Amount Of CH4 Research Articles

A rationale for higher ratios of CH4 to CO2 production in warmer anoxic freshwater sediments and soils

A rationale for higher ratios of <scp>CH₄</scp> to <scp>CO₂</scp> production in warmer anoxic freshwater sediments and soils

Revealing acetylene separation performances of anion-pillared MOFs by combining molecular simulations and machine learning

Acetylene is a crucial chemical feedstock that can be efficiently purified from CH4 and CO2 through adsorption-based separation methods. Combining advantages of organic and inorganic chemistry, metal–organic frameworks (MOFs) provide high separation performances in adsorption processes. In this work, anion-pillared (AP) MOFs were computationally investigated for C2H2/CH4 and C2H2/CO2 separations using Grand Canonical Monte Carlo (GCMC) simulations. Results of molecular simulations were used to compute selectivity, working capacity and regenerability, which were then combined to identify the top adsorbents and their structural features for C2H2/CH4 and C2H2/CO2 separations. The best adsorbents were computed to have C2H2 selectivities, working capacities, regenerabilities of 25.5–30.6 (6.1–7.3), 5.6–6 (4.9–5.8) mol/kg, 81.3–83 % (81.2–85.5 %) for C2H2/CH4 (C2H2/CO2) separation, respectively. We then developed machine learning (ML) models to accurately predict C2H2, CH4, and CO2 adsorption amounts in AP-MOFs for equimolar C2H2/CH4 and C2H2/CO2 mixtures by using pore-limiting diameter, surface area, isosteric heat of adsorption as the input features. ML-predicted gas adsorption amounts, separation performance metrics and adsorbent rankings were found to be in good agreement with those directly obtained from GCMC simulations. Therefore, ML models that we developed can be used to accurately and quickly screen large number of AP-MOFs and related materials to identify the top performing materials for C2H2/CH4 and C2H2/CO2 separations.

Effect of Residual Water in Sediments on the CO2-CH4 Replacement Process

CO2 replacement is a promising method of gas hydrate recovery. However, the influence of residual water in the replacement process and selections of a suitable mining area remain uncertain. To better understand this method, we examined the influence of the particle size and initial hydrate saturation on the replacement process while using the same amount of residual free water. The results showed that during the replacement process, two stages of rapid reaction and slow reaction occurred, which were manifested by the speed of pressure change in the reactor. The CO2 sequestration ratio decreased with the increase in sediment particle size and increased with the increase in initial hydrate saturation. During the replacement process, two reactions occurred: CH4 was replaced by CO2 and CO2 hydrate was formed, and the replacement amount and recovery efficiency of CH4 increased with a decrease in sediment particle size. When the sediment particle size was less than 166 μm, the CH4 recovery efficiency was significantly affected by the particle size. The replacement amount of CH4 increased with the increase in initial hydrate saturation, and the recovery efficiency decreased. This study provides a basis for selecting suitable hydrate-accumulation areas for on-site mining.

The influence of diesel contaminated soil on Miscanthus x giganteus biomass thermal utilization and pyrolysis products composition

The second-generation energy crop Miscanthus x giganteus (Mxg) demonstrated ability to produce adequate biomass yield even in marginal or contaminated soils. This renewable biomass can be utilized energetically or transformed into various biobased products and thus contribute to decrease of primary resources and fossil fuel use. To evaluate potential effects on energetic biomass properties Mxg was grown in diesel contaminated soils. Traces of total petroleum hydrocarbons were found solely in the leaves, however most likely resulting from air contamination. No differences were detected in the elemental composition of the raw biomass. Biomass combustion heat value reached average of 17.23 ± 0.21 MJ kg−1; contamination-originated leaves had slightly but significantly decreased heat values (14.41 ± 1.10 MJ kg−1) while heat of other parts was comparable to control. Thermogravimetric curves, simulating thermic utilization processes, were comparable both under oxygen (combustion) and nitrogen (pyrolysis). No diesel impacts were observed on the pyrolysis products yield. Higher amounts of CH4, C2H6, C3H4, C3H6 and C3H8 were detected in the pyrolysis gas from aboveground biomass from contaminated soil. Diesel contamination decreased significantly biochar surface. Concentrations of acids and esters in biooil were increased on the expense of concentrations of furans in the case of samples from contaminated soils. No significant effect on phenols and ketones concentrations in the biooil was observed. The amount of acetic acid, as the main biooil component, increased in the above- and below-ground plant parts along with the higher diesel concentrations in soil. Despite slight changes detected, the parameters of the biomass produced in diesel-contaminated soils present no obstacle to its energetic utilization and Mxg can be recommended for productive phytomanagement of such soils.

