CN115504495A - 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 comprises the steps of adding required carbonaceous raw materials according to the amount of the phosphogypsum to be treated, and then adding SO required to be obtained in the tail gas 2 Concentration calculation of CO content 2 The amount of gas introduced; a part of carbonaceous raw materials and all the phosphogypsum simultaneously enter the reducing furnace from the main feeding port, and the rest part of carbonaceous raw materials uniformly enter the reducing furnace from the secondary feeding port according to the reaction residence time of the phosphogypsum in the reducing furnace; containing CO 2 Gas is introduced from a gas inlet; decomposing phosphogypsum in a reducing furnace; the tail gas generated after the phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then used as CO needed by the next batch of phosphogypsum for decomposition 2 The tail gas is recycled until the introduced gas tends to be all CO 2 Equilibrium is reached.
Description
Technical Field
The invention relates to a method for decomposing phosphogypsum by recycling tail gas.
Background
The phosphogypsum is a solid waste generated in a wet-process phosphoric acid process, the composition of the phosphogypsum is complex, besides calcium sulfate hydrate, incompletely decomposed phosphorite, residual phosphoric acid, fluoride, acid insoluble substances, organic matters and the like are also included, wherein the existence of fluorine and the organic matters has the greatest influence on the resource utilization of the phosphogypsum, the stacking occupies a large amount of land, and the water resource and the land resource are polluted. According to the statistics of the China phosphorus fertilizer industry Association, the total emission amount of phosphogypsum in 2020 is about 7500-8000 million tons, and although many industries try to use the phosphogypsum, the utilization rate is low, the domestic stock of the phosphogypsum reaches more than 6 hundred million tons, and more than 60 hundred million tons in the world, and the phosphogypsum is recycled, safe and efficient, and has important significance for solving the problems of environmental pollution and resource waste caused by stacking treatment.
The phosphogypsum replaces limestone to be used as a CaO source to produce the cement clinker, which is a direction with challenge and significance for solving the resource utilization of the phosphogypsum, can ensure that CaO in the clinker is mainly provided by the phosphogypsum, improve the utilization rate of the phosphogypsum and reduce the problem of carbon dioxide emission of the limestone in the cement production. Portland cement clinker pair SO widely applied in market 3 The content has stringent requirements, but CaSO 4 Relative to CaCO 3 In other words, it needs to be decomposed and desulfurized completely at higher temperature, and in order to save energy, the phosphogypsum raw meal is not melted and blocked during decomposition, so that a reducing atmosphere needs to be provided to decompose and desulfurize the phosphogypsum in a low-temperature environment of 900-1100 ℃.
The control of the reducing atmosphere is the key to the decomposition of phosphogypsum, and the main reaction formula of the phosphogypsum decomposition is as follows:
the phosphogypsum is decomposed and desulfurized at the low temperature of 900-1100 ℃ mainly by the reaction 4, the reaction 5 is unfavorable for the desulfurization of the phosphogypsum, the reaction 6 needs to be carried out at the temperature of more than 1200 ℃ and has lower speed, and the CaS can be oxidized into CaO and CaSO under the high-temperature condition of subsequent calcined clinker 4 And carrying out a solid-solid reaction of reaction 6 to release SO 2 Adversely affecting the calcination of the clinker. A large number of documents and studies have shown that reactions 4 occur predominantly at CO concentrations below 10%, reactions 5 occur predominantly at CO concentrations above 10%, the reduction potential being P (CO)/P (CO) 2 ) Also influence the progress of each reaction, P (CO)/P (CO) 2 ) Below 0.20 the reaction 4, P (CO)/P (CO) occurs predominantly 2 ) Above 0.20, reaction 5 occurs mainly, while CaSO 4 Decomposition occurs to make SO in the atmosphere 2 Too high a concentration also inhibits the occurrence of reaction 4, but in order to make SO in the off-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%.
