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The global energy system is in transition. It is attempting to reach net‐zero greenhouse gas emissions by 2050. The systemic changes mean that the role of bioenergy will change. The potential of bioenergy to make a flexible contribution to the energy system is key for the achievement of global emission reduction ambitions and the functioning of the low‐carbon energy system and economy. As the volume of sustainably available biomass resources is limited, defining the contributions from bioenergy to a low‐carbon energy system and finding balances – and ideally synergies – between the different possible energy and climate system services that biomass can provide will be very important. The recognized system services include, among others, the flexible operation of bioenergy plants to integrate variable renewable energy sources and to provide negative carbon dioxide (CO2) emissions. Interest in flexible operation of bioenergy value chains, bioenergy with carbon capture and utilization as well as synergies with renewable hydrogen‐based value chains has increased recently. The objective of this paper is to present a holistic definition of flexible bioenergy as a system service based on the work conducted in International Energy Agency (IEA) Bioenergy Technology Collaboration Programme's Task 44 Flexible Bioenergy and System Integration, and to provide some practical examples. The paper also presents the different bioenergy system services and considers their definitions and interactions, as this is important in energy system design. The definition of flexible bioenergy shows that the flexibility provision from bioenergy goes far beyond the traditional definition of providing short‐term flexibility in the power sector. Indicators to demonstrate the value of services as well as further quantitative assessment of synergies and trade‐offs are needed to valorize the different services from bioenergy and create viable business cases. [ABSTRACT FROM AUTHOR]

• Concentrations of atmospheric CO2 and tropospheric ozone (O3) are rising concurrently in the atmosphere, with potentially antagonistic effects on forest net primary production (NPP) and implications for terrestrial carbon sequestration. • Using free-air CO2 enrichment (FACE) technology, we exposed north-temperate forest communities to concentrations of CO2 and O3 predicted for the year 2050 for the first 7 yr of stand development. Site-specific allometric equations were applied to annual nondestructive growth measurements to estimate above- and below-ground biomass and NPP for each year of the experiment. • Relative to the control, elevated CO2 increased total biomass 25, 45 and 60% in the aspen, aspen–birch and aspen–maple communities, respectively. Tropospheric O3 caused 23, 13 and 14% reductions in total biomass relative to the control in the respective communities. Combined fumigation resulted in total biomass response of −7.8, +8.4 and +24.3% relative to the control in the aspen, aspen–birch and aspen–sugar maple communities, respectively. • These results indicate that exposure to even moderate levels of O3 significantly reduce the capacity of NPP to respond to elevated CO2 in some forests. [ABSTRACT FROM AUTHOR]

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO2 and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi‐point hydrogen‐bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO2 reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi‐identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X‐ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO2 capture, activation, and reduction. [ABSTRACT FROM AUTHOR]

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO2 and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi‐point hydrogen‐bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO2 reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi‐identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X‐ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO2 capture, activation, and reduction. [ABSTRACT FROM AUTHOR]

Global warming has in recent years become a cause for serious concern. It is believed to result from the release of greenhouse gases into the atmosphere, particularly carbon dioxide. Upon assessing the recent developments, it can be learnt that attempts in relation to the reduction of anthropogenic carbon dioxide content and decreasing the emission of greenhouse gases appear to be among the key issues. Despite a range of technologies and approaches established over the years, the issue of separating carbon dioxide from gas streams still cannot be addressed. Notwithstanding having developed new methods, another substantial challenge identified in the area is the growth of adsorbents with relatively higher performance. It is worthy of note that they help balance an array of optimization‐needed factors which include efficiency, engineering feasibility and costs. Zeolites, metal‐organic frameworks, silica and activated carbon are among the adsorption materials which are widely discussed in the literature. Accordingly, recent studies focusing on such materials are comprehensively discussed and summarized in this review. Besides, the cost, carbon capture capacity and selectivity which are among the major concerns with respect to selecting adsorbents are compared in this paper. Furthermore, both the privileges and drawbacks of each type of adsorbent are presented in this manuscript. Despite the encouraging results achieved in this study, developing more effective adsorbents to capture carbon dioxide remains a fundamental challenge. Therefore, further innovations regarding the design and synthesis of adsorbents are essential for future applications. [ABSTRACT FROM AUTHOR]

