A denitrification method for producing oxidized pellets based on belt roasting process

Abstract

A denitrification method for producing oxidized pellets based on a belt roasting process, the method includes batching, pelletizing and pellet roasting; a double denitrification mechanism is established by installing an ammonia injection system in the smoke hood of the exhaust drying section and the first preheating section of the belt roaster, and an SCR denitrification system behind the wind box of the second preheating section, the roasting section and the soaking section, so as to achieve the purpose of ultra-low emissions. The method also adds composite fuels with different ignition points to the pellets, so that a small amount of low-ignition-point fuel in the added fuel can burn rapidly in the first preheating section, and abundant pores are formed on the pellets while providing heat to the pellets, which can effectively absorb NO in the flue gas. x and NH3, improving the denitrification efficiency and eliminating the need for end-of-pipe NO treatment x process and improve economic benefits.

Description

Technical Field

[0001] The invention relates to a denitration method of a belt roasting process, and in particular to a denitration method for producing oxidized pellets based on a belt roasting process, belonging to the field of pellet flue gas denitration. Background Art

[0002] Nitrogen oxides NO in the steel industry x and sulfur dioxide are the main pollutants that pollute the atmosphere. The steel industry now has mature desulfurization technology, but the removal technology of nitrogen oxides is still relatively lacking. Under the increasingly severe environmental situation, the development of steel industry nitrogen oxides NO x Prevention and control technology is of great significance.

[0003] The belt roasting process is one of the main processes for pellet production. At present, the flue gas denitrification of the belt roasting process mainly adopts the end-of-pipe treatment method, that is, the flue gas generated in the pellet production process is collected and dusted, and then the selective catalytic reduction method SCR and activated carbon adsorption method are used for denitrification. However, due to the large amount of flue gas and complex components in the belt roasting process, the end-of-pipe treatment method requires huge denitrification equipment and high operating costs. If the nitrogen oxides NOx can be removed during the process of generating nitrogen oxides NOx in the belt roasting process, there is no need to equip large-scale denitrification equipment at the end for denitrification, which can effectively reduce the denitrification cost.

[0004] In the existing belt roasting process, the hot air circulation path is as follows: a cooling fan is used to introduce ambient air to cool the pellets, and the high-temperature hot air generated in the first cooling section is sent to the equalizing section, roasting section and preheating section respectively through the smoke hood and the pipe; the high-temperature flue gas in the equalizing section and the roasting section is extracted by the heat recovery fan and returned to the exhaust drying section for use. After the hot air passes through the material layer, it is dedusted by the dust collector together with the flue gas in the preheating section, and then passes through the fan, the desulfurization and denitrification reaction tower, and is discharged into the atmosphere through the chimney; the hot air in the second cooling section is sent to the blast drying section through the blower fan and the pipeline system, and the exhaust gas after drying the material layer is dedusted by the dust collector and discharged into the atmosphere through the chimney through the fan.

[0005] A Chinese patent (publication number CN111004914A) discloses an enhanced method for denitrification by spraying ammonia during the iron ore pellet production process. This method is to prepare pellets with high burst temperature and good thermal stability by adding anti-bursting additives to the pellet binder bentonite, thereby increasing the thickness of the material layer in the pellet heat treatment process by 1.5 to 1.75 times, reducing the machine speed to 4 / 7 to 2 / 3, and reducing the exhaust wind speed of the drying stage II to 0.8 to 1.0 m / s, and evenly spraying ammonia water into the airflow of the drying stage II smoke hood for denitrification. This invention utilizes the thick material layer operation and the reduction of airflow speed to extend the time for the airflow to pass through the pellet material layer, thereby increasing the separation of the iron-containing minerals and NO in the denitrification catalyst. x, NH3 action time, thereby enhancing the efficiency of spraying ammonia denitrification in the drying section, but this method x It cannot react completely with NH3 between the material layers, so NO in the flue gas x The content still does not meet the requirements of ultra-low emissions.

[0006] The above schemes all utilize the catalytic properties of iron-containing minerals in the pellets. In the air drying section (300-500°C) of the pellet production process, the SCR process is used to pre-remove a portion of NO x , but in the above method, because NO x The reaction time with NH3 is still short, and NO x To achieve ultra-low emission standards, end-of-pipe treatment is still required. x The treatment cost is still high, so it is necessary to further improve the NO x The removal rate of NO x The content is reduced to meet the ultra-low emission standards, which can save the end-of-pipe treatment of NO x process. Summary of the invention

[0007] In view of the existence of NO in the prior art x In order to solve the problem of high processing cost, the present invention provides a denitration method for producing oxidized pellets based on a belt roasting process. The method establishes a dual denitration mechanism by installing an ammonia injection system in the smoke hoods of the exhaust drying section and the preheating section of the belt roaster, and installing an SCR denitration system behind the bellows of the preheating section, the roasting section, and the equalizing section, thereby achieving the purpose of ultra-low emissions. At the same time, composite fuels with different ignition points are added to the pellets, so that a small amount of low-ignition-point fuel in the added fuel can burn rapidly in the preheating section, forming abundant pores on the pellets while providing heat to the pellets, which can effectively absorb NO in the flue gas. x and NH3, improve the denitrification efficiency of the preheating stage, and save the end treatment of NO x process and improve economic benefits.

[0008] According to an embodiment of the present invention, a denitration method for producing oxidized pellets based on a belt roasting process is provided.

[0009] A denitration method for producing oxidized pellets based on a belt roasting process, the method comprising the following steps:

[0010] 1) Batching: mixing the iron ore concentrate and bentonite to obtain a mixed material;

[0011] 2) Pelletizing: Add calcium peroxide, water and composite fuel to the mixed material, and pelletize in a pelletizer to obtain green pellets;

[0012] 3) Pellet roasting: the raw pellets are placed on a belt roaster and processed in sequence through a drying section, a preheating section, a roasting section, a soaking section and a cooling section to obtain roasted pellets;

[0013] The drying section includes a forced air drying section and an exhaust air drying section. The preheating section includes a preheating section 1 and a preheating section 2. An ammonia spraying system is arranged in the smoke hoods of the exhaust air drying section and the preheating section 1. An SCR denitrification system is arranged behind the wind boxes of the preheating section 2, the roasting section and the soaking section.

[0014] Preferably, step 2) specifically includes:

[0015] 201) First stage pelletizing: firstly, calcium peroxide and water are added to the mixed material, and pelletizing is performed in a pelletizing machine to obtain pellet cores;

[0016] 202) Second stage pelletizing: After the first stage pelletizing is completed, water and composite fuel are continuously added to the pelletizing machine for pelletizing, and green pellets are obtained after screening;

[0017] Preferably, the particle size of the pellet core is 3-8 mm, preferably 4-6 mm. The particle size of the green pellet is 10-18 mm, preferably 12-15 mm.

[0018] Preferably, the iron ore concentrate and bentonite are both iron ore concentrate powder and bentonite powder pre-treated by high pressure roller mill. The particle size of the iron ore concentrate powder is -0.044mm and the content is greater than 60% (preferably -0.044mm and the content is greater than 70%). The specific surface area of ​​the iron ore concentrate powder is 1500-2000cm 2 / g (preferably 1600-1800cm 2 / g).

[0019] Preferably, the composite fuel includes a low ignition point fuel and a high ignition point fuel. The low ignition point fuel is one or both of lignite and bituminous coal. The high ignition point fuel is one or both of anthracite and coking coal. Preferably, the amount of the low ignition point fuel accounts for 3%-7% of the total mass of the composite fuel, and the amount of the high ignition point fuel accounts for 93%-97% of the total mass of the composite fuel.

[0020] Preferably, the amount of calcium peroxide is 0.1%-6.0% of the mass of the iron ore concentrate, preferably 0.5%-3.5%. The amount of the composite fuel is 1%-6.0% of the mass of the iron ore concentrate, preferably 3%-4.5%.

