Method to reduce power consumption in production of thermomechanical wood pulp by means of low-temperature grinding of wood pulp of low and medium concentration

FIELD: wood working industry.

SUBSTANCE: method for heat recuperation in grinding of wood pulp includes ejection of pressurised wood pulp from high-pressure refining machine; introduction of at least filtrate from pressurised wood pulp into pressurised expansion cyclone; transfer of heat from expansion cyclone to water for its heating, and usage of heated water in process of wood pulp grinding. Meanwhile wood pulp is a pressurised suspension of fibres in liquid, besides, wood pulp suspension is pressurised with 3 to 6 bar. Pressurised wood pulp is a suspension of low or medium concentration and has the temperature of not lower than 140°C in the refining machine. Expansion cyclone maintains pressure in wood pulp at the level of 3-6 bar. Heat exchanger is additionally used for heat transfer. Wood pulp is ground in pulp mill, and a separate flow from pressurised expansion cyclone is used in a separate process at pulp mill.

EFFECT: increased power consumption in process of production of mechanical wood pulp.

12 cl, 3 dwg

 

The technical field to which the invention relates.

The invention relates to the production of mechanical wood pulp, more specifically, to methods of heat recovery with this production.

The level of technology

Energy conservation in the process of obtaining mechanical wood pulp it is highly desirable from an economic and environmental point of view and can significantly improve the overall competitiveness of the pulp and paper industry.

One way to reduce energy consumption in the production process of conventional thermomechanical pulp (TMP) without reducing the quality of the wood pulp is grinding at low concentration (LC) at 70-90°C immediately after soaking in the pool wood pulp (to eliminate the twisting of the fibers). This method is usually achieved by reducing specific energy consumption by only 5-8%. Furthermore, the method usually causes a significant shortening of the fibers and the decrease in tensile strength. Chemical-mechanical wood pulp (HMM) and chemi-thermomechanical pulp (CTMP) provides significantly more opportunities for energy saving in LC-refining, since the softening temperature of lignin have lower, usually below 100°C., and more elastic fibers have a higher resistance to a greater intensity of the AZMOL and to the use of more specific energy on stage LC.

Both types of natural fibers for making paper, namely chemical wood pulp and mechanical wood pulp, have shortcomings: first (chemical) consumes a lot of wood, and the second (mechanical) consumes a lot of electricity. Power consumption when receiving mechanical wood pulp is about 20% of global energy consumption in the production of paper and is approximately equal to the consumption of electric energy by countries such as Austria and Switzerland combined.

Energy efficiency in obtaining mechanical wood pulp is low in comparison with other technological processes used in the manufacture of paper, such as pumping, drying, transport and electricity production. When discussing energy efficiency in obtaining mechanical wood pulp calculations and estimates range from 0,012% to a few percent and up to 40-60%. However, it should be assumed that the assessment of the efficiency of 40-60% wrong, because it is obvious that more than 90% of the energy milling in the production of thermomechanical pulp passes into the heat.

Less than 10% of the total energy consumed for the production of wood pulp for making paper, usually spent on division of wood into individual fibers. These individual fibers are then split (internal fibril the licensing), small particles are peeled off the middle of the plate, and the primary and secondary layers of the wall of the fiber and the remaining secondary wall are of fibrillation. At the same time fiber gain flexibility and even partially broken and separated. This is the result of many thousands of cycles of load change (contraction and relaxation). This process fatigue loading in compressible steam environment is called grinding.

Ways to improve the efficiency of the milling process in recent years has focused on optimizing the intensity of grinding, defined as the transfer of energy through shock and rapid and selective heating of the fibers to a temperature exceeding the softening temperature of lignin to make the fiber more sustainable and increase their ability to withstand tough handling. Thus, one of the newest technological strategies is that before grinding to expose the wood to effect sealing and transverse forces to create the optimum zones of separation and division in rich pulp areas of the walls of the fibers. Processing chips enzymes is another new direction of reducing electricity consumption. Optimization of intensity refining completes the increased speed of the refiner by increasing the diameter of the disk and the proper configuration of the plates of the refiner, such ka is Nerevarine displacement or turbine plate.

Disclosure of inventions

Developed original non-obvious system of milling TMM at low (LC) and secondary (MS) concentrations, at temperatures above 100°C, equal to or greater than the softening temperature of the lignin. The concentration of the pulp varies from 4% to 10%. Achieved significant energy savings when compared as a fibrous mass. The system can be used for the recovery of a significant proportion of energy spent on grinding at low and medium concentrations, in the form of high pressure steam. The system transmits heat produced by the pressurized surge cyclone water to produce steam that is fed back into the pressurized cyclone. Thus, the system allows to simplify the technological scheme of production TMM by reducing requirements for exposure in the pool and pulp filter.

