Solar chemical reactor technology for industrial production of lime

We developed the solar chemical reactor technology to effect the endothermic calcination reaction CaCO₃(s) → CaO(s) + CO₂(g) at 1200–1400 K. The indirect heating 10 kW_th multi-tube rotary kiln prototype processed 1–5 mm limestone particles, producing high purity lime that is not contaminated with combustion by-products. The quality of the solar produced quicklime meets highest industrial standards in terms of reactivity (low, medium, and high) and degree of calcination (exceeding 98%). The reactor’s efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184 kJ kg⁻¹) divided by the solar energy input, reached 30–35% for quicklime production rates up to 4 kg h⁻¹. The solar lime reactor prototype operated reliably for more than 100 h at solar flux inputs of about 2000 kW m⁻², withstanding the thermal shocks that occur in solar high temperature applications. By substituting concentrated solar energy for fossil fuels as the source of process heat, one can reduce by 20% the CO₂ emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant. The cost of solar lime produced in a 20 MW_th industrial solar calcination plant is estimated in the range 131–158 $/t, i.e. about 2–3 times the current selling price of conventional lime.     

Decomposition of CO2 emissions change from energy consumption in Brazil: Challenges and policy implications

This study evaluates the changes in CO₂ emissions from energy consumption in Brazil for the period 1970–2009. Emissions are decomposed into production and consumption activities allowing computing the full set of energy sources consumed in the country. This study aims to develop a comprehensive and updated picture of the underlying determinants of emissions change from energy consumption in Brazil along the last four decades, including for the first time the recently released data for 2009. Results demonstrate that economic activity and demographic pressure are the leading forces explaining emission increase. On the other hand, carbon intensity reductions and diversification of energy mix towards cleaner sources are the main factors contributing to emission mitigation, which are also the driving factors responsible for the observed decoupling between CO₂ emissions and economic growth after 2004. The cyclical patterns of energy intensity and economy structure are associated to both increments and mitigation on total emission change depending on the interval. The evidences demonstrate that Brazilian efforts to reduce emissions are concentrated on energy mix diversification and carbon intensity control while technology intensive alternatives like energy intensity has not demonstrated relevant progress. Residential sector displays a marginal weight in the total emission change.     

The social return on investment in the energy efficiency of buildings in Germany

The German government has developed a variety of policy instruments intended to reduce national CO₂ emissions. These instruments include a programme administered by KfW bank, which aims at improving the energy efficiency of buildings. It provides attractive credit conditions or subsidies to finance refurbishment measures which improve the energy efficiency of buildings significantly.     

Reducing energy-related CO2 emissions using accelerated weathering of limestone

The use and impacts of accelerated weathering of limestone (AWL; reaction: CO₂+H₂O+CaCO₃→Ca²⁺+2(HCO₃⁻) is explored as a CO₂ capture and sequestration method. It is shown that significant limestone resources are relatively close to a majority of CO₂-emitting power plants along the coastal US, a favored siting location for AWL. Waste fines, representing more than 20% of current US crushed limestone production (>10⁹ tonnes/yr), could provide an inexpensive or free source of AWL carbonate. With limestone transportation then as the dominant cost variable, CO₂ mitigation costs of $3-$4/tonne appear to be possible in certain locations. Perhaps 10–20% of US point–source CO₂ emissions could be mitigated in this fashion. It is experimentally shown that CO₂ sequestration rates of 10⁻⁶ to 10⁻⁵ moles/sec per m² of limestone surface area are achievable, with reaction densities on the order of 10⁻² tonnes CO₂ m⁻³day⁻¹, highly dependent on limestone particle size, solution turbulence and flow, and CO₂ concentration. Modeling shows that AWL would allow carbon storage in the ocean with significantly reduced impacts to seawater pH relative to direct CO₂ disposal into the atmosphere or sea. The addition of AWL-derived alkalinity to the ocean may itself be beneficial for marine biota.     

