Increase In Exergy Efficiency Research Articles

Thermal integration of reheated organic Rankine cycle (RH-ORC) with gas turbine exhaust for maximum power recovery

Reheating is a potential modification to the organic Rankine cycle architecture. Reheated ORC (RH-ORC) is integrated as bottoming cycle plant for topping high efficiency, recuperated gas turbine cycle with low exhaust temperature in the present study. The exit temperature of the working fluid after internal heat exchanger (IHE) sets the initial qualifying criterion. Cyclopentane, hexane and benzene qualify as potential working fluids and ORC with saturated operating conditions with these working fluids is considered as base cycle. For a power generating cycle, power recovery becomes priority over efficiency when connected to a waste heat recovery source. The performance of RH-ORC is studied at various reheat pressure ratios for different temperatures. Specific net work output of base cycle increases by retrofitting reheating and it leads to enhanced power recovery. Benzene, at a reheat pressure ratio of 0.558 produces maximum power output of 1292.033 kW and 4772.631 kW from the integration of SM-50 and Rolls-Royce WR-21 for a case of reheating at a temperature of 557.15K. The power recovery potential improves when reheating is carried out to a higher temperature. There is an increase in exergy efficiency because of reheating.

Exergy-Economic-Environment Optimization of the Waste-to-Energy Power Plant Using Multi-Objective Particle-Swarm Optimization (MOPSO)

This paper brings together the benefits of the results of exergy, exergoeconomic, exergoenvironmental analysis, and ‎optimization for a waste-to-energy (WTE) power plant. Initially, exergoeconomic balances for each stream were ‎calculated. For validating the current simulations, the actual data of the Amsterdam WTE power plant in working ‎conditions were examined. Moreover, the behaviors of the influential parameters on the objective functions were ‎evaluated. In order to perform multi-objective optimization, the Multi-Objective Particle-Swarm Optimization‎ ‎‎(MOPSO) algorithm is implemented. To obtain optimum operating conditions, 14 design parameters, and 3 ‎objective functions are considered, while the total cost rate, total exergy efficiency of the cycle, and environmental ‎impacts are the objective functions. Finally, the TOPSIS decision-making method determined optimum-operating ‎conditions. The results of exergy analysis indicated that the most exergy destruction belonged to the incinerator unit ‎at 66%. Instead, the pumps contributed the least in this field, (approximately 1%). Because of the optimization ‎process, the total exergy efficiency of the power plant increased from 30.89% to 38.9% while the total cost rate was ‎‎5188.05 USD/hour. By comparison between the obtained results from the optimization procedure, introducing ‎optimum working conditions has caused an increase in exergy efficiency and reduced exergy destruction for ‎components.

Flat-Plate Solar Collector Thermal Performance and Optimal Operation Mode by Exergy Analysis and Numerical Simulation

In this paper, the effect of a flat-plate solar collector components exergy destruction rates on the collector performance has been examined. A theoretical model based on energy and exergy balance for glass cover, absorber plate and working fluid resulted in nonlinear ordinary differentials non-autonomous system of equations that was solved numerically. Upon verification of the accuracy of the proposed model with experimental data, the effect of parameters such as solar radiation, mass flow rate, inlet fluid temperature and insulation thickness on the exergy destruction rates and exergy efficiency has been investigated. The model was used to optimize parameters, such as inlet fluid temperature, mass flow rate and number of collector tube. The results reveal that the highest exergy destruction rate occurs in the absorber plate, which is 79.23% of the total exergy destruction rate. Increasing the mass flow rate to 0.0087 kg/s leads to a decrease in the absorber plate exergy destruction rate to a minimum value of 575.74 W/m2 and to an increase in the exergy efficiency to a maximum value of 21.97%. When the inlet fluid temperature increases from 20 to 50 °C, the absorber plate exergy destruction rate reduces from 676.66 to 438.40 W/m2 resulting in a significant increase in the collector exergy efficiency from 6.80 to 37.86%. The optimum operating condition was found to be 37 °C for the inlet fluid temperature, 0.0087 kg/s for mass flow rate and fifteen for the number of tubes.

