Process for calcining high-activity calcium oxide in double-chamber kiln

Abstract

The invention relates to the technical field of chemical engineering, and particularly discloses a process for calcining high-activity calcium oxide in a double-hearth kiln. The process comprises the following steps: S1, pretreatment of raw materials: performing crushing, screening and washing pretreatment on limestone raw materials; s2, fuel adaptation, wherein blast furnace gas and coke oven gas mixed fuel is adopted; s3, carrying out partitioned calcination in a double-hearth kiln; s4, calcination control, wherein fuel and combustion-supporting air are introduced into the high-temperature decomposition area; s5, waste heat cascade recovery: introducing flue gas in a high-temperature decomposition area into a raw material preheater, and recovering heat energy from waste gas in a low-temperature cooling area through a third-stage heat exchanger; and S6, gas purification, wherein the kiln tail flue gas is subjected to the following purification processes in sequence. According to the method, the effects of improving the activity of calcium oxide and increasing the conversion efficiency of calcium are achieved by combining the partitioned temperature control of the double-hearth kiln and the calcination control that the CO2 concentration is smaller than or equal to 25 vol% and cooperatively optimizing the heat transfer efficiency, inhibiting the regeneration reverse reaction of calcium carbonate and avoiding the formation of an MgO-CaO solid solution.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of chemical industry, in particular to a high-activity calcium oxide calcination process by using a double-chamber kiln. BACKGROUND

[0002] Chemical technology is a comprehensive application discipline that studies the technology and methods used in the production process of chemical industry. It is theoretically supported by basic disciplines such as chemistry, physics and mathematics, combined with engineering practice, and is committed to realizing efficient, safe and environmentally friendly conversion from raw materials to chemical products. Its core content covers chemical reaction engineering, chemical unit operation, chemical process design and optimization, chemical materials and equipment, and also emphasizes the development of green chemical technology, and is widely used in petroleum chemical industry, fine chemical industry, biological medicine and new energy fields. The preparation of calcium oxide is an important part of the chemical industry.

[0003] The related preparation of calcium oxide adopts a single-chamber kiln structure for calcining raw materials. However, the single-chamber kiln cannot control the temperature in different zones, the calcination temperature fluctuates greatly, the local over-fired zone is coarsened, the under-fired zone is not completely decomposed, and the CO2 concentration in the kiln is high, which leads to high residual calcium carbonate content in the product, thereby resulting in low activity of calcium oxide and high energy consumption per ton of product. SUMMARY

[0004] In order to solve the problems of low activity of calcium oxide and high energy consumption per ton of product caused by the related preparation of calcium oxide using a single-chamber kiln structure for calcining raw materials, the application provides a high-activity calcium oxide calcination process by using a double-chamber kiln.

[0005] The application provides a high-activity calcium oxide calcination process by using a double-chamber kiln, which adopts the following technical scheme:

[0006] A high-activity calcium oxide calcination process by using a double-chamber kiln includes the following steps:

[0007] S1, raw material pretreatment: the limestone raw material is pretreated by crushing, screening and washing, the particle size after crushing and screening is controlled to be 30-120 mm, and the MgO content is ≤2%;

[0008] S2, fuel adaptation: using mixed fuel of blast furnace gas and coke oven gas;

[0009] S3, double-chamber kiln zoned calcination: using a parallel flow regenerative double-chamber kiln structure, the temperature of the high-temperature decomposition zone is controlled to be 1050±25℃, and the temperature of the low-temperature cooling zone is ≤300℃;

[0010] S4, calcination control: introducing fuel and combustion air into the high-temperature decomposition zone, controlling the CO2 concentration in the kiln to be ≤25 vol%, and controlling the residence time of the material to be 8-10 h;

[0011] S5, waste heat cascade recovery: the high-temperature decomposition zone flue gas is introduced into the raw material preheater, and the low-temperature cooling zone exhaust gas is recovered through three-stage heat exchanger;

[0012] S6, gas purification: the kiln tail flue gas successively passes through the following purification processes:

[0013] S601. Bag dust removal: the flue gas passes through the coated filter bag and captures the suspended particulate matter with particle size ≥1 μm in the flue gas, wherein the filtration wind speed is ≤0.8 m / min;

[0014] S602. SCR denitration: the flue gas treated in S601 is introduced into the denitration reactor;

[0015] S603. Sodium-based double-alkali desulfurization: the flue gas treated in S602 is introduced into the desulfurization tower, and the sodium alkali solution in the desulfurization tower is in countercurrent contact with the flue gas, and then the solution flows to the regeneration tank for recycling.

