Okihiro Tokunaga

Radiation chemical reactions in NOx and SO2 removals from flue gas

Abstract For the purpose of elucidation of radiation chemical reactions of No x and SO 2 removals in irradiation of flue gas, the reactions of NO x and SO 2 were studied under irradiation with electron beams in various systems ranging from a simple system (NO-nitrogen) to the complex (NO-SO 2 -water vapour-oxygen-nitrogen) which was close to the composition of an flue gas. Reaction mechanisms of NO x and SO 2 were changed markedly by oxygen and water vapour. In nitrogen, NO was decomposed to oxygen and nitrogenthrough reactions with N atom and NO 2 was also decomposed to NO, dinitrogen oxide, oxygen and nitrogen. The decompositions were retarded markedly in the presence of oxygen, and an oxidation of NO and a reduction of NO 2 became predominant reactions. In the moist mixture of oxygen and nitrogen, fast oxidation of NO took place through the reactions with O, OH and HO 2 radicals, leading to the formation of NO 2 , followed by oxidation of NO 2 to produce HNO 3 . The SO 2 was also oxidized to H 2 SO 4 through the reactions with O and OH radicals in the moist mixture. An addition of ammonia enhanced markedly the NO x and SO 2 removals in the moist mixture. Reactions of NO and SO 2 with NH 2 radical took place in irradiation of the moist mixture containing ammonia in addition to the oxidations of No and NO 2 . The HNO 3 and H 2 SO 4 produced through the oxidations were converted to solid NH 4 NO 3 and (NH 4 ) 2 SO 4 and some parts of SO 2 itself reacted with ammonia, leading to the SO 2 removal.

Pilot-scale test for electron beam purification of flue gas from coal-combustion boiler

Abstract A pilot-scale test for electron beam treatment of flue gas (12,000m3N/hr) from coal-fired boiler was conducted by Japan Atomic Energy Research Institute, Chubu Electric Power Company and Ebara Corporation, in the site of Shin-Nagoya Thermal Power Plant in Nagoya, Japan. During 14 months operation, it was proved that the method is possible to remove SO2 and NOX simultaneously in wide concentration range of SO2 (250–2,000ppm) and NOX (140–240ppm) with higher efficiency than the conventional methods, with appropriate operation conditions (dose, temperature etc.). The pilot plant was easily operated with well controllability and durability, and was operated for long period of time without serious problems. The byproduct, ammonium sulfate and ammonium nitrate, produced by the treatment was proved to be a nitrogenous fertilizer with excellent quality.

Radiation treatment of exhaust gases—I. Oxidation of NO and reduction of NO2

Abstract Nitrogen oxides were irradiated by electron beams at low concentrations ranging from 50–1000 ppm in nitrogen and the mixture of nitrogen and oxygen at 100°C. In nitrogen, the NO was decomposed to mainly nitrogen and oxygen with the G-value of 1.7. In the presence of oxygen, effects of initial concentrations of NO, NO2 and oxygen on the changes of NO and NO2 concentration were studied. Oxidation of NO and reduction of NO2 take place simultaneously and an empirical equation, (NO)/(NO)2)2 = 0.027 ppm-1, was found at 3% oxygen under irradiation above 4 Mrad when the NO2 concentration is higher than 60 ppm. These reactions are considered to proceed by oxygen atom produced by the irradiation of the mixture of nitrogen and oxygen.

Radiation treatment of exhaust gases. IV. Oxidation of NO in the moist mixture of O2 and N2

Abstract A NO-H2O-O2-N2 gaseous mixture was irradiated by electron beams of 1.5 MeV at various reaction conditions. The decrease in [NO] was much larger for the moist mixture than for the dry mixture. The NO was easily oxidized to NO2 and finally to HNO3 in the moist mixture. The rate of NO consumption in the mixture increased with increasing H2O- and O2-concentrations and with lowering irradiation temperature from 150 to 100°C. The G(-NO) obtained in lower dose was 7.5 in the moist mixture of NO(100–500 ppm), H2O(8.4%), O2(11.4%) and N2(80.2%) at 120°C. The formed HNO3 reacted with NO to form NO2.

