Packed Bed Temperature Research Articles

Partially Oxidative Torrefaction of Woody Biomass Pellets: Burning Behaviour and Emission Analysis

Non-conventional torrefaction under partially oxidative conditions is an emerging cost-effective thermochemical pre-treatment method to improve the quality of biomass for energy applications. The literature lacks data on the combustion of biomass torrefied under oxygen-deficient atmosphere with actual reactor conditions (inevitable non-uniformities in the thermal environment). In this work, a dual mode fixed-bed biomass (torrefaction) reactor and combustor was operated on Australian biomass pellets, to torrefy the fuels at 275 °C for 30 min using partially oxidative atmosphere (O2: 5 vol%, balance N2) and then to combust them. Combustion behaviour with a particular focus on gaseous emissions of raw, blended (25% torrefied), and torrefied (100%) pellet fuels in a batch-type combustor was investigated. The decomposition behaviour was analysed in a thermogravimetric analyser to understand the impact of biomass constituents on the direct combustion of the tested samples. Results indicate that unlike the combustion of raw biomass, the fuels torrefied under partially oxidative conditions burned 45% faster, attained high packed-bed temperatures (1382 °C) and exhaust gas temperatures (657 °C) then latter (bed: 1128 °C, exhaust: 574 °C) at similar airflow. Additionally, 100% torrefied pellets emitted 38% less NOx compared to raw biomass pellets. However, low CO values for torrefied biomass were attained at higher primary airflows compared to raw. The combustion of 100% torrefied biomass in a fixed-bed was dominated by both flaming and smouldering phases with a modified combustion efficiency (MCE) value of 91%, whereas raw biomass combustion occurred in flaming phase with an MCE value of 98% at same airflow (0.35 kg·m−2·s−1). The outcomes of this work provide useful insights into the viability of using biomass fuels torrefied under partially oxidative conditions alongside other industrial processes generating (waste) heat and flue gases.

Numerical study on the thermodynamic performance of a packed bed cryogenic energy storage system

• Developed a 3-D porous media model for cryogenic energy storage in a packed bed. • Studied the influence of key factors on cold charging performance of the packed bed. • Operating conditions of cryogenic gas charged packed bed were analyzed. Cold energy storage devices improve the round-trip efficiency of cryogenic energy storage systems, where a solid packed bed for cold energy storage (PBCES) is widely utilized. In this study, a three-dimensional transient porous media packed bed model was developed using computational fluid dynamics software ANSYS Fluent 2020 to study the thermodynamic characteristics of a solid PBCES system with cryogenic nitrogen as the working medium during the cold charging process. The effects of the superficial mass flow rate ( G in ), inlet temperature of nitrogen, packing materials, porosity on the packed bed temperature distribution, pressure drop, cold storage efficiency ( η s ), and cold exergy efficiency ( η Ex ) were investigated carefully. The results showed that the axial temperature distribution is a typical thermocline. The system performance is predominantly affected by the criterion of the complete charging (the minimum temperature difference between Face-2 and Face-1, Δ T F2-F1,min ) and the G in . The thermocline thickness decreased with a decrease in the G in . The η s and η Ex increased significantly with an increase in the Δ T F2-F1,min . The maximum η s and η Ex were 77.69% and 75.21% at the G in was 0.1 kg/(m 2 ·s) when the Δ T F2-F1,min was 100 K. The change in porosity had a limited influence on the cryogenic storage performance but considerably influenced the pressure drop; Basalt was recommended as the optimal packing material in the present study. The superficial mass flow rate of working medium and the complete charging indicator (Δ T F2-F1,min ) should be carefully determined to achieve high performance in a practical CES system. The developed simulation model would be promising and useful for the design and optimization of a practical packed bed for CES systems.

