CN109371231B - Method for pre-desulfurizing and pre-denitrating in pelletizing process of grate-kiln - Google Patents

Method for pre-desulfurizing and pre-denitrating in pelletizing process of grate-kiln Download PDF

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CN109371231B
CN109371231B CN201811567545.5A CN201811567545A CN109371231B CN 109371231 B CN109371231 B CN 109371231B CN 201811567545 A CN201811567545 A CN 201811567545A CN 109371231 B CN109371231 B CN 109371231B
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bentonite
desulfurization
flue gas
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CN109371231A (en
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龙红明
余正伟
春铁军
孟庆民
张中武
任志祥
钱立新
狄瞻霞
魏汝飞
王平
向爱平
王毅璠
罗云飞
章裕东
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Anhui University of Technology AHUT
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/216—Sintering; Agglomerating in rotary furnaces
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/2406—Binding; Briquetting ; Granulating pelletizing

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Abstract

The invention discloses a pelletizing process of a chain grate-rotary kilnA desulfurization and denitrification method, belonging to the field of ferrous metallurgy. According to the invention, the drying I section of the chain grate machine is dried by adopting air draft, the hot air source adopts mixed gas of the preheating I section and the cooling III section of the circular cooler, and the air draft drying II section is still dried by adopting air draft; ca is added in the preparation process of green pellets2+Chelating urea intercalation bentonite, setting a urea injection device on the preheating II section of the chain grate and injecting urea powder, so that the content of NOx and SOx in the flue gas is obviously reduced. Aiming at the conditions that the capacity of a grate-rotary kiln pellet flue gas desulfurization system is generally insufficient and flue gas denitration is not implemented temporarily under the new environmental protection standard, Ca is added in the green pellet preparation process2+Chelating urea intercalation bentonite, spraying urea powder in the preheating second stage of the chain grate, and controlling Ca2+The addition amount of the chelated urea intercalated bentonite and the spraying amount of the urea powder can control the effects of desulfurization and denitrification more flexibly.

Description

Method for pre-desulfurizing and pre-denitrating in pelletizing process of grate-kiln
Technical Field
The invention relates to the technical field of ferrous metallurgy, in particular to a method for pre-desulfurizing and pre-denitrating in a pelletizing process of a chain grate machine-rotary kiln.
Background
The pellet ore is one of iron-containing furnace charges commonly used for blast furnace smelting, and the acidic pellet ore is matched with the high-alkalinity sinter ore and is the main furnace charge structure of the blast furnace of key enterprises in China at present. The grate-rotary kiln method is the mainstream method for producing oxidized pellets in China and plays an important role in the blast furnace charge preparation process.
SO2The sulfur dioxide has a synergistic effect with smoke dust in the atmosphere, when the concentration of the sulfur dioxide in the atmosphere is 0.21ppm, the concentration of the smoke dust is more than 0.3 mg/L, the disease incidence of respiratory diseases can be increased, and the disease condition of chronic patients can be rapidly worsened2The emission concentration of (A) is strictly regulated and must be controlled at 200mg/m3The following.
NO based on nitric oxide and nitrogen dioxidexIs an important cause of photochemical smog and acid rain. The toxic smog formed by the reaction of nitrogen oxides in automobile exhaust and hydrocarbon through ultraviolet irradiation is called photochemical smog. Photochemical smog has a special odor, irritates the eyes, damages plants, and can reduce atmospheric visibility. In addition, nitric acid and nitrous acid generated by the reaction of nitrogen oxides with water in the air are acid rainThe composition of (1). Atmospheric nitrogen oxides are mainly derived from the combustion of fossil fuels and the incineration of plant material, as well as the conversion of nitrogen-containing compounds in farmland soils and animal waste. Meanwhile, nitrogen oxide can stimulate the lung, so that people are difficult to resist respiratory diseases such as cold, and people with respiratory problems, such as asthma patients, can be easily affected by nitrogen dioxide. In children, nitrogen oxides may cause impaired lung development. The limit value of the emission concentration of NOx in the current sintering and pelletizing industry is 300mg/m3。
With the increasing improvement of environmental protection standards, the emission standard of sintered pellet flue gas is in line with the power generation industry, and ultralow emission is gradually realized, SO2The emission concentration is required to be lower than 35mg/m3，NOxThe emission concentration is required to be lower than 50mg/m3And great challenges are brought to the environmental protection work of enterprises. From the domestic desulfurization system of pellet plants, because the design desulfurization capability is insufficient, the desulfurization capability of the currently operated desulfurization system has a certain gap with the ultralow emission requirement, and therefore, part of SO is removed in the production process2Reducing the burden on the terminal desulfurization system becomes particularly important; current NO in domestic pellet millxThe emission concentration of (A) is usually 60 to 280mg/m3No report of denitration of the tail end of pellet smoke is found, but along with the improvement of environmental protection standards, denitration in the pellet production process must be carried out on schedule. NO for pellet flue gasxThe concentration is relatively low, and the pellet flue gas NO is hopefully realized in a certain stage by a process control or emission reduction modexDischarge up to standard, compare the terminal treatment technique that the investment is huge, the high enterprise of working costs, the relevant work of process denitration has very big realistic meaning. The grate-rotary kiln method is used as a mainstream method for producing the oxidized pellet in China, and how to effectively realize the denitration mode in the process is imperative and has great significance.
