Consistency

Читайте также:

Pulp consistency affects the sodium hydroxide concentration at a given alkali

charge, and also the pumping costs. Increasing pulp consistency results in a

decreasing diffusion distance and in an increasing alkali concentration, both of

which lead to an increased delignification rate [60]. The relationship between

caustic concentration at a given alkali charge as a function of pulp consistency on

the one hand, and the correlation to the extent of lignin removal on the other

hand, is depicted in Fig. 7.41.

Pulp consistency plays an important role in terms of safety for a commercial

system. The gaseous reaction products (predominantly carbon monoxide and volatile

hydrocarbons) generated in the reaction must be removed from the oxygen

delignification system comprising the reactor, blow tank, and washers. The specific

carbon monoxide evolution is about 30% less at medium consistency as compared

to high consistency [61].

7.3.6

Pulp Components and Impurities

Effect of Metal Ion Concentration

The rather poor selectivity of oxygen delignification as compared to chlorine dioxide

is further impaired by the presence of transition metal ions. The wood used as

708 7Pulp Bleaching

0 20 40 60 80

oxygen pressure: 0.4 MPa 0.6 MPa 1.1 MPa

Remaining â-arylether [%]

Reaction time [min]

Fig. 7.44 Influence of oxygen pressure on the degradation

rate of a phenolic b-aryl ether compound at pH 11 and 100 °C

(according to [39]).

Consistency