Natural gas sweetening using tailored ionic liquid-methanol mixed solvent with selective removal of H₂S and CO₂

Natural gas is often preferred in various energy applications due to its many advantages over conventional fossil fuels such as oil and coal. However, the removal of pollutants from natural gas, particularly hydrogen sulfide (H2S) and carbon dioxide (CO2), requires complex treatment strategies, significantly impacting the cost of natural gas production. In this work, we propose a mixed solvent combining ionic liquid (IL) and methanol, which can selectively and simultaneously remove H2S and CO2 by customizing the IL structure and its ratio in the solvent. This purification process offers improved efficiency and energy savings compared to traditional methods. To determine the optimal IL structure in the mixed solvent, a computer-aided design method was employed. Through solving the formulated MINLP problem, the IL 1-methyl pyridinium trifluoroacetate ([C1OHPy][TFA]) was identified as having the highest affinity for H2S, making it suitable for use in the IL-methanol mixed solvent. Furthermore, the upgrading process of high-sulfur natural gas using the IL-methanol mixed solvent was simulated and evaluated, comparing it to the benchmark natural gas upgrading (Rectisol) process. The results demonstrate that the IL-methanol mixed solvent natural gas upgrading process achieved a 55.57 % power savings and reduced the annual total cost (TAC) by 23.90 % compared to the Rectisol process. These findings highlight the significant potential of our tailored IL-methanol mixed solvent in natural gas production.</p

Process Simulation and Optimization of Fluid Catalytic Cracking Unit’s Rich Gas Compression System and Absorption Stabilization System

In a fuel-based refinery, rich gas in the fluid catalytic cracking (FCC) unit is further processed to separate dry gas and refinery products (i.e., stabilized gasoline and liquified petroleum gas). The process is utility-intensive and costly and includes a two-stage compressor, pumps, an absorber, a stripper, a stabilizer, and a re-absorber. The optimization was conducted with respect to the compressor outlet pressure from the gas compression system (GCS) and the flow rate of absorbent and supplementary absorbent from the Absorption-stabilization System (ASS) using the process simulation software Aspen Plus. Compared to the base case of a 725 kt/a rich gas FCC unit, a refinery can save 2.42% of utility costs under optimal operation. Through optimized operation, medium-pressure steam consumption has been reduced by 2.4% compared to the base case, resulting in a significant improvement in total operational cost. The optimization strategy can provide insightful guidance for the practical operation of GCS and ASS.</p

Work Exchange Networks (WENs) and Work and Heat Exchange Networks (WHENs): A review of the current state of the art

This paper provides a current state-of-the-art review of literature on work exchange networks (WENs) and work and heat exchange networks (WHENs). Heat exchange networks (HENs) and mass exchange networks (MENs) have been widely adopted and extensively studied for heat and material recovery to save energy and other resources. However, work recovery can also result in significant energy savings in the process industries, such as oil refineries, petrochemical plants, and cryogenic processes (e.g., the production of liquefied natural gas (LNG) and air separation units (ASUs)). The concept of WENs was first proposed and identified as a new research topic in process synthesis in 1996. This research area has broadened considerably during the last 5–10 years, and it covers both flow work (material streams) and shaft work (energy streams or nonflow processes). Flow work recovery is referred to as direct work exchange and shaft work recovery is referred to as indirect work exchange. More recently, there has also been considerable development in the combined problem of WENs and HENs. This problem is referred to as work and heat exchange networks (WHENs). The WHENs problem is generally studied by pinch based methods and mathematical programming. The corresponding literature is reviewed, analyzed, and compared in this paper. The present review covers WENs (both flow work and shaft work) and WHENs (with a focus on both mechanical energy and thermal energy). The development progress, current state, challenges, and future research in WENs and WHENs are discussed and analyzed thoroughly.acceptedVersio

Model reformulations for Work and Heat Exchange Network (WHEN) synthesis problems

The Duran-Grossmann model can deal with heat integration problems with variable process streams. Work and Heat Exchange Networks (WHENs) represent an extension of Heat Exchange Networks. In WHEN problems, the identities of streams (hot/cold) are regarded as variables. The original Duran-Grossmann model has been extended and applied to WHENs without knowing the identity of streams a priori. In the original Duran-Grossmann model, the max operator is a challenge for solving the model. This paper analyzes four ways to reformulate the Duran-Grossmann model. Smooth Approximation, Explicit Disjunctions, Direct Disjunctions and Intermediate Temperature strategy are reviewed and compared. The Extended Duran-Grossmann model for WHEN problems consists of both binary variables and non-smooth functions. The Extended Duran-Grossmann model can be reformulated in similar ways. In this study, the performance of different reformulations of the Extended Duran-Grossmann model for WHEN problems are compared based on a small case study in this paper.publishedVersio

Identifying optimal thermodynamic paths in work and heat exchange network synthesis

The process synthesis problem referred to as work and heat exchange networks (WHENs) is an extension of the classical heat exchanger networks problem considering only temperature and heat. In WHENs, additional properties are pressure and work, and strong interactions exist between temperature, pressure, work, and heat. The actual sequence of heating, cooling, compression, and expansion for pressure changing streams (PCs) will affect the shape of the composite and grand composite curves, the Pinch point, and the thermal utility demands. Even stream identities (hot or cold) will sometimes change. The identification of the optimal thermodynamic path from supply to target state for PCs becomes a primary and fundamental task in WHENs. An MINLP model has been developed based on an extension of the Duran–Grossmann model (that can handle variable temperatures) to also consider changing stream identities. Three reformulations of the extended Duran–Grossmann model have been developed and tested for two examples. © 2018 American Institute of Chemical Engineers AIChE J, 2018. © 2018 American Institute of Chemical EngineersIdentifying optimal thermodynamic paths in work and heat exchange network synthesisacceptedVersio