Integrating mid-temperature solar heat and post-combustion CO2-capture in a coal-fired power plant

This article proposed a hybrid power system combining mid-temperature solar heat and a coal-fired power plant for CO₂ capture. In this system, solar heat at around 300 °C replaces the high-quality steam extractions of the Rankine cycle to heat the feed water, so the steam that was to be extracted can expand efficiently in the high-pressure turbines. In this hybrid system, the CO₂ capture penalty is completely compensated for by the enhanced work output contributed by the solar heat. The annual solar field cost is reduced to 10.8 $/ton-CO₂, compared to 25.8 $/ton-CO₂ in a system with solar heat for direct solvent regeneration. Additionally, the mid-temperature solar heat is converted into work with an improved efficiency of 27%. Thus, this system offers a promising approach to reduce the CO₂ capture penalty in CCS with attractive cost-effective utilization of mid-temperature solar heat.     

Quantitative analysis of potential power production and environmental benefits of Biomass Integrated Gasification Combined Cycles in the European Union

Biomass Integrated Gasification Combined Cycles (BioIGCC) are a promising technology, alternative to fossil fuels for power generation. Significant reduction of CO₂ emissions could be achieved, although important changes in the gas turbines and gasifiers design and further technological development would be necessary. The aim of this work is to study quantitatively the benefits of using BioIGCC plants instead of fossil fuel technologies, in terms of power supply and CO₂ emission avoidance, including the study of pre-combustion CO₂ capture. Different biomass substrates are analysed and compared and the required land use in each case and for different scenarios is also studied and quantified. The power generation and greenhouse gas emission avoidance potential of BioIGCC technology in Europe is also studied and the viability of this technology in different circumstances is discussed. In several cases BioIGCC plants are found to be viable from the point of view of availability of biomass resources and the cost of the produced kWh. In the whole EU-27 the potential hovers around 30 GW and a reduction of nearly 4% of the total EU emissions in 2009 in a conservative scenario, and up to 100 GW and 15% of emission reduction in a more optimistic one.     

Membrane processes for post-combustion carbon dioxide capture: A parametric study

Much of the research in the area of carbon dioxide recovery and storage focuses on minimizing the energy required for CO₂ capture, as this step corresponds to the major cost contribution of the overall process (capture, transportation, injection). Out of the three traditional methods of CO₂ capture (absorption, adsorption and membrane processes), absorption is considered to be the best available technology for post-combustion application. However, amine absorption requires 4–6 GJ/tonne of recovered CO₂, in a large part due to significant energy consumption associated with the regeneration step.In this paper, we perform a systematic analysis of the separation performances and associated energy cost of a single-stage membrane module. First, the operational limits are identified in terms of permeate composition and CO₂ recovery ratio via a systematic parametric study for CO₂/N₂ mixtures. The energy consumption of the capture step is then evaluated and compared with the performance of amine absorption. Next, the search for an optimal strategy in terms of compression energy for a combination of membrane capture and CO₂ injection has been addressed. The results allow the identification of an optimal membrane pressure ratio for a given set of conditions.     

China's 2020 carbon intensity target: Consistency,implementations, and policy implications

China has pledged to reduce its CO₂ emissions per unit of GDP by 40–45% by 2020 as of 2005 level. This research examines China's 2020 carbon intensity target and its interdependence with the overarching national economic and social development goals. The results show that, with annual GDP growth rate at 7% during the 12th Five-Year-Plan (FYP) period and 6% during the 13th FYP period, the 45% CO₂ intensity reduction target implies annual CO₂ emissions of 8600 million tonnes by 2020, close to 8400 million tonnes, the UNFCCC 450 ppm scenario for China. However, achieving only the 40% reduction target will lead to 9380 million tonnes CO₂ emissions in 2020 which largely surpass the UNFCCC 450 ppm scenario. We conclude that China's 45% CO₂ intensity reduction target is not only within international expectations but also self-consistent with its overall economic and social development strategy. Then primary energy and power planning for implementing the 45% carbon intensity reduction target is proposed. Related investment requirements are also estimated. To achieve the target, China needs to restructure the economic structure for significant improvements in energy conservation.     

