阅读说明：本技术 将木屑馈送到预水解反应器的方法 (Method for feeding wood chips to a prehydrolysis reactor ) 是由 马可·安德拉德 罗尼·盖格 韦萨·凯帕伊宁 奥沃·凯图纳 彼得里·塔扎沃里 维里蒂纳·维亚 于 2019-10-02 设计创作，主要内容包括：本发明涉及一种用于在生产溶解纸浆时将碎屑和液体组成的浆料馈送到预水解反应器的方法。通过使用至少一个泵,将该浆料泵送到所述反应器,并且,将碱馈送到所述至少一个泵5,以将所述浆料的pH调节到7到10的范围。(The present invention relates to a method for feeding a slurry of chips and liquid to a prehydrolysis reactor when producing dissolving pulp. The slurry is pumped to the reactor by using at least one pump, and a base is fed to the at least one pump 5 to adjust the pH of the slurry to the range of 7 to 10.)

1. A method for feeding a slurry of chips and liquid to a pre-hydrolysis reactor when producing dissolving pulp, in which method the slurry is pumped to the reactor by using at least one pump, characterized in that alkali is fed into the at least one pump to adjust the pH of the slurry to the range of 7 to 10.

2. The method according to claim 1, characterized in that alkali is fed to the inside of the pump.

3. A method according to claim 1 or 2, wherein the alkali is fed between the pump housing and the pump impeller.

4. Method according to claim 1, 2 or 3, characterized in that the pump is a centrifugal screw pump provided with a liner, wherein alkali is introduced into a gap or channel between the impeller and the liner.

5. The method according to any one of claims 1 to 4, wherein the pH is in the range of 8 to 9.5.

6. A method according to any of claims 1 to 5, wherein base is directed to the pump through a conduit and an opening in a wall of the pump housing.

7. The method of any one of claims 1 to 6, wherein the impeller is turned on or off.

8. The method according to any one of claims 1 to 7, wherein the base is white liquor or oxidized white liquor.

Technical Field

The present invention relates to a method for hydrolytic treatment and cooking of cellulosic fibre material, preferably wood chips. In particular, the present invention relates to a method of feeding a slurry of chips and liquid to a pre-hydrolysis stage.

Background

In conventional systems, wood chips (or other cellulosic or fibrous material) are subjected to hydrolysis in a first reactor vessel prior to introduction into a second vessel (e.g., a digester). One such system is described in US 20080302492. The wood chips are introduced from the chip feed assembly to an upper inlet in the pre-hydrolysis reactor vessel where the chips are hydrolyzed in an upper region of the reactor vessel by adding pressure and heat energy to the vessel. The hydrolysate is extracted from the cellulosic material through an extraction screen below the upper zone and in the first reactor vessel. A wash liquid is introduced into a lower region of the first reactor vessel where the wash liquid inhibits hydrolysis of the cellulosic material in the lower region. The washing liquid flows up through the cellulosic material to the extraction screen. The treated material is discharged from the lower outlet of the reactor vessel and introduced into a digester to digest the material, thereby producing pulp.

The high pressure in the conveying means typically provides the force to move the chips up to a top separator located at the top of the pre-hydrolysis reactor and to raise the pressure of the feed to substantially above atmospheric pressure. Such as sold by Andritz GroupThe conveying means may be one or more centrifugal pumps arranged in series. From these pumps, the feed and liquid are moved to a top separator in the upper region of the prehydrolysis reactor vessel.

In a continuous prehydrolysis kraft cooking process, water is typically only fed to the chip feed system to provide sufficient liquid to allow the chips to pass over the inverted top separator, successfully being transported into the prehydrolysis vessel. Since the crumb is weakly acidic after cooking in the crumb silo, the pH in the feed cycle is typically about 5. With regard to pre-hydrolysis, it is important to avoid the presence of an alkaline source in the feed system, as this slows down the acidic autohydrolysis reaction. It has been found that a weakly acidic pH has a negative effect on the operation of the debris pump. Under acidic conditions, needle-like debris can accumulate between the impeller and the liner of the debris pump, and the needle-like debris does not soften as under strongly alkaline (pH 12-14) conditions, such as in kraft cooking systems. The accumulated hard needle-like debris begins to create friction and wear on the impeller and bushing, which is indicated by an increase in pump motor load. In acidic pre-hydrolyzed kraft cooking systems, the wear rate of the crumb pump is typically 5 to 10 times faster than in alkaline kraft cooking feed systems.

