Combustion Of Pulverized Coal Research Articles

Oxy-fuel combustion of pulverized coal in an industrial boiler with a tangentially fired furnace

Numerical studies of the processes of oxy-fuel combustion of pulverized coal (PC) in an industrial boiler BKZ 500–140–1 (with a capacity of about 400 MW) were carried out in this work. The proposed comprehensive mathematical model was tested based on data from a full-scale experiment (2.4 MW laboratory stand) of oxy-fuel combustion of PC. The conducted comparison has shown a good agreement of the calculation results with the experimental data. A detailed comparative analysis of the effect of the operating modes of the BKZ 500–140–1 industrial boiler during oxy-fuel combustion of coal on physical and chemical processes and the level of harmful emissions (NOx, CO2) was performed for the first time. The effect of oxygen concentration and CO2/H2O ratio in the blast on the processes of ignition and combustion of fuel in a nitrogen-free environment has been studied. It is shown that when nitrogen in the blast composition is replaced with flue gases without changing the oxygen concentration in the boiler under study, the average temperature in the furnace volume declines, as well as the average heat flux at the walls decreases from 87.35 to 70.32 kW/m2. To achieve the standard operating parameters of the BKZ 500–140–1 industrial boiler, it is necessary to increase the oxygen concentration in the blast from 15.4 to 19.7 vol.% (i.e. by 28%). The implementation of the oxy-fuel combustion technology on a steam boiler leads to a decrease in the NOx concentration in flue gases from 480 to 273 mg/m3.

Numerical modelling of heat transfer processes in coal-fired vortex furnace with bottom-port secondary blowing: ecological performance comparison for two types of coal fuel

The work is devoted to numerical 3D modelling of aerodynamics and pulverized-coal combustion processes in a novel vortex furnace of a boiler unit for thermal power stations. A prospective retrofitting design of this furnace, featuring additional tangential blowing at the bottom part of the vortex combustion chamber, has been studied. The firing regimes using two types of siberian coal (black coal, brown coal) are considered. Numerical results for the studied combustion regimes in the modified vortex furnace are presented, including the fields of velocity, temperature, species and dispersed phase concentrations, and the comparative analysis of NOx emissions for two types of coal.

Thermal reactivity and flowability of pulverized coal blending with iron-bearing dust injection in blast furnace process

Pulverized coal (PC) blending with iron-bearing dust (IBD) injection technology in blast furnace (BF) iron-making process was proposed to valorize the IBD. Three aspects containing the co-flow property of PC and IBD, thermal reactivity and corresponding kinetics during the PC combustion process, as well as thermal variation and unburned PC distribution in BF were the main focuses of the present work. It has found that the Carr-flowability indexes of PC and IBD appear little difference. Their blends can be smoothly transported when adding portion of the IBD is less than 6%. In addition, comprehensive combustibility index (S), ignition index (Ci), and burnout index (Db) of the PC are improved when the mass fraction of the IBD enhances from 0% to 3%, and 6%, which proves that blending with the IBD can accelerate the PC combustion process. Moreover, the combustion activation energy (E) decreases after adding the IBD, which supports the improved thermal reactivity. Also, the accumulation of unburned PC in BF presents a decline tendency, which may promote the permeability of BF and help enhancing the pulverized coal injection dosage.

