A method for the co-disposal of baking soda desulfurization ash and wastewater sludge

Abstract

The present invention relates to a method for co-disposing sodium bicarbonate desulfurization ash and wastewater sludge. The wastewater sludge mass is spread on a hardened site to form a wastewater sludge spreading layer, and sodium bicarbonate desulfurization ash is sprinkled on the surface of the wastewater sludge spreading layer to form a wastewater sludge-sodium bicarbonate desulfurization ash layer; the wastewater sludge mass and sodium bicarbonate desulfurization ash are continuously spread on the surface of the wastewater sludge-sodium bicarbonate desulfurization ash layer in sequence, and after repeating n times, an n+1-layer wastewater sludge-sodium bicarbonate desulfurization ash layer mixture is obtained - left standing - coal powder is added and mixed evenly and then left standing - and then fed into a two-stage sludge dryer. The chemical properties of sodium bicarbonate desulfurization ash are used to modify the wastewater sludge, changing the characteristics of the wastewater sludge particles, thereby reducing the strength of the formed dried sludge after the two-stage drying process and obtaining a formed dried sludge product that is easy to pulverize.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for co-disposing sodium bicarbonate desulfurization ash and wastewater sludge. Background Art

[0002] During the wastewater treatment process, a large amount of wastewater sludge is generated by processes such as flocculation precipitation and pressure filtration. It is a common type of solid waste in industrial and municipal enterprises. To resourcefully utilize such solid waste, sludge is often subjected to drying pretreatment. The two-stage combined process is a typical sludge drying process that combines a thin-layer dryer and a belt dryer, which can give play to the advantages of high efficiency and compactness of the thin-layer dryer and safety and flexibility of the belt dryer. The dryness of the dried sludge can reach more than 90%, and the size of the formed dried sludge particles is 5-20 mm. However, due to the fast sludge drying speed, the compact microstructure of the sludge, the high strength of the formed dried sludge particles, it is not easy to further pulverize, the energy consumption for powdering is high, which is not conducive to the subsequent resource utilization of wastewater sludge in the form of powder, and the pretreatment cost is high.

[0003] In recent years, with the popularization of the national ultra-low emission requirements in the steel industry, gas boilers generally use the sodium bicarbonate dry desulfurization process to purify the flue gas generated after gas combustion. However, at the same time, during the process of solving the ultra-low emission of flue gas, the sodium bicarbonate dry desulfurization process also produces the problem of secondary pollution of the by-product desulfurization ash. Sodium bicarbonate desulfurization ash belongs to the by-product of the sodium-based desulfurization process, mainly containing substances such as NaHCO3, Na2SO4, and Na2SO3. Its composition is complex and variable, and there is little research on its resource utilization in the literature and lack of utilization means, which has become a new problem for the resource utilization of solid waste in steel enterprises. Summary of the Invention

[0004] Aiming at the problems in the prior art that the formed dried sludge is difficult to pulverize and the sodium bicarbonate desulfurization ash is difficult to utilize, a co-disposal method of sodium bicarbonate desulfurization ash and wastewater sludge that reduces the strength of the formed dried sludge particles is provided.

[0005] The purpose of the present invention is to provide a co-disposal method of sodium bicarbonate desulfurization ash and wastewater sludge, including the following steps:

[0006] 1) Spread the wastewater sludge mass on a hardened site to form a wastewater sludge spreading layer, and sprinkle sodium bicarbonate desulfurization ash on the surface of the wastewater sludge spreading layer to form a wastewater sludge-sodium bicarbonate desulfurization ash layer; continue to spread the wastewater sludge mass and sodium bicarbonate desulfurization ash on the surface of the wastewater sludge-sodium bicarbonate desulfurization ash layer in turn, and repeat n times to obtain an n+1-layer wastewater sludge-sodium bicarbonate desulfurization ash layer mixture;

[0007] 2) Let the n+1-layer wastewater sludge-sodium bicarbonate desulfurization ash layer mixture stand still;

[0008] 3) Add pulverized coal to the n + 1 layer of wastewater sludge - sodium bicarbonate desulfurization ash layered mixture after standing still, and obtain a mixture after mixing evenly and standing still.

[0009] 4) Feed the mixture into a two-stage sludge dryer (the two-stage sludge dryer is a combination of a thin-layer dryer and a belt dryer), and obtain formed dried sludge.

[0010] Furthermore, in the step 1), the mass fraction ratio of sodium bicarbonate desulfurization ash to the dry sludge basis in the wastewater sludge paving layer is 1:20 to 1:30.

[0011] Furthermore, in the step 1), the water content of the wastewater in the wastewater sludge lumps is 60 - 80%.

[0012] Furthermore, the thickness of each layer of the wastewater sludge paving layer is about 10 - 20 cm.