Estimation of Greenhouse Gas Emission and Global Warming Potential of Livestock Sector; Lake District, Türkiye

The calling on livestock is increasing fast because of the population and economic broadening. In recent years, the contribution of the livestock sector to greenhouse gas emissions and climate change has been a concern. This sector accounts for the second largest share of anthropogenic greenhouse gas emissions after the energy sector. The storage of animal manure is very important in this respect. Because gases such as nitrous oxide and methane, which are important greenhouse gases, are formed during storage. Therefore, it is very important to focus on this area to make manure management systems sustainable. In this study, greenhouse gas emissions that may occur in the provinces located in the region called Turkey's Lakes Region were estimated using the data on the number of different species of animals published in 2016-2020. Evolution by years has been evaluated on a provincial basis. The global warming potential created by greenhouse gas emissions has been determined. As an animal species in the study; dairy and beef cattle, buffalo, sheep, goat, donkey-mule, meat and laying chicken, turkey, duck, and goose were used. 1567000 tons of CH4 emission has occurred due to the total enteric fermentation of animal origin. The amount of CH4 calculated based on manure management is 22450 tons. The CO2 equivalent amount of CH4 emission due to manure management and enteric fermentation was calculated as 33380500 tons. The total amount of direct and indirect N2O emissions from manure management in 2016-2020 is 12566.10 tons. CO2 emission originating from N2O emission was obtained as 555743.46 tons.

Rigorous simulation of geothermal power plants to evaluate environmental performance of alternative configurations

Different studies highlighted the environmental impacts of geothermal power plants (GPPs), especially in the operational phase. Primary data are essential for reliable environmental assessments, but these are not available when considering alternative configurations. Rigorous simulation can offer such a degree of information, representing also a tool for a digital twin technology transition. Considering a GPP in Tuscany, Italy, four alternatives configurations are simulated in UniSim Design®, performing accurate refinements to the thermodynamic model to properly estimate the behavior of different pollutants (Hg, H2S, NH3, and SO2) among the various unit operations. The configurations alternate direct-contact and surface condensers as well as wet and dry towers as cooling systems, while a fifth one adopts an organic Rankine cycle. The actual plant model has been reconciliated with data collected during two different monitoring campaigns. Performance analysis shows a trade-off: the lowest pollutant emissions are obtained using the dry tower generating less net energy (20.17 MWe and 20.83 MWe), instead, adopting surface condenser and wet tower, 22.26 MWe are produced with NH3 emissions almost 3 times the measured ones. The CO2 and CH4 amount in the well fluid is not abated in any configurations and therefore their emissions are the same among them.

Eddy Covariance Data Reveal That a Small Freshwater Reservoir Emits a Substantial Amount of Carbon Dioxide and Methane

AbstractSmall freshwater reservoirs are ubiquitous and likely play an important role in global greenhouse gas (GHG) budgets relative to their limited water surface area. However, constraining annual GHG fluxes in small freshwater reservoirs is challenging given their footprint area and spatially and temporally variable emissions. To quantify the GHG budget of a small (0.1 km2) reservoir, we deployed an Eddy covariance (EC) system in a small reservoir located in southwestern Virginia, USA over 2 years to measure carbon dioxide (CO2) and methane (CH4) fluxes near‐continuously. Fluxes were coupled with in situ sensors measuring multiple environmental parameters. Over both years, we found the reservoir to be a large source of CO2 (633–731 g CO2‐C m−2 yr−1) and CH4 (1.02–1.29 g CH4‐C m−2 yr−1) to the atmosphere, with substantial sub‐daily, daily, weekly, and seasonal timescales of variability. For example, fluxes were substantially greater during the summer thermally stratified season as compared to the winter. In addition, we observed significantly greater GHG fluxes during winter intermittent ice‐on conditions as compared to continuous ice‐on conditions, suggesting GHG emissions from lakes and reservoirs may increase with predicted decreases in winter ice‐cover. Finally, we identified several key environmental variables that may be driving reservoir GHG fluxes at multiple timescales, including, surface water temperature and thermocline depth followed by fluorescent dissolved organic matter. Overall, our novel year‐round EC data from a small reservoir indicate that these freshwater ecosystems likely contribute a substantial amount of CO2 and CH4 to global GHG budgets, relative to their surface area.

