Minimum Specific Energy Consumption Research Articles

A comparative assessment of drying kinetics, energy consumption, mathematical modeling, and multivariate analysis of Indian borage (Plectranthus amboinicus) leaves

AbstractIn the current study, four drying methods, namely microwave (MD), vacuum (VD), hot air (HAD), and freeze drying (FD), were compared for drying of Indian borage (Plectranthus amboinicus) leaves for optimum energy consumption and bioactive compounds' retention. Effective moisture diffusivity for MD was about 100 times more than that of HAD and VD. MD at 600 W showed minimum specific energy consumption (4.04 kWh/kg), proving the most suitable drying condition. Moreover, it showed desirable energy values in terms of maximum specific moisture extraction rate (0.265 kg moisture/kWh) and maximum drying efficiency (15.85%). Bioactive compounds' retention in terms of phenols, antioxidants, and flavonoids was better in MD, followed by FD. Mathematical modeling of drying kinetics data revealed proper fitting of three drying models, namely, Aghbashlo, Modified Page‐II, and Page model, for explaining the drying behavior of Indian borage leaves. Multivariate characterization using principal component analysis revealed that FD and MD had a strong effect on bioactive compounds' retention, while VD and HAD showed least effect. Hence, based on optimum energy utilization and bioactive compounds' retention, MD at 600 W was selected for efficient drying of Indian borage leaves.Practical applicationsDrying of Indian borage leaves using microwave drying (MD) resulted in quicker drying with retention of bioactive compounds and color of dried leaves. The energy aspects were also favorable for industrial scale‐up. With due consideration to capacity enhancement in MD, it can prove to be a promising source of drying for culinary, medicinal, and aromatic plants.

Optimizing energy efficiency in brackish water reverse osmosis (BWRO): A comprehensive study on prioritizing critical operating parameters for specific energy consumption minimization

Reverse osmosis (RO) systems offer a viable solution for treating brackish water (BW), a common but underutilized water resource. However, the energy-intensive nature of brackish water reverse osmosis (BWRO) systems poses affordability challenges to water supply, necessitating a focus on minimizing their energy consumption to support SDG6's goal of providing safe and affordable drinking water for all. This study addresses the critical need to minimize the specific energy consumption (SEC) of a typical BWRO system, defined as the energy consumed per unit of water recovered, mathematically and experimentally. Empirical models were developed proving there is a global minimum SEC while adjusting the operating conditions. Furthermore, we identified the key operating factors influencing SEC and their priority levels, along with their interactive effects. Notably, no prior study has discussed the significance and interaction of these operating factors (e.g., feed water salinity, temperature, pressure, flowrate and membrane permeability) on SEC of a BWRO system. Employing a full factorial experimental design with mixed levels of operating parameters, the study developed regression models that elucidate the mechanistic interaction between these parameters and system performance. Moreover, the models were validated experimentally, with a new dataset demonstrating their accuracy and reliability. ANOVA statistical analysis identified feed salinity, pressure, flow rate, feed flow rate×pressure, salinity×pressure, and temperature as influential operating parameters in reducing SEC, in descending order of importance. Operating within the determined optimum range resulted in a 36 % decrease in SEC and a more than fourfold increase in water recovery. The study's systematic approach and findings can be extrapolated to optimize the performance of other desalination technologies and diverse feed water types, contributing significantly to global water sustainability efforts.

Analyzing the impact of vacuum level on the energy and exergy efficiency of a unique solar desalination unit driven by concentrating solar power technology

An in-depth analysis of a unique desalination unit based on concentrated solar energy was conducted in this study. A lab scale prototype was built and tested under variable vacuum levels between 0.3 bar and 0.7 bar to see how vacuum levels influence system performance. Results reveal a direct relationship between vacuum level and distillate production. Vacuuming of 0.7 bar produced a maximum distillate of 2520 ml/h. An average energy efficiency of 65.2 % was found for the brine heater. Moreover, the average exergy efficiencies were 88.2 % for the condenser, 17.2 % for the brine heater, and 41.6 % for the flash chamber. In order to determine the relationship between vacuum level and various system responses, mathematical models were also developed. Moreover, performance indicators such as energy utilization factor, gain output ratio, and specific energy consumption were also evaluated. The proposed device has a maximum energy utilization factor of 2.4, a maximum gain output ratio of 19.2, and a minimum specific energy consumption of 280.7 kWh/m3. The outcomes of this research are expected to provide valuable insights into the impact of vacuum level on solar-powered desalination systems and contribute towards advancing renewable energy into desalination systems.

