Search Results (24)

An electrical heating fluidized-bed thermal energy storage (EH-FB-TES) system is proposed for integration with a coal-fired power plant (CFPP) for deep peak shaving (DPS) due to its high energy storage density and extensive heat exchange performance. The primary objective of this study is to evaluate the thermodynamic performance and economic feasibility of the integrated EH-FB-TES system, specifically focusing on identifying the optimal coupling and heat recovery strategies for enhanced deep peak shaving performance. Since EH-FB-TES uses air flow for fluidization in the heating storage process, its coupling with the CFPP differs from other TES technologies, and the associated thermodynamic performance and cost are thereby analyzed. The results show that, in EH-FB-TES, the heat release efficiency is predominantly constrained by thermal losses. To increase the energy utilization efficiency, a two-stage heat recovery strategy is proposed to release the stored energy in the integration. The first stage is to heat up the feedwater extracted from the deaerator and the second one is to heat up the condensate water. The analyses also show that the selection of reinjection positions for the heated medium from EH-FB-TES greatly influences the system performance. Returning the stored thermal energy to heat up feedwater can effectively increase the output of the unit, while directly generating steam can be beneficial for coal saving. The integrated system achieves a maximum equivalent round-trip efficiency of 32.9% under 20 MW/800 °C conditions. An economic analysis reveals that, compared with other energy storage methods, EH-FB-TES can realize a relatively high energy storage density with a rather low cost. Under the present DPS compensation policy, for a 315 MW subcritical CFPP integrated with a 50 MW EH-FB-TES system, when heat storage is 8 h, heat release is 4 h per day, and the plant operates 100 days per year, the estimated static and dynamic payback periods are 3.06 years and 3.67 years, respectively. The integration of CFPP with EH-FB-TES could be promising for meeting DSP requirements. Full article

The methanol-to-olefins (MTO) process offers a viable alternative to traditional naphtha cracking for producing light olefins, providing flexibility in feedstock sources and the potential for reduced energy consumption. This study presents a detailed plant-wide design of an MTO process, developed and optimized to increase ethylene and propylene yields while reducing energy consumption. The methodology includes comprehensive reactor modeling of a fast fluidized-bed reactor–regenerator system, accounting for coke formation kinetics, along with rigorous process simulation for the subsequent separation and purification of products. A six-column distillation train has been designed and optimized for the recovery of polymer-grade ethylene and propylene, while dual-stage CO₂ absorption units ensure complete removal of carbon dioxide. Pinch analysis is used to identify opportunities for heat integration, resulting in an optimized heat-exchanger network that significantly reduces the need for external heating and cooling utilities. The results show that the optimized MTO design achieves a methanol conversion rate of over 99.9% and produces a propylene-rich product stream with a propylene-to-ethylene ratio of approximately 1.8, while maintaining a high purity level exceeding 99.5%. By implementing heat integration and recycling by-products, including using off-gas methane as furnace fuel and repurposing waste heat for steam generation, the plant reduces utility requirements by more than 85%, significantly improving energy efficiency. An economic evaluation shows a favorable payback period of approximately 5.4 years and an internal rate of return of 15–16%, confirming the viability and industrial potential of the integrated MTO process for sustainable olefin production. Full article

To ensure the safe operation of the external heat exchanger (EHE) in a circulating fluidized bed (CFB) boiler, it is essential to obtain real-time information on the flow conditions within the bed. This paper establishes a predictive model for the external heat exchanger of the high-temperature reheater in an ultra-supercritical CFB boiler by combining computational fluid dynamics (CFD) with model order reduction and artificial neural networks. The model enables rapid prediction of the solid volume fraction, solid temperature, and gas temperature within the external heat exchanger. The results show that the three predictive models can accurately forecast flow field information under unknown operating conditions. For inlet velocities of 0.225 m/s and 0.325 m/s, the calculation errors are 2.89%, 1.04%, 1.03% and 2.99%, 1.08%, 1.09%, respectively. The predictive models significantly save computational resources, reducing the computation time from 6000 min for the full-order model to approximately 1 s. This lays the foundation for real-time monitoring of the external heat exchanger. Full article