[0016] By adopting the above technical scheme, since the limestone raw material with a particle size of 30-120 mm is adopted, the size range ensures that the material has good heat transfer efficiency in the kiln, and prevents dust escape caused by too small particle size; at the same time, the MgO content in the limestone is not more than 2%, which can avoid the formation of low-activity solid solution of MgO and CaO in the high-temperature calcination process, thereby reducing the accumulation of impurities in the calcination process; and the temperature control in S3 is adopted, wherein the high-temperature decomposition zone is maintained at 1050±25℃, the temperature range has high CaCO3 decomposition efficiency, thereby realizing efficient conversion of CaCO3 to CaO, and the low-temperature cooling zone is controlled at a temperature not higher than 300℃, avoiding overcooling to cause product pulverization;

[0017] In S4, the mixed fuel of stable calorific value blast furnace gas and coke oven gas is introduced, wherein the low calorific value of the blast furnace gas is 3000-3500kcal / Nm 3 , and the low calorific value of the coke oven gas is 4200-4500kcal / Nm 3The complementary mixture of the two fuels ensures high combustion efficiency; at the same time, the CO2 concentration in the kiln is controlled to be no more than 25 vol%, which is below the critical point of the CaCO3 decomposition equilibrium curve, and can inhibit the regeneration reaction of CaCO3; and the material residence time is set to 8-10 h, which covers the minimum value of the reaction time required for complete decomposition of CaCO3 and the upper limit of the safety margin of the double-chamber kiln; in S5, the high-temperature flue gas is used for preheating the raw materials, so that the limestone temperature entering the kiln is increased to above 200 DEG C, thereby reducing the calcination energy consumption; and in S6, first, dust removal treatment is performed by a membrane filter bag with a filtering air speed controlled below 0.8 m / min, which can capture suspended particulate matter with a particle size of 1 μm or more; then, in the SCR denitration device, the ammonia reducing agent reacts with the nitrogen oxides in the flue gas on the surface of the vanadium-titanium catalyst to form N2 and H2O, realizing efficient removal of nitrogen oxides and providing a low-nitrogen-oxide gas environment for the subsequent desulfurization process; finally, in the desulfurization tower, the NaOH component in the sodium alkali solution reacts with SO2 to generate Na2SO3 through acid neutralization, so that the calcium conversion efficiency of the active calcium oxide product is high, the calcium oxide content is high, and the comprehensive energy consumption per ton of product is reduced.

[0018] Preferably, in step S1, the raw materials are washed by high-pressure water flow, and the washing water pressure is ≥0.5 MPa.

[0019] By adopting the above technical scheme, since the limestone raw materials are washed by high-pressure water flow, in the washing process, the high-pressure water flow can effectively strip the clay minerals and carbonate gangue attached to the surface of the limestone, and at the same time, the high-pressure water flow preferentially separates the magnesium-containing impurities with lower hardness, which makes the MgO content of the limestone raw materials after washing controlled to ≤2%, thereby avoiding the formation of CaO·MgO solid solution between MgO and CaO in the subsequent calcination process, which reduces the active sites of the raw materials; thus, the CaCO3 content of the calcined raw materials is increased, and the reaction activation energy of the high-temperature decomposition zone is reduced.

[0020] Preferably, in step S2, the oxygen concentration of the mixed fuel is ≥23 vol%.

