Temperature Distribution In Furnace Research Articles

Combustion characteristics and NOx release of sludge combustion with coal in a 660 MW boiler

This article analyses the effects of sludge moisture content and blending ratio on combustion characteristics, furnace temperature distribution and NOx release during co-firing with coal in a 660 MW tangentially fired boiler using CFD. When the sludge water content increases from 10 % to 30 %, the water in the fuel is rapidly released during the initial combustion process and absorbs the reaction heat, resulting in a 2.8 % decrease in the temperature of the main combustion zone and a gradual decrease in the heat flux density, while the presence of water leads to the intensification of the incomplete combustion, resulting in the increase of the NOx conversion rate. With the increase of sludge blending ratio from 5 % to 25 % and the increase of water, the combustion temperature in the main combustion zone decreased by 4.0 %, and the heat flow density decreased significantly in the whole furnace and MBR area, by 6.43 % and 12.78 %, respectively. However, the nitrogen content present in the sludge is much higher than that of coal, and the fuel-based NOx produced by the combustion process increased dramatically, which led to the boiler exit NOx increasing by 35.4 %. Reasonable selection of sludge blending ratio and water content is a key issue to be considered for boiler co-combustion.

Efficient online prediction and correction of 3D combustion temperature field in coal-fired boilers using GDNN

Predicting furnace temperature distribution is vital for coal-fired boiler safety. Existing methods, including finite element calculations and three-dimensional (3D) reconstruction still face limitations. A 3D combustion temperature field prediction method, GDNN, which utilizes offline-computed computational fluid dynamics (CFD) simulation results for online reconstructions of entire boiler, was proposed. GDNN method leverages the knowledge of the temperature field acquired by the base neural network model and Gaussian processes. Furthermore, a temperature field correction method is introduced, which employs intermediate variables of the GDNN model and measured values from temperature sensors to establish a correction model for the entire predicted temperature field. We compared GDNN's effectiveness with four well-established algorithms: Extreme Learning Machine (ELM), Least Absolute Shrinkage and Selection Operator (LASSO), Deep Neural Network(DNN), and Radial Basis Function (RBF) network, by also substituting these algorithms as the base model in our proposed method. The experimental results demonstrate that the proposed prediction method exhibits the highest performance, and the correction method effectively improves the overall results. The optimal parameters for predicting and correcting 3D furnace temperature field results were determined through experimental comparison, and the proposed method was applied to a 350 MW boiler, achieving an error of 2.41%, proving its real-world effectiveness.

Online monitoring instantaneous 2D temperature distributions in a furnace using acoustic tomography based on frequency division multiplexing

The online and accurate capture of dynamic changes in furnace temperature distribution is crucial for production efficiency improvement and international environmental policy compliance in power plants. To achieve this, a measurement system with a reliable online reconstruction capability and high temporal resolution is necessary. This paper presents a novel technique that can improve the temporal resolution of the currently existing acoustic tomography (AT) system using frequency division multiplexing (FDM). This method allows for concurrent transmissions of acoustic signals in several different frequency bands instead of a sequential manner, which leads to more efficient channel utilization and allows all acoustic signals to be acquired at the same time, so that a better temporal uniformity of multipath acoustic signals can be realized. Theoretical analysis and experiments have been conducted to verify the effectiveness of this technique. The results prove that the proposed method can significantly improve the temporal resolution of the AT system while maintaining the accuracy and robustness of the reconstruction.

Modeling effects of skid buttons and dislocated skids on the heating quality of slabs in an industrial walking-beam reheating furnace

The slab heating process inside a walking-beam reheating furnace is critical for slab quality. This paper presents a comprehensive CFD model simulating the fuel combustion, flow field, temperature distribution, and heating process of walking slabs in an industrial-scale furnace. It explicitly considers the effects of dislocated skids and skid buttons. After the model validation through industrial measurements, the model is used to analyze the influences of skid buttons and dislocated skids on the flow and temperature field and the slab heating process. The results show that the dislocated skids and skid buttons significantly affect the flow field and furnace temperature distribution. The simplifications on the structures of skid buttons and dislocated skids cause the neglect of shielding radiation of skids in the modeling. Overcoming this problem by the present model reduces the difference between the measured and predicted slab temperature by more than 20 K. Overall, the skid buttons reduce the sheltered area for slab heating by 86%, and the dislocated skids change the sheltered region of the slabs. These together favor a more uniform temperature of slabs. The results suggest that the CFD model can offer convenience to understanding, designing, controlling, and optimizing the slab heating process in a walking-beam reheating furnace.

