is below 450 K. When ζ is below 60 %, the NO mole fraction increases with the increase in ζ. However, at ζ = 80 %, the NO mole fraction is lower than at ζ = 40 %. Increasing T0 continually increases the NO mole fraction. Analysis of the NH3 reaction pathways indicates that NHi (i = 0, 1, 2) is closely related to the NO → N2 reduction reactions.
{"title":"The effects of NH3 pre-cracking and initial temperature on the intrinsic instability and NOx emissions of NH3/bio-syngas/air premixed flames","authors":"","doi":"10.1016/j.joei.2024.101873","DOIUrl":"10.1016/j.joei.2024.101873","url":null,"abstract":"<div><div>The study of the combustion characteristics of NH₃/bio-syngas/air under NH₃ partial cracking and elevated initial temperatures can enhance its feasibility as a practical fuel. The effects of NH₃ cracking rates (<em>ζ</em>) and initial temperature (<em>T</em><sub><em>0</em></sub>) on the laminar burning velocity (<em>S</em><sub><em>L</em></sub>), instability, and NO emissions of NH₃/bio-syngas/air premixed flames under different equivalence ratios are investigated. The results indicate that increasing <em>ζ</em> and <em>T</em><sub><em>0</em></sub> enhances the <em>S</em><sub><em>L</em></sub> of the premixed flame, with <em>ζ</em> having a more pronounced effect on combustion enhancement. Virtual gas analysis reveals that pre-cracking primarily strengthens combustion through chemical effect. An increase in <em>ζ</em> significantly shifts the peak <em>S</em><sub><em>L</em></sub> towards the fuel-rich region, while at any <em>T</em><sub><em>0</em></sub>, the peak <em>S</em><sub><em>L</em></sub> consistently occurs around Φ = 1.1. Increasing <em>ζ</em> and <em>T</em><sub><em>0</em></sub> reduces the critical radius (<em>r</em><sub><em>c</em></sub>) and the critical Peclet number (<em>Pe</em><sub><em>c</em></sub>) of the premixed fuel, with <em>r</em><sub><em>c</em></sub> decreasing more rapidly when <em>ζ</em> is below 30 %. The dimensionless growth rate (<em>∑</em>) increases with the rise in <em>ζ</em> and <em>T</em><sub><em>0</em></sub>, consistently remaining positive, indicating an unstable state. Additionally, <em>∑</em> varies more significantly with <em>T</em><sub><em>0</em></sub> when <em>T</em><sub><em>0</em></sub> is below 450 K. When <em>ζ</em> is below 60 %, the NO mole fraction increases with the increase in <em>ζ</em>. However, at <em>ζ</em> = 80 %, the NO mole fraction is lower than at <em>ζ</em> = 40 %. Increasing <em>T</em><sub><em>0</em></sub> continually increases the NO mole fraction. Analysis of the NH<sub>3</sub> reaction pathways indicates that NH<sub>i</sub> (i = 0, 1, 2) is closely related to the NO → N<sub>2</sub> reduction reactions.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-30DOI: 10.1016/j.joei.2024.101868
Achieving carbon neutrality necessitates the adoption of zero-carbon fuels in engine applications, with ammonia emerging as an up-and-coming candidate due to its favorable safety profile and advantages in storage and transportation. This study experimentally investigated the feasibility of an ammonia-gasoline dual-fuel (AGDF) engine to achieve comparable power output and satisfactory carbon reduction without changing the main structural parameters of the engine. A four-cylinder, naturally aspirated, spark ignition engine was used to investigate the impact of ammonia energy ratio (AER), engine base torque and engine speed on the engine performance, combustion evolution and emission characteristics. The findings reveal that the brake thermal efficiency (BTE) in AGDF mode is lower than in gasoline-only mode, primarily due to the reduced combustion activity. However, this efficiency decline becomes noticeable only when the AER exceeds 15 %. Additionally, at high AERs and high engine base torques, the delayed effect of ammonia fuel on the main combustion period results in a double-peak pattern, which limits the energy output but presents opportunities for phase optimization. The study also examined three incomplete combustion emissions, each exhibiting distinct behaviors. Except for ammonia slip, adding ammonia fuel does not significantly affect carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions, particularly at AERs below 25 %. Nevertheless, nitrogen oxide (NOx) emissions under AGDF combustion are significantly higher than under gasoline alone in most instances. Crucially, the study demonstrates the carbon reduction potential of ammonia fuel across different engine loads, with a maximum carbon dioxide (CO2) reduction of 46.8 % at a 35 % AER. It is anticipated that further optimization of the combustion phase will improve the capability for carbon reduction.
