Method for co-processing of kitchen waste biogas residue compost and pyrolysis

Abstract

The application discloses a kind of kitchen garbage marsh sludge compost-pyrolysis collaborative disposal methods, comprising the following processes: providing kitchen garbage marsh sludge, the product after kitchen garbage is treated by anaerobic fermentation technology;The kitchen garbage marsh sludge is divided into two parts, and the first part kitchen garbage marsh sludge is pyrolyzed, and marsh sludge charcoal, bio-oil and pyrolysis gas are obtained;The bio-oil and the pyrolysis gas are combusted to generate heat;Second part kitchen garbage marsh sludge and the marsh sludge charcoal are mixed to carry out aerobic composting, and fertilizer is obtained.The marsh sludge charcoal generated by pyrolysis is added to composting, which can significantly improve the composting temperature, not only can fully sterilize, but also can significantly speed up the composting maturity progress, shorten the composting time, improve the marsh sludge treatment efficiency, while also reducing odor emission.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of garbage disposal, more particularly, to a kitchen waste biogas residue composting-thermal decomposition collaborative disposal method. BACKGROUND

[0002] Kitchen waste is mainly edible residues (pig swill) generated by public catering service departments such as catering enterprises, government and school canteens. The characteristics of kitchen waste are mainly high water content, accounting for 80-90% of the total amount of garbage; high organic matter content, high oil content, high salt content; easy to rot, easy to ferment, easy to smell; easy to grow parasitic worms, eggs, pathogenic microorganisms and mycotoxins and other harmful substances. If kitchen waste is not specially classified and treated, it will cause serious harm to the environment.

[0003] The kitchen waste disposal methods mainly include landfill, incineration, aerobic composting, pyrolysis and anaerobic fermentation, etc. Among them, landfill occupies a large area, and there are safety risks such as air pollution and water pollution, so it is rarely used at present; due to the high water content of kitchen waste, incineration and pyrolysis will not only consume a lot of energy, but also have low utilization rate of organic matter; aerobic composting has the problems of long composting time and low disposal efficiency; kitchen waste contains various balanced nutrients required by anaerobic microorganisms, and using anaerobic fermentation method to resourceize it is a relatively appropriate treatment method. At present, more than 80% of kitchen waste is disposed by anaerobic digestion technology. The products of anaerobic fermentation method include biogas, biogas slurry and biogas residue. Biogas can be used for combustion to generate heat, and biogas slurry is discharged to a sewage treatment plant for sewage treatment. Due to the complex composition of kitchen waste and the high salt content, and the incomplete decomposition of biogas residue, the biogas residue obtained by anaerobic fermentation of kitchen waste is not allowed to be directly used as fertilizer.

[0004] The disposal methods of biogas residue obtained by anaerobic fermentation of kitchen waste include incineration, landfill, pyrolysis and aerobic composting. However, the water content of biogas residue obtained by anaerobic fermentation of kitchen waste is still relatively high, about 60%, and from the aspects of energy consumption and organic matter utilization rate, the methods of incineration and pyrolysis are still not suitable; aerobic composting has the problems of long composting time and low treatment efficiency. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned defects existing in the prior art, and to provide a kitchen waste biogas residue composting-thermal decomposition collaborative disposal method, which shortens the composting time, improves the disposal efficiency, and reduces the energy consumption of thermal decomposition.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A kitchen waste biogas residue composting-thermal decomposition collaborative disposal method, comprising the following processes:

[0008] The kitchen waste sludge is a product after kitchen waste is treated by an anaerobic fermentation technology;

[0009] The kitchen waste sludge is divided into two parts, pyrolysis is performed on the first part of the kitchen waste sludge to obtain sludge char, bio-oil and pyrolysis gas;

[0010] The bio-oil and the pyrolysis gas are combusted to generate heat;

[0011] The second part of the kitchen waste sludge is mixed with the sludge char to perform aerobic composting to obtain a fertilizer.

