NOx Emission Concentration Research Articles

Decoupled combustion of alcohol extracted herb residues with blending wasted activated coke: Insight into in-situ NOx emission control by pyrolysis products

By a self-established dual fluidized bed combustion apparatus, alcohol extracted herb residues (AEHRs), as well as their derived char and on-line volatiles, were firstly directly combusted to investigate and compare the characteristics of the resulting NOx emissions; and then, the AEHRs were subjected to decoupled combustion (DC) with addition of wasted activated coke (WAC), to realize their safe disposal/clean energy recovery. The result showed that, the DC exhibited a desirable NOx reduction effect, and the on-line volatiles, especially those from pyrolysis at 600 ℃, played a crucial role in the in-situ NOx control. The WAC inhibited NOx formation, due to its lower ash content and containing significantly fewer light metals (mainly K and Mg) than the AEHR char. When subjected to DC at the optimized conditions (600 °C pyrolysis, 850 °C combustion, excessive air ratio (ER) = 1.3 and secondary air proportion = 0.5), blending 20% WAC into the AEHR further reduced the NOx emission concentration from 217.03 to 163.82 mg m−3, corresponding to a 70.40% NOx reduction rate when compared to 553.41 mg m−3 for conventional combustion of the AEHR. Splitting the primary air revealed that the char + WAC contributed 18.81–26.51% of the total NOx reduction amount during the AEHR + WAC DC, justifying the necessity for DC to simultaneously make good use of the hot char and the on-line volatiles for reducing NOx.

Auto-encoder-extreme learning machine model for boiler NOx emission concentration prediction

An automatic encoder (AE) extreme learning machine (ELM)-AE-ELM model is proposed to predict the NOx emission concentration based on the combination of mutual information algorithm (MI), AE, and ELM. First, the importance of practical variables is computed by the MI algorithm, and the mechanism is analyzed to determine the variables related to the NOx emission concentration. Then, the time delay correlations between the selected variables and NOx emission concentration are further analyzed to reconstruct the modeling data. Subsequently, the AE is applied to extract hidden features within the input variables. Finally, an ELM algorithm establishes the relationship between the NOx emission concentration and deep features. The experimental results on practical data indicate that the proposed model shows promising performance compared to state-of-art models.

Investigation and Evaluation of Flue Gas Pollutants Emission in Waste-to-Energy Plant with Flue Gas Recirculation

The emissions of pollutants by waste-to-energy power plants, which contain more toxic substances owing to the complicated composition of municipal solid waste (MSW), such as NOx, SO2, HCl, HF, particulate matter, and heavy metals, has attracted increasing attention worldwide. To effectively control the pollutants, a flue gas cleaning system is indispensable in the operation of MSW incineration power plants. In this study, the flue gas cleaning system in a waste-to-energy power plant with flue gas recirculation (FGR) was evaluated. The concentrations of various pollutants were measured and compared with the standards at home and abroad. The results indicated that NOx emission can be effectively reduced by FGR, and that the emission concentration of NOx may meet the national emission standards only by adopting FGR. However, the emission levels of HCl and PM exceeded the limits in legislative standards; therefore, operation optimization or retrofit of a deacidification system and bag filter were proposed to comply with the international standards and near-zero-emissions goal.

Feasibility study on mornitoring NOx emissions of China-VI natural gas engines with the NOx sensor

Based on a heavy-duty stoichiometric natural gas engine which can meet the requirement of China-VI regulations, steady-state and transient cycles were carried out to measure the exhaust NOx concentration out of TWC by a NOx sensor and a gaseous emission analyzer simultaneously. The results show that the measurement results of NOx sensor are relatively higher when the NOx emission concentrations are lower than 50 ppm, and the accuracy is not high enough. Due to the obviously smaller proportion of lower NOx concentrations, especially for the concentrations below 10ppm, the average concentration measured by the NOx sensor was 24.3% higher than the average concentration measured by the emission analyzer during the whole testing process. When the NOx concentrations are higher than 50ppm, the frequency distributions of NOx concentration measured by NOx sensor and emission analyzer are almost the same, and the deviations of average NOx concentrations between these two measurement methods can be within ±4.5%, which represent a significantly high reliability of NOx sensor.