Conversion of surface CH4 concentrations from GOSAT satellite observations using XGBoost algorithm

Methane (CH4), the second most significant greenhouse gas after carbon dioxide, contributes significantly to global warming. Owing to its wide monitoring range and long observation time, satellite remote sensing has emerged as a popular method for monitoring CH4. Although the existing algorithm for satellite retrievals of CH4 column amount is mature, it has some drawbacks: the retrieval calculation process is complicated, and there is still a discrepancy between the satellite-retried column amount of CH4 and surface CH4 concentrations. To obtain more accurate near-surface CH4 concentrations from satellite observations, this paper proposed a conversion method based on the Extreme Gradient Boosting (XGBoost) algorithm, taking column amount retrieved by the Greenhouse Gas Observation SATellite (GOSAT) satellite, meteorological factors and near-surface methane concentrations as predictor variables. Using this method, we analyzed the importance of the characteristic factors and predicted methane concentrations at four ground monitoring sites in World Center for Greenhouse Gases (WDCGG), and reached the following conclusions: (1) The model performed well on the test set, with a sample-based cross-validation coefficient of determination (R2) of 0.79, a root mean square error (RMSE) of 0.0251 ppm and a mean absolute percentage error (MAPE) of 0.88%. (2) Of the five meteorological input features, surface net solar radiation had a greater impact on the construction of the model than the other four. (3) The CH4 monthly average concentrations predicted by this model are generally consistent with the trend of the CH4 concentrations of ground monitoring stations.

Decomposition of Benzene during Impacts in N2-dominated Atmospheres

Benzene is a simple neutral aromatic compound found in molecular clouds, comets, and planetary atmospheres. It has been confirmed on Jupiter, Saturn, Titan, and is expected on exoplanets. In this paper, the decomposition of benzene in a simulated asteroid or comet impact into an N2-dominated atmosphere was investigated. The impact plasma was simulated with laser-induced dielectric breakdown and the gas phase decomposition products were observed using high-resolution Fourier transform infrared spectroscopy. The gas phase decomposition products involve mainly HCN, C2H2, and smaller amounts of CH4 with yields of 3.1%–24.0%, 0–11.7%, and 0.5%–3.3%, respectively. Furthermore, in presence of water, benzene also produces CO and CO2 with yields of 2.4%–35.1% and 0.01%–4.8%, respectively. The oxidation state of the product mixture is proportional to the water content. Apart from that, a black-brownish solid phase is formed during the experiments, which makes up about 60% of the original carbon content. Our results therefore show that in anoxic N2-dominated planetary atmospheres, impacts might lead to the depletion of benzene and the formation of HCN, C2H2, and CH4 and, in the presence of water, to the formation of CO and CO2.

Improvement of Municipal Solid Waste Syngas Premixed Flame with Cellular Structure on a Flat Burner

This research was conducted to study the flame instability of syngas derived from raw municipal solid waste (MSW) and its potential as a natural gas (NG) replacement in power generation. MSW syngas is a mixture of various components such as methane (CH4), nitrogen (N2), oxygen (O2), and hydrogen (H2), whereas NG is mainly composed of CH4 (&gt;70%) and CO2 (&gt;10%). The flame characteristics of these two gases are quite different thus a direct replacement of NG with MSW syngas is impossible. Improvements to MSW syngas combustion are needed through the augmentation of the gas with CH4 and H2 active additives at various ratios so that its flame characteristics are comparable to those of NG. A typical MSW syngas composed of 16.2% methane (CH4), 13.5% hydrogen (H2), 69.1% nitrogen (N2), and 0.6% oxygen (O2) (by vol.) is available in Thailand with great potential for use as an NG replacement. In this study, this gas is used as a representative fuel for improvement and is referred to as simulated Syngas 1. Its premixed flame was studied using a McKenna flat burner to understand its flame instability. Various percentages of CH4 and H2 were added to Syngas 1. Its flame characteristics were measured and compared to those of NG. These characteristics included the cellular flame, cell size, flat flame, flammability limit, and flame temperature. The results showed that the flame instability of Syngas 1 was significantly suppressed by adding minimal amounts of CH4 and H2. The new composition of Syngas 1 consisted of 19.3% methane (CH4), 19.0% hydrogen (H2), 61.2% nitrogen (N2), and 0.5% oxygen (O2) (by vol.). It yielded flame characteristics that were comparable to those of an NG flame. This study shows that MSW syngas can potentially replace NG in power generation.