[0012] The embodiment of the present application has the following beneficial effects:

[0013] The embodiment of the present application uses part of the kitchen waste sludge for pyrolysis and part for composting, and adds the sludge char generated by pyrolysis to the composting, which can significantly improve the composting temperature, not only can kill pathogenic bacteria, but also can significantly speed up the composting maturation progress, shorten the composting time, and improve the sludge treatment efficiency. The main reason for improving the composting temperature is that the sludge char of the present application contains a larger amount of micropores and mesopores, which can effectively preserve the input aeration and moisture, nutrients, microorganisms and other substances, accelerate the growth rate of microorganisms, not only improve the composting temperature, but also shorten the composting time. In addition, due to the aromatic ring system structure and oxygen-containing functional groups formed by water participating in pyrolysis in the sludge char, ammonia gas and volatile sulfur-containing gas can be adsorbed, the odor exhaust volume (odor mainly includes ammonia gas and volatile sulfur-containing gas) can be significantly reduced, the odor generated in the disposal fermentation process can be reduced, the cost can be reduced, and air pollution can be reduced. Since the sludge char also contains metal elements such as Ca and Fe from the flocculant added in the anaerobic fermentation process, S and N elements can be combined to further reduce the odor exhaust volume.

[0014] Compared with the single pyrolysis method, the present application can also significantly reduce energy consumption and improve the utilization rate of organic matter. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0016] Among them:

[0017] Figure 1 is a flow chart of the kitchen waste sludge composting-pyrolysis combined disposal method of a specific embodiment of the present application.

[0018] Figure 2is a relationship diagram of pore size and pore volume of biogas residue char prepared by pyrolysis of biogas residue of kitchen waste with different moisture concentrations.

[0019] Figure 3 is a comparison relationship diagram of structure and functional groups of biogas residue char prepared by pyrolysis of biogas residue of kitchen waste with different moisture concentrations.

[0020] Figure 4 is a relationship diagram of the effect of the addition amount of biogas residue char on the temperature of the compost during the composting process.

[0021] Figure 5 is a relationship diagram of the addition amount of biogas residue char and cumulative ammonia gas emission during the composting process.

[0022] Figure 6 is a relationship diagram of the addition amount of biogas residue char and cumulative sulfur-containing gas emission during the composting process.

[0023] Figure 7 is a relationship diagram of net carbon emission of kitchen waste biogas residue during the composting and pyrolysis of the biogas residue according to a certain proportion.

[0024] Figure 8 is a relationship diagram of the germination rate and composting time of different addition amounts of biogas residue char during the composting process. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0026] REFERENCE Figure 1 The present application discloses a kitchen waste biogas residue composting-pyrolysis collaborative disposal method, comprising the following processes:

[0027] 1) Provide kitchen waste biogas residue, which is the product after the kitchen waste is treated by anaerobic fermentation technology, and the kitchen waste refers to edible residues (pig swill) generated by public catering service departments such as catering enterprises, government and school canteens.

[0028] In the above process, the anaerobic fermentation technology is a conventional technology, comprising the following processes:

[0029] First, pretreat the kitchen waste to separate impurities and obtain a first intermediate product;

[0030] Second, crush and sort the first intermediate product to make pulp and obtain a second intermediate product;

[0031] Third, oil-water separation is performed on the second intermediate product to separate out oil and fat, and a third intermediate product is obtained;

[0032] Fourth, hydrolytic acidification is performed on the third intermediate product to obtain a fourth intermediate product;

[0033] Fifth, fermentation is performed on the fourth intermediate product to obtain a solid-liquid mixture and biogas, and the biogas is collected for combustion to provide heat;

[0034] Sixth, a flocculating agent is added to the solid-liquid mixture, and pressure filtration dewatering is performed on the solid-liquid mixture to separate out biogas slurry and kitchen waste sludge. The flocculating agent usually includes CaO and / or FeCl3, and the mass of the flocculating agent is usually 0.03% to 0.1% of the mass of the solid-liquid mixture.

