Nitrogen Oxides In Flue Gases Research Articles

Collaborative removal of NOx and toluene in flue gas driven by aerobic denitrifying biotrickling filter

Nitrogen oxides (NOx) and volatile organic compounds (VOCs) may cause ozone formation and photochemical smog pollution, which may damage to human health and ecological environment seriously. An aerobic Denitrifying BioTrickling Filter (DBTF) for collaborative removal of nitrogen oxides (NOx) and toluene in flue gas was investigated. NOx and toluene removal efficiency were up to 90% and 95%, respectively. Mycobacterium, Comamonas and Pseudomonas were predominant bacteria; Mycobacterium, Pseudomonas, Comamonas, Microbacterium, Reyranella, Stenotrophomonas and Alicycliphilus were the core toluene oxidizing-denitrifying genera, denitrification genes (narGHI, nirK, nasB, napAB, nosZ and norC) and toluene oxidation genes (tom, E1.14.13.7, xyl, cat, todE, tes, mhp, pch, pob, pca, lig, gal) responsible for bacterial oxidation of toluene and NOx reduction, as shown by16S rDNA and metagenomic sequencing. Bacterial oxidation of toluene was coupled to NOx reduction in which toluene served as the electron donor while NOx served as the electron acceptor and thereby redox between toluene and NOx was formed, toluene was degraded through the classical aerobic aromatic compound degradation pathway. DBTF was capable of both toluene oxidation and NOx reduction by denitrification. These results show that the DBTF is achievable and open new possibilities for applying the DBTF to simultaneous removal of NOx and VOCs.

Case study of the application of pervious fly ash geopolymer concrete for neutralization of acidic wastewater

Coal-fired power plants generate electricity and produce pollutants, including sulfur dioxide and nitrogen oxides in flue gases, as well as particulates, i.e., fly ash and bottom ash. In addition, the processes for removing toxic gases from flue gas and scale from boilers generate the acid wastewater, which requires treatment before release to the environment. Hence, there are many wastes generated from these power plants, and well managed waste treatment is required. Due to the alkalinity of geopolymer, therefore, this research proposes the use of fly ash for the production of pervious geopolymer concrete to neutralize the acidic wastewater. Its high surface area and porosity makes pervious geopolymer concrete suitable for use in wastewater infiltration and neutralization. Crushed limestone to fly ash mass ratios of 8, 10 and 12 were used in the mix design to produce the pore of pervious geopolymer concretes. Samples of 10-cm cube and 30 × 30 × 5 cm were fabricated, and the physical properties and acid neutralization were tested. A 0.001 M HCl solution was used to represent acidic wastewater, and batch and continuous processes of acid neutralization were compared. Results show that the density of the pervious geopolymer concrete increased with the increasing limestone content from 2.32 to 2.57 g/mL, with the percent voids of 20–30% and water flow rate through the concrete of 3.4–3.9 L/min. The compressive strength of the pervious geopolymer concrete was in the range 5.7–8.3 MPa, conforming to the requirement for pervious concrete as a permeable base and edge drain in pavement applications. With the alkaline properties of the geopolymer, neutralization of acidic wastewater from the operational processes of a power plant could be achieved. For the batch operation, concrete with a crushed limestone to fly ash mass ratio of 8 was most efficient, as it provided the highest volume of acid neutralization of 450 L. Sustainable production of pervious geopolymer concrete is proposed by using waste heat from the combustion process in a power plant.

Predicting the thermodynamics of aluminum dross denitrification of flue gas

Existing alumina extraction and material production methods result in the formation of harmful ammonia gas or ammonia water originating from aluminum nitride (AlN) in dross. Therefore, in this study, aluminum dross was used as a denitration reagent to eliminate nitrogen oxides in flue gas and AlN in dross. Based on the proposed scheme, thermodynamic calculations were performed to investigate the denitrification effect and reduction of aluminum dross in flue gas. The results show that equilibrium concentrations of NO, NO2, and HF in the flue gas were influenced mainly by temperature; their concentrations increased with an increase in the temperature, reaching 4.4 × 10−20, 1.7 × 10−38, and 7.0 × 10−8 g/m3, respectively, at 923 K. The Gibbs free energy corresponding to the reaction of CO2 with Al/AlN in aluminum dross was −377/–120 kJ/mol. HF, originating from the reaction of NaF and water vapor, maintained an extremely low concentration of 6.99 × 10−8 g/m3 at 923 K. These results indicate that aluminum dross processing may clean the flue gas and increase the calorific value while eliminating the hazards of AlN. The results obtained herein will provide theoretical guidance toward new avenues of aluminum dross utilization.

