Processes and systems for the pulping of lignocellulosic materials

Abstract

A non-compression vessel, such as a digester, is employed for the chemical preconditioning of the chips followed by a fiberizing device to break the preconditioned chips down to fiber bundles, which are then washed before a high consistency chemical treatment. The digester may be one such as used in conventional chemical pulping of wood with or without screens for the extraction of chemical. If extracted this chemical could be recirculated to the digester with treatment in the circulation loop such as heating or the addition of dilution or other chemicals. This digester may be hydraulic or vapor phase (that is contain a vapor space within the digester), and operate in either a continuous or batch fashion. This digester allows for the discharge of material without the use of a screw mechanism. The digester treated material is then defiberized to convert the chips into course fiber bundles, which then is washed and dewatered. The washed and dewatered pulp is then treated with alkali peroxide chemicals to develop brightness and other pulp properties.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Accompanying FIGS. 1 through 3 illustrate three presently preferred embodiments in accordance with the present invention so as to apply the alkali peroxide chemicals, wherein,

FIG. 1 is a schematic illustration of a system in accordance with one embodiment of the present invention;

FIG. 2 is a schematic illustration of a system in accordance with another embodiment the present invention; and

FIG. 3 is a schematic illustration of a system in accordance with yet another embodiment of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

As shown in accompanying FIG. 1, chips are introduced to a chip washer, where dirt, tramp material, etc is removed from the chips in preparation for chemical addition in the digester. The process may include a chip bin before or after chip washer. The purpose of the digester is mainly to impregnate the chip with either stabilizers alone or stabilizers in combination with other chemicals traditionally used in pulp processing, such as alkali peroxide chemicals, alkaline chemicals (e.g., Na₂CO₃) and the like. The stabilizers include any organic chelating reagents (e.g. diethylene triamine pentaacetic acid (DTPAP), ethylene diamine tetraacetic acid (EDTA), nitriletriactic acid (NTA) and the like, or inorganic chemicals (e.g. silicate, MgSO₄ and the like) that reduces or stops transition metal reactivity toward peroxide chemicals. Preferably, the operation conditions for the digester are:

Pressure: 0-6 bar (preferably 3.5 bar)

Temperature: 30-120° C. (preferably 40-90° C.)

Time: 0.1-4 hours (preferably 1 hour)

Liquor to Wood ratio: 1.5:1 (preferably 2.5:1)

Liquor may be added to the digester to obtain the desired liquor to wood ratio. This liquor may be stabilizer dissolved in water with or without alkali and with or without peroxide. The fiberizer after the digester is designed to gently break the impregnated chips into fiber bundles so that the material can be easily washed with conventional washing equipment and be easily fed to a conventional high consistency refiner. Most or all the alkali peroxide chemicals are added either immediately before the refiner and/or a blow line immediately after the refiner. The chemical-mixed material (pulp) is then retained in a high consistency tower to allow the chemical reactions to complete. The treated pulp is then, with or without washing, refined using either a high, medium, or low consistency refiner, with at least one stage of refining, which may be one or more refiners run at the same consistency or a combination of refiners run at different consistencies. The refined pulp undergoes treatments as is conventional in mechanical pulping processes, such as latency removal, screening, cleaning, screen reject treatment, washing/dewatering, and the like.

The high consistency refiner performs both further defiberization and fibrillation as a conventional primary mechanical pulp system (e.g. either thermal mechanical pulping (TMP) or refiner mechanical pulping (RMP)), and mixing alkali peroxide chemicals either at the refiner or in the blow line after the refiner. The alkali chemicals include alkali and peroxide in various forms, and with or without peroxide stabilizers. Quantities of the chemicals used vary, and depend on the nature of the raw material and the product.

The high consistency tower is mainly to give the added chemicals enough reaction time to complete their reactions. The pulp consistency can be between about 12 to about 60% (e.g., between about 15 to about 45%, preferably between about 25 to about 30%), and the temperature can be between about 20 to about 100° C (e.g., between about 40 to about 100° C., preferably between about 70 to about 95° C.). The retention time may varies a few minutes to several hours (e.g., up to 7 hours), for example from about 15 minutes to about 4 hours, depending on the raw materials and the products.

