Method for recovering liquid-phase phosphorus and preparing solid fuel through co-hydro-thermal treatment of fish paste and PVC

Abstract

The invention provides a method for recovering liquid-phase phosphorus and preparing solid fuel through co-hydro-thermal treatment of fish mud and PVC, and provides an optimized hydro-thermal reaction process aiming at the problems that the recovery rate of the liquid-phase phosphorus is low and the performance of hydro-thermal carbon fuel is poor in the hydro-thermal treatment process of the fish mud (namely aquaculture bottom mud). The method specifically comprises the following steps: (1) pretreating fish paste; (2) mixing the treated fish paste and polyvinyl chloride (PVC) according to a certain proportion; and (3) carrying out hydrothermal carbonization treatment on the mixture obtained in the step (2). And (4) carrying out solid-liquid separation on the carbonized product in the step (3). And (5) a liquid-phase product can be directly used for phosphorus recovery. And (6) the solid-phase product can be used as solid fuel. The method has the advantages of being easy and convenient to operate, high in resource utilization rate, environmentally friendly and the like, and is suitable for efficient treatment and energy utilization of organic waste.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste resource utilization, and particularly relates to a method for co-hydrothermal treatment of fish sludge and PVC to recover liquid-phase phosphorus and prepare solid fuel. Background Art

[0002] With the rapid development of the aquaculture industry, the resource utilization of fish sludge (i.e., aquaculture bottom sludge), a solid waste with high organic matter and high phosphorus content, has attracted increasing attention. Fish sludge contains abundant organic matter and phosphorus resources. If directly discarded or improperly treated, it may cause environmental pollution and resource waste. Currently, the treatment methods of fish sludge mainly include land application, anaerobic digestion, composting, and pyrolysis treatment, etc. However, these traditional methods have certain limitations. For example:

[0003] 1. Land application and composting: Although directly using fish sludge for agricultural fertilization can recover some phosphorus resources, due to its high moisture content and perishable characteristics, it is easy to cause secondary pollution, and the phosphorus utilization rate is low.

[0004] 2. Anaerobic digestion: Although it can convert fish sludge into biogas to achieve energy recovery, the reaction time is long, and the phosphorus recovery effect is limited. It is difficult to effectively separate and recover the phosphorus resources therein.

[0005] 3. Pyrolysis treatment: Pyrolysis at high temperature can generate biochar with relatively high calorific value, but the phosphorus is mainly enriched in the solid phase and is difficult to be effectively utilized. And some elements such as nitrogen and sulfur may be converted into polluting gases, increasing environmental risks.

[0006] On the other hand, polyvinyl chloride (PVC) is a widely used plastic material, and the treatment of its waste is also a difficult problem in the field of environmental protection. PVC will release harmful gases such as hydrogen chloride (HCl) during conventional incineration or pyrolysis, and then generate chlorinated organic pollutants such as dioxins and polychlorinated biphenyls, resulting in serious air pollution. Therefore, how to effectively remove chlorine elements during the heat treatment process, reduce pollution, and at the same time improve the resource utilization value of by-products is also an urgent problem to be solved.

[0007] In recent years, hydrothermal treatment technology has received extensive attention due to its mild operating conditions and good resource utilization effect. However, existing hydrothermal treatment research mainly focuses on the conversion of single phosphorus-rich organic solid wastes (such as sludge, livestock manure, etc.), with problems such as low recovery rate of liquid-phase phosphorus, complex phosphorus recovery processes, the need for external chemical raw materials, and poor combustion performance of hydrothermal carbon. For example, in "A Method for Directional and Clean Recovery of Phosphorus in Sludge by Alkali Heat Treatment" CN113772905B by Dai Xiaohu, Ding Yanyan, and Wu Boran on September 9, 2022, calcium oxide or calcium hydroxide needs to be added to the sludge hydrothermal system. First, the phosphorus form in the solid-phase product is regulated to hydroxyapatite (AP)-state phosphorus, and then HCl or H2SO4 solution needs to be added to use acid leaching method to transfer the phosphorus in the solid-phase product to the liquid phase for further recovery and utilization; Xu Jin, et al. in "A Method for Hydrothermal Carbonization of Livestock Manure to Recover Phosphorus" CN109722264B on March 30, 2021. First, the livestock manure is hydrothermally treated. After solid-liquid separation, the biochar is acid-leached to transfer the phosphorus element from the solid phase to the liquid phase, and a phosphorus-rich filtrate is obtained after filtration for further recovery and treatment.

