By R. Nemenyi
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1 FLOW DIAGRAM FOR PREPARING HIGH-PURITY NITROGEN Nitrogen F I G . 2 33 HIGH-PURITY NITROGEN PREPARATION PLANT point (8). (7) The resultant gas which leaves the system at point 9 will be a high-purity N2 containing 0 2 < 1 ppm and approximately 5% of H 2 . The system is shown in the photograph of Fig. 2. Nitrogen can also be obtained by burning hydrocarbons in insufficient air. 1). e. from lean exogas, is higher than that of the N2 obtained from the air. 3 HYDROGEN The hydrogen does not react with metals but reduces oxides and decarburises steel.
Since no satisfactory method of effective quenching existed up to about 1960, quench hardening could not be carried out as part of vacuum heat treatments. Reliable quenching methods have been available since the early 1970s and two favoured systems exist. The first involves locating a quench tank in the base of the vacuum furnace, this tank uses very low vapour-pressure oil quenchant. A double-chamber furnace is typical of the second system class and after vacuum austenitising the steel inert gas is admitted into the chamber and the workpiece is transferred through an inner seal/door into the second chamber where it may be quenched in a variety of media including water, liquid metal or fused salts.
For perfect combustion the air factor Λ = 1 while for partial combustion it is less than 1 (Λ < 1). Referring to the diagram of Fig. 8 to 1 The limit of 5% combustibles (CO + H 2 ) can easily be reached using a slight deficiency of air, as shown on the graph. The main phases of prepared nitrogen-base or monogas production are: burning of the combustible base gas with a slight deficiency of air to give a very lean exogas; conversion of the CO content of the resulting atmosphere to carbon dioxide; removal of carbon dioxide formed during Prepared Nitrogen-base or Monogas Generators 59 F I G .