Municipal sludge pyrolysis co-processing waste plastic pollution control process

Abstract

The invention discloses a municipal sludge pyrolysis co-treatment waste plastic pollution control process. The process comprises the following steps: S01, mixing plastic particles with municipal sludge according to a mass ratio of 15-30%; wherein the mass ratio is the ratio of the plastic weight to the sum of the plastic weight and the dry weight of the municipal sludge; s02, putting the mixed material into a pyrolyzing furnace, and heating and pyrolyzing in a nitrogen or air atmosphere. In the step S02, the heating pyrolysis process adopts segmented heating, wherein in the first stage, the temperature is raised to 300-450 DEG C at the temperature raising rate of 30 DEG C / min; in the second stage, the temperature is increased to 600-750 DEG C at the speed of 10-20 DEG C / min; and then keeping the temperature constant for 30-90 minutes. According to the pollution control process for co-processing the waste plastics through municipal sludge pyrolysis, efficient treatment of the sludge and the waste plastics is achieved by optimizing pyrolysis process parameters and a co-processing mode, meanwhile, the quality of pyrolysis products and the energy utilization efficiency are improved, and remarkable environmental benefits and application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technologies, and particularly to a process for controlling the pollution of municipal sludge pyrolysis and co-disposal of waste plastics. Background Art

[0002] Municipal sludge is a solid waste generated during the sewage treatment process, containing a large amount of organic matter, heavy metals and pathogens. Traditional treatment methods such as landfilling and incineration have problems such as occupying land and generating harmful gases.

[0003] Waste plastic pollution refers to the pollution caused by plastic products being discarded or abandoned in the environment after use, which is difficult to degrade naturally. Under the action of external forces, the structure of plastic products will be damaged, generating a large number of plastic particles, making it difficult to recycle.

[0004] Among various sludge treatment methods, the sludge pyrolysis technology can not only effectively reduce the volume of sludge, but also degrade most of the organic matter and toxic and harmful substances in the sludge. Under the action of high temperature, microplastics in the sludge can also be effectively removed. However, the current research on how sludge and waste plastic particles synergize with each other during the pyrolysis process is not sufficient, and the effects of plastic particles on the combustion behavior, process parameters, gas emissions and ash properties during the sludge pyrolysis process have not been clarified. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for controlling the pollution of municipal sludge pyrolysis and co-disposal of waste plastics to solve the problems existing in the prior art.

[0006] To achieve the above purpose, the technical solution of the present invention provides a process for controlling the pollution of municipal sludge pyrolysis and co-disposal of waste plastics, including the following steps: S01. Mix plastic particles with municipal sludge at a mass ratio of 15%-30%; where the mass ratio is the ratio of the weight of plastic to the sum of the weight of plastic and the dry weight of municipal sludge; S02. Place the mixed material in a pyrolysis furnace and heat and pyrolyze it under a nitrogen or air atmosphere.

[0007] Further, in step S01, the particle size of the plastic particles ≤ 200 mesh, obtained by crushing and sieving the plastic.

[0008] Further, in step S01, the dry weight of the municipal sludge is the weight of the solid residue after all moisture is removed from the sludge after drying treatment.

[0009] Further, in step S01, the plastic particles are particles of any one or more plastics such as polyethylene and polyethylene terephthalate (PET).

[0010] Further, in step S01, the municipal sludge is pretreated, and the pretreatment includes crushing, sieving, and dewatering; in step S01, the water content of the municipal sludge is 15%-30%.

[0011] Further, in the heating pyrolysis process of step S02, staged heating is adopted, where the first stage is to heat up to 300-450 degrees at a heating rate of 30°C / min; the second stage is to heat up to 600-750 degrees at a heating rate of 10-20°C / min; and then keep it at a constant temperature for 30-90 minutes.

[0012] The municipal sludge pyrolysis collaborative disposal waste plastic pollution control process proposed by the present invention realizes the efficient treatment of sludge and waste plastics by optimizing the pyrolysis process parameters and collaborative disposal methods, while improving the quality of pyrolysis products and energy utilization efficiency, and has significant environmental benefits and application prospects. Specifically, in this application, through the optimization of process parameters and the addition of plastics, the combustion of sludge during pyrolysis can be effectively improved. The release of CO during the light volatile matter decomposition stage of the mixed sample is reduced, but the absorption intensities of functional groups such as C-H, CO, C=O, C-O, and C=C during the pyrolysis process of the mixed sample are also enhanced. At the same time, the addition of microplastics promotes the escape of S in MS. The addition of microplastics can reduce the fouling and slagging properties of sludge ash. 2 The release amount, but also enhances the absorption intensity of functional groups such as C-H, CO, C=O, C-O, and C=C during the pyrolysis process of the mixed sample. At the same time, the addition of microplastics promotes the escape of S in MS. The addition of microplastics can reduce the fouling and slagging properties of sludge ash. Description of the Drawings

[0013] Figure 1 It is a scanning electron microscope image of the pyrolysis product in Example 1 of the present invention.

[0014] Figure 2 It is a scanning electron microscope image of the pyrolysis product in Example 1 of the present invention.

