Non-catalytic Reduction Research Articles

Modeling De-NOx by Injection Ammonia in High Temperature Zone of Cement Precalciner

The quantity of NOx emission from cement production is second only to thermal power generation and vehicle exhaust. In this paper, a phenomenon found by Taniguchi is used to achieve NOx reduction in the cement precalciner. Based on his results, it is proposed to reduce NOx that ammonia is injected in the high-temperature and lean-oxygen zone (HT-DeNOx) during pulverized coal combustion. For a large cement precalciner (3200 t/d), numerical simulation is used to evaluate the technology of HT-DeNOx combined with the traditional selective non-catalytic reduction (SNCR) method. The results indicate that NH3 and HCN in HT-DeNOx can reduce NO during the reaction process. With very little ammonia injection (normalized stoichiometric ratio NSR=0.1, the normalized stoichiometric ratio), the efficiency of NO reduction by HT-DeNOx is 27.72%. Combining SNCR (NSR=1.1) and HT-DeNOx (NSR=0.1), the reduction efficiency will be improved to 60.05%, compared with 50.83% efficiency when using only SNCR at NSR=1.2.

Experimental kinetic studies on the effects of organic additives on ammonia-based selective non-catalytic reduction process.

The effect of organic components including ethanol, acetic acid, and benzene on ammonia-based selective non-catalytic reduction (SNCR) process has been investigated. Experiments were performed through a quartz tube reactor with simulated flue gas and conducted from 973 to 1373 K. The combustion and pyrolysis properties of organic components were carried out first, it was found that all the combustion processes were completed ahead of the pyrolysis, and the combustion and pyrolysis temperatures for benzene are the highest among the three organic components. Ethanol addition promoted the removal of NO in the temperature range of 973 to 1073 K, and the NO reaction temperature window was broadened, while NO removal was greatly inhibited under a higher temperature over 1100 K. With regard to the effect of addition of multiple organic components on NO removal, the combination of C2H6O and C2H4O2 significantly promoted this process, while the combination of C2H6O/C2H4O2 and C6H6 showed a negative effect on NO removal. The mechanism based on the radicals' reaction has been illustrated, showing the competition of these reactions under different situations.

Chemical Kinetics Modeling and Analysis of Monomethylamine for Power Plants Selective Non-Catalytic Reduction (SNCR) Systems

A study was performed to investigate monomethylamine (MMA) as an alternative or supplementary reagent for selective non-catalytic reduction (SNCR) of nitrogen oxides (NOx) for power plants especially the coal-fired type. A detailed chemical kinetics mechanism for MMA, related to the SNCR NOx reduction process, was modeled using a simplified plug flow reactor (PFR) approach using the CHEMKIN software. Model validation results were in line with reported experimental results. A model sensitivity analysis showed that the normalized MMA/NO stoichiometric ratio (NSR) and the initial NOx concentration are the most critical parameters that significantly affect MMA-based process performance. Additionally, a reduced reaction mechanism and its mechanism tree for this particular process are proposed, consisting of only 18 reactions and 21 species. Simulation comparisons with three other reagents (ammonia, urea, and cyanuric acid), under similar process conditions, indicate that MMA-based SNCR NOx reduction process has a superior performance at much lower temperatures (under 800 K) than conventional SNCR processes, with the added benefit that it does not suffer from ammonia slip problems. The MMA-based SNCR NOx removal system could be applied in cascade mode with other post-combustion NOx removal approaches to extend NOx control to lower temperatures and eliminate the temperature window limitation and potential ammonia slip of conventional SNCR systems. The cascade design is a perfect solution for coal power plants especially at partial load modes of operation which provides more flexibility in performance for such plants. The results of the simulations in this study show that the potential of MMA for SNCR NOx reduction systems at full-scale power plants has significant merit.