Abstract: A significant amount of global carbon dioxide emissions is due to steel mill gases. One promising approach for the reduction of these emissions is their chemical conversion. In this regard, the conversion to urea is very advantageous, since common urea processes are already using carbon dioxide as a feedstock. In the present paper, urea capacities are determined that can be realized using steel mill gases. The capacities are estimated based on new process concepts that are presented in this paper. Exemplarily, the steel mill of thyssenkrupp Steel in Duisburg, Germany, is considered. It could be shown that reasonable urea capacities can be reached. By this means, a great impact can be made on the reduction of steel mill carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

The regeneration reaction characteristics of the K2CO3/Al2O3 sorbent were investigated with a thermogravimetric apparatus. The effects of the gas composition and temperature on the regeneration conversion and reaction rate were analysed extensively. The results of the thermogravimetric experiment revealed that the regeneration characteristics of K2CO3/Al2O3 are better than those of pure K2CO3 and that temperature is the key parameter for the K2CO3/Al2O3 regeneration process. It was also observed that the regeneration process of K2CO3/Al2O3 occurred in three stages. As the regeneration temperature increased, regeneration occurred in the following sequence: KHCO3 on the external surface, KHCO3 on the internal surface and KAl (CO3)2(OH)2. The activation energy (E, kJ/mol) and pre‐index factor (A, min−1) of the three stages were 69.7, 73.8 and 84.5 and 1.36 × 107, 1.86 × 107 and 2.74 × 106, respectively. The reaction kinetic parameters were calculated by the thermal analysis method. A comprehensive model based on the Avrami–Erofeev reaction mechanism model was proposed for the regeneration process of K2CO3/Al2O3. The model data and test values agreed well, thereby establishing the model's accuracy. This paper provides fundamental data for further study on the capture of carbon dioxide from flue gas using potassium‐based sorbents. [ABSTRACT FROM AUTHOR]

As a new type of green environment‐friendly cementitious material, microbial‐induced mineralization products have garnered more and more attention. In this paper, the synthesis of mineralization products under microbial inducement was conducted. The composition and microstructure of mineralization products were studied using energy‐dispersive spectrometer (EDS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results showed that mineralization products were calcite, while the shape was similar to globular type, and particle size was about 5 μm. The effect of microbial culture solution, secretion solution, and concentration on the conductivity of the solution was compared and analyzed. During the formation of mineralization products, bacterial bodies not only played the role of nucleation sites but also accelerated the deposition of mineralization products. Thus, it could be seen that the bacterial bodies had a certain influence on the reaction kinetics. The adhesion force of mineralization products was evaluated by the interfacial adhesion properties between the mineralization products and glass slides. The results of the sonication test and scratch test indicated that the interfacial adhesion strength between mineralization products and glass slides was closely related to the mass of mineralization products deposited. The larger the mass of mineralization products deposited, the greater the interfacial adhesion strength. Based on the above research and analysis, the reaction process and mechanism model of microbial‐induced mineralization were defined. [ABSTRACT FROM AUTHOR]

