The acid gases (H2S and CO2) are unpleasant groups in the natural gas (sour gas) stream, which must be reduced. The presence of acid gases will have operational problems such as corrosion in the processing facilities and, environmental issues like air pollution and greenhouse effects. Therefore, the reduction of acid gases from sour gas is essential via a reliable process. The most common method for natural gas sweetening is the utilization of the amine solution. In the current work, the analytic hierarchy process (AHP) is employed to consider the advantages and disadvantages of each amine solution. The four process criteria and seven alternatives were intended based on the AHP procedure. Then, the natural gas sweetening process was simulated, and finally, operation conditions were optimized. MDEA as an alternative and cost as process criteria were introduced with 21% and 53% as the highest priority, respectively. The reduction of acid gas contents and reboiler duty were chosen as objective functions. The optimization results indicated that the best feed gas temperature and MDEA concentration are 30 ºC and 39 wt. %, respectively. The amount of H2S and CO2 as one of the optimization objectives of gas sweetening achieved 2. 4 and 88 ppm in the optimal condition. Accordingly, the MDEA solution consumption was reduced by 5%, and reboiler duty decreased by approximately 0. 04% compared to the conventional process.

In this research, a film-model-based for gas sweetening by alkanolamine is considered and three different approaches to the solution of the CO2 mass transfer- reaction in the liquid film are studied. Also the results are compared with each other and pilot plant data. The first approach is based on numerical method for solving nonlinear boundary value problem. The second approach requires a simplification of differential transport equation by assuming uniform amine concentration in liquid film and bulk of liquid. The third approach is polynomial method and furthers these two later methods, by taking advantage of an analytical technique. Numerical method was solved by complex matrix solution. Advantage and disadvantage of these methods are analyzed and investigated. The three models have good agreement with pilot plant data.

In sour gas flares, H2S content like any other components in inlet gas influences adiabatic flame temperature, which, in turn, impacts on the pollutant emission. Wherever flame temperature increases, the endothermic reaction between O2 and N2 is accelerated, which means higher NOx emission to the atmosphere. In this work, we developed an in-house MATLAB code to provide an environment for combustion calculations. Then, this written code was used to perform sensitivity analyses on H2S content, air temperature, and excess air ratio in sour gas flares. We used Environmental Protection Agency (EPA) reports to assign weighting indexes to each air contaminant according to its harmfulness to environment; thereafter, sour gas flaring conditions were optimized for two real field case studies, namely Ahwaz (AMAK) and South Pars, to reach the minimum integrated pollutant concentrations. The results show that each 2% increase in the H2S content of the entrance feed may produce 0. 3% additional SOx in the exhaust. The results also confirm that decreases of 20 ° F and 50 ° F in the oxidant temperature cause NOx emission to reduce by 0. 5% to 1% respectively. Finally, to verify and validate our results acquired from the written MATLAB code, FRNC 2012 industrial software was used to duplicate the oxidation results for the two sour flare case studies.

Use of amine solutions for the removal of acid gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) from natural gas is the most common method, and, in this process, operational problems because of foaming are reported. Foaming can lead to the entrainment of liquid into downstream process equipment and might result in a situation in which the process specifications cannot be met for acid gases. Alkanolamines in general have a negative effect on downstream process equipment, and the loss of amines has a negative effect on the health, safety, and environment (HSE). The foam reducing agents are often used to reduce the risk of heavy foaming in amine plants. This study concerns with foaming in amine-based CO2 plants. To investigate foaming related to CO2 removal from natural gas by amine solutions, the fundamental theory of foaming in gas-liquid contactors was first reviewed. Then, experimental techniques related to this phenomenon in diethanolamine (DEA)/CO2 absorbers were considered. After that, foaming of diethanolamine solution polluted with different impurities was noticed, and the tendency of foam was measured by considering their foaming indices. To analyze the experimental measurements and experimental observations, a mathematical model was developed too. The model could justify the experimental measurement reasonably.