CN113082962A - Secondary mixed magnesium method flue gas desulfurization process and device - Google Patents
Secondary mixed magnesium method flue gas desulfurization process and device Download PDFInfo
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Abstract
A secondary mixed magnesium method flue gas desulfurization process, the neutralization reaction process of a desulfurizer and absorption liquid is as follows: and leading out part of absorption liquid from the desulfurizing tower to be mixed with a magnesium oxide desulfurizing agent for the first time, leading the primary mixed liquid to enter the desulfurizing tower without solid-liquid separation to be mixed with the absorption liquid in the tower for the second time, leading magnesium oxide in the primary mixed liquid to be subjected to neutralization reaction with the absorption liquid in the tower, or/and dissolving magnesium sulfite crystals in the primary mixed liquid into the absorption liquid in the tower, and using the secondary mixed liquid for absorbing sulfur dioxide in flue gas. The problem that the desulfurization absorption liquid in the prior art is low in PH or/and low in concentration of effective absorption medium is solved, the desulfurization efficiency is improved, the spraying liquid-gas ratio is reduced, and the spraying energy consumption is saved; the utilization rate of the desulfurizer is improved, and the medicament cost is reduced; the solid content of the absorption liquid is reduced, and the problem of the operation reliability of a desulfurization system is solved; simultaneously solves the problems of desulfurization product oxidation and regeneration system scale which restrict the wide application of the desulfurization technology of magnesium sulfite liquid-cleaning method.
Description
Technical Field
The invention relates to flue gas desulfurization, in particular to improvement of the existing magnesium flue gas desulfurization process.
Background
The traditional magnesium-method flue gas desulfurization desulfurizing tower comprises three units of absorption, neutralization and spraying, wherein absorption liquid and flue gas are subjected to gas-liquid mass transfer to absorb sulfur dioxide in the flue gas in an absorption unit positioned in the middle of the desulfurizing tower, the absorption liquid for completing desulfurization absorption enters a neutralization unit (a tower bottom liquid storage section) to be subjected to neutralization reaction with a magnesium (hydrogen) oxide desulfurizing agent, and a spraying layer positioned on the upper part of the desulfurizing tower is introduced by a spraying pump of a circulating unit to be circularly used for desulfurization absorption of the flue gas. For the purpose of oxidizing the primary desulfurization product magnesium sulfite to magnesium sulfate, an oxidative aeration unit is generally provided in the liquid bottom stage to oxidize the primary desulfurization product.
In the traditional magnesium method flue gas desulfurization process, the desulfurizer is configured by mixing external process water and magnesium oxide powder, and introducing steam for digestion to generate magnesium hydroxide slurry so as to improve the absorption reaction activity of the magnesium hydroxide slurry. Because the evaporation capacity of the flue gas of the desulfurization system is less than the supplement amount of external process water, the preparation concentration of the desulfurizer slurry is usually controlled to be 10-20% (calculated by magnesium oxide) based on the purposes of reducing the discharge amount of wastewater and reducing the energy consumption of digestion reaction. The adding mode of the desulfurizer slurry is that the desulfurizer slurry is directly added to a liquid storage section (neutralization unit) at the bottom of a desulfurization tower to perform neutralization reaction with desulfurization absorption liquid, although the adding equivalent of the desulfurizer is larger than the absorption equivalent of sulfur dioxide (magnesium-sulfur ratio is 1.03), the absorption liquid leaving the neutralization unit and entering a spraying unit still contains a large amount of unreacted desulfurizer, the pH of the absorption liquid is still only 5.5-5.8, the gas-liquid mass transfer efficiency of the absorption unit is low, the requirement of desulfurization efficiency is met by increasing the gas-liquid mass transfer area, therefore, the spraying liquid-gas ratio (the ratio of spraying amount to flue gas amount) is larger and is usually 7-10 liters (absorption liquid)/standard cubic meter (flue gas), and the spraying energy consumption of a desulfurization system is high. Meanwhile, in order to maintain the material balance of the desulfurization system, the desulfurization system needs to discharge desulfurization products by discharging absorption liquid in the tower, and since the absorption liquid in the tower contains a large amount of unreacted desulfurizing agents, the larger the discharge liquid amount is, the larger the desulfurizing agent loss is. In order to reduce the loss of the desulfurizer to the maximum, the traditional magnesium method adopts that the solid content of the absorption liquid in the tower is accumulated to 5-10% and then discharged outside, so that the simultaneous discharge of the waste water and the waste residue is realized, the liquid discharge capacity of the desulfurization system is reduced to the maximum, and the loss of the desulfurizer is reduced, but the adverse effect is that the solid content of the absorption liquid in the tower is high, the abrasion and the blockage of equipment are serious, and the operation reliability of the desulfurization system is influenced.