Study on the Effect of Secondary Air Layout on CO Reduction Performance in a 75 t/h Biomass CFB Boiler Burning Wheat Straw

Biomass fuels play an important role in the field of fluidized bed combustion, but due to the diversity and uncertainty of fuels, there are usually some problems of high CO emission that cannot be directly solved by combustion adjustment. In this paper, a 75 t/h biomass fluidized bed was taken as the research object. It was observed from the field test that the gas incomplete combustion loss reached 12.13% when mono-combustion of wheat straw was conducted, and the CO concentration in the exhaust gas exceeded 30k ppm. Combined with the CPFD numerical simulation, the combustion characteristics and influence of secondary air layout on CO reduction performance were discussed in detail. The results revealed that the gas temperature gradually increased along furnace height under the initial condition, and the maximum temperature was more than 1000 °C at furnace outlet. The air curtain of the secondary air jets was insufficient, and the wheat straw rose rapidly as it entered into the furnace. By arranging adjacent secondary air ports above each fuel-feeding inlet, the residence time of particles in the furnace could be significantly increased, thus, the furnace temperature distribution was more reasonable and the CO emission was reduced by 58.6%.

Influence of fuel distribution on co-combustion of sludge and coal in a 660 MW tangentially fired boiler

The distribution method of coal and sludge is an important factor affecting co-combustion, but few studies have been carried out in most papers. The influence of different fuel distribution methods for municipal sewage sludge and coal on co-combustion in a furnace was studied using numerical computational fluid dynamics simulations in this paper. In the considered cases, the burners that inject sludge were artificially altered, while the masses and contents of sludge and coal remained unchanged. The combustion temperature, combustion characteristics, and the heat of the boiler were analysed. The concentrations of CO, CO2, and volatile matter were used as characteristic parameters. The conclusion shows that the co-combustion temperature in the main combustion region inevitably decreases compared to coal mono-combustion regardless of the fuel distributions being used. When coal and sludge are premixed, the furnace temperature distribution is more uniform. However, premixing has a greater influence on the boiler heat flux. Feeding sludge into the furnace from the top layer of burners individually can effectively reduce the adverse impact of premixed combustion, and the total heat flux of the furnace is reduced by 4.8%, the heat flux decreased by about 6% for other distribution methods. Considering the broad prospects of sludge co-disposal in boilers, these findings provide guidance and suggestions for the co-combustion of sludge and coal, and they provide theoretical support for the efficient operation of boilers.

An experimental investigation of ammonia/landfill/air mixtures' pollutant emissions and temperature distribution under non-preheated moderate or intense low-oxygen dilution combustion.

This paper investigates the non-preheated MILD combustion behavior of landfill/ammonia mixtures. The experiments were carried out in a laboratory-scale furnace. The effects of equivalence ratio variation, CO2 dilution, and ammonia on the furnace temperature distribution and exhaust gas emissions were analyzed attentively. The experiment results indicate that a non-preheated MILD combustion establishment can provide a uniform temperature distribution and lower pollutant emissions while maintaining the same thermal efficiency. According to the results, equivalence ratio changes affect the MILD temperature structure sensibly. Variation of equivalence ratio is also effective on the pollutant emissions. Moreover, the rich burn condition increases the CO emissions by bringing the HCN and H radicals into the related reactions. Whereas in lean-burn states, little amounts of CO are generated, while the NO concentrations are higher due to the NH2 pathways. The results also indicate that CO2 dilution reduces the furnace's peak temperature. However, CO2 dilution may also increase the O and OH radicals, allowing HCN molecules to react and generate NO. Regarding the ammonia addition experiments, it was figured out that ammonia increases NOx emissions, while decreasing CO2 concentrations affect the flame temperature profile.

