Low Temperature Section Research Articles

Study on the effect of valve openings and multi-stage throttling structures on the pressure and temperature during CO2 pipeline venting processes

The venting operation is an important measure for rapidly eliminating the risk of overpressure in CO2 transportation pipelines. However, the low-temperature phenomenon and vibration generated by the rapid discharge can affect structural reliability. Multi-stage throttle structures have been proven to effectively alleviate vibration phenomena, but their impact on low temperatures remains unclear. In this study, venting tests were conducted on eight groups of single-stage and two-stage throttle structures based on a large-scale pipeline. The results indicate that the nonlinear variation of the valve resistance coefficient when the valve opening changes is the fundamental reason affecting the downstream temperature. Two-stage throttle structures can effectively mitigate the low-temperature conditions in certain spaces within the pipeline. For the remaining low-temperature sections, three-stage throttle structures can provide effective compensation. However, this significantly reduces the pressure drop rate in the main pipeline, contradicting the original purpose of the venting operation. Additionally, considering the temperature of the throttle structure and the pressure within the main pipeline, this study recommends increasing the valve openings for the two-stage throttle structure. The results of this study provide important references for the design of throttle structures and the formulation of on-site venting schemes, with strong prospects for engineering applications.

Soret effect on the mixing of H2 and CO2 cushion gas: Implication for underground hydrogen storage

For underground hydrogen storage (UHS), hydrogen (H2) injection and withdrawal will create a temperature difference between the wellbore and the reservoir. The thermal diffusion driven by the temperature gradient (Soret effect) may enhance the mixing between H2 and cushion gas and affects the purity of the produced H2. In this work, the thermal diffusion process of H2 and CO2 under reservoir conditions is quantitatively observed for the first time. Results show that the Soret effect drives H2 accumulation in the high-temperature region, and is influenced by temperature, pressure, and concentration. There is significant concentration difference between the high- and low-temperature sections when minor quantities of gas are injected. From experimental observations, we obtain the Soret coefficients across different physical conditions and propose a correlation for their prediction. Additionally, while thermal diffusion slows down in porous reservoirs, the concentration difference established along the temperature gradient remains unchanged at steady state.

Kinetics and H2O Influence on NOx Trapping and Selective Catalytic Reduction over Ce/Pd Doping Catalyst.

In this paper, the removal effects and activation energy of Ce and Pd doping on pollutants (CO, C3H6, and NO) were comparatively analyzed by using characterization methods and constructed kinetic equations. Furthermore, the problems of the water influence mechanism on the NSR process were also discussed. The results show the following: (1) Pd doping effectively improves the removal of CO (80%) and C3H6 (71%) in the low-temperature section of the catalyst (150-250 °C) compared to Ce doping, while Ce doping exhibits excellent low-temperature conversion of NO. (2) The reaction activation energy of the LaKMnPdO3 catalyst was 9784 kJ/mol, which was significantly lower than that of the LaKMnCeO3 catalyst. (3) The presence of H2O has an important enhancement effect in the storage performance of the LaKMnPdO3 catalyst for NOx but decreases the catalytic reduction of NO. It provides a solution for the effective treatment of the increasing problems of particulate matter and ozone pollution.

Performance and mechanism of low-temperature NH3-SCR denitrification over Mn/CePO4-SiO2 catalysts

Preparation of low-temperature NH3-SCR catalysts by Si and Mn modification and Si and Mn co-modification of CePO4 catalysts using mixed roasting and hydrothermal methods. XRD,BET,SEM and other characterisation tools were used to investigate the effect of Si and Mn modification on the catalyst structure. A series of different Si and Mn loadings and changes in catalyst denitrification performance, sulfur and water resistance after co-modification with Si and Mn were tested using NH3-TPD, H2-TPR and XPS, and the reaction pathways were investigated and the reaction mechanism of the catalysts was explored by FTIR detection in situ. The results show that CePO4-SiO2 catalyst at 250℃∼400℃, denitrification rate of about 90%; The optimum temperature for denitrification activity of the Mn/CePO4 catalyst was reduced, with a denitrification rate of 82% at 150℃; Mn/CePO4-SiO2 catalyst denitrification activity with significantly lower temperature and wider range. The denitrification rates of the catalysts were greater than 90% at 50℃∼300℃, with an optimum denitrification rate of 95 % at 150℃. The N2 selectivity of the catalyst is greater than 95 % in the low temperature range (below 200℃), good resistance to sulfur and water. The CePO4, SiO2 diffraction peaks on the surface of the sample decreased under the combined effect of Si and Mn. More acid sites appeared on the surface of the catalyst with elevated ratios of Ce3+ and adsorbed oxygen Oα, which promoted the catalyst's oxygen migration and conversion ability. After Si modification, the proportion of Mn4+ was significantly increased, which promoted the redox cycling of the catalyst in the low-temperature section. In situ IR results show that the catalyst follows both the Eley-Rideal mechanism and the Langmuir-Hinshelwood mechanism at 150℃. A variety of nitrate species produced by NO adsorption of the Si and Mn co-modified samples reacted rapidly with NH4+ species adsorbed at the Brønsted acid sites, which favoured the NH3-SCR reaction on the catalyst surface and improved the low-temperature denitrification efficiency.

