阅读说明：本技术 一种利用链篦机-回转窑系统氧化球团生产工艺及系统 (Production process and system for oxidizing pellets by using grate-rotary kiln system ) 是由 胡兵 于 2019-07-22 设计创作，主要内容包括：一种链篦机-回转窑系统氧化球团生产工艺,该工艺包括以下步骤：1)生球团经过链篦机进行干燥、预热和氧化,然后将经过链篦机的物料输送至回转窑进行焙烧,再输送至环冷机进行冷却,获得球团矿；2)环冷一段排出的热风输送至回转窑,回转窑排出的热风被输送至预热二段,预热二段排出的热风通过抽风方式输送至抽风干燥段；3)环冷二段排出的热风通过鼓风的方式输送至预热一段；4)环冷三段排出的热风通过鼓风的方式输送至鼓风干燥段。本发明方案通过向预热一段中鼓入热风,使得预热一段内的气压大于预热二段的气压,从而使得无需对预热一段的气体进行脱硝；同时在预热一段内形成稳定热风区,保证了上下层球团的预热效果。(A production process of oxidized pellets by a chain grate-rotary kiln system comprises the following steps: 1) drying, preheating and oxidizing the green pellets by a chain grate, then conveying the materials passing through the chain grate to a rotary kiln for roasting, and then conveying the materials to a circular cooler for cooling to obtain pellets; 2) conveying hot air exhausted from the ring cooling section to the rotary kiln, conveying the hot air exhausted from the rotary kiln to the preheating section, and conveying the hot air exhausted from the preheating section to the air draft drying section in an air draft mode; 3) hot air discharged from the annular cooling second section is conveyed to the preheating first section in a blowing mode; 4) and hot air exhausted from the ring cooling three sections is conveyed to the air blowing drying section in an air blowing mode. According to the scheme, hot air is blown into the preheating section, so that the air pressure in the preheating section is greater than that in the preheating section, and the gas in the preheating section does not need to be denitrated; meanwhile, a stable hot air area is formed in the preheating section, so that the preheating effect of the pellets on the upper layer and the lower layer is ensured.)

1. A production process for oxidizing pellets by utilizing a chain grate-rotary kiln system, wherein the chain grate-rotary kiln system comprises a chain grate (1), a rotary kiln (2) and a ring cooling machine (3), wherein: according to the material trend, the chain grate (1) is sequentially divided into a blast drying section (UDD), an air draft drying section (DDD), a preheating section (TPH) and a preheating section (PH); the ring cooling machine (3) is sequentially divided into a ring cooling first section (C1), a ring cooling second section (C2) and a ring cooling third section (C3); the process comprises the following steps:

1) drying, preheating and oxidizing the green pellets by a chain grate (1), then conveying the materials passing through the chain grate (1) to a rotary kiln (2) for roasting, and then conveying the materials to a circular cooler (3) for cooling to obtain pellet ore;

2) hot air exhausted from the ring cooling section (C1) is conveyed to the rotary kiln (2), hot air exhausted from the rotary kiln (2) is conveyed to the preheating section (PH), and hot air exhausted from the preheating section (PH) is conveyed to the air draft drying section (DDD) in an air draft mode;

3) hot air discharged from the ring cooling section (C2) is conveyed to the preheating section (TPH) in a blowing mode;

4) the hot air discharged from the ring cooling three section (C3) is conveyed to the blast drying section (UDD) by means of blast.

2. The production process according to claim 1, characterized in that: and a denitration device is arranged in a bottom bellows of the air draft drying section (DDD), and the denitration device is an oxidant ejector (4).

3. The production process according to claim 2, characterized in that: an air outlet of the air draft drying section (DDD) is connected with a first conveying pipeline (L1); the first conveying pipeline (L1) is sequentially provided with a dust removal system (5) and an alkali liquor absorption device (6); the hot air in the ventilation drying section (DDD) reacts with the oxidant sprayed by the oxidant sprayer (4), and the oxidant oxidizes the nitrogen oxide in the hot air in the ventilation drying section (DDD) into NO₂And/or HNO₃(ii) a Then sequentially carrying out dust removal treatment by a dust removal system (5) and denitration treatment by an alkali liquor absorption device (6); wherein the alkali liquor absorption device (6) absorbs NO in hot air discharged from the air draft drying section (DDD)₂Or HNO₃。

4. The production process according to claim 2 or 3, characterized in that: the grate-kiln system further comprises an oxidant generating device (7); the oxidant generation device (7) comprises: an ozone generator (701); the outlet of the ozone generator (701) is connected to the oxidant ejector (4) via a second conduit (L2).

5. The production process according to claim 4, characterized in that: the oxidant generation device (7) further comprises a catalytic reactor (702); the outlet of the ozone generator (701) is communicated with the inlet of the catalytic reactor (702), and a second pipeline (L2) is connected with the outlet of the catalytic reactor (702) and the oxidant ejector (4); an ozone catalyst bed layer is arranged in the catalytic reactor (702).

6. The production process according to any one of claims 1 to 5, characterized in that: in the step 3), hot air exhausted from the ring cooling second section (C2) is conveyed to the preheating first section (TPH) in a blowing mode, mineral aggregate is preheated at low temperature, and the air pressure in the preheating first section (TPH) is greater than the standard atmospheric pressure; preferably, the air pressure in the preheating section (TPH) hood is 0-200Pa, preferably the air pressure in the preheating section (TPH) hood is 10-150Pa, and more preferably the air pressure in the preheating section (TPH) hood is 20-100 Pa.

