Burner Concept Research Articles

다공성세라믹버너의 화염안정화에 관한 연구

Typical boiler system consists of combustion chamber and heat exchanger in one housing, therefore the size of boiler system is large and the heat exchanging efficiency becomes low. At these boiler systems, because the combustible mixture fires as free flame in the combustion chamber, consequently the combusted hot gas heats the heat exchanger only as conductive and convective heat transfer. The present Porous Ceramic Burner concept is that combustion process is occurred at the gaps of the porous ceramic materials, and the heat exchanger is placed in the same porous materials. Therefore we can reduce the boiler size, and we can also use radiative heat transfer from ceramic material with conductive and convective heat transfer from combusted gas throwing the porous materials. The purpose of this study is to search the flame stability ranges at different fuel flow rate and excess air ratio burning in the <TEX>$Al_2O_3$</TEX> ceramic balls. We found out the stable excess air ratio range on given combustion intensity. And we can get clean porous ceramic combustion results compared with free flame.

NOx emissions and turbulent flow field in a partially premixed bluff body burner with CH4 and H2 fuels

The increased need for fuel flexibility and CO2 capture solutions (CCS) in the power and industrial sectors has led to higher focus on hydrogen containing fuels. The high reactivity and combustion temperature in hydrogen flames are a source of high nitrogen oxides (NOx) and a barrier to the implementation of traditional dry lean premixed low NOx burner technology. The present experimental study investigates emissions of NOx and characterises the turbulent flow field above a promising burner concept based on partially premixed bluff body (PPBB) strategy. The PPBB burner configuration allows for a rapid mixing of fuel and air through multiple fuel injection in the accelerating air stream, followed by a flame stabilization process controlled by a bluff body. The measurements were conducted using methane, hydrogen, and a methane–hydrogen mixture 50/50 mass fraction as fuels and at various burner thermal loads ranging from 10 kW to 25 kW. The turbulent flow field characterisation was made by Particle Image Velocimetry (PIV) without the combustion chamber and in selected operation modes. Several burner parameters were varied, as the position of the bluff body and the fuel distribution. Shifting the burner lance controlling the bluff body position to accelerate the air flow resulted in lower NOx emissions, although negatively affecting the flame stability and generating incomplete combustion. Supplying fuel through secondary fuel ports had opposite effect on NOx emissions depending on the fuel: an increase for methane and a decrease for hydrogen. The temperature of the chamber has significant impact on NOx emissions and was quantified in the study with a 50% increase from a chamber temperature of 700 °C–1050 °C. NOx emissions are generally higher as the hydrogen content in the fuel increases. The lowest achieved NOx emissions are 26 and 66 ppm at 3% O2 dry for methane and hydrogen respectively.

Large Eddy Simulation Modeling of Non-Premixed Turbulent Oxy-Fuel Combustion Supplied by Three Separated Jets

ABSTRACTThe continuity of evolving pollutant emission regulations requires the design and the development of new burners. The separated-jets burner concept is an example that implies a careful understanding of the turbulent oxy-fuel flames properties developing in a furnace. Modeling, such as turbulent combustion, is a challenge, as it combines complex flow and transport phenomena with combustion events including a vast amount of species and reactions. The flamelet generated manifold (FGM) method is a promising technique to model reacting flows using a tabulated chemistry approach. It is considered as a function of the mixture fraction (Z) and a reaction progress variable (Y). In this work, the interaction of three aligned separated jets is numerically investigated. The central jet provides the natural gas and the others side jets provide the pure oxygen. Turbulence is modeled using the large eddy simulation model in which the dynamic Germano approach is applied to determinate the sub-grid scale stress. In the reacting case, the turbulence chemistry interaction is achieved by coupling the FGM tabulated chemistry within the computational fluid dynamic code. The numerical results show a good agreement with experimental data notably in the isothermal case. In the reacting case, statistical flow field quantities for velocity, mixture fraction, and temperature are analyzed in detail.