We considered that: the traditional magnesium method does not effectively utilize the advantages of slightly solubility and alkalescence of the magnesium sulfite, which is shown in that the absorption liquid is used for spray absorption before neutralization reaction at the tower bottom is not finished, and the actual absorption process is a magnesium (hydrogen) oxide absorption reaction of gas-liquid-solid three-phase mass transfer rather than a magnesium sulfite absorption reaction (gas-liquid two-phase) with higher mass transfer efficiency. The absorption mass transfer efficiency can be effectively improved by improving the conversion rate of the tower bottom neutralization reaction, and the root reason for restricting the improvement of the conversion rate of the tower bottom neutralization reaction is as follows: 1) the mixing ratio of the tower bottom absorption liquid and the desulfurizer slurry in a liquid storage section (neutralization unit) at the bottom of the desulfurization tower is large; 2) the neutralization reaction at the bottom of the tower has short residence time. The smoke quantity of the conventional smoke desulfurization is generally at the level of 30-240 kilomega cubic meter/hour, the diameter of a corresponding desulfurization tower reaches 6-18 meters, the corresponding spraying quantity is 2000-16000 tons/hour, the spraying quantity is about 1000 times of the adding quantity of the desulfurizer slurry, and the aim of neutralization reaction can be fulfilled only by diluting the desulfurizer 1000 times in a liquid storage section at the bottom of the desulfurization tower. However, due to the huge spraying amount, even if the liquid storage section at the bottom of the desulfurization tower reaches the limit height of 7-8 m, the residence time of the mixture and neutralization reaction of the desulfurizer slurry and the absorption liquid in the tower can only reach about 5 minutes, and in addition, the large tower diameter and the laminar flow formed by lateral stirring are not beneficial to the mixture of the desulfurizer slurry and the absorption liquid in the tower, so that a large amount of desulfurizer and the absorption liquid are not completely mixed and neutralized and enter a spraying unit, and the result is that: although the equivalent of the desulfurizing agent in the absorption liquid is far higher than that of the magnesium bisulfite, the pH value of the absorption liquid is low, and the requirement of desulfurization efficiency is met by a larger spraying amount.
The inventor invents a technology for desulfurizing flue gas or waste gas by an external regeneration circulation magnesium sulfite method (an authorized patent CN200810124177), a regeneration unit is arranged outside a desulfurizing tower, partial or all absorption liquid is led out of the desulfurizing tower and then undergoes a neutralization reaction with a magnesium oxide desulfurizing agent, magnesium hydrogen sulfite in the absorption liquid is regenerated into magnesium sulfite, magnesium sulfite crystals and other solid impurities generated by the neutralization reaction are removed by solid-liquid separation, and the absorption liquid after the solid-liquid separation flows back to the desulfurizing tower to absorb sulfur dioxide in the flue gas. Above-mentioned patent is through the reaction of outside regeneration (neutralization), has improved neutralization reaction efficiency, has solved the incomplete problem of neutralization reaction in the tower, has improved the PH of absorption liquid, and the empty tower of system of will desulfurization sprays liquid-gas ratio and will be low nearly half. Meanwhile, as the neutralization reaction is completely carried out outside the tower, and the solid-liquid separation link completely removes the solid matters, the solid content of the absorption liquid in the tower approaches to zero, and the problems of equipment blockage, abrasion and the like caused by the high solid content of the absorption liquid are effectively solved. Based on the good application effect of the invention, the technology is named as flue gas desulfurization technology of magnesium sulfite liquid-removing method by the ministry of environmental protection and is listed as national important environmental protection practical technology.
