System and method for coal gangue single feeding calcination of cement clinker

Abstract

The present application belongs to the technical field of coal gangue application in cement production, in particular to a system and method for calcining cement clinker by feeding coal gangue alone, wherein the method comprises the following steps: feeding cement raw material other than coal gangue into a preheater; and feeding coal gangue into the last but one stage cyclone preheater discharge pipe, with fineness controlled to 80 microns, and the residue on a 10 micron sieve being less than or equal to 10%. The present application provides a system and method for calcining cement clinker by feeding coal gangue alone, which can increase the amount of coal gangue used and utilize more coal gangue in the cement production process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of application of coal gangue in cement production, and particularly relates to a system and method for separately feeding and calcining cement clinker from coal gangue. BACKGROUND

[0002] Prior art:

[0003] The mixture of coal and rock discharged in the coal washing plant and coal mining tunneling and the white gangue outside the coal system stacked together with the coal gangue is a mixture of carbonaceous, argillaceous and sandy shale, containing 20-30% of carbon and having a low calorific value.

[0004] The coal gangue is composed of inorganic matter (rock matter) and organic matter (carbon-containing matter), wherein the inorganic matter is mainly silico-alumina component, and the average content of SiO2 and Al2O3 respectively fluctuates between 40-60% and 15-30%, which can be used as a raw material for cement production to reduce the amount of clay in the cement production raw material; the organic matter in the coal gangue has a certain calorific value, which can reduce the amount of fuel used in cement production.

[0005] The conventional use method of coal gangue in cement production is to grind the coal gangue together with limestone and other cement raw materials to prepare cement raw materials, and the cement raw materials are sent into the cement pre-decomposition system after homogenization, the raw materials are preheated by the preheater and then enter the decomposition furnace, and the carbonates in the raw materials are decomposed and then enter the rotary kiln to complete the calcination of cement clinker under high temperature conditions.

[0006] The utilization mode of coal gangue brings a certain calorific value into the cement raw materials, and when the raw materials enter the second or third stage of the preheater, the combustible materials in the raw materials burn and release heat to cause local overheating, resulting in melting of part of the raw materials in the first, second or third stage of the preheater, and the molten materials and raw material dust adhere to the side wall of the preheater, causing blockage of the conical part or material pipe of the preheater, and in severe cases, the preheater is blocked and cannot produce normally. At the same time, the sulfur in the coal gangue is oxidized and decomposed to form SO2 gas which is discharged with the exhaust gas, resulting in excessive SO2 emission of the tail gas.

[0007] The above problems of preheater skinning and blockage and excessive SO2 emission seriously limit the use amount of coal gangue in cement production.

[0008] Therefore, based on these problems, it is of great practical significance to provide a system and method for separately feeding and calcining cement clinker from coal gangue, which can increase the amount of coal gangue and utilize more coal gangue in the cement production process. SUMMARY

[0009] The application aims to provide a system and method for increasing the amount of coal gangue and utilizing more coal gangue in the cement production process.

[0010] The technical scheme adopted by the embodiment of the application to solve the technical problems in the prior art is:

[0011] A method for separately feeding and calcining cement clinker with coal gangue, wherein the cement raw material comprises coal gangue, and the method comprises the following steps:

[0012] feeding the cement raw material other than the coal gangue into the preheater;

[0013] controlling the fineness of the coal gangue to be less than or equal to 10% of the 80-micron sieve residue, and feeding the coal gangue into the last-but-one cyclone preheater downpipe.

[0014] The embodiment of the application can also adopt the following technical scheme:

[0015] In the method for separately feeding and calcining cement clinker with coal gangue, further, the method comprises the following steps:

[0016] After the coal gangue is separately crushed, homogenized and ground, the coal gangue powder is fed into the mixing part of the last-but-one cyclone preheater downpipe according to the cement raw material ratio after the cement raw material other than the coal gangue falls into the last-but-one cyclone preheater downpipe, and then the coal gangue powder is fed into the kiln together with the cement raw material after mixing.

[0017] In the method for separately feeding and calcining cement clinker with coal gangue, further, the feeding point of the coal gangue is 0.5-1.0 meters away from the connection between the preheater downpipe and the kiln.

[0018] A system for separately feeding and calcining cement clinker with coal gangue, which comprises five or six preheaters and a kiln connected in sequence, a coal gangue grinding system and a coal gangue separate feeding unit, the feeding port of the coal gangue separate feeding unit is connected with the pneumatic conveying pipeline of the coal gangue grinding system through a pipeline and a valve, and the discharging port of the coal gangue separate feeding unit is connected with the kiln or the last-but-one cyclone preheater downpipe.