[0021] Preferably, the ammonia spraying system is a plurality of ammonia nozzles arranged in the fume hood. Preferably, the airflow direction sprayed from the ammonia nozzles is upward. That is, the airflow direction sprayed from the ammonia nozzles is opposite to the direction of the reheating airflow, and the reheating airflow is the high-temperature flue gas generated by the roasting section and the soaking section.

[0022] Preferably, the SCR denitration system comprises a flue gas mixer and an SCR catalytic reaction chamber. The flue gas mixer is also connected to an ammonia delivery pipeline.

[0023] Preferably, the first preheating stage bottom bellows and the second preheating stage bottom bellows are not connected to each other.

[0024] Preferably, burners are independently provided in the smoke hood of the second preheating stage, the smoke hood of the roasting stage, and the smoke hood of the soaking stage. The burner comprises an upper burner and a lower burner. Among them, the upper burner is a supplementary heat burner, which sprays low calorific value coal gas. The lower burner is a high-temperature burner, which sprays high calorific value coal gas. Preferably, the low calorific value coal gas is blast furnace gas and / or converter gas, and the high calorific value coal gas is coke oven gas and / or natural gas. Preferably, the gas flow of the upper burner and the lower burner in the smoke hoods of the second preheating stage, the roasting stage, and the soaking stage are independently adjusted.

[0025] Preferably, the flue gases exhausted from the bottom bellows of the exhaust drying section and the preheating section are collected, passed through the first electrostatic precipitator and the main exhaust fan in sequence, and then discharged through the chimney.

[0026] Preferably, the flue gas discharged from the second-stage preheating bottom wind box flows in the following specific directions:

[0027] A) If the burner of the second preheating stage has not been opened, the flue gas discharged from its bottom bellows will merge with the flue gas of the exhaust drying stage and the first preheating stage, and then pass through the first electrostatic precipitator and the main exhaust fan in sequence before being discharged through the chimney.

[0028] B) If the burner of the second preheating stage is turned on, the flue gas discharged from the bottom bellows will be transported to the flue gas mixer.

[0029] Preferably, the flue gases discharged from the bottom bellows of the roasting section and the soaking section are collected and transported to the flue gas mixer.

[0030] Preferably, the flue gas transported to the flue gas mixer is mixed evenly and then enters the SCR catalytic reaction chamber for denitration treatment. After the denitration flue gas is discharged from the SCR catalytic reaction chamber, it is collected with the flue gas of the exhaust drying section and the preheating section through the first bypass, and then passes through the first electrostatic precipitator and the main exhaust fan in sequence and then discharged through the chimney. Preferably, the denitration flue gas is also returned to the fume hood of the exhaust drying section and / or the preheating section through the exhaust reheat fan.

[0031] Preferably, the cooling section includes a cooling section 1 and a cooling section 2, and in the cooling section, cold air is drawn from the environment by a cooling fan to blow air to the pellet layer for cooling. The high-temperature flue gas generated in the cooling section 1 is returned to the preheating section 2, the roasting section and the soaking section. The high-temperature flue gas generated in the cooling section 2 is transported to the blast drying section by a blast drying heat recovery fan to dry the green pellets in the blast drying section, and the waste gas generated after drying passes through the second electrostatic precipitator and the blast drying exhaust fan in sequence and is discharged through the chimney.

[0032] Preferably, a first temperature detection device is provided at the flue gas outlet of the second cooling stage. When the temperature of the flue gas discharged from the second cooling stage is lower than the temperature of the flue gas required by the blast drying stage, part of the high-temperature flue gas after denitrification discharged from the SCR catalytic reaction chamber is introduced through the second bypass.

[0033] Preferably, a second temperature detection device is provided on the hood of the blast drying section. When the temperature on the hood of the blast drying section is low, part of the high-temperature flue gas discharged from the second cooling section is introduced into the hood of the blast drying section through the third bypass.

[0034] Preferably, when the temperature of the flue gas discharged from the second cooling stage is too high, cold air is introduced through a cold air inlet duct upstream of the drying and heat recovery blower.

[0035] Preferably, a third temperature detection device is provided at the air inlet of the first electrostatic precipitator. When the temperature of the flue gas extracted by the wind box of the exhaust drying and preheating stage is low, part of the high-temperature flue gas generated by the second cooling stage is collected with the flue gas of the exhaust drying stage and the preheating stage through the fourth bypass, and the collected flue gas passes through the first electrostatic precipitator and the main exhaust fan in sequence and then is discharged into the air through the chimney.

[0036] Preferably, the flue gas in the bottom bellows of the exhaust drying section and the first preheating section is transported to the first electrostatic precipitator through the first pipe. The flue gas in the bottom bellows of the second preheating section is transported to the flue gas mixer and the SCR catalytic reaction chamber through the second pipe. The flue gas in the bottom bellows of the roasting section and the equalizing section is transported to the flue gas mixer and the SCR catalytic reaction chamber through the third pipe. The SCR catalytic reaction chamber then transports the denitrified flue gas to the smoke hoods of the exhaust drying section and the first preheating section through the fourth pipe. A fifth pipe is also led out from the second pipe and is connected to the first pipe. The hot air from the second cooling section is transported to the blast drying section through the sixth pipe.

[0037] The first bypass is led out from the fourth pipe and connected to the first pipe. The second bypass is also led out from the fourth pipe located downstream of the first bypass and connected to the sixth pipe. The third bypass is led out from the sixth pipe located downstream of the drying and regenerating fan and connected to the hood of the drying section. The fourth bypass is also led out from the sixth pipe located between the drying and regenerating fan and the third bypass and connected to the first pipe.

[0038] Preferably, the second pipeline, the fourth pipeline, the fifth pipeline, the first bypass, the second bypass, the third bypass, the fourth bypass, the ammonia delivery pipeline, and the cold air inlet pipeline are independently provided with gas valves.

[0039] Preferably, the water content of the iron ore concentrate is 5%-12%, preferably 7%-10%. The amount of bentonite used is 0.5%-3% of the mass of the iron ore concentrate, preferably 1%-2.5%.

[0040] Before the green pellets are laid, the bottom material and the side material need to be laid on the belt roaster. The thickness of the bottom material and the side material is 50-90 mm, preferably 60-80 mm. The thickness of the green pellets is 250-400 mm, preferably 300-350 mm. Preferably, the bottom material and the side material are both roasted pellets.

[0041] The present invention is aimed at NO existing in the prior art x In order to solve the problem of high treatment cost, the design of pellet structure and improvement of flue gas circulation line are proposed. First, fuel is added inside the pellet to reduce the total demand of the pellet for external heat source, thereby reducing the heat supplied by the combustion gas, and the NO generated x In addition, according to the characteristics of the belt roasting process, the present invention simultaneously sets two denitration reaction points in the exhaust drying section and the preheating section, and behind the wind box in the preheating section, the roasting section, and the soaking section, thereby increasing NO x removal rate.

[0042] In the present invention, composite fuels with different ignition points are added to the pellets, so that a small amount of low-ignition-point fuel in the added fuel can be burned quickly during the preheating stage, and abundant pores are formed on the pellets while providing heat to the pellets. The formed pores can effectively absorb NO in the flue gas. x and NH3, thereby improving the denitrification efficiency of the preheating stage, and also improving the combustion efficiency of the pellets. The composite fuel used in the present invention includes a small amount of low-ignition-point fuel and a high-ignition-point fuel, the low-ignition-point fuel is such as lignite and bituminous coal, and the high-ignition-point fuel is such as anthracite and coke.

