In-Situ Measurements of Temperature and Emissivity during MSW Combustion using Spectral Analysis and Multispectral Imaging Processing

By using a novel multispectral imaging technology, the 2-D distributions of flame temperature and emissivity were measured in a 16 MW incinerator to co-fire municipal solid waste (MSW) and municipal sludge. A way to establish the relationship between the multispectral flame images and the temperature was proposed by combing the Newton iteration method and Hottel emissivity model. The results showed that the measured temperatures at different locations varied by 31.25% with a fixed steam evaporation rate, and 11.76% with different steam evaporation rates at a given port. The temperatures and emissivities decreased at upper locations due to the lower local soot particle concentration and the change of the measured flame temperatures with load were correlated with the MSW caloric values. Flame temperatures near the left wall were higher than those near the right wall. This deviation was caused by the high moisture content of municipal sludge that inhibited combustion. The emissivities of flame near the right wall were lower than those near the left wall due to the low fixed carbon in municipal sludge. The normalized flame emissivities between the left and the right walls indicated that obvious differences existed in the radiative characteristics of soot, which confirmed the uneven mixing of MSW and municipal sludge. Besides, a spectrometer system was used to measure the release of alkali metal elements including Na, K during the incineration process. The characteristic spectra showed that the alkali metal radiative intensity was related to the moisture content in the wastes. Overall, these results justified that the multi-wavelength thermometry was feasible for monitoring combustion in the MSW incinerator

Effects of Acetylene Addition to the Fuel Stream on Soot Formation and Flame Properties in an Axisymmetric Laminar Coflow Ethylene/Air Diffusion Flame

The effects of adding acetylene to the fuel stream on soot formation and flame properties were investigated numerically in a laminar axisymmetric coflow ethylene/air diffusion flame using the open-source flame code Co-Flame in conjunction with an elementary gas-phase chemistry scheme and detailed transport and thermodynamic database. Radiation heat transfer of the radiating gases (H2O, C2H2, CO, and CO2) and soot was calculated using a statistical narrow-band correlated-k-based wide band model coupled with the discrete-ordinates method. The soot formation was described by the consecutive steps of soot nucleation, surface growth of soot particles via polycyclic aromatic hydrocarbons (PAHs)-soot condensation or the hydrogen abstraction acetylene addition (HACA) mechanism, and soot oxidation. The added acetylene affected the flame structure and soot concentration through not only chemical reactions among different species but also radiation effects. The chemical effect due to the added acetylene had a significant impact on soot formation. Specifically, it was confirmed that the addition of 10% acetylene caused an increase in the peak soot volumetric fraction (SVF) by 14.9% and the peak particle number density by about 21.1% (z = 1.5 cm). Furthermore, increasing acetylene concentration led to higher concentrations of propargyl, benzene, and PAHs and consequently directly enhanced soot nucleation rates. In addition, the increased H mole fractions also accentuated the soot surface growth. In contrast, the radiation effect of the addition of 10% acetylene was much weaker, resulting in slightly lower flame temperature and SVF, which in turn reduced the radiant heat loss

Distributed parameter modeling and thermal analysis of a spiral water wall in a supercritical boiler

In this paper, a distributed parameter model for the evaporation system of a supercritical spiral water wall boiler is developed based on a 3-D temperature field. The mathematical method is formulated for predicting the heat flux and the metal-surface temperature. The results show that the influence of the heat flux distribution is more obvious than that of the heat transfer coefficient distribution in the spiral water wall tube, and the peak of the heat transfer coefficient decreases with an increment of supercritical pressure. This distributed parameter model can be used for a 600 MW supercritical-pressure power plant

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

Analysis of the Hydraulic Resistance of a Water Wall Based on a Distributed Parameter Model in a Supercritical Once-Through Boiler

Accurate prediction of the hydraulic resistance is helpful for the safe operation of a water wall in a supercritical boiler. In this paper, the density distribution for the resistance calculation of a water wall at the supercritical pressure is numerically analyzed, and a distributed parameter model of the hydraulic resistance is developed in a down-fired 600 MWe supercritical boiler using a three-dimensional temperature distribution. The results show that the difference in the density along the radial direction is small and that the hydraulic resistance of the water wall tubes at the supercritical pressure is affected by the critical phenomenon of the working fluid and the allocation of heat flux of the boiler. The simulation cases and in situ operation data demonstrate the model. The model provides a new analysis method for the hydraulic resistance characteristics of a water wall in this thermodynamic system, and the derived model builds a foundation for developing flow monitoring and a thermal-hydraulic design

