Reduce NOx Emissions Research Articles

Analysis of the influence of hydrogen co-firing on the operation and performance of the gas turbine and combined cycle

The effect of hydrogen co-firing on the performance and operating conditions of gas turbines (GTs) and gas turbine combined cycles (GTCCs) was investigated. Two operating scenarios were applied, and off-design analyses were conducted for three GTs with different turbine inlet temperatures (TITs). In the first scenario, the TIT was kept constant. As the hydrogen co-firing ratio increases, the pressure ratio of GT increased, and the power outputs of both GT and GTCC increased. With 100 % hydrogen in the 1650 °C GT, power output and efficiency improved by 5.36 % and 1.55 %p for GT, and 2.90 % and 0.72 %p for GTCC. In the second scenario, the power output was kept constant. The operating point moves toward lower pressure ratio and TIT regimes, and the efficiency of both GT and GTCC increased. With 100 % hydrogen in the 1650 °C GT, TIT decreased by 50.3K, and efficiency increased by 1.42 %p for GT, and 24.9K and 0.42 %p for GTCC. In both scenarios, the higher the TIT, the impact of hydrogen co-firing was more pronounced. It is expected that the second scenario might reduce NOx emissions while still increasing system efficiency in comparison to the NG fired case by operating the GT at a lower TIT and equivalence ratio.

Effect of fuel injection pressure on the performances of a CI engine using water-emulsified diesel (WED) as a fuel

BackgroundThe choice of energy sources is essential for sustainable development to combat different environmental issues caused by the consumption of fossil fuels. Though diesel engines are considered more efficient and reliable than other internal combustion engines, they emit different harmful pollutants which are detrimental to human health and the environment. Researchers are trying to find suitable alternative fuels for diesel engines with lower pollutant emissions and without much compromise in the efficiency of the engine. In this regard, water-emulsified diesel (WED) may be considered to be one of the most suitable alternative fuels. It is expected that the entire world will use electric vehicles in the long term. However, the complete replacement of IC engines in the near future is not feasible. In fact, different European countries have targeted to ban the use of diesel engine cars before the middle of the twenty-first century. Prior to that date, hybrid vehicles will be more popular and diesel engines will continue to play an important role. Hence, research involving improvements in diesel-operated IC engines is still relevant.MethodsAn experimental investigation was carried out using WED containing 10% water by volume as a fuel in a diesel engine at four different fuel injection pressures. The WED was prepared using an ultrasonicator.ResultsWith the increase of injection pressure, peak net heat release rate and in-cylinder pressure are found to have increased. Brake thermal efficiency is also found to have improved at higher injection pressure. The maximum efficiency was recorded when a WED at 210 bar of injection pressure is used, and it is about 3.3% higher than the maximum efficiency achieved when using normal diesel at the same pressure of fuel injection. At a higher load, neat brake-specific fuel consumption is found to be less compared to neat diesel, when only the amount of diesel contained in the emulsion as a fuel is considered. Maximum reduction in both NOx and smoke emission by using WED is recorded at 210 bar, and the average reductions are determined to be 32.6% and 51.9%, respectively.ConclusionsWED can be used as an alternative fuel for existing diesel engines without any retrofitting and with significant reduction in the emissions of pollutants compared to normal diesel fuel. It can also be concluded that at higher injection pressure, the combustion, performance and emission characteristics of compression ignition engines are improved when using emulsified diesel.

Assessing the performance of the transport sector within the global supply chain context: Decomposition of energy and environmental productivity

With globalization and industrialization, the supply chain of the transport sector has become increasingly complex and environmentally polluting. Consequently, the multidimensional and transnational nature of this sector presents numerous challenges in performance estimation, hindering previous studies. To address these issues, we propose an input-output modeling approach based on the Multi-region input-output model (MRIO) and Bounded-adjusted Measure (BAM). This approach allows for a comprehensive assessment of the sector's performance across various dimensions within a global context. Building upon this approach, we construct two indicators: the static transportation sustainability inefficiency (STSI) and the transportation sustainability productivity indicator (TSPI). Moreover, we introduce a systematic decomposition framework, encompassing both horizontal and vertical aspects, to analyze and break down the STSI and TSPI. Empirically, we apply this framework to study the sustainability performance of the global transport sector, encompassing 43 economies, over the period of 2005–2014. The results indicate that within transportation-related Global Supply Chains (GSCs), there is a potential for approximately 5% reduction in energy use, 7% reduction in CO2 emissions, 8% reduction in SO2 emissions, and 8% reduction in NOx emissions over the course of the decade. On average, a 1.0% increase in TSPI was observed, primarily driven by technological progress. From a global perspective, the sustainable development of the transport sector relies more on less developed economies. These findings point to the necessity of subsidizing these economies, which provide spillover effects through global supply chain.