7. A grate-rotary kiln system or a system for a production process according to any one of claims 1-6, comprising a grate (1), a rotary kiln (2), a ring cooler (3), wherein: according to the material trend, the chain grate (1) is sequentially divided into a blast drying section (UDD), an air draft drying section (DDD), a preheating section (TPH) and a preheating section (PH); the ring cooling machine (3) is sequentially divided into a ring cooling first section (C1), a ring cooling second section (C2) and a ring cooling third section (C3); the discharge hole of the chain grate machine (1) is connected with the feed inlet of the rotary kiln (2), and the discharge hole of the rotary kiln (2) is connected with the feed inlet of the circular cooler (3); the method is characterized in that: an air outlet of the annular cooling section (C1) is connected with an air inlet of the rotary kiln (2), an air outlet of the rotary kiln (2) is connected with an air inlet of the preheating section (PH), and an air outlet of the preheating section (PH) is connected with an air inlet of the air draft drying section (DDD) through a third conveying pipeline (L3); an air outlet of the annular cooling second section (C2) is connected with an air inlet of the preheating first section (TPH) through a fourth conveying pipeline (L4); the air outlet of the annular cooling three-section (C3) is connected with the air blowing drying section (UDD) through a fifth conveying pipeline (L5); an exhaust fan (8) is arranged on the third conveying pipeline (L3), a first air blower (901) is arranged on the fourth conveying pipeline (L4), and a second air blower (902) is arranged on the fifth conveying pipeline (L5).

8. The system of claim 7, wherein: a denitration device is arranged in a bottom bellows of the air draft drying section (DDD), and the denitration device is an oxidant ejector (4); and/or

An air outlet of the air draft drying section (DDD) is connected with a first conveying pipeline (L1); the first conveying pipeline (L1) is sequentially provided with a dust removal system (5) and an alkali liquor absorption device (6).

9. The system of claim 8, wherein: the grate-kiln system further comprises an oxidant generating device (7); the oxidant generation device (7) comprises: an ozone generator (701); the outlet of the ozone generator (701) is connected with the oxidant ejector (4) through a second pipeline (L2);

preferably, the oxidant generation device (7) further comprises a catalytic reactor (702); the outlet of the ozone generator (701) is communicated with the inlet of the catalytic reactor (702), and a second pipeline (L2) is connected with the outlet of the catalytic reactor (702) and the oxidant ejector (4); an ozone catalyst bed layer is arranged in the catalytic reactor (702).

10. The system of claim 9, wherein: NO is provided in the preheat stage (TPH)_xThe flow meter comprises a detector (10) and a flow detection device (11), wherein a flow control valve (12) is arranged on a second pipeline (L2); and/or

The system further comprises a chimney (13); the exhaust openings of the suction drying section (DDD) and/or the blower drying section (UDD) are connected to a chimney (13).

Technical Field

The invention relates to a preheating process, in particular to a production process for oxidizing pellets by utilizing a grate-rotary kiln system, belonging to the technical field of pellets; the invention relates to a chain grate-rotary kiln system.

Background

The pellet ore is the main iron-containing furnace burden generated by blast furnace ironmaking 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 carried out by a grate-rotary kiln-circular cooler process, and the yield of the pellets accounts for more than 60 percent of the total yield of the pellets. In recent years, with the increasing complexity of iron ore raw materials and fuels, the increase of the proportion of hematite (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 causes the NOx emission concentration of a plurality of enterprises in the pellet production process to be in an increasing trend; in addition, the increasingly severe environmental protection requirements of China are met, the emission of NOx is brought into an emission check system, and from 2012 onwards, NOx (produced by NO) is produced by pellets₂Meter) emission limit 300mg/m³The national environmental protection agency of 6 months in 2017 issues a revised notice of the emission standard of steel sintering and pelletizing industry atmospheric pollutants, and NOx (in NO form)₂Meter) emission limit from 300mg/m³Down-regulated to 100mg/m³The reference oxygen content of sintering and pellet roasting flue gas is 16%. So that part of enterprises can meet the national emission standard by adding denitration facilities.

Although pelletizing enterprises do a lot of work in the aspect of environmental protection, dust removal and desulfurization are effectively controlled, and emission requirements can be met, NOx is high in removal cost and complex in process at present, and under the environment with a low steel form, new challenges are brought to the pelletizing industry, and a part of enterprises have to reduce production greatly due to the fact that NOx exceeds the standard, and even face shutdown. From the current majority of pellet production situations, in order to meet new emission requirements, a tail end denitration device is additionally arranged after desulfurization, so that the investment cost and the operation cost are greatly increased. In addition, hot air in a grate-rotary kiln-circular cooler pellet process hot air system is recycled, so that the production and quality of pellets and energy conservation and emission reduction are very important, and under the existing hot air system, two-stage preheating is realized by adopting air draft preheating, so that the problem that the preheating of one-stage NOx is caused by the fact that two-stage preheating flue gas is mixed into the preheating of one-stage preheating is caused, and the product quality is greatly influenced by the difference of the strength and the oxidation degree of pellets on the upper layer and the lower layer caused by uneven preheating. If can follow the air current system and start, let preheating of upper and lower layer pelletizing tend to evenly and concentrate on preheating the two-stage process after handling NOx, can promote the quality of preheating the pelletizing when reducing denitration flue gas handling capacity to when can reducing the denitration cost, promote the pelletizing quality, it is significant to the production of grate-kiln oxidation pellet, be favorable to further improving the vitality and the competitiveness of pelletizing production.

