阅读说明：本技术 间歇式制浆工艺中的方法和布置 (Method and arrangement in a batch pulping process ) 是由 L·拉米 J·卡冯恩 S·米纳 H·兰德曼 B·寇特兹 J·沃兹 于 2020-03-09 设计创作，主要内容包括：本发明为在用于生产浆的间歇式蒸煮系统中提取水解产物的方法、水解产物提取布置和间歇式蒸煮系统。所述方法包括以下步骤：将木质纤维素原料提供给间歇式蒸煮容器；在间歇式蒸煮容器中进行木质纤维素原料的酸水解；从间歇式蒸煮容器中去除水解产物；以及将所去除的水解产物在从间歇式蒸煮容器去除后在其从间歇式蒸煮容器到水解产物提取罐的途中尽快冷却至低于140℃,其中所述冷却在水解产物离开间歇式蒸煮容器时起0-2分钟的时间段内进行。(The present invention is a method of extracting a hydrolysate in a batch cooking system for producing pulp, a hydrolysate extraction arrangement and a batch cooking system. The method comprises the following steps: providing a lignocellulosic feedstock to a batch digester vessel; acid hydrolysis of lignocellulosic feedstock in a batch digester vessel; removing the hydrolysate from the batch cooking vessel; and cooling the removed hydrolysate to below 140 ℃ as quickly as possible on its way from the batch cooking vessel to the hydrolysate extraction tank after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from when the hydrolysate leaves the batch cooking vessel.)

1. A method of extracting a hydrolysate in a batch cooking process for producing pulp, the method comprising the steps of:

-providing a lignocellulosic feedstock to a batch cooking vessel;

-performing an acid hydrolysis of the lignocellulosic feedstock in a batch cooking vessel;

-removing hydrolysate from the batch cooking vessel; and

-cooling the removed hydrolysate to below 140 ℃ as soon as possible on its way from the batch cooking vessel to the hydrolysate extraction tank after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from the moment the hydrolysate leaves the batch cooking vessel.

2. The method of claim 1, wherein the method further comprises the step of extracting sugars from the removed hydrolysate.

3. The process of claim 1 or 2, further comprising the step of alkaline cooking in a batch cooking vessel after removing the hydrolysate.

4. The method of any one of the preceding claims, wherein the batch cooking process is a process for producing dissolving pulp.

5. The process according to any one of the preceding claims, wherein the step of performing acid hydrolysis of the lignocellulosic feedstock in a batch digester vessel comprises steam hydrolysis and/or liquid hydrolysis.

6. A method according to any one of the preceding claims, wherein the step of cooling the removed hydrolysate comprises cooling the hydrolysate to below 120 ℃ or below 100 ℃.

7. The method of any one of the preceding claims, wherein the step of cooling the removed hydrolysate comprises cooling the hydrolysate over a period of 0 to 1 minute from the time the hydrolysate exits the batch cooking vessel.

8. A method according to any one of the preceding claims, wherein the step of cooling the removed hydrolysate comprises cooling the hydrolysate via a heat exchanger.

9. A batch cooking system (1) for producing pulp, the batch cooking system (1) comprising a batch cooking vessel (3) and a hydrolysate extraction arrangement (5), the hydrolysate extraction arrangement (5) being configured to extract hydrolysate in the batch cooking system (1), whereby the hydrolysate extraction arrangement (5) is connected to a hydrolysate outlet (11) of the batch cooking vessel (3) and comprises:

-a hydrolysate removal pipe (7) comprising a batch cooking vessel connector (8) configured to be connected to a hydrolysate outlet (11) of a batch cooking vessel (3) of a batch cooking system (1);

-a hydrolysate extraction tank (13) connected to the hydrolysate removal pipe (7) and configured to receive the hydrolysate removed from the batch cooking vessel (3) via the hydrolysate removal pipe (7); and

-a cooling device (15) configured to cool any hydrolysate removed from the batch cooking vessel (3) to 140 ℃ as soon as possible after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from when the hydrolysate leaves the batch cooking vessel, wherein the cooling device (15) is arranged in connection with the hydrolysate removal pipe (7) and cools the removed hydrolysate on its way from the batch cooking vessel to the hydrolysate extraction tank.

