Method and integrated equipment for treating municipal sludge using semi-carbonization coupled carbonization process

Abstract

The present invention belongs to the technical field of municipal sludge treatment, and particularly relates to a method and integrated equipment for treating municipal sludge using a semi-carbonization coupled carbonization process. The integrated equipment comprises a first heat treatment furnace (10) using direct heating and a second heat treatment furnace (20) using jacket heating. The second heat treatment furnace (20) is equipped with a second heat source (21). The air inlet of the first heat treatment furnace (10) is located at its discharge end. The first heat treatment furnace (10) is equipped with a first heat source (11), and the first heat source (11) is connected to the air inlet of the first heat treatment furnace (10). The air outlet of the first heat treatment furnace (10) is connected to a dry dust removal device (12), and the jacket of the second heat treatment furnace (20) is connected to an exhaust gas treatment device (22). The present invention introduces the concept of semi-carbonization and uses a direct contact heating method to achieve partial carbonization of the material, thereby improving the heat treatment efficiency and also helping to improve the dust removal efficiency of the gas.

Description

Technical Field

[0001] The invention belongs to the technical field of municipal sludge treatment, and in particular relates to a method and integrated equipment for treating municipal sludge using a semi-carbonization coupled carbonization process. Background Art

[0002] Municipal sludge is an inevitable byproduct of urban sewage treatment. In recent years, with the rapid growth of sewage treatment capacity, municipal sludge production has also increased dramatically. Sludge contains heavy metals, microorganisms, and various other pollutants. Improper sludge treatment and disposal can lead to secondary environmental problems such as greenhouse gas emissions, groundwater contamination, and soil pollution. Currently, municipal sludge drying and pyrolysis carbonization technology is attracting considerable attention due to its advantages, including high volume reduction and high heavy metal solidification rates.

[0003] Chinese patent document CN107200458A discloses a municipal sludge treatment method that utilizes a drying furnace and a pyrolysis carbonization furnace for dehydration and pyrolysis carbonization. Both the drying furnace and the pyrolysis carbonization furnace utilize jacketed rotary kilns for indirect heating. The material in the drying furnace is heated to a temperature of 100-150°C. The drying furnace is heated by auxiliary heating flue gas generated by the drying auxiliary combustion furnace and by the pyrolysis furnace jacket flue gas discharged from the pyrolysis carbonization furnace heating jacket. The pyrolysis carbonization furnace is heated by high-temperature heating flue gas generated by the mixed combustion furnace. The pyrolysis carbonization furnace is equipped with a pyrolysis gas exhaust port, which conveys pyrolysis gas generated within the pyrolysis carbonization furnace cavity into the mixed combustion furnace for combustion to generate high-temperature heating flue gas. This method results in relatively low drying efficiency due to the relatively low heating temperature within the drying furnace and the indirect heating method.

[0004] Chinese patent document CN214400194U discloses a municipal sludge drying and pyrolysis carbonization system. The system comprises a drying furnace and a pyrolysis carbonization furnace, both of which utilize heating jackets. The drying furnace is equipped with a drying gas outlet pipe, which connects sequentially to a spray tower, a condenser, and a heat exchanger. The pyrolysis gas outlet pipe is connected to the heat exchanger to facilitate heat exchange between the drying gas and the pyrolysis gas. After the heat exchanger, the drying gas outlet pipe branches into two branches, one leading to the combustion chamber and the other to the drying furnace. The drying furnace utilizes both internal and external heating methods. After spraying and heat exchange, the drying gas returns to the drying furnace, achieving partial circulation and internal heating. The high-temperature flue gas generated in the combustion chamber passes sequentially through the pyrolysis carbonization furnace and the drying furnace jacket, achieving external heating. This solution improves drying efficiency through internal circulation of the drying gas and helps reduce odor at the project site, representing a technological development trend. However, the condensation-first, then heat exchange process increases energy consumption. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for treating municipal sludge by a semi-carbonization coupled carbonization process on the basis of the existing technology, so as to reduce the odor at the project site on the basis of further improving the thermal treatment efficiency.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The method for treating municipal sludge by semi-carbonization coupled carbonization process, the municipal sludge is treated in the first heat treatment section and the second heat treatment section, the second heat treatment section is heated by a jacket, and the second heat treatment section is equipped with a second heat source to provide heat for the jacket:

[0008] (1) Control the moisture content of municipal sludge in the first heat treatment stage so that the moisture content at the feed end is greater than 60% and the moisture content at the discharge end is less than 30%;

[0009] (2) The air inlet end of the first heat treatment section is located at its discharge end. The first heat treatment section is equipped with a first heat source. The heated flue gas derived from the first heat source enters the first heat treatment section from the air inlet end and directly contacts the municipal sludge. The movement direction of the heated flue gas is opposite to the forward direction of the municipal sludge. The temperature of the heated flue gas at the air inlet end is not less than 450°C, so that the municipal sludge is partially carbonized in the latter part of the first heat treatment section.

