Selective Non-catalytic Reduction Research Articles

Life Cycle Assessment of Nitrogen Circular Economy-Based NOx Treatment Technology

Humans are significantly perturbing the global nitrogen cycle, leading to excess reactive nitrogen in the environment. Nitrogen oxides as a key reactive nitrogen species are mainly controlled by selective non-catalytic reduction and selective catalytic reduction. Converting nitrogen oxides to ammonia, defined as ReNOx, emerges as an alternative method under a disparate design concept. However, little is known about its overall environmental performance. In this study, we conducted for the first time a life cycle assessment of ReNOx. Compared with the eco-index in the condition of 200 °C with a conversion rate of 95%, it would increase substantially in the condition of 160 °C with a conversion rate of 80% and in the case without a sound NH3 treatment. Feedstock format change, adsorption material performance deterioration, and recovery rate decline would increase the eco-index by 8%, 12%, and 18%, respectively. The eco-index was decreased by 31% in the optimized scenario with a renewable energy source and an increased conversion rate. The environmental impacts were compared with traditional methods at impact, damage, and eco-index levels. Finally, the implications on process arrangement in the flue gas system, the externality for power generation, and the contribution to the nitrogen circular economy were examined. The results can serve as a reference for its developers to improve the technology from the environmental perspective.

Application of SNCR denitration technology in circulating fluidized bed boiler

In order to ensure the realization of NOX emission limit and implement the enterprise’s leading. the denigration principle, basic structure and application effect of SNCR (selective non-catalytic reduction) denigration system of circulating fluidized bed boiler in a power plant are introduced. The test results show that SNCR denigration technology can meet the NOx emission requirements of the new pollutant emission standard of thermal power plant.

Achieving an ultralow emission of nitrogen oxides by using activated carbon with hydrophobic modification

Selective noncatalytic reduction (SNCR) systems have been widely used for denitrification in small capacity boilers, such as biomass- and waste-fueled boilers. However, these systems cannot meet the requirements of ultralow emission regulations, i.e., 50 mg m−3. This work proposes a new solution that combines SNCR and activated carbon (AC). To solve the problem caused by the wettability of AC, which can significantly reduce the quantity of NOx that can be adsorbed and block active cites, hydrophobic modification was employed to amend the properties of AC. The influences of the key operating parameters on the denitrification of AC, including the reaction temperature, O2 concentration, feed gas flow rate, and contents of SO2 and CO2, have been investigated experimentally. A novel solution that combines AC and SNCR was proposed for industrial applications, and the economic feasibility has been verified. The results have demonstrated that this hybrid solution can achieve a low levelized cost of denitrification, which is 59.8% and 33.7% lower than those of SCR and hybrid SNCR/SCR.

Assessment of Hazard Due to Release of Gaseous Ammonia from the Fly Ash-Water Mixture Applied in Longwall Mine Gobs

Purpose The introduction of flue gas denitrification technologies by selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) in coal fired plants resulted in an increase of ammonia content in fly ash. The utilization of fly ash in fire and ventilation prevention of hard coal mines causes the release of ammonia from a fly ash-water mixture. In the applied technology of the ash and water mixture, ammonia in gaseous form is discharged and mixes with the air flowing through the mine airways. In this article, reference is made to the risk assessment of gaseous ammonia in the longwall area during the application of the fly ash-water mixture to the gobs in the U-tube ventilation system. Methods The test methods include: ammonia release from ash and water mixtures at various temperatures and in respect to different proportions of water to ash with use of a multigas analyzer with an FTIR detector. Results The results of the laboratory tests helped to determine the size of the ammonia stream released from the fly ash-water mixture in respect to different ratios of water to ash. Practical implications Laboratory studies allow for ventilation and gaseous analysis to assess the level of ammonia risk, in the mine airways, from exhaust air discharged from the longwall area. Originality/value Based on the literature review, this type of research has not been carried out so far.