CO2 emission and avoidance in mobile applications

The present paper analyzes the CO₂ emissions from mobile communications and portable wireless electronic devices in the Korea environment. The quantitative and qualitative contributions to CO₂ emission reduction of the substitution of renewable energy for traditional electricity as the power supply in these devices are also investigated.Firstly, the national CO₂ emission coefficient is temporarily estimated as 0.504 tCO₂/MWh, which can be regarded as the basis for calculating CO₂ emissions in mobile devices. The total annual CO₂ emissions from mobile devices is calculated as approximately 1.4 million tons, comprising 0.3 million tCO₂ for portable wireless electronic devices and 1.1 million tCO₂ for electric equipment required for mobile communication service.If renewable energy sources are substituted for traditional electricity sources in the supply for mobile devices, solar cell and wind turbine systems can reduce CO₂ emissions by about 87% and 97%, respectively. However, the use of fuel cell systems will only slightly reduce the CO₂ emissions. However, the use of the direct methanol fuel cell system can release 8% more CO₂ emissions than that emitted by using traditional electricity sources.     

Decarbonized hydrogen and electricity from natural gas

This paper discusses configuration, attainable performances and thermodynamic features of stand-alone plants for the co-production of de-carbonized hydrogen and electricity from natural gas (NG) based on commercially available technology.We focus on the two basic technologies currently used in large industrial applications: fired tubular reformer (FTR) and auto-thermal reformer (ATR). In both cases we assume that NG is pre-heated and humidified in a saturator providing water for the reforming reaction; this reduces the amount of steam to be bled from the power cycle and increases electricity production. Outputs flows are made available at conditions suitable for transport via pipeline: 60 bar for pure hydrogen, 150 bar for pure CO₂. To reduce hydrogen compression power requirements reforming is carried out at relatively high pressures: 25 bar for FTR, 70 bar for ATR. Reformed gas is cooled and then passed through two water–gas shift reactors to optimize heat recovery and maximize the conversion to hydrogen. In plants with CO₂ capture, shifted gas goes through an amine-based chemical absorption system that removes most of the CO₂. Pure hydrogen is obtained by pressure swing absorption (PSA), leaving a purge gas utilized to fire the reformer (in FTR) and to boost electricity production.For the power cycle we consider conventional steam cycles (SC) and combined cycles (CC). The scale of plants based on a CC is determined by the gas turbine. To maintain NG input within the same range (around 1200 MW), we considered a General Electric 7FA for ATR, a 6FA for FTR. The scale of plants with SC is set by assuming the same NG input of the corresponding CC plant.Heat and mass balances are evaluated by a model accounting for the constraints posed by commercial technology, as well as the effects of scale. Results show that, from a performance standpoint, the technologies of choice for the production of de-carbonized hydrogen from NG are FTR with SC or ATR with CC. When operated at high steam-to-carbon ratios, the latter reach CO₂ emissions chargeable to hydrogen of 10–11 kg of CO₂ per GJ_LHV—less than 20% of NG—with an equivalent efficiency of hydrogen production in excess of 77%.     

Reactivity study on oxygen carriers for solar-hybrid chemical-looping combustion of di-methyl ether

A power cycle with the solar-hybrid chemical-looping combustion can simultaneously provide a new insight for treating with the problem of large energy penalty for CO₂ capture in the energy system and achieve the efficient utilization of the mid-temperature solar thermal energy. Experiments were implemented on a thermo-gravimetrical reactor with di-methyl ether (DME) as fuel to identify suitable looping material for this system. Oxygen carriers, with Fe₂O₃, NiO, and CoO as solid reactants and Al₂O₃, MgAl₂O₄, and YSZ as binders, were prepared by dissolution method. Compared with Fe₂O₃ and NiO, CoO has higher reactivity in the research temperature range of 673–773 K, and the suitable reduction temperature of CoO with DME is around 723 K. Carbon deposition in the reduction process of DME with CoO/CoAl₂O₄ can be completely suppressed by adding water vapor to the gaseous reactant, and the optimal range of H₂O/DEM is around 1.5–2.0. Scanning electron microscopy was used to characterize the morphological features of the fresh and the cycling used oxygen carriers. For CoO/YSZ, big grains formed after cyclic reactions, but no apparent change was found for CoO/CoAl₂O₄. The findings of this paper provide a promising looping material candidate for the solar-hybrid chemical-looping combustion.     

Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal

Based on the results of previous studies, the efficiency of a Brayton/Hirn combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO₂ removal by chemical absorption reached 33.94%, considering also the separate CO₂ compression process. The specific CO₂ emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO₂ chemical absorption (38–39% efficiency, 130 kg/MW h specific CO₂ emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilisation. The LCA shows the important environmental advantages of biomass utilisation in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilisation.     

Influence of the required EEDI reduction factor on the CO2 emission from bulk carriers

In order to improve energy efficiency for ships International Maritime Organization (IMO) introduced Energy Efficiency Design Index (EEDI). For every new ship the attained EEDI has to be calculated and not higher than the required EEDI which is calculated from the reference line value and appropriate reduction factor. The reference line value represents the world fleet average and is dependent on the ship type and size. The reduction factor represents a reduction for the EEDI relative to the reference line value and is increased in a set of time intervals. However, the scheme of the reduction factor change seems to be rigidly set and could lead to design issues and ship under powering. This study estimates the CO₂ emission from bulk carriers based on the current reduction factor change policy. Other policies and some innovative approaches are also discussed and the CO₂ emission in every scenario is estimated. The results are then compared with the requirement of reaching mean global CO₂ stabilization level of 550 ppm in the atmosphere. It is concluded that policies which include feedback from the shipbuilding sector impose requirements that could be much easier to satisfy and which will lead to overall lower CO₂ emission.     

Assessment of cleaner electricity generation technologies for net CO2 mitigation in Thailand

The choice of electricity generation technologies not only directly affects the amount of CO₂ emission from the power sector, but also indirectly affects the economy-wide CO₂ emission. It is because electricity is the basic requirement of economic sectors and final consumptions within the economy. In Thailand, although the power development plan (PDP) has been planned for the committed capacity to meet the future electricity demand, there are some undecided electricity generation technologies that will be studied for technological options. The economy-wide CO₂ mitigations between selecting cleaner power generation options instead of pulverized coal-thermal technology of the undecided capacity are assessed by energy input–output analysis (IOA). The decomposition of IOA presents the fuel-mix effect, input structural effect, and final demand effect by the change in technology of the undecided capacity. The cleaner technologies include biomass power generation, hydroelectricity and integrated gasification combined cycle (IGCC). Results of the analyses show that if the conventional pulverized coal technology is selected in the undecided capacity, the economy-wide CO₂ emission would be increased from 223 million ton in 2006 to 406 million ton in 2016. Renewable technology presents better mitigation option for replacement of conventional pulverized coal technology than the cleaner coal technology. The major contributor of CO₂ mitigation in cleaner coal technology is the fuel mix effect due to higher conversion efficiency. The demand effect is the major contributor of CO₂ mitigation in the biomass and hydro cases. The embedded emission in construction of power plant contributes to higher CO₂ emission.     

The environmental impact of post-combustion CO2 capture with MEA, with aqueous ammonia, and with an aqueous ammonia-ethanol mixture for a coal-fired power plant

In this paper the authors compare monoethanolamine (MEA) to aqueous ammonia (AA) and a solvent mixture of aqueous ammonia and ethanol (EAA) with respect to their post-combustion CO₂ capture performance and their environmental impact. Simulation of all processes was carried out with Aspen Plus^® and compared to experimental results for CO₂ scrubbing with ammonia. Of special interest was the formation of stable salts, which could be observed in the experimental CO₂ capture with both ammonia solvents. If CO₂ can be captured in the form of ammonium salts, energy requirements are greatly reduced, since no energy is required for solvent regeneration and CO₂ compression. The environmental impact of CO₂ capture was investigated for a 500 MW pulverised coal power plant employing Life Cycle Assessment (LCA) using the software SimaPro^®. For a comprehensive evaluation of this impact, influencing factors such as solvent production and solvent emissions were included. With kinetics taken into account, no salt formation could be observed in CO₂ removal with aqueous ammonia. The necessary reduction of ammonia emissions leads to further energy requirements, and solvent production as well as the remaining ammonia losses to the environment have a more significant environmental impact than CO₂ removal with MEA.     