Pulverized coal combustion computational modeling approach: A review

CFD (Computational fluid dynamics) is a tool, through which, the entire combustion process for pulverized coal combustion (PCC) can be predicted. The solid fuel combustion modeling is not as simple as gaseous or liquid fuel combustion modeling. In the solid fuel combustion process, various physical transformations and chemical reactions occur simultaneously. Therefore in the computational modeling approach for PCC, basic physical and chemical processes such as; turbulence, radiation, devolatilization, gas-phase combustion, char reaction and soot formation/reduction are integrated to obtain the desired results. However, in order to reach the desired accuracy, different computational models should be chosen carefully. In this review, various common models that are widely used in PCC simulation are discussed scientifically along with their modeling aspects. The basic advantages and disadvantages of these models are also discussed in this study. Moreover, different models preferred by various authors for pulverized coal combustion simulation process are also summarized. From the review, it has been observed that the eddy viscosity based two-equation turbulent models and Eulerian-Lagrangian multiphase approach are mostly preferred due to better computational economy. Two competing rate devolatilization model from various finite rate models and FG-DVC devolatilization model from various phenomenological models are mostly used for PCC. Diffusion kinetic control and Intrinsic char combustion models are mostly chosen to predict the char reaction. Finite reaction rate models are preferred when the computational economy is a concern, whereas phenomenological models provide results with better accuracy because in phenomenological models realistic inputs are given as input for simulation whereas, in finite rate models, finite rate constants are mostly empirical. Most of the gas phase models are given almost equal importance. Discrete ordinate (DO) is mostly used for PCC due to its ability of volumetric radiation calculation and the ability to evaluate radiation effect on the particle phase.

Flame characterisation of gas-assisted pulverised coal combustion using FPV-LES

A multiphase flamelet/progress variable (FPV) model for the large eddy simulation (LES) of gas-assisted pulverised coal combustion (PCC) is developed. The target of the simulation is the Darmstadt turbulent gas-assisted swirling solid fuel combustion chamber. The coal particles are treated as Lagrangian point particles, the position, momentum and energy of which are tracked. The gas phase is described by the low-Mach Navier-Stokes equations alongside the Eulerian transport equations of the governing variables for the FPV model. The set of chemical states of the PCC flame is pre-tabulated in a six-dimensional flamelet table and determined by the mixing of the primary fuel stream, volatiles and char off-gases with the oxidising air, the progress of chemical reactions, the interphase heat transfer, as well as sub-grid scale variations. A presumed β-PDF approach for the total mixture fraction is applied to capture sub-grid scale effects. The discrete ordinate method (DOM) with the weighted sum of grey gases model (WSGGM) is employed to model radiation. The FPV-LES results are validated against the experimental evidence and a good agreement of the predicted mean and RMS velocities, as well as the mean gas temperature between experiments and simulations is obtained. The contributions of the pilot, volatile and char off-gas fuel streams to the coal flame are analysed. It is found that most regions of the furnace are dominated by either pilot or volatile combustion, while char conversion only occurs in the far downstream and outer furnace regions. The pilot gas dominates the near-wall region inside the quarl, whereas the volatile gas mainly released from small particles dominates a first volatile combustion zone in the interior of the internal recirculation zone. Larger particles heat up more slowly and release their volatile content further downstream, leading to a secondary volatile combustion zone.

Prediction of Pulverized Coal Combustibility by Measuring Chemi-luminescence of Radical Species around Tuyere

To develop novel technologies for reducing CO2 emission from ironmaking process, steelmaking companies in Japan are engaging in the national project called COURSE50. In this project, a large amount of H2 is co-injected into blast furnace (BF) with pulverized coal (PC). In order to clarify how the co-injection affects PC combustibility, PC combustibility should be measured in COURSE50 BF. However, it was difficult to measure PC combustibility in BF without bothering operation. Therefore, we developed the non-contact measurement method for PC combustibility (ηPC) by utilizing chemi-luminescence spectra of PC combustion field in the lab-scale combustion furnace. We also applied the method to the COURSE50 experimental BF to ensure the accuracy of the method. And then we found that

Effect of carbonation curing on physicochemical properties of mineral admixture blended belite-rich cement