NOx emission reduction of coal‐fired power plants through data‐driven model and particle swarm optimization

AbstractSeveral studies have aimed to predict and control carbon emissions from coal‐fired power plants. However, the highly complex combustion mechanisms in coal‐fired power plant boilers pose a significant challenge in direct modeling and optimization. To tackle this challenge, this study introduced a data‐driven approach along with model‐based process optimization to mitigate NOx emissions from coal‐fired power plants. The process involved collecting a 5‐month operational dataset containing 67 controllable parameters from a 500 MW coal‐fired power plant. Steady‐state data was isolated from the load output using a moving average method, followed by the application of an isolation forest algorithm to detect and remove anomalies. Correlation analysis was then used to evaluate parameter relationships and eliminate redundant ones. Subsequently, a NOx prediction model was developed, combining an extra tree regressor data‐driven prediction model with particle swarm optimization to optimize the most influential controllable parameters for reducing NOx emissions. Testing the proposed model across four different target loads consistently resulted in a reduction of over 20% in NOx emissions by optimizing boiler combustion parameters, representing a significant achievement in optimizing coal‐fired combustion.

Charge Shielding Effect of Sodium Ions in Improving The Hydrophobicity and Performance of Co/Na‐SSZ‐13 Zeolite for Passive NOx Adsorber

AbstractWith increasingly stringent regulations, the reduction of NOx emissions during vehicle cold start is a major challenge. Pd‐modified zeolites are considered as the most promising passive NOx adsorber (PNA) for cold start NOx control. Nevertheless, the scarcity and the high cost of Pd limit its practical application. Herein, a non‐precious metal modified Co/Na‐SSZ‐13 zeolite for low‐temperature NOx adsorption is reported. This one‐pot synthesized Co/Na‐SSZ‐13 exhibits an extraordinary NOx storage capacity (212 µmol gcat−1) under humid conditions (3% H2O v/v), which is more than double that of conventional Co or Pd‐modified SSZ‐13. This is attributed to the absence of the inert cobalt phyllosilicate commonly found in conventional Co‐SSZ‐13, as well as the highly dispersed Co and Na ions as the effective NOx adsorption sites in Co/Na‐SSZ‐13. Moreover, the presence of Na ions shields the negative charge generated by the Al center and weakens the local electric field strength of the Al and Co centers. This lowers the H2O adsorption energy and improves the zeolite hydrophobicity, which enhances the NO storage capacity of the Co/Na‐SSZ‐13 under humid conditions. This work highlights the Co/Na‐SSZ‐13, synthesize via a simple and high‐efficiency method, as a promising substitute for noble metal PNA materials.

Simulation Study on the Combustion and Emissions of a Diesel Engine with Different Oxygenated Blended Fuels

Aiming to achieve the goal of efficient and clean combustion in internal combustion engines, simulations are used to change the physicochemical properties and molecular configuration of fuels by adding oxygenated fuels such as alcohols, esters, ethers, etc., so as to achieve the purpose of improving combustion and reducing emissions. In this paper, blends of oxygenated fuels, including n-butanol, DME, DMC, and diesel fuel with different oxygen-containing functional groups, were selected for simulation to reveal the chemical mechanisms of fuel oxygen on combustion and pollutant generation in the combustion system and to deeply explore the mechanism and influence law of the different forms of oxygen bonding on the generation and oxidation of carbon smoke. At the same fuel oxygen content, the differences in the fuel physicochemical properties and reaction paths resulted in different effects of the different oxygenated fuels on the in-cylinder oxidative activity and different inhibition abilities of carbon smoke precursors. Compared with pure diesel, n-butanol, and DME, which promoted OH generation, DMC inhibited OH generation, so the oxidation activity of diesel/n-butanol was the highest, and that of diesel/DMC was the lowest; meanwhile, the two O atoms in the DMC molecule formed CO2 with one C atom, which reduced the utilization efficiency of the O atoms, whereas each O atom in the n-butanol and DME fuels took away one C atom, so the utilization efficiency of O atoms was higher. The individual oxygenated fuels themselves had different abilities to contribute to carbon smoke precursors, and the above combined factors led to reductions of 8.7%, 32.6%, and 85.4% in soot emissions from the addition of DMC, DME, and n-butanol compared to pure diesel fuel, respectively, at the same oxygen content. At a medium load, the addition of n-butanol, DME, and DMC reduced NOx emissions by 0.5%, 1.7%, and 3.3%, respectively. Thus, it is shown that DMC has a more significant effect on NOx emission reduction.

