Flue Gas Recirculation Research Articles

H2 – CH4 blending fuels combustion using a cyclonic burner on colorless distributed combustion

H 2 – CH 4 mixture fuels can be promising for reducing carbon-based emissions. However, because of higher pollutant emission (such as NO X ) problems during hydrogen combustion, a new combustion method can be favorable. Colorless distributed combustion (CDC) is emerging here. CDC enables ultra-low pollutant emissions along with reduced flame instabilities, combustion noise, improved combustion efficiency, etc. Considering those benefits, methane and the hydrogen-enriched methane (60% CH 4 – 40% H 2 , 50% CH 4 – 50% H 2 , 40% CH 4 – 60% H 2 ) fuels have been consumed using a cyclonic burner providing more residence time at an equivalence ratio of 0.83 under distributed regime. For the modelings, Reynolds Stress Model (RSM) turbulence model, the assumed-shape with β-function Probability Density Function combustion model, and P-1 radiation model have been selected. To seek CDC, the oxygen concentration in the oxidizer was reduced with N 2 or CO 2 diluent from 21% O 2 to 13% O 2 at an interval of 2%. The air and the fuel temperatures were kept constant at 300 K. Besides, for seeking high-temperature air combustion (HiTAC) conditions the oxidizer temperature was changed to 600 K to simulate flue gas recirculation. The results showed that the temperature distributions changed to be more uniform considerably with a decrease in oxygen concentration for all cases. CDC also provided a considerable decrease in NO X and a favorable reduction in CO at a certain oxygen concentration. It has been concluded that CO 2 as the diluent was more effective for reducing temperature levels and NO X levels due to its greater heat capacity. • H 2 – CH 4 blending fuels combustion have been examined in a cyclonic burner. • Colorless distributed combustion (CDC) was sought for H 2 – CH 4 blending fuels. • Reduced oxygen concentration affected considerably all combustion characteristics. • Combustion characteristics were changed with increase in hydrogen content. • Ultra-low pollutant emissions were achieved under CDC.

Thermogravimetric and kinetic study of thermal degradation of various types of municipal solid waste (MSW) under N2, CO2 and oxy-fuel conditions

Oxy-fuel combustion is one carbon capture and sequestration (CCS) technique that uses both O2 and recirculated flue gas as an oxidiser. As a result, the produced gas is composed mainly of CO2 and H2O, which makes its sequestration more cost-effective. Changing the atmosphere from N2 to CO2 affects combustion behaviour. To study the impact of the atmosphere on the combustion process, the thermal degradation of representative types of municipal solid waste (MSW) under N2, CO2, and O2/CO2 atmospheres was analysed using a thermogravimetric (TG) instrument. Nonisothermal degradation experiments were conducted, and three heating rates were examined. Isoconversional methods were employed to determine kinetic data. Comparing N2 and CO2 atmospheres, it was found that below 600 °C, the shape of TG curves was not affected significantly. However, above 600 °C under CO2 atmosphere, a second peak appeared, which indicated gasification reactions of the char with carbon dioxide. In the presence of oxygen, the second peak was shifted to lower temperatures, indicating that thermal decomposition with O2 was more rapid. The reported kinetic parameters provide fundamental information on the conversion of solid waste. Thus, they are essential for designing chambers dedicated to the oxy-combustion of waste.

Effects of flue gas recirculation on self-excited combustion instability and NOx emission of a premixed flame

