Control system and methods for reducing mercury emissions from cement kiln dust collectors.

Abstract

This invention discloses a control system and method for reducing mercury emissions from cement kiln dust collector ash discharge. A flue gas mercury analyzer installed on the chimney measures the mercury concentration in the flue gas and transmits the data to a computer. When the mercury concentration in the flue gas is lower than the environmental standard, the dust collector ash is not discharged. When the mercury concentration in the flue gas is higher than the environmental standard, the computer controls relevant equipment to discharge the dust collector ash to reduce the mercury concentration in the chimney. Solid powder samplers installed in the ash hopper of the baghouse dust collector and on the raw material elevator take samples at regular intervals and send them to a solid mercury analyzer. The solid mercury analyzer transmits the mercury content of the dust collector ash and the mercury content of the raw material entering the kiln to the computer. By comparing the input and output mercury levels, the computer calculates the amount of dust collector ash to be discharged. The computer then controls a bidirectional screw conveyor to transport the dust collector ash to a temporary storage silo via a second belt conveyor according to the calculated discharge amount, thereby reducing the mercury emission concentration from the chimney.

Description

Technical Field

[0001] This invention relates to the field of cement kiln flue gas treatment, specifically to a control method and control system for reducing mercury emissions from cement kilns. Background Technology

[0002] Mercury enters the cement industry primarily from raw materials, pulverized coal, and waste disposal; while its exit route is mainly through exhaust gas emissions, with a small amount entering cement products. After raw materials and fuel enter the preheater and kiln, the vast majority of mercury becomes gaseous and volatilizes, flowing with the exhaust gas. In the preheater, it comes into contact with the raw material powder and is mostly adsorbed. The mercury-adsorbed raw material powder enters the dust collector with the flue gas and is captured as recycled ash, which is then mixed into the raw materials. Most of the mercury re-enters the preheater system with the raw material powder, creating a cycle. A very small amount of recycled ash enters the cement mill as a blending material. Gaseous mercury not captured by the dust collector is emitted into the atmosphere with the cement exhaust gas, resulting in atmospheric mercury emissions.

[0003] like Figure 1 The diagram shows a simplified process for ordinary cement production in the prior art. Flue gas from preheater 1, after waste heat recovery, enters raw meal mill 2 as a drying heat source for the raw meal being ground in mill 2. The cooled flue gas is collected by bag filter 3 and then discharged through chimney 7. The dust collected by bag filter 3 is conveyed to raw meal silo 5 by belt conveyor 4. The raw materials from raw meal mill 2, after grinding, are stored in raw meal silo 5. Raw meal elevator 6 lifts the cement raw meal from raw meal silo 5 to the top of preheater 1 and feeds it into preheater 1.

[0004] Tang Xinyu, in his article "Current Status of Mercury in the Cement Industry and Progress in Emission Reduction Technology" (New Century Cement Herald, No. 4, 2022) and other articles, proposed that since mercury concentration continuously increases during the recycling process, discharging mercury-rich return ash from dust collectors can effectively reduce mercury emissions. The mercury content in dust collector return ash is approximately 10 times that in raw materials, and in some areas, it can even reach hundreds of times the level in raw materials. Therefore, utilizing mercury recycling and enrichment, combined with the operating intervals of raw material mills, to intermittently discharge high-mercury-concentration return ash for use as an admixture in cement products is a promising technological direction.

[0005] In Japanese Patent Application Publication No. 2011-88770, in order to remove mercury and other substances contained in the exhaust gas of cement kilns and to reuse the dust collected after removing mercury and other substances in cement raw materials, the following method was proposed: collecting dust from cement kilns, heating the exhaust gas from clinker coolers, and recovering the mercury that volatilizes through heating.

[0006] However, none of the aforementioned documents and patents have proposed effective methods for controlling the amount of dust discharged from dust collectors. This results in a large amount of dust discharged from dust collectors being wasted and energy consumption being too high in practical applications, or the amount of dust discharged from dust collectors being too small to control mercury emissions, and mercury emissions in flue gas still exceeding the standard. Summary of the Invention

[0007] The technical problem this invention aims to solve is to provide a control system and method for reducing mercury emissions from cement kiln dust collector ash discharge. This system reduces mercury emissions from flue gas by testing and calculating the amount of dust collector ash to be discharged. It is suitable for cement plants with long-term stable or minimal fluctuations in cement raw materials and fuels, but not for cement plants that suddenly need to handle small amounts of co-processed waste containing high concentrations of mercury.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for controlling mercury emissions from cement kiln dust collector ash discharge, comprising the following steps:

[0009] (1) Solid sample sampling and testing

[0010] Samples were taken from the raw materials entering the kiln and the dust collector ash, and the mercury content was tested using a mercury analyzer. The mercury content of the raw materials entering the kiln was A1, and the mercury content of the dust collector ash was A2.

