High Temperature Air Combustion Research Articles

Impact of Particle Size and Carrier Gas on Pulverized Bituminous Coal Emissions: Experimental and Computational Fluid Dynamics Analysis

This study explores the influence of particle size and carrier gas on the clean and efficient combustion of pulverized 'Barapukuria' bituminous coal. Both experimental and numerical analyses were conducted to examine the temperature and fluid flow in a 1400 mm long vertical furnace with a 344 x 344 mm² interior crosssection. High-Temperature Air Combustion (HTAC) was employed to minimize NOx emissions. The research focused on volatile matter and reactivity during combustion, evaluating their impact on NOx, CO2, and CO generation. CO2 was used as a carrier gas to inject coal particles with sizes ranging from 0.001 to 0.02 mm. Results showed flue gas recirculation and varied devolatilization patterns with different particle sizes. Smaller particles produced less NOx compared to larger particles, highlighting the potential for improved combustion and reduced emissions. Computational fluid dynamics (CFD) analysis also supported the experimental results. By optimizing combustion parameters, this study may contribute to achieve environmental sustainability. Journal of Engineering Science 14(1), 2023, 65-76

Development of a waste incinerator based on high-temperature air combustion technology

Development of a waste incinerator based on high-temperature air combustion technology

Four-step global kinetics mechanism for diluted combustion fueled with kerosene

The aim of the present study was to develop a global kinetics mechanism capable of predicting characteristics of the combustion of kerosene diluted with combustion gases. A four-step model of the Aachen mechanism was developed via modification of a mechanism for lower molecular weight hydrocarbons. A simplified fuel was used to simulate kerosene, the thermodynamic properties of which were estimated based on the surrogate fuel in the Aachen mechanism. Combustion of this model fuel in a perfectly stirred reactor (PSR) operating under high-temperature air combustion (HiTAC) conditions was simulated using inflow mixtures preheated and diluted with nitrogen. In this new mechanism, the activation energy for the fuel consumption reaction and the pre-exponential factor for the hydrogen oxidation reaction were adjusted. The resulting model accurately predicted variations in temperature and major species over time. The four-step mechanism was also validated under conventional flame and moderate or intense low oxygen dilution (MILD) combustion conditions. The PSR simulations with the four-step mechanism accurately predicted variations in temperature and major species under MILD combustion conditions. In addition, this four-step mechanism was confirmed to be superior to other global mechanisms with regard to predicting the mole fractions of various species. Experimental trials were carried out with diluted kerosene flames formed above parallel jet burners composed of a fuel spray nozzle and an oxidizer nozzle, and it was found that NOx emission decreased with increasing distance between nozzles even for spray combustion. These diluted flames were numerically simulated using the eddy dissipation concept model combined with the four-step mechanism. The temperature distributions obtained from the simulations showed good agreement with the experimental data in the downstream region.

Combustion regime identification and characteristics of nitrogen-diluted ammonia with hot air oxidizer: Non-premixed counterflow flame

In this study, a numerical investigation was done to study the characteristics of N2-diluted ammonia combustion in a counterflow diffusion configuration with an elevated oxidizer temperature. The flame structures have been characterized in a steady laminar, unidimensional configuration in which hot oxidant and diluted fuel are representative of recirculating flow required to achieve High Temperature Air Combustion (HiTAC) and moderately or intense low-oxygen dilution (MILD) combustion. Investigations were done from a combustion-regime viewpoint to find the effect of each regime on the ammonia flame structure and emission. The specific working conditions of each regime were also identified. The heat release rate typology and temperature rise were analyzed with respect to external parameters such as dilution, oxidizer temperature, and thermal power to determine the boundaries of each regime of ammonia combustion. The results suggest the desired fuel dilution and oxidizer temperature to achieve a favorable combustion regime. It has been found that a high dilution of 0.8 is at least required for the MILD combustion of ammonia to occur. An enhancement has been found in the heat release rate, temperature, and main intermediate and final species in correspondence with combustion regime transition. It is shown that ammonia combustion characteristics in HiTAC and MILD regimes can be favorable in terms of stability and Emissions.

