NOx Absorption Research Articles

NOx scrubbing with H2O2/HNO3 solutions achieved with a laboratory bubble contactor

In this work, the removal of dilute nitrogen oxides NOx from the gaseous effluents of Tunisian nitric acid plant by absorption into aqueous hydrogen peroxide solutions containing or not nitric acid was studied. All semi-continuous absorption tests were carried out at ambient conditions and at 40 Pa as NOx partial pressure. The effects of the gas flow rate, the initial H2O2 concentration and the presence of HNO3 on the NOx absorption efficiency (ANOx) were studied. The tests results revealed that ANOx increases with an increase in initial H2O2 concentration in the scrubbing liquid, but decreases with an increase of gas flow rate. Furthermore, the presence of nitric acid in the aqueous hydrogen peroxide solution has a positive effect on ANOx. These results confirmed that the removal of NOx liberated from the plants of the Tunisian Chemical Group (TCG) by absorption into H2O2 solution is a feasible and an effective solution.

ИСПОЛЬЗОВАНИЕ ЦИКЛОНА И ЭФФЕКТА "МИКРОВЗРЫВОВ" КАПЕЛЬ ВОДОТОПЛИВНОЙ ЭМУЛЬСИИ ПРИ КОМПЛЕКСНОЙ ОЧИСТКЕ ВЫХЛОПНЫХ ГАЗОВ ДВИГАТЕЛЯ ВНУТРЕННЕГО СГОРАНИЯ

Obtaining additional energy due to the deep utilization of the internal combustion engine (ICE) heat losses al-lows saving fuel used for the operation of the ship's power plant. This accordingly leads to a reduction of the emissions of harmful substances into the atmosphere, contributes to meet the more stringent standards of the International Maritime Organization (IMO) governing the limits of these emissions. The study aims to develop the system of complex exhaust gas cleaning for an internal combustion engine (ICE). For solving the tasks in the technology of proposed method there were 6 stages of technological process envisaged. Based on experimental and theoretical studies, a setup for complex exhaust gas cleaning using a cyclone and the effect of "microexplosions" of a water-fuel emulsion (WFE) droplet was developed. It has been established that as a result of activated WFE combustion we obtain at the engine outlet exhaust gases of a corresponding composition with a reduced amount of toxic ingredients down to 35 % and below and most importantly – an equimolar ratio of NO2 /NO to NOx. Experimental studies have shown that in the condensate acid under these conditions, an average concentration of about 57 % is established, which ensures a sharp increase in the absorption of SO2 and NOx. The presence of an equimolar (or almost this) NO2 /NO ratio in gases ensures the passivation of the condensation surface in exhaust gas boiler (EGB) from carbon steel. This ensures a sharp decrease in the low-temperature corrosion intensity, an increase in the operating reliability of condensation surfaces and the possibility of a sharp increase in the engine exhaust gas utilization depth to 80...90 °C instead of 160 °C. For the final gas cleaning, it was proposed to install a venturi scrubber and a cyclone-absorber on the gas path of ICE. Based on experimental studies, it has been established that the installation of a condensation heating surface in the EGB reduces the NOx content in gases by 55 %, SO2 - by 50 %, and the content of solid particles - by 3 times. The developed complex system can be used to clean the ICE gases to the level recommended by IMO.

Oxidation and absorption of SO2 and NOx by MgO/Na2S2O8 solution at the presence of Cl−

Based on advanced oxidation technology, a new method for the simultaneous removal of SO2 and NOx from industrial flue gas using Na2S2O8/MgO was proposed. The method does not require the body structure of the wet desulfurization device is changed but adds Na2S2O8 to the original equipment to realize simultaneous desulfurization and denitrification. After determining Cl− was additive, the effects of various reaction factors on the simultaneous removal of SO2 and NOx were investigated, including the Cl− concentration, the initial concentration of the oxidant, the initial pH value of the solution, and the reaction temperature. According to the characterization of removal products and the types of free radicals involved in the reaction by XRD, XPS, and EPR, the reaction mechanism was elucidated. The experimental results indicated that the removal products were mainly sulfates and nitrates. The free radicals involved in the reaction were SO4·−, ·OH, and Cl·, and the key free radical was Cl·.

