Method for evaluating carbon emission reduction potential in sludge building material resource utilization process

Abstract

The invention discloses a method for evaluating carbon emission reduction potential in a sludge building material resource utilization process, and belongs to the technical field of solid waste treatment and building materials. According to the method, pretreated dewatered sludge is treated by adopting a biological drying technology and a heat drying technology respectively, the treated dry sludge is incinerated, ground and sieved and is mixed with cement to obtain the cement substitute cementing material, and the total discharge amount of carbon dioxide in the cementing material production process is calculated comprehensively, so that the cement substitute cementing material is obtained. And obtaining unit compressive strength carbon emission according to the compressive strength of the mortar test block to evaluate the carbon emission reduction potential. According to the method, indexes for evaluating the carbon emission reduction potential of different treatment processes are provided for the building industry, so that low-carbon emission treatment processes and high-strength materials are selected, and the method has great significance on sustainable development of the building industry.

Description

Technical Field

[0001] The invention relates to a method for evaluating the carbon emission reduction potential in the process of resource utilization of sludge building materials, and belongs to the technical field of solid waste treatment and building materials. Background Art

[0002] The treatment and disposal of sludge has become an urgent issue in the field of environmental protection. As an effective sludge treatment method, biological drying can not only reduce the moisture content and volume of sludge, but also kill some pathogens. At the same time, traditional cement not only consumes a large amount of natural resources, such as limestone and clay, in the production process, but also emits a large amount of greenhouse gases such as carbon dioxide, which puts great pressure on the environment. At present, the main treatment technology for the resource utilization of dewatered sludge is thermal drying. Thermal drying will lead to high treatment costs due to the characteristics of high moisture content. The use of biological drying technology to treat dewatered sludge will greatly reduce the problem of high treatment costs caused by high moisture content. In addition, there is a lack of emission measurement standards for evaluating carbon emission reduction potential in the construction field, so it is not possible to distinguish the carbon emission reduction potential between different materials and different treatment processes. The unit compressive strength carbon emission measurement indicator introduced in this work is conducive to the selection of low-carbon emission and high-strength materials in the construction industry, which is of great significance to the sustainable development of the construction industry. Summary of the invention

[0003] The present invention provides a method for evaluating the carbon emission reduction potential in the process of resource utilization of sludge building materials, so as to realize the resource utilization of dewatered sludge while evaluating the carbon emission reduction potential between different treatment processes and maintain the sustainable development of the construction industry. The carbon emission reduction potential is evaluated by calculating using the following formula:

[0004] I x =1000×R x / P x (1)

[0005] In the formula, I x is the carbon emission per unit compressive strength, g CO2 / MPa; R x is the comprehensive carbon emission of dried sludge-cement-based cementitious materials required for making a single mortar test block, kg; P x It is the compressive strength of mortar made of dried sludge-cement-based cementitious material at 28 days, MPa.

[0006] Preferably, the R x The calculation formula is:

[0007] R x =N×P×(1-E C )+M r / M S ×N×E C (2)

[0008] Preferably, N is the mass of cement required for the production of a single mortar test block, kg; P is the carbon emission per unit mass of cement production, kg CO2 / kg, and P is 842kg CO2 / kg; E C is the proportion of sludge ash replacing cement, %; M r is the carbon emission of sludge drying, kg. When the sludge drying method is thermal drying, M r When the sludge is dried by biological drying, M r 438.61kg; M S The mass of ash after incineration of 1 ton of dehydrated sludge, kg.

[0009] Preferably, the M S The calculation formula is:

[0010] M S =1000×(1-MC)×(1-VS)(3)

[0011] Wherein, MC is the moisture content of dewatered sludge before drying, %; VS is the volatile solid content of fresh sludge, %.

[0012] Preferably, the preparation method of the dried sludge-cement-based gelling material is as follows:

[0013] (1) drying the fresh dehydrated sludge until the moisture content is 64% to 66% and then sieving to obtain pretreated dehydrated sludge;

[0014] (2) subjecting the dewatered sludge obtained in step (1) to biological drying or thermal drying to obtain dried sludge;

[0015] (3) drying and incinerating the dried sludge obtained in step (2) to obtain dried sludge ash;

[0016] (4) Grinding and sieving the dried sludge ash obtained in step (3), and mixing it with cement to obtain a cement-based cementitious material of biological dried sludge.

