Identification of early opportunities for CO2 sequestration—worldwide screening for CO2-EOR and CO2-ECBM projects

A study has been performed to identify potential worldwide opportunities for early application of CO₂ sequestration. An early opportunity is defined as a high-purity CO₂ point source, which can provide CO₂ at low costs to oil or coal fields, where the CO₂ is sequestered, and simultaneously enhance oil production (CO₂-EOR) or coal bed methane production (CO₂-ECBM). A Geographical Information System (GIS) was used to combine worldwide CO₂ point sources and oil and coal fields. This resulted in 429 potential source–oil field and 79 source–coal field combinations. A multi-criteria analysis (MCA), in which technical and socio-economic criteria are taken into account, was applied to rank the source–reservoir combinations generated by the GIS exercise. Some of the most promising cases were considered in more detail to select four illustrative cases for further study: two potential enhanced oil recovery (EOR) projects and two potential enhanced coal bed methane recovery (ECBM) projects. Case 1 consists of a hydrogen plant in Saudi Arabia, which could sequester 0.26 Mt/year CO₂ in a depleted oil reservoir at a net saving of approximately 3 €/t CO₂. EOR case 2 is a hydrogen plant in California, USA, which has to be retrofitted in order to generate a pure CO₂ stream. Approximately 0.28 Mt CO₂ could be stored annually. Mitigation costs have been estimated at 9–19 €/t CO₂, depending on the availability of steam for CO₂ regeneration. In cases 3 and 4, circa 0.68 and 0.29 Mt CO₂ from ammonia plants in China and Canada could be sequestered annually in coal fields for ECBM production at approximately 5 and 6 €/t CO₂, respectively.     

Production and consumption accounting of CO2 emissions for Xiamen,China

Consumption accounting of urban greenhouse gas emissions is preferable to production accounting, because cities are open systems which depend on the import of large quantities of externally produced goods. In this paper we use environmental input–output analysis to construct CO₂ production and consumption accounting inventories for Xiamen, a rapidly developing coastal city in southeast China. We found that, in 2007, total emissions embodied in production were 21.8 Mt CO₂, of which 17.1 Mt CO₂ were embodied in exports and 4.7 Mt CO₂ resulted from local demand on local production. If the large amounts of emissions embodied in the Xiamen reprocessing trade are excluded from the analysis, total imported emissions were 12.2 Mt CO₂, consumption emissions were 16.9 Mt CO₂, and Xiamen was a net exporter of 4.9 Mt CO₂. Although Xiamen's rapid economic growth is dependent on large-scale flows of embodied emissions, most of these emissions are not produced or consumed within the city system.     

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.     

A comparative analysis of woody biomass and coal for electricity generation under various CO2 emission reductions and taxes

Mitigating global climate change via CO₂ emission control and taxation is likely to enhance the economic potential of bioenergy production and utilization. This study investigated the cost competitiveness of woody biomass for electricity production in the US under alternative CO₂ emission reductions and taxes. We first simulated changes in the price of coal for electricity production due to CO₂ emission reductions and taxation using a computable general equilibrium model. Then, the costs of electricity generation fueled by energy crops (hybrid poplar), logging residues, and coal were estimated using the capital budgeting method. Our results indicate that logging residues would be competitive with coal if emissions were taxed at about US$25 Mg⁻¹ CO₂, while an emission tax US$100 Mg⁻¹ CO₂ or higher would be needed for hybrid poplar plantations at a yield of 11.21 dry Mg ha⁻¹ yr⁻¹ (5 dry tons ac⁻¹ yr⁻¹) to compete with coal in electricity production. Reaching the CO₂ emission targets committed under the Kyoto Protocol would only slightly increase the price of fossil fuels, generating little impact on the competitiveness of woody biomass. However, the price of coal used for electricity production would significantly increase if global CO₂ emissions were curtailed by 20% or more. Logging residues would become a competitive fuel source for electricity production if current global CO₂ emissions were cut by 20–30%. Hybrid poplar plantations would not be able to compete with coal until emissions were reduced by 40% or more.     

Research on photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV irradiation

The Pt/TiO₂ particles have been prepared by the photodeposition of Pt on TiO₂ surface and characterized by X-ray diffraction. Photocatalytic H₂ production from acetic acid (HAc) over Pt/TiO₂ in aqueous solution has been studied at ambient temperature under UV irradiation. The effects of operational variables such as Pt loading, photocatalyst concentration, HAc concentration, and solution pH, have been systematically investigated. The optimum conditions for H₂ production from HAc by Pt/TiO₂ were Pt loading 1.0 wt.%, Pt/TiO₂ concentration 0.22 g/L, HAc concentration 6.52 g/L and pH 1.0. The H₂ yield is 0.27 mol-H₂/mol-HAc obtained under prolonged time irradiation. Experimental results showed that the photocatalytic H₂ production activity could be enhanced remarkably by depositing a suitable amount Pt on TiO₂ surface. Based on our results, a new process for H₂ production from biomass can be achieved by coupling fermentative H₂ production with photocatalytic H₂ production. The process also provides a method for degradation of organic pollutants with simultaneous H₂ production. A possible mechanism for photocatalytic decomposition of HAc over Pt/TiO₂ was also proposed.     