Decomposition analysis of the sodium void reactivity of the Korean sodium-cooled fast reactor

Abstract To cope with increasing spent fuel disposals and limited domestic spent fuel storages in Korea, the Korea Atomic Energy Research Institute has developed an advanced sodium-cooled fast reactor for TRU transmutation with an electricity output of 600 MWe (called the KALIMER-600 TRU burner). The design philosophy of the KALIMER-600 TRU burner concept is highly focused on inherent safety mechanisms, i.e., passive responses to abnormal and emergency conditions, and thereby minimizes the need for engineered safety systems. Accordingly, the main concern is on the sodium coolant void reactivity, a very important safety parameter of the KALIMER-600 TRU burner. This study was therefore performed to analyze the sodium void reactivity of the KALIMER-600 TRU burner to the finest resolution possible, e.g., contributions from any isotope in each core region. Such detailed analysis could be valuable and applicable to further optimization of the core passive safety characteristics against severe coolant voiding accident conditions.

Proposal of a plutonium burner system based on HTGR with high proliferation resistance

An innovative plutonium burner concept based on high temperature gas cooled reactor (HTGR) technology, “Clean Burn”, is proposed by Japan Atomic Energy Agency (JAEA). That is expected to be as an effective and safe method to consume surplus plutonium accumulated in Japan. A similar concept proposed by General Atomics (GA), Deep Burn, cannot be introduced to Japan because of its adopting highly enriched plutonium, which shall infringe on a Japanese nuclear nonproliferation policy according to Japan–US reprocessing negotiation. The Clean Burn concept can avoid this problem by employing an inert matrix fuel (IMF) and a tightly coupled fuel reprocessing and fabrication plants. Both features make it impossible to extract plutonium alone out of the fabrication process and its outcomes. As a result, the Clean Burn can use surplus plutonium as a fuel without mixing it with uranium matrix. Thus, surplus plutonium alone will be incinerated effectively, while generation of plutonium from the uranium matrix is avoided. High neutronic performance, i.e., achievement of burn-up of about 500 GWd/t and consumption ratio of plutonium-239 reaching to about 95%, is also assessed. Furthermore, reactivity defect caused by the inert matrix is found to be negligible. It is concluded that the Clean Burn concept is a useful option to incinerate plutonium with high proliferation resistance.

Highly flexible burner concept for research on combustion technologies with recirculation of hot combustion products

This paper reports the development and testing of a research coflow burner that generates laminar flames in a hot and diluted environment, which is adequate for studying the operating conditions found in practical combustors that use flue gas recirculation techniques. The burner has two flame zones; the first is an annular laminar premixed flat flame stabilized by a perforated plate, which generates a hot oxygen-rich flue gas mixture. The second is a non-premixed laminar flame, which uses the hot oxygen-rich flue gas mixture as an oxidizer. A methodology based on coflow calculations, which is the most significant component, was designed to provide different temperatures and dilution levels. The burner was built based on this design and tested using both intrusive and non-intrusive measurement techniques. The device emulated several features of practical combustor systems but with a simpler geometry, well-defined boundary conditions and using the simplest configuration found in literature (laminar flames). In a preliminary study, the MILD combustion regime was emulated by generating methane laminar non-premixed flames at oxygen concentrations between 3% and 9% and temperatures between 973 K and 1173 K.

Study on the Operational Window of a Swirl Stabilized Syngas Burner Under Atmospheric and High Pressure Conditions

