CH4 Losses Research Articles

CARBON DIOXIDE CAPTURE BY USING HYBRID SYSTEM. PARAMETRIC SENSITIVITY ANALYSIS AND ENVIRONMENTAL AND ENERGY EVALUATION

Global warming is mainly caused by carbon dioxide (CO2). For natural gas streams that contain high lev-els of CO2, combining different technologies, such as absorption, adsorption, membrane, and cryogenic separation, may be more convenient for separating acid gas. This study focuses on a gas stream that con-tains 81.14 mole% of CO2. Two hybrid processes, membrane-absorption with amines and cryogenic-membrane, were evaluated for their capital cost, en-ergy and water consumption, and greenhouse gas (GHG) emissions under different operational condi-tions using ASPEN HYSYS V.12. The membrane-absorption system has the lowest CH4 losses, while the hybrid cryogenic-membrane system has lower energy and water requirements and 69% less GHG emissions than the membrane-amine hybrid system. The cryo-genic-membrane system is suitable for enhanced oil recovery (EOR) due to its high carbon dioxide purity and 30% lower operative costs, but requires a slightly higher initial investment.

The Danish national effort to minimise methane emissions from biogas plants

In total, 69 biogas plants representing 59 % of Danish biogas production participated in a national effort to reduce methane (CH4) emission. Measurements in terms of total plant CH4 emissions, quantification of emissions from point sources, leak surveys and conceptual design plans to mitigate emissions were performed. Plant-level CH4 emission rates varied between 1.3 and 81.2 kg CH4 h−1, and CH4 losses expressed in percentages of production varied between 0.3 and 40.6 %. Agricultural plants generally had lower CH4 loss rates compared to wastewater treatment plants. Biogas plants with a smaller gas production emitted a larger fraction of their production compared to larger plants, which was partly explained by the absence of gas collection from digestate storage tanks at smaller plants. A very commonly observed source of emission was pressure relief valves, where this source of leakage was observed at 53 % of the plants. A national emission factor (sum of CH4 emissions/sum of CH4 productions) was determined at 2.5 % for the Danish biogas production, whereof it was 2.1 % for agricultural biogas production and 6.7 % for biogas production at wastewater treatment plants. Measurements of total CH4 emissions at six plants performed before and after implementation of mitigating actions showed that emissions were reduced by 46 % by carrying out relatively minor technical fixes and adjustments. An economic evaluation showed that, in some cases, mitigating actions could be economically beneficial for the biogas plant (positive net present value over a 10 year time frame), due to an increase in revenue.

Is hydrogen production through natural gas pyrolysis compatible with ambitious climate targets in the United States? A location-specific, time-resolved analysis

Pyrolysis of natural gas to produce H2 and solid carbon through methane cracking can be characterized as a high-CH4, low-CO2 process. It results in low CO2 emissions because no direct CO2 is generated at the point of H2 generation if solid carbon is not combusted further. However, it results in high CH4 emissions because of its higher natural gas consumption compared to the direct use of natural gas and, thus, higher CH4 losses along the natural gas supply chain. Here, I analyzed whether this process can provide climate benefit in comparison to the direct, unabated utilization of natural gas and also in comparison with H2 produced from water electrolysis with grid electricity. To this end, Monte Carlo simulations of time-resolved and US state-specific emission profiles and their impact on mid-century global warming under different CH4 mitigation scenarios were conducted. It was found that the climate benefit of natural gas pyrolysis is highly dependent on plant location and the speed at which CH4 emissions can be abated. New York, Pennsylvania, and Ohio emerged as the most promising locations. This is because of their projected long reliance on natural gas for power generation, which renders electrolysis using grid electricity less attractive, as well as the relatively low estimate of current CH4 emissions from the natural gas supply chain. However, without fast action on CH4 emission mitigation, the climate benefit of natural gas pyrolysis is small or non-existent, irrespective of the plant location. Overall, the uncertainty in the relative climate benefit of natural gas pyrolysis was found to be large; however, this study developed an easy-to-adapt MS Excel/visual basic for applications (VBA) tool that can be updated as soon as more accurate data on CH4 emissions becomes available. Policymakers, businesspeople, and scholars can use this tool to estimate the climate impact within their own scenarios and locations.

