CN1225405C - Magnesium sulfate production method using magnesium oxide and desulfurated waste fluid - Google Patents
Magnesium sulfate production method using magnesium oxide and desulfurated waste fluid Download PDFInfo
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- CN1225405C CN1225405C CN 200310107026 CN200310107026A CN1225405C CN 1225405 C CN1225405 C CN 1225405C CN 200310107026 CN200310107026 CN 200310107026 CN 200310107026 A CN200310107026 A CN 200310107026A CN 1225405 C CN1225405 C CN 1225405C
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Abstract
The present invention provides a method of utilizing magnesium oxide desulphurization waste liquid for producing magnesium sulfate. The method comprises the procedures of oxidation, neutralization, extraction, evaporation and concentration, solid-liquid separation and drying packaging. By controlling different evaporation temperature, material discharge conditions and different equipment, the product of monohydrate magnesium sulfate and heptahydrate magnesium sulfate can be respectively produced. The present invention has the effect that the method not only can solve the problem that sideproduct waste liquid is drained into the sea, but also can extract the waste liquid of magnesium sulfate resources to manufacture the magnesium sulfate product. The present invention has the advantages of small evaporation capacity in technological process, low energy consumption, and high recovery rate, thereby having obvious social benefit and definite economic benefit. During preparing monohydrate magnesium sulfate, the present invention reaches the indexes that the content of magnesium oxide is larger than 27%, and the content of sulfur is larger than 20%, which are in an agriculture grade. During preparing heptahydrate magnesium sulfate, heptahydrate magnesium sulfate product with the purity of more than 97% can be obtained, and energy consumption and quality index are respectively superior to those of other technologies.
Description
Technical Field
The invention relates to a method for recycling a byproduct waste liquid resource in a wet magnesium oxide desulfurization process of flue gas, in particular to a method for producing magnesium sulfate by using magnesium oxide desulfurization waste liquid.
Background
In recent years, in the process of flue gas desulfurization, magnesium oxide is widely popularized as a desulfurizing agent, and has a tendency of replacing a calcium oxide desulfurizing agent, mainly because a magnesium compound desulfurizing device has low investment, low operation cost and good desulfurizing effect, and a byproduct waste liquid can be subjected to resource recovery. However, in the actual operation process of the magnesium oxide desulfurization device, the byproduct waste liquid containing magnesium sulfite as a main component has to be discharged due to no economic treatment method, thereby causing resource waste and secondary environmental pollution.
Some magnesium oxide desulfurization apparatuses, which are mainly used in japan abroad, adopt a double decomposition process to recover magnesium compounds for recycling in the desulfurization process, as described in japanese laid-open publication 155263/1996, by: the desulfurization waste liquid is subjected to forced oxygen exposure to oxidize magnesium sulfite into magnesium sulfate, calcium oxide emulsion is added, calcium hydroxide reacts with the magnesium sulfate to generate calcium sulfate and magnesium hydroxide, the mixture is physically separated, gypsum is prepared from calcium sulfate residues, and the magnesium hydroxide returns to a desulfurization device for recycling.
But the process obviously inherits part of the defects of a calcium oxide desulphurization device, such as large consumption of calcium oxide, low-value calcium sulfate as a byproduct, and magnesium oxide only used as a desulphurization carrier. One more important problem is that calcium sulfate particles and magnesium hydroxide generated in the double decomposition process are difficult to separate, and the actual operation is very difficult.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a method which can recover magnesium sulfate resources with low energy consumption, reduce discharge, eliminate secondary pollution and simultaneously can be separately prepared.
In order to achieve the purpose, the invention adopts the technical scheme that a method for producing magnesium sulfate by using magnesium oxide desulfurization waste liquid is provided, wherein the method comprises the following steps: the method comprises the following steps:
in the oxidation step,oxygen-enriched air is forcibly blown into the desulfurization waste liquid containing 10-30% of magnesium sulfite, the liquid is in a stirring state, and the temperature range is 20-50 ℃, so that the liquid is completely oxidized into magnesium sulfate.
And in the neutralization step, adding magnesium hydroxide emulsion into the fully oxidized magnesium sulfate solution according to the weight ratio of 1: 0.001-0.01, neutralizing sulfuric acid generated in the previous step, and adjusting the pH value to 6-8.
And in the impurity removal step, the neutralized solution is placed in separation equipment for mechanical impurity removal, so that liquid without solid-phase impurities is obtained.
