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Carbon reduction has become one of the most significant challenges for economic growth. This paper presents the preliminary analysis of undesirable output reduction targets and emission schedules in temporal–spatial comparisons based on Data Envelopment Analysis. The reduction targets of undesirable outputs are investigated, including the maximum, input, technical and ideal reduction targets. Four Data Envelopment Analysis models that are based on a sequential benchmark technology and variable returns to scale are introduced to measure these reduction percentages. In order to formulate the optimal emission schedule of undesirable outputs, an optimal model is provided without inflation. Data from the Australian construction industry from 2000 to 2010 are employed to develop the models. The results of the analysis indicate that the Australian Government could achieve its promised carbon reduction targets in the construction industry. Most Australian regions' construction industries possess carbon mitigation potential and some of them could increase their desirable outputs if carbon were decreased. This paper suggests that policymakers can benefit from formulating various suitable undesirable output reduction objectives and schedules through the models developed. The research method can be replicated for other sectors and regions focussing on undesirable output reduction. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the development of a decision support system for monitoring and diagnosis of the amine-based post-combustion carbon dioxide (CO2) capture process system at the International Test Centre for CO2 Capture (ITC) at the University of Regina. The amine-based CO2 absorption capture process system consists of dozens of components and generates more than a hundred different types of data. The vast amount of raw data produced by the system are measurements of the many reaction components, valves and pumps. The system operators often find it difficult to quickly detect, diagnose and correct any abnormal conditions that may arise during operation. Therefore, developing a decision support system for monitoring and diagnosis of the CO2 capture process system which aids the operator in monitoring and diagnosis of the system is a desirable objective. This paper describes development of the system based on the dual foundation of a domain ontology and an intelligent system framework in the domain of carbon dioxide capture process. The developed ontology provides the semantic knowledge foundation; it was implemented in the Knowledge Modeling System (KMS), and the knowledge was stored in the XML format. The intelligent system framework consists of system functions which can use the XML schema provided by the ontology and support the development process. A decision support expert system for process monitoring is a sample system developed on the dual foundation. [Copyright &y& Elsevier]

The selection of the social discount rate and the consideration of hurdle rates in energy systems optimisation models affect the creation of sound and comprehensive scenarios useful for energy modellers. Due to the lack of studies about the use of different discounting options in energy optimisation models, the goal of this paper is to fill that gap by establishing the foundations for a debate among energy modellers, policy-makers and stakeholders in this regard. So firstly, we introduced the concept of discount rates both social and technology-specific including a thorough literature review concerning figures, scopes and approaches. Secondly, two models, ETSAP-TIAM and TIMES-Norway, were used to assess the behaviour of the energy systems at different regionalisation levels, Europe and Norway respectively. Thirdly, we analysed the evolution of the electricity production mixes and system costs for both models and considering several values for the discount rates. Finally, results showed that the energy system is strongly affected by changes in the social discount rate. The lower the social discount rate is, the higher the renewable contribution. The social discounting exerts influence on capital intensive investments so it is quite important to look at the energy carriers pathways (fossil-renewable transition). This is what happens in the case of ETSAP-TIAM for Europe. Reversely, in the case of TIMES-Norway, as the electricity system is almost 100% renewable, it is important to take into account the hurdle rates of the technologies to enrich the competition by including their particular risks and barriers. In summary, we recommend using a value not higher than 4–5% for the social discount rate for the European countries as well as to include an exhaustive portfolio of hurdle rates for all the technologies included in the energy optimisation model. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion of pulverized fuels (PF), as a promising technology for CO 2 capture from power plants, has gained a lot of concerns and also advanced considerable research, development and demonstration in the past years worldwide. The use of CO 2 or the mixture of CO 2 and H 2 O vapor as the diluent in oxy-fuel combustion, instead of N 2 in conventional air–fuel combustion, induces significant changes to the combustion fundamentals, because of the great differences in the physical properties and chemical effects of the different diluents. Therefore, some fundamental issues and technological challenges need to be properly addressed to develop oxy-fuel combustion into an enabled technology. Computational Fluid Dynamics (CFD) modeling, which has been proven to be a very useful and cost-effective tool in research and development of conventional air–fuel combustion, is expected to play a similarly vital role in future development of oxy-fuel combustion technology. The paper presents a state-of-the-art review and an in-depth discussion of PF oxy-fuel combustion fundamentals and their modeling, which underpin the development of this promising technology. The focus is placed on the key issues in combustion physics (e.g., turbulent gas–solid flow, heat and mass transfer) and combustion chemistry (e.g., pyrolysis, gas phase combustion and char reactions), mainly on how they are affected in oxy-fuel conditions and how they are modeled and implemented into CFD simulations. The system performance of PF oxy-fuel combustion is also reviewed. Finally, the current status of PF oxy-fuel combustion fundamentals and modeling is concluded and the research needs in these regards are suggested. [ABSTRACT FROM AUTHOR]