{"title":"Experimental study of ammonia energy ratio on combustion and emissions from ammonia-gasoline dual-fuel engine at various load conditions","authors":"","doi":"10.1016/j.joei.2024.101868","DOIUrl":"10.1016/j.joei.2024.101868","url":null,"abstract":"<div><div>Achieving carbon neutrality necessitates the adoption of zero-carbon fuels in engine applications, with ammonia emerging as an up-and-coming candidate due to its favorable safety profile and advantages in storage and transportation. This study experimentally investigated the feasibility of an ammonia-gasoline dual-fuel (AGDF) engine to achieve comparable power output and satisfactory carbon reduction without changing the main structural parameters of the engine. A four-cylinder, naturally aspirated, spark ignition engine was used to investigate the impact of ammonia energy ratio (AER), engine base torque and engine speed on the engine performance, combustion evolution and emission characteristics. The findings reveal that the brake thermal efficiency (BTE) in AGDF mode is lower than in gasoline-only mode, primarily due to the reduced combustion activity. However, this efficiency decline becomes noticeable only when the AER exceeds 15 %. Additionally, at high AERs and high engine base torques, the delayed effect of ammonia fuel on the main combustion period results in a double-peak pattern, which limits the energy output but presents opportunities for phase optimization. The study also examined three incomplete combustion emissions, each exhibiting distinct behaviors. Except for ammonia slip, adding ammonia fuel does not significantly affect carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions, particularly at AERs below 25 %. Nevertheless, nitrogen oxide (NOx) emissions under AGDF combustion are significantly higher than under gasoline alone in most instances. Crucially, the study demonstrates the carbon reduction potential of ammonia fuel across different engine loads, with a maximum carbon dioxide (CO<sub>2</sub>) reduction of 46.8 % at a 35 % AER. It is anticipated that further optimization of the combustion phase will improve the capability for carbon reduction.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-29DOI: 10.1016/j.joei.2024.101870
The carbon neutrality strategy presents both challenges and opportunities for the metallurgical industry. Hydrogen, recognized as a green energy source, demonstrates significant potential for application in metallurgy. The negative impact of carbon deposition on catalysts is a significant challenge in the large-scale industrial application of methane dry reforming to produce hydrogen-rich reducing gases for ironmaking. This paper investigates the reaction mechanism through thermodynamic calculations and molecular dynamics simulations, systematically examining the effects of temperature, pressure, and feed ratio on the composition of gas products and the amount of carbon precipitation during the preparation process of hydrogen-rich reduction gas. The optimal conditions to produce high-quality reducing gas are identified to be a CO₂/CH₄ ratio of 0.8 at 1100K and 1 atm. At elevated temperatures, increasing the amount of carbon dioxide can reduce the amount of precipitated carbon, while the opposite is true at lower temperatures. The carbon absorbed by the nickel-based catalyst primarily originates from methane, while hydrogen ions activate carbon dioxide to produce carbon monoxide or carboxyl groups. By elucidating the reaction mechanism and quantifying the carbon precipitation, we provide theoretical guidance for industrial application.
