LPG treating

Most LPG treating applications require no mote than three beds of packing. In some cases, e.g., removal of carbon dioxide alone, a single bed of packing is adequate. Single stage con-... 

Figure 2-96 depicts a typical LPG treating system, hi this case the LPG feed is the condensed product of a refinery debutanizer cohmm. Ibe LPG is punqied on level control from the debutanizer colunm ovediead accumulator and flows to a countercnirent liquid-liquid contactor which contains three beds of random pacldng. The LPG entns the bottom of the cohimn, while filtered lean amine is fed to the top of the column at a controlled, constant flowrate. 

LPG/amine treaters can have significant amine losses. Veldman (1989) states that amine losses for well designed and operated LPG treaters due to amine entrainment and solubility amount to about 0.02 lb of amine per barrel of LPG treated. Washing the LPG with a dilute amine-water solution removes entrained amine from the LPG and reduces the concentratian of amine dissolved in the LPG because amine in the hydrocarbon phase establishes equilibrium with the dilute water wash phase. Figure 2-96 includes a typical water wash system. 

Fractions treated by this process are light products from the primary distillation LPG to Kerosene, or light products from thermal and catalytic cracking (visbreaking, coking, FCC). 

A large use of molecular sieves ia the natural gas industry is LPG sweetening, in which H2S and other sulfur compounds are removed. Sweetening and dehydration are combined in one unit and the problem associated with the disposal of caustic wastes from Hquid treating systems is eliminated. The regeneration medium is typically natural gas. Commercial plants are processing from as Htde as ca 30 m /d (200 bbl/d) to over 8000 m /d (50,000 bbl/d). 

Higher molecular weight hydrocarbons present in natural gases are important fuels as well as chemical feedstocks and are normally recovered as natural gas liquids. For example, ethane may be separated for use as a feedstock for steam cracking for the production of ethylene. Propane and butane are recovered from natural gas and sold as liquefied petroleum gas (LPG). Before natural gas is used it must be processed or treated to remove the impurities and to recover the heavier hydrocarbons (heavier than methane). The 1998 U.S. gas consumption was approximately 22.5 trillion ft. ... 

The LPG stream containing a mixture of C s and C4 s must be treated to remove hydrogen sulfide and mercaptan. This produces a noncorrosive, less odorous, and less hazardous product. The C s and C4 s from the debutanizer accumulator flow to the bottom of the H S contactor. The operation of this contactor is similar to that of the fuel gas absorber, except that this is a liquid-liquid contactor. 

In the LPG contactor the amine is normally the continuous phase with the amine-hydrocarbon interface at the top of the contactor. This interface level controls the amine flow out of the contactor. (Some liquid/liquid contactors are operated with the hydrocarbon as the continuous phase. In this case, the interface is controlled at the bottom of the contactor.) The treated C3/C4 stream leaves the top of the contactor. A final coalescer is often installed to recover the carry-over amine. 

In the extraction process, the LPG from the prewash tower enters the bottom of an extractor column. The extractor is a liquid/liquid contactor in which the LPG is counter-currently contacted by a caustic solution. Another option is the use of a fiber film contacting device. The mercaptans dissolve in the caustic (Equation 1-14). The treated LPG leaves the top of the extractor and goes on to a settler, where entrained caustic is separated. 

Drivers for investment are directly linked to market demand. In the European Union, gasoline demand is declining, whereas demand for diesel is increasing with modest increases for treating gas oil. Heavy fuel oil demand is also declining. Under such market forces, the E.U. product market is shifting and demand for middle distillates is increasing from 310 million tons (310 MMt) in 1997 to 390 MMt in 2015.15 Production of LPG, naphtha, and other products is expected to increase.15... 

If LPG containing olefins and diolefins is to be used as a feed for a cracking operation then it should be hydro-treated prior to use. This will prevent olefin polymerisation in the cracking furnace which would lead to coking. Hydro-treatment of LPG is becoming more common in refinery operations as the specifications for automotive LPG are tightened . 

USY), Ultrastable synthetic zeolite Y treated to reduce aluminum content and improve thermal and hydrothermal stability (see Section. 6.1). LPG = liquid propane gas. 

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