阅读说明：本技术 一种链篦机、链篦机回转窑氧化球团脱硝系统及方法 (Chain grate machine, and denitration system and method for oxidized pellets of rotary kiln of chain grate machine ) 是由 胡兵 于 2019-07-22 设计创作，主要内容包括：一种链篦机、链篦机回转窑氧化球团脱硝系统及方法,该链篦机脱硝系统包括链篦机,按照工艺走向,所述链篦机依次设有鼓风干燥段、抽风干燥段、预热一段和预热二段。抽风干燥段和/或预热一段的底部风箱内设有脱硝装置,所述脱硝装置为氧化剂喷射器。本发明提供的技术方案,通过将抽风干燥段和预热一段中的热风在风箱内与氧化剂接触反应；将热风内的NO氧化为NO<Sub>2</Sub>,有利于碱液对氮氧化物的吸收。从而在脱硝工艺过程中,实现NO<Sub>X</Sub>的减排。无需针对NO额外增加脱硝装置。即响应国家的节能减排号召,提高球团生产的生命力和竞争力,又降低生产成本。(A chain grate machine, a rotary kiln oxidized pellet denitration system of the chain grate machine and a method are provided, the chain grate machine denitration system comprises the chain grate machine, and the chain grate machine is sequentially provided with a blast drying section, an air draft drying section, a preheating section and a preheating section according to the process trend. And a denitration device is arranged in the bottom bellows of the air draft drying section and/or the preheating section, and the denitration device is an oxidant ejector. According to the technical scheme provided by the invention, hot air in the air draft drying section and the preheating section is in contact reaction with an oxidant in an air box; oxidizing NO in hot air to NO 2 Is favorable for absorbing the nitrogen oxide by the alkali liquor. Thereby realizing NO in the denitration process X And (4) emission reduction. And a denitration device does not need to be additionally arranged for NO. Namely responding to the national call of energy conservation and emission reduction and improving the vitality and the competitiveness of pellet productionAnd the production cost is reduced.)

1. a chain grate denitration system is characterized by comprising a chain grate (1), wherein according to the process trend, the chain grate (1) is sequentially provided with a blast drying section (UDD), an air draft drying section (DDD), a preheating section (TPH) and a preheating section (PH); and a denitration device is arranged in the bottom bellows of the air draft drying section (DDD) and/or the preheating section (TPH), and the denitration device is an oxidant ejector (2).

2. The grate denitration system of claim 1, wherein: the chain grate denitration system also comprises an oxidant generating device (3), wherein a first oxidant ejector (201) is arranged in a bottom air box of the air draft drying section (DDD); the oxidant generation device (3) comprises: an ozone generator (301); the outlet of the ozone generator (301) is connected with a first oxidant ejector (201) through a first pipeline (L1); and/or

The system also comprises an oxidant generating device (3), wherein a second oxidant ejector (202) is arranged in the bottom bellows of the preheating section (TPH); the oxidant generation device (3) comprises: an ozone generator (301); the outlet of the ozone generator (301) is connected with a second oxidant injector (202) through a second pipeline (L2); preferably, the second conduit (L2) branches off from the first conduit (L1).

3. The grate denitration system of claim 2, wherein: the oxidant generation device (3) also comprises a catalytic reactor (302); the outlet of the ozone generator (301) is communicated with the inlet of the catalytic reactor (302), and a first pipeline (L1) is connected with the outlet of the catalytic reactor (302) and the first oxidant ejector (201); an ozone catalyst bed layer is arranged in the catalytic reactor (302).

4. The grate denitration system of any one of claims 1 to 3, wherein: the chain grate denitration system also comprises an alkali liquor absorption device (6); an air outlet of the air draft drying section (DDD) and/or the preheating section (TPH) passes through a third pipeline (L3), a dust removal system (4) is arranged on the third pipeline (L3), and the flue gas passes through a main exhaust fan and then is connected with an inlet of an alkali liquor absorption device (6); preferably, the outlet of the lye absorption device (6) is connected to the chimney (5) via a fourth line (L4).

5. The grate denitration system of any one of claims 1 to 4, wherein: a first NO detector (701) is arranged in the ventilation drying section (DDD), a first flow detection device (801) is arranged in the ventilation drying section (DDD), a first flow control valve (901) is arranged on a first pipeline (L1), and the first flow control valve (901) is arranged at the downstream of the position of a second pipeline (L2) separated from the first pipeline (L1); and/or

A second NO detector (702) is arranged in the preheating section (TPH), a second flow detection device (802) is arranged in the preheating section (TPH), and a second flow control valve (902) is arranged on the second pipeline (L2).