Soil carbon sequestration is being considered as a potential pathway to mitigate climate change. Cropland soils could provide a sink for carbon that can be modified by farming practices; however, they can also act as a source of greenhouse gases (GHG), including not only nitrous oxide (N2O) and methane (CH4), but also the upstream carbon dioxide (CO2) emissions associated with agronomic management. These latter emissions are also sometimes termed "hidden" or "embedded" CO2. In this paper, we estimated the net GHG balance for Chinese cropping systems by considering the balance of soil carbon sequestration, N2O and CH4 emissions, and the upstream CO2 emissions of agronomic management from a life cycle perspective during 2000–2017. Results showed that although soil organic carbon (SOC) increased by 23.2 ± 8.6 Tg C per year, the soil N2O and CH4 emissions plus upstream CO2 emissions arising from agronomic management added 269.5 ± 21.1 Tg C‐eq per year to the atmosphere. These findings demonstrate that Chinese cropping systems are a net source of GHG emissions and that total GHG emissions are about 12 times larger than carbon uptake by soil sequestration. There were large variations between different cropping systems in the net GHG balance ranging from 328 to 7,567 kg C‐eq ha−1 year−1, but all systems act as a net GHG source to the atmosphere. The main sources of total GHG emissions are nitrogen fertilization (emissions during production and application), power use for irrigation, and soil N2O and CH4 emissions. Optimizing agronomic management practices, especially fertilization, irrigation, plastic mulching, and crop residues to reduce total GHG emissions from the whole chain is urgently required in order to develop a low‐carbon future for Chinese crop production. This is important to know what extent are greenhouse gas (GHG) emissions from intensive arable agriculture in China mitigated by sequestration of carbon in soil. We calculated the net GHG balance (kg C‐eq ha−1 year−1) between SOC stock change and emissions of N2O and CH4 and upstream CO2‐eq emissions associated with agronomic management. Despite the soil carbon sink found in Chinese cropland soils, it acted as a net GHG source because the emissions of total GHG are about one order of magnitude larger than the soil carbon sink under current farmers' practices. [ABSTRACT FROM AUTHOR]

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas ( GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta-analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential ( GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation. [ABSTRACT FROM AUTHOR]

Abstract: Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta‐analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation. [ABSTRACT FROM AUTHOR]

A process development unit (PDU) for amine-based post-combustion carbon capture located at Clean Coal Technologies Centre in Zabrze, Poland, was used to validate split-stream configuration. A PDU having capacity up to 100 m³n /h was designed to test the amine scrubbing carbon capture process from flue gases or mixtures of technical gases. Flexible process flow sheet of the unit allowed investigation of the split flow process. The split-flow flowsheet modification was compared with a standard system for chemical absorption-based CO2 capture. The tests were conducted using well-accepted baseline solvent: 30 wt% aqueous monoethanolamine solution. The flow sheet modification resulted in a decrease of reboiler heat duty by ~1.6% and an increase in CO2 recovery by ~1.2 p.p. Split-flow process modification was examined together with standard process flow sheet, and vast number of process parameters recorded during the trials have been presented. The explanation of beneficial effects of split-flow designs have been shown together with detailed analysis of experimental trials carried out using PDU for amine-based post-combustion carbon capture. This paper is also a valuable source of experimental data useful during validation of models. [ABSTRACT FROM AUTHOR]

Biochar as a carbon-rich coproduct of pyrolyzing biomass, its amendment has been advocated as a potential strategy to soil carbon (C) sequestration. Updated data derived from 50 papers with 395 paired observations were reviewed using meta-analysis procedures to examine responses of soil carbon dioxide (CO2) fluxes, soil organic C (SOC), and soil microbial biomass C (MBC) contents to biochar amendment. When averaged across all studies, biochar amendment had no significant effect on soil CO2 fluxes, but it significantly enhanced SOC content by 40% and MBC content by 18%. A positive response of soil CO2 fluxes to biochar amendment was found in rice paddies, laboratory incubation studies, soils without vegetation, and unfertilized soils. Biochar amendment significantly increased soil MBC content in field studies, N-fertilized soils, and soils with vegetation. Enhancement of SOC content following biochar amendment was the greatest in rice paddies among different land-use types. Responses of soil CO2 fluxes and MBC to biochar amendment varied with soil texture and pH. The use of biochar in combination with synthetic N fertilizer and waste compost fertilizer led to the greatest increases in soil CO2 fluxes and MBC content, respectively. Both soil CO2 fluxes and MBC responses to biochar amendment decreased with biochar application rate, pyrolysis temperature, or C/N ratio of biochar, while each increased SOC content enhancement. Among different biochar feedstock sources, positive responses of soil CO2 fluxes and MBC were the highest for manure and crop residue feedstock sources, respectively. Soil CO2 flux responses to biochar amendment decreased with pH of biochar, while biochars with pH of 8.1-9.0 had the greatest enhancement of SOC and MBC contents. Therefore, soil properties, land-use type, agricultural practice, and biochar characteristics should be taken into account to assess the practical potential of biochar for mitigating climate change. [ABSTRACT FROM AUTHOR]