Energy-saving effect assessment of various factors in container plant factories: A data-driven random forest approach

Plant factory is one of the controlled environment agriculture forms with huge potential to alleviate food crisis, but the high energy cost restricts its widespread adoption. Numerous researches have explored various factors for energy-saving in plant factories in their settings, but there is a lack of analysis of the importance of these factors in energy saving. In this work, the energy-saving effect assessment of various factors in the container plant factory is investigated. Four cities (Harbin, Taiyuan, Shanghai, and Guangzhou), three plant densities (cultivation area: floor area=100 %, 150 %, and 200 %), and two temperature/humidity setpoints (20/22 ℃, 60/70 %, and 16/22 ℃, 50/95 %) are selected as operating conditions to cover different weather conditions and plant heat loads. The energy-saving effect of each factor is calculated using a random forest algorithm based on large amounts of energy simulation data. We identify that envelope overall heat transfer coefficient (U), air conditioner coefficient of performance (COP), and light efficacy (Efficacy) are three factors that have the largest impact on energy-saving in plant factories, in which light efficacy is the most important factor. Simultaneous optimization of these three factors could possibly reduce electricity consumption by ∼50 % compared to the base case. Finally, employing weight-light intensity correlation, the minimum specific energy consumption is approximately 4.76 kWh/kg lettuce fresh weight. This study utilizes advanced machine learning methods to sort out important factors and shows that significant energy reduction may be achieved by optimizing dominant factors, which gives a general guidance for future designers to build energy-efficient plant factories.

A compression-free re-liquefication process of LNG boil-off gas using LNG cold energy

Re-liquefying boil-off gas (BOG) of LNG is of great significance for energy conservation and environmental protection. BOG is usually compressed before being liquefied with nitrogen reverse Brayton cycle, which makes the system's capital investment and energy consumption high. A novel compression-free re-liquefication process of BOG using liquid nitrogen (LN2) is proposed. BOG is liquefied with latent heat of LN2, reducing the heat-transfer temperature difference in BOG condenser and the required amount of refrigerant. LN2 is produced using LNG pre-cooled Joule-Thomson cycle. Overall optimization is performed using genetic algorithm. Thermodynamic, economic, and environmental assessments are conducted based on the optimized results. Sensitivity analysis of the principal design parameters is performed. It is found that the proposed process is significantly profitable because it fully utilizes the cold energy of LNG and LN2 and eliminates the required cost for BOG compressor, turbine expander, and LNG regasification process. The minimum specific energy consumption of 0.74 kWh·kg−1 is achieved, and the figure of merit is up to 34.95%. The payback period of total capital investment is only one month. Carbon dioxide emission is reduced by 36242.66 kg·h−1 compared to the direct emission of BOG. Pinch temperature difference of 3∼5 °C is recommended for cryogenic heat exchangers.

Salinity impacts on a unique desalination system embedded with concentrated solar energy for cleaner production

This research comprehensively analyzed a unique solar desalination unit that operates on concentrated solar energy. The analysis primarily focused on evaluating three crucial components: the condenser, flash chamber, and brine heater. Testing was initially performed using seawater sourced from the eastern region of Saudi Arabia. Subsequently, to investigate the influence of salinity on the system performance, the device was tested under variable salinity levels ranging from 15,000 ppm to 35,000 ppm. Key parameters, including condenser temperature, brine heater temperature, and distillate production, were measured throughout the experimentation. The findings unveiled an inverse correlation between salinity and distillate production, as increasing the salinity from 15,000 ppm to 35,000 ppm resulted in a decline in distillate production. The maximum distillate achieved was 2400 ml/h at a salinity level of 15,000 ppm, corresponding to a constant feed rate of 0.2 l/min. The average energy efficiency of the brine heater was determined to be 61.9%. Moreover, the average exergy efficiencies were calculated as 81.3% for the condenser, 4.4% for the brine heater, and 44.3% for the flash chamber. Mathematical models were subsequently developed to establish the relationships between salinity and various system responses. Furthermore, performance metrics such as gain output ratio, energy utilization factor, and specific energy consumption were evaluated. The proposed system has a maximum gain output ratio of 16, a maximum energy utilization factor of 2.2, and a minimum specific energy consumption of 299.3 kWh/m3.