Assessment of nitrogen fertilization for the CO2 balance during the production of poplar and rye

This study was designed to consider all nitrogen fertilizer-related effects on crop production and emission of greenhouse gases on loamy sandy soils in Germany over a period of nine years (1999–2007). In order to set up a CO₂ balance for the production of energy crops, different nitrogen pathways were investigated, such as direct N₂O emissions from the soil and indirect emissions related to NO₃ leaching and fertilizer production. Fluxes of N₂O were measured in an experimental field using closed chambers. Poplar (Populus maximowiczii × P. nigra) and rye (Secale cereale L.) as one perennial and one annual crop were fertilized at rates of 0 kg N ha^?1 yr^?1, 75 kg N ha^?1 yr^?1 and 150 kg N ha^?1 yr^?1. The mean N₂O emissions from the soil ranged between 0.5 kg N ha^?1 yr^?1 and 2.5 kg N ha^?1 yr^?1 depending on fertilization rate, crop variety and year. The CO₂ fixed in the biomass of energy crops is reduced by up to 16% if direct N₂O emissions from soil and indirect N₂O emissions from NO₃ leaching and fertilizer production are included. Taking into account the main greenhouse gas emissions, which derive from the production and the use of N fertilizer, the growth of poplar and rye may replace the global warming potential of fossil fuels by up to 17.7 t CO₂ ha^?1 yr^?1 and 12.1 t CO₂ ha^?1 yr^?1, respectively.     

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.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Nanoscale surface observation of feldspar dissolved under supercritical CO2–water–mineral system

As part of our assessment program on underground CO₂ storage, we studied the dissolution of feldspar in aqueous solutions of supercritical CO₂ at 25, 50, 65, and 80 °C with a constant CO₂ pressure of 10 MPa. Atomic force microscopy (AFM) was then used to observe nanoscale dissolution features on the feldspar surface. The average dissolution rates of anorthite during the initial 1 week of dissolution were estimated from surface retreat based on vertical cross-section profiles.     

CO2 separation during hydrocarbon gasification

Hydrocarbon can be gasified with steam into fuel gas, including CO, CO₂, H₂, CH₄, etc. For H₂ production, it is necessary to separate the other gases from hydrogen. In this study, hydrogen production by removal of carbon oxides during hydrocarbon gasification with CaO and other metal oxides was examined theoretically and experimentally.It was experimentally confirmed that when the hydrocarbon, water, and Ca(OH)₂ were set in a micro-autoclave at a temperature of 973 K and a pressure of 25 MPa, the only gas products were hydrogen along with a small amount of methane. CO was converted to CO₂, and CO₂ was absorbed by Ca(OH)₂ to form CaCO₃ completely. CaOSiO₂ can absorb CO₂ to form CaCO₃ under the same experimental conditions. Others such as MgO, SnO, and Fe₂O₃ were found to be unsuitable sorbents for CO₂ absorption in the gasifier at high temperature.By calcination, CaCO₃ can reform to CaO. Because the chemical energy contained in CaO can be released during hydrocarbon gasification, H₂ production efficiency as high as 70–80% can be expected.     

Negative pressure dependence of mass burning rates of H2/CO/O2/diluent flames at low flame temperatures

Experimental measurements of burning rates, analysis of the key reactions and kinetic pathways, and modeling studies were performed for H₂/CO/O₂/diluent flames spanning a wide range of conditions: equivalence ratios from 0.85 to 2.5, flame temperatures from 1500 to 1800 K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, and dilution concentrations of He up to 0.8, Ar up to 0.6, and CO₂ up to 0.4. The experimental data show negative pressure dependence of burning rate at high pressure, low flame temperature conditions for all equivalence ratios and CO fractions as high as 0.5. Dilution with CO₂ was observed to strengthen the pressure and temperature dependence compared to Ar-diluted flames of the same flame temperature. Simulations were performed to extend the experimentally studied conditions to conditions typical of gas turbine combustion in Integrated Gasification Combined Cycle processes, including preheated mixtures and other diluents such as N₂ and H₂O.Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves – up to a factor of three at high pressures. The present findings suggest the need for several rate constant modifications of reactions in the current hydrogen models and raise questions about the sufficiency of the set of hydrogen reactions in most recent hydrogen models to predict high pressure flame conditions relevant to controlling NO_x emissions in gas turbine combustion. For example, the reaction O + OH + M = HO₂ + M is not included in most hydrogen models but is demonstrated here to significantly impact predictions of lean high pressure flames using rates within its uncertainty limits. Further studies are required to reduce uncertainties in third body collision efficiencies for and fall-off behavior of H + O₂(+M) = HO₂(+M) in both pure and mixed bath gases, in rate constants for HO₂ reactions with other radical species at higher temperatures, and in rate constants for reactions such as O + OH + M that become important under the present conditions in order to properly characterize the kinetics and predict global behavior of high-pressure H₂ or H₂/CO flames.     

