Method and Arrangement for Impregnating Chips

Abstract

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.

Description

DESCRIPTION OF DRAWING

FIG. 1 shows an arrangement for impregnation of chips during the manufacture of chemical pulp according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The concept “untreated chips” will be used in the following detailed description. “Untreated chips” is here used to denote chips that have not passed through any form of pre-treatment by, for example, steam treatment or similar, before the chips are fed into an impregnation vessel to be impregnated.

The concepts “fluid level, LIQ_LEV” and “chips level, CH_LEV” will also be used. The term “fluid level, LIQ_LEV” is here used to denote the level that the impregnation fluid BL added to the impregnation vessel 101 has established in the vessel. The term “chips level, CH_LEV” is here used to denote the height of that part of the bed of chips (consisting of chips) that is located above the fluid level, LIQ_LEV.

FIG. 1 shows an arrangement for the impregnation of chips during the manufacture of chemical pulp. The arrangement comprises an essentially cylindrical impregnation vessel 101 arranged vertically, to which untreated chips/non-steamed chips are continuously fed to the top of the impregnation vessel through a feed arrangement, in the form of a small chip bin 102 without steam treatment, and a sluice feed/chip feed 103. The temperature at the top 109 of the vessel essentially corresponds to ambient temperature, 15-25° C., where steam ST may be added if the ambient temperature falls below normal ambient temperature and in such a quantity that a chip temperature within this interval is established. The chips that are fed to the impregnation vessel normally maintain the same temperature as the ambient air temperature ±5° C. The chips fed in establish a chips level CH_LEV in the upper part of the impregnation vessel.

According to the invention, a feed line 108 with impregnation fluid BL is connected to the impregnation vessel in order to establish a fluid level LIQ_LEV consisting of the said impregnation fluid. The impregnation fluid is fed directly in in association with the fluid level LIQ_LEV ±1 meter. The impregnation fluid BL is added at the centre of the impregnation vessel and is fed in to the impregnation vessel in such an amount and at such a temperature that the temperature at the fluid level CH_LEV is established within the interval 90-115° C. and preferably within the interval 95-105° C., whereby evaporation of fluid takes place up into the superior bed of chips locally above the fluid level, while at the same time steam is not driven through the superior bed of chips. The evaporation up into the superior bed of chips takes place over a distance that does not exceed half of the height of the superior chips level CH_LEV, it is preferable that the evaporation takes place up into the superior bed of chips over a distance that does not exceed 25% of the superior chips level CH_LEV.

The impregnation fluid BL added is constituted to more than 50% by cooking fluid after use in a cooking zone in a subsequent digester, which impregnation fluid BL has an alkali level of at least 15 g/l. The amount of impregnation fluid BL that is added to the vessel 101 lies between 5-10 m³/ADT, preferably between 7-9 m³/ADT, where “ADT” is an abbreviation for “Air-dry tonne” of pulp.

The temperature of the impregnation fluid BL in the feed line 108 maintains a temperature of 115-150° C. and the chips level CH_LEV lies at least 1-2 meters over the fluid level and preferably 3-5 meters over the fluid level LIQ_LEV, in order to facilitate the sinking of the chips in the impregnation fluid, where the chips are heated. In order to ensure that the temperature of the added impregnation fluid BL is not exceeded, a cooling means 111 may be preferably arranged in front of the impregnation vessel 101. The cooling means may be an indirect heat exchanger, a pressure-reduction cyclone or other evaporative cooling, or it may be the addition of cold fluid, preferably colder process fluids, alkali or washing filtrate.

Given non-steam treated chips that maintain 25° C. with their naturally occurring moisture level, 5 tonnes of fluid that maintains 139° C. are required in order to establish a temperature of approximately 115° C. in the chips mixture at the fluid level.

If a temperature of 100° C. is to be established in the chips mixture, given the same basic conditions, 5 tonnes of impregnation fluid that maintains 120° C. is required.

By adding the impregnation fluid in association with the fluid level CH_LEV, the air present in the chips will be flashed out, and the chips will sink in the impregnation fluid.

A withdrawal strainer 110 can, in one preferred embodiment, be used in order to withdraw impregnation fluid REC from the impregnation vessel 101, at the level of the fluid level LIQ_LEV.

In one preferred embodiment, the temperature of the material REC withdrawn is measured, and in this case either one of the temperature and the amount of added impregnation fluid BL is adjusted such that the target value desired for the withdrawn material REC is maintained.

The pressure in the vessel can be adjusted as required through a regulator valve 104 arranged in a ventilation line 105 at the top of the impregnation vessel. The ventilation line 105 may open directly into the atmosphere, for the establishment of atmospheric pressure. It is preferable that a pressure at a level of atmospheric pressure is established, or a slight negative pressure down to −0.2 bar (−20 kPa), or a slight excess pressure up to 0.2 bar (20 kPa). If necessary, an addition of a ventilating flow SW_AIR (sweep air) may be added at the top, which ventilating flow ensures the removal of any gases. However, this is not to be normally necessary during established operation.

The impregnated chips are continuously fed out through output means, here in the form of an outlet 107, combined where relevant with a bottom scraper (not shown in the drawing), at the bottom of the impregnation vessel 101.

The following advantages are achieved with the invention:

• • +The chips sink in the impregnation fluid, and there is no risk that they float.
  • +The quantity of steam added is lower.
  • +The quantities of NCGs and malodorous gases expelled are minimal.

The invention is not limited to the embodiments shown. Several variants are possible within the framework of the claims.

Claims

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 tons of an impregnation fluid per ton 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 15 g/l, establishing a pressure within the top of the impregnation vessel that is essentially at atmospheric pressure ±0.5 bar and a temperature essentially corresponding to ambient temperature, 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 m3/ADT (Air-Dry-Ton) 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 above the fluid level without driving steam through the superior bed.

4. The method according to claim 1 wherein the method further comprises only adding steam when a temperature of the chips is below 15-25° C.

5. The method a cording to claim 3 wherein the method further comprises evaporating the chips up to the superior bed at a level that does not exceed half a 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 chip 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 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.

13. The method according to claim 1 wherein the method further comprises adding 5-10 m3/ADT (Air-Dry-Ton) of the impregnation fluid.