Influence of Variable Swirl on Emissions in a Non-Premixed Fuel-Flexible Burner at Elevated Ambient Conditions

Abstract As alternative fuels are designated for future energy applications, flexible combustor designs require considerable development to ensure stable operation with reduced NOx emissions. A nonpremixed variable swirl burner was used to experimentally appraise changes in NO production pathways, with CH4 NH3 and H2 flames, alongside intermediate fuel blends. Maintaining an equivalent thermal power and flame temperature between fuels, preheated reactants (500 K) were supplied to the burner, with parametric changes made to pressure (1–6 bara) and swirl number (0.8–2.0). NO production was characterized, alongside variations in flame structure and topology, with a correlation demonstrated for exhaust emissions. NO production was shown to be sensitive to combustor pressure, providing an expected increase for CH4 and H2 flames. Emission profiles from both NH3 and H2 flames are shown to be significantly augmented by a change in swirl number. As NH3 fractions were increased in the H2 blend, a decaying trend in NO emissions was observed with an increase in pressure, and as a function of mixture ratio. However, this behavior was markedly augmented by a change in swirl number and suggests that further reductions may be possible at increased pressure. At the low swirl/high pressure condition, the NH3/H2 blend outperformed pure H2, providing lower NO concentrations. Emissions data were normalized using the traditional dry/O2 correction, alongside mass scaled by thermal power, with a comparison provided. The corresponding differences in emission formation pathways were investigated, alongside high-speed OH* chemiluminescence to further elucidate findings.

Emissions from the Construction Sector in the United Kingdom

The UK national atmospheric emissions inventory estimates of construction industry emissions use a top-down approach, based on fuel consumption and employment. It estimates that the sector is the 2nd largest emitter of PM2.5 (14%) and 4th largest emitter of NOX (7%). In this study, we have adopted a bottom-up approach to assess emissions of NOX from the sector and show that emissions are 39% higher than the existing estimates. By developing a novel fleet turnover model to predict the population and emission standard of construction machinery up to 2025, we demonstrate a significant shift in the quantity and types of machines used. The overall uncertainty of the model was calculated to be 55%. Applying the estimated uncertainties to the model, in 2018, the non-road mobile machinery fleet in the UK emitted 36.6 ± 10.0 kilo-tonnes of NOX, whilst the NAEI estimated 33.2 kilo-tonnes for the same sector. For the subsequent years 2019 and 2020, the NAEI estimate was within the model’s uncertainty prediction—28.0 kilo-tonnes compared with 32.7 ± 8.9 kilo-tonnes for 2019 and 23.2 kilo-tonnes compared with 29.5 ± 8.1 kilo-tonnes for 2020. Overall, the size of the non-road mobile machinery fleet in the UK is predicted to reduce by 4% in 2025 compared to 2018. Furthermore, the introduction of Stages IV and V emission regulations for new machines will lead to a 58% reduction in fleet NOX emissions over the same period. These emission regulations are targeted at the larger, more polluting machines, with smaller machines not required to meet tighter emissions standards under Stage V. As a result, mini-excavators are the most common machines and consequently become the dominant source of NOX emissions from the fleet, contributing 55% in 2025. Therefore, tighter emissions regulations, or the uptake of battery power in the form of electrification, for these small machines would yield significant emissions reductions.Graphical

Operating parameters analysis of a nitric acid plant to increase production and reduce NOx gases emission

