CN109226188B - A method for hydrothermal carbonization coupled with anaerobic digestion to treat kitchen waste - Google Patents

Abstract

The present invention provides a method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion. The method includes the following steps: (1) performing a hydrothermal carbonization reaction on the pulverized kitchen waste, and performing a hydrothermal carbonization reaction on the product of the hydrothermal carbonization reaction. Separation to obtain a hydrothermal liquid and a solid-phase product, and drying the solid-phase product to obtain a hydrothermal charcoal; (2) combining the hydrothermal charcoal, the hydrothermal liquid or the hydrothermal charcoal with the hydrothermal liquid obtained in step (1) The mixture is subjected to anaerobic digestion. The hydrothermal carbonization coupled anaerobic digestion method provided by the present invention couples the hydrothermal carbonization technology and the anaerobic digestion technology to process the kitchen waste, which can realize the recycling, harmlessness and reduction of the kitchen waste. .

Description

A method for hydrothermal carbonization coupled with anaerobic digestion to treat kitchen waste

technical field

The invention relates to a method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion, and belongs to the technical field of waste organic recycling and clean energy production and application.

Background technique

Kitchen waste refers to food residues in canteens, households and the catering industry, mainly including steamed bread, rice, peels, vegetables, oil and water and other substances. The chemical composition is mainly starch, protein, inorganic salts, lipids, cellulose, etc. It has the characteristics of high water content, high organic matter, salt and oil content. With the growth of the economy, while the catering industry is developing rapidly, the kitchen waste is also growing rapidly. According to statistics, in 2017, the amount of kitchen waste generated in the country reached 99.72 million tons. In the early stage, the country has started large-scale kitchen waste treatment facilities. The pilot construction work is planned to achieve the goal of 30,000 tons/day by the end of 2015, but the actual processing capacity is only 14,900 tons/day. It is estimated that the overall market space for the entire kitchen waste will reach 100-150 billion yuan in the next few years.

The improper disposal of kitchen waste will have a huge impact on social life and is a major hidden danger to food safety. Because kitchen waste contains a large amount of organic matter and oil and fat available components, if it can be effectively used, it will save resources and generate greater economic value. . At this stage, the main methods of processing kitchen waste in my country are incineration, landfill, and composting. These three processing methods are not efficient and will pollute the environment to a certain extent. Anaerobic digestion technology uses microorganisms to decompose complex organic macromolecules into complex organic small molecules and inorganic substances and generate biogas. The generated biogas can be used to generate electricity and supply energy. It is a good way to deal with kitchen waste. Anaerobic digestion treatment of kitchen waste has a high organic load, which will produce a large amount of difficult-to-treat biogas residue and biogas slurry. The hydrothermal carbonization technology uses an aqueous solution as the reaction medium in a closed reaction vessel, and directly converts substances into gaseous, liquid and solid products under heating conditions, so that normally insoluble or insoluble substances are dissolved and recrystallized.

Chinese patent CN107142296A discloses a method for producing ethanol from kitchen waste, which is to perform hydrothermal pretreatment on the sorted kitchen waste, and then use microorganisms to ferment the separated solid kitchen waste to prepare ethanol. The invention uses the solid component for the production of ethanol, but during the pretreatment process of the solid, a large amount of organic acid is generated by hydrolysis, and the invention ignores the utilization of this part of the liquid phase, resulting in a part of energy loss. Chinese patent CN105414158A discloses a method for anaerobic digestion of kitchen waste coupled with hydrothermal liquefaction to treat grease, which is to perform hydrothermal liquefaction of grease to prepare liquid phase fuel, and directly perform anaerobic digestion on solid phase. The invention directly performs anaerobic digestion on the solid phase, which will lead to acidification of the anaerobic environment caused by high load, affecting the treatment efficiency, and the large amount of biogas residue and biogas slurry produced is difficult to handle.

Therefore, it has become an urgent technical problem to be solved in the art to provide a method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion.

SUMMARY OF THE INVENTION

In order to solve the above shortcomings and deficiencies, the purpose of the present invention is to provide a method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion.

Another object of the present invention is to provide a hydrothermal charcoal.

