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AbstractThe integration of power plants and desalination systems has attracted increasing attention over the past few years as an effective solution to tackle sustainable development and climate change issues. In this light, this paper introduces a novel modelling and optimization approach for a combined-cycle power plant (CCPP) integrated with reverse osmosis (RO) and multi-effect distillation (MED) desalination systems. The integrated CCPP and RO–MED desalination system is thermodynamically modelled utilizing MATLAB and EES software environments, and the results are validated via Thermoflex software simulations. Comprehensive energy, exergic, exergoeconomic, and exergoenvironmental (4E) analyses are performed to assess the performance of the integrated system. Furthermore, a new multi-objective water cycle algorithm (MOWCA) is implemented to optimize the main performance parameters of the integrated system. Finally, a real-world case study is performed based on Iran's Shahid Salimi Neka power plant. The results reveal that the system exergy efficiency is increased from 8.4 to 51.1% through the proposed MOWCA approach, and the energy and freshwater costs are reduced by 8.4% and 29.4%, respectively. The latter results correspond to an environmental impact reduction of 14.2% and 33.5%. Hence, the objective functions are improved from all exergic, exergoeconomic, and exergoenvironmental perspectives, proving the approach to be a valuable tool towards implementing more sustainable combined power plants and desalination systems.

Wastewater containing ammonia nitrogen compounds is considered as a harmful material to environment due to eutrophication and toxicity effects; hence, finding practical methods for treating this type of wastewater seems necessary. In this study, performance of two sequencing batch reactors have been assessed for simultaneous nitrification and denitrification in treating synthesized wastewater containing ammonium nitrogen, using leachate obtained from cow dung as the biomass. The leachate obtained from cow dung as the source of bio‐sludge added to the reactors. Experiments were designed according to central composition design and response surface methodology with four operating variables including pH (6, 7.5, 9), cycle time (CT) (4, 12, 20 h), ratio (5, 10, 15) and carbon source (Sodium acetate: , Glucose: ). According to statistical analysis, experimental responses were in acceptable agreement with model predictions. CT was the most important operating variable in chemical oxygen demand (COD) and removal. The maximum percentage of ammonium nitrogen removal was attained at pH 7.5 and CT 21.5 h. The optimum conditions were composed of pH 7.67, CT 19.15 h, 10.95 and sodium acetate as carbon source, while COD, and total nitrogen removals were 94.96%, 94.93% and 93.60%, respectively. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1638–1646, 2018

Ammonia production through more efficient technologies can be achieved using exergy analysis. Ammonia production is one of the most important but also one of most energy consuming processes in the chemical industry. Based on a panel of solutions previously developed, this study helps to identify potential areas of improvement using an exergy analysis that covers all aspects of conventional ammonia synthesis and separation. The total internal and external exergy losses are calculated as 3,152 and 6,364 kJ/kg, respectively. The process is then divided into five main functional blocks based on their exergy losses. The reforming block contains the largest exergy loss (3,098 kJ/kg) and thus the largest potential for improvement including preheating cold feed through an economizer, developing technology towards isobaric mixing, and pressure drop reduction in the secondary reformer as the main contributors to the irreversibility (1,302 kJ/kg) in this block. The second largest exergy loss resides in the ammonia synthesis block (3,075 kJ/kg) where solutions such as reduced temperature rise across the compressor, proper compressor isolation, reducing undesired components such as argon in the reactor feed, and using lower temperatures for reactor outlet streams, are proposed to decrease the exergy losses. Throttling process in the syngas separator is the key contributing mechanism for the irreversibility (1,635 kJ/kg exergy losses) in the gas upgrading block. The exergy losses in the residual ammonia removal block (833 kJ/kg exergy losses) are mainly due to the stripper and the absorber column where a modified column design might be helpful. The highest exergy loss in the preheating block belongs to the compressors (518 kJ/kg exergy losses) where a lower inlet temperature and better system isolation could help to reduce losses.

Abstract This study presents and evaluates the feasibility of a novel hybridization of modified Kalina cycle, reverse osmosis desalination, and low-temperature water electrolysis utilizing geothermal energy to yield power, distilled water, and hydrogen, respectively. The scientific impact of the current work has been improved considering the features of Sabalan flash-binary geothermal wells in Iran as a real model through a case study. In addition to designing a novel setup, the smart use of multi-heat recovery technique, modifying the base cycle, and utilizing a part of generated distilled water to produce hydrogen by the electrolyzer are the other structural originalities, distinguishing the current work from the previous studies. The suggested system is scrutinized via a parametric study and optimized based on a genetic algorithm. The parametric study demonstrated that the highest sensitivity of varying the performance criteria of the whole system is attributed to the change in flash tank pressure. Moreover, the multi-objective optimization led to achieving the exergy efficiency and trigeneration gain output ratio as 51.3% and 1.7 for the system, respectively. Furthermore, the system was able to produce 4795 kW of power, 5.3 kg/h of hydrogen, and 19.9 kg/s of distilled water.

