Effect Of Flue Gas Recirculation Research Articles

Effect of flue gas recirculation on combustion instability and emission characteristics of premixed CH4/NH3/air flame

The hydrogen carrier ammonia is considered a prominent carbon-free alternative fuel. This paper examines the impact of flue gas recirculation (FR) on combustion instability and emission behavior of premixed CH4/NH3/air swirl flame at different equivalence ratios (Φ) and ammonia mole fractions (χNH3). Experimental results show that FR is beneficial to suppressing the self-excited pulsating pressure and pulsating heat release rate of CH4/NH3/air flame, and the pulsating frequency decreases monotonically with the increase of FR. Under fuel-lean and stoichiometric conditions, FR is beneficial to suppressing NOx formation but will increase CO and NH3 emissions. Under fuel-rich conditions, FR reduces CO emissions but increases NOx emissions. The NO emissions obtained from the chemical reactor network simulation are in qualitative agreement with the experimental results. The results show that the elementary reactions related to HNO and NHi radicals play a crucial role in the influence of FR on NO formation.

Numerical Study on Effect of Flue Gas Recirculation and Co-Firing with Biomass on Combustion Characteristics in Octagonal Tangentially Lignite-Fired Boiler

The octagonal tangentially fired boiler can be utilized for burning lignite with high moisture. Co-firing biomass in an octagonal tangential boiler is considered a promising approach. A numerical simulation is carried out in this study to analyze the impact of flue gas recirculation (FGR) and the biomass blending ratio on heat and mass transfer in an octagonal tangentially fired boiler. When the FGR rate increases from 0 to 30%, the maximum temperature in the boiler decreases from 2162.8 to 2106.5 K. Simultaneously, the average temperature of the center longitudinal section decreases from 1589.0 to 1531.9 K. The maximum fluctuation of the outlet flue gas temperature remains within 10.9 K for the four calculated working conditions. Consequently, the efficiency of the boiler is basically unchanged. However, the flue gas temperature at the furnace outlet decreases significantly from 1605.9 to 1491.9 K. When the biomass blending ratio increases from 0 to 20%, the mean temperature of the primary combustion zone decreases from 1600.5 to 1571.2 K.

The Effect of Flue Gas Recirculation on CO, PM and NOx Emissions in Pellet Stove Combustion

Pellet stoves are popular appliances because they are an affordable technology and because the fuel is easy to store and to use. The increasing concern for environmental issues, however, requires a continuous effort to reduce pollutant levels in the atmosphere. This experimental work focuses on flue gas recirculation (FGR) as a possible way to improve combustion and decrease the emissions of carbon monoxide CO, particulate matter PM, and nitrogen oxides NOx in order to fulfill European and Italian emission requirements, for NOx in particular. A pellet stove has been tested in several experimental sessions with and without FGR. Pollutant emissions have been measured and analyzed in terms of statistical summaries and instantaneous trends. With FGR, the average CO and PM emissions were found to be 80% and 45% lower than the corresponding emissions without FGR. Results for PM are significant since FGR reduces emissions well below the most restrictive limits enforced in Italy. The analysis of instantaneous emissions in relation to excess air indicated that FGR can considerably reduce emissions, especially at the extremities of the oxygen O2 content range. Optimal ranges of excess air, in terms of O2 in flue gas, were identified for both the tested configurations, in which CO and PM emissions are minimized. The optimal range is 8–9% without FGR, and it decreases to 5–7% with FGR. Finally, a reduction in NOx emissions by about 11% has been observed in the configuration with FGR. Although this reduction seems modest as compared to CO and PM, it is important in that it lowers the emission level to the most severe limit in Italian regulations and indicates an improved FGR system as the solution for further reduction.

