Thermodynamic Analysis of Liquefied Natural Gas （LNG） Production Cycle in APCI Process

The appropriate production of liquefied natural gas(LNG)with least consuming energy and maximum efficiency is quite important.In this paper,LNG production cycle by means of APCI Process has been studied.Energy equilibrium equations and exergy equilibrium equations of each equipment in the APCI cycle were established.The equipments are described using rigorous thermodynamics and no significant simplification is assumed.Taken some operating parameters as key parameters,influences of these parameters on coefficient of performance(COP)and exergy efficiency of the cascading cycle were analyzed.The results indicate that COP and exergy efficiency will be improved with the increasing of the inlet pressure of MR(mixed refrigerant)compressors,the decreasing of the NG and MR after precooling process,outlet pressure of turbine,inlet temperature of MR compressor and NG temperature after cooling in main cryogenic heat exchanger(MCHE).The COP and exergy efficiency of the APCI cycle will be above 2% and 40%,respectively,after optimizing the key parameters.     

Future forecast for life-cycle greenhouse gas emissions of LNG and city gas 13A

The objective of this paper is to analyze the most up-to-date data available on total greenhouse-gas emissions of a LNG fuel supply chain and life-cycle of city gas 13A¹ based on surveys of the LNG projects delivering to Japan, which should provide useful basic-data for conducting life-cycle analyses of other product systems as well as future alternative energy systems, because of highly reliable data qualified in terms of its source and representativeness. In addition, the life-cycle greenhouse-gas emissions of LNG and city-gas 13A in 2010 were also predicted, taking into account not only the improvement of technologies, but also the change of composition of LNG projects. As a result of this analysis, the total amount of greenhouse-gas emissions of the whole city-gas 13A chain at present was calculated to be 61.91 g-CO₂/MJ, and the life-cycle greenhouse-gas emissions of LNG and city-gas 13A in 2010 could be expected to decrease by about 1.1% of the current emissions.     

A new semi-closed gas turbine cycle with CO2 separation

In this work, a new Semi-Closed Gas Turbine Cycle (SCGT) configuration is presented, named Semi-Closed Gas Turbine/Regenerative Combined Cycle (SCGT/RCC). The SCGT/RCC is an hybrid combination of the SCGT/CC and SCGT/RE cycle concepts, including both partial regeneration of the gas turbine and coupling to a bottoming steam cycle by a small-size Heat Recovery Steam Generator (HRSG). An energy and exergy analysis is carried out for several configurations and operating conditions. A preliminary analysis of the RHE size, CO₂ absorption potential and related effects on the cycle performance is presented, at several operating conditions and investigating three possible plant operation modes. The performance of the SCGT/RCC is very interesting at optimized operating conditions (specific power exceeding 550 kJ/kg of compressor inlet flow rate, efficiencies close to 50% including a 80% CO₂ removal). This plant is a promising solution that combines the positive features of semi-closed gas turbines, allowing a drastic reduction of size and capital costs for both HRSG and RHE and maintaining high values of performance.     

Natural gas combined cycle with exhaust gas recirculation and CO2 capture at part-load operation

This paper aims to evaluate part-load operation of a natural gas combined cycle (NGCC) power plant with exhaust gas recirculation (EGR) and a CO₂ capture plant. Several studies have demonstrated the feasibility and the advantages of EGR at full load, but operation at part load is also important because it is a common condition when NGCC power plants are being used as backup for renewables. The results of this study show that the number of absorber trains is reduced from 4 to 3 with EGR. The efficiency of the NGCC plant with EGR was 0.5% points higher than a conventional NGCC at full load as a result of a higher CO₂ concentration in the flue gas. However, this efficiency advantage decreased as the load was reduced from 100% to 50%, with both cases presenting the same efficiency at 50% load. This means that there was no benefit from the effect of EGR at lower loads. The efficiency of a NGCC plant with EGR and CO₂ capture configuration decreased from 52.6% to 45.9% when the load was reduced from 100% to 50% compared with a conventional NGCC where the efficiency changed from 52.1% to 45.9%. It was concluded that a NGCC plant with EGR and CO₂ capture is viable, results in lower capital costs due to the smaller number of absorber trains and yields slightly higher efficiencies, for operation at part-load down to 50%.     

