A three-step progressive treatment method to improve sewage sludge activity index and its carbon reduction effect

Abstract

The present invention discloses a treatment method for improving the activity index of sewage sludge, aiming to realize the utilization of sewage sludge as building materials by adopting a more energy-saving and environmentally friendly treatment method, and to obtain sewage sludge with a high activity index under the condition of the lowest possible heat treatment temperature. The present invention combines mechanical grinding, medium and low temperature roasting and chemical activation to realize the activation treatment of sewage sludge from dried granular materials to active admixtures that can partially replace silicate cement, providing a feasible solution for new energy-saving applications of sewage waste, and proposing a method for quantitatively evaluating its pollution reduction and carbon reduction potential. Compared with the existing technology, the heat treatment temperature is reduced, the energy consumption in the sewage sludge treatment process is saved, and the carbon emission in the sewage sludge treatment process is further reduced; through the three-step combined progressive treatment of mechanical grinding, medium and low temperature roasting and chemical activation, the problem of too low activity index of medium and low temperature roasted sewage sludge is solved, while saving energy, the relevant requirements of cement active admixtures are met.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and in particular to a three-step combined progressive disposal and activation method for improving the activity index of sewage sludge and a carbon accounting method thereof. Background Art

[0002] Sewage sludge refers to the residual semisolid material formed as a byproduct of industrial or municipal wastewater treatment. As a byproduct of wastewater treatment, sewage sludge concentrates and collects 30% to 50% of the pollutants and organic matter in the wastewater, possessing both the properties of "pollution" and "resource." Given the growing production of sewage sludge, developing new applications for it within existing disposal and recycling options is a common challenge facing industry professionals.

[0003] Patent CN202310488308 discloses a grinding system for increasing the activity index of sludge ash. This system deeply grinds and physically activates incinerated sludge ash, reducing the average particle size while increasing the uniformity of the particles. Through mechanical activation, a highly activated sludge ash powder is produced, effectively replacing Portland cement. However, this patent uses incinerated sludge ash as the raw material for disposal, as the incineration process consumes significant energy and is not energy-efficient or environmentally friendly.

[0004] Patent CN202110779746 discloses a method for increasing the activity of sludge incineration ash. This method involves synergistic conditioning of sludge and soil to increase the active components in the ash. The active admixture is then prepared through modification methods such as grinding and chemical activation. Claim 1 of the patent states that the incineration activation temperature is 700-850°C, suggesting potential for reduction. Summary of the Invention

[0005] The purpose of the present invention is to realize the utilization of sewage sludge as building materials by adopting a more energy-saving and environmentally friendly disposal method, and to obtain sewage sludge with a high activity index under the lowest possible heat treatment temperature conditions. The present invention realizes the activation disposal of sewage sludge from dried granular material to active admixture that can partially replace silicate cement through three steps of mechanical grinding, medium and low temperature roasting and chemical activation, providing a feasible solution for new energy-saving applications of sewage waste.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a treatment method for improving the activity index of sewage sludge. The treatment method uses dried sludge as raw material and comprises the following three steps:

[0008] (1) Mechanical grinding: Add the dried sludge into a ball mill and grind it to a particle size of 100 μm;

[0009] (2) Medium-low temperature roasting: the dried sludge after the mechanical grinding step in step (1) is placed in a kiln for roasting at a temperature of 400°C;

[0010] (3) Chemical activation: Add the sewage sludge calcined in the low-temperature calcination step in step (2) to a chemical activator and mix well.

[0011] By mechanical grinding, the particle size of the dried sewage sludge material is controlled to 100 μm to increase the surface area of ​​the sludge particles, increase the reaction contact sites, and improve the activity of the sewage sludge volcanic ash at the physical level; under the premise of ensuring low energy consumption, the medium and low temperature roasting removes most of the phosphorus-containing organic matter in the sewage sludge that is not conducive to its own activity index through heat treatment; reduces the negative impact of phosphorus-containing organic matter on the activity of the volcanic ash; by combining medium and low temperature roasting with mechanical grinding, the roasting process is fully reacted to improve the activity index of the sewage sludge. Then, a small amount of chemical activator is added to the sewage sludge. The active admixture reacts with the calcium hydroxide generated by cement hydration to generate reaction products such as hydrated calcium silicate. The selected chemical activator is conducive to the positive reaction, further improving the activity index of the sewage sludge roasted in the medium and low temperature roasting step (2). Finally, the activity of the sewage sludge volcanic ash is greatly improved.

