Compression Energy Consumption Research Articles

Simulation study on a novel solid–gas coupling hydrogen storage method for photovoltaic hydrogen production systems

Compressed hydrogen storage in photovoltaic hydrogen production systems faces several challenges, including limitations in storage volume, compression energy consumption and safety concerns. To improve the comprehensive hydrogen storage performance, this study develops a novel solid–gas coupling hydrogen storage method that combines metal hydride and phase change material (MH-PCM). Firstly, a vertical MH-PCM solid storage model considering the natural convection effect is proposed and investigated. Building upon this model, the solid–gas coupling hydrogen storage is constructed and integrated into the photovoltaic hydrogen production system to evaluate its comprehensive storage performance. Results reveal that considering natural convection leads to an approximately 12.7 % increase in the average storage rate, but is also accompanied by an uneven storage process. To address this unevenness and further enhance the storage rate, it's advisable to focus on structural optimization at the bottom of the tank. Additionally, improving the PCM thermal conductivity and hydrogen inlet pressure (to approximately 1 MPa) are also proven effective strategies. The proposed solid–gas coupling hydrogen storage demonstrates comprehensive advantages, particularly compact size and reduced energy consumption. Furthermore, appropriately increasing the coupling ratio between solid and gaseous capacities can achieve the even smaller storage volume. These findings can provide valuable theoretical and engineering guidance for implementing such hydrogen production and storage systems.

TEMPERATURE OF THE COMPRESSOR SUCTION AIR AND ITS INFLUENCE ON THE EFFICIENT OPERATION OF THE COMPRESSOR UNIT

The climatic conditions of Uzbekistan are characterized by relatively long summers with air temperature of 40-45 0C and higher, which is the reason of significant heating of air suctioned by compressor. Increase in temperature and corresponding decrease inair density contributes to 8-10% decrease in compressor unit productivity, leading to significant economic losses in the process of compressed air production. By means of artificial cooling of suction air at the inlet to the compressor unit it is possible to increase the energy efficiency of operation of the mine reciprocating compressor unit.The effectiveness of artificial air temperature reduction depends on the amount of temperature reduction and the type of plant drive, as well as on the purpose -toreduce the specific electric energy consumption for compression or to increase the capacity of the reciprocating compressor.

Enhancing Energy Efficiency and Reliability in Floating LNG Operation: A Hydrofluoroolefin-Based SMR Cycle with Thermo-Economic Assessment and Uncertainty Analysis

Natural gas liquefaction is the most energy-intensive technique in floating liquefied natural gas (FLNG) operations. Hence, a hydrofluoroolefin-based single mixed refrigerant (SMR) technology was proposed to achieve energy-efficient and eco-friendly operations. The study was perfomed to enhance the SMR process by substituting expansion valves with hydraulic turbines to improve process reversibility and enhance energy efficiency. The proposed process was optimized using a sine–cosine concept-based algorithm that tuned the design variables which yielded an overall compression energy consumption of 0.2501 (kWh/kg-LNG), resulting in a 21.43% saving as compared to the conventionally used mixed refrigerant-based process. This resulted in a reduction of about 38.81% in overall exergy destruction. The economic analysis results draw curtains that the process saves about 26.02% of total annualized cost as compared to conventional study. Owing to the appropriate mixed refrigerant component mixture ratio and process design improvement. To determine the process reliability under uncertain conditions the optimal compression power and minimum approach temperature were determined. Further, uncertainty analysis reveals that the methane and butane refrigerant flow rates along with evaporation, and condensation pressure, were among the most influential parameters that influence the process most that may affect the whole operation in uncertain process inlet conditions. In summary, our approach presents immense promise for achieving energy efficiency, environmental responsibility, and economic viability in FLNG operations, offering a robust solution for the challenges of offshore plants.

