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19 pages, 7294 KiB

Open AccessArticle

Design and Performance Investigation of a Compact Catalytic Reactor Integrated with Heat Recuperator

by Qiang Chen, Mingming Mao, Min Gao, Yongqi Liu, Junrui Shi and Jia Li

Energies 2022, 15(2), 447; https://doi.org/10.3390/en15020447 - 9 Jan 2022

Cited by 1 | Viewed by 1743

Abstract

The catalytic combustion has the advantage of lower auto-ignition temperature and helps to expand the combustible limit of lean premixed gas. However, the intake needs to be preheated to certain temperature commonly through an independent heat exchanger. Similar to the principles of non-catalytic [...] Read more.

The catalytic combustion has the advantage of lower auto-ignition temperature and helps to expand the combustible limit of lean premixed gas. However, the intake needs to be preheated to certain temperature commonly through an independent heat exchanger. Similar to the principles of non-catalytic RTO combustion, this paper presents a similar approach whereby the combustion chamber is replaced by a catalytic combustion bed. A new catalytic reactor integrated with a heat recuperator is designed to enhance the heat recirculation effect. Using a two-dimensional computational fluid dynamics model, the performance of the reactor is studied. The reaction performances of the traditional and compact reactors are compared and analyzed. Under the same conditions, the compact reactor has better reaction performance and heat recirculation effect, which can effectively decrease the ignition temperature of feed gas. The influences of the inlet velocity, the inlet temperature, the methane concentration, and the thermal conductivity of porous media on the reaction performance of integrated catalytic reactor are studied. The results show that the inlet velocity, inlet temperature, methane concentration, and thermal conductivity of porous media materials have important effects on the reactor performance and heat recirculation effect, and the thermal conductivity of porous media materials has the most obvious influence. Moreover, the reaction performance of multiunit integrated catalytic reactor is studied. The results show that the regenerative effect of multiunit integrated catalytic reactor is further enhanced. This paper is of great significance to the recycling of low calorific value gas energy and relieving energy stress in the future. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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24 pages, 9629 KiB

Open AccessArticle

A Multi-Scale Numerical Model for Investigation of Flame Dynamics in a Thermal Flow Reversal Reactor

by Jia Li, Ming-Ming Mao, Min Gao, Qiang Chen, Jun-Rui Shi and Yong-Qi Liu

Energies 2022, 15(1), 318; https://doi.org/10.3390/en15010318 - 3 Jan 2022

Cited by 2 | Viewed by 1530

Abstract

In this paper, the flame dynamics in a thermal flow reversal reactor are studied using a multi-scale model. The challenges of the multi-scale models lie in the data exchanges between different scale models and the capture of the flame movement of the filtered [...] Read more.

In this paper, the flame dynamics in a thermal flow reversal reactor are studied using a multi-scale model. The challenges of the multi-scale models lie in the data exchanges between different scale models and the capture of the flame movement of the filtered combustion by the pore-scale model. Through the multi-scale method, the computational region of the porous media is divided into the inlet preheating zone, reaction zone, and outlet exhaust zone. The three models corresponding to the three zones are calculated by volume average method, pore-scale method, and volume average method respectively. Temperature distribution is used as data for real-time exchange. The results show that the multi-scale model can save computation time when compared with the pore-scale model. Compared with the volumetric average model, the multi-scale model can capture the flame front and predict the flame propagation more accurately. The flame propagation velocity increases and the flame thickness decreases with the increase of inlet flow rates and mixture concentration. In addition, the peak value of the initial temperature field and the width of the high-temperature zone also affect the flame propagation velocity and flame thickness. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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24 pages, 6595 KiB

Open AccessArticle

Effect of Burner Wall Material on Microjet Hydrogen Diffusion Flames near Extinction: A Numerical Study

by Aravind Muraleedharan, Jithin Edacheri Veetil, Akram Mohammad, Sudarshan Kumar and Ratna Kishore Velamati

Energies 2021, 14(24), 8266; https://doi.org/10.3390/en14248266 - 8 Dec 2021

Cited by 2 | Viewed by 2629

Abstract

Characteristics of microjet hydrogen diffusion flames stabilized near extinction are investigated numerically. Two-dimensional simulations are carried out using a detailed reaction mechanism. The effect of burner wall material, thickness, and thermal radiation on flame characteristics such as flame height and maximum flame temperature [...] Read more.

Characteristics of microjet hydrogen diffusion flames stabilized near extinction are investigated numerically. Two-dimensional simulations are carried out using a detailed reaction mechanism. The effect of burner wall material, thickness, and thermal radiation on flame characteristics such as flame height and maximum flame temperature are studied. Results show that the flame stabilizes at lower fuel jet velocities for quartz burner than steel or aluminum. Higher flame temperatures are observed for low conductive burners, whereas the flame length increases with an increase in thermal conductivity of the burner. Even though thermal radiation has a minor effect on flame characteristics like flame temperature and flame height, it significantly influences the flame structure for low conductive burner materials. The burner tip and its vicinity are substantially heated for low conductive burners. The effect of burner wall thickness on flame height is significant, whereas it has a more negligible effect on maximum flame temperature. Variation in wall thickness also affects the distribution of H and HO₂ radicals in the flame region. Although the variation in wall thickness has the least effect on the overall flame shape and temperature distribution, the structure near the burner port differs. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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11 pages, 1647 KiB

