生物炭对农田土壤CO2排放的影响研究进展

生物炭是生物质在缺氧或者限氧条件下经热解后产生的富碳产物。目前,生物炭被广泛应用于农业生产领域,可改善土壤质量,提高农田土壤碳汇。生物炭还田后,使土壤物理、化学和生物学等性质发生变化进而影响土壤CO₂的排放。本文从生物炭理化特性、土壤性质以及生物炭稳定性等角度综述生物炭对土壤CO₂排放的影响。主要内容包括不同炭化温度和生物质来源的生物炭特性(pH、比表面积、孔径、挥发分和灰分等)及其对土壤CO₂排放的影响;生物炭还田土壤特性变化及其对土壤CO₂排放的影响;生物炭稳定性及其对土壤CO₂排放的影响。本文基于以上三个方面综述了生物炭对农田土壤CO₂排放的影响,并在此基础上对生物炭的固碳减排效应进行展望,以期为生物炭的合理施用、农田固碳减排等提供基础和参考。     

Negative emissions of carbon dioxide through chemical-looping combustion (CLC) and gasification (CLG) using oxygen carriers based on manganese and iron

Carbon capture and storage (CCS) is an economically attractive strategy for avoiding carbon dioxide (CO₂) emissions from, e.g., power plants to the atmosphere. The combination of CCS and biomass combustion would result in a reduction of atmospheric CO₂, or net negative emissions, as plant growth is a form of sequestration of atmospheric carbon. Carbon capture can be achieved in a variety of ways, one of which is chemical looping. Chemical-looping combustion (CLC) and chemical looping gasification (CLG) are two promising technologies for conversion of biomass to heat and power or syngas/methane with carbon capture. There have been significant advances made with respect to CLC in the last two decades for all types of fuel, with much less research on the gasification technology. CLG offers some interesting opportunities for production of biofuels together with carbon capture and may have several advantages with respect to the bench mark indirect gasification process or dual-bed fluidized bed (DFBG) in this respect. In CLG, an oxygen carrier is used as a bed material instead of sand, which is common in indirect gasification, and this could have several advantages: (i) all generated CO₂ is present together with the syngas or methane in the fuel reactor outlet stream, thus in a concentrated stream, viable for separation and capture; (ii) the air reactor (or combustion chamber) should largely be free from trace impurities, thus preventing corrosion and fouling in this reactor; and (iii) the highly oxidizing conditions in the fuel reactor together with solid oxide surfaces should be advantageous with respect to limiting formation of tar species. In this study, two manganese ores and an iron-based waste material, LD slag, were investigated with respect to performance in these chemical-looping technologies. The materials were also impregnated with alkali (K) in order to gauge possible catalytic effects and also to establish a better understanding of the general behavior of oxygen carriers with alkali, an important component in biomass and biomass waste streams and often a precursor for high-temperature corrosion. The viability of the oxygen carriers was investigated using a synthetic biogas in a batch fluidized bed reactor. The conversion of CO, H₂, CH₄, and C₂H₄ was investigated in the temperature interval 800–950 °C. The reactivity, or oxygen transfer rate, was highest for the manganese ores, followed by the LD slag. The conversion of C₂H₄ was generally high but could largely be attributed to thermal decomposition. The K-impregnated samples showed enhanced reactivity during combustion conditions, and the Mangagran-K sample was able to achieve full conversion of benzene. The interaction of the solid material with alkali showed widely different behavior. The two manganese ores retained almost all alkali after redox testing, albeit exhibiting different migration patterns inside the particles. LD slag lost most alkali to the gas phase during testing, although some remained, possibly explaining a small difference in reactivity. In summary, the CLC and CLG processes could clearly be interesting for production of heat, power, or biofuel with negative CO₂ emissions. Manganese ores are most promising from this study, as they could absorb alkali, giving a better conversion and perhaps also inhibiting or limiting corrosion mechanisms in a combustor or gasifier.

