CN108706610A - A method of ammonia and high-quality gypsum are recycled by ammonium sulfate - Google Patents

Abstract

The invention discloses a method for recovering ammonia gas and high-quality gypsum from ammonium sulfate: first, the milk of lime solution and ammonium sulfate (or ammonium sulfate aqueous solution) are mixed and reacted to generate ammonia and calcium sulfate; the generated ammonia can be recovered from the gas phase After the reaction, the slurry rich in calcium sulfate crystals is steam stripped to completely recover ammonia; the calcium sulfate in the slurry is filtered, dried, and dehydrated to recover high-quality gypsum products. This technology adopts multi-stage stripping to distill ammonia to ensure the complete recovery of ammonia in the reaction mother liquor; the mixing and reaction in the process of this technology should be operated under pressurized or slightly positive pressure, and the temperature of subsequent steam stripping, solid-liquid separation and other processes Both should be kept higher than 95°C. On the one hand, it can prevent the formation of dihydrate gypsum and scarring, and at the same time, it can also ensure that the gypsum crystals are mainly low-binding water gypsum, reduce process energy consumption, and ensure the quality of gypsum products. The technology can efficiently recover ammonia gas and gypsum products with low bound water from ammonium sulfate, with low process energy consumption and good economic benefits.

Description

A method for recovering ammonia and high-quality gypsum from ammonium sulfate

technical field

The invention relates to a method for recovering ammonia and high-quality gypsum from ammonium sulfate, especially for the chemical process with ammonium sulfate as a by-product, which can realize the recycling of ammonia.

Background technique

Ammonium sulfate is a by-product of a chemical process, especially in the production process of caprolactam. For every ton of caprolactam product produced, about 1.5-2.0 tons of ammonium sulfate will be produced as a by-product. In recent years, with the promotion of ammonia desulfurization technology, the production of ammonium sulfate has increased significantly. Ammonium sulfate is mainly used as nitrogen fertilizer, but long-term application will cause soil acidification, and the market is limited. Therefore, the supply of ammonium sulfate has been exceeding the demand for a long time, and the price has been depressed. Each ton of ammonium sulfate by-product needs to consume 258kg of liquid ammonia. Based on the average price in 2017 (3,200 yuan/ton of liquid ammonia and 450 yuan/ton of ammonium sulfate), the production of one ton of ammonium sulfate needs to consume 825 yuan of liquid ammonia. It is obviously unreasonable to consume a large amount of expensive ammonia while producing low value-added ammonium sulfate by-product. Therefore, it is worth trying to recover ammonia from ammonium sulfate. Once the ammonia is recycled, it is expected to greatly improve the economic benefits of the related process.

So far, there are few relevant reports on attempts to recover ammonia from ammonium sulfate, and more research is on the recovery of ammonia by pyrolysis of ammonium sulfate. Chen Tianlang (Chemical Research and Application, 2002, 14(6): 737-739) investigated the pyrolysis law of ammonium sulfate under different atmosphere conditions through tube furnace experiments; Cao Fahai et al. ): 341-346) studied the pyrolysis reaction kinetics of ammonium sulfate by thermogravimetric method. Ammonium pyrosulfate and the decomposition of ammonium pyrosulfate to generate nitrogen and sulfur dioxide and other steps. The results show that the ammonium sulfate pyrolysis process has low ammonia recovery rate, high temperature and high energy consumption, so it is not feasible.

Patent CN207002285U provides a kind of method that utilizes industrial by-product ammonium sulfate to prepare potassium sulfate, mainly is to carry out metathesis reaction by heating ammonium sulfate and potassium chloride, and ammonium chloride is removed by vaporization, obtains potassium sulfate product. This method can only be used as a method for processing ammonium sulfate by-products containing organic impurities, because the energy consumption of the process is high, the equipment is complicated, the added value of potassium sulfate and ammonium chloride obtained is not high, and large-scale application has no economic benefits.