Disclosure of Invention

It is an object of the present invention to provide a method and system in which the wear rate of a debris pump can be reduced.

According to the present invention, the pH level in the pre-hydrolyzed kraft cooking feed system is raised to a range of 7 to 10, preferably 9.5 of 8, by the addition of white liquor or other alkali to prevent debris pump wear. Preferably, the base is added directly to the one or more debris pumps.

It has surprisingly been found that even very weakly alkaline conditions improve this from the point of view of pump wear. At pH levels of 8 to 9.5, the wear of the debris pump is already greatly reduced. At the same time, a very small amount of base is required to increase the pH of the feed system to the above-mentioned levels, and the negative impact on self-hydrolysis is very small. Thus, by maintaining the pH of the feed cycle at a level of 7 to 10, preferably 8 to 9.5, by adding small amounts of alkaline chemicals to the feed system, the wear rate of the debris pump can be significantly reduced without significant interference in the pre-hydrolysis stage.

Essentially any alkaline chemical can be used for pH control, but white liquor or oxidized white liquor is optimal since these chemicals are already available in (pre-hydrolyzed) kraft pulp mills. The alkali can be diluted with water fed into the feed system.

The base is added to the interior of the pump in which the crumb slurry flows. Preferably, the base is added between the pump housing and the pump impeller. The pump housing is provided with a conduit and an opening for introducing a base to the pump. The pump is typically a screw-type centrifugal pump having a housing including a conical suction housing portion, a spiral housing portion, an inlet opening, and an outlet opening. The impeller may be opened or closed. The closed impeller is provided with a conical shroud fixed to the outer periphery of the screw blades. The pump may further be provided with a liner between the suction housing and the impeller.

If the pump is provided with a liner, the preferred point of feeding the lye is the gap or channel between the pump impeller and the liner. In this case, the critical part of the pump encounters the highest alkali concentration. This minimizes wear.

The debris feed system may include one or more pumps for feeding debris. Two or more pumps may be connected in series or in parallel. The base is typically added to the first pump in the direction of the debris flow. The base may also be added to the other pumps after the first pump.

Drawings

FIG. 1 is a schematic view of a continuous pulping system having a crumb feed, a hydrolysis reactor, and a continuous digester reactor to which the present invention may be applied.

Fig. 2 shows a side view of a screw-type centrifugal pump for debris pumping.

Fig. 3a, 3b and 3c show partial cross-sectional views of a screw-type centrifugal pump.

Detailed Description

In a dual reactor vessel system, steam is introduced into the top of both vessels for heating and pressurization purposes. Hydrolysis occurs in the first reactor vessel. An extraction screen in the first reactor vessel removes the hydrolysate as the wood chips introduced at the top of the first vessel travel through the vessel and reach the lower extraction port of the vessel.

The second reactor vessel is a continuous digester vessel, such as a vapor phase or vapor phase digester. The first and second reactor vessels may be substantially vertical and have a height of at least 30 meters (e.g., 50 to 70 meters), an inlet in an upper portion of the vessel, and a discharge near the bottom of the vessel. The thermal energy added to the reactor vessels may be pressurized steam at or above atmospheric pressure.

Fig. 1 is a schematic diagram of an exemplary chip feeding and pulp processing system having a chip feeding system 24, a first reactor vessel 10 (hydrolysis reactor), and a continuous pulp digester 12. The first reactor vessel includes an inverted top separator 14 that receives a slurry of cellulosic material and liquid from a conventional chip feed assembly 24 via chip feed line 26.

These chips are conveyed through a chip feed line 11 and fed via a screw conveyor 13 to a chip bin 16. The crumb silo 16 may be a conventional crumb silo such as that supplied by Andritz Group (Andritz Group)And a scrap bin. Low pressure steam may be added to the crumb silo via a steam line so that the temperature and pressure of the crumb in the crumb silo may be controlled.

The crumb bin 16 is connected to a twin screw crumb meter 18 and a crumb trough 20. Hot water is added to the chips in the chip chute 20 via conduits 28 and 30 to form a slurry of chips.

The separated liquid exiting the overhead separator 14 and extracted to the conduit 30 may be mixed with hot water. The mixture flows through conduit 30 to the crumb tube 20. The mixture of liquid and hot water 28 exiting the overhead separator 14 is controlled to a temperature below the normal hydrolysis temperature of the chips (e.g., preferably 170 c). The temperature of the water and liquid discharged from the top separator is preferably in the range of 100 to 120 ℃.

