Environmental assessment of German electricity generation from coal-fired power plants with amine-based carbon capture

Background, aim, and scope  

One of the most important sources of global carbon dioxide emissions is the combustion of fossil fuels for power generation. Power plants contribute more than 40% of the worldwide anthropogenic CO₂ emissions. Therefore, the increased requirements for climate protection are a great challenge for the power producers. In this context a significant increase in power plant efficiency will contribute to reduce specific CO₂ emissions. Additionally, CO₂ capture and storage (CCS) is receiving considerable attention as a greenhouse gas (GHG) mitigation option. CCS allows continued use of fossil fuels with no or little CO₂ emissions given to the atmosphere. This could approve a moderate transition to a low-carbon energy generation over the next decades. Currently, R&D activities in the field of CCS are mainly concentrated on the development of capture techniques, the geological assessment of CO₂ storage reservoirs, and on economic aspects. Although first studies on material and energy flows caused by CCS are available, a broader environmental analysis is necessary to show the overall environmental impacts of CCS. The objectives in this paper are coal-based power plants with and without CO₂ capture via mono-ethanolamine (MEA) and the comparison of their environmental effects based on life cycle assessment methodology (LCA).     

Maximum impacts of future reforestation or deforestation on atmospheric CO2

There is scope for land‐use changes to increase or decrease CO₂ concentrations in the atmosphere over the next century. Here we make simple but robust calculations of the maximum impact of such changes. Historical land‐use changes (mostly deforestation) and fossil fuel emissions have caused an increase in atmospheric concentration of CO₂ of 90 ppm between the pre‐industrial era and year 2000. The projected range of CO₂ concentrations in 2100, under a range of emissions scenarios developed for the IPCC, is 170–600 ppm above 2000 levels. This range is mostly due to different assumptions regarding fossil fuel emissions. If all of the carbon so far released by land‐use changes could be restored to the terrestrial biosphere, atmospheric CO₂ concentration at the end of the century would be about 40–70 ppm less than it would be if no such intervention had occurred. Conversely, complete global deforestation over the same time frame would increase atmospheric concentrations by about 130–290 ppm. These are extreme assumptions; the maximum feasible reforestation and afforestation activities over the next 50 years would result in a reduction in CO₂ concentration of about 15–30 ppm by the end of the century. Thus the time course of fossil fuel emissions will be the major factor in determining atmospheric CO₂ concentrations for the foreseeable future.     

Diverting residual biomass to energy use: Quantifying the global warming potential of biogenic CO2 (GWPbCO2)

To calculate the global warming potential of biogenic carbon dioxide emissions (GWP_bCO2) associated with diverting residual biomass to bioenergy use, the decay of annual biogenic carbon pulses into the atmosphere over 100 years was compared between biomass use for energy and its business-as-usual decomposition in agricultural, forestry, or landfill sites. Bioenergy use increased atmospheric CO₂ load in all cases, resulting in a ¹⁰⁰GWP_bCO2 (units of g CO₂e/g biomass CO₂ released) of 0.003 for the fast-decomposing agricultural residues to 0.029 for the slow, 0.084–0.625 for forest residues, and 0.368–0.975 for landfill lignocellulosic biomass. In comparison, carbon emissions from fossil fuels have a ¹⁰⁰GWP of 1.0 g (CO₂e/g fossil CO₂). The fast decomposition rate and the corresponding low ¹⁰⁰GWP_bCO2 values of agricultural residues make them a more climate-friendly feedstock for bioenergy production relative to forest residues and landfill lignocellulosic biomass. This study shows that CO₂ released from the combustion of bioenergy or biofuels made from residual biomass has a greenhouse gas footprint that should be considered in assessing climate impacts.     

Carbon dioxide fixation by Chlorella kessleri, C. vulgaris, Scenedesmus obliquus and Spirulina sp. cultivated in flasks and vertical tubular photobioreactors

CO₂ at different concentrations were added to cultures of the eukaryotic microalgae, Chlorella kessleri, C. vulgaris and Scenedesmus obliquus, and the prokaryotic cyanobacterium, Spirulina sp., growing in flasks and in a photobioreactor. In each case, the best kinetics and carbon fixation rate were with a vertical tubular photobioreactor. Overall, Spirulina sp. had the highest rates. Spirulina sp., Sc. obliquus and C. vulgaris could grow with up to 18% CO₂.     

