DualOx® Enhanced Oxygen Delignification

DualOx® Enhanced Oxygen Delignification

Kempulp is a world leader in oxygen delignification, having supplied over one hundred forty medium consistency oxygen delignification installations worldwide.
Oxygen delignification has been done in several ways, high consistency, medium consistency, one stage or two stage. The state of the art design today is the GL&V DUALOX® system which delignification with oxygen is primarily intended to facilitate your next stage of the process, i.e. bleaching. More effective delignification enables you to reduce the use of hazardous and expensive chemicals in the bleach plant.

Efficient DUAL mixer solutions are available for steam, oxygen, chlorine dioxide and ozone. The compact design and convenient nozzle locations allows for easy and cost effective installation in new and existing mills. The Dual mixer consists essentially of housing and an extended rotor of compact design. Chemicals are added at the front end of the rotor, where the pulp is fluidised. Fluidisation is further intensified between the rotor and the stator at the outlet of the rotor. This process gives very good mixing of the chemicals.

The Kempulp patented DUALOX® design with a short retention time pre-reactor followed by a booster pump and a second stage 60 minute reactor. This concept offers to enhance performance of a two stage system with a lower investment cost. The oxygen delignification system is of the GL&V patented DUALOX type in two-reactors. The process was designed using reaction kinetic equations, which were translated into a mill context. The equations state that the oxygen delignification process proceeds via two different phases, a very rapid initial phase and a slow final phase. As a consequence, the retention time is divided unequally between the two reactors, with a short retention time of 5-10 minutes designed in the first reactor and a longer retention time of 60 minutes in the second reactor.

The temperature in the first reactor is kept at a lower level to treat the pulp more mildly here in order to retain as high a final viscosity as possible. In the second reactor a higher temperature to ensure that the desired outgoing kappa number is reached. In this second kinetic phase the temperature does not affect the selectivity of the process meaning that the temperature level does not compromise the high final viscosity. The pressure is kept at a high level throughout the whole of the system in order to make the oxygen dissolve easily stay in solution for as long as possible. In order to maintain a high pressure in the second reactor apart from a mixer also a booster-pump is placed between the two reactors. This way the pressure is increased to a high level again.

The DUALOX system is a compact two-reactor oxygen delignification system setting a standard for the state-of-the-art technology. It allows a high delignification degree to go hand in hand with a good selectivity.

  • Extended delignification feasible
  • More selective delignification
  • A simple design
  • Optimum conditions for the delignification process
  • Flexibility to adjust pressure and temperature in both reactors

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