RU2523973C1 - Method and system for pulp processing using cold caustic extraction with alkaline filtrate reuse - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for pulp processing using cold caustic extraction includes: delignifying organic materials in a digester and treating the resulting brown pulp to obtain semi-purified pulp for use in producing soluble pulp; extracting the semi-purified pulp with a caustic solution during a cold caustic extraction process; washing the purified pulp and collecting the obtained spent wash liquid by separating the hemicellulose-containing solution from the purified pulp; combining the spent wash liquid and the hemicellulose-containing solution to obtain an alkaline filtrate; concentrating the alkaline filtrate and using at least a portion of the concentrated alkaline filtrate in said digester to obtain a soluble pulp.

EFFECT: high content of alpha cellulose in soluble cellulose and high efficiency of using the filtrate.

50 cl, 5 dwg, 1 tbl, 4 ex

Description

FIELD OF THE INVENTION

The invention, in General, relates to the processing of pulp and, in particular, to an improved method and system for processing a stream leaving cold-alkaline extraction in a chemical method for producing kraft pulp

Prior art

Pulp from wood and plant materials has a large number of commercial applications. Although one of the most common uses is paper production, pulp can also be used to produce many other products, including rayon and other synthetic materials, as well as cellulose acetate and cellulose ethers, which are used, for example, in the manufacture of filter tows, fabrics, packaging film and explosives.

There are many chemical and mechanical methods for processing wood and plant materials for the production of pulp and paper. The main stages of processing include preparing raw materials (e.g., crushing and grinding), isolating wood fiber mechanically or chemically (e.g. grinding, refining, or cooking) to separate lignin and extractables from wood fiber pulp, remove dyes by bleaching, and form from the resulting recycled pulp of paper or other products. In addition, pulp and paper production at pulp and paper mills usually also has equipment for the production and recovery of chemicals, the collection and processing of by-products for energy production and the disposal and recycling of waste to minimize environmental impact.

"Pulping" generally refers to a process for achieving fiber release. Wood and other plant materials include cellulose, hemicellulose, lignin, and other minor components. Lignin is a network of polymers interspersed between individual fibers and functions as an intercellular adhesive to bond individual wood fibers together. During cellulose cooking, lignin macromolecules are fragmented, thereby releasing individual cellulosic fibers and dissolving impurities that can cause discoloration and subsequent decomposition of paper or other final product.

Sulphate pulping (kraft process) is a commonly used method of pulping. Sulphate pulp paper can be used, for example, for the production of bleached packaging board and lining board used in the packaging industry. In conventional sulphate pulping, wood is treated with an aqueous mixture of sodium hydroxide and sodium sulfide, known as white liquor. Processing destroys the bond between lignin and cellulose, and destroys most of the lignin and part of the hemicellulose macromolecules into fragments that are soluble in highly alkaline solutions. This process of removing lignin from the environment of cellulose is known as delignification. The soluble portion is then separated from the pulp.

Figure 1 is a flow diagram of a conventional sulphate pulping process 100. The process 100 involves feeding wood chips (or other organic cellulose-containing raw materials) 118 and alkaline solutions to a pressure vessel called an autoclave to carry out delignification, which is referred to as “cooking” stage 121. Wood chips are combined with white liquor 111, which can be produced in subsequent stages of the process or obtained from a separate source. Delignification can take several hours and the degree of delignification is expressed by the dimensionless "H factor", which is usually determined so that cooking for one hour at 100 ° C is equivalent to a factor of 1. Due to the high temperature, an increased pressure is often created in the reaction vessel the introduction of steam. At the end of the cooking step, the pressure in the reaction vessel is reduced to atmospheric, thereby removing steam and volatile products.

The white liquor used in cooking can be, for example, an alkaline solution containing sodium hydroxide (NaOH) and sodium sulfide (Na ₂ S). White liquor characterization is often expressed in units of effective alkali (EA) and sulfide. The effective alkali can be calculated as the weight of sodium hydroxide plus half the weight of sodium sulfide, and represents the equivalent weight of sodium hydroxide per liter of liquor, expressed in grams per liter. The effective alkali, in terms of sodium hydroxide, represents the equivalent weight of sodium hydroxide relative to dry wood, expressed as a percentage. Sulfide is the ratio of half the weight of sodium sulfide to the sum of the weight of sodium hydroxide and half the weight of sodium sulfide, expressed as a percentage.

After cooking, the brown solid pulp, also known as “unbleached pulp”, is removed from the autoclave used in cooking stage 121, and then sorted and washed in process 122. By sorting, the pulp is separated from the fire (bundles of wood fibers), knots (uncleared chips ), dirt and other residues. Materials separated from the pulp are sometimes referred to as "waste" and the pulp as a "product". Multistage cascade processes are often used to reduce the amount of cellulosic fibers in the waste stream while maintaining high purity in the product stream. Additional fiber extraction can be achieved in a refiner located downstream or by recycling bonfires and units in an autoclave.

Unbleached pulp can then be washed in several successive steps to separate spent cooking liquid and dissolved materials from cellulose fibers. The spent cooking liquid 112 from the autoclave used in the cooking step 121, and the liquid 113 collected during the washing and sorting process 122, are usually referred to as “black liquor” because of their color. Black liquor usually contains lignin fragments, carbohydrates from degraded hemicellulose and inorganic substances. Black liquor can be used in addition to white liquor in the cooking step, as shown, for example, in FIG. 1 with an arrow representing the black liquor 113 obtained in washing and sorting step 122 and transferred to cooking step 121. Black liquor 135 from a collection tank (not shown in FIG. 1) can also be fed into the autoclave as part of the cooking step 121, if an appropriate alkali concentration is to be achieved, or for other similar purposes.

The purified unbleached pulp 131 after washing and sorting 122 can then be mixed with white liquor 114 and fed to the reaction vessel to further separate dissolved materials such as hemicellulose and low molecular weight cellulose. An exemplary separation method is the so-called cold alkaline extraction ("CCE"), which is represented by the CCE reaction step 123 in FIG. 1. The temperature at which the extraction is carried out may vary, but is usually less than 60 ° C.

Then, the purified pulp mass 132, from the reactor used in the CCE reaction step 123, is separated from the spent cold alkaline solution and dissolved hemicellulose and washed several times and sorted in a second separation unit in the CCE washing step 124. The resulting refined unbleached pulp 133 with a relatively high alpha cellulose content, still containing a certain amount of lignin, is fed to a downstream bleaching unit for further delignification. In some methods of producing pulp, bleaching is performed prior to step 123 of the CCE reaction and step 124 of washing the CCE.

For many applications, such as the manufacture of synthetic materials or pharmaceutical products, pulp pulp of very high purity or quality is required. The quality of the pulp can be estimated by several parameters. For example, the percentage of alpha cellulose reflects the relative purity of the processed pulp. The degree of delignification and degradation of cellulose is measured by the Kappa number ("KN") and pulp viscosity, respectively. A higher pulp viscosity indicates a longer pulp chain and less degradation. The solubility of the pulp in 18% of the mass. aqueous sodium hydroxide solution ("S18") gives an estimate of the amount of residual hemicellulose. The solubility of the pulp in 10 wt.%, Aqueous sodium hydroxide solution ("S10") determines the total amount of soluble substances in alkaline solutions, which include the sum of hemicellulose and cellulose degradation products. Finally, the difference between S10 and S18 determines the amount of pulp destroyed.

