Method and arrangement for impregnating chips
The method is for the impregnation of chips during the manufacture of chemical pulp. The chips are continuously fed without preceding steam treatment to the top of an impregnation vessel that maintains atmospheric pressure. Impregnation fluid (BL) is added to the impregnation vessel and establishes a fluid level (LIQ_LEV). The chips that have been added establish a chips level (CH_LEV) that lies at least 3-5 meters over the fluid level. The temperature at the top of the vessel essentially corresponds to ambient temperature. Impregnation fluid BL is fed in to the impregnation vessel in such an amount and at such a temperature that the temperature that is established at the fluid level (LIQ_LEV) is established within the interval 90-115° C., preferably within the interval 95-105° C.
1. A method for the impregnation of chips during the manufacture of chemical pulp, comprising:
continuously feeding chips, without a preceding steam treatment, to a top of an impregnation vessel, the chips establishing a chips level,
feeding at least 5 tonnes of an impregnation fluid per tonne of chips into the impregnation vessel,
the impregnation fluid establishing a fluid level, the chips level being at least 1-2 meters above the fluid level, the impregnation fluid having a temperature in an interval of 115-150° C. and an alkali level exceeding 15g/l,
establishing a pressure within the top of the impregnation vessel that is essentially at atmospheric pressure ±0.5 bar and a temperature in a range of 15-25° C., and
establishing a fluid-wood mixture at the fluid level having a temperature within an interval of 90-115° C., and feeding out impregnated chips from a bottom of the impregnation vessel.
2. The method according to claim 1 , wherein the method further comprises withdrawing 0.1-1.5 m 3 /ADT (Air-Dry-Tonne) impregnation fluid for recycling.
3. The method according to claim 1 wherein the method further comprises evaporating impregnation fluid into a superior bed of chips located between the fluid level and the chip level.
4. The method according to claim 1 wherein the method further comprises adding steam at a top of the impregnation vessel when a temperature of the chips is below 15-25° C.
5. The method according to claim 3 wherein the method further comprises evaporating impregnation fluid up into the superior bed of chips at a level that does not exceed half of the height of the superior bed that is above the fluid level.
6. The method according to claim 5 , wherein the method further comprises evaporating the impregnation fluid up into the superior bed of chips at a level that does not exceed 25% of the height of the superior bed that is above the fluid level.
7. The method according to claim 1 wherein the method further comprises feeding the impregnation fluid at a position that is within one meter from the fluid level.
8. The method according to claim 1 wherein the method further comprises adding the impregnation fluid at a center of a cross-section the impregnation vessel.
9. The method according to claim 2 , wherein the method further comprises measuring a temperature of the withdrawn impregnation fluid.
10. The method according to claim 1 wherein the method further comprises including partially consumed cooking fluid, from a subsequent digester, into the impregnation fluid.
11. The method according to claim 1 wherein the method further comprises cooling a portion of the impregnation fluid in a cooler before feeding the impregnation fluid into the impregnation vessel.
12. The method according to claim 1 wherein the method further comprises heating a portion of the impregnation fluid in a heater prior to feeding the impregnation fluid into the impregnation vessel.