To create a reducing atmosphere with a CO concentration of less than 10% and to make P (CO)/P (CO) 2 ) Less than 0.20, allowing the CaSO to stand 4 Decomposing CaO, and using atmosphere bottle in various researches by using carbonaceous raw material and O 2 、CO、CO 2 However, in actual production, it is impossible to use an expensive atmosphere bottle, and only a carbon raw material and air can be used to create a reducing atmosphere, C can be considered as reaction 1 and then reaction 3, and air can be considered as O 2 21% and 79% inert gas, and increasing the amount of carbonaceous material and increasing the amount of CO by using only carbonaceous material and air 2 Discharge amount ofThe concentration of CO, P (CO)/P (CO) required by the atmosphere conditions cannot be satisfied at the same time 2 ) And SO in the exhaust gas 2 And (4) concentration.
How to utilize the existing low-price raw materials and gases in the actual production so as to reduce the dosage of the carbonaceous raw materials and reduce CO 2 The discharge amount and the realization of the perfect regulation and control of the 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 Discharge amount, and realizes the concentration of CO, P (CO)/P (CO) required by phosphogypsum decomposition atmosphere 2 ) While ensuring SO in the tail gas 2 The concentration is easier to recover to prepare H 2 SO 4 。
In order to achieve the purpose, the technical scheme is as follows:
a method for decomposing phosphogypsum by recycling tail gas comprises the following steps:
(1) Adding the required carbonaceous raw material according to the amount of the phosphogypsum to be treated, and then adding the SO required in the tail gas 2 Concentration calculation of CO content 2 The amount of gas introduced;
(2) A part of carbonaceous raw materials and all the phosphogypsum simultaneously enter the reduction furnace from the main feeding port, and the rest part of carbonaceous raw materials uniformly enter the reduction furnace from the secondary feeding port according to the reaction residence time of the phosphogypsum in the reduction furnace; containing CO 2 Gas is introduced from a gas inlet; decomposing phosphogypsum in a reducing furnace;
(3) The tail gas generated after the phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then used as CO needed by the next batch of phosphogypsum for decomposition 2 Gas use, such recycling of tail gas until the gas is fed in tends to be all 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 carbonaceous raw material and SO in phosphogypsum 3 Is x, x =0.5-0.8.
According to the scheme, the CO is contained in the step (1) 2 The gas is air after complete combustion, wherein the content of inert gas is d 0 ，CO 2 Content of A 0 (ii) a Setting SO in exhaust gas 2 Concentration W SO2 8 to 15 percent; x is known to be C and SO in phosphogypsum 3 The molar ratio of (a); given the set value W SO2 X, and d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculating to contain CO 2 Amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 The value of (c).
According to the scheme, in the step 2, a part of carbonaceous raw materials are 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 the phosphogypsum in the reduction furnace, so that the CO concentration is kept below 10%.
According to the scheme, SO is carried out in the step (3) 2 The recycled tail gas is continuously introduced from the gas inlet according to the calculated introduction amount in the step (1), SO that SO in the tail gas after the next batch of phosphogypsum is decomposed 2 The concentration is unchanged and the excess gas is vented to the atmosphere.
In the step (1), the catalyst contains CO 2 The amount of gas is calculated as air after complete combustion, where the inert gas is d 0 (79%) CO 2 Is A 0 (21%) of; let CaSO in phosphogypsum 4 The main reaction formula of decomposition is:
xC+A 0 CO 2 →2xCO+(A 0 -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
the general reaction formula is as follows: caSO 4 +xC+A 0 CO 2 →CaO+SO 2 +(2x-1)CO+(A 0 -x+1)CO 2
To decompose 1mol of CaSO 4 If the standard is satisfied, 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 the exhaust gas 2 Is easier to recycle to prepare H 2 SO 4 Thus SO in the tail gas 2 The concentration should be 8%From the above, the final known set value W SO2 X, and d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculating to contain CO 2 Amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 The value of (c).