Numerical Investigation on the Impact of Exergy Analysis and Structural Improvement in Power Plant Boiler through Co-Simulation

In current power station boilers, fuel burns at a low temperature, which results in low exergy efficiency. This research combined the second law of t with the boiler structure to maximize the efficiency of a 350 MW power plant boiler. A three-dimensional simulation of the combustion process at the power plant boiler is performed. A one-dimensional simulation model of the boiler is then constructed to calculate the combustion exergy loss, heat transfer exergy loss, and boiler exergy efficiency. Under the principle of high-temperature air combustion technologies, this paper also proposes a new structure and improved operating parameters to improve the exergy efficiency of boilers by reducing the heat exchange area of the economizer and increasing the heat exchange area of the air preheater. Simulation results show that the exergy efficiency of the boiler increased from 47.29% to 48.35% through the modified model. The simulation outcomes can instruct future optimal boiler design and controls.

H2 – CH4 blending fuels combustion using a cyclonic burner on colorless distributed combustion

H 2 – CH 4 mixture fuels can be promising for reducing carbon-based emissions. However, because of higher pollutant emission (such as NO X ) problems during hydrogen combustion, a new combustion method can be favorable. Colorless distributed combustion (CDC) is emerging here. CDC enables ultra-low pollutant emissions along with reduced flame instabilities, combustion noise, improved combustion efficiency, etc. Considering those benefits, methane and the hydrogen-enriched methane (60% CH 4 – 40% H 2 , 50% CH 4 – 50% H 2 , 40% CH 4 – 60% H 2 ) fuels have been consumed using a cyclonic burner providing more residence time at an equivalence ratio of 0.83 under distributed regime. For the modelings, Reynolds Stress Model (RSM) turbulence model, the assumed-shape with β-function Probability Density Function combustion model, and P-1 radiation model have been selected. To seek CDC, the oxygen concentration in the oxidizer was reduced with N 2 or CO 2 diluent from 21% O 2 to 13% O 2 at an interval of 2%. The air and the fuel temperatures were kept constant at 300 K. Besides, for seeking high-temperature air combustion (HiTAC) conditions the oxidizer temperature was changed to 600 K to simulate flue gas recirculation. The results showed that the temperature distributions changed to be more uniform considerably with a decrease in oxygen concentration for all cases. CDC also provided a considerable decrease in NO X and a favorable reduction in CO at a certain oxygen concentration. It has been concluded that CO 2 as the diluent was more effective for reducing temperature levels and NO X levels due to its greater heat capacity. • H 2 – CH 4 blending fuels combustion have been examined in a cyclonic burner. • Colorless distributed combustion (CDC) was sought for H 2 – CH 4 blending fuels. • Reduced oxygen concentration affected considerably all combustion characteristics. • Combustion characteristics were changed with increase in hydrogen content. • Ultra-low pollutant emissions were achieved under CDC.

Study of high-temperature oxygen combustion (HiTOx) and its heating performance using a laboratory-scale test furnace

Abstract High-temperature air combustion technology (HiCOT), which uses air preheated by heat recirculation, has had a great impact on reduction of CO2 and NOx emissions from combustion furnaces. In this study, a lab-scale test furnace was developed to examine the novel combustion method termed as high-temperature oxygen combustion, HiTOx. HiTOx uses combustion with a preheated mixture of oxygen and burned gas. Testing was conducted with liquefied petroleum gas. HiTOx has the following three characteristics because nitrogen is excluded from the working gas: (1) in principle, no thermal NOx is generated; (2) combustion gas is almost entirely water vapor and carbon dioxide, providing better heating performance because of its strong gas-phase radiation; and (3) the method has good compatibility with carbon dioxide capture, utilization and storage (CCUS) technologies because carbon dioxide can be separated easily from the combustion gas of HiTOx furnace by condensation of water vapor. Heating performance tests in a lab-scale test furnace were conducted using stainless steel rectangular rods as heating objects. Gas temperature, object temperature, and heat fluxes on the objects were measured. Compared to HiCOT, HiTOx enables stable operation with a lower flow rate of flue gas, better gas temperature uniformity in the furnace, faster heating, and higher heat flux. The heat flux of HiTOx was slightly higher than that of HiCOT (7%) when the furnace temperature was low (973 K) and the temperature difference between the gas and object was large (280 K). On the other hand, the heat flux of HiTOx was much higher than that of HiCOT (22%) when the furnace temperature was high (1323 K) and the temperature difference was small (60 K). Radiative heat transfer at high temperature was greater in HiTOx than in HiCOT at small temperature difference between the gas and object. A furnace body can be greatly downsized by the good radiation performance of combustion gas in HiTOx, resulting in a remarkable improvement in energy-saving performance.

