CN115504495B - Method for decomposing phosphogypsum by recycling tail gas - Google Patents
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Abstract
The invention discloses a method for decomposing phosphogypsum by recycling tail gas, which is prepared according to the amount of phosphogypsum to be treatedThe required carbonaceous raw material is then subjected to SO as required in the tail gas 2 Concentration calculation of CO content 2 The gas inlet amount; part of the carbonaceous raw materials and all phosphogypsum enter the reduction furnace from the main feed inlet at the same time, and the rest part of the carbonaceous raw materials uniformly enter the reduction furnace from the secondary feed inlet according to the reaction residence time of the phosphogypsum in the reduction furnace; containing CO 2 The gas is introduced from the gas inlet; decomposing phosphogypsum in a reduction furnace; the tail gas generated after phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then as the CO content required for the next phosphogypsum decomposition 2 The gas is used, and the tail gas is recycled until the introduced gas tends to be CO 2 Equilibrium is reached.
Description
Technical Field
The invention relates to a method for decomposing phosphogypsum by recycling tail gas.
Background
Phosphogypsum is a solid waste produced in a wet-process phosphoric acid process, the composition of phosphogypsum is complex, besides hydrated calcium sulfate, phosphorus ore which is not completely decomposed, residual phosphoric acid, fluoride, acid insoluble substances, organic matters and the like are also included, wherein the presence of fluorine and organic matters has the greatest influence on the recycling of phosphogypsum, and stacking occupies a large amount of land and causes pollution to water resources and land resources. According to statistics of the Chinese phosphate fertilizer industry association, the total discharge amount of phosphogypsum in 2020 is about 7500-8000 ten thousand tons, and although many industries try to use phosphogypsum, the utilization rate is low, the domestic stock amount is up to more than 6 hundred million tons, the world is up to more than 60 hundred million tons, the phosphogypsum is recycled, and the phosphogypsum is safely and efficiently utilized, so that the method has important significance in solving the problem of environmental pollution and resource waste caused by stacking treatment.
The phosphogypsum is used as a CaO source to produce cement clinker, so that the method has the advantages of solving the challenging and meaning direction of phosphogypsum resource utilization, enabling CaO in the clinker to be mainly provided by phosphogypsum, improving the utilization rate of phosphogypsum and reducing the carbon dioxide emission problem of limestone in cement production. Portland cement clinker pair SO with wide application in market 3 The content has stringent requirements, but CaSO 4 Relative to CaCO 3 In other words, it needs to be done at a higher temperatureFull decomposition and desulfurization, so that phosphogypsum raw material is not blocked by melting during decomposition, in order to save energy, it is necessary to provide a reducing atmosphere to decompose and desulfurize phosphogypsum in a low temperature environment of 900-1100 ℃.
The control of the reducing atmosphere is the key to decomposing phosphogypsum, and the main reaction formula of phosphogypsum decomposition is as follows:
the decomposition and desulfurization of phosphogypsum under the low-temperature environment of 900-1100 ℃ mainly depends on the reaction 4, the reaction 5 is unfavorable for the desulfurization of phosphogypsum, the reaction 6 needs to be carried out at the temperature of more than 1200 ℃ and has a slower speed, and CaS can be oxidized into CaO and CaSO under the high-temperature condition of the subsequent calcination of clinker 4 Solid-solid reaction of reaction 6 is carried out to release SO 2 Adversely affecting the calcination of the clinker. A great deal of literature and research show that the reaction mainly occurs when the concentration of CO in the reducing atmosphere is lower than 10%, and the reaction mainly occurs when the concentration of CO is higher than 10%, and the reaction mainly occurs 5, and the reduction potential is P (CO)/P (CO) 2 ) Can also affect the reactionsBy P (CO)/P (CO) 2 ) Below 0.20, reaction 4, P (CO)/P (CO) occurs predominantly 2 ) Above 0.20, reaction 5 mainly occurs, while CaSO 4 Decomposition takes place to bring about SO in the atmosphere 2 Too high a concentration will also inhibit the reaction 4 but in order to bring about SO in the tail gas 2 Is easier to recycle to prepare H 2 SO 4 Thus SO in the tail gas 2 The concentration should be above 8%.
In order to create a reducing atmosphere with a CO concentration below 10% and to let P (CO)/P (CO) 2 ) Below 0.20, let CaSO 4 Decomposing in CaO direction, adopting atmosphere bottle in various researches, and preparing the raw materials of carbon and O 2 、CO、CO 2 The inert gas is controlled to reach the atmosphere condition, however, in actual production, an expensive atmosphere bottle cannot be used, only a carbonaceous raw material and air can be used for creating a reducing atmosphere, C can be regarded as reaction 1 and then reaction 3, and air can be regarded as O 2 21% and 79% inert gas, the use of carbonaceous feedstock and air alone increases the amount of carbonaceous feedstock and increases the CO 2 Emission amount, and cannot meet the CO concentration, P (CO)/P (CO) required by the atmosphere condition at the same time 2 ) SO in tail gas 2 Concentration.