The change trend of the tail gas component in the step (3) can be calculated by setting the number of times of recycling the tail gas as n and introducing CO in the gas 2 Is set as A n Then the amount of inert gas is d n ＝(A 0 /21％)-A n CaSO in phosphogypsum 4 The main reaction formula of decomposition is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
the general reaction formula is as follows: caSO 4 +xC+A n CO 2 →CaO+SO 2 +(2x-1)CO+(A n -x+1)CO 2
To decompose 1mol of CaSO 4 As a standard, the tail gas is subjected to SO 2 Recycle system H 2 SO 4 Sometimes has O 2 The reaction is carried out, the temperature is 400-600 ℃, and the residual 2x-1 CO in the tail gas can be mixed with O 2 Reaction to CO 2 The CO concentration in the process is low and can be regarded as being converted into CO completely 2 The relation after recycling the tail gas can be obtained as follows:
A n+1 ＝{(A 0 /21％)/[(A 0 /21％)+x]}*(A n +x)，n＝0,1,2...
the general 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...
then d 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 (ii) a When n → + ∞ is reached, A n ＝A 0 /21％，d n =0. The relation shows that recycling the tail gas can lead the tail gas and CO in the introduced gas 2 Gradually increases the content of inert gas and gradually decreases until the gas is introduced and tends to be totally CO 2 Equilibrium is reached.
The amount of the carbonaceous feedstock divided into two in step (2) may be adjusted according to the calculated gas composition variation trend to decompose 1mol of CaSO 4 As a standard, set CaSO 4 The amount of the decomposition participating in the reaction is t, t epsilon [0,1]The main reaction formula is as follows:
xC+A n CO 2 →2xCO+(A n -x)CO 2
tCaSO 4 +tCO→tCaO+tSO 2 +tCO 2
the general reaction formula is as follows: tCaSO 4 +xC+A n CO 2 →tCaO+tSO 2 +(2x-t)CO+(A n -x+t)CO 2
The CaSO can be obtained along with 1mol 4 Gradually participate in the reaction and are decomposed, and the calculation formula of each gas quantity 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 Amount = 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。
The trend of the CO concentration in the atmosphere can be calculated at this time, and the initial value of the CO concentration is higher than 10 percent along with 1mol of CaSO 4 The carbon raw material is divided into two parts according to the change trend of the CO concentration calculated here, the first part is added firstly to ensure that the initial value of the CO concentration is lower than 10%, and then the second part is uniformly added according to the reaction residence time of each batch of phosphogypsum in a reducing furnace to ensure that the CO concentration is kept below 10%, thus being beneficial to CaSO 4 Decomposing and desulfurizing in the direction of CaO, and recycling CO after sufficient times of tail gas 2 Increased concentration of P (CO)/P (CO) 2 ) Will also be lower than 0.20, more beneficial to CaSO 4 Decompose and desulfurize in the direction of CaO, and suppress CaSO 4 Decomposing towards the direction of CaS, and improving the desulfurization rate of the phosphogypsum.
CaSO in the invention 4 The reaction formula of the decomposition is as follows:
in practice, reactions 1 and 2 predominate, and reactions 3 and 4 predominate, and are both endothermic and reversible reactions. Low CO concentration, high CO 2 The concentration can inhibit the generation of the reaction 3 to a great extent。
Although theoretically 0.5mol of C is sufficient for 1mol of CaSO to pass through reactions 1 and 2 4 Decomposition desulfurization, but considering that reaction 2 is a reversible reaction and will occur with partial reaction 3, there will actually be a residual of CO and CaSO 4 Can not meet the requirements of decomposition and desulfurization, so that CaSO 4 After the decomposition to a certain degree, surplus CO is needed to promote the reaction 2 to continue to carry out, thereby achieving the CaSO 4 High decomposition desulfurization rate of (1), SO that C in the carbonaceous raw material and SO in the phosphogypsum 3 Is suitably in the range of 0.5 to 0.8, too high increasing the CO concentration and the P (CO)/P (CO) 2 ) Thereby, reaction 3 occurs.
Compared with the prior art, the invention has the following beneficial effects:
the method for decomposing the phosphogypsum by recycling the tail gas simultaneously realizes the concentration of CO and the concentration of P (CO)/P (CO) required by the decomposing atmosphere of the phosphogypsum by using the existing low-price raw materials and gases in the actual production 2 ) And SO in the tail gas 2 The concentration is regulated and controlled, so that the phosphogypsum is decomposed towards CaO, and the use amount of carbonaceous raw materials and CO are reduced 2 The discharge amount further realizes the industrial application of phosphogypsum decomposition.