In order to achieve the above object, on the one hand, the present invention provides a method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion, wherein the method includes the following steps:

(1) carrying out the hydrothermal carbonization reaction of the pulverized kitchen waste, separating the hydrothermal carbonization reaction product, obtaining a hydrothermal liquid and a solid-phase product, and drying the solid-phase product to obtain a hydrothermal carbon;

(2) carrying out anaerobic digestion treatment on the hydrothermal charcoal, hydrothermal liquid or the mixture of hydrothermal charcoal and hydrothermal liquid obtained in step (1).

According to a specific embodiment of the present invention, in the described method, step (1) specifically comprises the following steps:

Mix the pulverized kitchen waste with deionized water, and place the resulting mixture in the inner tank of the reactor to carry out hydrothermal carbonization reaction;

After the reaction is completed, circulating water is introduced to cool to room temperature, and the hydrothermal liquid and the solid-phase product are obtained by separation, and then the solid-phase product is sent to an oven for drying to obtain hydrothermal charcoal.

According to specific embodiments of the present invention, the present invention does not make specific requirements on the drying temperature and drying time described in step (1) of the method, and those skilled in the art can reasonably set the drying temperature and time according to the needs of field operations , as long as it is guaranteed that the present invention can achieve the purpose of drying the solid-phase product to obtain hydrothermal carbon.

According to a specific embodiment of the present invention, in the method, the yield of the hydrothermal carbon is 42.33-49.33%, the calorific value is 28.36-31.11 MJ/kg, the O/C atomic ratio is 0.15-0.24, and the H/ The C atomic ratio is 1.10-1.30.

According to a specific embodiment of the present invention, in the method step (1), the temperature of the hydrothermal carbonization reaction is 180-260° C., and the reaction time is 2-4h;

Preferably, the temperature of the hydrothermal carbonization reaction is 180°C, and the reaction time is 2h.

According to a specific embodiment of the present invention, in the method step (2), the temperature of the anaerobic digestion is 37±1° C., the anaerobic digestion time is 45 days, and the pH is not adjusted.

According to a specific embodiment of the present invention, the method further comprises, before the anaerobic digestion treatment, continuously feeding nitrogen into the system to ensure that the system maintains the operation in an anaerobic environment;

Preferably, the time for introducing nitrogen gas is 1-3 min.

According to a specific embodiment of the present invention, in the method, based on the total volume of the inoculum used for the anaerobic digestion treatment, the added amount of the hydrothermal solution is 50-200 mL/L.

According to a specific embodiment of the present invention, in the method, based on the total volume of the inoculum used for the anaerobic digestion treatment, the addition amount of the hydrothermal charcoal is 5-15 g/L;

Preferably, the added amount of the hydrothermal carbon is 10 g/L.

According to the specific embodiment of the present invention, the present invention does not make specific requirements for the inoculum used in the anaerobic digestion treatment of the method. Those skilled in the art can select a suitable inoculum according to the needs of field operations, as long as it is ensured that the anaerobic digestion treatment of the present invention can be achieved. purpose can be. For example, the inoculum used in the method of the present invention may be biogas slurry, which includes biogas slurry obtained after fermentation of activated sludge, crop straw, aquaculture manure and kitchen waste; in the specific embodiment of the present invention, the inoculum used is It is the biogas slurry taken from Asuwei Landfill (Changping District, Beijing).

According to a specific embodiment of the present invention, the method further comprises the operation of recycling the hydrothermal liquid obtained in step (1) as the solvent used in the hydrothermal carbonization reaction;

Preferably, the number of cycles is 5-7 times.

Among them, the invention can improve the yield and calorific value of the hydrothermal char by recycling the hydrothermal liquid obtained after the hydrothermal carbonization reaction.

According to a specific embodiment of the present invention, in the method, the kitchen waste includes one or a combination of meat, vegetables, rice, steamed bread, noodles, fruit and oily water.

According to a specific embodiment of the present invention, in the method, the moisture content of the kitchen waste is 70-90%; preferably, it is 80%.

According to a specific embodiment of the present invention, the method further includes an operation of performing biomass conditioning on the hydrothermal char to prepare biofuel. Wherein, the biomass conditioning is a conventional technical means in the art, and those skilled in the art can select a suitable biomass conditioning process according to operational needs, as long as it is ensured that the purpose of preparing biofuels of the present invention can be achieved.