Single Crystal Growth of 4‐Aminobenzophenone (ABP) by Solution and Seeded Czochralski Pulling Techniques for Second Harmonic Generation Applications

AbstractHighly efficient 4‐aminobenzophenone (ABP) single crystals are grown from melt by employing the seeded Czochralski pulling technique for second harmonic generation (SHG) applications. The as‐grown seed crystals from solution with dominant (100) and (001) facets are utilized to trigger the directional solidification. For successive growth, initial measurements of the furnace temperature distribution, heat flow structure, and solidification temperature of ABP in correlation with differential scanning calorimetry (DSC) analysis are made. The controlled diffusion is ensured by monitoring the interfacial layer between the melt and the growing crystal and is maintained by optimizing the melt temperature and pulling and rotation rates. Color change of the melt due to thermal‐oxidation is prevented by appropriate control of the growth environment. A slow and steady growth rate affirms the good quality of the ABP single crystal. The anisotropic growth behavior of ABP from solution and melt is reported. Internal molecular structure, crystalline purity, molecular vibrational modes, optical transmission, and thermal behavior are studied using single crystal and powder X‐ray diffraction, FTIR, UV–vis–NIR and DSC analyses. The obtained higher SHG efficiency of the grown ABP in comparison with that of the organic and inorganic standards urea and KDP reveals its suitability for SHG applications.

Investigation on self-sustained combustion, NOx emissions, and ash characteristics of coal slime in a lab-scale fluidized bed

Incineration of coal slime in the fluidized bed boiler is an efficient means of energy recovery and environmental protection. In this study, combustion behaviors and NOx emissions of coal slime were studied using a lab-scale fluidized bed reactor. Besides, the fundamental characteristics of coal slime and its ash were explored coupled with a particle size analyzer, X-Ray Diffraction (XRD), thermogravimetric analysis (TGA), automatic specific surface, porosity analyzer, etc. It revealed that the range of 350–640 °C was the main mass loss stage with more than 92% of the total loss during combustion through the thermogravimetric analysis, guaranteeing good burnout performance. The challenges of fluidization and burnout of C-type particles accounting for 36.59% of coal slime were solved by mixing the water with coal slime to enhance its agglomeration and thermal explosion. Through the coupling of multiple operating parameters such as primary and secondary air rate, secondary air height, the oxygen content of flue gas, etc., reasonable furnace temperature and reduction zone distribution can be achieved. In addition, it was found that the migrations of most heavy metals are correlated with the proportion of fine particles in coal slime during combustion. The high content of alkaline substances of coal slime leads to a slightly slagging propensity below 900 °C due to the prevention of eutectics formation. Pore analysis implies that bottom ash and fly ash show different trends in the specific surface area and pore volume compared to the coal slime during combustion.

Numerical simulation of combustion of sulfide- biomass concentrate ingredients and contaminants in copper furnace smelting

Co-firing biomass and fossil fuels in industrial furnaces is a suitable way to reduce the environmental impact of human activities with acceptable investment. In this paper, the results of numerical simulation co-firing of sulfide concentrate and three auxiliary fuels, including gasoil, kerosene, and sawdust biomass, are compared in the flash furnace copper smelting. For modeling of turbulent flow and combustion, RNG, k-ε model, and probability density function model (pdf) have been used, respectively. This study has been carried out to investigate the furnace temperature and combustion pollutants distribution. The numerical simulation results show that the flame temperature resulting from the combustion of diesel fuel and sawdust as auxiliary fuel is the highest and lowest, respectively. In biomass combustion, despite that the flame temperature is low, but the NOx mass fraction increases because there is nitrogen in the sawdust chemical composition. Also in sawdust combustion, the oxygen content is high, the SO2 and SO3 sulfur pollutants increase in the high temperatures regions of the furnace and the lower temperature of the auxiliary fuel burner, respectively. Because SO2 is formed at high temperatures (> 1273K), oxygen-rich and SO3 species are produced at relatively low temperatures with excess oxygen. The amount of CO emissions in sawdust combustion is much lower than the amount of combustion of diesel and oil. In the peak of the flash furnace for sawdust and diesel auxiliary fuels, the temperature is 2.29E+03 K, and the distribution of NOx, CO2, O2, SO2, and SO3 are 1.51E-04, 9.72E-02, 2.33E-03, 1.71E-01 and 2.45E-02 respectively.

