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DumpmeAdrenaline

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- Homework Statement
- The vacuum residue fraction from an Albertan bitumen is hydroprocessed using an ebullated bed technology. The vacuum residue fraction has a density of 1030 kg/m3. The catalyst is a commercial sulfided CoMo/Al2O3 catalyst. The unit is operated at a constant reactor temperature of 428 °C and a total pressure of 10 MPa absolute. The H2-to-feed ratio is maintained at 1000 normal m3/m3 residue feed. The H2 consumption is 1.27 wt% of the residue feed and the average heat of reaction for hydrotreating and cracking expressed in terms of the H2 consumption is 62kJ/mol H2 consumed.

1.1) What is the H2 consumption by reaction in normal m3/m3 residue feed? (Normal conditions:273.15 K, 101.325 kPa).

1.2) Some gaseous products are produced during residue hydroconversion that cannot completely be removed as either liquid phase products, or through scrubbing, i.e. they end up in the H2recycle. For the process considered, these products are methane 1.2 wt%, ethane 0.3 wt%, H2S0.6 wt%, and CO2 0.1 wt% (wt% of the residue feed). If the H2 partial pressure in the H2 recyclemust be at least 8 MPa, what is the purge rate in normal m3/m3 residue feed? (Hint: Non-H2gases in the recycle must be purged at the rate of their formation).

1.3) What is the fresh feed rate of pure H2 in normal m3/m3 residue feed?

1.4) What must the preheater outlet temperature be for the combined feed, i.e. H2 and residue feed? Assume that the average heat capacity for all of the material in the reactor is 2.6 kJ/kg·K at the operating conditions. Consider this question independently of your answers to questions 1.2 and 1.3 and make the following assumption: assume that the ratio of non-H2 gases to H2 in the combined fresh plus recycled H2 feed is 1:6 molar ratio. (Hint: The ebullated bed reactor behaves like an adiabatic continuous stirred tank reactor and the reactions taking place during hydroprocessing are exothermic).

- Relevant Equations
- Material balance

Ideal gas Law

Energy Balance

1.1) 1 m3 of residue feed has a mass of 1030 kg.

Mass of H2 consumed=(1.27 kg of H2 consumed/100 kg of residue feed)*1030 kg of residue feed=13.081 kg

We can treat H2 as an ideal gas to calculate its volume at normal conditions

101325*V=(13.081/2.016)*1000*8.3145*273.15

V=145.436 m3 normal/m3 residue feed

1.2) To calculate the H2 mass in feed I used the ideal gas

1000*101325=n*8.3145*273.15

n=44614.8 mol H2 =44.6148 kmol

Mass of H2 in feed=44.6148*2.016=89.9434 kg

Mass of Unconverted H2=Mass of H2 in feed-Mass of H2 consumed=89.9434-13.081=76.8624 kg H2

We split the product stream into a low pressure purge stream and low pressure recycle stream to avoid the build up of non-condensables that decrease the partial pressure of H2. The composition of all three streams are the same. Given that the partial pressure of H2 in the recycle stream must be 8 MPa I am not sure how this information is enough to compute the purge rate

Mass of H2 consumed=(1.27 kg of H2 consumed/100 kg of residue feed)*1030 kg of residue feed=13.081 kg

We can treat H2 as an ideal gas to calculate its volume at normal conditions

101325*V=(13.081/2.016)*1000*8.3145*273.15

V=145.436 m3 normal/m3 residue feed

1.2) To calculate the H2 mass in feed I used the ideal gas

1000*101325=n*8.3145*273.15

n=44614.8 mol H2 =44.6148 kmol

Mass of H2 in feed=44.6148*2.016=89.9434 kg

Mass of Unconverted H2=Mass of H2 in feed-Mass of H2 consumed=89.9434-13.081=76.8624 kg H2

Component in product stream | wt% of residue feed | m(kg) | n (kmol) | y (mole fraction) |

CH4 | 1.2 | 12.36 | 0.7705 | 0.0006 |

C2H6 | 0.3 | 3.09 | 0.1027 | 0.0046 |

H2S | 0.6 | 6.18 | 0.1813 | 0.0026 |

CO2 | 0.1 | 1.03 | 0.02340 | 0.0197 |

H2 | 7.4624 | 76.8624 | 38.1262 | 0.9725 |

We split the product stream into a low pressure purge stream and low pressure recycle stream to avoid the build up of non-condensables that decrease the partial pressure of H2. The composition of all three streams are the same. Given that the partial pressure of H2 in the recycle stream must be 8 MPa I am not sure how this information is enough to compute the purge rate

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