Drawings
FIG. 1: the invention realizes a process diagram for decomposing phosphogypsum by recycling tail gas.
FIG. 2: x =0.7 and W SO2 =12%, the tail gas is sufficiently recycled, and the change curve of each gas concentration is obtained.
FIG. 3: x =0.7 and W SO2 =12%, the tail gas is sufficiently recycled, and P (CO) is P (CO) 2 ) The change curve of (2).
FIG. 4: x =0.6 and W SO2 =12%, the tail gas can be recycled sufficiently, and the concentration of each gasThe change curve of (2).
FIG. 5 is a schematic view of: x =0.6 and W SO2 =12%, the tail gas is sufficiently recycled, and P (CO) is P (CO) 2 ) The variation curve of (c).
Detailed Description
The following examples further illustrate the technical solutions of the present invention, but should not be construed as limiting the scope of the present invention.
In a specific embodiment, a method for decomposing phosphogypsum by recycling tail gas is provided, which is shown in the attached figure 1:
(1) Firstly, required carbonaceous raw materials are mixed according to the amount of phosphogypsum to be treated in each batch, and then SO required to be reached in tail gas is added 2 Calculating the amount of the introduced gas according to the concentration;
(2) All the phosphogypsum enters a reducing furnace from a main feeding hole according to batches; dividing carbonaceous raw materials required for decomposing each batch of phosphogypsum into two parts, wherein the first part of carbonaceous raw materials and the phosphogypsum enter the reduction furnace from the main feeding port or all enter the reduction furnace from the secondary feeding port, and the second part of carbonaceous raw materials 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; introducing all the introduced gas required for decomposing each batch of phosphogypsum from the gas inlet; decomposing phosphogypsum in a reducing furnace;
(3) The tail gas generated after the previous batch of phosphogypsum is decomposed is treated by SO 2 Recycle system H 2 SO 4 The tail gas is recycled until the introduced gas tends to be CO completely 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 carbonaceous raw material and SO in phosphogypsum 3 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% by weight); setting CaSO in phosphogypsum 4 The main reaction formula of decomposition is:
xC+A 0 CO 2 →2xCO+(A 0 -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
the general reaction formula is as follows: caSO 4 +xC+A 0 CO 2 →CaO+SO 2 +(2x-1)CO+(A 0 -x+1)CO 2
To decompose 1mol of CaSO 4 If the standard is satisfied, 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 the exhaust gases 2 Is easier to recycle to prepare H 2 SO 4 Thus SO in the tail gas 2 The concentration should be above 8%, and the final known set value W SO2 X, and d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+ 1+d 0 ) Calculating to contain CO 2 Amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 The value of (c).
Specifically, the tail gas is recycled in the step (3), and the tail gas is subjected to SO 2 The recycled tail gas is continuously introduced from the gas inlet according to the amount of the introduced gas calculated in the step (1), SO that SO in the tail gas after the next batch of phosphogypsum is decomposed 2 The concentration is unchanged, and the redundant gas is discharged into the atmosphere.
Specifically, the change trend of the gas components of the gas introduced 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 introduced gas 2 Is set as A n The amount of inert gas is then d n ＝(A 0 /21％)-A n CaSO in phosphogypsum 4 The main reaction formula of decomposition is:
xC+A n CO 2 →2xCO+(A n -x)CO 2
CaSO 4 +CO→CaO+SO 2 +CO 2
the general reaction formula is as follows: caSO 4 +xC+A n CO 2 →CaO+SO 2 +(2x-1)CO+(A n -x+1)CO 2
To decompose 1mol of CaSO 4 As a standard, the tail gas is subjected to SO 2 Recycle system H 2 SO 4 Sometimes has O 2 The reaction is carried out, the temperature is 400-600 ℃, and the residual 2x-1 CO in the tail gas can be mixed with O 2 Reaction to CO 2 The CO concentration in the process is low and can be regarded as being converted into CO completely 2 The relation formula after the tail gas is recycled is as follows:
A n+1 ＝{(A 0 /21％)/[(A 0 /21％)+x]}*(A n +x)，n＝0,1,2...
the general 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...
then d 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 (ii) a When n → + ∞ is reached, A n ＝A 0 /21％，d n And =0. The relation shows that recycling the tail gas can lead the tail gas and CO in the introduced gas 2 Gradually increases the content of inert gas and gradually decreases until the gas is introduced and tends to be totally CO 2 Equilibrium is reached.