Review on MILD Combustion of Gaseous Fuel: Its Definition, Ignition, Evolution, and Emissions

Combustion of fossil fuels has been continuously generating over 70% of the total energy for our human society, concurrently emitting vastly greenhouse gases and ecologically harmful pollutants. To mitigate the adverse issue, combustion technologies of a new type were successfully developed and debuted around 1990, associated with various terms of “flameless oxidation (FLOX)”, “flameless combustion (FLC)”, “high-temperature air combustion (HiTAC)”, and “moderate and intense low-oxygen dilution (MILD) combustion”. These combustion processes may be regarded as similar or the same class of combustion, because they all involve high preheat and deep dilution of individual reactants (non-premixed) or the reactant mixture (premixed), prior to main combustion reactions, with high-temperature flue gases (burnt products) internally and/or externally. Very significantly, all of these combustion technologies can simultaneously achieve high efficiency and ultralow emissions of nitric oxides (NOx), light, and noise. This class of combustion has been frequently unified as “MILD combustion”. Highly worthy to note, as a particular type of combustion, the MILD combustion has thus far been most extensively explored, resulting in many hundreds to 1000 academic articles published by various energy-related journals and conferences. The present review summarizes the research progress in the gaseous-fuel MILD combustion on its definition, ignition, evolution, and NOx emissions, specifically, through its aspects associated with open jet flames in hot coflow and industrial flames in combustion chamber or furnace. Also, discussions are provided on the relevant terminologies, existing problems, and further fundamental issues.

High temperature air combustion (HiTAC): How it all started for applications in industrial furnaces and future prospects

Over the last three decades, High Temperature Air Combustion (HiTAC) has contributed much to become the leading technology for fossil fuel conversion in industrial furnaces. Since then several other researchers have termed it MILD, Flameless or Distributed combustion and they all show much similarities with the HiTAC. This review underlines that the technology was developed through a cooperation between the Japanese government (NEDO, METI) and Nippon Furnace Kogyo (Japan) as well as the key role played by the University of Maryland (USA) and the International Flame Research Foundation (IFRF – the Netherlands). Tokyo Gas (Japan) also provided an important role, although indirect, in the development. The HiTAC technology development was revolutionary with simultaneous demonstration on significant energy savings (some 25%), reduced equipment size, much reduced pollution (50%, including CO2), and noise in industrial furnaces. The technology is now widely used in many modern industrial furnaces worldwide. Per METI some 39,000 HiTAC burners in 7867 industrial furnaces were installed worldwide that showed fuel savings of 1721 billion liters of crude oil/year. It is estimated that 68 Billion liters/year of fuel oil savings and 180 Billion tons/year of CO2 reduction will be realized by 2030 through the use of HiTAC technology in industrial furnaces. This revolutionary technology continues to be adapted by many countries worldwide. The authors provide a brief review on the HiTAC technology development and give their views on its potential applications on the horizon that will also contribute to cleaner and efficient combustion in many other applications, besides industrial furnaces. These include high intensity gas turbine combustion, portable power, and engines. We do not discuss MILD and Flameless combustion as they have been reviewed previously with proliferation of numerous scientific publications available in the literature on the subject.

