Oily water sewer system

A process oily water sewer system is a convenient location to direct oily wastes. The oily water system normally collects into a sump. If several lines connect into a common header, care should be taken to prevent backflow into another outlet source. In such cases use of an air gap, i.e., drainage in to a collection ftinnel has be advantageous. 

Where drainage provisions are provided to the battery room, the fluid should first collect into a neutralizing tank before entering the oily water sewer system (OWS). 

Process, chemical, or oily water sewer system branch and lateral lines should enter main lines through vapor-sealed and vented manholes. Branches and laterals in clean or storm water drainage systems may enter main lines without vapor seals if liquid-sealed catch basins are used on the inlets to these branches and laterals. 

This system picks up drains around boilers and steam drums and is run as a separate system, preferably to the battery limit. It is permissible to tie into a sewer box in the oily water sewer system as long as it is located downstream from any sewer box that collects... 

Sewer boxes Used in oily water sewer systems, sewer boxes ... 

Sanitary sewer systems should be entirely segregated from oily water sewer systems. Similarly, process venting or blowdown systems should not be connected to the sewer system. 

Common practice and a general guide is to prevent combustible vapors from transmitting from one process area to another process area, generally 15 m or (50 ft) or more away. Usually unsealed drainage receptacles, such as drain funnels, tundishes, and drain boxes, are routed to the nearest local water sealed catch basin and then directly into the oily water sewer system collection header. The unsealed receptacles are only allowed in the same process equipment area where if vapors were to be released, it would be considered immaterial due to the proximity to where the liquid is being drained, as the drainage process would emit these vapors anyways. 

In some cases a closed drainage system can be used which drains process components directly into the oily water sewer. This has the advantage of avoiding releases of vapors in any instance, but assurance must be obtained that back pressure from one drainage location will not backfeed liquids into another drain point when two valves are open simultaneously or other drainage valves can contain any backpressure on them from other drainage sources. 

In addition to a system for disposing of rain, fire, and wash-down water, many process units require special dedicated sewer systems (i.e., chemical and oily water sewers) for routine nonemergency drainage of process waste due to environmental, waste disposal, cross-contamination, or reactivity reasons. Chemical, process, or oily water sewers are usually not appropriate in capacity or purpose for use in drainage of large uncontrolled process spills, rain water, or fire water. 

The waste streams in most large plants can be classified under four basic sewer systems (1) Oily-water sewer, (2) acid (chemical) sewer, (3) storm-water sewer and (4) sanitary sewer. Typical sewer systems are shown in Figure 8-1. The design and operation of each type will be described in detail. 

The oily-water sewer main should be run to the battery limit as a separate system and there connected to the oily-water trunk sewer which runs to an oil-water separator. 

This seaion outlines the criteria and formulas that are commonly used for developing line sizing for oily and storm water sewer systems. 

Concrete pipe, which is commonly used in oily and storm water sewer systems in sizes of 15 in and larger, is illastrated in Exhibit 13-40, Use of cast iron pipe smaller than 15 in is determined by economics. 

An adequate drainage system should be provided for all locations where a large amount of hydrocarbon liquids has the possibility of release and may accumulate within the terms of the risk analysis frequency levels. Normal practice is to ensure adequate drainage capability exists at all pumps, tanks, vessels, columns, etc., supplemented by area surface runoff or general area catch basins. Sewer systems are normally gravity flow for either sanitary requirements or oily surface water disposal. Where insufficient elevation is available for the main header, lift stations are installed with a forced pressure outlet header to a disposal or treatment system. 

Oily water gravity and pressure sewer systems Ship, rail or truck loading facilities Storage Tanks for flammable liquids... 

The initial layout of any oily or storm water underground piping system usually takes place after the preliminary plot plan is generated. Even though some equipment locations may be tentative, the plant layout designer can begin to spot the oily water and storm water mains, locate sewer boxes, and establish the invert elevation of these systems at each end of the unit. 

Oily water gravity and pressure sewer systems... 

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