Coal combustion emissions and ash formation characteristics during oxy-fuel combustion in a 100 kWth pressurized circulating fluidized bed

Pressurised circulating fluidized bed oxy-fuel combustion (PCFB-OFC) is a promising technology for CO2 capture because of its high carbon capture efficiency and net efficiency. However, there is a lack of comprehensive experimental studies on PCFB thermal state experimental devices due to the complexity of their design, construction, and operation. In this study, a 100 kWth PCFB-OFC experimental device was developed, and a series of coal combustion experiments were conducted under 0.1 to 0.6 MPa at an average oxygen concentration of 30% with a fixed peroxygen coefficient β (1.1–1.3). The effect of combustion pressure was investigated to determine the influence of pressure on coal combustion efficiency, furnace temperature distribution, gaseous pollutant emissions, and fly ash chemical composition. The experimental results showed that the increase in pressure increased the particle concentration in the dilute phase zone and increased the temperature at the top of the furnace, with a more uniform temperature distribution. The carbon content in the fly ash and the CO emissions in the flue gas were gradually reduced, and the combustion efficiency increased to 97.3%. The emissions of NO and N2O gradually decreased with the increase in load, and the NO emissions reduced by approximately 70% at 0.6 MPa. The emission of SO2 showed a downward trend as the pressure increases. Affected by the increase in pressure, the self-desulfurization capability of fly ash was improved. In addition, lower K2O and Na2O contents may reduce the deposition of fly ash in the furnace.

Coal ash induced ring formation in a pilot scale rotary kiln for low-grade iron ore direct reduction process: Characterization and mechanism

For economic utilization of low grade iron ore resource, a pilot scale study of iron ore direct reduction by rotary kiln (ϕ1.5 m × 15 m) was carried out. In this work, the actual furnace burden and temperature distribution status in rotary kiln were in-situ measured. The location and typical physicochemical condition in rotary kiln for ring substances generation were verified. SEM equipped with EDX, XRD and optical microscopy were applied to analyze the characteristics of ring substances. Extra lab experiments and phase diagram calculation with the help of Factsage 7.0 were performed to reveal the ring formation mechanism. Results showed that ring substances emerged at 5 ∼ 6 m zone of rotary kiln, with high temperature, coal proportion, and metallic iron content of pellets in this region. Pellets bonded together by the sintering of metallic iron on surface, then, molten wrappage cemented them to refractory of rotary kiln forming the ring. Hedenbergite and fayalite produced by interaction of coal ash and iron ore powder developed the molten wrappage. The new understanding of ring formation promised potential for its application in coal fired rotary kiln operation.

PARAMETRIC STUDY OF THE NON-PREMIXED COAL COMBUSTION IN FURNACE FOR HEAT TRANSFER AND EMISSION CHARACTERISTICS

Steady-state turbulent non-premixed combustion of pulverized coal has been modeled in the two-dimensional furnace. Pulverized coal of three different types, low volatiles coal, medium volatile coal and high volatile coal, has been considered. The coal is injected through the center of the furnace and air is being supplied with two inlets (top inlet and bottom inlet) at different velocities. Taking advantage of the symmetry, only one half of the domain is considered. Results have been validated with the experimental data for furnace temperature distribution. Effect of variation of parameters such as top air velocity, bottom air velocity, air temperature, furnace wall temperature and mass flow rate of coal are discussed for all three different types of coal. The effect of these various parameters has been discussed upon peak temperature inside the furnace, heat transfer to/from the system to surroundings and emission of gases like compounds of NO, CO and CO2. The analysis has been carried out using Ansys-Fluent software.

