Co-firing NH3 in coal-fired power plants is an attractive method to accelerate the pace of global decarbonization. However, the contradiction between achieving elevated temperature within the furnace ...and maintaining low NOx emission constrains the utilization of NH3 as fuel. In this study, 3-dimensional numerical simulations on coal/NH3 co-firing cases were conducted in a full-scale boiler for the first time. The influences of NH3 blending ratio, O2 enrichment combustion and deep air-staging technology were investigated. The results show that the burnout properties of NH3 are excellent in co-firing boiler. Higher NH3 blending ratio leads to lower temperature in the furnace. Enriching O2 concentration to 30% in the secondary air can compensate the temperature decline caused by 50% NH3 co-firing, while it brings an undesired surge in NOx concentrations. The high temperature and strong reducing atmosphere (HT&SRA) could be created by combining the O2 enrichment and deep air-staging combustion. The NO emission drops by 49.6% due to HT&SRA. Then, high flue gas temperature and low NOx emission can be achieved simultaneously. HT&SRA improves the overall exergy efficiency for 50% NH3 co-firing case from 51.65% to 51.78%. The findings open up a promising strategy for utilizing NH3 as a stationary fuel.
•NH3 shows excellent burnout characteristics in the full-scale utility boiler.•The flue gas temperature drops by more than 100 K when NH3 blending ratio is 50%.•30% O2 compensates the temperature decline, but increases NO emissions by 47.2%.•NO emission drops by 49.6% under high temperature & strong reducing atmosphere.•HT&SRA improves the exergy efficiency from 51.65% to 51.78% for 50% NH3 case.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•Rice husk combustion was performed in a circulating fluidized bed system.•The single air-staging combustion can reduce NO concentration.•The single SNCR process increase in the CO emissions.•The ...combined air-staging and SNCR can reduce NO emissions.•The RHA recovered from secondary cyclone has completely amorphous silica ash.
Rice husk ash produced from rice husk combustion consists of mainly amorphous SiO2, which has economic applications in industry. However, the combustion technology for rice husk attributes to crystallization of SiO2 and environmental impacts associated with NOx emission as particulate matter precursors. In this study, the rice husk combustion in the circulating fluidized bed system was conducted to investigate the combustion characteristics, including temperature and pressure profiles, NO emissions combustion efficiency, and rice husk ash properties. The single and combined air-staging and selective non-catalytic reduction (SNCR) process was applied to suppress NO formation and reduce NO concentration, respectively. At air-staging combustion conditions of primary air/secondary air/tertiary air ratio (vol.%) of 60/10/30 for normalized stoichiometric ratio of 1.1, the synergetic effect was observed on the NO and CO emissions reduction compared to single NO reduction technologies. The highest combustion efficiency of 98.88 % was also found while rice husk ash was recovered as a completely amorphous form with low unburned carbon of 2.92 %. The combined air-staging and SNCR process in the circulating fluidized bed combustion of rice husk shows the technical feasibility to recover fully amorphous SiO2 and reduce NO emission by 65.6 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•NOx emissions modeling and in-furnace measurements in industrial biomass combustion.•Effects of air staging on NOx emissions clarified in a bubbling fluidized bed.•Conversion of fixed nitrogen to N2 ...of 90% demonstrated.
NOx emissions belong to the most critical gaseous emissions in thermal conversion of biomass and non-recyclable waste. Yet the role of air staging on NOx reduction is not fully understood in most combustion systems. This study investigates the effect of air staging on the NOx reduction in an industrial bubbling fluidized bed by means of a detailed kinetic mechanism and assuming gradual entrainment of flue gases (with NOx precursors) into the air jets. The computed data is compared to unique non-published experimental industrial-scale data, from a 107 MWth biomass-fired fluidized bed boiler. The air was staged via primary air (through the bed), and secondary and tertiary air jets with a high inlet velocity. NO, HCN and NH3 concentrations were measured inside the furnace at a depth of 1.8 m, below the secondary air jets, above the secondary air jets and above the tertiary air jets. The computed NOx values were in good agreement with the experimental values. Above the bed, the total NO + HCN + NH3 concentration was 1169 ppm. After the tertiary air staging the total NO + HCN + NH3 concentration was 76 ppm. The conversion of fixed nitrogen (NO + HCN + NH3) to N2 reached 65 % after the secondary air jets, and 90 % after the tertiary air jets. The study shows that exceptional reduction of NOx emissions can be achieved with air staging in this type of industrial combustion systems for biomass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
For developing technologies for innocent disposal of/energy recovery from high‐ash oil sludge char (OSC), it was continuously combusted in a 10 kg h−1 fluidized‐bed combustor. Addition of brown coal ...(BC) improved its combustion, but excessive BC was prone to cause slagging. Fine coke particles in OSC and volatiles in BC led to staged temperatures along the fluidized bed through air‐staging co‐combustion, enabling excellent combustion performance as well as efficient NOx reduction, especially when coupled with selective non‐catalytic reduction. Thus, there is a potential to cleanly recover energy from OSC by its co‐combustion with BC.