Coal serves as a cornerstone and stabilizer for China’s energy security; utilizing it in a clean and efficient manner aligns with the current national energy situation. The moisture content of coal is a crucial factor affecting its calorific value and separation efficiency. Therefore, enhancing the drying rate while simultaneously reducing the moisture content in coal is essential to improve separation efficiency. This paper primarily investigates the drying and separation characteristics of wet fine coal particles within a gas–solid fluidized bed system. A hot gas–solid fluidized bed was employed to study the particle fluidization behavior, heat–mass transfer, and agglomeration drying properties under varying airflow temperatures. The results indicate that as the airflow temperature increases, the minimum fluidization velocity tends to decrease. Additionally, with an increase in bed height, the particle temperature correspondingly decreases, leading to weakened heat exchange capability in the upper layer of the bed. Faster heating rates facilitate rapid moisture removal while minimizing agglomeration formation. The lower the proportion of moisture and magnetite powder present, the less force is required to break apart particle agglomerates. The coal drying process exhibits distinct stages. Within a temperature range of 75 °C to 100 °C, there is a significant enhancement in drying rate, while issues such as particle fragmentation or pore structure collapse are avoided at elevated temperatures. This research aims to provide foundational insights into effective drying processes for wet coal particles in gas–solid fluidized beds. Full article

This study focused on the small-scale dual fluidized-bed gasifier for hydrogen (H₂) production from sewage sludge. One of the current problems with the pyrolizer is tar condensation. Tar could reduce the efficiency of the H₂ yield by adhering and condensing on walls and pipes. It was revealed that more tar can be decomposed with higher reaction temperatures. Therefore, this study aimed to increase the tar decomposition efficiency with raising the heat carriers’ (HCs) temperature and analyzing the temperature distribution in the furnaces using a CFD simulation. The tar decomposition rate in the pyrolizer was +34.4%pt. by 100 °C of the HCs’ temperature rising. It is implied that less tar trouble and a longer lifetime of the H₂ production plant could be expected by raising the HCs’ temperature. However, comparing the heat transfer efficiency of the whole system, the lower HC inlet temperature of +7.4%pt., because of the hot gas, which supplies heat to the HCs, required more heat, making the thermal efficiency poorer. In addition, the environmental impact of the AGM was increased by 27.2% with the HCs’ temperature rising to 100 °C. Thus, the heat exchange efficiency of the preheater needs to be improved to raise the HCs’ inlet temperature and reduce the amount of hot gas required. Full article

In this study, a fluidized bed reactor for polyethylene production was employed using a dry mode approach, where the recycle stream may contain components of a nature that cannot be condensed through standard cooling. To analyze the behavior of the fluidized bed reactors during the copolymerization of ethylene with butene, a dynamic population balance model was employed. The study includes sensitivity analyses through computer simulations to examine the variations in reactor temperature, molecular weights, catalyst feed rate, and monomer/comonomer concentrations in the fluidized bed reactor. It is noteworthy that the reactor exhibits instability under normal operational conditions and is sensitive to changes in the catalyst feed rate and coolant temperature of the heat exchanger. The findings also highlight challenges such as temperature fluctuations above the polymer melting point. This underscores the importance of implementing a temperature control system to prevent issues like reactor shutdown due to elevated temperatures. Dynamic instabilities were observed under specific circumstances and were successfully controlled using Proportional Integral Derivative (PID) control strategies. The population balance model is essential for understanding the complexity of transient polymerization reactions. It enables researchers to simulate and optimize polymerization processes by utilizing the detailed kinetics of the reaction. Full article

Hydrogen-based fluidized bed direct reduction (H-FBDR) is an important and promising route for fossil-free ironmaking. In this study, to achieve the optimal operation state of energy use and exergy efficiency, the influences of the metallization process and the ratios of H₂ injected on the energy and exergy flows in the H-FBDR process are studied. The results show that the thermodynamically designed two-stage reduction process (first: Fe₂O₃→FeO; second: FeO→Fe) requires a smaller H₂ quantity than other metallization processes. According to the mass, energy, and exergy balance analyses, variations in the H₂ consumption, exergy destruction, and energy/exergy losses of the overall system, iron ore preheater (F1), fluidized bed reactor system (R), heat exchanger (E), and gas preheater (F2) with different ratios of H₂ injected (η) are derived. The total H₂ consumption, total exergy destruction, and energy/exergy losses rise with increasing η, and sharp increases are observed from η = 1.3 to η = 1.8. The exergy efficiencies (φ) can be ranked as φ_R > φ_E > φ_F1 ≈ φ_F2, and the exergy destruction in components F1 and F2 is mainly caused by the combustion reaction, whereas physical exergy destruction dominates for components R and E. The performances of components F1, E, and F2 degrade from η = 1.0 to η = 1.8, and significant degradation arises when η exceeds 1.3. Thus, considering the H₂ consumption, thermodynamic efficiency, and energy/exergy losses, the ratio of H₂ injected should be set below 1.3. Notably, although the energy loss in the H-FBDR system is 2 GJ/h at η = 1.3, the exergy loss is only 360 MJ/h, in which the recycled gases from component E occupy 320 MJ/h, whereas the total exergy destruction is 900 MJ/h. Therefore, improving the performance of operation units, particularly the components F1 and F2, is as important as recovering the heat loss from component E for optimizing the H-FBDR process. Full article