How to utilize the existing low-price raw materials and gases in actual production so as to reduce the consumption of carbonaceous raw materials and CO 2 The discharge amount and the perfect regulation and control of phosphogypsum decomposition atmosphere become technical problems to be solved urgently.
Disclosure of Invention
The invention aims to provide a method for decomposing phosphogypsum by recycling tail gas, which utilizes the existing low-price raw materials and gases in actual production to reduce the consumption of carbonaceous raw materials and CO 2 Emission amount, and CO concentration, P (CO)/P (CO) required by phosphogypsum decomposition atmosphere 2 ) At the same time ensure SO in the tail gas 2 The concentration is easier to recycle to prepare H 2 SO 4 。
In order to achieve the above purpose, the following technical scheme is adopted:
a method for decomposing phosphogypsum by recycling tail gas comprises the following steps:
(1) According to the instituteAdding the required carbon raw material into the phosphogypsum to be treated, and then according to the required SO in the tail gas 2 Concentration calculation of CO content 2 The gas inlet amount;
(2) Part of the carbonaceous raw materials and all phosphogypsum enter the reduction furnace from the main feed inlet at the same time, and the rest part of the carbonaceous raw materials uniformly enter the reduction furnace from the secondary feed inlet according to the reaction residence time of the phosphogypsum in the reduction furnace; containing CO 2 The gas is introduced from the gas inlet; decomposing phosphogypsum in a reduction furnace;
(3) The tail gas generated after phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then as the CO content required for the next phosphogypsum decomposition 2 The gas is used, and the tail gas is recycled until the introduced gas tends to be CO 2 Equilibrium is reached.
According to the scheme, the carbonaceous raw material in the step (1) is one or more of common coal, high-sulfur coal and coke; c in the carbonaceous raw material and SO in phosphogypsum 3 The molar ratio of (2) is x, x=0.5-0.8.
According to the above scheme, the CO-containing gas in the step (1) 2 The gas is air after complete combustion, wherein the inert gas content is d 0 ，CO 2 The content is A 0 The method comprises the steps of carrying out a first treatment on the surface of the Setting SO in tail gas 2 Concentration W SO2 8-15%; x is known to be C and SO in phosphogypsum 3 Molar ratio of (3); known set value W SO2 X, d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculated to contain CO 2 The amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 Is a value of (2).
According to the scheme, in the step 2, a part of carbonaceous raw material is firstly added to enable the initial value of the CO concentration to be lower than 10%, and then a second part is uniformly added according to the reaction residence time of phosphogypsum in a reduction furnace, so that the CO concentration is kept below 10%.
According to the scheme, SO is passed in the step (3) 2 The tail gas after recycling is continuously led in from the air inlet according to the calculated inlet amount in the step (1) to lead the next batch of phosphorusSO in tail gas after gypsum decomposition 2 The concentration is unchanged, and the redundant gas is discharged into the atmosphere.
In step (1) with CO 2 The amount of gas is calculated for the air after complete combustion, wherein the inert gas is d 0 (79%) CO 2 Is A 0 (21%); caSO in phosphogypsum 4 The main reaction formula of the decomposition is:
xC+A 0 CO 2 →2xCO+(A 0 -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
general reaction formula: caSO (Caso-like conductor) 4 +xC+A 0 CO 2 →CaO+SO 2 +(2x-1)CO+(A 0 -x+1)CO 2
To decompose 1mol of CaSO 4 Is standard, SO in the tail gas 2 Concentration W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) In order to make SO in tail gas 2 Is easier to recycle to prepare H 2 SO 4 Thus SO in the tail gas 2 The concentration is above 8%, and the set value W is finally known SO2 X, d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculated to contain CO 2 The amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 Is a value of (2).