The Fate of Protonated Guaiacol and Its Derivatives in the Gas Phase.

Guaiacol (2-methoxyphenol) and its derivatives are a class of semivolatile polar organic molecules possessing low molecular weights. Owing to their volatility, guaiacol and its derivatives can interact with atmospheric water and form protonated methoxyphenols through proton transfer. The aim of the present work is to study the dissociation of these protonated ions and hence, potentially, their atmospheric fate. Tandem mass spectrometry was employed to analyze the unimolecular dissociation of the protonated forms of guaiacol (2-methoxyphenol, 1), creosol (2-methoxy-4-methylphenol, 2), 4-ethylguaiacol (4-ethyl-2-methoxyphenol, 3), 4-vinylguaiacol (2-methoxy-4-vinylphenol, 4), eugenol (2-methoxy-4-prop-2-enylphenol, 5), and vanillin (4-hydroxy-3-methoxybenzaldehyde, 6). Density functional theory at the B3LYP/6-31G(d) (1-5) and B3LYP/6-311+G(d,p) (6) levels of theory were applied to determine the observed minimum energy reaction pathways, and reliable energetics were acquired using CBS-QB3 single-point energy calculations. All the protonated ions, with the exception of 6, exhibit the loss of CH3OH via a series of hydrogen transfers, followed by ring contraction to lose CO. This common dissociation pathway leads to the formation of a cyclopentadienyl ion as the main dissociation product. Conversely, 6 first exhibits the loss of CO, followed by sequential losses of CH3OH and CO to generate a cyclopentadienyl ion. Additionally, minor fragmentation channels are also observed for the different protonated ions: CH2 loss in 1; CH4 and H2O losses in 3; CH3 loss in 4, 5, and 6; C2H4 and CH2CHCH2 losses in 5; H loss in 6. Altogether, the protonated ions primarily lose CH3OH and CO as neutral molecules and generate a cyclopentadienyl ion as a dissociation product.

Purification and upgrading biogas from anaerobic digestion using chemical asborption of CO2 with amines in order to produce biomethane as biofuel for vehicles: a pilot-scale study

ABSTRACT Methane from biogas is a promising option for the transition to a circular economic system based on renewable and sustainable energy. Currently, there is a wide variety of technologies capable of efficiently extracting the impurities contained in biogas in order to produce biomethane. In the present study, work was carried out in a pilot plant for cleaning and upgrading real biogas from anaerobic digestion by means of the chemical absorption method. In contrast to other technologies, chemical absorption stands out for having the lowest CH4 losses, which was crucial for this study. The objective was to purify and upgrade the biogas from anaerobic digestion of a WWTP to achieve a high concentration of methane and use it as biofuel in vehicles. The two aqueous solutions used as absorbents were mono-ethanolamine (MEA) and N-methyldiethanolamine (MDEA), both at 20% and 40% concentrations. It was found that the most effective solution was the MEA at 20% concentration, since it has the highest CO2 removal efficiency (94%) and, therefore, CH4 richness (96%). Finally, for every 100 m3 of biomethane generated after the chemical absorption process, 62 Nm3 of biofuel were obtained.

Quantification of N and C cycling during aerobic composting, including automated direct measurement of N2, N2O, NO, NH3, CO2 and CH4 emissions