CO2 methanation enhanced with a cyclic SERP process using a commercial Ni-based catalyst mixed with 3A zeolite as adsorbent

Valorization of greenhouse gas CO2 is needed to mitigate and reduce climate change impact. The sustainable production of methane to obtain synthetic natural gas (SNG) is one of the most attractive solutions, given current needs. The methanation reaction, known as the Sabatier reaction, is limited by the formation of CO as an intermediate at high temperatures and the formation of H2O as a by-product. For this reason, recent research has focused on the use of catalysts/adsorbents mixtures capable of retaining the water produced as well as being methane-selective at low temperatures. In this work, the kinetic model of a commercial Ni/SiAl catalyst in an experimental reaction bed was obtained. Moreover, the water adsorption capacity of the catalyst has been studied in the typical reaction temperature range (473–623 K), and the adsorption equilibrium and diffusional parameters were determined. With the data obtained from these experiments, the methane production in a cyclic Sorption Enhanced Reaction Process (SERP) has been simulated, adding zeolite 3A as a water selective adsorbent. The process consists of three consecutive stages: an adsorption/reaction stage and two other stages, rinse and purge, to desorb the adsorbed water and remove it by condensation. A sensitivity analysis has been carried out to determine the effect of the operational variables on the process performance to obtain methane suitable for domestic natural gas consumption. A CO2 conversion of 99.7 %, methane selectivity of 99.9 %, molar purity of CH4 of 98.2 % as product, and compression energy consumption (6.97 kJ/mol CH4) 99 times lower than methane combustion energy has been obtained, proposing, therefore, a new process of methanation.

A novel nitrogen pipeline system for recycling pressure energy: System model and energy efficiency economic analysis

• Developed a novel nitrogen system with pressure energy recovery. • Reduced the energy consumption of compression by recovering the cold energy. • The exergy flow diagrams revealed the path of energy-saving and efficiency. • The exergy efficiency of the system increased from 48.92% to 65.78% mostly; • Guide system design by the sensitivity analysis of power generation pressure. The depressurization0 process by throttling causes a large amount of pressure energy loss in the nitrogen delivery process. We propose a novel nitrogen piping system (NNPS) and determine the key technical parameters to recover the pressure energy. The NNPS recovers nitrogen pressure energy for power generation and uses post-expansion cold energy to further reduce feedstock nitrogen temperature and compression energy consumption. We selected an NPS in China as a case study to analyze the performance of the NNPS under various operating conditions through energy, exergy, and economic analysis. In addition, a sensitivity analysis of the pre-expansion pressure was carried out. Results show that when the two throttling processes are replaced by the expansion process, the power generation per unit mass flow rate is 77.37 kW, and the energy consumption per unit mass flow rate of the compressor is reduced by 24.49 kW. Moreover, the energy efficiency and the exergy efficiency are 18.67% and 16.86% higher in NNPS compared with those in the NPS, respectively, with the shortest payback period of 113.2 days. When the expansion outlet pressure is 1.6 MPa, the system is suitable for construction when the pre-expansion pressure is higher than 2.0 MPa.

Hydrogen production from coke oven gas using pressure swing adsorption process − a mathematical modelling approach

Coal is playing a major role as a reductant and as an energy source in the present world steel production due to its low cost and widespread distribution around the world. At the same time, being the largest contributor to global CO2 emissions, coal faces significant environmental challenges in terms of air pollution and global warming. Hydrogen is a promising alternative for coal in lowering the steel industry’s CO2 footprint, but the availability of green hydrogen is currently limited by its high production cost. This research study focuses on developing a pressure swing adsorption (PSA) technology that will allow for continued use of coal for a smooth transition towards green hydrogen-based steel production, by better utilisation of its by-product coke oven gas to produce high purity hydrogen. A generic, fast and robust simulation tool for simulating a variety of PSA processes considering both equilibrium and kinetic effects using a detailed non-isothermal and non-isobaric model is developed in the study. The adsorption equilibrium data required for the model are calculated from experimental results using the non-linear regression data fitting method. A series of rigorous parametric studies and breakthrough tests are performed using the developed mathematical model for better understanding of the effects of different factors on the PSA process performance. With the better understanding obtained from the above-mentioned parametric studies, the model is optimised by performing several simulation tests to achieve a high process performance in terms of purity and recovery of the H2 product, productivity of the adsorbents and energy consumption for compression of gases. The optimised 14-step multi-bed PSA cycle developed in this study allows for an improved energy efficiency of coal usage by better utilisation of its by-product coke oven gas by converting it into valuable high purity (>99.999%) hydrogen product with a recovery of over 75%.

