Abstract Exhaust gases emitted from ships were regulated in MARPOL Treaty 73/78 Annex VI of IMO for air pollution control. In this paper, results of a fundamental development for an electrostatic precipitation (ESP) and a demonstration test for cleaning exhaust gases were described. In fundamental research, the characteristics of ESP with a heat exchanger were explained. It was described that ESP without a heat exchanger was able to remove dry soot and nano-particles, which were included with exhaust gas, in high efficiency. It was also indicated that particulate matters were generated due to condensation of gaseous soluble organic fraction and sulphate in the case of gas cooled by a heat exchanger, whereby these were also removed by ESP. In demonstration test, it was confirmed that high removal efficiency for 24 hours in ESP pilot plant was possible.
Due to recent higher quality requirement for refined petrochemical products, sulfur content increases even to the range of 4–8% in petrochemical residue, which may be used as boiler fuel from econimical reasons and viewpoint of effective resource utilization, as an alternative of usual heavy oil. When a fuel with high sulfur content is burnt in boiler, SO2 is partly oxidized to SO3 in flue gas, and at the outlet of wet FGD (Flue gas desulfurization) system, it takes the form of liquid mist (SO3 mist), which is ultrafine particulate matter (PM) classified into PM2.5, and causes problems such as sulfuric acid corrosion of the flue gas treatment system or visible bluish plume discharged from stack. In order to remove SO3 from flue gas, two practical methods have been developed firstly in Japan and applied for many years satisfactorily in actual plants using usual heavy oil so far. One is NH3 injection dry electrostatic precipitator (DESP) system and the other is wet electrostatic precipitator (WESP) system. However, these conventional systems may not be applied as they are for the recent cases of using petrochemical residue as boiler fuel, which causes very high SO3 content, over 60–130 ppm, in flue gas. A new technology “salt solution spray WESP system” is recently developed and firstly in Japan put into actual operation. SO3 concentration of the system is reduced from 130 ppm to 1 ppm, equivalent to 99.2% of removal efficiency. Together with the salt solution spray technology, WESP provides the most effective system for SO3 mist removal.
Diesel engines have contributed in industry and transportation because of high energy efficiency and durability. The serious drawback of diesel engines is emission of PM and gaseous pollutants, especially NOx. Due to tough regulation of emission, high efficiency and low pressure-drop apparatus for diesel exhaust after-treatment has been required. A potential candidate is an electrostatic precipitation, ESP, for PM (particulate matter) and non-thermal plasma, NTP, process for gaseous pollutants. Due to low electrical conductivity, diesel PM is difficult to remove. In this article, some of novel attempt in ESPs are introduced, together with the effectiveness of the combination of ESP and DPF (Diesel particulate filter).For regeneration, or oxidation of PM deposit, of DPF at low temperature condition can be possible using NTP in DPF. NO in exhaust gas can also be oxidized using NTP, resulting in higher removal efficiency of NOx using SCR (selective catalytic reduction) with ammonia. The engine test using JE05 mode proved the effectiveness of NTP for the after-treatment.
The removal of air pollutants containing nanoparticles using a wet-type plasma reactor is investigated by combining a wet-type electrostatic precipitator with a nonthermal plasma reactor. This reactor can simultaneously remove nanoparticles and hazardous gases such as nitrogen oxides (NOx) and sulfur oxides (SOx). In order to evaluate the performance of this reactor, a simulated exhaust gas is prepared using polystyrene latex particles having diameters of 29, 48, 100, 202, and 309 nm, and NO and SO2 gas cylinders. A collection efficiency of more than 99% is achieved for nanoparticles having diameters in the 27.9–216.7 nm range. Moreover, removal efficiencies of more than 99% and 77% are obtained for SO2 and NOx, respectively. From these results, it is confirmed that this wet-type discharge plasma reactor is useful for the simultaneous removal of nanoparticles, NOx, and SOx.
In order to investigate the processes of chemical transformations of aerosol transported from East Asia to Japan the concentrations of ionic species in size-segregated aerosols were measured in Cape Hedo, Okinawa, Japan. By use of a cascade impactor (Nano sampler) we collected aerosols at 5 stages. Throughout the observation periods, species originated from anthropogenic sources such as NH4＋ and nss-SO42- were dominant in fine mode particles (0.1–0.5 μm, 0.5–1 μm), whereas species originated from natural sources such as Na＋ and Cl- were dominant in coarse mode particles (2.5–10μm, ＞10μm). The (Cl-＋NO3-)/Na＋ ratio in coarse mode, 1.14 in equivalent basis, was very close to Cl-/Na＋ of sea water (1.17), which indicated that NH4NO3 was decomposed to gaseous NH3 and HNO3 during the long-range transport, and HNO3 deposited on sea-salt particles. The concentrations of NH4＋, nss-SO42- and nss-K＋ in fine mode were higher during high pressure episodes; it suggests that the fine particles emitted from anthropogenic sources (e.g. biomass burning) were transported with a migratory anticyclone. Increase of nss-Ca2＋ and nss-SO42- in coarse mode during Asian dust episode implied that surface reactions with gaseous species on CaCO3 particles occurred during the transport.
Atmospheric pollution by airborne particulate matter (PM) in Ulaanbaatar, particularly in the winter season, is very serious problem in Mongolia. The chemical compositions of PM samples were measured in Ulaanbaatar in the winters of 2012 and 2013. The concentration trends for both PM2.5 and PM10 in the city center were similar and the PM2.5/PM10 ratios were about 0.8. Arsenic, Pb and Zn were weighted toward the fine size range, whereas Ca, Fe and Mn dominated the coarse size range. The PM ratios for acidic ions, the ions assumed to be derived from coal combustion, were about 0.8, except for fluoride.The average winter concentrations for PM10 samples collected simultaneously at three separate locations in the city were 167 μg/m3 for the city center, 422 μg/m3 for an area dominated by Gers housing(traditional Mongolian yurt dwellings houses) and 155 μg/m3 for an area with traffic congestion. Total carbon represented the largest component of PM, accounting for approximately half of the total. The organic carbon (OC) concentration of PM10 samples in the Gers area was significantly higher than that of other areas. Within the five fractions of OC, the OC1 fraction with gasification at low temperature(120°C) in the Gers area was consistently higher than in other areas.
Both of the component measurement and the analysis based on Air Quality Model (AQM) are essential for the consideration of PM2.5 reduction measures. In order to collect more information regarding PM2.5 components, long-term weekly measurement for inorganic ions in PM2.5 had been conducted from August 2009 to August 2011 at Meisei University, located in Western Tokyo. The performance of AQM was also clarified based on the comparison between CMAQ simulation and the observation. Observed SO42- and NO3- showed higher concentration in summer and winter season, respectively. Since the ratio of total amount of inorganic ions in PM2.5 mass concentration reached up to 75% in each February, reduction measures for the inorganic ions seemed to be more effective to decrease PM2.5 mass concentration especially in winter season. As AQM performance, a correlation coefficient of around 0.8 was obtained by the comparison with observed SO42-. However, AQM did not show a reasonable performance for NO3- and NH4＋ due to both of the sampling artifact originated in the volatilization of NH4NO3 and the model uncertainties especially for the overestimation of NO2 and O3. As a result, it was suggested for the improvement of Nitrate prediction that further observation studies for the volatilization and the precursors such as HNO3 and NH3 were important as well as the evaluation of overestimated NO2 and O3.