نشریه مهندسی گاز ایران
پیاپی 9 (شهریور 1398)

In this paper complex fluid flow and transport phenomena in plate-fin heat exchanger for LNG process are investigated. Modeling and simulation of heat transfer and fluid flow has been done using ANSYS Fluent software. This software has limitation in simulation of multispecies biphasic flow; therefore, UDF.A 2D model was used for modeling aforementioned phenomena in one channel of heat exchanger. HYSYS software was used for calculation of species equilibrium concentration and it was linked to ANSYS using UDF. Results shows that vapor volume fraction, species composition and heat transfer coefficient for CFD and Aspen muse are in good agreement, but pressure drop is over predicted by Aspen Muse. Using the developed model, a good deal of information was obtained about transport phenomena and fluid flow in cryogenic heat exchangers, while other software packages could not provide that much information.

The most important elements in liquefaction process are heat exchangers that are Plate Fin or Spiral Wounded. In this paper, IRAN LNG liquefaction cycle is simulated using Aspen-Hysys software. Then a procedure for designing plate fin heat exchanger is developed. Moreover, the paper also presents a new method to select the best secondary surface. The obtained surfaces by traditional simulation for cold and warm ends of heat exchanger and overall heat transfer coefficient are 3001 m2, 1933 m2 and 425 W/m2.K. After designing the optimized heat exchanger using the newly developed Rapid Design Algorithm (RDA), the obtained surfaces for cold and warm ends and the overall heat transfer coefficients were 575 m2 and 842 W/m2.K, respectively. This study shows a significant reduction in designing a compact heat exchanger with cold end surface, warm ends surface, and an increase in overall heat transfer coefficient which are 2.5, 3.3 and 2 times lower and higher, respectively.

To purify and eliminate sulfur compounds from LPG molecular in an oil refinery, a molecular sieve is used; however, due to a change in the feed of the refinery, the amount of sulfur compounds which enters the LPG Unit has increased by 20 times. This change has disrupted the output compounds of the molecular sieve. In this study, it is suggested that a pre-wash process using Soda should be carried out prior to the molecular sieve adsorption process, to increase the efficiency of adsorption process by molecular adsorbents. In order to investigate the possibility of using Caustic to pre-wash the LPG Unit input, the piping of Naphtha Merox Unit was investigated; then, using the Promax software, the process was simulated and reviewed. By carefully examining the factors affecting the reactions, it was tried to select the best model and the optimal conditions. Using caustic, the amount of Mercaptan in the LPG was reduced from 1900 ppm to below 130 ppm and, in line with the original design, it entered the adsorption stage without disrupting the adsorbents performance, and the final values of Mercaptan and H2S reached zero.

Today, one of the problems in gas transmission lines is the phenomenon of gas hydrate, which, by combining light gases with water molecules under special conditions of temperature and pressure, forms a substance similar to ice that contains a large amount of gas. Therefore, it is very important to study the variables and factors affecting the formation and removal of hydrates. In this research, Soroush-Abuzar gas pipeline was simulated with Hysys software and the hydrate formation conditions in 30 kilometers of gas transmission were investigated. The results of this study reveals that in the studied pipelines, the temperature is 50 C and the pressure is 25 bar, the best process condition in which there is no possibility of hydrate formation. Also, the analysis of pressure and temperature profiles shows that as the pipe length increases, both parameters tend to descend.

In this study, gas condensate of Bandar Abbas, Kopet Dag and Qom (Central Iran) regions have been studied in organic geochemistry. In this regard, 7 gas condensate samples (3 samples from Bandar Abbas, 3 samples from Kopet Dag and 1 sample from Central Iran) were used to determine the geochemical characteristics of gas chromatography, gas chromatography-mass spectrometry, and Isotope of carbon studies. Based on the parameters obtained from the Biomarkers study, sedimentary environment source rock of the hydrocarbons of the Bandar Abbas with lithology carbonate and marl with kerogen type II and III, the hydrocarbon producing organic materials in the Kopet Dag basin is mainly deposited in the shallow marine and coastal areas (kerogen type III) and in comparison with other regions, it has higher maturity. The Biomarker’s parameters showed that the source rock of Central Iran (Serajeh Qom Field) is deposited in marine environment with shale and carbonate lithology and, compared to the other two studied regions, has the lowest degree of maturity. This study shows that the source rock age of the studied hydrocarbons in the Kopet Dag and Bandar Abbas areas belong to the second geological era, and the source rock of the hydrocarbons in the Serajeh Field is related to the third geological era. Also, the difference in maturation of gas condensate samples in these three areas indicates that the samples of the Kopet Dag region have the highest maturation and the samples related to Central Iran have the lowest maturation.

Tri-reforming is a synergetic combination of carbon dioxide reforming, steam reforming and partial oxidation of methane in a single unit to produce synthesis gas. In this research, the slurry bubble column tri-reformer reactor performance is compared with those of fluidized-bed and fixed-bed tri-reformer reactors. The process of slurry bubble column performance under steady state conditions was analyzed, and model validation was carried out by comparing the methanol synthesis reactor model results with Air Products’ (1991) RUN E-8.1. Slurry bubble column tri-reformer reactor has reduced methane conversion by 6.33% and 6.66%, relative to fixed-bed and fluidized-bed tri-reformer reactors; moreover, it has reduced hydrogen yield by 0.58% and 18% relative to fixed-bed and fluidized-bed tri-reformer reactors. In fixed-bed and fluidized-bed tri-reformer reactors, temperature in the catalytic bed for methanol feed unit was 1680 K and 1432 K, respectively. However, due to the unique mixing, the temperature in the catalytic bed for slurry bubble column tri-reformer reactor reduced to 1157.5 K. Slurry bubble column tri-reformer reactor suggested instead of fixed-bed and fluidized-bed tri-reformer reactors to produce synthesis gas, due to significant fall temperature in the catalytic bed and low repairs because of simple structure.

With increasing population, reducing the amount of pollutants in the environment is especially important. Oil and gas refineries are one of industrial units which cause environmental pollution. Since all the hydrocarbon components recovered from the reservoirs are not separable, therefore inevitably a significant amount of these compounds, which are generally of high economic value, are burn in flares. In addition to the loss of many beneficial hydrocarbon compounds, flaring has many environmental damages. The main purpose of this paper is to provide the best way to separate and minimize flare gases and reduce the loss of gas hydrocarbons. For this purpose, the separation of gases sent to Parsian refinery flare was simulated using Aspen HYSYS software and operational enhancements were applied. Different types of amines for carbon dioxide separation were investigated and the best type was selected with the highest recovery rate. Moreover, sensitivity analysis were performed on important operational parameters and the results were analyzed. Finally the application of separated carbon dioxide for gas injection in gas reservoirs for pressure stabilization and the separated sweet gas for GTL process and conversion to more valuable compounds were suggested.