[0011] (2) Gas sample collection and testing

[0012] A mercury analyzer was used to test the flue gas from the chimney, and the test result was recorded as A3.

[0013] (3) Judgment of dust discharge from dust collector

[0014] When A3 < A0, the dust collector ash is not discharged; when A3 ≥ A0, the dust collector ash is discharged.

[0015] When the dust collector ash needs to be discharged externally, the discharge volume is as follows:

[0016] ① When A1×M1×1000<A0×Q:

[0017] M3 = K(A3-A0) × Q ÷ A2 ÷ 1000

[0018] ②When A1×M1×1000≥A0×Q:

[0019] M3=K(1000×A1M1-A0×Q)÷A2÷1000

[0020] In the formula, A0: National standard for mercury emission limit, mg / m³ 3

[0021] A1: Mercury content in raw feed entering the kiln, mg / kg

[0022] A2: Mercury content in dust collector ash, mg / kg

[0023] A3: Mercury content in chimneys, mg / m³ 3

[0024] M1: System feed rate, t / h

[0025] M2: Total ash collected by the dust collector, t / h

[0026] M3: Dust collector ash discharge rate, t / h

[0027] Q: Emission volume, m 3 / h

[0028] K: Safety factor: 1.1 to 1.3.

[0029] A control system for reducing mercury emissions from cement kiln dust collector ash discharge includes a preheater, a raw material mill, a baghouse dust collector, a chimney, a first belt conveyor, a raw material elevator, and a raw material silo. A flue gas mercury analyzer is installed on the chimney to test the mercury concentration in the flue gas and transmit the data to a computer. A first solid powder sampler is installed below the ash hopper of the baghouse dust collector, and a second solid powder sampler is installed on the raw material elevator. Both samplers are connected to a solid mercury analyzer, which transmits the mercury content of the dust collector ash and the mercury content of the raw material entering the kiln to the computer. A bidirectional screw conveyor is installed between the baghouse dust collector and the first belt conveyor. The computer controls the bidirectional screw conveyor to transport the dust collector ash to the first belt conveyor or to the temporary storage silo via the second belt conveyor.

[0030] The beneficial effects of this invention are: reducing mercury emissions, enabling cement kiln flue gas emissions to meet environmental protection standards; clarifying the relationship between external dust collector ash and mercury emissions, reducing the amount of external dust collector ash emissions and disposal, reducing waste and energy consumption, and achieving a high degree of automation. Attached Figure Description

[0031] Figure 1 A simplified diagram of the existing ordinary cement production process;

[0032] Figure 2 This is a schematic diagram of the control system for reducing mercury emissions from the dust collector of a cement kiln according to the present invention.

[0033] Figure 3 This is a flowchart of the control method for reducing mercury emissions from the dust collector of a cement kiln according to the present invention;

[0034] In the diagram, 1 is the preheater; 2 is the raw material mill; 3 is the baghouse dust collector; 4 is the first belt conveyor; 5 is the raw material silo; 6 is the raw material elevator; 7 is the chimney; H-1 is the flue gas mercury analyzer; H-2 is the first solid powder sampler; H-3 is the second solid powder sampler; H-4 is the solid mercury analyzer; H-5 is the computer; H-6 is the bidirectional screw conveyor; H-7 is the second belt conveyor; and H-8 is the temporary storage silo. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] like Figure 3 As shown, the method for controlling mercury emissions from cement kiln dust collector ash discharge according to the present invention includes the following steps:

[0037] (1) Solid sample sampling and testing

[0038] Samples were taken from the raw materials entering the kiln and the dust collector ash, and the mercury content was tested using a mercury analyzer. The mercury content of the raw materials entering the kiln was A1, and the mercury content of the dust collector ash was A2.

[0039] (2) Gas sample collection and testing

[0040] A mercury analyzer was used to test the flue gas from the chimney, and the test result was recorded as A3.

[0041] (3) Judgment of dust discharge from dust collector

[0042] When A3 < A0, the dust collector ash is not discharged; when A3 ≥ A0, the dust collector ash is discharged.