Biological treatments of mercury and nitrogen oxides in flue gas: biochemical foundations, technological potentials, and recent advances.

Nitrogen oxides (NOx) and mercury (Hg) are commonly found coexistent pollutants in combustion flue gas. Ever-increasing emission of atmospheric Hg and NOx has caused considerable environmental risks. Traditional flue gas demercuration and denitration techniques have many socioeconomic, technological and environmental drawbacks. Biotechnologies can be a promising and prospective alternative strategy. This article discusses theoretical foundation (biochemistry and genomic basis) and technical potentials (Hg0 bio-oxidation coupled to denitrification) of bioremoval of Hg and NOx in flue gas and summarized recent experimental and technological advances. Finally, several specific technical perspectives have been put forward to better guide future researches.

A study of the effect of air temperature on the possibility and rate of formation of nitrogen oxides in boiler flue gases

We consider the mechanisms of formation of nitrogen oxides in boiler flue gases. Thermodynamic calculations are used to determine the possibility and rate of formation of nitrogen oxides in the temperature range from 25 to 2000°C. We apply the methods of geometric thermodynamics to demonstrate the changes in the Gibbs free energy of nitrogen oxides formation reactions and determine the conditions of achieving the chemical equilibrium for these reactions. An analysis of concentrations of formed nitrogen oxides and temperatures of the jet flame under different conditions of mixture formation was performed. We produced and analyzed a number of diagrams of distribution of the flame temperatures and nitrogen oxide concentrations in the calculation area for the temperatures of the oxidant of 20, 60, 100, 150 and 200°C. Mathematical simulation of the process of gaseous fuel combustion was performed using FlowVision software package. The analysis of the results showed that the decrease in the temperature of the air supplied as an oxidant results in a considerable drop in the concentration of nitrogen oxides in flue gases without any significant impact on the changes of the flame temperature. The results of the study can be used in addressing the problems of optimization of boiler plants in order to reduce harmful flue gas emissions.

Computer model of a gas path in a microturbine unit

Microturbine units are used for autonomous supply of buildings and engineering facilities with heat and electric energy. Gas path of a microturbine unit contains a combustion chamber and a set of gas-burners which provide mixing of the natural gas with the air, followed by total combustion of the obtained gas-air mixture. The known structures have two essential disadvantages which reduce operational efficiency of a gas turbine as part of the microturbine unit. The first disadvantage is caused by inhomogeneous nature of the “gas-air” flammable mixture, which leads to an incomplete combustion of fuel and emission of nitrogen oxides harmful for the environment. The second disadvantage is connected with a loss of mechanical strength of structural elements exposed to the impact of high-temperature products of combustion. The article proposes methods of boosting the resource of a combustion chamber by enhancing its mechanical durability with a simultaneous reduction of the content of nitrogen oxides in flue gases. The first method is in the use of power elements installed inside the combustion chamber. The second method of boosting the resource of the combustion chamber is connected with accurate profiling of windows through which cylindrical gas-burners get inserted. The third method is based on improving the quality of mixture formation in the casing of the gas-burner. Combined application of the proposed modification activities allows reducing the extent of harmful emissions as well as boosting the resource of the microturbine unit.

Сценарії розвитку джерел централізованого теплопостачання України, включених до Національного плану скорочення викидів

Emissions of nitrogen oxides are the main emissions of pollutants from the burning of natural gas at the boilers of district heating system of Ukraine and currently are to 200 – 240 mg/nm3 without the use of technologies for reduction. The integrated application of technologies that prevent the primary formation of nitrogen oxides with a total efficiency of their total reduction of 50-60% will ensure compliance with the requirements of Directive 2010/75/EC (the concentration of nitrogen oxides in flue gas cannot exceed 100 mg/nm3) at boilers district heating system of Ukraine, included in the National Plan for Reducing Emissions from Large Combustion Plants with a thermal power of 50 MW or more. The total specific costs for the integrated implementation of these technologies for reducing nitrogen oxide emissions are from 165.88 to 283.35 UAH/kW of installed heat power of a boiler or a boiler house. We formed scenarios for the development of these boiler houses of district heating to achieve compliance with the new, more stringent environmental requirements of Directive 2010/75/EC: progressive (technical re-equipment by replacing physically worn out and technologically obsolete boilers with modern energy-efficient ones), traditional (complete reconstruction of existing obsolete boilers with an extension of time of equipment operation), and conservative (modernization of existing boilers only to ensure compliance with new environmental requirements). For these boilers were determined the necessary capital expenditures for the implementation of proposed development scenarios. Under the progressive scenario, the capital costs of replacing boilers with a total heat output of 0.675 GW, which were put into operation before 1960, will be equal to 546.75 million UAH. According to the traditional scenario, the capital costs for complete reconstruction of existing boilers with a total thermal capacity of 3,518 GW, which were put into operation from 1960 to 1980, will be 1,424.79 million UAH. According to the conservative scenario, the capital expenditures for modernization of boilers with a total thermal capacity of 1.252 GW, which were put into operation from 1980 to 2011, will constitute 338.04 million UAH. The total capital expenditures for the development of 20 boiler houses of the district heating system of Ukraine with a total heat output of 5.445 GW included in the National Plan for Reducing Emissions from Large Combustion Plants, under these scenarios are ~ 2.31 billion UAH (85.54 million US dollars).