CO2 adsorption on porous NiO as a cathode material for molten carbonate fuel cells

Molten carbonate fuel cells (MCFC) are the systems suitable for large-scale energy production. The cathode material used in these cells is NiO. In this study the NiO cathode was synthesized by tape-casting method and the adsorption of CO₂, one of the cathode feeding gases, was investigated on it. The adsorption studies were carried out by the use of packed column and the adsorption analysis were performed using pulse response technique. There were two 1/4 in. diameter and 5 and 10 cm length columns prepared for the experiments and they were packed with 3 mm average particle sized NiO. The experiments were carried out with gas chromatography using He as a carrier gas. The response curves were taken after pulsing the columns with CO₂. The equilibrium constants and heat of adsorption of CO₂ on NiO were determined by the use of the first absolute moment equations corresponding to retention times. It was observed that the adsorption was physical in nature. From the adsorption constants determined at different temperatures and the heat of adsorption, ΔH⁰, was found as −1299 cal mol⁻¹.     

Using aluminum and Li2CO3 particles to reinforce the α-LiAlO2 matrix for molten carbonate fuel cells

The electrolyte substrate (matrix) of a molten carbonate fuel cell (MCFC) provides both ionic conduction and gas sealing. During the starting-up and operating of MCFC stacks at 923 K, the matrix can experience mechanical stresses that can cause cracking. In particular, the pure α-LiAlO₂ that is generally used for the MCFC possesses poor mechanical strength. In this study, we employed Al and Li₂CO₃ particles as reinforcement materials to increase the mechanical strength of the α-LiAlO₂ matrix for its stable long-term operation. The mechanical strength of the matrix increased dramatically after adding Al particles into the pure matrix. Moreover, we operated a single cell for 2000 h after adding Li₂CO₃ particles into the Al-reinforced matrix to prevent a Li-ion shortage caused by a lithiated Al reaction in the matrix.     

Gasification reactivity of biomass chars with CO2

In this study, carbon conversion was calculated from the data obtained with a real-time gas analyzer. In a lab-scale furnace, each biomass sample was pyrolyzed in a nitrogen environment and became biomass char. For preparation of the char, the furnace was electrically heated over 40 min up to the wall temperature of 850 °C, and maintained at the same temperature over 17 min. The furnace was again heated over 3 min to a temperature higher than 850 °C and then CO₂ was injected. The biomass char was then gasified with CO₂ under isothermal conditions. The reactivity of biomass char was investigated at various temperatures and CO₂ concentrations. The VRM (volume reaction model), SCM (shrinking core model), and RPM (random pore model) were used to interpret the experimental data. For each model, the activation energy (E) and pre-exponential factor (A) of the biomass char-CO₂ reaction were determined from gas-analysis data by using the Arrhenius equation. For the RPM, the apparent reaction order was determined. According to this study, it was found that the experimental data agreed better with the RPM than with the other two models. Through BET analyses, it was found that the structural parameter (ψ) of the surface area for the RPM was obtained as 4.22.     

The role of biofuels for transportation in CO2 emission reduction scenarios with global versus regional carbon caps

This study analyzes how international climate regimes affect cost-efficiency of fuel choices in the transportation sector. The analysis is carried out with a regionalized version of the Global Energy Transition model, GET-R 6.0. Two different carbon dioxide (CO₂) reduction scenarios are applied, both meeting an atmospheric CO₂ concentration target of 450 ppm by the year 2100. The first scenario, “global cap” (GC), uses a global cap on CO₂ emissions, and global emissions trading is allowed. In the second scenario, “regional caps” (RC), industrialized regions start to reduce their CO₂ emissions by 2010 while developing regions may wait several decades and emission reductions are not tradable across regions. In this second scenario, CO₂ emissions are assumed to meet an equal per capita distribution of 1.0 tC/capita, in all six regions, by 2040; emissions then follow a common reduction path, toward approximately 0.2 tC/capita by 2100. Three main results emerge from our analysis: (i) the use of biofuels in the industrialized regions is significantly higher in RC than in GC; (ii) the use of biofuels in RC actually increases the weaker (i.e., higher) the CO₂ concentration target (up to 550 ppm); and (iii) biofuels never play a dominant role in the transportation sector. We find that biofuels may play a more important role in industrialized countries if these take on their responsibilities and reduce their emissions before developing countries start reducing their emissions, compared to the case in which all countries take action under a global cap and trade emission reduction regime.     