<Emphasis Type="Italic">Tetraselmis suecica</Emphasis> culture for CO<Subscript>2</Subscript> bioremediation of untreated flue gas from a coal-fired power station

The accumulation of atmospheric CO₂, primarily due to combustion of fossil fuels, has been implicated in potential global climate change. The high rate of CO₂ bioremediation by microalgae has emerged as a favourable method for reducing coal-fired power plant emissions. However, coal-fired power station flue gas contains other chemicals such as SO_x which can inhibit microalgal growth. In the current study, the effect of untreated flue gas as a source of inorganic carbon on the growth of Tetraselmis in a 1000 L industrial-scale split-cylinder internal-loop airlift photobioreactor was examined. The culture medium was recycled after each harvest. Tetraselmis suecica grew very well in this airlift photobioreactor during the 7-month experiment using recycled medium from an electroflocculation harvesting unit. Increased medium SO₄ ^2? concentration as high as 870 mg SO₄ ^2??L^?1 due to flue gas addition and media recycling had no negative effect on the overall growth and productivity of this alga. The potential organic biomass productivity and carbon sequestration using an industrial-scale airlift PBR at International Power Hazelwood, Gippsland, Victoria, Australia, are 178.9?±?30 mg L^?1 day^?1 and 89.15?±?20 mg?‘C’?L^?1 day^?1, respectively. This study clearly indicates the potential of growing Tetraselmis on untreated flue gas and using recycled medium for the purpose of biofuel and CO₂ bioremediation.     

A comparison of the global warming effects of wood fuels and fossil fuels taking albedo into account

Traditionally, wood fuels, like other bioenergy sources, have been considered carbon neutral because the amount of CO₂ released can be offset by CO₂ sequestration due to the regrowth of the biomass. Thus, until recently, most studies assigned a global warming potential (GWP) of zero to CO₂ generated by the combustion of biomass (biogenic CO₂). Moreover, emissions of biogenic CO₂ are usually not included in carbon tax and emissions trading schemes. However, there is now increasing awareness of the inadequacy of this way of treating bioenergy, especially bioenergy from boreal forests. Holtsmark (2014) recently quantified the GWP of biogenic CO₂ from slow‐growing forests (GWP_bio), finding it to be significantly higher than the GWP of fossil CO₂ when a 100 year time horizon was applied. Hence, the climate impact seems to be even higher for the combustion of slow‐growing biomass than for the combustion of fossil carbon in a 100 year timeframe. The present study extends the analysis of Holtsmark (2014) in three ways. First, it includes the cooling effects of increased surface reflectivity after harvest (albedo). Second, it includes a comparison with the potential warming impact of fossil fuels, taking the CO₂ emissions per unit of energy produced into account. Third, the study links the literature estimating GWP_bio and the literature dealing with the carbon debt, and model simulations estimating the payback time of the carbon debt are presented. The conclusion is that, also after these extensions of the analysis, bioenergy from slow‐growing forests usually has a larger climate impact in a 100 year timeframe than fossil oil and gas. Whether bioenergy performs better or worse than coal depends on a number of conditions.     

Terrestrial fluxes of carbon in GCP carbon budgets

The Global Carbon Project (GCP) has published global carbon budgets annually since 2007 (Canadell et al. [2007], Proc Natl Acad Sci USA, 104, 18866–18870; Raupach et al. [2007], Proc Natl Acad Sci USA, 104, 10288–10293). There are many scientists involved, but the terrestrial fluxes that appear in the budgets are not well understood by ecologists and biogeochemists outside of that community. The purpose of this paper is to make the terrestrial fluxes of carbon in those budgets more accessible to a broader community. The GCP budget is composed of annual perturbations from pre‐industrial conditions, driven by addition of carbon to the system from combustion of fossil fuels and by transfers of carbon from land to the atmosphere as a result of land use. The budget includes a term for each of the major fluxes of carbon (fossil fuels, oceans, land) as well as the rate of carbon accumulation in the atmosphere. Land is represented by two terms: one resulting from direct anthropogenic effects (Land Use, Land‐Use Change, and Forestry or land management) and one resulting from indirect anthropogenic (e.g., CO₂, climate change) and natural effects. Each of these two net terrestrial fluxes of carbon, in turn, is composed of opposing gross emissions and removals (e.g., deforestation and forest regrowth). Although the GCP budgets have focused on the two net terrestrial fluxes, they have paid little attention to the gross components, which are important for a number of reasons, including understanding the potential for land management to remove CO₂ from the atmosphere and understanding the processes responsible for the sink for carbon on land. In contrast to the net fluxes of carbon, which are constrained by the global carbon budget, the gross fluxes are largely unconstrained, suggesting that there is more uncertainty than commonly believed about how terrestrial carbon emissions will respond to future fossil fuel emissions and a changing climate.     

