Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal

Based on the results of previous studies, the efficiency of a Brayton/Hirn combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO₂ removal by chemical absorption reached 33.94%, considering also the separate CO₂ compression process. The specific CO₂ emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO₂ chemical absorption (38–39% efficiency, 130 kg/MW h specific CO₂ emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilisation. The LCA shows the important environmental advantages of biomass utilisation in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilisation.     

Equality and CO2 emissions distribution in climate change integrated assessment modelling

The equity implications of alternative climate policy measures are an essential issue to be considered in the design of future international agreements to tackle global warming. This paper specifically analyses the future path of emissions and income distribution and its determinants in different scenarios. Whereas our analysis is driven by tools which are typically applied in the income distribution literature and which have recently been applied to the analysis of CO₂ emissions distribution, a new methodological approach is that our study is driven by simulations run with the popular regionalised optimal growth climate change model RICE99 over the 1995–2105 period. We find that the architecture of environmental policies, the implementation of flexible mechanisms and income concentration are key determinants of emissions distribution over time. In particular we find a robust positive relationship between measures of inequalities in the distribution of emissions and income and that their magnitude will essentially depend on technological change.     

Integrated gasification combined cycle and carbon capture: A risky option to mitigate CO2 emissions of coal-fired power plants

The power sectors of many big economies still rely on coal-fired plants and emit huge amounts of carbon dioxide. Emerging countries like Brazil, China and South Africa plan to expand the use of coal-fired thermal plants in the next decade. Integrated gasification combined cycle (IGCC) is an innovative technology that facilitates the implementation of carbon capture (CC). The present work analyzes the maturity and costs of the IGCC technology, with and without CC, and assesses the effect of the technology risk on its economic viability. Findings show that the inclusion of the risk in the economic analysis of IGCC plants raises the cost of CO₂ avoided from 36 US$/t_CO2 to 106 US$/t_CO2 in the case of Shell Gasifiers and from 39 US$/t_CO2 to 112 US$/t_CO2 in the case of GE Gasifiers. Thus, the introduction of IGCC with CC on a wider scale faces huge uncertainties. The feasibility of these plants will rely heavily on the overcoming of the technology risk. Besides, its implementation in the short run will depend on government incentives to bear with the additional cost incurred in the first-generation plants.     

South Patagonia: Wind/hydrogen/coal system with reduced CO2 emissions

Wind is a significant renewable energy source in Patagonia, which could generate a very large amount of electrical energy. However, it is not possible to put such a large amount of energy on to the grid due to instability issues. Electrolysis could facilitate the storage of such energy in the form of hydrogen, which could be used for peak power production or for vehicles. However, hydrogen storage and distribution are still very expensive.     

Part-load analysis of a chemical looping combustion (CLC) combined cycle with CO2 capture

This paper presents part-load evaluation of a natural gas-fired chemical looping combustion (CLC) combined cycle with CO₂ capture. The novel combined cycle employs an air-based gas turbine, a CO₂-turbine and a steam turbine cycle. In this combined cycle, the CLC reactors replace combustion chamber of the gas turbine. The proposed combined cycle has a net plant efficiency of about 52.2% at full-load, including CO₂ compression to 200 bar. The part-load evaluation shows that reducing the load down to 60% results in an efficiency drop of 2.6%-points. However, the plant shows better relative part-load efficiency compared to conventional combined cycles. The pressure in CLC-reduction and -oxidation reactors is balanced by airflow control, using a compressor equipped with variable guide vanes. A combination of control strategies is discussed for plant start-up and shutdown and for part-load when airflow reduction is not practically possible with current generation of compressors. The results show that the combined cycle has a promising efficiency even at part-load; however, it requires an advanced control strategy.     

Thermodynamic analysis and optimization of novel ejector-expansion TRCC (transcritical CO2) cascade refrigeration cycles (Novel transcritical CO2 cycle)

In this paper, two new CO₂ cascade refrigeration cycles are proposed and analyzed. In both these cycles the top cycle is an ejector-expansion transcritical cycle and the bottom cycle is a sub-critical CO₂ cycle. In one of these proposed cycles the waste heat from the gas cooler is utilized to drive a supercritical CO₂ power cycle making the plant a combination of three cycles. Using the first and second laws of thermodynamics, theoretical analyses on the performance characteristics of the cycles are carried out. Also a parametric study is conducted to optimize the performance of each cycle under various operating conditions. The proposed cycles exhibit a reasonable value of COP (coefficient of performance) with a much less value of compressor discharge temperature, compared to the conventional cycles.     

