منصور خانکی

Constructing peak-shaving liquefaction units with 600 times reduction in volume of natural gas, is the most desirable way to store surplus natural gas in the warm seasons and using it in cold seasons of the year. In this research, along with selecting Shahid Rajaee power plant in Qazvin as case study, the natural gas liquefaction cycle with mixed refrigerant with the purpose of supplying the fuel of total unit of this power plant for 60 days was established; and subjected to technical analysis. Then the amount of initial investment and current costs of the natural gas liquefaction unit is calculated. The economic evaluation of the project based on the net present value method and 12 percent discount rate assumption indicates the payback period is 4.3 years. Sensitivity analysis about variation in discount rate and initial investment cost is another consideration in this study. The results show that even with an increase in the discount rate up to 40% or 50% increase in the initial investment cost, the construction of liquefaction unit is economically justified, but by considering that the life cycle of project is 20 years, such a payback period is not much desirable.

Iran is using natural gas as the main energy carrier in many sectors. Establishing peak-shaving liquefaction units due to reduction in volume of natural gas, is the most desirable way to store surplus natural gas in the warm seasons and using it in cold seasons of the year. Due to the high cost of operating and maintenance of liquefaction cycles, inventing solutions aimed at reducing energy consumption and improving the economy of these units, is really important. In this research, along with selecting Shahid Rajaee power plant in Qazvin as case study, the natural gas liquefaction cycle with mixed refrigerant and absorption refrigeration pre-cooling with the purpose of supplying the fuel of total unit of this power plant for 60 days was established. Then, it was subjected to technical and economic analysis and in terms of operational parameters was compared with common single mixed refrigerant cycle (without precooling). Results show that in comparison to common single mixed refrigerant cycle the specific power consumption %43, the cost of liquefaction plant equipment %15, the flow rate of mixed refrigerant %69 decreased and the figure of merit %28.36 increased.

In the last decade, renewable energy sources have been proposed as an appropriate alternative to meet the energy needs of remote rural areas. The present work focuses on the feasibility of locally available renewable energy production systems development (including solar systems and biomass resulted from manure dung). The studied rural area, Eastern Alamut, located in Qazvin province and consists of three cold and impassable villages of Pichebon, Narmelat and Dinheroud. In order to fulfill energy supply of the rural region, three scenarios have been presented and related techno-economic analyses have been done. Firstly, all heating (cooking and hot water are included) and electricity demands have been met solely by photovoltaic system. In the second scenario, heating and electricity have been supplied by biogas as well as CHP system. Moreover, the heat loss of CHP has been used to warm up the digester. In the last survey, the electricity need has been supplied by photovoltaic system along with covering heating demand through biogas. In this scenario, the required heat to operate digester is provided using the photovoltaic system. In each scenario, volume of digester and equipment of solar system have been calculated. The techno-economic analysis shows that the second scenario that has a positive Net Present Value in each discount rate (5%, 10% and 15%) and Internal Rate of Return is 24.24% 23.26% and 38.6% for Pichebon, Narmelat and Dinehroud villages, respectively, is as a practical design and economic option.

Liquefied natural gas (LNG) is obtained by cooling the natural gas to −162℃ at the atmospheric pressure. Methane is the major chemical component of LNG which varies between 87.0–99.8% for different sources. The cryogenic power generation cycle using LNG as its heat sink is known to be one of the considerable ways for the LNG exergy recovery. A double-stage Rankine power generation cycle using the single component working fluid in each stage for liquefied natural gas (LNG) cold exergy recovery is used as a base case in the present study. To improve the recovery of LNG cold exergy, a three-stage Rankine power generation cycle has been proposed using mixture working fluid. Optimization is done using the particle swarm algorithm. The performance of three-stage Rankine power generation cycle is studied regrading to the effects of thermal efficiencies, exergy efficiencies, overall heat transfer coefficient of condensers and natural gas distribution pressure. Specific power production of the cycle is 100.45 , thermal efficiency is 12.76%, exergy efficiency is 27.92%. By decreasing the total coefficient of heat transfer, the condensers of different stages of the cycle reduce the maximum output power of the cycle with different trends. The results show that by decreasing the distribution pressure of natural gas, specific power production, thermal efficiency and exergy efficiency increases. So that their optimal values at 6 bar are 290.87 , 25.63% and 39.12%, respectively.