RESEARCH OF INFLUENCE OF AIR TEMPERATURE ON THE LEVEL OF NITROGEN OXIDES IN SMOKE GASES OF BOILER PLANTS

The analysis of the values of the concentrations of the formed nitrogen oxides and the temperatures of the jet plume under various conditions of mixture formation is carried out. The plots of the distribution of torch temperatures and concentrations of nitric oxide in the calculated area for oxidizer temperatures of 20, 60, 100, 150, and 200 ° C were obtained and analyzed. Mathematical modeling of the gaseous fuel combustion process was carried out using the FlowVision software package. An analysis of the results showed that a decrease in the temperature of the air supplied as an oxidizing agent leads to a significant decrease in the concentration of nitrogen oxides in flue gases, while not significantly affecting the change in the flame temperature. The research results can be used to solve the problems of optimizing boiler plants, in order to reduce harmful flue gas emissions. Further modeling is planned to determine the dependence of the influence of various factors on the degree of formation of nitrogen oxides in the flue gases of boiler plants.

Application of Non-Thermal Plasma for NOx Reduction in the Flue Gases

Over the years, ever more stringent requirements on the pollutant emissions, especially NOX, from combustion systems burning natural gas are introduced by the European Union (EU). Among all NOX reduction methods, the flue gas treatment by plasma is widely applied and could be used for both small scale and domestic combustion systems. However, the removal efficiency depends on concentrations of oxygen, water vapor, traces of hydrocarbons, and nitrogen oxides in flue gas. In order to analyze the application of the NOX reduction for small-scale or domestic combustion systems, experiments of NOX reduction by non-thermal plasma from real flue gases originating from premixed methane combustion at different equivalence ratio (ER) values were performed. It was determined that the residual oxygen in flue gas plays an important role for improvement of NO to NO2 oxidation efficiency when O2 concentrations are equal to or higher than 6%. The power consumption for the plasma oxidation constituted approximately 1% of the burner power. In the case of ozone treatment, the addition of O3 to flue gas showed even more promising results as NO formed during combustion was fully oxidized to NO2 at all ER values.

REVIEW OF TECHNOLOGIES FOR REDUCING OF NITROGEN OXIDES EMISSIONS ON COAL-FIRED POWER PLANTS

The paper discusses the technologies of reducing the concentration of nitrogen oxides in the exhaust flue gases during the combustion of coal in the boiler units of power plants that produce heat and electrical energy. According to the results of the analysis, the influence of the method of oxidizing gaseous nitrogen oxides on the efficiency of the treatment plant was revealed. It has been established that during the reconstruction of the gas cleaning system, the advantage is in the technology in which, at the first stage, a gaseous oxidizer is added to the gas flow to convert nitric oxide into heavier water-soluble compounds. At the second stage, an aqueous solution of alkali metal compounds or ammonia is injected into the gas mixture for chemical bonding of the products of oxidation reactions. Thus, this technology allows reducing the concentration of nitrogen oxides in flue gases by 90–95% and meeting the requirements of regulatory documents on emissions of pollutants into the environment. Bibl. 11, Fig. 4, Tab. 5.

Studying the Aerodynamics of the TPP-210A Boiler Furnace When It Is Shifted to Operate with Dry-Ash Removal and Vortex Fuel Combustion

