CN112322666A

CN112322666A - Method for preparing methane from pulping waste liquid

Info

Publication number: CN112322666A
Application number: CN202011315666.8A
Authority: CN
Inventors: 房桂干; 黄晨; 邓拥军; 田庆文; 焦健; 韩善明; 仇刚; 荀为农
Original assignee: Institute of Chemical Industry of Forest Products of CAF
Current assignee: Institute of Chemical Industry of Forest Products of CAF
Priority date: 2020-11-21
Filing date: 2020-11-21
Publication date: 2021-02-05

Abstract

The method for preparing the biogas from the pulping waste liquid comprises the steps of firstly washing the wood fiber raw material at room temperature and then collecting wet materials; introducing steam into the wet material, and preserving heat; performing solid-liquid separation on the steamed material, and respectively collecting steaming liquid and the material; adding sodium hydroxide, adding water to adjust the concentration of the material to 30wt.%, uniformly mixing, introducing steam, preserving heat again, collecting the material after heat preservation is finished, performing solid-liquid separation again, and collecting waste liquid and the material; adding clear water into the collected materials to adjust the mass concentration to 15wt.%, and collecting washing liquid and the materials after washing; mixing the liquids generated in the above process, adding fresh animal feces, adjusting solid concentration of the animal feces to 10wt.%, and C/N ratio to 25, and delivering into a fermentation tank for anaerobic fermentation to produce biogas. The invention has the advantages that the biogas yield is obviously increased, the methane content in the biogas is higher than that of the traditional biogas preparation technology, and the invention has the characteristics of high yield and good biogas quality.

Description

Method for preparing methane from pulping waste liquid

Technical Field

The invention relates to the technical field of biological methane preparation, in particular to a method for preparing methane from pulping waste liquid.

Background

In recent years, with the development of social economy, the living standard of residents is continuously increased, the demand of people on agricultural products is continuously increased, and the livestock breeding industry and the planting industry are rapidly developed. The development of animal husbandry produces a large amount of livestock manure, the annual production amount of the livestock manure exceeds 40 hundred million tons, the livestock manure is difficult to treat, and the livestock manure becomes an important pollution source in rural areas. At present, most of agricultural livestock manure is used as fertilizer, the utilization efficiency is low, and the problem of cleaning treatment of the livestock manure cannot be effectively solved. The livestock manure treated by the anaerobic fermentation technology can effectively solve the problem of livestock manure treatment, has the effect of clean production, and is a way for effectively treating rural livestock manure. The livestock manure contains a large amount of undigested plant fibers and proteins, and can meet the requirements of growth and metabolism of methane bacteria on a carbon source and a nitrogen source. However, in the traditional livestock manure fermentation, because the plant carbon source mostly exists in a fiber form, microorganisms cannot be directly utilized and need to be degraded to generate monosaccharide for reuse, the fermentation period is longer and the efficiency is lower.

Pulping and papermaking are important components of light industry in China, wherein chemi-mechanical pulp is popular due to the advantages of high yield, simple process, low investment and the like. However, the chemical-mechanical pulping process has high wastewater concentration, dark color and complex components, and thus is difficult to process. The traditional method for treating the pulping waste liquid of the chemi-mechanical pulp adopts a biological treatment technology of anaerobic and aerobic fermentation, but the technology cannot completely remove organic matters in the pulping waste liquid, the color of the treated waste water is high, the discharge requirement can be met only by combining secondary Fenton advanced treatment, and the production cost of enterprises is greatly increased by the waste water treatment no matter how the treatment is carried out; if the waste can be changed into valuable, the effective components in the pulping waste liquid can be recycled, and the enterprise burden can be greatly reduced.

The applicant finds that in the chemical mechanical pulping process, in the presteaming and alkaline impregnation steps, a large amount of carbohydrates such as hemicellulose and the like in the wood fiber raw material are degraded and mainly exist in waste liquid in the form of monosaccharide and oligosaccharide, wherein the monosaccharide and the oligosaccharide are high-quality carbon sources for methane fermentation, and the efficiency of methane bacteria for utilizing the monosaccharide and the xylooligosaccharide is far higher than the efficiency of methane bacteria for directly utilizing the cellulose and the hemicellulose. Therefore, if the process for preparing the biogas by fermenting the pulping waste liquid can be developed, the wastewater treatment cost of enterprises can be greatly reduced, and the fermented biogas slurry and biogas residues contain lignin and various trace elements required by plants and are natural organic fertilizers.

Disclosure of Invention

The technical problem to be solved is as follows: aiming at the defects of the prior art, the invention provides the method for preparing the methane by using the pulping waste liquid, and the method has the advantages of small pollution, small investment and quick response.