In one embodiment, the pressurized suspension of wood pulp expands under pressure expansion cyclone and the suspension passes through a heat exchanger where heat from the suspension of wood pulp is passed dilution water, which is used to located above the cyclone process of refining pulp of low concentration. In another example, the pressurized slurry of wood by weight of the s dewatered under pressure in a screw press and only the filtrate from the suspension expands under the pressure of the secondary cyclone. Expanded, the filtrate flows out of the cyclone in the heat exchanger, where it heats the process water, as will be discussed later. Compressed fibrous mass is transferred from the screw press for the next stage of processing.

In one embodiment, the invention features a method of heat recovery when grinding wood pulp, including the release of pressurized pulp from the refiner of high pressure, and finding under pressure groundwood is a pressurized slurry of fibers in a liquid, and the suspension of wood pulp is under pressure from 3 to 6 bar; introducing at least filtrate from the pressurized suspension of wood pulp in a pressurized expansion cyclone and surge cyclone maintains the pressure in the wood mass at the level of 3-6 bar; the transfer of heat from the expansion of the cyclone water for heating and the use of heated water in the process of refining wood pulp.

Brief description of drawings

Figure 1 - flow chart of installation for grinding wood pulp without recovery of high-pressure steam from the expansion of cyclones.

Figure 2 - flow chart of the first installation option of grinding wood pulp with recovery of the high-pressure steam from the expansion of cyclones.

3 - those the technological scheme of the second installation option of grinding wood pulp with recovery of the high-pressure steam from the expansion of cyclones.

The implementation of the invention

One way to reduce power consumption during normal production TMM is to install speed grinding at low concentration (LC) immediately after the first and second stages of grinding at high concentration and endurance in the pool wood pulp. It was reported that when this is achieved energy savings of 5-8%, and even more without deterioration of wood pulp. Reported similar values of resistance to tearing, and sometimes even slightly higher values of tensile strength and a reduced content of fibre bundles. The reduction of electricity consumption by 5-8% in the production of wood pulp for newsprint based on the total energy use of grinding, which in this case is about 2200 kWh/T. This principle of the third step of grinding at low concentration found relatively widespread use, particularly in North America, and normally provides increasing productivity in the production of TMM. However, we need more long quest to improve energy efficiency in the production of TMP.

As far as known to the applicant, before did not know why moderate consumption of energy of the order of 80 to 90 kWh/t when grinding TMM at a low concentration achieved results similar to the results obtained with the consumption of about 270 kWh/t p and grinding at high concentration. From this point of view it is very sharp decrease in energy consumption. Similar ratios of 1:3 were obtained when comparing grinding HMM at low and high concentrations. Lower energy consumption can probably be attributed to the relatively high intensity processing in the refiner at a low concentration and other influencing factors:

1. A sufficient quantity of water at low concentration promotes the formation of hydrates and the swelling of the fibers.

2. Smaller, but homogeneous and stable clearance plate and uniform load distribution due to a very stable mass flow.

3. As a rule, more efficient transfer of energy in an incompressible medium.

When on stage LC after soaking in the pool pulp at approximately 80°C is fed more and more energy and when to increase the intensity of grinding increases the tendency to shortening of the fibers. Accepted method of tightening or easing effect shortening of the fibers is to further increase the elasticity of the fibers by heating or chemical treatment to make them more resistant to harsh handling.

The basic idea of this study is therefore in rapid heating of the fibers in the liquid phase to the softening temperature of lignin or a higher temperature and in the refining of the fibers when iscoe or average concentration. The concept for "purely" mechanical wood pulp is also supported by the known effect of the successful application of LC refining to reduce energy consumption in the production of chemi-mechanical wood pulp, because the softening temperature of lignin is reduced, usually below 100°C due to alkaline swelling and/or culturali.

Some previous attempts at high temperature grinding at low concentration was unsuccessful due to the difficulties of rapid heating of the emulsion wood pulp by means of heat exchangers. So I chose the way of direct heating with steam. Usually laboratory system TMP/CTMP, even the most modern of them, do not work under pressure at low or medium consistency pulp.

