Coal Combustion Boiler Research Articles

Recovered Fly Ashes as an Anthropogenic Raw Material

Poland is a country where the commercial power industry mainly uses coal to produce energy. As a result of energy production processes, by-products of combustion are generated, primarily fly ashes. In Poland, these are mostly obtained from conventional coal combustion boilers. Fly ashes from coal combustion account for 1.2% of all industrial waste generated in Poland. In addition, fly ashes are produced by fluidized-bed boilers. These are classified as a mixture of fly ashes and solid calcium-based reaction waste from flue-gas desulphurization, and constitute almost 2% of Polish industrial waste. This paper describes the amounts of fly ashes generated in Poland and considers activities related to their recovery and disposal. The high recovery levels of fly ashes (about 90%) and fluidized ashes (about 98%) mean that these waste products can also be considered anthropogenic raw materials. The use of these materials in the cement industry is an example of industrial symbiosis. Such usage benefits not only the economy but also the environment and, therefore, society as a whole. To describe the use of recovered fly ashes in cement plants, the authors use the anthropogenicity index, which characterizes the level of technological advancement and the substitutability of primary raw materials for secondary raw materials.

Simulation of Pulverized Coal Combustion Process Considering Turbulence-Radiation Interaction.

In this paper, the combustion process of a 350 MW opposite pulverized coal combustion boiler is studied using a combined field test and numerical simulation. Considering the turbulence-radiation interaction (TRI) effect caused by turbulent particle pulsation during the combustion process, the TRI model is modified by introducing optical factors. The interaction between the optical thickness and the radiation pulsation of pulverized coal particles during the combustion process is studied to learn the influences of turbulent particle combustion on radiative heat transfer. According to the analysis of the TRI influence on pulverized coal combustion, the temperature of the cross section decreases with TRI. Compared with the traditional radiation model calculation, the time-average temperature of the cross section is reduced by 49.85 K, and the deviation from the experimental data is reduced by 1.54%. It is proved that the temperature distribution in the furnace considering TRI is closer to reality. In the numerical simulation of the TRI sensitivity to the optical thickness of the particles, it is found that with TRI, the increase of optical thickness will strengthen the effect of turbulent kinetic energy in the combustion area. Due to the increase in particle density, the content of the main radiation medium produced by combustion, H2O and CO2, increases and the radiation effect in the furnace is enhanced. In the fire area with dense particles, the average temperature of the cross section increases by 28 K. Hence, the change in optical thickness causes the change of TRI parameters, and the TRI effect becomes more significant with the increase of particle load.

Emission of nanoparticles from coal and diesel fired power plants on Svalbard: An electron microscopy study

Sub-micrometer aerosol particles were collected at the stack of two coal power plants (Barentsburg, Longyearbyen), two diesel power plants (Pyramiden, Sveagruva) and one small-scale coal-burning boiler (Pyramiden) on the Arctic archipelago of Svalbard (Norway). Primary particles (n = 5752) in the size range of 100–1000 nm were investigated by operator-controlled high-resolution scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). Based on morphology and chemical composition primary particles were assigned to one of the following groups: soot, carbonaceous, fly ash spheres, Hg-containing particles, and mineral particles. Soot is the dominating particle group in most samples with a relative number abundance between 69 and 98%. Two coal burning samples have significantly lower soot contents of about 12 and 31%. The relative number abundance of the other particle groups is highly variable.The chemical composition of soot, fly ash spheres and mineral particles was studied in more detail. Soot particles from coal burning are significantly enriched in the elements S, Na, and K compared to diesel soot. The P contents of soot, fly ash spheres, and mineral particles reflect the variable concentration of this element in the different coal seams. Fly ash spheres from coal burning consist of a Si-rich component (quartz or silica glass), alumosilicates or alumosilicate glass, Fe oxides and a Fe, Ca, Al component (most likely a mechanical mixture of spinel and gypsum or lime). Fly ash spheres from diesel burning have a similar composition except that the Fe, Ca, Al component does not occur. Mineral particles from coal burning may be divided into Si-rich (quartz or silica glass), Pb-rich, Fe oxides, alumosilicates or alumosilicate glass and Na-rich particles (most likely a mechanical mixture of Si-rich particles with aged sea salt). The relative number abundance of these subgroups of mineral particles is highly variable. Mineral particles are rare in diesel burning, and seem to be mostly Fe oxides.The observed differences in minor element contents can be used in source apportionment studies for discrimination of individual soot particles as well as fly ash spheres from coal and diesel burning. The highly variable abundance of soot and of mineral particles (especially those consisting predominantly of toxic metals as for example Pb) should be taken into account in exposure assessment.

