•The CO2 in pressurized flue gas of LNG-fired power plant is recovered cryogenically.•The cold energy needed is supplied by both flue gas expansion and LNG gasification.•The CO2 cryogenic capture system does not require excessive gasification of LNG.•The CO2 capture rate may reach 90% or higher at temperature −140 °C or lower.In the present paper, a CO2 cryogenic capture for flue gas of an LNG-fired power generation system is proposed, in which LNG cold energy can be fully utilized during the gasification process. First of all, the flue gas is compressed to facilitate the CO2 solid formation and separation. Sequentially, the CO2-removed flue gas expands to supply most of the cold energy needed for the cryogenic process. In comparison with traditional CO2-capture systems in LNG-fired power generation cycle, the new system does not require gasifying excessive amount of LNG. Based on the HYSYS simulation, the CO2 capture pressure and temperature are investigated as the key parameters to find the appropriate working conditions of the CO2-capture system. The results show that the system can achieve a 90% CO2 recovery rate or higher if the flue gas temperature can be lowered to less than −140 °C.

•Synthetic natural gas (SNG) liquefaction processes with H2 separation are proposed.•H2 separation must be adopted with liquefaction to ensure little H2 in liquefied SNG.•H2 separation ways by flash, distillation or a combination of both are analyzed.•Processes with distillation may yield LNG product with H2 content below 0.01%.•The process with combined H2 separation consumes less energy than the others.The fact that synthetic natural gas (SNG) contains hydrogen has a great impact on its liquefaction process. Aiming to produce liquefied natural gas (LNG) from SNG, hydrogen separation from SNG through cryogenic processes is studied. A new separation method combining distillation and flash is developed, resulting in higher liquefaction rate than that of distillation under same operating parameters. Process simulations are performed by combining one liquefaction part (a nitrogen expansion process or a mixed refrigerant one) and one distillation part (direct flash, atmospheric distillation, pressurized distillation or the new separation method). Compared to direct flash, distillation can reduce the hydrogen content of products to a very low level, increasing the temperature of products by 8 °C and reducing the unit power consumption by 3%; and, compared to the other three separation ways, the new separation method reduces the unit power consumption by 7–10%. Both nitrogen expansion and SMR liquefaction processes can be integrated with hydrogen separation, but power consumptions for SMR processes are less than those for nitrogen expansion ones.

•A seawater desalination prototype system utilizing LNG cold energy is developed.•R410a is chosen as the secondary refrigerant for heat transfer of LNG and seawater.•A flake ice-maker is adopted to produce desalinated ice from seawater.•The LNG cold energy utilization efficiency may reach 2 kg (fresh water)·kg (LNG)−1.•The one-cycle salt removal rate is about 50%, not enough to produce drinking water.The freeze desalination method is not being used widely, since it needs refrigeration system that consumes much electricity. On the other hand, liquefied natural gas (LNG) releases a lot of cold energy during its vaporization process. Thus, combining the two processes of LNG vaporization and seawater freezing may produce freshwater in an economical and environment-friendly way. In this paper, a seawater freeze desalination prototype system is designed and manufactured. In this system, R410A is chosen as the secondary refrigerant to transfer cold energy from LNG to seawater, and a flake ice-maker is adopted to produce ice. Experiments are conducted with the prototype system, with liquid nitrogen as the cold source. The results show that the system is able to reach the designed fresh water capacity of 150 L h−1, with the converted cold energy efficiency above 2 kg (fresh water)·kg (LNG)−1. The salt removal rate of the system is about 50%, indicating that one cycle of the freeze desalination is not enough for producing drinking water. The influences of some key factors, such as refrigerant evaporating temperature, number of spraying nozzles at the water distributing disk, and seawater flowrate, on the salinity of the formed ice are also tested.

In published literature, only very limited data for CO2 frost point in natural gas mixture can be found. Measurements and calculations for CH4 + CO2/CH4 + CO2 + N2/CH4 + CO2 + C2H6 mixtures over a wide range of temperature, pressure, and compositions were performed in this work. The measurements were conducted through a simple equilibrium cell by static analytic method utilizing sampling technique. The calculations were carried out by fugacity balance model based on Peng–Robinson (PR) equation of state (EoS) with van der Waals mixing rule. The calculated results agree well with the experimental results, demonstrating the reliability of PR EoS based model. By comparing data obtained from gas mixtures with different nitrogen contents and ethane contents, it is found that both nitrogen and ethane have little effect on CO2 frost point. However, the maximum pressure for CO2 frosting in CH4 + CO2 + N2 ternary mixture increases with nitrogen content; oppositely, it decreases with ethane content in CH4 + CO2 + C2H6 ternary mixture.

