Resource demand implications for US algae biofuels production scale-up

Photosynthetic microalgae with the potential for high biomass and oil productivities have long been viewed as a promising class of feedstock for biofuels to displace petroleum-based transportation fuels. Algae offer the additional benefits of potentially being produced without using high-value arable land and fresh water, thereby reducing the competition for those resources between expanding biofuels production and conventional agriculture. Algae growth can also be enhanced by the use of supplemental CO₂ that could be supplied by redirecting concentrated CO₂ emissions from stationary industrial sources such as fossil-fired power plants, cement plants, fermentation industries, and others. In this way, algae may offer an effective means to capture carbon emissions for reuse in renewable fuels and co-products, while at the same time displacing fossil carbon fuels to help bring about a net reduction in overall carbon emissions. Significant displacement of petroleum fuels will require that algae feedstock production reach large volumes that will put demands on key resources. This scenario-based analysis provides a high-level assessment of land, water, CO₂ and nutrient (nitrogen, phosphorus) demands resulting from algae biofuel feedstock production reaching target levels of 10 billion gallons per year (BGY), 20 BGY, 50 BGY, and 100 BGY for four different geographical regions of the United States. Different algae productivities are assumed for each scenario region, where relative productivities are nominally based on annual average solar insolation. The projected resource demands are compared with data that provide an indication of the resource level potentially available in each of the scenario regions. The results suggest that significant resource supply challenges can be expected to emerge as regional algae biofuel production capacity approaches levels of about 10 BGY. The details depend on the geographic region, the target feedstock production volume, and the level of algae productivity that can be achieved. The implications are that the supply of CO₂, nutrients, and water, in particular, can be expected to severely limit the extent to which US production of algae biofuel can be sustainably expanded unless approaches are developed to mitigate these resource constraints in parallel to emergence of a viable algae technology. Land requirements appear to be the least restrictive, particularly in the Western half of the country where larger quantities of potentially suitable classes of land exist. Within the limited scope and assumptions of this analysis, sustainable photosynthetic microalgae biofuel feedstock production in the US in excess of about 10 BGY will likely be a challenge due to other water, CO₂ and nutrient resource limitations. Developing algae production approaches that can effectively use non-fresh water resources and minimize both water and nutrient requirements will help reduce resource constraints. Providing adequate CO₂ resources for enhanced algae production appears the biggest challenge, and could emerge as a constraint at oil production levels below 10 BGY.     

CO2 emissions reduction of Chinese light manufacturing industries: A novel RAM-based global Malmquist–Luenberger productivity index

Climate change has become one of the most challenging issues facing the world. Chinese government has realized the importance of energy conservation and prevention of the climate changes for sustainable development of China's economy and set targets for CO₂ emissions reduction in China. In China industry contributes 84.2% of the total CO₂ emissions, especially manufacturing industries. Data envelopment analysis (DEA) and Malmquist productivity (MP) index are the widely used mathematical techniques to address the relative efficiency and productivity of a group of homogenous decision making units, e.g. industries or countries. However, in many real applications, especially those related to energy efficiency, there are often undesirable outputs, e.g. the pollutions, waste and CO₂ emissions, which are produced inevitably with desirable outputs in the production. This paper introduces a novel Malmquist–Luenberger productivity (MLP) index based on directional distance function (DDF) to address the issue of productivity evolution of DMUs in the presence of undesirable outputs. The new RAM (Range-adjusted measure)-based global MLP index has been applied to evaluate CO₂ emissions reduction in Chinese light manufacturing industries. Recommendations for policy makers have been discussed.     

Potential for reducing global carbon emissions from electricity production—A benchmarking analysis

We present five performance indicators for electricity generation for 129 countries using the 2005 data. These indicators, measured at the national level, are the aggregate CO₂ intensity of electricity production, the efficiencies of coal, oil and gas generation and the share of electricity produced from non-fossil fuels. We conduct a study on the potential for reducing global energy-related CO₂ emissions from electricity production through simple benchmarking. This is performed based on the last four performance indicators and the construction of a cumulative curve for each of these indicators. It is found that global CO₂ emissions from electricity production would be reduced by 19% if all these indicators are benchmarked at the 50th percentile. Not surprisingly, the emission reduction potential measured in absolute terms is the highest for large countries such as China, India, Russia and the United States. When the potential is expressed as a percentage of a country's own emissions, few of these countries appear in the top-five list.     