In a conventional method, the filtrate 116, also referred to as the CCE alkaline filtrate, from the washing step 124 and the CCE separation step includes both spent cold alkaline solution and spent washing liquid from the separation and washing step 124. This filtrate 116 often contains a substantial amount of high molecular weight hemicellulose. When a high hemicellulose filtrate is used as part of the cooking liquid in the autoclave of the cooking step 121, hemicellulose can be separated from the solution and deposited on cellulose fibers. This may impede the production of high quality pulp. On the other hand, in certain applications - such as high-quality yarn or synthetic fabrics, materials for liquid crystal displays, products made from acetate derivatives, products from viscose (such as tire cords and special fibers), filter tows used in cigarettes, and some food and pharmaceutical applications — pulp with a minimum amount of re-precipitated hemicelluloses and a certain alpha-cellulose content is required.

A portion of the alkaline filtrate 116 CCE can be reused at the cooking stage 121, the remainder can be sent to the regeneration zone 134 to prevent the risk of re-precipitation of hemicellulose at the cooking stage 121. In the regeneration zone 134, the discharged alkaline filtrate 116 CCE can be combined with an excess of black liquor, concentrated and burned in a soda recovery boiler to remove organic substances and recover inorganic salts, or it can be directed to another cooking line, or in both implementations. A new alkali source may then be needed to replace the CCE filtrate and black liquor fed to the regeneration zone 134 to maintain an adequate alkaline balance in the cooking stage 121. The process of regeneration and the provision of a new source of alkali leads to an increase in production costs.

There is a need for a method and system for processing pulp, which allows to obtain soluble cellulose with a very high content of alpha-cellulose. In addition, there is a need for a method and system for processing pulp that provides increased efficiency and cost-effective use of CCE filtrate while minimizing the deposition of hemicellulose in the cooking process.

Disclosure of invention

In one aspect, an improved method and system for the production of pulp includes, among other things, washing the purified pulp obtained by the cold alkali extraction process, collecting the alkaline filtrate resulting from this, concentrating the alkaline filtrate, for example by evaporation, and using at least a portion of the concentrated alkaline filtrate in the upstream cooking process.

According to one or more implementations, the method and system for the production of pulp using cold-alkaline extraction in combination with sulphate pulping includes autoclaving the delignification steps of cellulose-containing organic materials, treating the obtained unbleached pulp to obtain semi-refined pulp, and extracting the semi-refined pulp with an alkaline solution purified pulp and a solution containing hemicellulose, separating a solution containing hemicellulose, from the purified pulp, washing the purified pulp and collecting the alkaline filtrate obtained in this way, concentrating the alkaline filtrate and using at least a portion of the concentrated alkaline filtrate in the autoclave. Concentrated alkaline filtrate can gradually replace other cooking liquids that were originally used to start the cooking process, which leads to increased efficiency.

In some implementations, the alkaline filtrate is concentrated to obtain a solution containing, for example, 90 or more grams per liter of effective alkali in the form of sodium hydroxide. By using concentrated alkaline filtrate as part of the cooking liquor, the purity of unbleached pulp and the resulting purified pulp can be improved.

Further implementations, alternatives and options are also presented in the description or in the accompanying figures.

Brief Description of the Drawings

Figure 1 is a general flow diagram of a conventional sulphate cooking process with preliminary hydrolysis of the prior art used for the production of pulp.

Figure 2 is a flow diagram of a process for the production of pulp in accordance with one of the implementations, as described in the application.

FIG. 3 is a conceptual diagram of a system and a corresponding evaporation process after cold alkali extraction in accordance with the general principles presented in FIG. 2.

Figure 4 is a diagram of a conventional system and evaporation process that can be used, among other things, together with cold alkaline extraction.

FIG. 5 is a diagram of a system and a corresponding process for evaporation of a cold alkaline extraction filtrate in accordance with the general principles presented in FIGS. 2 and 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to one or more implementations, the pulp processing method and system used in a sulfate cooking (kraft process) comprises combining a first alkaline solution, such as white liquor, with some wood or other organic material containing cellulose in an appropriate tank or reaction vessel a vessel (autoclave) for cooking at a suitable temperature, for example from 130 to 180 ° C, to obtain unbleached pulp. Sorting and washing of unbleached pulp results in semi-refined pulp and by-products (such as black liquor) that are returned to the autoclave. The semi-purified pulp can be extracted with another alkaline solution (which can also be white liquor) at a suitable temperature, for example, below 60 ° C, to obtain a purified pulp. The solution containing hemicellulose can be separated from the purified pulp by additional washing, resulting in another alkaline solution in the form of an alkaline filtrate, which can be separately collected and stored. This CCE alkaline filtrate can be concentrated, for example, by evaporation or otherwise, and used alone or in combination with the first alkaline solution in an autoclave to process organic materials and resume the cycle.

According to a feature of one or more embodiments, wood chips or other cellulose-containing organic materials interact with an alkaline solution in a reaction vessel. At the end of the reaction, the reaction mixture contains released cellulose fibers. These fibers are further extracted with a second alkaline solution to dissolve hemicellulose. The spent alkaline solution together with the dissolved hemicellulose is separated from the extracted pulp and then the pulp is further washed to remove residual alkaline solution and hemicellulose. Wash liquids and spent alkaline solution containing hemicellulose are combined and concentrated to form concentrated CCE filtrate. Concentrated CCE filtrate can be used alone or in combination with another alkaline solution for treating wood in a reaction vessel.

All of the above steps can be performed on conventional equipment. After the steps described above, in accordance with the description, a concentrated CCE filtrate can be obtained with a concentration of effective alkali comparable to the concentration of effective alkali in white liquor commonly used for cooking.

The method according to one implementation is presented in figure 2. Method 200 begins with step 221, in which, like conventional sulphate pulping, wood chips or other cellulose-containing organic materials 218 are fed to an autoclave capable of withstanding high pressure. The autoclave may be of any suitable volume, such as, for example, about 360 cubic meters. In a typical industrial plant, several autoclaves can operate in parallel with various autoclaves operating at different stages of the pulp production process.

The specific choice of the type of wood or other plant or organic material may depend on the desired end products. For example, softwood, such as pine, spruce, and Canadian spruce, can be used for some derivative processes to produce high viscosity products like cellulose ethers (which can be used, for example, as additives in food, paint, drilling fluids, or sludge, paper, cosmetics, pharmaceuticals, adhesives, printing, in agriculture, ceramics, textiles, detergents and building materials). Hardwood, such as eucalyptus and acacia, may be preferred in applications that do not require very high viscosity pulp.