10. A batch cooking system according to claim 9, wherein the cooling device (15) is configured to cool the hydrolysate to below 120 ℃ or below 100 ℃.

11. A batch cooking system according to any one of claims 9-10, wherein the cooling device (15) is arranged in such a position that the cooling of the hydrolysate takes place during a period of 0-1 minutes from the moment the hydrolysate leaves the batch cooking vessel.

12. A batch cooking system according to any one of claims 9-11, wherein the cooling device (15) is a heat exchanger.

13. A batch cooking system according to any one of claims 9-12, wherein the batch cooking vessel (3) is a pressurized vessel, and wherein the batch cooking system further comprises a hydrolysis arrangement (21), which hydrolysis arrangement (21) is connected to the batch cooking vessel (3) and is configured for adding a fluid to the batch cooking vessel for hydrolysis of the lignocellulosic feedstock provided in the batch cooking vessel (3).

14. A batch cooking system according to claim 13, wherein the hydrolysis arrangement (21) is configured for adding steam and/or liquid to the batch cooking vessel (3) for hydrolysis.

15. A batch cooking system according to any one of claims 9-14, wherein the batch cooking system (1) further comprises a liquid addition arrangement (27) connected to the batch cooking vessel (3) and configured for adding lye into the batch cooking vessel (3) for alkaline cooking after hydrolysis in the batch cooking vessel (3) and after removal of the hydrolysate from the batch cooking vessel (3).

16. A batch cooking system according to any one of claims 9-15, wherein the batch cooking system (1) is a system for producing dissolving pulp.

17. A hydrolysate extraction arrangement (5) configured to extract a hydrolysate in a batch cooking system (1) for producing pulp, the hydrolysate extraction arrangement (5) comprising:

-a hydrolysate removal pipe (7) comprising a batch cooking vessel connector (8) configured to be connected to a hydrolysate outlet (11) of a batch cooking vessel (3) of a batch cooking system (1);

-a hydrolysate extraction tank (13) connected to the hydrolysate removal pipe (7) and configured to receive the hydrolysate removed from the batch cooking vessel (3) via the hydrolysate removal pipe (7); and

-a cooling device (15) configured to cool any hydrolysate removed from the batch cooking vessel (3) to 140 ℃ as soon as possible after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from when the hydrolysate leaves the batch cooking vessel, wherein the cooling device (15) is arranged in connection with the hydrolysate removal pipe (7) and cools the removed hydrolysate on its way from the batch cooking vessel to the hydrolysate extraction tank.

18. The hydrolysate extraction arrangement according to claim 17, wherein the cooling device (15) is configured to cool the hydrolysate to below 120 ℃ or below 100 ℃.

19. A hydrolysate extraction arrangement as claimed in any one of claims 17 to 18, wherein the cooling means (15) is provided in a position such that cooling of the hydrolysate takes place over a period of 0 to 1 minute from the time the hydrolysate leaves the batch cooking vessel.

20. A hydrolysate extraction arrangement as claimed in any one of claims 17 to 19, wherein the cooling device (15) is a heat exchanger.

Technical Field

The present invention relates to a method for extracting hydrolysate in a batch cooking process for producing pulp. The invention also relates to a hydrolysate extraction arrangement configured for extracting hydrolysate in a batch cooking system for producing pulp, and a batch cooking system for producing pulp.

Background

In some pulping processes, such as dissolving pulp production, lignocellulosic feedstock is first hydrolyzed to remove unwanted hemicellulose, and then subjected to alkaline cooking to remove lignin. Hydrolysis in batch cooking systems is typically carried out by adding steam to the lignocellulosic feedstock. During the hydrolysis process, hemicellulose (mainly C5 sugars) is degraded and released from the wood. If fructose should be extracted and processed, the hydrolysis product containing dissolved sugars needs to be removed from the vessel where the hydrolysis is carried out before changing the pH and carrying out the alkaline cooking. In the alkaline cooking process, the sugar is broken down into non-valuable ingredients.