Patent CN107686193A provides a method for recovering ammonium sulfate solids from high-concentration ammonium sulfate wastewater. Using the characteristics that ammonium sulfate is easily soluble in water but not ethanol at normal temperature and pressure, ammonium sulfate wastewater is mixed with absolute ethanol to make ammonium sulfate solids from For precipitation in waste water, the recovery rate of ammonium sulfate can reach more than 92%. The absolute ethanol in the mother liquor can be concentrated by rectification and recycled. Compared with the existing sulfuric acid evaporation crystallization technology, this method is more energy-saving and has lower operating costs.

It is also obvious to use strong alkaline substances (such as lime, NaOH or KOH) to react with ammonium sulfate to generate corresponding sulfate and ammonia for ammonia recovery, but it is not economical and not feasible to use expensive NaOH or KOH. The only strong alkali that can be used is cheap lime water, which can undergo metathesis reaction with ammonium sulfate to generate calcium sulfate and ammonia:

(NH ₄ ) ₂ SO ₄ +Ca(OH) ₂ →H ₂ O+2NH ₃ ↑+CaSO ₄ ↓ (1)

Patent CN107935016A discloses a method for preparing α-type hemihydrate gypsum from waste water containing ammonium sulfate: mixing waste water containing ammonium sulfate with calcium hydroxide, a metathesis reaction occurs, and crude calcium sulfate is obtained; after the crude calcium sulfate is mixed with water, it is mixed with sulfuric acid The pH value is adjusted to 6-8 to obtain a dihydrate gypsum solution; the dihydrate gypsum solution is mixed with the composite crystal transformation agent to undergo a phase change reaction to obtain α-type hemihydrate gypsum. The reaction of mixing ammonium sulfate aqueous solution with calcium hydroxide to generate calcium sulfate and ammonia is obvious, and the purpose of this patent is to obtain α-type hemihydrate gypsum products. In order to obtain α-type hemihydrate gypsum, it is necessary to add a variety of auxiliary chemical reagents, including adding sulfuric acid to adjust the pH value, adding crystal transformation agents such as aluminum potassium sulfate and sodium citrate, etc. The process is complicated, the cost is high, and industrial implementation is difficult. In particular, the patent does not recover the ammonia produced.

Contents of the invention

In order to solve the outlet problem of a large amount of by-product ammonium sulfate in industrial processes such as caprolactam, the invention proposes a method for recovering ammonia and high-quality gypsum by using ammonium sulfate. This technology can recover and recycle the low-value ammonia fixed in the ammonium sulfate by-product, realize the circulation of ammonia, reduce the ammonia consumption in the process, and improve economic benefits.

The method for recovering ammonia and high-quality gypsum from ammonium sulfate described in the present invention can refer to Figure 6 for a typical process, which specifically includes four steps of mixed reaction crystallization, stripping deamination, ammonia recovery, and gypsum recovery:

1) First, the milk of lime solution and ammonium sulfate are sent into the reaction crystallizer to fully mix and react to generate a gas phase rich in ammonia and a water slurry rich in calcium sulfate precipitation. The ammonia gas phase is sent to the ammonia recovery step;

2) Then, the water slurry rich in calcium sulfate precipitation generated by the reaction is subjected to steam stripping deammonification treatment, and the ammonia-containing steam obtained by stripping is sent to the ammonia recovery step, and the deammoniated slurry is sent to the gypsum recovery step;

3) Recovering high-concentration ammonia water and ammonia gas from the ammonia-containing steam generated by stripping and deammonification and the ammonia-containing gas phase generated by the reaction by means of rectification and condensation;

