Residual oxygen level

The efficiency of the condenser is reduced by poor air removal (and the presence of other noncondensable gases), so surface condensers usually are equipped with vacuum pumps but also may incorporate older style, single or multistage multielement, steam-jet air ejectors. Under most normal operations, the residual oxygen level is below 20 to 40 ppb 02. 

To achieve a proper de-aeration, the bleached oil is sprayed into a vessel under reduced pressure, before entering the heating section. The lower the pressure applied, the lower the residual oxygen level in the oil. Usually, the oil is heated to at least 80° C and sprayed in a tank, which is kept at a pressure below 50 mbar. Some refiners even use the low pressure of the deodorizer or add some sparge steam in the spraying vessel to improve de-aeration. 

Replace the oxygen-rich air with an anoxic (oxygen-less) air to the desired residual oxygen level and... 

The CAP process requires use of a high vacuum chamber machine incorporating a snorkel, which evacuates the pouch under mild external pressure (preventing blockage of channels), before increasing this pressure somewhat to expel the remaining air. The pack is then inflated with carbon dioxide to achieve residual oxygen levels less than 0.05% in a cycle time of approximately 30 s. 

FIG. 1 Residual oxygen level (ROL) impact on relative wetting time. (After R. Lea, Ref. [4], 1992). 

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