Combustion instability has been a common problem accompanied with the low NOx emission technologies for the industrial premixed burner. The effects of flue gas recirculation ratio (FR) on the characteristics of combustion instability and NOx emissions of a premixed flame in a 350 kW industrial boiler are investigated by experimental tests and numerical simulations. The cavity acoustic mode of the whole chamber is computed by a Helmholtz solver combined with CFD simulations. As the FR increased from 0 to 20%, the NOx emission is reduced by around 85% and self-excited combustion instability is trigged when the FR exceeds 10%. Four modes - combustion noise, limited cycle, intermittence and breathing - of combustion instability with the different FRs are recorded in the experiment. Two dominant pressure oscillation frequencies ranging from 21 to 25 Hz and from 1 to 2 Hz are observed when the FR is 10–20%. The measured pressure oscillation modes are compared with the acoustic simulation results. The results show that these two dominant frequencies are consistent with the first and second acoustic modes of the whole boiler cavity. The difference between the dominant oscillation frequency and the cavity acoustic eigenfrequency may be caused by the time delay of the response of the flame. The high amplitude pressure oscillations featured as ultra-low frequency (1–2 Hz) are caused by the periodic extinction and ignition of the flame under a high FR (>18%).

Effects of flue gas recirculation on nitrogen oxide formation in 1000 MW S-CO2 coal-fired boiler with partial expansion furnace

Abstract Since the heat transfer coefficient of supercritical carbon dioxide (S-CO2) is approximately 1/2–2/3 of traditional steam boiler, the S-CO2 boiler structure, cooling wall arrangement and combustion system is different from traditional boiler configuration. This paper takes a 1000 MW S-CO2 coal-fired boiler with partial expansion furnace and partial flow strategy arrangement for cooling wall as research object, the coal combustion and NOx generation characteristics in the furnace were numerically examined with the flue gas recirculation rate of 0–35%. The calculation results show that under staged combustion, the flue gas recirculation increases the ignition temperature of the pulverized coal and reduces the combustion temperature. And the expansion of the upper furnace further reduces gas temperature. Besides, as the flue gas recirculation rate increases, the gas temperature decreases. The flue gas recirculation may lower the production of NOx in the main combustion zone, and reduce the production of NOx further in the expansion zone. The average NOx concentration at the outlet decreases from 439 to 365 ppm when the flue gas recirculation rate increases from 0 to 27%. While the flue gas recirculation rate increases from 27% to 35%, the average NOx concentration is not changed obviously.

Numerical investigations on the aerodynamics and flue gas recirculation of cyclone-fired coal boiler

Cyclone-fired boilers have gained wide applications due to their ability to burn low ash fusion temperature coals that are unsuitable for pulverized coal (PC) firing. In comparison to PC boilers, cyclone-fired boilers exhibit significantly different aerodynamics and the molten slag layer plays a critical role in the operation of boilers. However, by far there are still lack of CFD models that are able to provide effective guidance to the design and operation of cyclone-fired boilers. In this paper a CFD model that was designed to solve the practical problems of cyclone-fired boilers was developed in which the capture of coal particles by the molten slag layer was considered through a slag layer capture model to remove the captured particles from calculation and release the combustion heat of the remaining combustibles. This model was then employed to investigate the aerodynamics and flue gas recirculation (FGR) optimization design of a 550 MW cyclone-fired boiler. The results demonstrated the highly nonuniform characteristics of furnace aerodynamics of cyclone-fired boilers due to the strong swirling flows created by the cyclones that frequently leads to the formation of localized high temperature zones and severe boiler fouling problems. Thus, it is critical to adapt the FGR design with the nonuniform furnace flow and temperature distributions. The simulation results showed that with the adapted FGR design the high temperature zones in the furnace could be effectively eliminated. This study is instrumental for the design of FGR system of cyclone boilers to avoid the potential severe boiler fouling problems.

Performance research and application of the vapor pump boiler equipped with flue gas recirculation system

To improve the boiler thermal efficiency and reduce oxynitride emissions, a novel flue gas waste heat recovery system is proposed. The vapor pump boiler equipped with a flue gas recirculation system is first applied for practical engineering. The oxidizing air is preheated and humidified before the combustion process, which causes the dewpoint temperature of the flue gas to increase. Thus, more waste heat in the flue gas can be recovered by the boiler feedback water. Heat recovery efficiency of the system can reach 82.6%, resulting in a 7–8% increase in the boiler efficiency. In addition, the increases in oxidizing air humidity and flue gas recirculation both reduce oxynitride production. As a result, oxynitride emission decreases from 129 mg/m3 to 23 mg/m3, resulting in a reduction of 82.3%. The gas-fired boiler realizes ultra-low oxynitride emission. For a 1.8 MW boiler, annual natural gas consumption can be saved by 7–8%. Given current energy prices in Beijing, the proposed system is economical with a static payback period of 1.2 years. An overall system performance is provided as evidence of the potential benefits. The proposed system is proved to have advantages in energy savings, pollutant reduction, and economic benefits.

