Low Nitrogen Combustion Research Articles

Effect of burner structural parameters on combustion characteristics and NOx emission of natural gas

The low-nitrogen combustion of natural gas has always been a crucial topic in environmental protection. Currently, small and medium-sized industries use straight-through pipelines as their burner nozzles. This design results in poor heat diffusion capacity after mixed combustion and a long time of temperature diffusion, leading to low combustion efficiency and high NOx emissions. To address this issue, a new type of natural gas low-nitrogen burner with a multi-port diffusion nozzle was developed. The burner’s structure was optimized through a combined approach of experiment and numerical simulation. The optimal structural parameters for the burner are a 40° swirl angle and 8 swirl blades, as indicated by the numerical simulation research results. The designed multi-port diffusion nozzle is matched with the appropriate swirl angle and number of blades to promote natural gas diffusion, forming an annular space region flames and a stable flame shape with a height of 0.64 m. After optimization, the average concentration of NOx at the outlet of the combustion chamber decreased from 61.5 ppm to 20.81 ppm. A natural gas low-nitrogen combustion experimental system was designed and constructed based on simulation results. The experimental results were analyzed in terms of flame structure characteristics, temperature distribution, and NOx emissions. The results indicate that the trend in temperature change is consistent with the simulation process. The NOx concentration at the outlet of the combustion chamber was measured by the flue gas analyzer to be 34.1 ppm, which was 5.3 ppm lower than the NOx concentration calculated by numerical simulation. The new burner exhibited better flame stability and a 12.6 % reduction in NOx emissions compared with a traditional straight-through pipeline burner of the same size. The designed natural gas low-nitrogen burner appears to be a suitable device for reducing NOx emissions in small and medium-sized industries.

Experimental Study on Flame Chemical Composition of Coal and Ammonia Gas-Solid Jet in Flat Flame Burner.

Ammonia as a fuel to partially or completely replace fossil fuels is one of the effective ways to reduce carbon dioxide, and the research on ammonia coal cocombustion is of great significance. The combustion characteristics of ammonia are very different from those of pulverized coal, resulting in the ignition and emission characteristics of ammonia and pulverized coal gas flow that is different from traditional pulverized coal flame. In this paper, the effect of pulverized coal concentration in coal and ammonia mixed combustion jet on the ignition distance and gas-phase components at different positions of the jet flame were studied experimentally on the flat flame burner, and the conditions of ignition and ignition stability of coal and ammonia gas-solid fuel were expounded. It was found that the ammonia mixed with pulverized coal changed the temperature field of the flat flame burner and therefore the ignition characteristics of the jet were changed. The ignition delay time at the same jet speed was positively correlated with the pulverized coal concentration, but when the pulverized coal concentration continued to decrease, the influence on the ignition delay time gradually became smaller. The composition of coal ammonia gas-solid fuel changed the heat transfer path and share during combustion, and finally, the flame temperature was negatively correlated with the concentration of pulverized coal. Therefore, the reduction of the pulverized coal concentration was conducive to the stable combustion of coal ammonia mixed fuel. When HAB = 100 mm, the conversion rate of fuel N to NOx per unit mass of coal ammonia mixture increased with the increase of pulverized coal concentration. The NOx production amount first increased and then decreased with the increase of pulverized coal concentration, and the amount of N2O and NO2 decreased rapidly with the increase of HAB. The proportion of NOx in NO exceeded 94%, which was conducive to achieving low nitrogen combustion of coal and ammonia gas-solid fuel. In general, the O2 concentration in the ammonia coal jet flame decreased, the flue gas temperature, and NOx and CO generation increased after mixing ammonia, and the optimal pulverized coal concentration in this experiment was 0.41 kgc/kga (mass ratio of pulverized coal to the sum of N2 and NH3).

