Pyrolusite and rhodochrosite absorb SO in sintering flue gas
It refers to a furnace steel conglomerate comprising coke, sinter, iron, steel, steel rolling - the long flow BOF steel producers. The long-process steel production process is also an iron- coal chemical process. Therefore, iron ore and coal are the main raw materials for steel production. The sulfur in the SO 2 emitted from the production process is mainly derived from iron ore and coal, and the sintering process consumes a large amount of iron ore and fuel coal. The annual amount of SO 2 emitted in this process accounts for about 40% to 60% of the annual emissions of steel companies. %. Therefore, in production, how to choose advanced, reliable, low-investment, low-cost, high-efficiency desulfurization technology to control and reduce SO 2 emissions according to actual conditions is an urgent problem for steel companies to achieve clean production. Desulfurization measures in the iron and steel industry mainly include low-sulfur raw material blending method, high chimney diffusion dilution method, and flue gas desulfurization method. Among them, the low sulfur raw material blending method is a method of controlling from the source, but it is often not fully realized due to various conditions such as resources; the high chimney diffusion dilution method can solve the pollution of SO 2 in the regional environment, but it is brought about by The secondary pollution problem is only a matter of expediency; the flue gas desulfurization method has been deeply studied and widely used for many years. At present, the desulfurization technology is divided into dry method and wet method according to its process. The dry desulfurization technology uses the adsorbent to remove SO 2 from the flue gas. The wet desulfurization technology converts into other substances by means of the chemical adsorption of the liquid state relative to the SO 2 in the gas phase, thereby achieving the purpose of removing sulfur. In the wet desulfurization technology, the lime milk absorption method and the sodium alkali method are currently employed. For more than 30 years, the most concerned and most invested by countries is the lime or limestone washing process. The technology is relatively mature, and the traditional wet process has been improved and improved. The wet process has been optimized from generation to generation. It mainly introduces various types of desulfurization equipment to improve the absorption conditions. Various additives are added to improve the slurry characteristics, and the pH of the slurry is controlled to improve the oxidation and crystallization conditions. Practice has proved that breakthroughs have been made in preventing corrosion and wear and improving the cost performance of the desulfurization system. However, the investment and operating costs are high, the pipelines and absorption towers are easily blocked, and the price of the desulfurization by-product gypsum is low. The application value of the waste residue is not large, and it is easy to cause secondary pollution, and the economic benefits are not obvious. Soft manganese ore, rhodochrosite Manganese Sulfate desulfurization technology, both capable of absorbing SO 2 gas, but wet dust, and manganese sulfate byproduct quality technical grade.
First, the reaction principle and the role of rhodochrosite
The main component of pyrolusite is manganese dioxide, which is a strong oxidizing agent with strong oxidizing properties in acidic solutions. SO 2 has a strong reducibility in aqueous solution, and 1 volume of water can dissolve 40 volumes of SO 2 . Wherein SO 2 is dissolved in water and reacted with water to form sulfurous acid. The absorption of SO 2 in flue gas by pyrolusite is mainly due to the oxidation of MnO 2 in pyrolusite and the reduction of sulfurous acid formed by the reaction of SO 2 with water to form sulfurous acid. The soft manganese ore slurry circulates and absorbs SO 2 gas in the packed absorption tower. A by-product manganese sulfate is produced. MnO 2 and SO 2 will undergo redox reactions in aqueous solution, and the relevant reaction mechanism is not consistent. It is generally believed that the reactions occurring during the flue gas desulfurization of soft manganese ore are as follows:
Combine equations (1) and (2) to get the total reaction:
According to the "thermodynamic data" manual, the standard Gibbs free energy of reaction (3) is ΔG°=-207.08 kJ·mol -1 and the equilibrium constant K°=1.88×10 36 , SO 2 at 298. 15 K. The equilibrium partial pressure is 5.39 × 10 -32 Pa.
It can be seen that the soft manganese ore slurry has strong flue gas desulfurization ability in thermodynamics.
However, when there is absorption of SO 2 SO 2 is absorbed very small part of the liquid oxygen is oxidized to SO 3, SO 3 dissolved in water after a reaction with water to form sulfuric acid, which reacts as follows:
Sulfuric acid can not directly react with MnO 2 . As the soft manganese ore slurry absorbs SO 2 gas, the sulfuric acid in the solution gradually enriches, causing the p H value of the solution to decrease. The decrease of the p H value of the solution reduces the solubility of SO 2 in the solution, thereby affecting the desulfurization rate of the absorption of SO 2 by the pyrolusite, and the acidification of the solution causes corrosion of the desulfurization equipment, which seriously affects the normal operation of the equipment.