Closing the carbon (C) and nitrogen (N) balance has yet to be achieved in aerobic bioprocess due to current methodological drawbacks in the frequency of sampling and detection and the challenge in direct measurement of instantaneous N2 emission. To address this issue, a novel system was developed enabling simultaneous and online determination of gaseous C and N species (N2, N2O, NO, NH3, CO2 and CH4) from aerobic composting at a high frequency of 120 times·d−1. A helium‑oxygen gas mixture was used to replace the air in the system to enable direct measurement of N2 emission, and three different gas exchange methods were assessed in their ability to minimize atmospheric background N2: 1) the N2-free gas purging method; 2) one cycle of the evacuation-refilling procedure; 3) one cycle of evacuating and refilling followed by N2-free gas purging. Method 3 was demonstrated as an optimum N2-removal method, and background N2 concentrations decreased to ~66 μmol·mol−1 within 11.6 h. During the N2-free gas purging period, low temperature incubation at 15 °C reduced CO2, CH4, NO, N2O and NH3 losses by 80.5 %, 41-fold, 10-fold, 11,403-fold and 61.4 %, respectively, compared with incubation at 30 °C. Therefore, a fast and low-perturbation N2 removal method was developed, namely the evacuating/refilling-low temperature purging method. Notably, all C and N gases exhibited large within-day variations during the peak emission period, which can be addressed by high-frequency measurement. Based on the developed method, up to 97.8 % of gaseous C and 95.6 % of gaseous N losses were quantified over a 43-day compost incubation, with N2 emission accounting (on average) for 5.8 % of the initial total N. This system for high frequency measurement of multiple gases (including N2) provides a novel tool for obtaining a deeper understanding of C and N turnover and more accurate estimation of reactive N and greenhouse gas emissions during composting.

Evaluation of a Tomato Waste Biofilter for the Retention of Gaseous Losses from Pig Slurry Hygienization by pH Modification

The use of pig slurry as organic fertilizer in intensive horticulture could be possible after hygienization to avoid contamination of products. This research aimed to evaluate a mixture of a tomato waste and rice husk as biofilter media to reduce NH3, N2O, CO2, and CH4 losses from a simple and low-cost solution for slurry hygienization by pH modification. The experiment was made in a system of laboratory scale biofilters connected to jars filled with raw slurry as control and three treatment methods: acidified slurry, alkalinized slurry, and neutralized slurry. The gas concentrations were measured for 35 days, and the composition of slurries and biofilters were determined. The results of this study showed that the mixture of biofiltering media, composed of tomato waste and rice husk, has the potential to retain NH3 and greenhouse gases (GHG) from a simple and low-cost solution for slurry hygienization by pH modification. Compared to the treatment raw slurry biofilter, the treatment neutralized slurry biofilter, subjected to a combined treatment by alkalinization/neutralization, retained 19% NH3, 4% CO2, and 83% CH4 losses and had no impact on N2O and global warming potential. Thus, the use of tomato waste biofilter during alkalinization did not increase the loss of NH3 and reduced GHG compared to raw slurry, avoiding the subsequent neutralization of slurry for environmental reasons, and could be used as an organic fertilizer in horticulture. However, using the combined alkalinization/neutralization treatment will improve the fertilizer value of the slurry by adjusting the pH from 9.5 to 7.5.

Climate impacts of fossil fuels in todays electricity systems

Oil, coal, and gas account for approximately 80% of global primary energy, but only a portion of total airborne CO2eq (approx. 35% at GWP20 to 65% at GWP100), even though they account for 95% of total measured CO2 emissions. The benefits of these energy sources, as well as their related costs, are not all incorporated in current energy policy discussions. Global greenhouse gas policies must include documented changes in measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears 'better for the climate' than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences and the switch from coal to natural gas, especially LNG, will not have the desired impact of reducing predicted future global warming; in fact, quite the contrary. A large portion of anthropogenic global warming is attributed by the IPCC and IEA to CH4, but it must be noted that CH4 emissions from natural sources and from agriculture account for approximately 40% and 25% of annual global CH4 emissions respectively. Energy accounts for about 20% of documented CH4 emissions. CO2 contributes only approximately 35% of annual airborne anthropogenic GHG emissions after accounting for CH4, over a 20-year horizon. At a 100-year horizon, the contribution of CO2 increases to approximately 60%. Energy policies that do not consider all GHG emissions along the entire value chain will lead to undesired economic and environmental distortions. All carbon taxation and CO2 pricing schemes are incorrect and need to be revised. At IPCC's GWP20 an approximately 2%1 higher loss of CH4 across the value chain prior to combustion of natural gas versus coal will lead to 'climate parity' of coal with natural gas. According to public data, natural gas value chains have high CH4 and undocumented CO2 losses. On a global average, using only IEA-documented CH4 data, natural gas emits approximately 15% more CO2eq than surface-mined coal, over a 20-year horizon. This difference will increase as the use of shale gas and LNG expands. Investors should support all energy systems in a manner that avoids an energy crisis, including intermittent renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install ultra-supercritical power plants with CCUS technology. However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its promotion of photosynthesis and plant growth effects (fertilization) need to be considered in energy policy decisions as well. The authors suggest that future research and development should concentrate on reducing net emissions from fossil fuel power plants and providing cost-effective and reliable new conventional power generation capacity, utilizing clean coal and clean natural gas technology.

