KR19980033485A - Sewage Sewage Treatment - Google Patents

Abstract

The present invention relates to a method for treating sewage sludge as a raw material for cement and a heat source in a cement manufacturing process, wherein the sewage sludge is dried to a water content of 15 to 35 wt% by a steam drying method in a sewage treatment plant to form cement. By mixing with raw materials for cement production in the range of 0.5 to 10% by weight of the total raw material, or by using the dried sludge as a secondary fuel in the cement manufacturing process, by transferring the sludge, the largest waste of the workplace to the cement factory while reducing transportation costs It is possible to utilize the existing facilities of the cement plant economically and stably without any additional facilities, and to prevent the leakage of leachate by landfill or the generation of secondary environmental pollution sources such as gas or incineration ash when incinerated. The landfill age of the landfill can be extended.

Description

Sewage Sewage Treatment

The present invention relates to a method for treating sludge, which is a waste generated after a water treatment in a sewage treatment plant, as a heat source in a cement raw material and cement manufacturing process. By using as a raw material of cement or a heat source in the cement manufacturing process, the present invention relates to a method for stably and economically recycling waste at low transportation costs and preventing generation of secondary environmental pollutants.

Increasing living standards due to economic development has led to an increase in domestic sewage, which inevitably increases sewage treatment plants to prevent pollution of rivers and rivers. With the increase of the treatment plant, the amount of sludge generated in the water treatment process continues to increase, and the effective treatment of the sludge has emerged as one of the main environmental policy tasks.

Sludge is a solid waste generated after removing particulate, colloidal and dissolved pollutants contained in sewage to prevent water pollution. In Korea, sludge accounts for 48.9% of the designated waste generated. Japan also accounts for the highest proportion of waste generation, and its effective treatment is urgently needed.

Existing sludge treatment methods have been mainly relied on landfills, which are simple and inexpensive, and other methods are generally treated by dumping or composting. In recent years, the reduction process by incineration is tried.

However, landfills or dumping at sea are likely to cause secondary pollution, which prevents long-term disposal.Incineration is also expected to result in excessive expenditures on facility investment and operating costs. do. Composting may be a good option for recycling, but it is not a fundamental solution due to the limitations of usage.

There is also the disposal of sludge by cement process, but it is not economically practical and practical use is impossible. This is because, in order to use the raw material with a high moisture content such as sewage sludge in the cement process, it is necessary to control the moisture content for economical and operational convenience in the transportation and cement manufacturing process.

That is, the mechanical dehydration can reduce the water content by 50 to 80% by weight, but further treatment is required to adjust to less than that. However, in the case of dehydration process using calcium oxide or lime hardener (see U.S. Patent Nos. 4,295,972 and 5,217,624), considering the raw material cost of the dehydrating agent used as dehydration aid and the transportation cost according to the weight increase after mixing treatment Justice is not realistic. In addition, there is a case where the waste was used in the cement process and then used directly in the cement factory (see US Patent Nos. 5,614,016 and 5,586,510), but transports sludge containing at least 80% by weight of water to be removed to the cement factory. That is a big burden on logistics costs. In addition, it requires additional drying facilities such as dry crushers and screw conveyors in cement plants, and introduces complex additional lines in the process for the treatment of dry gases. Many difficulties arise from the point of view.

Accordingly, the present inventors have diligently researched and found that the above-mentioned problems can be solved by efficiently transporting sewage sludge directly to a cement plant after being directly dried in a sewage treatment plant to a level suitable for future use while reducing transportation costs. This invention was completed.

It is an object of the present invention to provide a method of treating sewage sludge by using it as a raw material of cement or as a heat source in a cement manufacturing process in order to stably and economically recycle sewage sludge and prevent generation of secondary environmental pollution sources.

1 is a diagram illustrating a process for producing clinker after mixing, pulverizing and calcining by using dried sewage sludge as a raw material of cement after drying sewage sludge in a sewage treatment plant.

In order to achieve the above object, in the present invention, the sewage sludge is dried in a sewage treatment plant by a water vapor drying method in a water content of 15 to 35% by weight, and the raw materials for cement production in the range of 0.5 to 10% by weight of the total raw materials constituting cement. A method of treating sewage sludge is provided by blending or by using the dried sludge as auxiliary fuel in a cement manufacturing process.

Hereinafter, the present invention will be described in detail.

Sewage sludge collected through all the water treatment processes such as sedimentation, sedimentation, aeration, etc. in the sewage treatment plant contains 75 to 80% by weight of moisture when discharged through the final dehydration process. Consists of remaining minerals. According to the present invention, the organic matter of the sewage sludge having the above-described structure is used as fuel in the cement manufacturing process due to the calorific value of the sewage itself, and the inorganic matter is used as a raw material of cement.