Carbon dioxide emissions must be stabilized to mitigate the unfettered release of greenhouse gases into the atmosphere. The removal of carbon dioxide from flue gases, an important first step in addressing the problem of CO2 emissions, can be achieved through adsorption separation technologies. In most adsorption processes, the adsorbent is in contact with fluid in a fixed bed. Fixed-bed column mathematical models are required to predict the performance of the adsorptive separation of carbon dioxide for optimizing design and operating conditions. A comprehensive mathematical model consists of coupled partial differential equations distributed over time and space that describe material, energy, and the momentum balances together with transport rates and equilibrium equations. Due to the complexities associated with the solution of a coupled stiff partial differential equation system, the use of accurate and efficient simplified models is desirable to decrease the required computational time. The simplified model is primarily established based on the description of mass transfer within adsorption systems. This paper presents a review of efforts over the last three decades toward mathematical modeling of the fixed-bed adsorption of carbon dioxide. The nature of various gas-solid equilibrium relationships as well as different descriptions of the mass transfer mechanisms within the adsorbent particle are reviewed. In addition to mass transfer, other aspects of adsorption in a fixed bed, such as heat and momentum transfer, are also studied. Both single- and multi-component CO2 adsorption systems are discussed in the review. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a techno-economic analysis of carbon-negative algal biodiesel production routes that use currently available technologies. The production process includes the following stages: carbon–neutral renewable electricity generation for powering the plant, algal growth in photobioreactors, algae dewatering and lipid extraction, and biofuel conversion and refining. As carbon dioxide is consumed in the algal growth process, side products are not burned (with CO2 release), and the energy supplied to the entire production process is obtained from concentrated solar power, the whole system is assumed carbon footprint negative. Under assumptions related to economics of scale, the techno-economic model is extended to account for varying industrial scales of production. Verified data from a selection of commercially available technologies are used as inputs for the model, and the economic viability of the various production routes is assessed. From the various routes investigated, one scheme involving combined gasification and Fischer–Tropsch of algal solids to produce biodiesel along with conversion of algal lipids into biodiesel through transesterification was found to be promising. Assuming a typical economic scaling factor of 0.8, an algal biodiesel process with an annual production rate of 100Mt/year is identified to achieve a biodiesel price comparable to the current conventional diesel price (approximately £1.39/litre at the pump, or $114/barrel of crude) with a discounted break-even time of 6years. [Copyright &y& Elsevier]

Abstract: Power plants using Victorian brown coal operate at low efficiency. Being reactive and spontaneously combustible, dried brown coals cannot be exported either. Synthesis of dimethyl ether (DME) is one option for the production of liquid fuel, an exportable product for power generation and transportation. This paper presents a steady-state process model for DME production using brown coal including drying, gasification and DME synthesis. The yield of the DME was a maximum for H2 to CO molar ratio of 1.41 and 0.81 at the gasifier outlet and the DME reactor inlet respectively. A process efficiency of 32% and CO2 emission of 2.91kg/kg of DME was obtained. Improved yield of DME is achieved when CO2 is removed from the fuel gas prior to feeding to the synthesis reactor. Integration of waste heat and design of appropriate catalyst for gasification and DME synthesis can result in further improvements in the process. [Copyright &y& Elsevier]

