Carbon capture and storage using alkaline industrial wastes

Carbon capture and storage (CCS) is gaining momentum as a means for combating climate change. It is viewed as an important bridging technology, allowing emission targets to be met during fossil fuel dependence while sufficient renewable energy generation is installed. Mineral carbon sequestration is the only known form of permanent carbon storage and has the potential to capture and store CO₂ in a single step. It is based on the geologic process of natural rock weathering where CO₂ dissolved in rain water reacts with alkaline rocks to form carbonate minerals. While the reactions are thermodynamically favourable, in nature the process occurs over thousands of years. The challenge of mineral carbon sequestration is to accelerate carbonation and exploit the heat of reaction with minimal energy and material losses. Minerals commonly selected for carbonation include calcium and magnesium silicates. These minerals require energy-intensive pre-treatments, such as fine grinding, heat treatment, and chemical activation with strong acids, to provide adequate conversions and reaction kinetics. Industrial waste residues present alternative sources of mineral alkalinity that are more reactive than primary minerals and are readily and cheaply available close to CO₂ sources. In addition, the carbonation of waste residues often improves their environmental stability. This paper provides an overview of the types of industrials wastes that can be used for mineral carbon sequestration and the process routes available.     

Life cycle assessment of processes for hydrogen production. Environmental feasibility and reduction of greenhouse gases emissions

Decomposition of CH₄ (natural gas) is one of the alternatives under study to achieve the sustainable production of hydrogen. No CO₂ or other greenhouse gases emissions are produced in this route and carbon is obtained as a solid co-product at the end of the reaction (₄CH?C+2H₂${\text{CH}}_4?\text{C}+2{\text{H}}_2$). This process can be thermally or catalytically conducted and recent studies have demonstrated that the carbon obtained in the reaction can also show catalytic activity.     

CO2 dry-reforming of methane over La0.8Sr0.2Ni0.8M0.2O3 perovskite (M = Bi,Co, Cr,Cu, Fe): Roles of lattice oxygen on C–H activation and carbon suppression

La_0.8Sr_0.2Ni_0.8M_0.2O₃ (LSNMO) (where M = Bi, Co, Cr, Cu and Fe) perovskite catalyst precursors have been successfully developed for CO₂ dry-reforming of methane (DRM). Among all the catalysts, Cu-substituted Ni catalyst precursor showed the highest initial catalytic activity due to the highest amount of accessible Ni and the presence of mobile lattice oxygen species which can activate C–H bond, resulting in a significant improvement of catalytic activity even at the initial stage of reaction. However, these Ni particles can agglomerate to form bigger Ni particle size, thereby causing lower catalytic stability. As compared to Cu-substituted Ni catalyst, Fe-substituted Ni catalyst has low initial activity due to the lower reducibility of Ni–Fe and the less mobility of lattice oxygen species. However, Fe-substituted Ni catalyst showed the highest catalytic stability due to: (1) strong metal–support interaction which hinders thermal agglomeration of the Ni particles; and (2) the presence of the abundant lattice oxygen species which are not very active for C–H bond activation but active to react with CO₂ to form La₂O₂CO₃, hence minimizing carbon formation by reacting with surface carbon to form CO.     

Tackling CO2 reduction in India through use of CO2 capture and storage (CCS): Prospects and challenges

CO₂ capture and storage (CCS) is not currently a priority for the Government of India (GOI) because, whilst a signatory to the UNFCCC and Kyoto Protocol, there are no existing greenhouse gas emission reduction targets and most commentators do not envisage compulsory targets for India in the post-2012 phase. The overwhelming priority for the GOI is to sustain a high level of economic growth (8%+) and provision of secure, reliable energy (especially electricity) is one of the widely recognised bottlenecks in maintaining a high growth rate. In such a supply-starved context, it is not easy to envisage adoption of CCS—which increases overall generation capacity and demand for coal without increasing actual electricity supply—as being acceptable. Anything which increases costs—even slightly—is very unlikely to happen, unless it is fully paid for by the international community. The majority viewpoint of the industry and GOI interviewees towards CCS appears to be that it is a frontier technology, which needs to be developed further in the Annex-1 countries to bring down the cost through RD&D and deployment. More RD&D is required to assess in further detail the potential for CO₂ storage in geological reservoirs in India and the international community has an important role to play in cultivating such research.     