[0017] (5) preparing a mortar test block from the cement-based cementitious material obtained in step (4), and measuring its 28-day compressive strength;

[0018] (6) Calculate the carbon dioxide emissions of the entire treatment process, and use formulas (1)(2)(3) to calculate and analyze the carbon dioxide emissions per unit compressive strength, and comprehensively evaluate the carbon emission reduction potential of different treatment processes and materials.

[0019] Preferably, in step (1), a sieve with a pore size of 4 mm×4 mm is used for screening.

[0020] Preferably, the biological drying process in step (2) adopts continuous aeration, and the aeration rate is 2-2.5 L·min -1 The biological drying cycle is 12 days, and the moisture content of the obtained biologically dried sludge is 45% to 55%. The drying process mainly utilizes the metabolic heat of microorganisms to evaporate water, and uses flowing air to bring the water out to achieve the purpose of reducing the moisture content.

[0021] Preferably, the drying temperature in the step (3) is set to 105±5°C, the drying time is 24h, the muffle furnace is used for incineration, the incineration temperature is 700°C, the incineration time is 7h, the heating rate during the incineration process is 2.5°C / min, and the cooling rate is 5°C / min.

[0022] Preferably, the grinding in step (4) is performed using a ball mill at a rotation speed of 1500 r / min for 3 min, and the mixture is sieved through 100 mesh, 150 mesh, 200 mesh and 250 mesh metal sieves in sequence.

[0023] Beneficial effects of the present invention

[0024] The innovative indicator of carbon emissions per unit compressive strength can be used to better evaluate the carbon reduction potential of different treatment methods (traditional thermal drying technology and biological drying technology). At the same time, the method of using biological drying sludge-cement-based cementitious materials to replace pure cement is simple to operate and energy-saving and environmentally friendly. The strength of the mortar produced meets the requirements of national standards. The carbon emissions per unit compressive strength are reduced by 7.23%-17.29% within the replacement ratio range of 5%-15%. It not only reduces carbon emissions while realizing the resource utilization of organic solid waste, but also reduces the excessive consumption of natural resources in cement production, and provides a reliable measurement indicator for evaluating the potential for carbon reduction in the construction industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the biological drying device in Example 1 of the present invention.

[0026] Figure 2 This is a schematic diagram of the biological drying temperature change in Example 1 of the present invention.

[0027] Figure 3 This is a schematic diagram of the mortar strength of the sludge-cement-based cementitious material of Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0029] Example 1

[0030] A method for preparing an ecological cementitious material by using biologically dried sludge ash and cement comprises the following steps:

[0031] (1) Weighing 13 kg of pre-treated dewatered sludge and drying it until the moisture content is 65%;

[0032] (2) Place the pretreated dewatered sludge into a biological drying reactor (such as Figure 1 ), connect the air pump, and use the gas flow meter to control the gas flow rate at 2-2.5L·min -1 Wrap the reactor with a blanket to keep it warm, and wrap it with fireproof cotton to prevent fire. Set the laboratory air conditioner to a constant temperature of 27°C, insert a temperature probe to record the temperature change during the biological drying process (such as Figure 2 ), and then copy the temperature data once a day to prevent loss. After the temperature in the reactor drops to room temperature (about 12 days), the reaction device is dismantled, the dried sludge is weighed and the moisture content of the dried sludge is calculated to be 53.04%, thus obtaining the biological dried sludge.

[0033] (3) Weigh 1 kg of bio-dried sludge and place it in an oven for drying for 24 h at a temperature of 105 °C. After the dry sludge reaches a constant weight, cool it naturally and place it in a muffle furnace for incineration. The heating rate is 2.5 °C / min, the cooling rate is 5 °C / min, and the incineration time is 7 h at 700 °C. After the cooling process is completed, take it out and weigh it.

[0034] (4) The fresh dehydrated sludge is dried in an oven and incinerated in a muffle furnace. The treatment process is the same as that in experimental step (3). This process is another drying method of sludge: thermal treatment. Analysis shows that the volatile solid content VS of the fresh sludge before drying is 51.68%.