ИССЛЕДОВАНИЕ УСТАНОВКИ С ИНФРАКРАСНЫМ НАГРЕВОМ ЗЕРНА

Thermal post-harvest processing of grain currently intended to improve its quality is highly energy-intensive and expensive. The development of new means of mechanization with infrared heating of grain, capable of reducing specific energy costs for heat treatment processes, as well as ensuring resource conservation, is a pressing and important scientific and technical problem. To reduce the cost of drying, disinfection and micronization of grain, as well as improve the quality of its heat treatment, we have developed an experimental model of an installation with infrared heating. The study of the developed installation was carried out in grain drying mode. The technological process of drying wheat grain with an initial moisture content of 18...19% was chosen as the object of study. The total specific energy consumption for grain drying was taken as an optimization parameter. The rational values of the selected factors were determined as a result of a study of the developed installation with infrared heating of grain: grain drying time t1 = 1000C; the temperature created by the infrared heater inside the installation casing is tin = 650C. Next, a series of experiments was carried out on the developed installation in the above modes. In each experiment, measurements were taken of the heating temperature of the grain, the percentage of reduction in grain moisture content and the throughput of the installation were determined, and the total specific energy consumption was recorded. The heating temperature of the grain was in the range of 37 - 38.5 ºС, while the moisture content of the grain decreased by 2.56%. The developed installation provides the required quality of grain drying, maintaining a throughput of about 800 kg/h and a minimum total specific energy consumption, which amounted to 4342.3 kJ h/kg.

Electrochemical mechanism of synchronous ammonia and nitrate removal based on multi-objective optimization by coupling random forest with genetic algorithm

In this work, an electrochemical system was constructed for the simultaneous elimination of ammonia and nitrate using the prepared Ti foam/SnO2-Sb anode and a Cu foam cathode. The hybrid RF-GA method is proposed as a tool for the analysis and optimization of the simultaneous removal of ammonia and nitrate. The influence of independent variables including NaCl concentration, time, and current densities was studied. Results showed that the random forest (RF) model could successfully predict the behavior of electrochemical systems (R2 = 0.9751, RMSE = 0.4567 for the ammonia prediction model; R2 = 0.9772, RMSE = 0.0436 for the nitrate prediction model). The variable importance measures (VIM) analysis reveals that time has the maximum influence on the degradation rate of ammonia and nitrate. The RF model is used as an objective function for the genetic algorithm (GA) to determine the optimum conditions in combination with the calculated specific energy consumption. Based on the optimization results, the removal rates of ammonia and nitrate reach 94.4 % and 74.7 %, respectively, with a minimum specific energy consumption of 0.181 kwh·g−1. The electrochemical reaction mechanism of the composite pollutants in the Ti foam/SnO2-Sb and Cu foam electrode system is further elucidated. The results indicate that nitrate is reduced to nitrite, ammonia, or nitrogen gas at the cathode, accompanied by the mutual transformation of Cu(0), Cu(I), and Cu(II) on the Cu electrode. Ammonia is oxidized to nitrogen gas or nitrate at the anode. Ultimately, the nitrogen-containing composite pollutant is decomposed and discharged as nitrogen gas by cyclic redox reactions.