Direct biogas upgrading via CO2 methanation to high-quality biomethane over NiMg/CNT-SiO2 fiber catalysts

As an environmentally friendly and renewable alternative fuel, biomethane can be obtained from biogas upgrading; however, the commercial technologies for upgrading are currently an unsustainable global process by releasing CO2 into the atmosphere. Here, this research proposed a novel sustainable method for direct biogas upgrading to high-quality biomethane by catalytic CO2 methanation and focused on the performance improvement of Ni-based catalysts. Carbon nanotubes-silica fiber (CNT-SF) composite as a high-heat transfer fibrous support was successfully synthesized using the Ni/silica fiber (SF) catalyst as a core-fiber seeding structure in ethanol steam reforming. The Ni/CNT-SF catalyst was extensively characterized and investigated in the direct biogas upgrading by CO2 methanation. The results revealed that Ni/CNT-SF catalyst exhibited superior catalytic performance than the Ni/SF and conventional Ni/silica porous (SP) catalysts. This suggested that the Ni/CNT-SF catalyst easily accessed the reactant molecules and exhibited an enhanced metal-support interaction with smaller Ni crystalline size, leading to a higher dispersion of the Ni active site, enhancing the CO2 methanation. Furthermore, the addition of Mg (1–3%wt.) into the Ni/CNT-SF catalyst resulted in a stronger metal-support interaction and increased moderate basic sites, which could suppress the Ni sintering and promote the adsorption and activation of CO2. Under optimum conditions (350 °C, 10 bar, H2/CO2 molar ratio of 4, and GHSV of 24,000 mL⋅g−1⋅h−1), the Ni-2Mg/CNT-SF catalyst achieved the highest CO2 conversion, CH4 selectivity, producing high-quality biomethane with CH4 content at approximately 95%, without CH4 losses.

Evaluation of Tomato-Based Packing Material for Retention of Ammonia, Nitrous Oxide, Carbon Dioxide and Methane in Gas Phase Biofilters: A Laboratory Study

Biofilters are an effective air pollution control technology to break down gaseous contaminants and produce innocuous end products. This laboratory study aimed to evaluate a biofilter media, mainly composed by tomato waste, as packing material to reduce NH3, N2O, CO2 and CH4 losses from stored pig slurry. Three mixtures of packing materials, with and without oxalic acid, were arranged in treatments, namely: mixture of tomato waste, pine bark and agricultural compost; mixture of tomato waste and rice husk; tomato waste only. A control treatment (no biofilter) was also included. The experiments were conducted using a system of laboratory scale biofilters connected to jars filled with pig slurry and under a constant airflow rate. The gas concentrations were measured for 14 days and the physicochemical of the packing materials were assessed. Results showed that biofilter media mixtures had a potential for NH3 retention ranging from 51 to 77% and the addition of oxalic acid to these biofilters increased NH3 retention to 72–79%. Additionally, the biofilter media mixtures with and without oxalic acid showed a potential retention for CH4 (29–69%) but not for N2O, yet with no impact on the global warming potential. It can be concluded that tomato based biofilters had the potential to reduce gaseous emissions from slurry.