Fluidized bed reactors are essential in a wide range of industrial applications, encompassing processes such as Fischer–Tropsch synthesis and catalytic cracking. The optimization of performance and reduction in energy consumption in these reactors necessitate the use of efficient heat transfer mechanisms. The present work examines the considerable impact of tube end geometries, superficial gas velocity, and radial position on heat transfer coefficients within fluidized bed reactors. It was found that the tapered tube end configurations have been empirically proven to improve energy efficiency in fluidized bed reactors significantly. For example, at a superficial gas velocity of 0.4 m/s, the tapered end form’s local heat transfer coefficient (LHTC) demonstrated a significant 20% enhancement compared to the flat end shape. The results and findings of this work make a valuable contribution to the advancement of complex models, enhance the efficiency of fluidized bed reactor processes, and encourage further investigation into novel tube geometries. Full article

Adsorption systems are alternatives to compressor cooling systems. Apart from many advantages, these systems are characterized by low COP and SCP parameters. One of the most promising options to improve the performance of adsorption chillers is the replacement of the stationary bed with a fluidized one. A fluidized bed significantly increases the heat and mass transfer within the bed, enables better contact between gas and solid phases, and results in the proper mixing of adsorbent particles. This paper presents the possibility of using fluidized beds in adsorption chillers. This paper shows the results of CFD numerical modelling of the operation of a fluidized bed for an adsorption chiller and simulations of the bed temperature profiles during the adsorption and desorption processes of sorbent in a fluidized bed. This article presents an analysis of CFD simulation results for the optimal angle of heat exchangers. Full article

Increasing production of poultry litter, and its associated problems, stimulates the need for generating useful energy in an environmentally friendly and efficient energy system, such as the use of shell-and-tube heat exchangers (STHE) in a fluidized-bed combustion (FBC) system. A holistic approach which involves the integration of the First Law of Thermodynamics (FLT) and Second Law of Thermodynamics (SLT) is required for conducting effective assessment of an energy system. In this study, the STHE designed by the CAESECT research group, which was integrated into the lab-scale FBC, was investigated to determine the maximum available work performed by the system and account for the exergy loss due to irreversibility. The effects of varying operating parameters and configuration of the space heaters connected to the STHE for space heating purposes were investigated in order to improve the thermal efficiency of the poultry litter-to-energy conversion process. Exergy and energy analysis performed on the STHE using flue gas and water media showed higher efficiency (75–92%) obtained via energy analysis, but much lower efficiency (12–25%) was obtained when the ambient conditions were factored into the exergy analysis, thus indicating huge exergy loss to the surroundings. From the obtained experimental data coupled with the simulation on parallel arrangement of air heaters, it was observed that exergy loss increased with increasing flue gas flow rate from 46.8–57.6 kg/h and with increasing ambient temperature from 8.8 °C to 25 °C. To lower the cost of STHE during final design, a larger temperature difference between the hot and cold flue gas is needed throughout the exchanger, which further increases the exergetic loss while maintaining an energy balance. In addition, this study also found the optimal conditions to reduce exergy loss and improve energy efficiency of the designed STHE. This study shows the possibility to evaluate energy systems using integration of exergy and energy analysis. Full article

Industrial liquid/solid fluidized bed heat exchangers are commonly used with particle recycling systems to allow an increased superficial velocity and higher heat transfer rates. Here, experimental results are reported on a novel helical flow channel geometry for liquid/solid fluidized beds which allow higher heat transfer rates and reduced complexity by operating below the particle transport fluid velocity. This eliminates the complexity of particle recycle systems whilst still delivering a compact heat exchanger. The qualitative character of the fluidization was studied for a range of particle types and sizes under several inclinations of the helices and various hydraulic diameters. The best fluidization combinations were further studied to obtain heat transfer coefficients and pressure drops. Improvements over the heat exchange from a plain concentric tube in an annulus were obtained to the following degree: vertical fluidized bed, 27%; helical baffles, 34 to 54%; and fluidized bed with helical baffles, 69 to 89%. Full article

