Inlet Gas Temperature Research Articles

Design and operation of a radio-frequency heated micro-trickle bed reactor for consecutive catalytic reactions

A radiofrequency heated micro-trickle bed reactor with two adjacent thermal zones was designed. In the first thermal zone, citronellal is converted to isopulegol over a H-ZSM-5 catalyst at 80°C. This is followed by the second thermal zone where hydrogenation isopulegol to menthol occurs over a Pd/TiO2 catalyst at 70°C. The two catalytic zones are separated by heating zones made of nickel ferrite particles that produce heat under radiofrequency field at 180kHz. The position of the catalytic zones was determined based on a one dimensional heat transfer model, in which the actual flow pattern was approximated. Such configuration allows achieving desired temperatures in the catalyst beds whereas the inlet and outlet gas temperatures are close to ambient temperature which increases energy efficiency of the system. The overall product yield was increased by 9 times as compared with a single thermal zone configuration.

석탄의 고품위화를 위한 기류건조기와 로터리킬른 건조기의 성능 비교평가

Drying, which is the oldest and most energy-intensive process, is an essential process for treatment of solid product. The specific procedure to design and evaluate the dryers, which are a rotary kiln dryer and a flash dryer, in case of drying the high-moisture coal was described. From determination of size to the heat and mass balance in one-dimensional model were conducted to evaluate the performance of dryers. Heat consumption, inlet gas temperature and size of the dryers were compared between a rotary kiln dryer and a flash dryer. Further considerations to evaluate the reactor elaborately were also discussed. Performance simulation of dryers along with the design procedure described here will provide helpful basis for understanding the concept of reactor design.

Modeling and simulation of soot combustion dynamics in a catalytic diesel particulate filter

In the work presented in this paper, a two-dimensional mathematical model of soot regeneration was developed for a single-channel catalytic diesel particulate filter. The commercial computational fluid dynamics (CFD) code ANSYS Fluent 15.0 was used to simulate the gas flow field, whereas the regeneration kinetics was implemented through user-defined-subroutines. Both mechanisms of catalyzed and non-catalyzed (i.e., thermal) oxidation were used to describe combustion of the soot trapped inside the porous wall of the filter. Conversely, only non-catalyzed oxidation was assumed for the cake layer. The aim of the work was at investigating the effect of the catalyst activity on the regeneration dynamics of the filter in the light of the thermal interaction between combustion of the soot in the (catalytic) porous wall and combustion of the cake. To this end, computations were run by increasing the pre-exponential factor in the Arrhenius equation for the catalytic reaction rate, thus simulating the effect of increasing catalyst activity.Numerical results have shown that, as the catalyst activity is increased, a transition occurs from a regime of slow combustion, in which regeneration proceeds in a substantially uniform manner over the filter, to a regime of intense combustion, in which regeneration proceeds by a reaction front moving upstream and downstream. The regime of slow combustion is characterized by low temperature rise (difference between the maximum filter temperature, Tmax, and the inlet gas temperature, Tin, lower than 100K) and long time for cake consumption and, thus, filter regeneration (~1800s). It is established when the catalyst activity is too low to appreciably affect combustion of the cake. Thus, combustion of the cake occurs independently of what happens in the porous wall of the filter. In contrast, the regime of intense combustion is characterized by high temperature rise – (Tmax−Tin)~400K – and short time for regeneration (~100s). It is established when the catalyst activity is high enough to make the porous wall of the filter an effective pilot for the cake. For this regime, the highest temperature rise is found under conditions that maximize the synchronization between combustion of the soot in the porous wall of the filter and combustion of the cake. When such a synchronization is attained, the time for filter regeneration becomes substantially insensitive to variations in the catalyst activity.

CFD simulation of transient gas to particle heat transfer for fluidized and spouted regimes

The transient gas to particle heat transfer for fluidized and spouted regimes was studied using a Eulerian–Eulerian two-fluid model (TFM) in conjunction with the kinetic theory of granular flows (KTGF). The inlet gas temperature was transient which increased with time. Effect of modelling parameter of specularity coefficient on the simulation results was studied. It was found that specularity coefficient is a critical parameter which affects on the particles behaviour and the value of 0.025 leads to creation of incoherent spouting similar to the measurements. The temporal variation of particles concentration and temperature distribution in the spouted and fluidized regimes were compared with the corresponding experimental data for three distinct regions of spout, fountain and annulus. It was shown that the CFD model predicted the particles distribution properly for both regimes. In addition, the CFD predictions for particle temperature distribution for the spouted regime were in a better agreement with the measurements, when compared with that for the fluidized regime.