A long-term view of fossil-fuelled power generation in Europe

The paper presents a view into the long term future of fossil-fuelled power generation in the European Union, based on a number of alternative scenarios for the development of the coal, natural gas and CO₂ markets, and the penetration of renewable and nuclear technologies. The new fossil fuelled capacity needed and the likely technology mix are estimated using a cost optimisation model based on the screening curve method, taking into consideration the rate of retirement of the current power plant fleet, the capacity already planned or under construction and the role of carbon capture and storage technologies. This analysis shows that measures to increase both non-fossil-fuel-based power generation and the price of CO₂ are necessary to drive the composition of the European power generation capacity so that the European policy goal of reducing greenhouse gas emissions is achieved. Meeting this goal will however require a high capital investment for the creation of an optimal fossil fuel power plant technology mix.     

Analysis of oxy-fuel combustion power cycle utilizing a pressurized coal combustor

Growing concerns over greenhouse gas emissions have driven extensive research into new power generation cycles that enable carbon dioxide capture and sequestration. In this regard, oxy-fuel combustion is a promising new technology in which fuels are burned in an environment of oxygen and recycled combustion gases. In this paper, an oxy-fuel combustion power cycle that utilizes a pressurized coal combustor is analyzed. We show that this approach recovers more thermal energy from the flue gases because the elevated flue gas pressure raises the dew point and the available latent enthalpy in the flue gases. The high-pressure water-condensing flue gas thermal energy recovery system reduces steam bleeding which is typically used in conventional steam cycles and enables the cycle to achieve higher efficiency. The pressurized combustion process provides the purification and compression unit with a concentrated carbon dioxide stream. For the purpose of our analysis, a flue gas purification and compression process including de-SO_x, de-NO_x, and low temperature flash unit is examined. We compare a case in which the combustor operates at 1.1 bars with a base case in which the combustor operates at 10 bars. Results show nearly 3% point increase in the net efficiency for the latter case.     

Optimizing a CO2 value chain for the Norwegian Continental Shelf

This paper presents a mathematical model for designing a carbon dioxide (CO₂) value chain. Storage of CO₂ in geological formations is recognized as an important alternative for carbon abatement. When CO₂ is deposited in oil reservoirs it can sometimes be used to achieve additional oil production, enhanced oil recovery (EOR). The model determines an optimal CO₂ value chain from a fixed set of CO₂ emission points and a set of potential injection sites. It designs a transport network and chooses the best suited oil fields with EOR potential or other geological formations for storage. A net present value criterion is used. The model is illustrated by an example of a Norwegian case with 14 oil fields, two aquifers and five CO₂ sources. A sensitivity analysis is performed on the most important parameters.     

The environmental impact and risk assessment of CO2 capture, transport and storage - An evaluation of the knowledge base

In this study, we identify and characterize known and new environmental consequences associated with CO₂ capture from power plants, transport by pipeline and storage in geological formations. We have reviewed (analogous) environmental impact assessment procedures and scientific literature on carbon capture and storage (CCS) options. Analogues include the construction of new power plants, transport of natural gas by pipelines, underground natural gas storage (UGS), natural gas production and enhanced oil recovery (EOR) projects. It is investigated whether crucial knowledge on environmental impacts is lacking that may postpone the implementation of CCS projects. This review shows that the capture of CO₂ from power plants results in a change in the environmental profile of the power plant. This change encompasses both increase and reduction of key atmospheric emissions, being: NO_x, SO₂, NH₃, particulate matter, Hg, HF and HCl. The largest trade-offs are found for the emission of NO_x and NH₃ when equipping power plants with post-combustion capture. Synergy is expected for SO₂ emissions, which are low for all power plants with CO₂ capture. An increase in water consumption ranging between 32% and 93% and an increase in waste and by-product creation with tens of kilotonnes annually is expected for a large-scale power plant (1 GW_e), but exact flows and composition are uncertain. The cross-media effects of CO₂ capture are found to be uncertain and to a large extent not quantified. For the assessment of the safety of CO₂ transport by pipeline at high pressure an important knowledge gap is the absence of validated release and dispersion models for CO₂ releases. We also highlight factors that result in some (not major) uncertainties when estimating the failure rates for CO₂ pipelines. Furthermore, uniform CO₂ exposure thresholds, detailed dose-response models and specific CO₂ pipeline regulation are absent. Most gaps in environmental information regarding the CCS chain are identified and characterized for the risk assessment of the underground, non-engineered, part of the storage activity. This uncertainty is considered to be larger for aquifers than for hydrocarbon reservoirs. Failure rates are found to be heavily based on expert opinions and the dose-response models for ecosystems or target species are not yet developed. Integration and validation of various sub-models describing fate and transport of CO₂ in various compartments of the geosphere is at an infant stage. In conclusion, it is not possible to execute a quantitative risk assessment for the non-engineered part of the storage activity with high confidence.     