[0021] By adopting the above technical scheme, since the oxygen concentration of the mixed fuel is controlled to be no less than 23 vol%, in the combustion process of the high-temperature decomposition zone of the double-chamber kiln, oxygen as a gasification medium participates in the chain reaction of hydrocarbons, and when the oxygen concentration is ≥23 vol%, the CO component contained in the blast furnace gas can be completely oxidized to CO2, and the 55-60 vol% H2 component in the coke oven gas can efficiently release heat by following the reaction process of 2H2+O2=2H2O; this lower limit of oxygen concentration ensures that the fuel is fully combusted in an environment of 1050±25 DEG C, avoiding the loss of unburned CO due to lack of oxygen, thus reducing the temperature field uniformity deviation of the high-temperature decomposition zone and the fuel consumption per ton of product.

[0022] Preferably, the blast furnace gas and the coke oven gas in step S2 are mixed at a volume ratio of (2.5-3.5):1.

[0023] By adopting the above technical scheme, since the volume ratio of the blast furnace gas and the coke oven gas is controlled to be (2.5-3.5):1, the calorific value of the blast furnace gas ranges from 3000 to 3500 kcal / Nm 3 , and the calorific value of the coke oven gas ranges from 4200 to 4500 kcal / Nm 3 ; when the mixing ratio is maintained at 2.5-3.5:1, the two gases form a self-sustaining combustion chain, and the comprehensive calorific value of the mixed fuel is stabilized at 3700-3900 kcal / Nm 3 , and the actual kiln temperature is adjusted to the process target value through the ratio of the combustion-supporting air, thereby meeting the constant-temperature combustion requirement of 1050±25℃ in the high-temperature decomposition zone of the double-chamber kiln; therefore, the effect of improving the uniformity of the heat flux distribution in the high-temperature decomposition zone and saving fuel is achieved.

[0024] Preferably, in step S3, the kiln wall of the high-temperature decomposition zone is made of corundum-silicon carbide composite refractory material, and the content of Al2O3 is ≥85%.

[0025] By adopting the above technical scheme, since the corundum-silicon carbide composite material is used to construct the kiln wall of the high-temperature decomposition zone, in the continuous high-temperature environment of 1050±25℃, the corundum phase in the material forms a dense corundum-mullite crystal framework to maintain the high-temperature volume stability, and the silicon carbide component is dispersed in the corundum matrix in the form of particles and generates a SiO2 film through oxidation, which forms a eutectic protective layer with the corundum matrix to improve the refractory material load softening temperature and resist the structural stress damage caused by the temperature fluctuation in the kiln; since the high-purity corundum phase reduces the content of impurities such as Fe2O3 in the kiln wall, the speed of the fayalite generated by the eutectic and CaO is slowed down; therefore, the effects of reducing the heat loss rate of the kiln wall and prolonging the continuous operation period of the high-temperature zone are achieved.

[0026] Preferably, in step S5, the three-stage heat exchanger comprises: a steam generator for generating 0.8MPa saturated steam and feeding the steam into the raw material; an air preheater for heating the combustion-supporting air to ≥150℃; and a hot water heat exchanger for heating the washing water used in step S1.

[0027] By adopting the technical scheme, the low-temperature cooling zone waste gas is recovered in stages by using the three-stage heat exchanger, the steam generator generates saturated steam by using the waste gas for heating, the steam is introduced into the raw material crushing device to assist driving the stone crushing equipment, so as to reduce power consumption; then the waste gas enters the air preheater to heat the combustion-supporting air, thereby shortening the ignition time of the fuel; then the waste gas enters the hot water heat exchanger to heat the washing water to 80±5℃, the temperature range is determined according to the solubility curve of clay minerals on the surface of limestone, the increase of the water temperature increases the removal rate of MgO impurities by the hydrocyclone, and therefore, the effect of reducing the comprehensive energy consumption per ton of product is achieved.

[0028] Preferably, the combustion-supporting air in step S4 adopts a staged air supply design, the amount of primary air accounts for 30-40% of the total air volume, and the swirl angle of secondary air is 15-25°.