Prospect analysis of high temperature air combustion technology for low calorific value coalbed methane in Liupanshui area of Guizhou province

China’s coalbed methane resource is abundant, which ranks third in the world. The total amount of coalbed methane resources in Guizhou Province accounts for about 10% of China, which ranks second in the country. However, the utilization rate of coalbed methane in Guizhou Province is not only low, but also relatively single, especially the low calorific value coalbed methane extracted from underground mines which has a methane concentration of only 10-30%. And the main method to deal with low calorific value coalbed methane is discharging directly, which caused a huge waste of energy. High temperature air combustion technology (HTAC), which expands the utilization range of low calorific value fuels, has attracted wide attention due to its characteristics of extreme recovery of waste heat and ultra-low NOx emission. In this paper, the characteristics of high temperature air combustion of low calorific value coalbed methane are analyzed by theoretical and numerical calculation based on combustion theory and CFD method.

HIGH TEMPERATURE COMPACT CERAMIC REGENERATIVE HEAT EXCHANGER

The subject of the research is the high-temperature compact ceramic heat exchanger of a regenerative type with a honeycomb structure. In relation to high-temperature processes of basalt smelting and glass melting, the possibility of its application in a system of high-temperature air combustion is considered. It is noted that heating of the air pursues both energy goal – reduction of natural gas consumption, and technological goal – increasing the amount of free oxygen in the basalt processing zone. The methods of determining the transient temperature field in the wall of the solid heat-storing material of the regenerator and the operating time of the heat exchanger from the condition of ensuring the permissible surface temperature of the heat regenerator are given. It is established that for the range of the Fourier number Fo≤2.5, it is possible not to take into account the temperature distribution in the wall of the solid heat-storing material of the regenerator and to operate with its average temperature. Features of compact ceramic regenerative heat exchangers are given – heat exchanger efficiency, heat recovery coefficient, number of transfer units, power – as applied to the conditions of the heat engineering process. The heat exchanger efficiency is confirmed. The operating time of the heat exchanger and its effect on the surface temperature of the solid heat-storing material are determined. It is shown that in relation to the conditions of the basalt melting and glass melting processes, the material of the regenerative heat exchanger – mullite – is not an optimal solution. Only for one of the considered variants of the technological process, the surface temperature of the regenerative heat exchanger was lower than the permissible temperature of prolonged use of mullite. In other cases, the resulting temperature of the regenerator exceeded the permissible value of long-term use. It is advisable to use a material with a permissible temperature of application of 1525 °C and above as of the solid heat-storing material of the regenerator. Testing of the results of the research was carried out on pilot industrial samples of bath melting furnaces equipped with HiTAC (high-temperature air combustion system).

Experimental research on the application of HTAC in small-size heating furnace

High temperature air combustion (HTAC) technology, which is also known as regenerative combustion technology, has realized energy saving, CO2 and NOx emissions reduction and low-noise combustion. It has been widely applied in various types of heating furnace and has achieved good energy-saving effect. However, there is little application of this technology in small-size furnace. In this paper, a small-size regenerative heating furnace was built in the laboratory and experiments were carried out on it. The result shows that, if the transport frequency was set to a group per min, the center temperature of processed workpiece at the rated conditions (i.e. burner power is 300 kW and switching time is 60s) reached 1133°C. And the efficiency of the heating furnace was 36.8%. Then the derived comprehensive heat transfer coefficient was 168 W/(m2˙°C).

Numerical investigation towards HiTAC conditions in laboratory-scale ethanol spray combustion