{"title":"Thermodynamic and molecular dynamics study of methane dry reforming","authors":"","doi":"10.1016/j.joei.2024.101870","DOIUrl":"10.1016/j.joei.2024.101870","url":null,"abstract":"<div><div>The carbon neutrality strategy presents both challenges and opportunities for the metallurgical industry. Hydrogen, recognized as a green energy source, demonstrates significant potential for application in metallurgy. The negative impact of carbon deposition on catalysts is a significant challenge in the large-scale industrial application of methane dry reforming to produce hydrogen-rich reducing gases for ironmaking. This paper investigates the reaction mechanism through thermodynamic calculations and molecular dynamics simulations, systematically examining the effects of temperature, pressure, and feed ratio on the composition of gas products and the amount of carbon precipitation during the preparation process of hydrogen-rich reduction gas. The optimal conditions to produce high-quality reducing gas are identified to be a CO₂/CH₄ ratio of 0.8 at 1100K and 1 atm. At elevated temperatures, increasing the amount of carbon dioxide can reduce the amount of precipitated carbon, while the opposite is true at lower temperatures. The carbon absorbed by the nickel-based catalyst primarily originates from methane, while hydrogen ions activate carbon dioxide to produce carbon monoxide or carboxyl groups. By elucidating the reaction mechanism and quantifying the carbon precipitation, we provide theoretical guidance for industrial application.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-29DOI: 10.1016/j.joei.2024.101871
This paper presents a numerical investigation of premixed methane/oxygen heterogeneous reaction characteristics in a micro-catalytic combustion chamber under various boundary and wall thermophysical conditions. A 3-D model was simulated using ANSYS Fluent and validated against experimental data, with a maximum difference of only 1.92 % using a pure heterogeneous reaction. This study aims to analyze the wall boundary conditions and thermophysical factors that influence chemically and thermally during heterogeneous reactions. The results show that, with an increase in inlet velocity from 1 m/s to 10 m/s, the maximum heat produced by the reaction increases 52.67 % and the temperature of the channel as well as the outer wall increases accordingly. Using a 2.5 m/s inlet velocity, we found that the maximum external wall temperature uniformity coefficient was 0.1911. Furthermore, it was observed that as the heterogeneous reaction progresses, Platinum's surface coverage and the H(s) site coverage increase; however, the O(s), OH(s), CO(s), and C(s) site coverage decreases. Additionally, low convective heat transfer and wall thermal conductivity increase the efficiency of heterogeneous reactions and methane conversion. As a result of the low wall thermal conductivity, the outer wall temperature uniformity coefficient was 0.2863, while the methane conversion rate was 79.05 %. According to the results, higher thermal resistance increased the methane conversion rate from 68.18 % to 79.05 %, and the combustion process within the micro-catalytic combustor was uniform and controlled, thus enhancing its efficiency. The results of this study provide useful insights for optimizing micro-combustors, paving the way for future improvements in their design and operational efficiency.
{"title":"Effects of thermophysical properties on heterogeneous reaction dynamics of methane/oxygen mixtures in a micro catalytic combustion chamber","authors":"","doi":"10.1016/j.joei.2024.101871","DOIUrl":"10.1016/j.joei.2024.101871","url":null,"abstract":"<div><div>This paper presents a numerical investigation of premixed methane/oxygen heterogeneous reaction characteristics in a micro-catalytic combustion chamber under various boundary and wall thermophysical conditions. A 3-D model was simulated using ANSYS Fluent and validated against experimental data, with a maximum difference of only 1.92 % using a pure heterogeneous reaction. This study aims to analyze the wall boundary conditions and thermophysical factors that influence chemically and thermally during heterogeneous reactions. The results show that, with an increase in inlet velocity from 1 m/s to 10 m/s, the maximum heat produced by the reaction increases 52.67 % and the temperature of the channel as well as the outer wall increases accordingly. Using a 2.5 m/s inlet velocity, we found that the maximum external wall temperature uniformity coefficient was 0.1911. Furthermore, it was observed that as the heterogeneous reaction progresses, Platinum's surface coverage and the H<sub>(s)</sub> site coverage increase; however, the O<sub>(s)</sub>, OH<sub>(s)</sub>, CO<sub>(s)</sub>, and C<sub>(s)</sub> site coverage decreases. Additionally, low convective heat transfer and wall thermal conductivity increase the efficiency of heterogeneous reactions and methane conversion. As a result of the low wall thermal conductivity, the outer wall temperature uniformity coefficient was 0.2863, while the methane conversion rate was 79.05 %. According to the results, higher thermal resistance increased the methane conversion rate from 68.18 % to 79.05 %, and the combustion process within the micro-catalytic combustor was uniform and controlled, thus enhancing its efficiency. The results of this study provide useful insights for optimizing micro-combustors, paving the way for future improvements in their design and operational efficiency.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-28DOI: 10.1016/j.joei.2024.101867
Ammonia/methanol co-combustion is considered an effective liquid-liquid blending strategy to enhance the combustion performance of ammonia. However, both methanol and ammonia have high latent heats of vaporization, which necessitate significant heat absorption during the vaporization process. This often results in excessively low ambient temperatures before the ignition of the mixture, negatively affecting low-temperature ignition and combustion. To improve the combustion characteristics of ammonia/methanol blends, this study proposes the addition of nitromethane, forming a ternary blend of ammonia/methanol/nitromethane to enhance fuel performance. To evaluate the impact of nitromethane on the combustion mechanism of ammonia/methanol blends, this study utilizes synchronous vacuum ultraviolet photoionization mass spectrometry to analyze the oxidation reactions of the ammonia/methanol/nitromethane blends. Based on the Brequigny model, cross-reactions involving C-N bonds and reactions related to nitromethane were incorporated for model modification, resulting in the newly modified model, termed A-M. Pathway and sensitivity analyses, as well as ignition delay time simulations, were conducted to further understand the combustion process. The results indicate that the addition of nitromethane to the ammonia/methanol blend lowers the initial reaction temperature from 860 K to 740 K and increases nitrogen oxide (NOx) concentrations at 1050 K. At 800 K, nitromethane reduces the conversion of NH2 to NH3, thereby enhancing ammonia consumption and altering the NOx consumption pathway. Furthermore, at 1020 K, 98.6 % of H2NO reacts with H to form NH2, which is a crucial species in ammonia regeneration. Additionally, at 1020 K, 90.8 % of nitromethane decomposes through the reaction CH3NO2(+M) = CH3 + NO2(+M), contributing to increased NOx emissions. Moreover, the incorporation of nitromethane significantly reduces the ignition delay time of ammonia/methanol blends, demonstrating its potential to improve the overall combustion performance of these mixtures.