In the evaporation concentration and solid-liquid separation steps, preheating the liquid after impurity removal and the mother liquor returned after filtration, then sending the liquid into a two-effect or three-effect evaporation device for evaporation, wherein the evaporation temperature is 120-140 ℃, when magnesium sulfate monohydrate needs to be produced, the discharge temperature is controlled to be 120-140 ℃, directly carrying out solid-liquid separation on the discharged slurry to obtain wet magnesium sulfate monohydrate and the mother liquor, drying the wet magnesium sulfate monohydrate, and returning the mother liquor to preheating and evaporation; when magnesium sulfate heptahydrate needs to be produced, controlling the discharge temperature to be 120-130 ℃, carrying out negative pressure cooling on the discharged slurry, and then carrying out solid-liquid separation to obtain wet magnesium sulfate heptahydrate and mother liquor; or controlling the discharge temperature to be 55-70 ℃, mixing the discharged slurry with the liquid after impurity removal according to the weight ratio of 1: 0.1-10, converting at the temperature of 10-45 ℃, then carrying out solid-liquid separation to obtain wet magnesium sulfate heptahydrate and mother liquor, drying the wet magnesium sulfate heptahydrate, and returning the mother liquor to preheating and evaporating or to the desulfurization process for recycling.
Drying and packaging, namely drying wet magnesium sulfate monohydrate or magnesium sulfate heptahydrate obtained in the evaporation and concentration step respectively, wherein drying equipment used for drying the magnesium sulfate monohydrate is a quick flash evaporation type rotary dryer, and the drying temperature is 240-400 ℃; drying equipment adopted for drying the magnesium sulfate heptahydrate is mainly a fluidized bed type dryer, and the drying temperature is 50-100 ℃; and obtaining the dried magnesium sulfate monohydrate or magnesium sulfate heptahydrate, and packaging to obtain the finished product.
The separation equipment in the impurity removal step is a filter press.
Magnesium sulfate heptahydrate, and packaging to obtain the finished product.
The separation device in the impurity removal step may be a filter press.
The method has the advantages that the method not only solves the problem that the by-product waste liquid is discharged into the sea, but also can extract the magnesium sulfate resource in the waste liquid to prepare the magnesium sulfate product, and the evaporation capacity in the process is small, the energy consumption is low, the recovery rate is high, so the method has remarkable social benefit and certain economic benefit, the indexes reached when preparing the magnesium sulfate monohydrate are that the content of magnesium oxide is more than 27 percent, the content of sulfur is more than 20 percent, the method is agricultural grade, when preparing the magnesium sulfate heptahydrate, the magnesium sulfate heptahydrate product with the purity of more than 97 percent can be obtained once, and the energy consumption and the quality index are superior to those of other processes.
Drawings
FIG. 1 is a flow chart of a process for preparing magnesium sulfate monohydrate from a magnesium oxide desulfurization waste liquid;
FIG. 2 is a process flow chart (negative pressure cooling) for preparing magnesium sulfate heptahydrate from magnesium oxide desulfurization waste liquid;
FIG. 3 is a flow chart of a process for preparing magnesium sulfate heptahydrate from magnesium oxide desulfurization waste liquid (normal temperature conversion).
Detailed Description
The method for producing magnesium sulfate by using the magnesium oxide desulfurization waste liquid of the invention is explained by combining the attached drawings and the embodiment.
The method for producing magnesium sulfate by using the magnesium oxide desulfurization waste liquid comprises the following steps
The technical scheme is realized as follows:
1. in the oxidation step, oxygen-enriched air liquid is forcibly blown into the desulfurization waste liquid containing 10-30% of magnesium sulfite (containing a small amount of magnesium bisulfite) obtained in the desulfurization step and is in a stirring state, and the temperature range is 20-50 ℃, so that the oxygen-enriched air liquid is thoroughly oxidized into magnesium sulfate. The by-product part of the process is sulfuric acid, and the chemical reaction is as follows:
2. in the neutralization step, a proper amount of magnesium hydroxide emulsion is added into a fully oxidized magnesium sulfate solution to neutralize the sulfuric acid generated in the previous step, and the pH value is adjusted to 6-8, wherein the chemical reaction formula is as follows:
3. and in the impurity removing step, mechanical impurities in the neutralized solution are removed by using a separation device to obtain a liquid without solid-phase impurities, wherein the separation device is mainly a filter press.
