Direct Analytical Modeling for Optimal, On-Design Performance of Ejector for Simulating Heat-Driven Systems

This paper describes an ejector model for the prediction of on-design performance under available conditions. This is a direct method of calculating the optimal ejector performance (entrainment ratio or ER) without the need for iterative methods, which have been conventionally used. The values of three ejector efficiencies used to account for losses in the ejector are calculated by using a systematic approach (by employing CFD analysis) rather than the hit and trial method. Both experimental and analytical data from literature are used to validate the presented analytical model with good agreement for on-design performance. R245fa working fluid has been used for low-grade heat applications, and Engineering Equation Solver (EES) has been employed for simulating the proposed model. The presented model is suitable for integration with any thermal system model and its optimization because of its direct, non-iterative methodology. This model is a non-dimensional model and therefore requires no geometrical dimensions to be able to calculate ejector performance. The model has been validated against various experimental results, and the model is employed to generate the ejector performance curves for R245fa working fluid. In addition, system simulation results of the ejector refrigeration system (ERS) and combined cooling and power (CCP) system have been produced by using the proposed analytical model

Design and Energy Analysis of a Solar Desiccant Evaporative Cooling System with Built-In Daily Energy Storage

Heat storage with thermochemical (TC) materials is a promising technology for solar energy storage. In this paper, a solar-driven desiccant evaporative cooling (DEC) system for air-conditioning is proposed, which converts solar heat energy into cooling with built-in daily storage. The system utilises thermochemical heat storage along with the DEC technology in a unique way. Magnesium Chloride (MgCl2·6H2O) has been used, which serves as both a desiccant and a thermochemical heat storage medium. The system has been designed for the subtropical climate of Lahore, Pakistan, for a bedroom with 8 h of cooling requirements during the night. MATLAB has been employed for modelling the system. The simulation results show that 57 kg of magnesium chloride is sufficient to meet 98.8% of cooling demand for the entire month of July at an elevated cooling requirement. It was found that the cooling output of the system increased with increasing heat exchanger effectiveness. The heat exchangers’ effectiveness was increased from 0.7 to 0.8, with the solar fraction increased from 70.4% to 82.44%. The cooled air supplied to the building meets the fresh air requirements for proper ventilation

Sustainable economic growth potential of biomass-enriched countries through bioenergy production: State-of-the-art assessment using product space model

The current study aims to examine the economically viable biomass feedstocks for bioenergy generation and their export potential. The Product Space Model (PSM) is the primary tool used to achieve the aim by accomplishing certain objectives. The study’s findings show that Pakistan has abundant biomass resources for energy production. Canola oil, leather flesh wastes, and poultry fattening show the highest PRODY values, 46,735, 44,438, and 41,791, respectively. These have high-income potential and are considered feasible for export after meeting local energy demand. While goat manure, cashew nutshell, and cotton stalk show lower income potential having values of 3,641, 4,225, and 4,421, respectively. The biowastes having low-income potential are more beneficial to utilize in energy generation plants within the country. The United States is observed to make the most sophisticated products, indicated by an EXPY value of 36296.89. While the minimum level of sophistication is observed for Indonesia, as revealed by its EXPY value of 22235.41 among all considered countries. The PSM policy map analysis of the current study shows that Pakistan and Argentina are located in the Parsimonious Policy quadrant, suggesting shifting toward unexploited products closely related to the existing export baskets. Although the United States, China, India, Indonesia, and Brazil are found in the most desired Let-it-be Policy quadrant. They have more room to diversify their industries and enhance their export potential. The study has practical applications in economic, social, and environmental perspectives, focusing on economic, clean, and sufficient energy. Furthermore, exportable biomass feedstocks are identified to strengthen the economy. Further research must be conducted to evaluate other indicators of the PSM to explore the proximity aspect of PSM, as it would provide a clearer picture of bioenergy and biomass export prospects

Membrane-Assisted Removal of Hydrogen and Nitrogen from Synthetic Natural Gas for Energy-Efficient Liquefaction

Synthetic natural gas (SNG) production from coal is one of the well-matured options to make clean utilization of coal a reality. For the ease of transportation and supply, liquefaction of SNG is highly desirable. In the liquefaction of SNG, efficient removal of low boiling point impurities such as hydrogen (H2) and nitrogen (N2) is highly desirable to lower the power of the liquefaction process. Among several separation processes, membrane-based separation exhibits the potential for the separation of low boiling point impurities at low power consumption as compared to the existing separation processes. In this study, the membrane unit was used to simulate the membrane module by using Aspen HYSYS V10 (Version 10, AspenTech, Bedford, MA, United States). The two-stage and two-step system designs of the N2-selective membrane are utilized for SNG separation. The two-stage membrane process feasibly recovers methane (CH4) at more than 95% (by mol) recovery with a H2 composition of ≤0.05% by mol, but requires a larger membrane area than a two-stage system. While maintaining the minimum internal temperature approach value of 3 °C inside a cryogenic heat exchanger, the optimization of the SNG liquefaction process shows a large reduction in power consumption. Membrane-assisted removal of H2 and N2 for the liquefaction process exhibits the beneficial removal of H2 before liquefaction by achieving low net specific power at 0.4010 kW·h/kg·CH4