Through retrieval, the denitration technology of the rotary kiln system of the chain grate machine has patent publications, such as Chinese patent application numbers: 2018104409059, the name of invention creation is: the utility model provides a grate rotary kiln deNOx systems and denitration method, the grate rotary kiln deNOx systems of this application includes the grate that connects gradually, rotary kiln and ring cooling machine, the grate includes the dry section of air blast that connects gradually, the dry section of convulsions, first preheating section and second preheating section, deNOx systems still includes the denitration reactor, the second preheating section has the exhanst gas outlet, the dry section of convulsions has the flue gas entry, the denitration reactor is connected between the exhanst gas outlet of second preheating section and the flue gas entry of the dry section of convulsions, still be connected with reductant injection apparatus between the exhanst gas outlet of denitration reactor and second preheating section. The denitration method of the rotary kiln of the chain grate comprises the following steps: and leading out the flue gas in the second preheating section to the outside of the chain grate, spraying a reducing agent into the flue gas by using a reducing agent spraying device, carrying out denitration treatment on the flue gas by using a denitration reactor, and then conveying the denitrated flue gas to an air draft drying section. This application need not to heat the intensification to the flue gas, can the energy saving, improves denitration efficiency, does not nevertheless relate to desulfurization function, still has the space of further optimization.
Disclosure of Invention
1. Technical problem to be solved by the invention
The invention aims to provide a method for pre-desulfurizing and denitrating in a grate-rotary kiln pelletizing process aiming at the conditions that the grate-rotary kiln pelletizing flue gas desulfurization system under the new environmental protection standard generally has insufficient capacity and flue gas denitration is not implemented temporarily, wherein Ca is added in a green pellet preparation process2+Chelating urea intercalation bentonite, spraying urea powder in the preheating second stage of the chain grate, and controlling Ca2+The addition amount of the chelated urea intercalated bentonite and the spraying amount of the urea powder can control the effects of desulfurization and denitrification more flexibly.
2. Technical scheme
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the invention relates to a method for pre-desulfurizing and denitrating pellets in a grate-rotary kiln, which is characterized in that a drying section I at the front end of a drying section of a grate is dried by air draft, a hot air source adopts mixed gas for preheating the section I and a cooling section III of a circular cooler, and an air draft drying section II at the rear end of the drying section is still dried by air draft; ca is added in the preparation process of green pellets2+Chelating urea intercalation bentonite, arranging a urea injection device on the preheating II section of the chain grate and injecting urea powderFinally, the NOx and SOx content in the flue gas is obviously reduced.
Further, Ca2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 2.5-10 wt.% urea, 2.5-10 wt.% Ca (OH)2And 80-95 wt.% bentonite.
Further, Ca2+The chelate urea intercalated bentonite is powder, and the content of the particle size fraction of the chelate urea intercalated bentonite is less than 0.074mm and is more than or equal to 95 wt.%.
Further, 1.0-4.0 wt.% Ca is added during the preparation of green pellets2+Chelating urea intercalation bentonite.