3D high-quality temperature-field reconstruction method in furnace based on acoustic tomography

Reconstructed 3D high-quality temperature distribution in furnace can provide important information to better control boiler operations and to optimize the combustion process. Acoustic travel-time tomography is considered to be a promising method that uses the dependence of sound speed on temperature to reconstruct the temperature field. In this paper, a new 3D temperature field reconstruction method based on radial basis function approximation with polynomial reproduction (RBF-PR) and truncated generalized singular value decomposition (TGSVD) is proposed to solve the inverse problem. To improve the reconstruction quality, we consider the refraction effect of sound waves in the non-uniform temperature field and estimate the sound wave propagation path model in the reconstruction method. The shooting method with improved Powell algorithms is used to solve the propagation path model and obtain the relationship between the acoustic travel-time over the propagation path and temperature distribution. Simulations are implemented to evaluate the effectiveness of the proposed reconstruction method. The results indicate that compared with other methods, the new reconstruction method that considers the refraction effect can reconstruct temperature distribution with higher accuracy and better anti-noise ability. Experimental results also demonstrate that the temperature distribution can be reconstructed effectively by the proposed method.

Pulverized coal combustion application of laser-based temperature sensing system using computed tomography – Tunable diode laser absorption spectroscopy (CT-TDLAS)

The investigation of combustion phenomena in pulverized coal flames is significant for combustion optimization related to energy conservation and emission reduction. Real-time two dimensional (2D) temperature and concentration distributions play an important role for combustion analysis. The non-contact and fast response 2D temperature and concentration distribution measurement method was developed in this study. The method is based on a combination of computed tomography (CT) and tunable diode laser absorption spectroscopy (TDLAS). The accuracy evaluation of developed 32-path CT-TDLAS demonstrated its feasibility of 2D temperature measurement. 32-path CT-TDLAS was applied to CH4 and 5 kg/h coal combustion fields for 2D temperature measurement. The time-series 2D temperature distribution in coal combustion furnace was measured using 32-path CT-TDLAS measurement cell with kHz time resolution. The transient temperature field of combustion flame directly reflects the combustion mode and combustion stability. The measurement results demonstrate its applicability of CT-TDLAS to various types of combustor, especially the combustion fields with coal and ash particles. CT-TDLAS method with kHz response time enables the real-time 2D temperature measurement to be applicable for combustion analysis.

Assessment of radiative heat transfer impact on a temperature distribution inside a real industrial swirled furnace

Combustion systems will continue to share a portion in energy sectors along the cur-rent energy transition, and therefore the attention is still given to the further improvements of their energy efficiency. Modern research and development processes of combustion systems are improbable without the usage of predictive numerical tools such as CFD. The radiative heat transfer in participating media is modelled in this work with discrete transfer radiative method (DTRM) and discrete ordinates method (DOM) by finite volume discretisation, in order to predict heat transfer inside combustion chamber accurately. The DTRM trace the rays in different directions from each face of the generated mesh. At the same time, DOM is described with the angle discretisation, where for each spatial angle the radiative transport equation needs to be solved. In combination with the steady combustion model in AVL FIRE? CFD code, both models are applied for computation of temperature distribution in a real oil-fired industrial furnace for which the experimental results are available. For calculation of the absorption coefficient in both models weighted sum of grey gasses model is used. The focus of this work is to estimate radiative heat transfer with DTRM and DOM models and to validate obtained results against experimental data and calculations without radiative heat transfer, where approximately 25% higher temperatures are achieved. The validation results showed good agreement with the experimental data with a better prediction of the DOM model in the temperature trend near the furnace outlet. Both radiation modelling approaches show capability for the computation of radiative heat transfer in participating media on a complex validation case of the combustion process in oil-fired furnace.