The present study investigates the effect of CO2 curing on carbonation degree, CO2 uptake, mechanical and physicochemical properties of mineral admixtures blended with belite-rich cement (BRC). Pulverized coal combustion (PCC) ash, circulating fluidized bed combustion (CFBC) ash, and blast furnace slag (SG) were utilized as mineral admixtures. The results revealed that the PCC ash blended with BRC attained the highest compressive strength under CO2 curing. CFBC ash was comparable to PCC ash in terms of the ability to improve the mechanical and physicochemical properties. TG analysis revealed that CFBC ash blended BRC was excellent for promoting carbonation and CO2 uptake. TG, MIP, XRD, and 29Si NMR results showed that the SG was the least reactive mineral admixture with BRC under CO2 curing and negatively affects the strength attainment outcome, carbonation degree, and CO2 uptake. 29Si NMR confirmed the potential of PCC ash and CFBC ash in enhancing the reactivity of BRC under CO2 curing than the SG. Therefore, it is concluded that the blending of PCC ash and CFBC ash is beneficial in promoting the CO2 sequestration characteristics and compressive strength of BRC.

Decoupling Investigation of Furnace Side and Evaporation System in a Pulverized-Coal Oxy-Fuel Combustion Boiler

A distributed parameter model was developed for an evaporation system in a 35 MW natural circulation pulverized-coal oxy-fuel combustion boiler, which was based on a computational fluid dynamic simulation and in situ operation monitoring. A mathematical model was used to consider the uneven distribution of working fluid properties and the heat load in a furnace to predict the heat flux of a water wall and the wall surface temperature corresponding to various working conditions. The results showed that the average heat flux near the burner area in the air-firing condition, the oxy-fuel combustion with dry flue gas recycling (FGR) condition, and the oxy-fuel combustion with wet flue-gas recycle condition were 168.18, 154.65, and 170.68 kW/m2 at a load of 80%. The temperature and the heat flux distributions in the air-firing and the oxy-fuel combustion with wet FGR were similar, but both were higher than those in the oxygen-enriched combustion conditions with the dry FGR under the same load. This study demonstrated that the average metal surface temperature in the front wall during the oxy-fuel combustion condition was 3.23 °C lower than that under the air-firing condition. The heat release rate from the furnace and the vaporization system should be coordinated at a low and middle load level. The superheating surfaces should be adjusted to match the rising temperature of the flue gas while shifting the operation from air to oxy-fuel combustion, where the distributed parameter analytical approach could then be applied to reveal the tendencies for these various combustion conditions. The research provided a type of guidance for the design and operation of the oxy-fuel combustion boiler.

Bioenergy as a prospective energy source in the future

The issues of global warming and greenhouse gasses have raised the concern of the people and led to integrate ambitious of using bioenergy in many countries. In this paper, the issues of conventional energy are stated, and the different types of conventional energy resources are discussed including coal, petroleum and natural gas. The process of pulverized coal combustion (PCC) to generate electricity is also studied and discussed in this paper to have a better understanding of the process and the emission of greenhouse gas released from the use of coal to generate conventional energy. The reason of soil contamination and air pollution caused by the refinery process of petroleum is also discussed in this paper and several study cases of the social economic impact caused by the production of natural gas in development countries. Furthermore, the used of bioenergy and different type of bioenergy resource are discussed including biogas, algae biofuel, and biodiesel. The process of algae cultivation for algae biofuel and the study of toxic waste algae strains that can give a negative impact to the environment is studied to avoid harmful substances released to the environment. The potential algae application in different fields is also included to show the benefit of algae biofuel which is flexible and able to contribute to the global economic growth. Lastly, the advantages of using bioenergy are discussed including the mitigation of greenhouse gas emission, improve social economic growth, renewable energy resources and prevent prescribed burning of the forest.