The existing production process of oxidized pellets by a chain grate-rotary kiln is shown in figure 1, the chain grate is divided into an air blowing drying section (UDD), an air draft drying section (DDD), a preheating section (TPH) and a preheating section (PH), and a circular cooler is divided into a circular cooling section (C1), a circular cooling section (C2) and a circular cooling section (C3). Wherein, the air of the ring cooling first section (C1) directly enters the rotary Kiln (Kiln) to roast the pellet, heats the preheated pellet through the preheating second section (PH), then blows into the induced draft drying section (DDD) to carry out induced draft drying on the green pellet, and then is discharged outwards through the induced draft drying section (DDD) (the flue gas is purified before being discharged); the air of the annular cooling second section (C2) enters the preheating first section (TPH) to heat the preheating ball and then is discharged outwards; and air of the circular cooling three-section (C3) enters an air blowing drying section (UDD) to carry out air blowing drying on the green pellets, so that the efficient utilization of the grate-rotary kiln-circular cooler air flow system is realized.

In order to meet the requirements of NOx emission and pellet quality improvement in the production process of the grate-rotary kiln oxidized pellets and respond to the national energy-saving and emission-reduction calls, an advanced air flow system is invented from a hot air system, and meanwhile, the characteristics of the system are utilized to realize quality improvement and optimize a NOx purification process, reduce the denitration cost and improve the vitality and competitiveness of pellet production.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to blow second type hot air into the preheating section to ensure that the air pressure in the preheating section is greater than that of the preheating section, so that the gas in the preheating section cannot enter the preheating section through a gap or a hole between the preheating section and the preheating section, and the concentration of NO in the preheating section is reduced; meanwhile, the air pressure in the preheating section is positive pressure, so that the heating speed of the pellets on the upper layer and the lower layer is consistent, and the preheating effect of the pellets on the upper layer and the lower layer is ensured. Improving economic benefit, reducing pollution and improving product quality. The invention provides a production process for oxidizing pellets by using a grate-rotary kiln system, which comprises the following steps: 1) drying, preheating and oxidizing the green pellets by a chain grate, then conveying the materials passing through the chain grate to a rotary kiln for roasting, and then conveying the materials to a circular cooler for cooling to obtain pellets; 2) conveying hot air exhausted from the ring cooling section to the rotary kiln, conveying the hot air exhausted from the rotary kiln to the preheating section, and conveying the hot air exhausted from the preheating section to the air draft drying section in an air draft mode; 3) hot air discharged from the annular cooling second section is conveyed to the preheating first section in a blowing mode; 4) and hot air exhausted from the ring cooling three sections is conveyed to the air blowing drying section in an air blowing mode.

According to a first embodiment of the present invention, there is provided a process for the production of oxidized pellets using a grate-rotary kiln system:

a production process for oxidizing pellets by utilizing a chain grate-rotary kiln system, wherein the chain grate-rotary kiln system comprises a chain grate, a rotary kiln and a circular cooler, wherein: according to the material trend, the chain grate is divided into a blast drying section, an air draft drying section, a preheating section and a preheating section in sequence; the annular cooler is sequentially divided into an annular cooling first section, an annular cooling second section and a first cooling section; the process comprises the following steps: 1) drying, preheating and oxidizing the green pellets by a chain grate, then conveying the materials passing through the chain grate to a rotary kiln for roasting, and then conveying the materials to a circular cooler for cooling to obtain pellets; 2) conveying hot air exhausted from the ring cooling section to the rotary kiln, conveying the hot air exhausted from the rotary kiln to the preheating section, and conveying the hot air exhausted from the preheating section to the air draft drying section in an air draft mode; 3) hot air discharged from the annular cooling second section is conveyed to the preheating first section in a blowing mode; 4) and hot air exhausted from the ring cooling three sections is conveyed to the air blowing drying section in an air blowing mode.

Preferably, a denitration device is arranged in a bottom bellows of the air draft drying section, and the denitration device is an oxidant ejector.

AsPreferably, an air outlet of the air draft drying section is connected with the first conveying pipeline; the first conveying pipeline is sequentially provided with a dust removal system and an alkali liquor absorption device; the hot air in the air draft drying section reacts with the oxidant sprayed by the oxidant sprayer, and the oxidant oxidizes nitrogen oxides in the hot air in the air draft drying section into NO₂And/or HNO₃(ii) a Then sequentially carrying out dust removal treatment by a dust removal system and denitration treatment by an alkali liquor absorption device; wherein the alkali liquor absorption device absorbs NO in hot air discharged from the air draft drying section₂Or HNO₃。

Preferably, the grate-rotary kiln system further comprises an oxidant generation device; the oxidant generation device includes: an ozone generator; the outlet of the ozone generator is connected with the oxidant ejector through a second pipeline.

Preferably, the outlet is communicated with the inlet of the catalytic reactor, and the second pipeline is connected with the outlet of the catalytic reactor and the oxidant ejector; an ozone catalyst bed layer is arranged in the catalytic reactor.

Preferably, in step 3), the hot air discharged from the annular cooling section is conveyed to the preheating section by means of air blowing to preheat the mineral aggregate at a low temperature, and the air pressure in the preheating section is positive pressure.

Preferably, the air pressure in the preheating section of the smoke hood is 0-200Pa, preferably the air pressure in the preheating section of the smoke hood is 0-150Pa, and more preferably the air pressure in the preheating section of the smoke hood is 20-100 Pa.