[0043] When the dust collector ash needs to be discharged externally, the discharge volume is as follows:

[0044] ① When A1×M1×1000<A0×Q:

[0045] M3 = K(A3-A0) × Q ÷ A2 ÷ 1000

[0046] ②When A1×M1×1000≥A0×Q:

[0047] M3=K(1000×A1M1-A0×Q)÷A2÷1000

[0048] In the formula, A0: National standard for mercury emission limit, mg / m³ 3

[0049] A1: Mercury content in raw feed entering the kiln, mg / kg

[0050] A2: Mercury content in dust collector ash, mg / kg

[0051] A3: Mercury content in chimneys, mg / m³ 3

[0052] M1: System feed rate, t / h

[0053] M2: Total ash collected by the dust collector, t / h

[0054] M3: Dust collector ash discharge rate, t / h

[0055] Q: Emission volume, m 3 / h

[0056] K: Safety factor: 1.1 to 1.3.

[0057] like Figure 2 As shown, the control system for reducing mercury emissions from cement kiln dust collector ash discharge according to the present invention includes a preheater 1, a raw material mill 2, a baghouse dust collector 3, a chimney 7, a first belt conveyor 4, a raw material elevator 6, and a raw material silo 5. A flue gas mercury analyzer H-1 is installed on the chimney 7 to test the concentration of mercury in the flue gas and transmit the data to a computer H-5. A first solid powder sampler H-2 is installed below the ash hopper of the baghouse dust collector 3, and a second solid powder sampler H-3 is installed on the raw material elevator 6. The first solid powder sampler H-2 and the second solid powder sampler H-3 are connected to the solid mercury analyzer H-4. The solid mercury analyzer H-4 transmits the mercury content of the dust collector ash and the mercury content of the raw material entering the kiln to the computer H-5. A bidirectional screw conveyor H-6 is set between the bag dust collector 3 and the first belt conveyor 4. The computer H-5 controls the bidirectional screw conveyor H-6 to transport the dust collector ash to the first belt conveyor 4 or to transport the dust collector ash to the temporary storage bin H-8 via the second belt conveyor H-7.

[0058] Specifically, a flue gas mercury analyzer H-1 installed in chimney 7 tests the mercury concentration in the flue gas and transmits the data to computer H-5. When the mercury concentration in the flue gas is lower than the environmental standard, the dust collector ash is not discharged. When the mercury concentration in the flue gas is higher than the environmental standard, the computer controls relevant equipment to discharge the dust collector ash to reduce the mercury concentration in the chimney. A first solid powder sampler H-2 installed in the ash hopper of baghouse dust collector 3 and a second solid powder sampler H-3 installed in the raw material elevator 6 take samples at regular intervals and send them to a solid mercury analyzer H-4. The solid mercury analyzer H-4 transmits the mercury content of the dust collector ash and the mercury content of the raw material entering the kiln to computer H-5. Computer H-5 calculates the amount of dust collector ash discharged by comparing the input and output of mercury. It then controls a bidirectional screw conveyor H-6 to transport the dust collector ash to a temporary storage bin H-8 via a second belt conveyor H-7 according to the calculated discharge amount, thereby reducing the mercury emission concentration from the chimney.

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0060] Example 1

[0061] A cement plant has a clinker production line with a capacity of 2500 t / d, a feed rate of 165 t / h, a dust collector ash recovery rate of 12 t / h, and a chimney flue gas volume of 270,000 Nm³. 3 The production line has no co-processing waste system, but the production system is operating normally. Currently, the national standard for mercury emissions from cement kilns is A0 = 0.05 mg / m³. 3 To control mercury emissions from chimneys, the relevant equipment and systems of this invention are provided.

[0062] In the early stages of production operation, the H-1 mercury detector in the chimney measured the concentration A of mercury in the flue gas. 33 It is 0.03 mg / m³ 3 Since A3 < A0, dust collection and ash discharge are not carried out.

[0063] After a period of production operation, the mercury concentration A3 in the flue gas detected by the H-1 chimney mercury detector was 0.06 mg / m³. 3 If A0 < A3, then dust collector ash discharge is required to control mercury emissions.

[0064] Manually sample 20g of dust from the dust collector and raw material entering the kiln, and test the mercury content of the two solid samples as follows: A1 = 0.06mg / kg; A2 = 20mg / kg.

[0065] According to the method of this invention, taking a safety factor of 1.1, the mass of dust collector ash that needs to be discharged is:

[0066] A1×M1=0.06mg / kg×165000kg / h=9900mg / h

[0067] A0×Q=0.05mg / m 3 ×270000m³ / h=13500mg / h

[0068] Therefore, A1×M1<A0×Q:

[0069] Dust collector ash discharge rate M3 = K(A3-A0)×Q÷A2

[0070] = 1.1 × (0.06 - 0.05) mg / m³ 3 ×270000m 33 / h÷20mg / kg

[0071] =148.5kg / h

[0072] The computer-controlled bidirectional dust collector ash cutter discharges 148.5 kg of dust per hour. The discharged dust is temporarily stored in a storage bin and later added to the cement mill as a mixture.