After the high consistency tower, the pulp can either be washed with a pulp press first, or is refined using at least one of a high, medium, or low consistency refiner, with at least one stage of refining, which may be one or more refiners run at the same consistency or a combination of refiners run at different consistencies with or without a latency chest in between. The washed and dewatered (pressed) pulp can be refined using either high or low or medium consistency refiner.

After the main line refining, the pulp goes through normal pulping process stages, e.g. screening, cleaning (if necessary), thickening and washing, and final storage.

Another embodiment of the process system according to the present invention is depicted in FIG. 2. As can be seen, the process system depicted in FIG. 2 is similar to that depicted in FIG. 1, except that it has a medium consistency (8-15%) chemical treatment between fiberization refiner and high consistency refiner. The embodiment of FIG. 2 is mainly for the situation where a more aggressive chemical treatment than 1-stage high consistency treatment, is needed. The medium consistency tower utilizes recovered chemical residuals from the high consistency tower, together with some make-up alkali peroxide chemicals if necessary.

The process system depicted in FIG. 3 is also similar to the embodiment depicted in FIG. 1, except that a mixer, rather than a refiner, is used for adding the alkali peroxide chemicals for the high consistency chemical treatment. The mixer can be either of disc refiner type or other designs. The treated pulp was then, with or without washing, refined using either high, or medium, or low consistency refiner, with either one or multiple stages of refining which may be a combination of refiners run at different consistencies.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An alkaline peroxide mechanical pulping process comprising the steps of: (a) preconditioning a lignocellulosic chip material with chemical stabilizers in a non-compression vessel;(b) discharging the preconditioned lignocellulosic chip material to a fiberizer so as to mechanically break apart the preconditioned lignocellulosic material and obtain a fiberized lignocellulosic material;(c) washing the fiberized lignocellulosic material, and thereafter(c) treating the washed and fiberized lignocellulosic material with alkali peroxide chemicals for a time and under conditions sufficient to obtain a pulp of desired consistency therefrom.

2. The process of claim 1, wherein step (c) is practiced with a high consistency refiner.

3. The process of claim 2, wherein substantially all the alkali peroxide chemicals are added immediately before the fiberized lignocellulosic material is transferred to the refiner.

4. The process of claim 3, comprising washing the fiberized lignocellulosic material with a press.

5. The process of claim 1, wherein step (a) is practiced in a digester as a non-compression vessel.

6. The process of claim 1, wherein step (a) is practiced at a pressure of between 0 to 10 bar, a temperature of between 10 to 170° C., and for a time of between 0.1 to 7 hours.

7. The process of claim 6, further comprising adding liquor to the lignocellulosic chip material so as to achieve a liquor to wood ratio of between about 0.5:1 to about 5:1.

8. The process of claim 1, wherein the chemical stabilizers comprise organic chelating reagents.

9. The process of claim 8, wherein the organic chelating reagents comprise diethylene triamine pentaacetic acid, ethylene diamine tetraacetic acid, and nitriletriactic acid.

10. The process of claim 1, wherein the chemical stabilizers comprise inorganic chemicals.

11. The process of claim 10, wherein the inorganic chemicals comprise silicate and MgSO4.

12. The process of claim 1, further comprising discharging the pulp to a high consistency tower and retaining the pulp in the high consistency tower for a time and under temperature conditions sufficient to achieve a desired pulp consistency.

13. The process of claim 12, wherein the time and temperature conditions achieve a pulp consistency of between about 12 to about 60%.

14. The process of claim 13, wherein the pulp consistency is between about 15 to about 45%.

15. The process of claim 12, wherein the temperature condition within the high consistency tower is between about 20 to about 100° C. and wherein the pulp is retained within the high consistency tower for between about 15 minutes to about 4 hours.