High Efficient CO2 Separation at High Pressure by Grain-Boundary-Controlled CHA Zeolite Membrane Investigated by Non-Equilibrium Molecular Dynamics

The CO2 permeability and selectivity of CHA-type zeolite membranes in the separation of a CO2/CH4 mixture gas at high pressure were evaluated using non-equilibrium molecular dynamics (NEMD). It was found that in a perfectly crystalline, defect-free CHA membrane, the adsorption of CH4, which diffuses slowly in the pores, hinders CO2 permeation. Therefore, an increase in the amount of CH4 adsorbed at high pressure decreases the CO2 permeability and significantly reduces the CO2 selectivity of the CHA membrane. CHA membranes with grain boundaries parallel to the permeation direction were found to show higher CO2 selectivity than perfectly crystalline CHA membranes at high pressure, as the blocking effect of CH4 on CO2 permeation occurring within the grain boundary is not significant. This paper is the first to show that the CO2 permeability of CHA membranes with controlled grain boundaries can exceed the intrinsic performance of fully crystalline zeolite membranes at high pressure.

Important Role of Biogas and Secretions in the Formation of Biological Fluid Sediment under Cyanobacterial Bloom Biomass Degradation

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then accumulate on sediments, leading to the formation of biological fluid sediment. In this study, the formation process of biological fluid sediment was investigated in microcosm experiments by monitoring the variations in gas, sediment physicochemical properties, and microorganisms during 30 days. It was found that variations in sediment height reached the maximum value on day 8 (0.53 cm) with the minimum sediment density (1.04 g cm–3). Meanwhile, the amount of carbon dioxide (CO2) produced through fermentation was larger than methane (CH4) during the initial 4 days. Then, the amount of CH4 drastically increased, resulting in the release of gas from sediments. In addition, a high amount of extracellular polymer substances (EPSs) was produced and led to sediment particle agglomeration, which benefited in maintaining the structure of biological fluid sediment. Through the microbial community analysis, it was found that the strong symbiotic structure of the microbial community in the early stage provided favorable conditions for the formation of CH4 in sediments. The results of this study can clarify the formation mechanism of biological fluid sediment and provide help for understanding the effect of biogas and secretions on the sediment properties in shallow lakes.

Performance of Particulate and Structured Pt/TiO2-Based Catalysts for the WGS Reaction under Realistic High- and Low-Temperature Shift Conditions

The water–gas shift (WGS) activity of Pt/TiO2-based powdered and structured catalysts was investigated using realistic feed compositions that are relevant to the high-temperature shift (HTS) and low-temperature shift (LTS) reaction conditions. The promotion of the TiO2 support with small amounts of alkali- or alkaline earth-metals resulted in the enhancement of the WGS activity of 0.5%Pt/TiO2(X) catalysts (X = Na, Cs, Ca, Sr). The use of bimetallic (Pt–M)/TiO2 catalysts (M = Ru, Cr, Fe, Cu) can also shift the CO conversion curve toward lower temperatures, but this is accompanied by the production of relatively large amounts of unwanted CH4 at temperatures above ca. 300 °C. Among the powdered catalysts investigated, Pt/TiO2(Ca) exhibited the best performance under both HTS and LTS conditions. Therefore, this material was selected for the preparation of structured catalysts in the form of pellets as well as ceramic and metallic catalyst monoliths. The 0.5%Pt/TiO2(Ca) pellet catalyst exhibited comparable activity with that of a commercial WGS pellet catalyst, and its performance was further improved when the Pt loading was increased to 1.0 wt.%. Among the structured catalysts investigated, the best results were obtained for the sample coated on the metallic monolith, which exhibited excellent WGS performance in the 300–350 °C temperature range. In conclusion, proper selection of the catalyst structure and reaction parameters can shift the CO conversion curves toward sufficiently low temperatures, rendering the Pt/TiO2(Ca) catalyst suitable for practical applications.