Domestic Pyrolusite absorb SO 2 also carried out considerable research in order to generate sulfuric acid suppression, that is, in order not to affect Pyrolusite absorption desulfurization rate of SO 2, domestic researchers mainly take join in the absorption process in lime water and sulfuric acid. Although this method can reduce the desulfurization rate of SO 2 in the flue gas, the amount of leaching slag increases after the addition of lime water, and the concentration of manganese sulfate in the solution decreases, resulting in an increase in investment in subsequent process equipment, energy consumption and operating costs. Big. The problem still exists in the method is that the scale of CaSO 4 is mainly that the gypsum adheres to the inner wall of the washing tower and the tower gate, so that the pipeline and the equipment are clogged, and the desulfurization equipment cannot operate normally. In order to solve the above technical problems, the author creatively uses rhodochrosite to regulate and control the p H value of the slurry, and adds the sulfuric acid in the rhodochrosite to the slurry to form manganese sulfate. The reaction is as follows:
The added rhodochrosite effectively controls the p H value of the slurry, promotes the reaction (2), ensures the absorption rate of sulfur dioxide is above 95%, and achieves the emission of SO 2 in the flue gas; The new impurities also solved the problem of pipeline and equipment blockage and saved investment.
Second, test materials and methods
(1) Test materials
The flue gas used in the test is the sintering flue gas of a steel joint enterprise. According to the field test, the SO 2 concentration of the sintering flue gas varies with the fluctuation of the raw materials and fuel, and is generally 1 to 3 g/m 3 .
The granularity of the pyrolusite and rhodochrosite for the test is 0. 09～0. 15mm, and the soft manganese ore slurry is directly prepared with clear water. The pyrolusite and rhodochrosite were taken from Guizhou mine, and the X-ray energy spectrum analysis results of the components are shown in Tables 1 and 2.
Table 1 Chemical composition of pyrolusite (mass fraction, %)
Table 2 Chemical composition of rhodochrosite (mass fraction, %)
(two) process
The process mainly includes an absorption process, a purification process, and a crystallization process. The slurry reacts with the SO 2 in the flue gas in the packed absorption tower to form a mixture of the manganese sulfate solution and the slag. After filtration, purification, crystallization, centrifugation, and drying, an industrial secondary manganese sulfate product is obtained. The process flow is shown in FIG.
Fig.1 Flow chart of the process of absorbing the SO 2 in the sintered flue gas by the pyrolusite and rhodochrosite
The amount of manganese ore used in each test was 600 g, and the ratio of pyrolusite to rhodochrosite was 3:1. When the p H value of the absorbing liquid slurry decreased to 2.5 to 310, the rhombohedral ore was added at a stirring speed of 300 r/min.
Third, test results and analysis
Domestic scholars' research on the desulfurization of pyrolusite flue gas shows that the choice of liquid-solid ratio should consider factors such as equipment type, energy consumption, operating temperature and cycle time. The experimental results of Huang Qi and Liang Renjie are similar, that is, the liquid-solid ratio has little effect on the desulfurization rate. The author's test results are similar. From the perspective of energy consumption, for the same volume flow of circulating pulp, the liquid-solid ratio is increased, the circulating solid phase is reduced, and the energy consumption of the circulating pump is reduced; however, care must be taken to ensure the final filtrate. The concentration of manganese sulfate is above 25%. Otherwise, the investment in subsequent equipment and the energy consumption of the process will increase. Therefore, the ideal liquid-solid ratio is 3. Therefore, in this study, when studying the influence of other factors on desulfurization, the liquid-solid ratio was chosen to be 3. The SO 2 absorption rate during the test is equal to the ratio of the difference in concentration of SO 2 at the inlet and outlet of the absorption tower to the concentration of SO 2 in the inlet.
(1) Effect of pH on SO 2 absorption rate
Since the sintering flue gas contains a certain amount of oxygen, in the absorption process, oxygen is dissolved in the slurry to oxidize H 2 SO 3 to sulfuric acid. As time goes by, the p H value of the slurry decreases continuously. When it drops to 2~3, the concentration of sulfuric acid in the slurry increases, and sulfuric acid can not directly react with MnO 2 , which seriously affects the absorption of sulfur dioxide. Achieve standard discharge of sulfur dioxide waste gas. The process creatively uses rhodochrosite as a regulator to neutralize the sulfuric acid formed in the reaction, ensuring the stability of the pH value. It not only increases the absorption rate of sulfur dioxide, but also achieves the discharge of sulfur dioxide exhaust gas, while the neutralized product is manganese sulfate, which also increases the concentration of manganese ions, as shown in Figures 2 and 3.
Figure 2 Relationship between SO 2 absorption rate and pH value
Figure 3 Relationship between SO 2 emission concentration and pH
(II) Effect of absorption temperature on SO 2 absorption rate
From the relationship between the SO 2 gas absorption rate and the absorption temperature in Fig. 4, it can be seen that the absorption rate has a maximum value when the temperature changes from low to high. This is because the absorption of SO 2 by the soft manganese slurry is as low as possible in terms of physical dissolution, and in the case of the redox reaction, the reaction temperature of the solution is increased. This is because the temperature increases, the viscosity of the liquid decreases, the diffusion coefficient increases, and the number of molecules exceeding the average activation energy increases accordingly. However, after the temperature rises, the gas solubility of SO 2 decreases. Considering these two conditions, 40 ° C is an ideal absorption temperature.
