WO2005028743A1

WO2005028743A1 - Black liquor extracting method in manufacturing straw pulp

Info

Publication number: WO2005028743A1
Application number: PCT/JP2003/011870
Authority: WO
Inventors: Eiji Otsuba; Kiyohisa Ueda; Minoru Ikeda
Original assignee: Hitachi Zosen Corporation
Priority date: 2003-09-18
Filing date: 2003-09-18
Publication date: 2005-03-31

Abstract

An optimum design method for a horizontal belt type washing machine and an optimum operating method for the washing machine for extracting black liquor produced in the manufacturing of alkaline straw pulp at a high rate, wherein a backwashing is performed by using the horizontal belt type washing machine to extract the black liquor, the horizontal belt type washing machine is manufactured by the optimum design method led from the water filterability and washability of the straw pulp, and the washing machine is operated under optimum operating conditions formed by integrating the overall pulp manufacturing workshops, an alkali recovery workshop, and a drain treatment workshop, whereby an extraction rate of 90% or more and a reduction in pulp manufacturing cost can be achieved.

Description

Description Method of extracting black liquor in straw pulp production

In the production of straw pulp, first, straw is steamed with an aqueous solution of caustic soda, and then a liquid containing caustic soda (hereinafter referred to as black liquor) and an organic substance such as pulp fiber and lignin are produced. The black liquor is separated from the pulp fibers using water (this operation is called extraction), and the pulp fibers are bleached to bleached pulp.

The present invention relates to a method for extracting black liquor in straw pulp production.

The separated black liquor (hereinafter referred to as dilute black liquor) is sent to the alkaline recovery process, where it burns organic matter and recovers the molten material (smezoleto) generated during combustion as caustic soda by a causticization reaction. However, this can be reused for steaming.

At present, this black liquor extraction operation can only extract 80-85% of the soluble solids (hereinafter referred to as T S) in the black liquor. The present invention relates to technology for increasing the extraction rate to 90% or more to increase the alkali recovery rate, reduce the load on wastewater treatment, reduce pulp production costs, and reduce environmental pollution. is there. Background art

Figure 1 shows an outline of the Alkali-method straw pulp production site and the Alkali recovery site. In Fig. 1, the names of raw materials and intermediates are shown in the oval frames, and the processes of each workplace are shown in the rectangular frames. The upper dotted line shows the pulp manufacturing workplace, and the lower dotted line shows the alkali recovery workplace. Shown respectively.

The black liquor extraction step, which is the subject of the present invention, is a step of separating steamed product into unbleached pulp (hereinafter referred to as black pulp) and dilute black liquor using warm water. This dilute black liquor is sent to the evaporation process, which is the first step in the alkaline recovery workplace, where the TS concentration is increased and then sent to the combustion step. Therefore, it is desirable that the T S concentration of the diluted black liquor be high. That is, it is desirable that the amount of hot water used for the extraction be small. On the other hand, T S which did not migrate to the diluted black liquor is dissolved in the water contained in the black pulp coming out of the extractor (hereinafter, this black pulp and its containing liquid are collectively referred to as a black pulp stream). The TS in this black pulp stream is washed with plenty of water in the first half of the bleaching process. This wash wastewater is called the middle wastewater and is the main wastewater of the pulp mill. The C 0 D and B 0 D values of the middle wastewater are determined by the amount of unextracted TS in the extraction process and the amount of components generated in the bleaching operation.

Therefore, unextracted TS not only reduces the amount of alkali recovered, but also increases the pollution load of the wastewater treatment process.

As described above, the extraction rate in the extraction step (in the present specification and claims, the extraction rate is the ratio of the amount of TS in the dilute black liquor to the amount of TS in the steamed product). Is an important factor that governs

Conventionally, many processes and washing machines have been proposed to increase the extraction rate with the least amount of hot water. Since the late 1990s, vacuum drum type washing machines have been widely used as washing machines for straw pulp production. Also, before the use of vacuum drum type washing machines, horizontal band type washing machines have been used.