[0043] In the present invention, a two-stage pelletizing method is adopted. In the first stage, a pelletizing core is formed. In this stage, calcium peroxide and water are added to the mixed material obtained by fully mixing iron ore concentrate and bentonite for pelletizing, wherein the calcium peroxide is added entirely in the first stage. In the second stage, water and a composite fuel in the pellet are added when the pellets grow. The present method allows the calcium peroxide to be distributed entirely inside the pellets. During the production process of the belt roasting process, when the pellets enter the preheating roasting stage and the pellet temperature rises to above the decomposition temperature of calcium peroxide, the calcium peroxide decomposes to produce calcium oxide and oxygen. The newly generated CaO has high activity and can react with Fe2O3 in the iron ore concentrate to form a calcium ferrite system with good reducibility even at a slightly lower temperature, so that the pellets are consolidated, i.e., the inner layer of the pellets can react in a solid phase even at a relatively low roasting temperature (e.g., below 1250°C). This design creates conditions for using low calorific value fuels in subsequent processes. At the same time, the O2 produced by the decomposition of calcium peroxide inside the pellet can diffuse to the outside of the pellet through the pores after the combustion of a small amount of low-ignition-point fuel inside the pellet, ensuring that the outer layer of the pellet is in an oxidizing atmosphere. When the pellet enters the preheating section and roasting section of the belt roasting process, the fuel in the outer layer of the pellet can be fully burned to supply heat for the solid-phase reaction of the pellet, and also create conditions for the use of low calorific value fuels in subsequent processes.

[0044] In the present invention, the temperature of the hood in the blast drying section is 85-115°C, the temperature of the hood in the exhaust drying section is 335-350°C, and the drying time is 3-4 minutes. The ignition point of lignite is 300-400°C, and the ignition point of bituminous coal is 400-550°C. Lignite starts to burn in small quantities in the exhaust drying section, while the temperature of calcium peroxide is completely decomposed at 400-425°C, and calcium peroxide is distributed in the inner layer of the pellets. When the green pellets are dried, the temperature inside the green pellets reaches the highest at the end of the drying section of the belt roaster. Therefore, when the belt roasting process is adopted, the calcium peroxide inside the pellets is almost not decomposed in the drying section of the belt roaster. Because the temperature of the smoke hood in the exhaust drying section of the belt roasting process is 335-350℃, it is suitable for SCR denitrification. Therefore, an ammonia nozzle is set in the smoke hood of the exhaust drying section to spray ammonia for denitrification. The ammonia nozzle faces upward, and the sprayed ammonia is mixed in the smoke hood. The mixed flue gas passes through the material layer and undergoes SCR denitrification reaction under the catalytic action of the iron oxide of the pellet ore. Because the pellets used in the present invention contain internal fuel (lignite, with good adsorption performance), the internal fuel on the surface of the pellets can remove NO in the flue gas. x and NH3 are adsorbed on the surface of the pellets, and SCR denitrification reaction occurs under the catalysis of the iron oxide in the pellets.

[0045] In the present invention, the preheating section is divided into two sections, namely, preheating section one and preheating section two. The temperature of the smoke hood in preheating section one is 450-550°C, and the temperature of the smoke hood in preheating section two is 750-950°C. The bottom bellows of preheating section one and preheating section two are separated. An ammonia nozzle is also provided in the smoke hood in preheating section one, and the ammonia nozzle faces upward (ammonia is sprayed against the direction of the heat recovery air flow). The sprayed ammonia is mixed in the smoke hood, and the mixed flue gas passes through the material layer to cause SCR denitrification reaction under the catalytic action of iron oxide in the pellet ore. In the preheating section one, the low calorific value fuel in the composite fuel in the pellet begins to burn fully, and the calcium peroxide inside the pellet decomposes to release O2. The above reaction occurring in the preheating section can form abundant voids on the surface of the pellet, and the pellet adsorbs NO x The ability of NO x The SCR reaction with NH3 under the catalytic effect of iron oxide in the pellets has a good denitrification effect, and the pellets are fully burned at the same time. Since the temperature of the SCR denitrification flue gas in the exhaust drying section and the preheating section is appropriate, the SCR reaction does not require additional adjustment of the flue gas temperature, and the SCR denitrification is carried out by the catalytic effect of iron oxide in the pellets, and the denitrification effect is good. The flue gas in the exhaust drying section and the preheating section is collected and passed through the first electrostatic precipitator and the main exhaust fan, and finally discharged into the air through the chimney.

[0046] In the present invention, the hood temperature of the second stage of preheating is 750-950℃. The high calorific value fuel in the composite fuel added to the pellets in the second stage of preheating begins to burn fully. A burner is provided in the hood of the second stage of preheating, and the burner includes an upper layer of supplementary heat burner and a lower layer of high temperature burner, wherein the upper layer of supplementary heat burner sprays low calorific value gas, such as blast furnace gas and converter gas), and the lower layer of high temperature burner sprays high calorific value gas (i.e., high calorific value gas commonly used in existing belt roasting processes, such as coke oven gas and natural gas). The upper and lower burners are both provided with flow valves, and the air intake flow rate can be flexibly adjusted. The air intake flow rate of the upper and lower burners is determined by the amount of composite fuel added to the pellets. If the heat provided by the composite fuel added to the pellets and the upper layer of supplementary heat burner meets the heat required by the pellets in the second stage of preheating, the lower layer of high temperature burner is closed, otherwise the lower layer of high temperature burner is opened. The flue gas of the second stage of preheating has two paths after passing through the material layer. Which path the flue gas takes after passing through the material layer depends on the opening of the burner of the second stage of preheating. If the burner of the second stage of preheating is not turned on, there is almost no NO in the second stage of preheating. x If the preheating stage 2 flue gas is generated, the preheating stage 2 flue gas passes through the material layer and then merges with the exhaust drying and preheating stage flue gas, then passes through the electrostatic precipitator and the main exhaust fan, and finally is discharged into the air through the main chimney. If the preheating stage 2 burner is turned on, the preheating stage 2 flue gas passes through the material layer and is transported to the flue gas mixer.

[0047] In the present invention, when the pellets enter the roasting section, the fuel in the pellets has been completely burned, and the calcium peroxide inside the pellets has been completely converted into calcium oxide. Burners are also provided in the smoke hood of the roasting section. There are two sets of burners, including an upper supplementary heat burner and a lower high-temperature burner (the burner arrangement is the same as the second preheating stage). The upper supplementary heat burner sprays low calorific value gas (such as blast furnace gas, converter gas). The lower high-temperature burner sprays high calorific value gas (i.e., high calorific value gas commonly used in existing belt roasting processes, such as coke oven gas and natural gas). Since the flue gas temperature in the roasting section and the equalizing section is relatively high (can reach 1180-1240°C), it is easy to cause NO x Therefore, the flue gas from the roasting section and the soaking section is transported to the flue gas mixer after passing through the material layer. Among them, the temperature of the flue gas in the roasting section and the soaking section is 320-420℃. The SCR reaction does not require additional adjustment of the flue gas temperature, and the SCR denitrification is carried out by the catalytic effect of iron oxides in the pellets, with a good denitrification effect.

[0048] In the present invention, the flue gas (320-420°C) in the bellows of the roasting section and the equalizing section, the flue gas (210-250°C) in the bellows of the second preheating section, and ammonia (the ammonia flow rate can be controlled) are evenly mixed in the flue gas mixer (if the flue gas of the second preheating section does not enter the flue gas mixer, the temperature of the flue gas in the bellows of the roasting section and the equalizing section in the flue gas mixer after mixing with the ammonia is 350-380°C. If the flue gas of the second preheating section enters the flue gas mixer, the temperature of the flue gas in the bellows of the second preheating section in the flue gas mixer after mixing with the flue gas and ammonia in the bellows of the roasting section and the equalizing section is 300-330°C) and enter the SCR catalytic reaction chamber for denitration treatment. The denitrified flue gas passes through the exhaust heat recovery fan (the flue gas flow rate can be adjusted) and returns to the smoke hood of the exhaust drying section and the first preheating section. In addition, the flue gas after denitration in the SCR catalytic reaction chamber can also be directly collected with the flue gas from the exhaust drying section and the preheating section, and then pass through the first electrostatic precipitator and the main exhaust fan, and finally discharged into the air through the chimney. Among them, when the flue gas in the second-stage preheating bellows enters the SCR denitration system, the flue gas flow rate of the exhaust heat recovery fan is large. When the flue gas flow rate exceeds the total amount of appropriate flue gas required for the exhaust drying and preheating section, part of the flue gas can be diverted, and the flue gas from the exhaust drying section and the preheating section can be directly collected. Balanced airflow distribution is conducive to smooth production. In addition, the high-temperature flue gas after the SCR denitration reaction is collected with the flue gas from the exhaust drying section and the preheating section and then enters the first electrostatic precipitator, which can increase the temperature of the flue gas entering the first electrostatic precipitator and prevent condensation after entering the main electrostatic precipitator due to the low flue gas temperature (95-120℃) affecting the dust removal effect.