A special dual-tube reactor-dual fluidized bed reactor (DFBR), including an external heat exchanger (EHE) and a bypass, was designed to solve the problems that the waste heat of the hot fluid cannot be fully utilized and the reaction temperature cannot be accurately adjusted. Two connection schemes of DFBR and EHE with their thermodynamic equilibrium models and algorithms were proposed, and the optimal scheme was obtained by comparing the outlet temperature and thermal load. The results of the thermodynamic and operating characteristics of the optimal scheme showed that the hot fluid and the cold fluid had positive and negative effects on the heat transfer process, respectively. Increasing the cold fluid mass flow rate in the main stream can enhance the thermal load of the system and increasing the cold fluid mass flow rate in the bypass helped to increase the thermal load of DFBR, even exceeding that of EHE. Adding a bypass can adjust temperature precisely and increasing the inlet temperature can more effectively increase the adjustment range of the reaction zone temperature. The experimental results showed that introducing a bypass can significantly reduce the calculation deviation (12.8%), which decreased with the increasing temperature. Full article

Carbon capture, utilization, and storage (CCUS) is one of the key promising technologies that can reduce GHG emissions from those industries that generate CO₂ as part of their production processes. Compared to other effective CO₂ capture methods, the adsorption technique offers the possibility of reducing the costs of the process by setting solid sorbent with a high capacity of adsorption and easy regeneration and, also, controlling the performance of gas-solid contactor. In this work, an amine-functionalized mesoporous sorbent was used to capture CO₂ emissions in a confined-fluidized bed. The adoption of a confined environment allows the establishment of a homogeneous expansion regime for the sorbent and allows to improve the exchange of matter and heat between gas and solid phase. The results illustrate how the different concentration of the solution adopted during the functionalization affects the adsorption capacity. That, measured as mg of CO₂ per g of sorbent, was determined by breakthrough curves from continuous adsorption tests using different concentrations of CO₂ in air. Mesoporous silica functionalized with a concentration of 20% of APTES proves to be the best viable option in terms of cost and ease of preparation, low temperature of regeneration, and effective use for CO₂ capture. Full article

The sandTES technology utilizes a fluidized bed counter current heat exchanger for thermal energy storage applications. Its main feature is an imposed horizontal flow of sand (SiO₂) particles fluidized by a vertical air flow across a heat exchanger consisting of several horizontal rows of tubes. Past international research on heat transfer in dense fluidized beds has focused on stationary (stirred tank) systems, and there is little to no information available on the impact of longitudinal or helical fins. Previous pilot plant scale experiments at TU Wien led to the conclusion that the currently available correlations for predicting the heat transfer coefficient between the tube surface and the surrounding fluidized bed are insufficient for the horizontal sand flow imposed by the sandTES technology. Therefore, several smaller test rigs were designed in this study to investigate the influence of different tube arrangements and flow conditions on the external convective heat transfer coefficient and possible improvements by using finned tubes. It could be shown that helically finned tubes in a transversal arrangement, where the horizontal sand flow is perpendicular to the tube axes, allows an increase in the heat transfer coefficient per tube length (i.e., the virtual heat transfer coefficient) by a factor of 3.5 to about 1250 W/m²K at ambient temperature. Based on the literature, this heat transfer coefficient is expected to increase at higher temperatures. The new design criteria allow the design of compact, low-cost heat exchangers for thermal energy storage applications, in particular electro-thermal energy storage. Full article

The production of clean and efficient energy from municipal solid waste (MSW) is extremely urgent matter due to an increasing energy demand and environmental concerns. In this study, a high steam parameter (520 °C, 7.9 MPa) circulating fluidized bed (CFB) MSW incineration system, equipped with a mechanical, biological treatment and external heat exchanger systems, was introduced and a comparative study with a typical mechanical grate (450 °C, 5.3 MPa) incineration system and conventional CFB (485 °C, 5.3 MPa) incineration system was carried out from a life-cycle, environmental and exergetic perspective which could assess different energy and material outputs based on real operating data. Moreover, the potential system optimization of this advanced CFB system was proposed. The results showed that the advanced CFB system was more environmentally friendly and resource-efficient than conventional MSW incineration systems. The recovery of material should be given priority over energy recovery. According to the assessment of the environment, and energy and material recovery, a process improvement with an incinerated refuse-derived fuel and a semi-compost produced by MBT as a soil conditioner was highly recommended. Full article