[0012] Furthermore, the raw dried sludge is dehydrated and dried in a sewage treatment plant and then preliminarily crushed to obtain granular dried sludge with a particle size of 0.5-1.5 cm.

[0013] Furthermore, the mechanical grinding method uses a ball mill with a rotation speed of not less than 47 r / min and a grinding time of not less than 30 minutes. The cumulative distribution of the obtained material particle size at 100 μm is higher than 50%, so that it meets the activity index improvement requirements.

[0014] Furthermore, the medium-low temperature roasting method should maintain the roasting temperature in the kiln at 400°C, and roast the dried sludge obtained by grinding in the mechanical grinding step (1) in the kiln for a time of not less than 2 hours. After the roasting is completed, the sewage sludge is naturally cooled to room temperature.

[0015] Furthermore, the chemical activator selected for the chemical activation method is one of Na2SO4 or nano-SiO2. If Na2SO4 is selected as the chemical activator, its addition amount is in the range of 6-10% of the mass of the sewage sludge calcined in the medium-low temperature calcination step (2); if nano-SiO2 is selected as the chemical activator, its addition amount is in the range of 10-15% of the mass of the sewage sludge calcined in the medium-low temperature calcination step (2).

[0016] The present invention provides a method for quantitatively determining the emission reduction efficiency achieved by increasing the activity index of sewage sludge, namely, a method for calculating the reduction in carbon dioxide emissions after partial replacement of cement with sewage sludge. The calculation method includes the following two parts:

[0017] (a) Carbon dioxide emissions from cement replaced by sewage sludge, in tons;

[0018] (b) Carbon dioxide emissions from sewage sludge disposal, in tons.

[0019] The total amount of carbon emission reduction is (a)-(b), in tons.

[0020] Furthermore, the carbon dioxide emissions are based on 1 t of cement clinker.

[0021] Furthermore, the cement CO2 emissions mentioned in (a) include both direct and indirect CO2 emissions from the cement production process. Specifically, direct emissions include the decomposition of carbonates in the raw materials, the calcination of kiln dust in the cement kiln system, the combustion of organic carbon in the raw materials, and the combustion of fuel in the cement kiln; indirect emissions include emissions from electricity consumption in clinker production and emissions from cement grinding.

[0022] Furthermore, the carbon dioxide emissions from the sewage sludge described in (b) are the electricity consumption emissions from mechanical grinding and the combustion of fuel during medium and low temperature roasting during the sewage sludge treatment process. The present invention has the following advantages: (1) The present invention adopts a heat treatment method of medium and low temperature roasting, which is different from the existing method of calcining and chemical activation, further reducing carbon emissions during the sewage sludge treatment process. The three-step combined treatment of calcination and chemical activation solves the problem of too low activity index of sewage sludge from medium and low temperature roasting, saving energy while meeting the relevant requirements of cement active admixtures.

[0023] (3) The present invention uses quantitative carbon evaluation to intuitively reflect the reduction in carbon dioxide emissions after high activity index sewage sludge partially replaces cement, providing a new development direction for carbon reduction and emission reduction in the cement industry. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0025] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0026] The parts used in this embodiment are based on mass.

[0027] The main raw materials in this embodiment are as follows:

[0028] The dried sludge pellets were taken from a sewage treatment plant in Sichuan. After preliminary drying and crushing, the main element composition is shown in Table 1.

[0029] Table 1 Elemental composition of sewage sludge from Example

[0030]

[0031]

[0032] The nameplate information of the ball mill used for mechanical grinding in the examples is shown in Table 2.

[0033] Table 2 Ball mill nameplate parameters used in the examples

[0034]

[0035] In the embodiment, low temperature roasting was performed using a 1700-degree box-type high temperature furnace of model MXX1700-30 produced by Shanghai Weixing.