In this work the influence of some operating parameters of a medium pressure nitric acid plant producing 54,000 t/year was studied in order to evaluate its influence over the absorption column efficiency. The target is to increase nitric acid production and reduce NOx emissions. The nitric acid plant was simulated using ProSimPlus HNO3. The parameters considered in the analyses were: secondary air molar flow rate; absorption column operating pressure; cooling water temperature and absorption water molar flow rate. Parameters were evaluated individually and the best results were combined in a multi-parameter analysis evaluating different optimized scenarios, including the possibility of increasing the amount of ammonia injected in the system and the addition of a plug flow reactor (PFR), which is a new approach to improve NO oxidation. Considering a base case, the best scenario obtained was able to reduce NOx emissions in 55 % while increasing nitric acid production in 18 %, using the following set of parameters: 20 kmol.h − 1 of additional ammonia; a 40 m3 PFR; cooling water at 5 °C; 172 kmol.h − 1 of absorption water and 345 kmol.h − 1 of secondary air. The results obtained in this work contribute to provide practical insights for optimum absorption stage operation in a real nitric acid plant.

Reducing NOx emission from palm biodiesel/diesel blends in CI engine: A comparative study of cetane improvement techniques through hydrogenation and fuel additives

In this study, the trans-esterification process prepared palm oil biodiesel and 20% biodiesel blended with diesel (PB20) by volume as test fuel. Unsaturated fatty acids are majorly influenced by biodiesel cetane number. This work examines two-fuel reformulation methods of fuel hydrogenation and addition of fuel additive di-tert-butyl peroxide (DTBP) to enhance the engine characteristics of a PB20 blend while maintaining emission control. A reactor (autoclave) was utilized for hydrogenating the palm biodiesel and examining the change in fuel composition using gas chromatography. DTBP is selected as the cetane enhancer and combined with PB20 at a 2000 ppm concentration. Tamson FBT equipment was utilized to evaluate the test fuel's filterability. The filterability, engine characteristics, and emissions were investigated for diesel (D0), PB20, HPB20, and PB20 + DTBP fuel blends in the compression ignition test engine. The FBT results reveal that PB20 and HPB20 have better filtration quality, which aligns with the standard requirements (ASTM D2068-14). An improved NOx (10.2%) and brake thermal efficiency (6.7%) are seen at engine full loads when using modified B20 fuels. The hydrocarbon, carbon monoxide, and smoke emissions decreased by 8.3%, 6%, and 10.14% compared to diesel fuel. Hence, partial hydrogenation has been a better approach to improving biodiesel trade-off features than DTBP addition.

Ozone at Mace Head, Ireland from 1987 to 2021: Declining baselines, phase-out of European regional pollution, COVID-19 impacts

Just under three hundred thousand hourly O3 observations from the Mace Head, Ireland atmospheric monitoring station have been assembled into a complete dataset covering the thirty five-year period from April 1, 1987 through to May 31, 2022. Of these, seventy thousand hourly observations were assigned to baseline air masses over the 422 months in the study. Annual mean baseline mixing ratios rose from 34 ppb in 1988 to a peak of 42 ppb in 1999 before declining to 39 ppb in 2021. Monthly mean baseline mixing ratios reached a peak of 53 ppb in April 1999. Baseline O3 mixing ratios exhibit a marked seasonal cycle, with maxima in April and minima in August. A detailed examination of the differences between the baseline and complete monthly mean O3 mixing ratios revealed a set of monthly differences with some striking long-term changes. Wintertime differences were dominated by a series of O3 depletion events in which, during the early years of the study, reduced ozone to near zero in long-range transport events. European NOx emission reductions have reduced significantly the number and severity of these wintertime O3 depletion events. Summertime differences were dominated by a series of regional photochemical episodes. In the early years of the record, the regional photochemical episodes were intense enough to raise the monthly means in the complete record above the baseline means. European volatile organic compound (VOC) and NOx precursor emission reductions have dramatically reduced the number and intensity of these events. Episodic peak O3 levels have also fallen steadily as a result of concerted, European action on regional VOC and NOx emissions. Subsets of the baseline and complete ozone datasets between 2017 and 2022 were scrutinised for possible COVID-19 impacts. Baseline ozone levels were lower than expected during 2020 and 2021 but the statistical significance of these impacts is difficult to judge, and reduced stratosphere-troposphere exchange rather than COVID-19 emission reductions may be the cause.

