Liquid nitrogen supply

The DSC measurements reported in this book are performed with the power-compensating DSC-2 and DSC-7 systems from Perkin Elmer. The block surrounding the DSC sample holders is kept at -150°C + 1°C with the aid of a controlled liquid nitrogen supply, both cells are purged with helium (60 ml/minute). 

Figure 6 shows the external appearance of the assembled unit. External connections include liquid-nitrogen supply and vent tubes, a displacer drive input and helium-gas charging tube. The weight of the xmit, as shown, is approximately 10 lb. 

Airborne radioactive release -VolatQes in process cold traps, up to 5,000 to 70,000 curies -Fatigue ilure of container -Mishandling/procedural violation -Loss of liquid nitrogen supply -l ctemal event Local or central cold traps use liquid nitrogen and vacuum to tr process volatiles. Warming or venting before minimum decay could release excess volatiles. 

Broken, plugged, or shut off liquid nitrogen supply or exhaust lines Mechanical malfunction or worker error Control and monitoring system indications and periodic maintenance inspections Redundant cold traps provide multiple flow paths for vacuum. Loss of cold trapping for control of noble gas and potential release of noble gas. 

Ge detectors are operated at liquid nitrogen temperature to reduce the leakage current and to increase the mobility of the charge carriers. If liquid nitrogen supply... 

Normal stand-by of a storage vessel of this type is one week without replenishing of the liquid-nitrogen supply and without undue pressure rise in the product storage container. Tank design is such that in an emergency, storage up to 30 days is possible without loss of any fluorine to the atmosphere. 

Liquid Nitrogen, supplied from low pressure dewar. Required for cooling of the MCT detector. Dewar may be connected through an electronic solenoid to the MCT cooling reservoir for unattended operation. 

Fig. 1. Approximate economic range of nitrogen supply technologies (at median site conditions). Shaded area represents bulk liquid or PSA membrane plus...

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

On other occasions tank trucks have been filled with the wrong material. In particular, liquid oxygen or liquid air has been supplied instead of liquid nitrogen. One incident, the result of confusion over labeling, was described in Section 4.1 (f). 

I do not know of any case in which delivery of liquid oxygen instead of liquid nitrogen caused an explosion. But, as stated in Section 12.3.1. in one case the nitrogen was used to inert a catalyst bed. and the catalyst got hot in another case a high-oxygen-concentration alarm in the plant sounded, and in several cases check analyses showed that oxygen had been supplied. 

The consumption of power in this process is theo-etically very small, as much carbon monoxide should e liquefied in the coil in the vessel B as is volatilised lutside it (this is theoretically true when the pressure )f the gas passing through the coil is atmospheric) Towever, in practice, the necessity for power consump-lon arises from the fact that liquid nitrogen must )e continuously supplied to the vessel D in order to jrevent the temperature of the plant rising from ex-ernal infiltration of heat, which takes place in spite of he most effective lagging. 

Oxygen-free nitrogen can be obtained from cylinders, but must be filtered to remove oil contaminants. Liquid nitrogen provides a better supply of gas, but impurities accumulate at the bottom of the Dewar flask, so that the bottom 10% should not be used (Johnson, 1990). Accessories to monitor and purify nitrogen gas are available commercially. 

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