The variation trend of the tail gas component in the step (3) can be calculated as follows, the number of times of recycling the tail gas is set as n, and CO in the gas is introduced 2 The quantity of (A) is set as A n The amount of inert gas is d n ＝(A 0 /21％)-A n CaSO in phosphogypsum 4 The main reaction formula of the decomposition is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
general reaction formula: caSO (Caso-like conductor) 4 +xC+A n CO 2 →CaO+SO 2 +(2x-1)CO+(A n -x+1)CO 2
To decompose 1mol of CaSO 4 Is standard due to the tail gas passing through SO 2 Recycling H production 2 SO 4 When there is O 2 Takes part in the reaction, and the temperature is 400-600 ℃, CO with 2x-1 remaining in the tail gas can also be mixed with O 2 CO is generated by reaction 2 The low concentration of CO in the process can be regarded as being converted to CO entirely 2 The relationship after recycling the tail gas is as follows:
A n+1 ＝{(A 0 /21％)/[(A 0 /21％)+x]}*(A n +x)，n＝0,1,2...
the general term formula can be further solved as follows:
A n ＝(A 0 /21％)-[(A 0 /21％)-A 0 ]*{(A 0 /21％)/[(A 0 /21％)+x]}^n，n＝0,1,2...
d is then n ＝[(A 0 /21％)-A 0 ]*{(A 0 /21％)/[(A 0 /21％)+x]}^n，n＝0,1,2...
When n=0, a n ＝A 0 ，d n ＝d 0 ＝(A 0 /21％)-A 0 The method comprises the steps of carrying out a first treatment on the surface of the When n → +. In the case of infinity, the air conditioner is controlled, A is that n ＝A 0 /21％，d n =0. The relation indicates that recycling the tail gas can lead the tail gas and CO in the gas 2 Gradually increasing the inert gas content until the gas feed tends to be CO in its entirety 2 Equilibrium is reached.
The amount of the carbonaceous material divided into two in the step (2) can be adjusted according to the calculated trend of the gas composition to decompose 1mol of CaSO 4 For the standard, set CaSO 4 The amount of decomposed reaction is t, t E [0,1]The main reaction formula is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
tCaSO 4 +tCO→tCaO+tSO 2 +tCO 2
general reaction formula: tCaSO 4 +xC+A n CO 2 →tCaO+tSO 2 +(2x-t)CO+(A n -x+t)CO 2
Can be obtained with 1mol of CaSO 4 The reaction is gradually participated and decomposed, and the calculation formula of each gas amount and concentration is as follows:
CO amount = 2x-t;
CO concentration= (2 x-t)/(t+2x-t+A) n -x+t+d n )＝{[3x+(A 0 /21％)]/[t+x+(A 0 /21％)]}-1；
CO 2 Quantity=a n -x+t；
CO 2 Concentration= (a n -x+t)/(t+2x-t+A n -x+t+d n )＝1-{[2x+(A 0 /21％)-A n ]/[t+x+(A 0 /21％)]}；
SO 2 Quantity = t;
SO 2 concentration = t/(t+2x-t+a) n -x+t+d n )＝1-{[x+(A 0 /21％)]/[t+x+(A 0 /21％)]}；
Amount of inert gas d n ＝(A 0 /21％)-A n ；
Inert gas concentration = d n /(t+2x-t+A n -x+t+d n )＝[(A 0 /21％)-A n ]/[t+x+(A 0 /21％)]；
P(CO)/P(CO 2 )＝(2x-t)/(A n -x+t)＝[(A n +x)/(t+A n -x)]-1。
At this time, the change trend of the CO concentration in the atmosphere can be calculated, the initial value of the CO concentration is higher than 10 percent, and the CO concentration is 1mol of CaSO 4 Gradually participate in the reaction to be decomposed, and the concentration of CO is gradually reduced, so the carbonaceous raw material can be divided into two parts according to the calculated CO concentration change trend, the first part is added firstly to enable the initial value of the concentration of CO to be lower than 10 percent, and then the second part is uniformly added according to the reaction residence time of each batch of phosphogypsum in the reduction furnace, thereby keeping the concentration of CO below 10 percent, and being beneficial to CaSO 4 Decomposing and desulfurizing in CaO direction, recycling tail gas for a sufficient number of times, and then CO 2 Concentration is increased, P (CO)/P (CO) 2 ) Can be lower than 0.20, and is more beneficial to CaSO 4 Decomposing and desulfurizing in the direction of CaO and suppressing CaSO 4 Decomposing towards the CaS direction, and improving the desulfurization rate of phosphogypsum.
The invention is thatCaSO in 4 The reaction formula for decomposition is as follows:
in practical cases, the reaction 1 and the reaction 2 are mainly, and the reaction 3 and the reaction 4 are secondary, and are all endothermic reversible reactions. Low CO concentration and high CO content 2 The concentration can suppress the occurrence of reaction 3 to a large extent.
Reaction 1 has a chemical equilibrium constant k=c at 900-1100 °c 2 (CO)/c(CO 2 ) Larger, 3.597 x 10, 1.395 x 10 respectively 2 、4.408*10 2 Decomposition of CaSO 4 The required C can be approximately seen as initially being fully CO-capable 2 Generating CO by reaction, and recycling tail gas to make CO 2 An increase in concentration will allow reaction 1 to proceed more fully in the forward direction.