6. A grate-rotary kiln oxidized pellet denitration system, comprising the grate denitration system of any one of claims 1 to 5, characterized in that: the denitration system also comprises a rotary kiln (10) and a circular cooler (11); the ring cooling machine (11) comprises a ring cooling first section (C1), a ring cooling second section (C2) and a ring cooling third section (C3); the air outlet of the annular cooling section (C1) is communicated with the air inlet of the rotary kiln (10); the air outlet of the rotary kiln (10) is communicated with the air inlet of the preheating section (PH); the air outlet of the preheating section (PH) is communicated with the air inlet of the air draft drying section (DDD); the air outlet of the annular cooling second section (C2) is communicated with the air inlet of the preheating first section (TPH).

7. A chain grate denitration method comprises the following steps:

1) the green pellets enter a chain grate machine (1) and sequentially pass through a blast drying section (UDD), an air draft drying section (DDD), a preheating section (TPH) and a preheating section (PH);

2) spraying oxidant into the bottom of the draft drying section (DDD) and/or the preheating section (TPH), and reacting NO in hot air in the draft drying section (DDD) and/or the preheating section (TPH) with the oxidant to oxidize NO into NO₂Or HNO₃；

3) The hot air passing through the suction drying stage (DDD) and/or the preheating stage (TPH) is discharged from the respective outlets via a third duct (L3).

8. The method of claim 7, wherein: the method further comprises the following steps: step 4), the ozone generator (301) conveys the oxidant to a first oxidant ejector (201) in a bottom bellows of the induced draft drying section (DDD) through a first pipeline (L1), and the first oxidant ejector (201) ejects the oxidant in the induced draft drying section (DDD); and/or

The ozone generator (301) delivers oxidant via a second conduit (L2) to a second oxidant injector (202) in the bottom windbox of the preheating section (TPH), the second oxidant injector (202) injecting oxidant in the preheating section (TPH).

9. The method of claim 8, wherein: in step 4), the oxidant generated by the ozone generator (301) passes through the catalytic reactor (302) and is conveyed to the first oxidant injector (201) through a first pipeline (L1), and is optionally conveyed to the second oxidant injector (202) through a second pipeline (L2); and/or

The method further comprises the following steps: step 5), discharging hot air in the ventilation drying section (DDD) and/or the preheating section (TPH) from respective air outlets, conveying the hot air to an alkali liquor absorption device (6) through a third pipeline (L3) after dust removal, and absorbing NO in the hot air discharged from the ventilation drying section (DDD) and/or the preheating section (TPH) by the alkali liquor absorption device (6)₂Or HNO₃(ii) a Preferably, the hot air treated by the lye absorption devices (6) is discharged via a fourth line (L4) through a chimney (5).

10. The method according to any one of claims 7-9, wherein: a first NO detector (701) in the ventilation drying section (DDD) detects that the concentration of NO in the ventilation drying section (DDD) is P_D，mg/m³(ii) a The first flow detection device (801) in the ventilation drying section (DDD) detects that the gas flow in the ventilation drying section (DDD) is Q_D，m³H; calculating the flow rate U of oxidant delivered to the first oxidant ejector (201) based on the mechanism by which NO reacts with the oxidant_D，m³/h：

A second NO detector (702) in the preheat section (TPH) detects that the concentration of NO in the preheat section (TPH) is P_T，mg/m³(ii) a A second flow detection means (802) in the preheat section (TPH) detects the preheat section (TP)H) The gas flow rate in the gas chamber is Q_T，m³H; calculating the flow rate U of oxidant delivered to the second oxidant injector (202) based on the mechanism by which NO reacts with the oxidant_T，m³/h：

11. The method according to any one of claims 7-10, wherein: the method further comprises the following steps:

step 6), conveying air discharged from the ring cooling first section (C1) to a rotary kiln (10), conveying hot air discharged from the rotary kiln (10) to a preheating second section (PH), and conveying hot air subjected to heat exchange in the preheating second section (PH) to an air draft drying section (DDD); and the air subjected to heat exchange by the ring cooling second stage (C2) is conveyed to the preheating first stage (TPH).

12. The method according to any one of claims 7-11, wherein: the oxidant is strong oxidant, preferably ozone and Cl₂、ClO₂、H₂O₂、KMnO₄One or more of; and/or

An ozone catalyst bed layer is arranged in the catalytic reactor (302), and the ozone catalyst is transition metal and/or transition metal oxide with large specific surface area, looseness, porosity, high mechanical strength and good activity; preferably MnO₂、Cu/Al₂O₃、Cu/TiO₂(ii) a The ozone catalyst catalyzes ozone and water into OH; and/or

The alkali liquor adopted in the alkali liquor absorption device (6) is one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate and ammonia water.