Inventory of pollutant emissions into the atmosphere from gas turbine installations of gas pumping units

Development of a single method for inventory of pollutant emissions from installations based on the elaboration of existing methods for calculation of air pollution is an important scientific and practical task in the field of environmental safety.
 The main purpose of the study is to test and compare models of stationary emission sources and to assess air quality based on them.
 In the inventory of pollutant emissions, the following materials are used: direct measurements, which are based on direct instrumental measurements, and calculated measurements or combinations thereof.
 According to the direct measurements of NOx and CO emissions from the operation of gas turbines at the Valley compressor station with a nominal capacity of 1 to 50 MW, we found that: the actual emissions of NO and CO increase with the average load on the installation and the time of introduction into operation and date of issue and the actual values of the maximum allowable concentration of NOx (from 100.13 to 467 mg / m) and CO (from 16.08 to 444.88 mg / m) do not exceed the permissible levels of NO-500 mg / m and CO-250 mg / m according to the instructional documents.
 Comparison of these calculation methods showed the same results, which confirms the need for their systematization with the subsequent development of a single methodology.
 The distance of 106 m, where the maximum concentration of pollution in adverse weather conditions is expected, was obtained by the calculation method of determining the surface concentration of NOx and CO emissions from the installation.
 To assess the effectiveness of the methods for inventory of pollutant emissions into the atmosphere from gas turbines, we have developed a scheme of relationship between the object being assessed for efficiency and the object being serviced. Particularly noteworthy are the results and analysis of direct measurements of NOx and CO emissions, as well as the developed scheme for linking the inventory process for pollutant emissions into the atmosphere from installations.
 The actual concentration of pollutants can be estimated by measuring the background, although in this case it is impossible to exclude the influence of other neighboring and remote emission sources on the results of the air pollution assessment. Depending on the specific task, the results of computer simulation for given parameters of the external environment can also be used to assess the actual, retrospective or prospective conditions. Future conditions can be modeled only with the help of computer simulation.
 The method of air pollutant concentration calculation for emissions of enterprises does not consider all possible features of emission sources and, in terms of passive stationary sources and cold emissions, the algorithm needs to be clarified and the justifications in the paper indicate ways to make these improvements.
 Inventory is the first stage in the strategy of air quality regulation, as it provides information for the development, justification and decision-making in regulating the activities of gas turbines to reduce adverse effects on the environment and public health.

A Framework for Economically Optimal Operation of Explosive Waste Incineration Process to Reduce NOx Emission Concentration

Explosives, especially those used for military weapons, have a short lifespan and their performance noticeably deteriorates over time. These old explosives need to be disposed of safely. Fluidized bed incinerators (FBIs) are safe for disposal of explosive waste (such as TNT) and produce fewer gas emissions compared to conventional methods, such as the rotary kiln. However, previous studies on this FBI process have only focused on minimizing the amount of NOx emissions without considering the operating and unitality costs (i.e., total cost) associated with the process. It is important to note that, in general, a number of different operating conditions are available to achieve a target NOx emission concentration and, thus, it requires a significant computational requirement to compare the total costs among those candidate operating conditions using a computational fluid dynamics simulation. To this end, a novel framework is proposed to quickly determine the most economically viable FBI process operating condition for a target NOx concentration. First, a surrogate model was developed to replace the high-fidelity model of an FBI process, and utilized to determine a set of possible operating conditions that may lead to a target NOx emission concentration. Second, the candidate operating conditions were fed to the Aspen Plus™ process simulation program to determine the most economically competitive option with respect to its total cost. The developed framework can provide operational guidelines for a clean and economical incineration process of explosive waste.

The effect of first generation biofuel on emission characteristics under variable conditions of engine speeds and loads in diesel engine

Iraqi sunflower was used in the current study and blended with diesel fuel into different ratios. The results indicated that lowest level of gaseous emissions (CO, HC, and CO2) and PM produced from B100 compared with other fuels tests. Furthermore, the CO and unburnt HC decreased with high conditions of engine loads and speeds. The high concentration of NOX emissions was found from the combustion of B100, B50, and B20 compared with diesel fuel. The emissions of NOX and exhaust gas temperature improved from increasing the operating conditions of engine loads and speeds. The effect of biodiesel blends on the gaseous emissions and particulate matter (PM) was investigated under variable engine operating conditions of loads and speeds. The best reduction was achieved with medium conditions of engine loads and speeds compared with low and high loads and speeds for all fuels tests. The higher oxidation rate of soot particles inside combustion cycle from the burning of B100, B50, and B20 decreased the total concentration of PM.