The impact of CO2 taxation on the configuration of new refineries: An application to Brazil

This article evaluates the impact of pricing CO₂ emissions over the configuration of new refinery complexes in their conceptual phase. Two refineries’ schemes were simulated through a linear programming optimization model in order to compare the optimum configuration obtained before and after the input of different CO₂ prices. The cases analyzed represent refining projects to be located in Brazil, a growing market for fuels and petrochemical feedstocks, as well as an oil producing country with rising crude exports. After 2012, emerging countries, such as Brazil, may adopt carbon emission reduction targets. Therefore, it is worth analyzing the impact of pricing CO₂ emissions in these countries, where the majority of new refining projects will be located. Our findings indicate that the initial refinery configurations proposed are quite rigid technologically for CO₂ prices up to US$ 100/t CO₂. For CO₂ prices higher than US$ 100/t CO₂, refineries reduced their emissions by increasing the consumption of natural gas used to produce hydrogen, and through changes in the original configurations towards less-energy consuming process units. Promising technological advances, such as carbon capture and storage (CCS), can also diminish the rigidity of the model and facilitate actions to curb carbon emissions.     

Techno-economic evaluation of coal-to-liquids (CTL) plants with carbon capture and sequestration

Coal-to-liquids (CTL) processes that generate synthetic liquid fuels from coal are of increasing interest in light of the substantial rise in world oil prices in recent years. A major concern, however, is the large emissions of CO₂ from the process, which would add to the burden of atmospheric greenhouse gases. To assess the options, impacts and costs of controlling CO₂ emissions from a CTL plant, a comprehensive techno-economic assessment model of CTL plants has been developed, capable of incorporating technology options for carbon capture and storage (CCS). The model was used to study the performance and cost of a liquids-only plant as well as a co-production plant, which produces both liquids and electricity. The effect of uncertainty and variability of key parameters on the cost of liquids production was quantified, as were the effects of alternative carbon constraints such as choice of CCS technology and the effective price (or tax) on CO₂ emissions imposed by a climate regulatory policy. The efficiency and CO₂ emissions from a co-production plant also were compared to the separate production of liquid fuels and electricity. The results for a 50,000 barrels/day case study plant are presented.     

The economic and emissions benefits of engineered wood products in a low-carbon future

There has been rapid growth in the use of engineered wood products in the construction sector in recent decades. We evaluate the economy-wide impacts on CO₂ emissions from fossil energy use of replacing carbon-intensive construction inputs, such as steel and cement, with lumber products in the US under an emissions constraint. We find that the ability to substitute lumber-based building materials increases production from the lumber and forestry sectors and decreases production from carbon-intensive sectors such as cement. Under a carbon cap-and-trade policy, the ability to substitute lumber products lowers the carbon price and the GDP cost of meeting the carbon cap, with more overall emissions abatement in the construction industry. We briefly review the broader impact of forest harvest on carbon levels in forests, critical to determining the full life cycle impacts of greater lumber use, but do not add anything new to this literature.     

Measuring eco-efficiency based on green indicators and potentials in energy saving and undesirable output abatement

Nowadays, majority of organizations are seeking to achieve sustainable development with respect to “green” concept. One of the main criteria for assessing green performance is eco-efficiency. To identify all aspects of the eco-efficiency, inputs should be divided into energy and non-energy and outputs should be divided into good and bad outputs. To deal with this issue, a data envelopment analysis (DEA) model is developed to divide inputs into both energy and non-energy and outputs into both desirable (good) and undesirable (bad) outputs. Likewise, variables are separated into both discretionary and non-discretionary factors. Accordingly, a bounded adjusted measure (BAM) based on green indicators is developed to calculate the eco-efficiency of decision making units (DMUs). Besides, energy saving potentials and undesirable output abatement potentials are calculated to show correlation coefficient between energy consumption and undesirable output. Finally, proposed model is validated by assessing the eco-efficiency of some selected members of organization for economic cooperation and development (OECD). Australia, Finland, Ireland, New Zealand, and Switzerland are recognized as eco-efficient countries and the rest of countries are inefficient in terms of the eco-efficiency. High and positive Spearman correlation coefficient between energy consumption and undesirable outputs addresses that the more use of energy inputs, the more undesirable outputs.     