Providing better fuel flexibility for future gas turbine generations is a challenge as the fuel range is expected to become significantly wider (natural gas, syngas, etc.). The technical problem is to reach a wide operational window, regarding both operational safety and low emissions. In a previous paper, an approach to meet these requirements has already been presented. However, in this previous study it was difficult to exactly quantify the improvement in operational safety due to the fact that the flashback phenomena observed were not fully understood. The present continuative paper is focused on a thorough investigation of operational safety also involving the influence of pressure on flashback and the emissions of the proposed burner concept. To gain better insight into the character of the propagation and to visualize the path of the flame during its upstream motion, tests were done on an atmospheric combustion test rig providing almost complete optical access to the mixing section as well as the flame tube. OH* chemiluminescence, HS-Mie scattering and ionization detectors were applied and undiluted H2 was used as fuel for the detailed analysis. To elaborate on the influence of pressure on the stability behavior, additional tests were conducted on a pressurized test rig using a downscaled burner. OH* chemiluminescence, flashback and lean blow out measurements were conducted in this campaign, using CH4, CH4/H2 mixtures and pure H2. The conducted experiments delivered the assets and drawbacks of the fuel injection strategy, where high axial fuel momentum was used to tune the flow field to achieve better flashback resistance.

Porous Burner for Application in Stationary Gas Turbines: An Experimental Investigation of the Flame Stability, Emissions and Temperature Boundary Condition

A possible solution to ensure the stability of lean premixed flames over an extended operational range is to provide enhanced heat recirculation by employing porous inert material. A potential application of the porous burner concept is the generation of the pilot flames based on lean premixed combustion which is a prerequisite for ultra low NOx emission. For the optimization of the porous burner an experimental study investigating flame stability and emissions was conducted. In particular axial concentration profiles of the stable species and temperature within the porous burner reaction zone are presented. Furthermore the surface temperature of the burner having a 10 PPI SiSiC material was measured for various operating conditions using two colour pyrometry.

Cellular Ceramics in Combustion Environments

AbstractCellular materials have become increasingly interesting for applications in combustion environments. Improvements like high power efficiency and low emissions are the main targets of technological development in combustion processes. However, despite scientific and technical success in developing new or improved burner concepts over recent years, a lot of problems remain to be solved in the field of materials science: due to the high power density of the burners the materials are subjected to high loads in terms of thermal shock, temperature and corrosion, especially in so‐called porous burner technology. This article shows some examples of research and development strategies and results in developing improved cellular ceramics.

Pollutant emissions of burners for steam reformers for residential power supply

The cogeneration of heat and power by means of a fuel cell based CHP unit is a promising option for efficient residential power supply. For most applications natural gas is used as fuel. One main component of such a CHP unit is a fuel processor in order to generate hydrogen from the natural gas with hydrogen thermal power output of about 6 kW. Usually the steam reforming process is used for hydrogen production. In order to meet the heat demand of the endothermic steam reforming process the fuel processor is equipped with a burner, which has to work with natural gas during start up phase and mainly with the low calorific anodic off gas of the fuel cell stack during normal operation. The presented work is focused on aspects of the main pollutant emissions (carbon monoxide and nitrogen oxide) of burners integrated into the reformer. Experimental investigations of two different burners, which were developed and adapted to the steam reformer requirements, in a real fuel processor environment show, that it is possible to operate both burner concepts with high and low calorific gases with very low pollutant emissions in order to compete with emissions of current heating boilers, which are in the range of 15 mg kWh −1 for CO and of 20 mg kWh −1 for NO x by adjusting suitable excess air ratios in the range of 1.2–1.4. But it is also demonstrated, that the efficiency of the fuel processor is influenced by the excess air ratio. An increase of the air ratio from 1.05 to 1.45 leads to an decrease of the efficiency from 80% to 76%. This results in a conflict of objectives between low pollutant emissions and high system efficiencies. The choice of a suitable burner concept and the definition of a suitable operation strategy can be based on the presented results. Additionally, aspects like fuel processor geometry, flame monitoring, pressure drop in the burner feed gas line as well as in the flue gas duct, investment costs and safety items have also to be considered for the burner selection.