Numerical simulation of welding fume lung dosimetry

Exposures to airborne particles and toxic gases generated by welding fabrication activities will potentially lead to various diseases. Accurate information on the transport and deposition of such aerosols in the respiratory system is critically needed for precise health risk assessments. To address the data demand mentioned above, a multiscale computational fluid-particle dynamics (CFPD) model was developed in this study. Specifically, a virtual fabrication shop was integrated with a virtual human in the numerical model to evaluate the effects of ventilation condition, particle size, and gas species on the lung uptakes of those welding fume particles and gases. Welding fume particle and gases transmission, transport, and deposition have been simulated and analyzed starting from the emission source to the subject-specific human respiratory system via oral inhalation. Spherical iron particles with diameters of 100, 190, and 830 nm were simulated. The transport and absorption of NOx and CO were predicted too. Steady-state inhalation with 11.87 L/min was applied with two different air filter ventilation conditions. The numerical results indicate that the ventilation condition can significantly influence welding gas transport and deposition. The pulmonary gas absorption rate is much higher at poor ventilation conditions. The air-tissue absorption coefficient is another crucial factor that can impact pulmonary gas absorption. The total particle deposition fractions (TDFs) from mouth/nose to generation 6 (G6) are less than 18.0%, and particles mostly deposit in the oral cavity. Regional and local particle deposition data demonstrate that particles tend to enter the two upper lobes more than the other three lobes. In summary, this study paves the way to build a personalized in silico tool based on CFPD models for noninvasive precise health risk assessments associated with different welding activities.

Simulation Study of an Oxy-Biomass-Based Boiler for Nearly Zero Emission Using Aspen Plus

Bioenergy integrated CO2 capture is considered to be one of the viable options to reduce the carbon footprint in the atmosphere, as well as to lower dependability on the usage of fossil fuels. The present simulation-based study comprises the oxy bio-CCS technique with the objective of bringing about cleaner thermal energy production with nearly zero emissions, CO2 capture and purification, and with the ability to remove NOx and SO2 from the flue gas and to generate valuable byproducts, i.e., HNO3 and H2SO4. In the present work, a simulation on utilization of biomass resources by applying the oxy combustion technique was carried out, and CO2 sequestration through pressurized reactive distillation column (PRDC) was integrated into the boiler. Based on our proposed laboratory scale bio-CCS plant with oxy combustion technique, the designed thermal load was kept at 20 kWth using maize stalk as primary fuel. With the objective of achieving cleaner production with near zero emissions, CO2 rich flue gas and moisture generated during oxy combustion were hauled in PRDC for NOx and SO2 absorption and CO2 purification. The oxy combustion technique is unique due to its characteristic low output of NO sourced by fuel inherent nitrogen. The respective mechanisms of fuel inherent nitrogen conversion to NOx, and later, the conversion of NOx and SO2 to HNO3 and H2SO4 respectively, involve complex chemistry with the involvement of N–S intermediate species. Based on the flue gas composition generated by oxy biomass combustion, the focus was given to the fuel NOx, whereby different rates of NO formation from fuel inherent nitrogen were studied to investigate the optimum rates of conversion of NOx during conversion reactions. The rate of conversion of NOx and SO2 were studied under fixed temperature and pressure. The factors affecting the rate of conversion were optimized through sensitivity analysiês to get the best possible operational parameters. These variable factors include ratios of liquid to gas feed flow, vapor-liquid holdups and bottom recycling. The results obtained through optimizing the various factors of the proposed system have shown great potential in terms of maximizing productivity. Around 88.91% of the 20 kWth boiler’s efficiency was obtained. The rate of conversion of NOx and SO2 were recorded at 98.05% and 87.42% respectively under parameters of 30 °C temperature, 3 MPa pressure, 10% feed stream holdup, liquid/gaseous feed stream ratio of 0.04 and a recycling rate of the bottom product of 20%. During the simulation process, production of around four kilograms per hour of CO2 with 94.13% purity was achieved.

Nitrogen oxides absorption into aqueous nitric acid solutions containing hydrogen peroxide tested using a cables-bundle contactor

This work aims to study the removal of dilute nitrogen oxides from gaseous effluents by absorption into aqueous nitric acid solutions containing or not hydrogen peroxide. NOx absorption tests (pNOx = 50 Pa with a varying composition) were performed in a cables-bundle contactor at ambient conditions. Tests runs were carried out with the recycling of the absorbent solution (0–8 mol/l for HNO 3 and 0–2 mol/l for H 2 O 2 ) allowing to observe the temporal evolution of the absorption efficiency. The effects of the different operating conditions on the NO, NO 2 and NOx absorption performances (A) were investigated. Results revealed in all the cases that A NOx increases when increasing the proportion of more oxidized species in NOx. Without H 2 O 2 A NOx decreases when the HNO 3 concentration of the solution is increased and also with the recycling of the scrubbing liquid, leading to NOx desorption phenomena. When hydrogen peroxide is added to the nitric acid solution the NOx absorption performances are much higher and increase with the initial H 2 O 2 concentration and the HNO 3 concentration. • A NOx increases when increasing the proportion of more oxidized species in NOx. • Without H 2 O 2 , A NOx decreases when the HNO 3 concentration of the solution is increased and also with the recycling of the scrubbing liquid, leading to NOx desorption phenomena. • When H 2 O 2 is added to HNO 3 solution, A NOx is much higher and increases with the initial concentration of H 2 O 2 and HNO 3 .

