Computational modeling of a utility boiler tangentially-fired furnace retrofitted with swirl burners

The paper presents 3D numerical investigation of OP-380 boiler tangentially-fired furnace utilizing bituminous coal. The boiler was retrofitted by replacing traditional jet burners with RI-JET2 (Rapid Ignition — JET) swirl burners. This kind of solution is unique in power generation systems. The purpose of this work is to show how the flow, combustion performance and heat exchange in the furnace are affected by introducing rapid ignition phenomena in RI-JET2 burners instead of delayed ignition associated with the traditional jet burners. Results were compared to simulations of similarly designed boiler equipped with traditional jet burners. Furnace simulation was preceded with a single RI-JET2 burner simulation at the inlet to a virtual combustion chamber. The results have shown that pulverized coal (PC) concentrator separates the PC into two streams: concentric with fine particles and axial with coarse particles. Stable flame operation was noticed even without secondary and tertiary air swirl. 3D simulations of combustion chamber have shown that in a burner zone a visibly isolated, concentrated flame exists in the furnace axis. This kind of flame shape reduces corrosion risk and furnace walls slagging as a result of RI-JET2 burner's long range.     

Numerical simulation on flow, combustion and heat transfer of ethylene cracking furnaces

With the study object of an 100kt/a SL-II ethylene cracking furnace, this paper used Computational Fluid Dynamics (CFD) method to carry out coupled simulation studies on the flow, combustion, radiative heat transfer and thermal cracking reaction processes in the cracking furnace. The standard k–ε two-equation model was applied to turbulence simulation. The finite-rate/eddy-dissipation model was used for modeling of non-premixed combustion of the bottom burners and premixed combustion of the sidewall burners. The Discrete Ordinates (DO) model was applied to the simulation of radiative heat transfer of furnace. The simulation results show the detailed information about velocity, temperature and concentration fields in the furnace and heat flux distribution on the reactor tubes skin. This work will provide a theoretical basis for the optimization of the geometrical structure and operational parameters of the cracking furnace.     

Numerical simulations of the slagging characteristics in a down-fired, pulverized-coal boiler furnace

Numerical studies of the slagging characteristics under different operational conditions in a 300 MW down-fired boiler were carried out using slagging models coupled with gas-solid two phase flow and combustion models. Combined with the real operating conditions; comparative and detailed analysis on the slagging position, extent, and causes is presented. The results show that the serious slagging is mainly on the side walls of the lower furnace. Because of the more rapid expansion of the flue gas under the higher temperature, the flue gas in the furnace center makes the flue gas on both sides deflect and flow to the side walls; and the pulverized-coal flame impinges on the side walls. This results in the slagging on the side walls. Under off-design operating conditions, such as stopping some burners, the local flow field is asymmetric and impinges on the local arch burner, front and rear wall regions where the stopped burners are located. It leads to slight slagging on the arch burner regions and the front and rear wall regions of the lower furnace. Based on the investigation, it has been found that the serious slagging on the side walls can be effectively alleviated by cutting off the burners close to the side walls, reducing boiler load and burning low slagging-tendency coals.     

浅谈浮法玻璃熔窑用重油燃烧器的结构设计及其发展

燃烧器是浮法玻璃熔窑中极为关键的热工设备。以浮法玻璃空气助燃技术以及全氧燃烧工艺为背景,从结构类型、工作原理、燃烧状态、优缺点以及发展历程等方面对几种具有代表性的重油燃烧器进行了详细介绍。     

全氧燃烧玻璃纤维窑炉火焰空间的数值模拟

以研究和优化玻璃纤维窑炉的燃烧制度和火焰空间喷枪排列为目的,借助CFD软件FLUENT,建立了全氧燃烧玻璃纤维窑炉火焰空间的三维数学模型,针对现有燃烧制度的不足,利用模拟的方式进行改进。结果表明,碹顶处模拟值与实测值的平均相对偏差为8．70％,玻璃液面处模拟值与实测值的平均相对偏差为2．32％;第3、4对喷枪处气流分布不均匀,导致对应的碹顶处热负荷较高;改进后的火焰空间可以在保持温度场分布合理的情况下,有效的降低碹顶的热负荷,改善火焰空间的气流场分布。     

