Optimization of Natural Gas Liquefaction Process

This chapter provides a brief review of the developments in the optimization of Natural gas (NG) liquefaction techniques since 2001. NG liquefaction is energy intensive and small improvements in liquefaction efficiency brings huge cost benefits thus optimization is needed. To tackle the NG liquefaction optimization problem, two different optimization philosophies, i) deterministic and ii) stochastic, have been adopted. The limitations of the deterministic approach have paved the way for derivative-free stochastic approaches. Although both techniques work well for the reported problem, their application is limited to the specific problems and generalization is quite difficult. Therefore to overcome this problem, a third of the so called knowledge-inspired class have been evolved for NG liquefaction optimization. Thus, this chapter covers the major development that took place in NG liquefaction area and after reviewing the trends future research directions are given.

As demand for natural gas continues to grow, offshore liquefaction of natural gas (LNG) by floating production, liquefaction, storage and offloading (FPSO) vessels is becoming increasingly attractive. LNG FPSO solutions offer an economic and environmentally sound solution to exploiting the attractive stranded offshore gas fields and commercialising oil associated gas, reducing the need for flaring and giving an extended potential for oil production. For offshore applications different design criteria apply than for onshore plants and the Nitrogen Expander Cycle is meeting all these requirements. The "Aragon's Optimised Expander Cycle" has additional features that makes it highly applicable for offshore liquefaction. Introduction The history of the development of large scale natural gas liquefaction plant started in 1960's with technologies based on either the classic cascade cycle (by Marathon/Phillips) or simple mixed refrigerant cycles. At the beginning of this century, several new large scale processes have been demonstrated or proposed. These includes Air Products' AP-X process, Shell's propane pre-cooled Parallel Mixed Refrigerant process (PMR), Statoil/Linde's Mixed Fluid Cascade (MFC) and Conoco-Phillips' Optimised Cascade. Common for all these base load technologies are:Ultra-large train sizeHigh process efficiencies but variable overall thermodynamic efficiencyLarge and heavy equipmentRequirement for large construction areasHC Refrigerants These are features that are not advantageous for offshore applications. Through the last decades the industry has studied to find the most appropriate liquefaction technology for the offshore environment. The paper gives an overview of the evaluations related to the engineering and design of an LNG FPSO topside. It discusses the different selection criteria that apply for selecting offshore liquefaction systems and gives an introduction to the Nitrogen Expander liquefaction technology and in particular the "Aragon's Optimised Expander Technology". Where is offshore LNG attractive? There is a wide range of applications where offshore LNG production is attractive: Stranded Gas Field - These fields are typically located at significant distance from existing offshore or onshore production facilities or pipeline networks. Floating production units is a highly competitive choice compared to new build offshore production platforms and long distance pipeline tie-backs to onshore facilities. Associated Gas Field Applications - As environmental regulation are getting stricter the presence of oil associated gas in locations remote from existing infrastructure is an increased challenge to Governments and the Oil and Gas Industry Economic development of many of these resources is difficult, particularly for the offshore fields. The result is that 110 billion standard cubic meter of natural gas is being flared annually in the world5. Production of this gas in form of exported LNG adds economic value to an existing project, and provides an additional benefit to the environment by reduced emissions. Early Production System and Staged Development Applications - Floating liquefaction offers a fast-track project compared to an onshore plant. Current LNG FPSO projects show that the development time from project definition until first LNG is up to 50% of the time required for a traditional onshore LNG development. Hence the LNG FPSOs are capable of providing a viable alternative for an early production scheme generating revenues and creating value while the standard facilities are being approved and built.

Thermo-Economic Assessment and Uncertainty Quantification of Hydrofluoroolefin-Based Single Mixed Refrigerant Process for Natural Gas Liquefaction

Advanced natural gas liquefaction and regasification processes: Liquefied natural gas supply chain with cryogenic carbon capture and storage