However, the "magnesium sulfite liquid-cleaning method" also has three technical defects: 1) based on the slightly soluble characteristic of magnesium sulfite, the absorption liquid volume for external regeneration needs to reach 25-100% of the spraying volume in the tower, and the technical defects of large device scale and high site requirement caused by large external regeneration volume restrict the popularization and application of the technology. 2) Because the neutralization reaction product contains fine particles such as smoke dust, magnesium oxide impurities and the like, in order to prevent the accumulation of the small particles in a circulating system, the fine particles must be thoroughly separated from the absorption liquid in the solid-liquid separation process, and the magnesium sulfite crystals with larger particle size and the excessive magnesium oxide desulfurizer are also completely removed from the absorption liquid, so that the solid content of the reflux liquid of the actual reflux desulfurizing tower is close to zero, and the effective absorption medium magnesium sulfite is completely returned to the desulfurizing tower in the form of saturated solution. Under the condition of leading out 25% of absorption liquid for regeneration, the concentration of magnesium sulfite after the regeneration liquid is mixed with the absorption liquid in the circulating system can only reach about 55% of the saturation concentration, and the absorption liquid in the tower has low effective absorption medium concentration and low PH value, and still needs higher spraying liquid-gas ratio. Although the desulfurization efficiency can be improved by further increasing the regeneration amount, the regeneration system is further scaled up. 3) The method is limited by the amount of magnesium sulfite entering the tower, the magnesium sulfite cannot be oxidized into magnesium sulfate in the tower, the desulfurization product can only be separated from a desulfurization system from a solid-liquid separation link in the form of magnesium sulfite crystals, and the magnesium sulfite crystals are extremely difficult to oxidize after being separated from a desulfurization circulating system, so that the comprehensive utilization of the desulfurization product is difficult to realize. 4) In order to reduce the external regeneration amount to the maximum extent, a mode of adding excessive desulfurizer is usually adopted to improve the neutralization reaction rate and the neutralization reaction completion degree, although the PH of the regeneration liquid can reach a weak alkaline level of 7.2-7.8, the magnesium-sulfur ratio of a desulfurization system reaches more than 1.05, and the loss of the desulfurizer is large.
The invention content is as follows:
in order to overcome the defects of the prior art, the invention provides a secondary mixed magnesium flue gas desulfurization process, which has the following technical scheme:
a secondary mixed magnesium flue gas desulfurization process, the neutralization reaction of a desulfurizer and absorption liquid comprises the following steps:
step 1: leading out part of absorption liquid from the desulfurizing tower to be mixed with the magnesium oxide desulfurizing agent for the first time:
three possibilities can occur in the first mixing, 1) under the condition of no residence time in the mixing process, only magnesium oxide and no magnesium sulfite crystal are contained in the first mixed solution; 2) under the condition that the retention time is in the mixing process and the extracted absorption liquid is excessive relative to magnesium oxide, only magnesium sulfite crystals and no magnesium oxide exist in the primary mixed liquid; 3) in the case that the retention time is provided during the mixing process but the amount of the absorption liquid extracted is not excessive relative to the amount of the magnesium oxide, the primary mixed liquid contains both magnesium oxide and magnesium sulfite crystals.
Step 2: refluxing the primary mixed solution to a desulfurizing tower without solid-liquid separation, and carrying out secondary mixing on the primary mixed solution and absorption liquid in the tower;
the larger the primary mixed absorption liquid amount is, the smaller the secondary mixing ratio is, and the more favorable the neutralization reaction is to be carried out in the liquid storage section at the bottom of the tower.
And step 3: after the secondary mixing, carrying out neutralization reaction on the primary mixed unreacted magnesium oxide and magnesium bisulfite in the absorption liquid in the tower, or/and dissolving a magnesium sulfite crystal generated by the primary mixing in the absorption liquid in the desulfurizing tower;
and 4, step 4: and (3) the secondary mixed liquid neutralized and/or dissolved in the step (3) is used for absorbing sulfur dioxide in the flue gas.
In the secondary mixed magnesium flue gas desulfurization process, the desulfurization tower comprises an oxidation unit for oxidizing magnesium sulfite into magnesium sulfate;
because the magnesium sulfite crystal generated by primary mixing and the excessive magnesium oxide desulfurizer enter the absorption liquid in the tower, as long as the oxidation amount of the magnesium sulfite is controlled not to exceed the final magnesium sulfite amount generated by desulfurization absorption, the concentration of the liquid-phase magnesium sulfite in the absorption liquid can be maintained in a state close to saturation, thereby solving the problem that the magnesium sulfite crystal is difficult to oxidize after being separated from a circulating system and being beneficial to reducing the solid content of the absorption liquid of a desulfurization circulating system.
In the secondary mixed magnesium flue gas desulfurization process, the empty tower spraying liquid-gas ratio of the desulfurization tower is not more than 4 liters (absorption liquid)/standard cubic meter (flue gas);
because the absorption liquid has the advantage of high PH, the spraying liquid-gas is reduced by more than 50 percent compared with the traditional magnesium method, correspondingly, the retention time of the neutralization reaction is doubled, and the secondary mixing ratio of the desulfurizer and the absorption liquid is reduced by 1 time.