Performance analysis of a CCHP system based on SOFC/GT/CO2 cycle and ORC with LNG cold energy utilization

An innovative CCHP system based on SOFC/GT/CO₂ cycle and the organic Rankine cycle (ORC) with LNG cold energy utilization is proposed to achieve cascade energy utilization and carbon dioxide capture. The mathematical models are developed and the system performance is analyzed using the energy and exergy methods. The results illustrate that the comprehensive energy utilization, the net power generation and the overall exergy efficiencies of the system can reach about 79.48%, 79.81% and 62.29%, respectively, while the power generation efficiency of the SOFC is 50.96% and the CO₂ capture rate of the proposed CCHP system is 79.2 kg/h under the given conditions. It shows that the proposed CCHP system can reach a high energy utilization efficiency with near zero emissions. The influence of some key parameters, such as the fuel utilization factor, the air-fuel ratio, the oxygen concentration in the cathode feed and the compression ratio of the SCO₂ turbine on the performance of the entire system is studied.     

Life cycle CO2 emissions from power generation using hydrogen energy carriers

Hydrogen energy carriers such as liquid hydrogen (LH₂), methylcyclohexane (MCH), and ammonia (NH₃) are promising energy vectors in the clean energy systems currently being developed. However, their effectiveness in mitigating environmental emissions must be assessed by life cycle analyses throughout the supply chain. In this study, while focusing on hydrogen energy carriers, life cycle inventory analyses were conducted to estimate CO₂ emissions from the following types of power generation plants in Japan: a hydrogen (H₂) mono-firing power plant using LH₂ or MCH that originated from overseas renewable electricity; and NH₃ co-firing with fossil fuel and NH₃ mono-firing power plants using hydrogen energy carriers that originated from overseas natural gas or renewable electricity. Parameters related to the supply chains were collected by literature surveys, and the Japanese life cycle inventory database was primarily used to calculate the emissions. From the results, CO₂ hotspots of the target supply chains and potential measures are identified that become necessary to establish low-carbon supply chains.     

In-depth numerical analysis on the determination of amount of CO2 recirculation in LNG/O2/CO2 combustion

The determination of proper amount of CO₂ recirculation is one of the critical issues in oxy-fuel combustion technology for the reduction of CO₂ emissions by the capture and sequestration of CO₂ species in flue gas. The objective of this study is to determine the optimum value of O₂ fraction in O₂/CO₂ mixture to obtain similar flame characteristics with LNG–air combustion. To this end, a systematic numerical investigation has been made in order to resolve the physical feature of LNG/O₂/CO₂ combustion. For this, SIMPLEC algorithm is used for the resolution of pressure velocity coupling. And for the Reynolds stresses and turbulent reaction the popular two-equation (k–ε) model by Launder and Spalding and eddy breakup model by Magnussen and Hjertager were incorporated, respectively. The radiative heat transfer is calculated from the volumetric energy loss rate from flame, considering absorption coefficient of H₂O, CO₂ and CO gases. A series of parametric investigation has been made as function of oxidizer type, O₂ fraction and fuel type for the resolution of combustion characteristics such as flame temperature, turbulent mixing and species concentration. Further the increased effect of CO₂ species on the flame temperature is carefully examined by the consideration of change of specific heat and radiation effect. Based on this study, it was observed that the same mass flow rate of CO₂ with N₂ appears as the most adequate value for the amount of CO₂ recirculation for LNG fuel since the lower C_p value for the CO₂ relative to N₂ species at lower temperatures cancels the effect of the higher C_p value at higher temperatures over the range of flame temperatures present in this study. However, for the fuel with high C/H ratio, for example of coal, the reduced amount of CO₂ recirculation is recommended in order to compensate the increased radiation heat loss. In general, the calculation results were physically acceptable and consistent with reported data in literature. Further work is strongly recommended for a large-scale combustor such as coal-fired power plant to figure out important parameters caused by the effect of increased combustor size and the presence of particle phase, etc.     