Arrhenius activation energy of damage to catalase during spray-drying

The inactivation of catalase during spray-drying over a range of outlet gas temperatures could be closely represented by the Arrhenius equation. From this an activation energy for damage to the catalase could be calculated. The close fit to Arrhenius suggests that the thermally-induced part of inactivation of the catalase during the complex drying and particle-formation processes takes place at constant temperature. These processes are rapid compared with the residence time of the powder in the collecting vessel of the cyclone where dried catalase is exposed to a constant temperature equal to approximately the drying gas outlet temperature. A lower activation energy after spray drying with the ultrasonic nozzle was found than with the 2-fluid nozzle under otherwise identical spray drying conditions. It is feasible that the ultrasonic nozzle when mounted in the lid of the spray dryer heats up toward the drying gas inlet temperature much more that the air-cooled 2-fluid nozzle. Calculation of the Arrhenius activation energy also showed how the stabilizing efficacy of trehalose and mannitol on the catalase varies in strength across the range of drying gas inlet and outlet temperatures examined.

CFD modeling and experimental study of carbon dioxide removal in a lab-scale spray dryer

In a co-current lab-scale spray dryer absorber fitted with a two-fluid nozzle, the removal of carbon dioxide through chemical absorption with NaOH solution as absorbent was investigated experimentally and theoretically. Experimental results showed that in selected ranges of operating parameters, increasing the inlet gas temperature and absorbent concentration has the increasing–decreasing effect on the overall removal efficiency. Also increasing L/G ratio (liquid to gas flow rate), decreasing inlet CO2 concentration and decreasing the droplet mean diameter had favorable effects on overall removal efficiency. Process modeling was done through Computational Fluid Dynamics (CFD) method and using Ansys Fluent 13.0 software. In the three dimensional model of the process the gas phase was modeled as a continuum using the Euler approach and the droplet/particle phase was modeled by the Lagrange approach. An empirical correlation for reaction rate was obtained through experimental data and added to the CFD model of the process as a surface reaction via a user defined function. Predictions of the CFD model were compared to the experimental data. The model prediction in comparison to the experimental trends is fair.

Simulation of thermoelectric-hydraulic performance of a thermoelectric power generator with longitudinal vortex generators

This work investigates the feasibility of using LVGs (longitudinal vortex generators) to improve heat transfer in TEG (thermoelectric generator) systems. A coupled fluid-thermal-electric model is established with COMSOL Multiphysics® to study the effects of LVG height, LVG attack angle, and hot-side inlet gas temperature. We find that LVGs can significantly enhance the heat transfer performance, power output, and thermal conversion efficiency due to the generated longitudinal vortices, especially at small LVG attack angles. The performance of the thermoelectric generators with LVGs is best for LVGs that span the full height of the channel at the highest temperature examined (550 K), where the heat input, net power and thermal conversion efficiency are enhanced by 29%–38%, 90%–104% and 31%–36%, respectively, compared to smooth flow channel. As the hot-side inlet gas temperature decreases, the pumping power remains constant and requires a larger portion of the power output since the heat input and power output are significantly reduced. Therefore, it is not beneficial to use tall LVGs at lower hot-side inlet temperatures and higher inlet Reynolds numbers due to the large ratio of pressure drop to power output, but smaller LVGs are still useful under these conditions.