4) Finally, high-quality gypsum products are recovered from the calcium sulfate-containing precipitated slurry after stripping and deamination. Typical solid-liquid separation processes include filtration, washing, and drying.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the ammonium sulfate raw material added to the reaction crystallizer can be selected from ammonium sulfate solid or ammonium sulfate aqueous solution. Due to the needs of transportation, especially to meet the needs of fully mixing and reacting with milk of lime, the ammonium sulfate aqueous solution is preferably used as the raw material, and the saturated ammonium sulfate aqueous solution with a mass percentage greater than 30wt% is more preferred. Especially in the caprolactam production plant, the ammonium sulfate content in the ammonium sulfate solution stream from the ammonium sulfate unit is about 40 to 60 wt%, and this stock stream can be directly used as the ammonium sulfate raw material of the present technology.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the milk of lime solution from the milk of lime configuration unit is pumped into the reaction crystallizer, fully mixed with ammonium sulfate solution, reacted, crystallized, and crystallized by reaction The reactor adopts a tank reactor with an enhanced mixing device. In the reactor, the ammonium ions in the dissolved ammonium sulfate combine with hydroxide ions to form free ammonia, and part of it enters the gas phase in the form of ammonia gas; at the same time, the sulfate ions in the ammonium sulfate combine with calcium ions to form calcium sulfate precipitation. Under different reaction temperature and pressure conditions, the precipitated calcium sulfate will bind different proportions of water molecules. The main reactions involved are shown in formulas (1)-(4):

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the tank reactor is equipped with devices such as stirring or liquid-phase injection feeding, which strengthens mixing through liquid-phase stirring, and simultaneously prevents sulfuric acid solids from depositing and scabbing. The reaction crystallizer is operated under pressure, and the preferred temperature range is 90-150°C, so as to ensure that the precipitated calcium sulfate crystals are mainly hemihydrate gypsum or anhydrous gypsum or a mixture of the two.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the slurry from the bottom of the reaction crystallizer is rich in calcium sulfate precipitated particles, and at the same time, ammonia is saturated and dissolved, and steam stripping is required to remove the dissolved ammonia. Steam stripping deamination is carried out in a multi-stage stripping tower, the water slurry rich in calcium sulfate precipitated particles is added from the upper part of the tower, and steam is passed into the bottom of the tower. Slurry and steam undergo multi-stage countercurrent contact to remove dissolved ammonia, and the ammonia-containing steam collected from the top of the tower is sent to the ammonia recovery step to further recover high-concentration ammonia water and ammonia gas, and the water slurry after complete deamination is sent to the bottom of the tower Subsequent gypsum recovery steps. In order to prevent calcium sulfate precipitated particles from scabbing, the stripping tower must be operated at a temperature above 95°C, and the temperature control range at the bottom of the tower is 100-170°C, preferably 120-150°C.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the theoretical gas-liquid equilibrium stages of the multistage steam stripping deammonization tower can be selected from 2 to 20 stages, preferably 3 to 7 theoretical equilibrium stages. The tray components of the stripping column need to adopt anti-scarring design, and the optional anti-scarring tray structure has "conical cap" tray (shown in Figure 5).

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, a multi-stage rectification tower is used to concentrate the recovered gaseous ammonia, and the rectification tower can be a packed tower or a tray tower. The ammonia-containing vapor from the top of the stripping deamination tower is added from the bottom of the rectification tower, and the ammonia-containing gas phase from the reaction crystallizer is also fed into the rectification tower from a suitable position in the tower; the low-concentration ammonia water obtained at the bottom of the tower can be added to the reactor It can be used as dilution water, and can also be used as reflux water of the stripping tower; the gas phase at the top of the crystallization tower is condensed by a condenser, and part of the condensed liquid is refluxed; high-purity ammonia gas is recovered from non-condensable gas, and high-concentration ammonia water is recovered from the condensed liquid. The concentration of recovered ammonia water can be adjusted through the condensate reflux ratio and condenser load. The condensing temperature is low and the reflux ratio is high, so that higher concentration of ammonia water can be obtained, and the energy consumption of the system will also be increased. The condensate reflux ratio is selected from 0.1 to 3, preferably 0.5 to 1.5.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate described in the present invention, the stripping deammonization tower and the ammonia rectification tower involved can be integrated and designed, that is, two functions can be realized in one tower equipment, and the integrated The integrated design can simplify the process, reduce the number of equipment and save land. A typical integration scheme is to place the ammonia rectification tower above the stripping and deamination tower, that is, the slurry stripping is completed in the lower section of the tower, and the ammonia rectification is completed in the upper section of the tower, and the ammonia-containing steam in the stripping section directly enters the ammonia Ammonia rectification is carried out by rectification. At the same time, the condenser can be placed in the top of the tower, the condensate is directly refluxed, and the recovered ammonia gas and ammonia water are drawn out from the top of the tower. A typical integrated tower structure diagram is shown in Figure 5.