Further, Ca2+The chelate urea intercalated bentonite is prepared by the following steps:
p1, adding water to slake calcium lime to prepare Ca (OH)2Saturated solution, to which Ca (OH) is added2Urea with equal mass is fully and uniformly stirred;
p2, heating and stirring the mixed solution to evaporate the mixed solution until the reactant is molten;
p3, adding bentonite into the melt, adding water, and stirring uniformly;
p4, standing the mixture at room temperature for a period of time, performing microwave heating treatment to make the mixture agglomerate, and then finely grinding the agglomerated material into powder.
Furthermore, in the step P2, the mixed solution is stirred and heated at constant temperature of 100-120 ℃ for 0.5-3 h.
Further, the bentonite added in the step P3 is Ca (OH) in mass2And 4-19 times of the mass of the urea, adding 5-8 wt.% of water, and uniformly stirring.
Further, in the step P4, the mixture is placed for 10-14h at room temperature, then placed in a microwave heating oven, the temperature is controlled to be 80-100 ℃, the mixture is heated for 0.5-2h, and then the caking material is finely ground until the content of the particle fraction of less than 0.074mm is more than or equal to 95 wt.%.
Furthermore, the desulfurization and denitrification can be controlled respectively, which is as follows:
adding 1.0-4.0 wt.% Ca during the preparation of green pellets2+Chelating urea intercalation bentonite, preheating the II section and not spraying urea powder, wherein the method only realizes the pre-desulfurization of the flue gas;
when the molar weight of the urea powder sprayed in the preheating II section is less than or equal to 1/2 times of the molar weight of NO in the flue gas, Ca is not added in the preparation process of the green pellets2+When chelating urea intercalation bentonite, the method only realizes pre-denitration of the flue gas;
when the molar weight of the urea powder sprayed in the preheating II section is more than 1/2 times of the molar weight of NO in the flue gas, 1.0-4.0 wt.% of Ca is added in the green ball preparation process2+The method simultaneously realizes the pre-desulfurization and denitration of the flue gas and strengthens the pre-desulfurization effect.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:
(1) the method for pre-desulfurizing and pre-denitrating pellets in the pelletizing process of the chain grate-rotary kiln comprises the step of adding Ca in the preparation process of green pellets2+Chelating urea intercalation bentonite, SO that SO generated in the process of preheating and roasting the pellets in the rotary kiln2When the ammonia gas is circulated to the drying section of the chain grate, the ammonia gas reacts with the slow-release ammonia, is solidified and enters the fly ash, SO that SO in the waste gas is obviously reduced2Content (c); secondly, the used urea dry powder can realize SNCR denitration in a preheating II section and excessive NH3The subsequent drying section can play a role in desulfurization, and the problem of ammonia escape is avoided, so that the desulfurization and denitrification are realized in advance in the process.
(2) The invention relates to a method for pre-desulfurizing and pre-denitrating pellets in a grate-rotary kiln pelletizing process, Ca2+The particle size requirement of the chelating urea intercalated bentonite is that the content of-0.074 mm particle size fraction is more than or equal to 95 percent, so that the chelating urea intercalated bentonite is beneficial to being dispersed in pellets to fully play a bonding role on one hand; at the same time, the adverse effect of the decomposable substances on the strength of the pellets after pyrolysis can be minimized.
(3) The invention relates to a method for pre-desulfurizing and pre-denitrating pellets in a grate-rotary kiln pelletizing process, Ca2+The chelate urea intercalation bentonite has 20-50 deg.C higher than common urea decomposition temperature, high thermal stability, and reduced NH content3Release, prolong local area NH3With SO2、H2Reaction of OThe reaction is carried out fully in response time, and the aim of improving the desulfurization efficiency is fulfilled.
(4) According to the method for pre-desulfurizing and denitrating the pellets in the grate-rotary kiln, the temperature range of the preheating section II meets the temperature requirement of selective non-catalytic reduction, and the adverse effect of sprayed substances on the temperature in the furnace can be reduced to the greatest extent by spraying urea powder, so that the influence on the original process is reduced.
(5) The method for pre-desulfurizing and pre-denitrating pellets in the pelletizing process of the grate-rotary kiln of the invention is used for preparing Ca2+Microwave heating is adopted to carry out intercalation on the chelate urea and the bentonite, and Ca is added2+The chelating urea intercalation reaction has obvious promotion effect, the obtained urea with a composite structure has higher decomposition temperature, and the speed of releasing ammonia gas in a certain temperature range is slowed down, so that the aim of improving the desulfurization efficiency is fulfilled.