Study of the influence of adding Al2O3 nanoparticles to biodiesel on the performance and emissions characteristics of a diesel engine

The use of biodiesel in compression ignition (CI) engines has great potential to reduce emissions and the dependence on fossil fuels. However, the complete adoption of biodiesel in CI engines is limited by several drawbacks. A promising solution to these problems is the addition of nanoparticles to biodiesel or diesel-biodiesel blends. Hence, this paper studies the impact of adding aluminum oxide (Al2O3) nanoparticles on the performance and emission characteristics of a diesel engine running on biodiesel and a mixture of diesel and biodiesel. Al2O3 nanoparticles were added at concentrations of 50, 100 and 150 ppm to biodiesel (B100) and a mixture of 50 % biodiesel and 50 % commercial diesel (B50). The results indicated an increase in fuel conversion efficiency and a reduction in specific fuel consumption. The highest fuel conversion efficiency was 26.5 % for B50 with 100 ppm of Al2O3, indicating an improvement of around 28.6 % compared to diesel fuel (B0). In general, CO emissions were reduced with the addition of nanoparticles, with a maximum reduction of 42.8 % for B100 with 50 ppm Al2O3 compared to B0. The highest reduction in NOX emissions was 30.3 % for B50 with 100 ppm Al2O3 compared to pure diesel B0.

The mechanism of NOx removal in the sintering process based on source reduction of carbon emissions.

This study systematically investigates the mechanism of NOx emissions during the sintering process, with a focus on the utilization of biochar as an auxiliary fuel to replace a portion of the coke traditionally used in iron ore sintering. The research involved the simulation of sintering raw material ratios using iron ore, biochar, and coke powder. Substitution levels of biochar for coke were set at 0%, 20%, 40%, 50%, 60%, 80%, and 100%. NOx emissions during the sintering process were monitored using a sintering flue gas detection system. Simultaneously, a comprehensive analysis of the sintered ore was conducted with the aim of producing samples that meet sintered ore requirements while reducing NOx emissions. Experimental results revealed that when biomass charcoal substitution for coke reached 50%, the lowest NO emissions were observed during the sintering process, with a reduction of over 90% in accumulated NO emissions in the exhaust gas. In this process, due to the participation of biochar, CO2 emissions were reduced by approximately 50% compared to traditional sintering processes. The study also analyzed the physicochemical properties of the sintered ore using methods such as XRD, Raman, FTIR, and Vickers hardness testing. The results indicated that the hardness fluctuated within the range of 610 to 710N for sintered products with different levels of biochar substitution, and there were minimal changes in Fe element content and crystal phase transformations.

Pure ammonia flames with high thermal intensities through fuel and air staging under extreme rich-to-lean conditions

Ammonia combustion has gained significant attention due to its high hydrogen content and zero carbon emissions. It poses a challenge for stabilization due to their low energy content and limited flammability range, with the added concern of fuel NOx emissions. In the current study, a novel burner design equipped with four series of reactors is proposed to achieve stable pure ammonia-air flames with reduced NOx emissions. The impact of thermal intensity (∼0.7 MW/m3 to ∼4 MW/m3), number of stages, equivalence ratio (0.5–1.2), and fuel staging on flame stabilization and emissions were investigated in the proposed burner. Comprehensive emissions analysis is performed at various burner levels. Numerical simulations incorporating Large Eddy Simulation (LES) modeling are employed to enhance understanding of the impact of thermal intensity and equivalence ratios on ammonia dissociation, mixedness, and NO emissions. The results indicated that the present burner design improved reactant mixing, and flame stability, reduced NH3 emissions (∼ 0 PPM), and lowered NOx levels in non-premixed ammonia-air flames. The computational and experimental results demonstrated that the implementation of fuel staging is crucial for reducing NOx emissions for the flames with lean global equivalence ratios. Lower NO emissions were identified at a global equivalence ratio of 1.1 for all the considered flames in the range of 0.5–1.2. In the four-stage rich-lean combustion strategy employed in this study; it was observed that higher thermal intensity (4 MW/m3) with fuel staging resulted in lower NOx emissions per kW of energy input compared to lower thermal intensities 0.7 MW/m3. This finding underscores the significance of achieving uniform mixtures and ensuring local flame in rich conditions for achieving low NOx emissions in ammonia combustion. Exhaust gas analysis is conducted at three stages of the burner to enhance the understanding of emissions at various levels of the burner. The proposed combustor design has achieved a substantial reduction in NOx to ∼1 PPM/kW and ∼2.8 PPM/kW with and without fuel staging, respectively. This impressive outcome is attributed to the controlled ammonia consumption facilitated by uniform mixing generated through the use of tangential air inlets.