In the secondary mixed magnesium method flue gas desulfurization process, the absorption liquid led out from the desulfurization circulating system is firstly subjected to solid-liquid separation to remove solid matters and then is mixed with the magnesium oxide desulfurizer for the first time;
because the conversion rate of the neutralization reaction is improved and even approaches to complete reaction, the content of the absorbent extracted from the desulfurizing tower is greatly reduced, so that solid matters in the absorbent are removed in combination with the extraction process, the loss of the desulfurizing agent is extremely limited, and the larger the amount of the extracted absorbent for solid-liquid separation is, the lower the solid content in the desulfurizing circulation system is.
In the solid-liquid separation method, the pH value of the absorption liquid led out from the desulfurizing tower after solid-liquid separation is not more than 7; because the conversion rate of the neutralization reaction is improved, the PH of the absorption liquid after solid-liquid separation is less than 7, namely: magnesium oxide carried by the absorption liquid led out of the desulfurizing tower is still insufficient to neutralize magnesium bisulfite in the absorption liquid after complete reaction in the solid-liquid separation process, and the loss amount of the magnesium oxide in the solid-liquid separation process can be considered as zero.
According to the solid-liquid separation method, the solid content of the absorption liquid of the desulfurizing tower is not more than 0.15%.
The solid content of the absorption liquid in the desulfurizing tower is related to the solid-liquid separation amount of the extracted absorption liquid, and the solid-liquid separation amount is larger, and the solid content of the absorption liquid is lower. And the method of leading out the absorption liquid and the solid for separation and then refluxing the desulfurization tower is adopted, so that the absorption liquid and the solid content in the tower are reduced, and simultaneously, no waste water is discharged.
In the secondary mixed magnesium flue gas desulfurization process, the magnesium oxide desulfurizer is magnesium oxide powder or undigested magnesium oxide slurry;
because the conditions of the neutralization reaction are greatly improved, the magnesium oxide does not need to be digested into magnesium hydroxide with higher reaction activity to improve the neutralization reaction rate, and even the magnesium oxide powder and the absorption liquid can be directly mixed for one time.
In the secondary mixed magnesium flue gas desulfurization process, the volume ratio of the absorption liquid volume led out from the desulfurization tower to the spraying volume of the desulfurization tower is not less than 0.8%;
theoretically, only the absorption liquid and the desulfurizer are mixed for the first time, the dilution ratio of the secondary mixing can be reduced, the conversion rate of the secondary mixing neutralization reaction is improved, and the pH value of the absorption liquid of the desulfurization system is improved to be more than 6.0 under the condition that the ratio of the extracted absorption liquid to the spraying amount is not less than 0.8%.
In the secondary mixed magnesium flue gas desulfurization process, the volume ratio of the absorption liquid volume led out from the desulfurization tower to the spraying volume of the desulfurization tower is not less than 4.0%.
Under the condition that the ratio of the absorption liquid led out from the desulfurization tower to the spraying amount of the desulfurization tower is not less than 4%, the air-to-tower spraying liquid-gas ratio of the desulfurization system can be reduced to be not more than 4 liters (absorption liquid)/standard cubic meter (flue gas).
In the secondary mixed magnesium flue gas desulfurization process, the pH value of the secondary mixed liquid after neutralization or/and dissolution is more than 6.0,
based on the improvement of the conversion rate of the neutralization reaction, the PH of the absorption liquid is greatly improved, and even under the condition that the extracted absorption liquid only accounts for 0.8 percent of the spraying amount, the PH of the absorption liquid is improved to more than 6.0 from 5.8 of the traditional magnesium method.
In the secondary mixed magnesium flue gas desulfurization process, the start-up step of the desulfurizing tower exists before the absorption liquid and the desulfurizing agent are led out and mixed for the first time: continuously introducing the flue gas or waste gas containing sulfur dioxide into a desulfurizing tower, circularly absorbing the flue gas by using magnesium oxide slurry with solid content lower than 0.5%, removing the sulfur dioxide in the flue gas or waste gas, and completing the starting process when the pH of the absorption liquid is less than or equal to 6.