To feed the chips to the first reactor vessel, a slurry of cellulosic material is fed via one or more pumps 22, such as TurboFeed sold by Andritz Group^TMSystem) was pumped to the top separator of the first reactor.

The first reactor vessel 10 may be controlled based on one or both of pressure and temperature in the vessel. Pressure control may be achieved by using a controlled flow of steam via steam line 32 or additionally using an inert gas added to the first reactor vessel. The gaseous upper region in the first reactor vessel is above the upper level of the chip column.

The steam in line 32 is supplied at a temperature above the normal hydrolysis temperature (e.g., 170 ℃) to enable hydrolysis to occur in the cellulose pulp in the first reactor vessel. Steam is added in a controlled manner, which at least partially promotes hydrolysis in the first reactor vessel. Steam is added, for example, to the vapor phase of the vessel, via line 32 at or near the top of the first reactor vessel. The steam introduced into the first reactor vessel raises the temperature of the cellulose pulp to or above the normal hydrolysis temperature, for example above 150 ℃.

The cellulosic material slurry fed to the inverted top separator 14 in the first reactor vessel may have excess liquid to facilitate flow through the transfer conduit 26. Once in the vessel, excess liquid is removed as the slurry passes through the top separator 14. Excess liquid removed from the separator is returned to the chip feed system via conduit 30, e.g., to chip pipe 20 and reintroduced to the slurry to convey the cellulosic material to the top of the first vessel.

The overhead separator 14 discharges the fines or other solid cellulosic material into the liquid phase of the first reactor vessel (below the upper fines column). The top separator pushes the material from the top of the inverted separator 14 and into the gas phase. The pushed out material may fall through the gas phase in the vessel and fall into the upper column of chips and liquid contained in the first reactor vessel. The temperature in the gas phase (if such a phase is present) and in the first reactor vessel 10 is at or above the normal hydrolysis temperature, for example at or above 170 ℃. A slurry of cellulosic material gradually flows downwardly through the first reactor vessel. As the material progresses through the vessel, new cellulosic material and liquid is added to the upper surface from the top separator.

Hydrolysis occurs in the first reactor vessel 10, where the temperature is maintained at or above the normal hydrolysis temperature. By adding acid, hydrolysis will occur at lower temperatures (e.g. below 150 ℃), but preferably hydrolysis occurs at elevated temperatures above 150 ℃ or 170 ℃ using only water from the top separator of the first reactor vessel and recycled liquid. The hydrolysate is removed by means of an extraction screen 36 or a set of multiple heights of extraction screen 36. An extraction screen (not shown) may be located in the bottom region of the reactor 10, wherein hydrolysis occurs substantially above the screen. In fig. 1, an extraction screen 36 is provided in the upper portion of the reactor to allow less treated hydrolysate to be removed from the reactor. The retention time in the hydrolysis stage is typically 60 to 80 minutes before extraction, but in figure 1 the screen 36 is in place after 10 to 40 minutes, preferably 20 to 30 minutes of retention. The hydrolysis reaction is completed below the screen 36. There may be an additional screen below screen 36 to remove the hydrolysate.

The hydrolysate is a product of hydrolysis. The hydrolysate is removed by an extraction screen 36 and fed to a conduit 38. The hydrolysate or a portion thereof may be recovered by conventional hydrolysate recovery systems.

The amount of liquid added to the crumb slurry in the crumb grooves 20 may be controlled to avoid excessive changes in the pH of the crumb slurry, for example to avoid rendering the slurry too alkaline or too acidic. The addition of liquid to the cellulosic material in the crumb pipe 20 helps to convey the crumb slurry material through the crumb pump 22 and through the crumb slurry conduit 26 which extends between the crumb tank 20 and the top separator 14 of the first reactor vessel 10.

The treated chips are discharged through the bottom 34 of the prehydrolysis reactor vessel 10 and sent via a chip transfer conduit 40 to a top separator 42 of the digester vessel 12 (e.g., a continuous digester), e.g., to an inverted top separator.

Additional liquid from line 48 may be added to the bottom of the first reactor vessel. The additional liquid may be withdrawn from the overhead separator 42 of the second reactor vessel 12. This additional liquid may be recirculated by pumping (via pump 50) to the bottom 36 of the first container as part of the liquid used to assist in the evacuation of debris from the first container. White liquor is added via lines 44 and 46 to conduit 48 and further to the bottom of the first reactor.

Steam may be added to the top of digester 12 via conduit 52.

