Pulp drying with superheated steam under pressure – Part 1

The steam drier for beet pulp developed in Denmark was reported to the sugar industry for the first time at the CITS conference in Ferrera in 1987. Today, 11 driers are installed in European sugar factories. In the NIRO steam driers, beet pulp is dried in a celldivided fluid bed under pressure in superheated steam. This means that the drying takes place without energy consumption because the energy supplied leaves the drier as steam at e.g. 3.5 bar. Using this, almost 100% energy recovery is possible. This does also mean that air pollution is fully avoided. Loss of dry substance in the drying process does not occur and the digestibility of the dried pulp is improved. Over the last 4 years, further development have made the drier more reliable and the capacity has been increased. In German drying plants, in contrast to those on France, problems occurred on the rotary valves which take the pulp into and out of the drier. In 1994, these problems were closely analyzed and were found to be related to a very rapid condensation of the steam on the material to be fed into the drier. That was due to the larger surface area of the wellpressed German beet pulp (> 30% dry substance). Solutions to this problem were found already. Another problem was wear on the discharge rotary valve. The problem is met by a changed design and the selection of new materials.