Tube emptying under pressure

Gas samples are taken by equipment that draws the gas stream into empty vials or through tubes containing some absorbent that concentrates the sample. Many systems analyse the sample in situ using colour indicators, gas chromatographs, or solid state analysers. Other gas samples are transported in sealed containers for analysis, but they are rarely under pressure. 

In Canada, where parks of CANDU tube reactors have been built (up to eight 600 MWe reactors on the same site), vacuum building containment has also been used which consists in building, for each park of reactors, a central empty containment, connected with the containments of any single reactor by a duct provided with a rupture disc or similar device. In the event of a LOCA accident in one of the reactors, the corresponding rupture disc opens and the air-steam mixture under pressure has the whole volume of the vacuum building in which to expand. In this way, the containment of each reactor can be rather small with overall economic advantages. 

The outlet then is closed, and hydrogen is admitted until the water in the reservoir, washing tube, and overflow bottle is under a pressure about 0.5 atmosphere above that of the outside atmosphere. The stirrer is operated at such a speed that the catalyst is suspended to a height of 18-20 cm. Distilled water from the reservoir is allowed to flow through the suspended catalyst at a rate of about 250 ml. per minute. When the reservoir is nearly empty and the overflow bottle fuU, the drain cock and distilled-water inlet are opened simultaneously to an equal rate of flow such that, as the overflow bottle empties, the reservoir is filled, while the pressure in the system remains constant. 

Tube c and the one-neck Woulfe flask b are filled with water and the apparatus Is assembled as quickly as possible. All rubber stoppers and tubing should be held In place with clamps or wires. Then, Og-free hydrogen Is Introduced via e imtll the entire apparatus Is under a gage pressure of 0.5 atm. This pressure Is then maintained while stirring at such a rate that the catalyst Is fluidized to a height of 18-20 cm. above the bottom of tube c and the wash water flow rate from b Is 250 ml./mln. When the water reservoir b Is nearly empty, stopcocks g and a (the latter Is connected to a lai e pressurized water reservoir) are simultaneously opened, and b Is replenished at the same rate as water runs out at g (the flow rate Is checked by a differential manometer). 

There are no "nozzles for an even SOj/air distribution over all pipes. The pressure drop over the 6 m pipe can be calculated with the well-known Fanning equation for turbulent flow. For an SOa/air velocity of 30 m/s in an empty reactor pipe a value of 0.025 bar is found. In experiments with air and organic film (without any sulphonation reaction) a pressure drop of 0.1 bar was measured at an air velocity of 30 m/s. The interaction of the air with liquid film ripples and waves causes an increase of about a factor 4 in the pressure drop compared with the empty tube. Under real sulphonation conditions the pressure drop measured becomes even greater at 0.25 bar, due to the sharp increase of viscosity at high conversions. 

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