     

Biomass-based carbon capture and utilization in kraft pulp mills

Corporate image, European Emission Trading System and Environmental Regulations, encourage pulp industry to reduce carbon dioxide (CO₂) emissions. Kraft pulp mills produce CO₂ mainly in combustion processes. The largest sources are the recovery boiler, the biomass boiler, and the lime kiln. Due to utilizing mostly biomass-based fuels, the CO₂ is largely biogenic. Capture and storage of CO₂ (CCS) could offer pulp and paper industry the possibility to act as site for negative CO₂ emissions. In addition, captured biogenic CO₂ can be used as a raw material for bioproducts. Possibilities for CO₂ utilization include tall oil manufacturing, lignin extraction, and production of precipitated calcium carbonate (PCC), depending on local conditions and mill-specific details. In this study, total biomass-based CO₂ capture and storage potential (BECCS) and potential to implement capture and utilization of biomass-based CO₂ (BECCU) in kraft pulp mills were estimated by analyzing the impacts of the processes on the operation of two modern reference mills, a Nordic softwood kraft pulp mill with integrated paper production and a Southern eucalyptus kraft pulp mill. CO₂ capture is energy-intensive, and thus the effects on the energy balances of the mills were estimated. When papermaking is integrated in the mill operations, energy adequacy can be a limiting factor for carbon capture implementation. Global carbon capture potential was estimated based on pulp production data. Kraft pulp mills have notable CO₂ capture potential, while the on-site utilization potential using currently available technologies is lower. The future of these processes depends on technology development, desire to reuse CO₂, and prospective changes in legislation.

     

CO2 Capture in Pulp and Paper Mills: CO2 Balances and Preliminary Cost Assessment

This paper investigates overall CO₂ balances of combined heat and power (CHP) plants with CO₂ capture and storage (CCS) in Kraft pulp and paper mills. The CHP plants use biomass-based fuels and feature advanced gasification and combined cycle technology. Results from simple process simulations of the considered CHP plants are presented. Based on those results and taking into account the major direct and indirect changes in CO₂ emissions, the study shows that implementing CCS leads to steep emission reductions. Furthermore, a preliminary cost assessment is carried out to analyse the CO₂ mitigation cost and its dependence on the distance that the CO₂ must be transported to injection sites.     

木质生物燃料与其半焦的混燃实验研究

生物质半焦作为生物质气化的副产物,其固定碳含量和热值均高于原生物质.若将生物质半焦充分利用将大幅提高生物质利用的能量效率,具有很大的经济和环境效益.在综合热分析基础上,考察了生物质半焦添加比例(掺烧比)对生物质微米燃料旋风炉燃烧炉膛温度、烟气及灰分的影响.试验研究发现掺烧比为20%(空气当量比为1.2,粉体粒径在0.177 mm以下,生物质含水率控制在8.1%以下),燃烧效果最好,燃烧效率高达98%,燃烧烟气中有害气体NOx和SO2的含量较少.     

Avoiding CO2 capture effort and cost for negative CO2 emissions using industrial waste in chemical-looping combustion/gasification of biomass

