CN1709833A - Method and device for producing calcium ammonium nitrate by using calcium nitrate by-product of nitrophosphate fertilizer - Google Patents

Abstract

The invention relates to the technics method of producing ammonium nitrate calcium using nitric acid phosphate fertilizer by-produced rough calcium nitrate solution. It makes rough calcium nitrate filtrate and gas ammonia react in tubular reactor to produce ammonium nitrate calcium, adjust pH to 5, vaporize and inflating flash vaporize, gas-liquid separate under negative pressure, the produced material slurry get into rotor drum fluid bed grain producing machine to spread and produce grains, then obtain ammonium nitrate calcium grains. The invention applies rotor drum fluid bed grain producing and cooling technology to spread and produce grain, and uses fluid bed to improve cooling efficiency. The sizes of ammonium nitrate calcium grains can be adjusted, and they have good sphericity and big compressive strength. It's uneasy to agglomerate, and the performance of products is excellent.

Description

Method and device for producing calcium ammonium nitrate by using calcium nitrate by-product of nitrophosphate fertilizer

Technical field

The invention relates to a production method of calcium ammonium nitrate, in particular to a process for producing calcium ammonium nitrate by using crude calcium nitrate liquid produced by nitrophosphate fertilizer. The invention also relates to a device for carrying out the method.

Background technique

Calcium ammonium nitrate, also known as ammoniated calcium nitrate, has a molecular formula of 5Ca(NO ₃ ) ₂ ·NH ₄ NO ₃ ·10H ₂ O, a molecular weight of 1080, and a nitrogen content of 15.5%, of which more than 90% is nitrate nitrogen, and the rest is Ammonium nitrogen, containing 25% water-soluble calcium oxide. Calcium ammonium nitrate is mainly used as a chemical fertilizer. Because it mainly contains nitrate nitrogen and water-soluble calcium oxide, it has the advantages of quick effect, high utilization rate, easy absorption by crops, and suitable for calcium-loving crops. It is especially suitable for spraying as foliar fertilizer on Fruits, vegetables, melons.

There are many acidic soils in Europe, and many countries originally used nitric acid and limestone to react to produce calcium nitrate fertilizers. For example, Norway used the electric arc method to produce nitric acid in the early 20th century, and then processed it into calcium nitrate products. With the large-scale rise of the frozen nitrophosphate fertilizer industry in Europe, its by-product calcium nitrate can be economically processed into calcium ammonium nitrate for sale. Therefore, as early as the middle of the 20th century, calcium ammonium nitrate was widely produced in Europe.

The most original method of producing calcium ammonium nitrate from calcium nitrate, a by-product of freezing nitrophosphate fertilizer, is to send the calcium nitrate tetrahydrate crystals filtered out in the filtration process into the stirring tank, heat and melt them with steam, and then add ammonia gas to neutralize the nitric acid Nitric acid in the calcium melt to pH=4, add nitric acid and ammonia at the same time to make calcium nitrate:ammonium nitrate (molar ratio) 5:1, then evaporate and concentrate to reduce the water content of the melt from 30% to 15% ~16%, Ca(NO ₃ ) ₂ :NH ₄ NO ₃ :H ₂ O (molar ratio) is adjusted to 5:1:10, and finally the melt is unloaded on the cooling drum to generate 5Ca(NO ₃ ) ₂ · NH ₄ NO ₃ ·10H ₂ O flake crystal product. The disadvantage of this product is that it is extremely hygroscopic.

In the 1960s, Stamika, the Netherlands, specially developed an oil immersion granulation process for calcium ammonium nitrate. The granulation equipment is a vertical conical bottom circular oil tank, and the oil tank is filled with mineral oil. It also contains a very small amount of calcium ammonium nitrate seed crystals and paraffin. There is a rotating basket with holes above the oil tank. The molten liquid of calcium ammonium nitrate is sprayed through the rotating basket to the oil tank at a temperature of 45-50 ° C. When it touches ammonium nitrate The calcium seeds are immediately cooled and solidified into granules, the heat released is taken away by the oil, the mineral oil is circulated and cooled, and the calcium ammonium nitrate gathered at the bottom of the cone is put into a centrifuge, dried and made into finished products, and a small amount of finished products are ground It is then continuously added to the circulating mineral oil as seed crystals. The characteristic of the oil immersion granulation process is that the product is not easy to absorb moisture and agglomerate, but the disadvantage is that the production capacity is too small, it is not easy to be large-scale, the product particle size is small, and the particle size cannot be adjusted, and because it contains mineral oil, the scope of use is limited. Nutrient solution for soilless cultivation.