[0019] In the system for separately feeding and calcining cement clinker with coal gangue, further, the connection point between the discharging port of the coal gangue separate feeding unit and the last-but-one cyclone preheater downpipe is 0.5-1.0 meters away from the connection between the preheater downpipe and the kiln.

[0020] In the system for feeding and calcining cement clinker by using coal gangue alone, further, the coal gangue grinding system comprises a coal gangue crushing device, a homogenizing bin and a homogenizing and distributing device, a vertical roller mill or a ball mill or a roller press, a steel plate type or a concrete type storage bin with a metering and pneumatic conveying pipeline at the bottom of the bin.

[0021] The one or more technical solutions provided in the embodiments of the present application have at least the following beneficial effects:

[0022] 1. The coal gangue is crushed and ground alone for feeding, which solves the problem of skinning or even blocking caused by local overheating of the second or third stage of the preheater, and ensures low energy consumption and stable operation of the cement production system while fully utilizing the heat value contained in the coal gangue.

[0023] 2. The coal gangue is crushed and ground alone for feeding, which solves the problem of excessive sulfur emission in the kiln tail gas, and realizes green and environmental protection in the process of producing cement clinker by using coal gangue.

[0024] 3. The method of feeding the coal gangue into the last but one stage of the preheater feeding pipe can achieve good homogenization effect, thereby ensuring the stability of the clinker quality.

[0025] 4. The present application breaks through the conventional method of using coal gangue as a raw material for cement together with other raw materials to grind and prepare raw meal for calcining clinker, which greatly improves the utilization amount of coal gangue in the calcining process of cement clinker. BRIEF DESCRIPTION OF DRAWINGS

[0026] The technical solutions of the embodiments of the present application will be further described in detail below in combination with the drawings, but it should be known that these drawings are designed only for illustrative purposes, and therefore do not limit the scope of the present application. In addition, unless specifically indicated, these drawings are only intended to conceptually illustrate the structural configuration described herein, and are not necessarily drawn to scale.

[0027] Figure 1 is a coal gangue suspension combustion characteristic diagram of the embodiments of the present application;

[0028] Figure 2 is a schematic diagram of feeding coal gangue directly into a decomposing furnace;

[0029] Figure 3 is a schematic diagram of feeding coal gangue from a preheater feeding pipe into a decomposing furnace.

[0030] In the drawings:

[0031] 1. coal gangue grinding system, 2. coal gangue feeding unit alone;

[0032] C4, last but one stage of cyclone preheater, C5, last but one stage of cyclone preheater, 3, decomposing furnace, 4, flue chamber, 5, rotary kiln. DETAILED DESCRIPTION

[0033] The cement clinker preheating and pre-decomposing unit of the embodiment comprises five or six preheaters and an online decomposing furnace connected in sequence.

[0034] The coal gangue grinding system is a coal gangue separate crushing and grinding system, which comprises a coal gangue crushing device, a homogenizing bin and a homogenizing and distributing device, a vertical roller mill or a ball mill or a roller press, a steel plate or concrete storage bin with a metering and pneumatic conveying pipeline at the bottom of the bin.

[0035] The feeding inlet of the coal gangue separate feeding unit is connected with the coal gangue pneumatic conveying pipeline through a pipeline and a valve, and the discharging outlet of the coal gangue separate feeding unit is connected with the discharging pipe of the second last cyclone preheater, and the connection point is 0.5-1.0 meters away from the connection between the discharging pipe of the preheater and the online decomposing furnace.

[0036] The method for calcining cement clinker by feeding coal gangue separately comprises the following steps:

[0037] S1, after being separately crushed, homogenized and ground, the coal gangue has a fineness controlled to be less than or equal to 10% on an 80-micron sieve;

[0038] S2, after being finely ground according to the cement raw material ratio, the other raw materials except the coal gangue are fed into the preheater;

[0039] S3, after the material falls into the discharging pipe of the second last cyclone preheater, the coal gangue powder is fed into the mixing part of the discharging pipe of the second last cyclone preheater according to the raw material ratio, and then fed into the decomposing furnace after being mixed with the raw meal.

[0040] Working principle:

[0041] The traditional method for calcining cement clinker by feeding coal gangue is to grind the coal gangue and other cement raw materials together, then homogenize and meter, and then feed into the preheating and pre-decomposing system. The main problems are as follows, which seriously restrict the large amount of coal gangue utilization and the stable operation of the cement preheating and pre-decomposing production system:

[0042] (1) The combustible substances in the coal gangue in the raw meal are combusted and released heat at the second or third stage (C2 or C3) of the preheater, which causes local overheating and even clogging;

[0043] (2) The harmful elements such as sulfur elements in the coal gangue in the raw meal appear in a low-temperature cycle (between the preheater and the kiln tail dust collector), which causes the sulfur emission to exceed the standard.