Technical Field

The invention relates to a denitration method, in particular to a chain grate and a chain grate-rotary kiln oxidized pellet denitration system, belonging to the field of sintered pellet denitration; the invention also provides a denitration method for the grate-rotary kiln oxidized pellets.

Background

The pellet ore is the main iron-containing furnace charge for blast furnace ironmaking production in China, and the yield of the pellet ore in China is 12800 ten thousand tons in 2015. Compared with sintered ore, because the energy consumption in the pellet production process is low, the environment is relatively friendly, and the product has the advantages of good strength, high grade and good metallurgical performance, and can play the roles of increasing yield and saving coke, improving the economic index of the iron-making technology, reducing the pig iron cost and improving the economic benefit when being applied to blast furnace smelting, the pellet ore is vigorously developed in recent years in China.

The production of the pellets in China is mainly based on a grate-rotary kiln process, and the yield of the pellets accounts for more than 60 percent of the total yield of the pellets. In recent years, along with the increasing complexity of iron ore raw materials and fuels, the proportion of hematite is improved (resulting in the rise of roasting temperature), the scale utilization of low-quality fuels, the application of nitrogen-containing coke oven gas of a gas-based rotary kiln, and the like, so that NO is generated in the production process of pellets of a plurality of enterprises_xThe emission concentration is in an ascending trend; in addition, the increasingly severe environmental protection requirement of China is NO_xThe emission is included in the emission assessment system, and NO is produced from the pellets in 2015_x(with NO)₂Meter) emission limit 300mg/m³Therefore, the part of enterprises can meet the national emission standard by adding the denitration facility. The national environmental protection agency of 6 months in 2017 issues a revised notice of 'emission standards of atmospheric pollutants for the iron and steel sintering and pelletizing industry', and NOx (in NO form)₂Meter) emission limits from 300mg/Nm³Down-regulated to 100mg/Nm³The reference oxygen content of sintering and pellet roasting flue gas is 16%. And then the environmental protection requirement of ultra-low emission is put forward.

Although the pelletizing enterprises do a great deal of work in the environmental protection aspect, the dust removal and the desulfurization are effectively controlled, and the emission requirements can be met, the NO is currently_xBecause the removal cost is high and the process is complex, under the environment with a low steel form, the method brings new challenges to the pelletizing industry, and part of enterprises are caused by NO_xExceeding standard has to reduce production greatly, even facing shutdown. From the perspective of most pellet production situations at present, NO_xThe emission is generally 100 to 400mg/m³If the process can be started, NO is realized by using working condition_xThe emission reduction can save tail end denitration purification equipment or greatly reduce tail end denitration investment, and the pellet is processed on a chain grate-rotary kilnThe production significance is great, and the vitality and the competitiveness of the pellet production can be further improved.

In the prior art, the production process of the grate-rotary kiln pellets is low in NO because of NO systematic research and reliability_xGeneration and control techniques resulting in NO in the production process of a pellet mill_xEmission failure becomes one of the biggest challenges facing normality and enterprises. Therefore, enterprises can only reduce the injection amount of coal gas or coal powder and the strength requirement of the pellets by reducing the pellet output, thereby reducing the temperature of the rotary kiln and adopting lower NO_xRaw materials and fuels, etc. to reduce NO_xAnd (4) generating. The modes not only influence the pellet production in terms of yield and quality, have high quality requirements on raw fuel and cause the increase of cost, but also cannot radically solve the problem of low NO of pellets_xThe production problem is solved. In addition, a denitration device is additionally arranged after the main exhaust fan, such as Selective Catalytic Reduction (SCR) technology and non-selective catalytic reduction (SNCR) technology, although low NO can be achieved_xThe requirement of emission, but the investment cost is high, the equipment requirement is high, the energy consumption is large, the denitration cost is high, secondary pollution exists, the denitration method is not popularized and applied in pellet enterprises, and NO in pellet factories at home and abroad is currently used_xThe control mode is mainly realized by process control.

In order to meet the requirement of NO in the production process of the grate-rotary kiln pellets_xThe emission requirement is responded to the national energy conservation and emission reduction call, the vitality and the competitiveness of pellet production are improved, and the low NO is realized by starting from the process flow and utilizing the characteristics of the system_xAnd (4) pelletizing production.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to contact and react hot air in an induced draft drying section and a preheating section with an oxidant in an air box; oxidizing NO in hot air to NO₂Is favorable for absorbing the nitrogen oxide by the alkali liquor. Thereby realizing NO in the denitration process_xAnd (4) emission reduction. And a denitration device does not need to be additionally arranged for NO. The invention provides a chain grate denitration system, which comprises a chain grateThe drying and drying device is characterized in that the chain grate is sequentially provided with a blast drying section, an air draft drying section, a preheating section and a preheating section. And a denitration device is arranged in the bottom bellows of the air draft drying section and/or the preheating section, and the denitration device is an oxidant ejector.