[0008] The above methods have complex processes, all require further treatment after acid leaching, and have low recovery rates. Summary of the Invention

[0009] In view of the problems of low recovery rate of liquid-phase phosphorus and poor fuel performance of hydrothermal carbon during the hydrothermal treatment of fish mud (i.e., aquaculture bottom mud) in the prior art, the present invention provides an optimized hydrothermal treatment method. The aim is to improve the recovery rate of liquid-phase phosphorus and simultaneously prepare high-quality solid fuels. By adding polyvinyl chloride (PVC) for co-treatment and regulating the hydrothermal reaction conditions, optimizing the hydrothermal reaction temperature and raw material ratio, realizing the efficient release of phosphorus into the liquid-phase product, and reducing the chlorine residue by reasonably regulating the degradation behavior of PVC, thereby improving the combustion performance of hydrothermal carbon, preparing solid fuels with high calorific value, improving the resource utilization rate of waste, and meeting the application requirements of clean energy.

[0010] The object of the present invention can be achieved by the following technical solutions:

[0011] The present invention provides a method for co-hydrothermal treatment of fish mud and PVC to synchronously recover liquid-phase phosphorus and prepare solid fuels, and the specific steps are as follows:

[0012] (1) Pretreat the fish mud;

[0013] (2) Mix the treated fish mud and polyvinyl chloride PVC in a certain proportion;

[0014] (3) Perform hydrothermal carbonization treatment on the mixture in step (2);

[0015] (4) Separate the carbonized product in step (3) into solid and liquid phases;

[0016] (5) The liquid-phase product can be directly used for phosphorus recovery;

[0017] (6) The solid-phase product can be used as a solid fuel;

[0018] Among them, the mass ratio of fish sludge to PVC in step (2) is 9:1 - 1:9;

[0019] Among them, in step (3), the temperature of the hydrothermal carbonization treatment is 200°C - 300°C, and the reaction time is 1 h.

[0020] Further, the pretreatment of the fish sludge described in step ( ) is that the fish sludge is centrifuged at 5000 r / min for 5 min to remove part of the water, then dried to constant weight in an oven at 105°C, and sieved through a 60-inch sieve.

[0021] Further, the mass ratio of fish sludge to PVC in step (2) is 7:3 - 1:9.

[0022] Further preferably, the mass ratio of fish sludge to PVC in step (2) is 1:1.

[0023] Further, the temperature of the hydrothermal carbonization treatment in step (3) is 220°C - 240°C, and the reaction time is controlled to be 1 h.

[0024] Further preferably, in step (3), the temperature of the hydrothermal carbonization treatment is 220°C, and the reaction time is 1 h.

[0025] Further, the composition, ash content, and calorific value of the fish sludge in the present invention are: N: 4.27%; C: 27.42%; H: 4.56%; S: 1.06%; O: 30.53%; Ash: 32.16%; HHV: 10.33 MJ / kg.

[0026] The present invention utilizes the high-temperature and high-pressure environment of the hydrothermal reaction to achieve the synergistic conversion of fish sludge and PVC. The HCl in-situ generated after the hydrothermal dechlorination of PVC promotes the migration of phosphorus elements in the fish sludge into the liquid phase; at the same time, the hydrothermal residue of PVC with high calorific value and low ash content significantly improves the fuel performance of the hydrothermal carbon of fish sludge.

[0027] The main advantages of the present invention compared with the prior art are:

[0028] 1. Compared with the traditional phosphorus recovery technology system, the present invention simplifies steps such as hydrothermal carbonic acid leaching and directly migrates phosphorus into the liquid phase. After adding PVC to the fish sludge hydrothermal system, the phosphorus content of the liquid-phase product increases significantly, from 0.75 mg / g TS to 8.66 mg / g TS.

