NOx Removal Performance Research Articles

Electron beam treatment of gas stream containing high concentration of NOx: An in situ FTIR study

The NOx removal from gas stream by electron beam (EB) technique under flow through condition was investigated using two different reactors. Initially reactor type I was fabricated to investigate the NOx removal performance, based on its performance, the reactor type II was designed for further investigation on NOx removal efficiency. The influence of the applied current, O2, water vapour and gas flow rate on the removal of NO and NOx was studied. The FTIR spectrum of the NO gas samples acquired after EB irradiation indicated the formation of NO2 and N2O. It was observed that the NOx concentration could be reduced to 95% from the initial NO concentration of 1000ppm using reactor type II. The possible removal mechanism of NOx under EB irradiation is discussed. It is inferred that the EB irradiation accelerate the reduction of NO to N2 and O2 in the absence of O2. Addition of O2 and water vapour in the NO/N2 gas stream was found to influence the oxidation and reduction reaction, respectively under EB irradiation. The Na2SO3 scrubbing of the gas increased the NOx removal performance during EB processing. The N2O was observed to form mainly by the reduction of NO2 during EB irradiation.

Enhancement of NOx removal performance for (La0.85Sr0.15)0.99MnO3/Ce0.9Gd0.1O1.95 electrochemical cells by NOx storage/reduction adsorption layers

This study investigated the effect of adding a NOx adsorption layer to the cathode of an electrochemical cell on the removal of NOx from gaseous mixtures. The cathode was a composite of (La0.85Sr0.15)0.99MnO3 (LSM15) and Ce0.9Gd0.1O1.95 (CGO10). Two different kinds of adsorption layers, K–Pt–Al2O3 layer and Ba–Pt–Al2O3 layer (known as NOx storage/reduction (NSR) catalyst), were studied. The effects of the NSR adsorption layers on the electrode processes were characterized by electrochemical impedance spectroscopy (EIS). Both adsorption layers increased the reduction of NOx to N2 in an atmosphere that contained only NO. When O2 was present with NO in the atmosphere, the K–Pt–Al2O3 adsorption layer significantly enhanced the conversion of NOx to N2, but the Ba–Pt–Al2O3 adsorption layer had no effect. The selective removal of NOx under O2-rich conditions was achieved by modifying the LSM15/CGO10 cell with a suitable NSR adsorption layer. The improvement for NOx reduction by the adsorption layers was mainly contributed by the promotion of the adsorption and surface diffusion of NOx species at/near the triple phase boundary (TPB) regions of the electrode and probably the formation of a short and effective reaction path for NOx reduction. A stronger capability for oxidizing NO and/or trapping NOx under the test conditions may have contributed to the superior performance of the K–Pt–Al2O3 adsorption layer relative to the Ba–Pt–Al2O3 layer.

Improvement in $\hbox{NO}_{\rm x}$ Removal Performance of the Pilot-Scale Boiler Emission Control System Using an Indirect Plasma–Chemical Process

NOx removal from the flue gas of a smoke tube boiler using an ozonizer for NO oxidation and a Na2SO3 aqueous solution scrubber (diameter: 0.6 m; height: 3.7 m) was investigated. In this paper, in order to determine the correlation NOx removal performance, the height of the packing material layer in the scrubber was varied from 2.1 to 0 m. The performance tests were carried out using both a compressed natural gas (CNG) and a heavy oil. The flue gas flow rates were in the range of 455-1440 Nm3/h under CNG firing and 675-1330 Nm3/h under heavy oil firing, and the boiler NOx emission concentrations were approximately 40 and 100 ppm, respectively. A total packing height of 0.75 m resulted in NOx removal efficiencies of 70% and 60% for CNG and heavy oil, respectively. Moreover, the Na2SO3 consumption rate at 0.75 m was 10%-20% less than that at 1.2 m, although the NOx removal efficiency was nearly the same. The correlation between the NOx removal performance and the gas retention time in the scrubber was obtained, providing the design information of the scrubber for industrial applications.

Plasma-Chemical Hybrid NOx Reduction System for Commercial Cogeneration Boiler -Recent Status Report-

Operation tests of the smoke-tube boiler emission NOx treatment plant which consists of a plasma ozonizer using a pressure swing adsorption (PSA) oxygen generator and silent discharge for indirect NO oxidation and a Na2SO3 chemical scrubber are carried out for cogeneration boilers which uses a city gas and heavy oil as a fuel based on our proposed plasma-chemical hybrid NOx reduction principle. It is clear that amount of NO removed is almost same as the amount of corresponding O3 concentration to oxidize NO regardless of fuels and flow rates of flue gas. After the relation between oxidation-reduction potential (ORP) and the NOx removal efficiency is obtained, continuous operation tests of this plant are performed. For gas firing boiler emission, the NO complete removal and the decrease in NOx from 32 ppm to 3 ppm are achieved for 300 min by keeping -30 mV of ORP. For the treatment of heavy oil boiler emission, the decrease in NOx from 90 ppm to less than 25 ppm is maintained for 250 min. It is demonstrated that the high NOx removal performance can be maintained for a long time by keeping the optimum value of ORP.

光触媒を利用した透水性インターロッキングブロックのNOx除去性能に及ぼす各種要因の影響

Nitrogen oxides in exhaust gases from automobiles have been causing so serious air pollution in urban areas that building materials with a NOx removal performance have been required. We have developed a photocatalytic concrete with an oxidative NOx removal performance by means of a photocatalytic activity of titanium dioxide. The photocatalytic concrete is used for paving blocks. We researched the influence of various factors on the NOx removal performance of the photocatalytic paving blocks. As a result, it turned out that the paving blocks had the performance by which NOx was removed from the ambient air on a roadside.

Production of Activated Char from Illinois Coal for Flue Gas Cleanup

Activated chars were produced from Illinois coal and tested in several flue gas cleanup applications. High-activity chars that showed excellent potential for both SO2 and NOx removal were prepared from an Illinois No. 2 bituminous coal. The SO2 (120 °C) and NOx (25 °C) removal performance of one char compared favorably with that of a commercial activated carbon (Calgon Centaur). The NOx removal performance of the same char at 120 °C exceeded that of the Centaur carbon by more than 1 order of magnitude. Novel char preparation methods were developed including oxidation/thermal desorption and hydrogen treatments, which increased and preserved, respectively, the active sites for SO2 and NOx adsorption. The results of combined SO2/NOx removal tests, however, suggest that SO2 and NOx compete for similar adsorption sites and SO2 seems to be more strongly adsorbed than NO. A low-activity, low-cost char was also developed for cleanup of incinerator flue gas. A three-step method involving coal preoxidation, pyrolys...

SO2 and NOx Removal from Combustion Flue Gas by Corona Discharge in Laboratory Scale Experiment.

It is reported that SO2 and NOx in a flue gas can be removed by corona discharge and that pulse corona discharge is as energy-efficient as the electron-beam treatment. However a large amount of data are required to assess the industrial application of the corona discharge method to remove SO2 and NOx from combustion flue gas. In this study parametric experiments of SO2 and NOx removal from actual and simulated combustion gas have been performed on a laboratory scale, where combustion gas composition, temperature, residence time in a discharge duct and the polarity of high voltage electrode are changed for DC and pulsed corona discharge. The following experimental results are obtained : (1) the increase in H2O and O2 concentration improves the SO2 and NOx removal performance, (2) dendritic powders of (NH4)2SO4 are apt to deposit on a high-voltage electrode, and (3) the electrode polarity has a nominal effect on the removal performance under our experimental conditions.