Annular Furnace Research Articles

Simulation of gas-solid combustion characteristics in a 1000 MW CFB boiler for supercritical CO2 cycle

Supercritical CO2 (S-CO2) power cycle has become one of the most efficient and low-pollution cycle schemes to improve thermal power generation efficiency and reduce energy consumption around the world. In this study, the 3D physical model of a 1000 MW S-CO2 circulating fluidized bed (CFB) boiler with annular furnace is established to simulate the gas-solid combustion process based on the MP-PIC method under the Eulerian-Lagrangian framework. By comparing with the conventional water steam CFB boiler, the S-CO2 CFB boiler has a smooth and stable gas-solid flow pattern with good uniformity of the particle concentration and velocity distribution, indicating that the annular structure and the layout of the heating surfaces is conducive to the gas-solid flow uniformity. The gas-solid phase temperature distributes uniformly basically without sudden rise or sudden drop, and the temperature difference between the solid phase and the gas phase is not large, which reflects the good combustion uniformity of the S-CO2 CFB boiler. Compared with 300 MW and 600 MW S-CO2 CFB boilers, the 1000 MW one shows a higher carbon conversion rate, lower desulphurization effect, and lower nitrogen removal performance with the CO, NO, and SO2 outlet concentration of 0.002%, 5.8 mg/m3, and 125 mg/m3, respectively.

Mass Transfer Model of Oriented Silicon Steel Coil during the First Soaking in Annular Furnace

Mass Transfer Model of Oriented Silicon Steel Coil during the First Soaking in Annular Furnace

О РЕЗУЛЬТАТАХ ТЕРМОУСТАЛОСТНЫХ ИСПЫТАНИЙ ЧУГУНА И ОЦЕНКЕ ЕГО ДОЛГОВЕЧНОСТИ

The article notes that at present, despite numerous studies of thermal fatigue, the thermal fatigue strength of cast irons due to stresses in parts made of this material requires additional study. Issues of thermal fatigue strength are especially relevant for such heat-stressed parts of internal combustion engines of autotractor diesel engines as the cylinder head. Of particular importance for these parts in their design and restoration is the ability to predict thermal fatigue strength, which is the main criterion that determines their durability. The article describes an approach to solving the problem of predicting the thermal fatigue strength of cast iron parts based on the data on their stress state and the results of thermal fatigue testing of samples on a specially designed and manufactured installation. The setup consists of two massive plates mounted on racks, between which a sample with a hole was rigidly installed. During the tests, the sample was heated by a special annular furnace to a temperature of 550°C for two minutes, and then cooled with running water through the central hole. A sample bounded on both sides during heating and thermal expansion accumulated residual tensile stresses as a result of relaxation processes and, upon reaching critical values and the appearance of fatigue defects in the form of cracks, ruptured. The proposed mode quite accurately repeats the operating conditions of the heat-receiving surface of the cylinder heads in the area of the intervalve jumpers when changing the operating mode at rated power and subsequent engine shutdown. As a result of the tests, the curves of the number of cycles to failure depending on the achieved stresses were obtained and their approximation was carried out. On the basis of approximating expressions and dependences of "limited durability" under low-cycle loading of parts, the thermal fatigue strength of a part made of cast iron can be predicted when its stress state changes as a result of design changes or after restoration.

Gas–Solid Hydrodynamics and Combustion Characteristics in a 600 MW Annular CFB Boiler for Supercritical CO2 Cycles

The detailed operational performance, gas–solid hydrodynamics, and combustion characteristics in a 600 MW coal-fired CFB boiler with a novel annular furnace, which was designed to meet the signific...

The Heat Transfer Model of Oriented Silicon Steel Coil in Annular Furnace during the Heating Stage of High‐Temperature Annealing

A 2D numerical model is built to simulate the heat transfer across the oriented silicon steel coil in annular furnace during the heating stage of high‐temperature annealing. A new method is proposed to calculate the view factors in the radiation submodel. The numerical result is verified through the comparison with the results of in situ experiments. For a coil with 1710 mm outside and 510 mm inside diameters, the heat absorbed by the outer surface of the coil is the highest, but the heat flux density along the axial direction of the coil is larger than the radial direction. The heat flux density of the outer surface shows an 86% rise depending on the increase in radial thermal conductivity after 75% H2 and 25% N2 is applied as the protective atmosphere at a heating time of 37 h. The temperature difference inside the coil ranges from 143 to 476 °C till the furnace reaches its designate temperature at 58 h, but the heating rate is nearly the same across the coil above 700 °C. The difference of property inside the coil is probably related to the difference of heating rate during the first soaking.