The disposal of the hydrolysate can be problematic because it is very viscous and prone to fouling on, for example, piping, screens and tank surfaces. Connecting piping and tanks used in systems for extracting sugars often have fouling problems and require cleaning when removing hydrolysates from cooking vessels used for extracting sugars. Any cleaning and interruptions in the production process are of course negative.

Summary of The Invention

It is an object of the present invention to improve the efficiency of hydrolysate extraction in a pulping system.

This is achieved by a method of extracting a hydrolysate in a hydrolysate extraction arrangement and a batch cooking system according to the independent claims.

According to one aspect of the present invention, there is provided a method of extracting a hydrolysate in a batch cooking process for producing pulp, the method comprising the steps of:

-providing a lignocellulosic feedstock to a batch cooking vessel;

-performing an acid hydrolysis of the lignocellulosic feedstock in a batch cooking vessel;

-removing hydrolysate from the batch cooking vessel; and

-cooling the removed hydrolysate to below 140 ℃ as soon as possible on its way from the batch cooking vessel to the hydrolysate extraction tank after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from the moment the hydrolysate leaves the batch cooking vessel.

According to another aspect of the invention, a batch cooking system for producing pulp is provided. The batch cooking system comprises a batch cooking vessel and a hydrolysate extraction arrangement configured to extract a hydrolysate in the batch cooking system, whereby the hydrolysate extraction arrangement is connected to a hydrolysate outlet of the batch cooking vessel and comprises:

-a hydrolysate removal pipe comprising a batch cooking vessel connector configured to connect to a hydrolysate outlet of a batch cooking vessel of a batch cooking system;

-a hydrolysate extraction tank connected to the hydrolysate removal pipe and configured to receive the hydrolysate removed from the batch cooking vessel via the hydrolysate removal pipe; and

-cooling means configured to cool any hydrolysate removed from the batch cooking vessel to 140 ℃ as soon as possible after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from when the hydrolysate leaves the batch cooking vessel, wherein the cooling means is arranged in connection with the hydrolysate removal pipe and cools the removed hydrolysate on its way from the batch cooking vessel to the hydrolysate extraction tank.

According to another aspect of the present invention, there is provided a hydrolysate extraction arrangement configured to extract hydrolysate in a batch cooking system for producing pulp, the hydrolysate extraction arrangement comprising:

-a hydrolysate removal pipe comprising a batch cooking vessel connector configured to connect to a hydrolysate outlet of a batch cooking vessel of a batch cooking system;

-a hydrolysate extraction tank connected to the hydrolysate removal pipe and configured to receive the hydrolysate removed from the batch cooking vessel via the hydrolysate removal pipe; and

-cooling means configured to cool any hydrolysate removed from the batch cooking vessel to 140 ℃ as soon as possible after removal from the batch cooking vessel, wherein the cooling is performed during a period of 0-2 minutes from the moment the hydrolysate leaves the batch cooking vessel, wherein the cooling means (15)

Is arranged in connection with the hydrolysate removal pipe (7) and cools the removed hydrolysate on its way from the batch cooking vessel to the hydrolysate extraction tank.

Thus, a method and system for extracting hydrolysate in a pulping system is provided that is more efficient and reliable than prior art systems. The tendency of the hydrolysate to form scale is greatly reduced due to cooling after removal from the batch cooking vessel. When the hydrolysate is cooled, furfural formation is reduced and lignin degradation is also reduced. This will reduce the tendency for fouling to occur. Furthermore, the stability of the sugar solution is radically improved due to the reduced rate of sugar degradation and a more efficient sugar extraction may be provided. A more reliable process is provided due to little fouling and substantially no system cleaning, and a better sugar yield may be provided due to reduced sugar degradation.

In one embodiment of the invention, the method further comprises the step of extracting sugars from the removed hydrolysate.