[0029] By adopting the technical scheme, the staged air supply design is implemented, the primary air is introduced into the central area of the burner in the form of axial laminar flow to provide the reference oxygen amount required for initial oxidation of the fuel, and to ensure that the CH4 component in the coke oven gas completes the cracking reaction within 0.5 meters from the outlet of the burner; the secondary air is sprayed into the kiln through the swirl vanes at a tangential angle of 15-25°, and the swirl strength forms a centrifugal flow field with a negative pressure gradient of-80 to-50 Pa in the kiln, so that the flame length of the high-temperature decomposition zone is extended to fully cover the fuel, and the two work together to position the fuel combustion position in the middle of the kiln body, avoiding the local overheating at the kiln tail or the under-burning at the kiln head caused by single-stage air supply; therefore, the effects of improving the combustion efficiency of the high-temperature decomposition zone and reducing the fuel consumption per ton of product are achieved.

[0030] Preferably, the sodium alkali solution in step S603 is an 8-10wt% sodium carbonate solution.

[0031] By adopting the technical scheme, since the 8-10wt% sodium carbonate solution is used as the desulfurization medium in the desulfurization tower, the ions generated by the ionization of SO2 in the flue gas and sodium carbonate in the aqueous solution react as follows: 2HCO3 - +SO3=SO3 2- +H2O+2CO2↑; when the solution concentration is lower than 8wt%, the concentration of HCO3 - ions is insufficient, the reaction rate decreases; when the concentration is higher than 10wt%, the solution is supersaturated, which causes Na2CO3 to crystallize and waste; therefore, the effect of improving the flue gas desulfurization efficiency is achieved.

[0032] Preferably, the regeneration tank uses 10-12wt% lime milk.

[0033] By adopting the technical scheme, since the concentration of lime milk in the regeneration tank is controlled to be 10-12wt%, the Ca(OH)2 component in the lime milk reacts with the sodium sulfite discharged from the desulfurization tower: Na2SO3+Ca(OH)2=2NaOH+CaSO3↓, and in the 10-12wt% concentration range, the corresponding pH value range of the lime milk is 12.5-12.8, which can inhibit the side reaction, that is, inhibit the oxidation of sodium sulfite and prevent the co-precipitation of magnesium hydroxide; therefore, the recycling effect of the sulfur components in the flue gas is achieved.

[0034] Preferably, in the step S4, the negative pressure in the kiln is controlled to be-100 to-50Pa by adjusting the frequency of the flue gas exhaust fan, and the CO2 concentration is maintained to be≤25vol%.

[0035] By adopting the technical scheme, since the negative pressure in the kiln is controlled to be-100 to-50Pa by adjusting the rotating speed of the flue gas exhaust fan, when the absolute value of the negative pressure is lower than 50Pa, the gas residence time in the kiln is prolonged, which leads to the increase of the local CO2 concentration, and then triggers the reverse reaction of calcium carbonate regeneration, which leads to the increase of the loss rate of the active sites of calcium oxide, and then leads to the decrease of the activity of calcium oxide; when the absolute value of the negative pressure exceeds 100Pa, the air leakage rate at the kiln head is increased, and the excess cold air enters to dilute the oxygen concentration, which leads to the decrease of the burnout rate of the blast furnace gas; therefore, the effects of the increase of the free calcium content of the active calcium oxide and the decrease of the residual calcium carbonate per ton of product are achieved.

[0036] In summary, the present application has the following beneficial effects:

[0037] 1. Since the present application adopts the limestone raw material with a particle size of 30-120mm and an MgO content≤2%, and combines the temperature control in different zones of the double-chamber kiln and the calcination control with a CO2 concentration≤25vol%, the heat transfer efficiency is optimized, the reverse reaction of calcium carbonate regeneration is inhibited, and the formation of MgO-CaO solid solution is avoided, so that the effects of the increase of the activity of calcium oxide and the increase of the calcium conversion efficiency are achieved.

[0038] 2. In the present application, the blast furnace gas and the coke oven gas are mixed at a ratio of 2.5-3.5:1, and the staged air supply is used, so that the flame temperature field is stabilized and the fuel burnout rate is improved, and the energy-saving effect of the decrease of the comprehensive energy consumption per ton of product is achieved.