The influence and optimization of air distribution method on the boiler burns high-sulfur coal

A large amount of H2S will be generated during the operation of power plants mixed combustion with high-sulfur coal, causing high-temperature corrosion of the boiler water-cooled wa ll. In order to prevent it from pipes bursting due to high temperature corrosion during the operation of the unit, Air distribution was adjusted on a 350MW subcritical pulverized coal combustion boiler, especially for the opening of the secondary a ir valves of each layer of the burner, so as to reduce the volume fraction of H2S in the furnace and lower the corrosion of the water-cooled wall. The research results show that by adjusting the a ir distribution, the volume fraction of CO and O2 in the flue gas of the furnace is changed, and at the same time, it also has an influences on the change of the flue ga s temperature in the furnace, a nd effectively inhibits the generation of H2S, a lleviating the high temperature corrosion of water wall.

Effect of biomass co‐firing position on combustion and NOX emission in a 300‐MWe coal‐fired tangential boiler

AbstractCo‐firing biomass in an existing coal combustion boiler is a promising way to mitigate carbon emission in the context of global carbon neutrality. This paper investigated the effect of biomass injection location on combustion and NOX formation characteristics in a 300‐MWe tangential boiler co‐firing with coal. Numerical models have been validated against experimental measurement for both pure coal firing and biomass/coal co‐firing cases. Compared to pure coal firing, co‐firing case with biomass injected into the highest layer can sustain a comparable temperature distribution profile along the furnace height, and generate a lower NO emission by around 20 ppm. By moving the biomass injection location downward, the temperature difference between co‐firing and pure coal firing cases becomes larger, and the final NO emission increases continually from 222 to 240 ppm. When biomass is injected through the lowest layer, N element in biomass volatile is oxidized to NO directly because of the abundant oxygen; thus, NO emission turns to be the highest among all co‐firing cases. Contrarily, when biomass is injected through the highest layer, the majority of N in biomass volatile is released as NH3, and it further acts as a reduction agent for NO, thus leading to the lowest NO emission.

Numerical optimization of separated overfire air distribution for air staged combustion in a 1000 MW coal-fired boiler considering the corrosion hazard to water walls

Multigroup separated overfire air (SOFA) has been widely applied in large-scale coal-fired boilers for air staged combustion to reduce NOX emissions. However, unreasonable flow distribution in multigroup SOFA nozzles would cause boiler performance degradation, including decreased coal burnout rate, severe gas temperature inhomogeneity, and risks of high-temperature corrosion. In this study, six SOFA distribution modes including the reference case based on the field test were numerically investigated for operation optimization of a 1000 MW double-tangential circular coal-fired boiler. The combustion characteristics including flow field, temperature distribution, residual char particles, and gas species were comprehensively analyzed. Meanwhile, particular attention was paid to the reducing atmosphere near water walls of the upper furnace for ameliorating the problem of high-temperature corrosion. The numerical results show that SOFA distribution significantly determines the gas flow field in the burnout zone, which subsequently influences coal combustion behavior and boiler performance. The pagoda mode is suggested to be optimum for sufficient penetration of SOFA in the upper furnace, which features gradually decreasing air induced from SOFA nozzles along with the furnace height. Compared with the baseline scenario, the burnout rate is increased by about 0.2% due to the enhanced mixing of SOFA and combustibles, and the NOX emission is slightly decreased by about 8 mg/Nm3 in the pagoda mode. Besides, better temperature homogeneity is obtained at the furnace exit, which helps improve the heat transfer performance of downstream heat exchangers. Moreover, the reducing atmosphere near the water walls of the upper furnace is significantly weakened in this mode, contributing to the alleviation of the corrosion hazard to water walls.

Повышение экологичности и эффективности городской системы теплоснабжения с использованием водоугольного топлива

Coal-water slurry fuel is coming into use in heat generation facilities as an alternative to natural gas and heavy oil. The main advantage of coal slurry is its cost efficiency. Our project is devoted to improvement of heat generation using coal-water slurry fuel instead of investing in new construction of coal-burning boiler houses. As an example, we considered implementing this project in the city of Leninsk-Kuznetsky, Russia. The project implies partial burning of coal slurry along with conventional coal burning. This solution is cost efficient and environmentally friendly yet not requiring major heat generation equipment replacement or renovation. The total cost efficiency of the suggested project is estimated at least as 1.1 billion rubles per year.