Abstract: Oxy-fuel combustion is one of the promising options for carbon dioxide capture in future coal power plants. Radiative properties of combustion gases and heat transfer characteristics inside oxy-fuel furnaces are different from those found in air-fired furnace. Nowadays, few publications provide appropriate radiation property correlations for oxy-fuel conditions. The available correlations are based on previous versions of HITRAN database, which is not accurate for prediction of spectral intensities at high temperature in combustion applications or above 1000K. This paper considers the determination and evaluation of new correlations for the weighted-sum-of-gray-gases model to predict the radiative transfer in gases under oxy-fuel conditions. The new correlations are fitted from emittance charts calculated from the up-to-date HITEMP 2010 database for molar ratios of water vapor to carbon dioxide between 0.125 and 4, temperature range of 400–2500K, and pressure path-length varying from 0.001 to 60barm. The new correlations are validated by comparing the radiative source term with line-by-line calculations from HITEMP 2010 database for a one-dimensional slab system. The radiative transfer equation is solved with the discrete ordinate method. [Copyright &y& Elsevier]

Abstract: Favorable economics of electricity generation will be crucial to the successful implementation of post-combustion carbon capture. Hence, the US DOE has set a goal of <35% for the increase on the cost of electricity (COE) due to CO2 capture. For meeting this goal, there is thus a growing need to perform a cost analysis of emerging separation methods. This paper goes through a detailed modeling and cost-sensitivity study of a promising membrane-based process for carbon capture: the air-sweep process. We have studied the impact of membrane performance, selectivity and permeance, on the COE increase and the capture cost. The effects of operating parameters as well as the membrane price on the overall cost were determined. Cost calculations show a COE increase of about 33% along with a capture cost of <$24/t CO2 for the air-sweep process to achieve 90% CO2 recovery and 95% purity of the CO2 product. This process operates at close to atmospheric feed pressure and requires a low membrane module price of $27/m2, a CO2/N2 selectivity of about 140 combined with a high CO2 permeance of 3000GPU. Although the required membrane properties have not yet been achieved, this research emphasizes quantitatively the need to improve the present membranes to realize a purely membrane-based process for the above application. [Copyright &y& Elsevier]

Abstract: This paper deals with the simultaneously optimization of operating conditions (pressures, temperatures and flow-rates) and dimensions (diameter and height) of the amine regeneration unit in the post-combustion CO2 capture process. The proposed model takes into account the effect of kinetic reactions on the mass transfer, the hydraulics of the random packing and the pressure drop along the column. In addition, profiles of temperature, composition and flow-rate along the height of the regenerator are also predicted. The resulting mathematical model is implemented into the optimization environment General Algebraic Modeling System (GAMS) which is a high-level modeling system for mathematical programming and optimization. The benefits of the mathematical programming techniques (equation-oriented modeling tools) are exploited for the simultaneous optimization not only of the operating conditions but also the dimensions of the all piece of equipments (heat exchangers, regeneration unit, condenser and reboiler). The mathematical model was successfully verified by comparison of the obtained results with published experimental data and simulated solutions obtained by a process simulator (HYSYS). Once validated, the model was used for optimization purpose. Finally, in order to study the effect of the main process parameters on the optimized results a sensitivity analysis is also investigated and discussed in detail. [Copyright &y& Elsevier]

