Method for co-processing dioxin-polluted soil by cement kiln

Abstract

The invention provides a method for co-processing dioxin-polluted soil through a cement kiln, and relates to the technical field of dioxin treatment. The invention relates to a method for co-processing dioxin-polluted soil by using a cement kiln. The method comprises the following specific steps: firstly, pre-homogenizing cement clinker raw materials / ingredients and pulverized coal; the method comprises the following steps: firstly, uniformly mixing dioxin-polluted soil with a TiO composite carrier (TiO / pulverized coal) in a pretreatment process, and then treating the dioxin-polluted soil by utilizing a medium-low temperature microwave plasma fluidized bed reactor; and finally, the mixture is pneumatically conveyed to a decomposing furnace for cement kiln co-processing. The pretreatment process can effectively solve the problem of low co-processing efficiency of the high-concentration dioxin-polluted soil cement kiln, and TiO added in the pretreatment process can be used as a catalyst to reduce the dioxin decomposition temperature, so that the risk of secondary synthesis of dioxin at the low-temperature end in the cement rotary kiln by the dioxin-polluted soil is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of dioxin treatment, in particular to a method for co-disposing dioxin-contaminated soil with a cement kiln. Background Art

[0002] Dioxin is one of the first persistent organic pollutants listed by the United Nations Environment Programme as a priority for control and reduction in the Stockholm Convention on Persistent Organic Pollutants. It is a chlorinated tricyclic aromatic compound. Due to the different numbers and positions of chlorine atoms, it constitutes 75 polychlorinated dibenzo-p-dioxins and 135 polychlorinated dibenzofurans. Among these 210 compounds, 17 are considered to be extremely harmful to human health, with acute lethal toxicity, high carcinogenicity, teratogenicity, and mutagenicity, and belong to Class I carcinogens. Dioxin almost does not exist in nature, and mainly comes from the incineration of waste (including domestic waste, medical waste, hazardous waste, sewage plant sludge, etc.) and industries such as metal smelting, pulp and paper making, pesticide production, and specific organic chlorine industrial product production.

[0003] Waste incineration and metal smelting are the main sources of dioxin emissions in my country, accounting for more than 62% of the country's total dioxin emissions. Dioxins emitted into the atmosphere enter the soil through dry and wet atmospheric deposition, causing soil contamination by dioxins, which in turn poses a threat to human health. Once the soil is contaminated by dioxins and the risk is unacceptable, the dioxin-contaminated soil must be disposed of and treated.

[0004] At present, the main treatment methods that have been applied to dioxin-contaminated soil include thermal desorption, photodegradation, microbial remediation, and cement kiln co-treatment. However, the thermal desorption method for treating dioxin-contaminated soil has extremely high energy consumption (>800℃ continuous heating), long treatment time, high cost, and the collected dioxin tail gas needs to be properly treated to avoid secondary pollution; dioxins can absorb electromagnetic radiation in the near-ultraviolet region and undergo photodegradation, but the depth of the soil layer for photodegradation is extremely limited, generally within a few millimeters of the surface, and the organic matter component also has a great influence on the photolysis effect; the microbial remediation method for treating dioxin-contaminated soil has a long treatment cycle and can only degrade low-chlorinated homologues with an efficiency of less than 70%; conventional cement kilns for co-treatment of dioxin-contaminated soil have high energy consumption, and there is a barrier of low efficiency in treating high-concentration dioxin-contaminated soil, as well as the risk of re-synthesis of dioxins at the low-temperature end (such as the kiln tail waste heat utilization system), which causes the dioxin concentration in the flue gas discharged from the exhaust pipe to exceed the standard. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a method for co-disposing dioxin-contaminated soil in cement kilns, which solves the problem of low efficiency of co-disposing high-concentration dioxin-contaminated soil in existing cement kilns, and also solves the risk of secondary synthesis of dioxins at the low-temperature end during the co-disposal of dioxins in existing cement kilns, resulting in substandard flue gas emissions, thereby achieving simultaneous treatment of complex pollution and realizing a low-carbon and resource-based closed loop.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for co-disposing dioxin-contaminated soil by cement kilns, comprising the following specific steps:

[0009] S1. Firstly, the raw materials / ingredients of cement clinker and coal powder are pre-homogenized;

[0010] S2, the raw materials / ingredients of cement clinker are sent to the batching station after pre-homogenization treatment, and weighed at the batching station, i.e. the weight of the raw materials entering the mill, and then the weighed raw materials entering the mill are ground, and after grinding, they are treated in a preheater and sent to the rotary kiln;

[0011] S3, after the coal powder is pre-homogenized, it is ground, and the ground coal powder is stored and sprayed into the rotary kiln through the burner during use;

[0012] S4. The dioxin-contaminated soil is transported to the cement plant by a transfer vehicle and weighed. The weighed dioxin-contaminated soil is then crushed in a closed container and stored separately. Each separately stored dioxin-contaminated soil must be labeled with the specific weight, i.e., the weight of the dioxin-contaminated soil entering the kiln;

[0013] S5. Dioxin-contaminated soil needs to be pre-treated before being added to the rotary kiln. First, the dioxin-contaminated soil and the TiO2 composite carrier are mixed evenly using a fully enclosed double-shaft mixer (slightly negative pressure), and then the dioxin-contaminated soil mixed with the TiO2 composite carrier is transported to the microwave plasma fluidized bed reactor for treatment through a closed conveyor belt. The treatment time is 15 to 30 minutes. The reactor is fully enclosed, and the waste gas generated is connected to the decomposition furnace through a pipeline through a negative pressure system;

[0014] S6. The pre-treated dioxin-contaminated soil is conveyed into the decomposition furnace and then into the rotary kiln through a pneumatic conveying device in a sealed manner, and the addition ratio is not higher than 5%. The calculation formula of the addition ratio is as follows: addition ratio = weight of dioxin-contaminated soil entering the kiln / weight of raw material entering the mill × 100%;

[0015] S7. Dioxin-contaminated soil is completely decomposed after medium- and low-temperature microwave plasma degradation and cement kiln co-treatment, and finally forms cement clinker together with cement clinker raw materials / ingredients. After cooling, the cement clinker is temporarily stored in the clinker warehouse.

[0016] Preferably, the pre-homogenization treatment in S1 mainly adopts any one of yard pre-homogenization and warehouse pre-homogenization.

[0017] Preferably, the dioxin-contaminated soil in S4 should be clearly marked before being stored separately in the pretreatment workshop, and the name, nature, state, quantity, storage time should be recorded and archived. The contaminated soil should be stored separately from cement raw materials / ingredients.

[0018] Preferably, the TiO2 composite carrier in the S5 is 1.5-2.0wt% TiO2 / coal powder, wherein the TiO2 particle size is <50nm, and the microwave plasma fluidized bed reactor has a frequency of 915MHz, a power of 500-1500W, a gas of 1-3L / min air, and a temperature of 300℃-400℃.

[0019] Preferably, the kiln tail exhaust gas generated in the preheater is discharged into an external SP waste heat boiler for waste heat recovery.

[0020] Preferably, the kiln head exhaust gas generated in the grate cooler is discharged into an external AQC waste heat boiler for waste heat recovery.

[0021] (III) Beneficial effects

[0022] The present invention provides a method for co-disposing dioxin-contaminated soil by cement kiln. It has the following beneficial effects:

[0023] In the pretreatment process, the dioxin-contaminated soil is first mixed with the TiO2 composite carrier (TiO2 / coal powder) and then treated using a medium-low temperature microwave plasma fluidized bed reactor; finally, it is pneumatically transported to a decomposition furnace for cement kiln co-disposal. The pretreatment process can effectively solve the problem of low efficiency of cement kiln co-disposal of high-concentration dioxin-contaminated soil. At the same time, the TiO2 added in the pretreatment process can act as a catalyst to reduce the temperature of dioxin decomposition, effectively solving the risk of dioxin-contaminated soil re-synthesizing dioxins at the low temperature end of the cement rotary kiln. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart of a method for co-disposing of dioxin-contaminated soil by using a cement kiln proposed in the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example:

[0027] like Figure 1 As shown, the embodiment of the present invention provides a method for co-disposing dioxin-contaminated soil by cement kiln, comprising the following specific steps:

[0028] S1. First, the raw materials / ingredients of cement clinker and coal powder are pre-homogenized. The pre-homogenization in S1 mainly adopts yard pre-homogenization. The crushed raw materials are piled and taken in the pre-homogenization yard. The piler piles the raw materials in multiple layers on the yard in a certain way to form a herringbone material layer that overlaps up and down. The taker cuts the materials of each layer at the same time in a direction perpendicular to the longitudinal direction of the material pile to complete "flat laying and direct taking" and achieve material mixing and homogenization. The pre-homogenization yard has two layout modes: rectangular and circular.

[0029] S2, the raw materials / ingredients of cement clinker are sent to the batching station after pre-homogenization treatment, and weighed at the batching station, i.e. the weight of the raw materials entering the mill, and then the weighed raw materials entering the mill are ground, and after grinding, they are treated in a preheater and sent to the rotary kiln;

[0030] S3, after the coal powder is pre-homogenized, it is ground, and the ground coal powder is stored and sprayed into the rotary kiln through the burner during use;

[0031] S4. Dioxin-contaminated soil is transported to the cement plant by a transfer vehicle and weighed. The weighed dioxin-contaminated soil is then sealed and crushed and stored separately. Each separately stored dioxin-contaminated soil must be marked with the specific weight, that is, the weight of the dioxin-contaminated soil entering the kiln. In S4, the dioxin-contaminated soil must be clearly marked before being stored separately in the pretreatment workshop, and the name, nature, state, quantity, storage time, and records must be filed. The contaminated soil should be stored separately from the raw materials / ingredients of cement;

[0032] S5. Dioxin-contaminated soil needs to be pretreated before being added to the rotary kiln. First, the dioxin-contaminated soil and the TiO2 composite carrier are mixed evenly using a fully enclosed double-shaft mixer (slightly negative pressure), and then the dioxin-contaminated soil mixed with the TiO2 composite carrier is transported to a microwave plasma fluidized bed reactor for treatment through a closed conveyor belt. The treatment time is 15 to 30 minutes. The reactor is fully enclosed, and the waste gas generated is connected to the decomposition furnace through a pipeline through a negative pressure system. The TiO2 composite carrier in S5 is 1.5 to 2.0 wt% TiO2 / coal powder, wherein the TiO2 particle size is <50 nm. The microwave plasma fluidized bed reactor has a frequency of 915 MHz, a power of 500 to 1500 W, a gas of 1 to 3 L / min of air, and a temperature of 300°C to 400°C.

[0033] S6. The pre-treated dioxin-contaminated soil is conveyed into the decomposition furnace and then into the rotary kiln through a pneumatic conveying device in a sealed manner, and the addition ratio is not higher than 5%. The calculation formula of the addition ratio is as follows: addition ratio = weight of dioxin-contaminated soil entering the kiln / weight of raw material entering the mill × 100%;

[0034] S7. Dioxin-contaminated soil is completely decomposed after medium- and low-temperature microwave plasma degradation and cement kiln co-treatment, and finally forms cement clinker together with cement clinker raw materials / ingredients. After cooling, the cement clinker is temporarily stored in the clinker warehouse.

[0035] The kiln tail exhaust gas generated in the preheater is discharged into the external SP waste heat boiler for waste heat recovery, and the kiln head exhaust gas generated in the grate cooler is discharged into the external AQC waste heat boiler for waste heat recovery.

[0036] The above method is used to use production lines 1, 2, 3, and 4 for cement kiln co-treatment of dioxin-contaminated soil. The following is a table of relevant parameters:

[0037] Table 1 is the relevant parameters of cement rotary kiln

[0038]

[0039] Note: The toxic equivalent mass concentration of dioxins in contaminated soil in this table is the toxic equivalent (TEQ) mass concentration calculated using the International Toxicity Equivalent Factor (I-TEF).