Preferably, the ozone catalyst is transition metal andor transition metal oxide with large specific surface area, loose porosity, high mechanical strength and good activity. Preferably, the ozone catalyst is MnO₂、Cu/Al₂O₃Or Cu/TiO₂。

According to a second embodiment of the present invention, there is provided a grate-rotary kiln system comprising:

a grate-rotary kiln system or a system for use in the production process of the first embodiment, the grate-rotary kiln system comprising a grate, a rotary kiln, a ring cooler, wherein: according to the material trend, the chain grate is divided into a blast drying section, an air draft drying section, a preheating section and a preheating section in sequence; the ring cooling machine is sequentially divided into a ring cooling first section, a ring cooling second section and a ring cooling third section; the discharge hole of the chain grate machine is connected with the feed inlet of the rotary kiln, and the discharge hole of the rotary kiln is connected with the feed inlet of the circular cooler; the method is characterized in that: an air outlet of the annular cooling section is connected with an air inlet of the rotary kiln, an air outlet of the rotary kiln is connected with an air inlet of the preheating section, and an air outlet of the preheating section is connected with an air inlet of the air draft drying section through a third conveying pipeline; an air outlet of the annular cooling section is connected with an air inlet of the preheating section through a fourth conveying pipeline; the air outlet of the annular cooling section is connected with the air blowing drying section through a fifth conveying pipeline; an exhaust fan is arranged on the third conveying pipeline, a first air blower is arranged on the fourth conveying pipeline, and a second air blower is arranged on the fifth conveying pipeline.

Preferably, a denitration device is arranged in a bottom bellows of the air draft drying section, and the denitration device is an oxidant ejector.

Preferably, an air outlet of the air draft drying section is connected with the first conveying pipeline; the first conveying pipeline is sequentially provided with a dust removal system and an alkali liquor absorption device.

Preferably, the grate-rotary kiln system further comprises an oxidant generation device; the oxidant generation device includes: an ozone generator; the outlet of the ozone generator is connected with the oxidant ejector through a second pipeline.

Preferably, the oxidant generation device further comprises a catalytic reactor; the outlet of the ozone generator is communicated with the inlet of the catalytic reactor, and the second pipeline is connected with the outlet of the catalytic reactor and the oxidant ejector; an ozone catalyst bed layer is arranged in the catalytic reactor.

Preferably, the preheating section is provided with NO_xThe second pipeline is provided with a flow control valve.

Preferably, the system further comprises a chimney; and the air outlet of the air draft drying section and/or the air blowing drying section is connected to the chimney.

Preferably, NO in the updraft drying section DDD_xDetector for detecting NO in DDD (double-walled carbon dioxide) of air draft drying section_xIs at a concentration of P_D，mg/m³(ii) a DrawerThe flow detection device in the air drying section DDD detects that the gas flow in the air draft drying section DDD is Q_D，m³H; according to NO_xMechanism of reaction with the oxidant, calculating the flow rate U of oxidant delivered to the oxidant injector_D，m³/h：

Wherein: k is NO_xThe reaction coefficient with the oxidant is 0.5-1.0, preferably 0.6-0.95, and more preferably 0.7-0.9; c₁The concentration of oxidant, mg/m, is injected into the oxidant injector³(ii) a The flow control valve controls the flow rate to the oxidant ejector to be U_D。

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, the mineral aggregate is dried and preheated by a chain grate once, roasted by a rotary kiln and cooled by a circular cooler. The mineral aggregate is primarily dried in the forced air drying section of the chain grate. The mineral aggregate is deeply dried in the air draft drying section. The mineral aggregate is preliminarily preheated in the preheating section. The mineral aggregate is preheated at high temperature in the preheating section. And (4) fully roasting the mineral aggregate at high temperature after the mineral aggregate enters the rotary kiln. After roasting is finished, mineral aggregate enters a ring cooling first section, a ring cooling second section and a ring cooling third section to be cooled step by step. Hot air exhausted from the ring cooling section is introduced into the rotary kiln, so that air circulation in the rotary kiln is kept, and consumption of combustion energy is reduced. 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, particularly the flame temperature is high and generally exceeds 1300 ℃, 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. After the second type of hot air discharged from the annular cooling second section enters the preheating first section in a blowing mode, the preheating first section is in a positive pressure state, and the preheating second section is in a negative pressure state at the moment, namely the air pressure of the preheating first section is greater than that of the preheating second section. The air pressure in the preheating section can not enter the preheating section through a gap or a hole between the preheating section and the preheating section, so that the NOx products in the preheating section are prevented from entering the preheating section. The concentration of preheating one section of combustion gas NOx product is less than national emission standard, then need not to carry out denitration treatment to preheating one section of combustion gas, only needs to carry out denitration treatment after the dry section of convulsions to preheating two-section exhaust hot-blast. According to the scheme, through innovation on the process flow, the air pressure in the first preheating section is positive pressure, so that the air pressure in the first preheating section is larger than that in the second preheating section, the flue gas in the second preheating section only needs to be subjected to denitration treatment, the concentration of NOx products in the first preheating section is lower than the national standard, a denitration device does not need to be additionally connected to the downstream of the first preheating section, the investment of an enterprise for reaching the national environmental protection standard is reduced, and the production cost of the enterprise is reduced; meanwhile, the amount of flue gas required to be subjected to denitration treatment is greatly reduced. Has the effects of improving quality and optimizing the NOx purification process.

