Assignment 5 by nskW5k


									                               Petroleum Refining Processes CBE 4432/9152

Assignment 5                                                                                           Due date: April 5, 2010

Vacuum Gas Oil (VGO) as a byproduct of crude oil vacuum distillation is sent to a hydro-cracking unit for
upgrading. The flow rate of VGO is 30000 bbl/day. The flow rate of hydrogen rich gas (make-up
hydrogen and recycled hydrogen) is 4000 scf/bbl of VGO. Considering the following conditions, design
the hydro-cracking unit (diameter and height of the reactor).

     -    Operating temperature 350-400 C
     -    Operating pressure 10-14 MPa
     -    Catalysts are spherical in shape, diameter = 3 mm, bed voidage = 0.40
     -    Nitrogen and sulfur are completely converted to H2S and NH3
     -    Liquid hourly space velocity (LHSV) = 1 h-1
     -    Maximum allowable pressure drop = 20 kPa/m of the catalyst bed
     -    Length to diameter ratio of the catalyst bed should not be larger than 1.5 m
     -    Operational pressure drop should be kept much lower than maximum value for safe and
          continuous operation, take between 10 – 20% of maximum pressure drop.

          Feed conditions at 400 C and 12 MPa:
          Liquid phase:
                                Density: 720 kg/m3
                                Viscosity:1.778 x 10-5 Pa.s
          Gas phase:
                                Density: 12.68 kg/m3
                                Viscosity: 0.000134 Pa.s

          Assume 1 meter spacing between the beds for redistribution and heat transfer.
          Also assume 1.5 m on top and the bottom of the reactor.

          Ergun equation:

ε = voidage                        μ = fluid viscosity                 A = cross sectional area of the reactor

ρf = liquid density                     dp = Particle diameter                 Q = flow rate

1 bbl = 0.15898 m3                                          1 scf = 0.0283 m3

    -   Liquid hourly space velocity is the ratio of liquid flow rate to the volume of catalyst.
    -   Since a large amount of hydrogen is used, it is safe to assume that a gaseous flow (e.g. mist
        flow) is entering the reactor having average properties for the flow of gas and liquid to the
    -   You need to use Ergun’s equation to find the area. This requires a trial and error procedure.
        Use Excel spread sheet for this Part. Having found the area, the diameter and height of one
        bed will be estimated. The total height of the reactor is determined using the data given in
        the problem.

Please feel free to contact the TA or myself if you need help.

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