According to a specific embodiment of the present invention, the method further includes an operation of pre-processing the kitchen waste, wherein the pre-treatment method is a conventional method in the field. For example, in the specific embodiment of the present invention, the pre-treatment method includes the following Specific steps:

After the kitchen waste is collected and transported, it is first subjected to rough sorting to separate out substances that cannot undergo hydrothermal carbonization, such as glass, metal, stone, etc.; The biodiesel is sent to be processed, and the solid phase enters the next pulverization system for pulverization; after the pulverization is completed, it enters the preheating tank for stirring and preheating, and the preheating temperature is 80-90 °C. Among them, preheating the pulverized kitchen waste at 80-90°C is to preliminarily hydrolyze the kitchen waste, so as to prevent the kitchen waste from directly reacting in the hydrothermal reaction tank, resulting in the problem of uneven reaction. .

According to a specific embodiment of the present invention, in the method, the hydrothermal carbonization reaction is performed in a closed reaction vessel under heating conditions, using subcritical water to exhibit both acidic and basic properties, and use it as both Solvents and catalysts to improve the solubility of organic matter in water, hydrolyze normally insoluble or insoluble substances to generate small molecular substances, and then these small molecular substances are recrystallized under the catalysis of the subcritical water to form new polymers . For different raw materials, the hydrothermal carbonization products show different properties. For kitchen waste, it is rich in a large amount of organic matter, and the hydrothermal carbonization process has undergone dehydration, decarbonation, and polymerization, which significantly increases the C content of the solid-phase product, and the solid-phase product also has a higher calorific value. It can be used as a biofuel, it can also be used as an additive for anaerobic digestion reactions, and it can also be used as a carbon base, combined with fertilizers to prepare slow-release agents. The liquid phase (hydrothermal liquid) is rich in a large number of small molecular organic acids, which are mainly acetic acid, which is the fermentation substrate of methanogens in the anaerobic digestion process and can be used in the anaerobic digestion process; The liquid can also be recycled as the solvent required for the hydrothermal carbonization reaction.

The anaerobic digestion process is usually divided into three stages, namely the hydrolysis stage of organic matter, the stage of acid production and hydrogen production, and the stage of methane production. Based on the current research, adding biochar to the anaerobic digestion system can improve the direct electron transfer ability between microbial species, thereby increasing the methane production during the anaerobic digestion process. The method provided by the invention is to add the hydrothermal charcoal after the hydrothermal carbonization of kitchen waste into the anaerobic digestion system, and the added hydrothermal charcoal adsorbs the hydrolyzing bacteria and methanogens in the anaerobic system to the water through biochemical adsorption. The surface of the hot charcoal can improve the hydrolysis efficiency of the hydrolyzing bacteria and enhance the synergy between the microorganisms. At the same time, the hydrothermal charcoal itself can also be used as a fermentation raw material to increase the organic acid content in the system, thereby increasing the methane production.

In addition, the preparation raw material of the hydrothermal charcoal provided by the present invention is kitchen waste, the prepared hydrothermal charcoal is an environment-friendly substance, and the preparation cost is low, and the application effect is obvious; in the specific embodiment of the present invention, the organic In the anaerobic digestion biogas system in which the waste biogas slurry is the inoculum, the hydrothermal charcoal, the hydrothermal liquid, and the mixture of the two prepared by the invention are respectively added. The experimental results show that after the hydrothermal charcoal is added, the cumulative methane production and The rate of methane production increased significantly.

Therefore, the hydrothermal carbonization coupled with anaerobic digestion method provided by the present invention to process the kitchen waste by coupling the hydrothermal carbonization technology and the anaerobic digestion technology can realize the recycling, harmlessness and reduction of the kitchen waste. quantify.

Specifically, in the most preferred embodiment of the present invention, the temperature of the hydrothermal carbonization reaction is 180° C., the reaction time is 2 hours, and the moisture content of the kitchen waste raw material is 80%. At this time, the prepared hydrothermal charcoal and water The hydrothermal performance is the best. Among them, the calorific value of the hydrothermal carbon is 29.50MJ/kg, the O/C atomic ratio is 0.24, and the H/C atomic ratio is 1.30; the total amount of small molecular organic acids in the hydrothermal liquid is 2103 mg/L, The acetic acid content was 1499 mg/L. It can be seen that the combustion properties of the hydrothermal char obtained by using the hydrothermal carbonization technology to treat the kitchen waste are better than that of lignite, and the hydrothermal liquid is rich in organic acids, which can be used for anaerobic digestion.

