Bleaching fibrous material - uses gas reagent suspension with opened fibres for mechanical mixing for reaction and porous bed to complete reaction and remove surplus gas

摘要

Fibrous material is opened out within the gas reagent to form a gas suspension with the fibres. The material is mixed mechanically while in suspension with the gas reagent, until it has reacted with the fibres. The material is passed to a porous bed for gas to be extracted to finish the reaction and ensure that all surplus reagent is removed from the fibre material. The assembly to move the gas suspension of fibres has a longitudinal mixing chamber with a number of mixing paddles on a rotating axial shaft. A screw conveyor at the entry to the mixing chamber moves the gas and fibre suspension into the mixing chamber at a speed which gives the gas suspension a dwell time of up to about 10 secs. After the gas/fibre suspension has been fed into the mixing chamber it dwells in the chamber while mixing for a sufficient time to allow the major portion of the gas reagent to react with the fibres. The gas/fibre suspension is transferred into a degassing and reaction chamber to form a porous bed, where the reaction can continue until the reagent is wholly consumed. The fibre material is opened out with the gas reagent, using wood pulp with a consistency of 20-50%, and the reagent is a mixture of ozone in oxygen, with a dwell time of about 10 secs. in the mixing chamber. The screw conveyor generates a movement pressure against the mixing paddles in the mixing chamber, and gives a dwell time of about 10 secs. for the pulp gas suspension in the mixing chamber. USE/ADVANTAGE - Partic. to bleach pulp for use in papermaking, using gas reagents such as chlordioxide or ozone. The technique gives a thorough reaction between the gas and the fibre material, with lower reagent consumption