Cooking chemicals (e.g., white liquor 44) are added to the top of the second reactor vessel 12, for example, to an inverted top separator 42. A portion of these cooking chemicals may be introduced into recycle line 48 to extract liquid from the overhead separator and add the liquid to the bottom of the first reactor vessel. White liquor is added to the top separator of the second reactor vessel 12 to facilitate mixing of the white liquor with the cellulosic material in the separator, and the mixture of material and white liquor is then discharged from the separator to the second reactor vessel.

The temperature in the cooking vessel 12 is raised and controlled by adding medium pressure steam 52 and possibly also air or inert gas. The cooking vessel may be a vapor phase or hydraulic compatilizer operating at a pressure of: this pressure is in equilibrium with the pressure in the prehydrolysis reactor vessel 14. The pressure at the bottom of the pre-hydrolysis reactor vessel is a combination of the medium steam pressure in vessel 14 and the hydraulic pressure of the chips and liquid column. The combined pressure is greater than the pressure at the top of the cooking vessel, which may be at the pressure of the medium pressure steam 52. The pressure differential between the bottom of the prehydrolysis reactor vessel and the top of the digestion vessel moves the feed through line 40. Further, in the case of a hydraulic digester cooking vessel, a heating cycle may be used to heat the feed to the desired cooking temperature.

The cooking vessel 12 may have multiple zones of parallel flow and counter flow. The upper cooking zone 54 may allow for parallel flow of feed and liquid. A portion of the black liquor is extracted through a screen 62 at the bottom of the upper cooking zone. The extracted black liquor flows through line 68 to provide heat energy to reboiler 70. Clean low pressure steam generated in the reboiler flows via line 72 to provide heat energy to the crumb silo 16. Black liquor flows from the reboiler to black liquor filter 74. The filtered liquid flows into a weak black liquor tank for further treatment in a black liquor evaporation system. Other heat recovery systems (e.g., flash tank and heat exchanger) may be used with or in place of the reboiler 70, such heat recovery systems recovering heat from the hot black liquor.

In the intermediate cooking zone 56, the feed continues to move downward and a counter-current flow of black liquor flows upward through this zone 56. Additional white liquor is extracted through screen 64 to conduit 68'. White liquid 44 may be added to the black liquid stream. The combined flow of black and white liquor is recycled to the cooking vessel via a central conduit 82 which adds the combined flow at or below the screen 64.

The rate of addition of the combined stream through central conduit 82 and the rate of liquid extraction through screens 62 and 64 are adjusted so that the liquid flows upward through the intermediate cooking zone and downward through the lower cooking zone 58. The lower cooking zone may have a length that is one-third, one-half, or more of the vertical length of digester vessel 16.

The feed is washed in a washing zone 60 at the bottom of the digester vessel to extract black liquor. The wash liquid 84 flows through the wash line to the lower region of the wash zone and through the central conduit 82 to the wash zone. As the wash liquor flows upward through the wash zone, black liquor and other chemicals in the feed are entrained, flow upward and extracted through the screen 66.

Bottom drain assembly 78 drains washed feed from the cooking vessel via line 80 to a discharge chute (not shown). The pressure of the feed material is released in the discharge chute. The feed discharged from the discharge chute (now dissolved pulp) is pumped for further processing, such as a brown stock washer (not shown).

Fig. 2 shows a side view of a typical screw-type centrifugal pump for debris pumping. The pump has a housing 202 and a screw impeller 208 as well as an inlet opening 204 and an outlet opening 206 for a slurry of wood chips and liquid. The impeller may be opened or closed. The closed impeller is provided with a conical shroud 210 which is fixed to the outer periphery of the screw blades. The pump may further be provided with a liner between the suction housing and the impeller (fig. 3).

Fig. 3a, 3b and 3c show partial cross-sectional views of a screw-type centrifugal pump.

In fig. 3a, pump 300 has a suction housing portion 302, a wear ring 304, a closed screw impeller 306, and a bushing 308 between the suction housing and the impeller. The pump also has an inlet 320 and an outlet 322 for the flow of the debris slurry. An opening 310 and a conduit 312 are arranged in the suction housing for introducing a base 314 to the pump. The alkali is directed to the gap 316 between the impeller and the liner 308 where it contacts the wood chip slurry and the pH of the slurry will increase. This reduces the wear rate of the pump.

In fig. 3b, there is no bushing between the suction housing 302b and the closed impeller 318. In this case, the base 314 is introduced into the gap 316b between the impeller 318 and the suction housing 302 b.

In fig. 3c, the impeller 320 is open. The alkali 314 is directed between the impeller 320 and the liner 308 c.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.