On the other hand, the present invention also provides a hydrothermal charcoal, which is to perform a hydrothermal carbonization reaction on the pulverized kitchen waste at 180-260° C. for 2-4 hours, and then separate the hydrothermal carbonization reaction products to obtain The hydrothermal solution and solid phase product are obtained after drying the solid phase product.

According to a specific embodiment of the present invention, the hydrothermal charcoal is made by subjecting the pulverized kitchen waste to a hydrothermal carbonization reaction at 180° C. for 2 hours, and then separating the hydrothermal carbonization reaction products to obtain hydrothermal liquid and solid-phase products, and then The solid phase product is obtained after drying.

According to a specific embodiment of the present invention, the hydrothermal carbon has a yield of 42.33-49.33%, a calorific value of 28.36-31.11 MJ/kg, an O/C atomic ratio of 0.15-0.24, and a H/C atomic ratio of 1.10-1.30.

Description of drawings

Fig. 1 is a graph showing the influence of hydrothermal circulation times on hydrothermal char yield and calorific value in Example 2 of the present invention;

Fig. 2 is a graph showing the relationship between the cumulative methane production of experimental group A, experimental group B, and experimental group C as a function of fermentation time in Example 3 of the present invention;

3 is a graph showing the relationship between the methane production rates of experimental group A, experimental group B, and experimental group C as a function of fermentation time in Example 3 of the present invention;

FIG. 4 is a schematic structural diagram of a system used in the method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion according to Embodiment 1 of the present invention.

Description of the main reference numerals in Figure 4:

1. Oil removal tank;

2. Crushing system;

3. Preheating tank;

4. Hydrothermal reaction tank;

5. Steam generator;

6. External buffer tank;

7. Steam recovery tank;

8. Filtration system;

9. Anaerobic reactor;

10. Water washing tower;

11. Dryer.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solutions of the present invention are now described in detail below with reference to the following specific examples, but should not be construed as limiting the scope of the present invention.

Example 1

This embodiment provides a method for treating kitchen waste with hydrothermal carbonization coupled with anaerobic digestion, wherein the method is implemented by using the processing system as shown in FIG. 4 , and the method includes the following specific steps:

(1) Pretreatment of kitchen waste

After the kitchen waste is collected and transported, it is firstly subjected to rough sorting to separate out substances that cannot undergo hydrothermal carbonization, such as glass, metal, stone, etc.; and the solid phase, the oil phase is sent to process biodiesel, and the solid phase enters the next pulverization system 2 for pulverization; after the pulverization is completed, it enters the preheating tank 3 for stirring and preheating, and the preheating temperature is 80-90 °C.

(2) Hydrothermal carbonization of kitchen waste

The preheated kitchen waste is sent to the hydrothermal reaction tank 4 for hydrothermal carbonization reaction. The temperature of the hydrothermal carbonization reaction is 180-260° C. The reaction process is heated by steam, and the steam can be provided by the steam generator 5, or High temperature steam from a refinery boiler, the rotational speed was set at 150 rpm during the reaction. After the reaction is completed, the mixture is sent to the outer buffer tank 6 for cooling, the steam is recovered by the steam recovery tank 7, and sent to the preheating tank 3 for preheating the raw materials. The mixture is separated by filtration system 8 .

(3) Anaerobic digestion of products

A part of the separated hydrothermal liquid is used for mixing with kitchen waste for slurry mixing, and the rest is sent to the anaerobic reactor 9; a part of the hydrothermal charcoal is sent to the water washing tower 10 for washing, and the rest is sent to the anaerobic reactor 9 and the hydrothermal reactor. The liquid is co-digested, and the generated biogas can be used for power generation. The waste heat in the power generation process can be recycled, such as maintaining the temperature of the anaerobic reactor.