[0029] 2. PVC can undergo synergistic conversion with the organic matter in fish mud. When compared with the hydrothermal treatment of fish mud alone, the calorific value of the hydrothermal carbon product increases from 13.15 KJ / kg to 26.25 KJ / kg, optimizing the combustion performance of the solid fuel.

[0030] 3. This method avoids the dioxin pollution caused by direct incineration of PVC. At the same time, it realizes the resource utilization of fish mud, reducing the waste treatment cost and environmental burden.

[0031] The method of the present invention realizes the synergistic treatment of fish mud and PVC by optimizing the hydrothermal treatment process, improves the recovery rate of liquid-phase phosphorus and simplifies its recovery steps. At the same time, it significantly improves the quality of the solid fuel, providing an efficient and environmentally friendly solution for the high-value utilization of waste. Description of the Drawings

[0032] Figure 1 It is a comparison diagram of the phosphorus content of the liquid-phase products of the fish mud and PVC raw materials of the present invention under different ratios (reaction conditions: 240 °C, 1 h).

[0033] Figure 2 It is a comparison diagram of the phosphorus content of the liquid-phase products of the present invention at different reaction temperatures (reaction conditions: the ratio of fish mud to PVC raw material is 1:1, and the reaction time is 1 h). Specific Embodiments

[0034] Example 1:

[0035] (1) Take 0.6 g of pretreated fish mud and 0.6 g of PVC, mix them evenly, place them in a hydrothermal reaction kettle, and add 12 mL of deionized water.

[0036] (2) Carry out hydrothermal carbonization at 220 °C for 1 h.

[0037] (3) Separate the solid and liquid of the hydrothermal carbonization product in (2).

[0038] (4) The phosphorus content of the liquid-phase product is 12.73 mg / g TS.

[0039] Example 2:

[0040] (1) Take 0.6 g of pretreated fish mud and 0.6 g of PVC, mix them evenly, place them in a hydrothermal reaction kettle, and add 12 mL of deionized water.

[0041] (2) Carry out hydrothermal carbonization at 240 °C for 1 h.

[0042] (3) Separate the solid and liquid of the hydrothermal carbonization product in (2).

[0043] (4) The phosphorus content of the liquid-phase product is 8.66 mg / g TS.

[0044] (5) The calorific value of hydrothermal carbon is 24.28 MJ / kg.

[0045] Comparative Example 1:

[0046] The difference from Example 2 is that the raw material is 1.2 g of pretreated fish mud, and no PVC is added, and the rest are the same as in Example 2. Under the same conditions, the phosphorus content in the liquid-phase product of this comparative example is only 0.75 mg / g TS. The calorific value of hydrothermal carbon is 13.15 MJ / kg.

[0047] Compared with Comparative Example 1, the phosphorus content in the liquid-phase product in Example 2 increased from 0.75 mg / g TS to 8.66 mg / g TS, an increase of nearly 12 times; the calorific value of hydrothermal carbon increased from 13.15 MJ / kg to 24.28 MJ / kg. It shows that remarkable effects have been achieved in the co-hydrothermal treatment for recovering liquid-phase phosphorus by adding PVC to fish mud.

[0048] Example 3:

[0049] (1) Take 0.84 g of pretreated fish mud and 0.36 g of PVC, mix them evenly, place them in a hydrothermal reaction kettle, and add 12 mL of deionized water.

[0050] (2) Conduct hydrothermal carbonization at 240 °C for 1 h.

[0051] (3) Separate the solid and liquid of the hydrothermal carbonization product in (2).

[0052] (4) The phosphorus content in the liquid-phase product is 8.48 mg / g TS.

[0053] (5) The calorific value of hydrothermal carbon is 23.74 MJ / kg.

[0054] Example 4:

[0055] (1) Take 0.36 g of pretreated fish mud and 0.84 g of PVC, mix them evenly, place them in a hydrothermal reaction kettle, and add 12 mL of deionized water.

[0056] (2) Conduct hydrothermal carbonization at 240 °C for 1 h.

[0057] (3) Separate the solid and liquid of the hydrothermal carbonization product in (2).

[0058] (4) The phosphorus content in the liquid-phase product is 5.41 mg / g TS.

[0059] (5) The calorific value of hydrothermal carbon is 26.25 MJ / kg.

