High Temperature Air Combustion Technology Research Articles

Novel conceptual design of a supercritical pulverized coal boiler utilizing high temperature air combustion (HTAC) technology

Technical and ecological aspects of implementation of High Temperature Air Combustion to power station boilers fired with pulverized coal have been considered. Several boiler concepts have been examined in the context of the following three key points: existence of an intensive in-furnace recirculation, homogeneity of both the temperature and the chemical species fields, and uniformity of heat fluxes. CFD-based numerical simulations have been performed in order to determine the shape of the boiler and its dimensions, to optimize both the distance between burners and location of the burner block. It was concluded that HTAC technology could be a realizable, efficient and clean technology for pulverized coal fired boilers.

Experimental Research on Heat Transfer Performance of Honeycomb Heat Regenerator

Heat transfer characteristics of honeycomb ceramic regenerator has been examined experimentally. The influence of switching time, flow rate of air and fuel gas on temperature distribution under unsteady heat transfer process in regenerator has been investigated. The results obtained are of some reference value for application of high temperature air combustion (HTAC). Key words: honeycomb ceramic regenerator, heat transfer, HTAC technology, molten steel container

Sulfur Recovery from Acid Gas Using the Claus Process and High Temperature Air Combustion (HiTAC) Technology

Sulfur-bearing compounds are very detrimental to the environment and to industrial process equipment. They are often obtained or formed as a by-product of separation and thermal processing of fuels containing sulfur, such as coal, crude oil and natural gas. The two sulfur compounds, which need special attention, are: hydrogen sulfide (H2S) and sulfur dioxide (SO2). H2S is a highly corrosive gas with a foul smell. SO2 is a toxic gas responsible for acid rain formation and equipment corrosion. Various methods of reducing pollutants containing sulfur are described in this paper, with a focus on the modified Claus process, enhanced by the use of High Temperature Air Combustion (HiTAC) technology in the Claus furnace. The Claus process has been known and used in the industry for over 100 years. It involves thermal oxidation of hydrogen sulfide and its reaction with sulfur dioxide to form sulfur and water vapor. This process is equilibrium-limited and usually achieves efficiencies in the range of 94-97%, which have been regarded as acceptable in the past years. Nowadays strict air pollution regulations regarding hydrogen sulfide and sulfur dioxide emissions call for nearly 100% efficiency, which can only be achieved with process modifications. High temperature air combustion technology or otherwise called flameless (or colorless) combustion is proposed here for application in Claus furnaces, especially those employing lean acid gas streams, which cannot be burned without the use of auxiliary fuel or oxygen enrichment under standard conditions. With the use of HiTAC it has been shown, however, that fuel-lean, Low Calorific Value (LCV) fuels can be burned with very uniform thermal fields without the need for fuel enrichment or oxygen addition. The uniform temperature distribution favors clean and efficient burning with an additional advantage of significant reduction of NOx, CO and hydrocarbon emission.

High-Temperature Air Combustion Phenomena and Its Thermodynamics

Abstract The fundamentals and thermodynamic analysis of high-temperature air combustion (HiTAC) technology is presented. The HiTAC is characterized by high temperature of combustion air having low oxygen concentration. This study provides a theoretical analysis of HiTAC process from the thermodynamic point of view. The results demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-deficient combustion process that utilizes both gas and heat recirculations. HiTAC conditions reduce irreversibility. Furthermore, combustion with the use of oxygen (in place of air) is also analyzed. The results showed that a system, which utilizes oxygen as an oxidizer, results in higher first and second law efficiencies as compared to the case with air as the oxidizer. The entropy generation for an adiabatic combustion process is reduced by more than 60% due to the effect of either preheating or oxygen enrichment. This study is aimed at providing technical guidance to further improve efficiency of a combustion process, which shows very small temperature increases due to mild chemical reactions.

Dynamic simulation on effect of flame arrangement on thermal process of regenerative reheating furnace

By analyzing the characteristics of combustion and billet heating process, a 3-D transient computer fluid dynamic simulation system based on commercial software CFX4.3 and some self-programmed codes were developed to simulate the thermal process in a continuous heating furnace using high temperature air combustion technology. The effects of different switching modes on injection entrancement of multi burners, combustion and billet heating process in furnace were analyzed numerically, and the computational results were compared with on-site measurement, which verified the practicability of this numerical simulation system. The results indicate that the flow pattern and distribution of temperature in regenerative reheating furnace with partial same-side-switching combustion mode are favorable to satisfy the high quality requirements of reheating, in which the terminal heating temperature of billets is more than 1 460 K and the temperature difference between two nodes is not more than 10 K. But since the surface average temperature of billets apart from heating zone is only about 1 350 K and continued heating is needed in soaking zone, the design and operation of current state are still needed to be optimized to improve the temperature schedule of billet heating. The distribution of velocity and temperature in regenerative reheating furnace with same-side-switching combustion mode cannot satisfy the even and fast heating process. The terminal heating temperature of billets is lower than that of the former case by 30 K. The distribution of flow and temperature can be improved by using cross-switching combustion mode, whose terminal temperature of billets is about 1 470 K with small temperature difference within 10 K.