Desulfurization Characteristics of Fuel-Born Alkali and Alkali Earth Metal Compounds in Coal Ashes from Lab-Scale Experiment to Real-Scale Monitoring of CFBC and PC Boiler.

Previous research findings and experiential accounts have provided evidence that specific components of coal ash play a catalytic role in the dry desulfurization of flue gas such that their contributions need to be considered for determining the optimal amount of desulfurizing agent such as limestone. The purpose of this study was to quantify the desulfurization characteristics of coal ash in a 500 MW pulverized coal combustion (PC) boiler as well as a 1000 MW circulating fluidized bed combustion (CFBC) boiler. In parallel with a year-long data collection of coal blends and emission characteristics, a series of temperature-controlled fixed bed (lab scale) experiments were conducted for 11 individual (but representative) coal samples. The results indicated that desulfurization by fly ashes appeared to proceed roughly in proportion to the total alkali (TA) contents of the ash, which were consistent with our preliminary test result of the CFBC boiler. In the PC boiler, however, the desulfurization reaction seemed to be very kinetically limited, apparently deactivating the TA components. We developed a practical equation for a priori prediction of SO2 concentration based on the sulfur content of coal blends.

Development of Low NO<sub>x</sub> Burner for Coal Combustion Boiler during Low Load Operation

Development of Low NO<sub>x</sub> Burner for Coal Combustion Boiler during Low Load Operation

A Comprehensive Three-Dimensional Analysis of a Large-Scale Multi-Fuel CFB Boiler Burning Coal and Syngas. Part 1. The CFD Model of a Large-Scale Multi-Fuel CFB Combustion.

The paper is focused on the idea of multi-fuel combustion in a large-scale circulating fluidized bed (CFB) boiler. The article discusses the concept of simultaneous coal and syngas combustion. A comprehensive three-dimensional computational fluid dynamics (CFD) model is developed, which allows us to describe complex phenomena that occur in the combustion chamber of the CFB boiler burning coal and syngas produced from coal sludge.

A Comprehensive, Three-Dimensional Analysis of a Large-Scale, Multi-Fuel, CFB Boiler Burning Coal and Syngas. Part 2. Numerical Simulations of Coal and Syngas Co-Combustion.

This paper presents the results of numerical computations for a large-scale OFz-425 CFB (circulating fluidized bed) boiler utilizing coal and syngas. Four different operating scenarios are considered, including the reference variant, corresponding to the conventional, mono-combustion of bituminous coal, and three tests involving replacement of secondary air and part of the coal stream with syngas fed by start-up burners. Pressure, gas velocity, temperature, and carbon dioxide distribution in the combustion chamber are discussed in the paper. The results indicate that the syngas supply leads to an increase in local temperature and carbon dioxide concentrations. The proposed concept is not advisable as it may lead to frequent emergency stops of the CFB boiler.

The Relationship between Unburned Carbon Levels in Coal Combustion Ash and Volatile Matter Content in Coal

ABSTRACT In this study, considering a specific coal fired power plant, fly ash samples were analyzed in terms of unburned carbon (UBC) and amount of UBC in these samples were compared to coal volatile matter content. UBC which can be used as an expression to tell efficiency of power plants is basically reasoned by either coal properties or by the conditions of combustion environment in boiler. Coal combustion boilers are utilized in terms of their design conditions and they are really hard to utilize them out of these ranged conditions. That is why in order to investigate the effect of these abovementioned parameters, either laboratory scale or pilot scale combustion tests should be conducted. Briefly in this study, a period of same conditions of same boiler utilization of different types of coals considered, and different amounts of UBC in fly ashes were correlated with high or low amount of volatile matter content in coal. Obtained correlation between coal volatile matter and UBC in ash showed that volatile matter content of coal is dominantly affecting the coal burnout.

Kinetic Study of Long-Term T23 Tube Corrosion upon Low-Rank Coal Ash Deposition under Oxy-Fuel Combustion Conditions

The aim of this study was to understand the kinetics of high-temperature tube corrosion and its rate-limiting step in oxy-fuel combustion mode. Four different types of ash deposits collected from low-rank coal combustion boilers were tested, with varying contents of sulfur and metallic species. A typical stainless steel, low chromium ferritic alloy, T23, was tested at a metal surface temperature of 650 °C for up to 200 h. Compared with air-fired flue gas which is lean in SO2 and steam, the aggressive flue gases formed under oxy-firing conditions enhanced T23 tube corrosion but to a marginal extent in a comparison with the S-rich ash deposit. The study found a positive correlation between the sulfur content within ash deposit and the thickness of the tube oxide layer. The sulfate in the ash deposit promoted the formation of molten and mobile sulfate complex and sulfides. The former species are predominant on the tube’s outer surface, while sulfides are preferentially formed inside the oxide layer where oxy...