There are several types of horizontal band washer. One of them is a filter net and a caterpillar-type rubber cylinder for supporting and driving it. This is a horizontal rubber belt type washer using a root. This washer was often used for pre-washing of the bleaching process when black liquor was not recovered. However, high recovery rates have been demanded since the recovery of energy, and this type is rarely used. The stainless steel horizontal band type washer (see Science and Technology Achievement Appraisal Certificate (19997) No. 0700) was developed to improve the alkali recovery. It belongs to the horizontal spiral mesh type washer. In this washer, the spiral mesh was made of stainless steel and the extraction rate was improved. However, the price and life of the spiral mesh did not meet the requirements, and it did not spread.

The stainless steel net was changed to a synthetic fiber spiral net, and a horizontal spiral net washer that improved foaming measures and improved the problems of black liquor leakage from around the net came to be used.

The cleaning mechanism of the vacuum drum type washer and the horizontal band type washer is either dilution washing using washing water or replacement washing. On the other hand, it is a black liquor extraction device with a so-called compression dewatering mechanism that mechanically compresses the steamed product and squeezes the TS-containing liquid contained in the pulp fiber to extract TS. Extractors based on this principle include short-screw screws, twin-screw screws, twin-roll presses, and ZLJ-type double-chain net black liquor presses. The extraction by the press dewatering mechanism is rarely used alone, and is often used in combination with the above-mentioned vacuum drum type or horizontal band type washer.

These various types of black liquor extraction technology and equipment are described in Chugoku Paper Industry, 2002, First Phase (January), pp. 53-56. The current status of systems using a typical vacuum drum type washer and a horizontal band type washer and issues to be solved will be explained.

Extraction using a vacuum drum type washing machine (case of 5-stage backwashing) Figure 2 schematically shows the dispensing process.

In each stage in Fig. 2, (1) is a vacuum drum (1) whose inside is evacuated to a vacuum, and its surroundings are covered with a filtration net (4). (2) is a bucket concentrically arranged at a predetermined interval outside the vacuum drum (1), and the lower half of the space between the vacuum drum (1) and the bucket (2) is diluted. The pulp-containing liquid to be treated is stored. In the first stage, the raw material to be treated, that is, the effluent from the steaming process, is diluted to a pulp concentration of about 1% with the first stage filtrate, and the resulting liquid containing the pulp to be treated is sent into the batter (2). This liquid is sucked into the vacuum drum (1) and a pulp layer is gradually formed on the filter net (4). The pulp layer discharged from the pulp-containing liquid to be treated with the rotation of the drum (1) is dehydrated, washed with washing water at the upper part of the drum (1), and subsequently dehydrated. After washing, the pulp layer passes through the top of the drum, is separated from the filter net (4) by air pressure from inside the drum, falls into the pulp receiving tank (3) of the next vacuum drum washing machine, where it is washed with washing water. It is diluted to a pulp concentration of about 1%. The pulp is washed by repeating the above operation for a total of five stages. For the washing water, use the filtrate in the next step, and use warm water in the last step. In this way, so-called backwashing is performed, in which the washing water is caused to flow in the direction opposite to the pulp traveling direction.

For straw pulp 7 5 t date, filtration area 6 0 vacuum drum m ² (standard ZNK 3 1 1) consists of 5 consecutive cleaning machine is the Typical. Usually, the vacuum of the vacuum drum is maintained by increasing the height, but it is often assisted by a vacuum pump. The five large drums will be installed on the third floor with a floor height of about 10 m. The extraction rate in a vacuum drum washer is 80-85%.

Operational problems with vacuum drum cleaning machines include:

Peeling of the pulp layer on the vacuum drum occurs frequently and the vacuum is not stable. I

A large amount of black liquor leaks into high-order condensed water due to foaming of the liquid, leading to a decrease in extraction rate.