4. In the evaporation concentration and solid-liquid separation steps, the magnesium sulfate solution after impurity removal and the mother liquor returned after filtration are preheated and then sent into a two-effect or three-effect evaporation device for evaporation, and different evaporation temperatures and discharge conditions are controlled, so that magnesium sulfate monohydrate products and magnesium sulfate heptahydrate products can be produced respectively. When the magnesium sulfate monohydrate needs to be produced, the evaporation temperature is controlled to be 100-130 ℃, the discharge temperature is controlled to be 75-100 ℃, the discharged slurry is directly subjected to solid-liquid separation to obtain wet magnesium sulfate monohydrate and mother liquor, the wet magnesium sulfate monohydrate is dried, and the mother liquor returns to be preheated and evaporated, as shown in figure 1. When magnesium sulfate heptahydrate needs to be produced, the evaporation temperature is controlled to be 100-130 ℃, the discharge temperature is 65-100 ℃, the discharged slurry is cooled to 35-45 ℃ through a negative pressure cooler, and then solid-liquid separation is carried out toobtain wet magnesium sulfate heptahydrate and mother liquor, as shown in figure 2. Or controlling the discharge temperature to be 55-70 ℃, mixing the discharged slurry after short-time sedimentation with the liquid after impurity removal according to the weight ratio of 1: 0.1-10, converting at the temperature of 10-45 ℃, then carrying out solid-liquid separation to obtain wet magnesium sulfate heptahydrate and mother liquor, drying the wet magnesium sulfate heptahydrate, and returning the mother liquor to preheating and evaporation or to the desulfurization process for recycling, as shown in figure 3.
5. And (5) drying and packaging. Drying the wet magnesium sulfate monohydrate or magnesium sulfate heptahydrate obtained in the evaporation concentration and separation steps by using different drying equipment under different temperature conditions to obtain dried magnesium sulfate monohydrate or magnesium sulfate heptahydrate, and packaging to obtain a finished product, wherein the drying equipment used for drying the magnesium sulfate monohydrate is mainly a rapid flash type rotary dryer, and the drying temperature is 240-400 ℃; the drying equipment adopted for drying the magnesium sulfate heptahydrate is mainly a fluidized bed type dryer, and the drying temperature is 50-100 ℃.
The technical solution of the present invention is further illustrated by the following examples.
Example 1:
① oxidizing, namely putting 2000g of magnesium oxide desulfurization waste liquid (prepared by a magnesium sulfite reagent) containing 20% of magnesium sulfite into a beaker with a stirrer, heating to 35 ℃, blowing air inwards for 30 minutes, sampling and analyzing that the content of magnesium sulfate reaches 22.2%, the oxidation rate reaches 99%, the pH value of the solution is 6-7, and the neutralizing and impurity removing processes are omitted.
② evaporating, concentrating and separating, heating 2055g above solution in electric furnace under stirring at 125 deg.C for 10 min, dehydrating 1040g, stopping heating, standing for 2 min, pouring supernatant into another beaker, taking lower layer of slurry, filtering with filter cloth bag, and drying to obtain 366g wet magnesium sulfate monohydrate, and pouring the mother liquor and supernatant into the same beaker.
③ drying, namely, dispersing 360g of wet magnesium sulfate monohydrate in an electric heating drying oven, drying for 30 minutes at 320 ℃, taking out and weighing to obtain 275g of magnesium sulfate monohydrate product, and analyzing that the magnesium sulfate contains 27.82 percent of magnesium oxide and 22.25 percent of sulfur, and exceeds the export standard of the prior agricultural grade magnesium sulfate.
The clear solution, i.e. the mother liquor, decanted in the evaporation process in this example can be returned for re-evaporation to improve the yield. The yield of magnesium ions after one evaporation process was about 51% without taking into account the return of mother liquor.
Example 2:
① 1000 g of waste liquid containing 25% of magnesium sulfite by-produced in the wet magnesium oxide desulfurization process is taken, air is introduced into the waste liquid for 30 minutes, 8 g of emulsion containing 50% of magnesium hydroxide is added, the mixture is stirred for 30 minutes, the pH value is 7, the mixture is filtered, 3 g of filter cake is obtained, 1028 g of clear liquid is obtained, and two portions of clear liquid are obtained by the same method.
② the 1028 g supernatant was put into a beaker and evaporated at 120 deg.C to remove 300 g of water, followed by settling for 20 hours and pouring out 400 g of the supernatant to obtain 328 g of magnesium sulfate slurry.
③ and 1028 g of clear solution are taken, 328 g of magnesium sulfate slurry obtained above is added, stirring is carried out for 4 hours at 25 ℃, then filtering is carried out to obtain 300 g of wet magnesium sulfate heptahydrate, and 1056 g of filtrate is obtained, and 290 g of dry magnesium sulfate heptahydrate is obtained by drying the wet magnesium sulfate heptahydrate through hot air at 50 ℃.
④ 400 g of the decanted solution from step ② and 1056 g of the filtrate from step ③ were combined in a beaker and evaporated at 120 c to remove 438 g of water and then allowed to settle for 20 hours to decant 400 g of the supernatant to give 618 g of magnesium sulfate slurry.