(4) Hydrothermal carbon quenched and tempered as fuel

The hydrothermal charcoal washed by the water washing tower is dried by the dryer 11 and then screened to remove the large particulate matter that has not been hydrothermally carbonized, followed by biomass conditioning, and co-molding to prepare biofuel.

It can be seen that the method for treating kitchen waste by hydrothermal carbonization coupled with anaerobic digestion provided by the present invention has high treatment efficiency, and can realize the recycling, harmlessness and reduction treatment of kitchen waste.

Example 2

The present embodiment provides a method for reusing the liquid phase obtained after the hydrothermal carbonization of kitchen waste to improve the solid phase yield and calorific value, which includes the following steps:

(1) After the kitchen waste is collected and transported, it is firstly subjected to rough sorting to separate substances that cannot undergo hydrothermal carbonization, such as glass, metal, stone, etc.; then centrifugal deoiling is performed to separate the oil phase and the solid phase. , the oil phase is sent to process biodiesel, and the solid phase enters the next pulverization system for pulverization; after the pulverization is completed, it enters the preheating tank for stirring and preheating, and the preheating temperature is 80-90 °C.

Wherein, the kitchen waste described in step (1) includes meat, rice, steamed bread, fruits and vegetables, and the like.

(2) Mix 50g of the kitchen waste (moisture content 80%) obtained in step (1) with 25mL of deionized water, and place it in the inner tank of a high temperature and high pressure hydrothermal reactor. The rotational speed was set to 100 rpm, and after maintaining for 2 h, circulating water was introduced to cool the reactor to room temperature. The reacted mixture was separated to obtain a solid phase and a hydrothermal liquid, and the solid phase was sent to an oven for cooling for 24 hours to obtain a hydrothermal charcoal.

In this example, the obtained hydrothermal carbon has a calorific value of 29.50 MJ/kg, an O/C atomic ratio of 0.24, and a H/C atomic ratio of 1.30; the total amount of small-molecule organic acids in the hydrothermal solution is 2103 mg/L, and the acetic acid content is 1499mg/L;

(3) The liquid phase obtained after the hydrothermal carbonization reaction in step (2) is sent to the next batch of experiments for recycling, and the number of cycles is 6 times.

After testing, after the first 3 cycles of the hydrothermal solution prepared in this example, the solid phase yield of the hydrothermal carbonization reaction increased from 40% to 43.39%, 46.13%, and 46.97%, respectively; an increase of 3.39% respectively , 6.13%, 6.97%; from the 4th cycle, the solid phase yield remained basically unchanged; in addition, after the hydrothermal solution prepared in this example was recycled, the calorific value of the obtained hydrothermal carbon also had a certain degree of improve.

Among them, the influence curve of the number of hydrothermal liquid cycles on the yield and calorific value (HHV) of hydrothermal carbon is shown in Figure 1. It can be seen from Figure 1 that the hydrothermal liquid is recycled as the solvent used in the hydrothermal carbonization reaction. It can improve the yield and calorific value of hydrothermal carbon. The specific reasons are: recycling the hydrothermal liquid as the solvent used in the hydrothermal carbonization reaction can make the organic small molecular acid in the hydrothermal liquid regenerate during the circulating hydrothermal process. Polycondensation, secondary polymerization and other reactions can further improve the yield and calorific value of the obtained hydrothermal carbon.

Example 3

The present embodiment provides a method for fermenting the hydrothermal charcoal, hydrothermal liquid, and the mixture of hydrothermal charcoal and hydrothermal liquid obtained after the hydrothermal carbonization reaction, so as to increase the gas production, which comprises the following steps:

(1) Experimental group A: the fermentation raw material is the hydrothermal charcoal prepared in Example 1, the fermentation concentration is 10 g/L (calculated by the total volume of the inoculum used), the total reaction volume is 250 mL, and the inoculum is the biogas of the garbage dump. Liquid, such as biogas slurry from Asuwei Landfill (Changping District, Beijing), without any accelerator.

(2) Experimental group B: the fermentation raw material is the hydrothermal liquid prepared in Example 1, the fermentation volume is 100 mL/L (calculated by the total volume of the inoculum used), the total reaction volume is 250 mL, and the inoculum is the biogas of the landfill. Liquid, such as biogas slurry from Asuwei Landfill (Changping District, Beijing), without any accelerator.