According to a first embodiment of the present invention, there is provided a chain grate denitration system

The utility model provides a chain grate denitration system, this chain grate denitration system include the chain grate, according to the technology trend, the chain grate is equipped with air blast drying section, convulsions drying section in proper order, preheats one section and preheats the two-stage process. And a denitration device is arranged in the bottom bellows of the air draft drying section and/or the preheating section, and the denitration device is an oxidant ejector.

Preferably, the chain grate denitration system further comprises an oxidant generating device, and a first oxidant ejector is arranged in a bottom bellows of the air draft drying section. The oxidant generation device includes: an ozone generator. The outlet of the ozone generator is connected with the first oxidant ejector through a first pipeline.

Preferably, the system further comprises an oxidant generation device, and a second oxidant injector is arranged in the bottom air box of the preheating section. The oxidant generation device includes: an ozone generator. The outlet of the ozone generator is connected with the second oxidant ejector through a second pipeline.

Preferably, the second conduit branches from the first conduit.

Preferably, the oxidant generation means further comprises a catalytic reactor. The outlet of the ozone generator is communicated with the inlet of the catalytic reactor, and the first pipeline is connected with the outlet of the catalytic reactor and the first oxidant ejector. An ozone catalyst bed layer is arranged in the catalytic reactor.

Preferably, the chain grate denitration system further comprises an alkali liquor absorption device. An air outlet of the air draft drying section and/or the preheating section passes through a third pipeline, and the flue gas passes through the main exhaust fan and then is connected with an inlet of the alkali liquor absorption device.

Preferably, the outlet of the lye absorption device is connected with the chimney through a fourth pipeline.

Preferably, the third pipeline is provided with a dust removal system.

Preferably, a first NO detector is arranged in the air draft drying section, a first flow detection device is arranged in the air draft drying section, a first flow control valve is arranged on the first pipeline, and the first flow control valve is arranged at the downstream of the position of the first pipeline, from which the second pipeline is separated.

Preferably, a second NO detector is arranged in the preheating section, a second flow detection device is arranged in the preheating section, and a second flow control valve is arranged on the second pipeline.

According to a second embodiment of the invention, a grate-rotary kiln oxidized pellet denitration system is provided

A chain grate-rotary kiln oxidized pellet denitration system comprises the chain grate denitration system of the first embodiment, and further comprises a rotary kiln and a circular cooler. The ring cooling machine comprises a ring cooling first section, a ring cooling second section and a ring cooling third section. And the air outlet of the annular cooling section is communicated with the air inlet of the rotary kiln. And the air outlet of the rotary kiln is communicated with the air inlet of the preheating section. And the air outlet of the preheating two-section is communicated with the air inlet of the air draft drying section. And the air outlet of the annular cooling section is communicated with the air inlet of the preheating section.

According to a third embodiment of the present invention, there is provided a method for denitrating a grate

A chain grate denitration method comprises the following steps:

1) the green pellets enter a chain grate machine and sequentially pass through a blast drying section, an air draft drying section, a preheating section and a preheating section.

2) The oxidant is sprayed into the bottom of the air draft drying section and/or the preheating section, NO in hot air in the air draft drying section and/or the preheating section reacts with the oxidant, and the NO is oxidized into NO₂Or HNO₃。

3) The hot air passing through the air draft drying section and/or the preheating section is discharged from the air outlets of the air draft drying section and/or the preheating section through the third pipeline.

Preferably, the method further comprises: and 4) conveying the oxidant to a first oxidant ejector in a bottom bellows of the air draft drying section through a first pipeline by the ozone generator, and ejecting the oxidant in the air draft drying section by the first oxidant ejector.

Preferably, the ozone generator delivers oxidant via a second conduit to a second oxidant injector in the bottom windbox of the preheating section, the second oxidant injector injecting oxidant in the preheating section.

Preferably, in step 4), the oxidant generated by the ozone generator is conveyed to the first oxidant injector via a first pipe after passing through the catalytic reactor, and is optionally conveyed to the second oxidant injector via a second pipe.

Preferably, the method further comprises: and 5) discharging hot air in the air draft drying section and/or the preheating section from respective air outlets, conveying the hot air to an alkali liquor absorption device through a third pipeline after dust removal, and absorbing NO in the hot air discharged from the air draft drying section and/or the preheating section by the alkali liquor absorption device₂Or HNO₃。

Preferably, the hot air treated by the lye absorption device is discharged through a chimney via a fourth pipeline.