Working Fluids Optimization Based on Economical Performance and Thermodynamic Performance for 350kW ORC System

This paper established a 350kW level organic Rankine cycle(ORC) system with the 393.15K flue gas as heat source. Nine kinds of working fluids were selected based on comprehensive consideration of thermal physical properties, environmental performance and safety. The optimum one was selected from them by comparing and evaluating their thermodynamic performance and economic performance at different evaporation temperatures. The results show that the thermal efficiency of system using R236fa increased firstly and then decreased with the increase of evaporation temperature, while the exergy efficiency and economic performance increase gradually. The thermodynamic performance and economic performance of others increased with evaporation temperature increasing. When the exergy efficiency was taken as the evaluation index, isopentane was the best working fluid. However, the thermal efficiency, levelized electricity cost(LEC) and discounted payback period(DPP) of the system using butane better than others. Therefore, butane is considered to be the most appropriate working fluid for this system among the nine working fluids.

Energetic, economic, exergetic, and exergorisk (4E) analyses of a novel multi-generation energy system assisted with bagasse-biomass gasifier and multi-effect desalination unit

This study presents a novel multi-generation system (MGS) assisted by sugarcane bagasse to produce power, freshwater, and cooling. The proposed integrated MGS consisted of a bagasse-biomass based gasifier-Brayton cycle, a Rankine cycle, a Kalina cycle, an ejector refrigeration cycle, and a multi-effect desalination unit. Comprehensive energy, economic, exergy, exergorisk (4E) analyses of the proposed system were performed. The effects of operating parameters on thermodynamic performance and economic feasibility were investigated. An optimal configuration of the proposed system was determined via weighted multi-objective optimization approach considering exergorisk, exergy, and economic analyses. The results showed that bagasse-biomass flowrate was the dominant factor affecting variation in energy and exergy efficiencies, and total cost rate. An increase in bagasse-biomass flowrate from 1.5 kg/s to 10 kg/s led to decreases of 34.42% and 50.75% in overall energy and exergy efficiencies. The most substantial increase (43.07%) in exergy efficiency occurred at a high compression ratio. The optimization results showed that the total accidental risk impact was improved by 92.59% and energetic and exergetic efficiency was increased to 92.10% and 77.49%, respectively. The proposed optimum system can provide power, cooling, and freshwater at loads of 28.72 MW, 13.64 kg/s, and 3.43 MW, respectively.

Fluid selection and advanced exergy analysis of dual-loop ORC using zeotropic mixture

The comprehensive performance of a dual-loop organic Rankine cycle (DORC) is mainly influenced by working fluid pairs and key components. Based on multi-objective optimization, we conducted the working fluid selection and advanced exergy analysis for the DORC system driven by flue gas at 300℃. The exergy efficiency, payback period (PBP), and annual CO2 emission reduction (AER) were selected as the objective functions. Operating parameters and mass fraction of mixtures were optimized by non-dominated sorting genetic algorithm-II (NSGA-II). A suitable fluid pair for the DORC system was selected from 13 candidate fluid pairs. Then, the improvement potential of each component was estimated based on advanced exergy analysis. The results show that there is an optimal mass fraction for different zeotropic mixtures. When cyclohexane/cyclopentane (0.2/0.8) and butane/pentane (0.65/0.35) are used for the high-temperature (HT) loop and low-temperature (LT) loop respectively, the DORC system can achieve the best performance. Its exergy efficiency and AER increase by 14.7% and 19.1% respectively, while PBP only increases by 2.6%, compared with the fluid pair of cyclohexane-butane. There is 261.9 kW endogenous avoidable exergy destruction in the DORC system, accounting for 53.5% of the total exergy destruction. The HT turbine (HTT) is the first component that needs technical modifications, followed by the HT evaporator (HTE), intermediate heat exchanger (IHE), and LT turbine (LTT).

