Conceptual study of distributed CO2 capture and the sustainable carbon economy

Capture of carbon dioxide from distributed sources is often neglected as a viable solution to the global problem of CO₂ emissions management. Small scale power plants, including those applicable to the transportation sector, can be designed to capture their CO₂ exhaust stream, provided it is not heavily diluted with air. Liquefaction of carbon dioxide allows the captured CO₂ to be stored densely, with a minimal energetic penalty and space requirement, until it can be permanently sequestered. In this short-term solution, the energetic penalty for CO₂ capture can be further offset by exploiting novel energy conversion processes involving regeneration of the reaction product stream – a simple strategy that is not exploited in conventional systems. More importantly, in the long-term, as the renewable energy infrastructure is built up, the collected CO₂ can be recycled into synthetic carbon-based liquid fuels which act as energy carriers in the sustainable carbon economy.     

Integrated biomass energy systems and emissions of carbon dioxide

Electric Power Research Institute (EPRI) and the US Department of Energy (DOE) have been funding a number of case studies under the initiative entitled “Economic Development through Biomass Systems Integration”, with the objective of investigate the feasibility of integrated biomass energy systems, utilizing a dedicated feedstock supply system (DFSS) for energy production. This paper deals with the full fuel cycle for four of these case studies, which have been examined with regard to the emissions of carbon dioxide, CO₂. Although the conversion of biomass to electricity in itself does not emit more CO₂ than is captured by the biomass through photosynthesis, there will be some CO₂ emissions from the DFSS. External energy is required for the production and transportation of the biomass feedstock, and this energy is mainly based on fossil fuels. By using this input energy, CO₂ and other greenhouse gases are emitted. However, by utilizing biomass with fossil fuels as external input fuels, we would get about 10–15 times more electric energy per unit fossil fuel, compared with a 100% coal power system. By introducing a DFSS on former farmland the amount of energy spent for production of crops can be reduced, the amount of fertilizers can be decreased, the soil can be improved and a significant amount of energy will be produced compared with an ordinary farm crop. Compared with traditional coal-based electricity production, the CO₂ emissions are in most cases reduced significantly by as much as 95%. The important conclusion is the great potential for reducing greenhouse gas emissions through the offset of coal by biomass.     

CO2 utilization options, part II: Assessment of dimethyl carbonate production

In this paper, the potential to reduce CO₂ emissions from dimethyl carbonate production by switching from the traditional phosgene-based production to a urea-based CO₂ utilization process is assessed. The total CO₂ emission for each process is estimated, including emissions related to the carbon content of the products, energy consumption in the production process, and energy consumption in the production processes of the required reactants. Implementation of the CO₂ utilization process probably will reduce total CO₂ emissions. However, in order to achieve substantially reduced CO₂ emissions, serious consideration must be given to the optimization and design of the CO₂ utilization process. Furthermore, the fuel-mix employed is one of the factors that influences the total CO₂ emission the most.     

Cost effective integration of hydrogen in energy systems with CO2 constraints

The integration of hydrogen in national energy systems is illustrated in four extreme scenarios, reflecting four technological mainstreams (energy conservation, renewables, nuclear and CO₂ removal) to reduce C emissions. Hydrogen is cost-effective in all scenarios with higher CO₂ reduction targets. Hydrogen would be produced from fossil fuels, or from water and electricity or heat, depending upon the scenario. Hydrogen would be used in the residential and commercial sectors and for transport vehicles, industry, and electricity generation in fuel cells. At severe (50–70%) CO₂ reduction targets, hydrogen would cost-effectively supply more than half of the total useful energy demands in three out of four scenarios. The marginal emission reduction costs in the CO₂ removal scenario at severe CO₂ reduction targets are DFL 200/tCO₂ (ca $ 100/t). In the nuclear, renewable and energy conservation scenarios these costs are much higher. Whilst the fossil fuel scenario would be less expensive than the other scenarios, the possibility of CO₂ storage in depleted gas reservoirs is a conditio sine qua non.     

