Fluidized Bed Furnace Research Articles

Thermodynamic modeling of oxidative roasting of nickel concentrate from matte separation in fluidized layer furnaces

Processes of oxidative roasting of sulfide concentrates in fluidized bed furnaces are quite widely used in sulfide copper, copper-nickel and pyrite concentrates processing. After roasting, the calcine is usually either smelted or hydrometallurgically processed. The results of various laboratory studies and industrial practice of sulphide roasting published in literature. This article will focus on thermodynamic modeling of roasting of nickel concentrate from matte separation. By means of FactSage software thermodynamic modeling of oxidative roasting of nickel concentrate from matte separation has been performed within the temperature range of 300–1200 оC and lg pO2 range from -20 to -2. Areas of possible calcined products – sulfates, oxides, sulfides and metallic non-ferrous metals shown. According to calculation results, formation of sulfates of non-ferrous metals is observed in low-temperature area, the area is moving to high temperatures with an increase in the oxidizing capacity of gas phase. In the area of medium temperatures, oxide phases, including spinels, observed. Sulfide and metal phases exist at the upper limit of the investigated temperature range. Comparison of the calculation results with the research data of real calcines from fluidized bed furnaces made using SEM and EMPA methods. It is observed that processes in real furnaces can be successfully calculated based on the assumption of thermodynamic equilibrium in fluidized bed. It was determined that calculation of the oxidation process using FactSage algorithms and databases is quite correct and can be used, among other things, when implementing control systems for industrial furnaces.The authors would like to thank director of the Research & Development Department at Gipronikel Institute Doctor of Technical Sciences L. B. Tsymbulov for providing advisory support.The authors would like to thank Yu. A. Savinova, Candidate of Technical Sciences, senior researcher at Gipronikel Institute, for her contribution to the research work.

Oxidizing Roasting of Sulphide Copper-Nickel Concentrate: Thermodynamic Simulation

The process of oxidizing roasting of sulphide concentrates in fluidized bed furnaces finds a wide application when it comes to the processing of sulphide copper, copper-nickel and pyrite concentrates. The roasted product is then smelted or hydrometallurgically processed. The literature describes results of various laboratory studies and the industrial practice of sulphide roasting. This paper focuses on the thermodynamic modelling of roasting process in application to copper-nickel concentrate. Thermodynamic modelling was done with the help of the FactSage software. Thus, the simulation for coppernickel concentrate was performed in the temperature range of 300–1,200 oC and at lgpO2 from –20 to –2. Areas are shown where possible products of roasting – i.e. sulphates, oxides, sulphides and non-ferrous metals – can exist. The simulation results show that sulphates of non-ferrous metals tend to form in the low temperature region, and the region of their existence tends to move towards higher temperatures as the oxidizing power of the gas phase rises. Oxide phases (including ferrites) were observed in the medium temperature region, while sulphide and metallic phases existed at the upper limit of the temperature range studied. The simulation results were compared with the data obtained after actual roasted products had been examined by means of scanning electron microscopy and X-ray microanalysis. It is obvious that roasting processes can be simulated based on the bulk thermodynamic equilibrium assumption. It is established that the FactSage algorithms and databases for oxidation process simulation deliver coherent results. Thus, they can be used for building control systems for industrial furnaces.The authors would like to thank L. Sh. Tsemekhman and L. B. Tsymbulov for their contribution to this paper.

