Search

[Objective] Carbon capture, utilization and storage(CCUS) is an indispensable technology for achieving carbon neutrality,and CO2 pipeline transmission is a significant component of this technology. In the process of supercritical CO2 pipeline transmission,unintentional pipeline leakage or venting operations may cause localized low temperatures in the trunk pipelines and vent piping due to the strong throttling effect caused by CO2, resulting in dry ice that blocks the pipeline and makes it brittle. [Methods] In the study, the OLGA software was utilized to develop a high-pressure CO2 pipeline relief model. The simulation results obtained from the model were then compared against foreign experimental data. The comparative analysis indicated that the OLGA software provided relatively accurate calculations for pressure drop and tended to be more conservative in calculating temperature drop. These findings supported the software's suitability for performing calculations related to the design of CO2 pipelines. Building upon this foundation, a long-distance high-pressure CO2 pipeline venting model was established to simulate and analyze the effects of different valve openings, initial temperatures, and initial pressures on temperature decrease, phase state changes, and venting duration during the CO2 pipeline venting process. [Results] It was revealed that reducing the vent valve opening effectively prevented excessively low temperatures within the pipeline during venting. Under the venting simulation conditions selected for this study, 13.5% valve opening effectively prevented dry ice formation, and the valve opening below 4.5% could maintain the pipeline temperature at higher than-30 ℃. The venting process of the high-pressure CO2 pipeline exhibited low convective heat transfer intensity and significant temperature drops, predominantly observed away from the relief port. The initial temperature had a substantial impact on the temperature in the pipeline during venting. More specifically, a lower initial temperature resulted in a decrease in the temperature in the pipeline during venting, increasing the likelihood of dry ice formation. [Conclusion] Therefore, in engineering practice, it is crucial to focus on fuid temperature in sections far from the relief port along the trunk pipelines and automatically reduce the vent valve opening in response to temperature drops, aiming to slow down the temperature drop rate during the venting process. Special attention should be paid to protecting CO2 pipelines, especially when operating under low-temperature dense phase conditions.

[Objective] Pressure regulation systems, serving as one of the vital links between long-distance pipelines and urban gas pipeline networks, play a significant role in the successful implementation of the “Hydrogen Society” Program. However, the contrasting physical properties of hydrogen and natural gas impose challenges to the effectiveness of process control in pressure regulation. [Methods] This study employed a combined approach involving decompression and pressure regulation experiments conducted on pure hydrogen and hydrogen-enriched compressed natural gas(HCNG), along with dynamic simulations of pressure regulation. By establishing a foundation for assessing the pressure stabilization effect of the decompression and pressure regulation system, considering factors such as pressure stabilization accuracy, response time, and fitness function, a sensitivity analysis was performed to investigate the influence of various parameters, including hydrogen blending ratios, flow fluctuation cycles, downstream flow change ranges, pipeline transmission pressures, as well as proportional, integral, and derivative parameters(PID). [Results] The following results were obtained:(1) With more frequent disturbances, gas flow rates increased, leading to larger system fluctuation ranges. Consequently, achieving pressure stabilization became more challenging for the decompression and pressure regulation system. This finding highlighted the importance of restraining the movement of pure hydrogen and HCNG at high flow rates in transmission pipelines.(2) The flow rate of the pressure regulation system carried sinusoidal fluctuations. Setting the pressure stabilization accuracy at ±1.5% and the proportional and integral parameters within the range of 1 to 2, the decompression and pressure regulation experiments showed that the decompression and pressure regulation of pure hydrogen and HCNG could be substantially achieved within the required pressure range of urban gas pipelines.(3) Pure hydrogen exhibited greater instantaneous fluctuations compared to natural gas when flowing through pipelines at identical rates of transmission.As a consequence, the response time and adaptability function of the control system gradually increased with higher hydrogen blending ratios. Moreover, the instantaneous pressure fluctuation of pure hydrogen reached 1.15 times that of pure methane, resulting in a response time and adaptability function of the control system that increased to 1.13 and 2.68 times those of pure methane, respectively. Under the same proportional and integral parameters, it was more challenging to maintain the pressure stabilization for the hydrogen-containing gas. Hence, decreasing the integral parameter or increasing the proportional parameter proportionally to the hydrogen blending ratio is recommended, to attain the same or even better pressure stabilization effect as observed in natural gas scenarios. [Conclusion] The research findings provide theoretical insights to guide the pressure regulation practices of pipelines carrying pure hydrogen and HCNG.