Single-tank storage versus multi-tank cascade system in hydrogen refueling stations for fuel cell buses

Many countries in Europe are investing in fuel cell bus technology with the expected mobilization of more than 1200 buses across Europe in the following years. The scaling-up will make indispensable a more effective design and management of hydrogen refueling stations to improve the refueling phase in terms of refueling time and dispensed quantity while containing the investment and operation costs. In the present study, a previously developed dynamic lumped model of a hydrogen refueling process, developed in MATLAB, is used to analyze tank-to-tank fuel cell buses (30–40 kgH2 at 350 bar) refueling operations comparing a single-tank storage with a multi-tank cascade system. The new-built Aalborg (DK) hydrogen refueling station serves as a case study for the cascade design. In general, a cascading refueling approach from multiple storage tanks at different pressure levels provides the opportunity for a more optimized management of the station storage, reducing the pressure differential between the refueling and refueled tanks throughout the whole refueling process, thus reducing compression energy. This study demonstrates the validity of these aspects for heavy-duty applications through the technical evaluation of the refueling time, gas heating, compression energy consumption and hydrogen utilization, filling the literature gap on cascade versus single tank refueling comparison. Furthermore, a simplified calculation of the capital and operating expenditures is conducted, denoting the cost-effectiveness of the cascade configuration under study. Finally, the effect of different pressure switching points between the storage tanks is investigated, showing that a lower medium pressure usage reduces the compression energy consumption and increases the station flexibility.

Graphical approach for estimating and minimizing boil-off gas and compression energy consumption in LNG regasification terminals

Liquefied natural gas regasification terminal operations are energy-intensive where compression of boil-off-gas consumes most of the energy. Improving such a terminal's economic performance demands effective boil-off-gas management that depends on its accurate and early prediction. Boil-off-gas processing and management systems are available, but they tend to incorporate boil-off-gas estimations that are either in the context of computationally expensive models or involve full-scale dynamic simulation models that require process data and expertise. To simplify boil-off-gas estimation, this study proposes a generalized graph that provides a correct estimation of boil-off-gas and the minimum compression power required to handle that estimated quantity of boil-off-gas generated. The method can be applied to a wide range of the liquefied natural gas regasification terminals currently in operation. This graphical approach renders the estimates of boil-off-gas generated and associated compression energy requirements without recourse to simulation. It can also provide early estimates of a terminal's energy requirements before any detailed analysis.

Small-scale adiabatic compressed air energy storage: Control strategy analysis via dynamic modelling

The increasing capacity of variable renewable energy sources fosters the importance of electric energy storage. This paper is focused on exploring Compressed Air Energy Storage (CAES) as a suitable solution for small-medium size stationary applications. A small-scale Adiabatic Compressed Air Energy Storage system with an artificial air vessel has been analysed and different control strategies have been simulated and compared through a dynamic model in Simcenter AMESim®, by identifying the most appropriate ones to improve the performance in off-design conditions. The built dynamic model allows simulating the real fluids behaviour, heat exchange, and thermofluid-mechanical inertia of its components. The proposed system is equipped with a three-stage volumetric compressor and a four-stage radial turbine. The use of variable speed compressor and turbine for both charging and discharging processes and the introduction of throttling to improve the compressor working point have been compared. Regarding the variable speed, the advantages resulted negligible for the expansion phase (+0.1% on the generated energy), while they were remarkable in the compression one. An enhancement of about 1% on the roundtrip efficiency was achieved with the variable-speed compressor and this solution demonstrated to better follow a power profile. The throttling valve was introduced to enable the reciprocating compressor to work close to nominal conditions when the pressure of the air vessel is lower than the nominal one. It allowed to strongly reduce the compression energy consumption, reaching an enhancement of about 2.3% on the round-trip efficiency. The combined use of the variable speed and throttling valve in the charging process has proven to be the best solution to reduce the compression energy consumption (-3.3%). The roundtrip efficiency enhancement of this solution (+1.8%) is lower than that obtained with the exclusive use of the throttling valve (+2.3%) because of the presence of the inverter efficiency but, simultaneously, it enables the compression group more flexible and to follow a given power profile.

Hydrogen purification using nanoporous graphene membranes and its economic analysis

We show from molecular dynamics insights that the nanoporous graphene (NPG) is an efficient membrane in hydrogen purification for separating gaseous H2/CH4 mixtures with a high permeance and selectivity. The H2 permeance is as high as 106 GPU, extremely higher than those of polymer membranes; the selectivity of H2 over CH4 is up to 225, in the same order with those of polymer membranes. An economic analysis is performed from the aspects of compression energy consumption and required membrane area; it is shown that the NPG membrane requires less membrane area but a bit more compression energy compared with the polymer membranes. However, the slightly higher compression energy consumption can be totally offset by the remarkably smaller membrane area. In summary, the NPG membranes for hydrogen purification present an excellent separation performance with a high H2 permeance, ultimately resulting in an impressive economic index comparing to the polymer membranes.