Although theoretically 0.5mol of C is sufficient to pass reaction 1 and reaction 2 to make 1mol of CaSO 4 Decomposition desulfurization, however, given that reaction 2 is a reversible reaction and occurs with partial reaction 3, there is actually CO remaining and CaSO 4 Does not meet the requirements of decomposing and desulfurizing, thus CaSO 4 After decomposing to a certain extent, the CO needs to be rich to promote the reaction 2 to continue, thereby reaching CaSO 4 SO C in the carbonaceous raw material and SO in phosphogypsum 3 The molar ratio of 0.5 to 0.8 is suitable, and too high a concentration of CO and P (CO)/P (CO) increase 2 ) So that reaction 3 occurs.
Compared with the prior art, the invention has the following beneficial effects:
the method for decomposing phosphogypsum by recycling tail gas can simultaneously realize the concentration of CO and the concentration of P (CO)/P (CO) required by phosphogypsum decomposition atmosphere by utilizing the existing low-price raw materials and gases in actual production 2 ) SO in tail gas 2 The concentration is regulated to decompose phosphogypsum towards CaO direction, and the dosage of carbonaceous raw materials and CO are reduced 2 The discharge amount further realizes the industrialized application of phosphogypsum decomposition.
Drawings
Fig. 1: the invention realizes the process diagram for decomposing phosphogypsum by recycling tail gas.
Fig. 2: x=0.7 and W SO2 =12%, and the cyclic utilization of tail gas is enough, and the change curve of each gas concentration.
Fig. 3: x=0.7 and W SO2 The tail gas is recycled by 12 percent, and P (CO) is P (CO) 2 ) Is a change curve of (a).
Fig. 4: x=0.6 and W SO2 =12%, and the cyclic utilization of tail gas is enough, and the change curve of each gas concentration.
Fig. 5: x=0.6 and W SO2 The tail gas is recycled by 12 percent, and P (CO) is P (CO) 2 ) Is a change curve of (a).
Detailed Description
The following examples further illustrate the technical aspects of the present invention, but are not intended to limit the scope of the present invention.
In a specific embodiment, a method for decomposing phosphogypsum by recycling tail gas is provided, and is shown in fig. 1:
(1) Firstly, adding the required carbonaceous raw materials according to the amount of phosphogypsum to be treated in each batch, and then, according to the required SO (sulfur dioxide) in the tail gas 2 Calculating the amount of the gas introduced by concentration;
(2) Phosphogypsum enters a reduction furnace from a main feed inlet according to batches; dividing a carbonaceous raw material required for decomposing each batch of phosphogypsum into two parts, wherein the first part of carbonaceous raw material and phosphogypsum enter a reduction furnace from a main feeding port or enter the reduction furnace from a secondary feeding port, and the second part of carbonaceous raw material uniformly enter the reduction furnace from the secondary feeding port according to the reaction residence time of each batch of phosphogypsum in the reduction furnace; all the gas required for decomposing each batch of phosphogypsum is introduced from the gas inlet; decomposing phosphogypsum in a reduction furnace;
(3) The tail gas generated after the phosphogypsum of the previous batch is decomposed is subjected to SO 2 Recycling H production 2 SO 4 Then is used as the gas required by the decomposition of the next phosphogypsum, thus recycling the tail gas until the gas tends to be CO 2 Equilibrium is reached.
Specifically, the carbonaceous raw material in the step (1) is one or more of common coal, high-sulfur coal and coke; c in the carbonaceous raw material and SO in phosphogypsum 3 The molar ratio of (2) is x, x=0.5-0.8.
Specifically, the amount of the introduced gas in the step (1) is calculated according to the air after complete combustion, and the inert gas in the air after combustion is d 0 (79%) CO 2 Is A 0 (21%); caSO in phosphogypsum 4 The main reaction formula of the decomposition is:
xC+A 0 CO 2 →2xCO+(A 0 -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
general reaction formula: caSO (Caso-like conductor) 4 +xC+A 0 CO 2 →CaO+SO 2 +(2x-1)CO+(A 0 -x+1)CO 2
To decompose 1mol of CaSO 4 Is standard, SO in the tail gas 2 Concentration W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) In order to make SO in tail gas 2 Is easier to recycle to prepare H 2 SO 4 Thus SO in the tail gas 2 The concentration is above 8%, and the set value W is finally known SO2 X, d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculated to contain CO 2 The amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 Is a value of (2).