In one embodiment, the autoclave is heated during the cooking step 221 to a first predetermined temperature with steam or other appropriate means. This predetermined temperature may be from 110 to 130 ° C and, in particular, for example, may be 120 ° C. The heating in this separate example is performed for a period of time from 15 to 60 minutes (for example, 30 minutes), although other heating times may be used depending on the specific equipment and the nature of the heated organic materials.

Then, the autoclave is preferably further heated by steam or other means to a second temperature higher than the first predetermined temperature to carry out the preliminary hydrolysis step. This second pre-hydrolysis temperature is preferably about 165 ° C., although again, the exact temperature may depend on many variables, including equipment and organic materials. Heating for preliminary hydrolysis can be carried out for 30 to 120 minutes (for example, 60 minutes), although again the time can be changed if necessary. As soon as the temperature of the preliminary hydrolysis is reached, the autoclave is maintained at this temperature for a suitable period of time, for example, from 35 to 45 minutes or any other time sufficient to complete the preliminary hydrolysis.

In a preferred embodiment, the neutralization solution 210 is added to the autoclave as part of the cooking step 221. The neutralization solution 210 may consist of freshly prepared white liquor with the addition of black liquor, or it may consist of CCE filtrate with the addition of black liquor. White liquor may be, for example, a mixture of sodium hydroxide and sodium sulfide. In a preferred embodiment, white liquor contains from 85 to 150 grams per liter of effective alkali in terms of sodium hydroxide (NaOH), more preferably from 95 to 125 grams of NaOH per liter, and most preferably from 100 to 110 grams per liter of effective alkali in terms of hydroxide sodium. Sulfide white liquor can be 10-40%, preferably 15-35%, and most preferably 20-30%.

The concentration of effective NaOH in black liquor can range from 10 to 50 grams per liter, although it can vary in certain processes. In one embodiment, neutralization solution 210 210 contains both white liquor and black liquor, with an effective alkali concentration of from 85 to 150 grams of sodium hydroxide per liter for white liquor and an effective alkali concentration of from 20 to 50 grams of sodium hydroxide per liter for black liquor. In a preferred embodiment, the neutralization solution 210, including both white liquor and black liquor, with an effective alkali concentration of 95 to 125 grams per liter and 30 to 35 grams per liter, respectively, and more preferably an effective alkali concentration of 100 to 110 grams per liter and from 38 to 45 grams per liter, respectively. The concentration of effective alkali in the neutralization solution 210 can be from 38 to 48 grams of NaOH per liter of solution for combined liquors.

The neutralization solution 210 may be added to the autoclave in one portion or else may be added to the autoclave in several parts. In one embodiment, the neutralization solution 210, including both white liquor and black liquor, is added in two parts, first, white liquor is introduced into the autoclave, followed by the addition of black liquor. In one embodiment, the neutralization solution 210 is added at a temperature of from 130 to 160 ° C, and more preferably from 140 to 150 ° C. Addition can be carried out within 15-60 minutes, preferably within 30 minutes. In a preferred embodiment, the neutralization solution 210 is added in two parts, each for 15 minutes, at a temperature of 140 to 150 ° C.

Then, the first alkaline solution 211 can replace the neutralization solution 210 and is used for cooking wood in an autoclave. The first alkaline solution 211 may have the same composition as the neutralization solution 210, or may have a different composition. The range and preferred range of sodium hydroxide and sodium sulfide in the first alkaline solution 211 are the same as in the neutralization solution 210, and they are well known to those skilled in the art.

The autoclave can be heated to a cooking temperature by steam or in another way. The cooking temperature may be in the range of 140 to 180 ° C, and preferably in the range of 145 to 160 ° C. Heating may be carried out for 10 to 30 minutes or another suitable period of time. The autoclave is kept at the cooking temperature for a suitable period for the cooking process, for example, from 15 to 120 minutes. The temperature range and cooking time are selected for a given H factor, which is preferably in the range from 130 to 250.

Preferred methods of neutralization and cooking are described in simultaneously pending application US 12 / 789,307 (file number of patent attorney No. 161551-0003), filed simultaneously with the present and entitled "Method and system for the production of soluble pulp with a high content of alpha-cellulose", assigned the assignee of the present invention, and thereby is incorporated into the application by reference, as if it were fully set forth in the description.

As a result of cooking step 221, unbleached pulp 212 is obtained. Unbleached pulp 212 is washed and sorted in a process 222 similar to a conventional kraft process, whereby unbleached pulp 212 is sorted using various types of sieves or sieves or centrifugally cleaned. Unbleached pulp 212 is then washed in a washer during sorting and washing 222. The washer can be of any commercial type, including horizontal conveyor washers, rotary drum washers, vacuum filters, press filters, filters with a sealing wall, sprayers at atmospheric and high pressure. The washing installation may use a counterflow between stages so that the pulp moves in the opposite direction with respect to the movement of the wash water. In one embodiment, pressurized water is used to wash unbleached pulp 212. In another embodiment, a dilute alkaline solution is used to wash unbleached pulp 212. The concentration of effective alkali in the dilute alkaline solution may be, for example, less than 5 grams of NaOH per liter, more preferably less than 1 gram of NaOH per liter. The spent washing solution is collected and used as black liquor 213. In one embodiment, black liquor 213 is used as part of the cooking liquid or other alkaline solution 211 supplied to the autoclave in the cooking step 221.

The semifinished pulp from the sorting and washing process 222 is then pumped as a suspension into a reactor, which is used in the cold alkaline extraction step (“CCE”) 223, also similar to the conventional method, in which the semifinished pulp is mixed with a second alkaline solution 214 (which may be the same or different from the first alkaline solution 211) for further separation of hemicellulose from the desired cellulose fibers. Cold alkali extraction is a process known in the art. Examples of cold alkali treatment methods and systems are described in detail, for example, in AN et al., US 2004/0020854, and Svenson et al., US 2005/0203291, both of which are incorporated by reference, as if they were fully set forth in the description.

The hemicellulose extraction during the 223 CCE extraction is carried out at a suitable temperature, usually from 15 to 50 ° C, preferably about 30 ° C. The pH value of the pulp suspension is usually higher than 13, and the effective alkali content is from 60 to 90 grams of NaOH per liter. The pulp is immersed in cold alkaline solution 214 for a sufficient amount of time to achieve the desired degree of diffusion of hemicellulose into the solution. Typical aging times for extraction at 30 ° C and pH 13 are 30 minutes. Cold-alkaline extraction can mainly result in a purified pulp with an alpha-cellulose content of 92-96 percent, although it has historically been quite difficult to achieve purity at the upper end of this range or beyond, in particular while maintaining other required pulp characteristics (such as level viscosity). In addition, it was difficult to achieve high purity while maintaining high process efficiency.

The alkaline solution 214 used for mixing and extraction in the CCE extraction process 223 may include freshly prepared sodium hydroxide solution, recycle from the subsequent process steps, or by-products of a pulp and paper mill, for example semi-alkaline white liquor, oxidized white liquor, and the like. Other basic solutions, such as ammonium hydroxide and potassium hydroxide, may also be used.