Two-stage gasification process simulation and optimization of pulverized coal for hydrogen-rich production using Aspen plus

This study proposed a two-stage gasification (TSG) process of pulverized coal to allow for hydrogen-rich (HR) production. The balance flow of this process is constructed using Aspen Plus software. Gasification pressure (GP), steam-coal ratio (SCR), and oxygen-coal ratio (OCR) influences on the process are studied, and the operating conditions are optimized to achieve the maximum hydrogen production. The results show that the GP mainly affects the pyrolysis of pulverized coal in the low-temperature section. Reducing the GP is conducive to hydrogen production. However, it requires heat supplement to raise temperature and maintain the balance of the system. An increase in the SCR is better for hydrogen production, leading to a decrease in the gasification temperature. When the SCR is higher than 0.3, the steam utilization rate decreases obviously. With an increase in the OCR, the gasification temperature continues to increase, and hydrogen production first increases and then decreases, reaching its peak at approximately 0.5. The optimal parameter combination is as follows: the SCR is 0.3; the OCR is 0.53; water is used as the medium for temperature regulation uses, and the water supply is 0.12 kg/kg coal; oxygen is used to raise the temperature of the low-temperature section, and the oxygen supply is 0.18 kg/kg coal. The hydrogen production rate of the optimal working condition is 77.78 g/kg coal, which is 48.38% higher than that of single-stage gasification.

Distribution and Quasi-Simultaneous Measurement of Room-Temperature, High-Temperature, and Low-Temperature Sections Using a Single Optical Fiber with BOCDR

Distribution and Quasi-Simultaneous Measurement of Room-Temperature, High-Temperature, and Low-Temperature Sections Using a Single Optical Fiber with BOCDR

Mechanism of cordierite formation obtained by high temperature sintering technique

Cordierite (2MgO·2Al2O3·5SiO2) is a kind of important ceramic with low thermal expansion coefficient and low dielectric constant. In this study, the influence of raw material compositions and various sintering temperatures on the synthesis mechanism and reaction path of cordierite were studied. The results reveal that the binary compounds forsterite and magnesia-alumina spinel are firstly generated in the low-temperature section while using pure single oxide materials. Then, forsterite and magnesia-alumina spinel are respectively combined with Al2O3 and SiO2 to form cordierite. The reaction of magnesia-alumina spinel with SiO2 to form cordierite requires a higher temperature. The addition of CaO and TiO2 tends to form low melting point substances, thus promoting the formation of cordierite phase. This study has a certain guiding significance for the cordierite synthesizing from natural minerals and solid wastes.

Thermodynamic analysis of the Chemical Looping Electricity Storage system incorporating an electric heater

Chemical Looping Electricity Storage system is a new energy storage approach with satisfactory thermal efficiency and high capacity density, especially when the material with high decomposition temperature is selected as the storage medium. In this study, two CLES systems, one using an electric heater directly, the other using a compressor and an electric heater, were investigated. A comprehensively analysis were performed from the perspectives of first and second laws of thermodynamics. The feasibility of the system configuration, as well as the round-trip efficiency and exergy destruction of each part under different operation temperatures were determined. Finally, the approaches to further improving the round-trip efficiency were discussed. Results show that for the CLES system using an electric heater and a compressor for heating, the increase in the charge temperature will increase the exergy destruction rate of the electric heater and reduce the round-trip efficiency. The operating temperature range and the round-trip efficiency can be improved by placing two reactor vessels in series for charge and parallel for discharge. For the CLES system direct heating with an electric heater, the efficiency in the low temperature section is extremely low, and the exergy loss caused by heat removal during discharge can be up to 8.9 %. Multi-stage compression intercooling or isothermal compression can be used during discharge to reduce this loss and increase the round-trip efficiency by 8.2 %–16.3 %.