In the method for recovering ammonia and high-quality gypsum from ammonium sulfate according to the present invention, the slurry rich in calcium sulfate precipitation is stripped and deammoniated, and then a high-quality gypsum product is obtained through a multi-stage solid-liquid separation process. The multi-stage solid-liquid separation process is carried out at a temperature higher than 100°C to ensure that the final gypsum products are mainly high-quality anhydrite, hemihydrate gypsum or a mixture of the two. The adopted multi-stage solid-liquid separation sequence may include cyclone concentration, filtration, washing, and drying processes. The typical process can be referred to Figure 6. After the slurry is concentrated by the cyclone, the clear liquid can be recycled to the reactor; the concentrated slurry is filtered and washed, and the filter cake is sent to dry to obtain gypsum products; part of the filtrate and washing liquid is used as supplementary water Added to the lime emulsification tank, part of it can be discharged as waste water for further treatment.

Compared with the prior art, the technical advantages that can be obviously brought by the technology of the present invention include:

1) The present invention can reclaim two products of ammonia and high-quality gypsum from ammonium sulfate by-product;

2) The ammonia product obtained by the present invention is high-concentration ammonia gas and ammonia.

3) The gypsum product obtained by the present invention is hemihydrate gypsum or anhydrite gypsum with low bound water, and the intermediate process avoids the generation of dihydrate gypsum, the process is simple, and the energy consumption is low.

Description of drawings

The variation curve of solution pH and ion concentration over time under the typical conditions of Fig. 1 reaction crystallization process;

The XRD analysis result comparison of gypsum crystallization product under Fig. 2 different conditions, wherein, A-embodiment 1; B-embodiment 2; C-embodiment 3; D-embodiment 4; E-embodiment 5;

The particle size analysis result comparison of gypsum crystallization product under Fig. 3 different conditions, A-embodiment 1; B-embodiment 2; C-embodiment 3; D-embodiment 4; E-embodiment 5;

The comparison of gypsum crystal pictures under the different conditions of Fig. 4, wherein, A-embodiment 2 (calcium sulfate hemihydrate); B-embodiment 4 (calcium sulfate dihydrate);

Fig. 5 is a schematic structural diagram of the stripping and rectifying integrated tower equipment;

Fig. 6 is a simplified process flow diagram for recovering ammonia and high-quality gypsum from ammonium sulfate.