Open AccessArticle

A Steady State Model for Burning Coal Mine Methane in a Reverse Flow Burner

by Jinsheng Lv, Junrui Shi, Mingming Mao, Xiangjin Kong and Dan Zhou

Energies 2021, 14(23), 7957; https://doi.org/10.3390/en14237957 - 29 Nov 2021

Viewed by 1812

Abstract

In this study, a steady state model for burning of coal mine methane in a Reverse Flow Burner (RFB) with full kinetics was developed by analogy of a steady counter-flow reactor, and the developed model was used for quick prediction of the lean [...] Read more.

In this study, a steady state model for burning of coal mine methane in a Reverse Flow Burner (RFB) with full kinetics was developed by analogy of a steady counter-flow reactor, and the developed model was used for quick prediction of the lean combustibility limit (LCL). The model was successfully validated with experimental and numerical results, and it was shown that the developed model has excellent accuracy and computational efficiency. Good agreement between the predicted temperature, LCL, and the experiments was observed. The LCL of the equivalence ratio of 0.022 for methane/air mixture was obtained by the developed model. The model was then used to evaluate LCL for the RFB, focusing on the effect of heat loss and burner length on LCL. This indicated that the computational time using the developed model can be reduced by a factor of 1560 compared to the complete transient model. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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15 pages, 2906 KiB

Open AccessArticle

CFD Simulation of Syngas Combustion in a Two-Pass Oxygen Transport Membrane Reactor for Fire Tube Boiler Application

by Te Zhao, Chusheng Chen and Hong Ye

Energies 2021, 14(21), 7348; https://doi.org/10.3390/en14217348 - 4 Nov 2021

Cited by 1 | Viewed by 1871

Abstract

The oxygen transport membrane reactor technology enables the stable combustion of syngas and reduction in NO_x emission. Applying the syngas combustion membrane reactor to fire tube boiler can integrate oxygen separation, syngas combustion, and steam generation in a single apparatus. In this [...] Read more.

The oxygen transport membrane reactor technology enables the stable combustion of syngas and reduction in NO_x emission. Applying the syngas combustion membrane reactor to fire tube boiler can integrate oxygen separation, syngas combustion, and steam generation in a single apparatus. In this study, a CFD model for oxygen permeation and syngas combustion in a two-pass LSCoF-6428 tubular membrane reactor for fire tube boiler application was developed to study the effects of the inlet temperature, the sweep gas flow rate, and the syngas composition on the reactor performance. It is shown that the inlet temperature has a strong effect on the reactor performance. Increasing the inlet temperature can efficiently and significantly improve the oxygen permeability and the heat production capacity. A 34-times increase of oxygen permeation rate and a doubled thermal power output can be obtained when increasing the inlet temperature from 1073 to 1273 K. The membrane temperature, the oxygen permeation rate, and the thermal power output of the reactor all increase with the increase of sweep gas flow rate or H₂/CO mass ratio in syngas. The feasibility of the syngas combustion membrane reactor for fire tube boiler application was elucidated. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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12 pages, 2987 KiB

Open AccessArticle

Three-Dimensional Pore-Scale Simulation of Flow and Thermal Non-Equilibrium for Premixed Gas Combustion in a Random Packed Bed Burner

by Jinsheng Lv, Junrui Shi, Mingming Mao and Fang He

Energies 2021, 14(21), 6939; https://doi.org/10.3390/en14216939 - 21 Oct 2021

Viewed by 1858

Abstract

Pore-scale studies of premixed gas combustion in a packed bed is conducted to study the flow and thermal non-equilibrium phenomenon in packed bed. The 3D random packed bed is generated using the EDEM software and solid surface radiation is computed using Discrete Ordinates [...] Read more.

Pore-scale studies of premixed gas combustion in a packed bed is conducted to study the flow and thermal non-equilibrium phenomenon in packed bed. The 3D random packed bed is generated using the EDEM software and solid surface radiation is computed using Discrete Ordinates (DO) model. The simulations are carried out using a commercial software package based on the finite volume method. It is shown that the local variation of species mass fraction, reaction rate et al. in pores near the flame front is significant, the radiation heat flux is transferred layer-by-layer. Cold flow simulation without reaction reveals that flow non-equilibrium is one of the essential characteristics of packing bed and increase in flow velocity leads to intensify non-equilibrium phenomenon. The distributions for content of axial velocity and gas temperature are wave-like shape in the burner and vary with time. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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11 pages, 1941 KiB

Open AccessArticle

Emission Characteristics of Pollution Gases from the Combustion of Food Waste

by Haili Liu, Xu Zhang and Qingchao Hong

Energies 2021, 14(19), 6439; https://doi.org/10.3390/en14196439 - 8 Oct 2021

Cited by 8 | Viewed by 2683

Abstract

The emission characteristics of pollution gases produced via the combustion of food waste were studied through a laboratory-scale electrically heated tube furnace. The results showed that the pollution gases generated from the combustion of food waste were CO, H₂ and NO_x [...] Read more.