CO2 capture from the industry sector

It is widely accepted that greenhouse gas emissions, especially CO₂, must be significantly reduced to prevent catastrophic global warming. Carbon capture and reliable storage (CCS) is one path towards controlling emissions, and serves as a key component to climate change mitigation and will serve as a bridge between the fossil fuel energy of today and the renewable energy of the future. Although fossil-fueled power plants emit the vast majority of stationary CO₂, there are many industries that emit purer streams of CO₂, which result in reduced cost for separation. Moreover, many industries outside of electricity generation do not have ready alternatives for becoming low-carbon and CCS may be their only option. The thermodynamic minimum work for separation was calculated for a variety of CO₂ emissions streams from various industries, followed by a Sherwood analysis of capture cost. The Sherwood plot correlates the relationship between concentrations of a target substance with the cost to separate it from the remaining components. As the target concentration increases, the cost to separate decreases on a molar basis. Furthermore, the lowest cost opportunities for deploying first-of-a-kind CCS technology were found to be in the Midwest and along the Gulf Coast. Many high purity industries, such as ethanol production, ammonia production and natural gas processing, are located in these regions. The southern Midwest and Gulf Coast are also co-located with potential geologic sequestration sites and enhanced oil recovery opportunities. As a starting point, these sites may provide the demonstration and knowledge necessary for reducing carbon capture technology costs across all industries, and improving the economic viability for CCS and climate change mitigation. The various industries considered in this review were examined from a dilution and impact perspective to determine the best path forward in terms of prioritizing for carbon capture. A possible implementation pathway is presented that initially focuses on CO₂ capture from ethanol production, followed by the cement industry, ammonia, and then natural gas processing and ethylene oxide production. While natural gas processing and ethylene oxide production produce high purity streams, they only account for relatively small portions of industrial process CO₂. Finally, petroleum refineries account for almost a fifth of industrial process CO₂, but are comprised of numerous low-purity CO₂ streams. These qualities make these three industries less attractive for initial CC implementation, and better suited for consideration towards the end of the industrial CC pathway.     

CO2 emission balances for different black liquor gasification biorefinery concepts for production of electricity or second-generation liquid biofuels

Black liquor gasification (BLG) is currently being developed as an alternative technology for energy and chemical recovery at chemical pulp mills. This study examines how different assumptions regarding systems surrounding the pulp mill affect the CO₂ emission balances for different BLG concepts. The syngas from the gasification process can be used for different applications; this study considers production of renewable motor fuels and electricity generation. Both a market pulp mill and an integrated pulp and paper mill are considered as host mill for the BLG plant. Furthermore, the consequences of limited availability of biomass are shown, i.e., increasing the use of biomass in a mill is not necessarily CO₂-neutral. The results show that the potential to reduce CO₂ emissions by introducing BLG is generally much higher for a market pulp mill than for an integrated pulp and paper mill. Electricity generation from the syngas is favoured when assuming high grid electricity CO₂ emissions where as motor fuel production is favoured when assuming low grid electricity CO₂ emissions. When considering the consequences of limited availability of biomass, the CO₂ emission balances are strongly affected, in some cases changing the results from a decrease to an increase of the CO₂ emissions.     