Carbon abatement potential of solar home systems in India and their cost reduction due to carbon finance

About 78 million rural households in India reportedly lack access to grid electricity. About 67 million of them use kerosene for lighting. Government of India is promoting the use of solar home systems (SHS) as one of the options for meeting lighting requirements in households in remote and less inhabited villages. About 363,399 SHS were reportedly disseminated across the country by December 2007. Apart from meeting the basic lighting need of the households, SHS also help in abating the emissions of green house gases (GHGs) by directly displacing the use of kerosene in households that currently use it for lighting. This study has attempted at estimating the CO₂ mitigation potential of SHS in India by studying the potential for their diffusion and the appropriate baseline. Subsequently, the scope for cost reduction to the user due to carbon finance, if received, is also studied. It is found that carbon finance could reduce the effective burden of SHS to the user by 19% if carbon prices were $10/tCO₂² and no transaction costs were involved in getting the carbon revenues. These benefits are also estimated for scenarios where transaction costs are incurred by the project proponent in getting the carbon benefits.     

Decomposition analysis of CO2 emission in long-term climate stabilization scenarios

To achieve the stabilization of greenhouse gas (GHG) concentrations in the atmosphere, the international community will need to intensify its long-term efforts. Many EU countries have released national long-term scenarios toward 2050, and their ambitious targets for CO₂ emission reduction are aiming at a decrease of more than 50% of today's emission. In April 2004, Japan began a research project on its long-term climate policy. This paper discusses the long-term scenarios in other countries and the medium-term scenarios in Japan to support the development of a Japan's long-term climate stabilization scenario. In this study, CO₂ emission is decomposed with an extended Kaya identity (indexes: CO₂ capture and storage, carbon intensity, energy efficiency, energy intensity, economic activity) and a Reduction Balance Table is developed.     

A novel hybrid oxy-fuel power cycle utilizing solar thermal energy

An advanced oxy-fuel hybrid power system (AHPS) is proposed in this paper. Solar thermal energy is used in the AHPS to produce saturated steam as the working fluid, and natural gas is internally combusted with pure oxygen. It is in configuration close to the zero emission Graz cycle. The thermodynamic characteristics at design conditions of the AHPS are analyzed using the advanced process simulator Aspen Plus. The corresponding exergy loss analyses are also carried out to gain understanding of the loss distribution. The results are given in detail. The solar thermal hybrid H₂O turbine power generation system (STHS) is evaluated in this study as the reference. The comparison results demonstrate that the proposed cycle has notable advantages in thermodynamic performances. For example, the net fuel-to-electricity efficiency of the AHPS is 95.90%, which is 21.61 percentage points higher than that of the STHS. The exergy efficiency (based on the exergy input of fuel and solar thermal energy without radiation) of the AHPS is 55.88%, which is 2.13 percentage points higher than that of the STHS.     

Integrated fossil fuel and solar thermal systems for hydrogen production and CO2 mitigation

In most current fossil-based hydrogen production methods, the thermal energy required by the endothermic processes of hydrogen production cycles is supplied by the combustion of a portion of the same fossil fuel feedstock. This increases the fossil fuel consumption and greenhouse gas emissions. This paper analyzes the thermodynamics of several typical fossil fuel-based hydrogen production methods such as steam methane reforming, coal gasification, methane dissociation, and off-gas reforming, to quantify the potential savings of fossil fuels and CO₂ emissions associated with the thermal energy requirement. Then matching the heat quality and quantity by solar thermal energy for different processes is examined. It is concluded that steam generation and superheating by solar energy for the supply of gaseous reactants to the hydrogen production cycles is particularly attractive due to the engineering maturity and simplicity. It is also concluded that steam-methane reforming may have fewer engineering challenges because of its single-phase reaction, if the endothermic reaction enthalpy of syngas production step (CO and H₂) of coal gasification and steam methane reforming is provided by solar thermal energy. Various solar thermal energy based reactors are discussed for different types of production cycles as well.     

Experimental study on the performance of solar Rankine system using supercritical CO2

An experimental study is carried out to investigate the performance of a solar Rankine system using supercritical CO₂ as a working fluid. The testing machine of the solar Rankine system consists of an evacuated solar collector, a pressure relief valve, heat exchangers and CO₂ feed pump, etc. The solar energy powered system can provide electricity output as well as heat supply/refrigeration, etc. The system performance is evaluated based on daily, monthly and yearly experiment data. The results obtained show that heat collection efficiency for the CO₂-based solar collector is measured at 65.0–70.0%. The power generation efficiency is found at 8.78–9.45%, which is higher than the value 8.20% of a solar cell. The result presents a potential future for the solar powered CO₂ Rankine system to be used as distributed energy supply system for buildings or others.     