It should be noted that, this scheme is through the atmospheric pressure that improves the preheating section, reaches to prevent to preheat the NOx product in the second grade and gets into the preheating section. At the same time, the air pressure in the preheating section is positive. The gas entering the preheating section comes from the ring cooling section, belongs to medium-high temperature hot air, and is marked as second type hot air in the scheme. Due to the thermal effect of the gas, the hot gas will float upwards. After the second type of gas enters the preheating section, the second type of gas is filled above the preheating section to form a stable hot air area. The gas temperature of each part in the stable hot air area is equal, the stable hot air area formed by the whole second type of hot air can extend downwards and cover and permeate the whole preheated mineral aggregate layer, and the upper and lower pellets are in the stable hot air area. The upper and lower spheres are heated stably under the uniform hot air wrapping. Thereby the preheating of the upper and lower spheres is uniform.

It is further explained that the materials pass through the blowing drying section, the air draft drying section, the preheating section and the preheating section in sequence. The hot wind that carries to in the forced air drying section is the air blast mode, and the hot wind that carries to in the convulsions drying section is the convulsions mode, and the hot wind that carries to preheating in one section is the air blast mode, and the hot wind that carries to preheating in the two-stage process is the convulsions mode. The material is through whole chain grate machine, and hot-blast drying method does in proper order: blowing-draft-blowing-draft; the material is dried and heated in the forced air drying section and the preheating section by positive pressure gas. The materials are dried and heated by negative pressure gas in the air draft drying section and the preheating section. So that the material is uniformly preheated in the process of the chain grate under the condition of good drying.

In the prior art, the grate in the grate-rotary kiln-circular cooler air flow system is preheated by air draft at the preheating section and the preheating section, and a wind shielding wall between the two sections is too high or is perforated or cancelled, so that hot air containing high-concentration NOx in the preheating section is connected to the preheating section, and the flue gas at the preheating section are subjected to denitration treatment, so that the denitration flue gas treatment capacity is large, and the denitration investment and the operation cost are increased. In addition, the hot air conveyed to the preheating section adopts an air draft mode, so that the hot air entering the preheating section cannot be gathered in the preheating section, and a stable hot air area cannot be formed. The gas entering the preheating section quickly passes through the mineral aggregate, namely the upper pellet layer and the lower pellet layer. Because the hot air firstly contacts the upper surface of the upper pellet layer in the process of passing through the upper pellet layer and the lower pellet layer, the hot air quickly passes through the upper pellet layer and the lower pellet layer under the action of air pressure after contacting and exchanging heat with the upper pellet layer. So that the preheating of the upper and lower pellet layers is not uniform, namely the preheating of the upper surface is excessive, and the preheating of the lower surface is insufficient; even if the preheating of the upper pellet layer is enough, the strength of the upper pellet layer is too high due to the action of hot air, a hard shell is formed, the re-oxidation crystallization in the preheating section II and the rotary kiln is not facilitated, and the phenomenon of cold core is generated; namely, the outer shell is heated excessively, but the temperature of the pellet core is insufficient, oxygen is insufficient, and the phenomenon of cold core occurs. Meanwhile, the preheating effect of the lower pellet layer is seriously insufficient, namely the oxidation degree is insufficient, and the strength is lower than that of the upper pellet layer. Finally, the preheating effect of the pellet ore material at the preheating section does not reach the standard, and the roasting effect of the whole pellet ore material is greatly influenced. After the technology is implemented, the temperature of the first preheating section and the second preheating section can be reduced by 30-50 ℃, and the average strength of the preheating ball is improved by 50-100N compared with that of the traditional technology.

In the prior art process, 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, and 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 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 air box at the bottom of an air draft drying section, and the denitration device is specifically an oxidant injection device. Under the action of oxidant, NO in the exhaust drying section reacts with oxidant to generate NO₂. Is favorable for absorbing the nitrogen oxides. Thereby realizing NO in the denitration process_xAnd (4) emission reduction.

In the invention, the chain grate denitration system also comprises an oxidant generating device, and an oxidant ejector in the air box at the bottom of the air 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 oxidant ejector through a second 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 invention, ozone generated in an ozone generator is firstly introduced into a catalytic reactor, under the action of a catalyst, the ozone and water are degraded into OH (free radicals), and the oxidation of the OH (free radicals) is stronger than that of the ozone. 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 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 invention, a first air blower is added on a pipeline between an air outlet of the annular cooling second section and an air inlet of the preheating first section, so that the second type of hot air of the annular cooling second section can enter the preheating first section in an air blowing mode under the action of the first air blower, and the air pressure entering the preheating first section is positive pressure. Thus, the air pressure in the preheating section is larger than that in the preheating section, and the NOx products in the preheating section are prevented from entering the preheating section through the gaps or holes. Or the second type of hot air forms a stable hot air layer from top to bottom in the preheating section. Thereby achieving the purpose of uniformly heating the upper and lower pellet layers, ensuring the preheating effect of the pellet ore material in the preheating section, and achieving the purposes of uniformly preheating and uniformly oxidizing all parts in the pellet. The preheating effect of the pellet ore materials is ensured.

In the invention, the gas in the preheating section is discharged from the preheating section under the action of the exhaust fan. In the preheating two-section, due to the air draft effect, the air pressure in the preheating two-section is in a negative pressure state, so that the air pressure in the preheating two-section is smaller than that in the preheating one-section on the basis of the negative pressure. Namely, the difference of the gas pressure of the preheating section and the preheating section is increased under the action of the first air blower and the exhaust fan. So that the gas containing NOx products in the preheating section cannot enter the preheating section through the gaps or holes. Therefore, NOx products contained in the exhaust gas in the preheating section meet the national standard, and a denitration device does not need to be additionally arranged.