Optimization experiments of the SNCR denitrification system in circulating fluidized bed boiler after ultra-low emission transformation

The current work firstly aims to improve denitrification efficiency of the selective non-catalytic reduction (SNCR) denitrification system in a circulating fluidized bed (CFB) boiler after ultra-low emission transformation, to reduce the operating pressure of the subsequent selective catalytic reduction (SCR) denitrification system, and to extend the service life of the boiler. Secondly, it attempts to ensure that the concentration of nitrogen oxides (NOx) does not exceed the emission standard, to drop the consumption of the reducing agent, and to save operating costs. Therefore, some key factors, such as the number of spray guns affect denitrification efficiency and the amount of ammonia escape, were chosen as the operating parameters to be optimized. Meanwhile, a 150 MW CFB boiler in the Inner Mongolia Autonomous Region of China was employed for the experimentation. We then designed and implemented the optimization experiments of the SNCR denitrification system, including optimizing the operating parameters and deeply optimizing the SNCR denitrification process. The denitrification efficiency can reach 76.6% when there are four spray guns with valve opening of 50, 100, 100, and 50% respectively from top to bottom. The current work can be used as a frame of reference for carrying out relevant experiments on similar units.

Mechanism of N2O generation over chromium poisoned γ-Fe2O3 catalyst during selective catalytic reduction of NOx with NH3

Poisoning effect of Cr in flue gas on the remarkable generation of greenhouse gas N2O over γ-Fe2O3 catalyst during selective catalytic reduction of NOx with ammonia was firstly observed in this work. At low temperature, N2O generation over Cr poisoned γ-Fe2O3 catalyst was attributed to non-selective catalytic reduction (NSCR) of NOx. At high temperature, NSCR of NOx and ammonia peroxidation accompanying by weak NO disproportionation induced a more generation of N2O. The seeming promotion effect of Cr on NOx conversion of γ-Fe2O3 catalyst at low temperature was partly resulted from the NSCR of NO which also contributed to NOx conversion. At high temperature, the reduction of NOx to innocent N2 was far inhibited after chromium poisoning in view of the low selectivity of NO to N2. The formed FeCr2O4 in chromium poisoned γ-Fe2O3 catalyst was the induction factor for large N2O production, which enhanced the acidity and reducibility of catalyst. Transient DRIFTS results indicated that SCR and NSCR of NOx over chromium poisoned γ-Fe2O3 catalyst predominantly happened via Eley-Rideal mechanism. Moreover, O2 in flue gas determined the activation of adsorbed NH3 and which dictated the NSCR of NOx and ammonia peroxidation.

Modified selective non-catalytic reduction system to reduce NOx gas emission in biodiesel powered engines

Biodiesel fuels releases higher NOx emissions than fossil diesel. The Selective Catalytic Reduction (SCR) technique used in the OEM industry is not suitable for application in small engines due to back pressure and clogging problems. Selective Non-Catalytic Reduction (SNCR) is used in relatively large combustion operations. This study introduces a new design by combining SCR and SNCR systems, for use in low power density diesel engines. The system composed of injection-expansion pipe and swirl chamber. The working principle is maximum mixing of the injected fluid and exhaust gas in the expansion chamber, then creating a maximum turbulence in the swirl chamber. This way NOx emission can be reduced at relatively lower exhaust temperatures without using any catalyst. The CFD models of three design candidates were examined in terms of velocity magnitudes, turbulence intensity and particle residence time. The selected design was manufactured and tested. Distilled water and urea-water solution were injected separately at the same flow rate of 375 ml/min. Exhaust emissions of fossil diesel, sheep fat biodiesel – waste cooking oil biodiesel blend and chicken fat – cottonseed biodiesel blend were tested. No significant changes in CO2 and HC gases were observed. Distilled water injection reduced CO and NO emissions by about 10% and 6% for fossil diesel; and by about 9% and 7% for biodiesels operation respectively. The urea-water injection led to reductions in CO and NO emissions by about 60% and 13% for fossil diesel; and by about 45% and 15% for biodiesels respectively.