Specifically, the carbonaceous raw material is divided into two parts in the step (2), and is characterized in that the amount of the carbonaceous raw material divided into two parts is adjusted according to the calculated gas composition change tendency to decompose 1mol of CaSO 4 As a standard, let CaSO 4 The amount of the decomposition of the reaction is t, t is from [0,1 ]]The main reaction formula is as follows:
xC+A n CO 2 →2xCO+(A n -x)CO 2
tCaSO 4 +tCO→tCaO+tSO 2 +tCO 2
the general reaction formula is as follows: tCaSO 4 +xC+A n CO 2 →tCaO+tSO 2 +(2x-t)CO+(A n -x+t)CO 2
The CaSO can be obtained along with 1mol 4 Gradually participate in the reaction and are decomposed, and the calculation formula of each gas quantity 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 Amount = 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。
The trend of the CO concentration in the atmosphere can be calculated at this time, and the initial value of the CO concentration is higher than 10 percent along with 1mol of CaSO 4 The carbon raw material is divided into two parts according to the change trend of the CO concentration calculated here, the first part is added firstly to ensure that the initial value of the CO concentration is lower than 10%, and then the second part is uniformly added according to the reaction residence time of each batch of phosphogypsum in a reducing furnace to ensure that the CO concentration is kept below 10%, thus being beneficial to CaSO 4 Decomposing and desulfurizing in the direction of CaO, and recycling CO after sufficient times of tail gas 2 Increased concentration of P (CO)/P (CO) 2 ) Will also be lower than 0.20, more beneficial to CaSO 4 Decompose and desulfurize in the direction of CaO, and suppress CaSO 4 Decomposing towards the direction of CaS, and improving the desulfurization rate of the 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%, and d 0 ＝(A 0 /21％)-A 0 The following can be obtained:
A 0 ＝1.393，d 0 =5.2403, and the gas amount = A 0 +d 0 ＝6.6333；
The general formula can be further solved as follows:
A n ＝6.6333-5.2403*(6.6333/7.3333)^n，n＝0,1,2...
then d n ＝5.2403*(6.6333/7.3333)^n，n＝0,1,2...
Can calculate and recycle SO 2 As shown in Table 1, it was found that the number of cycles increased and the introduced C caused CaSO in the relation between the number of exhaust gas cycles n after absorption and the atmosphere 4 Decomposition of the CO formed 2 Gradually replacing inert gas in the atmosphere, and 1mol of SO in 8.3333mol of tail gas 2 Is absorbed and utilized to prepare H 2 SO 4 And the remaining CO is converted to CO 2 At this time, 7.3333mol of the tail gas remained, and 6.6333mol of the tail gas was used for the next decomposition of 1mol of CaSO 4 The excess 0.7mol of gas is discharged into the atmosphere, and after the cycle times reach enough, the introduced gas is basically all CO 2 Every 1mol CaSO 4 CO produced by decomposition 2 The amount discharged (i.e., the amount of C used) was 0.7mol.
Table 1 x =0.7 and W SO2 =12%, recycling of SO 2 The number n of times of tail gas after absorption is related to the atmosphere.