A numerical investigation of the flame stability in porous burners employing various ceramic sponge-like structures

In order to optimize the porous burner for the application as a pilot burner of stationary gas turbines aiming to reduce NO x emissions a fundamental study investigating the influence of the thermo-physical properties of the porous structure on the flame stabilization in a porous burner was conducted. This work presents a numerical study of the stability of one-dimensional laminar premixed flame in porous inert ceramic sponge structure. A set of steady computations are considered, using a numerical model that takes into account solid and gas energy equations as well as detailed chemistry. The model considers additionally the enhancement of both, thermal and species diffusivity by the flow dispersion, whereas the dispersion coefficients of the investigated structures have been determined from three-dimensional flow simulations using MRI (magnet resonance imaging) and CT (computer tomography) data to regenerate the real sponge structures. Hence, it was possible to calculate a thickened flame front as it was detected in experiments, too. The computations were conducted for different operational conditions and different burner configurations in respect to geometrical and material properties of the porous inert media. The numerical predictions showed very good agreement with the corresponding experimental stability data. The obtained numerical results were used for the formulation of a simple stability model based on the Pe number that enables a prediction of the lean blow-off limits in the combustion systems employing porous burner concept.

FLOX® Combustion at High Power Density and High Flame Temperatures

In this contribution, an overview of the progress in the design of an enhanced FLOX® burner is given. A fuel flexible burner concept was developed to fulfill the requirements of modern gas turbines: high specific power density, high turbine inlet temperature, and low NOx emissions. The basis for the research work is numerical simulation. With the focus on pollutant emissions, a detailed chemical kinetic mechanism is used in the calculations. A novel mixing control concept, called HiPerMix®, and its application in the FLOX® burner are presented. In view of the desired operational conditions in a gas turbine combustor, this enhanced FLOX® burner was manufactured and experimentally investigated at the DLR test facility. In the present work, experimental and computational results are presented for natural gas and natural gas+hydrogen combustion at gas turbine relevant conditions and high adiabatic flame temperatures (up to Tad=2000 K). The respective power densities are PA=13.3 MW/m2 bar (natural gas (NG)) and PA=14.8 MW/m2 bar(NG+H2), satisfying the demands of a gas turbine combustor. It is demonstrated that the combustion is complete and stable and that the pollutant emissions are very low.

Catalytic, hybrid lean combustion for gas turbines

In the CATHLEAN project (an EU Framework 5 project performed between 2003 and 2006) a consortium of researchers investigated the development of an advanced, ultra-low NO x, hybrid burner for heavy-duty gas turbines that combines catalytic and lean-premix combustion components. Catalytic elements were developed that preheat the incoming lean fuel/air mixture up to temperature of ca. 1100 K at the required high (20–30 m/s) operating velocities and inlet temperatures (670–690 K). High-pressure aging of a highly active Pd-based catalyst at 10 bars indicated that the catalyst activity decreases significantly in the first 200 h of operation, and that an optimal catalyst design should contain different regions (in the axial direction) to allow optimization of catalyst activity and material stability, e.g. higher activity at the flow entrance, greater thermal stability at the reactor outlet where temperatures are high. Full-scale burner investigations demonstrated the feasibility of the CATHLEAN hybrid catalytic burner concept, and provided an indication of performance enhancement due to catalytic conversion. Both NO x emissions and lean stability limit were improved (25% reduction in NO x emissions and reduction of lean blow-out limit of ca. 200 K).

Atmospheric low swirl burner flow characterization with stereo PIV

The lean premixed prevaporized (LPP) burner concept is now used in most of the new generation gas turbines to reduce flame temperature and pollutants by operating near the lean blow-off limit. The common strategy to assure stable combustion is to resort to swirl stabilized flames in the burner. Nevertheless, the vortex breakdown phenomenon in reactive swirling flows is a very complex 3D mechanism, and its dynamics are not yet completely understood. Among the available measurement techniques to analyze such flows, stereo PIV (S-PIV) is now a reliable tool to quantify the instantaneous three velocity components in a plane (2D–3C). It is used in this paper to explore the reactive flow of a small scale, open to atmosphere, LPP burner (50 kW). The burner is designed to produce two distinct topologies (1) that of a conventional high swirl burner and (2) that of a low swirl burner. In addition, the burner produces a lifted flame that allows a good optical access to the whole recirculation zone in both topologies. The flow is studied over a wide range of swirl and Reynolds numbers at different equivalence ratios. Flow statistics are presented for 1,000 S-PIV snapshots at each configuration. In both reactive and cold nonreactive flow, stability diagrams define the domains of the low and high swirl topologies. Due to the relatively simple conception of the physical burner, this information can be easily used for the validation of CFD computations of the burner flow global structure. Near field pressure measurements reveal the presence of peaks in the power spectra, which suggests the presence of periodical coherent features for almost all configurations. Algorithms have been developed to identify and track large periodic traveling coherent structures from the statistically independent S-PIV realizations. Flow temporal evolution is reconstructed with a POD-based method, providing an additional tool for the understanding of flow topologies and numerical codes validation.