The global warming is directly related to the increased greenhouse gas emissions from both natural and anthropogenic origins. There has been a drastic rise in the concentration of CO2 and other greenhouse gases since the industrial revolution primarily due to the intensifying consumption of fossil fuels. With the need to reduce carbon emissions and mitigate global warming certain strategies relating to carbon capturing and sequestration are indispensable. This paper comprehensively describes several physicochemical, biological and geological routes for carbon capture and sequestration. The trend of the increase in greenhouse gases over the years is illustrated along with the global statistics for fossil fuels usage and biofuels production. The physicochemical carbon capturing technologies discussed include absorption, adsorption, membrane separation and cryogenic distillation. The algal and bacterial systems, dedicated energy crops and coalbed methanogenesis have been vividly explained as the biological routes for carbon sequestration. The geological carbon sequestering route centers on biochar application and oceanic carbon storage. A systematic survey has been made on the origin and impact of greenhouse gases along with the potential for sequestration based on some fast-track and long-term sequestration technologies. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method based on real options theory for economic evaluation of the replacement of an old coal-fired thermal power plant (COAL) with a coal-fired thermal power plant that includes a CCS (carbon dioxide capture and storage) unit. We calculate the real option value (ROV) of CCS as the value of an American call option with dividend, treating the increased carbon cost of COAL due to the delay of replacement as opportunity cost. The appropriate construction time of a CCS unit is evaluated by binominal decision tree analysis for option exercise. We calculate the change of project ROV and the appropriate construction time according to the difference in carbon emission benchmarks and the variation of the maintenance cost of COAL. The effect of power station lifetime is also analyzed. We conclude that flexibility in the timing of decision making increases the value of a project. We also found that CCS is an economically justifiable technology option under forthcoming restrictions on carbon emissions. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 9-17, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21065 [ABSTRACT FROM AUTHOR]

Across many dryland regions, historically grass-dominated ecosystems have been encroached upon by woody-plant species. In this paper, we compare ecosystem water and carbon dioxide (CO2) fluxes over a grassland, a grassland–shrubland mosaic, and a fully developed woodland to evaluate potential consequences of woody-plant encroachment on important ecosystem processes. All three sites were located in the riparian corridor of a river in the southwest US. As such, plants in these ecosystems may have access to moisture at the capillary fringe of the near-surface water table. Using fluxes measured by eddy covariance in 2003 we found that ecosystem evapotranspiration (ET) and net ecosystem exchange of carbon dioxide (NEE) increased with increasing woody-plant dominance. Growing season ET totals were 407, 450, and 639 mm in the grassland, shrubland, and woodland, respectively, and in excess of precipitation by 227, 265, and 473 mm. This excess was derived from groundwater, especially during the extremely dry premonsoon period when this was the only source of moisture available to plants. Access to groundwater by the deep-rooted woody plants apparently decouples ecosystem ET from gross ecosystem production (GEP) with respect to precipitation. Compared with grasses, the woody plants were better able to use the stable groundwater source and had an increased net CO2 gain during the dry periods. This enhanced plant activity resulted in substantial accumulation of leaf litter on the soil surface that, during rainy periods, may lead to high microbial respiration rates that offset these photosynthetic fluxes. March–December (primary growing season) totals of NEE were −63, −212, and −233 g C m−2 in the grassland, shrubland, and woodland, respectively. Thus, there was a greater disparity between ecosystem water use and the strength of the CO2 sink as woody plants increased across the encroachment gradient. Despite a higher density of woody plants and a greater plant productivity in the woodland than in the shrubland, the woodland produced a larger respiration response to rainfall that largely offset its higher photosynthetic potential. These data suggest that the capacity for woody plants to exploit water resources in riparian areas results in enhanced carbon sequestration at the expense of increased groundwater use under current climate conditions, but the potential does not scale specifically as a function of woody-plant abundance. These results highlight the important roles of water sources and ecosystem structure on the control of water and carbon balances in dryland areas. [ABSTRACT FROM AUTHOR]