Experimental and Analytical Study on Optimal Spacing for Hard-Rock Breaking under Double-Indenter Impact

Abstract Rock breaking by double hydraulic hammers has a wide application prospect in hard-rock roadway excavation because of its environmental protection and strong rock-breaking ability, but the optimal spacing under double-indenter synchronous impact is not clear. Based on the rock-breaking experimental system under double-indenter synchronous impact established by combining a detachable double-indenter device and Hopkinson pressure bar, the impact tests of three kinds of rocks are carried out, and a theoretical model of specific energy consumption is derived to determine the optimal spacing. The results show that when the indenter spacing is 28 mm, 42 mm, and 14 mm, respectively—that is, when the cross section of the fragmentation crater is in the shape of a “peanut” with a fine middle and two large ends—the concrete, limestone, and sandstone specimens reach the minimum specific energy consumption, which is reduced by 22.55 %, 30.60 %, and 11.85 %, respectively, compared with single-indenter impact. The theoretical model, which explains and verifies the experimental phenomena and results well, can be divided into four zones, and the optimal spacing is in Zone III. The research can be helpful for actual hard-rock tunneling under double hydraulic hammers.

Soybean molasses has a positive impact on the pelleting process and physical quality of dairy feed pellets

The influence of soybean molasses (SBMo) addition in dairy cow feed on the pelleting process and pellet quality was assessed in this study. For purpose of optimising production process of dairy feed pellets the SBMo content was varied at three levels (30, 60 and 90 g/kg) together with moisture content (MC – 130, 150 and 170 g/kg) of mash prior the pelleting process and sieve opening diameter (SOD – 5, 6 and 7 mm) of the hammer mill that was used for grinding of dry ingredients. The SBMo and required amount of water were added by a two-phase nozzle during mixing of ingredients and pelleting was done using a flat die pellet press. Experimental runs were performed according to Box-Behnken experimental design. The determined responses were: specific energy consumption (SEC), quantity of fines (QoF), pellet hardness (PH), pellet durability index (PDI) and bulk density (BD). Significance of input factors and their interactions, corresponding contributions and sum of squares were determined by using the statistical method of analysis of variance (ANOVA). Addition of SBMo decreased the SEC, PH and BD, and higher MC also decreased the SEC, PH and BD. The increase of SOD decreased the BD. The strongest contribution on SEC had the addition of SBMo (64.1%), while the strongest contribution on BD originated from the MC (71.2%). Models obtained in this research were used to optimise the input parameters in order to get the minimum SEC, maximum PH and maximum BD. The results of the optimisation for the input parameters were: SBMo content = 89.9 g/kg, MC = 130 g/kg, and SOD = 6.0 mm; and for the responses were: SEC = 33.9 kWh/t, PH = 12 Kahl unit kg, BD = 595.1 g/L. The obtained results showed that inclusion of SBMo at level of 90 g/kg could lead to the reduction of SEC and without significant influence on the pellet physical quality.

Impact of SWMM Fouling and Position on the Performance of SWRO Systems in Operating Conditions of Minimum SEC.

Due to water stress in the world in general desalination technologies are becoming increasingly important. Among the available technologies, reverse osmosis (RO) is the most widespread due to its reliability and efficiency compared to other technologies. The main weakness of RO is the loss of performance due to membrane fouling, which usually affects the water permeability coefficient (A), causing it to decrease. In RO desalination plants, fouling does not affect all spiral wound membrane modules (SWMMs) in the pressure vessels (PVs) in the same way. This will depend on the type of fouling and the position of the SWMM inside the PV. In this study, the impact of A and the position of the SWMM on the performance of the RO system is analyzed. For this purpose, decrements of up to 50% have been assumed for the seven SWMMs in series considering nine commercial SWMM models. The operating point analyzed is that which minimizes the specific energy consumption (SEC), a point obtained in a previous work carried out by the authors. The results show how the impact of A on the SWMM in the first position is more significant than the impact on modules that are in another position for the nine SWRO models studied. A drop of 50% in the coefficient A of the first element produces a permeate loss in the pressure pipe between 0.67 and 1.35 m3 d-1. Furthermore, it was observed that the models with the lowest coefficient A exhibited the highest performance losses in terms of permeate production when A was decreased.