Low-medium temperature application of selective catalytic reduction denitration in cement flue gas through a pilot plant

Low-medium temperature application of selective catalytic reduction (SCR) denitration in cement flue gas was established and investigated in this study. The 2000 h continuous operation shows the concentration of NOx at the outlet can be maintained at 24 mg/Nm3 on average, while due to the increase of SO2 in flue gas, the NOx concentration increased to 57.5 mg/Nm3 after long time operation. The sulfur deposition is the main reason for catalyst deactivation, and SO2 is still a big obstacle for low-medium temperature SCR application in cement flue gas. The denitration efficiency was tested as fluctuated from 73.5% to 86.2%, and ammonia concentration after SCR was as still as high as 22.5–60.0 mg/Nm3 due to the excessive ammonia injection from selective non-catalytic reduction (SNCR), shows serious ammonia escape problem for SNCR, and the potential application of hybrid SNCR-SCR technology. In order to maintain the denitration efficiency above 85.0%, the gaseous hourly space velocity (GHSV) should not be exceeded 2800 h−1, the electrostatic precipitators (ESP) setting at 60 kV was relatively appropriate, the temperature of the flue gas should be kept at above 200 °C. The concentrations and toxic equivalent quantities (TEQs) of the PCDD/Fs congeners in the flue gas raised greatly after SCR reactor, indicating the PCDD/Fs concentration should be concerned during the application of low-medium temperature SCR, especially for the waste co-disposal processes.

Numerical study of the combustion and application of SNCR for NOx reduction in a lab-scale biomass boiler

In this paper, a numerical study of flow, reactions and NOx emissions from a biomass boiler is presented. Detailed reaction mechanisms for the decomposition of tar species, combustion of hydrocarbons and formation of NOx are employed by adopting appropriate reaction sets from literature. The proposed mechanism is used to perform CFD simulations of a laboratory-scale biomass boiler, and temperature and species concentrations are compared with the experimental data. NOx formation and emissions are studied in detail and the contribution of different pathways for NOx formation are identified. Furthermore, the CFD model is used to study the application of Selective Non-Catalytic Reduction (SNCR) method in this boiler. The effects of height and flow rate of ammonia injection on the performance of SNCR method are studied. It is observed that the SNCR, can reduce up to 63% of NOx emissions.

An Experimental Study on the Characteristics of NOx Distributions at the SNCR Inlets of a Large-Scale CFB Boiler

The unknown NOx distributions inside large-scale CFB (circulating fluidized bed) boilers have always hindered the economy of the SNCR (selective non-catalytic reduction) process. In this study, field tests were carried out on a typical 300 MW CFB boiler, where multi-level 316 L-made probe and Ecom-J2KN/Testo 350 analyzers were used to perform detailed two-dimensional distributions of flue gas composition at SNCR inlets for the first time. The penetration depth inside the horizontal flue pass was up to 7 m. The NOx distributions were analyzed in detail combining with the auxiliary test in the dilute phase zone. Key results show that the average O2 concentrations in #A and #C regions were 6.52% and 0.95%, respectively. The vertical NOx distributions of #A and #C SNCR inlets were similar, showing a trend of first increasing and then decreasing with peak value all appeared at 5 m depth, while the NOx distribution of #B SNCR inlet was basically increasing. Some local areas with extremely high NOx concentration (over 2000 mg/m3) were observed near the inclined edge of SNCR inlets, which has never been reported before. Based on this, the optimization of urea injections was conducted, which could save 15.7% of the urea solution consumption while ensuring ultra-low emission of NOx.

Surrogate Reaction Mechanism for Waste Incineration and Pollutant Formation

The incineration of municipal solid waste (MSW) is an attractive technology to generate thermal energy and reduce landfill waste volume. To optimize primary measures to ensure low emission formation during combustion, numerical models that account for varying waste streams and their impact on nitrogen oxide (NOx) formation are needed. In this work, the representation of the fuel by surrogate species is adopted from liquid fuel and biomass combustion and applied to solid waste devolatilization and combustion. A surrogate formulation including biomass components, protein, inorganics, and plastic species is proposed, and a comprehensive description of the heterogeneous and homogeneous reactions is developed. The presented work combines and extends available schemes from the literature for woody and algae biomass, coal, and plastic pyrolysis. The focus is set on the prediction of fuel NOx and its precursors, including cyclic nitrogen-containing hydrocarbons. Additionally, the interaction of NOx with sulfur and chloride species is accounted for, which are typically released during the devolatilization of MSW. The model allows for predicting thermogravimetric analysis measurement of waste fractions and different waste mixtures. The proposed kinetic mechanism well reproduces NOx formation from ammonia and hydrogen cyanide and its reduction under selective non-catalytic reduction conditions. The chemical model is successfully applied to predict the released gas composition along a grate-fired fuel bed using a stochastic reactor network.

