Flash Drying of Recycled Paper Pulp in a Mechanically Agitated Fluidized Bed
Hidén, Aleksi (2020)
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Hidén, Aleksi
Åbo Akademi
2020
Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2020052639173
https://urn.fi/URN:NBN:fi-fe2020052639173
Tiivistelmä
Flash drying of pulp is an interesting option for drying of market pulp, mainly due to its high thermal efficiency and relatively low operating and capital costs. Typical flash dryers consist of a series of high drying towers, and cyclones for solid-air separation. The purpose of the study was to find out if drying of particulate pulp could be carried out in a smaller and simpler system, compared to those currently found in the industry.
The aim of this study was to investigate a fluidized bed-type flash drying process for recycled paper pulp. The core of the analysis was the behaviour of the granular pulp material when suspended in air and pneumatically transported. In addition to that, the drying characteristics of the pulp in such conditions were investigated. Some considerations and suggestions for possible feeder systems and other auxiliary components for the dryer are also given.
In industrial drying applications, an accurate calculation of a specific drying process requires sufficient information about several characteristics regarding the material, its shrinkage and the transfer coefficients, which can really only be determined by adequate experiments. Therefore, a test unit in bench scale was built to carry out experiments about the drying kinetics and the material behaviour. The unit was built to be a fluidized bed -type flash fryer with an option to mechanical agitation. With a proper dryer and agitator design, highly efficient air-solid heat transfer properties can be achieved in this type of drying system.
The fluidization characteristics, as well as drying kinetics, were analysed in the test unit. The feed of coarsely shredded material disintegrated into individual fibres in the dryer, resulting in a good quality product without significant formation of flocs or nodules. The dry matter content of the dried pulp achieved in the experiments was between 69 and 81% for one-stage drying, and 84% for two-stage drying. In order to achieve dry matter contents of 85-90% in the product, a two-stage drying configuration is always preferable for this type of drying system. The specific dryer efficiency was calculated at 3500 kJ/kg evaporated water, which is lower than the typical values of 4000-6000 and 4000-9500 kJ/kg for fluid bed and flash dryers respectively.
The aim of this study was to investigate a fluidized bed-type flash drying process for recycled paper pulp. The core of the analysis was the behaviour of the granular pulp material when suspended in air and pneumatically transported. In addition to that, the drying characteristics of the pulp in such conditions were investigated. Some considerations and suggestions for possible feeder systems and other auxiliary components for the dryer are also given.
In industrial drying applications, an accurate calculation of a specific drying process requires sufficient information about several characteristics regarding the material, its shrinkage and the transfer coefficients, which can really only be determined by adequate experiments. Therefore, a test unit in bench scale was built to carry out experiments about the drying kinetics and the material behaviour. The unit was built to be a fluidized bed -type flash fryer with an option to mechanical agitation. With a proper dryer and agitator design, highly efficient air-solid heat transfer properties can be achieved in this type of drying system.
The fluidization characteristics, as well as drying kinetics, were analysed in the test unit. The feed of coarsely shredded material disintegrated into individual fibres in the dryer, resulting in a good quality product without significant formation of flocs or nodules. The dry matter content of the dried pulp achieved in the experiments was between 69 and 81% for one-stage drying, and 84% for two-stage drying. In order to achieve dry matter contents of 85-90% in the product, a two-stage drying configuration is always preferable for this type of drying system. The specific dryer efficiency was calculated at 3500 kJ/kg evaporated water, which is lower than the typical values of 4000-6000 and 4000-9500 kJ/kg for fluid bed and flash dryers respectively.