Above-mentioned secondary mixes magnesium method flue gas desulfurization device, the device include desulfurizing tower absorption unit A, desulfurizing tower spray unit B, desulfurizing tower neutralization unit C, spray pump D, primary mixing tank F. The desulfurizing tower comprises a desulfurizing tower spraying unit B, a desulfurizing tower absorption unit A and a desulfurizing tower neutralization unit C, wherein the desulfurizing tower spraying unit B, the desulfurizing tower absorption unit A and the desulfurizing tower neutralization unit C are sequentially arranged in a desulfurizing tower from top to bottom; the absorption unit A of the desulfurizing tower is provided with an original flue gas inlet, and the top of the spraying unit B of the desulfurizing tower is provided with a clean flue gas outlet; an absorption liquid outlet of the desulfurizing tower neutralization unit C is connected with an inlet of a spray pump D, and an outlet of the spray pump D is connected with an inlet of a desulfurizing tower spray unit B; the absorption liquid outlet of the desulfurizing tower neutralization unit C is connected with the inlet of the primary mixing tank F, the outlet of the primary mixing tank F is connected with the inlet of the desulfurizing tower neutralization unit C, and the primary mixing tank F is provided with the inlet of a desulfurizing agent.
Has the advantages that:
based on the research conclusion that the large mixing ratio of the desulfurizer slurry and the absorption liquid in the tower and the short residence time of the neutralization reaction are the root causes of low conversion rate of the neutralization reaction of the flue gas desulfurization by the traditional magnesium method, the mixing ratio of the desulfurizer and the absorption liquid in the tower is greatly reduced and the conversion rate of the neutralization reaction and the pH value of the absorption liquid are improved by adopting a mode of mixing the absorption liquid led out from the desulfurization tower and the desulfurizer for one time and then mixing the absorption liquid in the tower with the absorption liquid in the second time. More beneficially, the requirement for the spraying amount is significantly reduced due to the increase of the PH of the absorption liquid, and the reduction of the spraying amount not only further reduces the mixing ratio of the absorption liquid and the desulfurizing agent, but also increases the residence time of the neutralization reaction, further increases the conversion rate of the neutralization reaction and the PH of the absorption liquid, further reduces the spraying amount, and realizes beneficial circulation. The positive significance is shown in detail as follows:
compared with the traditional magnesium-method flue gas desulfurization, the invention adopts the technical means that the absorption liquid and the desulfurizer are mixed for the first time and then mixed for the second time with the absorption liquid in the tower, thereby effectively improving the conversion rate of neutralization reaction in the tower, improving the PH of the absorption liquid from 5.5-5.8 to 6.0-6.5, reducing the gas ratio of the spraying liquid from 8-10 liters per standard cubic meter to not more than 4 liters per standard cubic meter, and greatly saving the spraying energy consumption. The solid content of the absorption liquid of the desulfurization circulating system is reduced by more than 80% by combining the technical means of separating the solid from the liquid of the absorption liquid and removing the solid before primary mixing, so that the risks of corrosion, abrasion and blockage of the desulfurization system are effectively reduced.
Compared with the desulfurization technology of a magnesium sulfite clear solution method, the invention adopts the technical means that the primary mixed solution directly enters the desulfurization circulating system without solid-liquid separation (removal of magnesium sulfite crystals), so that the effective absorption medium magnesium sulfite crystals and the excessive magnesium oxide desulfurizer generated by neutralization reaction also enter the absorption liquid in the tower, the effective absorption medium concentration of the absorption liquid in the tower is effectively improved, the desulfurization absorption efficiency is improved, the desulfurization spray amount and the spray energy consumption are further reduced, and the loss of the desulfurizer is reduced. Meanwhile, based on the improvement of the concentration of the effective absorption medium of the absorption liquid in the desulfurization tower, the magnesium sulfite oxide in the desulfurization tower has sufficient feasibility, and the problem of desulfurization waste residue treatment restricting the technical application of a magnesium sulfite liquid cleaning method is solved. More importantly, the extraction amount of the absorption liquid is reduced by more than 50 percent compared with the magnesium sulfite clear liquid method, and the problem that the application of the magnesium sulfite method is restricted due to the huge external regeneration system is effectively solved. And the solid-liquid separation is carried out on the absorption liquid led out of the desulfurization system before primary mixing, and the solid content of the absorption liquid in the tower can be controlled to be at the level of clear liquid by combining the technical means of oxidizing magnesium sulfite in the desulfurization tower.
Description of the drawings:
FIG. 1 is a process flow chart of examples 1, 2 and 3 of the present invention
Fig. 2 is a process flow chart of the embodiment 4, the embodiment 5 and the embodiment 6 of the invention.