In order to cement the specific resources, it should not affect the quality of cement in use and there should be no secondary pollution in recycling. In addition, a stable supply must be made, economical and easy to handle in the factory. Accordingly, the present invention is based on the compositional similarity between waste sewage sludge and a general cement raw material. Table 1 shows the results of incineration ash analysis of clay and sewage sludge as raw materials for cement and cement.

Component (ppm) cement Clay Sewage SiO ₂ 22.0 61.30 28.24 Al ₂ O ₃ 5.2 17.80 11.84 Fe ₂ O ₃ 3.2 8.70 4.19 CaO 65.1 0.90 4.03 MgO 0.5 1.70 1.24 Na ₂ O 0.36 0.17 0.83 K ₂ O 0.58 3.04 0.91 P ₂ O ₅ 0.11 - 5.08 Cl 40 18 323 Loss in Incineration 0.5 6.30 43.13

1 is a diagram illustrating a process for producing clinker after mixing, pulverizing and calcining by using dried sewage sludge as a raw material of cement after drying sewage sludge in a sewage treatment plant.

According to the present invention, the sewage sludge (a) finally discharged from the sewage treatment plant is dried by a steam drying method in the sewage treatment plant. By this steam drying method, the sludge (a) is 5 to 30 tons / hr during the residence time of 10 to 30 minutes in the dryer 1 in which a vapor pressure of 7 to 10 kg / cm ² and a temperature of 200 to 350 ° C. are maintained. It is dried at a rate of to have a water content of 15 to 35% by weight from a water content of 75 to 80% by weight.

Sludges dried to contain 15 to 35% by weight of water can be added directly to raw mills in cement plants without being blown off during transportation, as well as 70% or more in weight loss due to the drying process. The cost per tonne of sludge can be reduced to less than a quarter, resulting in significant logistical savings. In addition, it is possible to suppress the generation of toxic gases by performing the drying under relatively low temperature conditions.

In addition, in the dryer 1 according to the present invention, a stirring blade centered on the axis is provided to continuously circulate the dried sludge to create a uniform flow in the dryer and to impart a grinding effect. In addition, by using the free methane gas generated from the digester in the sewage treatment plant as an auxiliary heat source for steam generation, the fuel cost can be greatly reduced, and the gas generated in the dryer is cooled and the soil deodorization facility in the sewage treatment plant is cooled. It can be induced to prevent the occurrence of odor occurrence in advance.

Then, the dried sludge (b) as described above is stored in a silo (2) in the sewage treatment plant and transported to a cement factory in a hopper (3), 0.5 of the total raw material in the cement manufacturing It is put into the raw material grinder 4 in the range of 10 weight%. In general, Portland cement is made by crushing, blending and firing clay, silica and iron oxide using limestone as a main raw material.In the cement factory, various raw materials are put into a certain amount of raw material grinder and pulverized. . Drying sludge (b) of the present invention can be directly introduced into the raw material grinder (4) without the addition of equipment in the factory, and further drying effect due to the exothermic effect of the mixing in the grinder (4) is also expected.

The dried sludge (b) according to the present invention is charged and pulverized, the raw material mixture (c) is contained in a silo (5) and then fired through a preheater (6), a calciner (7) and a kiln (8). . The mixture (c) preheated sequentially to 300 to 350 ° C., 500 ° C., 750 ° C. and 500 to 850 ° C. by several stages of preheater 6 passes through a calciner 7 having a temperature range of 800 to 900 ° C. The kiln 8 is calcined under 1500 ° C. in an inclined continuous sintering furnace to produce clinker, and at the sintering temperature used, dioxin is decomposed to generate a second source of environmental pollution.

According to the present invention, the kiln 8 necessarily requires a bypass line for sludge treatment of a predetermined amount (combination ratio 4%) or more. The bypass line is a device that can induce external release of chlorine or alkali that can generate or accumulate coating in the kiln to ensure the quality of cement products and the stability of equipment. P ₂ O ₅ , Cl, Mg, Na As it removes components in raw materials that may affect the quality of cement, such as K and K, it is possible to treat a large amount of various wastes introduced with sewage sludge.

Subsequently, the raw material mixture calcined by the kiln 8 may be passed through a cooler 9, cooled to 200 to 250 ° C., and then mixed and pulverized with gypsum and slag in a cement mill, thereby preparing cement. Cement is stored in product silos and shipped and used at the appropriate time.

According to the present invention, the sludge (b) dried by the steam drying method in the sewage treatment plant has a calorific value of 1,500 kcal / kg or more. Therefore, the sludge dried according to the present invention can also be used as auxiliary fuel in the kiln 8, which is a sintering furnace in a cement manufacturing process.

