The production of sewage sludge in Korea amounts to 2 million ton/y. It is disposed mainly by ocean dumping. At the London Convention, however, there was a strong demand for this practice to be stopped. Therefore, new treatment methods for sewage sludge should be found. One of the strong candidates for these new methods is the pyrolysis technique, which obtains oil from the organic part of sewage sludge. The pyrolysis oil, however, usually shows bad characteristics, mainly due to its low heating value and high contaminant content. In this study, digested and dried sewage sludge containing polymer flocculants was pyrolyzed in a temperature range of 446–720 °C in a pyrolysis plant equipped with a fluidized bed reactor. The mass balance was established in each experiment, and the produced gas and oil were analyzed with the aid of GCs and a GC-MS system. In the experiments, above 50 wt % pyrolysis oil was obtained with a maximum caloric value of 33 MJ/kg. In addition, the authors tried to reduce contaminants in the pyrolysis oil by using a char separation system composed of a cyclone and a hot filter and calcium oxide as an adsorbent, to capture the HCl liberated during the pyrolysis. The pyrolysis oil was almost free of hazardous metals, and its chlorine content was significantly reduced.
The production of sewage sludge in South Korea is continually increasing. Until now, much of the sewage sludge in the country has been disposed of by dumping it into the ocean, which the London Convention wants stopped. Therefore, new sewage sludge treatment methods should be sought. Sewage sludge can be energetically utilized through gasification, which produces combustible gases such as H 2 , CO, and CH 4 . During the gasification of a biomass, however, a large amount of tar is also formed. In this paper we report the results of the experiments that were conducted on the air gasification of dried sewage sludge in a newly developed two-stage gasifier. In such experiments, activated carbon was applied to reduce the tar components of the producer gas. The total amount of tar that was reduced was 6-fold when activated carbon was used in the upper reactor of the gasifier. The effects of the reaction conditions, such as the reaction temperature and the equivalence ratio, on the gas composition were also investigated. The producer gas was analyzed using gas chromatographs and a GC-MS system. The producer gases (inclusive of N 2 ) that were obtained with the application of activated carbon had high hydrogen contents (24 vol %), and their lower heating values amounted to 11.6 MJ/Nm 3 (Nm 3 ) normal cubic meter). The use of activated carbon led to a strong reduction of tar in the producer gases. In each of the experiments with activated carbon, the tar content of the producer gas was found to be below 10 mg/Nm 3 . At this tar level, the producer gas seems to be appropriate for use as a fuel gas in internal combustion engines.
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