Study on effects of molecule structure on exhaust emissions from RCCI engine fueled with low alcohol isomers

Due to the existence of reactivity stratification in mixture of Reactivity Controlled Compression Ignition (RCCI) engine, effects of molecule structure of low alcohols on exhaust emissions may be different. Three kinds of molecule structure, hydroxyl group position (OHP), methyl branches (MB) and straight carbon chain (SCC) are constructed through propanol and butanol isomers, and experimental data of exhaust emissions were drawn from RCCI engine under different oxygen mass contents (RO) and start of injections (SOI). Then, changes of exhaust emissions with OHP, MB, SCC, RO and SOI, and real influence factors and influence sequence of them on emissions are analyzed. The results show that: Although a certain emission changes with a certain impact factor, they may not be correlated with each other, which means the determination of real influencing factors and influence sequence is necessary. This determination is helpful to find out the strongest correlation influencing factors to optimize exhaust emissions. It is worth noting that, different emissions have different real influencing factors. NOX emission and particle mass concentration (PMC) are unrelated to molecule structure. On the contrary, they are only correlated to SOI. Moreover, all emissions are unrelated to OHP, and only HC emission is correlated to MB, while SCC is correlated to multiple emissions, and emission types correlated to Ro and SOI are the most.

Research on precise ammonia injection technology in thermal power plant

Under the situation of ultra-low emission in China, SCR denitration system generally has the problem of high ammonia escape from the reactor outlet, and the escape ammonia reacts with SO3 in flue gas to generate NH4HSO4, which will aggravate the blockage of air preheater and affect the denitration efficiency, so the ammonia injection has a great impact on the NOx emission concentration of power plant. In this paper, how to accurately spray ammonia in SCR denitration system is introduced in detail, that is, after the flow field partition optimization of denitration system, the corresponding advanced measurement system, advanced control system and actuator are added combined with the partition.

Mitigating combustion instability and NOx emissions with annular oxyfuel jets into the flame shear layer region

AbstractThe shear layer is a region between the internal and external recirculating zone of the flame, which is critical for combustion stabilization and emission. This study experimentally studied the effects of oxyfuel (CO2/O2) shear layer injections on combustion dynamics and pollutant emissions of a model gas turbine combustor. To evaluate the damping performances of ‘Oxy’ CO2/O2 shear layer jets on unsteady combustion and pollutant formation processes, four variables of the CO2/O2 shear layer injection system are studied—the flow rate, the inner diameter, the injection angle and the oxygen ratio. Experimental results show that thermoacoustic instability and NOx emissions can be suppressed with the ‘Oxy’ CO2/O2 shear layer injection method. The minimum inner diameter cases could achieve better control effectiveness of 80%, with the sound pressure amplitude drops from 27 to 5.4 Pa. The maximum inner diameter case could achieve better control effectiveness of 59.2%, with the concentration of NOx emissions drops from 25 to 10.2 ppm. Flame oscillation modes experienced shifting and switching under different shear layer angles and oxygen ratios. There exist extreme points that can be selected for a better control effect. The CO2/O2 shear layer injection splits the inner and outer recirculation zones of the flame. As the oxygen ratio of CO2/O2 varied from 36% to 46%, a flame flapping phenomenon emerged. The ‘Oxy’ CO2/O2 shear layer injection method could eliminate combustion instability and NOx emissions at a relatively lower cost and complexity, which will promote the development of high‐performance burners.