Characteristics of Hydrothermal Carbonization Hydrochar Derived from Cattle Manure

The characteristics of hydrothermal carbonization hydrochar derived from cattle manure including excrements and lignocellulosic biomass were analyzed. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures in the range of 180~240 °C. The hydrochars were evaluated with respect to their usefulness as renewable fuels via physicochemical analysis and pyrolysis processes. As reaction temperatures increased, the fractions of fixed carbon in proximate analyses, carbon elements in ultimate analyses, and higher heating values of hydrothermally carbonized biochars increased in correlation with the primary reactions of coalification. Various correlations were derived with the characteristics of hydrochars in order to be utilized for operating and designing HTC reactors for cattle manure. The correlation between the O/C and H/C ratios was deduced on the basis of a van Krevelen diagram. The interaction equation was represented with the increased fraction of HHV compared to the reaction temperature of hydrothermal carbonization. The ultimate correlation for the estimation of higher heating values was suggested for HTC hydrochars. Moreover, the pyrolysis characteristics and kinetic parameters of the cattle manure and hydrochar were deduced by utilizing a multi-step kinetic model scheme. As the HTC reaction temperature increased, the global activation energy and the pre-exponential factors of hydrochars decreased in the low-temperature section and increased in the high-temperature section.

Термоактиваційний аналіз температурної залежності твердості квазікристалів системи Al—Cu—Fe

The results of thermoactivation analysis of the temperature dependence of hardness for icosahedral quasicrystals (QC) of the Al—Cu—Fe system obtained as a coating, massive compact and ingot are presented. QC as well as covalent crystals at room temperature are brittle without signs of macroplastic deformation at standard methods of mechanical testing and only the method of local indenter loading makes it possible to deform QC to significant degrees of deformation without fracture. In the studied temperature range 77—1073 K, the HV(T) hardness dependences have the same character, despite the state in which the QC was obtained. The HV(T) dependence consists from two sections: an athermal low-temperature section (77—600 K) and a section (>600 K) where the hardness decreases sharply with increasing temperature. The presence of a low-temperature athermal section on the HV(T) dependence is explained by the phase transition of the QC to a more plastic approximant phase. Phase transition of this type can be associated with a high density of phason defects, which are formed during the deformation of the QC that leads to violations of the atomic structure. Based on the experimental data of the temperature dependences of the Vickers hardness (HV) obtained by the authors and the literature data, the values of the activation energy of the dislocation motion U and the activation volume V of a number of icosahedral quasicrystals were calculated. It is shown that the value of U  0,97—1,83 eV, and V is (65—132)∙10-24cm3. Previously, the method of thermoactivation analysis of tempera¬ture dependence of a flow stress was applied to materials with different crystal structures (BCC, FCC metals, covalent crystals, refractory compounds, intermetallics, high entropy alloys). In comparison with crystalline materials, the values of thermal activation parameters of the deformation process for QC are close to refractory compounds (carbides, borides) which have a covalent component in the interatomic bond. Keywords: quasicrystals, activation energy of dislocation motion, activation volume, hardness, temperature.

Effect of h-BN addition on thermo-physical properties and phonon mechanisms of C/C-BN composites

C/C-BN composites containing different contents of h-BN particles were prepared by chemical vapor infiltration (CVI), presenting different microstructures and pyrolytic carbon (PyC) textures. The effects of different microstructures and PyC textures on the thermo-physical properties and their phonon mechanisms at 30–900 °C were investigated. The temperature dependence of heat capacity follows Debye's phonon theory, especially in the low-temperature section (30–300 °C) and the temperature dependence of thermal conductivity is determined by heat capacity and mean free length of phonon. Due to the higher texture of h-BN and regenerative laminar PyC (ReL-PyC), h-BN addition causes higher Debye temperature (ΘD) and high sensitivity of thermal conductivity to temperature. Besides, h-BN addition significantly changes the microstructure of composites such as pore structure, PyC morphology, crack distribution and fiber/PyC interface bonding state, causing the transformation of thermal conductivity from anisotropy to isotropy. Finally, based on the different microstructures of composites, the microstructure model and thermal resistance formulas of composites were established and coincident with the experimental results.