[0013] Furthermore, in the step 2), the n + 1 layer of wastewater sludge - sodium bicarbonate desulfurization ash layered mixture is allowed to stand still for 12 - 48 h.

[0014] 6. The synergistic treatment method of sodium bicarbonate desulfurization ash and wastewater sludge according to claim 1, characterized in that: in the step 3), the added amount of pulverized coal is 1 - 1.5 times the total mass of the dry sludge basis in the n + 1 layer of wastewater sludge paving layer.

[0015] Furthermore, in the step 1), the chemical components of the wastewater sludge by mass percentage include: 5% ≤ TFe ≤ 20%, 15% ≤ CaO ≤ 30%, MgO ≤ 10%, 20% ≤ SiO2 ≤ 40%, 10% ≤ Al2O3 ≤ 20%, K2O ≤ 2% and Na2O ≤ 2%; the particle size of the sludge lumps is 5 - 10 cm.

[0016] Furthermore, in the step 1), the chemical components of the sodium bicarbonate desulfurization ash by mass percentage include:

[0017] NaHCO3 40 - 65%;

[0018] Na2SO4 30 - 50%;

[0019] Na2SO3 5 - 15%;

[0020] The balance is crystal water and impurities.

[0021] Furthermore, in the step 1), the particles with a particle size of less than 200 mesh (i.e., 75 μm) in the sodium bicarbonate desulfurization ash account for 90 - 98% of the total weight.

[0022] Further, in the step 3), the pulverized coal is anthracite or coke powder, with the C content accounting for 90 - 95% of the total weight; the weight of particles with a particle size below 100 mesh (i.e., 150 μm) accounts for 90 - 98% of the total weight.

[0023] Due to the high viscosity of the wastewater sludge mass, it is not easy to mix with the soda ash desulfurization ash. Therefore, the paving method is used to mix the two, and the effective reaction between the two is achieved by utilizing the solubility of the soda ash desulfurization ash itself and the moisture in the wastewater sludge. After adding the pulverized coal, due to the porosity of the pulverized coal, it can adsorb part of the moisture in the sludge, reducing the free water content of the mixture, thereby changing the rheological properties of the material and making it easier to feed the mixture into the dryer.

[0024] Since the wastewater sludge contains a large amount of flocculants and clay mineral phases, the microscopic particles (10 -9 ~10 -7 m size) are dendritic, and a large number of water molecules are filled between the dendritic particles. After conventional drying, when the water molecules volatilize, the dendritic particles crosslink with each other, forming a large force, resulting in high strength of the formed dried sludge particles (5 - 20 mm) macroscopically and being difficult to grind. On the one hand, the soda ash desulfurization ash has a large amount of charges, which can destroy the charge structure of the flocculant, causing the flocs to depolymerize and destroying the dendritic microstructure. On the other hand, the soda ash desulfurization ash is alkaline and can react with the clay mineral phases in the wastewater sludge, reducing the cohesive force of the material. The combined effect of the two reduces the strength of the formed dried sludge particles and makes them easier to pulverize.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1) Utilize the chemical properties of the soda ash desulfurization ash to modify the wastewater sludge, change the characteristics of the wastewater sludge particles, thereby reducing the strength of the formed dried sludge after the two-stage drying process, and obtaining a formed dried sludge product that is easy to pulverize;

[0027] 2) The present invention synergistically utilizes the soda ash desulfurization ash and the wastewater sludge to achieve "treating waste with waste". It not only turns the soda ash desulfurization ash into a sludge conditioning agent with certain added value, but also effectively reduces solid waste emissions and environmental pollution;

[0028] 3) Use the pulverized coal as a modifier to improve the rheology of the sludge, which is beneficial for subsequent drying feeding;

[0029] 4) The present invention uses the soda ash desulfurization ash for the pretreatment of wastewater sludge. The soda ash desulfurization ash contains substances such as NaHCO3, Na2SO4, and Na2SO3, all of which are soluble substances. They can enter the wet wastewater sludge solution environment and react with the flocculants in the sludge, destroying the charge structure of the flocs, making the dried sludge not easy to agglomerate, reducing the strength of the formed dried sludge particles, and being easy for subsequent blending and co-firing with coal. Specific embodiments

[0030] The device and process method of the present invention will be further described in detail below:

[0031] Example 1

[0032] 1) Spread the wastewater sludge mass with a water content of 65% on a hardened site to form a wastewater sludge spreading layer with a thickness of about 12 cm. Sprinkle sodium bicarbonate desulfurization ash on the surface of the wastewater sludge spreading layer to form a wastewater sludge - sodium bicarbonate desulfurization ash layer. The mass ratio of sodium bicarbonate desulfurization ash to the dry sludge basis in the wastewater sludge spreading layer is 1:20. Continuously spread the wastewater sludge mass and sodium bicarbonate desulfurization ash on the surface of the wastewater sludge - sodium bicarbonate desulfurization ash layer, and repeat 4 times to obtain a 5 - layer wastewater sludge - sodium bicarbonate desulfurization ash layered mixture;

