Andritz Inc.

Ahlstrom Machinery, Inc.

Andritz-ahlstrom Inc.

Andritz-ahlstrom Oy

Auvo K Kettunen

Kaj Henricson

C Bertil Stromberg

Hannu Olavi Ramark

Aki Hannu Vilpponen

Matti Lautala

J Robert Prough

Bruno S Marcoccia

Richard O Laakso

Jay J Miele

Jian E Jiang

The strength properties of chemical cellulose pulp (particularly kraft pulp) are improved by substituting a cold impregnation soak for conventional impregnation procedures. After steaming, wood chips are soaked in an alkaline liquid at a temperature of about 80-110&deg; C. (preferably 80-100&deg; C., or 90-105&deg; C.) for between one-half-72 hours (typically about 2-4 hours) at a pressure of about 0-15 bar (preferably about 1-5 bar), to dissolve at least about 8% of the wood (preferably about 10-20%) and at least about 15% of the lignin. The alkaline liquid used preferably contains sulfide (e.g. black liquor, green liquor, white liquor, or mixtures thereof), but almost any alkaline liquid having an alkali concentration of about 1.0 mole of NaOH/liter or less (typically about 0.75 m/l or less) is suitable. The wood chips are then raised to a cooking temperature of about 145-180&deg; C. and cooked to produce the cellulose chemical pulp. There may be an intermediate step, between soaking and raising the cooking temperature, of heating the wood chips to a temperature of about 110-150&deg; C. (preferably about 120-140&deg; C.) for about 10-90 minutes (preferably about 10-30 minutes). Alternatively or additionally the majority of the dissolved lignin (and/or other solids) may be removed before raising the wood chips to cooking temperature. The system for treating the wood chips need only include a low pressure soaking vessel (with an associated pump or other transfer device) in addition to conventional equipment.

Pretreatment of chips before cooking

By the utilization of a jet ejector (such as a thermocompresser) in a cellulose chemical pulp mill, it is possible to effectively increase the utilization of steam. The volume of steam from a flash tank which flashes black liquor from a pulp digester may be increased (e.g. at least about 10%), while the volume and temperature of the liquor discharged from the flash tank are decreased and its concentration increased, by operatively connecting the jet ejector to the steam discharge from a flash tank. The jet ejector is supplied with higher pressure steam from another source which can result in a low pressure or partial vacuum condition in the flash tank. The flash tank may be a single flash tank or one of a series of flash tanks, and an ejector can be associated with at least another flash tank in the series. The hot spent cooking liquor from the digester can be cooled in a heat exchanger (for example in indirect heat exchange relationship with a fresh cooking liquor) prior to introduction in to the flash tank or series of flash tanks. Alternatively a jet ejector may be used to increase the pressure of a low pressure steam flow in a pulp mill to make it suitable for alternative uses.

Flash tank steam economy improvement

In the feeding of a slurry of comminuted cellulosic fibrous material to a digester (continuous or batch) in the production of chemical pulp, one of the tanks used in the feed system (which preferably includes a high pressure feeder) may be eliminated without consequent loss of its function by providing a single tank with the combined functions of controlling the level of liquid in a slurrying conduit which supplies slurry to a slurry pump, and storing and substantially continuously supplying liquid to a make-up liquid pump connected to the digester. The single tank preferably surrounds the slurrying conduit and is substantially concentric, and in liquid communication, with it. A gap of 3-48 inches may be provided between the bottom of the conduit and a connection to the slurry pump. A screen or strainer may be provided in the gap, which is substantially surrounded by the tank. The return system from the low pressure outlet of the high pressure feeder to the slurrying device (like the conduit and tank surrounding it, or a conventional clip tube) may be devoid of one or more of an in-line drainer, level tank, centrifugal separator, and surge tank.

Chip feeding to a comminuted cellulosic fibrous material treatment vessel

A method of cooking pulp in an alkaline batch process (using one or more batch digesters) improves pulp bleachability. The wood material is supplied to the digester; the cellulosic material is pre-treated in the digester with a first liquor, the first liquor is displaced by a second liquor, the displaced first liquor is led to a further treatment, the cellulose material is treated with the second liquor, and the cooked pulp is removed from the digester. The second liquor is displaced as two consecutive parts, i.e. as strong black liquor and weak black liquor, and after cooling in a heat exchanger the strong black liquor thus obtained is fed into the digester as the first liquor in a subsequent batch (in the same, or a different, batch digester).

Batch cooking with black liquor pretreatment

The strength properties of chemical cellulose pulp (particularly kraft pulp) are improved by substituting a cold impregnation soak for conventional impregnation procedures. After steaming, wood chips are soaked in an alkaline liquid at a temperature of about 80-110&deg; C. (preferably 80-100&deg; C., or alternatively 90-105&deg; C.) for between one-half-72 hours (typically about 2-4 hours) at a pressure of about 0-15 bar (preferably about 1-5 bar), to dissolve at least about 8% of the wood (preferably about 10-20%) and at least about 15% of the lignin. The alkaline liquid used preferably contains sulfide (e.g. black liquor, green liquor, white liquor, or mixtures thereof), but almost any alkaline liquid having an alkali concentration of about 1.0 mole of NaOH/liter or less (typically about 0.75 m/l or less) is suitable. The wood chips are then raised to a cooking temperature of about 145-180&deg; C. and cooked to produce the cellulose chemical pulp. There may be an intermediate step, between soaking and raising the cooking temperature, of heating the wood chips to a temperature of about 110-150&deg; C. (preferably about 120-140&deg; C.) for about 10-90 minutes (preferably about 10-30 minutes). Alternatively or additionally the majority of the dissolved lignin (and/or other solids) may be removed before raising the wood chips to cooking temperature. The system for treating the wood chips need only include a low pressure soaking vessel (with an associated pump or other transfer device) in addition to conventional equipment.

Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking, preferably by adding the vast majority of cooking liquor (such as kraft white liquor) after the first removal of liquid from the digester so that the effective alkali concentration is high near the end of the cook. That is during at least the last minute (preferably at least the last 15 minutes and most preferably at least the last 30 minutes) before the cook is terminated the effective alkali concentration is between 15-50 g/l, more preferably between about 18-40 g/l, and most preferably between about 20-35 g/l. More than 50% (in fact most preferably more than 90%) of the total alkali added to the slurry in order to produce the chemical pulp is added after the first removal of liquid from the digester, and the alkali is added at two or more different locations so that the highest effective alkali concentration is within the range set forth above. The extracted liquors having a high effective alkali concentration are reused in the earlier stages of the cooking to avoid an increase in the addition and consumption of fresh alkali. Also a hydraulic or vapor phase continuous digester is provided with a quench circulation and alkali and heat are added to the quench circulation to control the final kappa number of the pulp, and so that the effective alkali concentration just before termination of the cooking zone is within the above ranges.

Cooking cellulose material using high alkali concentrations and/or high

Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking. After being impregnated with a first cooking liquor (e.g. white liquor) having low effective alkali, the first liquor is extracted from the pulp, and it is impregnated with a second cooking liquor having an effective alkali concentration of at least 25 g/l and cooked at cooking temperature (e.g. 140.degree.-190.degree. C.) to produce a spent second cooking liquor having a residual effective alkali concentration of at least about 15 g/l, which is then extracted from the pulp. The spent second liquor may be used to preheat incoming white liquor, and then flashed and used as the first liquor. The pH of the first liquor is typically less than about 13.0, and the residual pH of the spent second liquor is about 13.0 or more.

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Auvo K Kettunen