The emission characteristics of pollution gases produced via the combustion of food waste were studied through a laboratory-scale electrically heated tube furnace. The results showed that the pollution gases generated from the combustion of food waste were CO, H₂ and NO_x. Each emission curve of CO had a peak. When the combustion temperature rose from 400 °C to 1000 °C, the peak first increased (from 400 °C to 700 °C) and then decreased (from 800 °C to 1000 °C). However, the burnout time shortened with the increase in temperature. Therefore, food waste should be combusted at a higher temperature than 700 °C from the perspective of reducing CO emissions. The emissions of H₂ were similar to those of CO. In other words, if CO emissions increased, H₂ emissions also increased in the same temperature range. Some NO_x emission curves had two peaks (the combustion of cooked rice at 1000 °C; the combustion of vegetable leaves in the temperature range of 600 °C to 1000 °C). The higher the combustion temperature, the higher the second NO_x emission peak. NO_x emissions from the combustion of cooked rice were greater in the temperature range of 400 °C to 500 °C, whereas for vegetable leaves, that temperature range was from 600 °C to 700 °C. Hence, from the viewpoint of reducing pollution gases, food waste should be combusted at a higher temperature than 700 °C. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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12 pages, 2333 KiB

Open AccessArticle

Improvement of the Combustion Completeness of Hydrogen Jet Flames within a Mesoscale Tube under Zero Gravity

by Junjie Hong, Ming Zhao, Lei Liu, Qiuxiang Shi, Xi Xiao and Aiwu Fan

Energies 2021, 14(15), 4552; https://doi.org/10.3390/en14154552 - 28 Jul 2021

Cited by 5 | Viewed by 1790

Abstract

Microjet hydrogen flames can be directly used as micro heat sources or can be applied in micro propulsion systems. In our previous study, under zero gravity and without an active air supply, the combustion completeness of hydrogen jet flames within a mesoscale tube [...] Read more.

Microjet hydrogen flames can be directly used as micro heat sources or can be applied in micro propulsion systems. In our previous study, under zero gravity and without an active air supply, the combustion completeness of hydrogen jet flames within a mesoscale tube with an inner diameter of 5 mm was very low. In this study, we were dedicated to improving the combustion efficiency by using a convergent nozzle (tilt angle was around 68°) instead of the previous straight one, and the exit diameter was 0.8 or 0.4 mm. The numerical results demonstrate that the maximum combustion efficiency in the case of d= 0.8 mm was only around 15%; however, the peak value for the case of d = 0.4 mm was around 36%. This happened because with d = 0.4 mm, the fuel jet velocity was around four times that of the d = 0.8 mm case. Hence, the negative pressure in the combustor of d = 0.4 mm decreased to a much lower level compared to that of d = 0.8 mm, which led to an enhancement of the air entrainment ratio. However, the highest combustion efficiency of d = 0.4 mm was still below 36%; therefore, a slightly larger tube or an even smaller nozzle exit diameter will be necessary for further improvements to the combustion efficiency. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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Review

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46 pages, 152246 KiB

Open AccessReview

Effect of Different Technologies on Performance Enhancement of the Micro-Combustor for the Micro Thermophotovoltaic Application: A Review

by Dongli Tan, Guicheng Ran, Guangling Xie, Jie Wang, Jianbin Luo, Yuanxing Huang, Shuwan Cui and Zhiqing Zhang

Energies 2021, 14(20), 6577; https://doi.org/10.3390/en14206577 - 13 Oct 2021

Cited by 12 | Viewed by 3393

Abstract

With the improvement and development of micro-mechanical manufacturing technology, people can produce an increasing variety of micro-electromechanical systems in recent years, such as micro-satellite thrusters, micro-sensors, micro-aircrafts, micro-medical devices, micro-pumps, and micro-motors. At present, these micro-mechatronic systems are driven by traditional energy power [...] Read more.

With the improvement and development of micro-mechanical manufacturing technology, people can produce an increasing variety of micro-electromechanical systems in recent years, such as micro-satellite thrusters, micro-sensors, micro-aircrafts, micro-medical devices, micro-pumps, and micro-motors. At present, these micro-mechatronic systems are driven by traditional energy power systems, but these traditional energy power systems have such disadvantages as short endurance time, large size, and low energy density. Therefore, efforts were made to study micro-energy dynamical systems with small size, light gravity, high density and energy, and long duration so as to provide continuous and reliable power for these systems. In general, the micro-thermal photoelectric system not only has a simple structure, but also no moving parts. The micro-thermal photoelectric system is a micro-energy power system with good application prospects at present. However, as one of the most important structural components of micro-thermal photoelectric systems, the microburner, is the key to realize the conversion of fuel chemical energy to electric energy in micro-thermal photoelectric system. The studies of how to improve the flame stability and combustion efficiency are very necessary and interesting. Thus, some methods to improve the performance of micro-burners were introduced and summarized systematically, hoping to bring some convenience to researchers in the field. Full article

(This article belongs to the Special Issue Combustion and Energy Conversion under Small Scales)

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