Preferably, the hot air in the third pipeline enters the alkali liquor absorption device after being dedusted by the dedusting system.

Preferably, the first NO detector in the air draft drying section detects that the concentration of NO in the air draft drying section is P_D，mg/m³. The first flow detection device in the air draft drying section detects that the gas flow in the air draft drying section is Q_D，m³H is used as the reference value. Calculating the flow rate U of oxidant delivered to the first oxidant injector based on the mechanism by which NO reacts with the oxidant_D，m³/h：

Wherein: k is the reaction coefficient of NO and oxidant, and has the value of 0.5-1.0, preferably 0.6-0.95, and more preferably 0.7-0.9. C₁Injecting a concentration of oxidant, mg/m, into the first oxidant injector³. The first flow control valve controls the flow rate to the first oxidant injector to be U_D。

As a preference, the first and second liquid crystal compositions are,a second NO detector in the preheating section detects that the concentration of NO in the preheating section is P_T，mg/m³. The second flow detection device in the preheating section detects that the gas flow in the preheating section is Q_T，m³H is used as the reference value. Calculating the flow rate U of oxidant delivered to the second oxidant injector based on the mechanism by which NO reacts with the oxidant_T，m³/h：

Wherein: k is the reaction coefficient of NO and oxidant, and has the value of 0.5-1.0, preferably 0.6-0.95, and more preferably 0.7-0.9. C₂Injecting a concentration of oxidant, mg/m, into the second oxidant injector³. The second flow control valve controls the flow delivered to the second oxidant injector to be U_T。

Preferably, the method further comprises: and 6) conveying air discharged from the ring cooling section to the rotary kiln, conveying hot air discharged from the rotary kiln to the preheating section, and conveying hot air subjected to heat exchange in the preheating section to the air draft drying section. And conveying the air subjected to heat exchange in the annular cooling second section to the preheating first section.

Preferably, the oxidizing agent is a strong oxidizing agent, preferably ozone or Cl₂、ClO₂、H₂O₂、KMnO₄One or more of (a).

Preferably, an ozone catalyst bed layer is arranged in the catalytic reactor, and the ozone catalyst is transition metal andor transition metal oxide with large specific surface area, looseness, porosity, high mechanical strength and good activity. The ozone catalyst catalyzes ozone and water to OH.

Preferably, the ozone catalyst is MnO₂、Cu/Al₂O₃、Cu/TiO₂(ii) a The ozone catalyst catalyzes ozone and water to OH.

Preferably, the alkali liquor adopted in the alkali liquor absorption device is one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate and ammonia water.

In the first embodiment, during the process production, the NOx mainly comes from the rotary kiln system and comprises NOx (thermal NOx) generated by high-temperature flame, NOx (fuel NOx) generated by fuel combustion and NOx brought by fuel, and the NOx products enter the preheating section along with the roasting hot air, and due to gaps or holes between the preheating section and the preheating section, the NOx products in the preheating section enter the preheating section, so that the gas in the preheating section comprises a part of the NOx products. In addition, the first type of hot air coming out from the preheating second section is introduced into a denitration device for denitration before entering the air draft drying section. But also results in the gas in the suction dryer section containing NOx products due to incomplete denitrification. In conclusion, the NOx in the exhaust drying section and the preheating section exceeds the standard due to the reasons. Tests show that in the pellet production process, due to insufficient combustion, the produced NOx contains more than 95% of NO products, and the rest is mainly NO₂. NO hardly soluble in water, NO₂Is easily dissolved in water. And the gas temperature in the air draft drying section and the preheating section is between 100 and 200 ℃. The technical scheme provided by the invention is that a denitration device is arranged in an air box, wherein the denitration device is arranged in the bottom air box of an air draft drying section and/or a preheating section, and the denitration device is specifically an oxidant injection device. Under the action of oxidant, NO in the exhaust drying section and/or the preheating section reacts with the oxidant to generate NO₂. Is favorable for absorbing the nitrogen oxides. Thereby realizing NO in the denitration process_xAnd (4) emission reduction.

In the first embodiment, the chain grate denitration system further comprises an oxidant generating device, and the first oxidant ejector in the bottom wind box of the induced draft drying section is communicated with an oxidant outlet of the oxidant generating device. The oxidant generating device specifically comprises an ozone generator. The ozone generated by the ozone generator is connected with the first oxidant ejector through a first pipeline.

In a first embodiment, the second oxidant injector of the grate that preheats a bottom windbox communicates with the oxidant outlet of the ozone generator. The ozone generated by the ozone generator is connected with the first oxidant ejector through a second pipeline. The second pipeline is a branch branched from the first pipeline.