Removal of non-CO2 greenhouse gases by large-scale atmospheric solar photocatalysis

Large-scale atmospheric removal of greenhouse gases (GHGs) including methane, nitrous oxide and ozone-depleting halocarbons could reduce global warming more quickly than atmospheric removal of CO₂. Photocatalysis of methane oxidizes it to CO₂, effectively reducing its global warming potential (GWP) by at least 90%. Nitrous oxide can be reduced to nitrogen and oxygen by photocatalysis; meanwhile halocarbons can be mineralized by red-ox photocatalytic reactions to acid halides and CO₂. Photocatalysis avoids the need for capture and sequestration of these atmospheric components. Here review an unusual hybrid device combining photocatalysis with carbon-free electricity with no-intermittency based on the solar updraft chimney. Then we review experimental evidence regarding photocatalytic transformations of non-CO₂ GHGs. We propose to combine TiO₂-photocatalysis with solar chimney power plants (SCPPs) to cleanse the atmosphere of non-CO₂ GHGs. Worldwide installation of 50,000 SCPPs, each of capacity 200 MW, would generate a cumulative 34 PWh of renewable electricity by 2050, taking into account construction time. These SCPPs equipped with photocatalyst would process 1 atmospheric volume each 14–16 years, reducing or stopping the atmospheric growth rate of the non-CO₂ GHGs and progressively reducing their atmospheric concentrations. Removal of methane, as compared to other GHGs, has enhanced efficacy in reducing radiative forcing because it liberates more _°OH radicals to accelerate the cleaning of the troposphere. The overall reduction in non-CO₂ GHG concentration would help to limit global temperature rise. By physically linking greenhouse gas removal to renewable electricity generation, the hybrid concept would avoid the moral hazard associated with most other climate engineering proposals.     

Evaluation of energy saving potential in China's cement industry using the Asian-Pacific Integrated Model and the technology promotion policy analysis

Much of China's cement industry still uses outdated kilns and other inefficient technologies, which are obstacles to improving energy efficiency. Huge improvements in energy consumption intensity can be made by improving this technology. To evaluate the potential for energy-saving and CO₂ emissions reduction in China's cement industry between 2010 and 2020, a model was developed based on the Asian-Pacific Integrated Model (AIM). Three scenarios (S1, S2 and S3) were developed to describe future technology policy measures in relation to the development of the cement industry. Results show that scenario S3 would realize the potential for CO₂ emissions mitigation of 361.0 million tons, accounting for 25.24% of the predicted emissions, with an additional energy saving potential of 39.0 million tons of coal equivalent by 2020. Technology promotion and industrial structure adjustment are the main measures that can lead to energy savings. Structural adjustment is the most important approach to reduce the CO₂ emissions from the cement industry; the resulting potential for CO₂ emissions reduction will be increasingly large, even exceeding 50% after 2016.     

Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe

The energetic and environmental performance of production and distribution of the Brassica carinata biomass crop in Soria (Spain) is analysed using life cycle assessment (LCA) methodology in order to demonstrate the major potential that the crop has in southern Europe as a lignocellulosic fuel for use as a renewable energy source.The Life Cycle Impact Assessment (LCIA) including midpoint impact analysis that was performed shows that the use of fertilizers is the action with the highest impact in six of the 10 environmental categories considered, representing between 51% and 68% of the impact in these categories.The second most important impact is produced when the diesel is used in tractors and transport vehicles which represents between 48% and 77%. The contribution of the B. carinata cropping system to the global warming category is 12.7 g CO₂ eq. MJ⁻¹ biomass produced. Assuming a preliminary estimation of the B. carinata capacity of translocated CO₂ (631 kg CO₂ ha⁻¹) from below-ground biomass into the soil, the emissions are reduced by up to 5.2 g CO₂ eq. MJ⁻¹.The production and transport are as far as a thermoelectric plant of the B. carinata biomass used as a solid fuel consumes 0.12 MJ of primary energy per 1 MJ of biomass energy stored. In comparison with other fossil fuels such as natural gas, it reduces primary energy consumption by 33.2% and greenhouse gas emission from 33.1% to 71.2% depending on whether the capacity of translocated CO₂ is considered or not.The results of the analysis support the assertion that B. carinata crops are viable from an energy balance and environmental perspective for producing lignocellulosic solid fuel destined for the production of energy in southern Europe. Furthermore, the performance of the crop could be improved, thus increasing the energy and environmental benefits.     

National and regional generation of municipal residue biomass and the future potential for waste-to-energy implementation

Municipal residue biomass (MRB) in the municipal solid waste (MSW) stream is a potential year-round bioenergy feedstock. A method is developed to estimate the amount of residue biomass generated by the end-user at the scale of a country using a throughput approach. Given the trade balance of food and forestry products, the amount of MRB generated is calculated by estimating product lifetimes, discard rates, rates of access to MSW collection services, and biomass recovery rates. A wet tonne of MRB could be converted into about 8 GJ of energy and 640 kg of carbon dioxide (CO₂) emissions, or buried in a landfill where it would decompose into 1800 kg of CO₂ equivalent (in terms of global warming potential) methane (CH₄) and CO₂ emissions. It is estimated that approximately 1.5 Gt y^?1 of MRB are currently collected worldwide. The energy content of this biomass is approximately 12 EJ, but only a fraction is currently utilized. An integrated assessment model is used to project future MRB generation and its utilization for energy, with and without a hypothetical climate policy to stabilize atmospheric CO₂ concentrations. Given an anticipated price for biomass energy (and carbon under a policy scenario), by the end of the century, it is projected that nearly 60% of global MRB would be converted to about 8 EJ y^?1 of energy in a reference scenario, and nearly all of global MRB would be converted into 16 EJ y^?1 of energy by the end of the century under a climate policy scenario.     

An evaluation of greenhouse gas mitigation options for coal-fired power plants in the US Great Lakes States

We assessed options for mitigating greenhouse gas emissions from electricity generation in the US Great Lakes States, a region heavily dependent on coal-fired power plants. A proposed 600 MW power plant in northern Lower Michigan, USA provided context for our evaluation. Options to offset fossil CO₂ emissions by 20% included biomass fuel substitution from (1) forest residuals, (2) short-rotation woody crops, or (3) switchgrass; (4) biologic sequestration in forest plantations; and (5) geologic sequestration using CO₂ capture. Review of timber product output data, land cover data, and expected energy crop productivity on idle agriculture land within 120 km of the plant revealed that biomass from forestry residuals has the potential to offset 6% and from energy crops 27% of the annual fossil fuel requirement. Furthermore, annual forest harvest in the region is only 26% of growth and the surplus represents a large opportunity for forest products and bioenergy applications. We used Life Cycle Assessment (LCA) to compare mitigation options, using fossil energy demand and greenhouse gas emissions per unit electricity generation as criteria. LCA results revealed that co-firing with forestry residuals is the most attractive option and geologic sequestration is the least attractive option, based on the two criteria. Biologic sequestration is intermediate but likely infeasible because of very large land area requirements. Our study revealed that biomass feedstock potentials from land and forest resources are not limiting mitigation activities, but the most practical approach is likely a combination of options that optimize additional social, environmental and economic criteria.     