Effects of flue gas recirculation on the thermal performance of the gas remediation well

Gas thermal remediation (GTR) is a promising novel soil remediation technology. Many problems such as high energy consumption and unreasonable temperature distribution are still commonly found in the application of the gas remediation well. External flue gas recirculation (e-FGR) was applied to improve the thermal performance of the well. A 3D CFD model of the gas remediation well coupled with e-FGR was developed to analyze the heat transmission and combustion process. Four representative e-FGR ratios, 15 %, 30 %, 45 %, and 60 %, were selected to analyze the relationship between the e-FGR ratio and the well thermal performance. The results show that limited impact is obtained at a low e-FGR ratio and excellent results can only be achieved when the e-FGR ratio reaches 60 %. The maximum flame temperature was reduced by about 28 % at an e-FGR ratio of 60 % when compared with conventional combustion conditions. Localized high-temperature areas on the well surface are eliminated. The total heat transfer of the well increased from 4.69 kW to 6.16 kW when the e-FGR ratio increased from 0 to 60 %, which means a 23.9 % reduction in the remediation cycle and fuel consumption can be achieved at an e-FGR ratio of 60 %.

Effect of Flue Gas Recirculation and Oxygen Addition on Combustion Parameters in the Brayton Cycle

Effect of Flue Gas Recirculation and Oxygen Addition on Combustion Parameters in the Brayton Cycle

Enhanced removal of nitric oxide and carbon dioxide from flue gas in a biofilter: Effect of flue gas recirculation and Fe(II)EDTA addition

Flue gas emission from combustion of fossil fuel is a growing environmental concern. In this study the effect of flue gas recirculation and Fe(II)EDTA addition on CO2 and NO removal from flue gas was explored in a biofilter. The effect of SO2 on CO2 and NOx removal efficiencies were also studied herein. The optimal removal efficiencies of CO2 (88.1%) and NO (85.8%) were achieved with the flue gas recirculation of 2:1. The presence of SO2 showed little impact on CO2 or NO removal while induced the decline of NO removal. The addition of Fe(II)EDTA clearly enhanced NO removal (~85%). The Illumina sequencing results showed that abundant sulfur-associated bacteria (Desulfobulbus, Desulfococcus, Sulfurovum, Chlorobium), nitrogen-associated bacteria (Thauera), fermentative bacteria (Longilinea and Anaerovorax), and various iron-reducing bacteria (Geobacter) were detected in the biofilter with Fe(II)EDTA addition. The synergistic effect of denitrifying/iron-reducing bacteria dedicated to the sustainable NO removal.

Mathematical investigation of syngas fired burner with various configurations in the BERL combustor

This paper discusses the effect of burning syngas in a configuration similar to that of the BERL (Burner Engineering Research Laboratory) 300 KW swirl-stabilized combustor which has previously been used with methane as a fuel. Due to the axisymmetric configuration, only 15° from the burner angle is studied with periodic boundary. The model adopts RANS (Reynolds Averaged Navier–Stokes) technique including a realizable k-ε turbulent scheme. The non-premixed combustion model used is based on applying flamelet concept. The study shows that the structure of the flame is affected with changing the burner quarl angle and the inlet air swirl number. The detailed parametric study of this synthetic fuel in the BERL paradigm relates easily to the accumulated experimental and numerical studies available in this configuration and then acquiring add noval value to the present work. The study also shows the presence of different recirculation zones, one of which is central recirculation zone and an external recirculation zone. When increasing quarl angle, the central recirculation zone is shifted outward and the turbulent interaction between the central fuel jet and the recirculation zone induces small vortices between these two flow patterns. On the other hand, the effect of flue gas recirculation and air staging into the burner on the reduction of NOx formation is discussed. The flue gas data show that FGR reduces NOx emissions significantly while having no influence on flame stability, total combustion efficiency, or CO emissions. Changes in fuel composition are also taken into account. The results reveal that when the hydrogen blending in the fuel increases, the temperature rises.

Effects of flue gas recirculation on combustion and heat flux distribution in 660 MW double-reheat tower-type boiler

The ultra-supercritical double-reheat boiler has attracted more attention because of high parameters (steam with high temperature and pressure), low pollution and large capacity. However, there are some difficulties in the development of this technology, such as adjusting the reheat steam temperature. In this study, computational fluid dynamics simulation is used to analyze a 660 MW double-reheat tower-type pulverized coal-fired boiler. The influence of flue gas recirculation (FGR) on heat transfer characteristics and combustion process in the furnace (including heating surfaces in the upper parts of the furnace) are evaluated. The user-defined function approach predicates the CO reduction effect on NOx. The results show that the flow at the horizontal section through the centerline of recirculating flus gas nozzles is rotating. The velocity distribution changes into an elliptical rotating flow when FGR ratio is 20%. At higher FGR ratios, the high-temperature area (1565–1700 K) shrinks and both the NOx concentration at the low-temperature superheater outlet and the O2 concentration in the burner zone descend. The O2 concentration at the low-temperature superheater outlet first increases and then decreases. In the main combustion zone, the heat flux peak of water-cooled wall is about 330 kW m−2. As FGR ratio increases from 0% to 20%, the rate of heat absorption of water-cooled wall to that of total boiler decreases by 3.50%. These rates for reheater and superheater increase by 2.53% and 2.13%, respectively.