Low black liquor extraction rate by pulp layer washing water,

Fine pulp fibers are mixed into the dilute black liquor, causing scale formation on the evaporation surface during the evaporation process.

Due to the maintenance related to valve seals, etc., the operating rate decreases and the cost increases.

And the point that came.

As described above, the vacuum drum type washing machine cannot not only achieve the extraction rate of 90% of the target, but also increases the equipment cost and the construction cost, and in addition, there are many obstacles to stable production. Fig. 3 schematically shows the extraction process using a horizontal spiral mesh type washer (a 5-stage backwashing case), which is a typical horizontal band type washer.

In Fig. 3, (11) and (12) are left and right drums wrapped around a spiral mesh (13), right drum (U) is a driving drum rotated by an electric motor, and left drum (12) is a driven drum. . The spiral mesh (13) stretched over the left and right drums (11) and (12) is rolled without slipping by applying an appropriate tension, and has a relatively large opening. A filtration net (14) is arranged outside the spiral net (13), supported by the spiral net (13), and moves together with the spiral net (13). The filter net (14) does not allow pulp to pass through, but has openings suitable for allowing washing water to pass with low resistance. Under the spiral mesh (13) in the first to sixth compartments, suction boxes (15) to (20), which play a role in facilitating the passage of washing water, are arranged, and the spiral mesh (13) is provided by a blower. Is applied with a vacuum pressure on the lower surface. At the entrance of each section after the second stage, a washing water distribution mechanism (perforated pipe or overflow weir) is installed on the filtration network (14). Suction from spiral mesh (13) The liquid sucked into the box is guided to the washing water storage tanks (21) to (26) below the suction box and stored therein.

The raw material to be treated, that is, the effluent from the steaming process, is diluted to a pulp concentration of about 2% with the filtrate in the first section, and the resulting liquid containing the pulp to be treated is supplied to the head box (27). This liquid passes through the filtration net (14) in the first section, and the pulp remains on the filtration net (14) to form a uniform pulp layer. The pulp layer on the filtration network (14) enters the second compartment, and is washed by the filtrate in the next compartment that has passed through the washing water distribution mechanism (first washing stage).

The filtrate in the second compartment is a dilute black liquor and is sent to the evaporation step. If the filtrate in the first compartment becomes insufficient, replenish with this diluted black liquor. The pulp that has progressed to the third section is washed with the filtrate of the fourth section at the entrance, as in the second section. Thereafter, the same operation is performed up to the sixth section to wash the pulp. For the washing water, use the filtrate in the next step, and use warm water (sometimes using recovered hot water with few impurities) in the last step. The pulp at the outlet of the sixth section is dewatered to a pulp content of 10% or more (this pulp and the liquid are collectively referred to as a pulp stream). The pulp stream is separated from the filtration network (14) by water sprayed from below the filtration network (14), held in a black pulp storage tank, and sent to the bleaching process.

The role of the first compartment is to distribute the pulp-containing liquid to be treated evenly on the filter net (14). Therefore, in the case of a horizontal belt type washer such as a horizontal spiral net type washer, the number of stages obtained by subtracting 1 from the total number of sections is the number of stages of backwashing.

For straw pulp 7 5 t Z date, placing the effective filtration area (the total filtration area of all sections) 5 of 4 m ² horizontal spiral network washer parallel to the 2 groups. The extraction rate in the horizontal spiral net washer is around 85%. Regarding drivability, Easy operation and stable operation. Operation can be stopped and restarted easily,

Equipment improvements also helped to resolve black liquor leakage and poor cleaning from around the belt, which was said to be an early defect.

Regarding the life of the net, it will take about one month to properly select the net and modify the equipment. Network replacement is also possible within 8 hours of shift work, and there is no need to stop all operations due to network replacement.

Compared to vacuum drum type washing machines, the power, maintenance, and investment costs required for operation are smaller,

There is an advantage.