氨/甲醇共燃被认为是一种有效的液-液混合策略，可提高氨的燃烧性能。然而，甲醇和氨的汽化潜热都很高，因此在汽化过程中必须大量吸热。这通常会导致混合物点火前的环境温度过低，从而对低温点火和燃烧产生不利影响。为改善氨/甲醇混合物的燃烧特性，本研究提出添加硝基甲烷，形成氨/甲醇/硝基甲烷三元混合物，以提高燃料性能。为了评估硝基甲烷对氨/甲醇混合物燃烧机理的影响，本研究利用同步真空紫外光离子化质谱仪分析了氨/甲醇/硝基甲烷混合物的氧化反应。在布雷基尼模型的基础上，加入了涉及 C-N 键的交叉反应和与硝基甲烷有关的反应，对模型进行了修改，从而得到了新修改的模型，称为 A-M。为进一步了解燃烧过程，进行了路径和敏感性分析以及点火延迟时间模拟。结果表明，在氨/甲醇混合物中加入硝基甲烷可将初始反应温度从 860 K 降低到 740 K，并增加 1050 K 时的氮氧化物（NOx）浓度。此外，在 1020 K 时，98.6% 的 H2NO 与 H 反应生成 NH2，而 NH2 是氨再生过程中的关键物种。此外，在 1020 K 时，90.8% 的硝基甲烷通过反应 CH3NO2(+M) = CH3 + NO2(+M) 分解，导致氮氧化物排放量增加。此外，硝基甲烷的加入大大缩短了氨/甲醇混合物的点火延迟时间，证明了其改善这些混合物整体燃烧性能的潜力。
{"title":"Research on the impact of nitromethane on the combustion mechanism of ammonia/methanol blends","authors":"","doi":"10.1016/j.joei.2024.101867","DOIUrl":"10.1016/j.joei.2024.101867","url":null,"abstract":"<div><div>Ammonia/methanol co-combustion is considered an effective liquid-liquid blending strategy to enhance the combustion performance of ammonia. However, both methanol and ammonia have high latent heats of vaporization, which necessitate significant heat absorption during the vaporization process. This often results in excessively low ambient temperatures before the ignition of the mixture, negatively affecting low-temperature ignition and combustion. To improve the combustion characteristics of ammonia/methanol blends, this study proposes the addition of nitromethane, forming a ternary blend of ammonia/methanol/nitromethane to enhance fuel performance. To evaluate the impact of nitromethane on the combustion mechanism of ammonia/methanol blends, this study utilizes synchronous vacuum ultraviolet photoionization mass spectrometry to analyze the oxidation reactions of the ammonia/methanol/nitromethane blends. Based on the Brequigny model, cross-reactions involving C-N bonds and reactions related to nitromethane were incorporated for model modification, resulting in the newly modified model, termed A-M. Pathway and sensitivity analyses, as well as ignition delay time simulations, were conducted to further understand the combustion process. The results indicate that the addition of nitromethane to the ammonia/methanol blend lowers the initial reaction temperature from 860 K to 740 K and increases nitrogen oxide (NO<sub>x</sub>) concentrations at 1050 K. At 800 K, nitromethane reduces the conversion of NH<sub>2</sub> to NH<sub>3</sub>, thereby enhancing ammonia consumption and altering the NO<sub>x</sub> consumption pathway. Furthermore, at 1020 K, 98.6 % of H<sub>2</sub>NO reacts with H to form NH<sub>2</sub>, which is a crucial species in ammonia regeneration. Additionally, at 1020 K, 90.8 % of nitromethane decomposes through the reaction CH<sub>3</sub>NO<sub>2</sub>(+M) = CH<sub>3</sub> + NO<sub>2</sub>(+M), contributing to increased NO<sub>x</sub> emissions. Moreover, the incorporation of nitromethane significantly reduces the ignition delay time of ammonia/methanol blends, demonstrating its potential to improve the overall combustion performance of these mixtures.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-24DOI: 10.1016/j.joei.2024.101859
The yield and higher heating value (HHV) of bio-oil products are significant performance parameters for the hydrothermal conversion of high-water and high-lipid biomass. Machine learning (ML) modeling prediction is a fast and convenient means of obtaining performance parameters. An informative dataset with 243 samples was prepared, and two highly adapted ML algorithms were used: Random Forest (RF) and Extreme Gradient Boosting Tree (XGBoost). It is interesting to note that the developed ML models demonstrated great prediction ability; for example, the regression coefficient () of the XGBoost model for yield and HHV prediction was as high as 0.942 and 0.940, respectively. Furthermore, partial dependence plots (PDP) and SHapley Additive exPlanations (SHAP) interpretability methodologies were adopted to address the main contributions of the feature identification and response behavior analysis of the features. The results demonstrated that the biomass composition had the greatest effect on bio-oil yield, with fat contributing up to 40 %. In contrast, the elemental composition had the most significant effect on the HHV of bio-oil. Notably, hydrogen content affected the HHV of up to 4.5 units. The interaction response behavior showed that the interaction of the process parameters with feedstock properties was most common and significant. The information obtained from the response mechanism can be used to enhance the subsequent hydrothermal fuel preparation process for bio-oils.