The technical scheme is as follows: the method for preparing the methane by using the pulping waste liquid comprises the following specific steps: (1) firstly, washing a wood fiber raw material at room temperature and then collecting wet materials; (2) introducing steam at the temperature of 100-145 ℃ into the wet material, and preserving the heat for 10-60min at the temperature of 90-120 ℃; performing solid-liquid separation on the steamed material, and respectively collecting steaming liquid and the material; (3) adding sodium hydroxide into the materials obtained in the previous step according to the weight percentage of 1-10%, simultaneously adding water to adjust the concentration of the materials to 30wt.%, uniformly mixing, introducing steam, preserving heat at 90-120 ℃ for 10-60min, collecting the materials after heat preservation is finished, performing solid-liquid separation again, and collecting waste liquid and the materials; (4) adding clear water into the collected materials to adjust the mass concentration to 15wt.%, and collecting washing liquid and the materials after washing; (5) mixing the liquids generated in the above process, adding fresh animal feces, adjusting solid concentration of the animal feces to 10wt.%, and C/N ratio to 25, and delivering into a fermentation tank for anaerobic fermentation to produce biogas.

Preferably, the wood fiber raw material comprises agricultural straws and woody plants, wherein the agricultural straws are wheat straws, rice straws, cotton stalks or corn straws, and the woody plants are poplar, eucalyptus or metasequoia.

Preferably, the solid-liquid separation method is realized by a double-screw press.

Preferably, the steam temperature is 145 ℃.

Preferably, the heat preservation time of the steam introduction is 15 min.

Preferably, the sodium hydroxide is used in an amount of 5%, the chemical impregnation solid concentration is 30wt.%, and the holding time is 30 min.

During steaming and pre-impregnating processes of pulping by a chemical mechanical method, cell walls of the raw materials are damaged, part of polysaccharide and lignin are dissolved out at high temperature under the action of sodium hydroxide and exist in pulping waste liquid in the form of monosaccharide, oligosaccharide and micromolecular lignin, wherein the monosaccharide and the oligosaccharide are high-quality carbon sources for microbial fermentation. The pulping waste liquid is used for anaerobic fermentation to prepare the methane, can effectively replace the purpose of taking clear water as the livestock manure diluent in the prior art, and simultaneously solves the problem of difficult treatment of the pulping waste water.

Has the advantages that: the invention destroys the cell wall of the plant fiber by steaming and chemical dipping steps in the pulping process of chemimechanical pulp, so that the polysaccharide and part of lignin in the plant fiber are degraded and dissolved out into the pulping waste liquid. The invention replaces water in the prior art with the pulping waste liquid to be used as a diluent of the livestock manure for anaerobic fermentation to prepare the biogas, thereby realizing the purpose of clean and cyclic utilization of the pulping waste liquid and simultaneously realizing the high-efficiency conversion of carbohydrates in the pulping waste liquid. Because the pulping waste liquid is rich in low molecular weight carbohydrates such as oligosaccharide, monosaccharide and the like, microorganisms can better metabolize, compared with the prior art which only uses livestock manure as a microorganism carbon source, the biogas yield is obviously increased, and meanwhile, the methane content in the biogas is higher than that of the traditional biogas preparation technology, so that the method has the characteristics of high yield and good biogas quality. The process integrates the advantages of animal husbandry, light industry and energy industry, uses the wastes of animal husbandry and light industry as the raw materials of energy industry, greatly reduces pollution and realizes clean conversion of the wastes

Drawings

FIG. 1 is a schematic diagram showing the daily gas production variation of pulping waste liquor;

fig. 2 is a schematic diagram of the methane content in the daily biogas.

Detailed Description

The invention is further described below in connection with specific embodiments. The examples are intended to illustrate, but not to limit, the invention. Those of ordinary skill in the art will understand that these examples are not intended to limit the present invention in any way, and that appropriate modifications can be made without departing from the spirit and scope of the present invention.

Example 1

Wheat straw is pulped by a chemical mechanical method to obtain pulping waste liquid: the method comprises the following steps: (1) introducing 145 ℃ high-temperature steam into the washed wheat straws, steaming for 30min at 95 ℃ (material temperature) to soften the wheat straws, treating the softened wheat straws by using a double-screw extruder, and separating steaming liquid and materials; (2) adding 3% sodium hydroxide (in absolute dry material mass ratio) into the steamed material and simultaneously supplementing a proper amount of water to adjust the solid concentration of the material to be 35 wt.%. Introducing high-temperature steam into the material, and keeping the temperature at 95 ℃ for 20 min. After chemical impregnation, the material is added into a double-screw extruder for extrusion treatment, and impregnation liquid and the material are separated. (3) Adding a proper amount of clear water into the materials, adjusting the solid concentration of the system to be 15wt.%, and washing. And separating the eluate from the materials by using a dehydrator.

The pH values and the carbohydrate contents of the three spent pulping liquors generated in the above three steps are shown in table 1:

TABLE 1 pH of spent pulping liquors and respective carbohydrate content

The results show that the wastewater in each stage is weakly acidic in the pulping process of wheat straw chemi-mechanical pulp, and is respectively 5.9, 6.7 and 6.8. Wheat straw was steamed and sodium hydroxide soaked to partially dissolve out carbohydrates, which were mainly glucose, xylose and partially oligosaccharides. In the steaming stage, wheat straw softens at high temperature but less of the carbohydrates are dissolved out; the dissolution of carbohydrate mainly takes place in the sodium hydroxide impregnation stage, and the dissolved substances are mainly present in the impregnation liquid in the form of oligomers, the oligomer content reaching 6.99 g/L. In the high-consistency washing section, the oligomer concentration in the eluate was only 2.10g/L due to the addition of a large amount of water. In conclusion, in the pulping process of the chemi-mechanical pulp, carbohydrates, particularly hemicellulose is greatly degraded, and degradation products mainly exist in the form of oligomers, so that the degradation products are high-quality microbial carbon sources.