Isothermal vapor–liquid equilibrium data for CH4/H2/N2 system are determined by an experimental apparatus based on the static analytic method at a temperature range from 100.0 K to 125.0 K, corresponding to pressure above atmospheric pressure up to 4.5 MPa. Meanwhile, GERG-2008 equation of state is used to calculate the vapor–liquid equilibrium data for CH4/H2/N2 ternary system with a good consistence. The maximum absolute liquid composition deviations are 0.0033 and 0.0011 for hydrogen and nitrogen, respectively. And the maximum absolute vapor composition deviations are 0.0869 and 0.0203 for hydrogen and nitrogen, respectively. In addition, Peng–Robinson (PR) equation of state is used to correlate the experimentally measured pressure–temperature–liquid phase compositions (p–T–xi) for CH4/H2 binary system to propose a temperature-dependent interaction coefficient kij for CH4/H2 system which improves the calculation accuracy in vapor–liquid equilibrium for mixtures containing hydrogen and methane.

•Liquefied natural gas can be produced from coke oven gas with acceptable energy cost.•Hydrogen content exerts a great influence on the performance of liquefaction process.•Liquefaction process integrated with H2 distillation separation consumes 10% lower.Coke oven gas (COG) is a by-product when producing coke from coal. Producing liquefied natural gas (LNG) is an efficient way of utilizing COG. The amount of hydrogen in COG affects liquefaction process significantly, because its thermal properties are quite different from the other compositions (methane, carbon monoxide, etc.) of COG. Based on nitrogen expansion liquefaction process, a series of liquefaction processes of COG containing different amount of hydrogen are simulated in this paper. It turns out that the hydrogen content exerts a great influence on the unit power consumption and the liquefaction rate of the processes. In order to ensure very low concentration of hydrogen in LNG product, distillation is added to the process. The processes with or without distillation are compared. Furthermore, for the processes with distillation, the liquefaction process is integrated with distillation separation of hydrogen to upgrade the quality of LNG. Simulations indicate that LNG can be produced by improved nitrogen expansion processes with acceptable energy consumption. The unit power consumption increases with the increase of hydrogen content of COG and the increase of the methane recovery rate. And the unit power consumption of the process with distillation is about 10% lower than that of process without distillation, when the methane recovery rate is fixed.

Coalbed methane (CBM) is an atypical natural gas that may contain a large amount of nitrogen in addition to methane. When liquefying such CH4/N2 mixtures, knowledge of solid solubility is very important and, in particular, CO2 solubility data are essential for determining the CO2 purification index. Although experimental data for CO2 solubility in pure methane are available for various conditions, such experimental data for CH4/N2 mixtures are rare. In this paper, a solid–liquid equilibrium experimental apparatus using a static-analytic method is described. Data for CO2 solubility in pure liquid methane were obtained and their accuracy was verified by comparison with published values. Solubility of CO2 in CH4/N2 mixtures with nitrogen molar fractions of 10, 30, 50, and 70% were then measured at cryogenic temperatures between −190 and −150 °C.

The objective of the present study is to analyze the heat transfer correlations of supercritical CO2 cooled in horizontal circular tubes. In the paper, heat transfer correlations are first reviewed and compared with the experimental data at different heat fluxes. The results show that most of the previous correlations agree well with the experimental data under lower heat flux, but fail to predict the heat transfer coefficient well when the heat flux is as high as 33 kW/m2. The study of buoyancy effect on convective heat transfer shows that buoyancy effect significantly affects the heat transfer with the increase of heat flux, and both free and forced convections operate in the turbulence flow during supercritical CO2 cooling process. The influencing factors on heat transfer coefficient are summarized and the new correlation can be developed with the four dimensionless numbers.

Accurate CO2 solubility data are crucial for putting a proposal of pressurized liquefied natural gas (PLNG) project into practice. A solid–liquid equilibrium (SLE) apparatus, which is based on the static–analytic method, has been set up to measure the solubility of carbon dioxide in saturated liquid CH4/CH4 + N2/CH4 + C2H6 in the pressure region from atmospheric up to 3 MPa, corresponding to the temperature region from (112 to 170) K. In addition, Peng–Robinson (PR) and Suave–Redlich–Kwong (SRK) equations-of-state (EOS) are selected to calculate the solubility of carbon dioxide in CH4 + N2 and CH4 + C2H6 mixtures, and the results are consistent with the experimental data in the whole region. Two temperature-dependent correlations for the interaction coefficients kij on CH4 + CO2 system are derived by the experimental data for PR and SRK EOS, which can improve the calculation accuracy of the binary and ternary solid–liquid phase equilibrium.

Cooling heat transfer to supercritical CO2 in a horizontal circular tube has been numerically investigated using CFD code FLUENT in the present study. The purpose is to provide detailed information on heat transfer behavior which is hard to be observed in experimental studies and to help to better understand the heat transfer mechanism. Simulation starts with five key issues, including physical model, mathematical models, mesh independency, boundary conditions and solution methods. The results demonstrate that almost all models are able to reproduce the trend of heat transfer characteristics qualitatively, and LB low Re turbulence model shows the best agreement with the experimental data, followed by standard k–ɛ model with enhanced wall treatment. After the validation, further studies are discussed on velocity and turbulence fields, buoyancy effect, and heat transfer mechanism. It concludes that buoyancy significantly affects the turbulent flow, and evidently enhances the cooling heat transfer of supercritical CO2, especially in the vicinity of pseudo-critical point. The mixed convection is the main heat transfer mechanism during supercritical CO2 cooling process.