Chemical-looping combustion (CLC) is a combustion process with inherent separation of carbon dioxide (CO₂), which is achieved by oxidizing the fuel with a solid oxygen carrier rather than with air. As fuel and combustion air are never mixed, no gas separation is necessary and, consequently, there is no direct cost or energy penalty for the separation of gases. The most common form of design of chemical-looping combustion systems uses circulating fluidized beds, which is an established and widely spread technology. Experiments were conducted in two different laboratory-scale CLC reactors with continuous fuel feeding and nominal fuel inputs of 300 W_th and 10 kW_th, respectively. As an oxygen carrier material, ground steel converter slag from the Linz–Donawitz process was used. This material is the second largest flow in an integrated steel mill and it is available in huge quantities, for which there is currently limited demand. Steel converter slag consists mainly of oxides of calcium (Ca), magnesium (Mg), iron (Fe), silicon (Si), and manganese (Mn). In the 300 W unit, chemical-looping combustion experiments were conducted with model fuels syngas (50 vol% hydrogen (H₂) in carbon monoxide (CO)) and methane (CH₄) at varied reactor temperature, fuel input, and oxygen-carrier circulation. Further, the ability of the oxygen-carrier material to release oxygen to the gas phase was investigated. In the 10 kW unit, the fuels used for combustion tests were steam-exploded pellets and wood char. The purpose of these experiments was to study more realistic biomass fuels and to assess the lifetime of the slag when employed as oxygen carrier. In addition, chemical-looping gasification was investigated in the 10 kW unit using both steam-exploded pellets and regular wood pellets as fuels. In the 300 W unit, up to 99.9% of syngas conversion was achieved at 280 kg/MW_th and 900 °C, while the highest conversion achieved with methane was 60% at 280 kg/MW_th and 950 °C. The material’s ability to release oxygen to the gas phase, i.e., CLOU property, was developed during the initial hours with fuel operation and the activated material released 1–2 vol% of O₂ into a flow of argon between 850 and 950 °C. The material’s initial low density decreased somewhat during CLC operation. In the 10 kW, CO₂ yields of 75–82% were achieved with all three fuels tested in CLC conditions, while carbon leakage was very low in most cases, i.e., below 1%. With wood char as fuel, at a fuel input of 1.8 kW_th, a CO₂ yield of 92% could be achieved. The carbon fraction of C₂-species was usually below 2.5% and no C₃-species were detected. During chemical-looping gasification investigation a raw gas was produced that contained mostly H₂. The oxygen carrier lifetime was estimated to be about 110–170 h. However, due to its high availability and potentially low cost, this type of slag could be suitable for large-scale operation. The study also includes a discussion on the potential advantages of this technology over other technologies available for Bio-Energy Carbon Capture and Storage, BECCS. Furthermore, the paper calls for the use of adequate policy instruments to foster the development of this kind of technologies, with great potential for cost reduction but presently without commercial application because of lack of incentives.

     

Valuing power plant flexibility with CCS: the case of post-combustion capture retrofits

An important development in recent years has been increased interest in retrofitting CO₂ capture at existing power plants. In parallel, it has also been suggested that flexible operation of power plants with CO₂ capture could be important in at least some jurisdictions. It is likely that retrofitted power plants could have significant ??built-in?? flexibility, but this potential is often not considered in studies of the economic performance of power plants with CO₂ capture. This paper makes a contribution to filling this gap by developing methods for first order screening analysis of flexible operation of power plants with CO₂ capture and applying them to the case study example of an appropriately integrated retrofit of post-combustion capture at a coal-fired power plant. The quantitative analysis suggests that rich solvent storage could be an attractive option on a short-run basis for some fuel, CO₂ and electricity price combinations. Results from first order analysis can then be used to determine which operating modes should (and shouldn??t) be included in further, more detailed design studies.     

施用不同污泥堆肥品对土壤温室气体排放的影响

通过田间试验,分别施加两种不同的污泥堆肥品（A：含生物质炭堆肥品,B：不含生物质炭堆肥品）和不同施肥量,分析土壤CO₂、CH₄和N₂O动态变化特征和排放系数,研究施用污泥堆肥品对土壤温室气体排放的影响.结果表明,土壤CO₂和CH₄排放主要集中在生长期,生物质炭堆肥品低施用量能减少CO₂排放,而高施肥量增加CO₂排放.CH₄排放主要为负值,总体表现为土壤吸收CH₄,对照处理吸收量远高于其他处理（P<0.01）,A组处理CH₄吸收量随施肥量的增加而增加（P<0.05）.N₂O排放集中在发芽期和幼苗期,施肥量越高,排放量越大（P<0.01）.污泥堆肥品农用过程排放的温室气体主要是N₂O,施用A、B两种污泥堆肥品的土壤N₂O排放系数分别为1.02%~1.90%和1.28%~2.93%.生物质炭堆肥品具有显著的碳减排效果,其温室气体排放量比不含生物质炭堆肥品的土壤低19.49%~35.56%,且对于N₂O的减排效果较CH₄更为显著.     