[0010] (3) After being discharged from the first heat treatment section, the municipal sludge enters the second heat treatment section, where the municipal sludge is carbonized and a second pyrolysis gas is generated. The second pyrolysis gas is introduced into the second heat supply source and / or the first heat supply source for resource utilization;

[0011] (4) The first pyrolysis gas generated in the first heat treatment section is discharged through the outlet of the first heat treatment section, and after dry dust removal, part of the first pyrolysis gas is discharged to the first heat source so that part of the first pyrolysis gas circulates between the outlet of the first heat treatment section, the first heat source, and the inlet of the first heat treatment section. Part of the first pyrolysis gas is discharged to the second heat source so that part of the first pyrolysis gas is utilized as a resource by the second heat source and then discharged together with the heated flue gas of the second heat treatment section after exhaust gas treatment.

[0012] The "semi-carbonization" mentioned in the present invention means that in the latter part of the drying stage where the moisture content is relatively low, the material is partially carbonized by direct contact with high-temperature flue gas.

[0013] Compared with Chinese patent document CN214400194U, the main innovations of this application are:

[0014] (1) By increasing the temperature of the flue gas in the first heat treatment stage, partial carbonization is achieved in the first heat treatment stage. On the one hand, the high temperature accelerates the drying efficiency of the municipal sludge in the first heat treatment stage, and on the other hand, it is equivalent to improving the carbonization efficiency of the second heat treatment stage. Compared with the indirect heating mode of the jacket in the second heat treatment stage, the direct heating mode of the first heat treatment stage has a higher carbonization efficiency.

[0015] (2) Partial carbonization can decompose some of the organic matter in the drying gas, thereby reducing the viscosity of the drying gas and reducing the impact of the viscosity of the drying gas on the stability of dry dust removal, which is beneficial to the removal of particulate matter or dust in the first pyrolysis gas.

[0016] (3) The first pyrolysis gas is treated with dry dust removal, ensuring the water vapor content of the first pyrolysis gas. The specific heat capacity of liquid is greater than that of gas, which can improve the heat storage performance of the first pyrolysis gas, thereby improving the efficiency of the first heat treatment stage and reducing the equipment scale. If a spraying method is used, on the one hand, a large amount of organic wastewater will be generated, and the high-temperature water vapor in the first pyrolysis gas will also condense when it cools, thereby reducing the heat storage performance of the first pyrolysis gas; secondly, organic wastewater is also a major source of odor at the project site.

[0017] (4) The first heat treatment section is equipped with a first heat source, which, on the one hand, ensures that the heated flue gas in the first heat treatment section has a sufficiently high temperature, and on the other hand, can promptly remove the organic components in the circulating gas and make full use of the thermal energy of the organic components.

[0018] (5) The first pyrolysis gas is partially directed to the second heat source and then discharged after exhaust treatment along with the heated flue gas from the second heat treatment section. This is equivalent to transferring the water vapor precipitated during the drying gas spraying stage in the solution described in Chinese patent document CN214400194U to the exhaust gas treatment section. At this time, the organic matter content in the exhaust gas is very low after high-temperature oxidation, which can significantly reduce the generation of odor. In addition, the water vapor content in the exhaust gas is relatively high, which can reduce the amount of spray water used in subsequent exhaust gas treatment.

[0019] As an improvement, at least 50% of the first pyrolysis gas is directed to the first heat source to ensure that there is sufficient organic matter available for combustion in the first heat source.

[0020] As an improvement, the temperature of the first pyrolysis gas when it is discharged from the gas outlet of the first heat treatment section is not greater than 300° C., so as to meet the needs of subsequent dry dust removal.