Figure 1 shows a simplified flow scheme of the experimental setup 10 companies Afocel. Recently created a pilot installation TMP/CTMP in the company Afocel (depicted in figure 1) consists of feeder chips/wood pulp 12, such as a feed hopper 14, which contains two alternately operated valves 16 and can be filled with chips of any type or wood mass in any concentration. Emulsion wood pulp coming from the conveying device can be quickly heated in the steam boiler 18 with a stirrer and sent to the 12-inch is th sealed laboratory refiner 20 Andritz Sprout-Bauer driven by a motor 22 with a variable speed power of 45 kW. Control system (not shown) provides accurate measurement and recording of energy consumption and of production for some time. Of pressurized refiner wood pulp is discharged through the exhaust valve 24 and the cyclone 26.

For testing has been used pulp from the first stage of grinding in the installation of TMM company Stora Enso Corbehem. The degree of grinding was approximately 350 ml CSF (canadian standard device). Raw was a typical mixture of 80% coniferous wood and 20% poplar. Installation of TMM in Corbehem is a two-channel three-stage system with total capacity of 480-500 absolutely dry tons per day. Three-step installation TMM at high concentrations, including waste grinding on the second and third steps of the main grinding line, consumes 2800-2900 kWh absolutely dry ton to produce wholemeal wood pulp with a beating degree of 80-90 ml CSF for paper production class LWC (Lightweight coated).

The program included the following tests:

1. Normal TMP production at a pilot plant at different values of specific energy in order to compare the energy consumption with consumption for industrial installation SE Corbehem.

2. Grinding at low concentration (4-5%) at ordinary temperature 80°C and four different values of the specific energy is Gia.

3. Grinding at an average concentration (10%) at ambient temperature of 80°C and four different values of the specific energy.

4. Grinding at low concentration similarly to 2, but after a quick heated to 140-150°C. Before grinding wood pulp was pre-heated to about 80°C in a water bath. Here also the grinding was carried out at four different levels of specific energy.

5. Grinding with a median concentration of similar to 3, but after a quick heated to 140-150°C. And in this case, wood pulp was pre-heated to about 80°C in a water bath and the grinding was carried out at four different levels of specific energy.

In all cases, wood pulp was subject to control in accordance with TAPPI standards, and determined the degree of grinding on the canadian standard instrument (CSF), tensile strength, resistance to tearing, the coefficient of light scattering and gloss. The casting was done according to international standard T. The fiber characteristics and the content of the fibre bundles were measured using MorFi analyzer. Five "final" sample pulp was also tested for residual twist fibers.

Introduction high-temperature refining LC/MC in the industry facilitates the fact that wood pulp after the first stage of grinding at high the Oh concentration present in the exhaust line at a high temperature together with a sufficient quantity of process steam for to quickly heat the dilution water required at the stage of LC/MC. To conserve heat process steam can be generated by the heat recovered from the expansion of the cyclone.

Figure 2 shows a process diagram of the first variant of implementation of the installation 30 for grinding wood pulp, which is the recovery of high-pressure steam from the expansion of cyclones. Install 30 optimization improves the overall heat balance in the installation due to the recovery of most of the energy used during LC or MS, in the form of steam.

From the outlet line 32 primary refiner under pressure (see, for example, the exhaust valve 24 and the refiner 20 in figure 1) fibrous wood pulp is fed in under pressure cyclone 34, which is sealed below the water trap or separator 36 of the liquid phase. The liquid phase separators are used on some installations TMM in North America. In the upper part of the cyclone 34 par 38 is separated from the fibers and is routed to a heat recovery system (not shown). The steam part 38 can be used for heating to approximately 140°C dilution water, which is served in a water trap at the bottom of the cyclone.

A water stopper 36 hot wood pulp at a concentration of about 4-5% is pumped into the refiner 40 low concentration. The refiner can potrebi shall be approximately 150-250 kWh/T. Most of the energy milling is converted into heat which raises the temperature of the pulp in the refiner 40. Hot wood pulp is discharged from the refiner in under excessive pressure surge cyclone 42, where practically do not contain fiber pairs 44 is removed until the temperature in the expansion cyclone equal approximately to the temperature in under pressure in the cyclone 34.

Wood pulp, usually comes into the expansion cyclone 42 under pressure from 3 to 6 bar. Under the pressure of the expansion cyclone supports a relatively high pressure in the wood mass, for example 3-6 bar to provide steam to escape from the cyclone at high pressure and high temperature. Steam energy is regenerated, for example, through a heat exchanger that generates pure steam for under pressure of the cyclone. Expansion cyclones, known from the prior art, in contrast, generally operate at atmospheric pressure, and the steam from the cyclone is simply released into the atmosphere and is not used or is used to heat water to a relatively low temperature, for example up to a maximum of 90°C.