Thermal conductivity of Na2O–B2O3–SiO2 melts

ABSTRACT Borosilicate glasses are candidate materials for the immobilization of high-level radioactive waste. The values of thermal conductivity of different borosilicate melts are thus indispensable information when optimizing the temperature distribution in a glass melting furnace. In this study, the thermal effusivity of Na2O–B2O3–SiO2 melts was measured using a front heating–front detection laser-flash method. The thermal conductivity, which can be obtained by combining the measured thermal effusivity with the specific heat capacity and density, was calculated using the least-squares method; the values for the Na2O–B2O3–SiO2 melts either slightly decreased linearly with increasing temperature or remained almost constant over the investigated temperature range. The values of thermal conductivity of the Na2O–B2O3–SiO2 melts were higher than those of B2O3–SiO2 melts and lower than those of CaO–B2O3–SiO2 melts. Furthermore, the thermal conductivity of the Na2O–B2O3–SiO2 melts was compared with those of the B2O3–SiO2 and CaO–B2O3–SiO2 samples.

Effect of FGR position on the characteristics of combustion, emission and flue gas temperature deviation in a 1000 MW tower-type double-reheat boiler with deep-air-staging

Flue gas recirculation (FGR), which is widely adopted to control the steam temperature of ultra-supercritical (USC) double-reheat boiler, significantly affects the temperature distribution, NOx generation, and flue gas temperature deviation in furnace. This study presents a numerical study on the combustion process in a 1000 MW tower-type double-reheat boiler with deep-air-staging. The effect of FGR injection position on the temperature distribution, NOx emission, and gas temperature deviation was studied and discussed under 100% boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA), and 50% THA loads. The numerical model was validated by the in-house thermal calculation code and design parameters provided by the boiler manufacturer. The results show that, under the same load, when recirculating flue gas (RFG) is injected into the furnace from the nozzle blow the burner, the burner zone temperature is lower but the NO generation is higher than the case in which RFG is injected from the nozzle above the burner. Compared to the former, NOx emission of the latter reduced by 12.3%, 31.2%, and 33.8% under 100% BMCR, 75% THA, and 50% THA load, respectively. Both the inlet flue gas temperature and the heat flux of the primary superheater decrease when RFG was introduced from the nozzle above the burner. The case in which RFG is injected from the nozzle above the burner was found to be an applicable and effective method to control the NO generation and regulate the steam temperature of the double-reheat boiler.

Experimental Research on NOx Emission Characteristics During Coal Combustion in the Stoker-fired Boiler

In this paper, the combustion stability and nitrogen oxides (NOx) emissions test were made in two coal-fired chain grate boilers with hot water supplies of 29MW and 46MW. The investigations aim to clarify the key characteristics of NOx emission, e.g.instability of NOx emission, temperature and gaseous components profiles and the unsteady variation of NOx emission with power level changing. Main conclusions include: 1) In the process of stable combustion, NOx emissions still have±5% fluctuations, it is not stable. 2) The furnace temperature distribution show double temperature peaks. One peak (~1500°C) is located on the burning solid-fuel surface on the chain grate, and the other (~1050°C) is ~5.6m above the arch. 3) With increasing the thermal power, NOx emission shows a dramatic increase, higher around 1.25 times, as due to the rapid adjustment of coal feeding in grate furnace. Those above show the NOx control difficulty and the proper injector location of SNCR (selective non-catalytic reaction), which is key data collected for further NOx reduction retrofits.

Determination of thermal conductivities of B2O3-SiO2 and CaO-B2O3-SiO2 melts

The thermal conductivities of borosilicate melts, which have scarcely been measured, are one of the important thermophysical properties for optimization of temperature distribution in a glass melting furnace. In this study, the thermal effusivities of B2O3-SiO2 and CaO-B2O3-SiO2 melts were first measured using a front heating–front detection laser flash method. Then, the thermal conductivities, which were obtained by combining the measured thermal effusivity data with specific heat capacity and density, could be evaluated through an equation using the least-squares method. As such, the thermal conductivities of the B2O3-SiO2 and CaO-B2O3-SiO2 melts were found to slightly linearly decrease with increasing temperature over the investigated temperature range of 1248–1723 K. In addition, the thermal conductivities of the samples of CaO-B2O3-SiO2 melts were higher than those of the samples of B2O3-SiO2 melts. Furthermore, the network models of the thermal conductivities for the B2O3-SiO2 and CaO-B2O3-SiO2 melts were discussed using the boron-11 NMR spectra of the glassy samples for the B2O3-SiO2 and CaO-B2O3-SiO2 samples.