In the present invention, since the hot roasting wind in the preheating stage comes from the rotary kiln, the hot roasting wind contains a large amount of NOx products. The exhaust fan pumps the gas in the preheating second section out of the preheating second section and then leads the gas into the denitration device, and the invention only needs to independently denitrate the gas discharged from the preheating second section. After the denitration is finished, generating first-class hot air, and introducing the hot air into the air draft drying section to deeply dry the pellet ore material. Or, directly conveying hot air discharged from the preheating second section into the air draft drying section for waste heat utilization, and then performing denitration treatment on the hot air discharged from the air draft drying section.

In the invention, the first type of hot air is discharged out of the air box after drying the mineral aggregate and is introduced into the flue gas purification device. The second type of hot air is discharged out of the air box after preheating the mineral aggregate at low temperature and is introduced into the flue gas purification device. The first type hot air and the second type hot air can be respectively introduced into the flue gas purification device; or can be mixed and then introduced into the flue gas purification device together. The flue gas purification device removes dust from the first type hot air and the second type hot air. So that the discharged gas meets the national environmental protection standard.

In a first embodiment, hot air in a ring cooling section enters the rotary kiln to form the roasting hot air. The hot air at the ring cooling section belongs to the hot air for primary heat exchange of the roasted mineral aggregate, and the temperature of the hot air is high. The air is introduced into the rotary kiln to provide sufficient oxygen for the rotary kiln, and simultaneously, because the temperature of the hot air is high, the fuel consumption of the rotary kiln can be reduced while the sufficient oxygen is maintained.

It should be noted that the combustion of the rotary kiln fuel is used to provide high temperature inside the rotary kiln, so that the pellet ore material is subjected to oxidation reaction and recrystallization in a high temperature state, and the pellet strength is improved.

In the invention, the mineral aggregate is dried and preheated by a chain grate once, roasted by a rotary kiln and cooled by a circular cooler. The mineral aggregate is primarily dried in the forced air drying section of the chain grate. The mineral aggregate is deeply dried in the air draft drying section. The mineral aggregate is preliminarily preheated in the preheating section. The mineral aggregate is preheated at high temperature in the preheating section. And (4) fully roasting the mineral aggregate at high temperature after the mineral aggregate enters the rotary kiln. After roasting is finished, mineral aggregate enters a ring cooling first section, a ring cooling second section and a ring cooling third section to be cooled step by step. Hot air exhausted from the ring cooling section is introduced into the rotary kiln, so that air circulation in the rotary kiln is kept, and the loss of combustion energy is reduced. 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. And the second type of hot air discharged from the annular cooling second section enters the preheating first section in a blowing mode under the action of the first air blower. Because the preheating section is positive pressure under the action of blowing air, and the preheating section is negative pressure under the action of air draft, the air pressure of the preheating section is greater than that of the preheating section. The air pressure in the preheating section can not enter the preheating section through the clearance or the hole between the preheating section and the preheating section, thereby preventing the NOx products in the preheating section from entering the preheating section. The concentration of the NOx product of the gas discharged from the preheating section is lower than the national emission standard, so that the gas discharged from the preheating section is not required to be denitrated. According to the scheme of the invention, through innovation on the process flow, the air pressure entering the preheating section is positive pressure through the first air blower, the air pressure of the preheating section is negative pressure under the action of air draft, so that the air pressure of the preheating section is greater than that of the preheating section, the concentration of NOx products in hot air discharged from the preheating section is lower than the national standard, a denitration device is not required to be additionally connected to the downstream of the preheating section, the investment of an enterprise for reaching the national environmental standard is reduced, and the production cost of the enterprise is reduced. Meanwhile, the replacement and the modification are very convenient.

In the invention, the gas pressure in the preheating section is positive pressure due to the action of the blast air. Meanwhile, the size of the air pressure in the preheating section can be controlled by adjusting the air flow of the preheating section of the air inlet and the air outlet and/or adjusting the pressure head of the fan.

In the invention, a denitration device is arranged on a third conveying pipeline for communicating an air outlet of the preheating two-section with an air inlet of the air draft drying section. The denitration device is used for preheating NO in the two sections_xAnd removing the product in advance. Preventing NO in the preheat two stage_xAnd the product enters an air draft drying section through a third conveying pipeline. Therefore, an additional denitration device is not required to be arranged at the downstream of the air outlet of the air exhaust drying section. The production cost of enterprises is reduced.

In a second embodiment, the function of the suction fan is to introduce and discharge the gas in the preheating section and the suction drying section.

In the second embodiment, a flow regulating valve is also arranged at the downstream of the preheating section of the air outlet. The size of the gas volume discharged from the preheating section of the air outlet can be accurately adjusted through the flow adjusting valve. Under the combined action of the first air blower and the second air blower, the regulation of the air pressure in the preheating section is realized.

In a second embodiment, a flue gas cleaning device is provided for cleaning the gases exiting the suction drying section and the preheating section. After the flue gas is purified, the gas in the air draft drying section and the preheating section reaches the national environmental protection emission standard and is discharged outwards.

In conclusion, the scheme of the invention prevents the NOx products in the preheating section from entering the preheating section by adjusting the technological process of the chain grate-rotary kiln. Preheat one section and need not additionally to increase denitrification facility. The production cost of enterprises is reduced. Meanwhile, the method also enables the upper and lower pellet layers in the preheating section to be uniformly preheated, and improves the product quality.