[0044] In order to solve the problem of local overheating of the second or third stage of the preheater, which causes the formation of a skin and even a blockage, and the problem of excessive sulfur emissions, the coal gangue is separately ground and fed into the decomposing furnace, which can avoid the combustion and heat release of the combustible substances in the raw material brought by the coal gangue at the second or third stage (C2 or C3) of the preheater; at the same time, the coal gangue is fed into the decomposing furnace, and the sulfur elements released by combustion rapidly react with the calcium oxide decomposed from calcium carbonate in the decomposing furnace to generate calcium sulfate, so that the sulfur elements are absorbed, and the problem of excessive sulfur emissions is avoided.

[0045] S + O2→ SO2

[0046] CaCO3→ CaO + CO2

[0047] CaO + SO2+ O2→ CaSO4

[0048] The coal gangue is fed into the decomposing furnace as a component, and there may be a problem of uneven mixing with the raw material made of other materials. In order to avoid causing fluctuations in the quality of the cement clinker, the feeding point of the coal gangue is at the lowermost stage of the preheater, which can have a good mixing effect with the raw material, and the mixed raw material enters the decomposing furnace and is subjected to forced mixing again under the action of the decomposing furnace, so that the raw material entering the kiln has good uniformity, and the quality of the cement clinker is not affected by the separate feeding of the coal gangue.

[0049] Referring to the drawings in the specification Figure 1 According to the suspended combustion characteristics of the coal gangue, the ignition time of the coal gangue is 3-5 seconds, and the flow rate of the material in the lowermost stage of the preheater is generally designed to be 1 meter / second. In order to make the coal gangue mixed uniformly while avoiding the occurrence of a skin in the pipeline due to ignition, it is determined through theoretical calculation and experimental verification that the feeding point of the coal gangue is 0.5-1.0 meters away from the connection between the preheater and the on-line decomposing furnace.

[0050] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0051] Taking a 5000t / d cement plant before and after transformation as an example, the actual production raw materials of the plant are shown in Table 1, the set clinker rate values are shown in Table 2, the coal gangue completely replaces clay, and the raw material proportioning obtained through theoretical calculation is shown in Table 3. As can be seen from Table 3, the theoretical amount of coal gangue added can reach 8.08%. The conventional production method of feeding the raw material prepared by grinding the traditional coal gangue and other raw materials into the preheating and pre-decomposing system to produce cement clinker is used as a comparative example, which is compared with the embodiment of the present application.

[0052] Table 1 Chemical composition of raw materials and coal ash

[0053] Item L.O.I SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 Cl - ]]> Total Limestone 40.55 4.56 1.56 0.71 50.92 1.13 0.23 0.16 0.04 0.01 99.87 Silica 1.00 95.13 0.38 0.63 2.11 0.38 0.10 0.04 0.00 0.01 99.78 Clay 12.00 27.58 21.86 37.52 0.06 0.32 0.10 0.12 0.09 0.01 99.66 Coal gangue 1.69 65.47 20.06 5.42 2.29 1.61 2.02 0.18 1.15 0.04 99.93 Copper slag 0.00 37.00 4.80 45.15 8.66 3.38 0.46 0.29 0.20 0.04 99.98 Fly ash 0.00 51.82 20.26 8.58 7.92 2.31 1.95 1.88 4.20 0.02 98.94

[0054] Table 2 Clinker rate value setting

[0055] KH 0.91 SM 2.60 AM 1.60

[0056] Table 3 ingredient calculation

[0057] Limestone Silica Coal gangue Copper slag 85.91 3.94 8.08 2.08

[0058] Comparative example

[0059] According to the conventional production mode, the coal gangue is used to replace part of the clay to prepare the cement raw meal. The limestone, clay, coal gangue, silica and copper slag are co-milled according to the set ratio, and then sent into the preheating and pre-decomposition system after homogenization and metering. It is found in the actual production process that when the coal gangue is mixed in an amount less than 3%, although the temperature at the outlet of the uppermost cyclone is increased, the system can realize continuous and stable operation, the 3-day compressive strength of the clinker is 30.2 MPa, and the 28-day compressive strength is 59.8 MPa (see Table 4); when the coal gangue is mixed in an amount more than 3%, the outlet temperatures of the second and third stages of the preheater are obviously increased, the cyclone wall and the downcomer are covered with a skin, and the downcomer is seriously blocked, which affects the normal and stable operation of the system, and the SO2 in the kiln tail gas and the tail exhaust gas fluctuates greatly, which has a certain impact on the standard discharge of the exhaust gas.