{"title":"Hydrothermal bio-oil yield and higher heating value of high moisture and lipid biomass: Machine learning modeling and feature response behavior analysis","authors":"","doi":"10.1016/j.joei.2024.101859","DOIUrl":"10.1016/j.joei.2024.101859","url":null,"abstract":"<div><div>The yield and higher heating value (HHV) of bio-oil products are significant performance parameters for the hydrothermal conversion of high-water and high-lipid biomass. Machine learning (ML) modeling prediction is a fast and convenient means of obtaining performance parameters. An informative dataset with 243 samples was prepared, and two highly adapted ML algorithms were used: Random Forest (RF) and Extreme Gradient Boosting Tree (XGBoost). It is interesting to note that the developed ML models demonstrated great prediction ability; for example, the regression coefficient (<span><math><mrow><msup><mi>R</mi><mn>2</mn></msup></mrow></math></span>) of the XGBoost model for yield and HHV prediction was as high as 0.942 and 0.940, respectively. Furthermore, partial dependence plots (PDP) and SHapley Additive exPlanations (SHAP) interpretability methodologies were adopted to address the main contributions of the feature identification and response behavior analysis of the features. The results demonstrated that the biomass composition had the greatest effect on bio-oil yield, with fat contributing up to 40 %. In contrast, the elemental composition had the most significant effect on the HHV of bio-oil. Notably, hydrogen content affected the HHV of up to 4.5 units. The interaction response behavior showed that the interaction of the process parameters with feedstock properties was most common and significant. The information obtained from the response mechanism can be used to enhance the subsequent hydrothermal fuel preparation process for bio-oils.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-24DOI: 10.1016/j.joei.2024.101864
The application of ammonia (NH3) as a possible future fuel presents a plausible solution for green energy storage. It helps provide a carbon-neutral fuel alternative for industrial power generation and transportation. However, the combustion of NH3 presents a formidable challenge due to its low reactivity, inadequate flame stability, sluggish flame propagation, and high NOx emissions. Consequently, its integration into combustion systems necessitates substantial system and strategy modification to enable its deployment to industrial systems. The current study presents a novel fuel/air injection technique, which emphasizes the high recirculation of hot combustion products and the extended residence time of fuel/air mixtures. A comprehensive experimental and numerical investigation is conducted using a swirl air injection and offset fuel injection to achieve the flameless combustion mode for optimized NH3/H2 fuel blends. A range of mixture conditions (ϕ = 0.5–1.2) and NH3/H2 compositions (50/50–70/30) are experimentally examined. The investigations helped elucidate the effect of residence time and recirculation on NOx emissions through kinetic simulations using a reactor network model. Subsequently, 3-D numerical simulations helped identify regions of high recirculation, quantified through reactant dilution ratios and uniform temperature distribution. These aspects are determined using a new parameter, the temperature uniformity index along the axial direction of the combustor. The emissions of NOx, unburnt NH3, and unburnt H2 are quantified for different equivalence ratios and NH3 mole fractions in the fuel mixture. The investigations reveal that NOx emissions reached their minimum (450–654 ppm) and (344-211 ppm), when the burner operated at lean (ϕ = 0.5–0.8) and rich (ϕ = 1.0–1.2) conditions, respectively, for 70/30 NH3/H2 blend. The emissions of unburnt NH3 and H2 species remain minimal for lean conditions. Both lean and rich operational regimes demonstrated similar or superior emission characteristics in flameless combustion mode when compared to the conventional combustion mode.