Example 2

The production waste liquid generated in the embodiment 1 is uniformly mixed and then is fermented by methane, and the steps are as follows:

(1) mixing the above waste liquid, placing 2.5L into 3L jar, adding 10% fresh biogas slurry, and adding appropriate amount of fresh livestock feces to make C/N25.

(2) Adjusting the pH value of the system to about 8, placing the mixed solution at 38 ℃ for anaerobic fermentation for 30 days, sealing the system in the fermentation process, and stirring to ensure that the methane bacteria are fully contacted with a carbon source.

The amount of biogas produced and the methane content of the biogas in the above fermentation are shown in fig. 1 and 2, and the process of the present invention is compared with the conventional fermentation of animal manure.

The daily gas production of the pulping waste liquid biogas fermentation is shown in figure 1. As can be seen from the figure, the biogas fermentation is feasible by using the pulping waste liquid, and the gas production process has 2 times of gas production peak periods. From the view of gas production speed, the first 3 days are strain adaptation periods, and the gas production rate in the process is low; after the strain adaptation period of 3 days, the gas production rate gradually rises, and reaches a stable value of 567mL on the 10 th day, which is the first gas production peak period; the gas production rate is stable from the 10 th to the 16 th days and is between 550 and 600 mL. After 16 days, a second increase in gas production occurred and reached a maximum of 855mL on day 19, after which the gas production decreased slightly (796 mL on day 21); after 21 days, the gas production rate is in a remarkable descending trend, and at 30 days of fermentation, the daily gas production rate is only 189 mL. Compared with the traditional process which adopts water as a medium, the daily gas production amount of the process is obviously improved, mainly because the pulping waste liquid is rich in low molecular weight carbohydrate, and methane bacteria can be directly utilized, so the gas production efficiency is high.

The change in methane content in the gas during anaerobic fermentation is shown in FIG. 2. As can be seen from the figure, the methane content in the gas generally shows a steady rising trend, and 2 stationary phases occur. The methane content in the biogas rapidly increases to 25% the next day of fermentation, and within 2-10 days, the methane content is at a relatively stable level; after 10 days, the methane content entered the second ramp-up phase, reaching a steady value of 56% on day 14; then, the methane content in the gas slowly rises, and reaches a maximum value of 69% on the 24 th day of fermentation; the methane content of the gas then gradually decreased, and at day 30, the methane content of the gas was 41%. The result shows that the pulping waste liquid can be used for methane fermentation, the methane content in the produced methane is obviously higher than that in the traditional process (water is used as a medium), and the pulping waste liquid is used as a raw material to greatly reduce the pollutant emission of a pulping plant, thereby changing waste into valuable.

Claims

1. The method for preparing the methane by using the pulping waste liquid is characterized by comprising the following specific steps: (1) firstly, washing a wood fiber raw material at room temperature and then collecting wet materials; (2) introducing steam at the temperature of 100-145 ℃ into the wet material, and preserving the heat for 10-60min at the temperature of 90-120 ℃; performing solid-liquid separation on the steamed material, and respectively collecting steaming liquid and the material; (3) adding sodium hydroxide into the materials obtained in the previous step according to the weight percentage of 1-10%, simultaneously adding water to adjust the concentration of the materials to 30wt.%, uniformly mixing, introducing steam, preserving heat at 90-120 ℃ for 10-60min, collecting the materials after heat preservation is finished, performing solid-liquid separation again, and collecting waste liquid and the materials; (4) adding clear water into the collected materials to adjust the mass concentration to 15wt.%, and collecting washing liquid and the materials after washing; (5) mixing the liquids generated in the above process, adding fresh animal feces, adjusting solid concentration of the animal feces to 10wt.%, and C/N ratio to 25, and delivering into a fermentation tank for anaerobic fermentation to produce biogas.

2. The method for preparing biogas from pulping waste liquor according to claim 1, characterized in that: the wood fiber raw material comprises agricultural straws and woody plants, wherein the agricultural straws are wheat straws, rice straws, cotton stalks or corn straws, and the woody plants are poplar, eucalyptus or metasequoia.

3. The method for preparing biogas from pulping waste liquor according to claim 1, characterized in that: the solid-liquid separation method is realized by a double-screw press.

4. The method for preparing biogas from pulping waste liquor according to claim 1, characterized in that: the steam temperature was 145 ℃.

5. The method for preparing biogas from pulping waste liquor according to claim 1, characterized in that: the heat preservation time of the introduced steam is 15 min.

6. The method for preparing biogas from pulping waste liquor according to claim 1, characterized in that: the sodium hydroxide is used in an amount of 5%, the concentration of the solid chemical impregnation is 30wt.%, and the heat preservation time is 30 min.