Techno-economic and environmental assessment of the main biogas upgrading technologies

Five biogas-to-biomethane upgrading technologies were compared from the environmental and economic points of view: High-Pressure Water Scrubbing (HPWS), Amine Scrubbing (AS), Potassium Carbonate Scrubbing (PCS), Pressure Swing Adsorption (PSA) and Membrane Permeation (MP). Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods were used for the comparison. In order to provide a wider picture of the conversion system and its impacts, the biogas production processes, starting from source sorted organic fraction of municipal solid waste, were included. The intention was to maintain the same object for the LCA and the LCC, given that the cost of biogas production had to be included for the calculation of the economic indicators. The cost analysis included also the evaluation of the external costs, derived from the monetization of the air emissions of the systems. The selected functional unit was the upgrading of 1 Nm3 of raw biogas. Data were collected directly from companies providing upgrading plants and confirmed by literature review. A biogas-to-biomethane plant proved to have environmental and economic benefits and, as expected, for larger plant sizes the economic performances improved. AS showed the best environmental performances mainly due to its limited CH4 losses and lower electricity consumption. Considering the contribution from only the upgrading part, AS showed the lowest impacts for the global warming potential (GWP) indicator (respectively 13%, 1%, 23% and 3% less than HPWS, PCS, PSA and MP). However, the results changed for other impact categories: for human toxicity indicator PSA showed lower impacts compared to the other technologies, respectively 7%, 144%, 1% and 9% less compared to HPWS, AS, PCS and MP. For small size plants, HPWS proved to be slightly more cost-effective compared to other technologies. For large size plants, PCS showed the highest net present value. Moreover, the sensitivity analysis showed that the electricity consumption is a key parameter for the economic and environmental results. Its variation proved that for the 60% of cases AS was the best solution in terms of GWP, however 35% and 5% of cases respectively indicated that PCS and MP had the lowest GWP.

Design assessment of polymeric membranes modules to separate carbon dioxide from a binary mixture with methane

This work presents the performance assessment of diverse membrane arrangements to separate carbon dioxide (CO2) from a binary mixture with methane (CH4). For the purpose, we employ computer modeling to represent different polymeric modules, which are able to split an inlet CH4/CO2 gaseous mixture into sweet and acid products. Aim of the process is to achieve a high-purity CO2 permeate, reducing the CH4 losses. Novelty, we compare the performances of different existing commercial polymers, available for gas industries: cellulose acetate, polycarbonates, polyamides, polyamide-imides, polyamides thin-film composites, among others. The importance of the use of different materials is the possibility to replicate total membrane area, transport properties, and operating conditions. Finally, a comparative and integral discussion of the simulations considers three fundamental aspects: hydrocarbon recovery, residual gas quality, and compression power to carry out the separation.

Methane emissions from oil and gas platforms in the North Sea

Abstract. Since 1850 the concentration of atmospheric methane (CH4), a potent greenhouse gas, has more than doubled. Recent studies suggest that emission inventories may be missing sources and underestimating emissions. To investigate whether offshore oil and gas platforms leak CH4 during normal operation, we measured CH4 mole fractions around eight oil and gas production platforms in the North Sea which were neither flaring gas nor offloading oil. We use the measurements from summer 2017, along with meteorological data, in a Gaussian plume model to estimate CH4 emissions from each platform. We find CH4 mole fractions of between 11 and 370 ppb above background concentrations downwind of the platforms measured, corresponding to a median CH4 emission of 6.8 g CH4 s−1 for each platform, with a range of 2.9 to 22.3 g CH4 s−1. When matched to production records, during our measurements individual platforms lost between 0.04 % and 1.4 % of gas produced with a median loss of 0.23 %. When the measured platforms are considered collectively (i.e. the sum of platforms' emission fluxes weighted by the sum of the platforms' production), we estimate the CH4 loss to be 0.19 % of gas production. These estimates are substantially higher than the emissions most recently reported to the National Atmospheric Emission Inventory (NAEI) for total CH4 loss from United Kingdom platforms in the North Sea. The NAEI reports CH4 losses from the offshore oil and gas platforms we measured to be 0.13 % of gas production, with most of their emissions coming from gas flaring and offshore oil loading, neither of which was taking place at the time of our measurements. All oil and gas platforms we observed were found to leak CH4 during normal operation, and much of this leakage has not been included in UK emission inventories. Further research is required to accurately determine total CH4 leakage from all offshore oil and gas operations and to properly include the leakage in national and international emission inventories.