Drawings
FIG. 1 is a schematic diagram of the method for pre-desulfurization and denitrification in the pelletizing process of the grate-rotary kiln of the present invention.
The reference numerals in the schematic drawings illustrate:
100. a chain grate machine; 110. drying the I section; 120. drying the II section; 130. preheating the I section; 140. preheating a II section; 150. a drying section; 160. a preheating section; 200. a rotary kiln; 210. a roasting section; 220. a soaking section; 300. a circular cooler; 310. cooling the section I; 320. cooling the II section; 330. cooling the section III; 340. and cooling the IV section.
Detailed Description
For a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The present invention will be further described with reference to the following examples.
Example 1
As shown in fig. 1, in the method for pre-desulfurization and denitration in the pellet process of the grate-rotary kiln of the embodiment, the drying I section 110 at the front end of the drying section 150 of the grate 100 is dried by air draft, the hot air source is the mixed gas of the preheating I section 130 and the cooling III section 330 of the circular cooler 300, and the drying II section 120 at the rear end of the drying section 150 is still dried by air draft; and Ca is added in the preparation process of the green pellets2+Chelating urea intercalation bentonite, set up urea grinding, storage, spiral feed and dry powder injection device on preheating II section 140 of the chain grate 100, the injection device sprays urea powder to preheating II section 140, make NOx and SOx content in the flue gas reduce notably.
The grate-rotary kiln pellet production system in the embodiment comprises a grate 100, a rotary kiln 200 and a circular cooler 300 which are connected in sequence, wherein the grate 100 comprises a drying section 150 at the front end and a preheating section 160 at the rear end, the drying section 150 comprises a drying section I110 and a drying section II 120, the preheating section 160 comprises a preheating section I130 and a preheating section II 140, the rotary kiln 200 comprises a roasting section 210 and a soaking section 220, and the circular cooler 300 comprises a cooling section I310, a cooling section II 320, a cooling section III 330 and a cooling section IV 340.
In the method for pre-desulfurization and denitrification in the process of the embodiment, the drying I section 110 is adjusted from the traditional forced air drying to the air draft drying, the mixed gas of the preheating I section 130 and the cooling III section 330 is used as a hot air source, and meanwhile, 1.0-4.0 wt.% of specially-made Ca is added during green ball preparation2+The chelate urea intercalation bentonite replaces the conventional bentonite, urea powder is sprayed in the preheating II section 140 in a matching way, and a desulfurization reaction area A and a denitration reaction area B are respectively formed, so that the desulfurization and denitration can be effectively realized in advance.
Ca of this example2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 2.5-10 wt.% urea, 2.5-10 wt.% Ca (OH)2And 80-95 wt.% bentonite, and Ca2+The chelate urea intercalated bentonite is powdery, the content of the particle size fraction of the chelate urea intercalated bentonite is less than 0.074mm and is more than or equal to 95 wt%, and the chelate urea intercalated bentonite is prepared according to the following steps:
p1, adding water to slake calcium lime to prepare Ca (OH)2Saturated solution, to which Ca (OH) is added2Urea with equal mass is fully and uniformly stirred;
p2, heating and stirring the mixed solution to evaporate the mixed solution until the reactant is molten; specifically, the mixed solution is stirred and heated for 0.5 to 3 hours at the constant temperature of 100-120 ℃;
p3, adding bentonite into the melt, adding water, and stirring uniformly; specifically, the mass of the added bentonite is Ca (OH)24-19 times of the mass of the urea, 5-8 wt.% of water is added, and then the mixture is stirred uniformly;
p4, standing the mixture at room temperature for a period of time, performing microwave heating treatment to enable the mixture to be caked, finely grinding the caked material to be powdery, specifically, standing the mixture at room temperature for 10-14h, then placing the mixture in a microwave heating furnace, controlling the temperature to be 80-100 ℃, heating for 0.5-2h, and finely grinding the caked material until the grain fraction content of the caked material is less than 0.074mm and is more than or equal to 95 wt.%.
