Search

To realize the industrialization of the novel single-column air separation process proposed in previous work, steady-state simulation for four different configurations of the single-column process with ternary (nitrogen, oxygen and argon) is developed. Then, exergy analysis of the single-column processes is also carried out and compared with the conventional double-column air separation process at the same capacity. Furthermore, based on the steady-state simulation of single-column processes, the different heat exchanger networks (HENs) for the main heat exchanger and subcooler in each process are designed. To obtain better performance for this novel process, optimization of process configuration and operation is investigated. The optimal condition and configuration for this process is consisted as: feedstock is divided into two streams and the reflux nitrogen is compressed at the approximate temperature of 301 K. In addition, HEN is optimized to minimize the utilities. HENs without utilities are obtained for the four different configurations of single-column process. Furthermore, capital costs of the HEN for different cases are estimated and compared.

Fluidized bed reactor is promising for CO methanation owing to its excellent heat transfer performance. The gas flow distribution between the bubble and emulsion phases and mass transfer are important for such a solid-catalyzed fast reaction in fluidized bed but these are described simplistically in most conventional models. In this work, a novel model contemplating the gas flow distribution influenced by circulation flow and the interphase mass transfer coefficient influenced by bubble size variation is proposed. The simulation results of the proposed model and the classic Kunii–Levenspiel model were compared with experimental data of fluidized bed CO methanation. It was shown that the results of the proposed model have better agreement with experimental data. To evaluate the roles of gas flow distribution and interphase mass transfer coefficient, sensitivity analysis was carried out. The results indicated that in the proposed model, the effect of gas flow distribution is more important.

Gasification processes with complex reaction systems typically require stable operating condition. However, variations of feedstock flow, composition of feedstock, and environmental factors, as well as other factors, may cause abnormal operating conditions. This work proposes a novel systems modeling and analysis method by combining computational fluid dynamics (CFD) and process simulation for the Shell pulverized coal gasifier. The proposed method considers the Shell pulverized coal entrained-flow gasifier with two parts: a gasification core zone and a heat exchange and water gas shift zone. High-fidelity CFD models of gasification core zone is developed to obtain characteristics of flow field, temperature field and composition profiles within the gasification core zone. An equation-oriented process simulation model is further developed for the heat exchange & water gas shift zone. The proposed hybrid method is validated by comparing with industrial operating data. Three cases for abnormal operating condition are further investigated with the proposed hybrid model. The most significant factors that influence the process operability are found to be the characteristics of gas and particles hydrodynamic behaviors of the inner layer of the gasification core zone. The results show that obvious vortex for the gas and particles is beneficial to the normal and abnormal operating conditions. To improve the operability of the entrained-flow gasifier under abnormal operating condition, it is crucial to keep the swirl zone of the vortex at the center of the reactor. In the end, an improved design for gasifier is presented by adjusting the bias angle of the nozzle to make the swirl zone of the vortex more obvious. According to the simulation results, the optimal bias angle is 5.0*(π/180) rad for the gasifier under both nominal and abnormal conditions.

Fluidized bed reactor is promising for CO methanation owing to its excellent heat transfer performance. The gas flow distribution between bubble and emulsion phases, and the characteristics of heat removal are significant for such a solid-catalyzed exothermal reaction in fluidized bed but these are described simplistically in most conventional models. In this work, a two-phase model contemplating: (i) the effect of circulation flow on gas flow distribution, (ii) the effect of particle flow on reaction heat removal, was proposed. The proposed model was validated by comparison with experimental data of the fluidized bed CO-methanation reactor. Meanwhile, simulation results of the proposed model and Kunii–Levenspiel model were compared. Finally, sensitivity analysis of important parameters was carried out. The results indicate that: (i) particle flow has more significance than circulation flow; (ii) the effect of bubble size is limited within bubbling region and bed-wall heat transfer has obvious influence in freeboard.

This study is aimed at investigating the effective precursory information of coal sample instability and failure under uniaxial compression. To achieve this aim, first, the infrared radiation temperature (IRT) variations of coal sample under the same loading mode were analyzed. Next, the variations of IRT counts on the coal sample surface, numbers of IRT points in high-temperature and low-temperature zones and IRT differences in the two zones were analyzed based on the infrared thermal image. Furthermore, the variations of variance and autocorrelation coefficient of IRT were explored with reference to the critical slowing down theory. The following results were obtained. The changes in IRT exhibit different characteristics in different stages of loading. Before the main rupture occurs, both the maximum infrared radiation temperature (MIRT) and the average infrared radiation temperature (AIRT) present a cooling precursor and an IRT rise buffer section. When the main rupture occurs, the MIRT surges, while the AIRT plunges. The high-temperature zone in the infrared thermal image keeps expanding with the increase of stress, and the low-temperature zone also expands considerably before the main rupture. The number of IRT points in the high-temperature zone decreases first and then increases with the increase of stress, while the number of IRT points in the low-temperature zone increases continuously with it. The IRT differences in the high-temperature and low-temperature zones vary in a basically consistent way with the number of IRT points in the two zones, respectively. The MIRT curve, and the curve of number of IRT points in the high-temperature zone and the variance curve of MIRT can all be taken as the precursor signal for identifying coal sample instability and failure. Among the three, the variance curve of MIRT boasts the most superior effect.

The technology of coal to synthetic natural gas is important to relieve the energy crisis and improve the environment. During the coal to synthetic natural gas process, methanation plays a key role by converting CO and H2 into methane. A novel systematic analysis framework based on modeling and simulation is provided for optimization of the CO methanation process using novel high-temperature tolerant catalysts. In this framework, the reactor is described by the mass-balance, energy–balance, and pressure equations. Meanwhile, reactor integration and waste heat utilization are considered. Then, the model of methanation process is validated by the industrial data. Three schemes for methanation processes and two types of feedstocks are investigated. In addition, different operating temperatures are considered for different schemes and different feedstocks. Furthermore, the solution method is proposed to optimize the split and recycle ratios in different process schemes. To compare the performance of different schemes, economic analysis, including methane profit, steam profit, and compressing work consumption, is investigated. Comprehensively considering different profits, the total profit for different schemes is provided and the optimal scheme is obtained. The method for optimization of split and recycle ratios can be used in different methanation process of coal to synthetic natural gas industry.