Physical absorption of CO2 and H2S from synthetic biogas at elevated pressures using hollow fiber membrane contactors: The effects of Henry’s constants and gas diffusivities

The present study applies the mathematical model to investigate the physical absorption of CO2, H2S and CH4 from synthetic biogas at high pressure using hollow fiber membrane contactors. Henry’s constants are considered pressure and temperature dependent, while the polarity of H2S is included in the calculation of gas diffusivities. The model was validated with the experimental data using two hollow fiber membranes, i.e., polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE), to analyze membrane wetting. The effects of pressure and temperature on the CO2 and H2S absorption and CH4 loss were investigated. From the model validation, the experimental results using PVDF and PTFE at 1 bar are in good agreement with non-wetting mode. At elevated pressures, non-wetting mode results correspond with the experimental results using PTFE, while the partially wetting mode well predicts the results of PVDF. The modeling results also indicate that increasing pressure and reducing temperature improves the absorption fluxes of CO2 and H2S, while the CH4 losses in this work are lower than 5.5%.

Factors affecting methane loss from a water scrubbing based biogas upgrading system

Biogas upgrading is a vital step to produce high quality fuel called biomethane with above 90% methane (CH4). Among the various technologies available for biomethane production, water scrubbing is the most extensively implemented technology around the world. However, during the process of biogas upgrading, a some amount of CH4 is separated as CH4 loss through the water flowing out of the water scrubbing column. In this paper, various factors affecting CH4 loss from water scrubbing method are analysed. Some factors such as pressure, water flow rate and CH4 concentration in input gas are dependent upon the solubility and partial pressures of the gases are generally known. Apart from these factors CH4 losses due to bubble entrainment due to high pressure difference between water scrubbing column and desorption tank and gas short circuiting of the gas through the bottom section of the column due to no water sealing and water level maintencence also contribute to CH4 losses. Therefore, CH4 losses during the water scrubbing process due to these factors have been experimentally studied in this paper. A pilot scale water scrubbing system for biogas upgradation was used for the study. It was observed that CH4 % (v/v) in the upgraded biogas and CH4 loss % from the desorbed gas increased with the increase in pressure and increase in the concentration of CH4 in the input gas. Increase in water flow rates caused removal of larger quantities of water containing more absorbed CH4 and CO2 from the scrubbing column, thereby increasing CH4 loss of the system. Highest CH4 loss % of 9.9% (±0.1%), was obtained with raw biogas sample when water was desorbed at atmospheric pressures in the desorption tank, i.e. when pressure difference between the water scrubbing column and desorption tank was highest. A pressure vessel was installed in between scrubbing column and desorption tank to reduce the pressure difference for water leaving the column by varying the pressure in the pressure vessel from 1 to 9bar. With the increase in pressure in the pressure vessel, the pressure difference for water decreased which led to a saving in overall CH4 loss of the system. Water sealing and water level maintenance in the bottom section of the column also affected CH4 losses of the system. All the factors discussed in the article contribute to the CH4 losses from the scrubbing column and cannot be solely credited to a single factor.

Effect of ground soybean and starch on intake, digestibility, performance, and methane production of Nellore bulls