[0060] Based on the above embodiments, the present invention provides a specific method for co-hydrothermal treatment of fish mud and polyvinyl chloride (PVC) to recover liquid-phase phosphorus and prepare solid fuel. By adding PVC for co-treatment and regulating the hydrothermal reaction conditions, optimizing the hydrothermal reaction temperature and raw material ratio, the efficient release of phosphorus into the liquid-phase product is achieved. By reasonably regulating the degradation behavior of PVC, the chlorine residue is reduced, thereby improving the combustion performance of hydrochar. At the same time, solid fuel with high calorific value is prepared, improving the resource utilization rate of waste and meeting the application requirements of clean energy.

[0061] Through the above embodiments, the relationship between the amount of PVC added to fish mud and the liquid-phase phosphorus recovery rate under different hydrothermal conditions was verified. Through comparative examples, the different effects of adding PVC and not adding PVC to fish mud on the liquid-phase phosphorus recovery rate were verified.

[0062] In some embodiments, the addition ratio of fish mud to polyvinyl chloride (PVC) can be selected as 9:1 - 1:9, preferably 7:3 - 1:9, and most preferably 5:5. With this addition ratio, the phosphorus content in the liquid phase reaches 8.66 mg / g TS, achieving outstanding technical effects. See the appendix Figure 1 。

[0063] In some embodiments, the temperature of hydrothermal carbonization treatment can be selected as 200°C - 300°C, preferably 220°C - 240°C, and the optimal choice is 220°C. At the same reaction time, the phosphorus content in the liquid-phase product at a reaction temperature of 220°C reaches 12.73 mg / g TS, achieving outstanding technical effects. See the appendix Figure 2 。

[0064] The elemental analysis, ash content and calorific value (reaction conditions: 240°C, 1 h) of the fish mud and PVC raw materials of the present invention and their hydrochar products under different ratios are shown in Table 1.

[0065]

[0066] In Table 1: O% = 100% - C% - H% - N% - S% - Ash%; HHV = 0.3383C + 1.442(H – O / 8).

[0067] The method of the present invention has the advantages of simple operation, high resource utilization rate, environmental friendliness, etc. The liquid-phase product of the hydrothermal reaction can be directly used for phosphorus recovery, and the solid-phase product can be used as solid fuel, realizing the efficient treatment and energy utilization of fish mud organic waste.

[0068] It should be further noted that the above embodiments are only used for understanding the technical solutions of the present invention, and are not used to limit the protection scope of the present invention. Any obvious adjustments and modifications made to the technical solutions of the present invention that belong to the technical concept of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel, characterized in that, It includes the following steps: (1) Pretreat the fish paste; (2) Mix the treated fish paste and polyvinyl chloride (PVC) in a certain proportion; (3) Perform hydrothermal carbonization on the mixture in step (2); (4) Separate the solid and liquid of the carbonized product in step (3); (5) The liquid phase product can be directly used for phosphorus recovery; (6) The solid phase product can be used as solid fuel; Among them, in step (2), the mass ratio of fish paste to PVC in the mixture is 9:1 - 1:9; Among them, in step (3), the temperature of the hydrothermal carbonization treatment is 200°C - 300°C, and the reaction time is 1 h.

2. The method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: In step (1), the pretreatment of the fish paste is to centrifuge the fish paste at 5000 r / min for 5 min to remove part of the water, then dry it to a constant weight in an oven at 105°C, and screen it through a 60-inch sieve.

3. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: In step (2), the mass ratio of fish paste to PVC in the mixture is 7:3 - 1:

9.

4. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: In step (2), the mass ratio of fish paste to PVC in the mixture is 1:

1.

5. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: In step (3), the temperature of the hydrothermal carbonization treatment is 220°C - 240°C, and the reaction time is 1 h.

6. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: In step (3), the temperature of the hydrothermal carbonization treatment is 220°C, and the reaction time is 1 h.

7. A method for co-hydrothermal treatment of fish mud and PVC to recover liquid-phase phosphorus and prepare solid fuel according to claim 1, characterized in that: The composition, ash content and calorific value of the fish paste are: N: 4.27%; C: 27.42%; H: 4.56%; S: 1.06%; O: 30.53%; Ash: 32.16%; HHV: 10.33 MJ / kg.

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