In particular, the tail gas is recycled in the step (3),it is prepared by SO 2 Continuously introducing the recycled tail gas from the air inlet according to the amount of the introduced gas calculated in the step (1) to enable SO in the tail gas after decomposing the next batch of phosphogypsum 2 The concentration is unchanged, and the redundant gas is discharged into the atmosphere.
Specifically, in the step (3), the gas is introduced, the trend of the gas component is calculated as follows, the number of times of recycling the tail gas is n, and CO in the gas is introduced 2 The quantity of (A) is set as A n The amount of inert gas is d n ＝(A 0 /21％)-A n CaSO in phosphogypsum 4 The main reaction formula of the decomposition is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
general reaction formula: caSO (Caso-like conductor) 4 +xC+A n CO 2 →CaO+SO 2 +(2x-1)CO+(A n -x+1)CO 2
To decompose 1mol of CaSO 4 Is standard due to the tail gas passing through SO 2 Recycling H production 2 SO 4 When there is O 2 Takes part in the reaction, and the temperature is 400-600 ℃, CO with 2x-1 remaining in the tail gas can also be mixed with O 2 CO is generated by reaction 2 The low concentration of CO in the process can be regarded as being converted to CO entirely 2 The relationship after recycling the tail gas is as follows:
A n+1 ＝{(A 0 /21％)/[(A 0 /21％)+x]}*(A n +x)，n＝0,1,2...
the general term formula can be further solved as follows:
A n ＝(A 0 /21％)-[(A 0 /21％)-A 0 ]*{(A 0 /21％)/[(A 0 /21％)+x]}^n，n＝0,1,2...
d is then n ＝[(A 0 /21％)-A 0 ]*{(A 0 /21％)/[(A 0 /21％)+x]}^n，n＝0,1,2...
When n=0, a n ＝A 0 ，d n ＝d 0 ＝(A 0 /21％)-A 0 The method comprises the steps of carrying out a first treatment on the surface of the When n → +. In the case of infinity, the air conditioner is controlled, A is that n ＝A 0 /21％，d n =0. The relation indicates that recycling the tail gas can lead the tail gas and CO in the gas 2 Gradually increasing the inert gas content until the gas feed tends to be CO in its entirety 2 Equilibrium is reached.
Specifically, the carbonaceous raw material is divided into two parts in the step (2), characterized in that the amount of the carbonaceous raw material divided into two parts is adjusted according to the calculated trend of the gas composition to decompose 1mol of CaSO 4 For the standard, set CaSO 4 The amount of decomposed reaction is t, t E [0,1]The main reaction formula is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
tCaSO 4 +tCO→tCaO+tSO 2 +tCO 2
general reaction formula: tCaSO 4 +xC+A n CO 2 →tCaO+tSO 2 +(2x-t)CO+(A n -x+t)CO 2
Can be obtained with 1mol of CaSO 4 The reaction is gradually participated and decomposed, and the calculation formula of each gas amount and concentration is as follows:
CO amount = 2x-t;
CO concentration= (2 x-t)/(t+2x-t+A) n -x+t+d n )＝{[3x+(A 0 /21％)]/[t+x+(A 0 /21％)]}-1；
CO 2 Quantity=a n -x+t；
CO 2 Concentration= (a n -x+t)/(t+2x-t+A n -x+t+d n )＝1-{[2x+(A 0 /21％)-A n ]/[t+x+(A 0 /21％)]}；
SO 2 Quantity = t;
SO 2 concentration = t/(t+2x-t+a) n -x+t+d n )＝1-{[x+(A 0 /21％)]/[t+x+(A 0 /21％)]}；
Amount of inert gas d n ＝(A 0 /21％)-A n ；
Inert gas concentration = d n /(t+2x-t+A n -x+t+d n )＝[(A 0 /21％)-A n ]/[t+x+(A 0 /21％)]；
P(CO)/P(CO 2 )＝(2x-t)/(A n -x+t)＝[(A n +x)/(t+A n -x)]-1。
At this time, the change trend of the CO concentration in the atmosphere can be calculated, the initial value of the CO concentration is higher than 10 percent, and the CO concentration is 1mol of CaSO 4 Gradually participate in the reaction to be decomposed, and the concentration of CO is gradually reduced, so the carbonaceous raw material can be divided into two parts according to the calculated CO concentration change trend, the first part is added firstly to enable the initial value of the concentration of CO to be lower than 10 percent, and then the second part is uniformly added according to the reaction residence time of each batch of phosphogypsum in the reduction furnace, thereby keeping the concentration of CO below 10 percent, and being beneficial to CaSO 4 Decomposing and desulfurizing in CaO direction, recycling tail gas for a sufficient number of times, and then CO 2 Concentration is increased, P (CO)/P (CO) 2 ) Can be lower than 0.20, and is more beneficial to CaSO 4 Decomposing and desulfurizing in the direction of CaO and suppressing CaSO 4 Decomposing towards the CaS direction, and improving the desulfurization rate of phosphogypsum.