Natural gas liquefaction processes require a lot of investment and operation costs and are part of the energy consuming industries. In this research, parameters such as refrigerant component, inlet and outlet pressure to compressors were optimized in dual mixed refrigerant system to reduce operating costs. The optimized system was then evaluated by exergy to obtain the amount of exergy loss in various components of the system, , Exergy efficiency of the entire cycle was obtained 41/63%, finding illustrate the highest exergy losses were in compressors, heat exchangers, after coolers and throttle valves, respectively. The reason is the high exergy loss in the compressors due to their low polytrophic efficiency. In the analysis of exergy it was found that the exergy loss in the main cycle heat exchanger is 4% higher than that of the pre-cooling cycle heat exchanger, reason is the high temperature difference in the input and output of the currents in the converter. Choosing the right heat exchanger can help reduce investment costs. For this purpose, analysis of the effect of the size of the heat exchanger on the specific power consumption was carried out, results showed that changes in the size of the heat exchanger near the optimum point on the power consumption of the cycle are low and increases with the distance from the optimum point of this effect. However, the main cycle curve will have a greater impact on the power consumption of the cycle due to its lower slope.

In this investigation, performance enhancement of direct evaporative cooling system using storage reservoir of cold water has been studied. The water in the reservoir is aimed to store the cold energy overnight and use it during daytime to reduce the temperature of exhaust air from cooler. In this paper, at first stage, the governing equation of above mentioned hybrid direct evaporative cooler is extracted and then, the effect of water storage reservoir mass on the temperature of exhaust air from cooler is investigated. Take a typical summer day in Tehran for example; the results indicate that the use of storage reservoir containing water with a mass of three times larger than the mass of dry air passed through cooler per hour decreases the temperature of the cooled air by 2.02℃ at 14:00 clock. The major advantages of this system are shifting the hours for the maximum and minimum cooled air temperatures towards other hours of a day (e.g., from 05:00 and 14:00 to 06:00 and 18:00, respectively) as well as reducing the cooled air temperature range from 6 to 3.5℃.

In this study, the double stage mixed refrigerant LNG system is investigated, which is known for having the highest efficiency among the liquefaction cycles. The main purpose is to evaluate the performance double stage mixed refrigerant LNG system of point of view effect of variations the environmental and operating conditions of feed that has not been previously discussed. Such as variable environmental conditions during liquefaction processes, temperature, pressure and feed gas composition are. To view the response of the DMR liquefaction system to these changes, system which has been designed and implemented, was selected as the base case.The Results show that with decreasing temperature and increasing pressure feed natural gas, as an advantage, specific shaft work decreases and since in this case, minimum approach temperature in heat exchangers only slightly reduced than the allowed amount 3°C therefore with accepting a safety factor less (to insignificant amount) than the optimal case, can be used of this available advantage. Also, with increasing temperature and decreasing pressure of feed natural gas, while increasing the specific shaft work as well as temperature cross occurs in heat exchangers and means to from entering of the feed natural gas in the area prevented with special controls. Also, any changes in mole fraction of natural gas components make temperature cross in heat exchangers. And due to the change of the natural gas components mole percent, during the life of the well, should over time, the refrigerant composition in the cycle is optimized regarding to new conditions.