Enhanced Nox Reduction Performance in the I-Type Radiant Tube by Combining a Novel Triple Air-Staging with Flue Gas Recirculation

Enhanced Nox Reduction Performance in the I-Type Radiant Tube by Combining a Novel Triple Air-Staging with Flue Gas Recirculation

Investigations on the Spatial Distributions of Nox Formation Routes in the Low-Nox Combustion Processes with the Internal Flue Gas Recirculation Method

Investigations on the Spatial Distributions of Nox Formation Routes in the Low-Nox Combustion Processes with the Internal Flue Gas Recirculation Method

ОСОБЛИВОСТІ ЗАСТОСУВАННЯ РЕЦИРКУЛЯЦІЇ ДИМОВИХ ГАЗІВ ДЛЯ КОТЛІВ МАЛОЇ ТА СЕРЕДНЬОЇ ПОТУЖНОСТІ

The problems of using the method of flue gas recirculation into the combustion air for small-capacity boilers that are not equipped with air- heaters are described. An analysis of the thermal-humidity state of the gas-air mixture in different modes of a water-heating boiler with a heat output of 2 MW was carried out. The reasons for limiting the application of this method are determined and ways to solve problems are indicated.

Enhanced Removal of Co2 and No from Flue Gas in a Biofilter: Effect of Flue Gas Recirculation and Fe(Ii)Edta Addition

Enhanced Removal of Co2 and No from Flue Gas in a Biofilter: Effect of Flue Gas Recirculation and Fe(Ii)Edta Addition

Effects of Flue Gas Recirculation on Combustion and Heat Flux Distribution in 660 Mw Double-Reheat Tower-Type Boiler

Effects of Flue Gas Recirculation on Combustion and Heat Flux Distribution in 660 Mw Double-Reheat Tower-Type Boiler

Engine performance analysis for diesel engine using hydrogen as an alternative fuel

Interest in alternative fuels grows as oil prices climb. Concerns over pollution levels in many regions of the world have heightened the urgency of finding solutions. As the price of crude oil rises, alternative fuels become more competitive. The automobile sector is well-known for being one of the world's largest consumers of gasoline. As a consequence, Because H2 is clean, dependable, efficient, approachable, client, and cost-effective, it also has the ability becoming a sustainable transportation power source. The potential of hydrogen as a primary energy source for transportation systems is investigated in this research. Hydrogen has proven to be a promising chemical fuel that has the potential to partially replace carbon fuels in diesel engines due to a variety of characteristics such as high power density, abundant supply, easy portability, and a wide range of production methods from sustainable and inexpensive fuels with no or low carbon output. A study into directly injecting H2 or H2-rich gas into diesel engine via the EGR flue gas recirculation design to facilitate ignition, effectiveness, and reduced carbon emissions would be of enormous scientific and practical relevance. The result indicates that the engine is operating at full load, with a thermal efficiency of 23.50 percent without EGR. The main conclusion is that in order to fully exploit the benefits of H2 and fueling cells in the transportation sector, it is necessary to establish a stable, long-term regulatory framework and to coordinate efforts across sectors in order to benefit from economies of scale.