Life cycle greenhouse gas emissions analysis of catalysts for hydrotreating of fast pyrolysis bio-oil

Bio-oil from fast pyrolysis of biomass requires multi-stage catalytic hydroprocessing to produce hydrocarbon drop-in fuels. One process design currently in development involves fixed beds of ruthenium-based catalyst and conventional petroleum hydrotreating catalyst. As the catalyst is spent over time as a result of coking and other deactivation mechanisms, it must be changed out and replaced with fresh catalyst. A main focus of bio-oil upgrading research is increasing catalyst lifetimes to 1 year. Biofuel life cycle greenhouse gas (GHG) assessments typically ignore the impact of catalyst consumed during fuel conversion as a result of limited lifetime, representing a data gap in the analyses. To help fill this data gap, life cycle GHGs were estimated for two representative examples of fast pyrolysis bio-oil hydrotreating catalyst, NiMo/Al₂O₃ and Ru/C, and integrated into the conversion-stage GHG analysis. Life cycle GHGs are estimated at 5.5 kg CO₂-e/kg catalyst for NiMo/Al₂O₃. Results vary significantly for Ru/C, depending on whether economic or mass allocation methods are used. Life cycle GHGs for Ru/C are estimated at 80.4 kg CO₂-e/kg catalyst using economic allocation and 13.7 kg CO₂-e/kg catalyst using mass allocation. Contribution of catalyst consumption to total conversion-stage GHGs at 1-year catalyst lifetimes is 0.5% for NiMo/Al₂O₃ and 5% for Ru/C when economic allocation is used (1% for mass allocation). This analysis does not consider the use of recovered metals from catalysts and other wastes for catalyst manufacture and therefore these are likely to be conservative estimates compared to applications where a spent catalyst recycler can be used.     

The performance analysis of a two‐stage transcritical CO2 cooling cycle with various gas cooler pressures

A theoretical analysis of a two‐stage transcritical CO₂ cooling cycle is presented. The effect of a two‐stage cycle with intercooling process on the system coefficient of cooling performance is presented for various gas cooler pressures. However, the performance comparison between one‐stage and two‐stage cycles is presented for same operating conditions. Gas cooler pressure, compressor isentropic efficiency, gas cooler efficiency, intercooling quantity and refrigerant outlet temperature from the gas cooler are used as variable parameters in the analysis. It is concluded that the performance of the two‐stage transcritical CO₂ cycle is approximately 30% higher than that of the one‐stage transcritical CO₂ cycle. Hence, the two‐stage compression and intercooling processes can be assumed as valuable applications to improve the transcritical CO₂ cycle performance. Copyright © 2008 John Wiley & Sons, Ltd.     

Life cycle analysis of energy use and greenhouse gas emissions for road transportation fuels in China

Life cycle analysis is considered to be a valuable tool for decision making towards sustainability. Life cycle energy and environmental impact analysis for conventional transportation fuels and alternatives such as biofuels has become an active domain of research in recent years. The present study attempts to identify the most reliable results to date and possible ranges of life cycle fossil fuel use, petroleum use and greenhouse gas emissions for various road transportation fuels in China through a comprehensive review of recently published life cycle studies and review articles. Fuels reviewed include conventional gasoline, conventional diesel, liquefied petroleum gas, compressed natural gas, wheat-derived ethanol, corn-derived ethanol, cassava-derived ethanol, sugarcane-derived ethanol, rapeseed-derived biodiesel and soybean-derived biodiesel. Recommendations for future work are also discussed.     

Life cycle CO2 assessment of concrete by compressive strength on construction site in Korea

As research on the reduction in the life cycle carbon dioxide (LCCO₂) emissions of buildings has become increasingly important, the development of technologies that can quantitatively assess the LCCO₂ emissions of a building at the level of the construction materials is essential. In addition, concrete of various compositions, such as high-performance concrete mixed with fly ash and blast furnace slag and eco-concrete, has become readily available and thus, a quantitative evaluation of CO₂ basic units for these new materials is needed. However, basic units for various types of concrete are not provided by the National Life Cycle Inventory Database (LCI DB) in Korea. Therefore, thorough research on these materials has become an important priority.In this study, a method to assess LCCO₂ emissions using the compressive strength of concrete is proposed. Specifically, the compressive strengths of various mixes of concrete that are employed at construction sites in Korea were utilized to evaluate CO₂ emissions. Comparisons according to the characteristics of each mixture were also made.Approximately 560 concrete mix designs used at construction sites were first classified according to the compressive strength, admixture, and season. The concrete CO₂ emissions assessment process was carried out for the concrete raw materials production stage, the concrete raw materials transportation stage, and the concrete production stage; quantitative assessment methods are proposed for the CO₂ emissions at each stage. Based on the proposed assessment methods, an evaluation of the concrete CO₂ emissions was conducted and the obtained values were analyzed.     