The alkaline solution 214 used in the CCE extraction process 223 may contain a suitable concentration of hydroxide, for example, the alkaline solution 214 may contain 3-50% by weight. the concentration of hydroxide, and more preferably 6-18% of the mass. hydroxide concentration. The extraction can be performed with any suitable pulp density, for example about 2-50% by weight, preferably about 5-10% by weight. In this context, the term "density" refers to the concentration of cellulose fiber in the extraction mixture.

After the required residence time, the pulp is separated from the spent cold alkaline solution in a subsequent washing process 224. The spent cold solution includes extracted hemicellulose. The pulp is washed in a CCE washer. Examples of washers include horizontal conveyor washers, rotary drum washers, vacuum filters, press filters, septum filters, atmospheric and high pressure sprayers. The washing liquid may contain, for example, pure water or a dilute alkaline solution with a concentration of effective alkali, for example, below 1 g NaOH per liter. The spent washing liquid is collected in the usual way and it can be combined with the spent cold alkaline solution to form another alkaline solution 216, which, on the one hand, includes the alkaline filtrate obtained from the washing process 224. The extracted and washed pulp 233 is at the same time transported to the next stage for bleaching.

The third alkaline solution 216 is preferably sent to concentration 225, and it can, for example, be fed to the evaporation system for concentration. A conventional evaporator system may include several units or stages of the evaporator installed in series. The fluid moves through each stage of the evaporator and becomes more concentrated at the exit of the stage. Vacuum may be used to facilitate evaporation and concentration of solutions.

In the concentration process 225, weak black liquor 243 can also be concentrated to strong black liquor 244, for example, by evaporation using one or more stages of the evaporator installed in series, gradually increasing the concentration of weak black liquor 243 during the process. Strong black liquor 244 can be stored in the storage tank and used in the regeneration zone (soda recovery boiler) or for other purposes, thereby increasing the efficiency of the reuse or recycling of by-products of production.

The number of stages used during evaporation depends in part on the required concentration level, plant capacity and other factors. In one embodiment, the evaporation equipment of concentration step 225 comprises six stages capable of processing, for example, 740 tons of liquor per hour. The steps may, but need not be, of the same type as that used to concentrate the black liquor in the cooking step 221. It is common, for example, to use a series of steps to concentrate the weak black liquor remaining in the cooking stage and stored in the storage tank, in which it can either be returned to the cycle for use in the cooking process or sent to other processes for various purposes. As a rule, an excess of black liquor is obtained, which is burned in an incinerator for the purpose of generating electricity.

In a preferred embodiment (as shown in FIG. 3), the concentration of the alkaline extract solution 316 from the CCE washing step 224 takes place in two of six stages (in this example, the fifth stage 327 and the sixth stage 328) under reduced pressure to obtain a concentrated solution 330, those. concentrated alkaline filtrate CCE. The concentration of weak black liquor from the cooking stage 221 to concentrated black liquor occurs in four of six stages at a higher pressure. In this example, weak black liquor 313 is introduced into one stage (in this example, the fourth stage 326), and after preconcentration it is pumped to further concentrate on steps 329 located downstream. Concentration of the alkaline extract solution 316 of CCE washing stage 224, which may be a combination of spent washing liquid 314 and spent cold alkaline solution 315 can be carried out in the fifth and sixth steps 327 and 328 with the appropriate pressure and sufficient duration NOSTA to achieve the desired concentration, which in one example is about 85-110 grams of NaOH per liter, and more preferably 95-105 grams per liter of NaOH. In one embodiment, the alkaline extract solution 316 remains in the fifth step 327 at a negative pressure of about −0.84 bar (instrument) and in the sixth step 328 at a negative pressure of about -0.50 bar (instrument) to produce a concentrated solution of 330 s effective alkali concentration, for example, about 95-105 grams of NaOH per liter.

Advantageously, the technological installation can be configured to carry out the method according to the invention without significant additional costs for the necessary equipment. In the case where the installation uses, for example, six stages of concentration of weak black liquor remaining in the cooking stage, two of the stages can be transferred for use to concentrate the alkaline filtrate obtained in the CCE washing process. The reduced number of stages provided for concentrating black liquor is not significant, because while the efficiency of the evaporation of black liquor is reduced by about 20-30%, the quality of black liquor (final concentration of solids) can be preserved, which allows you to burn black lye obtained from four steps in a soda recovery boiler without significant consequences. However, the use of two degrees to concentrate the alkaline filtrate and return to the cycle, in accordance with the method of the invention described in the application, can have a significant impact on the efficiency of the installation. Since the same number of stages can be used for two different processes, the installation can be designed so that the operator can choose between using the usual process of evaporation of weak black liquor at all stages or, otherwise, can select some stages to concentrate the alkaline filtrate without noticeable negative consequences, but seeking improvement in terms of effectiveness.

Returning to FIG. 2, the concentrated alkaline filtrate solution 217 can be reused, in whole or in part, either as a neutralization solution 210 and / or as part of cooking liquor 211. In one embodiment, the neutralization solution 210 consists entirely of a concentrated alkaline filtrate solution 217. In another embodiment, the neutralization solution 210 contains both a concentrated alkaline filtrate solution 217 and white liquor that can be pre-added to the autoclave and also, if necessary, used to enrich the concentrated alkaline filtrate solution 217. In the third embodiment, the concentrated alkaline filtrate solution 217 is used as cooking liquor 211. In the fourth embodiment, the concentrated alkaline filtrate solution 117 is combined with white liquor for use as cooking liquor 211.

The concentrated alkaline filtrate solution 217, which is not reused in the cooking step 221, can be used for other purposes. For example, it can, if necessary, be directed to other purposes, for example, for use on an adjacent production line (such as white liquor), as shown by arrow 251 in the example of FIG. 2. At the same time, the concentrated alkaline filtrate solution 217 may also make it possible to use a higher concentration of liquor in the cooking step 221, thereby preventing re-deposition of hemicellulose on the fibers.

4 and 5 illustrate and compare a conventional system for the evaporation process associated with cold alkaline extraction, with one possible implementation, in accordance with the disclosure in the description. FIG. 4 is a schematic diagram of a conventional system 400 that depicts a evaporation process that can be used, inter alia, for cold alkali extraction. As shown in FIG. 4, system 400 includes a series of steps, 461A-D and 462-466. Weak black liquor 413 from the cooking process is fed to one of the steps, in this case the fourth step 464, where the evaporation process begins. Pipes 441 and 442 respectively connect the fourth stage 464 to the fifth stage 465 and the fifth stage 465 to the sixth stage 466. After processing at the sixth stage 466, the semi-concentrated black liquor is fed to the intermediate heat exchangers 450 and 452. From the heat exchanger 452, the semi-concentrated black liquor is fed to the third stage 463, the product of which is fed to another intermediate heat exchanger 454.