To reduce the amount of nitrogen oxide emissions and achieve more reliable operation of the TPP-210A boiler, a process arrangement for firing Grade TR Kuznetsk coal that involves using straight-flow burners and shifting the boiler from slag-tap to dry-ash removal is developed. Owing to a large burner downward slope angle and special arrangement of burners and nozzles, four large vertical vortices rotating in opposite directions are produced in the furnace lower part, as a result of which the combustion products dwell for a longer period of time in the burning zone and more complete fuel combustion is achieved. For verifying the operability and efficiency of the proposed combustion arrangement, investigations on a boiler furnace physical model were carried out using a technique for visualizing fuel jets and secondary and tertiary overfire air jets. The fuel jet temperature boundaries in the course of jet propagation in the furnace model are also determined. The study results have shown that staged fuel combustion will be set up with using the proposed arrangement of burners and nozzles. In addition, large vertical vortices produced in the furnace lower part will help to achieve more efficient use of the dry bottom hopper heating surfaces, due to which lower coal combustion product temperature in the furnace upper part and smaller content of combustible products in fly ash will be obtained. Owing to low values of air excess factor at the pulverized coal burner outlet and gradual admission of air into the vortex zone through a few nozzles with intense inner recirculation of combustion products to the jet initial section, staged combustion of pulverized coal and low nitrogen oxide emissions will be secured. Owing to expansion of fuel jets, a rapid growth of mass in the fuel jet is achieved, which is obtained both due to ejection of the jet itself and due to forced admission of hot fuel gases from other jets. Investigations carried out on the physical model have confirmed that the proposed combustion arrangement features high efficiency and that a low content of nitrogen oxides in flue gases is obtained.

TECHNICAL SOLUTIONS FOR DECREASING NOX EMISSIONS AT COAL THERMAL ELECTRIC POWER STATIONS

Most power-generating units at the Ukrainian thermal electric power stations were designed to burn hard coal mined in Ukraine, but today due to physical depreciation of the stations, those units are in non-project manoeuvring peaking operation what leads to the increase in both the specific fuel equivalent consumption and in harmful environmental emissions. The purpose of the research is to develop recommendations on the selection of optimal technical solutions aimed at reducing NOx emissions of oxides at the operating boilers of Burshtyn thermal electric power stations (TEPS) under the conditions of regime-technological measures. The article analyzes the main approaches to developing and selecting technological methods aimed at reducing emissions of coal thermal power stations and identifies prospects for their work in accordance with modern environmental requirements. The mechanisms of the transformations the organic fuel bound nitrogen undergoes when heated are determined. To reduce the amount of NOx emissions in combustion products, it is offered to apply the regime-technological mode of the preliminary heating the pulverized coal mixture. The results of thermo chemical studies of coal samples used at Burshtyn TEPS are presented. The temperature ranges are determined at which the maximum emissions of volatile combustible compounds takes place before to the upper flammability limit of the pulverized coal mixture is reached. It was determined that under the conditions of actual burning process, there is a clear sequence: a release of volatile components and burning of the coke residue; heating of the pulverized coal mixture; emission of volatile combustible compounds; their burning; heating of the coke residue up to initiation of its combustion; the coke residue burning-out. A pulverized coal stream is brought into the furnace without being preliminary mixed up with air. While burning the pulverized coal stream, fuel particles are heated and degassed in the zone immediately adjacent to the burner section where there is a shortage of oxygen, whereas the oxygen concentration in the flow is a gradually increasing. The regime-technological measures that are aimed at inhibiting NOx oxides formation by preliminary heat treatment of the pulverized coal mixture; they make it possible to obtain the maximum emissions of volatile combustible compounds before the upper flammability limit of the pulverized coal mixture is reached. It was found out that heat treatment should be carried out at temperature from 540-580° C. This is the temperatures range when the maximum emission of volatile combustible compounds takes place. After this combustion occur in an environment that is practically devoid of oxygen, where competing reactions of formation of volatile components and molecular nitrogen occur simultaneously. Thereafter, combustion can proceed in the practically oxygen-free environment with competing parallel reactions the forming volatile components and molecular nitrogen. This method allows to almost halving the concentration of nitrogen oxides in flue gases.

Removal of Nitrogen Oxide Based on Anammox through Fe(II)EDTA Absorption

Nitrogen oxides in flue gas cause considerable environmental and health problems. In this study, the NO removal through Fe(II)EDTA absorption based anaerobic ammonium oxidation (Anammox) reduction was first evaluated in batch tests. The removal efficiency and removal rate of NO reached 74.5%–85.4% and 1.62–15.48 μmol NO gVSS–1 h–1 with Fe(II)EDTA absorption, respectively. The optimal temperature and pH for Fe(II)EDTA absorption based Anammox reduction of NO was 30 °C and 7.0 in the range of temperature from 25 to 45 °C and pH from 6.5 to 8.0, respectively. The maximum specific substrate utilization rate and half-saturation constant of Fe(II)EDTA-NO were experimentally determined as 0.09 mmol N gVSS–1 h–1 and 1.338 mM, respectively. Then, a sequencing batch reactor (SBR1) performing Fe(II)EDTA absorption based Anammox reduction for NO removal was continuously operated for 35 days. The NO removal performance of SBR1 decreased gradually, and the NO removal efficiency and NO removal rate decreased from 86.65%...