Research: influence of air classification ratio on low nitrogen performance of natural gas burner

ABSTRACT An innovative low-nitrogen natural gas burner was developed, leveraging air-staged combustion as the primary mechanism, supplemented by swirl combustion and flue gas recirculation technology. This design enables adaptation to a multitude of combustion conditions through the adjustment of the secondary air ratio. A prototype burner with a power output of 60 kW was constructed for experimental study. The velocity field, gas concentration field, temperature field, and NO x concentration within the combustion zone were analyzed under different load, and the impact of the secondary air ratio on the burner’s low-nitrogen combustion performance was explored. Experimental results showed that the burner can maintain stable combustion and low NO x emissions and had good load adaptability. The introduction of secondary air resulted in a “W”-shaped distribution characteristic within the combustion zone’s velocity and concentration fields, and effectively suppressed the formation of high-temperature zones, thereby reducing the generation of thermal NO x . A secondary air ratio of 27% significantly enhanced the gas atmosphere within the combustion zone, leading to more uniform gas distribution and improved mixing of the gas mixture. Furthermore, it had a better low-nitrogen performance. With an increase in burner load, the NO x concentration within the combustion zone also increased, reaching a peak value of 31 mg·m−3 at full-load, which still complied with low-nitrogen emission requirements.

Effect of calcium-based additives on NO release of coals under different combustion modes

The nitrogen oxides and sulfur oxides released from coal combustion pose serious environmental hazards, but there exists a contradiction between low-nitrogen combustion and efficient desulfurization, necessitating a deeper understanding of the impact of calcium-based desulfurization agents on NOx release. Based on one-stage and two-stage horizontal furnaces, the effects of temperature, coal types and CaO on the release of NO were explored under the coupled combustion and the separated combustion. The experimental results indicate that: under both conditions, the NO emissions of coals decrease with the increase of temperature. The reaction time of separated combustion is shorter than that of coupled combustion. Under the coupled combustion, the order of NO emissions is: anthracite (AC) > bituminous coal (BC) > lignite (LC) > high chlorine coal (HC), and the order are mainly affected by the content of N in coal. At 800 °C, the fuel-N conversion rates of BC, AC, LC, and HC are all the highest, and the rates are 20.52 %, 25.93 %, 14.90 %, and 15.34 %, respectively. As the temperature rises, both volatile-N and char-N emissions show a downward trend. The NO emissions in the separated combustion are greater and the fuel-N conversion rates of BC, AC, LC, and HC are 44.11 %, 47.31 %, 40.44 % and 32.21 %, respectively. The reduction reaction between char and NO plays a crucial role. After the addition of CaO, there is a significant increase in NO release, indicating that CaO has a catalytic effect on the release of volatile-N and char-N. Under the separated combustion, the impact of CaO on NO emissions is relatively minor, and sometimes it leads to a reduction in NO emission. The role of CaO on the NO release is multifaceted.

Effect of ammonia on N migration and transformation characteristics during coal pyrolysis: Quantum chemical calculations and pyrolysis experiments

The co-firing of the non-carbon fuel, ammonia, with pulverized coal, is an effective way to reduce CO2 emissions in thermal power plants. However, the high nitrogen content of ammonia increases the risk of high NOx emissions during the co-firing process. To achieve low nitrogen combustion of ammonia-coal co-firing, it is necessary to study the impact of ammonia on the N migration and transformation characteristics, during the coal pyrolysis and combustion processes. In this work, the effects of ammonia on the release of N-containing products, during coal pyrolysis, were studied by quantum chemistry calculations and pyrolysis experiments. The theoretical calculation results showed that the mixing of hydrogen-rich ammonia fuel promoted the generation of HCN during coal pyrolysis and increased the energy consumption of HCN generation. Additionally, ammonia-N could be embedded into the coal char structure and exist in the form of N-6. The experimental results indicated that with the temperature increasing, the N content of the coal char and the pyridinic-N increased under the condition of ammonia-coal co-pyrolysis, confirming the microscopic mechanism of ammonia-N embedding into the coal char structure, as indicated by the theoretical calculations. Our work reveals the molecular paths of N migration and transformation and elaborates on the interaction mechanism of ammonia-N and coal-N during the ammonia-coal co-pyrolysis, which has a certain promoting effect on the development of ammonia-coal co-firing mechanism.