From the heat exchanger 454, the semi-concentrated black liquor is then fed to the second stage 462 (one casing is divided into two liquor circulating units “A” and “B”). After evaporation in the second stage 462, one part of the black liquor is pumped directly to the first stage (concentrator), and the other is subjected to flash evaporation in an evaporator 459 at atmospheric pressure and 432 is pumped for ash processing. The first stage may physically consist of four evaporators 461A-D. Evaporators can be evaporators with a falling film of tubular and surface type. All four evaporators 461A-D can be put into operation at the same time, which can allow the production of higher concentration black liquor. The liquor containing ash is pumped from the ash mixer tank to the 461D evaporator. After evaporation in the evaporator 461D, the concentrated heavy black liquor is instantly evaporated in an instant evaporator 459 and stored in a pressurized tank for heavy liquor (not shown in FIG. 4).

The products of the evaporation system 400 are heavy (strong) black liquor 430, as well as condensate 431, which is sent to the storage of liquor for washing. Strong black liquor 430 can be used for the purposes described above in the application. In the condensate tank 440A, steam condensate from the second, third and fourth stages 462, 463 and 464 are combined to form pure condensate (“A condensate”) and can be instantly vaporized in several stages, upon reaching a pressure equal to the vapor pressure at the inlet of the sixth stage 466. A-condensate is collected in a clean condensate tank (tank A of the condensate tank 440) and can be used in other places, for example, on a fiber production line.

The condensate from the clean side of the fourth and fifth stages 464 and 465 forms an intermediate condensate (“B-condensate”), the pressure of which is depressurized or reduced in stages until it reaches the same pressure as the pressure at the inlet of the sixth stage 466. The instantaneous vaporization condensate is combined with treated or untreated condensate from other parts of the evaporation system, for example, from the clean side of the sixth stage 466, the primary section of the separated surface of the condenser 470 and / or the processed condensate of the distillation column. This combined condensate can usually contain more impurities than A-condensate. B-condensate is collected in an intermediate condensate tank (tank B of the condensate tank 440) and can be used in other parts of the pulp production, for example in a causticization unit.

The dirty condensate (“C-condensate”), which usually contains more impurities than the A-condensate or B-condensate, can be collected from the dirty part of the fifth and sixth steps 465 and 466, the secondary section of the separated condenser surface, and the vacuum system. C-condensate is stored in a dirty condensate tank (tank C of the condensate tank 440).

FIG. 5 is a diagram of a system 500 reflecting a process for evaporating a cold alkaline extraction filtrate in accordance with the general principles of FIGS. 2 and 3. In this example, the system 500 uses the same equipment design and the same number of stages as the system 400 in FIG. .4, although this should not be mandatory in other implementations. Dashed lines in FIG. 5 show additional connections (including pipes and valves) that can be added to the equipment of FIG. 4 to achieve additional functionality for concentrating CCE filtrate. 5, system 500 also has several stages 561A-D and 562-566. Steps 561A-561D, 562, and 563 serve the same general purpose as the corresponding steps 461A-D, 462, and 463 in FIG. 4. However, in the system 500 of FIG. 5, after initially concentrating the weak black liquor 513 in the fourth stage 564, it is supplied via bypass line 537 (adjusted by added valve 536) to the heat exchanger 550 (which otherwise would be similar to the heat exchanger 450 of FIG. 4) . Thus, the concentration of weak black liquor bypasses steps 565, 566.

Unlike the 400 system of FIG. 4, in the 500 system of FIG. 5, the cold alkaline extraction (CCE) filtrate 516 from the CCE washing stage is supplied by a connecting pipe 541 to the fifth stage 565, after which it passes the first part of the concentration process. A new valve 538 was added to FIG. 4 to allow separation of the fourth stage 564 from the CCE of the filtrate 516. An optional bypass connection 539 may be added to connect the CCE filtrate 516 to the sixth stage 566 to allow the supply of CCE filtrate directly to the sixth stage 566 if, for example, less concentration is required. Otherwise, after evaporation at the fifth stage 565, a semi-concentrated CCE filtrate is fed to the sixth stage 566 via a connecting pipe 542, after which it is further concentrated by evaporation to the desired degree.

Concentrated CCE filtrate 560 can be sent via line 591 to tank C in condensate tank 540 or via line 592 to tank B of condensate tank 540. In connection with the above stages of the Kraft process, concentrated CCE filtrate 560 can be mixed with white liquor, black liquor or other solutions as part of the cooking step. If necessary, the semi-concentrated CCE filtrate can be sent to the heat exchanger 550 from the fifth stage 565 via another added connecting pipe 535, adjusted by valve 534. The connecting pipe 535 also provides the possibility of using five stages for concentrating weak black liquor and only one stage (sixth stage) for concentration CCE filtrate. This configuration provides, among other things, significant flexibility in terms of various mixtures and the concentration of cooking and washing solutions. In this embodiment, where the CCE filtrate is concentrated in the fifth and sixth stages 565 and 566, the condensate flows can be changed by switching valves: for example, the dirty side of the fourth stage 564 may be part of the dirty condensate (C-condensate); the condensate on the dirty side of the sixth stage 466 may be part of an intermediate condensate (B-condensate); and condensate from the primary section of the separated surface of the capacitor may be part of pure condensate (A-condensate).

Examples

Methods in accordance with implementations of the present invention are presented in the following examples. The analytical results described in the examples are obtained using the following methods.

The techniques used to measure S10 and S18 cellulose solubility at 25 ° C are based on the TAPPI T 235 cm-00 standard, incorporated by reference as if fully presented in the application. The pulp is extracted with 10% and 18% sodium hydroxide (NaOH) solution, respectively. The content of dissolved carbohydrates is determined by oxidation with potassium dichromate. Low molecular weight carbohydrates such as hemicelluloses and cellulose degradation products can be extracted from cellulose with sodium hydroxide solutions. The solubility of cellulose in alkali thus provides information on cellulose degradation and the loss or retention of hemicelluloses during cooking and bleaching. In the usual procedure for measuring the solubility of S10, 10 g of an absolutely dry pulp sample was placed in a beaker and 75 ml of 10% by weight was added. NaOH solution to the pulp. The mixture is stirred with a mixer for a time sufficient to achieve complete dispersion of the pulp. One example of a mixer may include a variable speed motor and a stainless steel mixer with a housing. The engine speed and the angle of the blades are controlled so that air is drawn into the pulp suspension with stirring. After complete dispersion of the pulp, another 25 ml of 10% NaOH is added to the mixture to ensure that all cellulose fibers are coated with an alkali solution. The beaker containing the mixture was kept in a water bath at a temperature of 25 ± 0.2 ° C for 60 minutes from the moment of the first addition of NaOH. After that, about 50 ml of the filtrate is collected in a clean and dry flask after filtration. An aliquot of 10.0 ml of the filtrate is mixed with 10.0 ml of a 0.5 N solution of potassium dichromate in a 250 ml flask. To this, 30 ml of concentrated sulfuric acid is added with stirring, while the solution is heated by chemical reactions. The solution is stirred for 15 minutes, keeping it hot. Then, 50 ml of water was added to the mixture, and the mixture was cooled to room temperature. Two to four drops of ferroin are added as an indicator to the mixture, and the mixture is titrated with 0.1 N solution of iron-ammonium alum (Mohr's salt). Titration is repeated using 10 ml of a 10% NaOH solution. S10 Solubility is calculated by the following formula:

S,% = [(V ₂ -V ₁ ) * N * 6.85 * 10] / (A * W),

where V1 is the volume of the solution of iron-ammonium alum used for titration of the filtrate, and the unit of measure is a milliliter, V2, also in milliliters, is the volume of the solution of iron-ammonium alum used for titration of a pure solution of 10% NaOH, N is the normality of the solution of iron-ammonium alum; A, in milliliters, is the volume of pulp filtrate used in the oxidation; and W is the weight of an absolutely dry pulp sample in grams.