The air‐lift photobioreactors with flow patterning for high‐density cultures of microalgae and carbon dioxide removal

A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO₂) into biomass. Using a microalgal photobioreactor as a CO₂ mitigation system is a practical approach to the problem of CO₂ emission from waste gas. In this study, a marine microalga, Chlorella sp. NCTU‐2, was applied to assess biomass production and CO₂ removal. Three types of photobioreactors were designed and used: (i) without inner column (i.e. a bubble column), (ii) with a centric‐tube column and (iii) with a porous centric‐tube column. The specific growth rates (μ) of the batch cultures in the bubble column, the centric‐tube and the porous centric‐tube photobioreactor were 0.180, 0.226 and 0.252 day^?1, respectively. The porous centric‐tube photobioreactor, operated in semicontinuous culture mode with 10% CO₂ aeration, was evaluated. The results show that the maximum biomass productivity was 0.61 g/L when one fourth of the culture broth was recovered every 2 days. The CO₂ removal efficiency was also determined by measuring the influent and effluent loads at different aeration rates and cell densities of Chlorella sp. NCTU‐2. The results show that the CO₂ removal efficiency was related to biomass concentration and aeration rate. The maximum CO₂ removal efficiency of the Chlorella sp. NCTU‐2 culture was 63% when the biomass was maintained at 5.15 g/L concentration and 0.125 vvm aeration (volume gas per volume broth per min; 10% CO₂ in the aeration gas) in the porous centric‐tube photobioreactor.     

The time aspect of bioenergy – climate impacts of solid biofuels due to carbon dynamics

The climate impacts from bioenergy involve an important time aspect. Using forest residues for energy may result in high initial emissions, but net emissions are reduced over time since, if the residues were left on the ground, they would decompose and release CO₂ to the atmosphere. This article investigates the climate impacts from bioenergy with special focus on the time aspects. More specifically, we analyze the climate impacts of forest residues and stumps where combustion related emissions are compensated by avoided emissions from leaving them on the ground to decompose. These biofuels are compared with fossil gas and coal. Net emissions are defined as emissions from utilizing the fuel minus emissions from a reference case of no utilization. Climate impacts are estimated using the measures radiative forcing and global average surface temperature. We find that the climate impacts from using forest residues and stumps depend on the decomposition rates and the time perspective over which the analysis is done. Over a 100 year perspective, branches and tops have lower climate impacts than stumps which in turn have lower impacts than fossil gas and coal. Over a 20 year time perspective, branches and tops have lower climate impacts than all other fuels but the relative difference is smaller. However, stumps have slightly higher climate impacts over 20 years than fossil gas but lower impacts than coal. Regarding metrics for climate impacts, over shorter time scales, approximately 30 years or less, radiative forcing overestimates the climate impacts compared with impacts expressed by global surface temperature change, which is due to the inertia of the climate system. We also find that establishing willow on earlier crop land may reduce atmospheric CO₂, provided new land is available. However, these results are inconclusive since we haven't considered the effects of producing the agricultural crops elsewhere.     