The electric transport properties of iridate Sr2-x Bi x IrO4 and Sr2-y Dy y IrO4

Sr2IrO4 is predicted to be a new superconductor in theory, and its electric transport properties have attracted much attention in the field of physics. Here we prepared a series of polycrystalline samples doped with Sr2-xBixIrO4 (x=0,0.02,0.04,0.06,0.08) and Sr2-yDyyIrO4 (y=0,0.02,0.04,0.06) respectively. The influence of the two ions on the lattice structure and electronic structure after the substitution of the Ir site is very similar, which makes the overall reduction trend of IrO6 octahedron and Ir-O1-Ir bond angle. The resistivity shows a non-monotonic change with doping and still maintains the insulation. The low-temperature section, medium-temperature section, and high-temperature section conform to three-dimensional variable range hopping (3D-VRH), thermal activation model, two-dimensional weak localization model respectively.

Experimental study on the interface shear performance of elastic polyurethane concrete–steel plate

The delamination and sliding failure of steel bridge deck pavements occur frequently due to insufficient shear resistance between their interface. Adopting an elastic polyurethane concrete (EPUC) bridge deck pavements can solve this problem. In this study, an interface shear experiment was conducted to investigate the interface shear performance of the EPUC–steel plate, in which 108 EPUC–steel plate composite specimens were divided into 36 groups. The emphasis of the research was to establish the interface failure mode, the shear stress–shear deformation curves characteristics and the constitutive model. Then, the impacts of temperature, loading rate and hygrothermal aging factors on the interface shear strength were determined. Test results showed that the interface failure mode was in the form of adhesion failure at the low-temperature section (−20 °C, −10 °C, 0 °C and 10 °C), mixed failure at 25 °C and 45 °C, and cohesive failure at 70 °C. The interface failure mode was changed from mixed failure to cohesive failure after hygrothermal aging. The shear stress–shear deformation curves at the low-temperature section, 25 °C and after hygrothermal aging exerted a two-stage development law, which could be described by an exponential function. Meanwhile, the curves at the high-temperature section (45 °C, 70 °C) exerted a three-stage development law, which can be described by the Popovics model. The interface shear strength decreased with the increase in temperature, whereas the interface shear strength remained at a high level at the high temperature. At the low-temperature section, the interface shear strength increased with the rise in shear rate, depicting a linear relationship. In the normal and high-temperature sections, the interface shear strength firstly increased and then decreased with the rise in the shear rate, depicting a quadratic parabolic relationship. The interface shear strength decreased with the increase in aging. Within the same age, the higher the temperature, the greater decrease in interface shear strength.The research results can provide experimental and theoretical support for the popularization and application of EPUC bridge deck paving materials.

A current reference with wide temperature operation range and low temperature drift

This work introduces a current reference with wide temperature operation range and low temperature drift, which can be used in high-performance intelligent power driver ICs. The core idea of the design is to use the non-linear characteristics of the drain current of MOSFET working in the sub-threshold region to realize the compensation of the reference current in low temperature and high-temperature section, then to reduce the fluctuation of reference current in the whole temperature range (TR). Compared with conventional structures, the temperature drift coefficient of this design is reduced by one order of magnitude. The proposed circuit is designed and verified under a 0.18 μm BCD technology, which occupies a footprint of about 0.085 mm2. Measured data shows that the output reference current at 1 μA has a temperature coefficient of 53.5 ppm/℃ during TR of −40–150℃.

Volume dependent fracture energy and brittle to quasi-brittle transition in intermetallic alloys

Intermetallic alloys such as titanium aluminide (TiAl) are lightweight with superior specific strength and high temperature oxidation resistance. They have a potential to replace heavier nickel based super alloys in low pressure high temperature sections of an aero engine. To facilitate an industry wide implementation, it is however indispensable to develop physically accurate computational methods which account for key deformation and fracture mechanisms. This assists the virtual prototyping required for the new product development using TiAl alloys. In this work, the quasi-brittle and volume dependent behavior of TiAl alloys is experimentally and numerically investigated. A total number of 29 geometrically identical TiAl specimens of three different sizes are tested in a three-point bending setup to investigate the volume dependence of fracture properties. In addition, three compact tension tests with identical specimen geometries are performed to analyze brittle to quasi-brittle transition and a switch in failure mechanism. Since the material fracture is observed to be preceded by plasticity, a theoretical and numerical framework of phase field ductile fracture which accounts for both elastic and plastic work densities is applied. The averaged fracture energy density for each test is evaluated numerically which is found to be lower for larger volumes. The work concludes with the proposal of an empirical law relating the fracture energy density with the specimen volume. Data from literature for different classes of materials is used for validation of the proposed empirical law. The mechanisms of transition from brittle to quasi-brittle fracture are investigated on the basis of local stress triaxiality in three-point and compact tension simulations.