As described above, the horizontal spiral net washer solves many problems of the vacuum drum type washer, and the black liquor extractor of a small-scale factory such as straw pulp with an annual production of about 50,000 tons or less. Suitable for.

However, an extraction rate of 85% is not enough. In particular, in order to respond to the tightening of wastewater discharge regulations, which have been strengthened with the recent rise in environmental protection philosophy, it is necessary to strengthen wastewater treatment facilities. To respond to this, instead of investing in wastewater treatment without reward, the idea is to reduce the wastewater load by collecting black liquor and respond to stricter regulations, and to reduce pulp production costs by improving the recovery rate of wastewater. ing. There is a strong need to achieve a black liquor extraction rate of 90% or more even with a horizontal spiral net washer, but this has not been met.

According to the operating conditions of the horizontal spiral mesh washing machine of the present inventors, if the amount of hot water is to be increased in order to increase the extraction rate, the filterability in the section before the final stage (hot water washing stage) is poor and dewatering is performed. It becomes defective and cleaning cannot be performed sufficiently. In order to solve this problem, it is necessary to increase the overall filtration area of the washer or add one horizontal spiral mesh washer. Or as shown in U.S. Patent No. 5,366,894. As shown in the figure, it is necessary to install a press dewatering mechanism at the outlet of the horizontal belt type washer.

It is desirable to develop an efficient improvement method and operation method for a horizontal spiral net washer that does not require such a large investment. Disclosure of the invention

The present inventors have intensively studied the filtration behavior of black liquor and the replacement washing property of the horizontal spiral net washer and performed a simulation.As a result, the horizontal spiral net washer was efficiently manufactured by the following method. The inventors have found a frequently used method and completed the present invention.

That is, according to the present invention, in extracting black liquor produced in the production of alkaline straw pulp by backwashing using a horizontal band washing machine,

(1) Divide the horizontal band type washer into 4 or 5 stages,

(2) These sections are numbered 1 to 4 or 1 to 5 sequentially from the upstream side of the pulp flow, and when the total number of stages is four, the filtration area of the second and third stages is the filtration area of the fourth stage When the total number of stages is 5, the filtration area from the second stage to the fourth stage is 1.3 to 2 times the filtration area of the fifth stage.

(3) The filtration area of the first stage should be 0.6 to 1.4 times the filtration area of the last stage.

This is a method for extracting black liquor in straw pulp production.

It is preferable that the filtration area of the portion where the pulp is present in the horizontal band type washer is 15 m ² to 45 m ² per ton of pulp to be treated.

The width of the band where the pulp is present in the horizontal band type washer (the length in the direction perpendicular to the traveling direction of the band) It is preferable to set the lm to 2.5 m per ton / hour and the driving speed of the band to be 10 m to 3 OmZ.

The horizontal band type washing machine includes a spiral net and a filter net supported by the net and moving together with the spiral net. The filter net has a ventilation capacity of 300 to 90 to prevent pulp from leaking. 0 cm is ³ cm ² Z s synthetic fibers net that having a, spiral network is a network woven vertical and horizontal lines made synthetic fibers having a diameter of 0.. 5 to 2 mm in a spiral shape, It is preferable that the number of vertical stitches is 13 to 20 lines Z25.4 mm, and the number of horizontal stitches is 3 to 8 lines Z25.4 mm.

It is preferable to supply washing water to multiple sections in each section of the horizontal belt type washer.