The treatment of sewage sludge according to the present invention is economical by utilizing existing facilities of a cement plant without additional equipment by drying the sludge, which is the largest waste generated in the workplace, to a level suitable for use in later processes and reducing transportation costs in the sewage treatment plant. In addition to being able to effectively and stably use the whole amount, it is possible to prevent the leakage of leachate by landfill or the generation of secondary environmental pollutants such as gas or incineration ash during incineration and to prolong the landfill length of the landfill.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example

The sewage sludge of the K material treatment plant was collected and dried for 5 tons per hour while maintaining a residence time of 20 minutes under a vapor pressure of 8 kg / cm ² and a temperature of 300 ° C. The water content of the sludge was reduced from 78 to 80% to 29 to 31%, and the dried sludge was combined with limestone, dolomite quartz and converter slag according to the mixing ratio of Table 2 below. The mineral composition and the content of the circulating material after blending are shown in Table 3 below.

Comparative example

Except for blending according to the mixing ratio of Table 2 without sewage, the same reaction as in the above embodiment was carried out to show the mineral composition and the content of the circulating material after the mixing in Table 3.

Raw material compounding ratio (%) Limestone Manjong Clay Oni Baiyun Kyu Seok Converter slag Comparative example 89.12 6.56 - 0.06 2.56 Example 88.72 - 4.18 2.26 3.14

Mineral composition (%) Circulating material content (%) C3S C2S C3A C4AF K ₂ O Na ₂ O Cl (ppm) Comparative example 51.48 25.54 8.97 10.39 1.51 0.14 57.29 Example 51.60 25.60 8.99 10.42 1.33 0.16 73.98 S: SiO ₂ , A: Al ₂ O ₃ , C: CaO, F: Fe ₂ O ₃

As can be seen from Tables 2 and 3, sludge can be a major substitute for clay, and it can be seen that there are no significant differences between Comparative Examples and Examples in mineral composition after mixing. Considering that the sewage sludge is composed of a large amount of impurities compared to the original raw material used as a product, it can be judged to be a relatively excellent characteristic, and the change in the content of circulating material may be a problem in the cement manufacturing process. However, the degree of change did not fall within the scope of process regulation, so the effect was insignificant.

Compressive strength test results of clinker

From the blends obtained from the examples and comparative examples, clinker and standard yarn (KSL5100 (for cement strength test)) prepared in a conventional manner were mixed at a weight ratio of 1: 2.45, and water was added to prepare a test body. The prepared specimens were stored in a damp or damp room for 20 to 24 hours, then taken out and placed in a hydraulic or screw type tester to apply a load to destroy the specimens. At this time, the maximum total load indicated by the tester was measured and the compressive strength was calculated, and the results of the compressive strength test (test specification: KSL5105) are shown in Table 4 below.

division flow(%) Compressive strength (kgf / cm ² ) 1 day 3 days 7 days 28 days Comparative example 85.3 56 245 336 378 Example 90.7 36 249 340 385 Reference Example - 153 255 316 388 * Reference example: Drying sludge by adding lime-based dehydrating agent * Flow: degree of spreading, degree of water added in preparation of test specimen

As can be seen from Table 4, the experimental results of the compressive strength of the clinker prepared from the examples and comparative examples were similar, similar results were obtained for the reference example of drying the sludge using a lime-based dehydrating agent.

According to the treatment method of sewage sludge according to the present invention, by directly drying the sludge, which is the largest waste generated in the workplace, in the sewage treatment plant, it is possible to economically and stably utilize the existing facilities of the cement plant without any additional facilities while reducing transportation costs. In addition, it is possible to prevent the outflow of leachate from landfill or secondary environmental pollutants such as gas or incineration ash when incinerated and to extend the landfill length of the landfill.

Claims (5)

After drying the sewage sludge to 15 to 35% by weight of water in the sewage treatment plant by steam drying method, the dried sludge is blended with raw materials for cement production in the range of 0.5 to 10% by weight of the total raw materials constituting the cement, or A method of treating sewage sludge by using dry sludge as an auxiliary fuel in a cement manufacturing process. The method of claim 1, A method for treating sewage sludge, characterized in that when drying sewage sludge, methane gas generated in the digester in the sewage treatment plant is used as an auxiliary heat source. The method of claim 1, Sewage sludge drying is carried out at a rate of 5 to 30 tons / hr for a residence time of 10 to 30 minutes in a dryer maintained at a vapor pressure of 7 to 10 kg / cm ² and a temperature of 200 to 350 ° C. How to treat sludge. The method of claim 1, The method of treating sewage sludge, characterized in that the dried sludge has a calorie of 1,500 kcal / kg or more. The method of claim 1, A method for treating sewage sludge, characterized in that the dried sludge is directly added to a raw mill without any additional process and mixed with cement raw materials.