[0035] The above anaerobic fermentation process does not include drying treatment, and the obtained kitchen waste sludge is wet, and the water content is still high, about 40wt.% to 80wt.%. In addition, the kitchen waste sludge contains a large amount of refractory organic and inorganic components (such as salt, etc.), which not only cannot fully utilize the rich organic matter resources contained therein, but also cause a threat to the air, soil and water body due to the high salt and ammonia nitrogen content, resulting in that the kitchen waste sludge cannot be directly used as a fertilizer.

[0036] 2) The kitchen waste sludge is divided into two parts, and pyrolysis is performed on the first part of the kitchen waste sludge to obtain sludge char, bio-oil and pyrolysis gas.

[0037] The above process directly pyrolyzes the wet kitchen waste sludge to obtain sludge char, and compared with the biochar obtained by drying the kitchen waste sludge and then pyrolyzing, the amorphous carbon structure, pore size and types of oxygen-containing functional groups on the carbon structure are improved, because the water in the wet kitchen waste sludge will participate in the pyrolysis reaction to improve the physicochemical properties of the sludge char, such as specific surface area, functional group types, etc. Therefore, the physicochemical properties of the sludge char obtained by directly pyrolyzing the wet kitchen waste sludge are also different from those of the sludge char obtained by directly pyrolyzing the dried kitchen waste sludge.

[0038] The above process directly pyrolyzes the wet kitchen waste sludge to obtain sludge char, and compared with the biochar obtained by drying the kitchen waste sludge without hydrolytic acidification and fermentation and then pyrolyzing, the amorphous carbon structure, pore size and types of oxygen-containing functional groups on the carbon structure are also different, because, first, the product after anaerobic fermentation of the kitchen waste is not the same as the kitchen waste; second, the sludge char also contains Ca, Fe and other metal elements from the flocculating agent added in the anaerobic fermentation process, which also changes the physicochemical properties of the sludge char.

[0039] In a specific embodiment, the temperature for pyrolysis is 500°C to 700°C, and the time for pyrolysis is 20 min to 60 min.

[0040] 3) Combustion of bio-oil and pyrolysis gas to generate heat, which can be used to generate electricity for the aerobic composting process.

[0041] 4) Aerobic composting of the second part of the kitchen waste slurry and slurry char to obtain fertilizer.

[0042] Specifically, the aerobic composting process includes a temperature rising stage, a high temperature stage, a temperature decreasing stage and a maturation stage.

[0043] Temperature rising stage: easy-degradable organic matter is decomposed to generate heat and CO2, and the composting body is heated.

[0044] High temperature stage: a large amount of organic matter is degraded, accompanied by emission of CO2, NH3 and sulfur-containing gas.

[0045] Temperature decreasing stage: organic matter decomposition slows down, and precursor of humus is formed.

[0046] Maturation stage: humus is formed, and the germination rate of the composting body can be increased to more than 80%.

[0047] The present application uses part of the kitchen waste slurry for pyrolysis and part for composting, and adds slurry char produced by pyrolysis to the composting process, which can significantly increase the composting temperature, not only kill bacteria, but also significantly speed up the composting maturation process, shorten the composting time, and improve the slurry treatment efficiency. The main reason for increasing the composting temperature is that the slurry char of the present application contains a large amount of micropores and mesopores, which can effectively preserve the input aeration and moisture, nutrients, microorganisms and other substances, accelerate the growth rate of microorganisms, not only increase the composting temperature, but also reduce the composting time. In addition, due to the presence of aromatic ring system structure and oxygen-containing functional groups formed by water participating in pyrolysis in the slurry char, ammonia and volatile sulfur-containing gas can be adsorbed, the odor exhaust volume (odor mainly includes ammonia and volatile sulfur-containing gas) can be significantly reduced, the odor generated during the fermentation process can be disposed of, the cost can be reduced, and air pollution can be reduced. Since the slurry char also contains metal elements such as Ca and Fe from the flocculant added during anaerobic fermentation, it can also combine with S and N elements to further reduce the odor exhaust volume.