Effects of elevated CO2 concentration and nitrogen supply on biomass and active carbon of freshwater marsh after two growing seasons in Sanjiang Plain, Northeast China

An experiments were carried out with treatments differing in nitrogen supply (0, 5 and 15 g N/m²) and CO₂ levels (350 and 700 μmol/mol) using OTC (open top chamber) equipment to investigate the biomass of Calamagrostis angustifolia and soil active carbon contents after two years. The results showed that elevated CO₂ concentration increased the biomass of C. angustifolia and the magnitude of response varied with each growth period. Elevated CO₂ concentration has increased aboveground biomass by 16.7% and 17.6% during the jointing and heading periods and only 3.5% and 9.4% during dough and maturity periods. The increases in belowground biomass due to CO₂ elevation was 26.5%, 34.0% and 28.7% during the heading, dough and maturity periods, respectively. The responses of biomass to enhanced CO₂ concentrations are differed in N levels. Both the increase of aboveground biomass and belowground biomass were greater under high level of N supply (15 g N/m²). Elevated CO₂ concentration also increased the allocation of biomass and carbon in root. Under elevated CO₂ concentration, the average values of active carbon tended to increase. The increases of soil active soil contents followed the sequence of microbial biomass carbon (10.6%) > dissolved organic carbon (7.5%) > labile oxidable carbon (6.6%) > carbohydrate carbon (4.1%). Stepwise regressions indicated there were significant correlations between the soil active carbon contents and plant biomass. Particularly, microbial biomass carbon, labile oxidable carbon and carbohydrate carbon were found to be correlated with belowground biomass, while dissolved organic carbon has correlation with aboveground biomass. Therefore, increased biomass was regarded as the main driving force for the increase in soil active organic carbon under elevated CO₂ concentration.     

生物质炭与有机物料混施对土壤温室气体排放和微生物活性的影响

土壤是温室气体的重要排放源,在土壤中施入生物质炭和有机物料对土壤微生物在土壤碳氮转化和微量气体代谢方面有着重要作用,不过迄今在生物质炭和有机物料混施对土壤温室气体排放和微生物活性的影响方面的研究尚少.本研究采用室内培养试验,利用土壤添加生物质炭和生物质炭与不同有机物料混施,探究生物质炭和有机物料混施对土壤温室气体排放及微生物活性的影响.共设5个处理:新鲜土壤(S)、新鲜土壤+2%生物质炭(SB)、新鲜土壤+2%生物质炭+1%大豆饼(SBS)、新鲜土壤+2%生物质炭+1%小麦秸秆(SBW)、新鲜土壤+2%生物质炭+1%鸡粪(SBC).研究表明:只添加生物质炭对温室气体的排放影响不明显;生物质炭与有机物料混施使土壤的CO2、N2O排放明显增加,而对CH4的排放影响不明显;从温室气体增温潜势(GWP)变化可以看出有机物料施用对温室效应具有明显的增强作用;生物质炭与有机物料混施在一定程度上增加微生物生物量碳和代谢熵(q CO2),各处理的代谢熵是对照处理S的0.18~4.37倍;不同有机物料对FDA水解酶、过氧化氢酶、脲酶和碱性磷酸酶活性都表现为激活作用.     

The oxycoal process with cryogenic oxygen supply

Due to its large reserves, coal is expected to continue to play an important role in the future. However, specific and absolute CO₂ emissions are among the highest when burning coal for power generation. Therefore, the capture of CO₂ from power plants may contribute significantly in reducing global CO₂ emissions. This review deals with the oxyfuel process, where pure oxygen is used for burning coal, resulting in a flue gas with high CO₂ concentrations. After further conditioning, the highly concentrated CO₂ is compressed and transported in the liquid state to, for example, geological storages. The enormous oxygen demand is generated in an air-separation unit by a cryogenic process, which is the only available state-of-the-art technology. The generation of oxygen and the purification and liquefaction of the CO₂-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be lowered by 8 to 12 percentage points, corresponding to a 21 to 36% increase in fuel consumption. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both the fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the steam generator require a moderation of the temperatures during combustion and in the subsequent heat-transfer sections. This is done by means of flue gas recirculation. The interdependencies among fuel properties, the amount and the temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are investigated. Expected effects of the modified flue gas composition in comparison with the air-fired case are studied theoretically and experimentally. The different atmosphere resulting from oxygen-fired combustion gives rise to various questions related to firing, in particular, with regard to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or the deposits that form. In particular, detailed nitrogen and sulphur chemistry was investigated by combustion tests in a laboratory-scale facility. Oxidant staging, in order to reduce NO formation, turned out to work with similar effectiveness as for conventional air combustion. With regard to sulphur, a considerable increase in the SO₂ concentration was found, as expected. However, the H₂S concentration in the combustion atmosphere increased as well. Further results were achieved with a pilot-scale test facility, where acid dew points were measured and deposition probes were exposed to the combustion environment. Besides CO₂ and water vapour, the flue gas contains impurities like sulphur species, nitrogen oxides, argon, nitrogen, and oxygen. The CO₂ liquefaction is strongly affected by these impurities in terms of the auxiliary power requirement and the CO₂ capture rate. Furthermore, the impurity of the liquefied CO₂ is affected as well. Since the requirements on the liquid CO₂ with regard to geological storage or enhanced oil recovery are currently undefined, the effects of possible flue gas treatment and the design of the liquefaction plant are studied over a wide range.     