Toward integrated energy and materials policies? A case study on CO2 reduction in the Netherlands

Energy and material flows are closely related. The materials system is of major significance from a national energy and CO₂ point of view. Integrated energy and materials studies can show significant new policy options for energy savings and CO₂ emission reduction through materials system improvements, shown in a case study on long-term CO₂ emission reduction in the Netherlands. An integrated energy and materials system MARKAL model is used for this analysis. The results show that, on one hand, CO₂ emission reduction costs are significantly reduced in the integrated approach and, on the other hand, the materials system is significantly influenced by CO₂ emission reduction. Consideration of dynamic interactions results in better understanding of future developments in both energy and materials systems.     

Natural gas fired combined cycle power plant with CO2 capture

A natural gas (NG) fired power plant is designed with virtually zero emissions of pollutants, including CO₂. The plant operates in a gas turbine-steam turbine combined cycle mode. NG is fired in highly enriched oxygen (99.7%) and recycled CO₂ from the flue gas. Liquid oxygen (LOX) is supplied by an on-site air separation unit (ASU). By cross-integrating the ASU with the CO₂ capture unit, the energy consumption for CO₂ capture is significantly reduced. The exergy of LOX is used to liquefy CO₂ from the flue gas, thereby saving compression energy and also delivering product CO₂ in a saleable form. By applying a new technique, the gas turbine efficiency is increased by about 2.9%. The net thermal efficiency (electricity out/heat input) is estimated at 45%, compared to a plant without CO₂ capture of 54%. However, the relatively modest efficiency loss is amply compensated by producing saleable byproducts, and by the virtue that the plant is pollution free, including NO_x, SO₂ and particulate matter. In fact, the plant needs no smokestack. Besides electricity, the byproducts of the plant are condensed CO₂, NO₂ and Ar, and if operated in cogeneration mode, steam.     

水合物法分离CO2工艺研究进展

随着温室效应加剧,CO₂减排行动已迫在眉睫。水合物法分离CO₂工艺作为一种发展前景广阔的新型CO₂分离技术,为CO₂减排提供了一种解决思路。水合物法分离CO₂工艺相比于化学吸收、物理吸附、深冷分离和膜分离等技术具有分离效率高、过程简单无副产物、条件温和的优势,为减缓CO₂排放增加对环境造成的影响提供了一个中短期解决方案,以此为前提将允许人类继续使用化石燃料直至可再生能源技术广泛应用。本文综合分析了国内外的相关文献,介绍了水合物法分离CO₂工艺的基本原理,并比较了水合物法分离CO₂不同工艺的优劣之处,为进一步优化水合物法分离CO₂工艺提供指导。     

CO2 emissions per individual based on a survey of university students

The amount of CO₂ produced by the daily activities of university students is estimated on the basis of statistical, questionnaire, and measurement data. The results reveal that a large proportion of CO₂ emissions occurs during energy consumption, food preparation and transport, and that the CO₂ emissions of dormitory residents are lower than those of students living in other situations. Practical methods for reducing student CO₂ emissions are also examined.     

二氧化碳在深部盐水层中溶解封存规律的研究进展

将二氧化碳埋存到深部盐水层中是目前缓解温室效应的可行性对策之一,在评价储层理论埋存量时,溶解封存量在总埋存量中占有很大的比例。本文通过对相关文献的调研,计算对比了Duan&Sun模型模拟数据与前人实验数据的误差,根据前人实验与本文模拟数据分析了二氧化碳在盐水层中溶解的动力过程和热力过程,二氧化碳通过扩散作用溶解到盐水中,引起盐水层密度的变化,计算系统瑞利数满足对流运动发生的基本条件后,系统产生对流,这有利于二氧化碳的溶解。分析了温度、压力和矿化度对二氧化碳溶解的影响。在前几百年内溶解缓慢易导致泄漏,低温高压、低矿化度下二氧化碳溶解度较高,小二氧化碳水滴更有利于二氧化碳封存。     

CO2 utilization options, Part I: An emission assessment framework

The utilization of CO₂ in various products and services must be carefully assessed in order to achieve reduced CO₂ emissions and simultaneously to add to the net economic benefit of society. In this paper, a framework for the assessment of CO₂ utilization options in the chemical industry is outlined in which the total CO₂ emission is estimated in four steps. First, the processes under study are surveyed to establish the consumption of different raw materials (reactants). Second, the CO₂ emission due to the content of fossil carbon in the reactants is determined, i.e. the material-related emission. Third, the CO₂ emission related to energy consumption in the studied processes is estimated, i.e. the direct energy-related emission. Fourth, the CO₂ emission related to energy consumption in the reactant production processes is estimated, i.e. the indirect energy-related emission.     