In one embodiment of the invention, the process further comprises the step of alkaline cooking in a batch cooking vessel after removal of the hydrolysate.

In one embodiment of the invention, the batch cooking process is a process for producing dissolving pulp.

In one embodiment of the invention, the step of performing acid hydrolysis of the lignocellulosic feedstock in a batch digester vessel comprises steam hydrolysis and/or liquid hydrolysis.

In one embodiment of the invention, the step of cooling the removed hydrolysate comprises cooling the hydrolysate to below 120 ℃. In one embodiment of the invention, the step of cooling the removed hydrolysate comprises cooling the hydrolysate to below 100 ℃.

In one embodiment of the invention, the step of cooling the removed hydrolysate comprises cooling the hydrolysate within a time period of 0 to 1 minute from the moment the hydrolysate leaves the batch cooking vessel.

In one embodiment of the invention, the cooling device is a heat exchanger.

In one embodiment of the invention, the batch cooking vessel is a pressurized vessel and the batch cooking system further comprises a hydrolysis arrangement connected to the batch cooking vessel and configured for adding fluid to the batch cooking vessel for performing hydrolysis of the lignocellulosic feedstock provided in the batch cooking vessel.

In one embodiment of the invention, the hydrolysis arrangement is configured for adding steam and/or liquid to the batch cooking vessel for hydrolysis.

In one embodiment of the invention, the batch cooking system further comprises a liquid addition arrangement connected to the batch cooking vessel and configured for adding lye into the batch cooking vessel for alkaline cooking after hydrolysis in the batch cooking vessel and after removal of the hydrolysate from the batch cooking vessel.

In one embodiment of the invention, the batch cooking system is a system for producing dissolving pulp.

Brief description of the drawings

FIG. 1 is a schematic diagram of a batch cooking system according to one embodiment of the present invention.

Fig. 2 is a flow diagram of a method of extracting a hydrolysate according to one embodiment of the present invention.

Figures 3a and 3b show graphs of furfural and HMF content in the hydrolysate at different temperatures.

Detailed description of the embodiments

Fig. 1 schematically shows a batch cooking system 1 for producing pulp according to one embodiment of the invention. The batch cooking system 1 comprises a batch cooking vessel 3 and a hydrolysate extraction arrangement 5 according to the invention, which hydrolysate extraction arrangement 5 is connected to a hydrolysate outlet 11 of the batch cooking vessel 3.

The batch cooking vessel 3 may be a conventional batch cooking vessel for producing pulp. Only some of the components and features of batch cooking vessel 3 relevant to the present invention will be described herein. The batch cooking vessel 3 comprises an inlet 4a for receiving the lignocellulosic feedstock and an outlet 4b for discharging the contents of the batch cooking vessel 3 after it has been treated in the vessel. The treatment of the lignocellulosic feedstock in the batch cooking vessel 3 comprises acid hydrolysis followed by alkaline cooking. The batch digester vessel 3 is a pressurized vessel. Acid hydrolysis of lignocellulosic feedstock is carried out by adding a fluid to batch cooking vessel 3. The added fluid may be steam and/or liquid added to the batch cooking vessel 3. The steam and/or liquid may be water and may optionally contain an acid component for improving the hydrolysis. In the case of water alone, the acid contained in the lignocellulosic material is considered sufficient to effect hydrolysis. In fig. 1, this is shown in a hydrolysis arrangement 21 connected to the batch cooking vessel 3, which hydrolysis arrangement 21 is configured to add at least one fluid to the batch cooking vessel to perform hydrolysis as described above. According to the invention, it is suitable to add a liquid for hydrolysis, which may have been previously steamed. The liquid may be, for example, water. According to the invention, which will be described in more detail below, the hydrolysate will be removed from the batch cooking vessel and extracted more efficiently by adding liquid for carrying out the hydrolysis. If sugar is extracted from the hydrolysate, such sugar extraction with the addition of liquid for carrying out the hydrolysis can be more efficient than hydrolysis achieved by adding only steam.