MgO-based adsorbents for CO2 adsorption: Influence of structural and textural properties on the CO2 adsorption performance

A series of MgO-based adsorbents were prepared through solution–combustion synthesis and ball-milling process.The prepared MgO-based powders were characterized using X-ray diffraction,scanning electron microscopy,N_2 physisorption measurements,and employed as potential adsorbents for CO_2 adsorption.The influence of structural and textural properties of these adsorbents over the CO_2 adsorption behaviour was also investigated.The results showed that MgO-based products prepared by solution–combustion and ball-milling processes,were highly porous,fluffy,nanocrystalline structures in nature,which are unique physico-chemical properties that significantly contribute to enhance their CO_2 adsorption.It was found that the MgO synthesized by solution combustion process,using a molar ratio of urea to magnesium nitrate(2:1),and treated by ball-milling during 2.5 hr(MgO-BM2.5h),exhibited the maximum CO_2 adsorption capacity of 1.611 mmol/g at 25℃ and 1 atm,mainly via chemisorption.The CO_2 adsorption behaviour on the MgO-based adsorbents was correlated to their improved specific surface area,total pore volume,pore size distribution and crystallinity.The reusability of synthesized MgO-BM2.5h was confirmed by five consecutive CO_2adsorption–desorption times,without any significant loss of performance,that supports the potential of MgO-based adsorbent.The results confirmed that the special features of MgO prepared by solution–combustion and treated by ball-milling during 2.5 hr are favorable to be used as effective MgO-based adsorbent in post-combustion CO_2 capture technologies.     

生物炭对塿土土壤温室气体及土壤理化性质的影响

通过田间小区试验,分别向塿土土壤中添加0、20、40、60、80 t·hm~(-2)的苹果果树枝条生物炭后,分析了生物炭对土壤温度、土壤团聚体、NO_3~--N、NH_4~+-N、微生物量碳以及土壤温室气体排放的影响.结果表明,生物炭可以缓解土壤温度的变化,增加土壤大团聚体的数量,尤其是5 mm、5~2 mm和1~0.5 mm的团聚体数量.与对照相比,随着生物炭施用量的增加,土壤NO_3~--N、NH_4~+-N、微生物量碳分别增加了4.9%~33.9%、9.1%~41.1%和11.8%~38.5%.本研究中生物炭对土壤温室气排放的影响主要表现为:添加生物炭后,土壤CO_2的排放量以及CH_4的吸收汇分别增加了6.73%~23.35%和3.62%~14.17%;施用20 t·hm~(-2)和40 t·hm~(-2)的生物炭降低了土壤N_2O的排放和综合增温潜势(GWP),而当生物炭施用量大于等于60 t·hm~(-2)时反而增加了土壤N_2O的排放和综合增温潜势(GWP).说明生物炭作为一种土壤改良剂和碳减排剂,能够改善土壤质量,提高土壤肥力,提高农田土壤增汇减排的作用,此外,选择合适的生物炭施用量至关重要.     

