Drains, liquid seals

On open drain piping leaving buildings, a liquid seal should be installed as further protection to assure that gases flashing from liquids from other locations in the drain system will not exit the system in the building. 

Catch basins should be provided for each fire zone of the process area to collect the flow from the floor drains and trenches. All catch basins within the process area battery limits should be sealed for vapor control. Catch basin seals should be of types that are easily cleaned out. P-traps should not be used. Catch basins require a periodic check to verify that a liquid seal is in place and clean-out plugs are installed. 

A) o-Nitrobenzenesulfonyl Chloride.—A 3-I. three-necked, round-bottomed flask is fitted with an efficient liquid-sealed stirrer, a reflux condenser, and an inlet tube for introducing chlorine well beneath the surface of the liquid. A glass outlet tube leads from the reflux condenser to the hood. In the flask are placed 200 g. (0.65 mole) of di-o-nitrophenyl disulfide (Org. Syn. Coll. Vol. 1, 215) 1 1. of concentrated hydrochloric acid (sp. gr. 1.18), and 200 cc. of concentrated nitric acid (sp. gr. 1.42). A stream of chlorine is passed into the mixture at the rate of about two bubbles per second, and the solution is warmed on a steam bath to 70°. In about thirty minutes the disulfide melts and the solution becomes orange-red in color. After the disulfide has melted, the heating and addition of chlorine are continued for one hour. The sulfonyl chloride is separated immediately from the supernatant liquid by decantation, washed with two 300-cc. portions of warm water (70°) and allowed to solidify. The water is drained from the solid mass as completely as possible. 

Traps in laboratory sinks and drains Traps should be checked and filled once a month with water to maintain liquid seal. If corrosive or toxic materials are known to be present, make sure the trap is flushed thoroughly with water. These precautions are taken to prevent backflow of gaseous wastes that may be hazardous. 

Figure 9.16 shows a typical flow arrangement. The fibers trap the acid mist and the liquid then trickles to the bottom of each candle. There, it must be collected and brought to a drain for removal. A liquid seal on the acid drain prevents bypassing of the chlorine gas. The tail pipes, usually of CPVC, can be sealed by maintaining a level of acid in the bottom of the vessel or each element can be sealed separately with an overflow cup attached to the bottom of the drain pipe. In the latter case, there still must... 

If there is not enough height available for a barometric installation, a pump has to be installed. Usually, such a pump is controlled by the hquid level above, so that there is always a liquid seal to prevent the inflow of air. Alternatively, a nonreturn valve must be mounted at the discharge side of the pump, but then cavitation has to be anticipated, if the drain pipe from the condenser is completely emptied by the pump. Collecting vessels are also used to collect the condensate under vacuum, discharging as required. For continuous operation, two or more alternating vessels are needed, and the ventilation and evacuation have to be considered. 

This is like unsealing a tray s downcomer in a distillation tower. If the bottom edge of the downcomer from a tray is above the top edge of the outlet weir on the tray below, then vapor can blow up through the unsealed downcomer. This will prevent the internal reflux ft om draining down the column. Tower flooding and loss of product separation efficiency will result. This is called liquid flooding or excessive downcomer backup due to loss of the dovmcomer liquid seal. 

The pressure in the vapour space of an incompletely full, sealed vessel containing liquid cannot be reduced by partially draining off liquid. 

Common practice and a general guide is to prevent combustible vapors from transmitting from one process area to another process area, generally 15.2 meters (50 ft.) or more away. Usually unsealed receptacles, such as drain funnels, tundishes, drain boxes, are routed to the nearest local sealed catch basin and then into the oily water sewer main. The unsealed receptacles are only allowed in the same process area equipment where if vapors where released from an adjacent unsealed receptacle it would be "immaterial" due to the proximity to where the liquid is being drained and would normally emit vapors. 

Process equipment liquid drains should be provided with a sealed drainage system where it is practical and backpressure from the system or containmenation is not a concern. Open drain ports should be avoided and separate sewage and oil water drains provided. Surface drainage should be provided to remove liquid spills immediate and effectively from the process area. Vents on drainage systems should be elevated so as to freely disperse hydrocarbon gases above congested areas that could be released from the system. 

Process equipment liquid drains should use a sealed drainage system. 

Steam sterilization is limited in the types of medical waste it can treat, but is appropriate for laboratory cultures and/or substances contaminated with infectious organisms. The waste is subjected to steam in a sealed, pressurized chamber. The liquid that may form is drained off to the sewer or sent for processing. The unit is then reopened after a vapor release to the atmosphere, and the solid waste is removed for further processing or disposal. One advantage of steam... 

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