Conventional natural gas (NG) liquefaction processes remove N2 near the tail of the plant, which limits production capacity and decreases energy efficiency and profit. Engineering calculations suggest that upfront N2 removal could have substantial economic benefits on large-scale liquefied natural gas (LNG) processes. This article provides an overview of the most promising technologies that can be employed for upfront N2 removal in the LNG process, focusing on the process selection and design considerations of all currently available upfront N2 removal technologies. The literature review revealed that although adsorption has proven to be a huge success in gas separation processes (efficiency ≥ 90%), most of the available adsorbents are CH4-selective at typical NG conditions. It would be more encouraging to find N2-selective adsorbents to apply in upfront N2 removal technology. Membrane gas separation has shown growing performance due to its flexible operation, small footprint, and reduced investment cost and energy consumption. However, the use of such technology as upfront N2 removal requires multi-stage membranes to reduce the nitrogen content and satisfy LNG specifications. The efficiency of such technology should be correlated with the cost of gas re-compression, product quality, and pressure. A hybrid system of adsorption/membrane processes was proposed to eliminate the disadvantages of both technologies and enhance productivity that required further investigation. Upfront N2 removal technology based on sequential high and low-pressure distillation was presented and showed interesting results. The distillation process, operated with at least 17.6% upfront N2 removal, reduced specific power requirements by 5% and increased the plant capacity by 16% in a 530 MMSCFD LNG plant. Lithium-cycle showed promising results as an upfront N2 chemical removal technology. Recent studies showed that this process could reduce the NG N2 content at ambient temperature and 80 bar from 10% to 0.5% N2, achieving the required LNG specifications. Gas hydrate could have the potential as upfront N2 removal technology if the is process modified to guarantee significant removals of low N2 concentration from a mixture of hydrocarbons. Retrofitting the proposed technologies into LNG plants, design alterations, removal limits, and cost analysis are challenges that are open for further exploration in the near future. The present review offers directions for different researchers to explore different alternatives for upfront N2 removal from NG.

Monoethylene glycol (MEG) is a widely used hydrate inhibitor in the oil and gas industry to reduce the risk of hydrate formation in pipelines that could cause a blockage. For flow assurance and hydrate inhibition purposes, large volumes of MEG are required to control the hydrate formation conditions in pipelines. Disposal of rich MEG after separation has considerable costs and poses significant environmental concerns. Therefore, the development of an effective process for MEG recovery has been gaining importance. The current study presents a systematic approach to develop, simulate, and optimize MEG recovery using Aspen Plus and ELEC-NRTL thermodynamic package. Two distinct MEG recovery process (MEG-R-P) designs, namely, the vacuum (design I) and atmospheric (design II) distillation, were tested. Both designs have demonstrated exceptional performance in recovering MEG from salts and water and producing lean MEG at a purity of 90 wt%. Design I operating at vacuum conditions outweighs design II in terms of MEG purity and energy requirements. The addition of MEG-R-P has the advantage of recovering and reusing significant amounts of MEG and removing the burden on the environment.

In the present study, the energy requirements, performance and economic feasibility of monoethylene glycol (MEG) recovery process (MEG-R-P) were establish based on Aspen Plus simulation. The simulation was carried out in two designs and four scenarios related to the composition (mono and divalent salts) of rich-MEG. The results revealed that, under optimized conditions, a process consists of a vacuum flash separator and distillation column operated at 0.05 bar recovered 99.7% of MEG with a purity of 99.9 wt% MEG for all scenarios. The concentration and type of dissolved solids showed a minimal effect on the process of energy and performance due to high dilution. The net present worth (20 years, 8%) of the capital and operating costs associated with MEG-R-P were 11.5 and 11.7 MMUSD, respectively, representing two to four folds saving compared with published results. The recovered MEG can be recycled 10 times with an estimated saving of 50% of the total MEG purchasing cost for one-time recycling, and up to 80% saving for five times recycling. Obtained results confirm the high economic and environmental benefits achieved by applying the proposed MEG-R-P. K E Y W O R D S economic evaluation, monoethylene glycol (MEG), process simulation 1 | INTRODUCTION Gas hydrates (GH) are ice-like clathrates of crystalline structure formed due to the freezing of water in the gas stream leading to pipeline plugging and discontinuing the transportation of gas. The formation of GHs has significant safety risks and economic challenges to gas transportation and processing that end up with operational shutdown for an extended period. Thus, careful measures to avoid, mitigate and control the formation of these hydrates are required for offshore production sites.

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