It is noted that ozone can react with NO to form NO₂. The reaction equation is as follows:

NO+O₃→NO₂+O₂

ozone conversion of NO to NO₂And is favorable for absorbing nitrogen oxides.

In the first embodiment, ozone generated in the ozone generator is first passed into the catalytic reactor, and the ozone and water are degraded into OH (free radicals) which are more oxidized than ozone under the action of the catalyst. Atomization of OH (free radical) and subsequent reaction with NO. The ozone catalyst bed layer in the catalytic reactor can effectively promote the catalysis of the catalyst on ozone.

The reaction equation of the degradation of ozone and water under the action of the catalyst is as follows:

H₂O+O₃→·OH

the equation for the reaction of OH (free radical) with NO is:

NO+·OH→NO₂

NO+·OH→HNO₃

NO₂+·OH→HNO₃。

in the present invention, the oxidant ejector includes a first oxidant ejector.

In the present invention, the oxidant injector comprises a second oxidant injector.

In the invention, NO in the air draft drying section is introduced into an alkali liquor absorption device after being fully reacted with an oxidant (ozone or OH) to absorb NO₂And HNO₃And (4) recovering. Due to NO₂Further reaction with free radicals produces nitric acid. The acid-base neutralization reaction is carried out in an alkali liquor absorption device, NO₂And HNO₃Is absorbed.

In the first embodiment, the waste gas absorbed by the alkali liquor absorption device is discharged to the atmosphere through a chimney, so that the influence of the waste gas on the surrounding environment is reduced.

In a first embodiment, the flue gas is first passed to a dedusting system for dedusting. And the gas after dust removal is subjected to denitration treatment, so that the environmental pollution is reduced.

In a first embodiment, the amount of NO can be monitored in real time by the first NO detector, the first flow sensing device and the first flow control valve during the updraft drying section, thereby better controlling the injection of the oxidant. Therefore, the reaction of NO and the oxidant in the air draft drying section can be accurately controlled, the oxidant is supplied according to the requirement, and the cost of the oxidant is saved.

In a first embodiment, the amount of NO can be monitored in real time by the second NO detector, the second flow sensing device and the second flow control valve during the preheat section, thereby allowing for better control of the oxidizer injection. Therefore, the reaction of NO and the oxidant in the preheating section can be accurately controlled, the oxidant is supplied according to the requirement, and the cost of the oxidant is saved.

In a second embodiment, hot air from the ring cooling section is passed into the rotary kiln to keep the air circulation in the rotary kiln and reduce the consumption of combustion energy. And (4) the roasting hot air in the rotary kiln enters a preheating second stage, and the mineral aggregate in the preheating second stage is preheated at high temperature. Because the rotary kiln is in a high-temperature environment, nitrogen in the air can react with oxygen to generate NOx products. The NOx products enter the preheating secondary section along with the circulation of the roasting hot air, so that the gas in the preheating secondary section contains a large amount of NOx products. The first type of hot air discharged from the preheating second section enters the air draft drying section to deeply dry the mineral aggregate. And then, the mineral aggregate enters a ring cooling second section, the second hot air after heat exchange discharged from the ring cooling second section enters a preheating first section through a pipeline, and the mineral aggregate in the preheating first section is preliminarily preheated. And finally, the mineral aggregate enters a ring cooling three-section for cooling, and low-temperature hot air generated by the ring cooling three-section enters a blast drying section for primary drying of the mineral aggregate. In the process of production, NOx mainly comes from a rotary kiln system and comprises NOx (thermal NOx) generated by high-temperature flame, NOx (fuel NOx) generated by fuel combustion and NOx brought by fuel, the NOx products enter the preheating section along with roasting hot air, and due to gaps or holes between the preheating section and the preheating section, the NOx products in the preheating section enter the preheating section, so that the gas in the preheating section contains a part of NOx products. In addition, the first type of hot air coming out from the preheating second section is introduced into a denitration device for denitration before entering the air draft drying section. But also results in the gas in the suction dryer section containing NOx products due to incomplete denitrification. In conclusion, the NOx in the exhaust drying section and the preheating section exceeds the standard due to the reasons. Tests show that in the pellet production process, due to insufficient combustion, the produced NOx contains more than 95% of NO products, and the rest is mainly NO₂. And the gas temperature in the air draft drying section and the preheating section is between 100 and 200 ℃. The technical scheme provided by the invention is that a first oxidant ejector is arranged in an air box at an air draft drying section, and a second oxidant ejector is arranged in an air box at a preheating section. The first oxidant injector and the second oxidant injector are in communication with the oxidant generator device. NO in the exhaust drying section and the preheating section reacts with the oxidant to generate NO₂. Then the nitrogen oxides are led into an alkali liquor recoverer to recover the nitrogen oxides.