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.

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

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

Experimental and numerical investigation of MILD combustion in a pilot-scale water heater

In the present study the effects of air preheating and dilution on stabilizing MILD (Moderate or Intense Low-oxygen Dilution) combustion of natural gas in a 100 kW jacket type water heater are investigated experimentally. The effects of FGR (flue gas recirculation) and flame heat loss on the self-ignition and extinction temperatures are analyzed numerically using a non-adiabatic WSR (Well-Stirred Reactor) model in the CHEMKIN software. Experimental results showed that the mechanical-process retrofitting techniques were successful to reach positive characteristics of the flameless combustion; e.g. uniform temperature distribution, improved efficiency (>10% increase), and lower NO emission (̴ 13% decrease), without the need to replace the conventional burner with modern flameless type or retrofitting the structure of combustion chamber. Based on the simulation results, a new combustion regime map for practical conditions encountering heat loss is developed. The new T-FGR-heat loss regime map shows that as heat loss increases the quasi-MILD region expands, whereas the MILD and MILD-like regions shrink and beyond a specific heat loss the HTC (high temperature combustion) zone disappears. The method of numerical visualization of experimental conditions on the combustion regime map is a simple powerful numerical tool to design practical flameless systems or retrofitting conventional devices.

Characteristics and flame appearance of oxy-fuel combustion using flue gas recirculation

The pollutant emissions resulting from combustion devices are considered one of the main concerns of many researchers due to their impact on the environment and people. Emissions of nitrogen oxides (NOx) and carbon dioxide (CO2) are considered two of the most important pollutant emissions. The present study is an experimental study to investigate the effect of flue gas recirculation (FGR) on non-premixed combustion for NOx reduction and CO2 capture and storage (CCS) using oxygen mixed with recycled flue gas as an oxidizer instead of fresh air. Flame stability, flame appearance, two-dimensional flame temperature, and exhaust gas analysis were investigated with different FGR percentages. The results show that the flame is stable up to 40% recycled flue gas, but the flame temperature is reduced by about 25%, and there is a reduction of NOx from 90 ppm to 5 ppm. By using oxy-fuel combustion, the flame exhibits the same general appearance for different FGR% and has the main characteristics of air combustion without FGR.

Effect of flue gas recirculation on efficiency of an indirect supercritical CO2 oxy-fuel circulating fluidized bed power plant

This paper deals with and oxy-fuel circulating fluidized bed (Oxy-CFB) power plant with air separate unit (ASU), CO2 compression and purification unit, and an indirect supercritical CO2 cycle. This novel power plant was designed and modeled by using Aspen Plus at commercial scale to investigate the possibility and the effect of recirculated flue gas conditions. The indirect S–CO2 oxy-CFB power plant had higher net efficiencies compared with oxy-CFB power plant with steam cycles because the phase of CO2 does not change during the operation. Also, the effect of the amount of water retained in flue gas stream generated at the CFB boiler on the overall net efficiency was analyzed. By decreasing the temperature of recirculated flue gas from 90 °C to 40 °C, water retained in flue gas decreased, and input O2 concentration in combustor increased from 34.7 to 38.5 vol%. When flue gas recirculation temperature was 40 °C, the boiler efficiency was 99.6%, and the overall net efficiency was 43.1%. Although approximately 20% of the total power is the power consumption of the ASU and CPU, high net efficiency was achieved in this novel power plant.