LOCAL REACTION ZONE STRUCTURE OF NON-PREMIXED FLAMES OF PROPANE WITH HIGHLY PREHEATED LOW-OXYGEN AIR

To investigate the instantaneous structure of the local reaction zone of the HiCOT (High Temperature Air Combustion Technology) flames, the characteristics of ion current obtained from the non-premixed flames of propane with highly preheated low-oxygen air have been closely examined. Nonluminous (bluish-green) region is seen in the upstream part and luminous (bright yellow) region is seen in the downstream part of the non-premixed flames of propane with highly preheated low-oxygen air, while only the luminous region is seen in the non-premixed flames of propane with highly preheated regular air. The ion current fluctuations, obtained from the nonluminous region of the HiCOT flames, look quite similar with those obtained from turbulent premixed flames in the reaction sheet regime, implying that the unburnt mixture, burnt gas and local reaction zone exist separately. It has been clearly shown from the ion current that homogenous combustion does not occur but the local reaction zone exists separately from burnt and unburnt gases. The thickness of the local reaction zone in the nonluminous region of HiCOT flames is not broadened but is similar to that of the laminar premixed flames. Thickness of the local reaction zone in the non-premixed flames of propane with highly preheated regular air is estimated approximately twice as much as that in the nonluminous regions of the HiCOT flames.

Advantages of Low Air-Ratio Combustion in a Stoker-Type Incinerator (With High Temperature Air Combustion Technology)

Low air-ratio combustion has become the major subject with enormous attention as a measure to reduce the amount of substances with environment impact from the waste incineration process, and to make the most effective use of energy. However, it has been thought that there would be considerable difficulty in utilizing low air-ratio combustion on the classic grate furnace due to fundamental problems in its process, which treats the wide range and heterogeneity of waste materials. The application of high temperature air combustion technology for enhancing sound combustibility provided solutions to these problems. In practice, a mixture of high-temperature air and flue gas is injected at high velocity from both sides of the furnace walls to form a stable high-temperature zone in the combustion initiation region above the waste. This prevents fluctuations or localized extinguishing of the flame, while heating the waste directly with the flame to promote gasification at the same time. A practical study was conducted at a 105-ton/day municipal solid waste stoker type incineration plant. The test demonstrated that stable low excess-air combustion operation is possible at a combustion air stoichiometry of 1.3 with EGR (Exhaust Gas Recirculation) and high temperature air combustion technology resulting in a 17% decrease in flue gas flow, an energy efficiency improvement of 10%, and more than 50% reduction in NOx emissions when compared with an air stoichiometry of 1.6.

Development of high temperature air combustion technology in pulverized fossil fuel fired boilers

High temperature air combustion (HTAC) is a promising technology for energy saving, flame stability enhancement and NO x emission reduction. In a conventional HTAC system, the combustion air is highly preheated by using the recuperative or regenerative heat exchangers. However, such a preheating process is difficult to implement for pulverized fossil fuel fired boilers. In this paper, an alternative approach is proposed. In the proposed HTAC system, a special burner, named PRP burner is introduced to fulfill the preheating process. The PRP burner has a preheating chamber with one end connected with the primary air and the other end opened to the furnace. Inside the chamber, gas recirculation is effectively established such that hot flue gases in the furnace can be introduced. Combustible mixture instead of combustion air is highly preheated by the PRP burner. A series of experiments have been conducted in an industrial scale test facility, burning low volatile petroleum coke and an anthracite coal. Stable combustion was established for burning pure petroleum coke and anthracite coal, respectively. Inside the preheating chamber, the combustible mixture was rapidly heated up to a high temperature level close to that of the hot secondary air used in the conventional HTAC system. The rapid heating of the combustible mixture in the chamber facilitates pyrolysis, volatile matter release processes for the fuel particles, suppressing ignition delay and enhancing combustion stability. Moreover, compared with the results measured in the same facility but with a conventional low NO x burner, NO x concentration at the furnace exit was at the same level when petroleum coke was burnt and 50% less when anthracite was burnt. Practicability of the HTAC technology using the proposed approach was confirmed for efficiently and cleanly burning fossil fuels.

Heat Saturation Time of Solid Spherical Regenerator of HTAC

In order to control the heat saturation time, the temperature field of the regenerators of high temperature air combustion (HTAC) technology after reheating furnace was studied. A one-dimensional unsteady mathematical model was established and discretized through finite difference method. The relationship between the heat saturation time and some factors was determined through the calculation of a program developed by language C. The heat saturation time decreases with the increase of heat convection coefficient, however, the increase of heat capacity, density and radius of regenerator all increase the heat saturation time approximately linearly.