Characteristics of cardboard and paper gasification with CO2

Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000 °C using CO₂ as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO₂ gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800 °C while at elevated temperatures of 900 and 1000 °C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H₂ to exhibit after few minutes into the gasification that changed with gasification temperature. At 800 °C gasification temperature peak in H₂ was displayed at 3 min into gasification while it decreased to only 2 min, approximately, at gasification temperatures of 900 and 1000 °C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (C+CO₂2CO). The results show important role of CO₂ gas for the gasification of wastes and low grade fuels to clean syngas.     

Sorbent enhanced hydrogen production from steam gasification of coal integrated with CO2 capture

In this work, CO₂ capture and H₂ production during the steam gasification of coal integrated with CO₂ capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H₂ (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H₂ to more than 80%, with almost all CO₂ was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H₂ and CO₂ through the water gas shift reaction. The steam gasification of coal integrated with CO₂ capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H₂ (81.7%) and minimum CO₂ concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.     

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.     

Biomass integrated gasification combined cycle power generation with supplementary biomass firing: Energy and exergy based performance analysis

A thermodynamic analysis of a Biomass Integrated Gasification Combined Cycle (BIGCC) plant has been performed based on energy and exergy balances in a proposed configuration. Combustion of supplementary biomass fuel is considered using the oxygen available in the gas turbine (GT) exhaust. The effects of pressure and temperature ratios of the GT system and the amount of fuel burned in the supplementary firing chamber on the thermal and exergetic efficiencies of the plant have been investigated. The plant efficiencies increase with the increase in both pressure and temperature ratios; however, the latter has a stronger influence than the former. Supplementary firing of biomass increases the plant efficiencies of a BIGCC plant till an optimum level of degree of firing. The other technical issues related to supplementary firing, like ash fusion in the furnace and exhaust heat loss maintaining a minimum pinch point temperature difference are accounted and finally a set of optimum plant operating parameters have been identified. The performance of a 50 MWe plant has been analyzed with the optimum operating parameters to find out equipment rating and biomass feed rates. Exergetic efficiencies of different plant equipments are evaluated to localize the major thermodynamic irreversibilities in the plant.     

CO2 emissions of Turkish manufacturing industry: A decomposition analysis

In this study, CO₂ emissions of Turkish manufacturing industry are calculated by using the fuel consumption data at ISIC revision 2, four digit level. Study covers 57 industries, for the 1995–2001 period. Log Mean Divisia Index (LMDI) method is used to decompose the changes in the CO₂ emissions of manufacturing industry into five components; changes in activity, activity structure, sectoral energy intensity, sectoral energy mix and emission factors. Mainly, it is found that changes in total industrial activity and energy intensity are the primary factors determining the changes in CO₂ emissions during the study period. It is also indicated that among the fuels used, coal is the main determining factor and among the sectors, 3710 (iron and steel basic industries) is the dirtiest sector dominating the industrial CO₂ emissions in the Turkish manufacturing industry.     

Cycle analysis of low and high H2 utilization SOFC/gas turbine combined cycle for CO2 recovery

A major factor in global warming is CO₂ emission from thermal power plants, which burn fossil fuels. One technology proposed to prevent global warming is CO₂ recovery from combustion flue gas and the sequestration of CO₂ underground or near the ocean bed. Solid oxide fuel cell (SOFC) can produce highly concentrated CO₂, because the reformed fuel gas reacts with oxygen electrochemically without being mixed with air in the SOFC. We therefore propose to operate multi-staged SOFCs with high utilization of reformed fuel to obtain highly concentrated CO₂. In this study, we estimated the performance of multi-staged SOFCs considering H₂ diffusion and the combined cycle efficiency of a multi-staged SOFC/gas turbine/CO₂ recovery power plant. The power generation efficiency of our CO₂ recovery combined cycle is 68.5%, whereas the efficiency of a conventional SOFC/GT cycle with the CO₂ recovery amine process is 57.8%.     

Simulation of a new biomass integrated gasification combined cycle (BIGCC) power generation system using Aspen Plus: Performance analysis and energetic assessment

A new biomass integrated gasification combined cycle (BIGCC), which featured an innovative two-stage enriched air gasification system coupling a fluidized bed with a swirl-melting furnace, was proposed and built for clean and efficient biomass utilization. The performance of biomass gasification and power generation under various operating conditions was assessed using a comprehensive Aspen Plus model for system optimization. The model was validated by pilot-scale experimental data and gas turbine regulations, showing good agreement. Parameters including oxygen percentage of enriched air (OP), gasification temperature, excess air ratio and compressor pressure ratio were studied for BIGCC optimization. Results showed that increase OP could effectively improve syngas quality and two-stage gasification efficiency, enhancing the gas turbine inlet and outlet temperature. The maximum BIGCC fuel utilization efficiency could be obtained at OP of 40%. Increasing gasification temperature showed a negative effect on the two-stage gasification performance. For efficient BIGCC operation, the excess air ratio should be below 3.5 to maintain a designed gas turbine inlet temperature. Modest increase of compressor pressure ratio favored the power generation. Finally, the BIGCC energy analysis further proved the rationality of system design and sufficient utilization of biomass energy.     