Development of PID based control strategy in maximum exergy efficiency of a geothermal power plant

The control strategy insures the efficiency, increased production and safety in new and complicated energy conversion systems. To this end, a thermodynamic model that simulates a real geothermal power plant is developed, and a new and optimal control strategy to increase exergy efficiency is presented on this model. In this study, real average daily data obtained during 2016 are used to verify the thermodynamic model of Sinem geothermal power plant in Turkey (S-GPP) and its control strategy. Thus, exergy efficiency of the system is maximized even under different and changed conditions by controlling flow rate, pressure and NCG percent content parameters in certain locations of S-GPP. Consequently, a new control strategy based on PID is developed. At the same time, different working conditions are provided by assigning disruptive values to these parameters. The thermodynamic model of S-GPP is used as a test system to demonstrate the efficiency of the proposed control strategy under various operating conditions. The results of the study prove that the model has a good statistical performance in terms of maximum exergy efficiency values. In addition, the proposed PID controller has a better performance compared to manual control, even in the presence of S-GPP. The effectiveness of the proposed control strategy is demonstrated by this case study, in which exergy efficiency of the system increased by 25% and power generation by 23%. Therefore, the proposed control strategy has the potential to create more reliable and controlled systems for geothermal and other power plants.

Development of a novel cogeneration system by combing organic rankine cycle and heat pump cycle for waste heat recovery

This paper presents a competitive cogeneration system, which combines the organic Rankine cycle with the heat pump cycle through a“built-in”evaporator. With this innovative structure, the input waste heat temperature in both the sub-cycles can simultaneously be maintained at a high level. The optimal working fluid is screened. Energy and economic advantages of the proposed system are proven. Moreover, the influence of main thermodynamic parameters on system performance is investigated. The results indicate that, compared with the traditional system, the thermal efficiency and waste heat recovery efficiency of the proposed system using the “built-in” evaporator increased by 6.4% and 1.2%, respectively. Meanwhile, it can be found that the thermal efficiency of the proposed system increased linearly, while the waste heat recovery efficiency showed a variation that followed a quadratic function with the increase of evaporation temperature. The peak value of the waste heat recovery efficiency was 9.9% for the evaporation temperature of 335 K. Moreover, the exergy performance of the system was very sensitive to the variation of evaporation temperature. An increase of 24 K in the evaporation temperature resulted in a drop in total exergy losses of nearly 76%, which resulted in an increase in the system exergy efficiency by about 27%.

Study on the Entropy Generation Distribution Characteristics of Molten Carbonate Fuel Cell System under Different CO2 Enrichment Conditions

The efficient and clean use of fuel is very important for the sustainable development of energy. In this article, a numerical study of molten carbonate fuel cell (MCFC) unit is carried out, and the source, distribution, and extent of six irreversible losses (fluid friction loss, mass transfer loss, ohmic loss, activation loss, heat transfer loss, the coupling loss between heat and mass transfer) are described and quantified. The effects of the operation temperature, current density, CO2 concentration, and cathode CO2 utilization rate on the exergy destruction and exergy efficiency during the power generation process are investigated. The results show that the main source of entropy generation in MCFC is the potential difference, which affects the ohmic and activation entropy generation, especially when the CO2 concentration is very low. The second is the temperature gradient, which causes the entropy production of the heat transfer. With the rise of the CO2 concentration at the cathode inlet, the exergy destruction reduces and the exergy efficiency increases. With the rise of the cathode CO2 utilization rate, the exergy destruction rises and the exergy efficiency reduces. Therefore, analyzing the irreversible process transfer mechanism in MCFC can provide the theoretical basis for its thermal performance optimization and structure design.