Kinetic study and optimization on SNCR process in pressurized oxy-combustion

Pressurized Oxy-combustion is one of the most promising technologies for carbon capture, utilization, and storage (CCUS) of coal utilization. In pressurized oxy-combustion, the removal of acid gas pollutants and the latent heat of moisture condensation are mainly carried out by an integrated direct-contact wash column (DCC). Recent studies have shown that the inlet concentration of NOx in the column is important for the combined removal of NOx and SOx, therefore, it is essential to control the NOx emissions before the DCC. Selective non-catalytic reduction (SNCR) is a promising and economical technology of NOx reduction; however, no study has been conducted on SNCR at elevated pressure, especially in pressurized oxy-combustion. In this paper, kinetic modeling is carried out to explore and optimize the NOx reduction by SNCR in pressurized oxy-combustion. First, the detailed mechanism used in this study is validated by the experimental results in literature. Based on the validation of the detailed mechanism, the effects of different parameters including temperature, oxygen concentration, moisture content, NH3 concentration, and SO2 concentrations on the SNCR performance are analyzed at higher pressures in oxy-combustion atmosphere. The modeling results show that by increasing the pressure from 1 atm to 15 atm, the SNCR de-NOx efficiency increased by 2–3%. The width of the optimum temperature window for maximum De-NOx is broadened from 1250K to 1450K with increasing the pressure from 1 atm to 10 atm. The increase of pressure has no significant effect on thermal de-NOx efficiency with increasing the NH3/NO ratio. At higher pressure (10 atm) the increase in O2 concentration from 1 to 20% the de-NOx efficiency decreases almost twice as much as at 1 atm. The increase of SO2 and moisture contents at high pressure have no significant effect on the de-NOx efficiency. Rate of production (ROP) and sensitivity analysis are performed to determine the dominant reaction paths of de-NOx in pressurized-oxy SNCR process. This study can provide guidance for the process optimization of de-NOx by SNCR in pressurized oxy-combustion.

Technical Route to Achieve Ultra-Low Emission of Nitrogen Oxides with Predictive Model of Nitrogen Oxide Background Concentration

As the most mature denitration technology in the cement clinker burning process, selective non-catalytic reduction (SNCR) has been unable to meet the requirements of ultra-low nitrogen oxide (NOX) emissions under low ammonia escape, thus a hybrid denitration process based on SNCR was established. The process had three steps: reducing the NOX background concentration (NBC), implementing staged combustion, and optimizing the effect of the SNCR. One of the keys to this process was the real-time acquisition of the NBC. In this paper, a multivariate linear regression model for the prediction of NBC was constructed and applied to one 12,000 t/d production line and one 5000 t/d production line. For the 12,000 t/d production line, NBC had a positive correlation with the temperature of the calciner outlet, the pressure, and the temperature of the kiln hood, and it had a negative correlation with the quantity of the kiln coal, the temperature of the smoke chamber, and the main motor current of the kiln. The influence degree of each parameter on the NBC is gradually weakened according to the above order. The determination coefficient (R2) of the model was 0.771, and the mean absolute error and maximum relative error between the predicted and measured NBC were 6.300 mg/m3 and 18.670 mg/m3 respectively.

Ultra-low emission transformation of 600 MW supercritical circulating fluidized bed boilers unit

With the introduction of ultra-low emission environmental protection policies in national and local coal-fired power plants, ultra-low emission transformation of coal-fired power plants is required to be carried out in an all-round way. Under this background, the first 600 MW supercritical circulating fluidized bed (SCCFB) boiler unit in the world have carried out the demonstration of the technical route of ultra-low emission transformation and the research of key technologies. By adopting limestone desulphurization and low nitrogen combustion in furnace, selective non-catalytic reduction (SNCR) technology outside furnace and the integrated desulfurization and dust removal process of flue gas circulating fluidized bed (CFB-FGD), the unit realizes the technical route of ultra-low emission, and has good investment and operation economy, which can adapt to the development trend of environmental protection in the future. The CFB-FGD and dust removal system can further improve the operation economy of the boiler by setting pre-electrostatic precipitator (pre-ESP), designing double-tower and optimizing the single-tower switching mode, optimizing the pressure margin of the induced draft fan, and adopting the coordinated desulphurization operation mode inside and outside the furnace. The research results can provide a reference for the selection of ultra-low emission transformation for 660MW ultra-supercritical CFB boiler unit.

