Method of delignification of wood chips in manufacturing of cellulose

FIELD: textiles, paper.

SUBSTANCE: method of delignification of wood chips is carried out in the digester during turbulisation of the pulp. For this a limited along the length fragment of the area of the brewing process in the digester is chosen, which is over the entire cross section of the stream of pulp is divided into a series of parallel and independent streams, in each of which turbulisation is created. The latter is carried out by periodic changes in the volume of each of the streams, which is implemented due to changes in cross-sectional area of these streams.

EFFECT: significant acceleration of delignification process, decrease in temperature of technological zones and pressure in them, and the reduced specific energy consumption of pulping, increased productivity of plants, weight and size characteristics of the digester are reduced several times.

3 cl, 1 dwg, 1 ex

 

The invention relates primarily to the pulp and paper industry, and more particularly to a method of obtaining three-dimensional pulp used for the manufacture of paper for various purposes and boards. In addition, it can be used in chemical, petrochemical, food and medical industries, as well as in the recycling of agricultural production and wastewater treatment.

The known method of delignification of wood chips in the production of pulp in the process of slow cooking in a continuously operating facility of the company "Kamyur". The main element of the installation is the digester cylindrical performance 450-500 tons per day, with a diameter of 4.7 m and a total height of 45 meters. In the digester installed screen belt. The height of the boiler there are three temperature zones: welding, melting and diffusion washing. Pulping in continuously operating boilers "Kamyur" is when completely filled with liquor digester and excessive hydraulic pressure (0.1-0.2 MPa higher than the pressure corresponding to the boiling temperature of the cooking solution). Working pressure in the boiler, thus, is equal to 1.0-1.2 MPa. The applied method allows to prevent boiling of the liquor and thereby create different temperatures in the haunted zone, the height of the boiler. After removal of chips of metal inclusions she enters the steam chamber. Chips proprivate pairs boiling generated in the cyclone evaporator, and fresh steam of low pressure. The pressure in the steam tank 0.06 to 0.17 MPa, temperature 105-120C. the steaming for 5 minutes. The air displaced from the chip, and a pair of turpentine from the steam tank with pairs boiling up from the cyclone evaporator is directed to heat-trapping unit (condenser) and further processing. Steamed chips from the tank enters the feeder high pressure rotary type, which provides power to the boiler wood chips and simultaneously a shutoff valve that separates the high-pressure boiler (1.0 to 1.2 MPa) from the area of low pressure in the steam chamber (0.07 to 0.15 MPa). After loading the rotor rotates in a horizontal position and chips washed away from the drive to the feed pipe liquor supplied by a high pressure pump. Liquor carries the chips in the boot device digester. Chips from the feed pipe is fed to the welding, and the excess liquor is filtered and returning the pump to the feeder high pressure. Necessary for cooking the amount of white and black liquor are served by pumps in the upper part of the boiler. The ratio of their strictly reguliruetsya under its own weight slowly moves downward and pass through the welding zone, melting and changed into the pulp suspension, zone diffuse leaching. At the beginning of the welding zone temperature is maintained at 115C (coming steamed wood chips and hot liquor). Advancing chips to sitonomy zone temperature rises to 150C due to the heating in the heater continuously circulating through him liquor. The last being sucked into the pump from the top sieve and passing the heater is returned in the same area. To a final temperature of cooking 170-172C continuously circulating liquor is heated in another heater. Liquor is drawn by the pump from the level of the sieve downstream relative to the first sieve and is also returned in this area. For washing pulp in the lower part of the boiler is served weak black liquor to a temperature not higher than 80C, which moves from the bottom up to meet the descending mass. Weak liquor, excluding black liquor, he gradually becomes stronger and is heated. Superseded strong black liquor is collected in the area of the screening zone, located in the lower part of the boiler, with a temperature of 160-170C. To prevent sudden drops of temperature rising liquor is first heated in a heat exchanger to 140-150C. the Pulp at the bottom of the digester is cooled weak liquor to a temperature of 80-85C, boiling is stopped and at a concentration of 14-16% after discharge elimination of the ETS the pulp enters the blowing device and then to the blow tank. Strong black liquor enters the cyclone evaporator. A pair of flashing going on steaming of wood chips. The cooking time of the pulp in the boiler 4.5 hours, with the time passing wood chips area of welding 1.5 hours, areas of cooking for 1.5 hours, the zone of leaching 1.5 hours.