Co‐combustion of oil sludge char (OSC) with brown coal (BC) was investigated in a continuous fluidized‐bed combustor. Addition of 10 wt % BC facilitated the combustion of OSC and achieved the expected reduction of NOx emission when air‐staging and selective non‐catalytic reduction were imposed into the freeboard. This exhibited the potential for clean energy recovery from OSC by its co‐combustion with low‐rank fuels rich in volatiles.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
To accomplish the goals of carbon peaking and carbon neutrality in China, coal-fired units are required to implement real-time responses to the requirements of intermittent renewable energy sources. ...Thus, they typically operate under ultra-low loads, resulting in unstable combustion and high NOX emissions. In this study, the combustion stability and NOX emission characteristics of a 300 MWe tangentially fired boiler operated under ultra-low loads of 90 MWe and 60 MWe and with two pulverized coal (PC)-staging strategies at 90 MWe were investigated by performing experiments and numerical simulations. The results indicate that as the boiler load decreases to 60 MWe, the ignition of the PC flow is delayed and the imaginary circle gradually disappears. At 90 MWe, the shorter ignition distance, lower ignition heat, and higher furnace fullness degree during three-mill operation compared to those during two-mill operation suggest that the combustion is more stable with wider PC staging. As the load decreases from 90 MWe to 60 MWe during two-mill operation, the ignition distance and flame boundary temperature change negligibly and the ignition heat decreases, indicating stable combustion at 60 MWe in the case of easily ignitable coal. The upper burner exhibits greater combustion stability than the lower burner under ultra-low loads. Furthermore, the local mean stoichiometric ratio (LMSR) can be employed to predict corrected NOX concentrations at stable ultra-low loads. The vast majority of NOX is fuel NOX, and the average corrected NOX concentration at 90 MWe and 60 MWe is 795 mg/m3 (O2 = 6%), which indicates that the deep-air-staging effect of the low-NOX combustion system is weakened, particularly when the LMSR is higher than 0.92.
•Imaginary circles disappear at ultra-low loads especially at narrower PC-staging.•Combustion stability with wider PC-staging is more ideal under ultra-low loads.•Combustion is stable at 60MWe primarily because of the easily ignitable coal.•The vast majority of NOX is fuel NOX and its quantity is great at ultra-low loads.•Deep-air-staging function is weakened especially with higher LMSR.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Low NOx burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NOx emissions in a low volatile coal fired 330 MWe boiler. Residual swirling flow in ...the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NOx combustion and SCR flow field optimization. Compared with the results before the optimization, the NOx emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330–430 mg/Nm³. The sample standard deviation of the NOx emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100–150 kg/h after optimization.
•Denitrification applied on a tangentially fired boiler burning low volatile coal.•Deep air staging, burner redesign and SCR flow field optimization were combined.•NOx at furnace exit decreased to 330–430 mg/Nm³ burning low volatile coal.•SCR Velocity profiles were smoothed and optimized based on numerical simulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
•The combination of self-preheating and reburning was conducive to NOx reduction.•Uniform preheated fuel could be an excellent fuel close to gas reburning effect.•Optimal reburning fuel fraction of ...preheated fuel ranged from 10.62% to 15.48%.•The residence time in the primary zone and reburning zone was optimally balanced.•Simply air staging was broken through to achieve ultra-low NOx emission and high η.