Detailed ways

Example 1

The crystallization law of the mixed reaction of ammonium sulfate and milk of lime was investigated experimentally in a 2L stirred tank. First, 900ml concentration of 1.1mol/L of Ca(OH) ₂ solution is loaded into the stirred tank, mechanically stirred, and the outer jacket of the reactor is passed into heat conduction oil to heat and control the temperature, and the temperature is controlled at 100°C; then, the 450ml concentration is 2.0mol/L (NH ₄ ) ₂ SO ₄ solution (21.2wt%) was quickly poured into the reactor at one time, and the milk of lime was kept in excess, and mixed uniformly by mechanical stirring. After the reaction starts, samples are regularly taken to measure the pH value, calcium ion concentration and sulfate ion concentration of the solution, and the crystal form and particle size of the generated gypsum crystals are analyzed at the same time. During the reaction process, 50ml/min of nitrogen gas is blown into the liquid phase, and the generated gas phase is absorbed by dilute hydrochloric acid solution in the subsequent absorption bottle, and the recovery rate of ammonia is determined by regularly sampling and detecting the concentration of ammonium ions in the absorption bottle. The PH value was measured by a pH meter; the concentration of calcium ions was measured by EDTA complexometric titration, and the concentration of sulfate ions was measured by barium sulfate turbidimetry; the concentration of ammonium ions in the absorption solution was measured by Nessler's reagent spectrophotometry; A laser particle size analyzer is used to measure the particle size of gypsum crystals, and an X-ray diffractometer is used to measure the XRD spectrum to determine the type of gypsum crystals.

The pH of the solution of this embodiment and the curve of ion concentration over time are shown in Figure 1, as can be seen from the figure, after mixing for 3 minutes, the concentration of sulfate ions in the liquid phase, the concentration of calcium ions and the pH value no longer change , which means that the reaction of ammonium sulfate and calcium hydroxide is a rapid equilibrium reaction, and the liquid phase reaction has reached equilibrium in a short time (<3min). After reacting for 60 minutes, analyze the concentration of ammonium ions in the tail gas absorption bottle. Based on the added ammonium sulfate, the calculated ammonia recovery rate is 99.1wt%, indicating that the amino group can be completely recovered. The XRD pattern of calcium sulfate obtained after 60 min of reaction is shown in Figure 2(A). It can be seen from Fig. 2(A) that the obtained calcium sulfate crystal form is hemihydrate gypsum (CaSO ₄ ·0.5H ₂ O). The particle size distribution is shown in Fig. 3(A), the average particle size is 27.7 μm, and there are a large number of fine-grain distributions with small particle sizes.

Example 2

The same as in Example 1, in a 2L stirred tank, the crystallization law of the mixed reaction of ammonium sulfate and milk of lime was experimentally investigated. The reaction temperature considered was also 100°C. The difference was the feeding method, and the milk of lime was added to sulfuric acid at one time under stirring conditions in ammonium solution. First in the stirred tank of 2L, it is the (NH ₄ ) ₂ SO ₄ solution (21.2wt%) of 2.0mol/L to load 450ml concentration, then the Ca(OH) ₂ solution (21.2wt%) with 1.1mol/L concentration in 900ml is one-time quickly Pour it into the reactor, keep the milk of lime in excess, add mechanical stirring to keep the mixture even, and at the same time blow 50ml/min of nitrogen into the liquid phase. After reacting for 60 minutes, the ammonium ion concentration in the tail gas absorption bottle was sampled and analyzed, and the ammonia recovery rate calculated based on the added ammonium sulfate was 98.5wt%, indicating that the ammonia was basically completely recovered. For solid sampling analysis, a Malvern particle size analyzer is used to measure the particle size, and an X-ray diffractometer is used to measure the XRD spectrum. The XRD pattern of calcium sulfate obtained after 60 min of reaction is shown in Figure 2(B). It can be seen from Fig. 2(B) that the obtained calcium sulfate crystal form is hemihydrate gypsum (CaSO ₄ ·0.5H ₂ O). The particle size distribution is shown in Figure 3(B), and there are a large number of fine-grain distributions with small particle sizes at the same time, and the average particle size is 32.5 μm. As shown in Fig. 4(A) under the microscope, the obtained calcium sulfate hemihydrate clusters are in the form of short rod-shaped crystals in a clustered state.