Assessment of the efficiency of the use of activating turbulent jets to eliminate the risk of the formation of unventilated zones in large premises

Strict requirements for microclimate parameters are imposed on food storage premises, which are equipped with artificial cooling systems. The experience of operating the refrigerated premises revealed the following disadvantages: uneven distribution and significant fluctuations in temperature and relative humidity; periodic precipitation of condensate in low-temperature sections. Elimination of the noted disadvantages is effectively achieved by using axial fans that form a swirling air stream that induces the ambient air. Swirling jets used to intensify the process of air circulation in a room in order to eliminate unventilated zones will be called activating jets. To assess the efficiency of the application of activating turbulent jets, an integral method based on the energy balance was used. Using the example of a representative object, it is shown that the distance of the effective application of an activating turbulent jet should be calculated taking into account the influence of environmental turbulence, which is determined by the amount of energy introduced and dissipated in the room.

Thermodynamic analysis of the heat pump steam system with medium-low temperature heat source

Heat Pump Steam technology driven by electric power has an important application value in the industrial thermal field. A cascade air source heat pump steam system (CASGHP) using in thermal workshop is proposed in this paper. A numerical model is established by EES software. The thermal performances of several feasible refrigerants in the cascade system are analyzed comparatively. The influences of intermediate cooling temperature (Tintc), the injection temperature (Tinje), the evaporating temperature (Tevap), the outlet steam temperature (Tout), gas-injection ratio (βg) and specific rate of compressors pressure ratio (PRR) on system power consumption of generating a ton steam (Wper) and system COP are studied. The conclusions are as follows: When R134a is used in low temperature section of the cascade system, R245fa, R1234ze(Z) and R1336mzz(Z) used in high temperature section respectively can meet the requirements of steam generation. The COP of the CASGHP adopted R1234ze(Z) is the largest, followed by R245fa and R1336mzz(Z). There exists a maximum COP, which is 2.268, 2.286 and 2.211, respectively. When Tevap is 10 °C and Tout is 120 °C, the optimal Tintc of CASGHP with these high temperature refrigerants is 53 °C, 50 °C and 53 °C, the optimal Tinje is 79 °C, 78.5 and 85.5, the optimal βg is 0.207, 0.18 and 0.165, and the optimal PRR is 0.77, 0.71 and 0.972, respectively. The COP increases by 18.4%, 18.2% and 17.9% respectively when Tevap increases from 10 °C to 30 °C, but it decreases by 14.4%, 14.2% and 10.2% respectively when Tout increases from 100 °C to 120 °C.

Study on NH3-SCR performance and mechanism of Fe/Mn modified rare earth concentrate