[0036] In the embodiment, the chemical activator Na2SO4 is anhydrous Na2SO4 with a purity greater than 99%, and the particle size of the chemical activator nano-SiO2 does not exceed 500nm.

[0037] The carbon dioxide emission data used in this example is derived from research data published in China Cement.

[0038] Example 1:

[0039] A method for improving the activity index of sewage sludge, using a chemical activator Na2SO4 activation, the specific steps are as follows:

[0040] (1) Add the sewage sludge pellets into a ball mill and mill for 30 minutes to obtain sewage sludge powder.

[0041] (2) The powder obtained in step (1) is placed in a box-type high-temperature furnace. The heating rate during the roasting process is set to 4°C / min. When the temperature in the furnace reaches 400°C, it is kept warm for 2 hours and then naturally cooled to room temperature.

[0042] (3) Weigh 100 parts by mass of the sewage sludge obtained in step (2) and mix it evenly with 10 parts of a chemical activator, Na2SO4, to obtain a sewage sludge active admixture.

[0043] (4) The carbon emission reduction calculation result of Example 1 is: 0.2656-0.0247=0.2409t

[0044] Example 2:

[0045] A treatment method for improving the activity index of sewage sludge, using a chemical activator nano-SiO2 with a particle size of 500nm, is described. The specific steps are as follows:

[0046] (1) Add the sewage sludge pellets into a ball mill and mill for 30 minutes to obtain sewage sludge powder.

[0047] (2) The powder obtained in step (1) is placed in a box-type high-temperature furnace. The heating rate during the roasting process is set to 4°C / min. When the temperature in the furnace reaches 400°C, it is kept warm for 2 hours and then naturally cooled to room temperature.

[0048] (3) Weigh 100 parts by mass of the sewage sludge obtained in step (2) and mix it evenly with 15 parts of a chemical activator, nano-SiO2, to obtain a sewage sludge active admixture.

[0049] (4) The carbon emission reduction calculation result of Example 2 is: 0.2656-0.0247=0.2409t

[0050] Comparative Example 1:

[0051] A method for improving the activity index of sewage sludge is provided. The method differs from the embodiment in that the roasting temperature is higher and chemical activation is not performed. The specific steps are as follows:

[0052] (1) Add the sewage sludge pellets into a ball mill and mill for 30 minutes to obtain sewage sludge powder.

[0053] (2) The powder obtained in step (1) is placed in a box-type high-temperature furnace, and the heating rate during the roasting process is set to 4°C / min. When the temperature in the furnace reaches 600°C, it is kept warm for 2 hours and naturally cooled to room temperature to obtain a sewage sludge active admixture.

[0054] (4) The carbon emission reduction calculation result of comparative example 1 is: 0.2656-0.0317=0.2339t

[0055] Comparative Example 2:

[0056] A method for improving the activity index of sewage sludge is different from the embodiment in that quicklime is selected for chemical activation. The specific steps are as follows:

[0057] (1) Add the sewage sludge pellets into a ball mill and mill for 30 minutes to obtain sewage sludge powder.

[0058] (2) The powder obtained in step (1) is placed in a box-type high-temperature furnace. The heating rate during the roasting process is set to 4°C / min. When the temperature in the furnace reaches 400°C, it is kept warm for 2 hours and then naturally cooled to room temperature.

[0059] (3) Weigh 100 parts by mass of the sewage sludge obtained in step (2) and mix it evenly with 15 parts of quicklime to obtain a sewage sludge active admixture.

[0060] (4) The carbon emission reduction calculation result of comparative example 2 is: 0.2656-0.0247=0.2409t

[0061] With reference to the standard "Fly ash used in cement and concrete" (GB / T 1596-2017), the sewage sludge active admixtures in the above embodiments and comparative examples were used instead of the standard fly ash to form sewage sludge cement mortar, and the strength activity index at the age of 28 days was tested to compare the differences in the activity index of sewage sludge between different embodiments and comparative examples.