It is preferable that the filtrate generated in the first section is not added to the filtrate generated in the second section, and only the filtrate generated in the second section is sent to the alkali recovery step as a dilute black liquid. It is known that the black liquor of straw pulp has a high viscosity due to silica present at a high concentration in the raw straw. It is known that straw pulp has a short fiber length and low strength. These basic properties of straw pulp make black liquor extraction more difficult than wood or bamboo pulp. On the other hand, when performing multi-stage reverse washing using a horizontal belt type washer, the amount of washing water in the last stage is determined by the smallest amount of filtered water among the amount of water that can be filtered in each stage. In the case of filtration of a liquid having a high viscosity such as black liquor of straw pulp, the filtration rate is low at a portion where the TS concentration is high, and the filtration speed is significantly different from that at a portion where the TS concentration is low due to washing. If the filtration area of each section of the horizontal zone is divided equally or almost equally, the amount of filtered water at the stage before the final stage will be decisive, and the amount of hot water will be limited. Also, cleaning at the stage before the last stage The effect is so small that the overall extraction rate does not increase. The amount of filtered water is determined by the product of the filtration speed and the filtration area.

The inventor of the present invention (1) divided the horizontal band type washer into four or five stages using a simulator originally created, and (2) assigned the numbers of these zones to the upstream side of the pulp flow. From 1 to 4 or from 1 to 5, and when the total number of stages is 4, the filtration area of the second and third stages is 1.3 to 2 times the filtration area of the fourth stage, and the total number of stages is 5 In the case of a stage, the filtration area from the second stage to the fourth stage is 1.3 to 2 times the filtration area of the fifth stage. (3) The filtration area of the first stage is 0. It was found that the optimal value was 6 to 1.4 times. To achieve extraction of 9 or higher 0%, a filtration area of the portion there is pulp in the horizontal band washer, the pulp 1 t Z during per ^{1 5 m 2 ~ 4 5 m} 2 for processing I found it preferable to do so. The upper limit of the above range is a value determined from economics.

The width and band speed of the horizontal band type washer are factors that determine the thickness of the pulp layer on the band, and this value is also required to achieve an extraction rate of 90% or more. The width of the band where the pulp is present (length in the direction perpendicular to the traveling direction of the band) is 1 m to 2.5 m per ton of pulp to be treated, and the driving speed of the band It has been found that it is preferable to set the temperature between 1 OmZ and 3 OmZ.

The type of the horizontal band type washer is not particularly limited, but a horizontal spiral net type washer is preferable. The horizontal spiral mesh type washer includes a spiral mesh and a filter mesh supported by the mesh and moving together with the spiral mesh, and the filter mesh has a ventilation capacity for preventing pulp from leaking. ~ 9 0 a 0 cm ³ / cm synthetic textile net having ² Z s, spiral network spirally vertical and horizontal lines of synthetic fibers of diameter 0.. 5 to 2 mm

0 It is preferable that the number of meshes in the vertical direction is 13 to 20 and Z25.4 mm, and the number of meshes in the horizontal direction is 3 to 8 Z25.4 mm.

As a method of supplying washing water to each section of the horizontal belt type washing machine, generally, various kinds of distribution mechanisms are provided at an inlet portion of each stage to supply the washing water, but the washing water is divided into a plurality of sections in each section. Supply. In other words, the cleaning effect can be improved by supplying a part of the cleaning water to the middle part of the section.

It was found that the filtration rate in the pulp layer was high at low pulp concentrations, but decreased exponentially with increasing pulp concentrations. In areas where the filtration rate is high, the wash water passes through with little contact with the pulp. Appropriate filtration speed is required to increase the washing efficiency. Split water supply makes this possible o

The fine fibers in the dilute black liquor, which is a defect of the drum-type vacuum cleaner, cause contamination of the evaporation surface in the evaporation process. Even in the horizontal belt type washer, a large amount of fine fibers are contained in the black liquor that has passed through the area where the pulp layer has not yet been sufficiently formed as in the first section. However, the filtrate in the second stage has passed through the pulp layer in its entirety, and the pulp layer becomes an effective filtration layer, and this filtrate contains almost no fine fibers. In a general horizontal strip type washer, the first and second filtrate storage tanks are shared to reduce the number of filtration storage tanks, and a part is supplied to the pulp dilution to the blower and the rest is supplied to the evaporation process. Therefore, fine fibers are mixed in the diluted black liquor. Preferably, the filtrate generated in the first section is not added to the filtrate generated in the second section, and only the filtrate generated in the second section is sent to the alkaline recovery section as a dilute black liquor. That is, the first-stage and second-stage filtrates are separated, and the first-stage filtrate is used to dilute the ejecta, and the second-stage filtration is performed. By supplying only the liquid as a dilute black liquor to the evaporation step, it is possible to avoid mixing of fine fibers into the dilute black liquor.