{"title":"A new low NOx emission technique for NH3/H2 blends in a flameless combustor through offset injection","authors":"","doi":"10.1016/j.joei.2024.101864","DOIUrl":"10.1016/j.joei.2024.101864","url":null,"abstract":"<div><div>The application of ammonia (NH<sub>3</sub>) as a possible future fuel presents a plausible solution for green energy storage. It helps provide a carbon-neutral fuel alternative for industrial power generation and transportation. However, the combustion of NH<sub>3</sub> presents a formidable challenge due to its low reactivity, inadequate flame stability, sluggish flame propagation, and high NO<sub>x</sub> emissions. Consequently, its integration into combustion systems necessitates substantial system and strategy modification to enable its deployment to industrial systems. The current study presents a novel fuel/air injection technique, which emphasizes the high recirculation of hot combustion products and the extended residence time of fuel/air mixtures. A comprehensive experimental and numerical investigation is conducted using a swirl air injection and offset fuel injection to achieve the flameless combustion mode for optimized NH<sub>3</sub>/H<sub>2</sub> fuel blends. A range of mixture conditions (ϕ = 0.5–1.2) and NH<sub>3</sub>/H<sub>2</sub> compositions (50/50–70/30) are experimentally examined. The investigations helped elucidate the effect of residence time and recirculation on NO<sub>x</sub> emissions through kinetic simulations using a reactor network model. Subsequently, 3-D numerical simulations helped identify regions of high recirculation, quantified through reactant dilution ratios and uniform temperature distribution. These aspects are determined using a new parameter, the temperature uniformity index along the axial direction of the combustor. The emissions of NO<sub>x</sub>, unburnt NH<sub>3</sub>, and unburnt H<sub>2</sub> are quantified for different equivalence ratios and NH<sub>3</sub> mole fractions in the fuel mixture. The investigations reveal that NO<sub>x</sub> emissions reached their minimum (450–654 ppm) and (344-211 ppm), when the burner operated at lean (ϕ = 0.5–0.8) and rich (ϕ = 1.0–1.2) conditions, respectively, for 70/30 NH<sub>3</sub>/H<sub>2</sub> blend. The emissions of unburnt NH<sub>3</sub> and H<sub>2</sub> species remain minimal for lean conditions. Both lean and rich operational regimes demonstrated similar or superior emission characteristics in flameless combustion mode when compared to the conventional combustion mode.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-18DOI: 10.1016/j.joei.2024.101858
The desorption kinetic parameters for pressurized combustion and gasification reactions were determined based on a C++ program coupled with the Langmuir-Hinshelwood (L-H) kinetic model developed and experimental data from pressurized char combustion, and the established L-H kinetic model for pressurized char-O2/H2O combustion was refined in the current paper. The activation energy for desorption in reactions involving pressurized char-O2 and char-H2O was determined to be 250.8 kJ/mol, accompanied by a pre-exponential factor of 5.42 × 1010 g/(m2 s). Using this foundation, the current research conducted simulations to investigate the impacts of temperature, pressure, and H2O concentration on the oxidation adsorption rate (Rads,oxi), desorption rate (Rdes), gasification adsorption rate (Rads,gas), and the competitive influences of kinetics and diffusion processes within the pressurized char-O2/H2O combustion. The simulation results indicate a gradual increase in Rdes and Rads,gas with char conversion to reach a peak, followed by a gradual decline. Conversely, the Rads,oxi varies smoothly throughout the char conversion process. At 1673 K/1.0 MPa, the char-O2/H2O reaction rate is primarily constrained by Rads,oxi and Rads,gas, with the adsorption reaction serving as the rate-controlling step. Moreover, it was noted that a rise in pressure resulted in a linear increase in Rads,oxi, Rdes, and Rads,gas. At elevated temperatures, the impact of pressure on them becomes more noticeable. However, the introduction of H2O mitigates this effect. Elevated temperature and pressure facilitate the competition on the kinetics of char-O2 combustion for O2 diffusion, resulting in the conversion of char being more susceptible to O2 diffusion rate limitation. With the addition of 20 % H2O, the competition effect was weakened. In the case of pressurized combustion involving char and O2/H2O, the char conversion is primarily constrained by the O2 diffusion rate and is scarcely influenced by the H2O diffusion rate.