Catalyst Heating Characteristics in the Traveling-Wave Microwave Reactor

Traveling-Wave Microwave Reactor (TMR) presents a novel heterogeneous catalytic reactor concept based on a coaxial waveguide structure. In the current paper, both modeling and experimental studies of catalyst heating in the TMR are presented. The developed 3D multiphysics model was validated from the electromagnetic and heat transfer points of view. Extrudes of silicon carbide (SiC) were selected as catalyst supports and microwave absorbing media in a packed-bed configuration. The packed-bed temperature evolution was in good agreement with experimental data, with an average deviation of less than 10%. Both experimental and simulation results show that the homogeneous temperature distribution is possible in the TMR system. It is envisioned that the TMR concept may facilitate process scale-up while providing temperature homogeneity beyond the intrinsic restrictions of microwave cavity systems.

Thermal performance of packed bed heat storage system for solar air heaters

Thermal performance of the packed bed solar heat storage system was studied under varying solar and ambient conditions in different months. The insulated packed bed heat storage unit was filled with 8500kg rock pebbles. The solar collection and heat retrieval efficiency of heat storage system ranged between 36–51% and 75–77%, respectively. Heat retrieval efficiency of the developed packed bed was found better as compared to the packed bed filled with phase change material (PCM). The experimental values were found in good conformity with predicted values of the packed bed temperature and hot air temperature retrieved from the bed.

Hydropyrolysis of Lignin Using Pd/HZSM-5

The aim of this work was to study the formation of cycloalkanes from hydropyrolysis of lignin with HZSM-5 and Pd/HZSM-5 catalysts. Cycloalkanes are high-octane-rating molecules and are a major component of jet fuels. We observed that palladium supported on HZSM-5 catalyzed hydrogenation and deoxygenation reactions that converted phenolic compounds into aromatic hydrocarbons and cycloalkanes. This in situ study analyzed the effect of the catalyst-to-lignin ratio, H2 partial pressure, and temperature on the yields of hydrocarbons with HZSM-5 and 1 wt % Pd/HZSM-5. Pd/HZSM-5 produced 44% more aromatic hydrocarbons than HZSM-5 at a catalyst-to-lignin ratio of 20:1, 650 °C, and a constant H2 partial pressure of 1.7 MPa. The presence of palladium led to a significant difference in yields only at 1.7 MPa H2 partial pressure. In addition, the hydropyrolysis temperature played a substantial role in the equilibrium conversion of hydrogenation reactions that led to cycloalkanes directly from lignin. In an attempt to bypass the thermal limitations of the in situ process, we performed ex situ catalytic upgrading experiments and also observed formation of cycloalkanes at a hydropyrolysis temperature of 650 °C, packed bed temperature of 300 °C, and H2 partial pressure of 1.7 MPa.

Aromatic hydrocarbons production from ex situ catalysis of pyrolysis vapor over Zinc modified ZSM-5 in a packed-bed catalysis coupled with microwave pyrolysis reactor

Ex situ catalytic pyrolysis of biomass through a packed-bed catalysis close coupled with microwave pyrolysis was investigated to convert Douglas fir sawdust pellets to aromatic hydrocarbons by Zn/ZSM-5 catalyst. A comparison test from five different Zn loadings (0, 0.5, 1, 2, 5wt.%) was first conducted, and it was found that the highest amount of aromatic hydrocarbons was produced from 0.5% Zn loaded on ZSM-5. Then a central composite experimental design (CCD) was used to optimize the upgraded bio-oil and syngas yields with 0.5% Zn loaded in ZSM-5. In comparison to the non-catalytic experiment, all the catalysts decreased the bio-oil yield and increased the syngas production. The product yields from Zn/ZSM-5 were sensitive with reaction conditions as the bio-oil yields varied between 22.3% and 44.8% compared with 32.2% and 37.8% over ZSM-5 catalyst, and syngas yields from 33.3% to 55.5% vs. 38.8% to 43.7% on ZSM-5 catalyst. GC/MS analysis showed that aromatic hydrocarbons become the most abundant compounds in the bio-oil. The high amount of aromatic hydrocarbons in the upgraded bio-oils from GC/MS analysis was confirmed by the FTIR analysis. The aromatic hydrocarbon was increased when the packed-bed temperature and inverse weight hourly space velocity (WHSV)−1 were increased. The comparison of coking on ZSM-5 and Zn/ZSM-5 catalysts at different reaction conditions showed that the coking increased with increasing (WHSV)−1 and decreasing packed-bed temperatures. Zn/ZSM-5 had lower coking than ZSM-5 on all the reaction conditions except packed-bed temperature at 269°C and (WHSV)−1 at 0.048.