In the past 25years high temperature air combustion (HiTAC) technology has been proved and utilized in industry as a promising way to increase thermal efficiency, create a relatively uniform temperature distribution, and reduce emissions of harmful pollutants such as NOX and CO. However, due to the complexity of fuel-oil combustion, to date HiTAC is mainly applied to gaseous fuel or coal, and little is known about spray combustion under HiTAC condition. In the present study, we numerically investigate the Delft Spray-in-Hot-Coflow (DSHC) using ethanol in high temperature diluted combustion air, and extend it to more co-flow conditions. We employ different temperatures and oxygen concentrations of the co-flow in order to dilute the oxidizer/fuel before it reacts with the fuel/ oxidizer. The pressure-swirl atomizer model with an Eulerian-Lagrangian approach was implemented for the spray modeling. Collision, coalescence, secondary breakup and evaporation of the drops were taken into account. The steady laminar flamelet model for the combustion of ethanol, the Discrete Ordinate model for radiation and the k-ε model for the turbulence with enhanced wall treatment were validated by the simulation of the NIST flame under conventional conditions and then used in the current study.The results indicate that the decreased peak temperature in many HiTAC applications with high temperature combustion air is mainly due to the reduced oxygen concentration by entraining flue gas.In the present study, a low oxygen concentration slows the evaporation process of droplets. It results in an enlarged combustion zone, a lowered peak temperature and minor NOX emission. However, decreasing the oxygen concentration may lead to problems of cracking, soot formation and flame extinction, especially for heavy oils. The optimization needs to be carried out based on the analysis of a specific fuel in order to create a HiTAC-like condition.Based on the results of the current study, the 1500K and 6%vol oxygen concentration case is considered as a HiTAC condition.

7-1-3 対向流型吹き込み方式を適用したストーカ式廃棄物焼却炉のNOx低減メカニズムに関する考察

7-1-3 対向流型吹き込み方式を適用したストーカ式廃棄物焼却炉のNOx低減メカニズムに関する考察

7-2-2 高温空気燃焼技術を適用したストーカ式焼却炉の性能向上(Session 7-2 環境対策)

7-2-2 高温空気燃焼技術を適用したストーカ式焼却炉の性能向上(Session 7-2 環境対策)

Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System

The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications [...]

対向流燃焼を適用したストーカ式焼却炉の低NOx化に関する性能評価

JFE Engineering has developed the advanced stoker-type incineration system “JFE Hyper 21 Stoker System”, which adopts high temperature air combustion technology. With this technology, the incinerator realizes stable combustion in the condition of low excess air ratio, which results in reduction of NOx formation. In this paper, we describe a newly developed stoker-type incinerator which utilizes counter flow combustion in addition to high temperature air combustion technology. Verification experiment was conducted and further reduction of NOx formation was achieved. Experiment and numerical simulation were carried out to consider the reduction mechanism of NOx. Flat combustion region which contributes to stable combustion was observed in both experiment and simulation. Oxygen concentration distribution in the furnace implies that effective two-staged combustion is formed. From the view of fluid analysis, strong turbulence region is formed in the downstream of the furnace. These factors are considered to interact with each other and contribute to suppress the NOx formation.

Numerical Investigation of Oxy-mild Combustion of Pulverized Coal in a Pilot Furnace

Abstract The Conventional coal-fired plants are large contributors to air pollution and greenhouse gas. The combustion generates pollutants such as oxides of sulphur, nitrogen, and carbon as well as fine organic and inorganic particulates. The new technologies able to reduce drastically the pollutant emissions and facilitate to use of coal in an environmentally more friendly way, are commonly known as clean coal technologies (CCT). In this context the CCS technologies play an important role to reduce the CO2 emissions. The only form with truly zero CO2 emissions in existence today is pre-combustion gas separation, namely, the combustion of fuel using oxygen instead of air. It is well known that burning pulverized coal in pure oxygen increases the flame temperatures, thus also increases NOx emissions. Therefore, to moderate the flame temperature and reduce NOx the oxygen is mixed with recycled flue gas (RFG). This approach to reduce CO2 emissions is often called oxy-firing or oxy-fuel combustion. The purified CO2 stream is then compressed and condensed to produce a manageable effluent of liquid CO2, which can be sequestered for storage (CCS) or for use in subsequent processes (CCR). MILD (Moderate or Intensive Low Dilution) or HiTAC (High Temperature Air Combustion) is an innovative combustion technology and probably the most important achievement of the combustion technology in recent years. In MILD combustion the reactions take place in almost the whole volume of the combustion chamber. This leads to temperature and species concentration fields uniform in the chamber. The fuel is oxidized in an environment that contains a substantial amount of inert gases (N2, CO2, H2O) and low oxygen concentrations. This is caused by an internal recirculation of combustion products generated by injecting preheated air jets into the combustion chamber with very high momentum, bringing the temperatures close to the combustion products temperature, reducing the NOx emissions. Because both technologies allow reductions of pollutant emissions, the aim of this work is to demonstrate the advantages of a combination of these two combustion technologies in order to analyze the temperature and specie concentrations field, the CO2 and NOx emissions by means of CFD. The goal is understand if it is possible to combine the MILD combustion and OXY one in order to reduce the NOx emissions, and capture the CO2.