The same procedure is used to determine S18 solubility, except that the 18% NaOH solution replaces the 10% NaOH solution used above.

The viscosity of the pulp in a solution of the copper ethylene diamine complex (CED) is determined using a procedure based on the SCAN standard CM 15-99, presented in the description by reference, as if it were fully disclosed in the application. The method determines the value of the intrinsic viscosity of the pulp in a dilute CED solution. In a conventional manner, a pulp sample is dissolved in a CED solution. The amount of pulp is selected taking into account the expected value of the characteristic viscosity. A weighted sample of pulp is placed in polyethylene containers (about 52 ml in volume), from which residual air is removed by compressing the container. 5-10 pieces of copper wire and 25 ml of deionized water are added to the pulp and the mixture is shaken with an appropriate shaking device until the pulp is completely disintegrated. A typical disintegration time interval is from 10 to 30 minutes. Another 25.0 ml of CED solution is added to the mixture. After squeezing out the residual air, the container is tightly closed and shaken again for about 30 minutes or until the pulp sample has completely dissolved. The temperature of the analyzed solution and viscometer was adjusted to 25 ° C. Part of the analyzed solution is drawn into the viscometer by suction. The expiration time, that is, the time required to reduce the meniscus from the upper to the lower mark of the viscometer, is determined. Relative viscosity is calculated using the following equation:

$$\left({\eta }_{ret}\right)=\frac{F}{Tced}\times T$$

where F is the calibration coefficient of the viscometer; T _ced , in seconds, is the expiration time of the 50% CED solution, T is the expiration time of the analyzed solution also in seconds. The equivalent value (η * s) can be found in the table attached to the SCAN standard, where η is the characteristic viscosity of the pulp in units of ml / g, and c is the concentration of the analyzed solution, calculated as the mass of dry pulp divided by the volume of the analyzed solution which is 50 ml in this example.

The kappa number (KN) is determined using a method similar to the method of the TAPPI standard T 236 om-99. KN corresponds to the volume (in ml) of a 0.1 N potassium permanganate solution used to oxidize one gram of dry pulp. Typically, a pulp sample is disintegrated or dissolved in about 300 ml of distilled water. A disintegrated or dissolved pulp sample is transferred to a beaker and a sufficient amount of water is added to the pulp mixture, bringing the total volume of the mixture to 795 ml. 100 ml of 0.1 N potassium permanganate solution and 100 ml of 4N sulfuric acid are mixed in a separate glass and the mixture is quickly brought to 25 ° C. An acidified potassium permanganate solution is immediately added to the analyzed pulp. After addition, the total volume of the mixture is about 1000 ± 5 ml. The mixture was allowed to react for ten minutes, after which 20 ml of 1 N potassium iodide solution was added to stop the reaction. The free iodine content in the mixture is determined immediately after titration of the pulp mixture with a 0.2 N sodium thiosulfate solution. The titration endpoint is determined with starch as an indicator added at the end of the reaction. Titration is carried out without removing cellulose fibers. Another titration is carried out with a blank solution without pulp. KN is calculated using the following formula:

KN = (p * f) / w,

where p is the amount of 0.1 N potassium permanganate in milliliters per sample, f is the conversion factor for the volume of 50% permanganate and depends on the "p" that can be found in the Tappi standard; w is the mass of the sample is absolutely dry pulp; and "p" is defined as follows:

p = [(b-a) * N] 0.1,

where b is the amount of thiosulfate, in milliliters, used to titrate the blank solution; and is the amount of thiosulfate used to titrate the pulp sample; and N is the normality of thiosulfate.

Example 1

Concentration of CCE filtrate

In accordance with the first example, a stream of a very dilute alkaline solution with an effective alkali concentration of 5.6 grams NaOH per liter is introduced into the fifth stage 327, as shown in FIG. 3, to start the installation and to observe its behavior at different levels of alkali concentration. Water is removed from the solution under reduced pressure of -0.73 bar at a temperature of 51.5-56.8 ° C. After 4 hours and 30 minutes, an alkaline solution with an effective alkali concentration of about 50 g NaOH per liter, similar to fresh CCE filtrate, is fed into the fifth stage, reaching about 50 grams of NaOH per liter at the outlet of the sixth stage inlet. The table shows the values of flow rate, temperature, concentration of effective alkali and vacuum level as a function of time.

Table I Time (min) Feed rate (m ³ / h) Temperature (° C) Effective alkali (gNaOH / L) Pressure (bar) Stage 5 Entrance Stage 6 output 0 350 51.5 5,6 -0.73 65 370 54.7 14.1 -0.73 105 370 56.8 36.6 -0.73 210 370 55.9 27.4 58.1 -0.73 270 400 53.6 49.8 106.9 -0.73 290 450 54.1 69.6 104.9 -0.73

Example 2

Normal craft process

According to the second example, an experimental craft process is carried out in a laboratory autoclave (with a volume of about 20 liters) to simulate an industrial process. The 20-liter laboratory autoclave is preheated with steam to 120 ° C for 30 minutes. An appropriate amount (e.g. 4.7 kg dry matter) of eucalyptus chips is added to the autoclave. The autoclave is heated to 165 ° C for 60 minutes and kept at 165 ° C for another 40 minutes to complete the preliminary hydrolysis step. For a typical Kraft process (without using CCE filtrates), 4.51 liters of the first white liquor ("WL1") with an effective alkali concentration of 124.7 g NaOH per liter is added to the autoclave for fifteen minutes at a temperature of 152 ° C. A typical alkali charge to neutralize is about 12% effective alkali (EA), calculated as NaOH based on the weight of dry wood chips. Then, the autoclave was filled with 10.8 liters of hot black liquor with an effective alkali concentration of 25.3 g of NaOH per liter ("HBL1") by addition over 15 minutes at a temperature of 140 ° C to complete the neutralization step. Ten liters of the second hot black liquor ("HBL2") of the same concentration is added to the autoclave to displace the neutralized liquor for 23 minutes at 146 ° C, followed by the addition of cooking liquor, consisting of a mixture of 1.0 liter of hot black liquor ("HBL2" ) and 4.16 liters of a second white liquor ("WL2") with an effective alkali concentration of 124.7 g of NaOH per liter for 12 minutes at 10 bar and 152 ° C. Typical alkali loading for the cooking phase is about 11% effective alkali (EA) in terms of NaOH based on the weight of dry wood chips. The cooking liquor is pumped at a rate of 3 liters per minute for 3 minutes at a pressure of 9.1 bar. Then the autoclave is heated to 160 ° C for 14 minutes and kept at 160 ° C for another 23 minutes. Then the autoclave is cooled and the reaction mixture is washed twice with a dilute alkaline solution. Each wash uses 15 liters of an aqueous solution containing about 0.2 g of NaOH per liter of solution. The Kappa number of the unbleached sulfate pulp obtained was 10.3, viscosity 988 ml / g, solubility S10 3.6% and solubility S18 2.7%. The reaction yield is 39.3%. When sorting in a mixture of 0.13% waste, which gives a sorting output of 39.1%.