Environmental performance of different end-of-life alternatives of wood fly ash by a consequential perspective

The increasing demand for bioenergy has intensified the pressure to utilise forest residues. Consequently, wood ash production has increased, which has prompted the need to find environmentally friendly alternatives for its end-of-life processes. However, studies assessing the environmental impacts of wood ash valorisation have assumed a static market while disregarding the potential environmental consequences and economic causalities of producing new products from wood ash. Therefore, this study assesses the outcomes of changing the conventional end-of-life of wood fly ash from its disposal in sanitary landfills to valorisation alternatives through its incorporation in construction materials (mortar and concrete) or soil amelioration. First, a consequential life cycle assessment was applied to identify the most environmentally sustainable choices for two types of wood fly ash (namely, those derived grate furnaces and fluidised bed furnaces). The characterisation factors used in this study are those that have been suggested for conducting a Product Environmental Footprint (PEF). The results show that mortar production is the best alternative for fly ashes generated in grate furnaces. Meanwhile, concrete and mortar production are the best alternatives for fly ashes generated in fluidised bed furnaces, concrete production has a slight advantage (smaller than 1%) over mortar production. Valorisation is less beneficial for soil amelioration than the incorporation in construction materials, and the impacts are higher than those of ash landfilling in some impact categories (human toxicity, freshwater eutrophication and ecotoxicity) due to the emission of trace elements into soil. A sensitivity analysis was carried out by changing the market trend of the conventional materials displaced from stable to strongly declining. This analysis showed that market trends could affect the net environmental performance of the investigated alternatives and modify their rankings.

Behaviour of SiO2 during a new process applied to nickel concentrate from matte separation at Kola MMC

Kola MMC has built a new nickel site that relies on chlorine leaching of nickel powder followed by electrowinning of nickel with insoluble anodes. After the new site had been commissioned, the operations of the refining facility saw changes, the electric anode furnaces were taken out of service, and a magnetic separation section was commissioned. The latter helps remove unreacted coal, metal oxides and other non-magnetic components from the tube kiln nickel powder thus ensuring its optimized quality. At the same time, once the electric furnaces had been removed from the process, it created the need for strict control over carbon and slag-forming constituent concentration in the nickel powder that goes to the chlorine leaching section. This paper looks at the history of the process behind the production of roasted nickel – the product of fluidized-bed furnaces – and describes the revamping stages witnessed by the Kola MMC site. The paper also analyzes certain features related to the current processing of nickel concentrates – from nickel matte separation to the production of nickel metal powder. The latter is further sent for chlorine leaching and in the presence of chlorine gas it gets dissolved. Then copper, iron, zinc and cobalt are removed from the resultant liquor and the purified sulphate-chloride solution goes in the electrolysis cells where high-purity nickel cathodes are produced. The authors analyzed the compositions of the key components in the studied materials of the nickel processing line. Special attention is given to the behaviour of silicon dioxide as one of the impurities causing most problems in the new process.

CFD modelling of coal gasification in a fluidized bed with the effects of calcination under different operating conditions

This paper investigates the thermochemical and physical conversion processes of coal gasification numerically with particular interest on calcination in a bubbling fluidized bed furnace. A comprehensive Eulerian-Eulerian three-dimensional model is developed for studying the gasification process. Three calcination cases are carried out under different operating conditions while one inert case is conducted to evaluate the effect of calcination. The presented numerical results aim at determining the mechanism of coal gasification in an air-steam environment with different flowrates. Evidence of particle segregation is found in the bed of coal and limestone due to density reduction and diameter shrinkage. Char conversion is investigated for different air-coal and steam-coal ratios, also the effect of bed temperature, fluid flowrate and fuel feeding rate on the carbon conversion is studied comprehensively. The highest char conversion rate is observed in the airflow rate of 17.0 kg/h where the bed temperature is found to be maximum. A noticeable impact of calcination is found in the gaseous emission while increasing CO2 concentration. Time averaged solid and gas temperature and species concentration profiles indicate the steady-state condition of numerical simulation.