Performance analysis and optimization of a new two-stage ejector-expansion transcritical CO2 refrigeration cycle

In this paper, a new two-stage configuration of ejector-expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. Based on the simulation results, it is found that, compared with the conventional two-stage transcritical CO₂ cycle, the COP and second law efficiency of the new two-stage cycle are about 12.5–21% higher than that of conventional two-stage cycle. It is also concluded that, the performance of the new two-stage transcritical CO₂ refrigeration can be significantly improved based on the presented new two-stage cycle. Hence the new two-stage refrigeration cycle is a promising refrigeration cycle from the thermodynamically and technical point of views. A regression analysis in terms of evaporator and gas cooler exit temperatures has been used, in order to develop mathematical expressions for maximum COP, optimum discharge and inter-stage pressures and entrainment ratio.     

The marginal cost of CO2 emissions

Haraden's model for estimating the economic cost of global warming is analysed. We change his method of discounting and some of his input parameters in a manner consistent with physical and economic theory as well as empirical data. We then find much higher costs than Haraden found. These costs are compared to the cost of reducing CO₂ emissions and we find that deep cuts of the emissions of CO₂ are preferable. A check of the sensitivity of our results with respect to some crucial parameter values does not alter that conclusion.     

CO2 emissions structure of Indian economy

This paper analyses carbon dioxide (CO₂) emissions of the Indian economy by producing sectors and due to household final consumption. The analysis is based on an Input–Output (IO) table and Social Accounting Matrix (SAM) for the year 2003–04 that distinguishes 25 sectors and 10 household classes. Total emissions of the Indian economy in 2003–04 are estimated to be 1217 million tons (MT) of CO₂, of which 57% is due to the use of coal and lignite. The per capita emissions turn out to be about 1.14 tons. The highest direct emissions are due to electricity sector followed by manufacturing, steel and road transportation. Final demands for construction and manufacturing sectors account for the highest emissions considering both direct and indirect emissions as the outputs from almost all the energy-intensive sectors go into the production process of these two sectors. In terms of life style differences across income classes, the urban top 10% accounts for emissions of 3416 kg per year while rural bottom 10% class accounts for only 141 kg per year. The CO₂ emission embodied in the consumption basket of top 10% of the population in urban India is one-sixth of the per capita emission generated in the US.     

Dynamic life cycle assessment (LCA) of renewable energy technologies

Before new technologies enter the market, their environmental superiority over competing options must be asserted based on a life cycle approach. However, when applying the prevailing status-quo Life Cycle Assessment (LCA) approach to future renewable energy systems, one does not distinguish between impacts which are ‘imported’ into the system due to the ‘background system’ (e.g. due to supply of materials or final energy for the production of the energy system), and what is the improvement potential of these technologies compared to competitors (e.g. due to process and system innovations or diffusion effects). This paper investigates a dynamic approach towards the LCA of renewable energy technologies and proves that for all renewable energy chains, the inputs of finite energy resources and emissions of greenhouse gases are extremely low compared with the conventional system. With regard to the other environmental impacts the findings do not reveal any clear verdict for or against renewable energies.Future development will enable a further reduction of environmental impacts of renewable energy systems. Different factors are responsible for this development, such as progress with respect to technical parameters of energy converters, in particular, improved efficiency; emissions characteristics; increased lifetime, etc.; advances with regard to the production process of energy converters and fuels; and advances with regard to ‘external’ services originating from conventional energy and transport systems, for instance, improved electricity or process heat supply for system production and ecologically optimized transport systems for fuel transportation.The application of renewable energy sources might modify not only the background system, but also further downstream aspects, such as consumer behavior. This effect is, however, strongly context and technology dependent.     

On the off-design of a natural gas-fired combined cycle with CO2 capture

During the last 15 years cycles with CO₂ capture have been in focus, due to the growing concern over our climate. Often, a natural gas fired combined cycle with a chemical absorption plant for CO₂ capture from the flue gases have been used as a reference in comparisons between cycles. Neither the integration of the steam production for regeneration of amines in the combined cycle nor the off-design behaviour of such a plant has been extensively studied before.     

Pilot scale autothermal gasification of coconut shell with CO2-O2 mixture

This paper explored the feasibility and benefit of CO₂ utilization as gasifying agent in the autothermal gasification process. The effects of CO₂ injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO₂/C ratio from 0.6 to 1.6. O₂ was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO₂ injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO₂-O₂ gasification with a CO₂/C ratio of 0.6–1.2. The progress of the expected CO₂ to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO₂/C ratio increased. The producer gas heating value of CO₂-O₂ gasification was consistently higher than that of air gasification. These results show the potential of CO₂-O₂ gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.