Moderate-pressure conversion of H2 and CO2 to methanol via adsorption enhanced hydrogenation

CO2 hydrogenation to methanol plays an increasingly important role in fields of chemical engineering, energy generation and H2/CO2 utilization, and the prohibitive costs result partially from the high operating pressures required for practical application. Thus, a hybrid catalyst/adsorbent consisting of Cu-ZnO-ZrO2 supported on hydrotalcite (named CZZ@HT) was synthesized, characterized and analyzed in this study with the intent that the adsorbent hydrotalcite would enhance the local concentration of CO2 and assist in catalyst dispersion. The as-prepared CZZ@HT catalyst containing 43.4 wt% of CuO-ZnO-ZrO2 in the form of well dispersed nanoparticles possessed a considerable BET surface area and external surface area after reduction. A remarkable copper dispersion of 58.7% was thereby achieved. This reduced catalyst displayed elevated uptakes of H2O and CO2 at 473 K compared to the reference adsorbent-free catalyst and presented enhanced adsorption capacities of CO2 at reaction temperatures due to collective effects of physisorption and chemisorption. Catalysis experiments on a fixed bed reactor using the rCZZ@HT catalyst showed a methanol selectivity of 83.4% and a SMeOH/SCO ratio of 5.0 in products. A control experiment in which hydrotalcite was replaced with quartz (named rCZZ&QS) showed considerably lower conversion at low pressure and demonstrated the enhancing effect of the hydrotalcite support. The new catalyst could achieve the same methanol productivity as the control catalyst at 2.45 MPa lower reaction pressure. This lower pressure corresponds to a ∼61.3% savings in energy consumption for compression. Accordingly, the CZZ@HT is a promising candidate for CO2 hydrogenation to methanol at moderate pressures.

Comparative experimental and numerical study on energy consumption of track-pin rubber bushing for high-speed tracked vehicles

During the running of high-speed tracked vehicles, the energy loss due to the rotation and tension-compression deformation of the rubber bushing between the track pin and the track plate causes the largest proportion of energy consumption in tracked vehicle propulsion systems; therefore, it is critical to study energy consumption of this component as it is the largest amount of energy loss of the system. First, the theoretical modeling and analysis of the torsional hysteresis and the tension-lag of the hanging glue on the pin of the track pin are conducted. Both energy loss of torsional hysteresis and energy loss of the hysteresis of tension and pressure are obtained when the rubber bushings pass the sprocket, the road wheel, and the idler. Second, a new and novel rubber bushing model based upon the rubber bushing elastic element, the friction element, and the viscoelastic element is proposed. Then the parameters (such as the static elastic stiffness and the maximum friction) of each unit are identified according to the dynamic characteristic experiment. Finally, the numerical simulation results of MATLAB with different stiffness and damping coefficient in addition to tension and compression energy consumption under different frequencies are obtained, and the comparisons are basically consistent with the experimental results; the average errors are less than 8%. The present analytical calculation model is practically useful and can meet the requirements of engineering applications.

Simulation study on the carbon capture system applying LNG cold energy to the O2/H2O oxy-fuel combustion

At present, the oxy-fuel combustion (O2/CO2 circulating combustion) is dominant in natural gas generating systems, but it consumes much energy for air separation oxygen generation and carbon capture, leading to a severe reduction of generating efficiency. The O2/H2O combustion system, as the new generation of an oxy-combustion system, is superior to the oxy-fuel combustion, and its pollutant emission is lower, but during its combustion, air separation oxygen generation is still needed, so CO2 compression energy consumption is still higher. In this paper, a set of carbon capture system applying LNG cold energy to the O2/H2O combustion was developed, and its mathematical model was established to calculate thermal efficiency and exergy efficiency. And then, it was compared with the COOLCEP system which also makes use of LNG cold energy for carbon capture. The combustion process of this system is operated under high pressure with H2O as the circulation medium, and LNG is utilized in a cascading pattern, so the energy consumption of air separation oxygen generation and carbon capture system is reduced, the generating efficiency of the system is increased and carbon capture is conducted at low cost. The thermal efficiency and energy efficiency of this system increase continuously as the inlet temperature of gas turbine rises. When the flow rate of circulating water is 13.5 kmol/s, the combustion pressure is 1.6 MPa, and the inlet temperature of gas turbine reaches 1328.1 °C, the thermal efficiency and exergy efficiency is 57.9% (maximum) and 42.7%, respectively. Compared with COOLCEP system, the O2/H2O combustion system is much lower in energy consumption and its thermal efficiency and exergy efficiency are 6.3% and 5.4% higher, respectively.