Groundwater and society: fresh submarine groundwater discharge and itsmanagement improvement

The issues of global warming and greenhouse gasses have raised the concern of the people and led to integrate ambitious of using bioenergy in many countries. In this paper, the issues of conventional energy are stated, and the different types of conventional energy resources are discussed including coal, petroleum and natural gas. The process of pulverized coal combustion (PCC) to generate electricity is also studied and discussed in this paper to have a better understanding of the process and the emission of greenhouse gas released from the use of coal to generate conventional energy. The reason of soil contamination and air pollution caused by the refinery process of petroleum is also discussed in this paper and several study cases of the social economic impact caused by the production of natural gas in development countries. Furthermore, the used of bioenergy and different type of bioenergy resource are discussed including biogas, algae biofuel, and biodiesel. The process of algae cultivation for algae biofuel and the study of toxic waste algae strains that can give a negative impact to the environment is studied to avoid harmful substances released to the environment. The potential algae application in different fields is also included to show the benefit of algae biofuel which is flexible and able to contribute to the global economic growth. Lastly, the advantages of using bioenergy are discussed including the mitigation of greenhouse gas emission, improve social economic growth, renewable energy resources and prevent prescribed burning of the forest.

Effect of Re-burn Fuel Stream Location on NO Reduction in a Model Pulverized Coal Combustor

I is missing this work, a computational simulation has been performed to investigate the positional effect of reburn fuel injection on NO-reburn. Reburn fuel methane is injected across the coal injection plane at different axial positions of the combustor. Various major NO source mechanisms are considered for NO formation and NO reburn mechanism is used for NO depletion. Temperature profile, species concentration are also investigated, as both NO formation and depletion rate depends on these parameters. It has been observed that, a high temperature flame exists near coal inlet, when the reburn fuel injection plane is closer to coal inlet. On the other hand, the temperature of the flame near the coal inlet decreases when the reburn fuel injection position is far away from coal inlet region. Moreover, NO sources are observed near coal inlet region, when the reburn fuel is injected closer to coal inlet. On the other hand, only Fuel-NO is observed near coal inlet, when the reburn fuel is injected away from the coal inlet. Maximum NO reduction efficiency is observed at outlet plane when reburn fuel is injected closer to inlet, whereas a relatively lower NO reduction efficiency has been observed at outlet plane when reburn fuel is injected far away from coal inlet region.

Effects of the fuel-lean coal/air flow damper opening on combustion, energy conversion and emissions in a supercritical down-fired boiler

In-situ trials were carried out to investigate the effects of the fuel-lean coal/air flow damper opening (FLD) on the pulverized-coal combustion and energy conversion efficiency in a 350-MW supercritical down-fired boiler. This boiler was operated with inferior coal, having a high ash content and low calorific value. The influence of combustion in furnace on steam temperature and coal consumption of a supercritical down-fired boiler were discussed innovatively. The experimental results indicate that, as the FLD was decreased from 100% to 25%, heating of the fuel-rich coal/air flow accelerated such that the overall furnace temperature increased and the thermal load gradually focused at the furnace center area. As a result, the maximum temperature of the water-wall in the lower furnace was reduced and the superheating degree rose significantly. Thus the superheated and reheated steam temperatures increased from 550.4 and 545.8 °C to 558.2 and 555.0 °C. Reducing the FLD also lowered the carbon in the fly ash and slag from 8.17% and 7.70% to 4.51% and 3.43%, respectively. Furthermore, the increase of boiler efficiency and the decrease of specific heat consumption both contributed to the reduction of the specific coal consumption, from 354.45 to 340.43 g·(kW·h)−1, thus the energy conversion efficiency of the unit was improved. However, adjustment of the FLD had only a minimal effect on NOx emissions, which remained in the range of 654–672 mg/m3 at 6% O2. Based on optimizing coal combustion characteristic and economic performance of the unit, an optimal FLD of 25% was recommended.

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.

