• Energy Research

The numerical simulation of the fluid flow and particle dynamics is presented by CFD technique to characterize the performance of two types of cyclones with the conventional single inlet (SI) and spiral double inlets (DI), respectively. The Reynolds-averaged Navier-Stokes equations with the Reynolds stress turbulence model (RSM) for fluid flow are solved by use of the finite volume method based on the SIMPLE pressure correction algorithm in the fluid computational domain. A Lagrangian method is employed to track the particle motion and calculate the gas–particle separation efficiency in the cyclones. According to the computational results, the differences of pressure, velocity and turbulence parameters of the gas flow are described to address the effects of the inlet geometry on the flow pattern of cyclones. Especially for the tangential velocity distribution, a key flow parameter in cyclones, are analysed using the classical Rankine vortex theories. Furthermore, the separation performances of cyclones are predicted, with the comparison of experimental data and theoretical model. The results indicate that the CFD method can effectively reveal the mechanism of gas–particle flow and separation in cyclone with different inlet configuration.

Numerical simulation was carried out on the High Temperature Air Combustion in an industrial furnace with a multi-jet burner. The effect of inlet oxygen concentration of the preheated air on the combustion characteristics was investigated. The standard k-e model was used to calculate the flow field and β function PDF was used to simulate the gas combustion. The radiation was simulated by a Discrete Ordinates method. NO was simulated by thermal NO model. The furnace was a rectangular chamber of 800 mm × 800 mm × 1400 mm. A circular fuel jet of a diameter of 10 mm is at the center of the wall. 5 circular air jets equably distributed around the fuel jet with different straddle angles. The results showed that inlet oxygen concentration of preheat air had a considerable influence on the local temperature, oxygen and NO distribution, resulting in a stable flame, an enlarged low-oxygen zone, an equable temperature distribution and a suppressed local high temperature, which led to the lower product of local NO. When the inlet oxygen concentration is 10%, the local NO concentration is lowered 2 factors than that under a 21% inlet oxygen concentration. The final NO emission is no more than 20 × 10-6 at an inlet oxygen concentration of 10%.

Abstract To improve the process and performance of CO2 capture with ammonia by chemical absorption, a vortex flow-based multistage spray reactor was designed to evaluate the enhancement effect for post-combustion CO2 capture with ammonia. The process intensification analysis based on flow patterns from a CFD (computational fluid dynamics) simulation indicated that the vortex flow presented multi-dimensional velocities including a V-shaped tangential velocity profile and non-uniform axial velocity profile, which resulted in enhancement of gas–liquid contact, mixing, mass transfer, and reaction compared to non-vortex flow. Furthermore, the CO2 capture characteristics were examined at varied operating parameters. It was found that the capture efficiency E increased with increasing ammonia concentration and liquid flow rate but decreased with increasing CO2 inlet concentration and gas flow rate. Meanwhile, the overall gas phase mass transfer coefficient Kga increased with increasing ammonia concentration, liquid flow rate, and gas flow rates but decreased with increasing CO2 inlet concentration. Within the measured range, the E and Kga varied from 72.05 to 86.72% and 0.31–0.49 × 10−3 kmol/m3 kPa s, respectively. Importantly, vortex flow presents relative enhancements of 7–15% in E and 18–33% in Kga compared with non-vortex flow depending on the operating parameters.

Abstract This paper presents a numerical study of the gas–solid flow in square cyclone separators with three types of inlet configuration. Three-dimensional Reynolds Stress Model (RSM) was used to simulate the turbulent flow of gas phase and a Lagrangian equation was used to simulate the particle motion. The resulting velocity, separation efficiency and pressure drops were verified by comparison with measured data. The effect of inlet configurations on the turbulent dynamics in the cyclone and the separation efficiency and pressure drop was analyzed. Results showed that inlet configurations influenced the turbulent dynamics in the cyclone and led to different pressure drop and separation efficiency. The separator with double declining inlets (DDI) had the minimum pressure drop and similar efficiency to the separator with double normal inlets (DNI). The separator with single normal inlet (SNI) had the best separation efficiency and the maximum pressure drop. When a baffle was installed in the inlet of separator SNI, the pressure drop increased by about 191% and 34% for the separator with a straight (SNI-1) and curved (SNI-2) baffle respectively on the basis of the pressure drop of separator SNI. The cut and critical diameter of particles were 2 μm and 14 μm for separator SNI-1 and 4 μm and 14 μm for separator SNI-2, while they were 8 μm and 30 μm for separator SNI at the same inlet conditions.

Abstract Algae-based bioenergy has been regarded as the next generation of renewable energy. To fix CO2 from flue gas and harvest algal biomass for energy conversion, three energy microalgae, Chlorella sp., Isochrysis sp. and Amphidinium carterae, were investigated in 1-L bubble column photobioreactors with an aeration of 15% CO2 at the flue-gas level. According to the potential on CO2 fixation and biomass production, Chlorella sp. was selected as the dominant species due to its superiority to the other species, with a specific growth rate of 0.328 d−1, a biomass production rate of 0.192 gL−1 d−1 and a CO2 fixation rate of 0.353 gL−1 d−1. Furthermore, Chlorella sp. was cultured under varied physicochemical parameters, including CO2 concentrations, aeration rates and toxic compounds (SO2, NO and Hg2+) to assess its performances. The maximum specific growth rate, biomass production rate and CO2 fixation rate were found to be 0.372 d−1, 0.268 gL−1 d−1 and 0.492 gL−1 d−1 at a CO2 concentration of 10%; 0.375 d−1, 0.274 gL−1 d−1 and 0.503 gL−1 d−1 at an aeration rate of 0.1 vvm; and 0.328 d−1, 0.192 gL−1 d−1 and 0.353 gL−1 d−1 in the absence of toxic compounds, respectively. The results provide a basis for microalgal-based CO2 emission reduction and bioenergy utilization in pilot-scale applications.