Energy Efficiency of Image Transmission in Embedded Linux based Wireless Visual Sensor Network

Wireless Visual Sensor Network (WVSN) is a system that consists of visual sensor nodes with an embedded processor. WVSN devices have limited resources of energy, computation capability, memory, and bandwidth. Due to these limitations the implementation of WVSN for large multimedia data, such as images, become a challenging task. Therefore, it is required compressed images prior to transmission. In addition to the limited resources, the system implementation strongly affects the efficiency of the working system.The main contribution of this research is to offer a technical solution of simpler image compression on the WVSN platform. JPEG 2000 is investigated as an alternative compression method to reduce the size of data transfer on WVSN using Embedded Linux as its operating system. Compressed images are transferred to a receiver on communication of IEEE 802.15.4.. This paper shows that the energy consumption for compression and transmission will reduce to only 10.48%, 13.60%, and 17.11% compared to raw image. BER will significantly reduce by implementing image compression. Therefore, it is demonstrated that this model significantly increases energy efficiency, memory utilization efficiency, and data transfer time with acceptable PSNR, compared to uncompressed images.

Effects of binders on the properties of bio-char pellets

Bio-char, produced from biomass pyrolysis, can be pelletized to improve its undesirable characteristics, such as low bulk and energy densities, poor transportation and storage properties, and troublesome to co-fire with coal. In this study, rice husk char was compressed into pellets with four kinds of binders (lignin, starch, calcium hydroxide and sodium hydroxide). The compressive process, mechanical strength, basic fuel properties, and combustion characteristics were investigated to elucidate the effect of binders on the properties of bio-char pellets. Results showed that starch pellets had good hydrophobicity, but low volume density and poor mechanical strength. The softening and morphological transition of lignin during compression may account for the high elastic modulus and good bonding of lignin pellets. The low saturated moisture content of Ca(OH)2 pellets is mainly ascribed to its hydration. NaOH pellets showed the highest compressive strength among all pellets, and also exhibited the highest moisture uptake that may worsen the handling and storage treatment of bio-char. Compared with raw bio-char, bio-char pellets had a lower ignition temperature, wider temperature interval, and higher oxidation activity according to the thermogravimetric analysis. The lignin and Ca(OH)2 pellets showed lower compression energy consumption and moisture uptake, enhanced mechanical strength and promoted combustion performance, which demonstrated more desirable properties for utilization as biofuels.

Co-pelletization of sewage sludge and biomass: The energy input and properties of pellets

Presently, most pellets are made of lignocellulose biomass. However, the rocketing development of demands and fierce competition of feedstock between biomass industries have resulted in local biomass supply insufficiency and rising prices of the raw material. Therefore, other kinds of raw materials should be involved in the production of pellets to improve the stable supply of feedstock. In this study, the pelletization of biomass materials mixed with sewage sludge (SS) was investigated. The effects of process parameters on energy consumption and pellet properties were studied. It was shown that the compression energy consumption was affected by applied pressure, die temperature and water content. Both temperature and water content had an influence on the above pellet properties to a different extent, which was found to be independent of pressure. Optimal parameters (55MPa for pressure, 90°C for temperature and 10–15% for water content) were recommended for co-pelletization.