Effect of CO2 diffusion on wettability for hydrocarbon-water-CO2 systems in capillaries

The importance of wettability in enhanced oil recovery with high pressure CO₂ has been demonstrated by some authors. When CO₂ diffuse in hydrocarbons, it promotes swelling and reduction in contact angle and surface tension, these changes improve the tendency to fill the corners of solid surfaces, therefore filaments arise in corners. In this work, hydrocarbon-water-CO₂ behavior was studied in cylindrical and square capillaries. Square capillaries were used in order to observe the wetting in corners. Cylindrical capillaries were used to determine if there is swelling in hydrocarbons due to the CO₂ mass transfer, first through the water and then through the hydrocarbon. Contact angle and interfacial tension were measured in an attemp to explain the results. It was demonstrated that the CO₂ diffusion occurs first through water and then through hydrocarbons. The CO₂ diffusion is evident due to the contact angle diminution and the displacement of water-hydrocarbon interfaces. In addition, it was found that the behavior of water-hydrocarbon interphase depends on contact angle and surface tension. Finally, when interfacial tension is lower, the displacement is different and contact angle increasing is higher, as it was concluded by Campbell and Orr [1].     

Mitigation assessment results and priorities for China''s energy sector

Energy-related CO₂ emission projections of China up to 2030 are given. CO₂ mitigation potential and technology options in main fields of energy conservation and energy substitution are analyzed. CO₂ reduction costs of main mitigation technologies are estimated and the multi-criteria approach is used for assessment of priority technologies.

The results of this study show (1) Given population expansion and high GDP growth, energy-related CO₂ emissions will increase in China. (2) There exists a large energy conservation potential in China. (3) Adjustment of industry structure and increase of shares of products with high added value have and will play a very important role in reducing energy intensity of GDP. (4) Energy conservation and substitution of coal by natural gas, nuclear power, hydropower and renewable energy will be the key technological measures in a long-term strategy to reduce GHG emission. (5) Identification and implementation of GHG mitigation technologies is consistent with China's targets of sustainable development and environmental protection. (6) Energy efficiency improvement is a “no-regret” option for CO₂ reduction, whereas an incremental cost is needed to develop hydropower and renewable energy.     

广东能源消费碳排放趋势与前景展望

能源消费是人类活动排放CO₂等温室气体的主要来源,碳减排已成为我国能源发展的一个重要约束因素。2012年全世界能源消费排放3.173 4×1010 t CO₂,中国能源消费排放的CO₂已占世界总排放量的26.0%。2012年全世界人均CO₂排放量4 510 kg,而中国人均CO₂排放量达到了6 093 kg。同年广东省人均CO₂排放量为5 224 kg,高于世界平均水平,低于全国平均水平。随着节能减排和应对气候变化工作的推进,广东的单位产值能耗水平逐年降低,能源结构不断改善,使得全省化石能源消费带来的CO₂排放量的增长势头得到抑制,2012年的排放量比2011年略有减少。按目前的发展趋势预测,到2020年,广东CO₂排放总量将达到1.606 2×108 t碳当量,比2012年增加9.69×106 t碳当量,人均CO₂排放量将达到5 287 kg,略高于2012年的5 224 kg。如果在“十三五”期间加快第三产业发展,则到2020年广东省化石能源消费总量将比2012年下降2.7%,CO₂排放总量将比2012年下降3.5%,人均CO₂排放量将由2012年的5 224 kg下降到2020年的4 795 kg,接近世界平均水平。     

Decomposition analysis of CO2 emission intensity between oil-producing and non-oil-producing sub-Saharan African countries