Elevated CO2-mediated plant VOCs change aggravates invasive thrips occurrence by altering their host-selection behaviour

Globally rising atmosphere CO₂ has been predicted to affect the emission of plant volatile organic compounds (VOCs) and the interaction with insect herbivores. CO₂-mediated plant VOCs change might contribute to develop effective management strategies for insect pests by using VOCs related biological control methods. In this study, we analysed the effect of elevated CO₂ on the host-selection behaviour of western flower thrips (Frankliniella occidentalis) and studied how they were affected by the release of VOCs from kidney bean plants (Phaseolus vulgaris). A four-chamber olfactometer was used to quantify the host-selection of F. occidentalis for P. vulgaris. Elevated CO₂ increased F. occidentalis' selection for P. vulgaris wounded by mechanical damage (MD) and thrips infestation (TI) that might via regulating the gene expression of CSP1, CSP1-q, OBP1 and OBP1-q in F. occidentalis. Besides, we cultivated kidney beans at ambient CO₂ (400 ppm) and elevated CO₂ (800 ppm), and quantified the emission of plant VOCs by using GC-MS. Thirty VOCs belonging to ten chemical groups were identified from P. vulgaris, including aromatic hydrocarbons, ethers, alkanes, cycloalkanes, alcohols, alkenes, aromatic derivatives, phenols, ketones and esters. Furthermore, six VOCs from P. vulgaris were significantly affected by CO₂ level, wounding way and the interaction between them, including ethyl benzene, 1,3-dimethyl benzene, 1,3-dimethyl-4-ethyl benzene, (E,E,E,E)-squalene, 2,6-ditert-butyl-4-methyl phenol and dioctyl phthalate. Our study indicates that elevated CO₂ might increase the host-selection of F. occidentalis for wounded P. vulgaris due to the changed plant VOCs.     

The effects of glacial atmospheric CO2 concentrations and climate on isoprene emissions by vascular plants

Isoprene (C₅H₈) emissions by terrestrial vegetation vary with temperature and light intensity, and play an important role in biosphere–chemistry–climate interactions. Such interactions were probably substantially modified by Pleistocene climate and CO₂ cycles. Central to understanding the nature of these modifications is assessment and analysis of how emissions changed under glacial environmental conditions. Currently, even the net direction of change is difficult to predict because a CO₂‐depleted atmosphere may have stimulated emissions compensating for the negative impacts of a cooler climate. Here, we address this issue and attempt to determine the direction of change from an experimental standpoint by investigating the interaction between isoprene emissions and plant growth of two known isoprene‐emitting herbaceous species (Mucuna pruriens and Arundo donax) grown at glacial (180 ppm) to present (366 ppm) CO₂ levels. We found a significant enhancement of isoprene emissions per unit leaf area in M. pruriens under subambient CO₂ concentrations relative to ambient controls but not for A. donax. In contrast, canopy emissions remained unaltered for both plant species because enhanced leaf emissions were offset by reductions in biomass and leaf area. Separate growth experiments with M. pruriens revealed that lowering day/night temperatures by 5°C decreased canopy isoprene emissions irrespective of the CO₂ level. Incorporation of these results into a simple canopy emissions model highlights their potential to attenuate reductions in the total isoprene flux from forests under glacial conditions predicted by standard models.     

Can biochar reduce soil greenhouse gas emissions from a Miscanthus bioenergy crop?

Energy production from bioenergy crops may significantly reduce greenhouse gas (GHG) emissions through substitution of fossil fuels. Biochar amendment to soil may further decrease the net climate forcing of bioenergy crop production, however, this has not yet been assessed under field conditions. Significant suppression of soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions following biochar amendment has been demonstrated in short‐term laboratory incubations by a number of authors, yet evidence from long‐term field trials has been contradictory. This study investigated whether biochar amendment could suppress soil GHG emissions under field and controlled conditions in a Miscanthus × Giganteus crop and whether suppression would be sustained during the first 2 years following amendment. In the field, biochar amendment suppressed soil CO₂ emissions by 33% and annual net soil CO₂ equivalent (eq.) emissions (CO₂, N₂O and methane, CH₄) by 37% over 2 years. In the laboratory, under controlled temperature and equalised gravimetric water content, biochar amendment suppressed soil CO₂ emissions by 53% and net soil CO₂ eq. emissions by 55%. Soil N₂O emissions were not significantly suppressed with biochar amendment, although they were generally low. Soil CH₄ fluxes were below minimum detectable limits in both experiments. These findings demonstrate that biochar amendment has the potential to suppress net soil CO₂ eq. emissions in bioenergy crop systems for up to 2 years after addition, primarily through reduced CO₂ emissions. Suppression of soil CO₂ emissions may be due to a combined effect of reduced enzymatic activity, the increased carbon‐use efficiency from the co‐location of soil microbes, soil organic matter and nutrients and the precipitation of CO₂ onto the biochar surface. We conclude that hardwood biochar has the potential to improve the GHG balance of bioenergy crops through reductions in net soil CO₂ eq. emissions.     