Drawings

FIG. 1 is a flow chart of a process for denitration of oxidized pellets of a grate-rotary kiln according to the present invention;

FIG. 2 is a flow chart of a denitration process of oxidized pellets of a grate-rotary kiln in the prior art;

FIG. 3 is a schematic diagram of the reaction of ozone as an oxidant in accordance with the present invention;

FIG. 4 is a reaction scheme of OH (radical) as an oxidizing agent according to the present invention.

Reference numerals:

1: a chain grate machine; UDD: a forced air drying section; DDD: an air draft drying section; TPH: preheating for one section; pH: a second preheating stage; 2: an oxidant ejector; 201: a first oxidant ejector; 202: a second oxidant injector; 3: an oxidant generating device; 301: an ozone generator; 302: a catalytic reactor; 4: a dust removal system; 5: a chimney; 6: an alkali liquor absorption device; 701: a first NO detector; 702: a second NO detector; 801: a first flow detection device; 802: a second flow detection device; 901: a first flow control valve; 902: a second flow control valve; 10: a rotary kiln; 11: a circular cooler; c1: cooling in a ring for one section; c2: a ring cooling section; c3: ring cooling for three sections;

l1: a first conduit; l2: a second conduit; l3: a third pipeline; l4: a fourth conduit.

Detailed Description

According to a first embodiment of the present invention, there is provided a chain grate denitration system

A chain grate denitration system comprises a chain grate 1, wherein according to the process trend, the chain grate 1 is sequentially provided with an air blowing drying section UDD, an air draft drying section DDD, a preheating section TPH and a preheating section PH; and a denitration device is arranged in the bottom bellows of the exhausting drying section DDD and/or the preheating section TPH, and the denitration device is an oxidant ejector 2.

Preferably, the chain grate denitration system further comprises an oxidant generating device 3, wherein a first oxidant ejector 201 is arranged in a bottom wind box of the induced draft drying section DDD; the oxidizing agent generation device 3 includes: an ozone generator 301; the outlet of the ozone generator 301 is connected to the first oxidant ejector 201 through a first pipe L1.

Preferably, the system also comprises an oxidant generation device 3, and a second oxidant ejector 202 is arranged in the bottom air box for preheating the section of TPH; the oxidizing agent generation device 3 includes: an ozone generator 301; the outlet of the ozone generator 301 is connected to the second oxidant injector 202 via a second conduit L2.

Preferably, the second conduit L2 branches off from the first conduit L1.

Preferably, the oxidant generation device 3 further comprises a catalytic reactor 302; the outlet of the ozone generator 301 is communicated with the inlet of the catalytic reactor 302, and a first pipeline L1 is connected with the outlet of the catalytic reactor 302 and the first oxidant ejector 201; an ozone catalyst bed is provided within catalytic reactor 302.

Preferably, the chain grate denitration system further comprises an alkali liquor absorption device 6; the air outlet of the DDD and/or the TPH preheating section is connected with the inlet of the alkali liquor absorption device 6 through a third pipeline L3 after dust removal. (the denitration system of the chain grate machine also comprises an alkali liquor absorption device 6. the air outlet of the DDD and/or TPH preheating section passes through a third pipeline L3, a dust removal system 4 is arranged on the third pipeline L3, the flue gas passes through a main exhaust fan and then is connected with the inlet of the alkali liquor absorption device 6. preferably, the outlet of the alkali liquor absorption device 6 is connected with a chimney 5 through a fourth pipeline L4.)

Preferably, the outlet of the lye absorption devices 6 is connected to the chimney 5 via a fourth conduit L4.

Preferably, a dust removal system 4 is provided on the third duct L3.

Preferably, the first NO detector 701 is arranged in the updraft drying section DDD, the first flow detection device 801 is arranged in the updraft drying section DDD, the first flow control valve 901 is arranged on the first pipeline L1, and the first flow control valve 901 is arranged downstream of the position where the second pipeline L2 is branched from the first pipeline L1.

Preferably, the second NO detector 702 is disposed in the preheat section TPH, the second flow detector 802 is disposed in the preheat section TPH, and the second flow control valve 902 is disposed on the second pipeline L2.

According to a second embodiment of the invention, a grate-rotary kiln oxidized pellet denitration system is provided

A chain grate-rotary kiln oxidized pellet denitration system comprises the chain grate denitration system of the first embodiment, a rotary kiln 10 and an annular cooler 11; the ring cooling machine 11 comprises a ring cooling first section C1, a ring cooling second section C2 and a ring cooling third section C3; the air outlet of the annular cooling section C1 is communicated with the air inlet of the rotary kiln 10; an air outlet of the rotary kiln 10 is communicated with an air inlet of the preheating section PH; the air outlet of the preheating section PH is communicated with the air inlet of the exhausting and drying section DDD; and the air outlet of the annular cooling section C2 is communicated with the air inlet of the preheating section TPH.