CFD modeling of biomass combustion and gasification in fluidized bed reactors using a distribution kernel method

A three-dimensional reactive multi-phase particle-in-cell (MP-PIC) model is employed to investigate biomass combustion and gasification in fluidized bed furnaces. The MP-PIC model considered here is based on a coarse grain method (CGM) which clusters fuel and sand particles into parcels. CGM is computationally efficient, however, it can cause numerical instability if the clustered parcels are passing through small computational cells, resulting in over-loading of solid particles in the cells. To overcome this problem, in this study, a distribution kernel method (DKM) is proposed and implemented in an open-source CFD code, OpenFOAM. In DKM, a redistribution procedure is employed to spread the solid volume and source terms of the particles in the parcel to the domain in which the particles are clustered. The numerical stiffness problem caused by the CGM clustering can be remedied by this method. Validation of the model was performed using data from different lab-scale reactors. The model was shown to be able to capture the transient heat transfer process in a lab-scale bubbling fluidized bed reactor under varying fluidization velocities and loads of sand. Then, the model was used to study the combustion/gasification process in a bubbling fluidized bed reactor under varying ambient temperatures, equivalent air ratios, and steam-to-biomass ratios. The performance of DKM was shown to improve the accuracy and the robustness of the model.

Extraction of silver in processing of dust from the firing of nickel concentrate in fluidized bed furnaces

In 2018 in order to prevent the accumulation of lead in the products of the main technology of JSC Kola MMC the technology of hydrometallurgical processing of fine dust from the nickel concentrate roasting in fluidized bed furnaces was implemented. In the process of roasting, along with lead, silver is concentrated in the fine dusts of electrostatic precipitators. The distribution of silver on intermediate products of the technology is studied and recommendations are given to exclude irreversible losses of this element. It was found that when water leaching of dust, silver is not extracted into the solution, while the treatment of the aqueous leaching residue with sodium chloride solutions under conditions that provide high recovery of lead, results in recovery up to 32% of silver in chloride solution. It is shown that it is not possible to quantitatively concentrate silver in the chloride leaching residue. It is recommended to send the chloride leaching residue based on nickel (II) oxide, free of lead and containing refractory silver compounds, for pyrometallurgical processing in the process of the main technology. It was found that the production of lead cake by interaction of chloride solution with sulfate-containing reagents is accompanied by coprecipitation of silver present in it to form a product containing up to 9.4% (wt.) of this element. The efficiency of treatment of lead cake with sodium sulfite solution for extraction of more than 90% of silver is shown. By treatment of sulfite silver-containing solutions with sodium sulfide, a rich silver-containing concentrate is obtained. A schematic diagram of extraction of silver from lead cake with obtaining of silver-containing concentrate for production of additional products with high added value, as well as suitable for the sale of lead cake. The results of the research allowed to identify the main channels of silver losses during hydrometallurgical processing of dust from nickel concentrate roasting and to recommend ways to prevent them, which will generally increase the complexity of the use of nickel raw materials. The authors are grateful to the staff of FRC KST RAS (N. Yu. Neradovsky, V. Ya. Kuznetsov, I.V. Glukhovskaya, E.S. Kshumaneva) and JSC Kola MMC (I.A. Basova), who took part in conducting research and analytical support of work.

Investigation of factors affecting thermal performance in a coal - fired boiler and determination of thermal losses by energy balance method

In this study, a coal-fired industrial type boiler's performance and emission tests were performed using the energy balance method. During the experiments, the directives in the test standard (ASME PTC - 4) were followed. This tested boiler has a capacity of 75 t/h and is used in the mining industry. This boiler is a steam drum boiler equipped with an atmospheric circulating fluidized bed furnace. The furnace chamber with a rectangular cross-section has its width of 4250 mm and a depth of 4100 mm. In order to minimize the height of the furnace chamber and whole boiler, the middle wing walls are built-in the furnace chamber. As a result of the performance test, the boiler efficiency (indirect method) was found to be 93.07% (base on the lower heating value of fuel). According to the indirect method, the first three significant losses in total boiler losses were, respectively; the conversion of H2 in the fuel to water after combustion by 4.036%, the loss of dry flue gas by 3.231%, and the proportion of unburned carbon in residual products at the end of combustion with 1.653%. Due to the fluidized bed boiler's structural characteristics, it was also shown in the test results that emissions were suppressed in the combustion chamber, which was kept in the temperature range of 850–950 °C.

