Gasoline splitter

Refinery group" = low pressure naphtha fractionators, gasoline splitters, crude flash towers, etc. 

A number of refiners split the debutanized gasoline into light and heavy gasoline. This optimizes the refinery gasoline pool when blending is constrained by sulfur and aromatics. In a few gasoline splitters, a third heart cut is withdrawn. This intermediate cut is low in octane and it is processed in another unit for further upgrading. 

Adding a downstream gasoline splitter can help when reducing gasoline sulfur by minimizing octane loss. Other towers may be expanded by using structured packing. 

The distillation section of the MTG unit consists of a deethaniser, stabiliser, gasoline splitter and lean oil/sponge absorber circuit for recovering gasoline from the deethaniser off-gas and product separator off-gas. 

Before the Net Liquid enters the gasoline stabilizer, we must heat the product to a temperature suitable for fractionation. In the actual refinery process, the product heater is often integrated with the bottoms outlet of the gasoline splitter or other columns. However, for the purposes of this simulation we use a simple heat exchanger instead. For more detailed simulations, we advise the use of cross exchangers to accurately model the model the duty required for the fractionation. 

Typically, we will use the reflux ratio, temperature of a particular stage and mole purity (either C4 or C5 in the overhead liquid or vapor) as specifications for the column. If the column is operating as a gasoline splitter, we may want to use the Reid vapor pressure (RVP) (i.e., the vapor pressure at 100 F of a product determined in a volume of air 4 times the liquid volume as determined by ASTM D-323) of the bottoms as a performance specification. If the column does not converge, we can use the alternate specifications of overhead draw rate, reflux ratio and bottoms draw to ensure that the column converges to a solution. Once we have a solution, it is quite easy to converge on a performance specification. 

The fat oil is fed to a splitter or stripping tower, where the absorbed tight constituents are separated from the oil by distillation. Usually the lean oil is the same material as the heavier part of the absorber feed, so that the bottoms from the stripper are split into lean oil, which is recycled to the absorber, and a stabilized gasoline product, which is passed on to subsequent processing operations. 

The methyl-acetylene and propadiene in the C3 cut are hydrogenated to propylene in a liquid-phase reactor. Polymer-grade propylene is separated from propane in a C3 splitter (16). The residual propane is either recycled for further cracking, or exported. C4s and light gasoline are separated in a debutanizer (17). 

The cracked gases are cooled and fractionated to remove fuel oil and water (2-5) then compressed (6), processed for acid-gas removal (8) and dried (9). The C3 and lighter material is separated as an overhead product in the depropanizer (10) and acetylene is hydrogenated in the acetylene converter (11). The acetylene converter effluent is processed in the demethanizer system (12-14) to separate the fuel gas and hydrogen products. The demethanizer bottoms is sent to the deethanizer (15) from which the overhead flows to the C2-splitter (16), which produces the polymer-grade ethylene product and the ethane stream, which is recycled to the furnaces as a feedstock. The deethanizer bottoms flows to the C3-splitter (18) where the polymer-grade propylene is recovered as the overhead product. The C3-splitter bottoms product, propane, is typically recycled to the furnaces as a feedstock. The depropanizer bottoms product, C4S and heavier, flow to the debutanizer (19) for recovery of the mixed-C4 product and aromatic-rich pyrolysis gasoline. 

In this approach, pyrolysis gasoline first enters a C5/C6+ splitter which passes the C5 fraction to a di-cyc/o-pentadiene unit which dimerises the cyc/o-pentadiene in the C5 stream and the dimer is extracted. Excess C5 is returned to the system via an isoprene extraction unit. The mixture is then hydrogenated and olefins are saturated to paraffins. 

However for the single-column scheme, both light and heavy naphtha fractions are fed to the main column. If they are taken together as overhead liquid product, there will need to be a downstream stabilizer and a naphtha splitter to produce the gasoline streams for treatment. 

A new process that converts propylene and water to diisopropyl ether (DIPE) was developed by Mobil Research Development Corp. DIPE is a high-octane gasoline blending agent which, unlike other ethers, utilizes propylene in its synthesis. The DIPE reaction takes place in a fixed-bed catalytic reactor via a series of reaction steps. Isopropyl alcohol (IPA) is an intermediate which is recycled within the process. A propane/propylene splitter is included in the feed purification section to increase the concentration of propylene in the feed and maximize the DIPE production. DIPE utilizes propylene from the refinery and does not depend on an outside supply of alcohol. DIPE has similar octane blending values of RON and MON as other ethers like MTBE and TAME. DIPE also has a lower Reid vapor pressure than that of MTBE. DIPE is virtually nontoxic and has not caused adverse systemic effects or tissue toxicity [66]. 

At 0215, operators had started to introduce raffinate into the raffinate Splitter Tower, which is used to distil and separate gasoline components. (The word raffinate means a product in the refining process. In this case the raffinate was naphtha -raw gasoline - from the crude distillation column.) The tower was more than 30 m tall. A single instrument (shown as LT) was available for liquid level indication at the bottom of tower which had a maximum indicated level 9 feet (about 3 m). Above this level the instrument just indicated 9 feet . However, operators routinely filled above this level during start-ups to avoid the possibility of low level causing furnace damage. 

To recap the accident involved the Splitter Tower becoming completely filled with hot liquid raffinate (naphtha or gasoline), when it should have been less than one-tenth full. Hot raffinate then overflowed into the blowdown drum and out through its vent. The Splitter Tower had been receiving raffinate feed for several hours without any apparent concern that it might be overfilling. The ineffective level instrumentation at the... 

A different scheme is offered by C. F. Braun and Co., which takes the effluent vapor from the acid gas removal system and, after drying and cooling, feeds it to the depropanizer [15]. The overhead from this column is compressed to around 540 psia, hydrogenated to remove the dienes, and chilled to separate a hydrogen stream from the condensed hydrocarbons. Liquid condensates contain methane, plus the C-2 and C-3 hydrocarbons present in the feed to the depropanizer. These liquids are fed to the demethanizer, which strips the methane overhead. The demethanizer bottoms serve as feed to the deethanizer. The overhead from that column goes to the C-2 splitter, while the bottoms is the feed to the 03 splitter. The bottoms liquid from the original depropanizer is sent to the debutanizer for separation of the C-4 hydrocarbons from the aromatic gasoline fraction. 

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