The objective of kerosene hydrotreating is to upgrade raw kerosene distillate to produce specification products suitable for marketing as kerosene and jet fuel. Sulfur and mercaptans in the raw kerosene cuts coming from the crude distillation unit can cause corrosion problems in aircraft engines and fuel handling and storage facilities. Nitrogen in the raw kerosene feed from some crude oils can cause color stability problems in the product. For aviation turbine fuels (ATF), the ASTM distillation, flash point, and freeze point of the hydro-treated kerosene cut has to be rigorously controlled to meet the stringent requirements. This is done by distillation in a series of columns to remove gases, light ends, and heavy kerosene fractions. The upgrading is achieved by treating hydrogen in the presence of a catalyst, where sulfur and nitrogen compounds are converted into hydrogen sulfide and ammonia.
Because of the very stringent product specifications, the ATF product can have only straight run kerosene or hydrotreated blend components. Another important property of aviation turbine fuel is its smoke point, which in turn is a function of the aromatic type hydrocarbons in the cut. Higher aromatic content yields lower smoke point kerosene cuts, which may not meet the aviation turbine fuel specification. Depending on the severity of hydrotreating, the smoke point of the kerosene may be improved by saturation of aromatics to corresponding naphthenes (see Figure 2-3).
Kerosene feed from storage is pumped via charge pump P-101 and preheated in effluent/feed exchanger E-103, followed by final heating in fired heater H-101. The effluent from H-101 next joins the recycle
Kerosene HDS unit. C.W.=cooling water.
hydrogen coming from compressor C-101 and is heated successively in feed/effluent exchanger E-102 and fired heater H-102. The heated kerosene feed and hydrogen mix stream next flow through reactor V-101, loaded with a Co-Mo or Mo-Ni catalyst. Hydrodesulfurization and hydrodenitrification reactions take place in the reactor. These reactions are exothermic. The reactor effluent is cooled in the effluent/ feed exchangers E-102, E-103, and E-104 by exchanging heat with incoming kerosene feed and hydrogen. The effluent is next cooled in air cooler E-105 before being flashed in high pressure separator drum V-l02 at 140°F.
The hydrogen-rich gas from the separator is compressed and recycled to the reactor section by centrifugal compressor C-101. Recycled hydrogen gas is preheated in effluent/hydrogen exchanger E-102. It is further heated in fired heater H-102 and joins the hydrocarbon feed to reactor V-101.
The hydrocarbon liquid from the separator drum is depressurized into flash drum V-l04. The flash gas is sent to the amine unit for H2S removal before being sent to refinery fuel system. The liquid from the flash drum is sent to a stabilizer column V-l05. The stabilizer overhead vapor is partially condensed in air cooler E-106 and flows into accumulator V-l06. A part of the accumulator liquid naphtha is returned to the column as reflux, the rest is withdrawn as wild naphtha.
The stabilizer bottom product is sent to fractionator column V-l07, where a high flash naphtha cut is taken as overhead product. Light kerosene base stock is withdrawn from the fractionator as a sidestream. It passes through kerosene side stripper V-l08 to adjust its flash point and cooled in E-lll and E-112 before sending to storage. The stabilizer column is reboiled by fired heater H-103.
Fractionator bottoms flow to splitter column V-l 10, where aviation turbine kerosene is withdrawn as an overhead product. Antioxidant is injected into the ATK product before it is finally sent to storage. The splitter column is heated in a forced recirculation-type reboiler, the heat provided by the H-106 fired heater.
The bottom product is pumped through air cooler E-l 14 and water trim cooler E-l 15 to storage as heavy kerosene. This product is used as a blend stock for diesel or as a cutter for various fuel oil grades.
The operating conditions of a kerosene hydrotreating unit are shown in Table 2-6. The corresponding feed and product properties, unit yields, and utility consumption are shown in Tables 2-7 to 2-10.
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