FIG. 4 illustrates a method for extracting black liquor in straw pulp production according to the present invention. Figure 4 shows a schematic flow diagram of the extraction process using a horizontal spiral mesh washing machine (case of three-stage backwashing). This flow is based on the fact that the number of washing stages is three, that a part of the washing water in each stage is also supplied from the middle part of each stage, and that the first and second stages It is the same as the flow shown in Fig. 3, except that the filtrate is completely separated. Each symbol in FIG. 4 means the one described with reference to FIG. Brief Description of Drawings

Figure 1 is a flow chart that schematically shows the processes and substances at the soda straw pulp production and recovery sites.

Figure 2 is a flow sheet schematically showing the extraction process using a vacuum drum-type washing machine (a case of five-stage backwashing).

Fig. 3 is a flow sheet schematically showing the extraction process using a horizontal spiral mesh washing machine (case of 5-stage backwashing).

Figure 4 is a flow sheet that schematically shows the extraction process using a horizontal spiral mesh washing machine (case of three-stage backwashing). BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be specifically described based on examples.

Example 1

Straw pulp was produced at 87 tons (air-dried) / day. In the black liquor extraction step, a horizontal spiral net extractor according to the method of the present invention was used. Data was collected for 5 days. The results are shown below.

2 1. Steaming process

In the step of preparing straw, a dry dust remover was used. The cooking process was used 4 0 m ³ and 2 5 m ³ of the earth can each four. The preparation operation conditions are as shown in the table below.

Steaming conditions (A line, B line) Steam pressure 0.6 MPa Heating time 2 hours

Retention time 0

Ejector outlet volume for 5 days (Value not including diluted black liquor for dilution)

Pulp 4 5 4.7 tons

T S amount 6 96.5 ton

Water 3 6 4 7 ton

Total 4 7 9 8 Ton

2. Extraction process

Equipment specifications

Horizontal spiral mesh washer; effective filtration area: 54 m ² , three-stage backwashing 2 units combined (29.8 m ² Z (1 ton / hour of pulp)) Area of each section of the machine: first stage 9 m ²

Second and third steps 16.8 m ²

Fourth stage 1 1. 4 m ²

Three (Area ratio with respect to the fourth stage; 0.79 for the first stage, 1.47 for the second and third stages)

Effective width of the airplane network; 3 m (1.66 m (at 1 ton of pulp)) Driving speed of the belt: 25 mZ min

Wash water supply method for each stage; 2nd and 3rd stages supply 2 Z3 at the stage entrance and 1 Z3 at the center of the stage

Specifications of the filtering net; permeability ^{^{4 0 0 cm 3 / cm 2}} Z s

Spiral mesh specifications; thread thickness 0.9 mm, number of spirals, length 13 threads Z 25.4 mm, number of weft threads 3 mm

Process flow of extraction process: A schematic flow of the extraction process using a horizontal spiral mesh type washing machine (case of three-stage backwashing) shown in Fig. 4 was implemented. This flow itself is based on the fact that the number of washing stages is three, that there is a mechanism in which part of the washing water in each stage is also supplied from the middle of each stage, and that the first and second stages are The procedure is the same as that shown in Fig. 3, except that the filtrate is completely separated. Each symbol in FIG. 4 means that described with reference to FIG. Operating conditions