(3) experimental group C: the fermentation raw material is the mixture of the hydrothermal liquid prepared in Example 1 and the hydrothermal charcoal, the hydrothermal liquid fermentation volume is 100mL/L, the hydrothermal charcoal fermentation concentration is 10g/L, and the total reaction volume is 250mL, the inoculum is the biogas slurry from the landfill, such as the biogas slurry taken from the Asuwei landfill (Changping District, Beijing), without any accelerator.

Among them, in experimental groups A-C, the fermentation temperature was 37±1°C, the anaerobic digestion time was 45 days, and the pH was not adjusted.

After testing, in the experimental group A of this example, the cumulative methane production was 360 mL, and the maximum methane production rate was 26.9 mL/d; in the experimental group B, the cumulative methane production was 69 mL, and the maximum methane production rate was 5.3 mL/d. d; In experimental group C, the cumulative methane production was 538.8 mL, and the maximum methane production rate was 56.8 mL/d.

Among them, the graph of the relationship between the cumulative methane production and fermentation time of experimental group A, experimental group B, and experimental group C of the present embodiment is shown in Figure 2; The relationship between the methane production rate and the fermentation time is shown in Figure 3. It can be seen from Figure 2-Figure 3 that adding the hydrothermal carbon after the hydrothermal carbonization of the kitchen waste The cumulative methane production and methane production rate of the system are greatly improved.

Claims (9)

1. A method for treating kitchen waste by hydrothermal carbonization coupled anaerobic digestion is characterized by comprising the following steps:

(1) carrying out hydrothermal carbonization reaction on the crushed kitchen waste, separating a hydrothermal carbonization reaction product to obtain hydrothermal liquid and a solid-phase product, and drying the solid-phase product to obtain hydrothermal carbon; the yield of the hydrothermal carbon is 42.33-49.33%, the heat value is 28.36-31.11MJ/kg, the atomic ratio of O/C is 0.15-0.24, and the atomic ratio of H/C is 1.10-1.30;

the step (1) further comprises the following steps:

mixing the crushed kitchen waste with deionized water, and placing the obtained mixture in a liner of a high-temperature high-pressure hydrothermal reactor for hydrothermal carbonization reaction;

after the reaction is finished, circulating water is introduced to cool to room temperature, hydrothermal liquid and solid-phase products are obtained through separation, and then the solid-phase products are sent to an oven to be dried to obtain hydrothermal carbon;

(2) carrying out anaerobic digestion treatment on the hydrothermal carbon, the hydrothermal liquid or the mixture of the hydrothermal carbon and the hydrothermal liquid obtained in the step (1);

the adding amount of the hydrothermal solution is 50-200mL/L based on the total volume of inoculation liquid used for anaerobic digestion treatment;

the adding amount of the hydrothermal carbon is 5-15g/L based on the total volume of inoculation liquid used for anaerobic digestion treatment;

in the step (2), the temperature of anaerobic digestion is 37 +/-1 ℃, the anaerobic digestion time is 45 days, and the pH value is not adjusted;

the method also comprises the operation of recycling hydrothermal liquid obtained in the step (1) as a solvent used for the hydrothermal carbonization reaction; the cycle number is 5-7.

2. The method as claimed in claim 1, wherein the temperature of the hydrothermal carbonization reaction in step (1) is 180-260 ℃ and the reaction time is 2-4 h.

3. The method according to claim 2, wherein the temperature of the hydrothermal carbonization reaction is 180 ℃ and the reaction time is 2 h.

4. The method of claim 1, further comprising continuing to introduce nitrogen into the system prior to anaerobic digestion to ensure that the system is maintained in an anaerobic environment.

5. The method according to claim 4, wherein the nitrogen is introduced for 1-3 min.

6. The method according to claim 1, wherein the amount of the hydrothermal charcoal added is 10 g/L.

7. The method according to claim 1, wherein the kitchen waste comprises one or more of meat, vegetables, rice, steamed bread, noodles, fruits and oily water.

8. The method according to claim 7, wherein the water content of the kitchen waste is 70-90%.

9. The method according to claim 8, wherein the water content of the kitchen waste is 80%.

Images