[0048] Compared with the separate pyrolysis method, the present application can also significantly reduce energy consumption and improve the utilization rate of organic matter.

[0049] In a specific embodiment, the moisture content of the kitchen waste biogas residue is 40wt.% to 80wt.%, so that the kitchen waste biogas residue does not need to be dried to save electric energy and deal with the odor generated in the drying process. In addition, experiments have shown that as the moisture content increases, the micropore structure and mesopore structure of the biogas residue char increase, which increases the pore volume and specific surface area, and significantly improves the treatment efficiency of aerobic composting. Water participates in pyrolysis, significantly increases the number of aromatic ring system structures and oxygen-containing functional groups, can adsorb ammonia and volatile sulfur-containing gases, significantly reduces the exhaust gas emission of odor (odor mainly includes ammonia and volatile sulfur-containing gases), and can not need to deal with the odor generated in the fermentation process, thereby reducing costs and air pollution.

[0050] In a specific embodiment, the mass ratio of the first part of the kitchen waste biogas residue to the second part of the kitchen waste biogas residue is 2:8 to 3:7. The net carbon emission generated by the synergistic treatment of pyrolysis and composting of the biogas residue in the above ratio is lower than that of separate composting or separate pyrolysis treatment.

[0051] In a specific embodiment, during aerobic composting, the added mass of the biogas residue char is 12.5% to 25% of the dry mass of the second part of the kitchen waste biogas residue, which can significantly improve the composting temperature and speed up the biogas residue treatment efficiency, while the net carbon emission is low.

[0052] In a specific embodiment, the kitchen waste biogas residue contains metal compounds. Specifically, the metal elements in the metal compounds can include one or more of Ca, Fe, Mg, Na, etc. The metal elements in the metal compounds can combine with S, N, etc. in the odor to reduce the emission of odor and avoid environmental pollution caused by composting. The mass percentage of metal elements in the kitchen waste biogas residue is 0.1% to 5%.

[0053] The following are specific embodiments.

[0054] Embodiment 1

[0055] The pore structure of the biogas residue char prepared by pyrolysis of kitchen waste biogas residue with different moisture concentrations was studied. As shown in FIG. 1, the pore size and pore volume of the biogas residue char obtained by pyrolysis of biogas residue with moisture content of 5wt.%, 20wt.%, 40wt.% and 60wt.% are shown, respectively. As shown in FIG. 2, it can be seen that as the moisture content of the biogas residue increases, the micropore structure and mesopore structure of the prepared biogas residue char increase, because water participates in the pyrolysis reaction of the biogas residue and reacts with more carbon elements to generate more pore structures. Figure 2 Figure 2 The pore structure and functional groups of the biogas residue char obtained by pyrolysis were further studied, as shown in FIG. 3. In FIG. 3, V is the volume of the functional group, and A is the surface area of the functional group.

[0056] The pore structure and functional groups of the biogas residue char obtained by pyrolysis were further studied, as shown in FIG. 3. In FIG. 3, V is the volume of the functional group, and A is the surface area of the functional group. Figure 3 ​​R represents methyl group on carbon structure, G R represents 3-5 aromatic ring structure on carbon structure, G L represents oxygen-containing functional group on carbon structure, S L represents para aromatic ring structure on carbon structure, each vertical stripe from left to right represents the pyrolysis experiment of biogas residue with water content of 5wt.%, 20wt.%, 40wt.% and 60wt.% respectively, it can be seen that with the increase of water content, the types of methyl group, aromatic ring structure, oxygen-containing functional group and para aromatic ring on amorphous carbon structure in biogas residue char increase, the reason may be that water promotes the degradation of polyaromatic ring system, generates more simple aromatic ring system structure, and further increases the amorphous carbon structure and oxygen-containing functional group structure.