Exergetic performance assessment of magnesium oxide–water nanofluid in corrugated minichannel heat sinks: An experimental study

To keep the temperature of miniature devices in the safe threshold, cooling of minichannel heat sinks via nanofluid has emerged as an effective technique. The prime focus of present work is to analyze the impact of channel configuration, nanoparticle concentration, Reynolds number, and heating power on the thermal and exergetic performances of the corrugated minichannel heat sinks by employing distilled water and MgO–water nanofluid as coolants. The heat sinks used in this study are made of aluminium. The volume fractions of nanoparticles used in the experimentation are 0.006%, 0.008%, and 0.01%. From experimental results, comparisons of thermal performance were made between the heat sinks employing different coolants. The heat sink with minimum wavelength (5 mm) and amplitude (0.5 mm) displayed the lowest wall temperature of 33.86°C, while 28.75% enhancement in Nusselt number for 0.01 vol.% nanofluid as compared to distilled water. The enhancement in nanoparticle concentration and Reynolds number showed an increase in exergy efficiency and outlet exergy of coolants, whereas a reduction in thermal resistance and logarithmic mean temperature difference of heat sinks.

Impact of different shape based hybrid nano additives in emulsion fuel for exergetic, energetic, and sustainability analysis of diesel engine

The energy, exergy, and sustainability analysis of a diesel engine with 5% water in diesel emulsion (5%WiDE) based hybrid nano fuel incorporated with various-shaped i.e., 25 ppm cylindrical carbon nanotube (CNT) and 25 ppm spherical Al2O3 nano-additives were investigated experimentally. The morphological characteristics of 5%WiDE based Al2O3-CNT fuel have been studied through scanning electron microscope (SEM) analysis. The analysis revealed an increase in brake thermal efficiency (BTE), exergy efficiency, engine sustainability, and exergy destruction rate on engine load, and engine speed. However, the 5%WiDE based Al2O3-CNT hybrid nano fuel showed a 2.86% increase in brake thermal efficiency and a 4.16% increase in exergy efficiency than diesel fuel at 1500 rpm engine speed and 5.6 kW engine load. Also, the energy, exergy, and sustainability parameters of the engine have been improved. Furthermore, the highest exergy based sustainability of the diesel engine has been observed at full engine load and 2000 rpm engine speed. The exergy destruction rate of the diesel engine with a 5%WiDE based Al2O3-CNT hybrid nano fuel has a 3.14% higher value than the diesel fuel. The experimental results conclude that the application of nano additive in water in diesel emulsion fuel improves the energy, exergy performance parameters, and the sustainability of the engine. Therefore, 5%WiDE based Al2O3-CNT hybrid nano fuel has a high potential to be an alternate conventional fuel for diesel engines without any design modification.

Development of a novel hybrid SOFC/GT system and transcritical CO2 cycle for CCHP purpose in the district scale

The main target of this work is to optimize a novel hybrid system which includes solid oxide fuel cell, gas turbine, and transcritical CO2 power cycle. The system is driven by the biomass gasification process and is supposed to supply thermal and electrical load of a residential subsector in Tehran (the capital of Iran). Furthermore, in order to maximize the waste heat utilization, a novel adaption of active thermal storage units and cooler of the transcritical cycle is proposed. The Aspen Plus V9 and Aspen HYSYS V9 software are utilized to simulate the proposed hybrid system. Also, the calculations of the loads are implemented by the TRNSYS software. In the final optimum model, about 10% of the total electrical load is generated by transcritical cycle and the rest of 90% is produced by SOFC/GT combination with the optimum ratio of power produced by fuel cell to gas turbine considered to be 50%. The results illustrated that by applying the transcritical CO2 cycle, the exergy and energy efficiency increase up to 4.7% and 1.3%, respectively. Also, the total cost reduces by 2.7%. Moreover, it was found that by using the 27.5% of anode and 50% of cathode of gas recirculation, the efficiency of fuel cell subunit is maximized. Finally, the optimum model is compared to the ones having the same configuration of fuel cell/gas turbine with different downstream models including the heat recovery steam generator unit and steam turbine (with and without transcritical cycle).

