فهرست مطالب حمیدرضا افشون

In the present study, brief review of the introduction of LNG, processes and equipment for its production and conversion to gas were done. Then mini LNG units were introduced and its maximum capacity (300 tons/day) was selected as the base unit. In the economic section, based on the selected scale and selection of the liquefaction process by the nitrogen expansion cycle method, price of the equipment was estimated and then updated according to the cost index for 2019. After that, the fixed and operating investment costs and finally total investment were estimated. According to assessments, the investment cost of the mini LNG unit with a capacity of 300 tons/day and a volume of 20,000 m3 of tanks is estimated at 101 MMUSD. Based on the calculations and according to the capacity of the proposed storage tanks and the consumption of a power plant, this mini LNG unit can supply gas for power plant for 60 hours of operation at its maximum power generation capacity. With the assumptions used for the price of electricity generated at peak times, the rate of return on investment was calculated and finally, based on the technical and economic evaluation, the feasibility of implementing this project was investigated.

Nowadays, natural gas pipeline is considered to be the most common way to satisfy heat demands of the Iranian. In this study, to satisfy the heat demands of some off-grid areas including Shahrag, Imam Gholi, Bardar, and Bajgiran, the areas in Khorasan Razavi province, the feasibility of implementing some methods are investigated. In this regard, three approaches consisting of virtual pipeline, substitution of electricity, and biogas are studied and compared to natural gas pipeline. Technical study reveals that the areas do not have a potential to be completely benefited from biogas. Afterward, other methods were financially studied. Moreover, form net present value standpoint, natural gas pipeline appears to be the best option among others.

As a clean energy source, the natural gas emits about 50 percent less CO2 than coal when burned normally. On the other hand, the global warming potential of the methane is 86 times greater than CO2 on a 20-year time frame. An increase in the methane emission can eliminate the advantage of minimal carbon dioxide emitted in the natural gas combustion. Hence, methane emission as an important environmental issue, has been evaluated in the various studies. Today, it has accelerated to progress of the mobile methane leak measurement in the various sectors of the natural gas industry. The most important achievement of this idea is increasing of the emission detection rate and also providing the potential for maximum coverage of leakage finding in the natural gas distribution network. In this study, the effort has been made to evaluate the new ideas of emission detection used in natural gas distribution infrastructure.

To pass the excess water and floodwaters from upstream to downstream of the dams, a structure called "spillway" is used. This structure is vital and integral as they should be ready for operation at any moment. Stepped spillways are introduced as a viable option for improvement of spillways facing problem when flowing the possible maximum flow rate. Stepped spillways consist of stairs which start near the crown and continue to lower heels. Increase of roughness leads to a uniform and continuous distribution energy of the flow over the spillway. This is of great benefit for designers as there is no longer need to the toe of the spillway to create facilities reducing flow energy such as stilling basins. In this study, to increase the roughness on the stepped spillway, barriers are used to increase the energy dissipation. For experimental tests, a flume with a 90 degree bend was used in Islamic Azad University of Ahvaz (IAU-A) and several different types of barriers on the stepped spillway in three shapes with three different lengths and widths as well as using barriers individually and in combination, with 5 different flow rates, a total of 140 tests were performed. After analyzing the results, it was found that in the stepped spillway combined with respectively a triangular, rectangular, and trapezoidal barrier, a decrease in dissipation and energy loss is observed. Triangular barriers, on average, increase the energy consumption by 15.9%, rectangular barriers, on the average, increase the energy consumption by 13.7% and tipping barriers by an average 11.2% increase in energy depreciation compared to the control model. An increase in the length and width of the barriers results in an increase in dissipation and energy loss. The two-step barriers have the highest energy dissipation and loss. By combining barriers on the two-stair stepped spillway, there is an average of 14.4 percent increase in energy dissipation. Based on the observations, rise in the Froude number from 0.32 to 1.71 leaded to a decrease in dissipation and energy losses which is due to the immersion of the stairs below the water level and the reduction of the roughness of the stairs and with the increase of the intensity of the inflow phenomenon. The simulation results with the Flow-3D math model are close to the physical model, and on average only 6.3% of errors are acceptable. After analyzing the results, it was found that in the combination of stepped spillway with triangular, rectangular and trapezoidal obstacles, we see a decrease in energy depreciation and energy loss. Also, comparing the simulation results and the physical model shows that the Flow-3D mathematical model find less bias with the physical model and closer to reality.

In this study, PES/Pebax composite membranes were prepared by coating the porous PES support layers by Pebax-1657. Film casting and pouring methods were used for coating Pebax layer. The effects of coating technique and conditions including coating solution concentration and curing temperature on CO2 and CH4 gas permeabilities of prepared composite membranes were investigated. SEM images were used to investigate the structure of the prepared membranes. Pure CH4 and CO2 gases were used to investigate the gas permeation properties of the prepared membranes at different trans-membrane pressures (1-11 bar) and feed temperatures (25-55°C). The obtained data showed that the prepared PES supports did not provide any CO2/CH4 selectivity. The results also showed the CO2/CH4 selectivity for the membrane prepared via pouring technique was higher than that of the film casting procedure due to the defect-free Pebax layer formation. CO2 and CH4 permeance increased as the feed temperature increased from 25 to 55°C. The results also showed that CO2 permeance increased from 6.8 to 10.1GPU with an increase in feed pressure from 2 to 12barg, while CH4 permeance remained almost constant and CO2/CH4 selectivity increased from 27 to 42.