Improvement of the Technology for Diesel Oil Fractions Hydrotreating

April 26, 2009

Key elements in the development of this technology include the following:

  • Selection of a reactor unit which would ensure the maximal contact of the catalyst with the initial raw stock and its uniform distribution;
  • Selection of a catalyst having stable hydrodesulfurization activity and high strength properties;
  • Selection of the optimal catalyst system in order to reduce the pressure differential;
  • Catalyst activation completeness;

Determination of the technological parameters in order to achieve the lowest initial process temperature.

   The reactor is the main device determining the efficiency of this process and the depth of the raw stock conversion; its technical design should ensure the specified productivity, have the necessary reaction capacity, develop the contact area of interacting phases required for the process, and maintain the necessary heat exchange during the process and the level of the catalyst activity. This design should have the minimal hydraulic resistance and ensure the uniform distribution of the gas-liquid stock flow over the whole reaction volume. Usually, reactors with axial infeed of the gas-liquid stock mixture are used at the domestic units for diesel oil hydrotreating.

   Practical experience of use of diesel oil fractions hydrotreating indicates that performance of the reactor with axial movement of the stock flow is characterized by non-uniform distribution of the gas-liquid stock mixture over the cross-section of the device and increasing hydraulic resistance of the catalyst layer, especially during long operation. Increase of differential pressure in the reactor results in decrease of its productivity and higher power consumption by the unit. To suppress the rise of differential pressure during the operating cycle, the following actions are usually undertaken: the top layer of the catalyst is periodically removed from the reactor; so-called filtering baskets, inert spherical materials (porcelain balls of variable diameter); combined protective catalyst layers, distribution devices are used. The listed methods make it possible to protect the main catalyst layer, but cannot solve the problem of the high hydraulic resistance.

   It is possible to reduce differential pressure in the hydrotreating reactor without the catalyst performance degradation by changing the scheme of the stock infeed in the reactor from axial to axial-radial (Table 1).
Non-uniformity of the reaction behavior is conditioned generally by the gradient of flow distribution over the layer cross-section and catalyst volume. The design of the inner components of the axial-radial reactor develops the cross movement of the reacting gas and liquid flows in the catalyst layer. At the same time, the hydrogenous gas is redistributed along the layer height, uniform catalyst layer performance and absence of dead zone for gas slippage are achieved; lower hydraulic resistance to the flow when it passes through the catalyst layer; improved distribution of the gas-liquid stock flow over the cross-section of the unit. The mentioned factors ensure (as practical experience proves) lower differential pressure in the axial-radial reactor during its long-time operation.

   In Russia, the first axial-radial reactors were installed at the second module of the standard double-flow hydrotreating unit L-24/6 of Salavatnefteorgsyntez. During the four-year service cycle