To decompose 1mol of CaSO 4 As a standard, let CaSO 4 The amount of the decomposition participating in the reaction is t, t epsilon [0,1]It is possible to obtain 1mol of CaSO 4 Gradually participate in the reaction and are 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 Amount = 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 sufficient to reach the balance, A n =6.6333, caSO according to calculation results 4 Gradually participate in the reaction and are decomposed, and the concentration of each gas, P (CO) and P (CO) are 2 ) Fig. 2 and 3 show the change curves of (a). Due to decomposition of CaSO 4 The initial CO concentration was 19.09%, the initial P (CO): P (CO) 2 ) 0.2360, higher, then with CaSO 4 The gradual decomposition shows an approximately linear relationship that the CO concentration is reduced to 4.80 percent and the P (CO) is P (CO) 2 ) To 0.0577. Thus, a method may be employed in which only a portion of the carbonaceous feedstock is first added to reduce the initial CO concentration and the initial P (CO): P (CO) 2 ) Then the remaining carbonaceous feedstock is added uniformly.
In this example, the carbonaceous material was used in the method of decomposing 1mol of CaSO based on the retention time of the reaction of phosphogypsum in the reduction furnace 4 For the standard, 0.3mol of carbonaceous feedstock was added first, 6.6333mol of total recycled tail gas was vented, and then another 0.4mol of carbonaceous feedstock was added uniformly according to half of the reaction residence time. By this method, the atmosphere can be stabilized at a better valueIs suitable for CaSO 4 Decomposition desulfurization.
Example 2
To decompose 1mol of CaSO 4 As a standard, when x =0.6 and W are set SO2 ＝1/(1+2x-1+A 0 -x+ 1+d 0 ) When =12%, and d 0 ＝(A 0 /21％)-A 0 The following can be obtained:
A 0 ＝1.414，d 0 =5.3193, the amount of gas introduced = A 0 +d 0 ＝6.7333；
The general formula can be further solved as follows:
A n ＝6.7333-5.3193*(6.7333/7.3333)^n，n＝0,1,2...
then d n ＝5.3193*(6.7333/7.3333)^n，n＝0,1,2...
Can calculate and recycle SO 2 As shown in Table 2, it was found that the number of cycles increased and the CaSO was caused by C introduced after the number of cycles increased in the relation between the number of times n of exhaust gas after absorption and the atmosphere 4 Decomposition of the CO formed 2 Gradually replacing inert gas in the atmosphere, and 8.3333mol of 1mol of SO in tail gas 2 Is absorbed and utilized to produce H 2 SO 4 And the remaining CO is converted to CO 2 At this time, 7.3333mol of the tail gas remained, and 6.7333mol of the tail gas was used as the next 1mol of CaSO 4 The excess 0.6mol of gas is discharged into the atmosphere, and after the cycle times reach enough, the introduced gas is basically all CO 2 Every 1mol CaSO 4 CO produced by decomposition 2 The amount discharged (i.e., the amount of C used) was 0.6mol.
Table 2x =0.6 and W SO2 =12%, recycling of SO 2 The number n of times of tail gas after absorption is related to the atmosphere.
To decompose 1mol of CaSO 4 As a standard, let CaSO 4 The amount of the decomposition of the reaction is t, t is from [0,1 ]]1mol of CaSO 4 Gradually participate in the reaction and are decomposed, and the quantity and the concentration of each gas are relatedThe system formula is:
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 Amount = 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 times of recycling tail gas are enough to reach balance, A n =6.7333, caSO according to the calculation result plotted with 1mol 4 Gradually participate in the reaction and are decomposed, the concentration of each gas, P (CO) 2 ) Fig. 4 and 5 show the change curves of (a). Due to decomposition of CaSO 4 Initial CO concentration of 16.36%, initial P (CO): initial CO concentration 2 ) 0.1957 higher, followed by CaSO 4 The gradual decomposition shows an approximately linear relationship that the CO concentration is reduced to 2.40 percent and the P (CO) is P (CO) 2 ) And reduced to 0.0280. Thus, a method may be employed in which only a portion of the carbonaceous feedstock is first added to reduce the initial CO concentration and the initial P (CO): P (CO) 2 ) Then the remaining carbonaceous feedstock is added uniformly.
In this example, the carbonaceous material was used in an amount calculated according to the residence time of phosphogypsum in the reduction furnace to decompose 1mol of CaSO 4 For the standard, 0.3mol of the carbonaceous raw material is added, 6.7333mol of the tail gas which is completely recycled is introduced, and then another 0.3mol of the carbonaceous raw material is uniformly added according to half of the reaction residence timeAnd (4) feeding. The method can better stabilize the atmosphere in a proper CaSO 4 Decomposition desulfurization.