Enhanced Removal of Nitric Oxide and Carbon Dioxide from Flue Gas in a Biofilter: Effect of Flue Gas Recirculation and Fe(Ii)Edta Addition

Enhanced Removal of Nitric Oxide and Carbon Dioxide from Flue Gas in a Biofilter: Effect of Flue Gas Recirculation and Fe(Ii)Edta Addition

Effect of the Flue Gas Recirculation Ratio on the Strengthened Low-Nox and High-Burnout Characteristics in a 600 Mwe W-Shaped Flame Furnace Firing Low-Volatile Coals

Effect of the Flue Gas Recirculation Ratio on the Strengthened Low-Nox and High-Burnout Characteristics in a 600 Mwe W-Shaped Flame Furnace Firing Low-Volatile Coals

Jet-Niche Technology Influence Potential on the Economic and Operating Parameters of the Fire-Engineering Equipment

The Power engineering is an inseparable part of the contemporary world that has a negative influence on the ecology; in particular it provokes the pollution of atmosphere with such harmful emissions as nitrogen and carbon oxides. Different methods are used to reduce the emission of harmful substances. The efficiency of such methods is increased when these are used in combination and not separately. The recirculation of flue gases and the use of contemporary technologies for municipal boilers, in particular jet-niche technology (JNT) enabled the reduction of NOx and СО emissions to the levels that meet the requirements of European standards simultaneously improving the efficiency of the operation of the fire-engineering facility. The principle of operation of the JNT is based on the formation of the compact stable self-controlled vortex structure and on the interaction system of flammable and oncoming oxidizer flows. This technology enables the operation at minimum recirculation values and it means that all boiler parameters can be retained, in particular starting characteristic, combustion stability and unavailability of vibration modes including a high level of fuel burnout. The obtained research data showed that NОх values were in the range of 80 to 140 mg/m3 when the oxygen content at the furnace inlet was 20% and lower for different boiler systems (DKBR-10, KVGM-6.5, PTVM-50) at CO values close to 50 mg/m2. Hence, the use of the burners of a JNT type enables the reduction of NОхemissions and retains the combustion process efficiency.

Decreasing NOx Emissions by Way of the Staged Fuel Combustion

The purpose of this scientific paper was to analyze the mathematical model built for the staged arrangement of the fuel combustion system and calculate the formation of nitrogen oxides throughout the boiler furnace height for the different distributions of thermal loadings along the full vertical extent of the combustion chamber. The obtained results enable the determination of the overall amount of nitrogen oxides formed in the boiler and it allows us to provide appropriate ecological indices for the boiler when regulating the air concentration in the burner rows. In practice, to suppress the formation of nitrogen oxides we often use such basic methods as low-toxic burners, staged fuel combustion, flue gas recirculation, etc. The analysis of the computations done allows us to draw a conclusion that the operation of the boiler with ecological indices that satisfy standard values of the European Directive 2010/75/EU is only possible for the load below 40 %. After reconstruction of the burner system and adjustment of the air supply system with the observation of above ecological norms the boiler power can be increased up to 80 % using the staged fuel burning with the ensurance of environmental performances during its operation. Computational and experimental data errors varied in the range of 8 % to 12 %. With the increase in the overall chemical incomplete combustion by 40 % to 60 % (q3) these losses are compensated by a decrease in absolute losses due to the boiler aggregate load and the losses through external walls (q5) due to an increase in the boiler power.

NO formation mechanism of CH4/NH3 jet flames in hot co-flow under MILD-oxy condition: Effects of co-flow CO2 and H2O

MILD-oxy combustion is an advanced technology for achieving carbon capture and low NOx emissions simultaneously. In its combustion process, the atmosphere comprises CO2 and H2O due to intense flue gas recirculation. This work numerically investigates the chemical effects of co-flow CO2 and H2O on the homogeneous fuel-NO formation mechanism of CH4/NH3 jet flames in hot co-flow under MILD-oxy condition. The results reveal that compared with H2O dilution, CO2 dilution alters the radical pool and thus lowers the overall oxidation rate, which favors achieving the MILD regime with a notably enlarged reaction zone. The increase in CO2 and H2O contents facilitates the formation of NO, wherein NH3 conversion into NO primarily occurs via four routes with HNO as the major N-containing intermediate. The addition of CO2 significantly promotes NH2 + O ↔ HNO + H and NH + CO2 ↔ HNO + CO, which enhances the oxidation of NH3 through the routes NH3 → NH2 → HNO → NO and NH3 → NH2 → NH → HNO → NO. The enhancement of H2O concentration accelerates NH + OH ↔ HNO + H and NH + OH ↔ N + H2O through the formation of abundant OH radical. The conversion of NH radical to HNO and N radical is consequently facilitated and strengthens the routes NH3 → NH2 → NH → HNO → NO and NH3 → NH2 → NH → N → NO.