Performance and cost assessment of Integrated Solar Combined Cycle Systems (ISCCSs) using CO2 as heat transfer fluid

In this paper, a performance and cost assessment of Integrated Solar Combined Cycle Systems (ISCCSs) based on parabolic troughs using CO₂ as heat transfer fluid is reported on. The use of CO₂ instead of the more conventional thermal oil as heat transfer fluid allows an increase in the temperature of the heat transfer fluid and thus in solar energy conversion efficiency. In particular, the ISCCS plant considered here was developed on the basis of a triple-pressure, reheated combined cycle power plant rated about 250 MW. Two different solutions for the solar steam generator are considered and compared.The results of the performance assessment show that the solar energy conversion efficiency ranges from 23% to 25% for a CO₂ maximum temperature of 550 °C. For a CO₂ temperature of 450 °C, solar efficiency decreases by about 1.5–2.0% points. The use of a solar steam generator including only the evaporation section instead of the preheating, evaporation and superheating sections allows the achievement of slightly better conversion efficiencies. However, the adoption of this solution leads to a maximum value of the solar share of around 10% on the ISCCS power output. The solar conversion efficiencies of the ISCCS systems considered here are slightly greater than those of the more conventional Concentrating Solar Power (CSP) systems based on steam cycles (20–23%) and are very similar to the predicted conversion efficiencies of the more advanced direct steam generation solar plants (22–27%).The results of a preliminary cost analysis show that due to the installation of the solar field, the electrical energy production cost for ISCCS power plants increases in comparison to the natural gas combined cycle (NGCC). In particular, the specific cost of electrical energy produced from solar energy is much greater (about two-fold) than that of electrical energy produced from natural gas.     

China's key role in climate protection

China is in the process of becoming the fourth main global player in the world economy, together with the US, the EU, and Japan. Due to an energy mix with 75% dependence on coal, a high energy intensity and low energy prices, it is, after the US, the world's second largest emitter of CO₂. China's recoverable fossil fuel reserves have a CO₂ emission potential of some 225 Gt (the current global CO₂ emission is about 22 Gt/yr). Under a business-as-usual (BAU) scenario, all of it would be released to the atmosphere by 2040. This emission may cause a significant disruption of the climate system, resulting in severe adverse climatic and ecological impacts on China and the world. To avoid this outcome, an equitable climate-protection strategy is introduced to explore an alternative energy/climate future. Using a macroeconomic approach, it is shown that under BAU conditions, the year 2100 emissions of CO₂ will increase above 1990 levels by 370 and 96% for China and the US, respectively. In contrast, for the climate-protection conditions required by the Climate Convention, CO₂ emissions must decrease by 36% for China and by 90% for the US below 1990 levels. Using a microeconomic-engineering approach, the total CO₂ reduction potential is found to be about 4600 Mt for 13 specific measures over a 10-yr period. The incremental costs range from US$ 0.09 to 18.55 per ton of CO₂ reduction for coal-saving stoves and solar cookers, respectively. The total reduction costs for China would be about US$ 2 billion per year or ∼0.4% of the 1994 GDP of China. This estimate does not allow for benefits from saved resources and avoided damages. We conclude with a discussion of various avenues for obtaining needed technological and financial support for China.     

Feasibility assessment of poplar bioenergy systems in the Southern Europe

A detailed reliability assessment of bioenergy production systems based on poplar cultivation was made. The aim of this assessment was to demonstrate the Economic feasibility of implementing poplar biomass production for power generation in Spain. The assessment considers the following chain of energy generation: cultivation and harvesting, and transportation and electricity generation in biomass power plants (10, 25 and 50 MW). Twelve scenarios were analysed in accordance with the following: two harvesting methods (high density packed stems and chip production in the field), two crop distributions around the power plant and three power plant sizes. The results show that the cost of biomass delivered at power plant ranges from 18.65 to 23.96 € Mg^?1 dry basis. According to power plant size, net profits range from 3 to 22 million € per yr.Sensibility analyses applied to capital cost at the power plant and to biomass production in the field demonstrate that they do not affect the feasibility of these systems. Reliability is improved if benefits through selling CO₂ emission credits are taken into account.This study clears up the Economic uncertainty of poplar biomass energy systems that already has been accepted as environmentally friendlier and as offering better energetic performance.