Small-scale devices of liquefied natural gas (LNG) have been widely applied in the natural gas industries, especially for stranded gas production. As the key equipment of LNG plants, the performance of the spiral wound heat exchanger (SWHE) influences operating costs, reliability and safety of the whole system. In order to obtain the accurate two-phase tube-side heat transfer model for small-scale LNG SWHE and analyze its thermal performance, an experimental device of dual mixed refrigeration (DMR) is constructed. A multi-phase multi- -stream calculation code for SWHE is developed to solve the energy balance equations among tube-side feed gas, tube-side refrigerant and shell-side refrigerant, based on experimental results and thermal property calculation. The results show that the homogeneous flow model can be applied to two-phase tube-side heat transfer calculation of feed gas and Bell and Ghaly’s model and Shah’s model can be both applied to the mixed refrigerant. The relative errors between the results of the experiment and program are all within the range of ±12%.

Pressurized liquefied natural gas (PLNG) is a new natural gas liquefaction solution proposed in recent years for reducing the construction and operating costs of floating liquefied natural gas (FLNG). For natural gas, the liquefaction temperature is strongly influenced by the pressure; when the pressure increases, the liquefaction temperature of natural gas increases accordingly. The increase in the liquefaction temperature of natural gas leads to a higher solubility of impurities such as carbon dioxide, which means that the pretreatment standards for liquefied natural gas can be reduced. Therefore, the use of PLNG technology can simplify pretreatment plants and significantly reduce construction and operating costs. In order to better apply PLNG technology to FLNG, it is necessary to understand the solubility of carbon dioxide in pressurized LNG and the phase change during liquefaction. To achieve this, experimental setups are needed to simulate the temperature and pressure environment of the LNG to obtain the relevant data and observe the relevant phenomena. After a literature research and analysis of the advantages and disadvantages of previous experimental setups, several improvements are proposed in this paper, and based on this, a visualization device is designed for studying the liquid–solid-phase equilibrium experiment of CO2 in PLNG. The device has a pressure resistance of 20 MPa, a minimum operating temperature of 77 K, and a variable volume function. It is also equipped with a sapphire window to be able to observe the inside of the device. In order to verify the superiority of the device, experiments were conducted using the device to verify the pressure resistance, variable volume, and visualization functions of the device. The experimental results show that the experimental device designed in this paper does have a certain superiority. [ABSTRACT FROM AUTHOR]

With the exploitation of oil and gas resources in the ocean, the application of FLNG is more and more extensive. The FLNG ships will face with sloshing, which will exert an influence on the performance of the system. In order to study the effect of sloshing on the double mixed refrigerant liquefaction process, a sloshing platform of six degrees of freedom is built to perform the sloshing experiment of DMR system. The experimental on yaw, roll and pitch is carried out by measuring the temperature, pressure, flow and pressure difference at key nodes to analyze the effects of three different sloshing forms on the overall liquefaction performance and the equipment. It can be found that sloshing will reduce liquefaction performance and increase power consumption. The sloshing has an adverse effect on the distribution of fluid in the heat exchanger and reduces the heat transfer effect. In addition, the sloshing has a greater impact on the wound tube heat exchanger than the plate fin heat exchanger. The effect of the yaw is negligible and the effect of the roll is biggest. The research results can provide reference and guidance for offshore FLNG production. [ABSTRACT FROM AUTHOR]