Shortcut Evaluation of Chemical Carbon Dioxide Utilization Processes

Chemical utilization of carbon dioxide seems to be an attractive option for the mitigation of greenhouse gas emissions. However, the respective processes themselves cause substantial greenhouse gas emissions. To achieve a good CO₂ balance, it is necessary not only to fix carbon but also to do this efficiently in terms of reactant supply and energy demand. An evaluation of the CO₂ balance requires detailed process simulation for the utilization reaction and the supply chain. To allow a quick evaluation of the potential to mitigate emissions, a number of estimation methods are presented.     

High Temperature Co-Electrolysis as a Key Technology for CO2 Emission Mitigation – A Model-Based Assessment of CDA and CCU

The mitigation of CO₂ emissions is a major challenge for modern society. While the mitigation of energy-related emissions can be achieved comparatively easy by switching to renewable energy sources, reduction of process-related industrial emissions is considerably more challenging. To reduce industrial CO₂ emissions, two basic routes are available: carbon direct avoidance (CDA) and carbon capture and utilization (CCU). It is shown that in terms of efficiency, CDA is to be favored when applicable. However, for applications where emissions cannot be avoided, CCU can be a viable approach allowing for emission mitigation.     

Emission Reduction of Regenerative Fuel Powered Co-Generation Plants with SCR- and Oxidation-Catalysts

Since the beginning of combustion engine development in this recent century various different fuels have been successfully tested. Diesel engines have been adapted to fuels made from mineral oils because of the rising importance and the cheapness in comparison to other fuels. On the other hand, it is possible to burn regenerative fuels in engines and achieve some significant advantages in comparison to fossil diesel fuel. This is, for example, a closed carbon dioxide (CO₂) cycle which causes no green house effect. It is possible to extract oil from various seeds like rapeseed. It is also possible to burn used oil from the food processing industry or waste grease and oil from food recycling companies. The great advantages: (1) food recycling oils can produce energy instead of use as animal food, and (2) as nobody knows exactly the consistency of the collected oils, poisonous pollution is possible. These regenerative fuels can be burned without any further processing in special adapted diesel engines, for example an Elsbett engine, or in precombustion engines with large swept volumes. Most researchers focused on operating diesel engines with regenerative fuels and reducing the emissions caring only about regulated exhaust components. In comparison to these studies it is necessary to learn more about the emissions beyond the exhaust regulations. Additionally emission reduction is possible by using an SCR-catalyst (selective catalytic reduction) to reduce the NO₂ combined with an oxidation-catalyst which reduces any kind of oxidisable emissions. The TU München, Lehrstuhl für Energie- und Umwelttechnik der Lebensmittelindustrie, operates a small co-generation plant with the ability of analysing the standard emission components (CO, NO₂, HC, particles, CO₂, O₂) and unregulated components (SO₂, NH₃, polycyclic aromatic hydrocarbons (PAH), aldehyde, ketone). The emissions show some significant differences in comparison to fossil diesel fuel which is caused by the diversity of each fuel. Results of an investigation on four different fuels (wastefat methyl ester (WME), rapeseed methyl ester (RME), rapeseed oil and diesel fuel) burned in a small co-generation plant with a SCR- and oxidation-catalyst will be presented. A comparison to the emissions before and after the catalysts will be shown additionally to the results of the different reduction potential of diesel fuel, methyl ester or untreated oils. The combination of regenerative fuel and catalyst shows good potential for reducing the emissions. Furthermore the use of regenerative fuels is a sustainable production of energy with an overall efficiency of almost 90%. Regenerative fuels based on vegetable oils and waste fat are a valuable form of energy and have some significant advantages in comparison to diesel fuel, like an almost closed carbon dioxide cycle, rapid biological decomposition and lower CO, HC and particle emissions. Regenerative fuels should also meet minimum standards discussed in the paper to avoid the risk of engine damage and to reduce emissions.     