Influences of ammonia co-firing on the NO generation characteristics of pulverized coal during different combustion stages

As an ideal carbon-free fuel, ammonia is a feasible choice to replace part of coal fuel to reduce carbon emissions from coal-fired power generation. This work used a constant temperature fixed bed experimental platform to study the effects of ammonia mixing on NO formation characteristics of pulverized coal. It was found that the peak time of NO precipitation decreases with the temperature increasing in ammonia-coal coupled combustion, and the increase of ammonia blending ratio promotes the NO formation. In the ammonia-coupled coal char combustion, NO production increases with the increase of ammonia co-firing ratio under different temperature conditions. Compared with coupled combustion, separation combustion can effectively reduced the NO formation, which was not conducive to the conversion of fuel-N to NO, and the ammonia mixing ratio and temperature have a significant impact on the range of NO generation reduction in separation combustion. At the temperature of 1300 °C and 1400 °C, the nitrogen conversion ratio of 0%, 4% and 20% ammonia co-firing ration was reduced by 19.64%, 9.23%, 0.22% and 13.35%, 1.86% and 0.15%, respectively, compared with that of coupled combustion. The results can provide theoretical support for the development of low nitrogen combustion technology of ammonia-coal co-combustion.

Experiment and Numerical Simulation Study of Low-Nitrogen Combustion Technology Inside Small Gas Boiler

Abstract This paper studies different experimental conditions for a 25t/h industrial boiler fueled with nature gas. In the meanwhile, numerical simulation is carried out using the commercial software of fluent. The different excess air coefficients of 1.05, 1.1, 1.15, 1.2, and 1.25 are studied. The different flue gas circulation rates of 5%, 10%, 15%, and 20% are studied compared with that rate of 0. The results show that the maximum temperature of the furnace and NOx emission concentration at the outlet increase first and then decrease with increasing excess air coefficient when flue gas circulation rate is 0, and the peak value of temperature and NOx emission concentration reaches 2071.93 K and 65.21 mg/m3 when excess air coefficient is 1.15, respectively. With increasing flue gas circulation rate, the average temperature of the furnace and the concentration of NOx at the outlet decreased, and the concentration of NOx decreased from 65.21 mg/m3 to 25 mg/m3. The higher the flue gas circulation, the smaller the high-temperature area of the furnace and the lower concentration of O2. However, excessively higher flue gas circulation rate and excess air coefficient can lead to incomplete combustion and lower coefficient. Hence, for optimizing the combustion conditions, the excess air coefficient and the flue gas circulation rate should be within an appropriate range.

Significantly mitigating PM2.5 pollution level via reduction of NOx emission during wintertime

Despite considerable decreases in fine particulate matter (PM2.5) in Chinese megacities over the past decade, many second- and third-tier cities that distribute abundant industrial enterprises are still facing great challenges for PM2.5 further reduction under the recent policy background of eliminating heavily-polluted weather. In view of core effects of NOx on PM2.5, the deeper reductions of NOx in these cities are expected to break the plateau of PM2.5 decline, however, the link between NOx emission and PM2.5 mass loading is currently lacking. Herein, we progressively construct an evaluation system for PM2.5 productions based on daily NOx emissions in a typical industrial city (Jiyuan), considering a sequence of nested parameters involving evolutions of NO2 into nitric acid and then nitrate, and contributions of nitrate to PM2.5. The evaluation system was subsequently validated to better reproduce real increasing processes for PM2.5 pollution based on 19 pollution cases, with root mean square errors of 19.2 ± 16.4 %, suggesting the feasibility of developing NOx emission indicators linked to goals of mitigating atmospheric PM2.5. Additionally, further comparative results reveal that currently high NOx emissions in this industrial city severely hinder the achievement of atmospheric PM2.5 environmental capacity targets, especially in the scenarios of high initial PM2.5 level, low planetary boundary layer height and long pollution duration. It is anticipated that these methodologies and findings would supply guidelines for further regional PM2.5 mitigation, in which source-oriented NOx indicators could also provide some orientations for industrial cleaner production such as denitrification and low nitrogen combustion.