Local Reaction Zone Thickness of Non-Premixed Flames of Propane with Highly Preheated Low-Oxygen Concentration Air

To investigate the instantaneous structure of the local reaction zone of the HiCOT (High Temperature Air Combustion Technology) flames, the characteristics of ion current obtained from the non-premixed flames of propane with highly preheated low-oxygen air have been closely examined. Luminous region is seen in the non-premixed flames of propane with highly preheated regular air and in the downstream part of the non-premixed flames of propane with highly preheated low-oxygen air. On the other hand, non-luminous region is seen only in the upstream part of the non-premixed flames of propane with highly preheated low-oxygen air. The ion current fluctuations, obtained from the non-luminous region of the HiCOT flames, look quite similar with those obtained from turbulent premixed flames in the reaction sheet regime. It has been clearly shown from the ion current that homogeneous combustion does not occur but the local reaction zone exists separately from burnt and unburnt gases. The thickness of the local reaction zone in the non-luminous region of HiCOT flames is not broadened but is similar to that of the laminar premixed flames. Thickness of the local reaction zone in the non-premixed flames of propane with highly preheated regular air is estimated approximately twice as much as that in the non-luminous region of the HiCOT flames.

Advantages of Low Air-Ratio Combustion in a Stoker-Type Incinerator (With High Temperature Air Combustion Technology)

Measures such as low air-ratio combustion have become the subject of a great deal of attention with a view to reducing the amount of environment impacting substances from the waste incineration process, and also to making the most effective use of energy. However, it has been understood there would be considerable difficulty utilizing low air-ratio combustion on the classic grate furnace due to fundamental problems in its process resulting from the wide range and heterogeneity of waste materials. The application of high-temperature air combustion technology for enhancing sound combustibility could provide solutions to these problems. In practice, a mixture of high-temperature air and flue gas is injected at high velocity from both sides of the furnace walls to form a stable high-temperature zone in the combustion initiation region above the waste. This prevents fluctuations or localized extinguishing of the flame, while at the same time heating the waste directly with the flame to promote gasification. A practical study was conducted at a 105 t/day municipal solid waste stoker type incineration plant. The test demonstrated that stable low excess-air combustion operation is possible at a combustion air stoichiometry of 1.3 with EGR (Exhaust Gas Recirculation) and high temperature air combustion technology resulting in a 17% decrease in flue gas flow, an energy efficiency improvement of 10%, and more than 50% reduction in NOx emissions when compared with an air stoichiometry of 1.6.

고온공기를 이용한 제트확산화염의 연소특성에 관한 실험

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions from the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.

Thermal Characteristics of Gaseous Fuel Flames Using High Temperature Air

Recent advances on high temperature air combustion (HiTAC) have demonstrated significant energy savings, higher and uniform thermal field, lower pollution, and smaller size of the equipment for a range of furnace applications. The HiTAC technology has evolved from the conception of excess enthalpy combustion (EEC) to high and ultra-high preheated air combustion. In the HiTAC method, combined heat regeneration and low oxygen methods are utilized to enlarge and control the flame thermal behavior. This technology has shown promise for much wider applications in various process and power industries, energy conversion, and waste to clean fuel conversion. For each application the flow, thermal, and chemical behavior of HiTAC flames must be carefully tailored to satisfy the specific needs. Qualitative and quantitative results are presented on several gas-air diffusion flames using high-temperature combustion air. A specially designed regenerative combustion test furnace facility, built by Nippon Furnace Kogyo, Japan, was used to preheat the combustion air to elevated temperatures. The flames with highly preheated combustion air were significantly more stable and homogeneous (both temporally and spatially) as compared to the flames with room-temperature combustion air. The global flame features showed the flame color to change from yellow to blue to bluish-green to green over the range of conditions examined. In some cases hybrid and purple color flame was also observed. Under certain conditions flameless or colorless oxidation of the fuel has also been demonstrated. Information on global flame features, flame spectral emission characteristics, spatial distribution of OH, CH, and C2 species and emission of pollutants has been obtained. Low levels of NOx along with negligible levels of CO and HC have been obtained using high-temperature combustion air. The thermal and chemical behavior of high-temperature air combustion flames depends on fuel property, preheat temperature, and oxygen concentration of air. Waste heat from a furnace in high-temperature air combustion technology is retrieved and introduced back into the furnace using regenerator. These features help save energy, which subsequently also reduce the emission of CO2 (greenhouse gas) to the environment. Flames with high temperature air provide significantly higher and uniform heat flux than normal air, which reduces the equipment size or increases the process material throughput for same size of the equipment. The high-temperature air combustion technology can provide significant energy savings (up to about 60%), downsizing of the equipment (about 30%), and pollution reduction (about 25%). Fuel energy savings directly translates to a reduction of CO2 and other greenhouse gases to the environment.