Bed-to-tube heat transfer characteristics with an immersed horizontal tube in the pressurized fluidized bed at high temperature

High-temperature and high-pressure conditions have great effects on the heat transfer characteristics of the immersed horizontal tube and understanding them will provide an industrial reference for the arrangement and optimization of heat exchanger in the pressurized fluidized bed furnace. In this study, the pressurized fluidized bed apparatus was developed to investigate the effects of factors such as pressure, temperature, particle size and gas velocity on the local and average heat transfer coefficients of the immersed horizontal tube. The experimental results showed the improved heat transfer at elevated pressure and high temperature. When the bed temperature increased from 400 °C to 800 °C, the proportion of the radiative heat transfer increased significantly, but it did not exceed 15%. The maximum heat transfer coefficients in the process of increasing the fluidization number were also measured in this study and fit well with the prediction results of the Shah model. The distribution of circumferential local heat transfer coefficients showed differences at low fluidization numbers and high fluidization numbers. The model proposed for the immersed horizontal tubes in the pressurized fluidized bed predicted the experimental data points from this study and other different sources well with the absolute average deviation of 11.86%.

Experimental measurements for Polish lignite combustion in a 1 MWth circulating fluidized bed during load changes

The conventional design of circulating fluidized beds mainly focuses on high process efficiency, while electricity markets increasingly target operating flexibility due to the increased penetration of renewable energy sources. In this work, the operational flexibility of the CFB furnace when applied to compensate for the feed-in fluctuations from renewable energies has been investigated experimentally. Employing a 1 MWth CFB test facility, Polish lignite was combusted over a wide range of transient operating conditions. The profiles of temperatures and pressures along the riser, the flue gas concentration and the temperature developments in the bed zone, and the outlet of the cyclone that identify the basis for operational flexibility and scale-up studies were shown. It was found that the circulating fluidized bed furnace can be operated with higher positive and negative load change rates up to ±25%/min, maintaining high combustion efficiency and low emissions. Furthermore, the temperature distribution along the riser was almost homogeneous at higher loads. By reducing the load, the temperature difference in the bed zone and after the cyclone was decreased and heterogeneous temperature distribution along the riser can be observed, resulting in a slight decrease in the combustion efficiency.

Preparation schemes of crushed coal for combustion in fluidized bed boilers using a gravity separator

The low concentration of nitrogen oxide during coal combustion in fluidized bed furnaces is due to the limited proportion of primary air in the combustion zone. The schemes applied for the preparation of crushed coal are mostly for the use of coal breakage screens with a fixed maximum particle size in the mixture. The primary air flow is limited to the conditions of the fluidization of the bed and can be reduced only by reducing the size of the particles fed into the furnace. With a constant particle size and lower boiler loads, the proportion of primary air and thus the concentration of nitrogen oxides in the flue gas increase. The use of separators to change the particle size has never been considered, since it is a priori assumed that the separators cannot provide the required disperse composition of crushed coal. To assess the possibility of using separators in the schemes of preparing crushed coal for combustion in a fluidized bed and to determine the necessary separation boundaries, variants calculations were carried out in respect to the coal preparation scheme for boiler No. 9 of the Novocherkasskaya hydro-power plant. It is shown that the disperse composition of the fine separation product in the gravity separator with overturning shelves along the 5 mm boundary is identical to the disperse composition of crushed coal obtained in the scheme with a screen and crusher. The dependence of the maximum particle size of crushed coal on the separation boundary of the separator is given. It is shown that in the scheme of preparation of crushed coal for combustion in a fluidized bed, replacement of screens with gravity separators will not lead to violation of the requirements for the dispersed composition of crushed coal. At the same time, the proposed replacement allows you to quickly change the maximum particle size of crushed coal during operational activity and thereby to maintain the optimal fraction of primary air when the boiler load changes.