Enhancing the thermal and economic performance of supercritical CO2 plant by waste heat recovery using an ejector refrigeration cycle

Supercritical CO2 cycle has an optimal performance when the cycle minimum temperature is around the critical temperature (31 °C), which is impossible at hot climatic conditions. To solve this problem, this work hybridizes a supercritical CO2 cycle with an ejector refrigeration cycle (ERC) to cool the minimum temperature of the cycle to be about 31 °C and hence achieving the highest possible performance. Comprehensive energy, exergy, and economic analyses are carried out to explore the mechanisms of performance improvement of the novel combined plant. Sensitivity analysis is performed to recognize the most influencing parameters on the performance of the combined plant. Based on the sensitivity analysis, the effect of different operating and design parameters on the system performance is investigated. Furthermore, a multi-objective optimization study is performed to find the trade-off between exergy efficiency and cost-saving. Among the different the five refrigerants used for ERC, the results illustrate that R717 is the most efficient one for the present hybridization. The exergy destruction in the precooler reduces from 15.5% to 0.7% when ERC is combined with the sCO2 cycle. Thus, the energy efficiency (ηth) and exergy efficiency (ηex) increase by 9.5%, while the levelized cost of energy (LCOE) declines by 10.7%. Compared with the standalone sCO2 cycle, the produced power, ηth, ηex, and LCOE of the optimized plant improve by 94.3%, 36.2%, 28.6%, and 18.3%, respectively.

Modeling and optimization of finless and finned tube heat recovery steam generators for cogeneration plants

AbstractThis article aims to model and optimize the fire tube Heat Recovery Steam Generator (HRSG) used in a gas microturbine cogeneration of heat and power system. Here, six cases including a finless and finned tube (solid and serrated) HRSGs with the inline and staggered arrangements are optimized and compared using techno‐economic assessment. Optimization of HRSG was carried out by applying two objective functions of minimizing the total annual cost as well as maximizing the exergy efficiency. Nondominated Sorting Genetic Algorithm II is used to find out the optimal values of design variables. The TOPSIS decision‐making process is employed to choose the optimum point of the Pareto front. A 600 kW gas microturbine cogeneration plant is considered as a case study. The results revealed that the finless tube HRSG with an inline arrangement has the lower pinch and approach temperatures (3.5°C and 3.1°C, respectively), the higher steam mass flow rate (12.7%), the lower total annual cost (64 096$/year), and the higher exergy efficiency (60.6%). It is also found that using the staggered arrangement tube banks along with the solid fins in HRSG leads the total annual cost, the steam mass flow rate, and exergy efficiency increase up to 41.6%, 100%, and 12.6%, respectively. This means that the thermodynamic performance improvement will compensate the total annual cost increment. Furthermore, it is demonstrated that HRSG with solid fins and staggered arrangement with total annual costs of (90 810$/year), exergy efficiency of (73.2%), and steam mass flow rate of (4680 kg/h) has the best performance in comparison with other finned tube cases.

Energetic and exergetic analysis of a heat pipe evacuated tube solar collector using MWCNT/water nanofluid

Increasing the energy demand and the limited availability of conventional energy sources are the main challenges to secure the human future. Solar energy is an attractive source of energy to ensure the sustainability of energy in this world for now and for the future. Evacuated tube solar collector is a solar thermal collector mostly used for domestic applications. The replacement of the working fluid with nanofluid can enhance the heat transfer even for low temperature applications. The effect of multi-walled carbon nanotubes and water nanofluid as working fluid in evacuated tube solar collector is used to experimentally investigate the energy and exergy efficiencies of the collector. Weight fractions of 0.005%, 0.01% and 0.05% were used in the investigation at flow rates from 1 to 3.5 L/min. The efficiency analysis of the collector was made as ASHRAE Standard 93–2010 stated. The results showed increase in energy and exergy efficiencies with the increase of volume flow rate and the concentration. The highest average energy and exergy efficiency achieved with 0.05 wt% MWCNT/water nanofluid were 55% and 10% respectively. The overall heat loss coefficient decreased with the increase of the concentration. It was found that 2 L/min were a critical flow rate and the behaviour of the system changed afterwards.