Transient dynamic response of solar diffusion driven desalination

The dynamic response for the solar diffusion driven desalination (DDD) process has been investigated. The heat and mass transfer within the direct contact evaporator is analyzed by one-dimensional conservation equations. The heat and mass transport models account for the transient variations within the packed bed due to time varying inlet water and air temperatures and humidity. The conservation equations are solved numerically using a finite difference scheme to predict water, air/vapor mixture and packed bed temperatures and humidity ratio within the evaporator and the condenser. The system dynamic response for the packed bed materials, wettability, and liquid hold-up, sudden increase–decrease in the inlet water temperature is investigated. It is found that the response time for the outlet water to reach the steady state temperature in the evaporator is shorter for lower liquid hold-ups. The response time is not sensitive to the packing material. Higher wettability does not affect the response time, but it does result in improved heat transfer with a higher exit air temperature and lower exit water temperature. The steady state temperature in the evaporator is not dependent on the heat capacity of the packing material, and liquid hold up. A delayed operating mode for the solar DDD is introduced to enhance the fresh water production rate. It is found that increasing the initial saline water temperature and decreasing the initial water volume in the seawater tank results in a higher fresh water production rate.

Transient analysis of direct contact evaporation and condensation within packed beds

Transient one-dimensional conservation equations have been developed to analyze the heat and mass transfer within direct-contact evaporators and condensers. The conservation equations are solved numerically to predict water, air/vapor mixture and packed bed temperatures and humidity ratio within the evaporator and the condenser. The heat and mass transport models account for the transient variations within the packed-bed due to time varying inlet air and water temperatures and humidity. Direct contact evaporator and condenser experimental facilities have been configured. The measured water and air/vapor mixture temperature differences agree well with those predicted using the transient model. The measured humidity difference is slightly greater than that predicted, and the maximum deviation is on the order of 20%.

Solar gasification of carbonaceous waste feedstocks in a packed‐bed reactor—Dynamic modeling and experimental validation

AbstractThermochemical gasification of carbonaceous waste feedstocks (specifically: scrap tire powder, industrial sludge, and sewage sludge) for high‐quality syngas production is numerically modeled and experimentally validated using concentrated solar process heat. The solar reactor consists of two cavities separated by a radiant emitter, with the upper one serving as the solar radiative absorber and the lower one containing the reacting packed bed. The reactor is modeled by considering combined heat transfer coupled to the reaction kinetics, driven by the applied solar flux at the reactor's aperture. Model validation is accomplished in terms of converted mass, reactor temperatures, efficiency, and solar upgrade based on experiments with an 8‐kW reactor subjected to solar fluxes up to 2560 suns and packed bed temperatures up to 1490 K. The transient operation of a 200‐kW pilot‐scale reactor for gasifying industrial sludge is simulated for a solar day, yielding a maximum solar‐to‐fuel energy conversion efficiency of 89%. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Comparing physisorption and chemisorption solid sorbents for use separating CO2 from flue gas using temperature swing adsorption

Abstract We have examined the capture of carbon dioxide from flue gas by adsorption on solid sorbents using an equilibrium model for a packed bed temperature swing adsorption (TSA) process for a wide range of sorbents. This model determines the working capacity of the sorbent by looking at the difference between the equilibrium adsorbed concentrations at the adsorption and desorption conditions, and uses the sensible and latent heating requirements to determine the minimum energy usage. Using the results of this model, a class of sorbents can be constructed that have nearly identical physical properties but variable heats of adsorption for carbon dioxide to mimic different adsorption mechanisms. Parametric studies are run to determine the calculated minimum energy requirements per ton of carbon dioxide captured for this class of sorbents and a global minimum is found. This paper also discusses the effect of heat of adsorption on adsorption isotherms and what isotherm shapes are most beneficial for minimizing energy usage in carbon capture.