Bagging based ensemble learning approaches for modeling the emission of PCDD/Fs from municipal solid waste incinerators

The conventional method for determining polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) emission concentrations from municipal solid waste incinerators (MSWIs) is accurate but complex, costly, and time-consuming. In this study, we utilized machine learning approaches to model International Toxic Equivalent Quality (I-TEQ) values of PCDD/Fs through chlorobenzene (CBz). Sampled data from a MSWI with a grate furnace and three MSWIs with fluidized bed furnaces were randomly divided into the training and test set. A two-step data preprocessing consists of Box-Cox transformation and standardization was applied to improve the model performances. The models including artificial neural network (ANN) and decision tree (DT). With the help of bagging, ANN and DT were stacked into bagging-based ensemble neural networks (BGNN) and random forest (RF) to improve the accuracy and robustness. BGNN was proved to be the best model with the relatively good perfomance in the test set. The Shapley additive explanation (SHAP) method was employed to improve the interpretability of BGNN. The results show that 1,2,3-trichlorobenzene (TrCBz), 1,4-dichlorobenzene (DiCBz), 1,2,4-TrCBz, and 1,3-DiCBz make positive contributions to I-TEQ values. Employing machine learning models, particularly BGNN, can be an effective method to determine the emission of PCDD/Fs within a wide range of I-TEQ values and in multiple MSWIs with strong generalization ability. It is helpful to realize the on-line measurement and controlling of PCDD/Fs emission.

SIMULATION OF CONTROL SYSTEM OF THE CHEMICAL-TECHNOLOGICAL PROCESSES

In this work is consider study and analysis of dynamic system for simulation of the technological process under uncertainty and complexity. To study and simulate a complicated technology process we carry out for consideration the technology of the process of roasting in fluidized bed furnaces of polymetallic sulphide ores. The choice is justified by the fact that, operation line producing of polymetallic sulphide ores represents a complex process, is characterized by a big number of transient processes, presence of process variables and deviations from technical regimes. To study process characteristics of any system functioning by means of mathematical methods the process should be formalized. This means, that adequate mathematical model needs to be developed. The choice of mathematical model depends a lot upon the features of the object and its controllability as well as of technological scheme and complexity of processes. Chemical engineering processes are complicated physical and chemical systems. Substance flows, which are part of these systems, are, as a rule, multicomponent. Therefore, for the purpose of study and qualitative control over chemical-engineering processes it is essential to apply the method of mathematic simulation, based on system analysis strategy, analysis of its structure, mathematical formulation development and evaluation of unknown parameters. Controllability means that such system attribute as having control actions, which make it possible to transfer the system from a pre-set initial state to the required condition during finite quantum of time. Therefore, the developed mathematical model of the process or control object should be controllable and stability.

Modern Technologies for the Thermal Treatment of Municipal Solid Waste, and Prospects for Their Implementation in Russia (Review)

The data on the state-of-the-art of the thermal processing of municipal solid waste (MSW) in the United States, China, Europe, and other countries are presented. The analysis of technologies for MSW incineration in layered furnaces using fire-grates and fluidized-bed furnaces, as well as using gasification and pyrolysis, is performed. It is shown that the best technology for the energy-producing MSW utilization consists in MSW incineration in layered furnaces with the use of mechanical shearing fire-grates. It is noted that, since all the enterprises for the energy-producing MSW utilization (in fact, these are TPPs, whose main fuel is municipal solid waste) are currently equipped with multistage gas purification facilities, the problems of their environmentally safe operation are completely solved. Therefore, research is mainly aimed at improving the energy efficiency of these enterprises, including through the integration of the units for MSW incineration into the thermal circuit of a TPP operating based on fossil fuel. Examples are given of foreign operating installations for the energy-producing MSW utilization with an electrical efficiency of 27–31% as well as those operating in a heating cycle with a high energy efficiency. The state-of-the-art of MSW thermal processing and the prospects for the implementation of modern technologies for the energy-producing MSW utilization in Russia are presented. Despite the fact that there is no sufficient experience in this field in Russia (only three plants have been constructed in Moscow, whose installed electric operating capacity does not exceed 12 MW), it is planned to construct four relatively large thermal power plants in Moscow oblast with an electric operating capacity of 70 MW each, in order to incinerate 700 000 t of solid waste per year. A TPP with the energy-producing utilization of 360 000 t of MSW per year with an installed electric operating capacity of 24 MW is the most promising for Russia. Such a TPP could already be in demand in more than two dozen large Russian cities.