Example 3

The same as in Example 1, in a 2L stirred tank, the crystallization law of the mixed reaction of ammonium sulfate and milk of lime was experimentally investigated. The difference was the reaction temperature and feeding method. The reaction temperature was 120 ° C. Under stirring conditions, the ammonium sulfate solution was pumped Continuously added to milk of lime. 900ml concentration is the Ca(OH) of 1.1mol/L earlier in the stirred tank of 2L ₂ solutions are loaded into, then the (NH ₄ ) ₂ SO solution ( _21.2wt %) of 2.0mol/L with 450ml concentration is 50ml/ The flow rate of min was continuously added to the reactor, and the ammonium sulfate solution was added in 9 minutes, and the mixture was kept uniform with mechanical stirring, and 50ml/min of nitrogen gas was blown into the liquid phase at the same time. The jacket of the reactor is heated and kept with heat conduction oil, and the temperature is controlled at 120°C. After reacting for 60 minutes, the ammonium ion concentration in the tail gas absorption bottle was sampled and analyzed, and the ammonia recovery rate calculated based on the added ammonium sulfate was 98.8wt%, indicating that the ammonia was basically completely recovered. For solid sampling analysis, a Malvern particle size analyzer is used to measure the particle size, and an X-ray diffractometer is used to measure the XRD spectrum. The XRD pattern of calcium sulfate obtained after reacting for 60 min is shown in Figure 2(C). It can be seen from Fig. 2(C) that the obtained calcium sulfate crystal form is calcium sulfate hemihydrate (CaSO ₄ ·0.5H ₂ O). The particle size distribution is shown in Fig. 3(C), the average particle size is 28.8 μm, and there are not many fine crystals with small particle sizes. Comparing Figure 3(C), 3(B) and Figure 3(A), it can be seen that under the conditions of Example 3, the generation of small particles and fine crystals of hemihydrate gypsum can be effectively reduced, which is beneficial to the subsequent filtration and washing processes.

Example 4

As in Example 1, the crystallization law of the mixed reaction of ammonium sulfate and milk of lime was experimentally investigated in a 2L stirred tank, except that the reaction crystallization temperature of 90° C. was used. At first in the stirring kettle, it is the Ca(OH) of _1.1mol /L that the 900ml concentration is loaded into solution, the ammonium sulfate solution (21.2wt%) of the 2.0mol/L of 450ml is disposablely added in the milk of lime under stirring condition, Add mechanical stirring to keep mixing evenly, and at the same time blow 50ml/min nitrogen gas into the liquid phase. The jacket of the reactor is heated and kept warm with heat conduction oil, and the temperature is controlled at 90°C. After reacting for 60 minutes, the ammonium ion concentration in the tail gas absorbing bottle was sampled and analyzed, and the ammonia recovery rate calculated based on the added ammonium sulfate was 100.5wt%, indicating that the ammonia was completely recovered. For solid sampling analysis, a Malvern particle size analyzer is used to measure the particle size, and an X-ray diffractometer is used to measure the XRD spectrum. The XRD pattern of calcium sulfate obtained after 60 min of reaction is shown in Figure 2(D). It can be seen from Fig. 2(D) that the obtained calcium sulfate crystal form is dihydrate gypsum (CaSO ₄ ·2H ₂ O). The particle size distribution is shown in Fig. 3(D), and the average particle size is 29.1 μm. As shown in the microscope photo in Figure 4(B), the obtained calcium sulfate product crystalline dihydrate gypsum is elongated rod-shaped crystals.

Example 5

The same as in Example 4, the crystallization law of the mixed reaction of ammonium sulfate and milk of lime was investigated experimentally in a 2L stirred tank, except that different feeding methods were used. First, 900ml concentration of 1.1mol/L Ca(OH) solution is charged into the stirred tank, and the 2.0mol/L ammonium _sulfate solution (21.2wt%) of 450ml is continuously added to the milk of lime by the pump under stirring conditions. Add the ammonium sulfate solution in 9 minutes, add mechanical stirring to keep the mixture uniform, and at the same time blow 50ml/min nitrogen gas into the liquid phase. The jacket of the reactor is heated and kept warm with heat conduction oil, and the temperature is controlled at 90°C. After reacting for 60 minutes, the ammonium ion concentration in the tail gas absorption bottle was sampled and analyzed, and the ammonia recovery rate calculated based on the added ammonium sulfate was 99.7wt%, indicating that the amino group was completely recovered. For solid sampling analysis, a Malvern particle size analyzer is used to measure the particle size, and an X-ray diffractometer is used to measure the XRD spectrum. The XRD pattern of calcium sulfate obtained after 60 min of reaction is shown in Figure 2(E). It can be seen from Fig. 2(E) that the obtained calcium sulfate crystal form is dihydrate gypsum (CaSO ₄ ·2H ₂ O). The particle size distribution is shown in Fig. 3(E), and the average particle size is 32.2 μm.