Physicochemical and Biochemical Approaches for Treatment of Gaseous Emissions Containing NOx

Nitrogen oxides (NOx) are the cause of severe environmental problems such as acid rain, smog formation, an increase in ground-level ozone, depletion of the ozone layer, and global warming and can indirectly affect human and animal health. Considering its severe polluting aspects, many approaches have been utilized so far for the development of a technology that efficiently removes NOx from the industrial gaseous emissions. These control techniques can be broadly classified as primary and secondary techniques. Primary control techniques modify the existing combustion methods to limit the production of NOx, which includes various physical and chemical approaches, whereas the secondary NOx control techniques involve chemical reduction of NOx in flue gas using a chemical reducing agent such as ammonia or urea, reacting on a specially engineered catalyst surface or by absorption of the NOx into a special chelating liquid, and then reducing the chelate-NOx complex to regenerate the chelate using chemical and biochemical approaches, which involve compost biofilters, trickling bed biofilters, packed bed reactors, and several other types of bioreactors. The overall efficiency of the process depends on the absorption efficiency of the chelating agent, the denitrification capacity of the microorganism and the process parameters and physicochemical conditions. The authors highlight the essential features of various physicochemical and biochemical NOx control strategies and techniques. Further, extensive research and development efforts are recommended to improve existing technology for effective NOx control.

Characteristics of Continuous Analyzers for Nitrogen Oxides in Flue Gas from Municipal Incinerators

Characteristics of Continuous Analyzers for Nitrogen Oxides in Flue Gas from Municipal Incinerators

CuO/NiO monolithic catalysts for NO x removal from nitric acid plant flue gas

The performance of copper/nickel oxide catalysts supported on ceramic monoliths of γ-alumina/silicate, for the selective catalytic reduction (SCR) of nitrogen oxides in flue gas from nitric acid plants ([NO]/[NO x ]=0.7) has been studied. The monoliths prepared were characterised by thermogravimetry, nitrogen adsorption–desorption, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), electron probe microanalysis wavelength dispersion spectroscopy (EPMA-WDS) and their mechanical strengths were measured. The support composition and heat-treatment temperature was optimised to obtain monolithic structures with satisfactory mechanical and textural properties. Thus, a monolith with a γ-alumina/silicate weight ratio of 2/3 was selected to give the best combination of textual and mechanical properties. The influence of active phase (CuO/NiO) content and operating conditions (residence time, [NH 3]/[NO x ] ratio) on the NO x conversion and ammonia slip was studied at laboratory scale to determine the optimum conditions for operation at pilot-plant scale. The maximum catalytic activity was achieved for a catalyst with CuO content of 6.3 wt.%. At higher active phase concentration a decrease in the catalytic activity was observed, related to the formation of copper oxides crystals detected by XRD. The presence of these species increase the reaction rate of the competitive ammonia oxidation reaction and thus, reduce the ammonia concentration in the outlet. The selected monolithic catalyst was tested at pilot-plant scale with real gases from a nitric acid production plant achieving NO x conversions of around 90 vol.%, with ammonia emissions lower than 10 ppm, at 230 °C and GSHV (NTP) of 10,600 h −1.

Reduction of nitrogen oxides in flue gases

In recent years there has been an unprecedented growth and development in flue gas control technologies capable of reducing NO x emissions to the low levels required by current legislation. Major post-combustion technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The current status of these technologies is summarised, and the advantages and disadvantages of both methods are reviewed. SCR offers the advantage of greater NO x reduction and has therefore been widely adopted in industrialised countries with stringent emission limits, while SNCR requires lower capital costs and is increasingly being applied by industries in developing countries. Other techniques, such as hydrocarbon-selective catalytic reduction (HC-SCR) and direct catalytic decomposition of NO x, although showing some promise in laboratory experiments, are still not commercially viable.

Catalysts for reduction of nitrogen oxides in flue gases

Catalysts for reduction of nitrogen oxides in flue gases

Catalyst for selective reduction of nitrogen oxides in flue gases

Catalyst for selective reduction of nitrogen oxides in flue gases

Selektive Reduktion von Stickoxiden in Rauchgasen – Stand der Technik und neue Wege

AbstractSelective reduction of nitrogen oxides in flue gas–state of the art and trends. The selective reduction of nitrogen oxides by ammonia may be catalyzed by different substances. The suitable choice of the catalyst is determined largely by where the reduction step is placed in the overall process. The technical problems and the required catalyst properties are demonstrated and discussed. A new process, based on a periodically operated reactor, avoids some of the difficulties otherwise encountered.