Experimental study on temperature characteristics and energy conversion in packed bed reactor with dielectric barrier discharge

The temperature characteristics and energy conversion in packed bed reactor combined with a dielectric barrier discharge (DBD) plasma was investigated experimentally. The pellet temperatures of two types packed bed reactor, cylindrical reactor and parallel-plate reactor, was measured in conditions of various inlet voltage of DBD plasma. The relationship between pellet temperature of the packed bed and applied voltage of DBD plasma was discovered. The experimental result indicates a tendency that the pellet temperature of packed bed increases as the applied voltage of inlet plasma increases. When the voltage of inlet plasma is high enough, the pellet temperature increment decreases. Simultaneously,the packed bed temperature is sensitive to the inlet plasma energy and there is a potential application to heat exchanger. Moreover the proportion of energy consumption of plasma inputting into packed bed reactor was analyzed and calculated. The mechanisms that electrical energy of inlet plasma is transformed into heat energy in the two phases, gaseous and pellets of the packed bed reactor are different. The energy consumption in pellet phase is dielectric polarization loss and depends on packed bed geometry and DBD plasma etc. The energy consumption in gaseous phase is plasma sheath procedure. The important factors effecting on gas discharge are gaseous component and voltage, frequency of power.

Kinetics of microbial growth and biodegradation of methanol and toluene in biofilters and an analysis of the energetic indicators

The kinetics of microbial growth and the biodegradation of methanol and toluene in (a) biofilters (BFs), and (b) biotrickling filters (BTFs), packed with inert materials, has been studied and analyzed. The specific growth rate, μ, for the treatment of methanol was 0.037 h −1 for a wide range of operating conditions. In the BF, μ was found to be a function of the methanol and toluene concentrations in the biofilm. In the BF used for treating methanol, μ was found to be affected by (1) the nitrogen concentration present in the nutrient solution, and (2) the kind of packing material employed. The kinetics of the methanol and toluene biodegradations were also analyzed using “mixed order” models. A Michaelis–Menten model type provided a good fit for the elimination capacity (EC) of the BTF treating methanol, while a Haldane model type provided a good fit to the EC of the BF treating methanol and toluene. The carbon dioxide production rate was related to the packed bed temperature and the content of the volatile solids within the biofilm. For the BF, the ratio of temperature/carbon dioxide production rate (PCO 2) was 0.024 °C per unit of PCO 2, and for the BTF it was 0.15 °C per unit of PCO 2.

Solar-Driven Coal Gasification in a Thermally Irradiated Packed-Bed Reactor

Coal gasification for high-quality synthesis gas production is considered using concentrated solar energy as the source of high-temperature process heat. The solar reactor consists of two cavities separated by a radiant emitter plate, with the upper one serving as the solar absorber and the lower one containing the reacting packed bed that shrinks as the reaction progresses. A 5 kW prototype reactor with an 8 cm depth, 14.3 cm diameter cylindrical bed was fabricated and tested in a high-flux solar furnace, subjected to solar flux concentrations up to 2600 suns and packed-bed temperatures up to 1440 K. The reactor is modeled by formulating the 1D unsteady energy conservation equation that couples conductive−radiative heat transfer with the reaction kinetics and solving it by the finite volume technique for a transient shrinking domain. The overall reaction rate was determined experimentally by thermogravimetry, while the effective thermal conductivity was determined experimentally in a radial heat flow ove...