Abstract Post-combustion CO 2 emissions caused by fossil fuel utilization have become a worldwide issue. To understand the macro-level status of research findings and impacts on post-combustion CO 2 capture, a publication-based survey since 2000 was performed using Web of Science™ Core Collection and Journal Citation Reports ® 2014. The number of articles published, citations and important publications were examined to assess the quantity and quality of scientific findings on post-combustion CO 2 capture. Results show that a total of 1025 articles were published during 2000–2013. A remarkable increase in publication numbers was found in 2011 and has remained high in the last three years. The United States and China are the top-two contributors of articles, far surpassing those of all other countries, with an approximate combined of 40% from these two countries. Post-combustion CO 2 capture approaches using absorption, adsorption and membrane techniques were dominant. Times Cited of articles regarding post-combustion CO 2 capture reached to peak in 2010 while the number of citing articles is continuously increasing. The most popular, most-cited and highest impact factor journals were found as International Journal of Greenhouse Gas Control , Industrial and Engineering Chemistry Research and Science , respectively.

Abstract The enhancement of particle separation is important for aerodynamic cyclones to reduce any extra or downstream capture process. To improve the particle separation performance, a new type of integrated compact-bend cyclone (ICBC) was proposed to achieve a non-homogeneous radial particle distribution at the cyclone inlet and hence reduce radial distance to the cyclone wall before performing the primary separation in the cyclone body. Experimental investigations and numerical simulation were performed to examine the enhancing effect of various integrated compact bends. The results proved the effectiveness of the integrated compact bends for improving particle separation performance. The grade efficiency for 1–5 μm particles was enhanced by up to 8.5% for 180° ICBC and 22.7% for 360° ICBC at 12 m/s inlet velocity, and by up to 8.0% for 180° ICBC and 20.5% for 360° ICBC at 20 m/s inlet velocity, respectively. Meanwhile, no significant difference in the gas flow pattern was observed for the different ICBCs. Furthermore, the results by computational fluid dynamics (CFD) simulation was demonstrated to reflect the enhancing effect of ICBs not included in other cyclonic separation theories. The result may provide a positive reference for cyclone-based intensified separation in the field of chemical and process engineering.

Abstract It has become an important energy and environmental issue how to effectively reduce NOx emissions from algae biomass combustion. To achieve advanced control of NO emission from algae biomass combustion, three kinds of iron-based additives, including Fe, Fe2+ and Fe3+, were physicochemical-loaded onto different algal biomasses using the immersion method which is different from the conventional physical blending. The effects of iron-based additives on NO emission were examined for various combustion temperatures, additive agents, and additive concentrations. Results showed that the higher the temperature, the greater the NO emissions from algal biomass combustion. However, the iron-based additives were able to inhibit NO emission in this process. The percentage drops in NO emission levels observed were 5.79–51.22%, 12.50–63.41%, and 14.06–80.49% for Fe, Fe2+ and Fe3+ based on a 1% loading rate. The inhibitory effects of Fe2+ and Fe3+ were comparable but better than those of Fe. Increasing the concentration of the iron-based additive load had a significant inhibitory effect. These results may provide a positive reference for combustion-, co-firing- and reburning-based NOx control for energy utilization of algae biomass.

Abstract Three-dimensional particle dynamics analyzer was employed to study the gas–solid flow in a square-shaped cyclone separator which was designed for large CFB application. Distribution of flow vector, fluctuating velocity, turbulent kinetic energy, turbulent intensity and particle concentration were discussed. The swirling flow inside the cyclone showed the Rankine vortex characteristics, i.e., strong swirling vortex at the central region of the cross-section and weak swirling quasi-free vortex near the wall. The quasi-laminar motion of particles enhanced the turbulent movement at the corners due to particle–particle/wall collision, which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner is one of the major region to cause pressure drop because the suspension at the corners consumed more energy of the flow. The corners were found to be beneficial to particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both the particle and the gas.

Abstract The thermochemical conversion of algae biomass into energy via direct combustion is an important and effective way but emits pollutants. To address the gas pollutant emissions and ash characteristics in this process, three species of algae biomass, namely, Enteromorpha (En), Sargassum (Sa) and Chlorella (Ch), were used to investigate the process behavior of real-time SO2/NOx emissions and ash formation at varied combustion temperatures. It was found that SO2/NOx emission peaks and concentrations highly depended on the combustion temperature in addition to algae species. The SO2 emission amount and conversion ratio generally increased with increasing sulfur content in the algae. The NOx emissions were not causally related to the nitrogen content in the algae biomass. The conversion ratio from N to NOx for each algae species was similar at 700–900 °C. In particular, it was relatively low for the algae En and Ch, which have relatively high N contents, implying that a large amount of N exists in the form of reductive intermediates. Moreover, the morphological and physicochemical properties of the ash were also found to be associated with the combustion temperature and algae species. The results may provide a positive reference for pollution assessment and control from algae biomass combustion.