Experiment and numerical study on combustion characteristics of low-nitrogen burners

Low nitrogen combustion has always been an essential topic in energy conservation and environmental protection. This paper proposes a new type of low-nitrogen burner, which aims to optimize the burner structure and reduce NOx emission. Fuel and air staged combustion and central swirl technology are adopted in the burner to reduce local high-temperature areas and NOx generation. The effects of the new low-nitrogen burner's structural parameters and operating parameters on the temperature distribution, velocity distribution and NOx concentration distribution in the furnace are analyzed by cold state experiment and numerical simulation. The results show that: the cyclone blade deflection angle of 30 and the main combustion stage gas nozzle of 3 are the optimal structural parameters. The secondary combustion stage gas ratio of 0.1, the excess air coefficient of 1.05, and the air preheating temperature of 298 K are the optimal working condition parameters. At this moment, the furnace has the highest average temperature, the best combustion efficiency and the lowest NOx emission. These indicates that the novel low-nitrogen burner can be a suitable device for reducing NOx emission.

Experimental Study on Denitration Transformation of CFB Boiler Burning Fujian Anthracite

Two 75 t/h medium-temperature separated circulating fluidized bed boilers burning Fujian anthracite were upgraded with low NOx combustion (LNC). By reducing the effective cross-sectional area of the air distributor (from 13.43 m2 to 11.38 m2), improving the secondary air rate (from 40% to 45%), adjusting the secondary air supply method (adding a layer of upper secondary air, raising the height of the lower secondary air nozzle (0.4 m), and increasing the secondary air speed (from 48 m/s to 54 m/s), the reform of low nitrogen combustion was carried out. The transformation achieved remarkable results, i.e., the original NOx emission concentration can be controlled between 140–160 mg/m3 after the transformation, and the lowest value is below 120 mg/m3.

Driving factors of NOX emission reduction in China's power industry: based on LMDI decomposition model.

Under the policy background of "joint prevention and control" of global greenhouse gas emission reduction and regional air pollutants, the power industry, as an important target industry of energy conservation and emission reduction policies, has become an effective choice to release dual pressures. In this paper, the "bottom-up" emission factor method was used to measure the emission of CO2 and NOX from 2011 to 2019. Then, the contributions of six factors to NOX emission reduction in China's power industry were identified using the Kaya identity and logarithmic mean divisia index (LMDI) decomposition methods. The research results show that (1) there is a significant synergistic emission reduction effect between CO2 emission reduction and NOX emission reduction; (2) the factor that inhibits the growth of NOX emissions reduction in the power industry is economic development factor; and (3) the main factors that promote the reduction of NOX emission from the power industry are synergy effect, energy intensity, power generation intensity, and power production structure factors. Several suggestions are proposed, which are the power industry should adjust its structure, improve energy intensity, focus on applying low-nitrogen combustion technology, and improve the air pollutant emission information disclosure system to reduce NOX emissions.

Simulation and Experimental Study on the Low NOx Combustion of 35 Kw Biomass Boiler with Air Staging

In the present research, numerical simulations and combustion experiments were carried out using a 35 kW biomass low nitrogen combustion furnace. For this purpose, the boiler structure and fluid area in the furnace were modeled. Subsequently, the grid was divided and the parameters such as speed and pressure were set using Gambit. Then, the model was introduced into Fluent in order to simulate the combustion process and for flow field output and analysis. By analyzing the distribution and changes in temperature field, velocity field, and NOx concentration field under different air supply schemes, and performing low nitrogen combustion experiments, the influence of different air supply schemes on fuel combustion and NOx emission was determined. Through the mutual verification of simulation and experimental research, the optimal air distribution scheme was obtained. The results showed that: without the air staged combustion, combustible gas and air were not properly mixed. As a result, the loss of mechanical incomplete combustion occurred. Under air-staged combustion, the addition of the secondary air reduced the “chimney flow” phenomenon in the furnace to a certain extent. The combustible gas and air were mixed more adequately and the reaction rate and efficiency significantly increased. In addition, with the introduction of the secondary air, the air and the flue gas in the furnace were more efficiently mixed. Moreover, the temperature in the upper combustion area of the furnace decreased by 300–500 K, which slowed down the rate of nitrogen oxides production. This effect was intensified when the proportion of the secondary air increased. The status of the combustion process and changes in the concentration of NOx in the flue gas were compared and analyzed under various working conditions. Data indicated that the optimal air distribution scheme was that with 70% of the primary air and 30% of the secondary air. In this case, the NOx emissions were 27% lower than those without the air staged combustion.