Experimental Study on Simultaneous Absorption and Desorption of CO2, SO2, and NOx Using Aqueous N-Methyldiethanolamine and Dimethyl Sulfoxide Solutions

MDEA+DMSO aqueous solutions, made up of N-methyldiethanolamine (MDEA) and dimethyl sulfoxide (DMSO), were explored for the simultaneous absorption of CO2, SO2, and NOx. Experiments in a semibatch a...

The role and mechanism of triethanolamine in simultaneous absorption of NOx and SO2 by magnesia slurry combined with ozone gas-phase oxidation

A novel absorption method was developed and used for the simultaneous removal of SO2 and NOx, whereby triethanolamine (TEA)-modified magnesia was utilized as an absorption slurry and combined with gas-phase oxidation by ozone. TEA was first used as the additive to magnesia slurry to facilitating the aqueous absorption of NOx and SO2. The injection of O3 increased the solubility of NOx considerably. Furthermore, the addition of TEA facilitated the absorption of NOx in wet combined desulfurization and denitrification processes. In addition, experiments on operating factors included initial pH, TEA concentration, and the effect of SO2 were performed in this study. The results show that after the addition of TEA to a magnesium-based slurry, the absorption efficiency of NO2 improved to almost 100% under alkaline conditions. However, the improvement effect of TEA was less evident in acidic conditions. Based on studies of operating factors and product analysis, the reaction mechanism of TEA-assisted magnesia slurry absorption was proposed. Under alkaline conditions, TEA served as the radical scavenger, terminated the excessive oxidation of sulfite, and then strongly promoted the reaction between NO2− and SO32−. Furthermore, TEA could react with NO2 and SO2 directly, and its alkalinity was beneficial for the absorption of NO2 and SO2. In acidic conditions, TEA reacted with H+ and formed +H-N(CH2CH2OH)3, and the antioxidant capability of TEA would be lost.

Utilization of super hydrophobic membrane contactor for NOx Absorption

NOx is produced from the reaction between nitrogen, oxygen and even hydrocarbons (during combustion), especially at high temperatures. Nitrogen oxide compounds are one of the harmful emissions that can result from fuel combustion. This research aims to find out the performance of super hydrophobic membrane contactors in the absorption process of N2O from its mixture with air using acid solution and hydrogen peroxide. N2O gas must be reduced from the exhaust gas especially to meet the regulations applicable to the environment due to the hazardous nature of the N2O gases. The experimental results showed that the amount of NOx absorbed and the absorption efficiency increased with increasing absorbent flow rate in the membrane contactor. Meanwhile, the concentration of NOX in the outlet gas decreased with increasing absorbent flow rate.

Selective Reversible Absorption of the Industrial Off-Gas Components CO2 and NOx by Ionic Liquids

Ionic liquids are promising new materials for climate and pollution control by selective absorption of CO2 and NOx in industrial off-gases. In addition pratical cleaning of industrial off gases seems to be attractive by use of ionic liquids distributed on the surface of porous, high surface area carriers in the form of so-called Supported Ionic Liquid Phase (SILP) materials. The potential of selected ionic liquids for absorption of CO2 and NOx will be demonstrated and the possible mechanism of absortion will be described on the molecular level. Our vision of application of these ionic liquids in the form of SILP filters to flue gas cleaning in power plants, waste incineration plants, cement and glass factories as well as unborad ships will be adressed.

Selective Reversible Absorption of the Industrial Off-Gas Components CO2 and NOx by Ionic Liquids

Ionic liquids are promising new materials for climate and pollution control by selective absorption of CO2 and NOx in industrial off-gases. In addition practical cleaning of industrial off gases seems to be attractive by use of ionic liquids distributed on the surface of porous, high surface area carriers in the form of so-called Supported Ionic Liquid Phase (SILP) materials. The potential of selected ionic liquids for absorption of CO2 and NOx are demonstrated and the possible interference of other gases influencing the stability and absorption capacity of the ionic liquids are investigated as well.