Review of the investigations of pulverized coal combustion processes in large power plants in laboratory for thermal engineering and energy: Part A

The paper presents an overview of the results of the investigations of the processes that take place in pulverized coal combustion boilers and power plants which, in a longer period of time, were realized in the Laboratory for Thermal Engineering and Energy of the "Vinca" Institute of Nuclear Sciences. The presented results were published in numerous studies realized for different users, Ph. D., M. Sc., and specialist thesis, in international and domestic scientific journals and monographs, presented at numerous international and domestic scientific meetings, etc. The main goal of the paper is to chronologically present the results of domestic research that at one time were at an enviable international level, with concrete practical applications for domestic users. This is especially important to contrast the present situation when domestic research in this area is scarce and when the energy sector relies practically only on imported technologies and foreign consultancy. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III42011, Grant no. III42010, Grant no. TR33018 and Grant no. TR33042] <br><br><font color="red"><b> This article has been corrected. Link to the correction <u><a href="http://dx.doi.org/10.2298/TSCI200127032E">10.2298/TSCI200127032E</a><u></b></font>

Feasible electricity price calculation and environmental benefits analysis of the regional nighttime wind power utilization in electric heating in Beijing

Facing the aggravation of air pollution and serious wind curtailment in North China, a new way to utilize excess wind power is presented, which is to use the excess nighttime wind from the surrounding areas to provide electric heating in Beijing at night. First, the mechanism of the nighttime electric heating price calculation and its environmental benefits are explained from both the supply side and the demand side. Second, considering the economic and environmental characteristics of electric heating, the electricity price-ceiling calculation model on the demand side, the electricity price-floor calculation model on the supply side, and the environmental benefit-analysis model are formed. Finally, the models are tested by practical data from Beijing, showing that the proposed models are scientific and practicable. The study shows several conclusions. (1) When no subsidy policy is carried out, the regenerative electric heater and the air-sourced heat pump are not economically justified to replace the rural-household coal-fired boiler and coal-burning boiler and the public coal-fired boiler. (2) With the existing subsidy policy, the regenerative electric heater is economically justified to replace the rural-household coal-fired boiler, self-owned coal-burning boiler, and public coal-fired boiler, and the air-sourced heat pump can be the substituted for the rural-household coal-fired boiler. Under different wind–thermal-power ratios, the feasible intervals for the electricity price are respectively [47.12, 48.62], [44.31, 48.62], and [41.51, 48.62]. (3) Compared with the traditional coal-fired heating, wind-sourced electric heating contributes fewer pollutant emissions and more environmental benefits.

Effects of momentum ratio and velocity difference on combustion performance in lignite-fired pulverized boiler

To study the effects of momentum ratio and velocity difference between primary and secondary air flow on boiler performance, simulation work was conducted on a lignite-fired boiler within a three dimension computational fluid dynamics model. Within the model, 8 cases were simulated where momentum ratio and velocity difference vary among cases. The distributions of combustion temperature, radiative heat flux, gas species concentration and residual particles’ concentration were analyzed. Results show that momentum ratio of primary and secondary air flow significantly determines coal combustion behavior and boiler performance, and a reasonably small momentum ratio is beneficial for boiler performance. The velocity difference between primary and secondary air also affects coal combustion performance, and a relatively large velocity difference is favorable in boiler operation. These findings reveal the effects of momentum ratio and velocity difference on boiler performance, and can be helpful in guiding the actual operation of lignite-fired boiler to avoid the unfavorable boiler performance degradation.