The main disadvantage of the cooking process in plants "Kamyur" is high energy and material equipment at low production in the digester (the diameter of the boiler with the daily capacity of 450-500 tons is 4.7 m and the total height of 47 meters). This situation is a consequence of the General conservative approach to the pulping process, in which the movement of the pulp is carried out under the action of gravitational forces, and the change in technological regimes worked for years, it is not currently possible. This is confirmed by the fact that the need to increase productivity is associated with an adequate increase in the volume of the digester. So, with daily capacity of 1,200 tons, the diameter of the boiler is increased to 6-7 m, and the height reaches 80-85 m

Promising in comparison with similar looks way delignification of wood chips almost any real thickness, which is achieved by the use of turbulence in the pulp mass in the cooking process. Hardware design shown in the last example, acid-saloon the th cooking, where used continuously active pulsation apparatus of the vertical type [VNIIM, Technology pulp and paper manufacture, volume 1, published Polytechnic University, St. Petersburg, 2003]. The design feature is that the height of the hollow column through certain intervals are fixed to the plate-shaped nozzles), which covers all the free section of the column. The plates have rectangular openings of small cross section, provided with a rectangular vanes. In the column provided for cylindrical pipes to move the chips from the plate on the plate from top to bottom. Oxygen is supplied to the lower part of the column and moves upward, i.e. counter-current relative to the direction of movement of the chips. In a steady process apparatus is completely filled with a mass of pulsating under the action of the pulsator connected to the lower part of the column. When oxygen is dispersed into small bubbles on each plate, passing through her holes up, aided and a layer of wood chips that are on it. From the pulsator to the liquid filling the column is constantly transmitting reciprocating motion in the vertical direction. The guide blades have small holes plates add to this vertical reciprocating movement and rotational structure is shining, which changes its direction on each plate, because the blades on adjacent plates in opposite directions. The movement from the fluid is transferred to the chips. As a result, the oxygen is dispersed on each plate over the entire cross section of the column, which creates very favorable conditions for the external mass transfer. Due to this, in the whole volume of the apparatus, the oxygen concentration in the liquor is close to equilibrium. Constant intense pulsating hydrodynamic effects on the chips, the friction of the strands about each other lead to the separation svalivshihsya fibers of the surface layer, delignification when cooking in the first place. When this chip is exposed new reaction surface. Svalivshiesja fibers fall into the same hole through which the bottom-up moves oxygen, is continuously removed from the apparatus with the flow of the circulating liquor and separated from him in a special discharge device. Partially cooked chips through nozzles located at the edges of the plates is moved downward until the complete transformation into the cooked fiber. The required degree of delignification of the pulp, in which the fibers are separated from the chips, is governed by the values of the factors of cooking, of which the main is the intensity of the pulsations, characterized by the work of daunosamine (in mm) on their frequency. This index is in the range of 1000-4000 mm/min

Turbulization or imposition of pulsations on the pulp mass in the digester and certainly theoretically and practically should lead to the intensification of the process of cooking.

However, the technology of turbulence, proposed in the above method does not achieve the full effect of the activation of physical and chemical processes that occur while cooking. The reason for this is the fact that the pulsation generated in the lower part of the boiler by means of the relevant system, even at low altitude digester will fade effect significant hydrodynamic resistance of pulp. The process of decay will also contribute to the compressibility (looseness) of the chip and the presence of the Poppet nozzles located along the height of the digester, which, in spite of through-perforations are purely physical obstacle to the spread of pulsations. On the other hand, the meaning of the pulsations is not in the usual creation of wave process in the pulp mass, and in its movement in the digester at a certain distance (20-30 mm) to improve the efficiency of delignification of wood chips from the interaction with the Poppet nozzles. This means that the pulsator must have sufficient power to lift "post" pulp on videocase the Noe distance. The weight of a pillar, in particular, in the above described apparatus Kamyur" reaches more than 300 tons. And when you consider that the drive pulsator in addition to the rise of "post" overcome hydrodynamic resistance must be calculated and to overcome inertia loads, then the total drive power of the pulsator can reach hundreds of kilowatts.

Thus, the proposed method delignification of wood chips, involving the imposition of pulsations on the pulp mass in the entire volume of the cooking space of the boiler is not able to solve the task efficiently and hardly will find practical application due to limited capacity, which is constrained by disproportionate growth of energy consumption for the organization of turbulence. In addition, it should be noted and significant structural complexity pulsation equipment.

Thus, the object of the invention is to increase the efficiency of turbulence in the pulp mass in the cooking process while simplifying the construction of the necessary equipment and reduction of the required energy consumption.

The problem is solved due to the fact that in the method of delignification of wood chips in the production of pulp, including the cooking process in the boiler, followed by the turbulization pulp, distinguish, at least, one is limited by the length of the fragment of the zone melting process in the boiler, mainly the actual cooking, which throughout the cross section of flow of the pulp is divided into a number of parallel and independent from each other flows, each of which create the turbulization. The last organized by periodically changing the volume of each of the independent streams within the selection zone of the cooking process. The volume change of each independent thread carried out by changing the cross-sectional area of the stream.

Attached to the description of the drawing given a schematic representation of a fragment of the zone melting process in the boiler when the flow of pulp is divided into a number of independent threads.