Cyclic CO2 capture performance of carbide slag

The carbonate looping process is a promising technology for CO₂ capture. The decay of sorbents reactivity over multiple cycles is an obstacle for realizing the carbonate looping process. In this work, the reactivity and stability of carbide slag for CO₂ capture have been examined. The results show that carbide slag exhibits superior CO₂ capture performance even at severe calcination temperatures in comparison with limestones, shells, pure CaCO₃, and Ca(OH)₂. X-ray diffraction analysis shows that there is mayenite (Ca₁₂Al₁₄O₃₃) formed in the calcination step for carbide slag, which is the main reason for its high stability in the carbonate looping process.     

Dissolution of steelmaking slags in acetic acid for precipitated calcium carbonate production

A promising option for long-term storage of CO₂ is to fixate carbon dioxide as magnesium- and calcium carbonates. Slags from iron and steel works are potential raw materials for carbonation due to their high contents of calcium silicates. Precipitated calcium carbonate (PCC) is used as filler and coating materials in paper. If slag could be used instead of limestone for producing PCC, considerable energy savings and carbon dioxide emissions reductions could be achieved. In this paper, the leaching of calcium from iron and steel slags using acetic acid was investigated. Thermodynamic equilibrium calculations at atmospheric gas pressures showed that extraction of calcium is exothermic and feasible at temperatures lower than 156 °C, while the precipitation of calcium carbonate is endothermic and feasible at temperatures above 45 °C. The formation of calcium- and magnesium acetate in the solution was found to be thermodynamically possible. Laboratory-scale batch experiments showed that iron and steel slags rapidly dissolve in acetic acid in a few minutes and the exothermic nature of the reaction was verified. While silicon was successfully removed by filtration using solution temperatures of 70–80 °C, further separation methods are required for removing iron, aluminum and magnesium from the solution.     

CCS: A future CO2 mitigation option for Germany?—A bottom-up approach

The role that carbon capture and storage (CCS) technologies could play within the framework of an overall CO₂ mitigation strategy is examined in the form of scenarios up to 2030 with the example of Germany. As the calculations show, the use of CCS can represent an interesting mitigation option in view of stringent CO₂ reduction goals. The scenarios, performed with the aid of the IKARUS optimization model, however, also show that according to cost-efficiency criteria a large number of measures would have to be taken covering all energy sectors. CCS can at best represent one element in an overall strategy. The model results show that a mitigation goal for 2030 corresponding to a 35% reduction of CO₂ as compared to 1990 is necessary to trigger a significant contribution of CCS. As an alternative to a CO₂ restriction, we also calculated reduction scenarios based on CO₂ penalties. These scenarios showed that a penalty price of approximately 30 €/tCO₂ is necessary before CCS can be included in the model.     

CO2 capture performance of calcium-based sorbent doped with manganese salts during calcium looping cycle

The effects of manganese salts including Mn(NO₃)₂ and MnCO₃ on CO₂ capture performance of calcium-based sorbent during cyclic calcination/carbonation reactions were investigated. Mn(NO₃)₂ and MnCO₃ were added by wet impregnation method. The cyclic CO₂ capture capacities of Mn(NO₃)₂-doped CaCO₃, MnCO₃-doped CaCO₃ and original CaCO₃ were studied in a twin fixed-bed reactor and a thermo-gravimetric analyzer (TGA), respectively. The results show that the addition of manganese salts improves the cyclic carbonation conversions of CaCO₃ except the previous cycles. When the Mn/Ca molar ratios are 1/100 for Mn(NO₃)₂-doped CaCO₃ and 1.5/100 for MnCO₃-doped CaCO₃, the highest carbonation conversions are achieved respectively. The carbonation temperature of 700-720 °C is beneficial to CO₂ capture of Mn-doped CaCO₃. The residual carbonation conversions of Mn(NO₃)₂-doped and MnCO₃-doped CaCO₃ are 0.27 and 0.24 respectively after 100 cycles, compared with the conversion of 0.16 for original one after the same number of cycles. Compared with calcined original CaCO₃, better pore structure is kept for calcined Mn-doped CaCO₃ during calcium looping cycle. The pore volume of calcined MnCO₃-doped CaCO₃ is 2.4 times as high as that of calcined original CaCO₃ after 20 cycles. The pores of calcined MnCO₃-doped CaCO₃ in the pore size range of 27-142 nm are more abundant relative to clacined original one. That is why modification by manganese salts can improve cyclic CO₂ capture capacity of CaCO₃.     