SORPTION AND THERMODYNAMIC PROPERTIES OF AROMATIC PLANTS AS DRYING OBJECTS

The high demand for aromatic herbs in the biotechnological, cosmetic, pharmaceutical and food industries led to increased requirements for the technological processes of processing aromatic raw materials to preserve biologically active substances and essential oils. Peppermint (Mentha piperita L.) is a well-known medicinal essential oil crop that is widely distributed throughout Ukraine. It is widely used due to its beneficial properties and therapeutic effect on the human body.
 The purpose of the article is studies of sorption and thermodynamic properties of aromatic plants to determine technological parameters of drying and storage processes, which ensure minimum specific energy consumption and maximum preservation of essential oils.
 The results of study on sorption properties of peppermint leaves are presented. Adsorption moisture isotherms of peppermint leaves were determined at three different temperatures 30, 40 and 50 ºC, using the standard gravimetric static method. The net isosteric heat of adsorption was calculated from moisture isotherms, using the Clausius-Clapeyron equation.
 The specific heat consumption for drying peppermint leaves at temperatures of 40 and 50 ºС was obtained experimentally, using the differential microcalorimeter of evaporation. The effect of volatile substances of peppermint essential oil on the heat of vaporization was revealed.
 The choice of drying temperature of aromatic plants is primarily determined by the thermal sensitivity of essential oils. The study of the effect of drying temperature on the removal of volatile aromatic compounds from peppermint leaves showed that the maximum allowable temperature of the material during dehydration should not exceed the melting point of menthol at 42,5 ºС.

In-depth insights on multi-ionic transport in Electrodialysis with bipolar membrane systems

Electrodialysis with Bipolar Membranes (EDBM) has become a key technology for valorising waste brine streams as a new chemical production route. Even though its application has been widely studied using single electrolyte solutions (e.g., NaCl or Na2SO4), there is still a lack of knowledge about using multi-ionic mixtures. For the first time, this work aims to evaluate the EDBM performance when treating synthetic solutions mimicking the waste brines produced in a integrated process for the valorisation of solar saltworks bitterns. The behaviour of a lab-scale EDBM unit was assessed using SUEZ ion exchange membranes (IEMs), operating at 300 A m−2, and the ion transport through IEMs was investigated, based on the calculation of apparent transport numbers and selectivities.The results highlighted that multi-ionic solutions barely affected the production of hydroxide ions. Chlorides were transported up to 7 times faster than sulphates across the anion-exchange membranes, while the cation-exchange membranes exhibited slightly higher selectivity for potassium than for sodium (∼1.2). The current efficiencies ranged between 70 % and 80 %, while a minimum specific energy consumption of 1.60 kWh kg-1NaOH was obtained for the most concentrated brine at 1 mol L-1 OH–.These results provide novel and valuable information to support the development and implementation of EDBM as a sustainable technology for supporting a resource-efficient and competitive economy through on-site and delocalized chemicals production routes.

Evaporation-Assisted Humidification–Dehumidification Cycles for Desalination Application in Tropical and Subtropical Regions

The present study aims to evaluate the performance of evaporation-assisted humidification–dehumidification (E-HDH) desalination, specifically direct evaporative (DE-HDH), indirect evaporative (IE-HDH), and Maisotsenko evaporative (ME-HDH) systems. To achieve this, a thermodynamic modeling approach is utilized, which incorporates the wet bulb effectiveness method, psychrometric relationships of humid air, and equations that govern heat and mass balance. The key performance indicators of the studied E-HDH desalination systems are estimated concerning operating parameters. The results show that the ME-HDH system is capable of producing a comparatively higher water production rate (WPR) ranging between 0.01 and 7.92 g/s as compared to the DE-HDH and IE-HDH systems. The sensible cooling flux was observed to be high at a dry-bulb temperature (Tdb) of 50 °C and relative humidity (RH) < 0.2, having a value of 5.26 kW for the DE-HDH system, followed by the ME-HDH system (3.23 kW) and the IE-HDH system (3.11 kW) due to relatively high mass flow rates. The latent heat flux was observed to be relatively high in the case of the ME-HDH system. Minimum specific energy consumption was observed from the ME-HDH system, and consequently, a maximum gain output ratio (3.32) was realized. In addition, the study realized that an increment in air velocity and wet bulb effectiveness significantly improves the WPR. In accordance with the climatic conditions of the studied Saudi Arabia cities, it has been realized that Al-Hofuf and Riyadh produce relatively high WPRs with minimum energy consumption. In the case of Al-Hofuf, the average WPR was recorded as 185.51 kg/day, followed by Riyadh (180.33 kg/day). The energy required was estimated to be 0.042 kWh/kg and 0.034 kWh/kg for both cities, accordingly.