Thermoeconomic evaluation of CO2 alkali absorption system applied to semi-closed gas turbine combined cycle

A new carbon dioxide separation system based on CO₂ absorption in aqueous solutions of alkaline salts (sodium and potassium carbonate) was studied with reference to semi-closed gas turbine/combined cycle (SCGT/CC), and compared to results obtained with existing technologies. Use of calcium hydroxide for the regeneration of the exhaust solution was studied in order to obtain a tail-end product, calcium carbonate in the form of precipitated calcium carbonate (PCC) with a wide spread and continuously growing market. The alkali CO₂ absorption process was compared with a conventional amine absorption process (DEA+MDEA), referring to the same SCGT/CC based on the same CO₂ removal efficiency. The comparison allows foregrounding of the possible goals of the CO₂ alkali absorption process with respect to previous amine cycle analyses. The modeling approach focuses on a thermodynamical and economical first comparison of the proposed cycle to previous studies carried out on CO₂ absorption (Energy Convers. Manage. 40 (1999) 1917; Absorption of CO₂ with amines in a semi closed GT cycle: plant performance and operating costs, ASME Paper 98-GT-395, American Society of Mechanical Engineers ASME Publishing, New York, 1998; Greenhouse Gas Control Technologies Conference, Interlaken, Switzerland, Pergamon, Oxford, 1999).     

Thermoeconomic analysis of a novel zero-CO2-emission high-efficiency power cycle using LNG coldness

This paper presents a thermoeconomic analysis aimed at the optimization of a novel zero-CO₂ and other emissions and high-efficiency power and refrigeration cogeneration system, COOLCEP-S (Patent pending), which uses the liquefied natural gas (LNG) coldness during its revaporization. It was predicted that at the turbine inlet temperature (TIT) of 900 °C, the energy efficiency of the COOLCEP-S system reaches 59%. The thermoeconomic analysis determines the specific cost, the cost of electricity, the system payback period and the total net revenue. The optimization started by performing a thermodynamic sensitivity analysis, which has shown that for a fixed TIT and pressure ratio, the pinch point temperature difference in the recuperator, ΔT_p1, and that in the condenser, ΔT_p2 are the most significant unconstrained variables to have a significant effect on the thermal performance of novel cycle. The payback period of this novel cycle (with fixed net power output of 20 MW and plant life of 40 years) was 5.9 years at most, and would be reduced to 3.1 years at most when there is a market for the refrigeration byproduct. The capital investment cost of the economically optimized plant is estimated to be about 1000 $/kWe, and the cost of electricity is estimated to be 0.34–0.37 CNY/kWh (0.04 $/kWh). These values are much lower than those of conventional coal power plants being installed at this time in China, which, in contrast to COOLCEP-S, do produce CO₂ emissions at that.     

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.     

Life cycle analysis of silicon-based photovoltaic systems

The analysis focuses on a comparative evaluation of emissions from conventional private passenger vehicles versus the environmental burdens of electric passenger vehicles. The batteries of electric passenger vehicles are loaded during daily working hours partly via silicon-based PV panels covering the vehicle parking areas (solar service stations), and partly via the public electric grid. The data base refers to Western Germany, and the tentative time period is around 2005. The analysis is based on detailed data collections for the fabrication of technical silicon, multi- and monocrystalline standard, MIS-I cells, and amorphous cells. The information on substance discharges into the environment permitted an environmental assessment to be made via evaluation criteria, quantitatively expressed as burden values. The results lead to the following main conclusions on the environmental impacts of Si-PV cells and to the major recommendations for PV development focuses: To substitute Si-PV for substance-emitting technologies is environmentally beneficial, but due to its manufacturing processes PV is not a zero emitter; supporting structures should be as low-weight as possible with minimized material requirements for low emissions from PV-system fabrication; PV only makes sense for applications relevant to the energy economy with high-efficiency modules and minimized electricity demand to enable solar supply shares to be as high as possible; and highest development priority should be given to the industrial fabrication maturity of high-efficiency modules.     