Innovative Design and Manufacturing Technology of High Temperature Air Combustion (HTAC) Municipal Solid Waste Incinerator

Incineration is a Thermal Treatment Technology (3Ts) that could be expressed as the way to get rid of waste effectively with the reduction of its mass and volume. However, to control the combustion process efficiently, especially combustion temperature, with low energy content in Municipal Solid Waste (MSW), an additional fuel is needed and leads to increase of operating cost compared with other disposal option. High Temperature Air Combustion (HTAC) has been successfully demonstrated in a lab-scale incinerator for energy saving and pollutant reduction, especially NOx. This article has the objective to design and manufacture the prototype scale High Temperature Air Incinerator with a capacity to treat MSW of 12 Ton per day. The system consists of an automatic feeding machine to feed the waste into the primary combustion chamber (PCC) where the combustion takes place. The push ram is used to push the burning waste and fall down to the lower hearth. Primary combustion air is supplied into PCC at the amount lower than the stoichiometric requirement to produce the combustible gas which is flown into the Secondary Combustion Chamber (SCC) located above PCC. Secondary combustion air is injected to react with combustible gas to convert to the product of complete combustion. A part of hot flue gas which is flew out from SCC is reverted and mixed with fresh air, in order to reduce oxygen concentration, before passing through the heat exchanger tube bundle which is placed inside SCC in order to exchange heat with hot flue gas. To manufacture the designed incinerator, the detail of materials used as well as the frabication method is explained. It has been shown that HTAC can be applied for thermal destruction of waste successfully, in term of energy saving and pollutant free. Benefits of this research work will promote the using of thermal treatment technology of dispose of MSW with lower operating cost and lower pollutants.

Application and research on Regenerative High Temperature Air Combustion technology on low-rank coal pyrolysis

Abstract Regenerative High Temperature Air Combustion (RHTAC) technology is composed of circular-ceramic regenerator, burners, small four-way reversing valve and control system. RHTAC technology works by using the regenerator in burners to complete heat exchange between the high-temperature fume exhausted and the combustion air. Based on RHTAC technology, Regenerative Radiant Tube Combustor (RRTC) has been developed, and was adopted by Shenwu Pyrolysis Process (SPP), which is a new pyrolysis technology with the heat-carrier-free rotating bed. SPP was researched and developed to upgrade low-rank coal into the upgraded coal, tar and pyrolyzing gas. Presently, various coals from China and other countries have been conducted, including Lignite and Long flame coal. To understand the function of the RRTCs in SPP, a pilot plant has been constructed and used to investigate the effects of the RRTCs on the fume and pyrolyzer temperature distributions and pyrolyzing products. The results show that low calorific value gas fuel (>700 kcal/Nm3) can be used, the heat loss in fume exhausted is low (temp. about 150 °C), so thermal efficiency of the RRTC is greatly improved; the RRTCs can realize accurate temperature control and the separation of volatile materials and fume in the pyrolyzer, so as to increase tar yield and improve gas quality. The tar yield is more than 90% of the Gray-King tar yield; the pyrolyzing gas contains high contents of CH4, H2 and CO. Moreover, SPP could solve some technical problems, such as high dust content in coal tar, likely blockage of pipeline and greatly increasing the subsequent tar processing cost.