Investigation of laminar pressurized flames for soot model validation using SV-CARS and LII

Quasi-simultaneous measurements of temperature and soot volume fraction in pressurized and atmospheric flames are presented. A dual-flame burner concept yielded stable laminar flames for a variety of equivalence ratios, pressures, and fuels, and permitted the investigation of flames without the influence of soot oxidation. A CARS-based technique (shifted vibrational CARS) for temperature measurements, which offers high accuracy over the entire relevant temperature and soot concentration range, is described. Comparison of temperature measurements in the nonsooting part of a laminar diffusion flame at atmospheric pressure by SV-CARS and conventional N 2 Q-branch CARS yielded excellent agreement. This new technique was applied to quasi-1D laminar flames with soot concentrations up to 10 ppm and pressures up to 5 bar. The temperature profiles measured in these flames were combined with soot concentration measurements using LII; calibration and correction for signal trapping yielded quantitative soot volume fraction data. The temperature and soot concentration data were combined to generate a comprehensive dataset for the validation of an improved kinetic soot model for the prediction of soot formation in premixed combustion at elevated pressure.

Lean Blowout Limit and NOx Production of a Premixed Sub-ppm NOx Burner With Periodic Recirculation of Combustion Products

The technological objective of this work is the development of a lean-premixed burner for natural gas. Sub-ppm NOx emissions can be accomplished by shifting the lean blowout limit (LBO) to slightly lower adiabatic flame temperatures than the LBO of current standard burners. This can be achieved with a novel burner concept utilizing spatially periodic recirculation of combustion products: Hot combustion products are admixed to the injected premixed fresh mixture with a mass flow rate of comparable magnitude, in order to achieve self-ignition. The subsequent combustion of the diluted mixture again delivers products. A fraction of these combustion products is then admixed to the next stream of fresh mixture. This process pattern is to be continued in a cyclically closed topology, in order to achieve stable combustion of, for example, natural gas in a temperature regime of very low NOx production. The principal ignition behavior and NOx production characteristics of one sequence of the periodic process was modeled by an idealized adiabatic system with instantaneous admixture of partially or completely burnt combustion products to one stream of fresh reactants. With the CHEMKIN-II package, a reactor network consisting of one perfectly stirred reactor (PSR, providing ignition in the first place) and two plug flow reactors (PFR) has been used. The effect of varying burnout and the influence of the fraction of admixed flue gas has been evaluated. The simulations have been conducted with the reaction mechanism of Miller and Bowman and the GRI-Mech 3.0 mechanism. The results show that the high radical content of partially combusted products leads to a massive decrease of the time required for the formation of the radical pool. As a consequence, self-ignition times of 1 ms are achieved even at adiabatic flame temperatures of 1600 K and less, if the flue gas content is about 50–60% of the reacting flow after mixing is complete. Interestingly, the effect of radicals on ignition is strong, outweighs the temperature deficiency and thus allows stable operation at very low NOx emissions.