Mixed refrigerant-based simplified hydrogen liquefaction process: Energy, exergy, economic, and environmental analysis

In current study, process of hydrogen liquefaction was proposed to overcome the transportation and storage issues associated with hydrogen. The proposed model is consisted of three refrigeration cycles which are coupled to liquefy hydrogen. Unique selection of mixed refrigerants was adopted in each refrigeration cycle to reduce the energy consumption of the process. The precooling cycle based on mixed refrigerant stream reduces the H-2 temperature from 25 to -160 degrees C. Whereas, cooling and liquefaction cycles reduce the hydrogen temperature up to -251 degrees C which then is further expanded in an expander to approach the liquefaction temperature (-252.1 degrees C) at 1.3 bar. As of authors' knowledge, this is the first study which demonstrates the 4 E's analysis (Energy, exergy, economic, and environmental) of hydrogen liquefaction process. Result of proposed study reveals that the specific energy consumption of proposed process was calculated as 9.477 kWh kg(-1) LH2 which is less than any commercial scale process. As a result, the exergy efficiency of the proposed process was increased by 34%. In addition, the estimated unit production cost was recorded as 5.54 $kg(-1) of LH2 at the capacity of 1TPD. Cost estimation of proposed model was evaluated at higher capacities 1 to 50 TPD with cost reduction of up to 3.2$ kg(-1) LH2. Life cycle assessment of proposed process revealed that the 67.85 kg of CO2eq emissions were observed against unit production of liquefied hydrogen for new plant at day 1 while 0.253 kg of CO2eq emissions at day 2. The simplicity and less energy consumption of proposed model built a basis for its development to commercial scale adoption

Improvement potential detection of integrated biomethane liquefaction and liquid air energy storage system

Biomethane (BM) is highly competitive bio-energy alternatives for lowering the dependency on fossil fuels globally. The form of BM that is most suitable for storage as well as shipping to far-flung areas of the world is liquefied biomethane (LBM). However, due to the significant power consumption by compressors used in BM liquefaction process (like natural gas), it is a cost-and energy-intensive operation. Additionally, because bio-methane is created at atmospheric pressure, unlike ordinary natural gas, liquefaction requires more power consumption because the pressure at which BM is produced is much less than corresponding critical pressure. Therefore, an integrated system of liquid air energy storage (LAES) system discharging end and a biomethane liquefaction process is introduced that is both economical and efficient in terms of energy use. The sub-cooling and liquefaction processes of biomethane are aided by the cold-exergy of liquid air at the time of regasification mode of LAES, which eventually lowers the refrigeration cycle duty of LBM process. On the other hand, gaining the additional advantage, the expansion stage of liquid air is aided by the thermal exergy of a compressed mixed refrigerant (MR). On the basis of conventional exergy analysis, composite curves analysis, advanced exergy analysis, and sustainability index, the impacts of novel integration of LBM and LAES are estimated in this study. Conventional exergy analysis determines that 15.9 % of exergy destruction is decreased in the proposed LBM-LAES system having additional power production of 4529 kW using gas turbine. Results based on advanced exergy analysis conclude that avoidable, endogenous and exogenous portions of exergy destructions are decreased by 28.9 %, 39.9 % and 43 %, respectively; which implies the significant improvement potential. Composite curves analysis depicts that the efficiency of primary cryogenic heat exchanger is improved in the proposed integrated scheme. Additionally, the overall sustainability index is increased from 1.55 to 2.13 for LBM-LAES process

An innovative high energy efficiency-based process enhancement of hydrogen liquefaction: Energy, exergy, and economic perspectives

Hydrogen liquefaction can be one of the effective and viable solutions to enhance its energy contents for storage and transportation purposes. However, liquefaction of H-2 is highly energy intensive where precooling is the most significant energy consumption section (similar to 50% of overall process) due to huge reduction in temperature (25 to-159.4 degrees C). In this context, in proposed study the precooling cycle is split into two cycles for reducing the energy consumption, 1) Hydrofluoroolefin-based mixed refrigerant stream which reduces the H-2 temperature to -30 degrees C and 2) Mixed refrigerant stream which tends to reduce the H-2 temperature up to-159.4 degrees C. This is the first study which utilizes the four refrigeration cycles with unique selection of HFO-based mixed refrigerants in precooling section to reduce the gaseous H-2 temperature. Results of proposed study reveal that the specific energy consumption of proposed process was reduced by 55.2 % and 29.5%, as compared to base case-I (10.15 kWh/kgLH(2)) and base case-II (6.45 kWh/kgLH(2)), respectively. The exergy efficiency of the proposed process was increased by 67%. In addition, results of economic evaluation depicted that the total annualized cost of proposed process was obtained as $1.89 x 10(6)/y where the CAPEX has share of similar to 71.7$5.18/kg of LH2 at the capacity of 1TPD. The simplicity and less energy consumption of proposed model built a basis for its development to commercial scale adoption