The desulfurization and denitrification processes in this embodiment can be controlled separately as follows:
adding 1.0-4.0 wt.% Ca during the preparation of green pellets2+When chelating urea intercalation bentonite and preheating the II section 140 without spraying urea powder, the method only realizes the pre-desulfurization of the flue gas;
when the molar weight of the urea powder sprayed into the preheating II section 140 is less than or equal to 1/2 times of the molar weight of NO in the flue gas, Ca is not added in the preparation process of the green pellets2+When chelating urea intercalation bentonite, the method only realizes pre-denitration of the flue gas;
when the molar weight of the excessive urea powder sprayed into the preheating II section 140 is more than 1/2 times of the molar weight of NO in the flue gas, NO matter whether Ca is added in the green ball preparation process or not2+Chelating urea intercalated bentonite, and the method realizes the pre-desulfurization and denitration of the flue gas at the same time, but simultaneously produces ballsAdding 1.0-4.0 wt.% Ca in the preparation process2+The chelating urea intercalation bentonite, the method effectively strengthens the pre-desulfurization effect.
This example was prepared by adding an amount of Ca during green pellet preparation2+When the chelated urea intercalated bentonite enters the drying I section 110 and the drying II section 120 of the chain grate 100, Ca2+The chelated urea intercalated bentonite starts to slowly release NH3In addition, a large amount of water is evaporated and enters the wind box and the pipeline at the lower part of the chain grate 100 and SO in the hot air2The following reactions occur:
NH3+H2O+SO2＝NH4HSO8
2NH8+H2O+SO2＝(NH4)2SO8
NH3+H2O+SO3＝NH4HSO4
2NH3+H2O+SO3＝(NH4)2SO4
by passing gaseous SO2Conversion to solid NH4HSO4、(NH4)2SO4、NH4HSO3Or (NH)4)2SO3Dust enters the subsequent dust removal process, SO that SO in the waste gas is generated2The content is obviously reduced, and the emission up to the standard is realized. Wherein, Ca2+The chelate urea intercalation bentonite has 20-50 deg.C higher than common urea decomposition temperature, high thermal stability, and reduced NH content3Release, prolong local area NH3With SO2、H2The reaction time of O ensures that the reaction is fully carried out, thereby achieving the purpose of improving the desulfurization efficiency. Ca2+The particle size requirement of the chelating urea intercalated bentonite is that the content of-0.074 mm particle size fraction is more than or equal to 95 percent, so that the chelating urea intercalated bentonite is beneficial to being dispersed in pellets to fully play a bonding role on one hand; at the same time, the adverse effect of the decomposable substances on the strength of the pellets after pyrolysis can be minimized. The urea is pulverized, stored and sprayed to the chain grate 100 to preheat the II section 140, and NH decomposed by heating is used as the urea by utilizing the selective non-catalytic reduction principle3As a reducing agent, at the temperature of 800-950 DEG CIn the range of NOxReduction to N2And the aim of flue gas denitration is fulfilled. The temperature range of the preheating II section 140 is 750-; when the ratio of the urea injection amount to the NOx molar amount is larger than 1/2, on the basis of the denitration of the preheating II section 140, the function of partial desulfurization can be realized when the circulating hot air enters the drying section 150, and the specific principle and the drying section 150 are added with Ca2+The chelating urea intercalation bentonite releases ammonia and is desulfurized the same.