[0073] Example 2

[0074] A cement plant has a clinker production line with a capacity of 6000 t / d, a feed rate of 425 t / h, a dust collector ash recovery rate of 24 t / h, and a chimney flue gas volume of 470,000 Nm³. 3 The production line has no co-processing waste system, but the production system is operating normally. Currently, the national standard for mercury emissions from cement kilns is A0 = 0.05 mg / m³. 3 To control mercury emissions from chimneys, the relevant equipment and systems of this invention are provided.

[0075] After normal production began, the mercury concentration A3 in the flue gas detected by the H-1 mercury detector in the chimney was 0.12 mg / m³. 3 If A0 < A3, then dust collector ash discharge is required to control mercury emissions.

[0076] Manually sample 50g of dust from the dust collector and raw material entering the kiln, and test the mercury content of the two solid samples as follows: A1 = 0.45mg / kg; A2 = 15mg / kg.

[0077] According to the method of this invention, taking a safety factor of 1.2, the mass of dust collector ash that needs to be discharged is:

[0078] A1×M1=0.45mg / kg×425000kg / h=191250mg / h

[0079] A0×Q=0.05mg / m3×470000m3 / h=23500mg / h

[0080] Therefore, A1×M1>A0×Q:

[0081] Dust collector ash discharge rate M3 = K(A1M1 - A0 × Q) ÷ A2

[0082] = 1.2 × (0.12 - 0.05) mg / m³ 3 ×470000m 3 / h÷15mg / kg

[0083] =2632kg / h =2.632t / h

[0084] The computer-controlled bidirectional dust collector ash cutter discharges 2.632 tons of dust per hour. The discharged dust is temporarily stored in a temporary storage silo. The subsequently discharged dust is sent to a special heating furnace for heating and mercury removal, and then returned to the raw material warehouse for use.

[0085] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The patent scope of the present invention should not be limited by these embodiments. That is, all equivalent changes or modifications made in accordance with the spirit of the present invention still fall within the patent scope of the present invention.

Claims

1. A method for controlling mercury emissions from cement kiln dust collector ash discharge, characterized in that, Includes the following steps: (1) Sampling and testing of solid samples Samples were taken from the raw materials entering the kiln and the dust collector ash, and the mercury content was tested using a mercury analyzer. The mercury content of the raw materials entering the kiln was A1, and the mercury content of the dust collector ash was A2. (2) Gas sample collection and testing A mercury analyzer was used to test the flue gas from the chimney, and the test result was recorded as A3. (3) Judgment of dust discharge from dust collector When A3 < A0, the dust collector ash is not discharged; when A3 ≥ A0, the dust collector ash is discharged. When the dust from the dust collector needs to be discharged externally, the discharge volume is as follows: ① When A1×M1×1000<A0×Q: M3 = K(A3-A0) × Q ÷ A2 ÷ 1000 ②When A1×M1×1000 ≥A0×Q: M3=K(1000×A1×M1-A0×Q)÷A2÷1000 In the formula, A0: National standard for mercury emission limit, mg / m³ 3 A1: Mercury content in raw feed entering the kiln, mg / kg A2: Mercury content in dust collector ash, mg / kg A3: Mercury content in chimneys, mg / m³ 3 M1: System feed rate, t / h M2: Total ash collected by the dust collector, t / h M3: Dust collector ash discharge rate, t / h Q: Emission volume, m 3 / h K: Safety factor: 1.1~1.3; This method employs a control system for reducing mercury emissions from cement kiln dust collectors. The control system includes a preheater (1), a raw material mill (2), a baghouse dust collector (3), a chimney (7), a first belt conveyor (4), a raw material elevator (6), and a raw material silo (5). A flue gas mercury analyzer (H-1) is installed on the chimney (7) to test the mercury concentration in the flue gas and transmit the data to a computer (H-5). A first solid powder sampler (H-2) is installed below the ash hopper of the baghouse dust collector (3), and a second solid powder sampler (H-2) is installed on the raw material elevator (6). -3), the first solid powder sampler (H-2) and the second solid powder sampler (H-3) are connected to the solid mercury analyzer (H-4). The solid mercury analyzer (H-4) transmits the mercury content of the dust collector ash and the mercury content of the raw material entering the kiln to the computer (H-5). A bidirectional screw conveyor (H-6) is set between the bag dust collector (3) and the first belt conveyor (4). The computer (H-5) controls the bidirectional screw conveyor (H-6) to transport the dust collector ash to the first belt conveyor (4) or to transport the dust collector ash to the temporary storage bin (H-8) through the second belt conveyor (H-7).

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