Example 1
To decompose 1mol of CaSO 4 As a standard, when x=0.7 and W is set SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) When=12%, d 0 ＝(A 0 /21％)-A 0 The method can obtain:
A 0 ＝1.393，d 0 5.2403 gas charge = a 0 +d 0 ＝6.6333；
The general term formula can be further solved as follows:
A n ＝6.6333-5.2403*(6.6333/7.3333)^n，n＝0,1,2...
d is then n ＝5.2403*(6.6333/7.3333)^n，n＝0,1,2...
Can calculate and recycle SO 2 As shown in Table 1, the relationship between the number of times n of the tail gas after absorption and the atmosphere shows that C introduced after the cycle number is increased causes CaSO 4 Decomposing the generated CO 2 Gradually replace inert gas in the atmosphere, and 8.3333mol of SO in 1mol of tail gas 2 Is absorbed and utilized to prepare H 2 SO 4 And the remaining CO is converted into CO 2 At this time, 7.3333mol remained in the tail gas, and 6.6333mol was used as the next 1mol CaSO for decomposition 4 The gas is introduced into the atmosphere, and the excess 0.7mol of gas is discharged into the atmosphere, and after the circulation times are enough, the introduced gas is basically all CO 2 Every 1mol of CaSO 4 Decomposition of generated CO 2 The amount of the discharged material (i.e., the amount of C used) was 0.7mol.
Table 1 x =0.7 and W SO2 =12% recycling of SO 2 Relationship between the number of times n of the tail gas absorbed and the atmosphere.
To decompose 1mol of CaSO 4 For the standard, set CaSO 4 The amount of decomposed reaction is t, t E [0,1]Can be obtained with 1mol of CaSO 4 The reaction is gradually participated and decomposed, and the relation between the gas quantity and the concentration is as follows:
CO amount = 1.4-t;
CO concentration= (1.4-t)/(t+1.4-t+A) n -0.7+t+d n )＝[8.7333/(t+7.3333)]-1；
CO 2 Quantity=a n -0.7+t；
CO 2 Concentration= (a n -0.7+t)/(t+1.4-t+A n -0.7+t+d n )＝1-[(8.0333-A n )/(t+7.3333)]；
SO 2 Quantity = t;
SO 2 concentration = t/(t+1.4-t+a) n -0.7+t+d n )＝1-[7.3333/(t+7.3333)]；
Amount of inert gas d n ＝6.6333-A n ；
Inert gas concentration = d n /(t+1.4-t+A n -0.7+t+d n )＝(6.6333-A n )/(t+7.3333)；
P(CO)/P(CO 2 )＝(1.4-t)/(A n -0.7+t)＝[(A n +0.7)/(t+A n -0.7)]-1。
When the number of times of recycling the tail gas is enough to reach the levelBalance time, A n = 6.6333, plotting CaSO with 1mol according to the calculation result 4 Gradually participate in the reaction and are decomposed, and the concentration of each gas, P (CO), is P (CO) 2 ) As shown in fig. 2 and 3, respectively. Due to decomposition of CaSO 4 The initial CO concentration at the time was 19.09%, and the initial P (CO): P (CO) 2 ) 0.2360, higher, followed by CaSO 4 Gradually decomposing to reduce CO concentration to 4.80%, P (CO): P (CO) 2 ) Reduced to 0.0577. Thus, the carbonaceous feedstock is only partially added to reduce the initial CO concentration and the initial P (CO): P (CO) 2 ) The remaining carbonaceous feedstock is then added uniformly.
The carbonaceous raw material of this example was converted to decompose 1mol of CaSO based on the residence time of phosphogypsum in the reduction furnace 4 As a standard, 0.3mol of the carbonaceous raw material was added first, 6.6333mol of the whole recycled tail gas was introduced, and then another 0.4mol of the carbonaceous raw material was added uniformly according to half of the reaction residence time. The method can better stabilize the atmosphere to be suitable for CaSO 4 In the range of decomposition desulfurization.
Example 2
To decompose 1mol of CaSO 4 As a standard, when x=0.6 and W is set SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) When=12%, d 0 ＝(A 0 /21％)-A 0 The method can obtain:
A 0 ＝1.414，d 0 5.3193 gas charge = a 0 +d 0 ＝6.7333；
The general term formula can be further solved as follows:
A n ＝6.7333-5.3193*(6.7333/7.3333)^n，n＝0,1,2...
d is then n ＝5.3193*(6.7333/7.3333)^n，n＝0,1,2...