It was hypothesized that replacement of corn with soybean hulls as the energy source, combined with ground soybean as the lipid source, would reduce methane emissions from feedlot animals without affecting their performance. This study aimed to evaluate the effects of including ground soybean combined with either a high or a low level of starch on intake, digestibility, performance, and methane emission of young Nellore bulls (n=28, initial weight=395±32kg) in the feedlot during the finishing phase. Diet treatments consisted of high (HS; approx. 250g/kg) or low (LS; approx. 110g/kg) starch levels, with (WSB) or without (NSB) soybean. Ground soybean was added as a lipid source to diets HS-WSB, LS-WSB, HS-NSB, and LS-NSB, representing 58.7, 64.6, 24.8, and 31.4g/kg ether extract in the total dry matter, respectively. Animals were distributed in a completely randomized design, in a 2×2 factorial arrangement. After 119days, the animals were slaughtered. Animals fed soybean demonstrated an average reduction of 11% in their intakes of dry matter, organic matter, and crude protein (P=0.01). There was a significant effect of the association between starch and soybean on neutral detergent fiber intake (P=0.01). Diets containing soybean affected the digestibility of the animals, reducing the apparent digestibility of dry matter by 3% (P=0.02) and the digestibility of organic matter by 2.8% (P=0.03). A significant interaction was detected between starch and soybean on the apparent digestibility of ether extract (P=0.02) and neutral detergent fiber (P=0.04); the lowest values for ether extract (750g/kg) and neutral detergent fiber (432g/kg) were obtained with HS-WSB. The animals that received WSB had their feed efficiency increased by 17% (P=0.01). The enteric CH4 emissions of the animals fed WSB reduced significantly (P=0.01), with 28% decrease in g CH4/d and g CH4/y, 16% decrease in g CH4 per kg of dry matter intake, and 23% decrease in CH4 losses per percent of gross energy intake. The inclusion of approximately 250g/kg of soybean in the diet of young Nellore bulls in the feedlot provides an increase in their feed efficiency and reduces their enteric methane emission, regardless of the level of starch in the concentrate.

Energy requirements, GHG emissions and investment costs in natural gas sweetening processes

Currently, different technologies are being employed to remove CO2 and H2S from the natural gas. Based on chemical phenomenon, the absorption using alkanolamines is probably the most extended process for the acid gas removal. However, membrane technologies are considered as an alternative in specific cases for their better performances, cleanness, energy requirements, operative costs and location flexibility.The aim of this article is to estimate, compare and analyze the energy requirements, greenhouse gases (GHG) emissions and investment costs of three Natural Gas Sweetening processes. For the study, a regular process using methyldiethanolamine (MDEA), the absorption process using recompressed vapor and a membrane system were simulated using Aspen Hysys v8.8. For the first case, real data from the gas plant Aguaragüe (Argentina) was used to validate the model. To establish a proper comparison, a natural gas with 4 mol.% of CO2 is considered as the inlet stream of each configuration. Specifically, compression and pump power, specific total heat, removed CO2, CH4 wastes and capital costs were estimated and compared for each case. Additionally, a discussion including different aspects in regard to the energy efficiency of the processes was conducted.Although the proposed membrane system demonstrated to reduce the energy requirements (77% and 72%) and emissions (80% and 76%) in respect to both absorption processes, the CH4 losses were higher by more than 6 factor. Moreover, the investment cost of the technology is 12% higher than the required capital of a conventional amine process.

Effects of rock fragments on yak dung greenhouse gas emissions on the Qinghai-Tibetan Plateau

Dung deposition is an important pathway of nutrient return and redistribution in alpine grasslands of the Qinghai-Tibetan Plateau. To date, information on the greenhouse gas emissions of yak dung on alpine grasslands, especially where there are large amounts of rock fragments, is limited. Our aim, therefore, was to evaluate variations in N2O, CH4, and CO2 emissions from yak dung (CCD), and compare it to dung placed on rock fragments (RCD), alpine steppe soil (CSD), and a soil and rock fragment mixture (RSD) over a 30-day incubation period. The results showed that the total N2O emissions from treatments without soil were significantly (P < 0.05) lower than those from treatments with soil. The highest total CH4 emissions were detected in the CSD treatment, while CH4 losses from treatments without rock fragments were significantly (P < 0.05) greater than those with rock fragments. The total CO2 emissions from the RSD treatment was 6.30%–12.0% lower than those in the other three treatments. The soil beneath yak dung pats elevated the global warming potential (GWP), while the addition of rock fragments to the soil significantly (P < 0.05) decreased the GWP by reducing emissions of the three greenhouse gases. We therefore suggest that interactions between rock fragments and alpine steppe soil are effective in decreasing yak dung greenhouse gas emissions. This finding indicates that rock fragments are an effective medium for reducing greenhouse gas emissions from dung pats, and more attention should therefore be paid to evaluate its ecological impact in future studies. These results should help guide scientific assessments of regional GHG budgets in agricultural ecosystems where the addition of livestock manure to soils with large amounts of rock fragments is common.