According to a third embodiment of the present invention, there is provided a method for denitrating a grate

A chain grate denitration method comprises the following steps:

1) the green pellets enter a chain grate machine 1 and sequentially pass through a blast drying section UDD, an air draft drying section DDD, a preheating section TPH and a preheating section PH;

2) spraying oxidant at the bottom of the DDD and/or the TPH, reacting NO in the hot air in the DDD and/or the TPH, and oxidizing NO into NO₂Or HNO₃；

3) The hot air passing through the draft drying section DDD and/or the pre-heated section TPH is discharged from the respective air outlets via the third duct L3.

Preferably, the method further comprises: step 4) the ozone generator 301 delivers the oxidant via a first conduit L1 to a first oxidant injector 201 in the bottom windbox of the updraft drying section DDD, the first oxidant injector 201 injecting the oxidant in the updraft drying section DDD.

Preferably, the ozone generator 301 delivers the oxidant via a second conduit L2 to a second oxidant injector 202 in the bottom windbox of the preheated section of TPH, the second oxidant injector 202 injecting the oxidant in the preheated section of TPH.

Preferably, in step 4), the oxidant generated by the ozone generator 301 passes through the catalytic reactor 302 and is then delivered to the first oxidant injector 201 via the first conduit L1, and optionally to the second oxidant injector 202 via the second conduit L2.

Preferably, the method further comprises: step 5) the hot air in the DDD and/or TPH section is discharged from the respective air outlet, and is conveyed to the alkali liquor absorption device 6 through a third pipeline L3, and the alkali liquor absorption device 6 absorbs NO in the hot air discharged from the DDD and/or TPH section₂Or HNO₃。

Preferably, the hot air treated by the lye absorption devices 6 is discharged via a fourth line L4 through the stack 5.

Preferably, the hot air in the third pipeline L3 enters the alkali liquor absorption device 6 after being dedusted by the dedusting system 4.

Preferably, in the induced draft drying section DDDThe first NO detector 701 detects that the concentration of NO in the DDD of the air draft drying section is P_D，mg/m³(ii) a First flow detection device 801 in ventilation drying section DDD detects that gas flow in ventilation drying section DDD is Q_D，m³H; calculating the flow rate U of oxidant delivered to the first oxidant ejector 201 based on the mechanism by which NO reacts with the oxidant_D，m³/h：

Wherein: k is the reaction coefficient of NO and oxidant, and has the value of 0.5-1.0, preferably 0.6-0.95, and more preferably 0.7-0.9; c₁Injecting a concentration of oxidant, mg/m, into the first oxidant injector 201³(ii) a The first flow control valve 901 controls the flow delivered to the first oxidant injector 201 to be U_D。

Preferably, the second NO detector 702 in the pre-heat segment of TPH detects the concentration of NO in the pre-heat segment of TPH as P_T，mg/m³(ii) a The second flow detection device 802 in the preheated section of TPH detects that the gas flow in the preheated section of TPH is Q_T，m³H; calculating the flow rate U of oxidant delivered to the second oxidant injector 202 based on the mechanism by which NO reacts with the oxidant_T，m³/h：

Wherein: k is the reaction coefficient of NO and oxidant, and has the value of 0.5-1.0, preferably 0.6-0.95, and more preferably 0.7-0.9; c₂Injecting a concentration of oxidant, mg/m, into the second oxidant injector 202³(ii) a The second flow control valve 902 controls the flow delivered to the second oxidant injector 202 to be U_T。

Preferably, the method further comprises:

step 6), conveying air discharged from the annular cooling first-stage C1 to a rotary kiln 10, conveying hot air discharged from the rotary kiln 10 to a preheating second-stage PH, and conveying hot air subjected to heat exchange of the preheating second-stage PH to an air draft drying stage DDD; and the air subjected to heat exchange by the annular cooling section C2 is conveyed to the preheating section TPH.

Preferably, the oxidizing agent is a strong oxidizing agent, preferably ozone or Cl₂、ClO₂、H₂O₂、KMnO₄One or more of (a).

Preferably, an ozone catalyst bed layer is arranged in the catalytic reactor 302, and the ozone catalyst is transition metal andor transition metal oxide with large specific surface area, looseness, porosity, high mechanical strength and good activity; the ozone catalyst catalyzes ozone and water to OH.

Preferably, the ozone catalyst is MnO₂、Cu/Al₂O₃、Cu/TiO₂。

Preferably, the alkali liquor adopted in the alkali liquor absorption device 4 is one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate and ammonia water.