[0039] 3. The method of the present application integrates the sodium-based double-alkali desulfurization and the three-stage waste heat gradient recovery, so that the SO2 emission concentration is reduced and the high waste heat utilization rate is achieved, and therefore the effects of low emission and energy efficient utilization in line with the industrial environmental protection requirements are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A flow chart of a double-chamber kiln calcination high-activity calcium oxide process is provided in the present application. DETAILED DESCRIPTION

[0041] The application is further described in detail below in combination with the drawings and examples.

[0042] Technical ideas:

[0043] The related calcium oxide preparation adopts a single-kiln structure for calcining raw materials, but the single-kiln cannot control temperature in different zones, the calcination temperature fluctuates greatly, the grains in the local over-burning zone are coarsened, and the decomposition in the under-burning zone is incomplete, and the CO2 concentration in the kiln is high, resulting in high residual calcium carbonate content in the product, thereby resulting in low activity of calcium oxide and high energy consumption per ton of product.

[0044] Referring to the accompanying Figure 1 The application adopts limestone raw materials with a particle size of 30-120 mm and an MgO content of ≤2%, combines the temperature control in different zones of a double-kiln and the calcination control with a CO2 concentration of ≤25 vol%, and obtains the effects of increasing the activity of calcium oxide and the calcium conversion efficiency by synergistically optimizing the heat transfer efficiency, inhibiting the reverse reaction of calcium carbonate regeneration, and avoiding the formation of MgO-CaO solid solution.

[0045] Example 1

[0046] The present embodiment provides a double-kiln calcination process for high-activity calcium oxide, comprising the following steps:

[0047] S1, raw material pretreatment: the limestone raw material is pretreated by crushing, screening and washing, the particle size after crushing and screening is controlled to be 30 mm, and the MgO content is 0.5%;

[0048] S2, fuel adaptation: a mixed fuel of blast furnace gas and coke oven gas is used, the volume ratio is 2.5:1, and the oxygen concentration is 23 vol%;

[0049] S3, double-kiln zone calcination: a parallel-flow regenerative double-kiln structure is used, the temperature in the high-temperature decomposition zone is controlled to be 1025℃, the kiln wall uses corundum-silicon carbide composite refractory material with an Al2O3 content of 85%, and the temperature in the low-temperature cooling zone is 295℃;

[0050] S4, calcination control: fuel and combustion air are introduced into the high-temperature decomposition zone, the primary air accounts for 30% of the total air, the secondary air swirl angle is 15°, the CO2 concentration in the kiln is controlled to be 22 vol%, and the material residence time is 8h; the kiln negative pressure is controlled to be -100Pa by adjusting the frequency of the exhaust gas fan;

[0051] S5, waste heat cascade recovery: the flue gas in the high-temperature decomposition zone is introduced into the raw material preheater, and the waste gas in the low-temperature cooling zone is heat-exchanged by three-stage heat exchangers to recover heat energy: 0.8MPa saturated steam generated by the steam generator is introduced into the raw material crushing system, the combustion air is heated to 150℃ by the air preheater, and the washing water used in S1 is heated to 80℃ by the hot water heat exchanger;

[0052] S6, gas purification: kiln tail gas in turn through the following purification process:

[0053] S601. bag filter: flue gas through the film filter bag, and capture the particle size of the flue gas ≥1 μm, wherein the filter wind speed 0.75 m / min;

[0054] S602. SCR denitration: the flue gas after S601 treatment into the denitration reactor, catalyst layer space velocity 4800 h-1;

[0055] S603. sodium-based double alkali desulfurization: the flue gas after S602 treatment into the desulfurization tower, 8wt% sodium carbonate solution in the desulfurization tower and flue gas countercurrent contact, liquid gas ratio 5.5 L / m 3 , then the solution flows to the regeneration pool using 10wt% lime milk for recycling.