Ca in this example2+When the chelate urea intercalated bentonite is prepared, urea is added into Ca (OH) with equal mass2The prepared saturated solution reacts to form Ca2+Chelating urea, and entering into the interlayer structure of bentonite during subsequent stirring, mixing and curing with excessive bentonite, so as to increase the decomposition temperature of urea by 20-50 deg.C, thereby improving desulfurization efficiency. In this example, the urea and the saturated limewater were mixed and heated at 100-120 deg.C, during which Ca was formed2+The chelate urea has obviously higher stability than common urea, higher decomposition temperature and lower decomposition speed. At the same time, by adding Ca2+Mixing chelated urea and bentonite, adding a certain amount of water for intercalation reaction, allowing dissolved urea molecules to enter into the inter-bentonite structure to form a stable structure, Ca2+Can promote the formation of a stable structure of the chelated urea intercalated bentonite, and two layers of stable water molecules can be formed between the layers. In cooperation, the microwave heating is different from the thermal radiation heating, so that the integral heating characteristic is realized, the heating efficiency is high, and the improvement of the production efficiency of the desulfurizer is facilitated; the existence of the microwave effect can also greatly influence the motion condition of polarized substance molecules, so that the effective collision among the molecules is increased, the chemical reaction speed is inevitably accelerated by the increase of the effective collision, and the frequency of the molecular rotation energy level transition is just in the microwave frequency range. Energy level transition is possible for corresponding molecules to acquire energy, so thatA metastable state exists in a microwave field, molecules in the state are quite active, and the change of molecules, chemical bonds and the like is very easy to occur, which is particularly shown in that the effective collision between the molecules is increased, the breakage of old bonds and the formation of new bonds are relatively easy, and the metastable state is Ca-resistant2+The chelating urea intercalation reaction has obvious promotion effect, the obtained urea with a composite structure has higher decomposition temperature, and the speed of releasing ammonia gas in a certain temperature range is slowed down, so that the aim of improving the desulfurization efficiency is fulfilled.
The method of this example was carried out by adding Ca during green pellet preparation2+Chelating urea intercalation bentonite, SO that SO generated in the preheating roasting process of the pellets of the rotary kiln 2002When the ammonia gas is circulated to the drying section 150 of the chain grate 100, the ammonia gas reacts with the slow-release ammonia, is solidified and enters the fly ash, SO that SO in the waste gas is obviously reduced2Content (c); secondly, the used urea dry powder can realize SNCR denitration in a preheating II section and excessive NH3The subsequent drying section 150 can play a role in desulfurization, and the problem of ammonia escape is avoided, so that desulfurization and denitrification are realized in advance in the process.
Example 2
The method for pre-desulfurization and denitrification in the pelletizing process of the grate-rotary kiln of this embodiment is basically the same as the above embodiment except that Ca is used in this embodiment2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 2.5 wt.% urea, 2.5 wt.% Ca (OH)2And 95 wt.% bentonite when prepared:
p2, stirring and heating the mixed solution at a constant temperature of 100 ℃ for 3 hours;
p3, adding bentonite Ca (OH) into the melt2And 19 times of the mass of the urea, adding 8 wt.% of water, and uniformly stirring;
p4, placing the mixture at room temperature for 10h, then placing the mixture in a microwave heating furnace, controlling the temperature at 80 ℃, heating for 2h, and then finely grinding the caking material until the content of the particle fraction smaller than 0.074mm is more than or equal to 95 wt.%.
When in use, 1.0 wt.% Ca is added in the preparation process of green pellets2+Chelating urea intercalation bentonite.
Example 3
The method for pre-desulfurization and denitrification in the pelletizing process of the grate-rotary kiln of this embodiment is basically the same as the above embodiment except that Ca is used in this embodiment2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 10 wt.% urea, 10 wt.% Ca (OH)2And 80 wt.% bentonite when prepared:
p2, stirring and heating the mixed solution at a constant temperature of 120 ℃ for 0.5 h;
p3, adding bentonite Ca (OH) into the melt24 times of the mass of the urea, adding 5 wt.% of water, and uniformly stirring;
p4, placing the mixture at room temperature for 14h, then placing the mixture in a microwave heating furnace, controlling the temperature at 100 ℃, heating for 0.5h, and then finely grinding the caking material until the content of the particle fraction smaller than 0.074mm is more than or equal to 95 wt.%.
When in use, 4.0 wt.% Ca is added in the preparation process of green pellets2+Chelating urea intercalation bentonite.
Example 4
The method for pre-desulfurization and denitrification in the pelletizing process of the grate-rotary kiln of this embodiment is basically the same as the above embodiment except that Ca is used in this embodiment2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 5 wt.% urea, 5 wt.% Ca (OH)2And 90 wt.% bentonite when prepared:
p2, stirring and heating the mixed solution at a constant temperature of 110 ℃ for 2 hours;
p3, adding bentonite Ca (OH) into the melt29 times of the mass sum of the urea, adding 6 wt.% of water, and uniformly stirring;
p4, placing the mixture at room temperature for 12h, then placing the mixture in a microwave heating furnace, controlling the temperature at 90 ℃, heating for 1h, and then finely grinding the caking material until the content of the particle fraction of less than 0.074mm is more than or equal to 95 wt.%.