High efficiency heat-recirculating domestic gas burners

Existing designs of most conventional domestic burners (CB) have typically relied on open combustion flame, where a large amount of energy loss with the flue gas arises, resulting in relatively low thermal efficiency (<30%). Against this background, a novel semi-confined porous radiant recirculated burner (PRRB) concept based on heat-recirculating combustion using the porous medium technology was developed for energy savings in domestic use and in the small-scale food processing industry. Performance of the new burner using the same ring burners as those in the CB, i.e. the PRRB(CB) were evaluated by comparing thermal efficiencies and the combustion characteristics with those of the conventional one (CB). Operating parameters such as heat input, flow type of the ring burners (conventional radial flow (CB) or swirling central flow (SB)) were clarified. The proposed PRRB(CB) is very effective in establishing a heat-recirculation mechanism from the hot exhaust gas to the combustion air, resulting in efficient combustion air preheating with maximum combustion air temperature of 300 °C. Thermal efficiency of the proposed PRRB(CB) is increased to about 12% higher than that of the conventional one (CB). Further improvement in thermal efficiency of the burner can be realized by combining the PRRB with the swirling central flame ring burner (SB), i.e. the PRRB(SB), yielding a maximum thermal efficiency of about 60% and, thus, energy saving of about 50% in average over the operating range. The proposed PRRB(SB) provides not only high thermal efficiency and considerable improvement in energy saving but also environmentally compatible emissions. With the model proposed, the calculated thermal efficiencies of the PRRB(SB) can be predicted and agree well with the experimental ones.

Studies on Plutonium Burning in the Prototype Fast Breeder Reactor Monju

Studies have been performed on plutonium burning in the Japanese prototype fast breeder reactor Monju. The main aims of these studies were to illustrate the plutonium-burning capabilities of fast reactors and to investigate the consequences of the related core design measures on the main core characteristics of Monju. Burner cores with diluting pins, with diluting subassemblies (also called diluents), and with an internal slice of inert material have been investigated; these require an increased average plutonium enrichment and thus offer an enhanced plutonium-burning rate. On the other hand, the consequences of the elimination of the radial and/or axial blanket have been investigated.Among the burner concepts, the B4C containing diluents have been found to be preferable because they cause the smallest maximum linear rating increase and offer the largest flexibility to adapt their reactivity via a modification of the B4C content. They also do not require a new fuel subassembly concept.For the case of the blanket elimination, the replacement of the blankets by steel reflectors has been found to be the best solution. The main consequence of the elimination of both blankets is the increase of the maximum linear rating by up to 11%. Whether this increase may lead to problems will depend on the actual linear power level of the core.

Research and development to improve naval shipboard waste management using a compact closed-loop-controlled waste incinerator

Research has been conducted into the application of forced acoustics for enhancing the performance of a pyrolyzed waste afterburner configured as a dump combustor. Subscale studies showed that acoustic forcing of an air jet entering a dump chamber could trigger the formation of coherent vortices generated by entrainment of ambient gases. Subsequent studies showed that combustible gases could be introduced into the coherent vortices, and with additional modulation this configuration would lead to an enhanced combustion rate with low emissions of pollutants. The acoustically forced burner concept was scaled up to practical levels and tested as an afterburner on a commercial waste incinerator operating in pyrolysis mode. Results show that the afterburner can promote both compactness, due to the rapid combustion rate, and low pollutant emissions resulting from enhanced mixing prior to combustion.

Emission behaviour of a catalytic burner fuelled with mixtures of hydrogen and methanol

A catalytic radiant burner was chosen as the process heat source in a fuel cell drive system. The advantage of a catalytic burner is the low level of harmful substances in the flue gas. Besides the production of process heat, another task of the burner is to convert different gas mixtures effectively from the system into CO2 and H2O. The basic burner structure is a ceramic cylinder to which the fuel gas, pre-mixed with air, is internally supplied. On the outer surface of the cylinder, a wire mesh coated with noble metal is provided on which the combustion takes place catalytically. The emission behaviour of the burner was investigated under different operation conditions concerning the gas mixture and the catalyst. From the results, the mechanisms of the formation of pollutants are discussed and the suitability of the burner concept is checked by comparing the measured emissions with the emission standards. The operation condition ranges are determined under which the burner works in the drive system without exceeding the emission standards.