Effects of CO2 gas as leaks from geological storage sites on agro-ecosystems

Carbon capture and storage in geological formations has potential risks in the long-term safety because of the possibility of CO₂ leakage. Effects of leaking gas, therefore, on vegetation, soil, and soil-inhabiting organisms are critical to understand. An artificial soil gassing and response detection field facility developed at the University of Nottingham was used to inject CO₂ gas at a controlled flow rate (1 l min⁻¹) into soil to simulate build-up of soil CO₂ concentrations and surface fluxes from two land use types: pasture grassland, and fallow followed by winter bean. Mean soil CO₂ concentrations was significantly higher in gassed pasture plots than in gassed fallow plots. Germination of winter bean sown in gassed fallow plots was severely hindered and the final crop stand was reduced to half. Pasture grass showed stress symptoms and above-ground biomass was significantly reduced compared to control plot. A negative correlation (r = −0.95) between soil CO₂ and O₂ concentrations indicated that injected CO₂ displaced O₂ from soil. Gassing CO₂ reduced soil pH both in grass and fallow plots (p = 0.012). The number of earthworm castings was twice as much in gassed plots than in control plots. This study showed adverse effects of CO₂ gas on agro-ecosystem in case of leakage from storage sites to surface.     

Carbon Dioxide Disposal via Carbonation

Abstract

Carbonation is a solidification/stabilization process. The availability of a carbon dioxide (CO₂) fixation technology would serve as insurance in case global warming causes severe restrictions on CO₂ emissions. In order to prevent rapid climate change, it will be necessary to stabilize CO₂ as carbonate by the carbonation process. Carbonation of the widely occurring mineral olivine (Mg₂SiO₄) converts CO₂ into an environmentally benign mineral magnesite (MgCO₃).     

An advanced zero emission power cycle with integrated low temperature thermal energy

An innovative zero emission hybrid cycle named HICES (hybrid and improved CES cycle) is presented in this paper. It can utilize fossil fuel and low quality thermal energy such as waste heat from industrial processes and solar thermal energy for highly efficient electric power generation. In the HICES cycle, natural gas is internally combusted with pure oxygen. External low quality thermal energy is used to produce saturated steam between 70 and 250 °C as part of the working fluid. The thermodynamic characteristics at design conditions of the HICES cycle are analyzed using the advanced process simulator Aspen Plus. The influences of some key parameters are investigated. The results demonstrate that the thermodynamic performances of the HICES cycle are quite promising. For example, when the external heat produced saturated steam is at 70 °C, the net fuel-to-electricity efficiency is 54.18% even when taking into account both the energy penalties to produce pure oxygen and to liquefy the captured CO₂. The incremental low temperature heat to electric efficiency is as high as 14.08% at the same time. When the external heat produced saturated steam is at 250 °C, the net fuel-to-electricity efficiency reaches 62.66%. The incremental low temperature heat to electric efficiency achieves 48.92%.     

Sulphur impacts during pulverised coal combustion in oxy-fuel technology for carbon capture and storage

The oxy-fuel process is one of three carbon capture technologies which supply CO₂ ready for sequestration - the others being post-combustion capture and IGCC with carbon capture. As yet no technology has emerged as a clear winner in the race to commercial deployment. The oxy-fuel process relies on recycled flue gas as the main heat carrier through the boiler and results in significantly different flue gas compositions. Sulphur has been shown in the study to have impacts in the furnace, during ash collection, CO₂ compression and transport as well as storage, with many options for its removal or impact control. In particular, the effect of sulphur containing species can pose a risk for corrosion throughout the plant and transport pipelines. This paper presents a technical review of all laboratory and pilot work to identify impacts of sulphur impurities from throughout the oxy-fuel process, from combustion, gas cleaning, compression to sequestration with removal and remedial options. An economic assessment of the optimum removal is not considered. Recent oxy-fuel pilot trials performed in support of the Callide Oxy-fuel Project and other pilot scale data are interpreted and combined with thermodynamic simulations to develop a greater fundamental understanding of the changes incurred by recycling the flue gas. The simulations include a sensitivity analysis of process variables and comparisons between air fired and oxy-fuel fired conditions - such as combustion products, SO₃ conversion and limestone addition.     