In the present invention, NO is passed through the air draft drying section_xThe detector, the flow detection device and the flow control valve can monitor NO in hot air in the air draft drying section in real time_xIn order to better control the injection of the oxidizing agent. Thereby accurately controlling NO in the air draft drying section_xThe reaction with the oxidant supplies the oxidant as required, and saves the cost of the oxidant.

Through experimental analysis and engineering application, the fact that ozone is adopted as an oxidant, the reaction speed of the ozone and NO is high at the temperature of 100-200 ℃, and the reaction rate is high, therefore, the ozone is sprayed into the air draft drying section, and the NO in the flue gas generated by the grate can be efficiently removed. The invention is also feasible with other oxidizing agents, the purpose of which is to oxidize NO to NO₂. Preferably, NO can be oxidized to NO at temperatures of 100-₂The oxidizing agent of (2) can be used in the present invention.

The application injects oxidant (preferably ozone) in the air draft drying section, and has the following effects: firstly, oxidizing NO which is insoluble in water in smoke in the air draft drying section into NO₂(or nitrous or nitric acids obtained by further reaction), NO₂(or nitrous acid or nitric acid obtained by further reaction) is easily dissolved in water and can be fully absorbed by alkali liquor; secondly, the temperature of 100-200 ℃ in the air draft drying section is fully utilized, the method is suitable for oxidizing NO by an oxidant, and heating or cooling treatment on the part of smoke is not needed; III,The invention can reasonably spray the amount of the oxidant according to the content of NO in the air draft drying section, and efficiently remove NO in the flue gas in the air draft drying section and the preheating section.

As a preferred scheme, the catalytic reactor is additionally arranged, the catalytic reactor catalyzes ozone and water into OH, the OH is a high-activity free radical, the reaction with NO can be performed higher, the reaction activity is higher, the reaction efficiency and the reaction rate of NO are greatly improved, and the removal of NO in smoke in the air draft drying section is further ensured.

As a preferred scheme, an alkali liquor absorption device is adopted to treat hot air discharged from the air draft drying section, and NO in the discharged hot air is absorbed by using alkali liquor₂Nitrous acid or nitric acid. Using alkaline liquor ratio of water to NO₂The absorption of nitrous acid or nitric acid is more thorough, and the removal effect is better.

The alkali liquor may be one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate, and ammonia water. Hydroxide ions and NO in the lye₂Acid radical ions generated after being dissolved in water are combined to generate acid-base neutralization reaction, so that nitrogen oxides in hot air are absorbed.

Compared with the prior art, the invention has the following beneficial effects:

1. the existing grate-rotary kiln air flow system is changed, hot air in the ring cooling two-stage section is blown into the grate through an air blowing mode to preheat the first section (TPH), and meanwhile, the air temperature in the ring cooling two-stage section can be reduced, so that the air temperature in the ring cooling one-stage section and the air temperature in the ring cooling three-stage section can be improved, and the roasting system is more advanced. Prevent to preheat two-stage Process (PH) high concentration's NOx flue gas and cluster into to improve the preheating temperature of lower floor pellet, thereby can reduce the flue gas volume that needs the denitration, also can suitably reduce the heat that the preheating section provided, the fuel of consumption also can reduce simultaneously, and the quality index of pellet can be promoted.

2. Aiming at the problem that the pellets on the upper layer and the lower layer of the chain grate are not uniformly preheated, the introduced blowing and pumping are combined with a preheated pellet production hot air system, the preheating temperature of the pellets on the lower layer can be increased, the oxidation degree and the strength of the pellets are enhanced, and meanwhile, extra energy consumed by the lower layer of the pellets reaching the required preheating temperature is avoided, so that the aims of reducing energy consumption and improving the overall metallurgical performance of the pellets are finally fulfilled.

3. The scheme of the invention combines the characteristic of high air temperature in the air draft drying section in the actual production process, and innovatively adds the oxidant in the air draft drying section to oxidize NO in the air draft drying section into NO₂Thereby being very easy to be absorbed by the alkali liquor. The method for improving the enterprise already put into production is provided, and the investment is small. But also can lead the emission to reach the national standard.

Drawings

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

FIG. 2 is a schematic diagram of the reaction of ozone as an oxidant in accordance with the present invention;

FIG. 3 is a reaction scheme of OH (radical) as an oxidizing agent according to the present invention;

fig. 4 is a flow chart of a process for producing oxidized pellets by using a grate-rotary kiln system in the prior art.

Reference numerals:

1: a chain grate machine; 2: a rotary kiln; 3: a circular cooler; 4: an oxidant ejector; 5: a dust removal system; 6: an alkali liquor absorption device; 7: an oxidant generating device; 701: an ozone generator; 702: a catalytic reactor; 8: an exhaust fan; 901: a first blower; 902: a second blower; 10: NO_xA detector; 11: a flow detection device; 12: a flow control valve; 13: a chimney; UDD: a forced air drying section; DDD: an air draft drying section; TPH: preheating for one section; pH: a second preheating stage; c1: cooling in a ring for one section; c2: a ring cooling section; c3: ring cooling for three sections;

l1: a first delivery conduit; l2: a second conduit; l3: a third delivery conduit; l4: a fourth delivery conduit; l5: and a fifth delivery conduit.