[0015] Figure 3 It is a scanning electron microscope image of the pyrolysis product in Example 2 of the present invention.

[0016] Figure 4 It is a scanning electron microscope image of the pyrolysis product in Example 3 of the present invention. Detailed Embodiments

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] The present invention relates to a municipal sludge pyrolysis and coordinated disposal of waste plastic pollution control process, comprising the following steps: S01, mixing plastic particles with municipal sludge at a mass ratio of 15%-30%; wherein the mass ratio is the ratio of the weight of plastic to the sum of the weight of plastic and the dry weight of municipal sludge; S02, placing the mixed material in a pyrolysis furnace, and heating it in stages at a heating rate of 10-30°C / min under a nitrogen or air atmosphere: in the first stage, heating to 300-450 degrees at a heating rate of 30°C / min; in the second stage, heating to 600-750 degrees at a heating rate of 10-20°C / min, and keeping the temperature constant for 30-90 minutes.

[0019] In the step S01, the particle size of the plastic particles is ≤200 mesh, and is obtained by crushing and sieving the plastic.

[0020] The dry weight of municipal sludge in step S01 is the weight of the solid residue after all moisture is removed from the sludge after drying. Specifically, in the embodiment of the present application, the sludge sample is placed in a cool and ventilated place to dry and then dried in an oven at 65°C for 24 hours to obtain the sludge dry weight data. In step S01, the municipal sludge is pretreated, and the pretreatment includes crushing, screening, and dehydration. The crushing, screening, and dehydration adopt existing mature processes. In step S01, the water content of municipal sludge is 15%-30%. After the plastic particles are mixed, the sludge dry weight data and the sludge water content are first obtained by sampling, and then the sludge dry weight is calculated according to the total weight of the water-containing sludge, and then the amount of plastic particles added is calculated.

[0021] The plastic particles in step S01 are particles of any one or more of polyethylene and polyethylene terephthalate (PET).

[0022] The following examples are provided in this application to further illustrate the present invention.

[0023] During the laboratory verification phase, the sludge used in this application was taken from a domestic sewage treatment plant in Foshan City. The sludge (MS) was crushed, sieved, and dehydrated. Microplastics were selected from high-density polyethylene powder (HDPE, Shanghai McLean Pharmacy) and polyethylene terephthalate powder (PET, Shandong Yawanglai Chemical).

[0024] The plastic particles and sludge were thoroughly stirred and mixed to obtain the following mixed sample.

[0025]

[0026] In the laboratory verification stage, a tube furnace (SX-G12123, China) was used to simulate the pyrolysis process. The experimental device included a gas cylinder, the main body of the tube furnace, and a tail gas purification device. The tube furnace was the heating main body, with a corundum tube inside that was 1000 mm long and 50 mm in diameter. The experimental sample would be placed in a corundum boat with dimensions of 100×40×20 mm and heated in the central area of the corundum tube. Rubber rings were used to seal both ends of the corundum tube to prevent gas leakage. A rotameter was installed between the gas cylinder and the tube furnace to control the gas flow. The tail gas purification device was an absorption bottle filled with 10% HNO3. Hoses were used to connect all parts to ensure the flow of gas.

[0027] Before the experiment, high-purity nitrogen was introduced into the tube furnace at a flow rate of 0.5 L / min for 20 min to evacuate the air in the furnace. 3.0000 ± 0.1000 g of the sample was loaded onto the corundum boat, which was then pushed into the central position of the furnace body. After that, the temperature-rising program was started. After the pyrolysis program was completed, the pyrolytic carbon in the furnace was allowed to continue cooling in a nitrogen atmosphere to below 150 °C, and then transferred to a drying dish to continue cooling to room temperature. The pyrolytic carbon sample was collected to evaluate the pyrolysis results.

[0028] The characterization of pyrolytic carbon included X-ray fluorescence spectrometry (XRF, AxiosmAX Petro, PANalytical B.V., Netherlands) and scanning electron microscopy (SEM, HITACH SU8010, Japan).

[0029] Example 1 For samples SH7030, SH8515, SP7030a, and SP8515, in the first stage, the temperature was raised to 400 °C at a heating rate of 30 °C / min; in the second stage, the temperature was raised to 600 °C at a heating rate of 15 °C / min and held constant for 60 minutes. The analysis results of the sample bottom slag are as follows.

[0030] The elemental composition of the sample ash was obtained by XRF analysis, and the results are shown below. SiO2, Al2O3, P2O5, and Fe2O3 were the main components in MS, and the content of SiO2 and Al2O3 accounted for about 70%. Generally speaking, after the incorporation of HDPE and PET, the types and contents of each component in the mixed samples did not change much compared with MS because almost no ash residue remained after the combustion of HDPE and PET. However, SO3 was an exception. With the incorporation of microplastics, its content in the mixed samples decreased significantly, indicating that the addition of microplastics promoted the escape of S.