Effects of hydrogen peroxide, sodium carbonate, and ethanol additives on the urea-based SNCR process

The issue of secondary pollutants represents a classic problem in the urea-based selective non-catalytic reduction (SNCR) process. Therefore, this study took to investigate the evolutions of secondary pollutants when including additives during the urea-based SNCR process. Results indicated that additives, namely hydrogen peroxide, sodium carbonate, and ethanol, clear improved denitration efficiency between 750 °C - 925 °C due to the increase of OH groups. Compared to rates without any additives, the “temperature window” width of hydrogen peroxide, sodium carbonate, and ethanol increased by 30%, 30%, and 52%, respectively. The temperature at the maximum denitration efficiency was decreased by 25 °C with the addition of ethanol. The addition of hydrogen peroxide, sodium carbonate, and ethanol decreased the amount of ammonia leakage at 725 °C - 900 °C. Besides, the emissions of HNCO and N2O were decreased by adding sodium carbonate during 725 °C - 900 °C. Therefore, the addition of sodium carbonate proved to be beneficial for reducing the secondary pollutant emissions in SNCR. This study aims to provide a deeper understanding of the urea-based SNCR process in combustion.

Pilot test of the low temperature SCR technology in cement plant

The low temperature selective catalytic reduction (SCR) was used for deep De-NOx in a cement kiln. The SCR pilot plant with a flue gas of 10000 m3/h was designed and constructed. To meet the emission standard, selective non-catalytic reduction (SNCR) technique was carried out and the concentration NOx in flue gas was ca. 270mg/m3. The De-NOx efficiency of SCR decreased with the increase of space velocity and exceeded 77.7% without the ammonia injection. When space velocity was 2500h-1, the de-NOx efficiency of SCR has been further improved by the addition of ammonia injection. After a long time of test, it suggested that the proposed De-NOx technology scheme could stably and effectively control the NOx emission in flue gas, and could meet the ultra-low emission standard.

Nitrogen oxide emissions reducing in cement production

In the European Union, the Russian Federation, as well as in a number of other countries, cement production is regulated by legislation on the best available technologies. Mandatory requirements (technological parameters, BAT-AELs) are imposed, first of all, on the emissions limitation of inorganic dust, nitrogen and sulfur oxides. The majority of Russian cement plants are currently characterized by the nitrogen oxide emissions state-established technological indicators‘ excess. The technological indicators of the best available technologies and methods for reducing nitrogen oxide emissions operating in the Russian Federation and the EU countries are considered. It is demonstrated that the most efficient technologies are the staged fuel combustion and selective non-catalytic reduction (SNCR) of nitrogen oxides.

Low Temperature SCR Cost Evaluation in Solid Waste Incineration Power Plant

To meet the increasingly strict emission control requirement, low temperature selective catalytic reduction (SCR) system is adopted in some waste incineration power plant because of the limited denitrification capability of selective non-catalytic reduction (SNCR) system in boiler furnace. The article evaluated the increased cost per ton of waste when SCR system is equipped on a 2×400t/d waste incineration power plant in Henan province. The total cost of SCR system, including construction period and operation period, per ton of solid waste is about 37 yuan.

Analysis of Oscillating Combustion for NOx−Reduction in Pulverized Fuel Boilers

Thermal power plants in different fields are regularly adapted to the state-of-the-art emissions standards, applying “The Best Available Techniques Reference”. Since 2016 in the power plant area new, more stringent limits for power plant units with a thermal output of more than 300 MW operated with black coal are valid. Usually, in order to reach the new limits e.g., for NOX emissions, downstream reduction processes (Selective Non-Catalytic Reduction, SNCR or Selective Catalytic Reduction) are applied, which use of operating resources (essentially ammonia water) thereby increase. By the means of an experimentally validated process, by which pulverized fuel is fed by oscillation through a swirl burner into a pilot combustion chamber with a thermal output of 2.5 MW, nitrogen oxides can be reduced without further activities, for instance from 450 mg/mN3 in non-oscillation operation mode (0 Hz) to 280 mg/mN3 in oscillation operation mode (3.5 Hz), normalized to an O2–content of 6% each. These findings were patented in EP3084300. Particularly promising are the experiments which utilize oscillation of a large portion of the burn out air instead of the fuel in order to minimize the fatigue of the pulverized fuel oscillator, amongst others. Thereby, the nitrogen conversion rate, which describes the ratio of NOX to fuel nitrogen, including thermal NOX can be reduced from 26% for non-oscillation operation mode down to 16%. The present findings show that fuel oscillation alone is not sufficient to achieve nitrogen oxides concentrations below the legislative values. Therefore, a combination of different primary (and secondary) measures is required. This paper presents the experimental results for oscillating coal-dust firing. Furthermore, an expert model based on a multivariate regression is developed to evaluate the experimental results.