[0060] This is because the combustible substances in the coal gangue are combusted at a certain temperature, the local overheating causes the liquid phase in the raw meal to appear in advance, the liquid phase condenses in the cyclone side wall and the downcomer at a lower temperature, and the raw meal dust is bonded to form a skin. When the coal gangue mixing amount is increased, this skin phenomenon gradually becomes serious, thereby causing the downcomer to be blocked and other production accidents, and affecting the normal production; the sulfur element in the coal gangue is volatilized and oxidized to form SO2, which circulates in the preheater and the kiln tail dust collector, and once a large fluctuation occurs, the tail gas SO2 is out of standard.

[0061] Example 1

[0062] A set of coal gangue crushing, grinding, storage and feeding system is built, the fineness of the coal gangue powder is controlled to be 10% on the 80-micron sieve, and the coal gangue feeding point is arranged on the side wall of the decomposing furnace above the coal injection pipe; the limestone, silica and copper slag are used to prepare the raw meal by the raw material grinding system, and the fineness of the raw meal is controlled according to the convention. The raw meal is fed into the preheating and pre-decomposition system from the air inlet pipe of the uppermost preheater, and the coal gangue powder is also directly fed into the decomposing furnace after the raw meal enters the decomposing furnace. The coal gangue and the raw meal are mixed in the decomposing furnace, the coal feeding amount of the decomposing furnace is adjusted, and the outlet temperature of the decomposing furnace is controlled to be consistent with that in the conventional operation.

[0063] It is found in actual production that when the amount of coal gangue is up to 5%, the system can realize continuous and stable operation, the compressive strength of clinker is 28.5 MPa after 3 days and 57.6 MPa after 28 days (see Table 4). Because the combustible material brought by coal gangue is combusted in the decomposing furnace, part of the coal used in the decomposing furnace is saved, and the second and third stage preheaters and the feeding pipe of the preheater do not appear to be covered with skin, the SO2 in the kiln tail gas does not exceed the standard, but because the coal gangue is directly fed into the decomposing furnace, the raw meal and the coal gangue cannot be completely homogenized in the decomposing furnace, which has a certain influence on the quality of the cement clinker, and the compressive strength of the clinker is reduced.

[0064] Example 2

[0065] A set of coal gangue crushing, grinding, storage and feeding system is built, the fineness of the coal gangue powder is controlled to be 10% on the 80 micron sieve, the coal gangue feeding point is set at 2 meters from the connection point of the last second stage preheater feeding pipe and the decomposing furnace, the limestone, silica and copper slag are used to prepare raw meal by the raw material grinding system, and the fineness of the raw meal is controlled according to the conventional method. The raw meal is fed into the preheating and pre-decomposing system from the air inlet pipe of the uppermost preheater, and the coal gangue powder is fed into the coal gangue feeding point at the same time after the raw meal enters the last second stage preheater feeding pipe of the preheating and pre-decomposing system. The coal gangue and the raw meal are mixed and then enter the decomposing furnace, the coal feeding amount of the decomposing furnace is adjusted, and the outlet temperature of the decomposing furnace is controlled to be consistent with that in the conventional operation.

[0066] It is found in actual production that when the amount of coal gangue is up to 5%, the system can realize continuous and stable operation, the compressive strength of clinker is 28.5 MPa after 3 days and 57.6 MPa after 28 days (see Table 4). Because the combustible material brought by coal gangue is combusted in the decomposing furnace, part of the coal used in the decomposing furnace is saved, and the second and third stage preheaters and the feeding pipe of the preheater do not appear to be covered with skin, the SO2 in the kiln tail gas does not exceed the standard, but because the coal gangue is directly fed into the decomposing furnace, the raw meal and the coal gangue cannot be completely homogenized in the decomposing furnace, which has a certain influence on the quality of the cement clinker, and the compressive strength of the clinker is reduced.

[0067] But it is found in production that the last second stage preheater feeding pipe of the coal gangue feeding appears to be covered with skin, which has a certain influence on normal production, and needs to be cleaned regularly, because the coal gangue stays in the feeding pipe for too long, and the heat released by the combustion of the combustible material in the coal gangue causes the feeding pipe to be covered with skin.