Indirect carbon dioxide emissions from producing bioenergy from forest harvest residues

Forest harvest residues are important raw materials for bioenergy in regions practicing forestry. Removing these residues from a harvest site reduces the carbon stock of the forest compared with conventional stem‐only harvest because less litter in left on the site. The indirect carbon dioxide (CO₂) emission from producing bioenergy occur when carbon in the logging residues is emitted into the atmosphere at once through combustion, instead of being released little by little as a result of decomposition at the harvest sites. In this study (1) we introduce an approach to calculate this indirect emission from using logging residues for bioenergy production, and (2) estimate this emission at a typical target of harvest residue removal, i.e. boreal Norway spruce forest in Finland. The removal of stumps caused a larger indirect emission per unit of energy produced than the removal of branches because of a lower decomposition rate of the stumps. The indirect emission per unit of energy produced decreased with time since starting to collect the harvest residues as a result of decomposition at older harvest sites. During the 100 years of conducting this practice, the indirect emission from average‐sized branches (diameter 2 cm) decreased from 340 to 70 kg CO₂ eq. MWh^?1 and that from stumps (diameter 26 cm) from 340 to 160 kg CO₂ eq. MWh^?1. These emissions are an order of magnitude larger than the other emissions (collecting, transporting, etc.) from the bioenergy production chain. When the bioenergy production was started, the total emissions were comparable to fossil fuels. The practice had to be carried out for 22 (stumps) or four (branches) years until the total emissions dropped below the emissions of natural gas. Our results emphasize the importance of accounting for land‐use‐related indirect emissions to correctly estimate the efficiency of bioenergy in reducing CO₂ emission into the atmosphere.     

Utilization of the cyanobacteria Anabaena sp. CH1 in biological carbon dioxide mitigation processes

Before switching totally to alternative fuel stage, CO₂ mitigation process has considered a transitional strategy for combustion of fossil fuels inevitably. In comparison to other CO₂ mitigation options, such as oceanic or geologic injection, the biological photosynthetic process would present a far superior and sustainable solution under both environmental and social considerations. The utilization of the cyanobacteria Anabaena sp. CH1 in carbon dioxide mitigation processes is analyzed in our research. It was found that an original developed photobioreactor with internal light source exhibits high light utilization. Anabaena sp. CH1 demonstrates excellent CO₂ tolerance even at 15% CO₂ level. This enables flue gas from power plant to be directly introduced to Anabaena sp. CH1 culture. Double light intensity and increased 47% CO₂ bubble retention time could enhance CO₂ removal efficiencies by 79% and 67%, respectively. A maximum CO₂ fixation rate of 1.01 g CO₂ L⁻¹ day⁻¹ was measured experimentally.     

Carbon dioxide biofixation by Chlorella vulgaris at different CO2 concentrations and light intensities

In order to develop an effective CO₂ mitigation process using microalgae for potential industrial application, the growth and physiological activity of Chlorella vulgaris in photobioreactor cultures were studied. C. vulgaris was grown at two CO₂ concentrations (2 and 13% of CO₂ v/v) and at three incident light intensities (50, 120 and 180 μmol m^?2 s^?1) for 9 days. The measured specific growth rate was similar under all conditions tested but an increase in light intensity and CO₂ concentration affected the biomass and cell concentrations. Although carbon limitation was observed at 2% CO₂, similar cellular composition was measured in both conditions. Light limitation induced a net change in the growth behavior of C. vulgaris. Nitrogen limitation seemed to decrease the nitrogen quota of the cells and rise the intracellular carbon:nitrogen ratio. Exopolysaccharide production per cell appeared to be affected by light intensity. In order to avoid underestimation of the CO₂ biofixation rate of the microalgae, exopolysaccharide production was taken into account. The maximum CO₂ removal rate (0.98 g CO₂ L^?1 d^?1) and the highest biomass concentration (4.14 g DW L^?1) were determined at 13% (v/v) CO₂ and 180 μmol m^?2 s^?1. Our results show that C. vulgaris has a real potential for industrial CO₂ remediation.     