The need to decompose CO₂ emission intensity is predicated upon the need for effective climate change mitigation and adaptation policies. Such analysis enables key variables that instigate CO₂ emission intensity to be identified while at the same time providing opportunities to verify the mitigation and adaptation capacities of countries. However, most CO₂ decomposition analysis has been conducted for the developed economies and little attention has been paid to sub-Saharan Africa. The need for such an analysis for SSA is overwhelming for several reasons. Firstly, the region is amongst the most vulnerable to climate change. Secondly, there are disparities in the amount and composition of energy consumption and the levels of economic growth and development in the region. Thus, a decomposition analysis of CO₂ emission intensity for SSA affords the opportunity to identify key influencing variables and to see how they compare among countries in the region. Also, attempts have been made to distinguish between oil and non-oil-producing SSA countries. To this effect a comparative static analysis of CO₂ emission intensity for oil-producing and non oil-producing SSA countries for the periods 1971–1998 has been undertaken, using the refined Laspeyres decomposition model. Our analysis confirms the findings for other regions that CO₂ emission intensity is attributable to energy consumption intensity, CO₂ emission coefficient of energy types and economic structure. Particularly, CO₂ emission coefficient of energy use was found to exercise the most influence on CO₂ emission intensity for both oil and non-oil-producing sub-Saharan African countries in the first sub-interval period of our investigation from 1971–1981. In the second subinterval of 1981–1991, energy intensity and structural effect were the two major influencing factors on emission intensity for the two groups of countries. However, energy intensity effect had the most pronounced impact on CO₂ emission intensity in non-oil-producing sub-Saharan African countries, while the structural effect explained most of the increase in CO₂ emission intensity among the oil-producing countries. Finally, for the period 1991–1998, structural effect accounted for much of the decrease in intensity among non-oil-producers, while CO₂ emission coefficient of energy use was the major force driving the decrease among oil-producing countries. The dynamic changes in the CO₂ emission intensity and energy intensity effects for the two groups of countries suggest that fuel switching had been predominantly towards more carbon-intensive production in oil-producing countries and less carbon-intensive production in non-oil-producing SSA countries. In addition to the decomposition analysis, the article discusses policy implications of the results. We hope that the information and analyses provided here would help inform national energy and climate policy makers in SSA of the relative weaknesses and possible areas of strategic emphasis in their planning processes for mitigating the effects of climate change.     

The efficiency-renewable synergism

Improving energy efficiency is the most effective and least expensive way to reduce carbon dioxide (CO₂) emissions in most industrialized nations— including the UK. A report from the UKAEA's own Energy Technology Support Unit concludes that energy efficiency can displace nearly four times more CO₂ than nuclear power can - more quickly and more cost-effectively. Each pound invested in efficient lighting can displace four to five times as much CO₂ as a pound invested in new nuclear power. Meanwhile, given recent dramatic progress in renewable energy technologies, the most promising long-term CO₂-abatement strategy may be a synergistic combination of energy efficiency and renewable energy.     

Review on cryogenic technologies for CO2 removal from natural gas

CO₂ in natural gas (NG) is prone to condense directly from gas to solid or solidify from liquid to solid at low temperatures due to its high triple point and boiling temperature, which can cause a block of equipment. Meanwhile, CO₂ will also affect the calorific value of NG. Based on the above reasons, CO₂ must be removed during the NG liquefaction process. Compared with conventional methods, cryogenic technologies for CO₂ removal from NG have attracted wide attention due to their non-polluting and low-cost advantages. Its integration with NG liquefaction can make rational use of the cold energy and realize the purification of NG and the production of by-product liquid CO₂. In this paper, the phase behavior of the CH₄-CO₂ binary mixture is summarized, which provides a basis for the process design of cryogenic CO₂ removal from NG. Then, the detailed techniques of design and optimization for cryogenic CO₂ removal in recent years are summarized, including the gas-liquid phase change technique and the gas-solid phase change technique. Finally, several improvements for further development of the cryogenic CO₂ removal process are proposed. The removal process in combination with the phase change and the traditional techniques with renewable energy will be the broad prospect for future development.     

A comparison of electricity and hydrogen production systems with CO2 capture and storage—Part B: Chain analysis of promising CCS options