Оценка технико-экономической эффективности пирометаллургической технологии переработки пылей электросталеплавильного производства

An evaluation of technical and economic efficiency parameters of a previously proposed technological solution for processing dust from electric steel production by the pyrometallurgical method is presented. The technological approach consists in the reduction of iron and zinc from their oxygen-containing forms (ZnFe 2 O 4 and ZnO) by active carbon-containing materials. Experiments were carried out on samples with a 26.02 and 37.7%wt. of ZnO and Fe 2 O 3 , respectively, to evaluate the processing of industrial dust of PJSC Magnitogorsk Iron and Steel Works in a laboratory facility based on the LHT 08/17 high-temperature furnace (Nabertherm, Germany). "Small long-flame nut" brand charcoal was applied as a carbon reducing agent, with lime and quartz sand serving as sources of slag-forming components. Commercial products were obtained in the form of granular cast iron (96.75 and 2.92%wt. of Fe and C, respectively) and a zinc oxide product (90.21%wt. of ZnO). The extraction of iron and zinc in cast iron comprised the values of 94.0 and 91.0%, respectively. As a result, an annular hearth furnace is recommended as the main technological unit for the industrial implementation of the process. The basic technological scheme is proposed including dosing raw materials, preparing charge briquettes, performing reduction smelting, separation of smelting products (cast iron and slag) and trapping zinc-containing sublimates. To assess the technical and economic efficiency of the developed technology on an industrial scale, the costs of building a dust processing plant involving one annular furnace with an average diameter of 12 m having a steel production capacity of 15 000 tonnes per year were taken into account. The proposed technology was shown to be capable of supporting commercial granular cast iron and zinc oxide products in the amount of 33264 and 4435 tonnes per year, respectively. Considering the investment period, the estimated payback period is determined to be 34 months with the expected net profit equal to 535.59 million rubles/year.

Two-phase technology of titanium slag production from ilmenite concentrates

Titanium slag is a basic raw material for production of titanium dioxide, widely used in various branches of national economy. Titanium slag is produced out of ilmenite concentrate. In Russian Federation there are several ilmenite deposits of ledge and placer type under various stages of development. Laboratory studies of ilmenite concentrates of Malyshevskoye, Irshanskoye and Medvedevskoye deposits processing technologies carried out. Two-phase technological scheme proposed, including ilmenite-coal briquettes reducing in an annular furnace and smelting of hot metallized briquettes in an ore-smelting furnace resulting in titanium slag and pig iron obtaining. Ilmenite concentrates were mixed with anthracite, bonding agent, briquetted and reduced in an annular furnace. After reducing the hot metallized briquettes were smelted in an electric furnace at 1650 ° С and the smelting products were casted into molds. The chemical and size composition of ilmenite concentrates and chemical composition of metallized briquettes presented. Technical indices of the annular furnace operation at metallized briquettes production and chemical composition of titanium slag and pig iron obtained out of the mentioned deposits ilmenite concentrates cited. It was determined, that the production of briquettes with high degree of metallization in the annular furnace is possible at heat treatment mode, providing a quick heating until the temperature of 1400-1500 °С. The cycle of the briquettes heat treatment in the annular furnace can be 15-30 min, including the phases of charging, heating, roasting, cooling and discharging. To study the heat treatment parameters effect on the process of coal-thermal reducing of ilmenite concentrates briquettes, a heat-physical model was elaborated. The model was based on studies of coal-thermal reducing kinetics of briquettes comprising ilmenite and anthracite, as well as zonal heat and material balances of oxidizing-reducing processes in the annular furnace. A technological scheme of titanium slag from ilmenite concentrates of Malyshevskoye, Irshanskoye and Medvedevskoye deposits proposed.

Investigating the thermal work and construction of annular furnace on “Chelyabinsk pipe-rolling plant” PJSC to improve heat technical indicators of its work

