The chemical structure of asphaltene was investigated as a model for coal with the aim of acquiring clues to the polymerization of coal macromolecules. Akabira coal hydrogenation asphaltene was separated according to the molecular weight of its components by means of GPC into 8 fractions (As. GPC-Fr. 1-8). The average molecular weight of fractions measured by VPO decreased smoothly from 1360 for As. GPC-Fr.1 to 200 for As. GPC-Fr. 8 with increasing fraction numbers. Regardless of the large variation in molecular weight among the GPC fractions, H/C atomic ratios and characteristic structural parameters such as fa and Hau/Ca showed much lower differences. From these results, the chemical structure of asphaltene may be considered to consist of approximately similar unit structures of clusters of 2 to 3 aromatic rings with alkyl and naphthenic ring structures of similar size. From NCa-Ncba correlation diagrams which were proposed previously, the average aromatic ring structure of units and the numbers of units making up asphaltene oligomer structure could be estimated. Secondary hydrogenation reactions were performed on asphaltene GPC fractions and the chemical structures of product oils (O. (GPC-Fr. 1-7)) were elucidated according to the same procedure adopted to original asphaltene GPC fractions. The molecular weight of product oils diminished greatly to nearly constant values between 320 and 370 regardless of the molecular weight of the feedstock. Structural analyses also suggested that slight hydrogenation of aromatic rings occurred, causing minor changes, including a slight increase of H/C and Hau/Ca and a slight decrease of fa. Comparison of results of structural analyses between As. GPC-Fr. 1-8 and O. (GPC-Fr. 1-7) showed that asphaltene oligomer structure degraded to 1 or 2 unit structure after rupture of linkage between aromatic units. Infrared analyses of oxygen groups suggested that the ether group is an important bonding structure between structural units and essential in the degradation of asphaltene polymers to oils.
This paper describes the low NOx combustion technology for a compact boiler. In the bench-scale experiment, the NOx emission from the flame stabilized by a bluff body was lower than the 1/3 of that from the flame stabilized by a pilot flame while the volumetric heat release was nearly twice as much as the conventional combustion method. The NOx emission at the air ratio above 1.1 was reduced less and less as the fuel and air mixture became more and more homogeneous. The NOx emission at the air ratio of about 1.1 was reduced as the ratio of the diameter of a bluff body (D1) to that of a premixed gas nozzle (D2) increased, because the maximum temperatures of the flames were lower with increasing values of D1/D2. In the case of full-scale burners, when the fuel was injected from a fuel nozzle perpendicularly to the flow of air, the fuel made the most homogeneous mixture. In the combustion test of the full-scale boiler, the NOx emission from single burner was equal to that of the bench-scale experiment. But in the case of the multiple burners, the flames influenced each other, and the NOx emission was higher than that of the single burner. When the multiple burners were separated each other as far apart as possible, the NOx emission was reduced as much as one burner. From the results of above experiments, the NOx emission could be reduced to below 60ppm (O20%) at 10%-100% load of the 10t/h compact boiler.
In order to develop a NOx-free catalytic combustor, a catalytic combustion using a platinum group catalyst supported on a honeycomb substrate has been examined. Measurements were made with kerosene/air mixture of 1-10 excess air ratio, 100-200mg/s of kerosene consumption rate. The measured quantities were substrate temperature, NOx, CO, CO2 concentration in the exhaust gas. The results obtained are as follows: 1. The catalytic combustor operated on a transitional region between a flame region and a entirely heterogeneous reaction region, forms a reaction zone in the gas phase of the channel without a visible flame. 2. The entirely heterogeneous reaction region and the transitional region, are practically available on the viewpoint of thermal durability of the catalyst and NOx formation. 3. Increasing of the catalyst thickness makes it possible to complete the catalytic combustion, because of decrease in the SV value and increase in the catalytic temperature. The effect of SV value appears mainly when the combustor is operated on the entirely heterogeneous reaction region, but the effect of the temperature mainly appears on the transitional region.