Hydrogen amplification from coke oven gas using a CO2 adsorption enhanced hydrogen amplification reactor

To improve coke oven gas (COG) energy conversion, alternative configurations for amplifying hydrogen from COG are proposed in this paper. In these new configurations, a CO₂ adsorption enhanced hydrogen amplification reactor is combined with a pressure swing adsorption separation unit (PSA) to produce pure hydrogen. Hydrogen production was integrated with desorption gas utilization, in situ CO₂ capture and waste heat recovery to improve COG energy conversion efficiency and decrease CO₂ emissions. To analyze the advantages of the flowsheet modifications, technical and economic performance indicators were used to evaluate and compare the performances of the various system configurations. Simulation results show that the alternative configurations proposed in this paper have higher energy conversion efficiencies, higher hydrogen yields and shorter dynamic payback periods. The variation of technical performance with reaction temperature, pressure, sorbent to carbon ratio and steam to carbon ratio were also analyzed using a sensitivity study. Optimal operating conditions for the CO₂ adsorption enhanced hydrogen amplification reactor were obtained based on the simulation results.     

Chemical recycling of carbon dioxide emissions from a cement plant into dimethyl ether,a case study of an integrated process in France using a Reverse Water Gas Shift (RWGS) step

Recycling of carbon dioxide (CO₂) and hydrogen (H₂) into liquid fuel technology has recently gained wide public interest since it is a potential pathway to increase the liquid fuel supply and to mitigate CO₂ emissions simultaneously.     

Analysis of energy service systems in urban areas and their CO2 mitigations and economic impacts

Three kinds of energy service system were examined as alternative energy systems in urban areas. A comparison of these energy systems was performed by finding Pareto optimum solutions for a multi-objective model. The model had two objective functions: CO₂ emission and cost to consumer. Various energy pricings were provided in the model as variables.     

Photocatalytic degradation of DBSNa using solar energy

This paper reports experimental results on photocatalytic degradation of sodium dodecylbenzene sulfonate (DBSNa), using the solar energy concentrator for photocatalysis studies (SECPS). The SECPS operation is based on the concentration of ultraviolet solar radiation on a reactor that contains contaminated water and a catalyst where the photocatalytic effect occurs. This effect produces ruptures in the toxic molecules, until transforming them into harmless compounds. The study focuses on determining how great is the contribution of the catalyst itself and the oxidant agent to the DBSNa photocatalytic degradation. Finally, three conditions were found as optimal for the photocatalytic degradation of DBSNa using the SECPS, which are 0.2 wt% TiO₂, 3000 ppm H₂O₂ and 60 min exposure time.     

Investigation of n-type Cu2O layers prepared by a low cost chemical method for use in photo-voltaic thin film solar cells

A low cost and simple chemical method of boiling copper plates in CuSO₄ solution is used to prepare Cu₂O layers. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES) and optical absorption have been used to characterise these layers. It has been found that the layers consist of Cu₂O phase with a thickness of about 1.4 μm for 60 minutes boiling in CuSO₄ solution. The largest grain sizes are in the order of 1 μm and the layers contain cubic Cu₂O phases. The layers are n-type in electrical conduction and the optical band gap observed is 2.2 eV.     

Modelling the impacts of a carbon emission-differentiated vehicle tax system on CO2 emissions intensity from new vehicle purchases in Ireland

The increasing awareness of the effects of climate change on the environment and the economic pressure on oil supply has focused international attention on reducing CO₂ emissions and energy usage across all sectors. In order to meet their Kyoto protocol commitments and in line with European Union policy, the Irish government has introduced a carbon-based tax system for new vehicles purchased from the 1st of July 2008. This new legislation aims to reduce carbon emissions in the transport sector, a sector which is responsible for a significant proportion of both. This paper presents the results of the development, calibration, and application of a car choice model which predicts the changes in CO₂ emissions intensity from new vehicle purchases as a result of the changes in vehicle tax policy and fuel price in Ireland. The model also predicts the impact of such changes on tax revenue for the Irish government and the changes in the split between the number of diesel and petrol vehicles purchased. The investigation found that the introduction of these new carbon-based taxes in Ireland will result in a reduction of 3.6–3.8% in CO₂ emissions intensity and a reduction in annual tax revenue of €191 M.     