Example 3

Use of low concentration CCE filtrate as a neutralization solution and a cooking solution

According to the third example, the same cooking process is repeated as described in Example 2, except that the white liquor for the neutralization and cooking stages is replaced with the CCE stage filtrate with EA 54 g NaOH per liter ("CCE54"). The neutralizate has a pH of 11.0 and the EoC of the cooking mixture is 18.5 g of NaOH per liter. The P coefficient for preliminary hydrolysis is 297 and the H coefficient for the cooking reaction is 419. In this example, the total equivalent alkali loading relative to wood is 12% EA in terms of NaOH for the neutralization phase and 11% EA in terms of NaOH for the cooking phase .

The Kappa number of the unbleached pulp obtained is 10.8, a viscosity of 1118 ml / g, a solubility of S10 of 4.5% and a solubility of S18 of 3.6%. The reaction yield is 40.4%. When sorting in a mixture of 0.09% waste, which gives a sorting yield of 40.3%.

Example 4

The use of highly concentrated CCE filtrate as a neutralization solution and a cooking solution

According to the fourth example, the same cooking process is repeated as described in Example 2, except that two thirds of WL1 and WL2 are replaced by concentrated CCE filtrate with an effective alkali concentration of 110 g of NaOH per liter. The Kappa number of the resulting unbleached pulp is 9.5, a viscosity of 990 ml / g, S10 solubility 4.1% and S18 solubility 3.0%. The reaction yield is 39.5%. When sorting in a mixture of 0.10% waste, which gives a sorting output of 39.43%.

Compared to the conventional Kraft process, in which two-thirds of the white liquor is replaced by concentrated CCE filtrate, a pulp with a viscosity (about 990 mg / L in this example) and Kappa number similar to the values in the traditional Kraft process is obtained. It is expected that a similar technique will work in a wider range, for example, where 60 - 75% of the white liquor is replaced by concentrated CCE filtrate. Slightly lower Kappa numbers achieved with concentrated CCE filtrate suggest that replacing white liquor with concentrated CCE filtrate does not adversely affect delignification. The ratio of viscosity to Kappa number, a measure of selectivity at the cooking stage, is higher in a process with concentrated CCE filtrate (104 relative to 96 in a traditional process), which indicates better cooking selectivity using concentrated CCE filtrate.

S18 solubility increases from 2.7% to 3.0% and S10 solubility increases from 3.6% to 4.1% when a concentrated CCE filtrate replaces part of the white liquor, indicating a re-precipitation of hemicellulose. If necessary, S18 solubility can be further controlled by other means.

It should be possible to further optimize by slightly lowering the cooking temperature to achieve the same Kappa number (about 10.8) and higher viscosity. Based on various experiments, it is expected that minor changes in the process can be made, including alkali content, relative amounts of white liquor and concentrated CCE filtrate, cooking temperature and time, which could be determined by routine calculations or optimization based on the principles and methods described in the application, while maintaining the amount of unbleached pulp obtained in a potentially desirable range. For example, it is expected that the resulting unbleached pulp may have a Kappa number of up to 10.0, a viscosity of up to 1000 ml / g, S18 with a solubility of not more than 3.0% and / or a ratio of viscosity to Kappa number of more than 100.

According to some implementations disclosed in the description, it is possible to cook to the same or similar levels of viscosity and Kappa number using a concentrated CCE filtrate as in a traditional Kraft process that uses only fresh white liquor, which leads to increased efficiency.

Although preferred embodiments of the invention have been disclosed in the description, many changes are possible that do not go beyond the concept and scope of the invention. Such changes will become apparent to those skilled in the art after reviewing the description and drawings. Thus, the invention should not be limited except by the nature and scope of the attached claims.

Claims (40)