• In this paper, a green, environmentally friendly and efficient NH3-SCR catalyst was prepared using rare earth minerals. • This paper explores the relationship between transition metals Fe, Mn and rare earth concentrates and their influence on the catalytic performance of NH 3 -SCR. • In this paper, the synergistic catalytic reaction process between Ce, Fe and Mn on the surface of rare earth concentrates is explored. In this paper, the transition metals Fe and Mn are doped on the surface of rare earth concentrates by the impregnation method to prepare NH 3 -SCR catalyst active powder. SEM, XRD, BET, XPS, H 2 -TPR, NH 3 -TPD, NO-TPD, FTIR and other characterization methods are used to explore the surface properties and mechanism of rare earth concentrates doped with transition metals, and at the same time determine its catalysis in a simulated flue gas device performance. The results showed that the NO x conversion rate of Fe and Mn doped rare earth concentrates reached 94.8% at 200 °C. The specific surface area of the rare earth concentrate increases after Fe and Mn are doped. Fe and Mn are uniformly dispersed on the surface of the rare earth concentrate. The combined effect of Fe, Mn and the rare earth concentrate provides more weak acid sites for the reaction and promotes desorption of NO in the low temperature section. The redox performance of rare earth concentrates has also been greatly improved. Rare earth concentrates doped with Fe and Mn mainly follow the L -H mechanism in the low temperature section, and mainly follow the E-R mechanism in the high temperature section. In general, the introduction of transition metals Fe and Mn effectively improves the NH 3 -SCR catalytic activity of rare earth concentrates, and the rare earth concentrates themselves have good resistance and tolerance, which is useful for preparing NH 3 -SCR catalysts from natural minerals. It has important theoretical significance and practical value, and at the same time has a pioneering role in the application of Baiyun Obo rare earth minerals in industrial production. In this paper, the transition metals Fe and Mn are doped on the surface of rare earth concentrates by the impregnation method to prepare NH 3 -SCR catalyst active powder. SEM, XRD, BET, XPS, H 2 -TPR, NH 3 -TPD, NO-TPD, FTIR and other characterization methods are used to explore the surface properties and mechanism of rare earth concentrates doped with transition metals, and at the same time determine its catalysis in a simulated flue gas device performance. The results showed that the NO x conversion rate of Fe and Mn doped rare earth concentrates reached 94.8% at 200℃. The specific surface area of the rare earth concentrate increases after Fe and Mn are doped. Fe and Mn are uniformly dispersed on the surface of the rare earth concentrate. The combined effect of Fe, Mn and the rare earth concentrate provides more weak acid sites for the reaction and promotes desorption of NO in the low temperature section. The redox performance of rare earth concentrates has also been greatly improved. Rare earth concentrates doped with Fe and Mn mainly follow the L-H mechanism in the low temperature section, and mainly follow the E-R mechanism in the high temperature section. In general, the introduction of transition metals Fe and Mn effectively improves the NH 3 -SCR catalytic activity of rare earth concentrates, and the rare earth concentrates themselves have good resistance and tolerance, which is useful for preparing NH 3 -SCR catalysts from natural minerals. It has important theoretical significance and practical value, and at the same time has a pioneering role in the application of Baiyun Obo rare earth minerals in industrial production .

Porous Ni-Cr-Mo-Cu alloys fabricated by elemental powder reactive synthesis

Fabrication of porous Ni-Cr-Mo-Cu alloys is available through Ni, Cr, Mo and Cu elemental powder reactive synthesis at the sintering temperature of 1150 °C. The pore structures, including swelling behavior, open porosity, pore size and viscous permeability of the porous Ni-Cr-Mo-Cu alloys are systematically investigated. The results revealed that the parameters of pore structure firstly increased, and then decreased with the increase of the sintering temperature. When the sintering temperature rose to 1000 °C, the volume expansion, open porosity and viscous permeability of porous Ni-Cr-Mo-Cu alloys reached the peak value of 8.0%, 41.6% and 17.2 μm2, respectively. In addition, it was confirmed that the pore structure evolution was based on three stages, that is, in the low temperature section before stearic acid decomposition, the formation of pores was initiated by the volatilization of pore-forming agent and the interstitial pores of green compact; when the temperature was lower than 1083 °C, the increase of open porosity was mainly due to the Kirkendall effect caused by solid partial diffusion; while, when the temperature is within the range of 1083 ∼ 1150 °C, the shrinkage behavior at high temperature and a small amount of metal solution formed by the unreacted Cu led to decrease in pore structure parameters.

Design and optimization of integrated single mixed refrigerant processes for coproduction of LNG and high-purity ethane

Abstract In this study, two novel integrated single mixed refrigerant (SMR) processes are proposed to coproduce liquefied natural gas (LNG) and high-purity liquid ethane, which are suitable for improving the economic benefits of high ethane-containing natural gas. In Process 1, cryogenic distillation and conventional SMR process are integrated to separate ethane while producing LNG. Since the distillation pressure is below the critical pressure of methane, heat transfer temperature difference in the low temperature section may be relatively large. Therefore, in Process 2, the pressure of natural gas is increased by adding a compressor after the distillation column. Aspen HYSYS is used to simulate the proposed processes, and the key parameters of the refrigeration cycles are optimized by genetic algorithms. Based on the comprehensive consideration of initial investment and operating cost, Process 2 is recommended for large-scale plant, while Process 1 for small-scale plant and situations with requirement of simple system, for example floating LNG production (FLNG). Furthermore, a simplified Process 1, with propane eliminated from the mixed refrigerant, is presented for better adaption to FLNG conditions.