Thermal and environmental performance of CI engine using CeO2 nanoparticles as additive in water–diesel–biodiesel fuel blend

The aim of this study was to find out the thermal and environmental performance of a four-stroke, single-cylinder, direct injection 10-kW CI engine at varying engine load conditions using different test fuels. The formulated fuels, viz. CeO2 nanoparticles-dispersed water–diesel–biodiesel fuel blend (CNWEDB) and water–diesel–biodiesel fuel blend (WEDB), were prepared using emulsification technique using CeO2 nanoparticles and water as additives in diesel–biodiesel blend (B20). The measured fuel properties of CNWEDB and WEDB satisfied the criteria of Indian Standard for biodiesel indicating their suitability for use in CI engine. The engine was run at various loads (0, 20, 40, 60, 80 and 100%) randomly to assess its thermal and environmental performance with all test fuels. Thermal performance of CI engine was evaluated by measuring the parameters such as brake thermal efficiency (BTE), brake-specific fuel consumption (bsfc), exhaust gas temperature (EGT) and heat balance for all test fuels. The environmental performance of engine was assessed by measuring CO, HC and NOx emissions for all test fuels. Adding water and CeO2 nanoparticles into B20 improved BTE of engine by 7.65% over diesel. Also, the minimum heat losses were observed at 80% engine load for CNWEDB indicating a better conversion of fuel energy to useful work. EGT and bsfc of engine reduced with CNWEDB over WEDB and B20 fuels. Engine fueling with CNWEDB emitted 12.82%, 14.46% and 14.20%; and 30.77%, 43.67% and 26.80% lesser concentration of CO, HC and NOx emissions over WEDB and diesel, respectively.

NOx emission from the combustion of mixed fuel pellets of Fenton/CaO-conditioned municipal sludge and rice husk

Sludge incineration technology is facing the problem of gaseous pollutant discharge. The control of NOx emissions is the key to reducing the impact of sludge combustion on environmental pollution. In this study, Fenton/CaO was used to condition municipal sludge, which was subsequently mixed with rice husk to fabricate briquette fuel for combustion experiments. The effects of the conditioner dosages, mass ratios of the rice hull to sludge, and the combustion temperatures on NOx emissions from briquette combustion were studied. The results showed that the NOx emissions decreased with increasing doses of conditioned sludge. In addition, with an increase in the rice husk ratio in the briquette, the NOx emissions decreased and the conversion rate increased. Additionally, with an increasing combustion temperature, the combustion of molded fuel became more complete. The NOx emission of conditioned sludge combustion was reduced by approximately 1.3 times compared with that of the sludge alone. Using the response surface methodology, the optimized conditions were obtained as follows: the rice husk mixing ratio is 43.8%, the Fenton/CaO conditioner dosage is 220 mg/g, and the temperature is 829 °C. The minimum NOx emission concentration was predicted to be 0.845 mg/g. The NOx emission laws observed from the combustion of mixed fuel pellets are believed to provide basic data for a new sludge treatment method.

Combined operation mode of sub-critical W-flame boiler and coal mill optimized numerical simulation

The flow, combustion, heat transfer and NOx emission characteristics of a 600 MW subcritical W-flame boiler were numerically simulated under different combined operation modes of coal mills, and compared with the measured results. The results show that the combustion, average residence time, burnout rate, NOx emission characteristics and temperature distribution near the side wall of pulverized coal particles in the furnace have different effects on the combined operation mode of pulverized coal. In the combustion efficiency of give attention to two or more things, screen superheater section of fly ash carbon content and flue gas temperature of entrance at the same time, compared with six coal mill run at the same time, 5 coal mill run, shut down near the side wall of the coal mill is beneficial to reduce NOx emission concentration, to achieve the emission reduction, at the same time under the wing wall and side wall area chamber of a stove or furnace slagging significantly reduce.

Incineration experiment of medical waste of novel coronavirus pneumonia (COVID-19) in a mobile animal carcass incinerator

Incineration experiment of medical waste was carried out in a mobile animal carcass incinerator. Simulated medical waste (69% cotton, 1.5% wood product, 4.5% mask and 25% moisture) was used as raw material. The temperature trend of first and second combustion chamber, the operating conditions and the emission characteristics of gaseous pollutants were studied. The results indicated that the temperature of first combustion chamber can be maintained at 550–650 °C without external heating, while in the final stage a burner was used to realize the burnout of material. The temperature of the second combustion chamber was always lower than that of the first combustion after the burner stopped working. The concentration of CO emission in flue gas was high due to the low disposal efficiency of the mobile incinerator, while NOX and SO2 emission concentrations were far below the standard limit value (GB 18484-2001).