Pulp concentration in extractor; 2%

Material supply amount of the extractor; 9 0. 7 m ³ Z when & 1 group

Hot water flow rate: 20.3 ton / hour · 1 unit

Hot water temperature: 35 to 40 ° C

Suction box pressure; Suction side pressure car at suction port of 10 kPa 5 days operating results

Black pulp production: 455 tons

Concentration of pulp discharged from the extractor: 11.3% (After thoroughly washing the pulp, dry it at 105 ° C for 2 hours and weigh it)

Four TS concentration of the pulp-containing liquid from the extractor; 1.33% (The liquid is dried at 105 ° C for 2 hours and weighed)

Unextracted TS amount: 47.5 tons

Dilute black liquor volume for evaporation process; 540 m ³

T S concentration in diluted black liquor going to the evaporation process; 1.43% (B e = 6.12, 59 ° C)

T S amount in dilute black liquor for evaporation process; 645 ton

Washer extraction rate *; 93.1%

Extraction rate of extraction process **; 92.6%

In addition,

Formula for estimating the concentration of the dilute black liquor from the degree of Be: T S concentration = (B e + 0.05 2 X (T-20)) X I. 5 1—0.9 (%)

Formula for calculating the extraction rate * of the washing machine

Extraction rate = Ts amount in dilute black liquor going to evaporation step (TS amount in dilute black liquor going to evaporation step + unextracted Ts amount)

Formula for extraction rate ** of extraction process

Extraction rate = TS amount in dilute black liquor going to evaporation process Z output from ejector TS amount Horizontal spiral net washer; effective filtration area 5 4 m ² , with three-stage backwash

(29.8 m ² Z (1 ton of pulp))

Area of each section of the Aircraft;

First stage 9 m ²

Second and third steps 16.8 m ²

Fourth stage 1 1. 4 m ²

(Area ratio for the 4th stage; 0.79 for the 1st stage, 1.47 for the 2nd and 3rd stages)

As described above, as a result of operating the horizontal spiral net washer by the method of the present invention, a washing machine extraction rate of 93% was achieved, and stable operation was achieved.

Five The above embodiments are merely examples of the present invention, and do not limit the scope of the present invention. Comparative Example 1

Steaming process

Same as in the first embodiment. However, the measurement period was 1 day, and the number of active lines A = 18 balls and the number of active lines B = 21 balls.

Amount of ejector outlet per day (Value not including diluted black liquor for dilution) Pulp 70 ton

T S amount 104 ton

^ 5 3 9 tonnes

Total 7 1 3 Ton Extraction process

Equipment specifications

Horizontal spiral mesh washing machine; Effective filtration area: 5 4 m ² , 5-stage backwashing 2 units combined (29.8 m ² / (1 ton of pulp Z)) Area of each section of the machine;

First stage 9 m ²

2nd to 5th tiers 8.4 m ²

Sixth stage 1 1. 4 m ²

(Area ratio for 6th stage; 0.79 for 1st stage, 0.73 7 for 2nd to 5th stages)

Washing water supply method at each stage: All of the 2 to 6 stages were supplied to the inlet of each stage.

Process flow of the extraction process; Others are the same as the first embodiment.

6 Operating conditions

Pulp concentration in extractor; 2.3%

Material supply amount of the extractor; 6 0. 4 m ³ o'clock-1 group

Hot water flow rate: 14.7 tons per hour · 1

Hot water temperature; 55-60 ° C

Suction box pressure: Suction side suction side pressure — 1 O k Pa

1 Operating results

Black pulp production: 70 tons

Concentration of pulp discharged from the extractor: 11.4% (After pulp is thoroughly washed, dried at 105 ° C for 2 hours and weighed)

T S concentration of the pulp-containing liquid from the extractor: 2.2% (The liquid is dried at 105 ° C for 2 hours and weighed)

