Purification of air

摘要

Process of reducing water, CO2 and N2O in feed air, which: a first adsorbent such as alumina (25-40% volume) and a second adsorbent such as X zeolite (60-75% volume) are used; the online time of the adsorbent is determined by determining the concentration measured by an analyzer for CO2 concentration at a position within the length of the second adsorbent when a maximum level of N2O is simultaneously obtained at the downstream end of the second adsorbent in the feed direction, wherein the online time is the time taken from commencing passing the feed air to the first and second adsorbents to the measurement by the analyzer of the determined concentration of CO2; at least the second adsorbent is regenerated by heated regeneration gas at a temperature of 140° C.-220° C.; and the molar ratio of the regenerating gas to feed air supplied during one iteration of the cycle is 0.08-0.5.

主权项

1. A method for determining conditions for the reduction, prior to cryogenic distillation, of the level of water, carbon dioxide and nitrous oxide in a feed air stream in a process comprising:
(a) passing said feed air stream at a feed pressure in a feed direction through a first adsorbent which has a Henry's Law selectivity for carbon dioxide over nitrous oxide measured at 30° C. of at least 12.5, and subsequently through a second adsorbent whose Henry's Law constant for the adsorption of N2O measured at 30° C. is less than 500 mmol/g/atm and whose Henry's Law selectivity for CO2 over N2O is at most 5; (b) ceasing to pass said feed air stream to said first and second adsorbents after a first time period; (c) depressurising the gas in contact with the first and second adsorbents to a second pressure less than the feed pressure; (d) passing regenerating gas at the second pressure and at a first temperature which is in the range 140 to 220° C. to at least the second adsorbent in a direction opposite to the feed direction for a second time period, and subsequently passing the regenerating gas at the second pressure and a second temperature less than the first temperature to the second and first adsorbents in a direction opposite to the feed direction for a third time period; (e) ceasing passing regenerating gas to the first and second adsorbents; (f) repressurising the gas in contact with the first and second adsorbents to the feed pressure; (g) repeating steps (a) to (f); wherein the first adsorbent occupies from 25% to 40% by volume of the total volume occupied by the first and second adsorbents; and wherein the molar ratio of the regenerating gas to the feed air supplied during each iteration of the steps (a) to (f) is from 0.08 to 0.5; which method comprises: (i) placing an analyser for CO2 concentration measurement at a chosen position within the length of the second adsorbent; (ii) determining the threshold concentration measured by the CO2 analyser when a desired maximum level of N2O is simultaneously obtained at the downstream end of the second adsorbent in the feed direction; (iii) using the result of step (ii) to determine the maximum duration of the first time period, such that the maximum duration of the first time period is the time taken from commencing passing the feed air stream to the first and second adsorbents to the measurement by the analyser of the determined threshold concentration of CO2.