Turbulent multi-regime methane-air flames analysed by Raman/Rayleigh spectroscopy and conditional velocity field measurements

In this study the characteristics of multi-regime combustion are investigated using a multi-regime burner with well-defined inflow boundary conditions. Based on previous findings, the range of operating conditions is extended. Fluid dynamical and thermochemical states are analysed for a variety of fuel/air ratios. Based on comprehensive Raman/Rayleigh and combined particle image velocimetry and SO2 laser-induced fluorescence measurements, two selected operating conditions are compared in detail. To gain insight into the stabilization mechanism, results from flow field measurements and flame front tracking are conditionally analysed in a statistical approach. In this configuration flame stabilization is dominated by recirculation of hot flue gases from a premixed flame enveloping the jet-type lifted flame exhibiting extended zones of multi-regime combustion.

Influence of gas composition and properties on the combustion and heat transfer characteristics of pulverized oxy-coal boiler

This paper presents a numerical study on the influences of gas composition and properties on the combustion and heat transfer characteristics of pulverized oxy-coal boiler. Previous studies were primarily focused on impacts of gas mass flow rate under different flue gas recirculation (FGR) rates while the important influences of gas composition and physical properties were overlooked. The results show that the changes in the gas composition and physical properties under different combustion modes, such as density, heat capacity and gas absorption coefficient, can significantly affect the flow, temperature, and heat transfer distributions in the furnace. Specifically, due to the differences in the heat capacities of CO2, H2O and N2, the gas heat capacity of oxy-coal combustion is considerably higher than that of air-coal combustion. As a result, oxy-coal combustion attains furnace temperature comparable to that of air-coal combustion at remarkably lower gas mass flow rate. Moreover, because of the differences in the radiation properties of CO2, H2O and N2, the gas absorption coefficient of oxy-coal combustion is higher than that of air-coal combustion, especially at the near-wall region, which hinders the radiation heat transfer between the high temperature flame and furnace wall. Consequently, oxy-coal combustion needs higher furnace temperature at further lower gas mass flow rate to achieve matched wall heat absorption with that of air-coal combustion. Therefore, the differences in the gas composition and physical properties under different combustion modes need to be comprehensively considered in the design of oxy-coal combustion systems or retrofit of existing air-coal combustion systems.

Research of coupling technologies on NOx reduction in a municipal solid waste incinerator

The controlling of NOx emission remains the focus and motivates research in municipal solid waste incineration nowadays. The denitrification process in municipal solid waste incinerator based on coupling technologies of flue gas recirculation, over-fired air and selective non-catalytic reduction were conducted by numerical simulation in this work. The effects of different flue gas recirculation ratios, two paths of applying flue gas recirculation and application of coupling technologies on NOx emission and combustion characteristics were studied. The results indicated approximately 23.54% of initial NOx was reduced with flue gas recirculation ratio of 20% (injected through path 1), and the boiler efficiency was increased gradually from 80.16% to 83.78 %, as the flue gas recirculation ratio increased from 13% to 20%. The improvement of NOx removal efficiency was maintained at about 16% when flue gas recirculation ratio was 13% to 20% (injected through path 2). Moreover, the NOx removal efficiency was 33.68% when selective non-catalytic reduction technology was applied separately but increased by 13.51% when over-fired air technology was combined. With coupling technologies applied, the total NOx removal efficiency reached the highest of 76.48%, indicating flue gas recirculation coupling with over-fired air and selective non-catalytic reduction technologies is feasible to achieve lower NOx emission in municipal solid waste incineration.