[0049] In the present invention, after the pellets enter the first cooling stage, the pellet material layer is cooled by the cooling fan, and the generated high-temperature flue gas (750-1000°C) is returned to the second preheating stage, the roasting stage and the equalizing stage through the smoke hood. The high-temperature flue gas (250-270°C) generated in the second cooling stage is blown into the bellows of the blast drying stage by the blast drying heat recovery fan to dry the raw balls in the blast drying stage. The dried waste gas passes through the pellet material layer, passes through the second electrostatic precipitator and the blast drying exhaust fan, and is finally discharged into the air through the chimney. A first temperature detection device is provided at the flue gas outlet of the second cooling stage. When the temperature of the flue gas discharged from the second cooling stage is lower than the temperature of the flue gas required by the blast drying stage, the high-temperature flue gas after denitration discharged from the SCR catalytic reaction chamber is introduced through the bypass pipeline, and the amount of the introduced flue gas is controlled by the air valve. A bypass pipe is also provided between the gas pipeline where the drying heat recovery fan is located and the pipeline for conveying the exhaust drying and preheating stage flue gas. When the temperature of the flue gas extracted from the exhaust drying and preheating stage bellows is low, the bypass pipe can be used to supplement the heat with the high-temperature hot air blown out from the cooling stage 2, effectively preventing the flue gas from condensing after entering the second electrostatic precipitator due to the low temperature. A third temperature detection device is provided on the smoke hood of the drying stage. When the temperature on the smoke hood of the drying stage is low and causes condensation, the high-temperature flue gas discharged from the cooling stage 2 is directly introduced into the smoke hood of the drying stage through the drying heat recovery fan, so as to avoid the temperature of the high-temperature flue gas from decreasing after passing through the material layer. When the temperature of the gas discharged from the cooling stage 2 is too high, it is easy to cause the pellets in the drying stage to burst due to high moisture content and too fast drying of the pellets. Cold air is introduced upstream of the drying heat recovery fan to reduce the flue gas temperature. The amount of cold air introduced is controlled by the air valve, so as to avoid the hot air temperature entering the drying stage being too high and causing the pellets to dry too fast.

[0050] In the present invention, an ammonia injection system is arranged in the smoke hood of the exhaust drying section and the preheating section; an SCR denitrification system and two-stage pelletizing and internal composite fuel are arranged behind the wind box of the preheating section, the roasting section and the soaking section, so that NO generated during the roasting process can be effectively controlled. x , reducing the total amount of NOx produced at the source and achieving NO x Ultra-low emissions. In the belt roasting process, NO x It is mainly produced at the gas burner. The existing belt roasting process generally uses high calorific value coke oven gas or natural gas. When the high calorific value gas burns at the burner, the temperature at the burner can reach about 1500℃. At high temperature, nitrogen and oxygen in the air react to form NO x The pellets of the present invention are equipped with fuel inside, so the heat required to be provided by gas combustion is reduced, and the amount of gas burned at the burner is reduced to generate NO xAt the same time, the burner system of the preheating and roasting section of the present invention is different from the existing belt roasting process. An upper layer of supplementary heat burner and a lower layer of high temperature burner are designed in the smoke hood of the preheating section and roasting section. The upper layer of supplementary heat burner burns low calorific value gas (such as blast furnace gas, converter gas) to provide part of the heat for the pellets. The low calorific value gas is burned at a temperature of only about 1300°C at the burner, and the NO generated is x Because the upper heat supplement burner burns low calorific value gas to provide heat for the pellets, the lower high-temperature burner burns less high calorific value gas. Only a small amount of high calorific value gas needs to be burned to meet the roasting requirements, which can reduce NO from the source. x In addition, according to the characteristics of the belt roasting process, the present invention cleverly designs two SCR denitrification reaction points in the production process, NO x The removal rate is high. NO x It is mainly generated at the burner in the smoke hood of the second preheating stage and the roasting stage. Because the flue gas temperature coming out of the bellows of the second preheating stage and the roasting stage is just between 300-400℃, it is suitable to use SCR denitrification, which has high denitrification efficiency and low cost. First, the flue gas generated by the second preheating stage and the roasting stage is collected and mixed in the flue gas mixer before entering the SCR reaction chamber for denitrification. After the high-temperature flue gas after the denitrification reaction is returned to the exhaust drying section and the first preheating section through the exhaust heat recovery fan, ammonia is sprayed in the smoke hood of the exhaust drying section and the first preheating section, and the catalytic effect of the iron oxide in the pellets is used to promote the removal of residual NO in the flue gas. x After the secondary denitrification reaction, NO in the flue gas x It can be almost completely removed and can meet ultra-low emission standards.

[0051] In the present invention, the reheated air is the hot air generated by the high-temperature flue gas generated in the cooling stage returning to the second preheating stage, the roasting stage and the soaking stage through the fume hood.

[0052] In the present invention, the distance between the lower burner and the material surface is 1650mm-1950mm, and the distance between the upper burner and the material surface is 2150mm-2300mm. The low calorific value gas sprayed by the upper burner mainly has a heat preservation effect. After the upper low calorific value gas is burned to heat the upper flue gas, the lower burner can reduce the amount of high calorific value gas used, and the nitrogen oxides produced are less (energy conservation, the required total calorific value is constant).

[0053] Compared with the prior art, the present invention has the following beneficial technical effects:

[0054] 1. The present invention mixes composite fuels with different ignition points inside the pellets, so that a small amount of low-ignition-point fuel in the mixed fuel can be burned quickly during the preheating stage, and abundant pores are formed on the pellets while providing heat to the pellets. The formed pores and the fuel with good adsorption performance on the outer layer of the pellets can effectively absorb NO in the flue gas.x and NH3, thereby improving the denitrification efficiency of the preheating stage, and also improving the combustion efficiency of the pellets;

[0055] 2. The present invention adopts a two-stage pelletizing method to distribute calcium peroxide completely inside the pellets. The newly generated CaO has high activity and can react with Fe2O3 in the iron concentrate to form a calcium ferrite system with good reducibility even at a slightly lower temperature. In addition, the generated O2 ensures that the outer layer of the pellets is in an oxidizing atmosphere, and the fuel added to the outer layer of the pellets can be fully burned, creating conditions for using low calorific value fuels in subsequent processes.

[0056] 3. The belt roasting process of the present invention can effectively control the NO generated during the roasting process. x Achieve NO x Ultra-low emissions. Reduce NO from the source x The total amount of production, fuel is added to the pellets to reduce the amount of fuel used, and secondary denitrification is set up to meet the ultra-low emission standards;

[0057] 4. The present invention can recycle the hot air generated in the production process through reasonable pipeline design, effectively reducing the energy consumption of the belt roasting process. In addition, the present invention can timely and conveniently adjust the flue gas temperature in the flue through reasonable design of bypass on the hot air circulation pipeline, effectively preventing accidents such as flue gas condensation. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a structural schematic diagram of a system corresponding to a denitration method for producing oxidized pellets based on a belt roasting process of the present invention.

[0059] Figure 2 The present invention is a schematic diagram of a pelletizing process of a denitrification method for producing oxidized pellets based on a belt roasting process.