1. The method of production of pulp using cold-alkaline extraction to obtain soluble pulp, including:
delignification of organic materials in an autoclave and processing of the obtained unbleached pulp to obtain a semi-refined pulp for use in the production of soluble pulp;
extraction of the semi-purified pulp with an alkaline solution during the process of cold-alkali extraction to obtain purified pulp and a solution containing hemicellulose;
washing the cleaned pulp and collecting the resulting spent washing liquid, while separating the hemicellulose-containing solution from the cleaned pulp;
combining spent washing liquid and a solution containing hemicellulose to obtain an alkaline filtrate;
concentrating the alkaline filtrate to obtain a concentrated alkaline filtrate without purifying the hemicellulose-containing solution or alkaline filtrate to substantially remove hemicellulose from it; and
use of at least a portion of the concentrated alkaline filtrate in said autoclave in connection with the production of soluble pulp. 2. The method according to claim 1, in which the concentration of the alkaline filtrate is carried out by the evaporation process. 3. The method according to claim 2, in which the evaporation process is carried out on several series-connected steps. 4. The method according to claim 2, in which the specified process of evaporation is carried out at a temperature of from about 50 to 60 ° C. 5. The method according to claim 2, in which the evaporation process is carried out at a pressure of -0.5 bar and -0.84 bar. 6. The method according to claim 2, in which the evaporation process is carried out until the concentration of effective alkali in the specified concentrated alkaline filtrate is from about 95 to 125 grams of NaOH per liter. 7. The method according to claim 2, in which the evaporation process is carried out until the concentration of effective alkali in the specified concentrated alkaline filtrate is from about 100 to 110 grams of NaOH per liter. 8. The method according to claim 1, further comprising adding white liquor to the concentrated alkaline filtrate used in said autoclave. 9. The method of claim 8, in which the ratio of white liquor to the concentrated alkaline filtrate is from about 1: 1.5 to 1: 2.5. 10. The method according to claim 1, wherein said alkaline solution contains NaOH and Na ₂ S. 11. A method of producing pulp in a Kraft process using cold-alkali extraction, including:
cooking the first batch of organic materials in an autoclave to produce unbleached pulp;
washing and sorting unbleached pulp to obtain a semi-refined pulp;
extraction of the semi-purified pulp using cold-alkaline extraction to obtain purified pulp and a solution containing hemicellulose;
washing the purified pulp and collecting the resulting spent washing liquid, while separating the hemicellulose-containing solution from the purified pulp obtained by cold-alkali extraction;
combining spent washing liquid and a solution containing hemicellulose to obtain an alkaline filtrate;
evaporation of the alkaline filtrate in a controlled environment to obtain a concentrated alkaline solution without purification of the solution containing hemicellulose or alkaline filtrate to substantially remove hemicellulose from it; and
using at least a portion of the concentrated alkaline solution as at least one cooking liquid for cooking a second batch of organic materials in connection with the production of soluble pulp. 12. The method according to claim 11, further comprising using the second part of the concentrated alkaline filtrate on another pulp production line. 13. The method according to claim 11, in which the evaporation process is carried out on several stages connected in series. 14. The method according to claim 11, in which the specified process of evaporation is carried out at a temperature of from about 50 to 60 ° C. 15. The method according to claim 11, in which the evaporation process is carried out at a pressure of -0.5 bar and -0.84 bar. 16. The method according to claim 11, in which the evaporation process is carried out until the concentration of effective alkali in the specified concentrated alkaline filtrate is from about 95 to 125 grams of NaOH per liter. 17. The method according to claim 11, in which the evaporation process is carried out until the concentration of effective alkali in the specified concentrated alkaline filtrate is from about 100 to 110 grams of NaOH per liter. 18. The method according to claim 11, further comprising adding white liquor to the concentrated alkaline filtrate used in said autoclave. 19. The method according to p, in which the ratio of white liquor to the concentrated alkaline filtrate is from about 1: 1.5 to 1: 2.5. 20. The method according to claim 11, in which the alkaline solution used for cold-alkaline extraction contains NaOH and Na ₂ S. 21. The method according to claim 11, further comprising the steps of:
obtaining a second unbleached pulp by cooking a second batch of organic materials in an autoclave;
washing and sorting the second unbleached pulp to obtain a semi-refined pulp; and
the use of cold-alkali extraction for the extraction of semi-purified pulp obtained from the second unbleached pulp, to obtain a second purified pulp and a second solution containing hemicellulose. 22. The method according to item 21, in which S18 the solubility of the second unbleached pulp is not more than 3.0% before cold alkaline extraction. 23. The method according to item 22, in which the Kappa number of the second unbleached pulp is less than 10.0 before cold alkaline extraction. 24. The method according to item 22, in which the viscosity of the second unbleached pulp is about 1000 milliliters per gram before cold alkaline extraction. 25. The method according to item 22, in which the ratio of viscosity to Kappa number of the second unbleached pulp is 100 or higher before cold alkaline extraction. 26. An improved method for the production of pulp in a Kraft process using cold-alkaline extraction to obtain soluble pulp, including boiling organic materials in an autoclave to produce unbleached pulp, washing and sorting unbleached pulp to produce pulp and extracting raw pulp using cold-alkali extraction to obtain a purified pulp and a solution containing hemicellulose, the improvement includes:
washing the purified pulp and collecting the resulting spent washing liquid, while separating the hemicellulose-containing solution from the purified pulp obtained by cold-alkali extraction;
combining spent washing liquid and a solution containing hemicellulose to obtain an alkaline filtrate;
concentrating the alkaline filtrate to obtain a concentrated alkaline filtrate without purifying the hemicellulose-containing solution or alkaline filtrate to substantially remove hemicellulose from it; and
using at least a portion of the concentrated alkaline filtrate in the autoclave to neutralize or cook additional organic materials in connection with the production of soluble pulp. 27. A method for the production of pulp in a kraft process using cold-alkaline extraction to obtain soluble pulp, including:
cooking organic materials in a series of batch autoclaves using at least a portion of a concentrated alkaline solution obtained in the downstream cold alkaline extraction step, and thereby obtaining unbleached pulp;
washing and sorting unbleached pulp to obtain a semi-refined pulp;
extraction of the semi-purified pulp using cold-alkaline extraction to obtain purified pulp and a solution containing hemicellulose;
washing the purified pulp and collecting the resulting spent washing liquid, while separating the hemicellulose-containing solution from the purified pulp obtained by cold-alkali extraction;
combining spent washing liquid and a solution containing hemicellulose to obtain an alkaline filtrate;
evaporation of the alkaline filtrate in a controlled environment to obtain a concentrated alkaline solution without purification of the solution containing hemicellulose or alkaline filtrate to substantially remove hemicellulose from it; and
returning at least a portion of the concentrated alkaline solution to at least one of the batch autoclaves as at least one cooking liquid in connection with obtaining a soluble pulp. 28. The method according to claim 3, in which the evaporation process is carried out at a pressure of about - 0.84 bar in the first stage, and at a pressure of about - 0.5 bar in the second stage, located downstream from the specified first stage. 29. The method according to 14, in which the evaporation process is carried out at a pressure of about - 0.84 bar in the first stage, and at a pressure of about - 0.5 bar in the second stage, located downstream from the specified first stage. 30. A method of obtaining a pulp in a Kraft process to obtain a soluble pulp, including:
neutralization of the first batch of organic materials using a neutralization solution containing a portion of white liquor and a second second alkaline liquid following it, other than it;
cooking the first batch of organic materials in an autoclave to produce unbleached pulp;
washing and sorting unbleached pulp to obtain a semi-refined pulp;
extraction of the semi-purified pulp using cold-alkaline extraction to obtain purified pulp and a solution containing hemicellulose;
washing the purified pulp and collecting the resulting spent washing liquid, while separating the hemicellulose-containing solution from the purified pulp obtained by cold-alkali extraction;
combining spent washing liquid and a solution containing hemicellulose to obtain an alkaline filtrate without substantially removing hemicellulose components from it;
evaporation of the alkaline filtrate in a controlled environment to obtain a concentrated alkaline solution without purification of the solution containing hemicellulose or alkaline filtrate to substantially remove hemicellulose from it; and
using at least a portion of the concentrated alkaline solution as at least one neutralization solution or cooking liquid for treating a second batch of organic materials in connection with the production of soluble pulp. 31. The method according to item 30, in which the neutralization solution for the second batch of organic materials contains the second part of the white liquor and the next concentrated alkaline solution. 32. The method according to item 30, in which the evaporation process is carried out on several series-connected steps. 33. The method according to p, in which the specified process of evaporation is carried out at a temperature of from about 50 to 60 ° C. 34. The method according to p, in which the evaporation process is carried out at a pressure of about -0.84 bar in the first stage, and at a lower pressure in the second stage, located downstream from the specified first stage. 35. The method according to clause 34, in which the evaporation process is carried out until the concentration of effective alkali in the specified concentrated alkaline filtrate from about 100 to 110 grams of NaOH per liter. 36. The method according to clause 30, further comprising adding white liquor to the concentrated alkaline filtrate used for cooking the specified second batch of organic materials. 37. The method according to clause 36, in which the concentrated alkaline filtrate is from 60 to 75% of the combination of concentrated alkaline filtrate and white liquor. 38. The method of claim 30, further comprising the steps of:
obtaining a second unbleached pulp by cooking a second batch of organic materials in an autoclave;
washing and sorting the second unbleached pulp to obtain a semi-refined pulp; and
using cold-alkaline extraction of the semi-refined pulp obtained from the second unbleached pulp to obtain a second refined pulp and a second solution containing hemicellulose. 39. The method of claim 30, wherein said second alkaline liquid used to neutralize the first batch of organic materials comprises black liquor. 40. The method according to clause 30, in which the white liquor has a concentration of effective alkali from 95 to 125 grams per liter, and the specified second alkaline liquid has a concentration of effective alkali from 30 to 35 grams per liter.

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