Considering its clean and environmental characteristics, natural gas has gradually attracted attention from countries around the world. China’s coal-to-gas project has significantly increased the country’s demand for, and supply of, natural gas. Liquefied natural gas (LNG) has also been gradually promoted, owing to its advantages of easy storage and transportation. However, the natural gas liquefaction process includes multiple phases, and each phase generates substantial industrial pollutants, such as CO2, SO2, and NOx. Despite this, the resulting environmental impacts have not been quantitatively assessed. Therefore, based on the production process of a liquefaction plant in the Shanxi Province, China, in this study, the Life Cycle Assessment (LCA) model was used to analyze the pollutant discharge in the unit’s natural gas liquefaction production process. By collecting data on the production capacity and composition reports of the eight major LNG-producing provinces, such as Henan, Sichuan, Inner Mongolia, Shaanxi, Xinjiang, Shanxi, Ningxia, and Hebei, the total amount of pollutants discharged from the natural gas liquefaction process in China was estimated. Finally, the environmental impact of the natural gas liquefaction process was evaluated according to the results of the environmental impact of pollutants. Our study arrived at the following conclusions: (i) 93.60% of China’s natural gas liquefaction output is concentrated in eight provinces; (ii) in terms of the unit’s LNG production, the Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), Photochemical Ozone Creation Potential (POCP) and Dust Potential (DP) proportions of each province explained the gas composition of LNG production gas sources in each province; (iii) the environmental problems caused by natural gas liquefaction were different in each provinces. In addition, we suggested relevant policy recommendations. First, the formulation of LNG-related policies should consider environmental pollution produced during the liquefaction stage. Second, if the problem of pollutant discharge in the liquefaction of natural gas is properly solved, it will not only reduce environmental pollution, but also generate additional income. Third, different provinces should optimize production technology based on the different gas qualities.

With the requirement of energy decarbonization, natural gas (NG) and hydrogen (H2) become increasingly important in the world’s energy landscape. The liquefaction of NG and H2 significantly increases energy density, facilitating large-scale storage and long-distance transport. However, conventional liquefaction processes mainly adopt electricity-driven compression refrigeration technology, which generally results in high energy consumption and carbon dioxide emissions. Absorption refrigeration technology (ART) presents a promising avenue for enhancing energy efficiency and reducing emissions in both NG and H2 liquefaction processes. Its ability to utilize industrial waste heat and renewable thermal energy sources over a large temperature range makes it particularly attractive for sustainable energy practices. This review comprehensively analyzes the progress of ART in terms of working pairs, cycle configurations, and heat and mass transfer in main components. To operate under different driven heat sources and refrigeration temperatures, working pairs exhibit a diversified development trend. The environment-friendly and high-efficiency working pairs, in which ionic liquids and deep eutectic solvents are new absorbents, exhibit promising development potential. Through the coupling of heat and mass transfer within the cycle or the addition of sub-components, cycle configurations with higher energy efficiency and a wider range of operational conditions are greatly focused. Additives, ultrasonic oscillations, and mechanical treatment of heat exchanger surfaces efficiently enhance heat and mass transfer in the absorbers and generators of ART. Notably, nanoparticle additives and ultrasonic oscillations demonstrate a synergistic enhancement effect, which could significantly improve the energy efficiency of ART. For the conventional NG and H2 liquefaction processes, the energy-saving and carbon emission reduction potential of ART is analyzed from the perspectives of specific power consumption (SPC) and carbon dioxide emissions (CEs). The results show that ART integrated into the liquefaction processes could reduce the SPC and CE by 10~38% and 10~36% for NG liquefaction processes, and 2~24% and 5~24% for H2 liquefaction processes. ART, which can achieve lower precooling temperatures and higher energy efficiency, shows more attractive perspectives in low carbon emissions of NG and H2 liquefaction.

A natural gas liquefaction and liquid recovery sequence is proposed for top-side offshore floating liquefied natural gas processing. During liquefaction, a single mixed refrigerant is separated into heavy and light key components, separately compressed after the main cryogenic heat exchanger and then mixed again to make a single mixed refrigerant. The proposed liquefaction cycle has a simple, compact structure and is suitable for power-efficient, offshore, floating liquefied natural gas liquefaction. The natural gas liquid recovery process employs space- and energy-efficient dividing wall columns for the integration of depropanization and debutanization. The columns were optimized by response surface methodology. A compact top dividing wall column configuration could reduce total annual costs. A combined process integrating natural gas liquefaction and liquid recovery is finally proposed.

The increasing demand for primary energy leads to a growing market of natural gas and the associated market for liquefied natural gas (LNG) increases, too. The liquefaction of natural gas is an energy- and cost-intensive process. After exploration, natural gas, is pretreated and cooled to the liquefaction temperature of around −160°C. In this paper, a novel concept for the integration of the liquefaction of natural gas into an air separation process is introduced. The system is evaluated from the energetic and exergetic points of view. Additionally, an advanced exergy analysis is conducted. The analysis of the concepts shows the effect of important parameters regarding the maximum amount of liquefiable of natural gas and the total power consumption. Comparing the different cases, the amount of LNG production could be increased by two thirds, while the power consumption is doubled. The results of the exergy analysis show, that the introduction of the liquefaction of natural gas has a positive effect on the exergetic efficiency of a convetional air separation unit, which increases from 38% to 49%.