Can calculate and recycle SO 2 As shown in Table 2, the relationship between the number of times n of the tail gas after absorption and the atmosphere shows that the introduced C causes CaSO after the cycle number is increased 4 Decomposing the generated CO 2 Gradually replace inert gas in the atmosphere, and 8.3333mol of tail gas is 1mSO of ol 2 Is absorbed and utilized to prepare H 2 SO 4 And the remaining CO is converted into CO 2 At this time, 7.3333mol remained in the tail gas, and 6.7333mol was used as the next 1mol CaSO for decomposition 4 The gas is introduced into the atmosphere, and the excess 0.6mol of gas is discharged into the atmosphere, and after the circulation times are enough, the introduced gas is basically all CO 2 Every 1mol of CaSO 4 Decomposition of generated CO 2 The amount of the discharged material (i.e., the amount of C used) was 0.6mol.
Table 2x =0.6 and W SO2 =12% recycling of SO 2 Relationship between the number of times n of the tail gas absorbed and the atmosphere.
To decompose 1mol of CaSO 4 For the standard, set CaSO 4 The amount of decomposed reaction is t, t E [0,1]Can be obtained with 1mol of CaSO 4 The reaction is gradually participated and decomposed, and the relation between the gas quantity and the concentration is as follows:
CO amount = 1.2-t;
CO concentration= (1.2-t)/(t+1.2-t+A) n -0.6+t+d n )＝[8.5333/(t+7.3333)]-1；
CO 2 Quantity=a n -0.6+t；
CO 2 Concentration= (a n -0.6+t)/(t+1.2-t+A n -0.6+t+d n )＝1-[(7.9333-A n )/(t+7.3333)]；
SO 2 Quantity = t;
SO 2 concentration = t/(t+1.2-t+a) n -0.6+t+d n )＝1-[7.3333/(t+7.3333)]；
Amount of inert gas d n ＝6.7333-A n ；
Inert gas concentration = d n /(t+1.2-t+A n -0.6+t+d n )＝(6.7333-A n )/(t+7.3333)；
P(CO)/P(CO 2 )＝(1.2-t)/(A n -0.6+t)＝[(A n +0.6)/(t+A n -0.6)]-1。
When the number of times of recycling the tail gas is enough to reach balance, A n = 6.7333, plotting CaSO with 1mol according to the calculation result 4 Gradually participate in the reaction and are decomposed, and the concentration of each gas, P (CO), is P (CO) 2 ) As shown in fig. 4 and 5, respectively. Due to decomposition of CaSO 4 The initial CO concentration at the time was 16.36%, and the initial P (CO): P (CO) 2 ) 0.1957, higher, followed by CaSO 4 Gradually decomposing to reduce CO concentration to 2.40%, P (CO): P (CO) 2 ) Reduced to 0.0280. Thus, the carbonaceous feedstock is only partially added to reduce the initial CO concentration and the initial P (CO): P (CO) 2 ) The remaining carbonaceous feedstock is then added uniformly.
The carbonaceous raw material of this example was converted to decompose 1mol of CaSO based on the residence time of phosphogypsum in the reduction furnace 4 As a standard, 0.3mol of the carbonaceous material was added first, 6.7333mol of the entire recycled tail gas was introduced, and then another 0.3mol of the carbonaceous material was added uniformly according to half of the reaction residence time. The method can better stabilize the atmosphere to be suitable for CaSO 4 In the range of decomposition desulfurization.