Coal Particle Devolatilization and Soot Formation in Pulverized Coal Combustion Fields

In this paper, recent developments of the devolatilization model and soot-formation model for the numerical simulations of pulverized-coal combustion fields, and the technology used to measure soot particles in pulverized-coal combustion fields are reviewed. For the development of new models, the validation of the developed models using measurement is necessary to check the accuracy of the models because new models without validation have a possibility to make large errors in simulations. We have developed the tabulated devolatilization process model (TDP model) that can take into account the effect of particle heating rate on the volatile matter amount and the devolatilization-rate parameters. The accuracy of the developed TDP model was validated by using the laser Doppler velocimetry data for the bench-scale coal combustion test furnace. The soot-formation model combined with TDP model for the large eddy simulation (LES) has been also developed. The spatial distributions of both the soot-volume fraction and the polycyclic aromatic hydrocarbons were measured by virtue of laser-induced incandescence (LII) and laser-induced chemiluminescence (PAHs-LIF). The accuracy of the developed soot-formation model was validated by using the measured data.

Effect of Large Amount of Co-injected Gaseous Reducing Agent on Combustibility of Pulverized Coal Analyzed with Non-Contact Measurement

Nowadays, reduction of amounts of CO2 from ironmaking process is important from the aspect of prevention of the global warming. COURSE50 is Japanese national project which aims to reduce the amount of CO2 emission from ironmaking process by 30% by 2050. In COURSE50, we try to reduce iron oxide with H2 to decrease amounts of carbon use, by injecting large amount of gas containing H2 and pulverized coal (PC) from tuyere. In that case, PC combustibility can be different from that in general blast furnace condition, due to high co-injected reducing gas ratio. Though a large number of researches about PC combustion around tuyere of blast furnace has been carried out, the effect of large amounts of co-injected reducing gas on PC combustibility was hardly investigated. To evaluate that, we conducted experiments with two experimental furnaces equipped with various non-contact measurement apparatus and found that

Utilization of Boiler Slag from Pulverized-Coal-Combustion Power Plants in China for Manufacturing Acoustic Materials

The potential utilization of boiler slag generated in large amounts from pulverized-coal-combustion (PCC) power plants has recently drawn much attention due to the serious problems caused to ecosystems. In order to make maximal use of the boiler slag and reduce the environmental risk it poses, this study focused on manufacturing acoustic materials using boiler slag from Chinese PCC power plants. Three promising acoustic materials were successfully manufactured from up to 80% boiler slag with different grain sizes, with the addition of 20% Portland cement. The density and compressive strength of the products were inversely proportional and the sound absorption coefficient was positively proportional to the grain size of the boiler slag. The best sound absorption coefficient was obtained in products made from the coarsest fraction of the boiler slag (MS-C). Nonetheless, all the boiler-slag-based acoustic products still demonstrated compressive strength and densities comparable to those of other acoustic materials made of Spanish bottom ash or other conventional/recycled materials. The acoustic products made from the coarsest fraction (MS-C) and medium fraction (MS-M) of the boiler slag presented good noise absorption characteristics, like those of the commercial coarse porous cement that is traditionally used as an acoustic product. Furthermore, the acoustic products were characterized by very low leach ability of potentially hazardous elements. Consequently, the manufacture of acoustic materials is a very promising application for boiler slag. On the one hand, it consumes huge amounts of boiler slag that is generated in large amounts in China. On the other hand, the acoustic products can be used extensively to produce road acoustic barriers with a high sound absorption efficiency, no significant physical or mechanical limitations and no environmental implication.

Kinetic Simulation of Fine Particulate Matter Evolution and Deposition in a 25 kW Pulverized Coal Combustor

In this paper, fine particulate matter (PM) evolution and deposition in pulverized coal combustion are simulated by solving the population balance equation using a quadrature-based method of moment...