Greenhouse gas emissions of bioenergy from agriculture compared to fossil energy for heat and electricity supply

Increasing the use of bioenergy is one promising option to reduce greenhouse gas emissions. Hence it is important to know the greenhouse gas emissions of bioenergy systems in comparison to fossil fuel systems. A life cycle analyses of biomass and fossil fuel energy systems is made to compare the overall greenhouse gas emission of both systems for heat and electricity supply. Different bioenergy systems to supply electricity and heat from agriculture are analysed for the Austrian situation in 2000. Total emissions of greenhouse gases (CO₂, N₂O, CH₄) along the fuel chain, including land use change and by-products, are calculated. The systems taken into consideration are different conversion technologies and different fuels from agriculture. The methodology was developed within the International Energy Agency (IEA) Bioenergy Task 25 on `Greenhouse Gas Balances of Bioenergy Systems'. In this paper the results of selected bioenergy systems for heat supply and combined supply of electricity and heat shown as emission of CO₂-equivalents per kWh for bioenergy systems in comparison to fossil fuel systems, and as a percentage of CO₂-equivalent reduction. The results demonstrate that some of the bioenergy systems reduce greenhouse gas emission already because of avoided emissions of the reference biomass use and/or because of certain substitution effects of by-products. In general the greenhouse gas emissions of bioenergy systems are lower compared to the fossil systems. Therefore a significant reduction of greenhouse gases is possible by replacing fossil energy systems with bioenergy systems. This comparison should help policy makers, utilities and industry to identify effective agricultural biomass options in order to reach emission reduction targets. This revised version was published online in August 2006 with corrections to the Cover Date.     

Carbon capture from stationary power generation sources: A review of the current status of the technologies

The world will need greatly increased energy supply in the future for sustained economic growth, but the related CO₂ emissions and the resulting climate changes are becoming major concerns. CO₂ is one of the most important greenhouse gases that is said to be responsible for approximately 60% of the global warming. Along with improvement of energy efficiency and increased use of renewable energy sources, carbon capture and sequestration (CCS) is expected to play a major role in curbing the greenhouse gas emissions on a global scale. This article reviews the various options and technologies for CO₂ capture, specifically for stationary power generation sources. Many options exist for carbon dioxide capture from such sources, which vary with power plant types, and include post-combustion capture, pre-combustion capture, oxy fuel combustion capture, and chemical looping combustion capture. Various carbon dioxide separation technologies can be utilized with these options, such as chemical absorption, physical absorption, adsorption, and membrane separation. Most of these capture technologies are still at early stages of development. Recent progress and remaining challenges for the various CO₂ capture options and technologies are reviewed in terms of capacity, selectivity, stability, energy requirements, etc. Hybrid and modified systems hold huge future potentials, but significant progress is required in materials synthesis and stability, and implementations of these systems on demonstration plants are needed. Improvements and progress made through applications of process systems engineering concepts and tools are highlighted and current gaps in the knowledge are also mentioned. Finally, some recommendations are made for future research directions.     

Simultaneous optimization of CO2 emissions reduction strategies for effective carbon control in the process industries

Concerns about global warming have led governments to regulate CO₂ emissions, including through emissions caps, trading and penalties, thus creating economic incentives to reduce CO₂ emissions. This paper presents a mathematical model based on a MINLP formulation to address the problem of CO₂ emissions from large-scale sites in the process industries. The proposed approach considers the interactions between process units, associated heat exchanger networks and the site utility system. The CO₂ emissions reduction strategies considered include retrofit of heat exchanger networks (HENs), operational optimization of the utility system and fuel switching. The mathematical model captures interactions between the HEN and the utility system; the optimization explores these interactions systematically within a superstructure of CO₂ reduction options. The optimization objective is to determine suitable CO₂-mitigation options for a given emissions reduction target and available capital for investment, taking carbon trading issues into account. The proposed approach is applied to a published industrial case study; the results demonstrate the applicability of the approach to finding cost-effective solutions for CO₂ emissions reduction. Results show that the best solution CO₂ emissions reduction is affected by carbon trading. Therefore, opportunities to sell CO₂ allowances, if practically achievable, play an important role in the process economics.     