Abstract: This paper presents a study that shows the effect of key environmental and operational factors on the Canadian Oil Sands operations for the production of synthetic crude oil (SCO) and commercial bitumen. Using an integrated energy optimization model developed in the GAMS platform, the present study determined the most economical oil schemes and energy commodities configurations at different CO2 capture levels, natural gas prices and steam-to-oil ratios (SOR). The sensitivity of these factors on the different aspects of the Oil Sands operations are explicitly discussed in this work, i.e., SCO unitary energy costs, energy commodity prices, energy plant''s configuration. According to the CO2 emission target planned by the Canadian federal government for year 2020 (50 MT of CO2 eq/yr), 38% of CO2 emission reduction with respect to the baseline emission is required from the Oil Sands industry. Similarly, the natural gas price is the operational factor that affects the energy costs associated to every product considered in this study. Furthermore, the SOR factor has a significant impact on the energy production costs of SAGD SCO and commercial bitumen. [Copyright &y& Elsevier]

Abstract: Carbon dioxide capture from energy systems will likely become a necessity as the European Union regulations are becoming increasingly more stringent. The greatest disadvantage of the existing methods of CO2 separation is the high energy intensity. In the Integrated Gasification Combined Cycle (IGCC) system, the carbon dioxide capture process is conducted before combustion, which facilitates the separation. In this paper, two methods of CO2 capture are compared. The first is the most frequently considered, known as chemical absorption. The second is membrane CO2 separation, which is not as commonly deployed but has the potential to be an even more efficient process. The models of CO2 capture installations were built in Aspen software. The two processes used in the analyses were primarily compared with respect to the energy intensity of each method. The results of the analysis show that the use of membranes allows for a significant decrease in the energy intensity of the capture process compared with the absorption process. However, the purity of the separated CO2 significantly depends on the type and surface of the membrane and on the process parameters. Nevertheless, it is clear that the development of membrane techniques will enable the most competitive CO2 capture solutions, in terms of effectiveness and cost, compared with other methods. [Copyright &y& Elsevier]

Abstract: Coal based polygeneration, a technology that couples power generation and chemical production, is a promising solution to the challenges of fossil fuel depletion and greenhouse gas emissions. Carbon monoxide shift process is a key unit in polygeneration, which adjusts hydrogen and CO ratio according to the requirements of downstream processes. Usually steam is added to shift the gas composition extensively, which contributes considerably to the energy efficiency penalty. This paper presents a polygeneration system with a low steam demand CO shift process, based on a recently developed catalyst QDB-04. Compared with a conventional CO shift, the proposed process is characterized by a low steam to CO ratio in the feeding syngas, and the steam required for the CO shift can be significantly reduced. A model of the proposed CO shift process was developed and its performance was compared with a conventional CO shift. Key system parameters were chosen to integrate the low steam CO shift process in a methanol/power polygeneration system. Based on flowsheet simulation, an energy assessment was performed to compare the proposed polygeneration system with a conventional one. Results show that the polygeneration with the low steam CO shift process has considerable energy savings over the conventional scheme. [Copyright &y& Elsevier]

Abstract: Understanding the physics of injection techniques required for large scale geological sequestration of CO2 is very important in order to mitigate the global warming in an effective and economical manner. In this paper, an analytical solution is presented to formulate the size of the CO2 droplets in terms of process parameters for Ex Situ Dissolution Approach (ESDA). The proposed solution is valid for turbulent bubbly flow regime and explicitly accounts for mass transfer and pressure changes along the pipeline length. Some technical and economic aspects of the ESDA are also addressed. In addition, the governing equation of mass transfer was numerically solved using the MATLAB® software. Comparison of the numerical and analytical results shows a good agreement for wide ranges of thermodynamic and flow conditions. The proposed analytical solution is very useful to estimate the length of pipeline required for full dissolution of CO2 droplets prior to injection into the ground. Results presented in this study indicate that the wellbore tubing could eliminate the need of horizontal mixing pipe in the ESDA. [Copyright &y& Elsevier]

Abstract: Carbon emission reduction targeting is an important and effective effort for industry to contribute in controlling greenhouse gases concentration in atmosphere. Graphical approach has been proposed for CO2 emissions reduction targeting via HEN retrofit and fuel switching. However, it involves potentially time consuming manual procedures and the quality of solutions produced greatly depends on designer’s experience and judgment. Besides, graphical approach hardly account for the cost factor during the design phase, thus potentially generate complex design. This paper introduces an MINLP model for simultaneous CO2 emissions reduction targeting via fuel switching and HEN retrofit. A sequential model execution was proposed along with the proposed model. The application of the model on a crude preheat train case study has demonstrated its workability to generate optimal solution for targeted CO2 emissions reduction at minimum payback period. [Copyright &y& Elsevier]

