Full Running Sewers

Full Running Sewers. Some trunk sewer systems rely on the sewer s running full to maintain a seal between operating areas. This is particularly true in the older sections of many plants. As the plants are modernized, many of the older units become obsolete and are taken out of service. If the spent cooling water and process water to these trunk sewers is thereby reduced, the sewer may flow only partially full. Under these conditions a fire in one section could be spread to other areas through the sewer. 

When there is a possibility that the sewer may flow only partially full, it is probably wise to provide some positive means of sealing the system. Gas-trap manholes can be installed in the existing system. Weirs installed in manholes to back up the flow and keep the sewer full provide another means of sealing the system. 

Sewers, in general, are designed for gravity flow. In a tightly sealed system, a rise in water level will reduce the vapor space and cause an increase in pressure. Such a tendency will, in turn, reduce the sewer s design capacity. Under these circumstances, vents are necessary to release vapors and to prevent vapor lock. Vents are functionally designed to maintain atmospheric pressure in the sewer and to release vapors to safe locations. 

A wide range of hydrocarbons enter the sewer system. Many of the lighter fractions will vaporize immediately. In addition, the warmth of the effluent will cause some heavier fractions to vaporize. Under normal conditions, there will always be some venting of hydrocarbon vapors. 

Discharge to areas that are apart from furnaces and other permanent sources of ignition. 

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Figure 8-9. Capacity of sewer pipes running 3/4 full. Sizes 4-inch to 24-inch inclusive. Turbulent flow e = 0.00085. Darcy formula Q = 19.65 fh[5"...

Flow capacities, velocities and slopes (for sewers running 3/4 full) can be coordinated so that the curves shown on Figures 8-9 and 8-10 will give the size of the sewer line required for the assumed slope and velocity at the desired flow capacity in gallons per minute. 

The electrolyte circulating pump is turned on and the inlet valve to the cell is opened just enough to move the rotometer float. Pumping is continued in this fashion until the cell compartment is full and water is running down the sewer drain. 

Some chemical fume hoods have a small cup sink located inside the cabinet. Water should be run into this sink periodically to maintain it free of obstruction and to keep the P-trap full and thereby prevent sewer gas back up. 

The results of the laboratory experiments were confirmed in various, sometimes very extensive investigations in treatment plants and water-courses. Earlier reviews were published by Heinz and Fischer [77] in 1962, and by Husmann, Malz and Jendreyko [78] in 1963. Full-scale tests on percolating filter plants confirmed the values found in the laboratory for the degradation of linear alkylbenzenesul-fonate [79]. During these tests, it was also observed that a part of the surfactant is already degraded, before it reaches the treatment plant, while the effluent runs along the sewer system [80]. 

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