Review of CO2 recovery methods from the exhaust gas of biomass heating systems for safe enrichment in greenhouses

Novel approaches to practice CO₂ enrichment in greenhouses from the exhaust gas of a biomass heating system are reviewed. General CO₂ enrichment benefits for greenhouse plant production are described along with optimal management strategies to reduce fuel consumption while improving benefits. Alternative and renewable fuels for CO₂ enrichment, landfill biogas and biomass, are compared with traditional methods and fuels. Exhaust gas composition is outlined to address the challenges of CO₂ enrichment from biomass combustion and leads to a comparison between combustion and gasification to improve boiler efficiency. In terms of internal modifications to a biomass heating system, syngas combustion, following biomass gasification, presents good potential to achieve CO₂ enrichment. Regarding external modifications to clean the exhaust gas, CO₂ can be extracted from flue gases via membrane separation that has shown a lot of potential for large industries trying to reduce and isolate CO₂ emissions for sequestration. Other research has optimized wet scrubbing systems by extracting SO₂ and NO emissions from flue gases to form ammonium sulphate as a by-product valuable to fertilizer markets. The potential of these techniques are reviewed while future research directions are suggested.     

GHG balance of crude palm oil for biodiesel production in the northern region of Brazil

Biomass has become important as an alternative to fossil fuels and as a means to decrease greenhouse gas (GHG) emissions, particularly in tropical regions such as Brazil. Therefore, the demand for energy crops has increased strongly, and among such crops, palm oil is distinctive because of its productivity and well-developed production techniques. This paper intends to evaluate crude palm oil's GHG balance through a life-cycle assessment approach. This study is based on the average data of an ideal palm oil system in the northern region of Brazil. In the production of crude palm oil, a large amount of CO₂ sequestration occurs during the growth of palm oil trees. In contrast, the greatest emissions are biotic CO₂, which returns to the atmosphere and emissions from fertilizer production. The GHG balance of an oil palm plantation is approximately −208 kg CO₂-equiv./1000 kg crude palm oil per year.     

Modeling of current and future energyintensity and greenhouse gas emissions ofthe Lebanese industrial sector: assessmentof mitigation options

Greenhouse gas emissions in Lebanon mainly come from energy activities, which are responsible for 85% of all CO₂ emissions. The CO₂ emissions from energy use in manufacturing industries and construction represent 24% of the total emissions of the energy sector. Lebanese manufacturers' accounted for 39.15 million gigajoules of fuel consumption for heat and power generation in 1994, including both fuel used directly and fuel burned remotely to generate electricity used in the sector. In addition to being processed by combustion, CO₂ is generated in calcining of carbonates in the manufacture of cement, iron and glass. Electricity, the most expensive form of energy, represented 25.87% of all fuel used for heat and power. Residual fuel oil and diesel, which are used mainly in direct combustion processes, represent 26.85 and 26.55% of all energy use by industry, respectively. Scenarios for future energy use and CO₂ emissions are developed for the industrial sector in Lebanon. The development of the baseline scenario relied on available data on major plants' outputs, and on reported amounts of fuels used by the industrial sector as a whole. Energy use in industry and the corresponding greenhouse gas (GHG) emissions for Lebanon are projected in baseline scenarios that reflect technologies, activities and practices that are likely to evolve from the base year 1994 to year 2040. Mitigation work targets a 15% of CO₂ emissions from the baseline scenario by year 2005 and a 20–30% reduction of CO₂ emissions by year 2040. The mitigation options selected for analysis are screened on the basis of GHG emissions and expert judgement on the viability of their wide-scale implementation and economic benefits. Using macroeconomic assessment and energy price assumptions, the final estimates of potential GHG emissions and reduction costs of various mitigation scenarios are calculated. The results show that the use of efficient electric motors, efficient boilers and furnaces with fuel switching from fuel oil to natural gas has the largest impact on GHG emissions at a levelized annual cost that ranges from −20 to −5 US$/tonne of CO₂ reduced. The negative costs are indicative of direct savings obtained in energy cost for those mitigation options.     

CO2-free hydrogen production via microwave-driven methane pyrolysis

Hydrogen will play an integral role in achieving net-zero emissions by 2050. Many studies have been focusing on green hydrogen, but this method is highly electricity intensive. Alternatively, methane pyrolysis can produce hydrogen without direct CO₂ emissions and with modest electricity inputs, serving as a bridge from fossil fuels to renewable energies. Microwaves are an efficient method of adding the required energy for this endothermic reaction. This study introduces a new method of CO₂-free hydrogen production via non-plasma methane pyrolysis using microwaves and carbon products of this process. Carbon particles in the fluidized bed absorb microwave energy and create a hot medium (>1200 °C) in contact with flowing methane. As a result, methane decomposes into hydrogen and solid carbon achieving over 90% hydrogen selectivity with ∼500 cumulative hours of experiments This modular pyrolysis system can be built anywhere with access to natural gas and electricity, enabling distributed hydrogen production.     