[0021] As an improvement, the temperature of the heated flue gas generated by the second heat supply source at the air inlet end of the jacket is not less than 850°C.

[0022] As an improvement, a bag dust collector is used for dust removal in step (4).

[0023] As an improvement, the dust outlet of the bag filter is connected to the feed end of the second heat treatment section.

[0024] As an improvement, in step (4), the first pyrolysis gas is subjected to dust removal treatment and then heat exchanged with the heated flue gas exhaust discharged from the jacket to increase the temperature of the first pyrolysis gas.

[0025] As an improvement, the first heat source and the second heat source are equipped with combustion-supporting air, and the combustion-supporting air exchanges heat with the heated flue gas exhaust gas derived from the jacket to reduce the temperature of the heated flue gas exhaust gas.

[0026] As an improvement, the tail gas treatment in step (4) includes deacidification treatment.

[0027] The present invention also provides an integrated device for treating municipal sludge by a semi-carbonization coupled carbonization process, comprising a first heat treatment furnace and a second heat treatment furnace, the second heat treatment furnace being an indirect thermal desorption furnace heated by a jacket, the second heat treatment furnace being equipped with a second heat source to provide a heat source for the jacket, the first heat treatment furnace being a direct thermal desorption furnace, the air inlet end of the first heat treatment furnace being located at its discharge end, the first heat treatment furnace being equipped with a first heat source, the first heat source being connected to the air inlet end of the first heat treatment furnace; the air outlet end of the first heat treatment furnace being connected to a dry dust removal device, the air outlet end of the dry dust removal device being connected to the first heat source and the second heat source, the jacket of the second heat treatment furnace being connected to an exhaust gas treatment device, the pyrolysis gas outlet of the second heat treatment furnace being connected to the second heat source and / or the first heat source.

[0028] As an improvement, the dust outlet of the dry dust removal device is connected to the feed end of the second heat treatment furnace.

[0029] As an improvement, a first heat exchanger for increasing the temperature of the first pyrolysis gas generated by the first heat treatment furnace is provided between the jacket of the second heat treatment furnace and the tail gas treatment device.

[0030] As an improvement, the tail gas treatment device includes a deacidification tower equipped with an alkaline liquid pool.

[0031] In summary, this invention introduces the concept of semi-carbonization, achieving partial carbonization of the material through direct contact heating, improving heat treatment efficiency and also contributing to enhanced gas dust removal efficiency. Furthermore, the use of dry dust removal instead of spray scrubbing not only reduces heat loss but also helps further reduce odor at the project site. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of the invention;

[0033] 10. First heat treatment furnace; 11. First heat source; 12. Dry dust removal device; 20. Second heat treatment furnace; 21. Second heat source; 22. Exhaust gas treatment device; 30. First heat exchanger; 40. Second heat exchanger; 50. Gas supply device. DETAILED DESCRIPTION

[0034] Example 1

[0035] like Figure 1 As shown, the integrated equipment for treating municipal sludge using a semi-carbonization coupled carbonization process according to the present invention comprises a first heat treatment furnace 10 and a second heat treatment furnace 20. The first heat treatment furnace 10 is a direct thermal desorption furnace and is equipped with a first heat source 11, which is a drying hot air furnace. The first heat source 11 is connected to the air inlet of the first heat treatment furnace 10, which is located at its discharge end. The air outlet of the first heat treatment furnace 10 is connected to a dry dust removal device 12. The air outlet of the dry dust removal device 12 is connected to a first heat exchanger 30. The second heat treatment furnace 20 is an indirect thermal desorption furnace using a jacket for heating and is equipped with a second heat source 21, which is a combustion chamber. The jacket of the second heat treatment furnace 20 is connected in sequence to the first heat exchanger 30, the second heat exchanger 40, and the exhaust gas treatment device 22. Furthermore, the first heat treatment furnace 10 and the second heat treatment furnace 20 are equipped with a gas supply device 50 .

[0036] Heating flue gas from the first heat source 11 enters the first heat treatment furnace 10 from its inlet port, where it comes into direct countercurrent contact with the municipal sludge. The initial moisture content of the municipal sludge at the inlet port of the first heat treatment furnace 10 is 75-85%, and at the outlet port, it is 15-20%. The heating flue gas temperature at the inlet port is 450-550°C, resulting in partial carbonization of the municipal sludge in the latter part of the first heat treatment stage.

