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Ethylene Glycol Elimination in Amine Loop for More Efficient Gas

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Ethylene Glycol Elimination in Amine Loop for More Efficient Gas  Hajilary and Rezakazemi Chemistry Central Journal (2018) 12:120 Chemistry Central Journal https://doi.org/10.1186/s13065-018-0493-3 RESEARCH ARTICLE Open Access Ethylene glycol elimination in amine loop for more efcient gas conditioning Nasibeh Hajilary1* and Mashallah Rezakazemi2 Abstract The gas sweetening unit of phase 2 and 3 in South Pars Gas Field (Asalouyeh, Iran) was frst simulated to investigate the efect of mono ethylene glycol (MEG) in the amine loop. MEG is commonly injected into the system to avoid hydrate formation while a few amounts of MEG is usually transferred to amine gas sweetening plant. This paper aims to address the points where MEG has negative efects on gas sweetening process and what the practical ways to reduce its efect are. The results showed that in the presence of 25% of MEG in amine loop, H­ 2S absorption from the sour gas was increased from 1.09 to 3.78 ppm. Also, the reboiler temperature of the regenerator (from 129 to 135 °C), amine degradation and required steam and consequently corrosion (1.10 to 17.20 mpy) were increased. The energy consumption and the amount of amine make-up increase with increasing MEG loading in amine loop. In addition, due to increasing benzene, toluene, ethylbenzene and xylene (BTEX) and heavy hydrocarbon solubility in amine solution, foaming problems were observed. Furthermore, side efects of MEG presence in sulfur recovery unit (SRU) such as more transferring BTEX to SRU and catalyst deactivation were also investigated. The use of total and/or partial fresh MDEA, install insulation and coating on the area with the high potential of corrosion, optimization of opera- tional parameters and reduction of MEG from the source were carried out to solve the problem. The simulated results were in good agreement with industrial fndings. From the simulation, it was found that the problem issued by MEG has less efect when MEG concentration in lean amine loop was kept less than 15% (as such observed in the indus- trial plant). Furthermore, the allowable limit, source and efects of each contaminant in amine gas sweetening were illustrated. Keywords: CO2 and ­H2S absorptions, Mono ethylene glycol, Amine gas sweetening, Corrosion, Foaming Introduction prevention of catalysts poisoning in downstream facilities Natural gas is produced from wells with a range of impu- [9]. rities and contaminants such as sulfur dioxide (SO­ 2), Many methods have been employed to remove hydrogen sulfde ­(H2S) and carbon dioxide ­(CO2) [1–4]. acidic components (primarily H­ 2S and ­CO2) from Tese contaminants should be removed from the natural hydrocarbon streams including adsorption, absorp- gas to meet typical specifcations for use as commercial tion [10, 11], membrane [12–16], hybrid system and fuel or feedstock for natural gas hydrate, liquefed natu- etc. [17–20]. From these methods, the amine absorp- ral gas (LNG) plants, gas turbines, industrial and domes- tion attracts increasing attention due to higher H­ 2S tic use [5–8]. Removal of these contaminants is required and ­CO2 removal and environmental compliance. An from point of safety, environmental requirements, corro- amine gas treating plant is commonly faced with two sion control, product specifcation, decreasing costs, and major problems: corrosion and instability of opera- tion [6]. Furthermore, the purity of amine has a con- siderable efect on the efciency of the gas sweetening unit. In most amine based sour gas treating process, *Correspondence: [email protected]; [email protected] the conventional alkanol amines such as monoethan- 1 Department of Chemical Engineering, Faculty of Engineering, Golestan olamine (MEA), diethanolamine (DEA), methyl dieth- University, Gorgan, Iran Full list of author information is available at the end of the article anolamine (MDEA), disopropanolamine (DIPA), and © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat​iveco​mmons​.org/licen​ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat​iveco​mmons​.org/ publi​cdoma​in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Hajilary and Rezakazemi Chemistry Central Journal (2018) 12:120 Page 2 of 15 diglycolamine (DGA) is used to separate H 2S and CO 2 Gas sweetening unit description from natural gas [19, 21]. MDEA is commonly used in Phases 2 and 3 of South Pars Gas Field were designed for industrial plants because it has some advantages over processing of sour gas by means of four MDEA based other alkanol amines