Cumulative energy demand and cumulative emissions of photovoltaics production in Europe

Studies of popular renewable energy systems show that cumulative energy demand (CED) can be understood as a kind of simplifying life cycle assessment [1] where the accounting of energy and material inputs is seen as part of an inventory analyses and the calculation of CED as a rough form of impact assessment.Within this research project, three grid-connected photovoltaic systems (sc-Si, pc-Si and a-Si based) are examined in regard to CED and cumulative emissions. The production of these systems was chosen to take place in seven European countries: Germany, France, Spain, Italy, Netherlands, Austria and Sweden.Due to the fact that electricity demand does play a major role in production of photovoltaics and that power generation differs throughout these countries CED varies from about 23,200 to 65,200 MJ/kWp. The cumulative emissions (CEm) were found to lie between about 900 and 4000 kg CO₂/kWp, 1.9 and 5.5 kg NO_x/kWp and 2.4 and 4.8 kg SO₂/kWp.     

An innovative indicator of carbon dioxide emissions for developing countries: A study of Taiwan

Ever since the Kyoto Protocol entered into force, the issues of climate change and greenhouse gas (GHG) emissions have drawn more and more attention globally. However, the major concern of the Kyoto Protocol to reduce the overall GHG emissions might be inaccessible for most developing countries, which rely heavily on the energy-intensive industries for exports and economic growth. In this study, an innovative indicator of net carbon dioxide (CO₂) emissions, which excludes the emissions corresponding to the exports, is proposed to explicitly reveal domestic situations of developing countries. By introducing the indicator of net CO₂ emissions to top five energy-intensive industries in Taiwan, the analysis indicates that the increase in CO₂ emissions from 1999 to 2004 is mostly contributed by the expanded exports rather than the domestic demand. The distinct growth patterns of the apparent and net CO₂ emissions also imply the transformation of the industrial sector. It is expected that, for developing countries, the concept of net emissions may not only serve as a proper interim target during the process of international negotiations over GHG reductions but also highlights the prominence of addressing the emissions from the industrial sector as the top priority.     

An overview of solar decarbonization processes,reacting oxide materials,and thermochemical reactors for hydrogen and syngas production

Solar decarbonization processes are related to the different thermochemical conversion pathways of hydrocarbon feedstocks for solar fuels production using concentrated solar energy as the external source of high-temperature process heat. The main investigated routes aim to convert gaseous and solid feedstocks (methane, coal, biomass …) into hydrogen and syngas via solar cracking/pyrolysis, reforming/gasification, and two-step chemical looping processes using metal oxides as oxygen carriers, further associated with thermochemical H₂O/CO₂ splitting cycles. They can also be combined with metallurgical processes for production of energy-intensive metals via solar carbothermal reduction of metal oxides. Syngas can be further converted to liquid fuels while the produced metals can be used as energy storage media or commodities. Overall, such solar-driven processes allow for improvements of conversion yields, elimination of fossil fuel or partial feedstock combustion as heat source and associated CO₂ emissions, and storage of intermittent solar energy in storable and dispatchable chemical fuels, thereby outperforming the conventional processes. The different solar thermochemical pathways for hydrogen and syngas production from gaseous and solid carbonaceous feedstocks are presented, along with their possible combination with chemical looping or metallurgical processes. The considered routes encompass the cracking/pyrolysis (producing solid carbon and hydrogen) and the reforming/gasification (producing syngas). They are further extended to chemical looping processes involving redox materials as well as metallurgical processes when metal production is targeted. This review provides a broad overview of the solar decarbonization pathways based on solid or gaseous hydrocarbons for their conversion into clean hydrogen, syngas or metals. The involved metal oxides and oxygen carrier materials as well as the solar reactors developed to operate each decarbonization route are further described.     