Combustion and Pyrolysis Reactions in a Naphtha Cracking Furnace

Numerical simulation on combustion and pyrolysis reactions in a tubular reactor is carried out on a 100,000 t/a naphtha cracking furnace. A complex arrangement of bottom burners is contained in the furnace model. The hydrodynamic and radiation models are included for calculating the flue gas flow pattern and heat transfer. A molecular reactions model is applied on the basis of a two‐dimensional tubular reactor model. The results calculated indicate that there is recirculation of the flue gas at each side of the reactor tubes due to the high inlet velocity from the bottom burners, which contributes to the uniformity of flue gas temperature in the furnace. Higher temperature profiles of the tube skin are mainly located 15–20 m along the tubular reactor. The calculated pyrolysis product yield and the tube skin temperatures are in good agreement with experimental data.     

Mathematical modelling of straw combustion in a 38 MWe power plant furnace and effect of operating conditions

As one of the most easily accessible renewable energy resources, straw can be burned to provide electricity and heat to local communities. In this paper, mathematical modelling methods have been employed to simulate the operation of a 38 MWe straw-burning power plant to obtain detailed information on the flow and combustion characteristics in the furnace and to predict the effect on plant performance of variation in operating conditions. The predicted data are compared to measurements in terms of burning time, furnace temperature, flue gas emissions (including NO_x), carbon content in the ash and overall combustion efficiency. It is concluded that straw burning on the grate is locally sub-stoichiometric and most of the NO is formed in the downstream combustion chamber and radiation shaft; auxiliary gas burners are responsible for the uneven distribution of temperature and gas flow at the furnace exit; and fuel moisture content is limited to below 25% to prevent excessive CO emission without compromising the plant performance. The current work greatly helps to understand the operating characteristics of large-scale straw-burning plants.     

Low NOx heavy fuel oil combustion with high temperature air

For an industrial-scale test furnace, the development and investigation of a heavy-oil-fired burner in a highly preheated air combustion system are discussed. The 1200 °C highly preheated combustion air was achieved by burners equipped with regenerators in high-cycle reciprocal firing. It was observed that the high-cycle reciprocal firing enhanced convective heat transfer to the furnace wall. Reduction of nitric oxide emissions was achieved by fuel directly injected into furnace (F2 mode) and mixed with combustion products. In previous studies of natural gas combustion in reciprocal firing, two injectors located at the burner quarl have been utilized to achieve low nitric oxide combustion. In this study, reduction of nitric oxide was investigated using single or paired atomizers located in the upper and lower position of burner quarl. It was found that buoyant forces were important for the mixing of fuel oil with high temperature air and for the resultant nitric oxide emission. Nitric oxide emission was found to be low with the paired atomizers in the F2 firing mode. Nitric oxide emission can be further reduced by use of a single atomizer rather than using paired atomizers.     

Combustion of low-calorific waste liquids in high temperature air

Waste liquids with low-calorific values are not easy to burn. In this experiment, a furnace with a pair of burners for high-cycled alternate firing was utilized to burn the low-calorific value liquids. In a 1383 K furnace, 1173 K preheated air was achieved via these burners equipped with regenerators. It was observed that the alternate firing with highly preheated air was an effective way to ignite and burn the low-calorific value liquids. The preheated air temperature was higher than the auto-ignition temperature of the flammable mixture of the waste liquids. The combustion gas temperature in the furnace was quite uniform via the high-cycled alternate firing, resulting in a longer residence time of combustion in the furnace as compared to the conventional incinerator. The convective heat transfer in this furnace was higher than that of the conventional incinerator, and more useful energy was extracted from the waste liquids for end users. For the waste liquids with lower heating values of 15.0 MJ/kg (19 wt.% water) and 10.4 MJ/kg (42 wt.% water), it was found that 49% and 10% of the heating values of the waste liquids, respectively, could be used for utility energy. Furthermore, the waste liquid with a lower heating value of 7.1 MJ/kg (45 wt.% water) could burn itself in this furnace without the need of co-firing of any auxiliary fuels. NO_x and CO emissions were lower than 60 ppmv (6% O₂) and 50 ppmv (6% O₂), respectively, for all tests.     