Application of a Waste Carbon Material as the Carbonaceous Reductant During Silicon Production

It is important to study the application of alternative carbon reductants for industrial silicon smelting to reduce consumption of carbonaceous reducing agents, electricity, and CO₂ emissions during silicon production. In this study, an industrial experiment was carried out in an 8 MVA submerged arc furnace using waste carbon material in place of approximately 20% partial reducing agents. The system was analyzed for silicon yield, power consumption, overall energy efficiency, CO₂ emissions, and the utilization rate of carbonaceous materials. The system improved the efficiency of carbonaceous materials and decreased power consumption using alternative carbon reductants. The results have showed that use of waste carbon materials reduced carbon emissions per ton silicon by more than 19.14% and specific CO₂ emissions decreased to 0.865 t.     

Verfahrenstechnische Möglichkeiten zur Verringerung des Anstiegs von Kohlendioxid in der Luft

Engineering Solutions for Limiting the Increase of Carbon Dioxide in Air This article describes engineering solutions for limiting the increase of carbon dioxide in air. Fossile power plants are taken as a model for the source of CO₂. The global mass balance shows that the oceans play a most important role in the storage of the CO₂. The hypothesis is that it is not the absolute value of carbon dioxide concentration that is the real problem but rather its change. Keeping this in mind the present emissions should not be converted but stored for future times. This strategy is called ?hiding the CO₂“. The reduction of the emission is not very likely. It is believed that present actions to reduce the private power consumption will not really change the situation. A number of strategies for the sequestration of CO₂ are reported in the contribution. One proposal is to use shallow waters which form a thermohaline current for the sequestration. In this case, the injection of CO₂ is quite simple but the carbon dioxide travels hundreds of years in a deep sea current. Several scenarios are discussed for the fate of this CO₂‐enriched current. The environmental impact is briefly reported. This contribution describes the actual research needs, taking into account that similar research in Japan and in the U.S. is much more developed.     

Design and operation of pilot plant for CO2 capture from IGCC flue gases by combined cryogenic and hydrate method

This project is a trial conducted under contract with CO₂CRC, Australia of a new CO₂ capture technology that can be applied to integrated gasification combined cycle power plants and other industrial gasification facilities. The technology is based on combination of two low temperature processes, namely cryogenic condensation and the formation of hydrates, to remove CO₂ from the gas stream. The first stage of this technology is condensation at −55 °C where CO₂ concentration is expected to be reduced by up to 75 mol%. Remaining CO₂ is captured in the form of solid hydrate at about 1 °C reducing CO₂ concentration down to 7 mol% using hydrate promoters. This integrated cryogenic condensation and CO₂ hydrate capture technology hold promise for greater reduction of CO₂ emissions at lower cost and energy demand. Overall, the process produced gas with a hydrogen content better than 90 mol%. The concentrated CO₂ stream was produced with 95-97 mol% purity in liquid form at high pressure and is available for re-use or sequestration. The enhancement of carbon dioxide hydrate formation and separation in the presence of new hydrate promoter is also discussed. A laboratory scale flow system for the continuous production of condensed CO₂ and carbon dioxide hydrates is also described and operational details are identified.     

Global estimates of potential mitigation of greenhouse gas emissions by agriculture

Technologies to reduce net emissions of carbon dioxide, methane and nitrous oxide within the agriculture sector were reviewed to estimate the global potential for mitigation of these radiatively active greenhouse gases. Our estimates of the potential reduction of radiative forcing by the agricultural sector range from 1.15-3.3 Gt C equivalents per year. Of the total potential reduction, approximately 32% could result from reduction in CO₂ emissions, 42% of carbon offsets by biofuel production on 15% of existing croplands, 16% from reduced CH₄ emissions and 10% from reduced emissions of N₂O. Agriculture encompasses large regional differences in management practices and rates of potential adoption of mitigation practices. Acceptability of mitigation options will depend on the extent to which sustainable production will be achieved or maintained and benefits will accrue to farmers. Technologies such as no-till farming and strategic fertilizer placement and timing are now being adopted for reasons other than concern for climate change issues. This revised version was published online in August 2006 with corrections to the Cover Date.     