[0057] Therefore, preferably, the water content of the kitchen waste biogas residue is 40%-80%.

[0058] Example 2

[0059] Effect of the addition amount of biogas residue char on the temperature in the composting process

[0060] In the kitchen waste biogas residue composting process, biogas residue char with mass of 6.25wt.% (R2), 12.5wt.% (R3) and 25wt.% (R4) of the dry weight of kitchen waste biogas residue was added respectively, and biogas residue char with 0wt.% (R1) was used as a control, and the results are shown in Figure 4 It can be seen that the addition of biogas residue char can increase the temperature of the composting body, and the effect of temperature increase is more obvious with the increase of the addition amount of biogas residue char, indicating that the addition of biogas residue char is beneficial to the temperature increase of the composting body.

[0061] The odor (including ammonia and volatile sulfur-containing gas) of each fermentation process was collected to study the effect of the addition amount of biogas residue char on the emission of ammonia and volatile sulfur-containing gas in the composting process.

[0062] Reference Figure 5 With the increase of the addition amount of biogas residue char, the cumulative ammonia emission is reduced by 5%-21%, the reason may be that the functional groups in the biogas residue char have adsorption effect on ammonia, and the porous structure of the biogas residue char promotes the growth of nitrifying bacteria, accelerates the conversion of ammonium nitrogen to nitrate nitrogen, reduces the conversion of ammonium nitrogen to ammonia, and further reduces the emission of ammonia.

[0063] The cumulative emission of volatile sulfur-containing gas in the kitchen waste biogas residue composting process is shown in Figure 6 It can be seen that the addition of biogas residue char can reduce the emission of sulfur-containing gas by 16%-20%. The reason may be that the porous structure and metal elements in the biogas residue char have adsorption effect on volatile sulfur-containing gas.

[0064] Therefore, preferably, in the aerobic composting process, the mass percentage of biogas residue char in the mixture of biogas residue char and the second part of kitchen waste biogas residue is 12.5% ​​to 25%. This can not only significantly increase the composting temperature, fully sterilize, and shorten the composting time, but also significantly reduce odor emissions by about 20%.

[0065] Example 3

[0066] The net carbon emissions were studied by co-processing food waste biogas residue with composting and pyrolysis in a certain proportion. The results are as follows: Figure 7 As shown, E0 represents all treatment using composting, E1 represents a composting to pyrolysis ratio of 9:1, E2 represents a composting to pyrolysis ratio of 8:2, E3 represents a composting to pyrolysis ratio of 7:3, E4 represents a composting to pyrolysis ratio of 6:4, and E5 represents a composting to pyrolysis ratio of 5:5.

[0067] The specific experimental process was as follows: using the same food waste biogas residue, composting and pyrolysis were carried out in different proportions. The pyrolysis process involved placing the food waste biogas residue in a tubular furnace at 600℃ for 60 minutes to obtain biogas residue char, bio-oil, and pyrolysis gas. The aerobic composting process involved mixing the biogas residue char and food waste biogas residue and then composting it. The compost entered four stages: heating stage, high temperature stage, cooling stage, and maturation stage. The temperature in the high temperature stage should exceed 55℃. During the maturation stage, the germination rate of the compost exceeded 80%, at which point the composting was considered complete, yielding fertilizer and addressing the odor generated during the composting process.

[0068] Net carbon emissions include indirect carbon emissions and direct carbon emissions. Indirect carbon emissions refer to the amount of carbon emitted due to the net energy consumed in the process of producing biogas residue, while direct carbon emissions refer to the amount of carbon directly emitted during the process of biogas residue treatment.

[0069] Specifically, the calculation of indirect carbon emissions includes: calculating the electrical energy Q1 required for the pyrolysis process, calculating the energy Q2 that can be released after the bio-oil and pyrolysis gas produced in the pyrolysis process are burned, calculating the electrical energy Q3 consumed by aeration in the composting process, calculating the net energy consumption Q using Q1-Q2+Q3, and converting the net energy consumption Q into the amount of carbon released in the process of burning fuel to obtain energy Q.