Detailed Description

According to a first embodiment of the present invention, there is provided a process for the production of oxidized pellets using a grate-rotary kiln system:

a production process for oxidizing pellets by utilizing a chain grate-rotary kiln system, wherein the chain grate-rotary kiln system comprises a chain grate 1, a rotary kiln 2 and a circular cooler 3, wherein: according to the material trend, the chain grate 1 is sequentially divided into an air blowing drying section UDD, an air draft drying section DDD, a preheating section TPH and a preheating section PH; the ring cooling machine 3 is sequentially divided into a ring cooling first section C1, a ring cooling second section C2 and a ring cooling third section C3; the process comprises the following steps:

1) drying, preheating and oxidizing the green pellets by a chain grate 1, then conveying the materials passing through the chain grate 1 to a rotary kiln 2 for roasting, and then conveying the materials to a circular cooler 3 for cooling to obtain pellets;

2) hot air exhausted from the annular cooling first-stage C1 is conveyed to the rotary kiln 2, the hot air exhausted from the rotary kiln 2 is conveyed to the preheating second-stage PH, and the hot air exhausted from the preheating second-stage PH is conveyed to the exhausting and drying section DDD in an exhausting mode;

3) hot air exhausted from the ring cooling section C2 is conveyed to the preheating section TPH in a blowing mode;

4) the hot air discharged from the ring cooling three section C3 is sent to the forced air drying section UDD by means of air blowing.

Preferably, a denitration device is arranged in a bottom wind box of the induced draft drying section DDD, and the denitration device is an oxidant ejector 4.

Preferably, an air outlet of the DDD is connected with the first conveying pipeline L1; the first conveying pipeline L1 is sequentially provided with a dust removal system 5 and an alkali liquor absorption device 6; the hot air in the DDD in the air draft drying section reacts with the oxidant sprayed by the oxidant sprayer 4, and the oxidant oxidizes the nitrogen oxide in the hot air in the DDD in the air draft drying section into NO₂And/or HNO₃(ii) a Then sequentially carrying out dust removal treatment by a dust removal system 5 and denitration treatment by an alkali liquor absorption device 6; wherein the alkali liquor absorption device 6 absorbs NO in the hot air discharged from the DDD of the air draft drying section₂Or HNO₃。

Preferably, the grate-kiln system further comprises an oxidant generation device 7; the oxidant generation device 7 includes: an ozone generator 701; the outlet of the ozone generator 701 is connected to the oxidant ejector 4 through a second pipe L2.

Preferably, the outlet communicates with the inlet of the catalytic reactor 702, and a second conduit L2 connects the outlet of the catalytic reactor 702 and the oxidant ejector 4; an ozone catalyst bed is provided in the catalytic reactor 702.

Preferably, in step 3), the hot air discharged from the loop cooling section C2 is conveyed to the preheating section TPH by blowing to preheat the mineral aggregate at a low temperature, and the pressure in the preheating section TPH is higher than the standard atmospheric pressure.

Preferably, the air pressure in the preheating section of the TPH smoke hood is 0-200Pa, preferably the air pressure in the preheating section of the TPH smoke hood is 10-150Pa, and more preferably the air pressure in the preheating section of the TPH smoke hood is 20-100 Pa.

According to a second embodiment of the present invention, there is provided a grate-rotary kiln system comprising:

a grate-rotary kiln system or a system for use in the production process of the first embodiment, the grate-rotary kiln system comprising a grate 1, a rotary kiln 2, a ring cooler 3, wherein: according to the material trend, the chain grate 1 is sequentially divided into an air blowing drying section UDD, an air draft drying section DDD, a preheating section TPH and a preheating section PH; the ring cooling machine 3 is sequentially divided into a ring cooling first section C1, a ring cooling second section C2 and a ring cooling third section C3; the discharge hole of the chain grate machine 1 is connected with the feed inlet of the rotary kiln 2, and the discharge hole of the rotary kiln 2 is connected with the feed inlet of the circular cooler 3; the method is characterized in that: an air outlet of the annular cooling section C1 is connected with an air inlet of the rotary kiln 2, an air outlet of the rotary kiln 2 is connected with an air inlet of the preheating section PH, and an air outlet of the preheating section PH is connected with an air inlet of the exhausting and drying section DDD through a third conveying pipeline L3; an air outlet of the annular cooling section C2 is connected with an air inlet of the preheating section TPH through a fourth conveying pipeline L4; an air outlet of the annular cooling section C3 is connected with the air blowing drying section UDD through a fifth conveying pipeline L5; an exhaust fan 8 is arranged on the third conveying pipeline L3, a first air blower 901 is arranged on the fourth conveying pipeline L4, and a second air blower 902 is arranged on the fifth conveying pipeline L5.

Preferably, a denitration device is arranged in a bottom wind box of the induced draft drying section DDD, and the denitration device is an oxidant ejector 4.

Preferably, an air outlet of the DDD is connected with the first conveying pipeline L1; the first conveying pipeline L1 is sequentially provided with a dust removal system 5 and an alkali liquor absorption device 6.

Preferably, the grate-kiln system further comprises an oxidant generation device 7; the oxidant generation device 7 includes: an ozone generator 701; the outlet of the ozone generator 701 is connected to the oxidant ejector 4 through a second pipe L2.

Preferably, the oxidant generation device 7 further comprises a catalytic reactor 702; the outlet of the ozone generator 701 communicates with the inlet of the catalytic reactor 702, and a second pipe L2 connects the outlet of the catalytic reactor 702 and the oxidant ejector 4; an ozone catalyst bed is provided in the catalytic reactor 702.

Preferably, the preheating section of TPH is provided with NO therein_xThe flow rate control valve 12 is arranged on the second pipeline L2 of the detector 10 and the flow rate detection device 11.

Preferably, the system further comprises a chimney 13; the exhaust outlets of the updraft drying section DDD and/or the forced draft drying section UDD are connected to a chimney 13.