Under the background of carbon peak and carbon neutrality, cleanandefficientutilization ofcoal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broadprospectsforapplication, nevertheless, previous studies have mainly focused on limiting NOx generation by simply applying air staging method in the combustor, which made further NOx reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOx emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the self-preheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%∼15.48% and 600 mm ∼ 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 ∼ 0.99 s and 0.87 ∼ 1.11 s, respectively. What’s more, under the same reburning parameters, Alxa lignite coal had the largest NOx reduction rate (32.15%), with NOx emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOx reduction rate (5.34%) and the highest NOx emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOx emission (45.75 mg/m3, @6%O2) with the NOx reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
In order to meet the ultralow emission standard of NOx, the combustion system of a 600 MWe tangentially-fired lignite boiler was retrofitted using air-staged combustion technology. The retrofit ...scheme is described in detail. Combustion and NOx emission characteristics of the original and retrofitted boiler were numerically studied and compared. Optimization simulations for retrofitted boiler were carried out under different over-fired air ratios. The moisture content in lignite was specially considered in simulations by simplified coal compositions method. The results show that the ignition of lignite particles is delayed due to the high moisture content. After retrofit, the temperature level in furnace rises owing to the reduction of total excess air coefficient in furnace, and the high temperature region moves upward due to the introduction of separated over-fire air. The NOx emission is reduced by approximately 40% through retrofitting, which proves that the low-NOx retrofit for the lignite-fired boiler is successful. With over-fired air ratio increasing from 15% to 25%, the NOx emission for retrofitted design decreases from 394 mg/Nm3 to 317 mg/Nm3 (at 6% O2). OFA ratio of 20% is the most economical case, and OFA ratio of 25% is the most environmentally friendly case. Taking NOx emission and boiler thermal efficiency into account, the practical operating condition with OFA ratio of 20% is optimal for retrofitted boiler. The results can be beneficial for the retrofit and practical operation of similar lignite-fired boilers.
•A tangentially-fired lignite boiler was retrofitted using air-staged combustion technology•Combustion and NOX emission in the 600MWe tangentially-fired lignite boiler were numerically studied.•The moisture content in lignite was specially considered by a simplified coal compositions method.•After boiler retrofit better NOX emission performance was achieved.•The optimal OFA ratio in retrofitted boiler was obtained by optimization simulation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Co-firing ammonia in coal units is a promising approach for the phasedown of coal power. In this paper, we demonstrate the feasibility of burning ammonia with coal and biomass in a 25- kW down-fired ...furnace with a swirl-stabilized burner. Ammonia is injected from the central tube at thermal ratios ranging from 0 to30% and can be completely burnt out in most co-firing cases. We investigate the NOx emission, unburnt carbon in fly ash, particulate matter formation and ash deposition behaviors when co-firing NH3 with either SH lignite coal or the coal/biomass blend. With a fixed air staging ratio, the NOx emission increases linearly with the NH3 fuel ratio. By increasing the percentage of secondary air, the emitted NOx can be reduced to 300 ppm with an NH3 thermal ratio of 30%. The unburnt carbon is affected by NH3 addition in a complex manner. With a 30% (thermal) NH3 addition, the unburnt carbon increases from 0.4% to 5.6% for the SH coal mainly due to a temperature drop, but decreases from 2.2% to 0.7% for the SH coal/biomass blend. As for the ash-related issues, the addition of NH3 to either coal or coal/biomass blend is found to alleviate both the fouling intensity and the ultrafine particulate matter formation ability. This is a major advantage over biomass combustion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•NOx concentration increases obviously before the burnout air injection at coal reburning cases.•The conversion rate of fuel-N to NOx in the whole reburning process is higher than that at air-staged ...cases.•The release rate of fuel-N from bituminous coal is significantly higher than that from anthracite.•The nitrogen release rate is faster than the carbon consumption rate in the reburning zone.
This paper presents some experimental results on the integral reburning process including all reburning stages in a down-fired furnace. A kind of high volatile bituminous coal (DT coal) and a kind of low volatile anthracite (SX coal) were focused. Natural gas as reburning fuel was also chosen when DT coal used as the main fuel. Reburning fuel fractions and residence times of reburning zone were considered. The deep and middle degree air-staged combustion cases were also conducted. Results show that the NOx reduction efficiency at the cases with natural gas as reburning fuel is significantly higher than that at the cases with two kinds of coal as reburning fuel. At the residence time of 0.82 s and 1.0 s, the conversion ratio of fuel nitrogen to NOx is reduced by 30–70%. At the coal reburning cases, the reduction of NOx and the oxidation of volatile and char to form NOx occur simultaneously in the reburning zone. The NOx concentration values at the reburning stage of DT coal rise faster and reach higher than that of SX coal. The NOx emission values at air-staged combustion cases are lower than that at all reburning cases. Air staging is more likely to inhibit or dissolve the conversion of fuel nitrogen to NOx during the combustion process. Further analysis shows that the release rate of fuel nitrogen from DT coal is significantly higher than that from SX coal, which leads to a faster and higher increase of NO formation at the latter stage of reburning zone.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