Indirect integration of thermochemical energy storage with the recompression supercritical CO2 Brayton cycle

Dispatchability is a major technological obstacle for concentrated solar power (CSP) plants. Calcium looping (CaL) is a potential solution for storing solar energy for long periods using raw materials (e.g., natural limestone or dolomite) which are high energy density, widespread availability, and low cost. This study aimed to propose a CSP-CaL plant indirectly integrated with the recompression supercritical CO2 Brayton cycle to realize carbonation under atmospheric pressure. To understand this indirect integration, the thermodynamic models are developed in Aspen and Matlab. The results show that the considered system can achieve storage exergy efficiency in the range of 8.26–16.34%, and power exergy efficiency in the range of 13.6–23.85%. In addition, a sensitivity analysis reveals that the storage exergy efficiency is largely determined by reaction temperature and conversion. Its value decreases with calcination temperature, and increases with carbonation temperature and CaCO3 conversion. Besides, it is found that the power exergy efficiency increase with an increase in power conditions (cycle low pressure, intermediate cycle pressure, and cycle high pressure) initially. However, above a certain pressure (80, 170, 210 bar, respectively), further increase leads to a decrease in power exergy efficiency. The results also indicate that high reaction temperature has a positive effect on power exergy efficiency. Compared to the molten-salt-based and direct integration, this CSP-CaL indirect integration offers competitive performance and promising potential for the commercialization of CSP-CaL systems in the near future.

Exergy and economic analyses of nanoparticle-enriched phase change material in an air heat exchanger for cooling of residential buildings

This paper studies the energy, exergy, and economic analyses of phase change material (PCM)-air heat exchangers filled with SiO2 based Nano-PCM of RT25 on enabling storage of night-time free-cooling from outdoor air or indoor air during off-peak hours, numerically. The stored cooling is subsequently utilized during a day-time or peak hours as auxiliary cooling, resulting in a reduction of the day-time refrigeration requirements. A computer model for seven days from June 22 to June 28 has been created using ANSYS FLUENT 18.2, to simulate the operation of PCM-air heat exchanger for domestic application. The setpoint temperature is considered at 23–25 °C, 23–26 °C, 24–25 °C, and 25–25 °C. The inlet airflow rate is varied between 2.5 m/s and 7.5 m/s. The PCM-air heat exchanger system is studied by varying the PCM thickness (10, 20, and 30 mm) and slab length (250, 500, and 750 mm). The nanoparticles volume fraction is from 0 to 5%. The maximum cooling power, exergy efficiency, and exergy destruction increase for the nanoparticles volume fraction of 5% is 9.4%, 4.1%, and 6.3%, respectively. To obtain the best balance between the exergy destruction cost rate and the capital cost rate, the exergoeconomic factor is defined for different cases.