CO2 and H2O reduction by solar thermochemical looping using SnO2/SnO redox reactions: Thermogravimetric analysis

The thermochemical dissociation of CO₂ and H₂O from reactive SnO nanopowders is studied via thermogravimetry analysis. SnO is first produced by solar thermal dissociation of SnO₂ using concentrated solar radiation as the high-temperature energy source. The process targets the production of CO and H₂ in separate reactions using SnO as the oxygen carrier and the syngas can be further processed to various synthetic liquid fuels. The global process thus converts and upgrades H₂O and captured CO₂ feedstock into solar chemical fuels from high-temperature solar heat only, since the intermediate oxide is not consumed but recycled in the overall process. The objective of the study was the kinetic characterization of the H₂O and CO₂ reduction reactions using reactive SnO nanopowders synthesized in a high-temperature solar chemical reactor. SnO conversion up to 88% was measured during H₂O reduction at 973 K and an activation energy of 51 ± 7 kJ/mol was identified in the temperature range of 798-923 K. Regarding CO₂ reduction, a higher temperature was required to reach similar SnO conversion (88% at 1073 K) and the activation energy was found to be 88 ± 7 kJ/mol in the range of 973-1173 K with a CO₂ reaction order of 0.96. The SnO conversion and the reaction rate were improved when increasing the temperature or the reacting gas mole fraction. Using active SnO nanopowders thus allowed for efficient and rapid fuel production kinetics from H₂O and CO₂.     

Solar thermal aided power generation

Fossil fuel based power generation is and will still be the back bone of our world economy, albeit such form of power generation significantly contributes to global CO₂ emissions. Solar energy is a clean, environmental friendly energy source for power generation, however solar photovoltaic electricity generation is not practical for large commercial scales due to its cost and high-tech nature. Solar thermal is another way to use solar energy to generate power. Many attempts to establish solar (solo) thermal power stations have been practiced all over the world. Although there are some advantages in solo solar thermal power systems, the efficiencies and costs of these systems are not so attractive. Alternately by modifying, if possible, the existing coal-fired power stations to generate green sustainable power, a much more efficient means of power generation can be reached. This paper presents the concept of solar aided power generation in conventional coal-fired power stations, i.e., integrating solar (thermal) energy into conventional fossil fuelled power generation cycles (termed as solar aided thermal power). The solar aided power generation (SAPG) concept has technically been derived to use the strong points of the two technologies (traditional regenerative Rankine cycle with relatively higher efficiency and solar heating at relatively low temperature range). The SAPG does not only contribute to increase the efficiencies of the conventional power station and reduce its emission of the greenhouse gases, but also provides a better way to use solar heat to generate the power. This paper presents the advantages of the SAPG at conceptual level.     

Energy and environmental potential of solid waste in Brazil

The economic progress and sustainable developments are linked to the optimization and energy conservation. Conventional methods of production and energy utilization usually embed harmful environmental impacts, and hence the challenge to scientists to seek for mechanisms of energy production and use which are less harmful or better still free of unfavorable environmental impacts. Studies point out that municipal solid waste has great energy potential and its reuse, specifically the production of biogas from landfills and the recycling of solid waste presents a favorable mechanism to optimize energy use and preserve it. The present investigation includes the energy savings and the avoided emissions of CO₂ to the atmosphere as a result of recycling and production of biogas from landfills in one metropolitan with more than one million inhabitants and in Brazil. The results show that the rate of CH₄ production from the Brazilian waste landfills can avail for Brazil about 41.7 MW and the reuse of recyclables can avail to the energy system an additional quantity of 286 GJ/month enough for the consumption of 318,000 families.     

Measurement of CuInSe2 solar cell AC parameters

The AC parameters (cell capacitance and cell resistance) of Copper Indium Diselenide (CuInSe₂) solar cell are measured using time-domain technique. The cell capacitance is calculated from the open circuit voltage decay (OCVD) and cell resistance with solar cell I–V characteristics measured in dark. The solar cell exhibits high parallel resistance and low parallel capacitance. The doping concentration and built in voltage are derived from the 1/C_P² versus bias voltage graph. The built-in voltage of the solar cell shows good agreement with measurements published in the literature.     

Solar module using dye-sensitized solar cells with a polymer electrolyte

Dye-sensitized TiO₂ solar cells assembled with a polymer electrolyte were investigated, aiming at the construction of an 8 V solar module. The individual solar cells were assembled with 4.5 cm² active area and were characterized under outdoor conditions, exhibiting an average efficiency of 0.9% per cell (at 12:00 noon). The solar module was built by connecting 13 cells in series. The integrated average daily power was estimated to be 183 mW. The present paper discusses the performance of the individual cells and the module.