Discharged from the expansion of the cyclone wood pulp 46 passes through the heat exchanger 48, giving thermal energy to the process water 50, also proteleuse is through the heat exchanger 48. Pressure wood pulp emerging from the expansion of the cyclone, is controlled by the valve. This valve can automatically maintain the set manually to a fixed value of pressure is selected so that the pressure and the steam temperature consistent with the purpose for which is generated in the expansion cyclone pairs.

Using the described method and installation, you can use steam, for example, in a paper machine for drying, where usually applied pressure up to 3 bar. Hot process water flows through the pipe 52 to the cyclone 34, in which the dilution water is supplied under pressure in a pressurized water gate 36. Chilled wood pulp 54 of the heat exchanger 48 enters the pool 56 for further processing, for example, the final removal of twisting fibers and filtering.

In the grinding installation LC 30 shown in figure 2, which finds under pressure emulsion wood pulp expands under pressure expansion cyclone 42, and then passes through the heat exchanger 48, in which the heat from the emulsion is passed dilution process water 50 that is used to located above the cyclone 34 process of refining wood pulp LC. In the example shown in figure 3, the grinding install MS 58 directs finding the Yuexiu under pressure emulsion wood pulp from the refiner 40 in the screw press 60, under pressure dehydrate the emulsion. The filtrate from 64 emulsion expands under pressure expansion cyclone 42, and compressed wood pulp 63 of the screw press is transmitted to the other stages of the process. Advanced filtrate from the expansion of the cyclone 42 is supplied to the heat exchanger 48 where it heats the process water 50, which is supplied to the water gate of the cyclone 34.

Figure 3 shows the process scheme of the second variant of implementation of the installation 58 for grinding wood pulp, which is the recovery of high-pressure steam from the expansion of cyclones. To the extent that the installation of 58 figure 3 has common elements with the installation of 30 presented in figure 2, these are common to both figures, the elements denoted by the same numbers.

Technological scheme of figure 3 depicts different from that shown in figure 2, the process further includes the washing of the pulp. The process implemented on the unit 58 and is presented in figure 3, can be applied in the refining process at a mean concentration (MS), and the process implemented at the facility 30 of figure 2, is in the process of grinding at low concentration (LC). The difference between these two processes is that the process implemented at the facility 30, wood pulp prog is the CIO through the expansion of the cyclone and the heat exchanger, and in the process implemented at the facility 58, no.

In the process implemented at the facility 58 under pressure emulsion wood pulp flows from the pressurized cyclone 34 with water bolt 36 and preferably pumped at a mean concentration (MS) in the refiner 40. Of refiner groundwood MS enters the screw press 60, provided with a casing 62 for collecting the compressed mass. Hot pressed wood pulp 63 in the form of fiber is discharged from the screw press and fed to further processing. For example, hot groundwood 63 extending from the screw press at a concentration of 30-35%, can be mixed with the heated "white water" and pumped to filter after processing twisting the fibers.

The filtrate 64 of the screw press is fed in under pressure in the expansion cyclone 42. The filtrate is essentially water that is extracted from the emulsion wood pulp in a screw press. The filtrate may be under pressure, for example, ranging from 3 to 6 bar. Under pressure from the filtrate 46 flows from the expansion of the cyclone 42 in the heat exchanger 48, in which process water 50 is heated to a temperature required for dilution under pressure cyclone 34. Partially cooled filtrate 66 leaves the heat exchanger and can b shall be returned to the refining process or after further cooling "white water" partly aimed at cleaning, because it contains most of COD generated in the TMP. The energy transferred to the suspension of wood pulp in the refining process when MS (inasmuch as it is in the form of heat passed into the filtrate), regenerated from the expansion of the cyclone in the form of steam 44 and the heated filtrate.

Technological scheme presented in figure 2 and 3 provide a simple mass balance and energy. Both processes provide a significant reduction of energy consumption thermochemical grinding fibrous mass and make possible the recovery of energy expended when LC or MS grinding, in the form of steam, suitable for drying paper. The second process that is implemented at the facility 58, requires much capital because it needs a screw press, but imposes lower requirements for heat exchange between the effluent and process water compared to the heat transfer between the wood mass at low concentrations and process water in the process implemented at the facility 30. The second process, in addition, provides an additional advantage of the ability to effectively flush wood pulp.