Mathematical modeling of polyethylene terephthalate pyrolysis in a spouted bed

A model has been developed for pyrolysis of polyethylene terephthalate (PET) in a spouted bed reactor based on the conservation equations for heat, mass, and momentum transports. A spouted bed has been constructed and the kinetic parameters have been obtained within the temperature range of 723–833 K, using two particle size ranges, (0.1–1.0) × 10−3 and (1.0–3.0) × 10−3 m. The model' predictions for the radial distributions of temperature and concentration confirm the excellent mixing of particles. Thus, spouted beds are appropriate equipments for performing kinetic studies of PET pyrolysis. The inlet gas temperature and the mass of PET highly affect PET conversion. The amount of inert particles has a negligible effect on the conversion and it can be reduced as far as a stable spouting is preserved. The gas flow suffices to eliminate the external heat and mass‐transfer limitations. It can be reduced to the minimum value to decrease the energy consumption. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1900–1911, 2015

Transport membrane condenser for water and heat recovery from gaseous streams: Performance evaluation

Using a tubular ceramic membrane as the transport membrane condenser for simultaneous water and heat recovery from gaseous streams is experimentally investigated in the current study. The effects of several important operational parameters (e.g. gas flow rate, coolant flow rate, transmembrane pressure and inlet gas temperature) on the process performance in terms of mass and heat transfer across the membrane are systematically studied. It is found that mass and heat transfer rates can be enhanced by increasing the gas flow rate, coolant water flow rate and the temperature of the inlet gas stream. To improve the water and heat recovery, a low gas flow rate but a high coolant flow rate should be maintained. Increasing the transmembrane pressure difference decreases the mass and heat transfer mainly due to the reduced inlet gas humidity, enthalpy and flow rate. However, water and heat recovery does not change significantly with the change in transmembrane pressure. 20–60% water recovery and 33–85% heat recovery are achievable when using cold water as the coolant. The mass transfer mechanism in membrane condensation is complex and needs further exploration. These findings offer significant implications in using transport membrane condensers for water and heat recovery from gas streams with high moisture.

Effect of precooled inlet gas temperature and mass flow rate on final state of charge during hydrogen vehicle refueling

Short refueling time and high final state of charge are among the main hydrogen car user's requirements. To meet these requirements, without exceeding the tank materials safety limits, hydrogen precooling is needed. Filling experiments with different inlet gas temperatures and mass flow rates have been executed using two different types of on-board tanks (type 3 and 4). State of charge has a strong dependency on the inlet gas temperature. This dependency is more visible for type 4 tanks. Lowest precooling temperature (−40 °C) is not always required in order to meet user's requirements, so energy savings can be achieved if the initial conditions of the tank are correctly identified. The results of the experiments performed have been compared with the SAE J2601 look-up tables for non-communication fillings. A big safety margin has been observed in these tables. Refueling could be performed faster and with less demanding precooling requirements if the initial conditions and the configuration of the hydrogen storage system are well known.

Bed Pressure Drop in a Draft‐Tube Conical Spouted Bed for Thermal Treatment of Wastes

AbstractAn experimental study of operating bed pressure drop was performed in thermal treatment of coarse waste particles of different size, density, and sphericity in conical spouted beds by introducing a nonporous draft tube. The influence of introducing a nonporous draft tube as well as of operating conditions on bed pressure drop was determined. Bed pressure drop in conical spouted beds with a nonporous draft tube was found to be lower than that without any device, which allows for saving operating costs. The most important factor influencing the bed pressure drop was the stagnant bed height. The bed pressure drop was reduced when stagnant bed height, particle density, particle sphericity or inlet gas temperature were decreased. Likewise, the bigger the particle diameter, the lower was the bed pressure drop.

Influences of exhaust gas temperature and flow rate on optimal catalyst activity profiles

This paper presents an optimization of an axial catalyst distribution for the two types of optimal axial catalyst distributions: continuous exponential and discrete two-zone, to enhance the light-off of a catalytic converter with a fixed amount of a catalyst. The influences of exhaust gas temperature and mass flow rate on the two types of optimal active component distribution profiles are identified and hence an optimum value for each of the operating conditions is quantitatively established. The catalyst surface area of the optimal distribution in the upstream section is greater, and in the downstream is lower than that of the uniform distribution. As an inlet exhaust gas temperature becomes lower than the catalyst light-off temperature, i.e., about 600K, the catalyst surface area of the optimal distribution at the monolith inlet increases greatly to attain high reaction rates at the monolith entrance. In contrast, at temperatures above 600K, it decreases slightly and hence its variation becomes negligibly small, as compared to the variation of the inlet gas temperature. The catalyst surface area at the monolith entrance decreases gradually with the increasing mass flow rate at gas temperatures above 550K.