Carbon dioxide capture by solvent absorption using amino acids: A review

The emission of large amounts of carbon dioxide is of major concern with regard to increasing the risk of climate change. Carbon capture, utilisation and storage (CCUS) has been proposed as an important pathway for slowing the rate of these emissions. Solvent absorption of CO₂ using amino acid solvents has drawn much attention over the last few years due to advantages including their ionic nature, low evaporation rate, low toxicity, high absorption rate and high biodegradation potential, compared to traditional amine solvents. In this review, recent progress on the absorption kinetics of amino acids is summarised, and the engineering potential of using amino acids as carbon capture solvents is discussed. The reaction orders between amino acids and carbon dioxide are typically between 1 and 2. Glycine exhibits a reaction order of 1, whilst, by comparison, lysine, proline and sarcosine have the largest reaction constants with carbon dioxide which is much larger than that of the benchmark solvent monoethanolamine (MEA). Ionic strength, pH and cations such as sodium and potassium have been shown to be important factors influencing the reactivity of amino acids. Corrosivity and reactivity with impurities such as SO_x and NO_x are not considered to be significant problems for amino acids solvents. The precipitation of CO₂ loaded amino acid salts is thought to be a good pathway for increasing CO₂ loading capacity and cutting desorption energy costs if well-controlled. It is recommended that more detailed research on amino acid degradation and overall process energy costs is conducted. Overall, amino acid solvents are recognised as promising potential solvents for carbon dioxide capture.     

Verwendung von Kohlendioxid bei technischorganischen Synthesen

Use of carbon dioxide in industrial organic syntheses . Although carbon dioxide is important as an abundant carbonaceous raw material, its utilization in chemical processes so far has been rather limited. This review covers the reactions of CO₂ employed in industry, such as the production of urea, the Kolbe-Schmitt reaction, the synthesis of cyclic organic carbonates, and the use of CO₂ in methanol synthesis. Interesting recent developments in CO₂ chemistry, especially the transition metal catalyzed reactions, are also elucidated. In addition to the synthesis of polymers and hydrocarbons, the production of oxygen-containing chemicals seems to be very profitable and attractive for future industrial applications. Not only can derivatives of formic acid and carbonic acid be formed but longer-chain carboxylic acids and their derivatives are also accessible by reactions of carbon dioxide with hydrocarbons such as alkynes, alkenes, and 1,3-dienes.     

Ein nachhaltiges Konzept zur Bereitstellung von reinem CO2 als C‐Quelle für Solarfuels – Synergien zwischen Biokohle und Biogas

In times of the German energy transition (“Energiewende”) chemical storage technologies achieve an increasing interest because only with their help the energy of the excess electricity from wind‐ and solar plants can be stored in huge quantities in form of hydrocarbons. The hydrogen generated by water electrolysis can be converted with carbon dioxide to hydrocarbons. In addition, pure CO₂ must be available at a reasonable price. For this CO₂ supply a sustainable concept is presented.     

Biomass-coal co-combustion: opportunity for affordable renewable energy

This investigation explores the reasons for and technical challenges associated with co-combustion of biomass and coal in boilers designed for coal (mainly pulverized coal) combustion. Biomass-coal co-combustion represents a near-term, low-risk, low-cost, sustainable, renewable energy option that promises reduction in net CO₂ emissions, reduction in SO_x and often NO_x emissions, and several societal benefits. Technical issues associated with cofiring include fuel supply, handling and storage challenges, potential increases in corrosion, decreases in overall efficiency, ash deposition issues, pollutant emissions, carbon burnout, impacts on ash marketing, impacts on SCR performance, and overall economics. Each of these issues has been investigated and this presentation summarizes the state-of-the-art in each area, both in the US and abroad. The focus is on fireside issues. While each of the issues can be significant, the conclusion is that biomass residues represent possibly the best (cheapest and lowest risk) renewable energy option for many power producers.     

Nonlinear optimization of steel production using traditional and novel blast furnace operation strategies

The high energy requirements in primary steelmaking make this industrial sector a major contributor to the global emissions of carbon dioxide. Ways to suppress the use of fossil reductants and the emissions from the processes should therefore be developed. The present work applies simulation and optimization for studying the economic feasibility of recycling blast furnace top gas to the combustion zones after CO₂ stripping. The study comprises the unit processes in an integrated steel plant, paying special attention to the blast furnace and the preheating of the blast or the recycled top gas. The system is optimized with nonlinear programming with respect to some central variables under different CO₂ sequestration and emission costs, which yields information about the economic feasibility of the concept. It is demonstrated that the optimal states of the plant show complex transitions, where the costs play a decisive role. It is also shown that hot gas recycling with CO₂ capture and storage would dramatically reduce the harmful emissions from the process. The conditions under which top gas recycling is economically feasible are also reported, as well as the effect of omitting oil injection in a blast furnace with top gas recycling.     