A study of the methanation of carbon dioxide on Ni/Al2O3 catalysts at atmospheric pressure

The hydrogenation of carbon dioxide producing methane and CO has been investigated over Ni/Al₂O₃ catalysts. The as prepared catalysts have been characterized by XRD and Temperature Programmed Reduction. Spent catalysts have been characterized by XRD and Field Emission SEM. Catalytic activity needs the presence of Ni metal particles which may form in situ if the Ni loading is higher than that needed to cover the alumina surface with a complete monolayer. If Ni content is lower, pre-reduction is needed. Catalysts containing very small Ni particles obtained by reducing moderate loading materials are very selective to methane without CO formation. The larger the Ni particles, due to higher Ni loadings, the higher the CO production. Cubic Ni metal particles are found in the spent catalysts mostly without carbon whiskers. The data suggest that fast methanation occurs at the expense of CO intermediate on the corners of nanoparticles interacting with alumina, likely with a “via oxygenate” mechanism.     

Cost and performance of fossil fuel power plants with CO2 capture and storage

CO₂ capture and storage (CCS) is receiving considerable attention as a potential greenhouse gas (GHG) mitigation option for fossil fuel power plants. Cost and performance estimates for CCS are critical factors in energy and policy analysis. CCS cost studies necessarily employ a host of technical and economic assumptions that can dramatically affect results. Thus, particular studies often are of limited value to analysts, researchers, and industry personnel seeking results for alternative cases. In this paper, we use a generalized modeling tool to estimate and compare the emissions, efficiency, resource requirements and current costs of fossil fuel power plants with CCS on a systematic basis. This plant-level analysis explores a broader range of key assumptions than found in recent studies we reviewed for three major plant types: pulverized coal (PC) plants, natural gas combined cycle (NGCC) plants, and integrated gasification combined cycle (IGCC) systems using coal. In particular, we examine the effects of recent increases in capital costs and natural gas prices, as well as effects of differential plant utilization rates, IGCC financing and operating assumptions, variations in plant size, and differences in fuel quality, including bituminous, sub-bituminous and lignite coals. Our results show higher power plant and CCS costs than prior studies as a consequence of recent escalations in capital and operating costs. The broader range of cases also reveals differences not previously reported in the relative costs of PC, NGCC and IGCC plants with and without CCS. While CCS can significantly reduce power plant emissions of CO₂ (typically by 85–90%), the impacts of CCS energy requirements on plant-level resource requirements and multi-media environmental emissions also are found to be significant, with increases of approximately 15–30% for current CCS systems. To characterize such impacts, an alternative definition of the “energy penalty” is proposed in lieu of the prevailing use of this term.     

Technoeconomic assessment of China’s indirect coal liquefaction projects with different CO2 capture alternatives

ICL (Indirect coal liquefaction), an alternative fuel-supplying technology, has drawn much attention and caused considerable debate in China’s energy sector. The hurdles to its development include the high risk of investment into large-scale installations, the high CO₂ emissions and water resource consumption. A comprehensive assessment of ICL is urgently needed. This study provides an economic assessment and a technical analysis based on process simulations. To address the future challenge of curbing CO₂ emissions, three absorption methods are compared for capturing the CO₂ released from the ICL process: DMC (a novel absorbent), MEA and Rectisol. The comparative results suggest that physical absorbents, represented by Rectisol and DMC, have a remarkable advantage over chemical absorption processes, represented by MEA. The Rectisol process costs the least, while the DMC process is close to the same level. As a novel absorbent, DMC has the potential to be widely used in the future. The economic analysis of ICL predicted a high capital cost of over 35 billion yuan and an overall product cost of approximately 3800 yuan/ton for the baseline. In addition, via a sensitivity analysis, coal price, electricity price and capacity factor were identified as the three most influential factors affecting the overall product cost.     

Heat optimisation of a staged gas–solid mineral carbonation process for long-term CO2 storage

Carbonation of magnesium silicates offers an interesting option for CO₂ emission mitigation in Finland, a country with large resources of serpentine-type minerals. Wet processes using aqueous solutions show reasonable chemical kinetics combined with poor energy economy. A dry, gas–solid process with slower chemical kinetics (demonstrated previously), but better energy economy could be an alternative. This paper addresses the energy economy of a two- or three-stage gas–solid process for magnesium silicate carbonation. It involves production of reactive magnesium as magnesium oxide or hydroxide in an atmospheric pressure step, followed by carbonation at elevated pressures that allow for reasonable carbonation reaction kinetics under conditions where magnesium carbonate is thermodynamically stable. For a feasible large-scale process the kinetics in the individual reactors must be fast enough, while the heat produced in the carbonation step must be sufficient to compensate for energy inputs to the preceding step(s). Results give reactor temperature combinations that allow for operation at a negative or zero energy input, for given carbonation reactor pressure and degree of carbonation conversion, and other process energy requirements. Softwares used were HSC and Aspen Plus. Also, some results from gas–solid kinetics studies with magnesium oxide-based materials at the pressures considered are included.