The Greenhouse Gas Balance of a Dairy Farm as Influenced by the Uptake of Biogas Production

The production of energy crops for farm-scale anaerobic digestion (AD) can affect emissions of greenhouse gases (GHG) in a number of ways. Some examples are: fugitive CH₄ emissions from the digester and the storage of the digestate, emissions of N₂O from soil and emissions of CO₂ from farm machinery. Moreover, uptake of AD may be accompanied by changes in the way the farm is operated, which may affect GHG emissions. The scale of these emissions was assessed from published data for the biogas feedstocks cattle slurry and grass silage. Emissions were compared to references representing current farm operation and energy generation by fossil fuels. Feeding the digester with cattle slurry for the entire year did not result in reduced emissions due to relatively high emissions from stored raw slurry in summer. If grass was used for digester feedstock, the level of N₂O emissions from the crop was the most important factor for the GHG balance of farm-scale AD. If N₂O emissions were low, biogas realised substantial savings of GHG in the order of 1 t CO₂ equivalents per hectare per year. At a high level of N₂O emissions, energy cropping might even result in increased GHG emissions compared to fossil fuels.     

Carbon balance indicator for forest bioenergy scenarios

A carbon (C) balance indicator is presented for the evaluation of forest bioenergy scenarios as a means to reduce greenhouse gas (GHG) emissions. A bioenergy‐intensive scenario with a greater harvest is compared to a baseline scenario. The relative carbon indicator (RC) is defined as the ratio between the difference in terrestrial C stocks – that is the C debt – and the difference in cumulative bioenergy harvest between the scenarios, over a selected time frame T. A value of zero indicates no C debt from additional biomass harvests, while a value of one indicates a C debt equal to the amount of additionally harvested biomass C. Multiplying the RC indicator by the smokestack emission factor of biomass (approximately 110 t CO₂/TJ) provides the net cumulative CO₂ emission factor of the biomass combustion as a function of T, allowing a direct comparison with the emission factors of comparable fossil fuels. The indicator is applied to bioenergy cases in Finland, where typically the rotation length of managed forests is long and the decay rate of harvest residues is slow. The country‐level examples illustrate that although Finnish forests remain as a C sink in each of the considered scenarios, the efforts of increasing forest bioenergy may still increase the atmospheric CO₂ concentrations in comparison with the baseline scenario and use of fossil fuels. The results also show that the net emission factor depends – besides on forest‐growth or residue‐decay dynamics – on the timing and evolution of harvests as well. Unlike for the constant fossil C emission factor, the temporal profile of bioenergy use is of great importance for the net emission factor of biomass.     

Simultaneous flue gas bioremediation and reduction of microalgal biomass production costs

A flue gas originating from a municipal waste incinerator was used as a source of CO₂ for the cultivation of the microalga Chlorella vulgaris, in order to decrease the biomass production costs and to bioremediate CO₂ simultaneously. The utilization of the flue gas containing 10–13% (v/v) CO₂ and 8–10% (v/v) O₂ for the photobioreactor agitation and CO₂ supply was proven to be convenient. The growth rate of algal cultures on the flue gas was even higher when compared with the control culture supplied by a mixture of pure CO₂ and air (11% (v/v) CO₂). Correspondingly, the CO₂ fixation rate was also higher when using the flue gas (4.4 g CO₂ l⁻¹ 24 h⁻¹) than using the control gas (3.0 g CO₂ l⁻¹ 24 h⁻¹). The toxicological analysis of the biomass produced using untreated flue gas showed only a slight excess of mercury while all the other compounds (other heavy metals, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and dibenzofurans, and polychlorinated biphenyls) were below the limits required by the European Union foodstuff legislation. Fortunately, extending the flue gas treatment prior to the cultivation unit by a simple granulated activated carbon column led to an efficient absorption of gaseous mercury and to the algal biomass composition compliant with all the foodstuff legislation requirements.     