Comparative example 1
Air (O) is used for each gas introduction 2 21% of the total, the others being considered as inert gases), without recycling the off-gas, to decompose 1mol of CaSO 4 As a standard, C in the carbonaceous raw material and SO in the phosphogypsum are set 3 In a molar ratio of x 0 + x, first C and all O in the air 2 Reaction to CO 2 Then excess C and CO 2 CO is generated by reaction, and the main reaction formula is as follows:
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
the general reaction formula is as follows: caSO 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 An amount of x 0 Amount of inert gas d 0 ＝(x 0 /21％)-x 0 ；
When setting x =0.7 and W SO2 ＝1/(1+2x-1+x 0 -x+ 1+d 0 ) =12%, the following can be obtained:
x 0 ＝1.393，d 0 =5.2403, and the gas flow = x 0 +d 0 ＝6.6333；
The atmosphere was varied in the same manner as in example 1, but 1mol of CaSO was decomposed 4 The amount of substance required of C is x 0 +x＝1.393+0.7＝2.093mol。
To decompose 1mol of CaSO 4 For the purpose of reference, air (O) was used for each gas introduction in comparative example 1 2 21% of the total amount of the carbon-containing gas, and the balance being inert gas), the exhaust gas was not recycled, and the amount of the carbon used was 2.093mol, which is significantly higher than 0.7mol in example 1, in order to achieve the same atmospheric conditions as those in example 1 in which the exhaust gas was not recycled; c of exhausting tail gas into atmosphereO 2 The discharge was 2.093mol, which is also significantly higher than 0.7mol in example 1; the reason is SO in the tail gas 2 When the concentration is 12%, the amount of gas to be introduced is large, and O in the air is large 2 The ratio is 21%, and the higher the ratio is, the air is fully used in the introduced gas to cause O 2 Is too high, thereby obviously increasing the dosage of C, and the tail gas is completely discharged into the atmosphere to ensure that CO is generated 2 Can not be utilized, thereby obviously increasing CO 2 And (4) discharging the amount.
A large number of literature studies have used bottles of inert gas atmosphere to reduce O 2 In a concentration of or using CO 2 Atmosphere bottle exclusion of O 2 The effect of consuming more C is needed, but the use of expensive atmosphere bottles is not allowed in the actual production, and after the method of recycling tail gas in the embodiment 1 and the embodiment 2 is adopted, the CO concentration and the SO 2 The concentration variation trend remains unchanged, CO 2 The concentration is gradually increased until the gas is introduced to the reactor and tends to be CO in all 2 An equilibrium is reached when CO is present 2 Increase in concentration and P (CO)/P (CO) 2 ) Further benefit CaSO 4 Decompose and desulfurize in the direction of CaO, and inhibit CaSO 4 Decomposing towards the direction of CaS, and improving the desulfurization rate of the phosphogypsum.
Next, examples 1 and 2 were conducted by a method of charging carbonaceous raw materials into a reduction furnace in two parts, the first part was charged so that the initial CO concentration was less than 10%, and then the second part was uniformly charged according to the reaction residence time of each batch of phosphogypsum in the reduction furnace so that the CO concentration was maintained below 10%, while P (CO)/P (CO) was charged 2 ) SO in tail gas below 0.20 2 The concentration was maintained at 12%.
The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention should not be limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are intended to be covered by the claims.
Claims (5)
1. A method for decomposing phosphogypsum by recycling tail gas is characterized by comprising the following steps:
(1) Adding the required carbonaceous raw material according to the amount of the phosphogypsum to be treated, and then adding the SO required in the tail gas 2 Concentration calculation of CO content 2 The amount of gas introduced;
(2) A part of carbonaceous raw materials and all the phosphogypsum simultaneously enter the reducing furnace from the main feeding port, and the rest part of carbonaceous raw materials uniformly enter the reducing furnace from the secondary feeding port according to the reaction residence time of the phosphogypsum in the reducing furnace; containing CO 2 Gas is introduced from a gas inlet; decomposing phosphogypsum in a reducing furnace;
(3) The tail gas generated after the phosphogypsum is decomposed passes through SO 2 Recycle system H 2 SO 4 Then used as CO needed by the next batch of phosphogypsum for decomposition 2 The tail gas is recycled until the introduced gas tends to be all CO 2 Equilibrium is reached.