金網を通過する低レイノルズ数流れ場と伝熱特性(一般セッション 対流熱伝達 II)

Radiation converter made of a wire mesh is proposal for heat transfer enhancement of HiCOT (high temperature air combustion technology) furnace. Heat transfer and fluid flow characteristics through a wire mesh at low Reynolds number are investigated by numerical simulation. Detailed model at various condition are necessary for performance prediction and modeling for design. It is confirmed that flow resistance results agree well with existing experimental data. Empirical formula of fluid resistance and heat transfer coefficient through a wire mesh was obtained.

ストーカ式廃棄物焼却炉における低空気比燃焼特性(燃焼・ガス化(1),廃棄物処理技術)

Measures such as low air-ratio combustion and exhaust gas recirculation have become the subject of a great deal of attention with a view to reducing the amount of environment impacting substances from the waste incineration process, and also to making the most effective use of energy. However, it has been understood there would be considerable difficulty utilizing low air-ratio combustion on the conventional grate furnace. The application of high-temperature air combustion technology for enhancing sound combustibility could provide solutions to these problems and it was studied before now. A practical test was conducted at a 105ton/day municipal solid waste stoker type incineration plant. The test demonstrated that stable low air-ratio combustion operation is possible at the stoichiometry of 1.3 with EGR (Exhaust Gas Recirculation) and high temperature air combustion technology resulting in a 17% decrease in flue gas flow, an energy efficiency improvement of 10%, and a significant reduction of toxic products emission when compared with a stoichiometry of 1.6 as conventional method.

Industrial applications of advanced high-temperature air combustion technology : Miyata, K. Kagaku Kogaku, 2002, 66, (5), 286–289. (In Japanese)

Industrial applications of advanced high-temperature air combustion technology : Miyata, K. Kagaku Kogaku, 2002, 66, (5), 286–289. (In Japanese)

316 高温空気燃焼を用いた重油のクリーン燃焼技術の開発

Combustibility of heavy oil was investigated with high temperature air combustion technology. The combustion with low NOx and soot emission was achieved even using heavy oil C and LCO as fuels. Strong luminous flame observed at high air ratio enlarged became transparent with some pale luminous flame at low air ratio. The NOx emission level for the combustion of heavy oil C was ∿100ppm keeping the low soot emission level. Introducing the high temperature (∿1000℃) steam could decrease the NOx emission even in the combustion of heavy oil C. Under the low NOx combustion condition, uniform distribution of temperature ure was confirmed.

F152 高温空気燃焼技術による微粉炭燃焼の低 NOx 化、高燃料比炭適用

High temperature air combustion technology (HiCOT) has demonstrated high effectiveness in significantly enhancing the performance of industrial furnaces, achieving advantages such as energy savings, CO2 reduction and reduced emission of NOx for gaseous fuels. This technology is expected to be applicable not only for gaseous fuels but also for solid fuels like pulverized coal, with the same advantages. To ascertain the advantages, the combustion behavior of pulverized coal in high temperature air using various coal combustion furnaces have been studied. As the results, we can ascertain the advantages of HiCOT applied to pulverized coal combustion, low NOx emission and stabilized combustion of low volatile coal.

H213 高温空気燃焼技術のストーカ式焼却炉への応用

High-Temperature Air Combustion Technology is an attractive method for producing surplus electric power and reducing environmental disruption materials such as NOx and dioxins especially in combustion process of Municipal Solid Waste (MSW) incinerator. The objective is to develop an energy-saving system for the MSW incinerator and to lower the emission pollutants. The experimental study is carried out systematically with simulated MSW furnaces (500kg-waste/h and commercial plant) to study the thermal degradation and the distributions of temperature and gas concentrations in the furnaces. Blowing the mixture of high temperature air and the flue gas to the primary combustion space brings extremely stable combustion. Moreover, it reduces not only the NOx, CO and the other toxic products, but also more than 20% of the excess air.

312 高温空気燃焼技術を用いた石油燃料の環境低負荷燃焼技術の開発

Combustibility of petroleum was investigated with high temperature air combustion technology. Ultra low NOx emission (∿10ppm) was achieved both for the kerosene and heavy oil A as fuels using a 0.4MW class test furnace. Thermal NOx was extremely reduced as decreasing the air ratio and fuel NOx was also reduced when the combustion was conducted at low oxygen concentration. Introducing the high temperature (∿1000℃) steam could decrease the NOx emission. As decreasing the air ratio, the flame was enlarged and flameless oxidation was observed. Under the low NOx combustion condition uniform distribution of temperature and chemical species were confirmed.