Simultaneous desulfurization and denitrification of sintering flue gas via composite absorbent

Experiments on simultaneous absorption of SO2 and NOX from sintering flue gas via a composite absorbent NaClO2/NaClO were carried out. The effects of various operating parameters such as NaClO2 concentration (ms), NaClO concentration (mp), molar ratio of NaClO2/NaClO (M), solution temperature (TR), initial solution pH, gas flow (Vg) and inlet concentration of SO2 (CS) and NO (CN) on the removal efficiencies of SO2 and NO were discussed. The optimal experimental conditions were determined to be initial solution pH=6, TR=55°C and M=1.3 under which the average efficiencies of desulfurization and denitrification could reach 99.7% and 90.8%, respectively. Moreover, according to the analysis of reaction products, it was found that adding NaClO to NaClO2 aqueous solution is favorable for the generation of ClO2 and Cl2 which have significant effect on desulfurization and denitrification. Finally, engineering experiments were performed and obtained good results demonstrating that this method is practicable and promising.

Valorization of Flue Gas by Combining Photocatalytic Gas Pretreatment with Microalgae Production.

Utilization of flue gas for algae cultivation seems to be a promising route because flue gas from fossil-fuel combustion processes contains the high amounts of carbon (CO2) and nitrogen (NO) that are required for algae growth. NO is a poor nitrogen source for algae cultivation because of its low reactivity and solublilty in water and its toxicity for algae at high concentrations. Here, we present a novel strategy to valorize NO from flue gas as feedstock for algae production by combining a photocatalytic gas pretreatment unit with a microalgal photobioreactor. The photocatalytic air pretreatment transforms NO gas into NO2 gas and thereby enhances the absorption of NOx in the cultivation broth. The absorbed NOx will form NO2(-) and NO3(-) that can be used as a nitrogen source by algae. The effect of photocatalytic air pretreatment on the growth and biomass productivity of the algae Thalassiosira weissflogii in a semicontinuous system aerated with a model flue gas (1% CO2 and 50 ppm of NO) is investigated during a long-term experiment. The integrated system makes it possible to produce algae with NO from flue gas as the sole nitrogen source and reduces the NOx content in the exhaust gas by 84%.

Process intensification in manufacture of nitric acid: NOx absorption using enriched and pure oxygen

Absorption column occupies a dominant place in the manufacturing of nitric acid. A mathematical model has been developed for the absorption of NOx gases using air and enriched oxygen in packed columns. For the first time, this paper considers the kinetics of nitrous acid decomposition and oxidation in the liquid phase. Till date, the published literature considers the instantaneous decomposition of nitrous acid in the liquid phase. The same case has also been considered in this paper as the base case. In addition, three more cases have been considered: (1) decomposition and oxidation kinetics of nitrous acid with a typical concentration of oxygen which is usually employed in nitric acid plants (2) complete decomposition and oxidation with enriched oxygen (3) complete conversion of nitrous to nitric acid by liquid phase nitrous acid oxidation. Enriched oxygen results in substantial reduction in column volume and/or the operating pressure. The enriched oxygen enhances the rate of nitrous acid oxidation (to nitric acid) and hence the nitrous acid available for decomposition reduces throughout the column. This implies that lesser quantity of nitric oxide gets desorbed to the gas phase. This feature has crucial implication because the need for gas phase oxidation of NO reduces and hence the absorption column becomes compact due to reduction in oxidation volume. Thus, the enriched oxygen plays a significant role in process intensification and equipment miniaturization. Additionally, the liquid phase oxidation of nitrous acid carried out in a suitable oxidizer was found to give substantial additional reduction in the column volume.For packed column absorber, the effects of design parameters viz. column diameter, heights of packed and empty sections, and operating parameters such as pressure and temperature have been examined.

Abatement of SO2–NOx binary gas mixtures using a ferruginous active absorbent: Part I. Synergistic effects and mechanism

A novel ferruginous active absorbent, prepared by fly ash, industrial lime and the additive Fe(VI), was introduced for synchronous abatement of binary mixtures of SO2–NOx from simulated coal-fired flue gas. The synergistic action of various factors on the absorption of SO2 and NOx was investigated. The results show that a strong synergistic effect exists between Fe(VI) dose and reaction temperature for the desulfurization. It was observed that in the denitration process, the synergy of Fe(VI) dose and Ca/(S+N) had the most significant impact on the removal of NO, followed by the synergy of Fe(VI) and reaction temperature, and then the synergy of reaction temperature and flue gas humidity. A scanning electron microscope (SEM) and an accessory X-ray energy spectrometer (EDS) were used to observe the surface characteristics of the raw and spent absorbent as well as fly ash. A reaction mechanism was proposed based on chemical analysis of sulfur and nitrogen species concentrations in the spent absorbent. The Gibbs free energy, equilibrium constants and partial pressures of the SO2–NOx binary system were determined by thermodynamics.