Dilution effects of CO2, Ar, N2 and He microjets on the combustion dynamic and emission characteristics of unsteady premixed flame

To evaluate the control effectiveness of jet in cross flow on thermoacoustic instability of lean premixed flame, the dilution effects of CO2, Ar, N2 and He microjets on the dynamic and emission characteristics of premixed flame were experimentally studied in a laboratory-scale gas turbine combustor. Three factors of jet in cross flow were investigated—Injection flow rate, inner diameter of injector and injecting medium. CO2 performs better than other three gas medium in both combustion instability and NOx emissions control. Results denote that an optimal sound pressure damping ratio can be reached as 80.3% with injection flow rate of 3.5 L/min. And the damping ratio of heat release rate can be as high as 75%. NOx emissions concentration can be reduced to 15.9 ppm. The NOx emission damping ratio can be as high as 35.4%. Flame becomes dispersed and flat under microjets with high flow rate. The flame length is reduced to 54 mm when both the sound pressure amplitude and the NOx emission concentration are all at the bottom, Flame length after passive control only equals to 40% of the original. The results confirmed that suppression effectiveness of combustion instability is associated with the relative molecular masses of the jet in cross flow. However, the detailed triggering mechanism and the coupling of combustion instability with jet in cross flow still needs exploration. This study demonstrated that the passive control with microjets has the potential to be applied to combustion systems under combustion instability.

Pollutants emission characteristics and emission reduction potential of crematoria flue gas in Beijing-Tianjin-Hebei region, China

There is a large population and high number of death in the Beijing-Tianjin-Hebei (BTH) region, therefore the amount of cremation and the incineration of sacrificial offerings is also high. Due to the loose pollution control in crematoria, the surrounding environment and human health were affected by the pollutants emitted from crematoria. To further explore the characteristics of pollution emissions from the BTH crematoria, this study carried out on-site emission monitoring of 19 cremators and 6 incinerators of sacrificial offerings in 19 crematoria in this region. The concentrations and chemical components of PM2.5 and volatile organic compounds (VOCs) and the emission levels of other gaseous pollutants from crematoria flue gas were obtained. The emission factors of air pollutants were calculated. Based on the activity level data, the emission inventory of atmospheric pollutants from the crematoria was established and its emission reduction potential was analyzed. Results showed that:(1) The average emission concentrations of TSP, CO and NOx from the crematoria in the BTH were seriously exceeding the national standard limits. Flue gas purification devices had significant effect on the removal of pollutants. (2) PM2.5/TSP=0.73 indicated that fine particles accounted for a large proportion in the flue gas of cremator; the concentration of organic matter (OC) was high and accounted for 25.3% in PM2.5. (3) The concentrations of benzene and benzene series, olefins, alkane were high in VOCs, accounting for 88.7%, which might pose health risks to exposed populations. (4) According to the emission inventory, the emissions of TSP, PM10, PM2.5 and CO in the BTH crematoria in 2016 decreased by 47.8%, 47.8%, 47.9% and 26.1% respectively compared with those for 2007. The proportion of installation purification devices for crematorium was low in the BTH region and it was common that flue gas discharged directly into atmosphere which had considerable potential of emission reduction.

Experimental Trails on Diesel Engine Performance and Emission Characteristics of Waste Cooking Oil Combinations at Varying Injection Pressures

Progressive rising of conventional fuel prices, as well as the high strengthened necessities of the environmental norms to reduce the atmospheric pollution levels, are flattering great challenges to scientists and researchers all over the world. In this regard, biofuels have become one of the best alternative fuels for conventional IC engine operation with reduced emissions and improved performance. Goal of paper is to study the influence on emissions and performance variables in one cylinder CI engine fueled accompanied by diesel-waste cooking oil mixtures. The test rig was operated at rated speed 1500 rpm, CR 17.5 and at variable injection operating pressure of 200, 225 and 250 bar correspondingly. Different fuel mixtures of diesel-waste cooking oil i.e., B10, B20 and B30 on mass basis were used for this study. As compared to neat diesel at standard Injection Operating Pressure (IOP) 200 bar, increased IOP 225 bar exhibits utmost BTE, nominal quantity BSFC, minimum CO and HC pollutions with the superior concentration of NOx emissions. In contrast, by using WCO blends, the performance of the engine reduced along with the emissions except HC.