Comparing Examples 1 to 5 comprehensively, it can be seen that under the condition of a slight excess of milk of lime, the ammonia in ammonium sulfate can be completely converted and recovered, and the recovery rate of ammonia is close to 100%. The continuous addition of ammonium sulfate solution helps to obtain calcium sulfate crystals with uniform particle size distribution. At a temperature higher than 100°C, the calcium sulfate crystals formed are mainly hemihydrate gypsum containing 0.5 crystal water, and at a temperature lower than 100°C, the calcium sulfate crystals obtained are mainly ammonium dihydrate gypsum containing 2 crystal water . However, converting dihydrate gypsum into hemihydrate gypsum products requires more energy consumption in subsequent processing. Therefore, in order to ensure the stability of the hemihydrate gypsum product, the reaction crystallization and subsequent solid-liquid separation must be kept at a temperature above 100°C.

Example 6

Adopt the technology of the present invention to build a set of pilot plant with an annual processing capacity of 10,000 tons of ammonium sulfate at the site of a certain caprolactam industrial device, and recycle 1280 tons of ammonia and by-product 11,000 tons of calcium sulfate hemihydrate. The main equipment of the device includes: lime milk tank, reactor, ammonia recovery tower, condenser, cyclone, filter and dryer, etc. The main process flow diagram is shown in Figure 6.

Quicklime and water are mixed and digested in a lime milk tank to prepare lime milk. The CaO content in the lime milk is 11.2wt%, and the processing capacity of the lime milk is 5.0 tons/hr. The lime milk tank is a stirred container with a volume of 10m ³ . The saturated sulfuric acid aqueous solution (45.0wt%) that comes from the ammonium sulfate unit of the caprolactam plant is sent into the reactor and the lime milk (5.6wt%) from the lime milk tank is stirred and mixed in the reactor, and the added ammonium sulfate aqueous material flow rate is It is 2.78ton/hr, and the amount of milk of lime added is 5.0 tons/hr. The volume of the reactor with multi-layer stirring device is 20m ³ , the reaction crystallization temperature is 100-110°C, operated under slight positive pressure, equipped with a gas-phase washing and collecting device, and the gas generated by the reaction is sent to the rectification section of the ammonia recovery tower from the top outlet It is used as gas phase feed, and the liquid phase slurry generated is sent from the bottom of the reactor to the ammonia recovery tower as feed to the upper part of the stripping section. The ammonia recovery tower is composed of an upper distillation section and a lower stripping section. The upper distillation section has a diameter of 0.60m and a height of 3m, filled with structured packing; the lower stripping section has a diameter of 0.80m and a height of 5m, and is covered with 8 mushroom caps. tray. The ammonia-rich gas phase generated in the reaction crystallizer is fed from the middle of the distillation section on the upper part of the tower, and a condenser is installed on the top of the tower. The condensate is refluxed from the top of the distillation section, and the reflux ammonia water and the steam containing ammonia are contacted in countercurrent through the distillation section to realize ammonia The gas and ammonia water are concentrated, and the ammonia gas and ammonia water recovered from the top of the tower add up to 246kg/hr (about 65.0wt% of ammonia content) and are sent to the neutralization unit of caprolactam to be used as neutralizing ammonia. The water slurry rich in calcium sulfate precipitate generated from the reactor is sent to the uppermost tray of the stripping section in the lower part of the ammonia recovery tower, and the ammonia-containing steam recovered from the top of the stripping section directly enters the upper distillation section for recovery ammonia. The low-pressure steam (1.6bar) is introduced from the bottom stripping section of the ammonia recovery tower to strip and remove ammonia. The ammonia nitrogen content in the liquid is less than 20ppm. The hot water slurry rich in calcium sulfate precipitate recovered from the bottom of the stripping section at the bottom of the ammonia recovery tower is sent to the cyclone through the slurry pump, and the calcium sulfate precipitate dense phase obtained by the cyclone is sent to the subsequent filtration step , the water phase is returned to the reactor as dilution water. Calcium sulfate hemihydrate (high quality gypsum) product is obtained after filtering, washing and drying. Ensure that the operating temperature of filtration, washing and other processes is higher than 95°C to prevent scabbing and the formation of calcium sulfate dihydrate.