[0056] Example 2

[0057] This embodiment provides a kind of double chamber kiln calcination high activity calcium oxide process, comprising the following steps:

[0058] S1, raw material pretreatment: limestone raw material is pretreated by crushing, screening and washing, control the particle size of 75 mm after crushing and screening, and MgO content 1.0%;

[0059] S2, fuel adaptation: using blast furnace gas and coke oven gas mixed fuel, volume ratio 3.0:1, oxygen concentration 25vol%;

[0060] S3, double chamber kiln partition calcination: using parallel flow regenerative double chamber kiln structure, high temperature decomposition zone temperature control is 1050 DEG C, kiln wall uses Al2O3 content 89% corundum-silicon carbide composite refractory material, low temperature cooling zone temperature 280 DEG C;

[0061] S4, calcination control: in high temperature decomposition zone, fuel and combustion air are introduced, primary air volume accounts for 35% of total air volume, secondary air swirl angle 20 DEG, control kiln CO2 concentration 24vol%, material residence time is 9h; by adjusting the frequency of exhaust fan to control the negative pressure in kiln is-75Pa;

[0062] S5, waste heat cascade recovery: high temperature decomposition zone flue gas is introduced into raw material preheater, low temperature cooling zone waste gas is recycled by three-stage heat exchanger: 0.8 MPa saturated steam is generated in steam generator and introduced into raw material crushing system, combustion air is heated to 170 DEG C by air preheater, and washing water used in S1 is heated to 85 DEG C by hot water heat exchanger;

[0063] S6, gas purification: kiln tail gas in turn through the following purification process:

[0064] S601. Bag filter: flue gas passes through the membrane filter bag, and the suspended particulate matter with a particle size of ≥1 μm in the flue gas is captured, wherein the filtration wind speed is 0.65 m / min;

[0065] S602. SCR denitration: the flue gas treated in S601 is introduced into a denitration reactor, and the catalyst layer space velocity is 4500 h-1;

[0066] S603. Sodium-based double-alkali desulfurization: the flue gas treated in S602 is introduced into a desulfurization tower, and 9wt% sodium carbonate solution in the desulfurization tower is contacted with the flue gas in countercurrent, and the liquid-gas ratio is 6.0 L / m 3 , and then the solution flows to a regeneration tank for recycling by using 11wt% lime milk.

[0067] Example 3

[0068] The present embodiment provides a process for calcining high-activity calcium oxide in a double-chamber kiln, comprising the following steps:

[0069] S1, raw material pretreatment: the limestone raw material is pretreated by crushing, screening and washing, the particle size after crushing and screening is controlled to be 120 mm, and the MgO content is 2.0%;

[0070] S2, fuel adaptation: mixed fuel of blast furnace gas and coke oven gas is used, the volume ratio is 3.5:1, and the oxygen concentration is 28vol%;

[0071] S3, partition calcination in double-chamber kiln: a parallel flow regenerative double-chamber kiln structure is used, the temperature in the high-temperature decomposition zone is controlled to be 1075℃, the kiln wall uses corundum-silicon carbide composite refractory material with Al2O3 content of 92%, and the temperature in the low-temperature cooling zone is 250℃;

[0072] S4, calcination control: fuel and combustion air are introduced into the high-temperature decomposition zone, the primary air accounts for 40% of the total air, the secondary air swirl angle is 25°, the CO2 concentration in the kiln is controlled to be 25vol%, and the material residence time is 10h; the kiln negative pressure is controlled to be-50Pa by adjusting the frequency of the exhaust fan;

[0073] S5, cascade recovery of waste heat: the flue gas in the high-temperature decomposition zone is introduced into a raw material preheater, and the waste gas in the low-temperature cooling zone is recovered by a three-stage heat exchanger: 0.8MPa saturated steam generated by a steam generator is introduced into a raw material crushing system, an air preheater heats the combustion air to 190℃, and a hot water heat exchanger heats the washing water used in S1 to 90℃;

[0074] S6, gas purification: the kiln tail flue gas sequentially passes through the following purification processes:

[0075] S601. Bag filter: flue gas passes through the membrane filter bag, and the suspended particulate matter with a particle size of ≥1 μm in the flue gas is captured, wherein the filtration wind speed is 0.65 m / min;

[0076] S602. SCR De-NOx: The flue gas treated in S601 was introduced into a De-NOx reactor, and the catalyst layer space velocity was 5000 h-1;

[0077] S603. Na-based double-alkali desulfurization: The flue gas treated in S602 was introduced into a desulfurization tower, and 10wt% sodium carbonate solution in the desulfurization tower was contacted with the flue gas countercurrently, with a liquid-gas ratio of 6.5 L / m 3 , and then the solution flowed into a regeneration tank for recycling using 12wt% lime milk.

[0078] Comparative Example 1

[0079] This comparative example was compared with Example 1, and only the following change was made in step S1: the particle size after crushing and screening was controlled to be 25 mm, and the remaining step contents were the same as those of Example 1.

[0080] Comparative Example 2

[0081] This comparative example was compared with Example 1, and only the following change was made in step S1: the MgO content was controlled to be 3.0%, and the remaining step contents were the same as those of Example 1.

[0082] Comparative Example 3

[0083] This comparative example was compared with Example 1, and only the following change was made in step S2: the volume ratio of blast furnace gas to coke oven gas was 2.0:1, and the remaining step contents were the same as those of Example 1.

[0084] Comparative Example 4

[0085] This comparative example was compared with Example 1, and only the following change was made in step S3: the temperature in the high-temperature decomposition zone was controlled to be 1000°C, and the remaining step contents were the same as those of Example 1.

[0086] Comparative Example 5

[0087] This comparative example was compared with Example 1, and only the following change was made in step S4: the negative pressure in the kiln was controlled to be -40 Pa by adjusting the frequency of the exhaust fan, and the remaining step contents were the same as those of Example 1.

[0088] Comparative Example 6

[0089] This comparative example was compared with Example 1, and only the following change was made in step S603: the concentration of the sodium carbonate solution in the desulfurization tower was 7wt%, and the remaining step contents were the same as those of Example 1.

[0090] The results of the key performance test of Examples 1-3 and Comparative Examples 1-8 are shown in Table 1.

[0091] Table 1:

[0092]

[0093]

[0094] 1. Test standard of calcium oxide activity (mL): GB / T 5762-2012 "Determination of lime activity";

[0095] 2. Test standard of SO2 emission concentration (mg / Nm3): HJ 57-2017 "Determination of sulfur dioxide in waste gas from stationary sources by constant-potential electrolysis method"; 3

[0096] 3. Test standard of comprehensive energy consumption per ton of product (kgce): GB / T 2589-2020 "General rules for calculation of comprehensive energy consumption";

[0097] 4. Test standard of calcium conversion efficiency (%): YB / T 042-2014 "Chemical analysis method of metallurgical lime".

[0098] Example conclusion:

[0099] It can be seen from Examples 1-3 and Comparative Example 1 in combination with Table 1 that when the particle size of limestone is less than 30 mm, the increase in bulk density of the material leads to a decrease in heat transfer efficiency, and the gas-solid contact area in the calcium carbonate decomposition process is reduced, thereby reducing the activity of calcium oxide, proving the role of controlling particle size in ensuring uniformity of heat exchange.

[0100] It can be seen from Examples 1-3 and Comparative Example 2 in combination with Table 1 that when the MgO content is >2%, magnesium ions form a solid solution with calcium oxide at a high temperature of 1050°C, and the crystal lattice distortion leads to a loss of active sites, reducing the activity, proving the role of limiting MgO to maintain the integrity of the crystal structure.

[0101] It can be seen from Examples 1-3 and Comparative Example 3 in combination with Table 1 that deviating the fuel volume ratio from the range of 2.5-3.5 leads to an imbalance in heat value, and insufficient combustion increases the loss of CO, increasing the energy consumption per ton of product, proving the role of optimizing fuel ratio in stabilizing the combustion temperature field.