[0035] (5) The biologically dried sludge obtained in step (3) and the thermally dried sludge ash obtained in step (4) are put into a ball mill in batches for grinding. The speed of the ball mill is set to 1500 r / min and the grinding time is 3 min. The ground dried sludge ash is sieved through metal sieves of 100 mesh, 150 mesh, 200 mesh and 250 mesh in sequence to obtain sludge ash. The obtained sludge ash is mixed with cement according to the mixing ratio in Table 1, and the total mass is weighed to be 450 g (this mass is the mass N of cement required for preparing a single mortar test block) to obtain a sludge-cement-based cementitious material.

[0036] (6) Add the sludge-cement-based cementitious material obtained in step (5) into a mortar mixer, take 225 ml of ultrapure water and 1350 g of standard sand, stir slowly for 1 min, then stir quickly for 2 min, take out the mortar, put it into a mold, and vibrate it twice.

[0037] (6) Wrap the compacted mortar and mold with plastic wrap to prevent water loss, and place in a shaded place for curing for 24 hours.

[0038] (7) After 24 hours of curing, the ecological mortar was demoulded and placed in a saturated calcium hydroxide solution. When the curing time was 3 days, 7 days and 28 days (the surface moisture of the wipe block was taken and dried in the shade one day before the test), the flexural and compressive strengths were measured using a compression and flexural testing machine ( Figure 3 ).

[0039] (8) Comprehensive analysis of the total carbon emissions from the treatment of 80% water content sludge per ton (after consulting the carbon emissions of thermal drying treatment M r The carbon emission of biological drying treatment is 601kg. r At the same time, the carbon emission per unit mass of cement production P is 842kg CO2 / kg, and the carbon emission per unit compressive strength is calculated based on the 28d compressive strength data. It is analyzed that biological drying can reduce carbon emissions by 27.03%, and at a replacement ratio of 5%, 10%, and 15%, it can reduce carbon emissions per unit compressive strength by 7.23%, 14.42%, and 17.29% (the calculation process is shown in Table 2).

[0040] After the strength test of sludge-cement-based cementitious materials, the results are as follows Figure 3 As shown in the figure, the 3d compressive strength of the mortar specimen after replacing cement is slightly lower than that of pure cement (control group), but it increases after 28d and is slightly higher than that of the control group. The compressive strengths at 3d and 28d are in line with national standards, which also shows that the replacement of biological dried sludge will not affect the 28d strength of cement mortar, and the strength has little to do with the treatment process. In fact, the replacement of sludge can help improve its strength.

[0041] Table 1 Mixing ratio of mixed cement slurry

[0042]

[0043] Table 2 Carbon emissions per unit compressive strength

[0044]

[0045]

Claims

1. A method for evaluating the carbon emission reduction potential in the process of resource utilization of sludge building materials, characterized by: The carbon reduction potential is assessed using the following formula: I x =1000×R x / P x In the formula, I x is the carbon emission per unit compressive strength, g CO2 / MPa; R x is the comprehensive carbon emission of dried sludge-cement-based cementitious materials required for making a single mortar test block, kg; P x It is the compressive strength of mortar made of dried sludge-cement-based cementitious material at 28 days, MPa.

2. The method for evaluating the carbon emission reduction potential in the process of resource utilization of sludge building materials according to claim 1 is characterized by: The R x The calculation formula is: R x =N×P×(1-E C )+M r / M S ×N×E C Where N is the mass of cement required for the production of a single mortar test block, kg; P is the carbon emission per unit mass of cement production, kg CO2 / kg; E C is the proportion of sludge ash replacing cement, %; M r is the carbon emission of sludge drying, kg; M S It is the mass of ash after incineration of 1 ton of dehydrated sludge, kg.

3. The method for evaluating the carbon emission reduction potential in the process of resource utilization of sludge building materials according to claim 2 is characterized by: The M S The calculation formula is: M S =1000×(1-MC)×(1-VS) Wherein, MC is the moisture content of dewatered sludge before drying, %; VS is the volatile solid content of fresh sludge, %.

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