⑤ and 1028 g of clear solution are again taken and 618 g of magnesium sulphate paste obtained above are added thereto, stirred for 4 hours at 25 ℃ and then filtered to obtain 590 g of wet magnesium sulphate heptahydrate, and 1056 g of filtrate is obtained, the wet magnesium sulphate heptahydrate is dried by hot air at 50 ℃ to obtain 570 g of dry magnesium sulphate heptahydrate.
And repeating ④⑤ steps to obtain magnesium sulfate heptahydrate by evaporating, converting and drying the clear solution after impurity removal.
The embodiment can show that the method for preparing the magnesium sulfate by using the wet method magnesium oxide desulfurization waste liquid byproduct waste liquid not only solves the problem that the byproduct waste liquid is discharged into the sea, but also can extract the magnesium sulfate resource in the waste liquid to prepare the magnesium sulfate product, and moreover, the evaporation amount in the process is small, the energy consumption is low, and the recovery rate is high, so that the method has remarkable social benefit and certain economic benefit, and has popularization and application prospects.
Claims (2)
1. A method for producing magnesium sulfate by using magnesium oxide desulfurization waste liquid is characterized by comprising the following steps: the method comprises the following steps:
in the oxidation step, oxygen-enriched air is forcibly blown into the desulfurization waste liquid containing 10-30% of magnesium sulfite, the liquid is in a stirring state, the temperature range is 20-50 ℃, and the liquid is completely oxidized into magnesium sulfate;
in the neutralization step, adding magnesium hydroxide emulsion into fully oxidized magnesium sulfate solution according to the weight ratio of 1: 0.001-0.01, neutralizing sulfuric acid generated in the previous step, and adjusting the pH value to 6-8;
in the impurity removal step, the neutralized solution is placed in separation equipment for mechanical impurity removal to obtain a liquid without solid-phase impurities;
in the evaporation concentration and solid-liquid separation steps, preheating the liquid after impurity removal and the mother liquor returned after filtration, then sending the liquid into a two-effect or three-effect evaporation device for evaporation, wherein the evaporation temperature is 120-140 ℃, when magnesium sulfate monohydrate needs to be produced, the discharge temperature is controlled to be 120-140 ℃, directly carrying out solid-liquid separation on the discharged slurry to obtain wet magnesium sulfate monohydrate and the mother liquor, drying the wet magnesium sulfate monohydrate, and returning the mother liquor to preheating and evaporation; when magnesium sulfate heptahydrate needs to be produced, controlling the discharge temperature to be 120-130 ℃, carrying out negative pressure cooling on the discharged slurry, and then carrying out solid-liquid separation to obtainwet magnesium sulfate heptahydrate and mother liquor; or the discharge temperature can be controlled to be 55-70 ℃, the discharged slurry and the liquid after impurity removal are mixed according to the weight ratio of 1: 0.1-10, the conversion is carried out at the temperature of 10-45 ℃, then the solid-liquid separation is carried out to obtain wet magnesium sulfate heptahydrate and mother liquor, the wet magnesium sulfate heptahydrate is dried, and the mother liquor is filtered and then returned to the preheating evaporation or the desulfurization process for recycling;
drying and packaging, namely drying wet magnesium sulfate monohydrate or magnesium sulfate heptahydrate obtained in the evaporation and concentration step respectively, wherein drying equipment adopted for drying the magnesium sulfate monohydrate is mainly a rapid flash evaporation type rotary dryer, and the drying temperature is 240-400 ℃; drying the magnesium sulfate heptahydrate by using a fluidized bed dryer at 50-100 ℃; and obtaining the dried magnesium sulfate monohydrate or magnesium sulfate heptahydrate, and packaging to obtain the finished product.
2. The method for producing magnesium sulfate by using the magnesium oxide desulfurization waste liquid as set forth in claim 1, characterized in that: the separation equipment in the impurity removal step is a filter press.
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Cited By (1)
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| CN102745725A (en) * | 2012-04-06 | 2012-10-24 | 北京世能中晶能源科技有限公司 | Method for producing magnesium sulfate monohydrate by using desulfurization wastewater |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102745725A (en) * | 2012-04-06 | 2012-10-24 | 北京世能中晶能源科技有限公司 | Method for producing magnesium sulfate monohydrate by using desulfurization wastewater |
| CN102745725B (en) * | 2012-04-06 | 2017-09-26 | 中晶环境科技股份有限公司 | The method that magnesium sulfate monohydrate is produced using desulfurization waste liquor |
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