Simulation of a 100-MW solar-powered thermo-chemical air separation system combined with an oxy-fuel power plant for bio-energy with carbon capture and storage (BECCS)

The combination of concentrated solar power–chemical looping air separation (CSP-CLAS) with an oxy-fuel combustion process for carbon dioxide (CO₂) capture is a novel system to generate electricity from solar power and biomass while being able to store solar power efficiently. In this study, the computer program Advanced System for Process Engineering Plus (ASPEN Plus) was used to develop models to assess the process performance of such a process with manganese (Mn)-based oxygen carriers on alumina (Al₂O₃) support for a location in the region of Seville in Spain, using real solar beam irradiance and electricity demand data. It was shown that the utilisation of olive tree prunings (Olea europaea) as the fuel—an agricultural residue produced locally—results in negative CO₂ emissions (a net removal of CO₂ from the atmosphere). Furthermore, it was found that the process with an annual average electricity output of 18 MW would utilise 2.43% of Andalusia’s olive tree prunings, thereby capturing 260.5 k-tonnes of CO₂, annually. Drawbacks of the system are its relatively high complexity, a significant energy penalty in the CLAS process associated with the steam requirements for the loop-seal fluidisation, and the gas storage requirements. Nevertheless, the utilisation of agricultural residues is highly promising, and given the large quantities produced globally (~?4 billion tonnes/year), it is suggested that other novel processes tailored to these fuels should be investigated, under consideration of a future price on CO₂ emissions, integration potential with a likely electricity grid system, and based on the local conditions and real data.

     

秸秆生物炭对河套灌区膜下滴灌玉米农田生态系统碳足迹的影响

为探究生物炭对干旱地区膜下滴灌玉米农田生态系统温室气体排放和碳足迹的影响.设置不同施用量的生物炭处理［0（CK）、15（C15）、30（C30）和45 t ·hm^-2（C45）］,连续2 a监测覆膜滴灌条件下一次性施用秸秆生物炭后玉米农田生态系统土壤温室气体（CO₂、N₂O和CH₄）排放的季节变化及其综合增温潜势,利用生命周期评估法估算农业生产活动引起的碳排放量,并进行碳足迹的分析.施用生物炭当年的作物生长季土壤CO₂累积排放量比CK下降17.6%~24.7%,N₂O累积排放量下降71.1%~110.4%,综合增温潜势降低19.5%~25.9%.生物炭施用后第2 a作物生长季的CO₂累积排放量比CK减少19.2%~40.6%,N₂O累积排放量减少38.7%~46.7%,综合增温潜势减少19.7%~40.5%.连续2 a处理C15和C30均不同程度增加了CH₄累积吸收量,而处理C45显著降低了CH₄累积吸收量.C15和C45分别为生物炭施用当年和翌年单位产量碳足迹最少的处理,其单位产量碳足迹较CK分别降低10.1%和26.2%.土壤温室气体排放量对玉米农田生态系统碳足迹贡献率最大（38.1%~59.2%）,其次为氮肥生产（19.8%~33.4%）,而后为电能生产（6.7%~8.8%）和地膜覆盖（4.4%~7.4%）.生物炭对生态系统碳足迹贡献率为5.7%~13.8%.施用30 t ·hm^-2生物炭对农田生态系统减排固碳增产效果更好.改善生物炭制作工艺及运输途径、提高氮肥利用效率和发展节水节能灌溉技术,是减少旱区农田生态系统碳足迹的重要途径.     

Gaseous emissions from Canadian boreal forest fires

CO₂-normalized emission ratios (ΔX/ΔCO₂; V/V; where ΔX and ΔCO₂ = the enhancement of trace gas and CO₂, respectively, above background levels) for carbon monoxide (CO), hydrogen (H₂), methane (CH₄), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N₂O) were determined from smoke samples collected during low-altitude helicopter flights over two prescribed fires in northern Ontario, Canada. The emission ratios determined from these prescribed boreal forest fires are compared to emission ratios determined over two graminoid (grass) wetlands fires in central Florida and are found to be substantially higher (elevated levels of reduced gas production relative to CO₂) during all stages of combustion. These results argue strongly for the need to characterize biomass burning emissions from the major global vegetation/ecosystems in order to couple combustion emissions to their vegetation/ecosystem type. Such a process should improve the quality of any assessments of biomass burning impacts on atmospheric chemistry and climate.     