[0037] After partial carbonization in the first heat treatment furnace 10, the municipal sludge is introduced into the second heat treatment furnace 20 for secondary complete carbonization. This secondary complete carbonization occurs within the second heat treatment furnace 20. The heated flue gas generated by the second heat source 21 has a temperature of 850-950°C at the jacket inlet. After carbonization is complete, the municipal sludge is discharged.

[0038] The first pyrolysis gas generated by the first heat treatment furnace 10 is subjected to dust reduction treatment by a dry dust removal device 12. The dust removal device is a bag filter. The first pyrolysis gas, when discharged from the outlet of the first heat treatment furnace 10, has a temperature of 200-230°C and a moisture content of 60-70%. Particulate matter or dust generated during the dust removal process is transported to the second heat treatment furnace 20 for harmless treatment. Conventional dust removal processes typically experience a decrease in dust removal efficiency after operation begins due to the presence of sticky organic matter in the first pyrolysis gas, the low heat capacity of the flue gas, and the tendency for the gas to cool during circulation. Furthermore, tar-like substances easily adhere to the inner walls of the first pyrolysis gas pipeline and fan, typically resulting in a limited operating life of one to two weeks. However, the first heat treatment stage utilizes pyrolysis gas generated by semi-carbonization. Under similar conditions, the dust collector efficiency can maintain over 95% for extended periods, requiring no cleaning or maintenance. The first pyrolysis gas pipeline, fan, and heat exchanger require maintenance every three months.

[0039] After dust removal, the first pyrolysis gas passes through the first heat exchanger 30 to exchange heat with the heated flue gas in the jacket of the second heat treatment furnace 20. 70-80% of the first pyrolysis gas is distributed to the first heat source 11 for combustion, and 20-30% of the first pyrolysis gas is distributed to the second heat source 21 for combustion and water vapor exhaust.

[0040] The second pyrolysis gas generated by the second heat treatment furnace 20 is introduced into the second heat source 21 as fuel for supplementary combustion. The gas supplied by the gas supply device 50 is natural gas, and the amount of natural gas is adjusted to control the temperature of the first heat source 11 and the second heat source 21.

[0041] The heated flue gas in the jacket of the second heat treatment furnace 20 exchanges heat with the first pyrolysis gas after dust removal through the first heat exchanger 30. Before the heat exchange, the temperature of the heated flue gas is 750-820°C, and the temperature of the first pyrolysis gas is 190-220°C. After the heat exchange, the temperature of the heated flue gas is about 270-350°C, and the temperature of the first pyrolysis gas is 450-550°C. Therefore, after the heat exchange, the temperature of the first pyrolysis gas is sufficient to support the partial carbonization of the sludge in the first heat treatment furnace 10. The first heat source 11 equipped in the first heat treatment furnace 10 is mainly used to remove organic components in the first pyrolysis gas and perform precise temperature adjustment to keep the temperature of the heated flue gas at the air inlet end stable at 450-550°C.

[0042] The heated flue gas continues to exchange heat with the combustion-supporting air through the second heat exchanger 40. The combustion-supporting air then enters the first heat source 11 and the second heat source 21, respectively. After two heat exchanges, the heated flue gas reaches a temperature of 150-200°C. The heated flue gas enters the exhaust gas treatment unit 22 for treatment before being discharged. The exhaust gas treatment unit 22 includes a deacidification tower equipped with an alkaline solution tank. Since the heated flue gas contains a high amount of water vapor, this water can be condensed and recycled.

[0043] Since the organic components in the drying gas circulate in the system and are burned by the first heat source 11 or the second heat source 21, the organic matter will not escape into the environment in gaseous or liquid form, greatly reducing the odor at the project site.

[0044] The system is used at a certain project site with a daily municipal sludge processing capacity of 60t / d. The specific material parameters are: moisture content 75-85%, dry basis organic matter content 50-80%, and dry basis calorific value 2200Kcal / kg.

[0045] The municipal sludge resides in the first heat treatment furnace 10 for 45 minutes, 20-25 minutes shorter than in conventional drying furnaces. The municipal sludge resides in the second heat treatment furnace 20 for 25 minutes, 10-15 minutes shorter than in conventional carbonization furnaces, shortening the total heat treatment time by approximately 30-40 minutes. The pyrolysis product meets national standards, with a thermal reduction rate of less than 8%.