The use of agricultural wastes as livestock feed is an appropriate method to convert these materials into high value-added materials. These wastes have low nutritional value per unit volume and high transportation, storage and labor costs when they are used in original form. Compaction of wastes in the form of pellet is a proper solution to solve these problems. The pellet drying stage is one of the most important pellet production processes that affect the quality of the pellets. In the present study, the impacts of moisture content, particle size, inlet air temperature of dryer and infrared power of dryer were investigated on properties of physical (unit and bulk density and shrinkage) and thermal (effective moisture diffusivity and specific energy consumption) properties of pellets produced from food and agriculture wastes. The results indicated that all independent variables had a significant negative effect on unit and bulk densities. The effective moisture diffusivity increased with the increase in particle size, infrared power and air temperature dryer. Also specific energy consumption in infrared-convection drying of pellets increased with finer grinding of raw materials.

Abstract In hot and humid regions, vapor-compression cooling systems impose high power demand to grid and increase peak of the load. While thermally activated cooling systems can be a sustainable solution, they are even more beneficial when driven by waste heat. In this paper, a multi-generation system including gas engine, desiccant cooling system and thermal desalination system is studied under three different weather conditions. In the desiccant system, two innovative cycles are applied in which the humidity of regeneration air is higher than conventional systems. Therefore, dew point temperature will be high enough for water condensation. The results show it can compensate for 121% of consumed water in humid areas. Moreover, thermal COP is within range of 0.61–1 in studied cities. While the cooling system uses the jacket water heat, desalination system is powered by the flue gasses. It can annually desalinate 1,122 and 1,817 m3 water by heats of the engines with powers of 33 and 55 kVA. Economic investigation shows levelized cost of cooling is within range of 1.5 to 20 US cents depending on the system size and weather conditions. Besides the water price, the difference between electricity and gas prices plays a key role in system economic feasibility.

Biomass (especially algae) is a renewable energy source that can be a great alternative to fossil fuels. Wet algal biomass converts into products such as solid, aqueous, and gaseous phases as well as biocrude in hydrothermal liquefaction (HTL). The aim of this work was to provide detailed exergy analyses of the production of biocrude from Nannochloropsis sp. by HTL. Physical and chemical exergy of the HTL products, exergy losses, exergy efficiency, and exergy distribution of the HTL process were determined in this research. The highest exergy loss and the lowest efficiency values obtained for the heat exchanger were 65,856.83 MJ/hr and 66.64%, respectively, which was mainly caused by the irreversibility of the heat transfer process. Moreover, the HTL reactor had high efficiency (99.9%) due to the complex reactions that occurred at high temperature and pressure. Also, the optimum operating conditions of the reactor were obtained at 350 °C and 20 MPa by using sensitivity analysis. The high overall exergy efficiency of the process (94.93%) indicated that HTL was the most effective process for the conversion of algae. In addition, the exergy recovery values of the overall exergy input values in the HTL process for biocrude, as well as the aqueous, solid, and gas phases, were nearly 74.88%, 18.42%, 0.86%, and 0.76%, respectively. Exergy assessment provides beneficial information for improving the thermodynamic performance of the HTL system.

Abstract A novel integrated energy system based on a geothermal heat source and a liquefied natural gas heat sink is proposed in this study for providing heating, cooling, electricity power, and drinking water simultaneously. The arrangement is a cascade incorporating a flash-binary geothermal system, a regenerative organic Rankine cycle, a simple organic Rankine cycle, a vapor compression refrigeration cycle, a regasification unit, and a reverse osmosis desalination system. Energy, exergy, and exergoeconomic methods are employed to analyze the suggested system. A parametric study based on decision variables is carried out to better assess the system performance. Four different multi-objective optimization problems are also carried out. At the most excellent trade-off solution specified by the TOPSIS method, the system attains 29.15% exergy efficiency and 1.512 $/GJ total product cost per exergy unit. The main output products are consequently calculated to be 101.07 kg/s cooling water, 570.44 kW net output power, and 81.57 kg/s potable water.

Abstract In this study, the process of carbon dioxide (CO2) desorption from two saturated solutions of monoethanolamine (MEA) and diethanolamine (DEA) was performed in a microchannel made of stainless-steel grade 316 with a circular cross-section (diameter: 800 μm, length: 35 cm). The operating variables in this study were temperature (55, 75 and 95 °C), rich solvent flow rate (0.3, 0.9 and 1.5 ml/min), and inlet solvent concentration (10, 20 and 30 wt% of the amine). The mass transfer efficiency was determined based on the desorption percentage, volumetric liquid-side mass transfer coefficient (kLaV), volumetric overall mass transfer flux (NCO2aV), and energy consumption per unit mass CO2 (R). The results showed that the use of a microchannel significantly increased the mass transfer rate and decreased energy consumption per removed CO2. The results also showed that the amount of kLaV for the two solvents of MEA and DEA was 1.91 and 3.48 1/s, respectively. Moreover, the R-value for the two solvents of MEA and DEA was 1.3 and 1.63 MJ/kg CO2, respectively, which is at least three times lower than that of other mass transfer devices.