Abstract: Post-combustion capture of CO2 is regarded as a possible technology in order to reduce CO2 emission to the atmosphere. This paper provides a dynamic analysis of the absorption/desorption loop of a carbon capture plant with the help of a simulation model, built using the object-oriented Modelica Library Thermal Separation. The solvent used is an amino-acid salt. The dynamic behaviour is investigated for a reduction in regeneration heat flow rate but constant flue gas flow rate. Hereby four different control strategies are compared, one keeping the lean solvent loading constant, one keeping the solvent flow rate constant, one where flue gas bypasses the capture plant and a last one where an additional solvent tank is introduced. The simulation shows i.e. that for a constant lean solvent loading the response of the absorbed CO2 flow rate is much faster than for a constant solvent flow rate. Also the effect on the dynamic behaviour is investigated, comparing the whole cycle model to a stand-alone desorber model and to a stand-alone absorber model respectively. It was found that the dynamic responses on a short time scale are very similiar, but different on a long time scale. [Copyright &y& Elsevier]

This paper deals with the modeling and optimization of the chemical absorption process to CO2 removal using monoethanolamine (MEA) aqueous solution. Precisely, an optimization mathematical model is proposed to determine the best operating conditions of the CO2 post-combustion process in order to maximize the CO2 removal efficiency. Certainly, the following two objective functions are considered for maximization: (a) ratio between the total absorbed CO2 and the total heating and cooling utilities and (b) ratio between total absorbed CO2 and the total amine flow-rate. Temperature, composition and flow-rate profiles of the aqueous solution and gas streams along the absorber and regenerator as well as the reboiler and condenser duties are considered as optimization variables. The number of trays or height equivalent to a theoretical plate (HETP) on the absorber and regenerator columns as well as the CO2 composition in flue gas are treated as model parameters. Correlations used to compute physical-chemical properties of the aqueous amine solution are taken from different specialized literature and are valid for a wide range of operating conditions. For the modeling, both columns (absorber and regenerator) are divided into a number of segments assuming that liquid and gas phases are well mixed. GAMS (General Algebraic Modeling System) and CONOPT are used, respectively, to implement and to solve the resulting mathematical model. The robustness and computational performance of the proposed model and a detailed discussion of the optimization results will be presented through different case studies. Finally, the proposed model cannot only be used as optimizer but also as a simulator by fixing the degree of freedom of the equation system. [ABSTRACT FROM AUTHOR]

Oxy-coal combustion is one of the leading technologies for carbon capture and storage. This paper presents a review of the opportunities and challenges surrounding the development of oxy-coal combustion models and discusses historical and recent advances in specific areas related to computational fluid dynamics (CFD), including char oxidation, radiation, pollutant formation and removal (Hg, NOx and SOx), and the impact of turbulence. CFD can be used to assess and optimise full-scale retrofit designs and to provide data on matching air-fired heat duties. In addition, CFD can also be used to improve combustion efficiency and identify potential reductions in corrosion, slagging, fouling and trace pollutant emissions. Transient simulations are becoming more computationally affordable for coal combustion, providing opportunities for model development. High concentrations of CO2 and H2O in oxy-coal can influence chemical kinetic rates, burnout and ash properties. The modelling can be improved by incorporating detailed kinetic mechanisms of gasification reactions. In addition, pollutant formation and removal mechanisms must be understood during oxy-coal firing to aid the selection of flue-gas cleaning strategies. Radiative heat transfer using spectral models for gaseous properties may be necessary in oxy-coal modelling because CO2 and H2O molecules have strong emission bands. Finally this review provides a coherent near-term and long-term oxy-coal specific CFD sub-models development strategy to simulate the complex oxy-coal combustion processes, heat transfer and pollutant emissions in power generation systems. [ABSTRACT FROM AUTHOR]

