Lean Oil Absorption Vapor Recovery Equipment
Process Description
Lean Oil Absorption systems, along with Refrigeration Condensation, were among the earliest vapor control technologies to be utilized in the terminal industry for the control of vapors generated by product transfer operations. The theory of operation of lean oil absorption is relatively uncomplicated. The lean oil is forced to make intimate contact with the hydrocarbon contaminated air stream. This is usually accomplished in a column where the vapor rises through the column counter flow to the liquid coming down the column. As part of the column, a packing material, trays or spray nozzles are used to "break-up" the liquid so that the contact between the liquid lean oil and the vapor is enhanced.
The liquid absorbent or lean oil is so named because it is initially deplete (lean) of the compounds found in the vapor stream. As the lean oil and the vapor are brought into contact, the hydrocarbon compounds in the vapor are absorbed into the liquid and the liquid absorbent is now comprised partly of the hydrocarbons found in the vapor stream. If this liquid is re-circulated for a long enough period, the hydrocarbons found in the vapor begin to make-up a sizable portion of its composition. In time the liquid and vapor reach equilibrium and the liquid is no longer able to absorb any more vapor hydrocarbons, the liquid is said to be saturated or "rich." If the liquid absorbent is to be reused in the absorption column it must be regenerated before it becomes saturated. Regeneration is usually accomplished thermally and the vapor hydrocarbons are flashed out of the liquid and recovered. The liquid can then be re-used as an absorbent. In certain applications, the absorbent can be circulated on a "once through" basis and then returned to storage for further use in a different application, such as feed stock to various refinery processes.
For Lean Absorption technology to function within the required emission limits for any vapor phase hydrocarbon pollutant, the absorbent must be correctly chosen, the severity of the regeneration and its frequency must also be correctly determined.