Energy Consumption Monitoring with Evaluation of Hidden Energy Losses

This article presents a computational method for monitoring the energy consumption of technological systems with the assessment of their hidden energy losses caused by erroneous actions of personnel or equipment failures. Herewith, energy losses are calculated as the difference between the actual energy consumed and the minimum energy required to conduct the process in all operating modes. The minimum required energy is determined by the machine learning method based on stationary consumption precedents. Two approaches to the implementation of energy consumption monitoring with the assessment of hidden energy losses are considered – hardware and software. The hardware approach is based on the preliminary definition of normative, or minimum specific energy consumption in each technological mode. The software approach is based on the modeling of stationary areas of energy consumption in the form of precedents and their further analysis in the space of influential technological parameters. The paper notes the advantages and disadvantages of the proposed monitoring method, it is emphasized that the method is able to work with both linear and non-linear functions of energy dependence on the parameters of the technological process. It is noted in the paper that the advantage of the proposed method is the automated construction of the minimum energy function.

Numerical Study on the performance of a heat pump-driven-DCMD for sustainable desalination

The study presents an energy-efficient desalination system that combines direct contact membrane distillation (DCMD) and a heat pump to improve thermal efficiency and integrate with photovoltaics. DCMD is a sort of thermal desalination process, and it requires a lot of thermal energy. A heat pump is a device that produces both hot and cold energy simultaneously with less electrical energy input compared to other heating devices, such as a boiler and an electrical heater. A hollow-fiber DCMD and a 10-kW water-to-water heat pump were considered for a numerical simulation in this study. Numerical models were established for each device and validated against the results obtained from the literature. The simulation was first carried out to identify the performance of the system based on the baseline. After that, a series of simulations were carried out in order to investigate the performance of the proposed system in terms of specific energy consumption (SEC), gained output ratio (GOR), and the coefficient of performance (COP) under various operating conditions. Results showed that the minimum SEC and the maximum GOR were achieved at the inlet feed water temperature of 66.5°C with a mass flow rate of 20 kg/min and the inlet permeate temperature of 19.8°C with a mass flow rate of 10 lpm. On the other hand, it was found that the maximum COP can be observed at the inlet feed water temperature of 23.6°C with a mass flow rate of 10 lpm and at the inlet permeate temperature of 8.9°C with a mass flow rate of 20 lpm.

Surfactant-assisted ultrasonic fragmentation of mixed fruit and vegetable biomass: Its impact on biomethane yield and energy analysis

The present study examines the effect of Tween- 80 assisted ultrasonic fragmentation (TUF) method for efficient disintegration of mixed fruit and vegetable (MFV) biomass with minimum energy consumption. In TUF method, tween 80 at different dosages was used to remove the biomass barrier (lignin), then it was exposed to ultrasonic fragmentation (UF). TUF was assessed based on SCOD release and specific energy consumption (SEC). At minimum SEC (4628 kJ/kg TS), TUF achieved a higher SCOD release (26 %) than UF (15.6 %). Bioacidogenic studies and biomethane potential assay (BPA) revealed higher volatile fatty acids (VFA) accumulation and biomethane production (2000 mg/L vs 550 mL/g COD) in TUF compared to UF (1200 mg/L vs 320 mL/g COD). From energy analysis, a higher energy ratio of 1.2 was obtained for TUF indicating combined fragmentation method could reduce the energy demand of UF and signifying the economic feasibility of TUF on practical usage.

Opportunities of Reducing the Energy Consumption of Seawater Reverse Osmosis Desalination by Exploiting Salinity Gradients.