Particulate Matter and NOx Reduction Techniques for Internal Combustion Engine: A Review

Exhaust emission from vehicles contains toxic gases, such as carbon monoxide due to incomplete combustion; hydrocarbons from unburnt fuel; oxides of nitrogen due to higher temperatures in the combustion chamber; oxides of sulfur and particulate matter (mostly soot). These toxic pollutants are responsible for air pollution which further becomes the cause of respiratory diseases in living beings. To curb this problem of air pollution from vehicles, India is preparing to enforce Bharat Stage-VI norms by the year 2020. This policy to leapfrog to BSVI from BSIV, eliminating BS V emission standard, has inspired/challenged inventors to find new ways and means for reducing the levels of pollution drastically. In this paper, technology involved in reducing tailpipe emission mainly particulate matter (PM) and nitrogen oxides (NOx) are discussed. The reviewed NOx reduction techniques involve fuel blending, modified engine design/combustion process and after-treatment of exhaust gases, while for PM reduction, Catalytic convertor techniques PM traps/filters technique, PM centrifugal separators technique are analyzed. It is found through this review that for NOx reduction, SNCR—selective non-catalytic reduction technique is very useful, without any use of a catalyst as remarkable results have been obtained through treating exhaust gases with Urea. Diesel particulate filter (DPF) is the technique used at the commercial level wherein centrifugal particulate separator technique is under development stage.

Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner

Combustion of ammonia (NH3) presents a number of challenges due to its low reactivity, poor flame stability, very low flame speed and high NOx emissions in a range of burning conditions. Therefore, its application in combustion systems requires device modifications, either by adapting existing systems or developing new ones. In this work, a novel combustor fired by a swirl and bluff-body stabilized burner was designed and tested. Initially, flame stability diagrams were established for NH3/H2 fuel mixtures. Then, emissions of NOx and unburnt NH3 were measured for a range of equivalence ratios and NH3 mole fractions in the fuel mixture. In addition, in-flame data for O2 and NOx concentrations and gas temperature were measured for five combustor operating conditions. A parallel mathematical modelling exercise was performed to obtain a qualitative knowledge of the burner aerodynamics and assist the interpretation of the experimental results. The predicted aerodynamic pattern suggests the establishment of an extended central recirculation zone that allows long residence times in the near burner region (NBR) that are critical to ensure stable combustion of the NH3/H2/air mixtures. The measurements revealed that the burner presents a wide range of stable flames for xNH3 between 0.6 and 0.8, showing the positive effects of adding relatively small amounts of H2 to the fuel mixture. The in-flame data show that the flame initiates close to the burner inlet and presents two main reaction zones. NOx is formed in the NBR and is consumed afterwards, through selective non-catalytic reduction reactions. Overall, the present laboratory combustor performs well in terms of flame stability and both NOx and NH3 emissions, and it is foreseen that industrial combustors based on the present design would be able to ensure flame stability and NOx and NH3 emissions control with simple complementary systems.

Simultaneous NOx and Dioxin Removal in the SNCR Process

Nitrogen oxides, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans are pollutants formed during thermal processes, in particular during the combustion of various fuels, including waste. They are classified as dangerous and highly toxic environmental pollutants whose emissions are strictly regulated. Many methods for reducing their emissions are known, but all involve additional production costs. For this reason, effective and cheap methods for removing these pollutants from exhaust gases are still sought. Selective non-catalytic reduction of nitrogen oxides is one of the more effective and cheaper methods for reducing these emissions. However, an alternative to expensive methods for dioxin and furan removal (catalysis, adsorption, etc.) may include using dioxin synthesis inhibitors. The authors propose a method for the simultaneous removal of both pollutants from flue gases using selective non-catalytic reduction technologies with dioxin synthesis inhibitors used as reducing agents.

Ammonia emission estimation for the cement industry in northern China

To quantitatively illustrate the ammonia (NH3) emissions from the cement industry in northern China, 14 cement lines were tested with 26 obtained NH3 emission data, and the average NH3 emission concentration was calculated as 35.29 mg/Nm3. The NH3 emissions of 84.62% of cement lines were above the standard of 8 mg/Nm3. Factors affecting NH3 emissions were analyzed; the ammonia injection amount in the selective non-catalytic reduction (SNCR) and the operation of raw mills were the main factors, and the NH3 emissions increased as the amount of injected ammonia increased, while it decreased with the running of the raw mill. The average NH3 emission factor (EF) was calculated as 0.07 kg NH3/t clinker, which was higher than the official recommended data, meaning more attention should be paid to NH3 emissions in the cement industry. Effective efforts should be made to prevent more NH3 emissions.

Reducing the Formation of Secondary Pollutants in the Process of NonCatalytic Purification of Flue Gases from Nitrogen Oxides

The possibilities of the technology of non-catalytic reduction of nitrogen oxides (SNCR) to reduce the possible formation of secondary pollutants: ammonia, carbon monoxide and nitric oxide (I) are considered. The conditions for the process of reduction of nitrogen oxides by the thermal decomposition products of urea with a minimum formation of the above pollutants are determined.