In this study, the method of molecular dynamics simulation is performed to investigate the effect of voids on shockwave propagation in solid argon. The case study is a non-interactive solid modeled by Buckingham potential function. The shockwave is generated using the motion of a piston with different velocities in the solid that leads to increase the temperature after its propagation. The resulted shockwave velocity is in good agreement with the experimental data and the Hugoniot curve. It is also found that voids with different geometries and sizes lead to have the same temperature increment with less initiation piston velocity (less threshold initiation).

In this study, the method of molecular dynamics simulation is performed to investigate the shockwave propagation in a solid. The simulation cell contains 51840 atoms at 5 K interacting by means of a pairwise potential. The shockwave is generated using the motion of a piston with different velocities in the solid and the resulted shockwave velocity is in good agreement with the experimental data and the Hugoniot curve. The piston hited the sample from one side of the simulation box, at speeds ranging from 1.2 to 1.3 times the speed of sound in solid argon at the chosen density. Some thermodynamics properties such as density, temperature and pressure are measured during propagation of shockwave. It is found that those thermodynamics properties (density, temperature and pressure) are remarkably and significantly increase when the shockwave passed through the solid. We also show that creating initial strain in the solid up to 6.5% can enhance the pressure increment in the solid up to 9%. The results can be useful in enhancing of the shockwave power by giving a detailed microscopic description of the process.

Due to energy crisis and shortage of fossil fuels and emissions from those that have arisen serious concerns in relation to environmental issues, the use of renewable energy, especially solar energy has many attentions. A significant part of energy used in buildings is consumed by air conditioning systems. According to temperature of the generator, renewable and solar energy can be used as thermal driver in absorption refrigeration systems. In this study, two effects lithium bromide-water solar absorption cooling systems is simulated to be used in Tehran in summer. It is shown that coefficient of performance is increased by increasing temperature of high pressure generator until 130°C significantly and after that remain approximately constant. Since the high temperature generator has high energy consumption, temperature of 130 oC is recommended for high pressure generator. Collectors used in this system are fixed axis parabolic ones. Because the average heat absorbed by the collector varies each month, parallel arrangement are used. Required collector area is determined due to needed solar energy. For 20 kW cooling capacity, 52.5 m2 collector area is required with a 4 m3 storage tank.

One of the most efficient systems for transferring the thermal energy from the power plants to the environment is the wet cooling towers. Dissolved impurities, which are entered into the cooling tower by makeup water, can be limited by the blowdown system. In the present paper, the water quality in the wet cooling towers was studied. Analyses showed that the continuous blowdown is more efficient than periodic one. Furthermore, a group of the wet cooling towers with a certain amount of blowdown, the blowdown system of towers can be utilized to reduce the dissolved impurities. For a special case, the effectiveness of the blowdown in a group of five cooling towers has been investigated, and it was shown that with 20 percent blowdown, the average impurity levels in towers can be reduced from six times of the dissolved impurities in water-supply to 2.74.

Existence of huge reserves of natural gas in the country and also the extent of its distribution lines has caused the use of natural gas as the main energy carrier. Seasonal fluctuations in gas consumption in domestic sector and giving priority to this sector has led that the gas supply to other sectors such as thermal power plants is faced with many problems in the cold season. One way to deal with this issue (shortage of natural gas) is the liquefaction and storage of surplus natural gas in the summer, using peak-shaving gas liquefaction plants. In this study, SMR and N2-expander processes have been evaluated. Changing in operational and environmental parameters (such as changes in flow rate, pressure, temperature and composition of the feed gas and working fluid of the cycle) are the main problems that peak-shaving plants will be permanently encountered with them, thus low sensitivity to changing conditions is the one of the important criteria in the selection of suitable process for peak-shaving. In this study, the sensitivity of liquefaction processes has been investigated using normalized sensitivity analysis. The results indicate that SMR process, despite lower power consumption is more sensitive to changes of the environmental and operational parameters and even, in some cases, the applied perturbation in the probable error range of measurement devices (such as 20 kPa uncertainty or fluctuation in compressor suction pressure), causes malfunction of the liquefaction process (wet entering the compressor).