8.4 Hydrocracking

8.4.1 Process summary

• • Cycle oils and coker distillates are the typical feedstocks.

• • High quality jet fuel and diesel production is targeted.

• •
• verall reaction is exothermic.

• • Cracking is promoted on silica-alumina sites of the catalyst.  Hydrogenation promoted by palladium, molybdenum sulphide or tungsten sulphide compounds.

• • Since catalyst gets poisoned with organic nitrogen compounds, hydrotreater catalytic reactors are used before hydrocracking reactors to safeguard the hydrocracking catalysts.

• • Excess hydrogen also aids in preventing catalyst coking.

• • Operating conditions of the hydrocracking reactor: 340 – 425°C and 70 – 200 bar.

8.4.2 Process Technology (Figure 8.3)

Figure 8.2 Fixed Bed and Moving Bed

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• • Reactors use fixed or moving bed reactors in which fixed beds are more common.

• Packed beds: Cold shot reactors are used in which cold H₂ is used to cool the hot streams. Guard reactors are used before hydrocracking catalyst within the reactor column itself

• Moving beds: Feed allows movement of the catalyst for good mixing.

• After reaction, the product gets mixed with water and enters a three phase separator.

Figure 8.3 Flow sheet of hydrocracking

• • The three phase separator generates three streams namely sour water stream, organic stream and a gas stream.

• The gas stream again enters a phase separator to remove entrained organic stream after cooling.

• The gas stream is subjected to H₂S removal using amine scrubber. The organic stream eventually enters a steam stripper further stabilize the organic stream.  In this fractionator, a gas stream and a sour water stream are generated.

• Eventually, the stabilized organic stream is sent to a multi-product fractionators to generate light naphtha, heavy naphtha, kerosene, diesel and residue. Steam is used to enhance the product quality.