[0070] The calculation of direct carbon emissions includes: calculating the amount of carbon in the flue gas released from the combustion of bio-oil and pyrolysis gas, and calculating the amount of carbon in the CO2 produced during composting.

[0071] from Figure 7 It can be seen that when pyrolysis and composting are carried out in a suitable ratio (2:8 to 3:7), the net carbon emissions generated by the treatment of kitchen waste sludge are lower than those of composting or pyrolysis alone, which can reduce net carbon emissions and improve environmental protection.

[0072] Example 4

[0073] Reference Figure 8 , which is a graph of the germination rate and the composting time of different amounts of biogas residue carbon added in the composting process, R1 is the control group (no biogas residue carbon added), R2, R3 and R4 groups add 6.25%, 12.5% and 25% of biogas residue carbon respectively, and each group of data includes a bar graph from left to right representing R1, R2, R3 and R4. As can be seen from the figure, the germination rate of R4 exceeds 100% at the 35th day, while the germination rate of the control group (R1) is still less than 40% at the 50th day, indicating that it still needs a longer time to improve the germination rate. From the current results, adding 25% of biogas residue carbon can improve the composting time by more than 30% ((50-35) / 50*100%) compared to adding 6.25%, 12.5% of biogas residue carbon, and can significantly shorten the composting time compared to the control group.

[0074] The above-described embodiments only express several embodiments of the present application, which are described in more detail and in more detail, but cannot be understood as limiting the scope of the application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application patent should be subject to the appended claims.

Claims

1. A method for co-processing of kitchen waste biogas residue compost and pyrolysis, characterized in that, The process comprises the following steps: providing kitchen waste sludge, which is the product of kitchen waste treated by anaerobic fermentation technology, and the moisture content of the kitchen waste sludge is 40wt%-80wt%; dividing the kitchen waste sludge into a first part and a second part, wherein the mass ratio of the first part to the second part is 2:8-3:7; pyrolyzing the first part of the kitchen waste sludge at a temperature of 500-700℃ for 20-60min to obtain sludge char, bio-oil and pyrolysis gas; combusting the bio-oil and the pyrolysis gas to generate heat; mixing the second part of the kitchen waste sludge and the sludge char to perform aerobic composting to obtain fertilizer, wherein the added mass of the sludge char is 12.5%-25% of the dry mass of the second part of the kitchen waste sludge.

2. The method according to claim 1, wherein, The kitchen waste sludge contains metal compounds.

3. The method according to claim 1, wherein the method is characterized by, The anaerobic fermentation technology comprises the following steps: pretreating the kitchen waste to separate impurities and obtain a first intermediate product; crushing and sorting the first intermediate product to obtain a second intermediate product; separating oil from the second intermediate product to obtain a third intermediate product; hydrolyzing and acidifying the third intermediate product to obtain a fourth intermediate product; fermenting the fourth intermediate product to obtain a solid-liquid mixture and biogas; adding a flocculating agent to the solid-liquid mixture, and performing pressure filtration dewatering on the solid-liquid mixture to obtain sludge and kitchen waste sludge.

4. The kitchen waste biogas residue composting-pyrolysis synergistic disposal method according to claim 3, characterized in that, The flocculating agent comprises CaO and / or FeCl3, and the added mass of the flocculating agent is 0.03%-0.1% of the mass of the solid-liquid mixture.

5. The method according to claim 1, wherein the method is characterized by, The aerobic composting comprises the following steps: a temperature rising stage: easy-degradable organic matter is decomposed to generate heat and CO2, and the composting body is heated; a high-temperature stage: a large amount of organic matter is decomposed, accompanied by the emission of CO2, NH3 and sulfur-containing gases; a temperature falling stage: the decomposition of organic matter slows down, and precursor substances of humus are formed; a maturation stage: humus is formed, and the germination rate of the composting body reaches more than 80%.

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