Section B Fire and Explosion - Scale Modeling of Biomass Fire Associated with Hydrogen-Producing Bacteria

Abstract

This paper details a fundamental study for developing a safe handling system for waste biomass fuels, especially for the prevention of fires and explosions associated with refuse-derived fuels (RDF). Unlike conventional solid fuel, RDF is a living fuel that contains various kinds of bacteria among which flammable gases such as hydrogen and methane may be produced during biological fermentation in the proper circumstances. The RDF storage silo at the Mie prefectural RDF power plant unexpectedly exploded in 2003, and firefighter deaths and injuries were reported. Though flammable gas production was the suspected cause of the explosion, there is disagreement about whether the flammable gas was produced by the biological fermentation or by thermal decomposition of the RDF materials. Due to the difficulties in conducting both the experiments and numerical simulations in a full-scale mock-up silo, the detailed explosion mechanism has not been explained since 2003. On the basis of scale modeling principles, this study begins with determining the physical or chemical laws which govern the phenomena of the accident. For this purpose, flammable gas production tests were conducted using two kinds of RDFs, which were provided from two manufacturers: Kuwana and Sakura. The RDF hydrogen production ability was affected by pH, moisture, and ambient temperature. The microbial colony count method revealed that aerobes occupied a dominant position in RDF on the second or third day from the beginning, whereas anaerobes occupied a dominant position hereafter. Bacillus sp. was superior to Clostridium sp. in Kuwana, whereas Clostridium sp. was superior to Bacillus sp. in Sakura after 3 days of cultivation. Scale effects on the temperature rise of RDF due to biological activities were examined using three different amounts of RDFs. It was found that the higher the amount of RDF, the higher the maximum temperature obtained after 50–85 h cultivation.