Experimental investigation of low temperature combustion in a diesel engine depending on injection advance and injection pressure

In this study, the performance parameters and emissions of a pre-mixed charge compression ignition were investigated under different injection pressures and injection advances. After the peak engine power was reached, reasonable decreases occurred in brake mean effective pressure at certain injection advances with the increase of injection advance, and dramatic decreases observed when interval was so exceeded. In addition mean indicated pressure and peak in-cylinder pressure were investigated. Considering the emissions, dramatic increases were observed in CO and total hydrocarbon, depending on the increase in the low temperature combustion regime. The NOx started a rapid downward trend after a certain injection advance value in the experimental region, but this effect did not occur at the de?sired level for specific NOx. It was observed that the NO2 to NOx ratio increased as the pre-mixed charge compression ignition became dominant and NO2 production increased among the total NOx. In the operating region where the low temperature combustion regime was dominant, the targeted reduction in NOx and particulate matter emissions was observed, but the desired reduction in specific emissions did not occur. In the low temperature combustion region, the combustion process was prolonged, initially reasonable changes occurred at performance parameters, but unacceptable results were observed at high injection pressures with excessive injection advances.

Effects of the secondary air on the combustion characteristics of turbulent premixed CH4/NH3/air flames in a two-stage swirl combustor

This study experimentally investigates the effects of secondary air injection on the flame structure and CO/NO emission characteristics of turbulent premixed CH4/NH3/air flames in a two-stage swirl combustor. The equivalence ratio (ϕp) and velocity (Up) of the primary fuel/air jet and the injection location (Ls) and velocity (Us) of the secondary air jet are varied. The location of the secondary air injection of 30 and 250 mm are adopted to investigate two interaction cases in two-stage combustion (TSC): 1) a strong interaction where the secondary air is directly injected into the primary premixed flame and strongly affects the flame, and 2) a weak interaction where the secondary air is injected after the primary reaction is completed. A single-stage combustion (SSC) is also tested for comparison. It is found from averaged OH-PLIF images that the strong interaction cases of TSC with ϕp > 1 can produce a significant amount of NO emissions due to the direct interaction between the primary flame and the secondary air, while the weak interaction cases can produce an appreciable amount of CO emissions due to the incomplete combustion of the secondary flames. This result is further confirmed by CO/NO measurements that the strong interaction cases produce higher NO emissions than the weak interaction cases, while the CO emissions of the weak interaction cases become significant and peak at ϕp = 1.1 ∼ 1.2. Based on the OH-PLIF images and CO/NO emission characteristics of TSC, the optimal conditions of the primary and secondary jets are proposed to ensure the reduction of NOx emissions with low level of CO emissions.

APPLICATION OF DIESEL-RK SIMULATION TOOL FOR REDUCING NOX EMISSION FROM BIODIESEL BLEND FUELS AT RETARDED INJECTION CONDITION

In renewable energy resources, although biodiesels have occupied the top place as an alternative for compression ignition engines, their high NO<sub>x</sub> discharge causes concern. Retarded fuel injection is a probable solution to reduce NO<sub>x</sub> emission. In the present work, tests are conducted with corn seed methyl ester (CSME) blend at standard and retarded fuel injection timings. Improvement in brake thermal efficiency and reduction in NO<sub>x</sub> emissions are observed due to the retardation of fuel injection timing. DIESEL-RK engine simulation software is used as a potential tool to simulate retardation conditions, and simulation results are compared with experimental values. It is seen that along with the performance and combustion parameters, the simulated NO<sub>x</sub> emission results are in good agreement with experimental values. Hence, the modeling used in the DIESEL-RK software captures the experimental observations well.