Comparative example 1
Air (O) is adopted for each air inlet 2 21% by weight, otherwise considered as inert gas), without recycling tail gas, to decompose 1mol of CaSO 4 Taking C in the carbonaceous raw material and SO in phosphogypsum as standards 3 Is x in molar ratio 0 +x, firstly C and all O in air 2 CO is generated by reaction 2 Then superfluous C and CO 2 CO is generated by reaction, and the main reaction formula is:
x 0 C+x 0 O 2 →x 0 CO 2
xC+x 0 CO 2 →2xCO+(x 0 -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
general reaction formula: caSO (Caso-like conductor) 4 +(x 0 +x)C+x 0 O 2 →CaO+SO 2 +(2x-1)CO+(x 0 -x+1)CO 2
O in air 2 The amount is x 0 Amount of inert gas d 0 ＝(x 0 /21％)-x 0 ；
When x=0.7 and W is set SO2 ＝1/(1+2x-1+x 0 -x+1+d 0 ) When=12%, it is possible to obtain:
x 0 ＝1.393，d 0 5.2403 gas charge = x 0 +d 0 ＝6.6333；
The atmosphere was changed in the same manner as in example 1, but 1mol of CaSO was decomposed 4 The mass of C required is x 0 +x＝1.393+0.7＝2.093mol。
To decompose 1mol of CaSO 4 As a standard, in comparative example 1, air (O) was used for each gas passage 2 21% by weight, otherwise regarded as inert gas), the tail gas was not recycled, and the amount of C was 2.093mol, which was significantly higher than 0.7mol in example 1, in order to achieve the same atmosphere conditions as in example 1 when the tail gas was not recycled; CO with exhaust gas discharged to atmosphere 2 The discharge amount was 2.093mol, which was also significantly higher than 0.7mol in example 1; the reason is that SO in the tail gas 2 When the concentration is 12%, the amount of the gas to be introduced is large, and O in the air 2 The ratio is 21 percent, and when the air is introduced, the air is used for the whole process to lead O to be 2 The amount of the catalyst is too high, so that the amount of C is obviously increased, and the tail gas is completely discharged into the atmosphere to enable CO to be discharged 2 Is not utilized, thereby obviously increasing CO 2 Discharge amount.
In the research of a large number of documents, the inert gas atmosphere bottle is adopted to reduce O 2 Concentration of or use CO 2 Atmosphere bottle exclusion O 2 The method of recycling the tail gas in example 1 and example 2 is adopted, and the concentration of CO and SO are as follows 2 The change trend of the concentration is kept unchanged, and CO 2 The concentration gradually increases until the gas tends to be CO 2 When reaching equilibrium, at this time CO 2 Increased concentration and P (CO)/P (CO) 2 ) Is further beneficial to CaSO 4 Toward CaODirectional decomposition and desulfurization, and inhibition of CaSO 4 Decomposing towards the CaS direction, and improving the desulfurization rate of phosphogypsum.
Next, in example 1 and example 2, the carbonaceous raw material was fed into the reduction furnace in two portions, the first portion was fed so that the initial value of the CO concentration was lower than 10%, and then the second portion was uniformly fed according to the residence time of each phosphogypsum in the reduction furnace so that the CO concentration was maintained at 10% or less, while P (CO)/P (CO) 2 ) At most 0.20 SO in the tail gas 2 The concentration was kept at 12%.
The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.
Claims (3)
1. A method for decomposing phosphogypsum by recycling tail gas is characterized by comprising the following steps:
(1) Adding the required carbonaceous raw materials according to the required amount of phosphogypsum to be treated, and then obtaining SO according to the required amount of the tail gas 2 Concentration calculation of CO content 2 The gas inlet amount; c in the carbonaceous raw material and SO in phosphogypsum 3 The molar ratio of (2) is x, x=0.5-0.8; the CO containing 2 The gas is air after complete combustion, wherein the inert gas content is d 0 ，CO 2 The content is A 0 The method comprises the steps of carrying out a first treatment on the surface of the Setting SO in tail gas 2 Concentration W SO2 8-15%; x is known to be C and SO in phosphogypsum 3 Molar ratio of (3); known set value W SO2 X, d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculated to contain CO 2 The amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 Is a value of (2);
(2) Part of the carbonaceous raw materials and all phosphogypsum enter the reduction furnace from the main feed inlet at the same time, and the rest part of the carbonaceous raw materials uniformly enter the reduction furnace from the secondary feed inlet according to the reaction residence time of the phosphogypsum in the reduction furnace; containing CO 2 Gas slaveThe air inlet is communicated; decomposing phosphogypsum in a reduction furnace; firstly adding a part of carbonaceous raw materials to enable the initial value of the concentration of CO to be lower than 10%, and then uniformly adding a second part according to the reaction residence time of phosphogypsum in a reduction furnace, so that the concentration of CO is kept below 10%;
(3) The tail gas generated after phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then as the CO content required for the next phosphogypsum decomposition 2 The gas is used, and the tail gas is recycled until the introduced gas tends to be CO 2 Equilibrium is reached.
2. The method for decomposing phosphogypsum by recycling tail gas as set forth in claim 1, wherein the carbonaceous raw material in the step (1) is one or more of common coal, high sulfur coal and coke.
3. The method for decomposing phosphogypsum by recycling tail gas as set forth in claim 1, wherein SO is passed through in step (3) 2 The tail gas after recycling is continuously led in from an air inlet according to the calculated inlet amount in the step (1), SO that SO in the tail gas after decomposing the phosphogypsum of the next batch 2 The concentration is unchanged, and the redundant gas is discharged into the atmosphere.
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