Temporal CO2 emissions associated with electricity generation: Case study of Singapore

Studying temporal patterns in emissions associated with electricity generation is increasingly important. On the supply side, there is interest in integrating renewable energy sources (solar, wind), which are known to vary daily and hourly. On the demand side, the concept of demand response is driving a need to better understand the impact of peak versus off-peak loading, with the objective of maximizing efficiency. In this study, we examine the case of electric power generation in Singapore, and aim to assess the half-hourly variation in associated average carbon dioxide emissions. Given the country’s serious push for clean energy solutions and a possibility of adopting carbon trading in the future, we feel the need to address the currently existing gap in research on daily CO₂ emissions patterns. By associating representative electricity generation data with the characterized fleet of power plants, half-hourly emissions are found to range between 415 and 455 kg CO₂ per MW h. Marginal emission factors show a fluctuating daily pattern between 390 and 800 kg CO₂/MW h. Policy makers able to work with real generation data can use this approach to understand the carbon footprint of short-term supply and demand interventions.     

Nanocrystalline TiO2 (anatase) for Li-ion batteries

Nanocrystalline TiO₂ (anatase) was synthesized successfully by the direct conversion of TiO₂-sol at 85 °C. The as-prepared TiO₂ at 85 °C were calcined at different temperatures and time in order to optimize the system with best electrochemical performance. The particle sizes of the synthesized materials were found to be in the range of 15–20 nm as revealed by the HR-TEM studies. Commercial TiO₂ anatase (micron size) was also studied for its Li-insertion and deinsertion properties in order to compare with the nanocrystalline TiO₂. The full cell studies were performed with LiCoO₂ cathode with the best performing nano-TiO₂ as anode. The specific capacity of the nanocrystalline TiO₂ synthesized at 500 °C/2 h in a half-cell configuration was 169 mAh g⁻¹ while for the cell with LiCoO₂ cathode, it was 95 mAh g⁻¹ in the 2 V region. The specific reversible capacity and the cycling performance of the synthesized nano-TiO₂ anode in full cell configuration across LiCoO₂ cathode are superior to that reported in the literature. Cyclic voltammetry measurements showed a larger peak separation for the micro-TiO₂ than the nano-TiO₂, clearly indicating the influence of nano-particle size on the electrochemical performance.     

Natural convective flow and heat transfer of supercritical CO2 in a rectangular circulation loop

Fluid dynamics and heat transfer of supercritical CO₂ natural convection are important for nuclear engineering and new energy system design etc. In this paper, in order to study the flow and heat transfer behavior of supercritical CO₂ natural circulation system, a computational simulation on a closed natural circulation loop (NCL) model has been carried out. The fluid temperature in the loop varies between 298.15 K and 323.15 K, which is across the CO₂ critical temperature, and the density is found to be in the range of 250–800 kg/m³. The results show a small temperature difference of 25 °C between heating and cooling sources can induce a mass flow with the Reynolds number up to 6 × 10⁴ using supercritical CO₂ fluid. A periodic reversal flow pattern is found and presented in this paper. Enhanced heat transfer phenomenon is also found for the supercritical CO₂ natural convective flow. The mechanisms to this enhancement and the heating effect on the flow are also discussed in detail in the present study.     

Physical properties of the CNT:TiO2 thin films prepared by sol–gel dip coating

Uniform and highly adherent thin films of CNT:TiO₂ were synthesized by sol–gel dip coating method. Both TiO₂ and CNT:TiO₂ films showed very identical structural characteristics and no significant changes in the lattice values were observed. The crystalline size decreased from 20 nm for TiO₂ film to 17 nm for the 4%CNT:TiO₂ film. The film surface was very smooth and compact, as indicated by the roughness data obtained from AFM measurements; the root mean square (rms) average of the roughness was as low as 3 nm. The HRTEM showed that the CNTs are embedded in the matrix of TiO₂ indicating the formation of a composite. In Raman spectra the characteristic vibrations of the TiO₂ are identified, the increase in the FWHM of main anatase peak (144 cm^?1) in the case of the 4%CNT:TiO₂ film is interpreted as due to the incorporation of CNTs in the film. At the wavelength of 600 nm the refractive index of pure TiO₂ was 2.07 and the 4%CNT:TiO₂ showed a value of 2.29. The photoresponse curves showed typical features of charge trapping centers in the band gap of the films.