Effects of reactants stratification and pre-heating on the stabilization and emissions of partially cracked ammonia swirl flames

Ammonia is an easy solution for the transportation and storage of hydrogen. To achieve combustion properties similar to those of methane, ammonia can be partially cracked on site to introduce hydrogen and nitrogen in the fuel mixture. In this work, an atmospheric pressure dual-swirl ammonia-hydrogen burner is used to study different configurations of stratified flames of ammonia cracked at 28 %. First, flame stabilization is evaluated in terms of the overall equivalence ratio and the distribution of air between the hydrogen and ammonia streams. This is done for both cases where either hydrogen or ammonia occupies the central part of the burner or its periphery. The configuration of the burner is adjusted in such a way that several stratification levels are scrutinized, depending on where the two streams meet. Seven types of flames are identified and described. A stability map is measured. The results show that the configuration with ammonia flowing centrally and hydrogen occupying the periphery enhances stability. Second, measurements of NOx, N2O, unburnt ammonia, and unburnt hydrogen in the exhaust gases are performed. Full stratification reduces NOx emissions, but both lean overall equivalence ratio and lean ammonia equivalence ratio increase N2O emissions. The flame with ammonia in the center and hydrogen at the periphery with an overall equivalence ratio of 0.55 gives the best results in terms of stability and low pollutant emissions. This condition is further investigated by changing the reactants temperature. The reactants preheating is beneficial for N2O emissions but comes with a strong NOx penalty.

Experimental study on municipal sludge/coal co-combustion preheated by self-preheating burner: Self-preheating two-stage combustion and NOx emission characteristics

To achieve efficient and low-pollution sludge treatment, this study explored the first-time application of self-preheating combustion technology in sludge/coal co-combustion, and subsequently investigated the influences of sludge blending ratio (BR) and tertiary air types on self-preheating two-stage combustion and NOx emission characteristics in a 30 kW self-preheating combustion system with a novel two-stage down-fired combustor (DFC). This system was well adaptable for fuels, and still ran steadily even if BR was as high as 50 %. During preheating, properly increasing BR improved carbon microcrystalline structure of preheated carbon-based fuel and increased its specific surface area, but its carbon microcrystalline structure was gradually deteriorated at BR>20 %. Fuel properties of preheated coal gas were deteriorated with increasing BR. During combustion, combustion efficiency (η) increased first and then decreased with increasing BR, while NOx emission increased. For tertiary air nozzle located at top of burnout region, the structures of center symmetry and ring hedge had less effect on η and NOx emission, both of which remained at high levels, exceeding 98.5 % and 160 mg/m3. Notably, properly shifting injection position down reduced NOx emission significantly, albeit at the expense of reduction in η. Excessively low injection position had less effect on further NOx emissdddction.

A multi-indicator prediction method for NOx emission concentration and ammonia escape value for cement calciner system

It is particularly important to accurately predict NOx emission concentration in cement production. As the cement industry is a process industry, there are many chemical reactions, coupling of front and back processes, and large fluctuations in production, resulting in time-delayed denitration data, strong coupling, and uncertainty, which makes it difficult to adequately extract the characteristics of the denitration data to achieve accurate prediction of NOx concentration. At the same time, excessive ammonia is used in production to reduce NOx concentration, resulting in increased ammonia escape and secondary hazards to the environment, therefore it is necessary to perform accurate multi-step prediction of NOx concentration and ammonia escape. To address these issues, this paper presented a new multicriteria deep learning hybrid model MI-ITBA. The model is constructed by connecting an improved causal dilated temporal convolutional network (ITCN) with bidirectional gated recurrent units (BiGRU) and a special attention mechanism, which enhances the ability to extract features from denitration sequence, using the attention mechanism to weigh the importance of different time steps and highlight the influence of key features on the prediction results. In addition, the time series (TS) of denitration containing time-delay information is designed in the input of the model to minimize the influence of time delay. Dynamic information support for denitration control was provided by multi-step prediction of NOx concentration at seven moments and ammonia escape value at three moments to retain the dynamics of the data. Compared with TCN, BiGRU, and TCN-BiGRU, MI-ITBA has a high prediction accuracy, which can provide an effective guide to realizing NOx emission reduction and accurate ammonia injection.