When in use, the green ball is prepared2.5 wt.% Ca was added2+Chelating urea intercalation bentonite.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims (7)

1. The method for pre-desulfurizing and pre-denitrating in the pelletizing process of the grate-rotary kiln is characterized by comprising the following steps of: the drying I section (110) at the front end of the drying section (150) of the chain grate machine (100) is dried by adopting air draft, the hot air source adopts mixed gas for preheating the I section (130) and the cooling III section (330) of the circular cooler (300), and the air draft drying II section (120) at the rear end of the drying section (150) is still dried by adopting air draft; ca is added in the preparation process of green pellets2+Chelating urea intercalation bentonite, arranging a urea injection device on a preheating II section (140) of a chain grate (100) and injecting urea powder, so that the content of NOx and SOx in the flue gas is obviously reduced;
Ca2+the chelate urea intercalated bentonite is prepared by the following steps:
p1, adding water to slake calcium lime to prepare Ca (OH)2Saturated solution, to which Ca (OH) is added2Urea with equal mass is fully and uniformly stirred;
p2, stirring the mixed solution at constant temperature of 100-120 ℃, heating and stirring to evaporate the mixed solution until the reactants are molten;
p3, adding bentonite into the melt, adding water, and stirring uniformly;
p4, standing the mixture at room temperature for a period of time, performing microwave heating treatment to make the mixture agglomerate, and then finely grinding the agglomerated material into powder.
2. The method for pre-desulfurization and denitrification in the pelletizing process of the chain grate-rotary kiln as claimed in claim 1, wherein the method comprises the following steps: ca2+The chelate urea intercalated bentonite comprises the following components in percentage by mass: 2.5-10 wt.% urea, 2.5-10 wt.% Ca (OH)2And 80-95 wt.% bentonite.
3. The method for pre-desulfurization and denitrification in the pelletizing process of the chain grate-rotary kiln as claimed in claim 1, wherein the method comprises the following steps: ca2+The chelate urea intercalated bentonite is powder, and the content of the particle size fraction of the chelate urea intercalated bentonite is less than 0.074mm and is more than or equal to 95 wt.%.
4. The method for pre-desulfurization and denitrification in the pelletizing process of the chain grate-rotary kiln as claimed in claim 1, wherein the method comprises the following steps: adding 1.0-4.0 wt.% Ca in the preparation process of green pellets2+Chelating urea intercalation bentonite.
5. The method for pre-desulfurization and denitrification in the pelletizing process of the chain grate-rotary kiln as claimed in claim 1, wherein the method comprises the following steps: the mass of the bentonite added in the step P3 is Ca (OH)2And 4-19 times of the mass of the urea, adding 5-8 wt.% of water, and uniformly stirring.
6. The method for pre-desulfurization and denitrification in the pelletizing process of the chain grate-rotary kiln as claimed in claim 1, wherein the method comprises the following steps: and step P4, placing the mixture at room temperature for 10-14h, then placing the mixture in a microwave heating furnace, controlling the temperature at 80-100 ℃, heating for 0.5-2h, and then finely grinding the caking material until the content of the particle fraction smaller than 0.074mm is more than or equal to 95 wt.%.
7. The method for pre-desulfurization and denitrification in the pelletizing process of the grate-kiln as recited in any one of claims 1 to 6, wherein: the desulfurization and denitrification can be respectively controlled, and the method specifically comprises the following steps:
adding 1.0-4.0 wt.% Ca during the preparation of green pellets2+When chelating urea intercalation bentonite and preheating the II section (140) without spraying urea powder, the method only realizes the pre-desulfurization of the flue gas;
when the molar weight of the urea powder sprayed into the preheating II section (140) is less than or equal to 1/2 times of the molar weight of NO in the flue gas, the flue gas is generatedNo Ca is added during the preparation of the balls2+When chelating urea intercalation bentonite, the method only realizes pre-denitration of the flue gas;
when the molar weight of the urea powder sprayed into the preheating II section (140) is more than 1/2 times of the molar weight of NO in the flue gas, 1.0-4.0 wt.% Ca is added in the green ball preparation process2+The method simultaneously realizes the pre-desulfurization and denitration of the flue gas and strengthens the pre-desulfurization effect.
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