Description method and device included in the accompanying document "Energy efficiency in the production of TMP by high-temperature refining at low and medium concentration, t is decomposing part of this application.

Although the invention is described with reference to the options that are currently the most feasible and preferred, it should be borne in mind that it is not limited to the described variants of implementation, but rather covers various modifications and equivalent devices, as appropriate for the nature and volume formulas.

1. Method heat recovery with the grinding wood pulp, comprising the following operations:
the release of the pressurized pulp from the refiner of high pressure, and wood pulp is a pressurized slurry of fibers in a liquid, and the suspension of wood pulp is under pressure from 3 to 6 bar;
introduction at least filtrate from the pressurized pulp in a pressurized expansion cyclone and surge cyclone maintains the pressure in the wood mass at the level of 3-6 bar;
the transfer of heat from the expansion of the cyclone water to heat it, and
the use of heated water in the process of refining wood pulp.

2. The method according to claim 1, wherein the wood pulp is supplied from the refiner directly into pressurized expansion cyclone.

3. The method according to claim 1, characterized in that the heat transfer in addition use a heat exchanger receiving dasouza under pressure from the wood pulp of pressurized expansion cyclone and dilution water.

4. The method according to claim 3, characterized in that the heat transfer in addition use a heat exchanger receiving the wood pulp from the expansion of the cyclone and dilution water, and heated dilution water is fed in under pressure cyclone, located in front of the refiner.

5. The method according to claim 4, characterized in that the dilution water is fed into a water trap cyclone.

6. The method according to claim 1, characterized in that the pressurized groundwood is a suspension of low concentration and has refiner temperature not lower than 140°C.

7. The method according to claim 1, characterized in that the pressurized wood pulp has a concentration of fibers in the suspension of wood pulp, comprising from 4 to 5%.

8. The method according to claim 1, characterized in that the pressurized groundwood is a suspension medium concentration and has refiner temperature not lower than 140°C.

9. The method according to claim 1, characterized in that the pressurized groundwood has a fiber concentration of at least 10% in a liquid suspension, and optionally remove the filtrate from the suspension in the press, unload the filtrate from the press in the expansion of the cyclone and discharged compressed wood pulp concentration of fibers constituting from 30 to 35%.

10. The method according to claim 1, characterized in that miss j is muusa under pressure wood pulp through a screw press to extract separately the filtrate from the slurry and compressed wood pulp, the filtrate is injected into the expansion cyclone.

11. The method according to claim 1, characterized in that the grinding wood pulp is carried out on wood-pulp factory, and a separate stream of pressurized expansion cyclone is used in a separate process on wood-pulp factory.

12. The method according to claim 4, characterized in that the grinding wood pulp is carried out on wood-pulp factory, and a separate stream of pressurized cyclone is used in a separate process on wood-pulp plant.



 

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EFFECT: increased efficiency of method.

12 ex, 1 tbl, 1 dwg

FIELD: textile, paper.

SUBSTANCE: method relates to production of mechanical or chemical-mechanical wood pulp applied as raw material for manufacturing of paper or cardboard, and may be used and pulp and paper industry. According to this method wood pulp is exposed to fibrillation. Produced wood pulp is screened to separate wastes from acceptable materials. At the same time wastes are removed in amount of maximum 60% of overall amount of wood pulp. Wastes and acceptable material are bleached separately. Wastes are bleached with the help of peroxide or peroxy acid. After that bleached wastes are mixed with bleached acceptable material. After combination they are exposed to finishing grinding, at the same time amount of consumed energy makes approximately 10-1000 kW-hr/ton. Finishing grinding is carried out at low concentration. Then wood pulp is batched into paper- or cardboard-making machine. Wastes are bleached in alkaline medium.

EFFECT: improved strength of wood pulp and reduction of energy consumed for grinding.

12 cl, 1 dwg, 1 ex

FIELD: engineering industry.

SUBSTANCE: device includes housing installed on shock absorbers and rotor hinged to it, the working surfaces of which are made in the form of flattened circular cones, which differs by the fact that lower rotor base is made in the form of ellipse formed with sectional plane passing through lower point of generatrix of side rotor surface and inclined to base plane at an angle of α=15°…45°.

EFFECT: providing optimum condition which is determined by giving variability to width and area of crescent outlet gap during rotor rolling motion, possibility of providing optimality of values of these parametres, provided that generatrixes of side surfaces of rotor and stator, which are opposite to outlet gap, are mated.

1 dwg

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