such as high selectivity to the H 2S, amine units (licensed by ELF Aquitaine which does not high equilibrium loading capacity (1 mol CO 2 per 1 mol need to remove all CO2; resulting in high H 2S content in amine) and less heat of reaction with CO2, and lower acid gas for Claus SRU). Te composition of sour gas feed energy consumption in regeneration section. is reported in Table 1. Te sour feed gas contains 0.6% Mono ethylene glycol (MEG) is commonly injected H2S and 2% CO2. into the system from two diferent points (wellhead and Te objective of the gas treatment unit is to meet the gas receiving facilities) as corrosion and hydrate inhibi- design sweet gas specifcation which must contain less tor especially during winter time when the potential of than 4 ppmv H2S and 1 mol% CO 2 and produce suit- condensation corrosion and hydrate formation are high. able acid gas for processing in the SRU’s. Tis certain In phases 2 and 3 through the gas path, MEG is injected specifcation of product in industrial plants is commonly at sea line, before HIPPS valve, and after the High-pres- achieved through an amine unit including absorption sure separator drum. A few amounts of MEG is usually and a regeneration sections. In the absorber, amine solu- transferred to the amine gas sweetening plant. Te MEG tion absorbs H 2S and CO2 from the sour gas to produce concentration gradually increases in amine gas sweet- a sweetened gas stream and a rich amine (a rich amine ening plant even to more than 25%. A large build-up of is an aqueous solution which has absorbed the H2S injection chemicals can eventually lead to fouling and can cause changes in solution physical properties, such as viscosity and mass transfer. South Pars is a giant gas reservoir shared with Qatar Table 1 Characteristics of sour gas feed to the gas with more than 20 phases. Te phases 2 and 3 of South sweetening unit (units 101 and 108) of phases 2 and 3 in South Pars Gas Field (Asalouyeh, Iran) Pars gas refnery has been planted to treat the produced gas through four gas treating trains and stabilize the Components Mole% accompanied condensate from the gas reservoir. Nowa- H S 0.5548 days, about 2500 million standard cubic feet per day 2 CO 1.8303 (MMSCFD) of gas is fed to this plant. In phases 2 and 2 C 85.1012 3, the untreated gas is transferred via two 30″ pipelines 1 C 5.4372 to onshore facilities for treatment. MEG is transferred 2 C 1.9888 by means of two 4″ piggy back lines to the wellhead for 3 i-C 0.368 hydrate prevention and low dosage hydrate inhibitor 4 n-C 0.5709 (LDHI) is being used as a backup. 4 i-C 0.1766 Te main purpose of the current study is to fnd where 5 n-C 0.1574 MEG has negative efects on gas sweetening process 5 Benzene 0.0194 and what the practical ways to reduce its efect are. Te N 3.4754 efects of MEG injection on amine gas sweetening and 2 n-hexane 0.0674 sulfur recovery unit (SRU) units were also studied. Since Cyclo hexane 0.0299 the presence of MEG was not predicted in the design Methyl cyclo pentane 0.0195 of gas sweetening unit, it seems the phases 2 and 3 was toluene 0.0046 the frst gas plants to deal with this problem. Other gas Methyl cyclo hexane 0.0094 refneries in South Pars Gas Field which used MEG as a Heptane 0.0604 hydrate inhibitor are gradually encountering this prob- Octane 0.0324 lem. Furthermore, a certain value was not found in the literature for the maximum allowable of MEG content in Ort-xylene 0.0048 amine loop. To overcome the problems issued by MEG in Nonane 0.003 amine loop, four diferent methods including: (1) chang- Decane 0.0003 ing operational parameters in the presence of MEG in Carbonyl sulphide 0.003 amine loop; (2) reducing MEG loading in amine loop Methyl mercaptans 0.0021 by total or partial discharging of amine; (3) enhancing Ethyl mercaptans 0.0137 resistant to corrosion; (4) developing a strategy to track Propyl mercaptans 0.0037 the source of MEG in amine loop were suggested and Butyl mercaptans 0.0008 investigated. Ort-xylene 0.0048 Hajilary and Rezakazemi Chemistry Central Journal (2018) 12:120 Page 3 of 15 and CO2). Te rich amine after passing through a fash and SULSIM (version 6) simulators and a schematic of drum and increasing its temperature in some exchang- the simulations are shown in Fig. 2. Te process simula- ers routed into the MDEA regenerator (a stripper with a tions were used to perform a parametric study to pre- reboiler) to produce lean amine (a lean amine is a solu- dict the operational parameters change as a function of tion regenerated from acid gases) that is come back to the MEG content in amine loop and also to better identifying absorber.
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