“ALL FREE” — a novel design concept of applying partial oxidation process to vehicle engine

With the rapid expansion of the global motor vehicle population, the transportation sector has taken up a growing proportion among all the carbon dioxide emission-related sectors. To contribute to solutions of the carbon dioxide-oriented problem in transportation, this paper proposes the “ALL FREE” concept that applies partial oxidation process instead of the conventional complete oxidation to vehicle engines. In such an engine, the fuels are partially oxidized into corresponding chemical products, which, as a result, enable the process to be theoretically free of CO₂, while the heat output of the partial oxidation could drive the vehicle. On the other hand, the resulting products are of great value, which could decrease or even counteract the cost of fuels in transportation. In this paper, the thermodynamic and kinetic data (e.g., the heat output and heat release rate) of five selected partial oxidation reactions were calculated at length to demonstrate and exemplify the theoretical feasibility of the “ALL FREE” concept. It turned out that the partial oxidation of n-butane to maleic anhydride has the most potential to meet the basic requirements of this concept. To sum up, this design concept is of significant application potential for the reduction of CO₂ emissions in the transportation industry, although there remain many technical challenges.     

Canadian greenhouse gas mitigation options in agriculture

In 1991, on farm management practices contributed 57.6 Tg CO₂ equivalent in greenhouse gas emissions, that is, about 10% of the anthropogenic GHG emissions in Canada. Approximately 11% of these emissions were in the form of CO₂, 36% in the form of CH₄ and 53% in the form of N₂O. The CO₂ emissions were from soils; CH₄ emissions were from enteric fermentation and manure, and N₂O emissions were primarily a function of cropping practices and manure management. With the emissions from all other agricultural practices included, such as the emissions from fossil fuels used for transportation, manufacturing, food processing etc., the agricultural sector's contributions were about 15% of Canada's emissions. In this publication, several options are examined as to their potential for reducing greenhouse gas emissions. These involve soil and crop management, soil nutrient management, improved feeding strategies, and carbon storage in industrial by-products. The Canadian Economic Emissions Model for Agriculture (CEEMA) was used to predict the greenhouse gas emissions for the year 2010, as well as the impact of mitigation options on greenhouse gas emissions from the agricultural sector. This model incorporates the Canadian Regional Agricultural sub-Model (CRAM), which predicts the activities related to agriculture in Canada up to 2010, as well as a Greenhouse Gas Emissions sub-Model (GGEM), which estimates the greenhouse gas emissions associated with the various agricultural activities. The greenhouse gas emissions from all agricultural sources were 90.5 Tg CO₂ equivalent in 1991. Estimates based on CEEMA for the year 2010 indicate emissions are expected to be 98.0 Tg CO₂ equivalent under a business as usual scenario, which assumes that the present trends in management practices will continue. The agricultural sector will then need to reduce its emissions by about 12.9 Tg CO₂ equivalent below 2010 forecasted emissions, if it is to attain its part of the Canadian government commitment made in Kyoto. Technologies focusing on increasing the soil carbon sink, reducing greenhouse gas emissions and improving the overall farming efficiency, need to be refined and developed as best management practices. The soils carbon sink can be increased through reduced tillage, reduced summer fallowing, increased use of grasslands and forage crops, etc. Key areas for the possible reduction of greenhouse gas emissions are improved soil nutrient management, improved manure storage and handling, better livestock grazing and feeding strategies, etc. The overall impact of these options is dependent on the adoption rate. Agriculture's greenhouse gas reduction commitment could probably be met if soils are recognized as a carbon sink under the Kyoto Accord and if a wide range of management practices are adopted on a large scale. None of these options can currently be recommended as measures because their socio-economic aspects have not been fully evaluated and there are still too many uncertainties in the emission estimates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influences of free-air CO2 enrichment (FACE), nitrogen fertilizer and crop residue incorporation on CH4 emissions from irrigated rice fields