Transport sector CO2 emissions growth in Asia: Underlying factors and policy options

This study analyze the potential factors influencing the growth of transport sector carbon dioxide (CO₂) emissions in selected Asian countries during the 1980–2005 period by decomposing annual emissions growth into components representing changes in fuel mix, modal shift, per capita gross domestic product (GDP) and population, as well as changes in emission coefficients and transportation energy intensity. We find that changes in per capita GDP, population growth and transportation energy intensity are the main factors driving transport sector CO₂ emission growth in the countries considered. While growth in per capita income and population are responsible for the increasing trend of transport sector CO₂ emissions in China, India, Indonesia, Republic of Korea, Malaysia, Pakistan, Sri Lanka and Thailand; the decline of transportation energy intensity is driving CO₂ emissions down in Mongolia. Per capita GDP, population and transportation energy intensity effects are all found responsible for transport sector CO₂ emissions growth in Bangladesh, the Philippines and Vietnam. The study also reviews existing government policies to limit CO₂ emissions growth, such as fiscal instruments, fuel economy standards and policies to encourage switching to less emission intensive fuels and transportation modes.     

Effects of nuclear power plant shutdowns on electricity consumption and greenhouse gas emissions after the Tohoku Earthquake

This study analyzes how the substitution of fossil fuels for nuclear power due to the shutdown of nuclear power plants after the Tohoku Earthquake affects electricity consumption and greenhouse gas emissions in Japan. Results indicate that Japan generated 4.3 million metric tons (or 0.3%, with a 95% confidence interval) of additional CO₂ emissions in 2011 following the earthquake. The increase in CO₂ emissions stemmed from the combined effects of decreased electricity consumption due to energy conservation efforts and the substitution of fossil fuels for nuclear power following the Tohoku Earthquake. Results also show considerable spatial variation in the impacts of the earthquake on net CO₂ emissions. A majority of the prefectures (40 of 47 prefectures, or 85%) were predicted to experience higher CO₂ emissions after the Tohoku Earthquake while the remaining (7 prefectures) were predicted to experience lower CO₂ emissions. Our findings suggest that Japan and countries under similar risks may want to reformulate energy policy by emphasizing utilization of diverse power and energy sources, including more renewable energy production and electricity conservation. The policy reform should also consider spatial variation in the combined effects of reduced reliance on nuclear power and increased CO₂ conversion factors.     

Thermal cracking of methane into Hydrogen for a CO2-free utilization of natural gas

The transition to a low-Carbon Hydrogen production will unavoidably follow a path where fossil fuels are going to play a fundamental role in the short term. The technological development of Hydrogen production based on sustainable, renewable energies (wind, solar, biomass) will most likely characterize the gradual substitution of fossil-based Hydrogen production in the long term. In this transition, the environmental concerns regarding greenhouse gas emissions to the atmosphere are a crucial issue, fostering the development of Hydrogen production scenarios in which either carbon capture and sequestration or decarburation could be implemented as mitigation or adaptation measures in order to avoid CO₂ release from the utilization of fossil fuels. Therefore, the development of CO₂-free technologies enabling fossil fuels exploitation is a must to make compatible their utilization with emission reductions. New innovative solutions should be put into practice. In this regard, methane cracking is a promising alternative and its potentials are highlighted and analyzed in this paper.     

Integration of methane cracking and direct carbon fuel cell with CO2 capture for hydrogen carrier production

Hydrogen fuel production from methane cracking is a sustainable process compared to the ones currently in practice due to zero greenhouse gas emissions. Also, carbon black that is co-produced is valuable and can be marketed to other industries. As this is a high-temperature process, using solar energy can further improve its sustainability. An integrated solar methane cracking system is proposed where hydrogen and carbon products are sent to fuel cells to generate electricity. The CO₂ exhaust stream from the carbon fuel cell is captured and reacted with hydrogen in the CO₂ hydrogenation unit to produce liquid fuels – Methanol and dimethyl ether. The process is simulated in Aspen Plus®, and its energy and exergy efficiencies are evaluated by carrying out a detailed thermodynamic analysis. In addition, a sensitivity analysis is performed on various input parameters of the system. The overall energy efficiency of 41.9% and exergy efficiency of 52.3% were found.