Chunli Tang

Supercritical CO₂ pipeline transportation is a critical component of the carbon capture, utilization and storage (CCUS) industry chain, where long distance operation introduces inherent risks of accidental leakage. During the leakage process of supercritical CO₂ pipelines, throttling pressure reduction and the Joule–Thomson effect generate distinct negative pressure wave characteristics. The magnitude of the leakage directly impacts localization effectiveness, particularly under small leakage conditions where negative pressure wave signals are less pronounced, so the leakage is difficult to effectively detect. To solve this problem, the mutual correlation function model for pipeline leakage was developed by using the mutual correlation analysis method, and it was verified by the dense-phase CO₂ leakage data from Trondheim University of Technology. Based on the TGNET software, the actual pipeline model of the Yanchang oilfield is established, and the captured leakage signal is imported into MATLAB for differential pressure conversion, using the verified cross-correlation function model of the differential pressure signal to calculate the time difference between the arrival of the negative pressure wave at the two ends of the pipeline. Finally, the actual leakage location was determined. The simulation results indicate that the leakage detection method based on mutual correlation analysis of negative pressure wave signals exhibits varying localization performance under different leakage rates. By enhancing negative pressure wave characteristics and utilizing mutual correlation analysis, this method effectively addresses the challenges of indistinct negative pressure wave features and difficult localization during small leakage conditions. When leakage exceeds 5%, the relative error is controlled within ±5.40%, meeting the preliminary localization requirements for rapid identification and regional determination in engineering applications. Through the application of actual engineering cases, it is shown that this method has high accuracy in pipeline leakage detection. These findings provide theoretical and methodological support for supercritical CO₂ pipeline leakage detection in the CCUS projects currently under construction.

Supercritical-dense phase CO₂ pipeline transportation has been proven to have excellent economic and safety benefits for long-distance CO₂ transportation in large-scale. Hydrates are easily generated in the high-pressure and low-temperature sections, resulting in blockage, so it is necessary to build the prediction model for hydrate formation in the long-distance CO₂ pipeline transportation. In the prediction model of hydrate formation of our work, the phase equilibrium was determined by the Chen-Guo model, and the lateral growth of hydrate was calculated by the comprehensive growth model, and the hydrate growth was estimated by analogy with the condensation process. Subsequently, the prediction model for hydrate volume in the CO₂ pipeline was established considering the process of hydrate growth and water droplet distribution. The effects of thermodynamic conditions, impurities, and operating conditions on the hydrate formation were analyzed. The impurities can expand the temperature and pressure ranges for hydrate generation. The increase in the moisture content, the increase in the pressure, the decrease in the temperature, or the increase in the fluid velocity could increase the volume of hydrates in the pipeline. After running for 10 h, the hydrates volume in the pipeline with the moisture molar fraction of 0.05% is over 10 times that with the moisture molar fraction of 0.005%. In addition, by using the proposed hydrate formation prediction model, the hydrate formation in a supercritical-dense phase CO₂ long-distance pipeline was predicted, and a suggested cleaning cycle was achieved. This study can guide the operation of CO₂ long-distance transportation pipelines.

A novel design for the energy storage by adsorption-absorption for the partial CO₂ capture of the energy supply buildings with fixed CO₂ emission is proposed. The new design successfully utilizes the attainment of the low energy consumption and implements energy storage through adsorption part, overcoming the deficiencies of poor selectivity through absorption part. Numerical approaches have been developed for modeling the adsorption-absorption procedure, while attaining satisfactory agreement with experimental data. The adsorption process is modeled based on the finite volume method, and the absorption process is simulated based on the double-film theory and the rate-based model. The issue of operating parameters upon system assessments has received considerable critical attention by numerical implementations. The results show that the mass fraction of CO₂ in the flue gas has been increased to 39.0%. The comprehensive enhancement effects are instrumental at a height of 20 m in the absorption tower. As the CO₂ concentration of the flue gas increases from 5.0% to 20.0%, the absorbent flow, absorber diameter, and reboiler specific load decrease by 13.0%, 42.1%, and 16.6%, in respective. The present analysis and design will provide guidance and gain fresh prominence with advantages in the CO₂ capture and purification.