High performance of rolling and tube rolling mills, good quality of finished metal products can be obtained by heating metal billets with minimal oxidation and decarburization in heating furnaces. Such conditions can be provided by annular furnaces, which are widely used in the rolling production of pipes, railway wheels and tires. High-quality heating allows us to obtain the structure of metal products with given thermal and working properties, as well as the plasticity necessary for subsequent mechanical processing. In this paper, we consider thermal engineering features of the operation of an annular furnace for heating billets before rolling at “Chelyabinsk Tube Rolling Plant” PJSC (ChTPZ). The problems arising during the operation of thermal unit were analyzed: high specific fuel consumption for billets heating; high temperatures of walls external surfaces and roof external surfaces; low heating rate of the billet; large amount of air leaks into the furnace working space. Also design of gas-burning devices does not provide the possibility of regulating gas supply in a large range of loads, up to a periodic complete shutdown. And thermal energy of waste gases is practically not used. Metal heating has been analyzed and annular furnace heat balance has been compiled. Analysis of the results of computational studies has revealed factors that reduce energy efficiency of the existing furnace design. The measures were proposed for its modernization in order to reduce fuel consumption and to increase productivity (use of fibrous refractory materials, regenerative burners, non-water-cooled partitions, etc.). To assess impact of the proposed measures, the furnace heat balance after its systems reconstruction and assembly has been compiled, the main indicators of the furnace heat operation have been determined. When implementing proposed measures, significant economic effect is expected, including improvement in quality of metal heating while reducing fuel consumption and increasing productivity of the unit. In particular, after furnace reconstruction it is expected to increase the total (by 18.1 %) and heat (by 31.0 %) efficiency of the furnace, and to decrease (to48.3 kgconditional fuel/ton) specific fuel consumption.

Improving the Performance of the Annular Furnace at PAO ChTPZ

Abstract—The productivity of rolling and pipe-rolling mills and the product quality may be improved by heating the metal billet in furnaces with minimum oxidation and decarburization. That is possible in annular furnaces, which are widely used in the rolling of pipe and railroad wheels. High-quality heating permits the creation of metal structure with specified thermophysical and operational properties, as well as the plasticity required for subsequent machining. In the present work, the operation of an annular furnace used to heat pipe blanks before rolling at PAO Chelyabinskii Trubokatnyi Zavod (ChTPZ) is analyzed. Thermal problems are considered: in particular, the high fuel consumption in heating blanks and high external temperatures of the walls and roof; the low rate of blank heating; and the serious leakage of air into the furnace’s working space. In addition, a defect of the gas-burner design is that the gas supply cannot be regulated, despite the wide load range (including periodic shutdown). Finally, practically no use is made of the thermal energy in the exhaust gases. In the analysis of these problems, the heating of the metal is calculated, and the thermal balance of the annular furnace is formulated. The analysis reveals factors that decrease the energy efficiency of the existing furnace design. Measures are proposed for furnace modernization so as to decrease the fuel productivity and increase the productivity: for example, the use of fiber refractories; regenerator burners; and barriers that are not water-cooled. To assess the effectiveness of these measures, we formulate the thermal balance of the redesigned annular furnace and analyze its thermal operation. The proposed measures are expected to provide significant economic benefit and to improve the heating of the metal, with decrease in fuel consumption and increase in productivity. In particular, after reconstruction, increase in the furnace’s total efficiency (by 18.1%) and thermal efficiency (by 31.0%) is expected, as well as decrease in fuel consumption by 48.3 kg CF/t.

Simulation of temperature distribution in the oriented silicon steel coil in the heating stage of annealing process

Annular furnace is widely used for high temperature annealing of oriented silicon steel coils. The coils are placed under a cover in a protective atmosphere. The heating rate of the process must be strictly controlled to prevent magnetic property variations of the products. In this work, temperature distribution in the coil at the heating stage is simulated using finite method. Effects of fuel flux at burners on temperature distribution in the furnace are also analysed. Experiments are carried out to measure the parameters needed in simulations and to verify the simulation results. For a coil of 510 mm inside and 1710 mm outside diameters, the largest temperature difference in the coil is found to be as high as 438 °C, which occurs at about 8 h of heating. A total of 72 h is needed for the temperatures across the coil to reach a target level of 1170 °C. The temperature difference in the coil can be greatly reduced if N2 is replaced by H2 as protective atmosphere and the gap between sheet layers in the coil is reduced. Temperature distribution on the cover during heating is found to be rather uniform with the largest difference being within 30 °C.