[0102] It can be seen from Examples 1-3 and Comparative Example 4 in combination with Table 1 that calcination temperature below 1025°C increases the activation energy of calcium carbonate decomposition, and then the decomposition rate constant k decreases, reducing the calcium conversion efficiency, proving the role of maintaining calcination temperature to accelerate the decomposition of calcium carbonate.

[0103] It can be seen from Examples 1-3 and Comparative Example 5 in combination with Table 1 that negative pressure >-50 Pa causes a decrease in the diffusion rate of CO2, and then triggers the reverse reaction CaO+CO2→CaCO3, at which point the activity decreases, proving the role of controlling negative pressure in the range of-100 to-50 Pa to inhibit the regeneration of calcium carbonate.

[0104] ​It can be seen from the combination of Examples 1-3 and Comparative Example 6 and Table 1 that: the concentration of sodium carbonate < 8wt% makes HCO3 - The ion concentration is less than 1.0mol / L, and the SO2 absorption mass transfer coefficient is reduced, which makes the SO2 emission exceed the standard, proving that the concentration of 8-10wt% maintains the role of desulfurization reaction rate.

[0105] The specific embodiment is only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiment without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A process for calcining highly active calcium oxide in a double-chamber kiln, characterized in that, Includes the following steps: S1. Raw material pretreatment: Limestone raw materials are pretreated by crushing, screening and washing. The particle size after crushing and screening is controlled to be 30-120mm and the MgO content is ≤2%. S2. Fuel compatibility: Uses a mixture of blast furnace gas and coke oven gas as fuel; S3. Double-chamber kiln zoned calcination: The kiln adopts a parallel-flow regenerative double-chamber structure, with the high-temperature decomposition zone temperature controlled at 1050±25℃ and the low-temperature cooling zone temperature ≤300℃. S4. Calcination control: Fuel and combustion air are introduced into the high-temperature decomposition zone to control the CO2 concentration in the kiln to ≤25 vol%, and the material residence time to 8-10 h. S5. Waste heat recovery in stages: The flue gas from the high-temperature decomposition zone is introduced into the raw material preheater, and the waste gas from the low-temperature cooling zone recovers heat energy through a three-stage heat exchanger. S6. Gas purification: The kiln tail flue gas undergoes the following purification processes in sequence: S601. Bag filter: Flue gas passes through a membrane filter bag, which captures suspended particulate matter with a particle size ≥1μm in the flue gas, wherein the filtration velocity is ≤0.8m / min; S602.SCR Denitrification: The flue gas treated by S601 is passed into the denitrification reactor; S603. Sodium-based double alkali desulfurization: The flue gas treated by S602 is passed into the desulfurization tower, where the sodium alkali solution comes into countercurrent contact with the flue gas. The solution then flows to the regeneration tank for recycling.

2. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S1, the raw material is washed with high-pressure water flow, and the washing water pressure is ≥0.5MPa.

3. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S2, the oxygen concentration of the mixed fuel is ≥23 vol%.

4. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S2, the volume ratio of blast furnace gas to coke oven gas in the mixed fuel is (2.5-3.5):

1.

5. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S3, the kiln wall in the high-temperature decomposition zone is made of corundum-silicon carbide composite refractory material, wherein the Al2O3 content is ≥85%.

6. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S5, the three-stage heat exchanger includes: a steam generator that generates 0.8MPa saturated steam and introduces the steam into the raw material area; an air preheater that heats the combustion air to ≥150℃; and a hot water heat exchanger that heats the washing water used in S1.

7. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S4, the combustion air adopts a staged air supply design, with the primary air volume accounting for 30-40% of the total air volume and the secondary air swirl angle being 15-25°.

8. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S603, the sodium alkali solution is an 8-10 wt% sodium carbonate solution.

9. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, The regeneration tank uses 10-12 wt% lime slurry.

10. The double-chamber kiln calcination process for highly active calcium oxide according to claim 1, characterized in that, In step S4, the negative pressure inside the kiln is controlled to be -100 to -50 Pa by adjusting the frequency of the exhaust fan, maintaining the CO2 concentration ≤25 vol%.

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