Low-NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Firing Systems with Swirl Burners Installed on Boilers PK-39-IIM and BKZ-420-140-5

The paper presents basic technical solutions for the firing system and design of the burners of boilers PK-39-IIM and BKZ-420-140-5 when firing Ekibastuz coal. The developed low-NO _x firing systems ensure low nitrogen oxide emissions both at low cross-section heat release rates and high furnace cross-section heat release rates. Technical solutions developed for the firing systems are based on the simulation of coal combustion in furnaces of the mentioned boilers using ANSYS Fluent software.     

Laser-based investigations of flow fields and OH distributions in impinging flames of domestic cooker-top burners

A thermal performance of impinging flames of widely-used cooker-top burners depends on a complex interaction between flow field and combustion. The critical situation is placed on two typical cooker-top burners having almost the same configurations, but yielding about 10% point difference in thermal efficiency. Therefore, in situ flame measurements of averaged velocity using particle image velocimetry (PIV) and image of averaged OH radicals using planar laser-induced fluorescence (OH-PLIF) are required to obtain insight into the coupling mechanisms during the combustion and heat transfer, and to develop a comprehensive experimental data base to support a phenomenological understanding of the differences in flames of the two burners. A combined study of flow field and combustion forms the basis of a much better understanding of the casual links that couple fluid mechanics, combustion and heat transfer in the two burners. This can provide guidelines for efficient burner design to meet future regulatory requirements.     

Predictions of CO and NOx emissions from steam cracking furnaces using GRI2.11 detailed reaction mechanism – A CFD investigation

This investigation develops a three-dimensional Computational Fluid Dynamics (CFD) model to simulate the turbulent diffusion flame on the fire-side of the radiation section of a thermal cracking test furnace coupled with a non-premixed low NO_x floor burner. When this type of burners which uses the internal Flue Gas Recirculation (FGR) technique is coupled with large scale furnaces, both the turbulent mixing and chemical reaction rates are comparable and hence this should be considered in the model. Different combustion models are used to simulate the turbulence–chemistry interactions for this flame. The CFD model, based on the Eddy Dissipation Concept (EDC) combustion model coupled with the detailed GRI2.11 reaction mechanism, gives the most reasonable predictions compared with the available experimental data or empirical correlations for the diffusion flame in the thermal cracking test furnace, especially for the flame length and the CO and NO_x emissions.     

乙烯裂解炉燃烧器技术进展

综述了乙烯裂解炉燃烧器技术开发的最新进展情况,介绍了燃烧器布置优化、底部燃烧器和侧壁燃烧器等新技术以及CFD模拟技术在燃烧器设计和操作等方面的应用情况,这些新技术的成功应用将降低裂解炉烟气中NOx的排放,提高燃烧器的效率和裂解炉的操作稳定性.     

Numerical study of co-firing coal and Cynara cardunculus in a 350 MWe utility boiler

In this work, a CFD numerical study of co-firing coal and cynara in a 350 MWe utility boiler is presented. The most influent operational factors related to the biomass feeding conditions such as biomass mean particle size, level of substitution of coal by biomass and feeding location in the furnace, are analyzed, determining their influence in the combustion process. Validation of the simulations is performed using measurements gathered at the plant. Results from the study show interesting conclusions for their implementation in the power plant, suggesting recommendable limits in the maximum biomass substitution level and particle size in order to keep a reasonable boiler efficiency, and pointing out the outstanding influence of the biomass injection location discussing thermal and fluid-dynamic implications and the possibility of introducing retrofitted or specific biomass burners.     