Thermodynamic analysis of the difference in adsorption characteristics of CH4 and CO2 on continental shale

In order to explain the difference in adsorption characteristics of CH4 and CO2 on continental shale from the perspective of thermodynamics, the isothermal adsorption experiments of CH4 and CO2 adsorbed by shale in Yanchang Formation in Ordos Basin were carried out, and the excess adsorption capacity was corrected to absolute adsorption capacity. Then the Clausius-Clapeyron equation was used to analyze the isosteric heat of adsorption of CH4 and CO2 on shale. The results show that, for calculating the absolute adsorption capacity, Ozawa empirical formula or Van der Waals approximation method should be used to calculate the adsorption phase density. The absolute adsorption capacity should be selected as the basic data for calculating the isosteric heat of adsorption. The reason is that the excess isosteric heat of adsorption has a negative value in the low adsorption capacity stage, which is contradictory to the fact that the adsorption process is exothermic, and is significantly higher than the absolute isosteric heat of adsorption. There is a good linear positive correlation between the isosteric heat of adsorption and the adsorption amount of CH4 and CO2 adsorbed by continental shale, and the isosteric heat of adsorption of CH4 is greater than that of CO2. The absolute initial isosteric heat of adsorption of CH4 and CO2 adsorbed by shale is 52.04 kJ/mol and 27.71 kJ/mol, indicating that the adsorption force of CH4 on Yanchang Formation shale is stronger than that of CO2.

Recent advances in constructed wetlands methane reduction: Mechanisms and methods.

Constructed wetlands (CWs) are artificial systems that use natural processes to treat wastewater containing organic pollutants. This approach has been widely applied in both developing and developed countries worldwide, providing a cost-effective method for industrial wastewater treatment and the improvement of environmental water quality. However, due to the large organic carbon inputs, CWs is produced in varying amounts of CH4 and have the potential to become an important contributor to global climate change. Subsequently, research on the mitigation of CH4 emissions by CWs is key to achieving sustainable, low-carbon dependency wastewater treatment systems. This review evaluates the current research on CH4 emissions from CWs through bibliometric analysis, summarizing the reported mechanisms of CH4 generation, transfer and oxidation in CWs. Furthermore, the important environmental factors driving CH4 generation in CW systems are summarized, including: temperature, water table position, oxidation reduction potential, and the effects of CW characteristics such as wetland type, plant species composition, substrate type, CW-coupled microbial fuel cell, oxygen supply, available carbon source, and salinity. This review provides guidance and novel perspectives for sustainable and effective CW management, as well as for future studies on CH4 reduction in CWs.

Energy and Exergy Analysis of Palm Tree Pruning Residues Gasification

Gasification is the process of obtaining syngas containing combustible gases such as H2, CO and small amounts of CH4 from biomass by performing partial combustion with a limited oxygen supply or with the help of suitable oxidants such as CO2 and water vapor. The efficiency of the gasification process is the most important parameter that determines the success of the system. In this study, the performance of the system in the gasification of palm pruning residues was evaluated by energy and exergy analysis methods. The gasification process was carried out at 7.6 Nm3/h and 10.2 Nm3/h air flow rates in the laboratory type fixed bed downdraft gasification unit manufactured in the Biosystems Engineering Department. The lower heating value of the syngas obtained as a result of gasification was found to be 4.09 MJ/Nm3 at 7.6 Nm3/h air flow rate and 3.76 MJ/Nm3 at 10.2 Nm3/h air flow rate. It has been observed that the lower heating value of the syngas is lower at high air flow rate. Energy efficiencies of the gasification system at 7.6 and 10.2 Nm3/h air flow rate were calculated as 47.6% and 52.8%, and exergy efficiencies were calculated as 43.7% and 48.1%, respectively. Exergy efficiencies were found to be lower than energy efficiencies in both air flow rates. However, as the air flow rate increased, the energy and exergy efficiencies also increased. The results obtained are similar to the results of previous studies on gasification of biomass.

Thermodynamic Equilibrium Study of Anaerobic Digestion through Helmholtz Equation of State

The growing attention regarding a more sustainable future, and thus into energy recovery and waste reduction technologies, has intensified the interest towards processes which allow to exploit waste and biomasses to generate energy, such as the anaerobic digestion. Improving the efficiency of this industrial application is crucial to increase methane production, and is essential from the economic, environmental and safety point of view. This study focuses on the thermodynamic modelling of a steady-state reactor as a flash unit, in order to determine the best operating conditions to produce the maximum amount of pure bio-methane. To this purpose, a new hybrid approach based on the Peng–Robinson cubic equation of state and on the Multi-Parameter Helmholtz-Energy EoS has been proposed. The simulations, performed using the developed algorithm at temperatures between 20 and 55 °C and at pressure values between 0.3 atm and 1.5 atm, point out that the fugacity of the mixture evaluated with the proposed technique is much more accurate and reliable than the one calculated with the PR EoS. In addition, this research has shown not only that the purity and the production of the biogas can be optimised by working at mesophilic conditions and at pressure between 1 atm and 1.5 atm, but also that it is not convenient to operate in a temperature range of 42 °C–45 °C, since about 20 % more H2S goes into the exiting biogas, reducing the CH4 amount and raising the post-treatment costs. Lastly, it has been seen that there is a significant water content in the vapour phase (∼5 %wt.), and this is a factor to be taken into account in order to improve the process.