Innovation evolution of industry-university-research cooperation under low-carbon development background: In case of 2 carbon neutrality technologies

Offsetting carbon emissions by various means is carbon neutrality. Technological innovation is an important path to carbon neutrality and has been framed in China’s policy planning, such as innovations about cleaner combustion technologies. To understand the current innovation of clean technology in gas boilers, this paper selects 2 Carbon Neutrality Technologies (CNT) identified in China, respectively low nitrogen combustion and catalytic combustion, to obtain relevant patent data of innovative technology. Besides, social network analysis (SNA) and community detection algorithms are used to show the evolution of three stages from 2005 to 2020. On the whole, several enterprises which dominate the network in the innovation cooperation of clean combustion technology in China exist at all stages, and the participation consciousness of scientific research institutions in universities is not strong. Network analysis shows that the network average degree fluctuates (1.172–1.962–1.442) with no obvious changes, and the network becomes sparse gradually. The analysis of the two-mode network shows that B01J refers to the most technical field involved in the cooperation except the first stage. B01D, F23G, and F23D are the key areas of technological innovation in the three stages except for B01J. The current innovations in clean combustion technology are not so much about combustion itself, instead, they focus on general physical and chemical methods. But at Stage2 and Stage3, more attention has begun to shift to burner innovation.

Research on the Modification of Coal Adaptability and Carbon Emissions Reduction Technology for Coal-Fired Boilers

In order to solve the problems of the high temperature of flue gas, low boiler efficiency, and the high concentration of nitrogen oxide (NOx) emissions for a 330 MW boiler fired with lean coal in a power plant, an adaptation modification by using different type of coals in the power generation unit (including pulverizing system, burners, heating surface, and so on) was carried out. The performances of boilers were tested under different combustion conditions before and after the modification. The results of the test show that the volatile content is higher and easy to burn out, and the combustible content of fly ash and slag are greatly reduced after the change in coal type (while lean coal is changed into bituminous coal). At the same time, the low-temperature economizer can greatly reduce the flue gas temperature, thus increasing the efficiency from 90.36% (lean coal, corrected) to 92.71% (bituminous coal). After the change in coal type (lean coal to bituminous coal) and the shift to low-nitrogen combustion (using low-nitrogen burner and OFA technology), the flame temperature in the main combustion area of the boiler decreases, the thermal-type NOx is reduced, and the volatile content of bituminous coal is higher in the anoxic atmosphere of the main combustion zone where the excess air coefficient is small. The intermediate reductive products tend to produce more, which can restrain and reduce NOx. Therefore, the concentration of NOx emissions can be greatly reduced. NOx average emissions at the economizer outlet decreased by 68%, from 864 mg/Nm3 to 279.4 mg/Nm3. A low-temperature economizer uses waste heat to heat feed water, which reduces coal consumption by about 1.32 g/(kW·h). The coal consumption for power supply after modification is reduced by 9.83 g/(kW·h) and the annual energy saving is 16,776 tons of standard coal, while the total carbon dioxide emissions reduction is 41,213.60 tons after the unit modification.

Influence mechanism of ammonia mixing on NO formation characteristics of pulverized coal combustion and N oxidation in ammonia-N/coal-N

Through ammonia-coal co-firing, ammonia as a carbon-free fuel can be used to effectively reduce CO2 emissions in coal-fired power generation. However, ammonia can also act as an N source that allows NOx to be generated through more reaction paths. Therefore, it is highly necessary to explore the N oxidation mechanism in the ammonia-coal co-firing process to achieve low nitrogen combustion. In this study, the N oxidation mechanism in the ammonia-coal co-firing process was explored through an experiment with a high-temperature furnace, XPS testing, and calculations based on quantum chemical theory. The experimental results show that both temperature and ammonia mixing ratios have a significant impact on NO formation. When the combustion temperature is 1200℃, the NO yield increases gradually as the ammonia mixing ratio increases from 20% to 40% and then to 60%; when the combustion temperature is higher than 1300℃, the NO yield increases first and then decreases as the ammonia mixing ratio increases. In addition, the XPS testing demonstrates that the content of char-N resulting from ammonia-coal co-firing at 1200℃ is higher than that resulting from pure coal combustion at 1200℃. This indicates that the N atoms in ammonia can be adsorbed or embedded in char. The theoretical calculations at the molecular level further reveal that the amino groups in the ammonia-coal co-firing system can be oxidized to produce NO, NO2, and HNO via different paths. Both the experimental data and the theoretical calculations confirmed that NO is the main oxidation product. Moreover, the amino groups can stably exist on the char surface under the effects of different adsorption mechanisms, which is consistent with the characterization test. This work lays a foundation for deepening the understanding of the N migration and transformation mechanism in ammonia-coal co-firing. It provides theoretical support for developing methods to ensure low nitrogen combustion in ammonia-coal co-firing.