Claims

1. A method for treating municipal sludge by a semi-carbonization coupled carbonization process, wherein the municipal sludge is treated in a first heat treatment section and a second heat treatment section, wherein the second heat treatment section is heated by a jacket, and a second heat source is provided in the second heat treatment section to provide heat for the jacket, characterized in that: The following steps are included: (1) Control the moisture content of municipal sludge in the first heat treatment stage so that the moisture content at the feed end is greater than 60% and the moisture content at the discharge end is less than 30%; (2) The air inlet end of the first heat treatment section is located at its discharge end. The first heat treatment section is equipped with a first heat source. The heated flue gas derived from the first heat source enters the first heat treatment section from the air inlet end and directly contacts the municipal sludge. The movement direction of the heated flue gas is opposite to the forward direction of the municipal sludge. The temperature of the heated flue gas at the air inlet end is not less than 450°C, so that the municipal sludge is partially carbonized in the latter part of the first heat treatment section. (3) After being discharged from the first heat treatment section, the municipal sludge enters the second heat treatment section, where the municipal sludge is carbonized and a second pyrolysis gas is generated. The second pyrolysis gas is introduced into the second heat supply source and / or the first heat supply source for resource utilization; (4) The first pyrolysis gas generated in the first heat treatment section is discharged through the outlet of the first heat treatment section, and after dry dust removal, part of the first pyrolysis gas is discharged to the first heat source so that part of the first pyrolysis gas circulates between the outlet of the first heat treatment section, the first heat source, and the inlet of the first heat treatment section. Part of the first pyrolysis gas is discharged to the second heat source so that part of the first pyrolysis gas is utilized as a resource by the second heat source and then discharged together with the heated flue gas of the second heat treatment section after exhaust gas treatment.

2. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: At least 50% of the first pyrolysis gas is directed to a first heat source.

3. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: The temperature of the first pyrolysis gas when it is discharged from the gas outlet end of the first heat treatment section is no more than 300°C.

4. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: The temperature of the heating flue gas generated by the second heat source at the air inlet end of the jacket is not less than 850°C.

5. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: In the step (4), a bag dust collector is used for dust removal.

6. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 5, characterized in that: The dust outlet of the bag filter is communicated with the feed end of the second heat treatment section.

7. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: In the step (4), the first pyrolysis gas is subjected to dust removal treatment and then heat exchanged with the heated flue gas exhaust discharged from the jacket to increase the temperature of the first pyrolysis gas.

8. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: The first heat source and the second heat source are equipped with combustion-supporting air, and the combustion-supporting air exchanges heat with the heated flue gas exhaust gas led out from the jacket to reduce the temperature of the heated flue gas exhaust gas.

9. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, characterized in that: The tail gas treatment in step (4) includes deacidification treatment.

10. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 1, wherein the integrated equipment for implementing the method comprises a first heat treatment furnace (10) and a second heat treatment furnace (20), wherein the second heat treatment furnace (20) is an indirect thermal desorption furnace heated by a jacket, and the second heat treatment furnace (20) is equipped with a second heat source (21) to provide heat for the jacket, and wherein: The first heat treatment furnace (10) is a direct thermal desorption furnace. The air inlet of the first heat treatment furnace (10) is located at its discharge end. The first heat treatment furnace (10) is equipped with a first heat source (11), and the first heat source (11) is connected to the air inlet of the first heat treatment furnace (10); the air outlet of the first heat treatment furnace (10) is connected to a dry dust removal device (12), and the air outlet of the dry dust removal device (12) is connected to the first heat source (11) and the second heat source (21). The jacket of the second heat treatment furnace (20) is connected to the tail gas treatment device (22), and the pyrolysis gas outlet of the second heat treatment furnace (20) is connected to the second heat source (21) and / or the first heat source (11).

11. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 10, characterized in that: The dust outlet of the dry dust removal device (12) is connected to the feed end of the second heat treatment furnace (20).

12. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 10, characterized in that: A first heat exchanger (30) for increasing the temperature of the first pyrolysis gas generated by the first heat treatment furnace (10) is provided between the jacket of the second heat treatment furnace (20) and the tail gas treatment device (22).

13. The method for treating municipal sludge by a semi-carbonization coupled carbonization process according to claim 10, characterized in that: The tail gas treatment device (22) includes a deacidification tower equipped with an alkaline liquid pool.

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