MATHEMATICAL SIMULATION AND STUDY OF CONTROL STABILITY OF THE CHEMICAL-ENGINEERING PROCESSES IN INDUSTRY

In this work is consider study and analysis of dynamic system for simulation of the technological process under uncertainty and complexity. To study and simulate a complicated technology process we carry out for consideration the technology of the process of roasting in fluidized bed furnaces of polymetallic sulphide ores. The choice is justified by the fact that, operation line producing of polymetallic sulphide ores represents a complex process, is characterized by a big number of transient processes, presence of process variables and deviations from technical regimes. To study process characteristics of any system functioning by means of mathematical methods the process should be formalized. This means, that adequate mathematical model needs to be developed. The choice of mathematical model depends a lot upon the features of the object and its controllability as well as of technological scheme and complexity of processes. Chemical engineering processes are complicated physical and chemical systems. Substance flows, which are part of these systems, are, as a rule, multicomponent. Therefore, for the purpose of study and qualitative control over chemical-engineering processes it is essential to apply the method of mathematic simulation, based on system analysis strategy, analysis of its structure, mathematical formulation development and evaluation of unknown parameters. Controllability means that such system attribute as having control actions, which make it possible to transfer the system from a pre-set initial state to the required condition during finite quantum of time. Therefore, the developed mathematical model of the process or control object should be controllable and stability.

CLEARANCE OF SOLID HOUSEHOLD WASTE WITH THE RECEPTION OF ALTERNATIVE TYPES OF ENERGY CARRIERS

The research is devoted to improving the technology of obtaining alternative types of energy carriers by applying methods of pyrolysis of unclaimed types of solid domestic wastes of biological origin, which also allow solving the tasks of improving the ecological situation in the places of formation. The practical value and relevance of this research lies in the development of advanced technology for obtaining alternative fuels. The proposed pyrolysis unit allows producing gaseous and liquid hydrocarbons in a continuous cycle. In the atmosphere of the gasifying agent (air, oxygen, water vapor, carbon dioxide or their mixture), the gasification process is primarily performed in vortex reactors or fluidized bed furnaces at temperatures of 600-1100°C. Accordingly, the production (extraction) of AT from them requires pre-treatment, often quite serious: separation, grinding, mixing, drying, etc., which ultimately guarantees the consistency of its composition and quality.

Energy recovery of solid waste disposal in Russia, State of the Art and operation experience

For Russia, there is no alternative way of a civilized solution to the problem of municipal solid wastes (MSW): through combustion (energy utilization) to complex processing. The government of the Russian Federation in 2017 adopted some decisions aimed at thermal processing of MSW. The order defines the construction of renewable energy facilities on the basis of MSW with a total electric capacity of 280 MW in Moscow region and one object with an electric capacity of 55 MW in the Republic of Tatarstan. In Russia, only three plants where the energy potential of MSW is converted into electricity were built. The results of the operation experience of fluidized bed furnaces for MSW incineration at Rudnevo plant in Russia are done. The main problems were connected with ash properties, deposit formation, and corrosion of superheater tubes. Also, the data of mathematical modeling of dynamic behavior near gas burners, chemical composition and material balance of solids, and the influence of secondary air injection on NOx formation are given. A special test rig was designed for the investigation of the corrosion mechanism. Also, the main corrosion factors (temperature of the tube surface, rates of O2, HCl, SO2, and H2O in flue gas, contains chloride and alkali metals in deposits) were found during the tests. Experience of energy recovery from waste incineration of pulp and paper mill plants is presented. Considerable attention is paid to improving the efficiency of waste incineration and bed particle agglomeration. Special experiments were carried out to optimize the bed drain flow rate. The influence of secondary air supply improvement on mixing with the main flow and boiler efficiency is given. Semi-empirical three-zone method of engineering heat calculations for fluidized bed furnaces of biomass boilers was proposed to predict both the value of outlet furnace temperature and the value of fluidized bed temperature. The method based on empirical values and relationships of the share of heat release in fluidized bed zone.