[0033] 2) Let the 5 - layer wastewater sludge - sodium bicarbonate desulfurization ash layered mixture stand for 13 h;

[0034] 3) Add pulverized coal to the 5 - layer wastewater sludge - sodium bicarbonate desulfurization ash layered mixture after standing. The addition amount of pulverized coal is 1.1 times the total mass of the dry sludge basis in the 5 - layer wastewater sludge spreading layer, and mix the materials evenly. After mixing evenly, let it stand for 40 minutes to obtain a mixture;

[0035] 4) Feed the mixture into a two - stage sludge dryer to obtain formed and dried sludge.

[0036] Among them, the particle size of the sludge mass is 5 - 10 cm. The weight of particles with a particle size of less than 200 mesh (i.e., 75 μm) in the sodium bicarbonate desulfurization ash accounts for 90 - 95% of the total weight. The pulverized coal is anthracite or coke powder, and the C content accounts for 90 - 92% of the total weight; the weight of particles with a particle size of less than 100 mesh (i.e., 150 μm) accounts for 90 - 95% of the total weight.

[0037] Example 2

[0038] 1) Spread the wastewater sludge mass with a water content of 71% on a hardened site to form a wastewater sludge spreading layer with a thickness of about 15 cm. Sprinkle sodium bicarbonate desulfurization ash on the surface of the wastewater sludge spreading layer to form a wastewater sludge - sodium bicarbonate desulfurization ash layer. The mass ratio of sodium bicarbonate desulfurization ash to the dry sludge basis in the wastewater sludge spreading layer is 1:25. Continuously spread the wastewater sludge mass and sodium bicarbonate desulfurization ash on the surface of the wastewater sludge - sodium bicarbonate desulfurization ash layer, and repeat 3 times to obtain a 4 - layer wastewater sludge - sodium bicarbonate desulfurization ash layered mixture;

[0039] 2) Let the 4 - layer wastewater sludge - sodium bicarbonate desulfurization ash layered mixture stand for 24 h;

[0040] 3) Add pulverized coal to the 4-layer waste water sludge-sodium bicarbonate desulfurization ash layered mixture after standing still. The added amount of pulverized coal is 1.3 times the total dry basis mass of the sludge in the 4-layer waste water sludge spreading layer. Mix the materials evenly, and let it stand still for 60 minutes after mixing evenly to obtain a mixture;

[0041] 4) Feed the mixture into a two-stage sludge dryer to obtain formed and dried sludge.

[0042] Among them, the particle size of the sludge agglomerates is 5-10 cm. The weight of the particles with a particle size of 200 mesh (i.e., 75 μm) or less in the sodium bicarbonate desulfurization ash accounts for 92-98% of the total weight. The pulverized coal is anthracite or coke powder, and the C content accounts for 92-95% of the total weight; the weight of the particles with a particle size of 100 mesh (i.e., 150 μm) or less accounts for 93-98% of the total weight.

[0043] Example 3

[0044] 1) Spread the waste water sludge agglomerates with a water content of 78% on a hardened site to form a waste water sludge spreading layer. The thickness of the waste water sludge spreading layer is about 20 cm. Sprinkle sodium bicarbonate desulfurization ash on the surface of the waste water sludge spreading layer to form a waste water sludge-sodium bicarbonate desulfurization ash layer. The mass ratio of the sodium bicarbonate desulfurization ash to the dry basis mass of the sludge in the waste water sludge spreading layer is 1:30; continue to spread waste water sludge agglomerates and sodium bicarbonate desulfurization ash on the surface of the waste water sludge-sodium bicarbonate desulfurization ash layer in turn, and repeat 2 times to obtain a 3-layer waste water sludge-sodium bicarbonate desulfurization ash layered mixture;

[0045] 2) Let the 3-layer waste water sludge-sodium bicarbonate desulfurization ash layered mixture stand still for 45 h;

[0046] 3) Add pulverized coal to the 3-layer waste water sludge-sodium bicarbonate desulfurization ash layered mixture after standing still. The added amount of pulverized coal is 1.5 times the total dry basis mass of the sludge in the 3-layer waste water sludge spreading layer. Mix the materials evenly, and let it stand still for 120 minutes after mixing evenly to obtain a mixture;

[0047] 4) Feed the mixture into a two-stage sludge dryer to obtain formed and dried sludge.