Measurement of Mechanical Compressive Properties and Densification Energy Requirement of Miscanthus × giganteus and Switchgrass

Lignocellulosic biomass in bale form has a low bulk density. Current in-field balers can achieve a bulk density of merely 120 to 180 kg dry matter (DM) m−3, whereas modern high-compression cutting balers produce up to 230 kg m−3. Mechanical compression is a straightforward technique to increase the material density, which significantly improves the efficiency of transportation and storage, and simplifies handling. Traditional compression technology mainly produces pellets, but conceivably bales could be compressed to a higher density as well. To design compression machinery in general, it is essential to determine the mechanical properties of biomass under compression and compression energy consumption. In addition, the material rebound percentage after compression is needed to design low-cost containerization methods for highly compressed bales. In this research, we established pressure–bulk density relationships and calculated Poisson’s ratio for Miscanthus (Miscanthus × giganteus, Poaceae/Gramineae) and switchgrass (Panicum virgatum L. Poacea/Gramineae). We also calculated rebound percentages for Miscanthus in two particle sizes. The results showed that the energy consumption for compression of Miscanthus and switchgrass is low, ranging from 0.01 to 0.05 % of the inherent heating value of the materials. Poisson’s ratios of Miscanthus and switchgrass ranged from 0.2 to 0.3 for various particle sizes. The rebound percentage was found as 28 % for unground Miscanthus and 23 % for Miscanthus ground to 6.35-mm particles. A common opinion is that high-level compression of biomass may reduce its energy content. Although in this research some of the biomass was exposed to an extreme pressure of 750 MPa, microscopic imagery revealed no fractions in the cell walls, leading to the conjecture that compression does not negatively impact the conversion potential of the biomass.

Exergy analysis of a high pressure multistage hydrogen gas storage system

This study presents a parametric study on the performance aspects, through exergy analysis, of the multistage hydrogen gas storage subsystem in a hydropower-based-hydrogen gas fueling station producing 3 kg of hydrogen per hour and storing it. In order to perform an exergy analysis, the following parameters are taken into consideration: (i) mass flow rate of hydrogen (3 kg/h), (ii) inlet pressure of hydrogen (ranging from 1 to 200 bar), (iii) hydrogen storage pressure (ranging from 200 to 900 bar), (iv) dead state temperature (at 25 °C), (v) efficiency of electrical motor (90%), (vi) mechanical efficiency (95%), and (vii) polytropic efficiency (90%). It is obtained that increasing inlet pressure of hydrogen gas decreases the energy consumption for compression and storage process while increasing exergy efficiency. Moreover, it is noticed that increasing storage pressure increases the exergy content of hydrogen gas.

Algorithm for determining optimum sequestration depth of CO2 trapped by residual gas and solubility trapping mechanisms in a deep saline formation

AbstractAn algorithm is proposed here for determining the optimum sequestration depth (in terms of depth corresponding to maximum net income per unit rock volume) in a saline formation for CO2 trapped by residual gas and solubility trapping mechanisms. The Peng–Robinson equation of state was used to determine the density and fugacity of sequestered CO2 and the compression energy required for CO2 injection. Geochemist’s Workbench®, a commercial geochemical software package, was used to estimate CO2 solubility in groundwater. Operational costs and CO2 emissions due to compression energy consumption were estimated. A hypothetical reference case was constructed to illustrate the proposed algorithm, assuming constant values of geothermal gradient, hydrostatic pressure gradient, sweep efficiency and initial groundwater chemistry, with a depth‐dependent porosity and porosity‐dependent saturation of residual gas. In general, the algorithm was illustrated successfully for the hypothetical reference case and produced the following results. The depth corresponding to maximum trapping capacity was approximately 3000 m, but the depth representing maximum net income was approximately 1300 m. CO2 emissions due to compression energy consumption per unit mass of CO2 sequestration cannot be ignored, but may be <0.15, even down to a depth of 7000 m. Both the trapping capacity and net income of CO2 sequestration decreased with geothermal gradient, but the corresponding optimum depths increased with geothermal gradient.

E241 O_2/CO_2 循環燃焼による CO_2 無放出発電システムの可能性の検討

Improvement of CO_2 Recovery Power Plant with O_2/CO_2 Combustion is studied. In O_2 production process, the following optimizations are proposed, (i) single rectification column is adopted instead of double rectification column to reduce the energy consumption for compression of air, (ii) optimum operating pressure and O_2 purity are determined to minimize the total energy consumption. And energy consumption for O_2 production is calculated. In result, energy consumption in optimized process is reduced by 13% compared with conventional ones. In natural gas fired power generation plant, cold exergy of LNG is available for O_2 production process, and the reduction of energy consumption goes up to 37%. The net power generation efficiency of O_2/CO_2 combustion system can be improved by 3∿4% compared with reference values.