[0060] Reference numerals:

[0061] A: belt roaster; A1: blast drying section; A2: exhaust drying section; A3: preheating section 1; A4: preheating section 2; A5: roasting section; A6: soaking section; A7: cooling section 1; A8: cooling section 2; 1: ammonia nozzle; 201: upper burner; 202: lower burner; 3: first electrostatic precipitator; 4: main exhaust fan; 5 chimney; 6: flue gas mixer; 7: SCR catalytic reaction chamber; 8: exhaust heat recovery fan; 9: cooling fan; 10: blast heat recovery fan; 11: second electrostatic precipitator; 12: blast exhaust fan; 13: first temperature detection device; 14: second temperature detection device; 15: third temperature detection device Device; 16: gas valve; 17: combustion-supporting fan; 18: low calorific value gas transportation pipeline; 19: high calorific value gas transportation pipeline; A: belt roasting machine; A1: forced air drying section; A2: exhaust air drying section; A3: preheating section one; A4: preheating section two; A5: roasting section; A6: equalizing section; A7: cooling section one; A8: cooling section two; L1: first pipeline; L2: second pipeline; L3: third pipeline; L4: fourth pipeline; L5: fifth pipeline; L6: sixth pipeline; L7: cold air inlet pipeline; L8: ammonia transportation pipeline; P1: first bypass; P2: second bypass; P3: third bypass; P4: fourth bypass. DETAILED DESCRIPTION

[0062] According to an embodiment of the present invention, a denitration method for producing oxidized pellets based on a belt roasting process is provided.

[0063] A denitration method for producing oxidized pellets based on a belt roasting process, characterized in that the method comprises the following steps:

[0064] 1) Batching: mixing the iron ore concentrate and bentonite to obtain a mixed material;

[0065] 2) Pelletizing: Add calcium peroxide, water and composite fuel to the mixed material, and pelletize in a pelletizer to obtain green pellets;

[0066] 3) Pellet roasting: the raw pellets are placed on a belt roaster and processed in sequence through a drying section, a preheating section, a roasting section, a soaking section and a cooling section to obtain roasted pellets;

[0067] The drying section includes a forced air drying section and an exhaust air drying section. The preheating section includes a preheating section 1 and a preheating section 2. An ammonia spraying system is arranged in the smoke hoods of the exhaust air drying section and the preheating section 1. An SCR denitrification system is arranged behind the wind boxes of the preheating section 2, the roasting section and the soaking section.

[0068] Preferably, step 2) specifically includes:

[0069] 201) First stage pelletizing: firstly, calcium peroxide and water are added to the mixed material, and pelletizing is performed in a pelletizing machine to obtain pellet cores;

[0070] 202) Second stage pelletizing: After the first stage pelletizing is completed, water and composite fuel are continuously added to the pelletizing machine for pelletizing, and green pellets are obtained after screening;

[0071] Preferably, the particle size of the pellet core is 3-8 mm, preferably 4-6 mm. The particle size of the green pellet is 10-18 mm, preferably 12-15 mm.

[0072] Preferably, the iron ore concentrate and bentonite are both iron ore concentrate powder and bentonite powder pre-treated by high pressure roller mill. The particle size of the iron ore concentrate powder is -0.044mm and the content is greater than 60% (preferably -0.044mm and the content is greater than 70%). The specific surface area of ​​the iron ore concentrate powder is 1500-2000cm 2 / g (preferably 1600-1800cm 2 / g).

[0073] Preferably, the composite fuel includes a low ignition point fuel and a high ignition point fuel. The low ignition point fuel is one or both of lignite and bituminous coal. The high ignition point fuel is one or both of anthracite and coking coal. Preferably, the amount of the low ignition point fuel accounts for 3%-7% of the total mass of the composite fuel, and the amount of the high ignition point fuel accounts for 93%-97% of the total mass of the composite fuel.

[0074] Preferably, the amount of calcium peroxide is 0.1%-6.0% of the mass of the iron ore concentrate, preferably 0.5%-3.5%. The amount of the composite fuel is 1%-6.0% of the mass of the iron ore concentrate, preferably 3%-4.5%.

[0075] Preferably, the ammonia spraying system is a plurality of ammonia nozzles 1 arranged in the fume hood. Preferably, the airflow direction sprayed from the ammonia nozzles 1 is upward.

[0076] Preferably, the SCR denitration system comprises a flue gas mixer 6 and an SCR catalytic reaction chamber 7. The flue gas mixer 6 is also connected to an ammonia gas delivery pipeline L8.

[0077] Preferably, the first preheating stage bottom bellows and the second preheating stage bottom bellows are not connected to each other.

[0078] Preferably, burners are independently provided in the smoke hood of the second preheating stage, the smoke hood of the roasting stage, and the smoke hood of the soaking stage. The burner includes an upper burner 201 and a lower burner 202. Among them, the upper burner 201 is a supplementary heat burner, which sprays low calorific value coal gas. The lower burner 202 is a high-temperature burner, which sprays high calorific value coal gas. Preferably, the low calorific value coal gas is blast furnace gas and / or converter gas, and the high calorific value coal gas is coke oven gas and / or natural gas. Preferably, the gas flow of the upper burner 201 and the lower burner 202 in the smoke hoods of the second preheating stage, the roasting stage, and the soaking stage are independently adjusted.

[0079] Preferably, the flue gases exhausted from the bottom bellows of the exhaust drying section and the preheating section are collected, passed through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence, and then discharged through the chimney 5.

[0080] Preferably, the flue gas discharged from the second-stage preheating bottom wind box flows in the following specific directions:

[0081] A) If the burner of the second preheating stage has not been turned on, the flue gas discharged from the bottom bellows will merge with the flue gas of the exhaust drying stage and the first preheating stage, and then pass through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence before being discharged through the chimney 5;

[0082] B) If the burner of the second preheating stage is turned on, the flue gas discharged from the bottom bellows is transported to the flue gas mixer 6.

[0083] Preferably, the flue gases discharged from the bottom bellows of the roasting section and the soaking section are collected and transported to the flue gas mixer 6.

[0084] Preferably, the flue gas transported to the flue gas mixer 6 is mixed evenly and then enters the SCR catalytic reaction chamber 7 for denitration treatment. After the denitration flue gas is discharged from the SCR catalytic reaction chamber 7, it is collected with the flue gas of the exhaust drying section and the preheating section through the first bypass P1, and then passes through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence and then discharged through the chimney 5. Preferably, the denitration flue gas is also returned to the fume hood of the exhaust drying section and / or the preheating section through the exhaust heat recovery fan 8.

[0085] Preferably, the cooling section includes a cooling section 1 and a cooling section 2, and in the cooling section, cold air is drawn from the environment by a cooling fan 9 to blow air to the pellet layer for cooling. The high-temperature flue gas generated in the cooling section 1 is returned to the preheating section 2, the roasting section and the soaking section. The high-temperature flue gas generated in the cooling section 2 is transported to the blast drying section by a blast drying heat recovery fan 10, and the green pellets in the blast drying section are dried. The waste gas generated after drying passes through the second electrostatic precipitator 11 and the blast drying exhaust fan 12 in sequence and is discharged through the chimney 5.

[0086] Preferably, a first temperature detection device 13 is provided at the flue gas outlet of the second cooling stage. When the temperature of the flue gas discharged from the second cooling stage is lower than the temperature of the flue gas required by the blast drying stage, part of the high-temperature flue gas after denitrification discharged from the SCR catalytic reaction chamber 7 is introduced through the second bypass P2.

[0087] Preferably, a second temperature detection device 14 is provided on the hood of the blast drying section. When the temperature on the hood of the blast drying section is low, part of the high-temperature flue gas discharged from the second cooling section is introduced into the hood of the blast drying section through the third bypass P3.

[0088] Preferably, when the temperature of the flue gas discharged from the second cooling stage is too high, cold air is introduced upstream of the drying and heat recovery fan 10 through the cold air inlet duct L7.

[0089] Preferably, a third temperature detection device 15 is provided at the air inlet of the first electrostatic precipitator 3. When the temperature of the flue gas extracted by the exhaust drying and preheating first stage bellows is low, part of the high-temperature flue gas generated by the second cooling stage is collected with the flue gas from the exhaust drying stage and the preheating first stage through the fourth bypass P4, and the collected flue gas then passes through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence and is discharged into the air through the chimney 5.