234U, 238U, 226Ra, 228Ra and 40K concentrations in feed coal and its combustion products during technological processes in the Upper Silesian Industrial Region, Poland

Hard coal is the predominant energy source in Poland. The unavoidable consequence of coal combustion is the production of huge amounts of ash which can be concentrated in radionuclides. The ashes from coal combustion are utilized or stored and may affect the quality of the environment. Therefore, the estimation of radionuclides in hard coal and by-products is of crucial importance. The analyzed samples included ashes produced in ash furnaces, power plants and individual home furnaces operating in the Upper Silesian Industrial Region, Southern Poland, during the hard coal burning. This paper presents radioactivity concentrations of 228Ra, 226Ra and 40K in hard coal, bottom and fly ash samples from Polish coal-fired power plants obtained during various technological coal combustion processes and generated in individual domestic furnaces, determined using the HPGe gamma spectrometry technique. The measurements of 234,238U concentrations were performed after sample preparation using alpha-particle spectrometer. The concentrations of the obtained radionuclides differ greatly in the fly and bottom ash samples. The lowest concentrations of 226Ra, 228Ra, 234U, 238U were observed in bottom ashes from the co-firing of hard coal and biomass in a fluidized-bed furnace, whereas the highest concentrations of 226Ra (163 ± 6 Bq/kg), 228Ra (100 ± 2 Bq/kg) isotopes were found in the ashes from individual household furnaces. This means that both the feed coal type and combustion techniques have a direct impact on the concentration of radionuclides in ash. Hard coal silt samples may be enriched in radionuclides and the radioactive equilibrium between 226Ra and 238U even in the case of coal is not always achieved. The concentrations of the analyzed isotopes in ashes are 5-7-fold higher than in feed coal. Given that combustion by-products are utilized as construction products, it should be noted that for some ash samples, the radiological hazard indices approach or exceed the maximum permitted levels.

Dynamic process simulation for Polish lignite combustion in a 1 MWth circulating fluidized bed during load changes

In this study, a sophisticated dynamic process model of a circulating fluidized bed furnace has been developed. The model describes the 1 MWth test facility, erected at the Technical University of Darmstadt, with a high level of detail including the air supply, the circulating fluidized bed, the flue gas path, the water-cooling system, and the control structures. The developed model was tuned using the experimental data at 82% load. After that, the load is decreased to 63% and the obtained numerical results were compared with the measurement data. Then, the dynamic load increases from 63% to 88% to 100%, followed by dynamic load decreases from 100% to 89% to 68% were simulated. During the load change, the pressure and temperature profiles along the riser were compared with measurement data, showing good agreement. Furthermore, the flue gas concentrations at the outlet of the cyclone agree very well with the values of the test facility. Using the validated model, the transient behaviour of the process variables (pressure, temperature, composition, and mass flow rates) of solids and gas flows during the combustion can be determined. Furthermore, the solid circulating, the inertia, and a variety of parameters that cannot be fully measured in the test facility were numerically obtained.

Co-firing of Rice Straw and Natural Gas in Fluidized Bed Furnace (Dept. M)

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