Coke deposition and run length in industrial naphtha thermal cracking furnaces via a quasi-steady state coupled CFD model

Mathematical modelling of the thickness of the coke layer growing over months in millisecond cracking reactors is a dilemma in computational fluid dynamics (CFD) simulation. To address the time scale issue, a quasi-steady state (QSS) approach was employed through a comprehensive coupled reactor/firebox CFD model in the current study. The model was applied to predict the time-dependent behaviour of coke deposition and to determine the appropriate operating conditions for maximum olefin yields over an industrial furnace run length. A novel algorithm was designed to overcome the complexity of QSS simulation of the CFD model, which is a combination of reactive turbulence flow, combustion, and radiation models. The furnace parameters were studied as a function of two variables: the dilution steam-to-feed ratio and the liberated heat by the burners. The results indicated that the run length can be extended by up to 20% while retaining the main product yields. This study offers practical suggestions to maximize the run length in the operation.     

Coupled simulation of an industrial naphtha cracking furnace equipped with long-flame and radiation burners

A coupled reactor/furnace simulation has been conducted for a 100 kt/a SL-II naphtha cracking furnace containing both long-flame and radiation burners. The computational fluid dynamics approach was used to simulate the flow, combustion and radiative heat transfer in the furnace. The software packages COILSIM1D and SimCO were used to account for the cracking process in the reactor coils. The simulation provides for the first time detailed information about concentration, velocity, and temperature fields for these types of furnaces. Comparison of the calculated product yields against measured industrial data validates the simulation and shows that the difference with using a predefined normalized heat flux profile is limited. The results show that the design of radiation section outlet leads to an asymmetric flue gas-temperature, concentration and velocity profile. Large recirculation zones exist near the reactor tubes, making the temperature in the middle of furnace more uniform.     

HIGH TEMPERATURE TESTING FURNACE1

A surface combustion furnace lined with alundum and fed by seven burners supplied from a mixture box in which an explosive mix. Of gas and air is made by a special inspirator melts down cone 36 in one hour using 156 cu. Ft. of city gas. The max. temp., 3400°F, attained is within 200°F, of the theoretical max. Advantages claimed are: Simplicity, low fuel consumption, ease of observation and measuring temperatures and ability to produce either neutral, reducing or oxidizing atmosphere.     

燃烧法快速合成黄色可控轻质纳米氧化铈

以硝酸铈为氧化剂和抗坏血酸为燃烧剂,采用燃烧法快速合成纳米氧化铈,并用XRD、IR、UV、SEM等技术进行表征.同时进行燃烧剂、煅烧温度、盐助溶剂的考察.得出燃烧法的最佳实验条件为:n(硝酸铈)∶n(抗坏血酸)=1∶2,可以不加助溶剂,不经洗涤、煅烧.在此条件下所制备的氧化铈质量轻,颗粒细.     

Premixed metal fibre burners based on a Pd catalyst

As an alternative to previously developed catalytic FeCrAlloy fibre mat burners based on perovskite catalysts, new catalytic burners have been developed based on Pd catalyst on lantana-stabilised Al₂O₃ and different fibre structures (NIT100A, NIT100S and NIT200S by ACOTECH NV). All development steps are considered, shifting from catalyst preparation (based on combustion synthesis of γ-Al₂O₃) to the optimisation of lantana and Pd loadings, from the definitions of the best catalyst-deposition conditions (washcoating) to the catalytic burners performances, determined in an ad hoc developed combustion chamber. The results show almost half pollutants emissions and better performance compared to various non-catalytic counterparts, especially as far as CO and NO_x emissions are concerned. Some flame instability problems were though registered, especially for one of the catalytic burner mattresses employed, at low specific power inputs and excesses of air (<375 kW/m² and <12%, respectively). Further, PdO/Pd transition is shown to influence the dynamic behaviour of the catalytic burners.