The batch cooking vessel 3 further comprises a liquid addition arrangement 27 configured to add lye to the batch cooking vessel 3 for alkaline cooking in the batch cooking vessel 3. The hydrolysis is followed by alkaline cooking in a batch cooking vessel. According to the invention, alkaline cooking is also carried out after removal of the hydrolysate from the batch cooking vessel 3. If, for example, the sugar should be extracted from the hydrolysate, it is necessary to remove the hydrolysate containing dissolved sugar from the batch cooking vessel in which the hydrolysis is carried out before changing the pH and carrying out the alkaline cooking. In the alkaline cooking process, the hydrolyzed dissolved sugars are destroyed into valueless components.

According to the invention, the hydrolysate should be removed from the batch cooking vessel 3 after the hydrolysis has been carried out and before the alkaline cooking step is started. The hydrolysate is removed via a hydrolysate outlet 11 arranged in the batch cooking vessel 3. The hydrolysate outlet 11 may for example be arranged in the upper half of the batch cooking vessel. However, it may also be arranged in the lower half of the batch cooking vessel. The hydrolysate can be pushed out of the bottom of the batch cooking vessel 3, e.g. from the bottom of the batch cooking vessel 3, by increasing the pressure in the batch cooking vessel, e.g. by adding another fluid (e.g. water or liquid) to the batch cooking vessel. Another option is to pump or discharge the hydrolysate from the batch cooking vessel 3.

The batch cooking system 1 may be a system for producing dissolving pulp. In the production of dissolving pulp, hemicellulose is removed from lignocellulosic feedstock by acid hydrolysis before lignin is removed in the alkaline cooking step.

According to the present invention, a hydrolysate extraction arrangement 5 is provided, which is configured to extract hydrolysate in a batch cooking system 1 for producing pulp. The hydrolysate extraction arrangement 5 is during use connected to the hydrolysate outlet 11 of the batch cooking vessel 3 in the batch cooking system 1 as described above. The hydrolysate extraction arrangement 5 comprises a hydrolysate removal pipe 7, which hydrolysate removal pipe 7 comprises a batch cooking vessel connector 8 configured to be connected to a hydrolysate outlet 11 of the batch cooking vessel 3. The hydrolysate extraction arrangement 5 further comprises a hydrolysate extraction tank 13 and a cooling device 15, the tank 13 being connected to the hydrolysate removal pipe 7 and arranged for receiving the hydrolysate removed from the batch cooking vessel 3 via the hydrolysate removal pipe 7, the cooling device 15 being configured for cooling any hydrolysate removed from the batch cooking vessel 3. The cooling device 15 may be arranged in connection with the hydrolysate removal pipe 7 as shown in fig. 1. The hydrolysate should preferably be cooled as quickly as possible after removal from batch cooking vessel 3. For example, the cooling means 15 may be arranged in a position such that the cooling of the hydrolysate is performed within a time period of 0-2 minutes from the moment the hydrolysate leaves the batch cooking vessel or within a time period of 0-1 minute from the moment the hydrolysate leaves the batch cooking vessel.

The cooling means 15 may be configured to cool the hydrolysate to below 140 ℃ or below 120 ℃ or below 100 ℃. A typical temperature of the contents of the batch cooking vessel 3 may be, for example, about 170 ℃. In one embodiment of the invention the cooling means 15 is configured to cool the hydrolysate to a temperature of 70 to 140 ℃ and in one embodiment of the invention the cooling means 15 is configured to cool the hydrolysate to a temperature of 80 to 120 ℃ or 90 to 100 ℃. By cooling the hydrolysate, the hydrolysate can be extracted more efficiently. The hydrolysate is usually very viscous and difficult to handle. For example, severe fouling can occur in tanks, pipes, recycle lines, screens, etc. in equipment used to treat the hydrolysate. The stickiness of the hydrolysate and its tendency to form scale may be due to furfural and lignin produced by the dissolved sugars. The production of furfural is a function of time, i.e., the longer the sugar exposure to such conditions, the higher the concentration of furfural in solution. The lignin content also increases during the hydrolysis time. The scale is mainly composed of lignin and furfural and sugars.