Experimental study on structural optimization of a supercritical circulating fluidized bed boiler with an annular furnace and six cyclones

Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was carried out in the cold-test rig of an annular furnace CFB with six cyclones. The influence of furnace structure and cyclone arrangement on the non-uniformity of gas-solid flow was obtained. On the basis of these findings, the structure of the annular furnace CFB with six cyclones was optimized, and an optimal structure was obtained. The results show that for newly designed annular furnace CFBs, the non-uniformity of gas-solid flow among loops is no greater than that of traditional CFBs. In terms of uniformity, side cyclones rotating inward are superior to those rotating outward. The position of the side cyclones determines the basic solid circulating rate distribution trend and can dramatically improve flow non-uniformity. The middle cyclone positions and the symmetric modes of the cyclones do not determine the solid circulating rate distribution trend and have less effect onDEV Gs. Forty-five degree chamfers of outer ring walls can reduce wall erosion and the non-uniformity of gas-solid flow in the circulating fluidized bed. Regarding the operating and structural conditions in this work, the optimal structure of annular furnace CFBs is Type 6: side cyclones rotating inward and b = a/2, d = 0.1c; the center of the middle cyclone inlet located at the centerline of the furnace cross-section; cyclones on the two sides of the furnace in an axisymmetric arrangement; and a furnace corner shape of 45° chamfers. Under the given operating conditions, the DEV Gs for the optimal structure are approximately 4.0%~10.3%.

Hydrodynamics in a circulating fluidized bed with annular furnace and six parallel cyclones

Systematic measurements were conducted on a cold CFB with annular furnace and six parallel cyclones to study gas-solids flow in the annular furnace and flow non-uniformity among six cyclones. The results show that axial solids holdup in the annular furnace decreases exponentially with height, similar to the conventional rectangular furnace. The uniform transverse distribution of solids holdup suggests a good gas-solids mixing in the annular furnace. The annular furnace presents the core/double-annulus flow structure, and it results in enhanced gas-solids back-mixing than the conventional core/annulus flow structure. The gas-solids flow of the inner wall-layer and the outer wall-layer is very close at most part of the furnace height, and the wall-layer thickness decreases with height. Flow non-uniformity exists among six parallel cyclones in the annular furnace CFB. But non-uniform distribution of solids circulating rates and cyclone pressure drops show no regularity, and the flow non-uniformity is no larger than the CFBs with conventional furnace. Under typical operating conditions, the relative deviation of six solids circulating rates is 8.0%.

Numerical analysis on the flow instability of parallel channels in water wall of an ultra-supercritical CFB boiler

Abstract A general calculation model based on the time-domain method is established for analyzing flow instability in parallel channels. In this model, the governing equations of mass, momentum, and energy are discretized and solved using the first-order upwind scheme. A numerical computational program called Dynsys is developed in Fortran language to analyze the flow instability occurring in the water wall of an ultra-supercritical CFB boiler with annular furnace. Comparing the calculation results of Dynsys with the experimental results shows that the model is reasonable and accurate for practical engineering application. On the basis of the validated model, the typical parallel channels in water wall of ultra-supercritical CFB boiler are simulated. Results show that, under the condition of invariable inlet pressure, temperature, and total mass flow rate, as well as 1.2 times heat flux disturbance applied on the parallel channels of ultra-supercritical CFB boiler, the fluctuation of inlet flow rate versus time in two channels is out of phase. In addition, the amplitude of flow pulsation decreases with time first and then returns to the steady state. Therefore, the flow in the parallel channels of ultra-supercritical CFB boiler with annular furnace is stable. Compared with the flow instability in single channel, the calculating results show that the flow in parallel channels was more stable within the range of parameters in the present paper.

Processing of converter slurry by coking with coal

Processing of the industrial waste formed at steel plants is of great importance. In the converter production of steel, 12–25 kg of fine dust is formed in the production of 1 t of steel, depending on the composition of the raw materials, the furnace design, and the smelting conditions. Wet cleaning of the waste gases converts the dust into a slurry containing 46–50% Fe2O3. It is difficult to process such slurry because of its high water content, the small particle size, and the presence of zinc oxides. Standard dehydration technology is complex. It is also associated with thermal drying, which poses an explosion risk, while briquetting or granulation does not resolve the problem posed by the presence of zinc oxides and is complicated by a lack of acceptable binders. Researchers at Siberian State Industrial University have developed complex conditioning of iron-bearing slurry by nonthermal adsorptive dehydration and subsequent thermochemical agglomeration, with simultaneous reduction of the iron and zinc oxides. Adsorptive dehydration to a moisture content of 2‒3% is possible by contact with porous lignite semicoke produced by Termokoks technology. Then the lignite semicoke is pneumatically separated and sent for use in energy systems, while the iron-bearing product is mixed with GZh or Zh coal and sent for thermooxidative coking in a furnace of special design (an annular furnace with a rotating hearth), where large and strong pieces of ferrocoke are obtained at 1050–1100°C. The ferrocoke contains 55–60% of the iron-bearing product. The oxides of iron and zinc are almost completely reduced. The zinc passes to the vapor phase and is removed with the combustion products of the volatile coking components. On cooling to 850°C, the zinc vapor condenses. The ferrocoke obtained is suitable for blastfurnace use, thereby reducing the consumption of sinter and coke. The heat obtained on cooling the ferrocoke and the energy of the combustion products after the deposition of zinc are utilized in a gas-turbine system.