Cost-benefit evaluation of different low NOx combustors of natural gas boilers in Beijing

This study focuses on establishing a cost-benefit evaluation model of low NOx combustion technology and the environmental benefits and economic benefits evaluation of technology operation were carried out as well. Results showed that: (1) The operation cost per unit calorific supply of the low NOx combustor with larger capacity (14 MW) boilers was 1.5-2.1 yuan/GJ, which was 22.3% to 26.2% as much as that of boilers with smaller capacity (0.7 MW). Compared with scattered boilers with smaller capacity, it is more economical to use boilers with larger capacity for centralized heating. (2) The lower the NOx emission concentration was, the greater the NOx emission reduction was. Furthermore, the lower the NOx emission benefits of low NOx combustor per unit calorific supply was, the greater the economic benefit of NOx reduction per unit calorific supply was. Based on the environmental and economic benefits analysis, the lean premixed combustor is recommended for natural gas boilers with capacity of 7 MW and below, and flue gas recirculation combustor (FGR-30) could be selected for natural gas boilers with capacity above 7 MW to achieve the NOx retrofits requirements of 30 mg/m3 or 80 mg/m3.

Analysis of Air Pollutant Emission Differences and Emission Reductions of Coal-fired Stoves of Different Residents

In order to explore the differences in air pollutant emissions of different types of stoves, this study selected five common new types of residential coal-fired stoves (square coal stoves, baffle heat exchange stoves, kang heating and cooking integrated stoves, Gasification forward burning and gasification reverse burning stoves) Simulated combustion and atmospheric pollutant emission level monitoring in the laboratory to quantitatively evaluate the environmental effects of different stoves, identify the influencing factors and causes of differences in pollution emission levels, and propose furnaces Suggestions for improvement of pollution reduction such as R & D and design. The results show that: ① The emission of air pollutants differs greatly among different stoves, and the intensity of pollution emitted by the stoves with kang heating and cooking is the largest. The emission intensity of the three types of atmospheric pollutants (SO2, NOx and particulate matter) is 2.9 kg t-1 It is 1.6 times the average value; stoves using square coal technology have the lowest air pollutant emission intensity, which is 65% of the average value. ②The emission of gaseous pollutants in different furnaces at different combustion stages also showed obvious differences and characteristics. During the fire stage, the NOx emission concentration of the square coal stove is 0.49mg ⋅ m-3, which is 45% ∼ 72% lower than that of other types of stoves; the SO2 emission concentration of the gasification anti-burning stove is 1.38mg ⋅ m- 3. Compared with other types of stoves, the maximum reduction is 28%. ③The factors that affect the emission of atmospheric pollutants of the stove include the application technology and the type of combustion. The stoves with square coal and gasification anti-burning technology have better environmental benefits, but the economic costs of the two types of stoves are 20,000 yuan and 18,000 Yuan, significantly higher than other types of stoves. ④Considering the differences in pollution emissions from different stoves, it is recommended to adopt differentiated economic policies and strict emission and product standards, promote the use of energy-saving and environmentally friendly stoves, and reduce the emission of atmospheric pollutants from coal-fired stoves.

Influence Study of Ammonia-Nitrogen Molar Ratio on SNCR Denitrification

The influences of different ammonia-nitrogen molar ratios (Normalized Stoichiometric Ratio, NSR) on the NOx emission concentration, ammonia escaping amount, and selective non-catalytic reduction (SNCR) denitrification efficiency were measured through a field test. The results show that with the increase of NSR, the NOx emission concentration changes little, the ammonia escaping amount is gradually increased, and the SNCR denitrification efficiency is basically kept stable after increasing firstly. In full consideration of the ultralow emission limit and reducing agent consumption, it is believed that 2.01 is the optimal NSR value under the test load.