Slag tapping cyclone furnace is suitable and promising for the utilization of low-ash-melting-point coals without worrying about the fouling and slagging problems, but its high NOx emission has limited its application. In this study, the temperature profiles, species concentration distributions, and slag tapping behavior of the cyclone barrel were explored on a self-built 100 kW cyclone furnace system. A reasonable slag capture ratio of 0.70 can be achieved for the cyclone barrel even under air-staged conditions. The coincidence of high temperature and high O-2 concentration in the annular near-wall area of the cyclone barrel can lead to a large amount of NOx formation, while a NOx reduction area with high CO concentration is formed in the central and lower zones of the cyclone barrel due to strong swirling effect. The NOx emission of cyclone staged combustion is lower than that of laminar drop-tube staged combustion in either air-staged or nonstaged cases, which could be attributed to the swirling effect. The NOx reduction area can be expanded by decreasing the cyclone stoichiometric ratio (SR) or reducing the primary air rate (PAR). Compared with the limit effects on the reduction of NOx emission by overall-SR, NOx formation can be greatly dropped by 56% when the cyclone-SR decreases from 1.1 to 0.7. The swirling intensity in cyclone barrel increases from 1.23 to 12.81 as PAR reduces from 0.4 to 0.2, which results in a reduction of NOx formation at the outlet of the cyclone barrel by half. Besides, the O-2 concentration in the annular near-wall region can be remarkably reduced by the decentralized secondary air supply, resulting in a 23% reduction in NOx formation in the cyclone barrel.

Very few studies have been reported on the fundamental mechanism analysis the augmentation of heat and mass transfer for the convection and condensation processes in the slit finned tube heat exchanger under dehumidifying conditions. By developing a 3D numerical model for the condensation of the slit finned tube heat exchanger under dehumidifying conditions, the heat and mass transfer characteristics were investigated under different the geometrical and operational parameters. The models neglecting convective mass flux or neglecting the water vapor loss can greatly enlarge the deviations of numerical results with respect to experimental data. The synergy angles are smaller in the windward and leeward sides of slits where the velocity field has a better synergy with both temperature field and the mass field. The slits on the fin not only increase the disturbance of fluid but continuously destroy the developments of thermal and mass concentration boundary layers, greatly enhancing the heat and mass transfer. The latent heat transfer is significantly greater than the sensible heat transfer, which accounts for 71.7% of the total heat transfer rate when inlet velocity is 1 m·s⁻¹and volume fraction of water vapor is 15%. The increases in the inlet velocity, and the volume fraction of water vapor can enhance the heat and mass transfer coefficient of wet flue gas. Whereas, the increase in inlet velocity can reduce the difference of synergy for the velocity field and the temperature or mass concentration gradient field of different fin tubes.

The cyclone-fired boiler has become a very competitive boiler type for utilizing coal with a low ash melting point and high alkali. Because of the higher combustion intensity in the cyclone barrel, good flow and combustion performances are of great significance to the safe and efficient operation of the cyclone-fired boiler. The flow and combustion characteristics in a vertical cyclone barrel were numerically investigated, which has never been done before to the author’s knowledge. The results showed that the pulverized coal particles are spun forward in the cyclone barrel driven by the tangentially rotating airflow, and the maximum velocity in the cyclone barrel is in the annular zone near the barrel wall. With the decrease in the swirl-vane angle of the primary air inlet or the increase in the particle diameter, the location where the particles collided with the barrel wall moves up along the axial direction of the cyclone barrel and the colliding chance increases. For the vertical cyclone barrel, the optimum particle diameter range is 70–110 μm, so the capture ratio of particles is greater than 99.4%.

This paper accomplishes a numerical investigation on the effect of two-level over-fire air (OFA) on the combustion and NO_x emission in a supercritical 600 MW wall-fired boiler. Different arrangements of two-level OFA nozzles and different airflow ratios between the two layers are set to examine NO_x emission and the carbon content in fly ash. According to the simulation results, the two-level OFA case releases the NO_x between the single upper layer and the single lower layer of the two-level OFA nozzles in operation. Moreover, the two-level OFA arrangement gives a lower carbon content in fly ash than the single-level OFA cases. In addition, both low NO_x emissions and low carbon content in fly ash can be obtained simultaneously when the two levels of OFAs are injected from Layers 1 and 4 with r_lower at 0.5.