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

Modes of Occurrence of Fluorine by Extraction and SEM Method in a Coal-Fired Power Plant from Inner Mongolia, China

In this study, an extraction method and environmental scanning electron microscopy (SEM) are employed to reveal the changes in the occurrence mode of fluorine in a coal-fired power plant in Inner Mongolia, China. The different occurrence states of fluorine during coal combustion and emission show that fluorine in coal mainly assumes insoluble inorganic mineral forms. The results illustrate that the three typical occurrence modes in coal are CaF2, MgF2 and AlF3. The fluorine in fly ash can be captured by an electrostatic precipitator (EPS) or a bag filter. In contrast, the gaseous fluorine content in flue gas is only in the range of several parts per million; thus, it cannot be used in this study. The occurrence mode of fluorine in bottom ash and slag is inorganic villiaumite (e.g., soluble NaF, KF and insoluble CaF2) which is difficult to break down even at high temperatures. The occurrence mode of fluorine with the highest content in fly ash is physically adsorbed fluorine along the direction of the flue gas flow. The insoluble inorganic mineral fluoride content in fly ash is also high, but the gradually increasing fluorine content in fly ash is mainly caused by physical adsorption. Fluorine in the coal-fired power plant discharges mostly as solid products; however, very little fluorine emitted into the environment as gas products (HF, SiF4) cannot be captured. The parameters used in this study may provide useful references in developing a monitoring and control system for fluorine in coal-fired power plants

Experimental Study on Co-Firing of Coal and Brewery Wastewater Sludge

The environmental pollution and high energy consumption caused by the coal-dominated energy structure in China have been the focus of attention for a long time. The co-firing of biomass with coal can save coal resources and realize effective utilization of biomass. In this paper, brewery wastewater sludge (SD) and bituminous coal (BC) were blended for an experimental study which aimed to provide basic experimental data and operational guidance as a reference for practical application in power plants. The co-firing characteristics of sludge and bituminous coal were studied. The results show that the burnout temperature and ignition temperature decrease with an increase in the sludge blending ratio. The Comprehensive Combustion Index (CCI) first rises, then decreases, reaching a maximum at about 15%. Compared with the atmosphere with 79% N2/21% O2, under the 79% CO2/21% O2 atmosphere, ignition is delayed and the burnout temperature is higher. Under an O2/CO2 atmosphere, as the O2 concentration improves, the thermo-gravimetric (TG) curve shifts to the low-temperature region, the burnout temperature drops significantly, and the comprehensive combustion characteristics are improved. With an increment of the heating rate, the curve of TG analysis shifts to the high-temperature region and the CCI increases. This study could provide helpful information on practical blending in coal-fired power plants for energy savings and emission reductions

In-Situ Measurements of Temperature and Emissivity during MSW Combustion using Spectral Analysis and Multispectral Imaging Processing

By using a novel multispectral imaging technology, the 2-D distributions of flame temperature and emissivity were measured in a 16 MW incinerator to co-fire municipal solid waste (MSW) and municipal sludge. A way to establish the relationship between the multispectral flame images and the temperature was proposed by combing the Newton iteration method and Hottel emissivity model. The results showed that the measured temperatures at different locations varied by 31.25% with a fixed steam evaporation rate, and 11.76% with different steam evaporation rates at a given port. The temperatures and emissivities decreased at upper locations due to the lower local soot particle concentration and the change of the measured flame temperatures with load were correlated with the MSW caloric values. Flame temperatures near the left wall were higher than those near the right wall. This deviation was caused by the high moisture content of municipal sludge that inhibited combustion. The emissivities of flame near the right wall were lower than those near the left wall due to the low fixed carbon in municipal sludge. The normalized flame emissivities between the left and the right walls indicated that obvious differences existed in the radiative characteristics of soot, which confirmed the uneven mixing of MSW and municipal sludge. Besides, a spectrometer system was used to measure the release of alkali metal elements including Na, K during the incineration process. The characteristic spectra showed that the alkali metal radiative intensity was related to the moisture content in the wastes. Overall, these results justified that the multi-wavelength thermometry was feasible for monitoring combustion in the MSW incinerator