Figure 4 Relationship between SO 2 absorption rate and temperature
(III) Effect of liquid-gas ratio on SO 2 absorption rate
The liquid-gas ratio was changed to study its effect on SO 2 absorption rate under the same conditions as other test conditions.
SO 2 absorption rate of the liquid to gas ratio and the relationship seen in Figure 5, the liquid-gas ratio is less than 30, the SO 2 absorption rate is low, because the flue gas flow with increasing, although the unit time into the liquid The amount of gas in the phase increases, but because the residence time of the SO 2 gas in the liquid phase is shortened, it is not sufficiently contacted with the slurry, and the initial large amount of SO 2 rapidly consumes the pyrolusite, so that the SO 2 is excessive in the subsequent reaction process. The desulfurization rate is lowered, and the too small liquid-gas ratio may also cause the "pan-liquid point" of the absorption tower. At this time, the absorption is no longer a bubbling behavior, which seriously affects the gas absorption. When the liquid-gas ratio is greater than 40, the SO 2 absorption rate does not increase much. Therefore, the liquid-gas ratio cannot be too large, otherwise the absorption equipment is too large and the investment cost is high. In order to achieve the emission of sulfur dioxide exhaust gas, the impact of the two is considered comprehensively. When the liquid-gas ratio is 40, the SO 2 absorption rate is higher.
Figure 5 Relationship between SO 2 absorption rate and liquid to gas ratio
(4) Desulfurization effect
The flue gas obtained by desulfurization of pyrolusite and rhodochrosite was prepared. The results are shown in Table 3. It can be seen that the absorption rate of soot in the process is over 90%.
Table 3 Flue Gas Monitoring Report
Note: Test method: HJ/T57-2000.
(5) Suppressing the formation of manganese disulfate
In the pyrolusite and rhodochrosite, the absorption of SO 2 to produce manganese sulfate products is accompanied by the formation of manganese dimanganese sulfate, and its presence seriously affects the production of manganese sulfate products, so it is essential to effectively inhibit the formation of manganese disulfate. The experimental results show that proper increase of the slurry reaction temperature is beneficial to reduce the formation of S 2 O 6 2 - , but considering the energy consumption problem, the fresh pulp does not need to be heated specially because the temperature of the flue gas is generally high and the slurry is in contact with the flue gas. At the same time of mass transfer, it will be heated and heated. Generally, the absorption temperature is 40~50 °C. In addition, the formation of manganese disulfate is related to the p H value of the slurry. When the p H value is decreased, it is beneficial to reduce S 2 O 6 . 2 - generation, because as the absorption process progresses, sulfuric acid is continuously produced, the acidity of the slurry increases, and the S 2 O 6 2 - is reduced, but the SO 2 absorption rate after the decrease of the p H value, Mn is considered. The recovery rate is low, and the test shows that the p H value is in the range of 2.0 to 3.5, which inhibits the formation of manganese disulfate. Therefore, rhodochrosite has an important role in inhibiting the formation of manganese disulfate.
Fourth, the purification of leachate
Pyrolusite and rhodochrosite contain impurities such as Fe, Al, Ca, and Pb in addition to Mn. In the process of leaching SO 2 from pyrolusite, leaching of Fe, Al, Ca, Pb impurities is also accompanied. The leaching reaction formula is:
Formula, Me represents a metal impurities Fe, Al, Ca, Pb and the like. Since the SO 2 is excessive during the reaction, after the iron is leached, the remaining SO 2 reduces Fe 3 + to Fe 2 + , and thus the iron in the leachate mainly exists in the form of Fe 2+ . In order to obtain a qualified manganese sulfate product, impurities must be removed. In the test, the neutralization method was used to increase the p H value of the solution, so that metal impurities such as iron and aluminum were hydrolyzed to form a precipitate and removed. After the impurity removal process, a portion of CaSO 4 , a small amount of MgSO 4 , and some unprecipitated H 2 SiO 3 colloids, small particles of Fe(OH) 3 and Al(OH) 3 are present in the manganese sulfate solution. These colloids and impurities need to stand for 48 h to be precipitated and removed. Finally, the quality of the MnSO 4 ·H 2 O product obtained by filtration and thermal crystallization (see Table 4) meets the national secondary standard (GB1622-79).
Table 4 Analysis results of manganese sulfate products (mass fraction, %)
V. Conclusion
(1) The use of soft manganese ore and rhodochrosite to absorb SO 2 from the sintering flue gas of steel plants to obtain manganese sulfate is technically feasible and is a novel and unique wet desulfurization technology.
(II) The test results show that the manganese sulfate ore can be used to desulfurize to obtain manganese sulfate, and the SO 2 absorption rate can reach over 95%.
(3) The process also has the characteristics of wet dust removal, the absorption rate of soot is over 90%, and the quality of by-product manganese sulfate can reach the national secondary standard (GB1622-79).
(4) Using rhodochrosite to regulate and control the p H value of the slurry to ensure the absorption rate of SO 2 in the desulfurization process.
(5) Desulfurization with pyrolusite and rhodochrosite, with good social and economic benefits, can not only control environmental pollution, but also produce high-value by-product manganese sulfate.
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