This work presents a performance assessment of three seawater reverse osmosis-pressure-retarded osmosis (SWRO-PRO) hybrid schemes for energy consumption reduction in seawater desalination applications by using an external low salinity water source. For comparison purposes, another arrangement based on the conventional SWRO process combined with brackish water RO (BWRO) and desalination was analyzed. Reverse osmosis system analysis software environments were used to select the best SWRO configuration and operating conditions. A purposely developed model was used to evaluate the PRO system. Two different cases were assessed depending on the origin of the external low-salinity resource for the PRO process: industrial wastewater and urban treated wastewater. In the case of the industrial wastewater, due to regulations on wastewater reclamation, the best arrangement would be the first SWRO-PRO scheme which was analyzed with a specific energy consumption of 1.54 kWh/m3. If urban treated wastewater is available as an external resource, the results obtained show that this scheme, leading to the minimum specific energy consumption of 1.46 kWh/m3, is the conventional SWRO combined with BWRO. Therefore, hybrid SWRO-PRO systems are recommended to reduce the specific energy consumption of seawater desalination if an industrial wastewater source with low osmotic pressure is available.

Reduction in Specific Energy Consumption of Overall Biogas Upgrading and Biomethane Liquefaction Process: Energy and Exergy Analysis

Biogas is considered one of the most promising alternative renewable fuels, but raw biogas needs to be upgraded before its use in vehicles or injection into the natural gas grid, and the resulting biomethane be liquified to be transported to distant areas. Both, absorption for upgrading, and compression for liquefaction are energy-intensive processes that require performance enhancement in terms of reduction of specific energy consumption. For the commissioning of biogas upgrading and biomethane liquefaction at a single plant, it is indispensable to optimize the overall process of biogas upgrading and biomethane liquefaction. According to the best of the authors’ knowledge, the overall process has not yet been optimized for minimum specific energy consumption. This study proposes a fast-converging teaching learning self-study optimization approach to the overall process with a careful selection of decision variables and their bounds without breaching the process constraints. The results of optimization are compared with the base case in terms of parametric and composite curves analysis. The parametric analysis shows that teaching–learning self-study optimization has reduced the specific energy consumption of the overall process by 15.4 % as compared to the base case that optimized the upgrading and liquefaction processes independently. The individual-specific energy consumption of upgrading and liquefaction sections is reduced by 20.4 % and 5.8 %, respectively. The composite curves analysis reveals that the gap between hot and cold composite curves is reduced as compared to the base case that depicts the reduction in specific energy consumption. Moreover, the detailed thermodynamic evaluation revealed that the exergetic efficiency of the upgrading process compared to the base case significantly increased from 51.43 % to 92.98 % while the exergetic efficiency of the liquefaction section slightly increased from 80.23 % to 80.83 %, thus, resulting in an increase in exergetic efficiency of the overall process by 20.9 % compared to the base case. Additionally, the overall sustainability index of the upgrading and liquefaction processes has increased from 3.78 to 9.04. This study would be significantly helpful for the process engineers to overcome the challenges related to the reduction in specific energy consumption in the biogas upgrading and liquefaction industry.

Evaluation of low energy consumption control for seawater desalination on Penghu Island

In fact, current water supplies due to natural constraints or lack of infrastructure (or both) cannot be provided in a sustainable manner for all increasing and competing uses (e.g. residential, industrial, agricultural). While promoting Penghu's low-carbon islands, in a water-scarce environment, it is the motivation of this research to take into account the development of water resources and lower energy consumption costs. The seawater desalination plant water production technology is improved, the cost of water production is reduced. This research uses a genetic algorithm (GA) to optimize the recovery rate to solve the minimum Specific energy consumption (SEC) value, and then, according to the required water production, the optimal flow rate of raw seawater of the high-pressure pump is obtained, so as to minimize the energy consumption of the reverse osmosis (RO) system. The energy recovery device has a great effect on reducing the energy consumption of the RO system, and it can be seen from the results that the higher efficiency does greatly reduce the energy consumption of the SEC and water production under the different energy recovery device efficiency. Calculated using genetic algorithms, and the SEC is 3.275 and the recovery rate is 45.1%, and the water production energy consumption is 2.35 kWh/m3. Scheme B changed the efficiency of the energy recovery unit to 97.22%, resulting in a SEC of 1.819 and a recovery rate of 25.3%, and a water production energy consumption of 1.31 kWh/m3. Finally, challenges and research gaps are also proposed.