Wherein: a is a desulfurizing tower absorption unit, B is a desulfurizing tower spraying unit, C is a desulfurizing tower neutralization unit, D is a spraying pump, E is a magnesium oxide batching tank, F is a primary mixing tank, G is a solid-liquid separator, and H is an oxidation fan
The specific implementation mode is as follows:
examples 1 to 3: as shown in the attached figure 1 of the specification: raw flue gas enters a desulfurizing tower absorption unit A through a pipeline (1), clean flue gas after gas-liquid mass transfer is carried out between the desulfurizing tower absorption unit A and absorption liquid sprayed out of a desulfurizing tower spraying unit B is discharged outside through a pipeline (2), and the absorption liquid enters a desulfurizing tower neutralization unit C through an absorption unit A in the tower. The magnesium oxide of the desulfurizer enters a magnesium oxide mixing tank E from a pipeline (5) and is prepared into magnesium oxide slurry with process water entering the magnesium oxide mixing tank E from a pipeline (6), the magnesium oxide slurry enters a primary mixing tank F from a pipeline (7) and is primarily mixed with absorption liquid introduced into the primary mixing tank F from a desulfurizing tower neutralization unit C from a pipeline 8, the primary mixed liquid flows back to the desulfurizing tower neutralization unit C from a pipeline (9) and is secondarily mixed with the absorption liquid in the tower, and the secondary mixed liquid is pumped into a spraying unit B from a spraying pump D through a pipeline (4) through a pipeline (3). The absorption liquid (desulfurization product) is discharged from the desulfurizing tower neutralization unit C through a line (10).
According to the process flow shown in the figure 1, flue gas desulfurization is carried out on an industrial kiln, the flue gas volume of the kiln is 600000 standard cubic meters per hour, the concentration of flue gas sulfur dioxide is 1800 mg per cubic meter, the diameter of a desulfurizing tower is 9 meters, the height of a neutralizing unit of the desulfurizing tower is 7 meters, the volume of the neutralizing unit of the desulfurizing tower is 397 cubic meters, and the effective volume of a primary mixing tank is designed into primary mixing residence time setting according to the table 1. And discharging desulfurization products in a mode of discharging absorption liquid outwards, wherein the discharge absorption liquid is discharged by 20 tons/hour. The examples 1 to 3 and the operation of the conventional magnesium method (comparative technique) were carried out by adjusting the ratio of the amount of the absorption liquid drawn from the desulfurization tower to the amount of the spray, and the desulfurization system was started by: continuously introducing the flue gas or waste gas containing sulfur dioxide into a desulfurizing tower, circularly absorbing the flue gas by using magnesium oxide slurry with solid content lower than 0.5%, removing the sulfur dioxide in the flue gas or waste gas, and completing the starting process when the pH of the absorption liquid is less than or equal to 6. The desulfurization system operating parameters are as shown in table 1:
table 1: EXAMPLES 1-3 operating parameter tables
From the comparison of the example 1 with the conventional magnesium desulfurization operation parameters, it can be seen that under the condition of the same spraying liquid-gas ratio (corresponding to the same residence time of neutralization reaction at the bottom of the tower), even under the condition that the extracted liquid amount accounts for only 0.8% of the spraying amount ratio and the residence time of the primary mixing is close to zero (magnesium oxide does not undergo neutralization reaction with the absorption liquid and magnesium sulfite crystals are not generated), the dilution ratio of the secondary mixing is reduced from 1067 times to 111 times by the conventional magnesium method, the pH of the absorption liquid is increased from 5.80 to 6.02, and the sulfur dioxide concentration of the corresponding desulfurization system is reduced from 86.2 mg/cubic meter to 66.6 mg/cubic meter. Namely: the conversion rate of the tower bottom neutralization reaction can be effectively improved only by leading out the absorption liquid to be mixed for one time, the PH of the absorption liquid is improved, the desulfurization efficiency is effectively improved, and the emission concentration of sulfur dioxide is reduced.
As is clear from comparison between example 2 and example 1, when the amount of the drawn-out absorption liquid is the same, the PH of the absorption liquid can be further increased by decreasing the spraying liquid/gas to increase the residence time of the neutralization reaction at the bottom of the tower and decrease the dilution ratio of the secondary mixing, and the emission concentration of sulfur dioxide is substantially unchanged. The positive significance of the method is to reduce the power consumption of spraying.