Optimizing in-situ char gasification kinetics in reduction zone of pulverized coal air-staged combustion

Reliable kinetics of char gasification are of great importance for accurate prediction of the reductive atmosphere in air-staged combustion of pulverized coal, which is critical in controlling nitrogen and sulfur species for the optimized design and operation of boilers and burners. In this study, a new method of obtaining char gasification kinetics from realistic air-staged combustion experiments is proposed. Firstly, a real combustion atmosphere, including the temperature and concentration fields of air-staged combustion in an actual boiler, is simulated in an electric-heated down-firing furnace by controlling the stoichiometric ratio of air to coal. In-situ char gasification is observed by obtaining gas and solid reaction data from staged combustions with stoichiometric ratios in the range of 0.6–0.9 at temperatures of 1200–1400 °C. Secondly, a detailed char combustion/gasification model with emphasis on coupling between the discrete phase and gas phase is developed and verified. The single film model based on nth order Arrhenius-type equations is used in the char combustion/gasification model, with consideration of particle boundary layer diffusion. The effect of reduced reactivity of the char at high degrees of conversion is included in the kinetic model. Thirdly, the in-situ char gasification kinetics are determined via a CFD-aided rigorous mathematical optimization process. A direct search algorithm is used to accelerate the optimization process. Finally, the determined kinetics are verified at wide ranges of temperatures, residence times, and stoichiometric ratios. Compared with char gasification kinetics from ex-situ char gasification experiment using the same coal, it is demonstrated that the kinetics of in-situ char gasification are very different from kinetics derived from ex-situ char gasification experiment. Therefore, reliable kinetics of in-situ gasification are necessary when predicting the fuel conversion and gas phase species in modern air-staged pulverized coal combustion boilers.

New-Generation Aluminum Composite with Bottom Ash Industrial Waste

Industrial waste bottom ash (BA) from a pulverized coal combustion boiler containing hard wear-resistant particles was utilized in this study to form an aluminum composite through a liquid metallurgy route. Composites comprising 5 wt.% and 10 wt.% bottom ash were characterized for their physiochemical, microstructural, mechanical, as well as tribological properties, along with pure aluminum. Scanning electron microscopy (SEM) microstructure revealed uniform distribution of BA particles throughout the matrix of the composite, whereas x-ray diffraction (XRD) analysis confirmed presence of aluminosilicate phase. Addition of 10 wt.% BA improved the Brinell hardness number (BHN) from 13 to 19 and ultimate tensile strength (UTS) from 71 MPa to 87 MPa, whereas ductility was adversely reduced after 5% BA addition. Incorporation of BA particles resulted in reduced dry sliding wear rates examined up to 80 N load compared with aluminum. Hence, such composites having lower cost could be applied as significantly hard, wear-resistant materials in applications in the automotive industry.

Laboratory study of H2SO4/H2O nucleation using a new technique – a laminar co-flow tube

Nucleation of aerosol particles from gaseous precursors is an important stage in the formation of atmospheric secondary aerosols or in industrial applications, particularly coal burning boilers. We introduce a novel laboratory device for studying binary or ternary nucleation – a laminar co-flow tube (LCFT) – and provide first data for the H2SO4/H2O system, showing that LCFT is able to cover a wide range of nucleation rates. The experimental set-up and the underlying transport processes are explained. Advantages of LCFT over methods employing turbulent mixing are suppression of wall losses and an accurate mathematical model. The determined nucleation rates are by about two orders of magnitude lower than typical literature values. Results of various nucleation experiments often show systematic differences unexplained by the present level of knowledge. Introduction of the LCFT technique based on a well-defined laminar diffusion process may help to identify the method-related biases.

Микроэлементный состав снежного покрова в окрестностях угольных и газовых котельных как показатель экологичности используемого топлива

Emissions of rural villages’ boiler houses remain insufficiently studied in comparison with emissions of big urban heat power engineering objects. In this paper have been presented the results of comparative analysis for a dust pollution level and trace element composition of solid particles in vicinity of rural villages’ boiler houses distinguishing by technological parameters and the fuel’s type (coal or gas) based on the snow cover’s trace element composition study. It has been established that the dust load value relating to background in vicinity of different coal-burning boiler houses is varying and depends on fuel consumption volumes, availability of dust and gas trapping system, coal depository and vehicle park. The dust load value does not exceeded background in vicinity of gas- burning boiler houses no matter of their technological parameters. It has been demonstrated that the trace elements accumulation level in the samples from vicinity of coal-burning and gas-burning boiler houses depends on type, composition and flow rates of fuel, as well as from the fly ash composition and local emissions sources. Have been marked general tracer elements (Hg, Zn, Ni, Mo, Co, Ba, Sr) and specific ones (Cd, As, Sb, Pb, V) of man-made impact for different coal-burning boiler houses. Hg, As, Cd have been proposed as general tracer elements of man-made impact for coal-burning boiler houses. It has been stated that natural gas is the most environmental friendliness fuel in comparison with coal regardless of boiler house’s technological parameters.