{"title":"Experimental and modeling studies on char combustion under pressurized O2/H2O conditions","authors":"","doi":"10.1016/j.joei.2024.101858","DOIUrl":"10.1016/j.joei.2024.101858","url":null,"abstract":"<div><div>The desorption kinetic parameters for pressurized combustion and gasification reactions were determined based on a C++ program coupled with the Langmuir-Hinshelwood (L-H) kinetic model developed and experimental data from pressurized char combustion, and the established L-H kinetic model for pressurized char-O<sub>2</sub>/H<sub>2</sub>O combustion was refined in the current paper. The activation energy for desorption in reactions involving pressurized char-O<sub>2</sub> and char-H<sub>2</sub>O was determined to be 250.8 kJ/mol, accompanied by a pre-exponential factor of 5.42 × 10<sup>10</sup> g/(m<sup>2</sup> s). Using this foundation, the current research conducted simulations to investigate the impacts of temperature, pressure, and H<sub>2</sub>O concentration on the oxidation adsorption rate (<em>R</em><sub>ads,oxi</sub>), desorption rate (<em>R</em><sub>des</sub>), gasification adsorption rate (<em>R</em><sub>ads,gas</sub>), and the competitive influences of kinetics and diffusion processes within the pressurized char-O<sub>2</sub>/H<sub>2</sub>O combustion. The simulation results indicate a gradual increase in <em>R</em><sub>des</sub> and <em>R</em><sub>ads,gas</sub> with char conversion to reach a peak, followed by a gradual decline. Conversely, the <em>R</em><sub>ads,oxi</sub> varies smoothly throughout the char conversion process. At 1673 K/1.0 MPa, the char-O<sub>2</sub>/H<sub>2</sub>O reaction rate is primarily constrained by <em>R</em><sub>ads,oxi</sub> and <em>R</em><sub>ads,gas</sub>, with the adsorption reaction serving as the rate-controlling step. Moreover, it was noted that a rise in pressure resulted in a linear increase in <em>R</em><sub>ads,oxi</sub>, <em>R</em><sub>des</sub>, and <em>R</em><sub>ads,gas</sub>. At elevated temperatures, the impact of pressure on them becomes more noticeable. However, the introduction of H<sub>2</sub>O mitigates this effect. Elevated temperature and pressure facilitate the competition on the kinetics of char-O<sub>2</sub> combustion for O<sub>2</sub> diffusion, resulting in the conversion of char being more susceptible to O<sub>2</sub> diffusion rate limitation. With the addition of 20 % H<sub>2</sub>O, the competition effect was weakened. In the case of pressurized combustion involving char and O<sub>2</sub>/H<sub>2</sub>O, the char conversion is primarily constrained by the O<sub>2</sub> diffusion rate and is scarcely influenced by the H<sub>2</sub>O diffusion rate.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-18DOI: 10.1016/j.joei.2024.101857
For the purpose of achieving global CO2 reduction, decarbonization at the source of fuels is a practical approach. The transition phase of blending fossil fuels with carbon-free fuels for combustion is a hot topic in the current carbon emission reduction process. In order to achieve efficient and low-pollution combustion of NH3/CH4, the combustion and emission characteristics of NH3/CH4 under single-stage and air-staged combustion methods were numerically investigated in this work. The emissions were compared for different equivalence ratios and different ammonia content conditions. Rate of production (ROP) and sensitivity analysis were performed for NOx, and the reaction path of NH3/CH4 was analyzed. The results indicate that the C-N interaction of the NH3/CH4 mixed combustion process is not significant and turns weaker in the lean flames. HNO intermediate is an important specie for NO generation, and HCN together with HCO intermediate, are essential species for CO generation. NH2 and NH almost dominate the promotion and inhibition of NO generation. Given the contrasting NOx and CO emission behavior of NH3/CH4 in rich and lean flames, the single-stage combustion approach is not suitable. Air-staged combustion achieves both, ensuring the complete burning of NH3 and CH4 while reducing NOx and CO emissions. Moreover, the results suggest that Φpri = 1.2/Φtotal = 0.6 is the optimal NH3/CH4 combustion staging method for controlling NOx emissions.