Effect of Change of Forest Carbon Storage on Net Carbon Dioxide Balance of Wood Use for Energy in Japan

This study analyzed the net carbon dioxide (CO₂) emission reductions between 2005 and 2050 by using wood for energy under various scenarios of forest management and energy conversion technology in Japan, considering both CO₂ emission reductions from replacement of fossil fuels and changes in carbon storage in forests. According to our model, wood production for energy results in a significant reduction of carbon storage levels in forests (by 46% to 77% in 2050 from the 2005 level). Thus, the net CO₂ emission reduction when wood is used for energy becomes drastically smaller. Conventional tree production for energy increases net CO₂ emissions relative to preserving forests, but fast‐growing tree production may reduce net CO₂ emissions more than preserving forests does. When wood from fast‐growing trees is used to generate electricity with gas turbines, displacing natural gas, the net CO₂ emission reduction from the combination of fast‐growing trees and electricity generation with gas turbines is about 58% of the CO₂ emission reduction from electricity generation from gas turbines alone in 2050, and an energy conversion efficiency of around 20% or more is required to obtain net reductions over the entire period until 2050. When wood is used to produce bioethanol, displacing gasoline, net reductions are realized after 2030, provided that heat energy is recovered from residues from ethanol production. These results show the importance of considering the change in carbon storage when estimating the net CO₂ emission reduction effect of the wood use for energy.     

Life cycle inventory for electricity generation in China

Background, Goal and Scope The objective of this study was to produce detailed a life cycle inventory (LCI) for the provision of 1 kWh of electricity to consumers in China in 2002 in order to identify areas of improvement in the industry. The system boundaries were processes in power stations, and the construction and operation of infrastructure were not included. The scope of this study was the consumption of fossil fuels and the emissions of air pollutants, water pollutants and solid wastes, which are listed as follows: (1) consumption of fossil fuels, including general fuels, such as raw coal, crude oil and natural gas, and the uranium used for nuclear power; (2) emissions of air pollutants from thermal power, hydropower and nuclear power plants; (3) emissions of water pollutants, including general water waste from fuel electric plants and radioactive waste fluid from nuclear power plants; (4) emissions of solid wastes, including fly ash and slag from thermal power plants and radioactive solid wastes from nuclear power plants. Methods Data were collected regarding the amount of fuel, properties of fuel and the technical parameters of the power plants. The emissions of CO₂, SO₂, NO_x, CH₄, CO, non-methane volatile organic compound (NMVOC), dust and heavy metals (As, Cd, Cr, Hg, Ni, Pb, V, Zn) from thermal power plants as well as fuel production and distribution were estimated. The emissions of CO₂ and CH₄ from hydropower plants and radioactive emissions from nuclear power plants were also investigated. Finally, the life cycle inventory for China’s electricity industry was calculated and analyzed. Results Related to 1 kWh of usable electricity in China in 2002, the consumption of coal, oil, gas and enriched uranium were 4.57E-01, 8.88E-03, 7.95E-03 and 9.03E-08 kg; the emissions of CO₂, SO₂, NO_x, CO, CH₄, NMVOC, dust, As, Cd, Cr, Hg, Ni, Pb, V, and Zn were 8.77E-01, 8.04E-03, 5.23E-03, 1.25E-03, 2.65E-03, 3.95E-04, 1.63E-02, 1.62E-06, 1.03E-08, 1.37E-07, 7.11E-08, 2.03E-07, 1.42E-06, 2.33E-06, and 1.94E-06 kg; the emissions of waste water, COD, coal fly ash, and slag were 1.31, 6.02E-05, 8.34E-02, and 1.87E-02 kg; and the emissions of inactive gas, halogen and gasoloid, tritium, non-tritium, and radioactive solid waste were 3.74E+01 Bq, 1.61E-01 Bq, 4.22E+01 Bq, 4.06E-02 Bq, and 2.68E-10 m³ respectively. Conclusions The comparison result between the LCI data of China’s electricity industry and that of Japan showed that most emission intensities of China’s electricity industry were higher than that of Japan except for NMVOC. Compared with emission intensities of the electricity industry in Japan, the emission intensities of CO₂ and Ni in China were about double; the emission intensities of NO_x, Cd, CO, Cr, Hg and SO₂ in China were more than 10 times that of Japan; and the emission intensities of CH₄, V, Pb, Zn, As and dust were more than 20 times. The reasons for such disparities were also analyzed. Recommendations and Perspectives To get better LCI for the electricity industry in China, it is important to estimate the life cycle emissions during fuel production and transportation for China. Another future improvement could be the development of LCIs for construction and operation of infrastructure such as factory buildings and dams. It would also be important to add the information about land use for hydropower.