Abstract: The paper analyzes nonlinear optimal control of integral–differential equations that describe the optimal management of a forest taking into account intra-species competition and carbon sequestration. The objective function includes the revenues from timber production, operational expenses, and the net benefits from carbon sequestration. A dual system is derived and a necessary extremum condition is established. [Copyright &y& Elsevier]

This paper serves two purposes: it provides a summarized scientific history of carbon sequestration in relation to the soil-plant system and gives a commentary on organic wastes and SOC sequestration. The concept of soil organic carbon (SOC) sequestration has its roots in: (i) the experimental work of Lundegårdh, particularly his in situ measurements of CO2 fluxes at the soil-plant interface (1924, 1927, 1930); (ii) the first estimates of SOC stocks at the global level made by Waksman [Waksman, S.A., 1938. Humus. Origin, Chemical Composition and Importance in Nature, second ed. revised. Williams and Wilkins, Baltimore, p. 526] and Rubey [Rubey, W.W., 1951. Geologic history of sea water. Bulletin of the Geological Society of America 62, 1111–1148]; (iii) the need for models dealing with soil organic matter (SOM) or SOC dynamics beginning with a conceptual SOM model by De Saussure (1780–1796) followed by the mathematical models of Jenny [Jenny, H., 1941. Factors of Soil Formation: a System of Quantitative Pedology. Dover Publications, New York, p. 288], Hénin and Dupuis [Hénin, S., Dupuis, M., 1945. Essai de bilan de la matière organique. Annales d’Agronomie 15, 17–29] and more recently the RothC [Jenkinson, D.S., Rayner, J.H., 1977. The turnover of soil organic matter in some of the Rothamsted classical experiments. Soil Science 123 (5), 298–305] and Century [Parton, W.J., Schimel, D.S., Cole, C.V., Ojima, D.S., 1987. Analysis of factors controlling soil organic matter levels in great plains grasslands. Soil Science Society of America Journal 51 (5), 1173–1179] models. The establishment of a soil C sequestration balance is not straightforward and depends greatly on the origin and the composition of organic matter that is to be returned to the system. Wastes, which are important sources of organic carbon for soils, are taken as an example. For these organic materials the following factors have to be considered: the presence or absence of fossil C, the potential of direct and indirect emissions of non-CO2 greenhouse gases (CH4 and N2O) following application and the agro-system which is being used as a comparative reference. [Copyright &y& Elsevier]

Cost effectiveness of CO2 sequestration, especially into aquifers, strongly depends on the sequestration capacities and the routes to connect CO2 sequestration sites and recovery sites. This site dependency of CO2 sequestration makes its evaluation difficult. In order to evaluate the cost effectiveness of CO2 sequestration in parallel with other carbon mitigation options in Japan, a new mathematical model of optimization type has been developed. The energy systems and the processes of CO2 recovery, transportation and sequestration are modeled in the bottom-up fashion. To pay due consideration to the site dependency, the land area of Japan is divided into 20 regions and the offshore area also into 20 regions. The land regions have various kinds of energy supply-side facilities and CO2 recovery and transportation facilities. The final energy demand is grouped into four types of energy: solid fuel, gaseous fuel, liquid fuel and electricity. On the other hand, the offshore regions have aquifers for CO2 sequestration. In addition, CO2 sequestration into ocean is taken into account. These model regions are inter-linked with each other, and inter-regional CO2 transportation and energy transportation are considered. The total cost of energy systems and CO2 sequestration in Japan between the years 2000 and 2050 is minimized in this model. This paper describes the structure of this new model for evaluation of CO2 sequestration in Japan, and presents model-based optimization solutions as to when, where and how much CO2 sequestration and other carbon mitigation options should be implemented under assumed carbon mitigation policy options. [Copyright &y& Elsevier]