Innovative use of membrane contactor as condenser for heat recovery in carbon capture.

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.

Nanoporous membrane tube condensing heat transfer enhancement study

A Transport Membrane Condenser (TMC), made from nanoporous membrane tube bundles, was developed to recover the water vapor and its significant amount of latent heat from boiler flue gases to improve boiler efficiency and save water. Experiments have been carried out to study the phenomena for both a nanoporous membrane tube bundle and an impermeable stainless steel tube bundle with the same characteristic dimensions. Flue gas streams with water vapor mass fraction 11.3%, temperature range from 65°C to 95°C are used for the experimental study, which covers the typical TMC waste heat recovery application parameter ranges. Results show convection Nusselt numbers of the membrane tube bundle are 50–80% higher than that of the impermeable stainless steel tube bundle at typical condensation heat transfer conditions. The parametric study has been done by varying cooling water inlet flow rate, water inlet temperature, flue gas inlet flow rate, inlet temperature, and inlet dew point. The condensing heat transfer enhancement effect gives a good perspective for using nanoporous membrane surface to design high efficiency condensing heat exchangers to recover both water vapor and its latent heat from high moisture content low grade waste heat streams.

Influence of Granule Porosity during Fluidized Bed Spray Granulation

Fluidized bed spray granulation is an important process for the transformation of liquids into solid materials. Especially product properties like final particle size and structure of the granules are important. These properties are closely related to the selected process parameters such as temperature and spraying rate. By knowing the relationship between the thermal process conditions and resulting particle structure, the final product can be designed according to the wishes of the consumers. In the presented work, a correlation between the thermal process conditions and the achieved shell porosity, which is relevant for the particle structure, is revealed. Therefore two experimental series with different materials (non-porous glass particles and porous alumina) were performed in a lab-scale fluidized bed spray granulator. The lab-plant allows the precise measurement of the inlet and outlet temperatures and moisture contents of the gas. All process parameters were kept constant except the inlet gas temperature and the spraying rate. Although the amount of initial material as well as the amount of injected solution was the same for all experiments, the final particle size distribution and the structure of the formed shell were clearly different. The obtained experimental results were compared with a process model including a new expression for the growth kinetics, which takes into account an acceleration of the growth velocity due to the formation of a porous structure. The used model also considers the separation of the fluidized bed into two different zones, namely the spraying zone and the drying zone. With the given initial process conditions, the model calculates the time evolution of the particle size distribution, the theoretical outlet temperature and the moisture content of the gas. The introduction of the shell porosity into the growth kinetics reduces the underestimation of the particle size in the model, which occurs if the formed layer on the particle surface is assumed to be compact.

Computational Fluid Dynamics Simulation: Hydrogen Production from Biogas Autothermal in Monolithic Catalyst Reactor

Abstract This research aims to find out the characteristic of autothermal biogas on catalyst monolithic reactor especially the influence of inlet gas temperature and H 2 O/C ratio. Monolithic catalyst has dimension 45 mm × 45 mm × 225 mm with cell density 600 cpsi. The research with Computational Fluid Dynamics (CFD) simulation involved four reactions: oxidation, steam reforming, water gas shift, and decomposition. This result elucidated that the higher inlet gas temperature, the higher methane conversion, hydrogen concentration, and carbon monoxide including the lowering H 2 /CO ratio. In addition, this research resulted that the higher H 2 O/C ratio, the higher is the hydrogen concentration with the lowering carbon monoxide concentration involving the increase of H 2 /CO ratio.