2. The method for decomposing phosphogypsum by recycling tail gas according to claim 1, wherein the carbonaceous raw material in step (1) is one or more of common coal, high-sulfur coal and coke; c in carbonaceous raw material and SO in phosphogypsum 3 Is x, x =0.5-0.8.
3. The method for decomposing phosphogypsum by recycling exhaust gases according to claim 1, wherein the CO-containing gas in step (1) 2 The gas is air after complete combustion, wherein the content of inert gas is d 0 ，CO 2 With a content of 0 (ii) a Setting SO in exhaust gas 2 Concentration W SO2 8 to 15 percent; x is known to be C and SO in phosphogypsum 3 The molar ratio of (a); given the value W SO2 X, and d 0 ＝(A 0 /21％)-A 0 By the formula W SO2 ＝1/(1+2x-1+A 0 -x+1+d 0 ) Calculating to contain CO 2 Amount of gas introduced (A) 0 +d 0 ) And A 0 、d 0 The value of (c).
4. The method for decomposing phosphogypsum by recycling tail gas according to claim 1, wherein in the step (2), a part of carbonaceous raw material is added to make the initial CO concentration lower than 10%, and then a second part is uniformly added according to the reaction residence time of the phosphogypsum in the reduction furnace, so that the CO concentration is kept below 10%.
5. The method for decomposing phosphogypsum by recycling tail gas according to claim 1, characterized in that SO is used in step (3) 2 The recycled tail gas is continuously introduced from the gas inlet according to the calculated introduction amount in the step (1), SO that SO in the tail gas after the next batch of phosphogypsum is decomposed 2 The concentration is unchanged and the excess gas is vented to the atmosphere.
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| CN101708826A (en) * | 2009-11-25 | 2010-05-19 | 四川大学 | Method for reducing and decomposing phosphogypsum by sulfur |
| CN103072949A (en) * | 2012-12-07 | 2013-05-01 | 云天化集团有限责任公司 | Method for preparing calcium sulfide through reductive decomposition of phosphogypsum by fluidized bed |
| CN103466675A (en) * | 2013-09-03 | 2013-12-25 | 昆明理工大学 | Decomposition method of ardealite |
| US20200377375A1 (en) * | 2017-11-22 | 2020-12-03 | Ocp Sa | Phosphogypsum Decomposition Process |
| CN115073030A (en) * | 2022-07-13 | 2022-09-20 | 华新水泥股份有限公司 | Process for desulfurization and co-production of cement by using phosphogypsum |
| CN115108744A (en) * | 2022-07-13 | 2022-09-27 | 华新水泥股份有限公司 | Process for decomposing phosphogypsum and co-producing cement |
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Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101708826A (en) * | 2009-11-25 | 2010-05-19 | 四川大学 | Method for reducing and decomposing phosphogypsum by sulfur |
| CN103072949A (en) * | 2012-12-07 | 2013-05-01 | 云天化集团有限责任公司 | Method for preparing calcium sulfide through reductive decomposition of phosphogypsum by fluidized bed |
| CN103466675A (en) * | 2013-09-03 | 2013-12-25 | 昆明理工大学 | Decomposition method of ardealite |
| US20200377375A1 (en) * | 2017-11-22 | 2020-12-03 | Ocp Sa | Phosphogypsum Decomposition Process |
| CN115073030A (en) * | 2022-07-13 | 2022-09-20 | 华新水泥股份有限公司 | Process for desulfurization and co-production of cement by using phosphogypsum |
| CN115108744A (en) * | 2022-07-13 | 2022-09-27 | 华新水泥股份有限公司 | Process for decomposing phosphogypsum and co-producing cement |
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