Prospects for carbon-neutral housing: the influence of greater wood use on the carbon footprint of a single-family residence

This paper examines the energy and carbon balance of two residential house alternatives; a typical wood frame home using more conventional materials (brick cladding, vinyl windows, asphalt shingles, and fibreglass insulation) and a similar wood frame house that also maximizes wood use throughout (cedar shingles and siding, wood windows, and cellulose insulation) in place of the more typical materials used – a wood-intensive house. Carbon emission and fossil fuel consumption balances were established for the two homes based on the cumulative total of three subsystems: (1) forest harvesting and regeneration; (2) cradle-to-gate product manufacturing, construction, and replacement effects over a 100-year service life; and (3) end-of-life effects – landfilling with methane capture and combustion or recovery of biomass for energy production.The net carbon balance of the wood-intensive house showed a complete offset of the manufacturing emissions by the credit given to the system for forest re-growth. Including landfill methane emissions, the wood-intensive life cycle yielded 20 tons of CO₂e emissions compared to 72 tons for the typical house. The wood-intensive home's life cycle also consumed only 45% of the fossil fuels used in the typical house.Diverting wood materials from the landfill at the end of life improved the life cycle balances of both the typical and wood-intensive houses. The carbon balance of the wood-intensive house was 5.2 tons of CO₂e permanently removed from the atmosphere (a net carbon sink) as compared to 63.4 of total CO₂e emissions for the typical house. Substitution of wood fuel for natural gas and coal in electricity production led to a net energy balance of the wood-intensive house that was nearly neutral, 87.1 GJ energy use, 88% lower than the scenario in which the materials were landfilled.Allocating biomass generation and carbon sequestration in the forest on an economic basis as opposed to a mass basis significantly improves the life cycle balances of both houses. Employing an economic allocation method to the forest leads to 3–5 times greater carbon sequestration and fossil fuel substitution attributable to the house, which is doubled in forestry regimes that remove stumps and slash as fuel. Thus, wood use has the potential to create a significantly negative carbon footprint for a house up to the point of occupancy and even offset a portion of heating and cooling energy use and carbon emissions; the wood-intensive house is energy and carbon neutral for 34–68 years in Ottawa and has the potential to be a net carbon sink and energy producer in a more temperate climate like San Francisco.     

Biochar addition to agricultural soil increased CH4 uptake and water holding capacity – Results from a short-term pilot field study

Biochar addition to agricultural soil has been suggested to mitigate climate change through increased biogenic carbon storage and reduction of greenhouse gas emissions. We measured the fluxes of N₂O, CO₂, and CH₄ after adding 9 t ha^?1 biochar on an agricultural soil in Southern Finland in May 2009. We conducted these measurements twice a week for 1.5 months, between sowing and canopy closure, to capture the period of highest N₂O emissions, where the potential for mitigation would also be highest. Biochar addition increased CH₄ uptake (96% increase in the average cumulative CH₄ uptake), but no statistically significant differences were observed in the CO₂ and N₂O emissions between the biochar amended and control plots. Added biochar increased soil water holding capacity by 11%. Further studies are needed to clarify whether this may help balance fluctuations in water availability to plants in the future climate with more frequent drought periods.     

Amine reclaiming technologies in post-combustion carbon dioxide capture

Amine scrubbing is the most developed technology for carbon dioxide (CO₂) capture. Degradation of amine solvents due to the presence of high levels of oxygen and other impurities in flue gas causes increasing costs and deterioration in long term performance, and therefore purification of the solvents is needed to overcome these problems. This review presents the reclaiming of amine solvents used for post combustion CO₂ capture (PCC). Thermal reclaiming, ion exchange, and electrodialysis, although principally developed for sour gas sweetening, have also been tested for CO₂ capture from flue gas. The three technologies all have their strengths and weaknesses, and further development is needed to reduce energy usage and costs. An expected future trend for amine reclamation is to focus on process integration of the current reclaiming technologies into the PCC process in order to drive down costs.     

Breakthrough CO2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO₂ adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO₂ activation and Potassium hydroxide (KOH) activation. CO₂ adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25–65°C and inlet CO₂ concentration range of 10–30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N₂ and CO₂ adsorption at 77 and 273 K, respectively. Central composite design was used to evaluate the combined effects of temperature and concentration of CO₂ on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm³/g and surface area of 1400 m²/g had the highest CO₂ adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO₂ and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO₂ activated carbons remained remarkably stable after 50 cycles with low temperature (160°C) regeneration.