Liquefaction of natural gas and simulated process optimization – A review

Natural gas liquefaction using the high-pressure potential in the gas transmission system

Natural gas, even more biogas, comply with this requirement but gas wells in the most areas are rather economically not accessible due to infrastructural or legislative requirements. The demands of small-scale module natural gas liquefaction plant have been gained considering attentions in recent years. In natural gas liquefaction plant, the core heat transfer equipment - efficient heat exchanger design and cold box systems integration technology promote the system design more compact and efficient. However, traditional plate-fin heat exchanger that be widely adopted as the core heat exchanger has strict purification standard definition, <50ppm for CO2 and <10ng/Nm3 for mercury, to prevent carbon dioxide (CO2) freezing and mercury corrosion inside aluminum material heat exchanger, which cause pretreatment system to large dimension and high cost. In this paper, a novel cold box with brazed plate heat exchangers (BPHE) for small-scale module LNG plant is proposed and designed. Firstly, the methane (CH4) /CO2 gas mixture cooling-down process are experimental conducted in a typical BPHE. The influences of carbon dioxide concentrations on solid precipitation from room temperature to liquid CH4 temperature are investigated, considering the flow resistance and heat transfer efficiency for natural gas liquefaction process. The maximum allowable carbon dioxide concentrations without clogging the flow channel of the plate heat exchanger and deteriorating the heat transfer efficiency under different pressures (2.5-5.5MPa) during the cooling process are obtained. Based on the research results, an optimized technology package of the cold-box has been designed and fabricated to achieve the practical application in a small-scale skid-mounted natural gas liquefaction process including cryogenic CO2 separation. First results and further optimization points will be discussed as well.

Liquefied natural gas (LNG) has become an important part in the energy industry on account of its high energy density, low carbon emission, and convenient transportation. In recent years, with the discovery of unconventional natural gas resources, the situation of the world’s natural gas liquefaction plants using conventional natural gas as feedstock is changing. Unlike traditional LNG plants, unconventional natural gas liquefaction processes require special considerations in design and manufacturing. This review summarizes and analyzes the characteristics and differences of several typical unconventional natural gas liquefaction processes compared to traditional natural gas liquefaction processes, including coalbed methane liquefaction, synthetic natural gas liquefaction, LNG-FPSO, and PLNG (pressurized liquefied natural gas). Moreover, a state-of-the-art review of the recent progress on design and optimization of unconventional natural gas liquefaction processes is presented.

Simulation based Heuristics Approach for Plantwide Control of Propane Precooled Mixed Refrigerant in Natural Gas Liquefaction Process

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 23261, ’Development of CO2-Tolerant LNG-Production System,’ by JungHan Lee, Jeheon Jung, and Kyeongmin Kim, SPE, Daewoo Shipbuilding and Marine Engineering, prepared for the 2012 Offshore Technology Conference, Houston, 20 April-3 May. The paper has not been peer reviewed. During natural gas liquefaction, CO2 must be removed to prevent icing and plugging in the system. The CO2-removal system may be the most important part of the gas-treatment system. CO2 removal systems require complicated amine contactor and regeneration systems with substantial heat sources. The CO2-tolerant natural-gas-liquefaction system called cluster liquefaction accepts approximately 1% of CO2 for the liquefaction and related systems. The CO2-tolerant characteristics of this liquefaction process will provide a multifold safety margin against CO2 problems in cryogenic systems and valves. CO2-Tolerant Liquefied-Natural-Gas (LNG) Production System Considerations. Natural gas liquefaction at higher pressures and equivalent higher liquefaction temperatures has the advantages of reducing liquefaction energy and adopting more-efficient refrigerant. Despite the advantages, the higher-pressure storage requirement for the produced LNG has been a cost burden in overall LNG chains. For that reason, natural gas liquefaction at higher pressures has not been adopted by the industry. The specific weight ratio (SWR) of natural gas, defined as the natural gas weight divided by the containment system weight, is an important indication of capital expenditures. The typical SWR of conventional LNG is approximately 10–20 times that of compressed natural gas (CNG). Even for the increased- pressure LNG, the SWR is typically 10 times that for CNG. Hence, storage as a liquid after cooling and insulation is far more efficient than CNG. For increased-pressure LNG, the main cost contributor has been the cryogenic material for the higher pressure. However, if a cost-effective solution for increased-pressure containment is developed, it may become a viable option. Examples. Intermediate-Pressure LNG (20 bara, 1% CO2). Substantial CO2 can be dissolved in LNG produced at increased pressure. CO2 in the LNG should be liquid, not solid or as two phases. During cool down at a predetermined pressure, the feed gas can pass through the solid formation region in the interim stage. Hence, this region should be avoided by liquefying the natural gas at a higher pressure before reducing the pressure. If the CO2 level is sufficiently lowered during the gas treatment, the solid formation can be avoided regard-less of the liquefaction temperatures and processes.

Design optimization of single mixed refrigerant LNG process using a hybrid modified coordinate descent algorithm