Molecular Simulation of Methane Adsorption Properties of Coal Samples with Different Coal Rank Superposition States.

Obvious differences exist in the structures of different coal rank coals, resulting in many differences and similarities in the amount of methane (CH4) gas adsorbed by coal and the control mechanism. In this study, we conducted adsorption simulations of three different coal rank coals in the superposition state using the Materials Studio software with simulated temperatures of 293.15, 313.15, and 333.15 K and adsorption pressures ranging from 0 to 10 MPa. We used the grand canonical ensemble Monte Carlo calculation method to calculate and study the adsorption amount, adsorption process, isosteric heat, and diffusion coefficient of CH4 in detail. We found that the adsorption of CH4 by coal samples of three coal rank coals (i.e., anthracite, bituminous coal, and lignite), which were mixed and stacked separately, was concentrated in the effective pores of coal molecules. Their effect on the amount of CH4 adsorption was dominated by the coal samples with more effective pores in the coal molecules. The isosteric heat of the coal samples showed an obvious exponential relationship with the adsorption pressure, and the isosteric heat of coal samples as a nonhomogeneous adsorbent gradually decreased with an increase in adsorption pressure. During the transformation of free-state CH4 into an adsorbed state, we obtained the best adsorption effect for bituminous-lignite superposition-state coal samples, and the diffusion coefficient of CH4 was the lowest.

Synthesis Gas Production with Gasification Technology from Municipal Solid Waste

This study aims to develop, test performance, and evaluate the environmental pollution of garbage fuel with gasification technology. Heat conduction from municipal solid waste (MSW) burning from the gasification process was studied to dispose of solid waste and produce energy for communities. There were four types of solid waste in the total amount of 5 kg (including 0.5 kg of charcoal and firewood, 1.5 kg of paper, 2.0 kg of leaf litter, 0.5 kg of plastic, and 0.5 kg of others) with 2 tested ranges of average humidity: 10–20% and 50–55%. It was found that all waste could be converted for gas production with different gas amounts. From the experiment, dried MSW with 10–15% moisture content produced synthesis gas compositions (mole percent) that were H2, CO2, N2, O2, and CH4 at 1.9–2.4, 1.8–3.2, 56.5–60.2, 3.4–4.6, and 1.2–1.6, respectively. When fuel gas composition at the equivalent ratio between 0.2–0.34 was obtained from the MSW burning test with 10–15% average humidity, MSW burning in various equivalent ratios resulted in different amounts of synthesis gas. In addition, the optimal amounts of CH4 and the heating value of the gas were in the equivalent ratio of 0.28, and the highest production efficiency of synthetic gas (ηg) was 33.46%.

Aerothermodynamic analysis of Neptune ballistic entry and aerocapture flows

An aerothermodynamic analysis of representative aerocapture (29 km/s) and entry (18 km/s) flows in Neptune is discussed. Two 60° and 45° sphere-cone shapes are considered, and chemically-reactive, nonequilibrium flowfield solutions are computed for the forebody region, yielding surface heat fluxes from convective heating. A radiative transfer calculation using a line-by-line approach coupled with a ray-tracing routine, yields surface heat fluxes from radiative heating.If the trace amounts of CH4 in Neptune’s atmosphere are accounted for, they dramatically enchance radiative heating, as a result of strong radiative emission from carbonaceous species in the shock layer. For the 18 km/s entry point, radiative heat fluxes accordingly increase by several orders of magnitude, from 0% to about 50% of the total heat fluxes.The post-shock flow features further differ significantly depending on the capsule shape. The sonic line is near the sphere-cone transition zone for the 45° shape and starts detaching from the boundary layer for angles above 55°. The post-shock flow becomes entirely subsonic up to the spacecraft shoulder at 60°. More streamlined shapes will accordingly be more aerodynamically stable.