Analysis and evaluation of the influence of heat storage material on coke oven flue gas exothermic process

Sufficient heat storage and proper flue-gas outlet temperature were prerequisites for selective non-catalytic reduction denitrification in coke oven regenerators. This work performed an energy balance analysis on the established regenerator model to obtain a new thermal storage evaluation index ? total thermal storage temperature. Furthermore, ten cases of thermal storage parameters were set to analyze the effects of thermal effusivity and thermal diffusivity on heat storage and transfer. The transient simulation results shown that the channel shape of the lattice brick limited the uniformity of fluid-solid heat transfer and temperature distribution during the 30 minutes commutation period, and the temperature window (1100~1300 K) suitable for selective non-catalytic reduction denitration slowly moved down. The increase of thermal effusivity led to the rise of heat storage and reduction of flue-gas outlet temperature. However, the transform in thermal diffusivity did not contribute substantially to the heat storage performance. Besides, the temperature-time-height equation obtained by fitting was used for predicting the suitable location of selective non-catalytic reduction denitration temperature. The total thermal storage temperature was positively correlated with the flue-gas outlet temperature and negatively correlated with the heat storage capacity. The total thermal storage temperature evaluated the effects of material properties on heat storage and flue gas outlet temperature.

Numerical Simulation of Urea Based SNCR Process in a Trinal-Sprayed Precalciner

In order to study the combustion characteristics, NOx emission and NH3 slip in a new trinal-sprayed precalciner, the simulations of combustion and aqueous urea solution based selective non-catalytic reduction (SNCR) process were conducted by computational fluid dynamics in this precalciner, the effects of different injection heights, different injection flow rates and stratified injection under different flow rates on SNCR process were studied. The results showed that the flow field was symmetrically distributed in the precalciner, and the flue gas from the rotary kiln formed the recirculation region on both sides of the cone body, which increased the residence time of the solid particles. The temperature was mainly between 1100 K and 1250 K in the middle and upper column of the precalciner, which met the demand of the pulverized coal combustion and raw material decomposition. The concentration of NO at the outlet of the precalciner was 559 ppm, moreover, different injection heights and different injection flow rates had a strong influence on NOX removal efficiency and NH3 slip. The aqueous urea solution should be injected at SNCR-1 to prolong the residence time of NH3, and injection flow rate had an optimal flow rate but not the higher the better. When the injection flow rate under stratified injection was 0.019 kg/s, which could play a better optimization role on NO removal efficiency on the basic of the injection flow rate. In consideration of cost effective, a stratified injection with an injection flow rate of 0.019 kg/s and an injection height of 20 m, 25 m and 30 m was suggested as a compromise of a satisfactory NOx reduction rates and reasonable NH3 slip. Under this condition, numerical simulation result showed that NOx concentration at the outlet of precalciner was 297.27 mg/Nm3 and NH3 slip was 4.67 mg/Nm3, meeting emission standard.

Mathematical support for the control system for nitrogen oxide emissions in boilers with furnaces with liquid slag removal

When burning high-calorie low-volatile brands of coal in furnaces with liquid slag removal to achieve the standard concentration of nitrogen oxides in the outlet gases of the boiler, it is necessary to use two methods of reducing the concentration, for example, staged combustion and selective non-catalytic reduction. For optimal control of the two-stage process of successive concentration reduction, it is necessary to develop appropriate mathematical support that guarantees the maintenance of the standard concentration at any load of the boiler and minimizes the operating costs of reducing emissions. The scheme of mathematical support functioning is presented, which is an information processing system, the input of which is a signal from the steam load sensor of the boiler, and the output is a tasks for the regulators of the degree of stepwise combustion of fuel and urea supply, which ensure the optimal mode of operation of the emission control subsystem. The key issues of system development and operation are considered.

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.