为了实现全球二氧化碳减排目标，从燃料源头进行脱碳是一种切实可行的方法。化石燃料与无碳燃料混合燃烧的过渡阶段是当前碳减排过程中的热点话题。为了实现 NH3/CH4 的高效低污染燃烧，本研究对 NH3/CH4 在单级燃烧和空气分级燃烧方式下的燃烧和排放特性进行了数值研究。比较了不同当量比和不同氨含量条件下的排放情况。对氮氧化物的生成率（ROP）和敏感性进行了分析，并分析了 NH3/CH4 的反应路径。结果表明，NH3/CH4 混合燃烧过程中的 C-N 相互作用并不明显，而且在贫焰中会变弱。HNO 中间体是生成 NO 的重要物质，HCN 和 HCO 中间体是生成 CO 的重要物质。NH2 和 NH 几乎主导了 NO 生成的促进和抑制作用。鉴于 NH3/CH4 在富焰和贫焰中的氮氧化物和一氧化碳排放行为截然不同，单级燃烧方法并不合适。空气分级燃烧可同时实现这两个目标，既能确保 NH3 和 CH4 的完全燃烧，又能减少 NOx 和 CO 的排放。此外，研究结果表明，Φpri = 1.2/Φtotal = 0.6 是控制氮氧化物排放的最佳 NH3/CH4 分级燃烧方法。
{"title":"Numerical investigation of NOx emission characteristics in air-staged combustion system fueled by premixed ammonia/methane","authors":"","doi":"10.1016/j.joei.2024.101857","DOIUrl":"10.1016/j.joei.2024.101857","url":null,"abstract":"<div><div>For the purpose of achieving global CO<sub>2</sub> reduction, decarbonization at the source of fuels is a practical approach. The transition phase of blending fossil fuels with carbon-free fuels for combustion is a hot topic in the current carbon emission reduction process. In order to achieve efficient and low-pollution combustion of NH<sub>3</sub>/CH<sub>4</sub>, the combustion and emission characteristics of NH<sub>3</sub>/CH<sub>4</sub> under single-stage and air-staged combustion methods were numerically investigated in this work. The emissions were compared for different equivalence ratios and different ammonia content conditions. Rate of production (ROP) and sensitivity analysis were performed for NO<sub>x</sub>, and the reaction path of NH<sub>3</sub>/CH<sub>4</sub> was analyzed. The results indicate that the C-N interaction of the NH<sub>3</sub>/CH<sub>4</sub> mixed combustion process is not significant and turns weaker in the lean flames. HNO intermediate is an important specie for NO generation, and HCN together with HCO intermediate, are essential species for CO generation. NH<sub>2</sub> and NH almost dominate the promotion and inhibition of NO generation. Given the contrasting NO<sub>x</sub> and CO emission behavior of NH<sub>3</sub>/CH<sub>4</sub> in rich and lean flames, the single-stage combustion approach is not suitable. Air-staged combustion achieves both, ensuring the complete burning of NH<sub>3</sub> and CH<sub>4</sub> while reducing NO<sub>x</sub> and CO emissions. Moreover, the results suggest that <em>Φ</em><sub>pri</sub> = 1.2/<em>Φ</em><sub>total</sub> = 0.6 is the optimal NH<sub>3</sub>/CH<sub>4</sub> combustion staging method for controlling NO<sub>x</sub> emissions.</div></div>","PeriodicalId":17287,"journal":{"name":"Journal of The Energy Institute","volume":null,"pages":null},"PeriodicalIF":5.6,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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