管状火炎を用いた二段燃焼のNO<sub>x</sub>低減効果

The recuperative burner and the regenerative burner that applied exhaust heat recirculation are proposed as energy-saving technology in furnaces in a practical use. Although, heating efficiency has the proportional to the rate of the exhaust heat recirculation, the burned gas temperature and NOx emission increases in the conditions of high exhaust heat recirculation. The newly developed two-stage combustion method was proposed in this research for improving NOx reduction. The two-stage combustion method is often applied as low NOx technology with using exhaust heat recirculation. This research proposed a tubular flame for the first stage of two-stage combustion. Since the tubular flame can sustain a stable premixed flame in rich mixture in the first stage, NOx generated in the primary burner suppresses due to low flame temperature in this proposed system. In addition, the inlet gas temperature in the secondary burner can be adjusted by intermediate cooling section that placed between the primary burner and secondary burner. This reduction of the inlet gas temperature is also contributed to reduction of NOx in the secondary burner. Results show that the first flame was successfully formed until equivalence ratio 1.7 by using tubular flame in the primary burner. The smallest NOx emission appeared in the condition that the adiabatic flame temperature become equilibrium to the amount of heat reduction calculated from the intermediate cooling section. The NOx emission is reduced to 16.3 ppm (O2=0%) at the equivalence ratio of 1.67 in the primary burner without intermediate cooling tube. This value is about 1/6 of the single-stage combustion with Bunsen flame, and about 1/4 of the two-stage combustion with partially premixed flame in the primary burner.

Analysis on three-dimensional flow and heat transfer in a cross wavy primary surface recuperator for a microturbine system

In this paper, 3-D periodic numerical model for fully developed flow in a cross wavy primary surface recuperator for a microturbine system is built. The performance of flow and heat transfer is analyzed. The fields of flow and temperature in a gas and air channel are obtained. Different working conditions are numerically simulated. Numerical results are compared with experimental data concerned. Analysis results show that the flow in the gas and air channel is anti-symmetry along the centre of channel. The flow of fluid is fluctuant. The flow velocity of gas is much higher than that of air. The thermal ratio of cross wavy primary surface recuperator can reach 95.2%. The thermal ratio decreases with the improvement of gas inlet temperature. When gas inlet temperature increases by 100 K, the thermal ratio decreases by about 1%. The thermal ratio increases with the reduction of flow rate in the channel. When flow rate reduces by 40%, the thermal ratio increases by about 4%. The research results can be used to guide checking the performance of a recuperator.

Process simulation of ammonia-based CO<SUB align="right">2 capture and regeneration in packed column

Post-combustion CO2 capture using aqueous ammonia offers advantages over the conventional amines solvent, including lack of corrosion, an enhanced CO2 loading capacity and low energy input requirement for solvent regeneration. In this paper, an aqueous ammonia-based CO2 absorption-desorption process integrated with washing column is modelled and simulated in Aspen Plus®. The predicted results agreed with published experimental results. The effect of performance parameters such as the ammonia concentration in lean solution, CO2 fraction in the flue gas, inlet feed gas temperature, stripper operating temperature and pressure, lean solution temperature and flow rates of the flue gas, were investigated. The gas temperature showed trivial effect on CO2 absorption efficiency; therefore the absorber column can be fed with hot flue gases, eliminating the need for cooling. The results show that the washing columns coupled at top of the absorber and stripper columns enabled the system to maintain ammonia slip within permissible level.

Numerical Investigation of Adiabatic Film Cooling Effectiveness over a Flat Plate Model with Cylindrical Holes

Film cooling is one of the cooling techniques used in gas turbines to protect the blades from high temperature. The efficiency of gas turbine can be increased by increasing the inlet gas temperature. The present study aims at numerical investigation of adiabatic film cooling effectiveness over the cylindrical hole exit flat plate test model. The hole inclination angle of 20° with stream wise direction is considered. The test model has 35 film cooling holes arranged in two rows in a staggered configuration with the coolant hole length to diameter ratio of 5.4 and pitch to diameter ratio of 4. During the experimental analysis, the adiabatic film cooling effectiveness is found at five different blowing ratios in the range of 0.5 to 2.5 with the coolant to mainstream density ratio at 1.6. The laterally averaged film cooling effectiveness is calculated along the stream wise direction at these blowing ratios. The realizable k-epsilon turbulence model with enhanced wall function is used to solve the flow field. The CFD obtained results are validated with the experimental results at a blowing ratio of 1.0. Further, the CFD analysis is done for other blowing ratios in the range of 0.5 to 4.0 at density ratios of 1.6, 1.8 and 2.0. From the CFD results, the laterally averaged film cooling effectiveness is found to be increasing with the increase in blowing ratio up to 1.5 immediately downstream of the coolant holes. For the blowing ratios of 2.0 to 4, the adiabatic film cooling effectiveness is less immediately downstream of coolant holes up to x/d=15 and then increases with increase in the blowing ratios considered.