Absorption lean oil

The oldest kind of gas plants are absorption/lean oil plants, where a kerosene type oil is circulated through the plant as shown in Figure 9-1. The lean oil is used to ab.sorb light hydrocarbon components from the gas. The light components are separated from the rich oil and the lean oil is recycled. 

Absorption Lean Oil Requirement for Fixed Component Recovery in Fixed Tower [18]... 

The butane-containing streams in petroleum refineries come from a variety of different process units consequently, varying amounts of butanes in mixtures containing other light alkanes and alkenes are obtained. The most common recovery techniques for these streams are lean oil absorption and fractionation. A typical scheme involves feeding the light hydrocarbon stream to an absorber-stripper where methane is separated from the other hydrocarbons. The heavier fraction is then debutanized, depropanized, and de-ethanized by distillation to produce C, C, and C2 streams, respectively. Most often the stream contains butylenes and other unsaturates which must be removed by additional separation techniques if pure butanes are desired. 

The bottoms, consisting of absorption oil, absorbed propane, and higher boiling hydrocarbons, are fed to the lean-oil fractionator. The LPG and the natural gas Hquids are removed as the overhead product from the absorption oil which is removed as a ketde-bottom product. 

This procedure has been applied to the absorption of C5 and lighter hydrocarbon vapors into a lean oil, for example. 

FIG. 14-9 Graphical design method for multicomponent systems absorption of hiitane and heavier components in a soliite-free lean oil. 

When A is very much larger than unity and when N is large, the right-hand side or Eq. (14-55) becomes equal to unity. This signifies that the gas will leave the top of the tower in equiUbrium with the incoming oil, and when Xo = 0, it corresponds to complete absorption of the component in question. Thus, the least volatile components may be assumed to be at equiUbrium with the lean oil at the top of the tower. 

Conversion of Lean Oil Absorption Process to Extraction Process for Conditioning Natural Gas, U.S. Patent 4.696,688, Sep. 29, 1987. 

Enhancing the Profitability of Lean Oil Absorption Through Simulation, GasTIPS , Fail 1996, Volume 2, Number 3, p.38... 

Basically, a gas absorption tower is a unit in which the desirable light ends components are recovered from the gas feed by dissolving them in a liquid passing through the tower countercurrently to the gas. The liquid absorbent is called lean, oil, and it usually consists of a hydrocarbon fraction in the gasoline boiling range. After the absorption step, the liquid which now contains the desired constituents in solution is referred to as fat oil. A similarly descriptive nomenclature is applied to the gas, which is referred to as wet gas when it enters the tower and as dry gas when it leaves the absorber. 

Instead of condensing out the ethylene at extremely low temperatures, as described above, the absorption process uses a very light, lean oil, such as Cj, at moderately low temperature to scrub the ethylene out of the gas. By stripping the fat oil, the ethylene and heavier cuts can be recovered as desired. 

Absorbent Flow Failure - For lean oil absorption generally, no relief requirement results from lean oil failure. However, in a unit where large quantities of inlet vapor may be removed in the absorber, loss of absorbent could cause a pressure rise to relief pressure, since the downstream system may not be adequate to handle the increased flow. In such cases, the effect of this additional vapor flow into downstream equipment must be analyzed. 

Many operations in petrochemical plants require the absorption of components from gas streams into lean oils or solvents. The resultant rich oil is then stripped or denuded of the absorbed materials. The greatest use of this operation utilizes hydrocarbon materials, but the basic principles are applicable to other systems provided adequate equilibrium data are available. 

This method [18] is well suited to handling the details of a complicated problem, yet utilizing the concept of average absorption and stripping factors. It also allows for the presence of solute components in the solvent and the loss of lean oil into the off gas. Reference 18 presents more details than are included here. Reference 18 is Edmister s original publication of the basic method for absorbers and strippers. Reference 18 also generates the... 

If the result does not yield the desired amount of the key component absorbed, then reassume the lean oil quantity, Lq, and recalculate. Adjustments may have to be made separately or simultaneously in the assumed absorption quantity until an acceptable result is obtained. After two or three trials a plot of the key variables will assist in the proper assumptions. 

The total intercooler duty is the difference between the total heat in of the rich gas and lean oil and the total heat out of the off gas and rich oil all at the terminal calculated or design conditions. The total duty is often divided between several coolers placed to re-cool the oil as it passes down the column. If intercoolers are not used, then the absorption cannot meet the design terminal outlet conditions and the quantity of material absorbed will be reduced. If the intercooling is too great so as to sub-cool, then greater absorption may be achieved, but this can be controlled by the intercooler operation. 

A second approach to the same result involves the same requirements as for a balanced heat design the heat of absorption of the actual components absorbed must equal the sum of the heat added to the lean oil and to the lean... 

For a new design a study should be made of number of trays against required lean oil for a given absorption. 

Kremser-Brown-Sherwood Method — No Heat of Absorption, 108 Absorption — Determine Component Absorption in Fixed Tray Tower, 108 Absorption — Determine Number of Trays for Specified Product Absorption, 109 Stripping — Determine Theoretical Trays and Stripping or Gas Rate for a Component Recovery, 110 Stripping — Determine Stripping-Medium Rate for Fixed Recovery, 111 Absorption — Edmlster Method, 112 Example 8-33 Absorption of Hydrocarbons with Lean Oil, 114 Inter-cooling for Absorbers, 116 Absorption and Stripping Efficiency, 118 Example 8-34 Determine Number of Trays for Specified Product Absorption, 118 Example 8-35 Determine Component Absorption in Fixed-Tray Tower, 119 Nomenclature for Part 2, 121... 

Two sources of absorption oil are normally utilized in this tower. The first is the hydrocarbon liquid from the main fractionator overhead receiver. This stream, often called wild, or unstabilized, naphtha, enters the absorber a few trays below the top tray. The second absorbent is cooled debutanized gasoline, which generally enters on the top tray. It has a lower vapor pressure and can be considered a trim absorbent. The expression lean oil generally refers to the debutanized gasoline plus the unstabilized naphtha from the overhead receiver. 

The absorption process is exothermic. To improve C3+ recovery, liquid from one or more of the middle trays is pumped through an intercooler and returned to the tray below. In some FCC units, the lean oil feed is chilled. 

A presaturator to provide lean oil/gas contact prior to feeding the lean oil into the tower can be a good way to get more out of an older tower. Absorber tray efficiences run notoriously low. A presaturator that achieves equilibrium can provide the equivalent of a theoretical tray. This can easily equal 3-4 actual trays. Some modem canned computer distilla-tion/absorption programs provide a presaturator option. 

Lean oil absorption oil from which gasoline fractions have been removed oil leaving the stripper in a natural-gasoline plant. 

A lean oil is to be used as the absorbing medium for removing a component of a gas. As part of the design for the absorption unit, it is necessary to estimate the size of the motor necessary to pump the oil to the top of the absorption tower. The oil must be pumped from an open tank with a liquid level 10 ft above the floor and forced... 

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