Reduced chemical reaction mechanisms for simulating sodium emissions by solid-fuel combustion

Starting from a reference and comprehensive chemical mechanism for alkali metal emissions (Glarborg and Marshall, 2005), combined with an hydrocarbon oxidation described with a skeleton mechanism (Kazakov and Frenklach, 1994), reduced and optimized chemical kinetics are derived. The objective is to provide a set of chemical schemes useful for three-dimensional (3D) numerical simulations of alkali metal emissions by pulverized solid-fuel combustion systems. An automated procedure relying on one-dimensional (1D) premixed flames is applied to obtain a combined reduced mechanism, whose performance is then evaluated in one-dimensional strained diffusion flames, micro-mixing based canonical problems and three-dimensional carrier-phase direct numerical simulation (DNS) of coal combustion. Predictions of the reduced mechanism on major sodium species, i.e., Na, NaOH, NaCl and Na2SO4 agree well with that of the detail reference scheme under all the considered conditions. A parametric study with 14 two-dimensional (2D) DNS cases is then performed to better understand the reactive flow properties and estimate the prediction capabilities of the reduced mechanism for various Na/Cl/S ratio in the volatiles. After pursuing the chemistry reduction, a global sodium mechanism with only 9 species and 8 reaction-steps is also discussed. The systematic comparison between the 3D DNS results obtained with the reference chemical scheme against those with the reduced ones confirm the validity of the reduction strategy. A reduction of up to 84% in computational cost is reached with the optimized global scheme, thus allowing for addressing real pulverized-coal combustion systems.

Utilization of low sulfur fly ash from circulating fluidized bed combustion burner as geopolymer binder

Circulating fluidized bed combustion (CFBC) is a newer type of burner that employ a circulating process to burn fuel effectively. CFBC burning process is gaining more popularity due to its compact size, high efficiency and lower burning temperature compared to the pulverized coal combustion (PCC) burner. The CFBC burner produces fly ash with different physical properties compared to the PCC burner, i.e. the fly ash is not rounded, and required higher water content for comparable workability. The CFBC fly ash also has a high sulfur content that is detrimental for hardened concrete. Due to its drawbacks, the CFBC hardly used as cementitious material and geopolymer precursor. This study focuses on comparing variations in the concentration of NaOH solution and variations in the ratio of alkaline activators to the setting time and compressive strength of geopolymer mortars on a new class of CFBC fly ash, which have low sulfur content. The concentrations of NaOH solution were 6M, 8M, 10M, and 12M, while the alkaline activator ratios used were 3.0, 2.5, 2.0, 1.0, and 0.5. It was concluded that the low sulfur CFBC fly ash has a potential to be utilized as geopolymer precursor, however, with a shortcoming in its high water demand. The CFBC fly ash used in this study resulted in a geopolymer matrix with good compressive strength and stability. The water demand varies with the fly ash sampling time shows the challenges in the utilization of the fly ash. The highest mortar’s compressive strength, 33.4 MPa at 90 days was achieved at NaOH concentration of 8M and ratio of sodium silicate solution to sodium hydroxide solution of 2.5 with excellent stability.

Influence of the Inner and Outer Secondary Air Ratios on the Combustion Characteristic and Flame Shape of a Swirl Burner with a Prechamber

The swirl burner with a prechamber was used in a 14 MW pulverized-coal combustion experiment to investigate the influence of inner and secondary air ratios (ISA/OSA) on the combustion characteristic and flame shape in this work. The temperatures and species concentrations in the prechamber were measured via the flue gas analyzer and thermocouples. The flame shape beyond the prechamber outlet was captured by using a high-speed camera. The results showed that the combustion efficiency was increased and low nitrogen combustion was achieved by adopting the swirl burner with a prechamber. The high temperature corrosion and slagging phenomenon did not occur in the prechamber. The influence of ISA/OSA on temperature and species concentration profiles at different areas in the prechamber was different. The flame shape size exhibited an inflection point with increasing ISA/OSA. Considering, comprehensively, the temperature peak, near wall temperature, oxygen-free zone, CO concentration, flame length, flame diameter, and divergence angle, the case of ISA/OSA =1 : 2 had great processing on combustion efficiency and NOx emission. Thus, ISA/OSA = 1 : 2 was selected as the optimized case under experiment conditions.