It has surprisingly been found that by cooling the hydrolysate to e.g. below about 140 ℃ or below 120 ℃ or below 100 ℃, the stickiness and the tendency to form scale is greatly reduced and the extraction of the hydrolysate from the pulping process can be greatly improved. Thereby also improving the extraction of sugars from the hydrolysate. The positive effect of cooling, i.e. the reduction of scale, is surprisingly high even when the temperature drop is relatively small.

Furthermore, in these types of cooking systems for producing pulp, it is traditionally very important to maintain the high temperature of the material to avoid energy losses. Thus, the solution of using such a cooled hydrolysate is not obvious to the skilled person.

The cooling device 15 may be a heat exchanger. Another option may be to add cold fluid to the hydrolysate as it is removed from the batch digester vessel 3. However, this dilutes the hydrolysate, which may not be advantageous in all applications.

FIG. 2 is a flow diagram of a method according to an embodiment of the invention. The method is a method of extracting a hydrolysate in a batch cooking process for producing pulp, comprising the steps of:

s1: the lignocellulosic feedstock is supplied to a batch digester vessel 3.

S2: acid hydrolysis of lignocellulosic feedstocks is carried out in a batch digester vessel. This step may include steam hydrolysis and/or liquid hydrolysis as described above. It is appropriate to add liquid to batch cooking vessel 3 for hydrolysis to improve the hydrolytic extraction.

S3: the hydrolysate is removed from the batch cooking vessel 3.

S4: the removed hydrolysate was cooled. This step may include cooling the hydrolysate to less than 140 ℃ or less than 120 ℃ or less than 100 ℃, as described above. In one embodiment of the invention, this step may comprise cooling the hydrolysate to a temperature of 70 to 140 ℃ or a temperature of 80 to 120 ℃ or a temperature of 90 to 100 ℃. Furthermore, it is desirable that the cooling should be carried out as soon as possible after removal from batch cooking vessel 3 to avoid fouling in the equipment. The hydrolysate is cooled on the way from the batch cooking vessel 3 to the hydrolysate extraction tank 13. The step of cooling the removed hydrolysate may comprise cooling the removed hydrolysate over a period of 0-2 minutes from when the hydrolysate leaves the batch cooking vessel or over a period of 0-1 minute from when the hydrolysate leaves the batch cooking vessel. The step of cooling the removed hydrolysate may comprise cooling the hydrolysate by means of a heat exchanger 15.

According to some embodiments of the invention, the method further comprises step S5: extracting sugars from the removed hydrolysate. This step is performed after step S4 of cooling the removed hydrolysate. When the hydrolysate has been cooled as described above according to the present invention, the extraction rate of sugars from the hydrolysate is greatly increased. Since the rate of sugar degradation is reduced after cooling of the hydrolysate, the stability of the sugar solution is fundamentally improved and a more efficient sugar extraction can be provided. In some embodiments of the invention, lignin may also be extracted from the hydrolysate.

According to some embodiments of the invention, the method further comprises step S6: after removal of the hydrolysis products, alkaline cooking is carried out in a batch cooking vessel 3. Step S6 may be performed at any time after step S3 as described above.

Figure 3a is a graph of furfural content in the hydrolysate after 0, 2, 4 and 6 hours at different temperatures. It clearly shows that the amount of furfural starts to increase when the temperature is above 140 ℃. Below 140 ℃, the amount of furfural is very limited.

Fig. 3b is a graph of HMF (hydroxymethylfurfural) content in the hydrolysate at different temperatures. Likewise, the HMF content increases at temperatures above 140 ℃, but is very limited at lower temperatures. Furfural and HMF can form sticky scale in the equipment together with lignin, so that when the hydrolysate is cooled to a temperature below 140 ℃ as soon as possible after removal from the batch digester vessel according to the invention, the scale can be greatly reduced.