[0040] Table 2 is a list of original ingredients and dioxin-contaminated soil dosage

[0041]

[0042] Table 3 is a summary of the dioxin monitoring results of the exhaust pipe of the cement rotary kiln tail waste heat utilization system at random time periods

[0043]

[0044] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for co-disposal of dioxin-contaminated soil by cement kilns, characterized in that: The specific steps include: S1. Firstly, the raw materials / ingredients of cement clinker and coal powder are pre-homogenized; S2, the raw materials / ingredients of cement clinker are sent to the batching station after pre-homogenization treatment, and weighed at the batching station, i.e. the weight of the raw materials entering the mill, and then the weighed raw materials entering the mill are ground, and after grinding, they are treated in a preheater and sent to the rotary kiln; S3, after the coal powder is pre-homogenized, it is ground, and the ground coal powder is stored and sprayed into the rotary kiln through the burner during use; S4. The dioxin-contaminated soil is transported to the cement plant by a transfer vehicle and weighed. The weighed dioxin-contaminated soil is then crushed in a closed container and stored separately. Each separately stored dioxin-contaminated soil must be labeled with the specific weight, i.e., the weight of the dioxin-contaminated soil entering the kiln; S5. Dioxin-contaminated soil needs to be pre-treated before being added to the rotary kiln. First, use a fully enclosed double-shaft mixer (slightly negative pressure) to evenly mix the dioxin-contaminated soil with the TiO2 composite carrier, and then use a closed conveyor belt to transport the dioxin-contaminated soil mixed with the TiO2 composite carrier to the microwave plasma fluidized bed reactor for treatment. The treatment time is 15 to 30 minutes. The reactor is fully enclosed, and the waste gas generated is connected to the decomposition furnace through a pipeline through a negative pressure system; S6. The pre-treated dioxin-contaminated soil is sent into the decomposition furnace and then into the rotary kiln through pneumatic conveying equipment in a closed manner, and the addition ratio is not higher than 5%. The calculation formula of the addition ratio is as follows: addition ratio = weight of dioxin-contaminated soil entering the kiln / weight of raw material entering the mill × 100%; S7. Dioxin-contaminated soil is completely decomposed after medium- and low-temperature microwave plasma degradation and cement kiln co-treatment, and finally forms cement clinker together with cement clinker raw materials / ingredients. After cooling, the cement clinker is temporarily stored in the clinker warehouse.

2. The method for co-disposal of dioxin-contaminated soil by cement kiln according to claim 1, characterized in that: The pre-homogenization treatment in S1 mainly adopts any one of yard pre-homogenization and warehouse pre-homogenization.

3. The method for co-disposal of dioxin-contaminated soil by cement kiln according to claim 1, characterized in that: The dioxin-contaminated soil in S4 must be clearly labeled before being stored separately in the pretreatment workshop, and the name, nature, state, quantity, storage time must be recorded and archived. The contaminated soil should be stored separately from cement raw materials / ingredients.

4. The method for co-disposal of dioxin-contaminated soil by cement kiln according to claim 1, characterized in that: The TiO2 composite carrier in S5 is 1.5-2.0 wt% TiO2 / coal powder, wherein the TiO2 particle size is less than 50 nm, and the microwave plasma fluidized bed reactor has a frequency of 915 MHz and a power of 500-1500 W; Gas: air 1~3 L / min; Temperature: 300℃~400℃.

5. The method for co-disposal of dioxin-contaminated soil by cement kiln according to claim 1, characterized in that: The kiln tail exhaust gas generated in the preheater is discharged into the external SP waste heat boiler for waste heat recovery.

6. The method for co-disposal of dioxin-contaminated soil by cement kiln according to claim 1, characterized in that: The kiln head exhaust gas generated in the grate cooler is discharged into the external AQC waste heat boiler for waste heat recovery.

Images