[0062] Table 3 Intensity activity index and carbon emission reduction efficiency per ton of product of the embodiments and comparative examples

[0063]

[0064] The strength activity index of sewage sludge refers to the ratio of the compressive strength of a mortar specimen containing 30% sewage sludge active admixture to the compressive strength of a pure cement mortar specimen at 28 days of age under the conditions required by the standard. This index can be used to intuitively and simply characterize the activity index of sewage sludge active admixtures. As shown in Table 3, Example 1 (medium-low temperature calcination, Na2SO4 activation) and Example 2 (medium-low temperature calcination, nano-SiO2 activation) both exhibit high activity indices. Comparative Example 1 (higher temperature calcination, no chemical activation) has a strength activity index of less than 5%, indicating that even with a moderately increased calcination temperature, chemical activation cannot produce a sewage sludge admixture with good activity. Comparative Example 2 (medium-low temperature calcination, quicklime) has a strength activity index that is slightly higher than that of Comparative Example 1, but far lower than that of the examples, indicating that quicklime is not suitable as a chemical activator for sewage sludge.

[0065] In terms of carbon emissions, the two embodiments and two comparative examples, except for comparative example 1 (higher temperature calcination) which used different heat treatment temperatures to increase carbon emissions, the carbon emission reductions in other groups were the same and the emission reduction values ​​were relatively considerable, indicating that this disposal method has a good guiding role in the development of carbon reduction and emission reduction in the cement industry.

[0066] The above descriptions and embodiments are provided to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these contents and apply the general principles described herein to other embodiments without requiring inventive effort. The present invention is not limited to the above descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for improving the activity index of sewage sludge, characterized in that: This treatment method uses dried sludge as raw material. The dried sludge is dehydrated and dried in a sewage treatment plant and then initially crushed to obtain granular dried sludge with a particle size of 0.5-1.5 cm. It includes the following three steps: (1) Mechanical grinding: Add the dried sludge into a ball mill at a speed of not less than 47 r / min and a grinding time of not less than 30 min, and the cumulative distribution of the obtained material particle size at 100 μm is greater than 50%; (2) Medium-low temperature roasting: the powder obtained in step (1) is placed in a box-type high-temperature furnace, and the heating rate during the roasting process is set to 4°C / min. When the temperature in the furnace reaches 400°C, it is kept warm for 2 hours and then naturally cooled to room temperature; (3) Chemical activation: adding a chemical activator to the sewage sludge calcined in the low-temperature calcination step in step (2), mixing them uniformly, and obtaining a sewage sludge activated admixture; The chemical activator is Na2SO4 or nano-SiO2; The Na2SO4 is used as a chemical activator, and its dosage range is 6-10% of the mass of the sewage sludge calcined in the low-temperature calcination step in step (2); The nano-SiO2 is used as a chemical activator, and its particle size does not exceed 500nm. Its dosage range is 10-15% of the mass of the sewage sludge calcined in the low-temperature calcination step in step (2); The activity index of sewage sludge refers to the ratio of the compressive strength of a mortar specimen mixed with 30% sewage sludge active admixture to the compressive strength of a pure cement mortar specimen at 28 days of age under the conditions required by the standard.

2. A carbon emission reduction accounting method for the treatment method for improving the activity index of sewage sludge according to claim 1, characterized in that: The method comprises the following steps: (a) Carbon dioxide emissions from cement replaced by sewage sludge, in tons; (b) CO2 emissions from sewage sludge disposal, in tons; The total amount of carbon emission reduction is (a)-(b), in tons.

3. The carbon emission reduction accounting method according to claim 2, characterized in that: The carbon dioxide emissions mentioned above are based on 1 ton of cement clinker.

4. The carbon emission reduction accounting method according to claim 2, characterized in that: The carbon dioxide emissions from cement in step (a) include direct and indirect emissions of carbon dioxide during the cement production process. Specifically, direct emissions include decomposition of carbonates in the raw materials, calcination of kiln dust in the cement kiln system, combustion of organic carbon in the raw materials, and fuel combustion in the cement kiln; indirect emissions include emissions from electricity consumption in clinker production and emissions from cement grinding.

5. The carbon emission reduction accounting method according to claim 2, characterized in that: The carbon dioxide emissions from the sewage sludge in step (b) are the electricity consumption emissions from mechanical grinding and the combustion of medium and low temperature roasting fuel during the sewage sludge treatment process.

Images