Numerical Study on the Denitrification Efficiency of Selective Noncatalytic Reduction Technology in Decomposing Furnace

In order to reduce the nitrogen oxide emission of cement plant, the denitrification of decomposing furnace is studied in this paper. Based on Fluent software platform, the 2500 t/d new dry-process cement kiln decomposing furnace of a plant is modeled and simulated by using air fractional combustion technology combined with selective noncatalytic reduction technology. The model and simulation methods are verified by the field test. The effects of the urea injection position and ammonia-nitrogen molar ratio on NO, NH3, and denitrification efficiency are studied by numerical simulation. The results show that the optimal injection position of the urea solution is 12 m, the optimal ammonia/nitrogen molar ratio is 1.8, and the optimal injection velocity of the urea solution is 40 m/s. The simulation results obtained under the optimal parameters are as follows: NO concentration is 187.60 mg/m3, NH3 escape is 32.40 mg/m3, and denitrification efficiency is 74.75%.

Numerical research on the SNCR method in a grate boiler equipped with the innovative FJBS system

Abstract The paper describes numerical simulations of processes occurring in the combustion chamber of a stoker boiler. The main topic of CFD analysis presented in this paper is the process of reducing nitrogen oxides emission using the patented Furnace Jet Boiler System (FJBS) in combination with the selective non-catalytic reduction (SNCR) method (FJBS+). The presented method is characterized by introducing a compressed urea-air mixture into the furnace. The reagent is injected through supersonic nozzles, the operating conditions of which are shown on a separate CFD model. The developed model enabled optimization of the existing NOx reduction system, especially in the case of a boiler operating at maximum load. The overall effect of the operation of FJBS + technology is a significant reduction of NOx emissions, by approximately 57%. The results achieved are comparable to those obtained from measurements. It was also confirmed that the operation of FJBS + has a positive effect on the equalization of temperature distribution in the furnace and the concentration of flue gas components. Finally, a sensitivity analysis on the basis of two parameters, specific heat of the fuel and thermal conductivity is presented.

Effect of Combustible Gas Components on SNCR Reaction with Reducing Agent in Ceramic Kiln

Selective non-catalytic reduction (SNCR) is a denitration method used in NOx process-control of ceramic kiln. In this study, the effect of combustion gas components (CO, H2, CH4) on NOx removal in the SNCR process was investigated, using ammonia and urea as reducing agent in a lab-scale experimental platform. The results showed that the addition of CO slightly promoted the NOx removal efficiency when ammonia was used as reducing agent, while when urea was used as reducing agent, the addition of CO inhibited the denitrification. The increase of H2 and CH4 addition ratio in the simulated flue gas reduced the de-NOx efficiency. With the same addition ratio, the effect of CH4 on the reduction of denitration efficiency was much more obvious than that of H2. When ammonia was used as reducing agent, the ammonia escape was much greater than that of urea.

Decreasing the NOx Emissions at Coke Plants

Various approaches to decreasing toxic emissions of nitrogen oxides at coke plants are described: stepwise air supply; recirculation of smokestack gases; and selective catalytic and noncatalytic reduction of the nitrogen oxides.

Experimental Investigation into NO Removal over Circulating Ash in Selective Noncatalytic Reduction during Circulating Fluidized Bed Combustion

Selective noncatalytic reduction with NH3 (NH3-SNCR) is an important method to control NO emission during circulating fluidized bed (CFB) combustion in which the circulating ash can affect the NO r...