As can be seen from the comparison between example 3 and example 1, the ratio of the drawn absorption liquid to the spraying amount is increased from 0.8% to 4%, the dilution ratio of the secondary mixing is further reduced, the pH of the absorption liquid is increased, the gas-liquid ratio of the spraying liquid is reduced, and as the gas-liquid ratio of the spraying liquid is reduced from 8L/cubic meter to 4L/cubic meter, the dilution ratio of the neutralization reaction is reduced by 50%, the residence time of the neutralization unit is increased by 1 time, the pH of the absorption liquid is increased from 6.02 to 6.28, and the emission concentration of sulfur dioxide is reduced from 66.6 mg/cubic meter to an ultralow emission level of 32.8 mg/cubic meter.
It should be noted that: although the problem of desulfurizer loss caused by the traditional magnesium method desulfurization product discharging mode is solved by improving the conversion rate of neutralization reaction, the solid content of absorption liquid in the tower still reaches 7.93 percent due to the limitation of the amount of discharged wastewater, the risk of equipment abrasion and blockage is high, and excessive wastewater discharge is caused at the same time.
Examples 4 to 6: as shown in the attached figure 2 in the specification: the raw flue gas enters a desulfurizing tower absorption unit A through a pipeline (11), gas-liquid mass transfer is carried out between the absorption unit A and absorption liquid sprayed out of a desulfurizing tower spraying unit B, the purified flue gas after the gas-liquid mass transfer is finished is discharged outside through a pipeline (12), and the absorption liquid after the gas-liquid mass transfer is finished enters a desulfurizing tower neutralization unit C through the desulfurizing tower absorption unit A. Part of absorption liquid led out from the neutralization unit C of the desulfurizing tower enters a solid-liquid separator G for solid-liquid separation through a pipeline (15), waste residues generated by the solid-liquid separation are discharged outside through a pipeline (19), the absorption liquid without solid-phase impurities enters a primary mixing tank F through a pipeline (16) and is mixed with magnesium oxide powder fed into the primary mixing tank F through a pipeline (17) for the first time, primary mixed liquid which is mixed for the first time returns to the neutralizing unit C of the desulfurizing tower through a pipeline (18) to be mixed with the absorption liquid in the tower for the second time, and secondary mixed liquid of the neutralizing unit C of the desulfurizing tower is pumped into a spraying unit B of the desulfurizing tower through a pipeline (13) and a spraying pump D through a pipeline (14). The oxidation fan H sends oxidation air from line (20) to the thionizer neutralization unit C.
According to the process flow shown in the figure 2, flue gas desulfurization is carried out on an industrial kiln, wherein the flue gas volume of the kiln is 600000 standard cubic meters per hour, the concentration of flue gas sulfur dioxide is 1800 mg per cubic meter, the diameter of a desulfurizing tower is 9 meters, the height of a liquid storage section at the bottom of the desulfurizing tower is 7 meters, the volume of the liquid storage section at the bottom of the desulfurizing tower is 397 cubic meters, and the volume of a primary mixing tank is 80 cubic meters. And an oxidation fan is arranged to oxidize the absorption liquid in the neutralization unit of the desulfurizing tower, and the air volume of the oxidation fan is 1500 cubic meters per hour. Before primary mixing, solid-liquid separation is carried out on the extracted absorption liquid in the tower by adopting a sedimentation tank, and the surface area of the sedimentation tank is 72 square meters. The operation of examples 4 to 6 was carried out by adjusting the ratio of the amount of the absorption liquid drawn from the desulfurization tower to the amount of the spray, and the on/off of the oxidation fan, and the operating parameters of the desulfurization system were as shown in Table 2:
table 2: EXAMPLES 4-6 operating parameter tables
Comparing example 4 with example 3, it can be seen that the solid content of the circulating absorption liquid can be reduced from 7.93% to 1.38% and by more than 80% by adopting a mode of first removing the solid content from the absorption liquid led out of the desulfurization system through solid-liquid separation and then mixing the absorption liquid once.
As can be seen from comparison of examples 5 and 4, the oxidation of the desulfurization product was solved by oxidizing the absorbent in the neutralization unit, and the solid content of the circulating absorbent was further reduced to 0.15% or less, thereby reaching the same level of the clear solution as in the "magnesium sulfite process".
It can be seen from comparison between example 6 and example 5 that the residence time of the primary mixing is ensured by increasing the extraction amount of the absorption liquid in the tower, the neutralization reaction can be completely completed outside the tower, and the secondary mixing in the tower only comprises the dissolution process of the magnesium sulfite crystals, but does not comprise the neutralization reaction process, thereby further improving the PH and desulfurization efficiency of the absorption liquid, and reducing the spray liquid-gas ratio and the solid content of the absorption liquid. Meanwhile, the beneficial effect that the pH value of the absorption liquid after solid-liquid separation is less than 7.0 is created, namely, no desulfurizer is lost in the solid-liquid separation process, and the utilization rate of the desulfurizer is close to 100%.