Radiation treatment of exhaust gases—II. Oxidation of sulfur dioxide in the moist mixture of oxygen and nitrogen

Abstract Moist and dry mixtures (1400 ppm SO 2 , 20% O 2 , ca . 80% N 2 ) were irradiated by electron beams at 100°C. In the dry mixture, SO 2 was not consumed by irradiation. On the other hand, SO 2 was oxidized to H 2 SO 4 with G (-SO 2 ) of 5.3 in the presence of moisture. The G (-SO 2 ) was reduced to a limiting value of 0.9 in the presence of a radical scavenger such as NO 2 , C 2 H 4 , C 2 H 6 , C 3 H 8 , or 1,3-C 4 H 6 . The G (-SO 2 ) was not affected by the addition of SF 6 . The radiolytic oxidation of SO 2 is induced mainly by the OH radical and the O atom.

Oxygen gas dosimeter for flow systems

Abstract Oxygen was used as a high dose gas phase dosimeter by measuring the concentration of ozone formed with electron beam irradiation in a flow system. The formed ozone was measured by an ultraviolet absorption ozone detector. A part of the formed ozone was decomposed during irradiation. The decomposition of ozone is mainly caused by radical reactions of OH and HO 2 with ozone, and the rate of decomposition can be estimated easily by computer calculations. It is therefore possible to use this method as a gas phase dosimeter with a correction for the decomposition. The dose rate obtained by this method was in good agreement with that of the nitrous oxide dosimeter.

The study of electron beam flue gas treatment for coal-fired thermal plant in Japan

Abstract The fundamental research work with simulated coal-fired flue gas was performed in JAERI to get basic data for electron beam treatment of flue gas from thermal power plants in Japan. The standard condition of the experiments was set to be the same as that of next large scale pilot test in Nagoya. The concentrations of NOx and SOx were 225 ppm and 800 ppm, respectively. The temperature of the system was 65°C. The effect of multiple irradiation was observed for NOx removal. The target SOx and NOx removals (94% and 80%, respectively) with low NH3 leakage (less than 10 ppm) were achieved at 9 kGy irradiation with 0.9 NH3 stoichiometry during 7 hours continuous operation. The facility for the pilot plant (12,000 Nm3/hr) has just built at the site of Shin-Nagoya power plant of Chubu Electric Power Company and will be started in full operation in November 1992.

Enhancement of removal of SO2 and NOx by powdery materials in radiation treatment of exhaust gases

Abstract We studied the effect of powdery silica on radiation removal of SO 2 and NOx from mixtures of SO 2 , NOx, water vapour, oxygen and nitrogen under irradiation by electron beams of 1.5 MeV at 120°C. The SO 2 and NOx concentrations decreased when powdery silica was fed without irradiation. Decrements of SO 2 and NOx concentrations were markedly enhanced when powdery silica was fed together with the irradiation. The enhancement of SO 2 - and NOx-removal is attributed to the adsorption of SO 2 and NO on the water-covered surface of powdery silica, and the effective removal of NO 2 due to the reaction with water adsorbed on the surface of powdery silica. The results obtained show that the addition of powdery silica under irradiation is an effective method of enhancing the removal of SO 2 and NOx.

Kinetics of SO2 removal from flue gas by electron beam technique

Abstract Laboratory scale experiments were carried out in order to get more information about the oxidation of SO 2 by OH radicals (homogeneous reaction) and the oxidation of SO 2 at aerosol surfaces (heterogeneous reaction). For the experiment of homogeneous reaction, SO 2 was added to synthetic flue gas without initial NO and without ammonia and the mixture was irradiated with electron beam. The SO 2 removal was measured as a function of temperature and water vapour concentration at constant dose. For the experiment of heterogeneous reaction, SO 2 was added to nucleating sulfuric acid aerosol. No SO 2 removal was observed in this case. So, it can be concluded that the heterogeneous oxidation of SO 2 is negligible in the absence of ammonia. Therefore, the oxidation of SO 2 must be interpreted merely by homogeneous gas phase chemistry. The gas phase kinetics are derived from comparison of experimental results and computer modelling.

Material balance of nitrogen and sulfur components in simulated flue gas treated by an electron beam

Abstract The material balance of nitrogen and sulfur components in simulated flue gas (NOSO 2 H 2 OO 2 NH 3 N 2 ) treated by an electron beam was measured using 15 N labeled NO (250 ppm). Combinations of chemical analysis, instrumental analysis and mass analysis were used to identify and quantify the nitrogen-containing products as well as to determine the ratio of 15 N in each product. The products 15 N 14 N, 15 NO 3 − , 15 NO 2 , 15 N 14 NO and 15 N 15 NO were detected after electron beam treatment of the gas. Perfect material balance of 15 N (103%) was obtained. The material balance of the sulfur components was measured using two different chemical analysis methods. All the removed SO 2 was converted to SO 4 2− by electron beam treatment, and both methods yielded a satisfactory balance (103 and 105%).