The environmental cost of recovering energy from municipal solid waste

Municipal solid waste (MSW) incinerators require effective flue gas treatment (FGT) to meet stringent environmental regulations. However, this in turn generates additional environmental costs through the impacts of materials and energy used in the treatment – these impacts are currently scarcely known. Therefore, this study uses life cycle assessment to estimate the impacts of different FGT systems typically found in modern MSW incinerators. A total of 12 scenarios are modelled to consider different combinations of the following eight technologies: electrostatic precipitators and fabric filters for removal of particulate matter; dry, semi-dry and wet scrubbers for acid gases; selective non-catalytic and catalytic reduction of nitrogen oxides (NOx); and activated carbon for removal of dioxins and heavy metals. The data are sourced from 90 full-scale incinerators operating in France. The results reveal that a dry system using sodium bicarbonate and selective non-catalytic reduction (SNCR) is the best option for seven out of 18 impacts, including climate change (37.1 kg CO2 eq./t MSW). By contrast, a dry system with calcium hydroxide and selective catalytic reduction (SCR) has the highest impacts in six categories, including climate change (102 kg CO2 eq./t MSW). The wet systems have higher impacts than the dry alternatives, with the semi-dry options being in between. Compared to SNCR, the use of SCR decreases the NOx-related impacts (fine particulate matter formation, terrestrial acidification and photochemical ozone formation) but increases other impacts. For example, the SCR systems have 49–284% greater climate change and 43–150% higher depletion of fossil resources than their SNCR counterparts. Overall, all FGT systems reduce significantly fine particulate matter formation (by 81–88%), photochemical ozone formation (76–90%) and terrestrial acidification (83–90%). However, they also cause 14 other impacts which would not be generated if the flue gas was left untreated, thus creating additional environmental costs. These include climate change, resource depletion and human and ecotoxicities. Therefore, these trade-offs should be considered carefully to minimise the unintended environmental consequences of flue gas treatment from incineration of MSW.

Catalytic oxidation of NH3 over circulating ash in the selective non-catalytic reduction process during circulating fluidized bed combustion

Selective non-catalytic reduction (SNCR) with NH3 as the reducing agent is widely used for the denitrification of flue gas in circulating fluidized bed combustion (CFB) process, where the circulating ash can cause the oxidation of NH3. In this study, the behaviors and mechanisms of NH3 catalytic oxidation over circulating ash were systematically investigated. The results revealed that NH3 could be catalytically oxidized to form NO efficiently by circulating ash. Along with the temperature increasing from 550 °C to 950 °C, the formation of NO increased at first and then decreased. Oxygen was crucial to NH3 catalytic oxidation, while its effects on NO formation were slight at high concentrations. Meanwhile, as the initial NH3 concentration increased, the concentration of NO in the flue gas increased while the selectivity of NO decreased because of the enhanced homogeneous reduction between the residual NH3 and NO. Fe2O3 was confirmed to be one of the principal mineral components in circulating ash to catalyze NH3 oxidation. In addition, the mechanisms of NH3 oxidation over circulating ash were also investigated. It was validated that NH2 on Lewis acid sites were the main NH3 adsorbed species (ad-species), and the main oxidation intermediates of NH3 ad-species were bidentate and bridged nitrates in the presence of O2.

Економічні аспекти впровадження заходів зменшення викидів з димовими газами на ТЕС України

The results of technical and economic calculations of the implementation of environmental technologies at the existing power units of coal-fired TPPs in Ukraine are presented in accordance with the National Plan for Reducing Flue Gas Emissions. The following technologies for cleaning flue gases are considered: capture of solid particles – electrostatic filters and cloth filters; reduction of nitrogen oxide emissions – selective catalytic reduction and selective non-catalytic reduction; reduction of sulfur dioxide emissions – half-dry desulfurization, wet limestone desulfurization, and the latest integrated desulfurization. We calculate capital costs for each technology and total costs as well as changes in the cost of electric energy over the life cycle. We analyze investment expenditures and increase in the cost of electric energy at the implementation of technological measures for flue gases cleaning from the emissions of dust particles, sulfur dioxide, and nitrogen oxides at all power units of Ukrainian TPPs. It is shown that the introduction of technologies for flue gases cleaning from the main air pollutants requires significant investment in environmental measures. Finally, we determine variants of cleaning systems that are in good agreement with the European Community emission standards for the main pollutants and the most economical combination of different technologies, namely wet limestone for sulfur dioxide removal, electrostatic filter for dust removal, selective catalytic reduction for removal of nitrogen oxides.

Study on ultra-low NOX emission technology of 660 MW ultra-supercritical circulating fluidized bed boiler

For the first 660MW ultra-supercritical circulating fluidized bed boiler in China, the original NOX emission concentration would be controlled and maintained below 50mg/Nm3, by improving the uniformity of bed temperature and bed pressure, strengthening the secondary air fractional combustion, optimizing the combustion temperature and operating oxygen and so on. Meanwhile, selective non-catalytic reduction (SNCR) technology with urea as reducing agent is selected as the auxiliary method to ensure the boiler achieves ultra-low NOX emission under full load conditions.