Claims (12)
1. A secondary mixed magnesium method flue gas desulfurization process is characterized in that: the neutralization reaction of the desulfurizer and the absorption liquid comprises the following steps:
step 1: leading out part of absorption liquid from the desulfurizing tower to be mixed with the magnesium oxide desulfurizing agent for the first time:
step 2: refluxing the primary mixed solution to a desulfurizing tower without solid-liquid separation, and carrying out secondary mixing on the primary mixed solution and absorption liquid in the tower;
and step 3: after the secondary mixing, carrying out neutralization reaction on the primary mixed unreacted magnesium oxide and magnesium bisulfite in the absorption liquid in the tower, or/and dissolving a magnesium sulfite crystal generated by the primary mixing in the absorption liquid in the tower;
and 4, step 4: and (3) the secondary mixed liquid neutralized and/or dissolved in the step (3) is used for absorbing sulfur dioxide in the flue gas.
2. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the desulfurization tower comprises an oxidation unit for oxidizing magnesium sulfite into magnesium sulfate.
3. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the ratio of the spraying liquid to the gas of the empty tower of the desulfurizing tower is not more than 4 liters (absorption liquid)/standard cubic meter (flue gas).
4. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the absorption liquid led out from the desulfurizing tower is firstly subjected to solid-liquid separation to remove solid matters and then is mixed with the magnesium oxide desulfurizing agent for the first time.
5. The solid-liquid separation method according to claim 4, characterized in that: the pH value of the absorption liquid led out from the desulfurizing tower after solid-liquid separation is not more than 7.
6. The solid-liquid separation method according to claim 4, characterized in that: the solid content of the absorption liquid in the desulfurizing tower is not more than 0.15 percent.
7. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the magnesium oxide desulfurizer is powder or undigested magnesium oxide slurry.
8. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the volume ratio of the absorption liquid amount led out from the desulfurizing tower to the spraying amount of the desulfurizing tower is not less than 0.8%.
9. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the volume ratio of the absorption liquid amount led out from the desulfurizing tower to the spraying amount of the desulfurizing tower is not less than 4.0%.
10. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the pH of the secondary mixed solution after neutralization or/and dissolution is more than 6.0.
11. The secondary mixed magnesium flue gas desulfurization process according to claim 1, characterized in that: the start-up step of the desulfurizing tower exists before the absorption liquid and the desulfurizing agent are led out for one time to be mixed: continuously introducing the flue gas or waste gas containing sulfur dioxide into a desulfurizing tower, circularly absorbing the flue gas by using magnesium oxide slurry with solid content lower than 0.5%, removing the sulfur dioxide in the flue gas or waste gas, and completing the starting process when the pH of the absorption liquid is less than or equal to 6.
12. The utility model provides a secondary mixes magnesium method flue gas desulfurization device which characterized in that: the device comprises a desulfurizing tower absorption unit A, a desulfurizing tower spraying unit B, a desulfurizing tower neutralization unit C, a spraying pump D and a primary mixing tank F; the desulfurizing tower comprises a desulfurizing tower spraying unit B, a desulfurizing tower absorption unit A and a desulfurizing tower neutralization unit C, wherein the desulfurizing tower spraying unit B, the desulfurizing tower absorption unit A and the desulfurizing tower neutralization unit C are sequentially arranged in a desulfurizing tower from top to bottom; the absorption unit A of the desulfurizing tower is provided with an original flue gas inlet, and the top of the spraying unit B of the desulfurizing tower is provided with a clean flue gas outlet; an absorption liquid outlet of the desulfurizing tower neutralization unit C is connected with an inlet of a spray pump D, and an outlet of the spray pump D is connected with an inlet of a desulfurizing tower spray unit B; the absorption liquid outlet of the desulfurizing tower neutralization unit C is connected with the inlet of the primary mixing tank F, the outlet of the primary mixing tank F is connected with the inlet of the desulfurizing tower neutralization unit C, and the primary mixing tank F is provided with the inlet of a desulfurizing agent.
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| JP2000084351A (en) * | 1998-09-09 | 2000-03-28 | Toyo Eng Corp | Desulfurization of waste gas |
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