[0068] Example 3

[0069] A set of coal gangue separate crushing, grinding, storage and feeding system is built, the fineness of the coal gangue powder is controlled to be 80 microns with a residue of 10%, and the coal gangue feeding point is arranged at a position 1 meter away from a connecting point of a feeding pipe of a preheater of a penultimate stage of a preheating and pre-decomposing system and a decomposing furnace. Limestone, silica and copper slag are prepared into raw meal by using a raw material grinding system, and the fineness of the raw meal is controlled according to the conventional method. The raw meal is fed into the preheating and pre-decomposing system from an air inlet pipe of the preheater of the uppermost stage, and the coal gangue powder is fed into the coal gangue feeding point at the same time after the raw meal enters the feeding pipe of the preheater of the penultimate stage of the preheating and pre-decomposing system. The coal gangue and the raw meal are mixed and then enter the decomposing furnace, the amount of the coal fed into the decomposing furnace is adjusted, and the outlet temperature of the decomposing furnace is controlled to be consistent with the outlet temperature of the decomposing furnace in the conventional operation.

[0070] It is found in the actual production process that when the amount of the coal gangue added reaches 6%, the system can realize continuous and stable operation, the compressive strength of the clinker is 30.6 MPa after 3 days and 60.5 MPa after 28 days (see Table 4), the coal gangue and the raw meal are mixed in the feeding pipe of the preheater and then enter the decomposing furnace, the spray and homogenization effect of the mixed material in the decomposing furnace is good, the 28-day compressive strength of the cement clinker is obviously improved compared with the conventional production method, and the SO2 in the kiln tail gas does not exceed the standard. Because the combustible substances brought by the coal gangue are burned in the decomposing furnace, part of the coal used in the decomposing furnace is saved, and there is no skinning phenomenon in the second and third stages of the preheater and the feeding pipe.

[0071] Table 4 Strength properties of cement clinker in different schemes

[0072] No. 3-day compressive strength MPa 28-day compressive strength MPa Comparative Example 30.2 58.8 Example 1 28.5 57.6 Example 2 30.5 59.2 Example 3 30.6 60.5

[0073] In summary, the present application provides a system and method for separately feeding coal gangue to calcine cement clinker to increase the amount of coal gangue and utilize more coal gangue in the cement production process.

[0074] The above embodiments have been described in detail, but the content described is only the preferred embodiments of the present application and cannot be considered as limiting the scope of the implementation of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A method of coal gangue-only fed calcination of cement clinker, the cement raw material comprising coal gangue, characterized in that: The method for calcining cement clinker by feeding the coal gangue alone comprises the following steps: feeding the cement raw material other than the coal gangue into the preheater; The coal gangue with a fineness of 80 microns or less than 10% is fed into the last but one cyclone preheater downpipe, and the feeding point of the coal gangue is 0.5-1.0 meters away from the connection between the preheater downpipe and the decomposing furnace, and the ignition time of the coal gangue is 3-5 seconds.

2. The method of claim 1, wherein the coal gangue is used as a sole feed material for the sintering of cement clinker. The method for calcining cement clinker by feeding the coal gangue alone comprises the following steps: After the coal gangue is separately crushed, homogenized and ground, the coal gangue powder is sent to the mixing part of the last but one cyclone preheater downpipe according to the cement raw material ratio after the other raw material other than the coal gangue is fed into the last but one cyclone preheater downpipe, and then the coal gangue powder is fed into the decomposing furnace together with the raw material.

3. A system for coal gangue single feeding calcining cement clinker, characterized in that: The system for calcining cement clinker by feeding the coal gangue alone comprises five or six preheaters and decomposing furnaces connected in sequence, a coal gangue grinding system and a coal gangue separate feeding unit, the feeding inlet of the coal gangue separate feeding unit is connected with the pneumatic conveying pipeline of the coal gangue grinding system through a pipeline and a valve, and the discharging outlet of the coal gangue separate feeding unit is connected with the last but one cyclone preheater downpipe.

4. The system for separately feeding coal gangue to calcine cement clinker according to claim 3, characterized in that: The connection point between the discharging outlet of the coal gangue separate feeding unit and the last but one cyclone preheater downpipe is 0.5-1.0 meters away from the connection between the preheater downpipe and the decomposing furnace.

5. The system for separately feeding coal gangue to calcine cement clinker according to claim 3, characterized in that: The coal gangue grinding system comprises a coal gangue crushing device, a homogenization bin and a homogenization distribution device, a vertical roller mill or a ball mill or a roller press, a steel plate or concrete storage bin with a metering and pneumatic conveying pipeline at the bottom.

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