[0048] Among them, the particle size of the sludge agglomerates is 5-10 cm. The weight of the particles with a particle size of 200 mesh (i.e., 75 μm) or less in the sodium bicarbonate desulfurization ash accounts for 90-98% of the total weight. The pulverized coal is anthracite or coke powder, and the C content accounts for 90-95% of the total weight; the weight of the particles with a particle size of 100 mesh (i.e., 150 μm) or less accounts for 90-98% of the total weight.

[0049] The formed and dried sludge obtained from the above embodiments was compared with the formed and dried sludge obtained without using soda desulfurized ash for drying, and the strength of the formed and dried sludge (pellets) was detected by the dropping method. Two groups (20 pieces in each group) of samples with comparable sizes were selected from each sample for comparison. They were dropped from a fixed height of 0.5 m, and the number of drops before each sample was broken was recorded, and the average value was recorded in Table 1.

[0050] Table 1. Comparison of the dropping strength of the formed and dried sludge in the examples and comparative examples

[0051] Dimension 1 Number of drops Dimension 2 Number of drops Example 1 5 - 10 mm 3 10 - 20 mm 6 Example 2 5 - 10 mm 4 10 - 20 mm 7 Example 3 5 - 10 mm 4 10 - 20 mm 6 Comparative example 5 - 10 mm 12 10 - 20 mm 17

[0052] As can be seen from the data in Table 1, after treatment with soda desulfurized ash, the strength of the formed and dried sludge decreased significantly compared with that without using soda desulfurized ash, indicating that the soda desulfurized ash has an obvious effect on sludge modification.

Claims

1. A co-disposal method of baking soda desulfurization ash and wastewater sludge, characterized in that: The co-disposal method includes the following steps: 1) Spread the wastewater sludge mass into a wastewater sludge spreading layer on a hardened site, and sprinkle sodium bicarbonate desulfurization ash on the surface of the wastewater sludge spreading layer to form a wastewater sludge - sodium bicarbonate desulfurization ash layer; continue to spread the wastewater sludge mass and sodium bicarbonate desulfurization ash on the surface of the wastewater sludge - sodium bicarbonate desulfurization ash layer in turn, and repeat n times to obtain an n + 1 - layer wastewater sludge - sodium bicarbonate desulfurization ash layer mixture; the mass ratio of sodium bicarbonate desulfurization ash to the dry sludge basis in the wastewater sludge spreading layer is 1:20 - 1:30; By mass percentage, the chemical composition of the sodium bicarbonate desulfurization ash includes: NaHCO3 40 - 65%; Na2SO4 30 - 50%; Na2SO3 5 - 15%; The balance is crystal water and impurities; 2) Let the n + 1 - layer wastewater sludge - sodium bicarbonate desulfurization ash layer mixture stand still; 3) Add pulverized coal to the n + 1 - layer wastewater sludge - sodium bicarbonate desulfurization ash layer mixture after standing still, and mix evenly and then let it stand still to obtain a mixture; the addition amount of pulverized coal is 1 - 1.5 times the total mass of the dry sludge basis in the n + 1 - layer wastewater sludge spreading layer; 4) Feed the mixture into a two - stage sludge dryer to obtain shaped dried sludge.

2. The co-disposal method of baking soda desulfurized ash and wastewater sludge according to claim 1, characterized in that: In the step 1), the water content of the wastewater in the wastewater sludge mass is 60 - 80%.

3. The co-disposal method of sodium bicarbonate desulfurized ash and wastewater sludge according to claim 1, wherein: The thickness of each wastewater sludge spreading layer is 10 - 20 cm.

4. The co-disposal method of sodium bicarbonate desulfurized ash and wastewater sludge according to claim 1, wherein: In the step 2), let the n + 1 - layer wastewater sludge - sodium bicarbonate desulfurization ash layer mixture stand still for 12 - 48 h.

5. The co-disposal method of sodium bicarbonate desulfurized ash and wastewater sludge according to claim 1, characterized in that: In the step 1), by mass percentage, the chemical composition of the wastewater sludge includes: 5% ≤ TFe ≤ 20%, 15% ≤ CaO ≤ 30%, MgO ≤ 10%, 20% ≤ SiO2 ≤ 40%, 10% ≤ Al2O3 ≤ 20%, K2O ≤ 2% and Na2O ≤ 2%; the particle size of the sludge mass is 5 - 10 cm.

6. The co-disposal method of sodium bicarbonate desulfurized ash and wastewater sludge according to claim 1, characterized in that: In the step 1), the weight of the particles with a particle size of less than 200 mesh in the sodium bicarbonate desulfurization ash accounts for 90 - 98% of the total weight.

7. The co-disposal method of baking soda desulfurized ash and wastewater sludge according to claim 1, characterized in that: In the step 3), the pulverized coal is anthracite or coke powder, the C content accounts for 90 - 95% of the total weight; the weight of the particles with a particle size of less than 100 mesh accounts for 90 - 98% of the total weight.