Performance evaluation of a pressurized oxy-combustion power plant according to wet and dry flue gas recirculation

In a pressurized oxy-combustion (POXY) power plant, it is essential to control the furnace temperature using flue gas recirculation (FGR) as an oxy-combustion environment produces an extremely high temperature in the furnace. However, FGR decreases the plant efficiency as it causes exergy loss in the furnace and increases the power consumption of the FGR booster fan. Therefore, to analyze a POXY plant, the effect of FGR on plant efficiency and performance should be evaluated. In this paper, an advanced supercritical pressure (A-USC) POXY power plant with a distributed pressurized oxy-combustion (DPOC) furnace is simulated and its performance for wet/dry FGR is analyzed. The furnace was modeled using an in-house code, and the whole power plant was simulated using commercial process simulation program. Plant efficiency with the wet FGR is 3.5% higher than that of the dry FGR system owing to the higher latent heat recovery of the FGC and reduction in the exergy loss. In addition, we demonstrated that variation of the plant efficiency for various flowrates of the recirculated gas was not significant in case of the wet FGR system, while considerable decrease in plant efficiency was observed for higher recirculation in the dry FGR cases. Accordingly, we presented an optimal A-USC POXY power plant system with a wet FGR system; the plant net efficiency improved by approximately 10% compared with that of a first-generation oxy-combustion power plant at atmospheric pressure.

Effects of flue gas recirculation on energy, exergy, environment, and economics in oxy‐coal circulating fluidized‐bed power plants with CO2 capture

SummaryCO2 capture and storage(CCS) are required for coal‐fired power plants, which are major sources of anthropogenic CO2 emission. In this study, energy, exergy, environment, and economic (4E) analyses were performed for a 500‐MWe oxy‐coal ultra‐supercritical circulating fluidized‐bed (CFB) power plant with CO2 capture. The effect of the location of flue‐gas recirculation (FGR) on the 4E values was investigated for wet FGR (wFGR) at 170°C, dry FGR (dFGR) at 68°C, and 80% wet and 20% dry FGR (wdFGR). The net electricity efficiencies of the wFGR and dFGR power plants were 37% and 36%, respectively. The exergy loss was the largest in the combustor and boiler area, where process improvement was possible. The levelized cost of electricity was approximately 60 $/MWh. The return on investment was 6.7% and 6.1%/y for the wFGR and dFGR plants, respectively. The CO2 emission rate decreased by 90% (from 690 to 76 kg‐CO2/MWh) in the oxy‐coal power plants with CO2 capture. Relative to the wFGR, the dFGR was advantageous for preventing material corrosion because of the lower sulfur content in the FGR stream. For the wdFGR power plant, the process performance was intermediate, that is, between that of the wFGR plant and that of the dFGR plant. The study provided an effective tool for identifying the technological and economic effects of the FGR location for the oxy‐coal power plant with CCS via 4E analyses.

Effect of Flue Gas Recirculation on Nitrogen Oxide Emission of Coal-Fired Unit Boiler

Taking the flue gas recirculation system of 220MW coal-fired unit as the test object, effects of the operation mode of the flue gas recirculation system on the operating characteristics of the boiler under different working conditions was studied.The results show: the operation of flue gas recirculation system will suppress the amount of NOx generated in the furnace, and the best way to restrain the formation of NOx is to send the recycled flue gas into the furnace through primary and secondary air simultaneously. The flue gas recirculation system can effectively improve the inlet flue gas temperature of SCR, especially when the secondary flue gas recirculation system is put into operation, and the effect of increasing the inlet flue gas temperature of SCR is obviously better than that of the other two operation modes. The operation of flue gas recirculation system can effectively save net coal consumption.

Effect of Flue Gas Recirculation on Operating Performance of Coal-Fired Unit Boiler

Taking the flue gas recirculation system of 220MW coal-fired unit as the test object, effects of the operation mode of the flue gas recirculation system on the operating characteristics of the boiler under different working conditions was studied. The results show: To a certain extent, the operation of flue gas recirculation system will reduce boiler efficiency, which is more obvious under low load conditions. However, The operation of the flue gas recirculation system can effectively increase temperatures of reheat steam and superheated steam.Comparing the economics of the front and rear units of the flue gas recycling system, it can be find that net coal consumption of the unit under the load of 200MW and 140MW can be reduced by up to 1.51g/kW·h and 1.86g/kW·h respectively.