STP1018

    The Behavior of Dispersed and Nondispersed Fuels in a Sewer System

    Published: Jan 1989


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    Abstract

    A small-scale model sewer was constructed to determine the behavior of dispersed and nondispersed fuel flushed or spilled into sewers. The system included a headbox containing a concrete pad with a drain in the middle. The drain fed into a sewer pipe. Six vapor sensors were positioned in ports or simulated manholes at intervals along the pipe length. The vapor sensors were connected to a computer which generated a continuous data record of vapor concentrations at each port. Liquid samples were also taken at different intervals under the vapor sensor ports.

    Vapors in a sewer system have two distinct origins: the first is vapor evaporating from the liquid fuel as it is transported with the water and the remainder is vapor that formed upstream and is in the process of moving downstream at a slower rate than the underlying liquid. The latter movement is caused by the pumping action of the water flow, but is slower than the liquid flow as a result of the drag of the walls and the low gas-to-liquid friction coefficient. Gasoline, whether treated with dispersant or not, produces two sharply different vapor peaks at the sensor ports because it evaporates rapidly upon entering the sewer and thus produces a slowly moving vapor cloud. Diesel fuel does not evaporate as rapidly and produces only a single vapor peak at the ports.

    The use of dispersants at the beginning of the sewer increases the volatilization rate of the smaller fuel molecules and thus increases the amount of vapor present in the sewer system. This occurs irrespective of the amount or brand of dispersant employed. When dispersants are applied, the vapor concentration and duration is increased at each subsequent port. An increasing amount of dispersant or dispersant/water mixture increases this effect. If dispersants are mixed with the fuel in a very vigorous manner the vapor concentration may not be increased in the first ports, but it will not be decreased and the concentrations are increased 5 min downstream. In no case is the vapor concentration at any port reduced by the use of dispersants.

    The results from the small-scale model show that dispersants do not reduce the explosion risk of fuels in sewers. In fact, the use of dispersants will in most cases greatly increase the potential for explosions and their magnitude. Dispersants increase the rate of volatilization of small fuel molecules and increase the total amount of those released. This is consistent with the results obtained by other authors who have conducted static experiments of similar nature.

    Keywords:

    fuels, dispersants, sewers, explosions


    Author Information:

    Fingas, MF
    Head of Chemistry and Physics, chemical technologist, and senior chemist, Conservation and Protection, Environment Canada, River Road Environmental Technology Centre, Ottawa, Ontario

    Hughes, KA
    Head of Chemistry and Physics, chemical technologist, and senior chemist, Conservation and Protection, Environment Canada, River Road Environmental Technology Centre, Ottawa, Ontario

    Bobra, AM
    Head of Chemistry and Physics, chemical technologist, and senior chemist, Conservation and Protection, Environment Canada, River Road Environmental Technology Centre, Ottawa, Ontario


    Paper ID: STP18667S

    Committee/Subcommittee: F20.21

    DOI: 10.1520/STP18667S


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