In the drawing illustrating the proposed method is depicted: the digester 1, the pulp 2, a fragment of the 3 zones of the cooking process in the boiler 1, movable in the transverse direction of the plate 4-7, located in the fragment 3 throughout the cross-section of the digester, independent, parallel threads 8 pulp 2, formed by plates 4-7, wood chips 9, the arrows 10 indicate the direction of movement of the pulp in the digester, the arrow 11 indicates the direction of movement of the plates 4-7, which provides the change in cross-sectional flow 8.

Implementation of the proposed method for the delignification of wood shch is dust on the example of slow cooking in a continuously operating facility "Kamyur", described above

The location of the fragment of the 3 zones of the cooking process selected area actually boiling in the boiler 1, located below the zone of welding and the upper sieves (not shown). After the pulp 2 drops under the action of gravitational force in the direction of arrow 10 and will be in the area of cooking, it will go to frame 3. The total flow is divided into a number of independent and parallel threads 8 formed by the movable plates 4-7, the length of which is chosen experimentally. Each of the plates 4-7 mounted in the boiler 1 with a reciprocating movement, so that the even-numbered plates (4, 6) perform an oscillatory motion in the direction opposite to the oscillation of odd plates (5, 7). This character of the mutual displacements of the plates leads to the fact that the cross-sectional area of each of the threads 8 varies with frequency, and this, in turn, leads to a periodic change in the volume of these flows. The minimum change in cross-sectional area of each of the threads 8 can be recommended level of at least +/- 5% of the original area or cross-sectional area of flow outside (stationary) state. Thus, there is a local pressure fluctuations in the flows of 8, i.e. volumes, limited movable plates. Given the low total is korost move the pulp within the digester 1, the pressure fluctuations in independent threads 8 will cause a considerable amount of hydrodynamic disturbance (turbulization), which will find expression in the phenomenon of "high tide - low tide", but made for a very short period of time, for example one second, which corresponds to oscillatory process a frequency of one Hertz. The proposed method provides the pressure fluctuations in the flow 8 with frequencies of tens of Hertz, which implies a very high degree of turbulence in the pulp mass. Next, wood chips 9, the past treatment of steaming and brewing, if it happened in one of the threads 8 are exposed to the active turbulence arising from local high-speed flow of a liquid medium during the aforementioned "tides" in the threads 8. This leads to a significant intensification of the process of separation svalivshihsya fibers of the surface layer and exposure of new reactive surfaces. An equally important factor that accelerates the delignification process is the impact on chips variables pressure, changing in a positive asymmetric cycle. Taking into account the working pressure in the digester at 1.0-1.2 MPa oscillatory motion of the plates will contribute to the creation of the fluctuation of pressure in the threads 8.

It should be noted that the pressure drop in the end is th result depends mainly on the amplitude of oscillation of the plates, frequency fluctuations and hydrodynamic resistance of the walls of the channels independent 8 threads.

Wood chips has a deep structure with a significant number of closed cavities especially when its in the zone of welding. The impact of the variable component of the pressure in the liquid medium surrounding the chips, changes its geometrical dimensions, causing the alternating internal threads of alkali and result in the leaching of lignin from the internal channels of the chip.

Changing the geometric dimensions of the chips to the beat of pressure changes affect the internal communication chips. However, as with any material object, the action of variable loads has a damaging effect due to the manifestations of fatigue phenomena, dramatically reducing the strength of internal connections.

Given the circumstances contribute to a significant intensification of the process of separation and delignification of wood chips during cooking of cellulose. The proposed method is applicable also in other technological operations in the production of pulp, such as bleaching, finishing, etc.

Simple calculations show that the criterion used in the method prototype to characterize the efficiency of delignification in the case of turbulence in the pulp mass can be increased, as is inimum, on order and can reach 40000-70000 mm/min and even more (prototype - from 1000 to 4000 mm/min).

The proposed method of intensification of pulping process pulp can significantly reduce the temperature of the process zones, and hence the pressure in them. When you do this 2-3 times can be reduced specific energy consumption pulping, 1.5-2 times higher performance installations, as well as the application of the proposed method makes it possible to reduce the weight and dimensional characteristics of the digester.

1. The way delignification of wood chips in the production of pulp, including the cooking process in the boiler, followed by the turbulization pulp, characterized in that allocate at least one limited by the length of the fragment of the zone melting process in the boiler, mainly the actual cooking, which throughout the cross section of flow of the pulp is divided into a number of parallel and independent from each other flows, each of which create the turbulization.

2. The method according to claim 1, characterized in that the turbulization create by periodic changes of the volume of each of the independent streams within the selection zone of the cooking process.

3. The method according to claims 1 and 2, characterized in that the volume change of the independent flow carried out at the expense of the ISM is in the cross-section of this thread.



 

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