Exergy analysis of a steam-turbine power plant using thermocombustion

This paper deals with the exergy analysis of a thermal power plant using different fuels, including biodiesel. The main goal is to understand the effect of design parameters and chemical dissociation of combustion products on energy and exergy efficiencies. Mass, energy and exergy analyses are made of the main components of the system, considering six different sources of irreversibilities: combustion chamber, heat transfer process, steam condensation, flue gas emission to the atmosphere, pump and frictional reheat at the steam turbine. Grassmann diagrams highlight the exergy flows and where the potential improvements exist. Results are obtained through ThermoCombustion, a virtual lab for combustion processes. The exergy analysis shows that the maximum source of exergy destruction is the boiler, followed by chimney exhaust, then steam turbine, and the condenser. Unlike the traditional methods, in this work, it was possible to distinguish between the irreversibilities thermal (due to the heat transfer) of the intrinsic irreversibility of the adiabatic combustion (associated with the chemical reactions and the viscous friction) in the steam boiler. The exergy loss distribution indicates that boiler irreversibility yields the highest exergy loss in the power plant. The use of the fuels with a simple molecular structure containing oxygen molecules will reduce the exergy destruction. The destruction of exergy in the reactive process decreases if the combustion temperature is increased, although this would lead to increases in NOx emissions. The regenerative cycle reduces total irreversibilities, increasing exergy efficiency.

The effect of air humidity on the exergy efficiency of domestic heat pumps

Heat pump systems have been used for decades in refrigeration and the upgrading of heat to temperature levels demanded by consumers. Private housing in Northern Europe and other countries is moving away from direct electric heating, combustion-based heating and even district heating in favour of heat pumps that use a cheap renewable heat source and electricity. The system purchase is motivated by an attractive coefficient of performance (COP), the option to reverse the heat pump operation from heating during winter to cooling during summer, and the increasing availability of (cheap) zero-CO2 electricity. Assessment of the energy efficiency of heat pump systems using exergy analysis is complicated by features of the heat reservoirs, such as humidity of air in a building envelope, becoming important besides temperature levels. In modern buildings, exhaust air heat recovery (EAHR) systems replace the air inside a building every few hours, with a net in- or outflux of humidity as side-effect. In this paper, an exergy analysis is presented that quantifies energy efficiency of a heat pump system as partly determined by the humidity of a building envelope being heated using a ground source or air source heat pump. Humidity control introduces a significant energy penalty. As shown, an EAHR unit can result in a significant increased exergy efficiency, adding to the benefits offered by the heat pump, depending on indoor versus outdoor temperature and humidity, and whether a ground source or air source heat pump is used. Using weather data for 2018, during the coldest months a ground heat source heat pump is clearly more efficient than an air source heat pump for maintaining a modern housing space in Finland at 22 °C and 50% relative humidity year-round. Exergy (in practice electricity) consumption is 20% higher for an air source heat pump compared to a ground source heat pump, with maximum exergy efficiencies of 14% and 11.5%, respectively. Integration with an EAHR system can add up to 20%-points to the exergetic efficiency, irrespective of the type of heat pump making also that a powerful investment.

Propane and iso-butane pre-cooled mixed refrigerant liquefaction process for small-scale skid-mounted natural gas liquefaction

The development of a small skid-mounted natural gas liquefaction plant can economically, environmentally-friendly, and efficiently collect natural gas in mountainous areas where are not easy to lay pipelines. A propane and iso-butane pre-cooled mixed refrigerant liquefaction process (C3&C4-MR) is proposed in this paper. Compared with the propane pre-cooled mixed refrigerant liquefaction process, the improved liquefaction process can reduce system energy consumption and increase exergy efficiency greatly. Genetic algorithm is applied to optimize energy consumption of C3&C4-MR process. The optimized specific energy consumption STotal is 0.301 kW·h/kg, which is 18.0% lower than the optimized C3-MR process. And compared with the optimized R410a pre-cooled mixed refrigerant liquefaction process, STotal of C3&C4-MR process is 5.64% lower than that of R410a-MR process. Besides, mixed propane and isobutane as pre-coolant is easier to obtain from the feed gas. By analyzing the temperature sensitivity of mixed refrigerant and calculating the unit compression power consumption of a single refrigerant, the guidance and recommendations for mixed refrigerant ratio are summarized. Due to the property of iso-butane, the optimal percentage of iso-butane in the pre-coolant was analyzed. In conclusion, C3&C4-MR process is energy-saving and advanced in terms of system operating costs to recycle scattered natural gas in remote areas.