[0090] Preferably, the flue gas in the bottom wind box of the exhaust drying section and the first preheating section is transported to the first electrostatic precipitator 3 through the first pipe L1. The flue gas in the bottom wind box of the second preheating section is transported to the flue gas mixer 6 and the SCR catalytic reaction chamber 7 through the second pipe L2. The flue gas in the bottom wind box of the roasting section and the equalizing section is transported to the flue gas mixer 6 and the SCR catalytic reaction chamber 7 through the third pipe L3. The SCR catalytic reaction chamber 7 then transports the denitrified flue gas to the smoke hood of the exhaust drying section and the first preheating section through the fourth pipe L4; the second pipe L2 also leads to a fifth pipe L5 connected to the first pipe L1. The hot air from the second cooling section is transported to the blast drying section through the sixth pipe L6.

[0091] The first bypass P1 is led out from the fourth pipe L4 and connected to the first pipe L1. The second bypass P2 is also led out from the fourth pipe L4 located downstream of the first bypass P1 and connected to the sixth pipe L6. The third bypass P3 is led out from the sixth pipe L6 located downstream of the drying and reheating fan 10 and connected to the hood of the drying section. The fourth bypass P4 is also led out from the sixth pipe L6 located between the drying and reheating fan 10 and the third bypass P3 and connected to the first pipe L1.

[0092] Preferably, the second pipeline L2, the fourth pipeline L4, the fifth pipeline L5, the first bypass P1, the second bypass P2, the third bypass P3, the fourth bypass P4, the ammonia delivery pipeline L8, and the cold air inlet pipeline L7 are all independently provided with gas valves 16.

[0093] Preferably, the water content of the iron ore concentrate is 5%-12%, preferably 7%-10%. The amount of bentonite used is 0.5%-3% of the mass of the iron ore concentrate, preferably 1%-2.5%.

[0094] Before the green pellets are laid, the bottom material and the side material need to be laid on the belt roaster. The thickness of the bottom material and the side material is 50-90 mm, preferably 60-80 mm. The thickness of the green pellets is 250-400 mm, preferably 300-350 mm. Preferably, the bottom material and the side material are both roasted pellets.

[0095] Example 1

[0096] A denitration method for producing oxidized pellets based on a belt roasting process, characterized in that the method comprises the following steps:

[0097] 1) Batching: mixing the iron ore concentrate and bentonite to obtain a mixed material;

[0098] 2) Pelletizing: Add calcium peroxide, water and composite fuel to the mixed material, and pelletize in a pelletizer to obtain green pellets;

[0099] 3) Pellet roasting: the raw pellets are placed on a belt roaster and processed in sequence through a drying section, a preheating section, a roasting section, a soaking section and a cooling section to obtain roasted pellets;

[0100] The drying section includes a forced air drying section and an exhaust air drying section. The preheating section includes a preheating section 1 and a preheating section 2. An ammonia spraying system is arranged in the smoke hoods of the exhaust air drying section and the preheating section 1. An SCR denitrification system is arranged behind the wind boxes of the preheating section 2, the roasting section and the soaking section.

[0101] Example 2

[0102] Repeat Example 1, except that step 2) specifically includes:

[0103] 201) First stage pelletizing: firstly, calcium peroxide and water are added to the mixed material, and pelletizing is performed in a pelletizing machine to obtain pellet cores;

[0104] 202) Second stage pelletizing: After the first stage pelletizing is completed, water and composite fuel are added to the pelletizing machine to continue pelletizing, and green pellets are obtained after screening;

[0105] The particle size of the pellet core is 5 mm. The particle size of the green pellet is 13 mm.

[0106] Example 3

[0107] Example 2 was repeated, except that the iron ore concentrate and bentonite were both iron ore concentrate powder and bentonite powder pre-treated by high pressure roller mill. The particle size of the iron ore concentrate powder was -0.044 mm and the content was greater than 70%. The specific surface area of ​​the iron ore concentrate powder was 1600-1800 cm 2 / g.

[0108] Example 4

[0109] Example 3 is repeated, except that the composite fuel includes a low ignition point fuel and a high ignition point fuel. The low ignition point fuel is lignite or bituminous coal. The high ignition point fuel is anthracite or coking coal. The amount of the low ignition point fuel accounts for 5% of the total mass of the composite fuel, and the amount of the high ignition point fuel accounts for 95% of the total mass of the composite fuel.

[0110] Example 5

[0111] Example 4 was repeated, except that the amount of calcium peroxide used was 2% of the mass of the iron ore concentrate and the amount of the composite fuel used was 4.0% of the mass of the iron ore concentrate.

[0112] Example 6

[0113] Example 5 is repeated, except that the ammonia spraying system is a plurality of ammonia nozzles 1 arranged in the fume hood. The airflow direction of the ammonia nozzles 1 is upward.

[0114] The SCR denitration system comprises a flue gas mixer 6 and an SCR catalytic reaction chamber 7. The flue gas mixer 6 is also connected to an ammonia delivery pipeline L8.

[0115] The first preheating stage bottom wind box and the second preheating stage bottom wind box are not communicated with each other.

[0116] Example 7

[0117] Example 6 is repeated, except that burners are independently provided in the smoke hood of the second preheating stage, the smoke hood of the roasting stage, and the smoke hood of the equalizing stage. The burner includes an upper burner 201 and a lower burner 202. Among them, the upper burner 201 is a supplementary heat burner, which sprays low calorific value coal gas. The lower burner 202 is a high-temperature burner, which sprays high calorific value coal gas. The low calorific value coal gas is blast furnace gas and converter gas, and the high calorific value coal gas is coke oven gas and natural gas. The gas flow of the upper burner 201 and the lower burner 202 in the smoke hoods of the second preheating stage, the roasting stage, and the equalizing stage are independently adjusted.

[0118] Example 8

[0119] Example 7 is repeated, except that the flue gases exhausted from the bottom bellows of the exhaust drying section and the preheating section are collected, passed through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence, and then discharged through the chimney 5.

[0120] The specific flow direction of the flue gas discharged from the bottom wind box of the second preheating stage is:

[0121] A) If the burner of the second preheating stage has not been turned on, the flue gas discharged from the bottom bellows will merge with the flue gas of the exhaust drying stage and the first preheating stage, and then pass through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence before being discharged through the chimney 5;

[0122] B) If the burner of the second preheating stage is turned on, the flue gas discharged from the bottom bellows is transported to the flue gas mixer 6.

[0123] Example 9

[0124] Example 8 is repeated, except that the flue gases exhausted from the bottom bellows of the roasting section and the soaking section are collected and transported to the flue gas mixer 6.

[0125] The flue gas transported to the flue gas mixer 6 is mixed evenly and then enters the SCR catalytic reaction chamber 7 for denitration. After being discharged from the SCR catalytic reaction chamber 7, the denitrated flue gas is collected with the flue gas of the exhaust drying section and the preheating section through the first bypass P1, and then passes through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence and then discharged through the chimney 5. The denitrated flue gas is also returned to the smoke hood of the exhaust drying section and / or the preheating section through the exhaust heat recovery fan 8.

[0126] Example 10

[0127] Example 9 is repeated, except that the cooling section includes a cooling section and a cooling section. In the cooling section, cold air is drawn from the environment by a cooling fan 9 to blow air to the pellet layer for cooling. The high-temperature flue gas generated in the cooling section is returned to the preheating section, the roasting section and the equalizing section. The high-temperature flue gas generated in the cooling section is transported to the blast drying section by a blast drying heat recovery fan 10 to dry the green pellets in the blast drying section. The waste gas generated after drying passes through the second electrostatic precipitator 11 and the blast drying exhaust fan 12 in sequence and is discharged through the chimney 5.

[0128] Embodiment 11

[0129] Example 10 is repeated, except that a first temperature detection device 13 is provided at the flue gas outlet of the second cooling stage. When the temperature of the flue gas discharged from the second cooling stage is lower than the temperature of the flue gas required by the blast drying stage, part of the high-temperature flue gas after denitrification discharged from the SCR catalytic reaction chamber 7 is introduced through the second bypass P2.

[0130] A second temperature detection device 14 is provided on the hood of the blast drying section. When the temperature on the hood of the blast drying section is low, part of the high-temperature flue gas discharged from the second cooling section is introduced into the hood of the blast drying section through the third bypass P3.