To investigate the response of methane (CH₄) emissions to an elevated atmospheric carbon dioxide (CO₂) concentration (200?±?40???mol?mol^?1 higher than the ambient atmosphere), we performed a 4-year multi-factorial experiment at a subtropical rice paddy that contained sandy loam soil in the Yangtze River Delta from 2004 to 2007 using free-air CO₂ enrichment (FACE) technology. Our results revealed that the elevated atmospheric CO₂ increased the seasonal cumulative CH₄ emissions by 15?% on average during the 4-year period. The increase was insignificant and much weaker than the previous studies, which might be primarily attributed to the absence of a significant difference in the rice biomass between the two CO₂ levels in half of the field treatments. Crop residue incorporation hindered the stimulatory effects induced by the elevated CO₂, which were 37, 14 and 6?% for the fields that were incorporated with none, half or all of the wheat straws that were harvested in the preceding winter wheat season, respectively. Nitrogen fertilizers application also hindered the stimulatory effects of the elevated CO₂ on the CH₄ emissions. The CO₂ stimulatory effect was 39?% for the field without nitrogen fertilizers, and reduced to 17, 7 and 5?% for the field with nitrogen fertilization of 125, 250 and 350?kg?N?ha^?1, respectively. The regulation of nitrogen fertilizers on the CO₂ effects in this experiment does not well agree with the previous studies, which might because the soil type was different from those of the previous studies. Thus, further studies are necessary to evaluate the role of soil properties in regulating the effects of elevated atmospheric CO₂ on CH₄ emissions from managed and natural wetlands. There were no significant interactions between the atmospheric CO₂ and the incorporations of nitrogen fertilizer and crop residue. Appropriate experiments are necessary for better understanding of the interact influences of the elevated CO₂ and farm managements.     

Engineering Solutions for Limiting the Increase of Atmospheric Carbon Dioxide

The article describes possible engineering solutions that can reduce the carbon dioxide (CO₂) content of the air. To demonstrate the point fossil fuel power plants will be taken as a model for the source of CO₂. The global mass balance shows that the oceans play a major role in storing CO₂. The hypothesis presented states that the real problem is not the absolute CO₂ content, rather its change. Consequently, present emissions should be stored for future release. Under the current worldwide measures to reduce power consumption CO₂ emissions are unlikely to decrease. A number of strategies for the maritime sequestration of CO₂ are reported in the contribution. One proposal for sequestration is the use of shallow waters which form a thermohaline current: the dissolved gas will travel for hundreds of years in deep sea currents. In the latter case, CO₂ injection is easily achieved. Several scenarios are considered for the fate of this CO₂‐enriched current. The environmental impact is briefly reported. The article will describe current research requirements, demonstrating that similar research in the US and Japan is presently more advanced in comparison to that in Europe. The sequestration of carbon dioxide on land will be the subject of a second publication. It is obvious that the sequestration of CO₂ is the method after all rational chances to save energy.     

Biogenic versus abiogenic emissions from agriculture in the Netherlands and options for emission control in tomato cultivation

In this paper, present-day emissions of greenhouse gases and acidifying compounds from agriculture are analysed at the farm level. Quantitative estimates are given for these emissions from three nested systems in the Netherlands: the agricultural sector, greenhouse horticulture, and tomato cultivation under glass. Total emissions are subdivided into emissions from biogenic sources and abiogenic sources. We conclude that, although most of the emissions from the agricultural sector have biogenic sources, those from abiogenic sources should not be neglected. Abiogenic emissions are mainly from greenhouse horticulture. The cost-effectiveness of options to reduce carbon dioxide (CO₂) and nitrogen oxides (NO_x) emissions from on-farm combustion of natural gas in tomato cultivation under glass is analysed. An inventory is given of technical reduction options that are presently available in practice. Based on information about the costs and the reduction potential of each option, cost-efficiency curves are derived for both types of emissions. Relative to a situation where none of the described options were applied (early nineties), CO₂ and NO_x emissions from tomato cultivation can be reduced at most by about 70% and 75%, respectively, by combinations of technical options. This revised version was published online in August 2006 with corrections to the Cover Date.