Claims (9)

1. a kind of method recycling ammonia and high-quality gypsum by ammonium sulfate, which is characterized in that include the following steps：

(1) lime milk solution is sent into ammonium sulfate in reaction crystalizer and is sufficiently mixed, is reacted, generate the gas phase rich in ammonia With with the water slurry rich in crystal of calcium sulfate；

(2) water slurry that will be enriched in crystal of calcium sulfate strips deamination by steam multistage, obtains steam containing ammonia and gypsum slurry；

(3) steam containing ammonia that the gas phase rich in ammonia and step (2) that step (1) obtains obtain recycles high concentration ammonium hydroxide through rectifying And/or ammonia；

(4) gypsum slurry that step (2) obtains recycles high-quality gypsum product through multistage separation of solid and liquid process.

2. according to the method described in claim 1, it is characterized in that, the ammonium sulfate is selected from ammonium sulfate solids or ammonium sulfate Aqueous solution, preferred mass percentage are more than the ammonium sulfate solution of 20wt%, can be selected from the by-product sulphur ammonium of caprolactam process Material stream.

3. according to the method described in claim 1, it is characterized in that, in step (1), the reaction crystalizer is equipped with reinforcing The tank reactor of mixing arrangement strengthens mixing arrangement and can be selected from stirring, liquid phase sprayed feed；Reaction crystalizer operation temperature Ranging from 90~150 DEG C.

4. according to the method described in claim 1, it is characterized in that, in step (2), the steam multistage is stripped in multistage vapour It is carried out in stripper, water slurry is added by tower top, and bottom of tower is passed through steam, slurry and steam and sloughs dissolving by multi-stage countercurrent contact Ammonia.

5. method as claimed in claim 4, which is characterized in that in the stripper, column bottom temperature ranging from 100~~ 160 DEG C, the column plate component of stripper is designed using preventing scaring.

6. the method as described in claim 1 and 4, which is characterized in that in step (4), the multistage solid-liquid of the gypsum slurry Separation process 100~~160 DEG C under the conditions of carry out, multistage be separated by solid-liquid separation include concentrate, be filtered, washed, drying process.

7. method as described in claim 1 or 4, which is characterized in that in step (3), the optional self filler of device of the rectifying Tower or plate column；Steam containing ammonia is added by rectifying column bottom, overhead condensate reflux, by recovered overhead high concentration ammonium hydroxide and ammonia.

8. the method as described in claim 1,4 or 7, which is characterized in that the reaction generated mutually also can be together containing ammonia It is passed through the rectifier unit, by recovered overhead high concentration ammonium hydroxide and ammonia.

9. such as claim 4~7 any one of them method, which is characterized in that the multistage stripper and ammonia rectifying column can It carries out ammonia rectifying column in integrated, integrated tower to be placed in above stripper, the steam containing ammonia of stripper is straight It taps into ammonia rectifying column.