Promising electricity and hydrogen production chains with CO₂ capture, transport and storage (CCS) and energy carrier transmission, distribution and end-use are analysed to assess (avoided) CO₂ emissions, energy production costs and CO₂ mitigation costs. For electricity chains, the performance is dominated by the impact of CO₂ capture, increasing electricity production costs with 10–40% up to 4.5–6.5 €ct/kWh. CO₂ transport and storage in depleted gas fields or aquifers typically add another 0.1–1 €ct/kWh for transport distances between 0 and 200 km. The impact of CCS on hydrogen costs is small. Production and supply costs range from circa 8 €/GJ for the minimal infrastructure variant in which hydrogen is delivered to CHP units, up to 20 €/GJ for supply to households. Hydrogen costs for the transport sector are between 14 and 16 €/GJ for advanced large-scale coal gasification units and reformers, and over 20 €/GJ for decentralised membrane reformers. Although the CO₂ price required to induce CCS in hydrogen production is low in comparison to most electricity production options, electricity production with CCS generally deserves preference as CO₂ mitigation option. Replacing natural gas or gasoline for hydrogen produced with CCS results in mitigation costs over 100 €/t CO₂, whereas CO₂ in the power sector could be reduced for costs below 60 €/t CO₂ avoided.     

System analysis of hydrogen production from gasified black liquor

Hydrogen produced from renewable biofuel is both clean and CO₂ neutral. This paper evaluates energy and net CO₂ emissions consequences of integration of hydrogen production from gasified black liquor in a chemical pulp mill. A model of hydrogen production from gasified black liquor was developed and integration possibilities with the pulp mill's energy system were evaluated in order to maximize energy recovery. The potential hydrogen production is 59 000 tonnes per year if integrated with the KAM reference market pulp mill producing 630 000 Air dried tonnes (ADt) pulp/year. Changes of net CO₂ emissions associated with modified mill electric power balance, biofuel import and end usage of the produced hydrogen are presented and compared with other uses of gasified black liquor such as electricity production and methanol production. Hydrogen production will result in the greatest reduction of net CO₂ emissions and could reduce the Swedish CO₂ emissions by 8% if implemented in all chemical market pulp mills. The associated increases of biofuel and electric power consumption are 5% and 1.7%, respectively.     

China’s pre-2020 CO2 emission reduction potential and its influence

China achieved the reduction of CO₂ intensity of GDP by 45% compared with 2005 at the end of 2017, realizing the commitment at 2009 Copenhagen Conference on emissions reduction 3 years ahead of time. In future implementation of the “13th Five-Year Plan (FYP),” with the decline of economic growth rate, decrease of energy consumption elasticity and optimization of energy structure, the CO₂ intensity of GDP will still have the potential for decreasing before 2020. By applying KAYA Formula decomposition, this paper makes the historical statistics of the GDP energy intensity decrease and CO₂ intensity of energy consumption since 2005, and simulates the decrease of CO₂ intensity of GDP in 2020 and its influences on achieving National Determined Contribution (NDC) target in 2030 with scenario analysis. The results show that China’s CO₂ intensity of GDP in 2020 is expected to fall by 52.9%–54.4% than the 2005 level, and will be 22.9%–25.4% lower than 2015. Therefore, it is likely to overfulfill the decrease of CO₂ intensity of GDP by 18% proposed in the 13th FYP period. Furthermore, the emission reduction potentiality before 2020 will be conducive to the earlier realization of NDC objectives in 2030. China’s CO₂ intensity of GDP in 2030 will fall by over 70% than that in 2005, and CO₂ emissions peak will appear before 2030 as early as possible. To accelerate the transition to a low-carbon economy, China needs to make better use of the carbon market, and guide the whole society with carbon price to reduce emissions effectively. At the same time, China should also study the synergy of policy package so as to achieve the target of emission reduction.     

Hydrogen no longer a high cost solution to global warming: New ideas

This paper contains brief statements about three new low-cost methods of obtaining clean hydrogen in massive amounts.

In the first method, new technology for converting solar energy and water to hydrogen at a price of $2.50 for an amount of hydrogen equal in first law energy to that in a gallon of gasoline seems to follow from a company's announcement of their new technology, already working, in one fully industrialized plant, producing electricity at a price corresponding to that from coal.

In the second method, pure hydrogen (no accompanying CO₂) can be obtained from natural gas and heat. The cost would be a little less than that of the low-cost hydrogen from water decomposition (and avoid storage of hydrogen for the 18 h/day of zero solar light).

In the third method, CO₂ is extracted from the atmosphere and combined chemically with the low-cost hydrogen to produce methanol. On being used to produce heat or electricity (fuel cell), CO₂ is left over. However, the amount of CO₂, thus added to the atmosphere is just equivalent to the amount removed. The presence of low-cost hydrogen from water means that the resulting methanol will also be of low cost and be a cure for global warming without a radical change of distribution method.