Oxidation mechanism of ammonia-N/coal-N during ammonia-coal co-combustion

Ammonia-coal co-combustion is a feasible approach to reduce CO2 emissions during thermal power generation, it is necessary to study NO formation mechanism in ammonia-coal co-firing to realize low-carbon and low-nitrogen combustion. The experimental results showed that temperature and ammonia ratio have a significant effect on the NO formation. Under the same ammonia blending amount, the NO production increased first and then decreased with temperature increasing. Theoretical calculations revealed that the formation of NH in NH3→NH→NO is one of the factors restricting ammonia combustion. NH oxidation on the char surface first occurred in the NH/coal/O2 combustion system, and realized the conversion of N to NO, HNO and NO2 through different reaction paths. Combined with the experimental and theoretical calculation results, it was concluded that the reduction of NO by ammonia/char is enhanced at high temperature (>1300 °C), which reduces the conversion of ammonia-N/coal-N to NO.

Technical Research on Widening the Adaptability of Coal Types after Low-nitrogen Combustion Transformation of 300MW Lean Coal Boiler

<p>In view of the problems such as poor adaptability of coal types, frequent slagging of boilers, and difficulty in mixing and burning after low nitrogen combustion transformation of lean coal units, the boiler shall be transformed to improve the safety and economy of boilers by improving the boiler power field and combustion stability.</p>

Application of Low Nitrogen Combustion Technology in Coal-fired Boiler

Application of Low Nitrogen Combustion Technology in Coal-fired Boiler

Effect of low-nitrogen combustion system with flue gas circulation technology on the performance of NOx emission in waste-to-energy power plant

NOx as a major gaseous contaminant, reducing NOx emissions has become a pressing concerns. At present, the SNCR process is preferred for waste-to-energy power plants. In this paper, a method of low-nitrogen combustion system with flue gas circulation combined with SNCR was proposed to reduce NOx emissions. A portion of the hot flue gas at the tail of the furnace is extracted as circulation flue gas, and the circulation flue gas is sprayed into the SNCR as tertiary air. The experimental research was conducted in a 500 t/d waste-to-energy power plant. Firstly, the air distribution of the incinerator with the low-nitrogen combustion system is discussed, the circulation flue gas can completely replace the secondary air to reach the boiler rated evaporating capacity and reduce NOx emissions. Next, the supply position of the tertiary air was studied, and the supply position worked best in the upper of SNCR. Finally, the usage of the low-nitrogen combustion system can reduce urea consumption by around 35%. The circulation flue gas extracted in the incinerator contains a small amount of particulate matter. It is a problem to be considered for further industrial application.

Failure Mechanism of Water Wall Coating Prepared by Supersonic Arc Spraying

In order to meet the requirements of environmental protection, low nitrogen combustion is widely used in thermal power plants, which causes serious high temperature corrosion of water wall on fire side. At present, some power plants use water wall anti-corrosion coating to improve their service life. n this paper, a power plant water wall coating off to explore, analysis of water wall corrosion mechanism and coating failure reasons. The results show that: The direct reason for the large-scale peeling off water wall coating is that S element penetrates through the pores of the coating and corrodes the coating, resulting in the decrease of the adhesion between the coating and the substrate and the generation of a large number of microcracks. The microcracks continue to expand and extend under the action of thermal stress and S corrosion, which eventually leads to the large-scale peeling off the coating.