Numerical analysis of flow instability in the water wall of a supercritical CFB boiler with annular furnace

In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.

Mathematical modeling and thermal–hydrodynamic analysis of vertical water wall in a SCFB boiler with annular furnace

In this study, a mathematical model for a 660MW SCFB boiler design with annular furnace was deduced and thermal–hydrodynamic analysis was performed to improve the design and operation of water wall. Based on the water wall structure and heat flux distribution of the SCFB boiler, the connection style, pressure drop, mass flux, metal temperature, and phase transition position in water wall were optimally selected and numerically analyzed. The calculation results show that the minimum deviation of mass flux among water wall presents at connection style 1, in which outer-front wall, outer-left (right) wall, inner-front wall, and inner-left (right) wall are connected to the same steam-water separator. The gravitational pressure drop decreases while the frictional pressure drop increases with the rise of fluid temperature. Moreover, vertical upward parallel tubes present positive flow response characteristic with low mass flow rate. The subcooled length and superheated length shrink while the saturated length expands with the reduction of partial loads.

Thermal–hydraulic calculation and analysis of a 600 MW supercritical circulating fluidized bed boiler with annular furnace

The development of supercritical Circulating Fluidized Bed (CFB) boiler has great economic and environmental value. An entirely new annular furnace structure with outer and inner ring sidewalls for supercritical CFB boiler has been put forward by Institute of Engineering Thermophysics (IET), Chinese Academy of Sciences and Dongfang Boiler Group Co., Ltd. (DBC). Its outer and inner ring furnace structure makes more water walls arranged and reduces furnace height availably. In addition, compared with other additional evaporating heating surface structures such as mid-partition and water-cooled panels, the integrative structure can effectively avoid the bed-inventory overturn and improve the penetrability of secondary air. The conditions of the 600 MW supercritical CFB boiler including capability, pressure and mass flux are harsh. In order to insure the safety of boiler operation, it is very necessary to analyze the thermal–hydraulic characteristics of water-wall system. The water-wall system with complicated pipe arrangement is regarded as a network consisting of series-parallel circuits, pressure nodes and linking circuits, which represent vertical water-wall tubes, different headers and linking tubes, respectively. Based on the mass, momentum and energy conservation, a mathematical model is built, which consists of some simultaneous nonlinear equations. The mass flux in circuits, pressure drop between headers, outer vapor temperature of water-wall system and metal temperature data of tubes at the boiler maximum continuous rating (BMCR), 75% BMCR and 30% BMCR loads are obtained by solving the mathematical model. The results show that the vertical water wall design with smooth tubes in the 600 MW supercritical CFB boiler is applicable.

Система управления обжигом анодов в открытой кольцевой печи

Система управления обжигом анодов в открытой кольцевой печи

Modeling, Prediction, and Control of Heating Temperature for Tube Billet

Annular furnaces have multivariate, nonlinear, large time lag, and cross coupling characteristics. The prediction and control of the exit temperature of a tube billet are important but difficult. We establish a prediction model for the final temperature of a tube billet through OS-ELM-DRPLS method. We address the complex production characteristics, integrate the advantages of PLS and ELM algorithms in establishing linear and nonlinear models, and consider model update and data lag. Based on the proposed model, we design a prediction control algorithm for tube billet temperature. The algorithm is validated using the practical production data of Baosteel Co., Ltd. Results show that the model achieves the precision required in industrial applications. The temperature of the tube billet can be controlled within the required temperature range through compensation control method.

Annular Heating Furnace Temperature Control Based on the Fuzzy-PID Algorithm and Cascade Double-Cross Limiting Control

Annular heating furnace temperature control is a typical and complex industrial process control system,with the characteristics of multivariable,time-varying parameters,nonlinear,coupling, large inertia and pure delay,so it is difficult to obtain satisfactory control effect when using conventional PID control. In view of the above problems, adopting fuzzy PID algorithm and cascade double-cross limiting control, combustion control effect is greatly improved, self-tuning of PID parameters is realized, and control quality is enhanced. The experimental results show that, fuzzy PID control shows good dynamic and steady performance, its control effect is significantly improved when compared with conventional PID control, and it has better overall performance.