[0131] When the exhaust gas temperature of the second cooling stage is too high, cold air is introduced upstream of the drying heat recovery fan 10 through the cold air inlet duct L7.

[0132] Example 12

[0133] Example 11 is repeated, except that a third temperature detection device 15 is provided at the air inlet of the first electrostatic precipitator 3. When the temperature of the flue gas extracted by the exhaust drying and preheating first stage bellows is low, part of the high-temperature flue gas generated by the second cooling stage is collected with the flue gas of the exhaust drying stage and the preheating first stage through the fourth bypass P4, and the collected flue gas then passes through the first electrostatic precipitator 3 and the main exhaust fan 4 in sequence and is discharged into the air through the chimney 5.

[0134] Example 13

[0135] Example 12 is repeated, except that the flue gas in the bottom bellows of the exhaust drying section and the first preheating section is transported to the first electrostatic precipitator 3 through the first pipe L1. The flue gas in the bottom bellows of the second preheating section is transported to the flue gas mixer 6 and the SCR catalytic reaction chamber 7 through the second pipe L2. The flue gas in the bottom bellows of the roasting section and the equalizing section is transported to the flue gas mixer 6 and the SCR catalytic reaction chamber 7 through the third pipe L3. The SCR catalytic reaction chamber 7 then transports the denitrified flue gas to the smoke hoods of the exhaust drying section and the first preheating section through the fourth pipe L4. A fifth pipe L5 is also led out from the second pipe L2 and is connected to the first pipe L1. The hot air from the second cooling section is transported to the blast drying section through the sixth pipe L6.

[0136] The first bypass P1 is led out from the fourth pipe L4 and connected to the first pipe L1. The second bypass P2 is also led out from the fourth pipe L4 located downstream of the first bypass P1 and connected to the sixth pipe L6. The third bypass P3 is led out from the sixth pipe L6 located downstream of the drying and reheating fan 10 and connected to the hood of the drying section. The fourth bypass P4 is also led out from the sixth pipe L6 located between the drying and reheating fan 10 and the third bypass P3 and connected to the first pipe L1.

[0137] The second pipeline L2, the fourth pipeline L4, the fifth pipeline L5, the first bypass P1, the second bypass P2, the third bypass P3, the fourth bypass P4, the ammonia delivery pipeline L8, and the cold air inlet pipeline L7 are all independently provided with gas valves 16.

[0138] Embodiment 14

[0139] Example 13 was repeated, except that the water content of the iron ore concentrate was 8% and the amount of bentonite used was 2.0% of the mass of the iron ore concentrate.

[0140] Before laying the green pellets, the bottom material and the side material must be laid on the belt roaster. The thickness of the bottom material and the side material is 70mm respectively. The thickness of the green pellets is 330mm. The bottom material and the side material are all roasted pellets.

Claims

1. A denitration method for producing oxidized pellets based on a belt roasting process, characterized in that: The method comprises the following steps: 1) Batching: mixing the iron ore concentrate and bentonite to obtain a mixed material; 2) Pelletizing: Add calcium peroxide, water and composite fuel to the mixed material, and pelletize in a pelletizer to obtain green pellets; 3) Pellet roasting: The raw pellets are placed on a belt roasting machine (A) and processed in sequence through a drying section, a preheating section, a roasting section, a soaking section and a cooling section to obtain roasted pellets; The drying section includes a forced air drying section (A1) and an exhaust air drying section (A2); the preheating section includes a preheating section (A3) and a preheating section (A4); an ammonia spraying system is arranged in the smoke hoods of the exhaust air drying section and the preheating section; an SCR denitrification system is arranged behind the wind boxes of the preheating section (A5) and the equalizing section (A6); The composite fuel includes a low ignition point fuel and a high ignition point fuel; wherein the low ignition point fuel is one or both of lignite and bituminous coal; the high ignition point fuel is one or both of anthracite and coking coal; the amount of the low ignition point fuel accounts for 3%-7% of the total mass of the composite fuel, and the amount of the high ignition point fuel accounts for 93%-97% of the total mass of the composite fuel.

2. The method according to claim 1, characterized in that: Step 2) specifically includes: 201) First stage pelletizing: firstly, calcium peroxide and water are added to the mixed material, and pelletized in a pelletizing machine to obtain pellet core; 202) Second stage pelletizing: After the first stage pelletizing is completed, water and compound fuel are added to the pelletizing machine to continue pelletizing, and green pellets are obtained after screening.

3. The method according to claim 2, characterized in that: The particle size of the pellet core is 3-8 mm; the particle size of the green pellet is 10-18 mm.

4. The method according to claim 3, characterized in that: The particle size of the pellet core is 4-6 mm; the particle size of the green pellet is 12-15 mm.

5. The method according to any one of claims 1 to 4, characterized in that: The iron ore concentrate and bentonite are both iron ore concentrate powder and bentonite powder pre-treated by high pressure roller mill; wherein the particle size of the iron ore concentrate powder is -0.044mm and the content is greater than 60%; the specific surface area of ​​the iron ore concentrate powder is 1500-2000cm 2 / g.

6. The method according to claim 5, characterized in that: The particle size of the iron ore concentrate is -0.044mm and the content is greater than 70%; the specific surface area of ​​the iron ore concentrate is 1600-1800cm 2 / g.

7. The method according to any one of claims 1 to 4 and 6, characterized in that: The amount of calcium peroxide used is 0.1%-6.0% of the mass of the iron ore concentrate; the amount of the composite fuel used is 1%-6.0% of the mass of the iron ore concentrate.

8. The method according to claim 7, characterized in that: The amount of calcium peroxide used is 0.5%-3.5% of the mass of the iron ore concentrate; the amount of the composite fuel used is 3%-4.5% of the mass of the iron ore concentrate.

9. The method according to any one of claims 1 to 4, 6 and 8, characterized in that: The ammonia injection system comprises a plurality of ammonia nozzles (1) arranged in the fume hood; and / or The SCR denitration system comprises a flue gas mixer (6) and an SCR catalytic reaction chamber (7); the flue gas mixer (6) is also connected to an ammonia gas delivery pipeline (L8).

10. The method according to claim 9, characterized in that: The direction of the airflow ejected from the ammonia nozzle (1) is upward.

11. The method according to claim 9, characterized in that: The bottom bellows of the first preheating stage (A3) and the bottom bellows of the second preheating stage (A4) are not connected to each other.

12. The method according to claim 9, characterized in that: Burners are independently provided in the smoke hood of the second preheating stage (A4), the smoke hood of the roasting stage (A5), and the smoke hood of the equalizing stage (A6); the burners include an upper burner (201) and a lower burner (202); the upper burner (201) is a supplementary heat burner, which sprays low calorific value coal gas; the lower burner (202) is a high temperature burner, which sprays high calorific value coal gas.

13. The method according to claim 12, characterized in that: The low calorific value coal gas is blast furnace gas and / or converter gas, and the high calorific value coal gas is coke oven gas and / or natural gas.

14. The method according to claim 13, characterized in that: The gas flow rates of the upper burner (201) and the lower burner (202) in the respective smoke hoods of the second preheating section (A4), the roasting section (A5) and the equalizing section (A6) are independently adjusted.

15. The method according to claim 9, characterized in that: The flue gas discharged from the bottom bellows of the exhaust drying section (A2) and the preheating section (A3) is collected, passed through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence, and then discharged through the chimney (5); and / or The specific flow direction of the flue gas discharged from the bottom wind box of the second preheating stage (A4) is as follows: A) If the burner of the second preheating stage (A4) has not been turned on, the flue gas discharged from the bottom bellows merges with the flue gas from the exhaust drying stage (A2) and the first preheating stage (A3), and then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence before being discharged through the chimney (5); B) If the burner of the second preheating stage (A4) is turned on, the flue gas discharged from the bottom bellows is transported to the flue gas mixer (6); and / or The flue gases discharged from the bottom bellows of the roasting section (A5) and the equalizing section (A6) are collected and transported to the flue gas mixer (6); and / or The flue gas transported to the flue gas mixer (6) is mixed evenly and then enters the SCR catalytic reaction chamber (7) for denitration treatment. The denitrated flue gas is discharged from the SCR catalytic reaction chamber (7) and then passes through the first bypass (P1) to be combined with the flue gas from the exhaust drying section (A2) and the preheating section (A3), and then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence before being discharged through the chimney (5).