Unextracted solid content; 12.0 tons

Volume of dilute black liquor going to evaporation process; 7 5 7 m ³

T S concentration in dilute black liquor for evaporation process; 1 1.2%

TS amount in dilute black liquor going to evaporation process; 88.7 tons

Washer extraction rate; 88.1%

Extraction rate in the extraction process: 85.3% During the operation of the comparative example, the entire amount of the filtered water in the 6th stage could not be used as the washing water in the 5th stage. Used as washing water in 5 stages. The remaining 6th stage filtered water was mixed with the 1st stage filtered water. The reason why the washing water must be flowed in such a manner is that the filtration speed in the fifth and lower stages is slow, and the filtration area in the fifth and lower stages is insufficient. In addition, the black liquor loss was large and the extraction rate in the extraction process was low.

7 Industrial applicability

The following effects are achieved by the present invention.

(1) By the method of the present invention, an extraction rate of 90% or more, which was not achieved by the vacuum drum type washing machine, can be achieved.

(2) The horizontal band type washer that solved many other problems of the vacuum drum type washer had an extraction rate of only 85%. With an appropriate allocation and an appropriate setting of the total filtration area, an extraction rate of 90% or more can be achieved with three or four backwash steps.

(3) By the method of the present invention, an extraction rate of 90% or more can be achieved at a high concentration of Be degree 8 or higher at a TS concentration of 20 ° C. of the dilute black liquor, and energy can be saved at a workplace for recovering energy. Can contribute.

(4) As a result of achieving an extraction rate of 90% or more by the method of the present invention, the amount of C 0 D and B 0 D of middle-stage wastewater can be significantly reduced, and the amount of capital investment in the wastewater treatment workplace can be reduced. It can save energy and contribute to reducing operating costs.

(5) According to the method of the present invention, the loss of black liquor can be significantly reduced, the stable operation of the extraction process can be achieved, and the capital investment can be reduced.

8

Claims

The scope of the claims

1. When the black liquor produced in the alkaline straw pulp production is extracted by backwashing using a horizontal band type washer,

(1) Divide the horizontal band type washer into 4 or 5 stages,

(2) These sections are numbered from 1 to 4 or 1 to 5 sequentially from the upstream side of the pulp flow, and when the total number of stages is four, the filtration area of the second and third stages is the filtration area of the fourth stage When the total number of stages is 5, the filtration area from the second stage to the fourth stage is 1.3 to 2 times the filtration area of the fifth stage.

(3) The filtration area of the first stage should be 0.6 to 1.4 times the filtration area of the last stage

Black liquor extraction in straw pulp production

Ά

2. The filter area of a portion where there is pulp in the horizontal band washer, to claim 1, processing said pulp 1 t Z 1 5 per time m. ^² ~ 4 5 m ² and child Extraction method as described.

3. The width of the band where the pulp is present (the length in the direction perpendicular to the traveling direction of the band) in the horizontal band type washer is processed. The extraction method according to claim 1 or 2, wherein the band driving speed is 1 OmZ to 3 OmZ.

4. The horizontal band type washing machine includes a spiral net and a filter net supported by the net and moving together with the spiral net, and the filter net has a ventilation capacity of 300 to 9 for preventing pulp from leaking. 0 0 cm ³ is Z cm synthetic textile net having ² Z s, spiral network is a network woven vertical and horizontal lines of synthetic fibers of diameter 0.. 5 to 2 mm in a spiral shape,

9 The method according to any one of claims 1 to 3, wherein the number of vertical stitches is 13 to 20 pieces Z25.4 mm, and the number of horizontal stitches is 3 to 8 pieces 25.4 mm. Extraction method.

5. The extraction method according to any one of claims 1 to 4, wherein the washing water is supplied to each section of the horizontal band type washer in a plurality of parts.

6. The filtrate produced in the first compartment is not added to the filtrate produced in the second compartment, and only the filtrate produced in the second compartment is sent to the alkaline recovery process as dilute black liquor. The extraction method according to any one of claims 1 to 5, wherein