Gas-Tracer Experiment for Evaluating the Fate of Methane in a Coastal Plain Stream: Degassing versus in-Stream Oxidation.

Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements. In this study, dissolved gases (methane, krypton) were injected into a coastal plain stream in North Carolina to quantify stream CH4 losses at the watershed scale. Stream-reach modeling yielded gas transfer and oxidation rate constants of 3.2 ± 0.5 and 0.5 ± 1.5 d-1, respectively, indicating a ratio of about 6:1. The resulting evasion and oxidation rates of 2.9 mmol m-2 d-1 and 1,140 nmol L-1 d-1, respectively, lie within ranges of published values. Similarly, the gas transfer velocity (K600) of 2.1 m d-1 is consistent with other gas tracer studies. This study illustrates the utility of dissolved-gas tracers for evaluating stream methane fluxes. In contrast to point measurements, this approach provides a larger watershed-scale perspective. Further work is needed to quantify the magnitude of these fluxes under varying conditions (e.g., stream temperature, nutrient load, gradient, flow rate) at regional and global scales before reliable bottom-up estimates of methane evasion can be determined at global scales.

Increasing harvest maturity of whole-plant corn silage reduces methane emission of lactating dairy cows

The objective of this study was to investigate the effects of increasing maturity of whole-plant corn at harvest on CH4 emissions by dairy cows consuming corn silage (CS) based diets. Whole-plant corn was harvested at a very early [25% dry matter (DM); CS25], early (28% DM; CS28), medium (32% DM; CS32), and late (40% DM; CS40) stage of maturity. In a randomized block design, 28 lactating Holstein-Friesian dairy cows, of which 8 were fitted with rumen cannula, received 1 of 4 dietary treatments designated as T25, T28, T32, and T40 to reflect the DM contents at harvest. Treatments consisted of (DM basis) 75% CS, 20% concentrate, and 5% wheat straw. Feed intake, digestibility, milk production and composition, energy and N balance, and CH4 production were measured during a 5-d period in climate respiration chambers after an adaptation to the diet for 12 d. Corn silage starch content varied between 275 (CS25) and 385 (CS40) g/kg of DM. Treatments did not affect DM intake (DMI), milk yield, or milk contents. In situ ruminal fractional degradation rate of starch decreased linearly from 0.098 to 0.059/h as maturity increased from CS25 to CS40. Apparent total-tract digestibility of DM, organic matter, crude protein, neutral detergent fiber, crude fat, starch, and gross energy (GE) decreased linearly with maturity. Treatments did not affect ruminal pH, volatile fatty acids, and ammonia concentrations, and volatile fatty acids molar proportions. The concentration of C18:3n-3 in milk fat decreased linearly, and the concentration of C18:2n-6 and the n-6:n-3 ratio increased linearly with maturity. A quadratic response occurred for the total saturated fatty acid concentration and total monounsaturated fatty acid concentration in milk fat. Methane production relative to DMI (21.7, 23.0, 21.0, and 20.1g/kg) and relative to GE intake (0.063, 0.067, 0.063, and 0.060 MJ/MJ; values for T25, T28, T32, and T40, respectively) decreased linearly with maturity. Also, CH4 emission relative to fat- and protein-corrected milk tended to decrease linearly with maturity (13.0, 13.4, 13.2, and 12.1g/kg of fat- and protein-corrected milk, for T25, T28, T32, and T40, respectively). Intake of GE and metabolizable energy, and energy retained, all expressed per unit of metabolic body weight, did not differ among treatments. Nitrogen intake, N use efficiency (milk N/N intake), and N balance were not influenced by treatments. Increasing maturity of whole-plant corn at harvest may offer an effective strategy to decrease CH4 losses with feeding CS without negatively affecting cow performance.