16. The method according to any one of claims 10 to 14, characterized in that: The flue gas discharged from the bottom bellows of the exhaust drying section (A2) and the preheating section (A3) is collected, passed through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence, and then discharged through the chimney (5); and / or The specific flow direction of the flue gas discharged from the bottom wind box of the second preheating stage (A4) is as follows: A) If the burner of the second preheating stage (A4) has not been turned on, the flue gas discharged from the bottom bellows merges with the flue gas from the exhaust drying stage (A2) and the first preheating stage (A3), and then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence before being discharged through the chimney (5); B) If the burner of the second preheating stage (A4) is turned on, the flue gas discharged from the bottom bellows is transported to the flue gas mixer (6); and / or The flue gases discharged from the bottom bellows of the roasting section (A5) and the equalizing section (A6) are collected and transported to the flue gas mixer (6); and / or The flue gas transported to the flue gas mixer (6) is mixed evenly and then enters the SCR catalytic reaction chamber (7) for denitration treatment. The denitrated flue gas is discharged from the SCR catalytic reaction chamber (7) and then passes through the first bypass (P1) to be combined with the flue gas from the exhaust drying section (A2) and the preheating section (A3), and then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence before being discharged through the chimney (5).

17. The method according to claim 15, characterized in that: The flue gas after denitration is also returned to the fume hood of the exhaust drying section (A2) and / or the preheating section (A3) through the exhaust heat recovery fan (8).

18. The method according to claim 16, characterized in that: The flue gas after denitration is also returned to the fume hood of the exhaust drying section (A2) and / or the preheating section (A3) through the exhaust heat recovery fan (8).

19. The method according to claim 15, characterized in that: The cooling section comprises a cooling section (A7) and a cooling section (A8). In the cooling section, cold air is drawn from the environment by a cooling fan (9) to blow air to the pellet layer for cooling. The high-temperature flue gas generated by the cooling section (A7) is returned to the preheating section (A4), the roasting section (A5) and the equalizing section (A6). The high-temperature flue gas generated by the cooling section (A8) is transported to the blast drying section (A1) by a blast drying heat recovery fan (10) to dry the raw pellets in the blast drying section (A1). The waste gas generated after drying passes through a second electrostatic precipitator (11) and a blast drying exhaust fan (12) in sequence and is discharged through a chimney (5).

20. The method according to claim 16, characterized in that: The cooling section comprises a cooling section (A7) and a cooling section (A8). In the cooling section, cold air is drawn from the environment by a cooling fan (9) to blow air to the pellet layer for cooling. The high-temperature flue gas generated by the cooling section (A7) is returned to the preheating section (A4), the roasting section (A5) and the equalizing section (A6). The high-temperature flue gas generated by the cooling section (A8) is transported to the blast drying section (A1) by a blast drying heat recovery fan (10) to dry the raw pellets in the blast drying section (A1). The waste gas generated after drying passes through a second electrostatic precipitator (11) and a blast drying exhaust fan (12) in sequence and is discharged through a chimney (5).

21. The method according to claim 19 or 20, characterized in that: A first temperature detection device (13) is provided at the flue gas outlet of the second cooling stage (A8), and when the temperature of the flue gas discharged from the second cooling stage (A8) is lower than the temperature of the flue gas required by the blast drying stage (A1), part of the high-temperature flue gas after denitration discharged from the SCR catalytic reaction chamber (7) is introduced through the second bypass (P2); and / or A second temperature detection device (14) is provided on the hood of the blast drying section (A1), and when the temperature on the hood of the blast drying section (A1) is low, part of the high-temperature flue gas discharged from the second cooling section (A8) is introduced into the hood of the blast drying section (A1) through the third bypass (P3); and / or When the temperature of the flue gas discharged from the second cooling stage (A8) is too high, cold air is introduced upstream of the drying heat recovery fan (10) through the cold air inlet duct (L7).

22. The method according to claim 15, characterized in that: A third temperature detection device (15) is provided at the air inlet of the first electrostatic precipitator (3); when the temperature of the flue gas extracted from the wind boxes of the exhaust drying section (A2) and the first preheating section (A3) is low, part of the high-temperature flue gas generated by the second cooling section (A8) is collected with the flue gas from the exhaust drying section (A2) and the first preheating section (A3) through a fourth bypass (P4), and the collected flue gas then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence and is discharged into the air through a chimney (5).

23. The method according to claim 19, characterized in that: A third temperature detection device (15) is provided at the air inlet of the first electrostatic precipitator (3); when the temperature of the flue gas extracted from the wind boxes of the exhaust drying section (A2) and the first preheating section (A3) is low, part of the high-temperature flue gas generated by the second cooling section (A8) is collected with the flue gas from the exhaust drying section (A2) and the first preheating section (A3) through a fourth bypass (P4), and the collected flue gas then passes through the first electrostatic precipitator (3) and the main exhaust fan (4) in sequence and is discharged into the air through a chimney (5).

24. The method according to claim 22 or 23, characterized in that: The flue gas in the bottom wind box of the exhaust drying section (A2) and the first preheating section (A3) is transported to the first electrostatic precipitator (3) through the first pipe (L1); the flue gas in the bottom wind box of the second preheating section (A4) is transported to the flue gas mixer (6) and the SCR catalytic reaction chamber (7) through the second pipe (L2); the flue gas in the bottom wind box of the roasting section (A5) and the equalizing section (A6) is transported to the flue gas mixer (6) and the SCR catalytic reaction chamber (7) through the third pipe (L3); the SCR catalytic reaction chamber (7) then transports the denitrified flue gas to the smoke hoods of the exhaust drying section (A2) and the first preheating section (A3) through the fourth pipe (L4); the second pipe (L2) also leads to a fifth pipe (L5) connected to the first pipe (L1); the hot air of the second cooling section (A8) is transported to the blast drying section through the sixth pipe (L6); The first bypass (P1) is led out from the fourth pipeline (L4) and connected to the first pipeline (L1); the second bypass (P2) is also led out from the fourth pipeline (L4) located downstream of the first bypass (P1) and connected to the sixth pipeline (L6); the third bypass (P3) is led out from the sixth pipeline (L6) located downstream of the drying heat recovery fan (10) and connected to the hood of the drying section (A1); the fourth bypass (P4) is also led out from the sixth pipeline (L6) located between the drying heat recovery fan (10) and the third bypass (P3) and connected to the first pipeline (L1).

25. The method according to claim 24, characterized in that: The second pipeline (L2), the fourth pipeline (L4), the fifth pipeline (L5), the first bypass (P1), the second bypass (P2), the third bypass (P3), the fourth bypass (P4), the ammonia delivery pipeline (L8), and the cold air inlet pipeline (L7) are all independently provided with air valves (16).

26. The method according to any one of claims 1-4, 6, 8, 10-15, 17-20, 22-23, 25, characterized in that: The water content of the iron ore concentrate is 5%-12%; the amount of the bentonite used is 0.5%-3% of the mass of the iron ore concentrate.

27. The method according to claim 26, characterized in that: The water content of the iron ore concentrate is 7%-10%; the amount of the bentonite used is 1%-2.5% of the mass of the iron ore concentrate.

28. The method according to any one of claims 1-4, 6, 8, 10-15, 17-20, 22-23, 25, 27, characterized in that: Before laying the green pellets, the bottom material and the side material must be laid on the belt roaster.

29. The method according to claim 28, characterized in that: The thickness of the bottom material and the side material is 50-90mm respectively; the thickness of the raw pellets is 250-400mm.

30. The method according to claim 29, characterized in that: The thickness of the bottom material and the side material is 60-80mm respectively; the thickness of the raw pellets is 300-350mm.

31. The method according to claim 28, characterized in that: The base material and the side material are both made of roasted pellets.

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