Modeling the Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems

A rate-based model is developed to elucidate the chemistry behind the simultaneous absorption of NOx and SOx under pressurized conditions (pressures up to 30 bar) that are applicable to the flue gases obtained from CO2 capture systems. The studied flue gas conditions are relevant to oxy-fuel and chemical-looping combustion systems. The kinetics of the reactions implemented in the model is based on a thorough review of the literature. The chemistry of nitrogen, sulfur, and N–S interactions are evaluated in detail, and the most important reaction pathways are discussed. The effects of pH, pressure, and flue-gas composition on the liquid-phase chemistry are also examined and discussed. Simulations that use existing kinetic data reveal that the pH level has a strong influence on the reaction pathway that is followed and the types of products that are formed in the liquid phase. In addition, the pressure level and the presence of NOx significantly affect the removal of SO2 from the flue gas.

Research on the Simultaneous Desulfurization and Denitrification of Fumes by Combining Ozone Oxidation and the Double Alkali Method

This paper introduced the fundamental principle of the simultaneous desulfurization and denitrification by combining ozone oxidation and the NaOH double alkali method. And the total chemical reaction equations were achieved by analyzing the process of the absorption of the productions of ozone oxidation by NaOH double alkali method. Then, based on thermodynamic principle, the partial pressure of SOx, NOx and CO2 when reactions reached equilibrium were calculated respectively. This paper also studied the reaction mechanism of the absorption of SOx and NOx and analyzed the absorption characteristic of SOx and NOx in absorption solution. The results showed that the simultaneous desulfurization and denitrification by combining ozone oxidation and NaOH double alkali method was feasible. Not only the elimination ratio of SOx and NOx were almost up to 100%, but also CO2 was removed on a considerable scale. The partial pressure of SOx and NOx was very important to the pH value of the absorption solution which affected the elimination ratio of SOx and NOx greatly.

Mercury re-emission in flue gas multipollutants simultaneous absorption system.

Recently, simultaneous removal of SO2, NOx and oxidized mercury in wet flue gas desulfurization (WFGD) scrubber has become a research focus. Mercury re-emission in traditional WFGD system has been widely reported due to the reduction of oxidized mercury by sulfite ions. However, in multipollutants simultaneous absorption system, the formation of a large quantity of nitrate and nitrite ions as NOx absorption might also affect the reduction of oxidized mercury in the aqueous absorbent. As such, this paper studied the effects of nitrate and nitrite ions on mercury re-emission and its related mechanism. Experimental results revealed that the nitrate ions had neglected effect on mercury re-emission while the nitrite ions could greatly change the mercury re-emission behaviors. The nitrite ions could initially improve the Hg(0)-emission through the decomposition of HgSO3NO2(-), but with a further increase in the concentration, they would then inhibit the reduction of bivalent mercury owing to the formation of Hg-nitrite complex [Hg(NO2)x(2-x)]. In addition, the subsequent addition of Cl(-) could further suppress the Hg(0) emission, where the formation of a stable Hg-SO3-NO2-Cl complex was assumed to be the main reason for such strong inhibition effect.

(Invited) Absorption of Flue-Gas Components by Ionic Liquids

Gas separation by ionic liquids (ILs) is a promising new research field with several potential applications of industrial interest. Thus cleaning of industrial off gases seems to be attractive by use of ILs and Supported Ionic Liquid Phase (SILP) materials. The potential of selected ILs for absorption of NOX, CO2 and SO2 are demonstrated and the possible mechanism of absorption described on the molecular level. Special focus regards the interaction of the ILs with water vapor, which is an important feature in envisaged application of flue gas cleaning in power plants, waste incineration plants, cement and glass factories as well as on board ships.

Absorption of Flue-Gas Components by Ionic Liquids

Gas separation by ionic liquids is a promising new research field with several applications of industrial interest. Thus cleaning of industrial off gases seems to be attractive by use of ionic liquids and Supported Ionic Liquid Phase (SILP) materials. The potential of selected ionic liquids for absorption of NOx, COx and SOx will be demonstrated and the possible mechanism of absortion will be described on the molecular level. Our vision of application of these ionic liquids to flue gas cleaning in power plants, waste incineration plants, cement and glass factories as well as unborad ships will be adressed.