#2 Naphtha Hydrotreater Unit (NHU) / Naphtha Splitter Unit (NSU) / CatalyticReformer Unit (CRU) & Isomerization Unit (Isom)

This unit, Unit 24, effectively consists of four sections: The Hydrobon section where sulphur and other contaminants are removed; The Prefractionator section where the full range feed naphthas are split into light feed to the Isomerization section and a heavy naphtha feed to the Reformer section; The Isomerization section where predominantly C5 & C6 components are Isomerized to increae octane and saturate the benzene; The Reformer section where the treated heavy naphtha is converted to a high octane Reformate for gasoline blending. Note that the effluents from both the Isomerization section reactor and the Reformer section reactors is combined for cooling and stabilization. The unit thus produces a single high octane gasoline blending component, the so called Iso-Reformate. The unit has a nominal design capacity of 14,500 BPSD at 90 RONC. The Hydrobon section consists of an absorber, charge heater, reactor, high pressure separator, and a stripper. The Prefractionator consist of a single distillation column, with feed surge drum, overheads reflux system and a fired reboiler. The Isomerization section is effectively a single reactor with feed preheat exchangers. The Reformer section consists of three reactors and heaters, high and low pressure separators, and a stabilizer.

In the Hydrobon section, the naphtha is fed to the absorber where it is contacted with a Hydogen rich gas stream from the Reformer. The feed is then heated and fed to the reactor where the main reaction is the conversion of sulphur to hydrogen sulphide. Nitrogen contaminants in the feed are also converted to ammonias. The reactor effluent enters the HP separator where a hydrogen rich stream is separated and recycled back to the Hydrobon feed with the fresh make-up hydrogen. In the stripper, Sour Fuel gas containing Hydrogen Sulphides and light ends are removed.

In the Prefractionator the treated full range naphthas from the Hydrobon section are separated into light and heavy naphtha components. Controlling the split in the prefractionator column allows the benzene and benzene precursors (components which form benzene in the reforming process) to be directed into the light naphtha feed going to the Isomerization reactor. This allows production of a high octane gasoline blend component with lower benzene contents as required to meet the gasoline specifications.

In the Isomerization section the light naphtha from the prefractionator overheads accumulator is contacted with hydrogen from the reformer nad preheated to reaction temperation. The preheat is first against Isomerization reactor effluent, then by condensing 150 psig steam and finally in electric heater exchangers. The Isomerization reactor contains a Zeolite type catalyst which promotes the isomerization of the straight chain paraffins and saturates any benzene aromatic rings. The effluent from the reactor after heat exchange with the incoming feed is routed into the reformer section for further cooling and stabilization in combination with the reformate.

In the Reformer section, the reactor charge is mixed with a hydrogen rich recycle gas stream, heated in exchangers and a fired heater, and charged to the reactors. Here, the naphtha is converted to reformate, a high octane gasoline blending component, in the presence of a catalyst. Because the chemical reactions are for the most part endothermic, the reactors have interstage heaters which reheat the effluent before entering the next reactor. After the effluent from the last reactor is cooled by exchanging heat with the reformer reactor charge, it is mixed with the Isomerization reactor effluent and further cooled before entering the low pressure separator to be separated into a liquid stream and a hydrogen rich gas stream. The gas stream is recompressed in the recycle gas compressor and is then combined with pumped liquid from the low pressure separator to maximize recovery. The combined gas and hydrocarbon streams are further cooled before entering the HP products separator. In the separator, the hydrogen rich gas stream separates from the condensed hydrocarbons. The majority of the gas stream is recycled back to the reactors with a net gas stream drawn off for supply to the Distillate Desulphurizer unit, to Hydrogen Sales, to the Hydrobon section as makeup and the excess is routed to fuel gas. The liquid stream is charged to the stabilizer where light ends are removed to control the RVP of the Iso-Reformate.