Thermodynamic analysis of a transcritical CO2 power cycle driven by solar energy with liquified natural gas as its heat sink

This paper proposes a transcritical CO₂ power cycle driven by solar energy while utilizing the cold heat rejection to an liquified natural gas (LNG) evaporation system. In order to ensure a continuous and stable operation for the system, a thermal storage system is introduced to store the collected solar energy and to provide stable power output when solar radiation is insufficient. A mathematical model is developed to simulate the solar-driven transcritical CO₂ power cycle under steady-state conditions, and a modified system efficiency is defined to better evaluate the cycle performance over a period of time. The thermodynamic analysis focuses on the effects of some key parameters, including the turbine inlet pressure, the turbine inlet temperature and the condensation temperature, on the system performance. Results indicate that the net power output mainly depends on the solar radiation over a day, yet the system is still capable of generating electricity long after sunset by virtue of the thermal storage tank. An optimum turbine inlet pressure exists under given conditions where the net power output and the system efficiency both reach maximum values. The net power output and the system efficiency are less sensitive to the change in the turbine inlet temperature, but the condensation temperature exerts a significant influence on the system performance. The surface area of heat exchangers increases with the rise in the turbine inlet temperature, while changes in the turbine inlet pressure have no significant impact on the heat exchanging area under the given conditions.     

湿化燃气轮机循环的性能分析

能源危机和环境污染的问题使人们对能源利用效率和环保的要求日益增加,同时经济的快速发展也使人们对电能的需求量越来越大。据国际能源协会(IEA)预测,电能的消耗将以平均每年2·4%的速度增长,因此效率高、比功输出大、对环境污染少成为目前发电技术所努力追求的目标。随着分布     

Performance analysis of open cycle gas turbines

In this study, the performance of ideal open cycle gas turbine system was examined based on its thermodynamic analysis. The effects of some parameters, such as compressor inlet temperature (CIT), pressure ratio (PR) and the turbine inlet temperature (TIT), on the performance parameters of open cycle gas turbine were discussed. The turbine net power output, the thermal efficiency and the fuel consumption of the turbine were taken as the performance parameters. The values of these parameters were calculated using some basic cycle equations and variables values of thermodynamic properties. Other variables such as lower heating value, combustion efficiency and isentropic efficiencies of compressor and turbine were assumed to be constant. The result showed that the net power output and the thermal efficiency increased by a decrease in the CIT and increase in the TIT and PR values. If it is aimed to have a high net power output and the thermal efficiency for the turbine, the CIT should be chosen as low as possible and the TIT should be chosen as high as possible. Copyright © 2008 John Wiley & Sons, Ltd.     

Life cycle analysis of processes for hydrogen production

Hydrogen is considered to be an ideal energy carrier in the foreseeable future and can play a very important role in the energy system. A variety of technologies can be used to produce hydrogen. One of the most remarkable methods for large-scale hydrogen production is thermo-chemical water decomposition using heat energy from nuclear, solar and other sources. Detailed simulations of the two most promising water splitting thermo-chemical cycles (the Westinghouse cycle and the Sulphur-Iodine cycle) were performed in Aspen Plus code and obtained results were used for life cycle analysis. They were compared with two different processes for hydrogen production (coal gasification and coal pyrolysis). Some of the results obtained from LCA are also reported in the paper.     

Life cycle cost analysis of a car,a city bus and an intercity bus powertrain for year 2005 and 2020

The international economy, in the beginning of the 20th century, is characterized by uncertainty about the supply and the price of oil. Together with the fast decrease of electrical propulsion component prices, it becomes more and more cost effective to develop vehicles with alternative powertrains. This paper focuses on two questions: Are alternative powertrains especially cost effective for specific applications?; How does an increased fossil fuel price influences the choose of powertrain? To assess these questions, a computer tool named THEPS, developed in a Ph.D. project, is used. Three applications and three scenarios are analysed. The applications, a car, a city bus and an intercity bus, are vehicles all assumed to operate in Sweden. One scenario represents year 2005, the other two year 2020. The two future scenarios are characterized by different fossil fuel prices. The study, presented in the paper, indicates that alternative powertrains can be competitive from a cost perspective, in some applications, already in year 2005. It is for example cost effective to equip a city bus, running in countries with a high fuel price, with a hybrid powertrain. The study also indicates that pure electric, hybrid and/or fuel cell cars will probably be a more cost effective choice than conventional cars in year 2020. Another indication is that it will not be clear which powertrain concept to choose. The reason is that many cost effective powertrain concepts will be offered. The best choice will depend on the application.