[0031]

[0032] The microscopic morphologies of the pyrolytic biochars of samples SH8515 and SP8515 at different magnifications under a scanning electron microscope are asFigure 1 As shown in the figure. Compared with MS, the pyrolytic biochar of SH8515 has a looser structure, with more and larger irregular voids on the surface and lower overall density. For the pyrolytic biochar of SP8515, its surface morphology presents a dense plate-like structure with irregular pores. During the pyrolysis process, the pyrolysis intermediate products of the sludge react with PET, generating cross-links with each other, making the overall structure of the biochar tighter than that of the sludge biochar.

[0033] In order to more accurately analyze the emission law of gases during the combustion process, three-dimensional spectra as shown in the figure were plotted for each sample in Example 1, and the corresponding temperatures of the DTG peaks of all mixed samples were analyzed in detail. The results are as Figure 2 shown in the figure. The main combustion stage of the mixed samples can be roughly divided into two stages. The first stage is below 400 °C, and the second stage is 400 - 600 °C. The functional groups of the gas products of all mixed samples are basically the same in the two stages, including CO Figure 2 , O-H, C-H, CO-C=O, C=C, and C-O. 2

[0034] For the MS-HDPE mixed sample, the types of gas products in the first stage are more abundant than those in the second stage. Various light volatile components such as lipids, proteins, and hydrocarbons decompose in this stage, resulting in many functional groups such as C-H, C-O, and C=O in the gas products of this stage. The absorption peak intensities of these functional groups all decrease in the second stage, which also corroborates the oxidative decomposition of these volatile components. For the MS-PET mixed sample, the overall gas emission situation is similar to that of MS-HDPE. However, different from MS-HDPE, the intensities of the C=O absorption peaks (1850 - 1600 cm-1) in its two combustion stages are almost the same because PET will start to react and crack in the second stage, generating gas products containing C=O. In the second stage, compared with MS-HDPE, MS-PET has a higher intensity of the CO 2 absorption peak, which is attributed to the fact that the combustion of PET will release more CO 2 .

[0035] Example 2 For the sample SH8515, it was heated to 400 °C at a heating rate of 30 °C / min in the first stage; in the second stage, it was heated to 600 °C, 750 °C, and 900 °C at a heating rate of 15 °C / min respectively and held for 60 minutes. As shown in the figure Figure 3 are the results of scanning electron microscope analysis of the sample bottom slag. It can be seen that the pyrolytic biochar structures obtained from SH8515 at different pyrolysis temperatures are different. The higher the pyrolysis temperature, the looser the biochar. When the temperature is relatively high (900 °C), the biochar structure is damaged, and the higher the temperature, the more severely the overall structure of the biochar is damaged.

[0036] Example 3 For samples SP7030a, SP7030b, and SP7030c, they will be heated to 400 degrees at a heating rate of 30 °C / min in the first stage; and then heated to 650 degrees at a heating rate of 15 °C / min in the second stage and held at a constant temperature for 60 minutes. Attached Figure 4 As the scanning electron microscope analysis results of the bottom slag of the samples, it can be seen that under different sludge moisture contents, the less the moisture content, the denser the pyrolytic biochar. When the moisture content is relatively high (50%), it will damage the biochar structure and affect its subsequent use.

[0037] It should be noted that unless otherwise clearly specified and limited, terms such as "installation", "connection", "linkage", "fixation", "setting", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Claims

1. A municipal sludge pyrolysis and coordinated disposal of waste plastic pollution control process, characterized in that: The following steps are involved: S01. Mix the plastic particles with municipal sludge at a mass ratio of 15%-30%; The mass ratio is the ratio of the weight of the plastic to the sum of the weight of the plastic and the dry weight of the municipal sludge; S02. Place the mixed material in a pyrolysis furnace and heat it to pyrolysis under a nitrogen or air atmosphere.

2. According to claim 1, a municipal sludge pyrolysis and coordinated treatment of waste plastic pollution control process is characterized in that: In the step S01, the particle size of the plastic particles is ≤200 mesh, and is obtained by crushing and sieving the plastic.

3. According to claim 1, a municipal sludge pyrolysis and coordinated treatment of waste plastic pollution control process is characterized in that: The dry weight of the municipal sludge in step S01 is the weight of the solid residue after all moisture is removed from the sludge after drying.

4. According to claim 1, a municipal sludge pyrolysis and coordinated treatment of waste plastic pollution control process is characterized in that: The plastic particles in step S01 are particles of any one or more of polyethylene and polyethylene terephthalate.

5. According to claim 1, a municipal sludge pyrolysis and coordinated treatment of waste plastic pollution control process is characterized in that: In the step S01, the municipal sludge is pretreated, and the pretreatment includes crushing, screening, and dehydration; in the step S01, the water content of the municipal sludge is 15%-30%.

6. According to claim 1, a municipal sludge pyrolysis and coordinated treatment of waste plastic pollution control process is characterized in that: The heating and pyrolysis process in step S02 adopts segmented heating, wherein the first stage is to heat up to 300-450 degrees at a heating rate of 30°C / min; the second stage is to heat up to 600-750 degrees at a heating rate of 10-20°C / min; and then the temperature is kept constant for 30-90 minutes.

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