Norwegian Hydro Company used a disc granulator to produce calcium ammonium nitrate in the early stage. The disc granulation process is to install a large amount of return material in a turntable with an inclination angle, and the calcium ammonium nitrate melt is sprayed on the tumbling return material particles. On the surface, the returned material is continuously grown, then screened and classified, cooled to obtain the finished product, and the fine particles and broken large particles are recycled to the pan granulator as the returned material. The feature of this process is that the particle size can be adjusted, but the equipment occupies a large area, the production capacity is small, and the operating environment is poor.

Later, in order to adapt to large-scale production, Hydro developed the tower spray granulation technology for large-scale production of more than 200,000 tons. The tower spray granulation process is to pump the calcium ammonium nitrate molten liquid into the feed tank of the prilling tower, and inject it into several groups of nozzles on the top of the prilling tower through the spray pump, and at the same time, dry air blows the calcium ammonium nitrate into the nozzles. Seed crystal, the molten liquid comes out from the nozzle and becomes a droplet of a certain size, falling from the top of the tower tens of meters high, the droplet is cooled by countercurrent dry air, crystallized into granules, comes out from the bottom of the tower, and then cooled and wrapped by dry air That is the finished product. The characteristic of this process is that the production capacity is large, but the product particles are small, the particle size cannot be adjusted, and the equipment investment is large, so it is only suitable for large-scale production.

The patent 02146785.4 jointly applied by China Petroleum & Chemical Corporation and Tsinghua University provides a drum fluidized bed granulation technology. A fluidized bed is arranged along the axial direction in the center of the drum, and the seed particles are fed continuously from the feeding end of the drum. One side of the spraying direction of the slurry nozzle flows down along the overflow port to form a continuous and uniform material curtain, and on the other hand, the granular material is moved from the inlet end to the outlet end. The drum axis is perpendicular to the side of the material curtain, and there are multiple nozzles installed, and equipped with atomizing air. The nozzles atomize the slurry into liquid droplets, which are sprayed on the particle material curtain. The liquid droplets collide with the moving particles and wrap on the surface of the particles. Covering and solidification, the enlarged particles fall to the bottom of the drum, and are copied into the fluidized bed again. The above process is repeated, so that the particles grow gradually during the spiral advancement process. The function of the fluidized bed is to cool and take away the crystallization. latent and sensible heat. Drum fluidized bed granulation technology belongs to melt granulation, that is, there is no excess water in the feed liquid, and there is no need for drying and dehydration after granulation. The whole granulation process is coating granulation, and the particles are coated and cooled layer by layer. , so the product particles have good sphericity, adjustable size, high compressive strength, and can produce large particle products that are not easy to agglomerate. However, this technology has only been applied in urea production at present, and has not been promoted and implemented in other fields. Because the physical and chemical properties of calcium ammonium nitrate are quite different from those of urea, this granulation technology cannot be directly applied to the granulation production of calcium ammonium nitrate.

Contents of the invention

The purpose of the present invention is to provide a new process for producing calcium ammonium nitrate by utilizing nitrophosphate by-product calcium nitrate, and a production device suitable for the process.

The processing method of utilizing nitrophosphate fertilizer byproduct calcium nitrate provided by the invention to produce calcium ammonium nitrate comprises the following steps:

1) The by-product thick calcium nitrate liquid from the nitrophosphate fertilizer plant is squeezed into the filter press for continuous filtration;

2) the filtrate obtained by filtering is passed into a tubular reactor in proportion to gas ammonia, and a neutralization reaction occurs to generate calcium ammonium nitrate;

3) make the above-mentioned calcium ammonium nitrate solution enter in at least two neutralization stirring tanks connected in series, pass into gas ammonia, adjust the pH=5 left and right of the calcium ammonium nitrate solution;

4) After preheating, the calcium ammonium nitrate solution adjusted in the previous step is introduced into an evaporator, heated to boiling point and evaporated;

5) The evaporated vapor-liquid mixture enters the evaporation separator, where the vapor-liquid mixture expands and flashes to realize gas-liquid separation under negative pressure;

6) Let the evaporated liquid accumulated at the bottom of the evaporation separator flow into the granulation feeding tank by itself, and become a slurry for granulation, and the evaporated gas is recovered after being cooled by the condenser;

7) The slurry from the granulation feeding tank enters the drum fluidized bed granulator together with the atomizing air, calcium ammonium nitrate seed crystals, and fluidization gas. After being atomized by the atomizing air, it is coated on the ammonium nitrate Calcium seed crystal surface is granulated, then cooled and fluidized by fluidizing gas to make calcium ammonium nitrate particles;

8) The calcium ammonium nitrate particles made are lifted to the double-layer vibrating screen through the bucket elevator, and the qualified particle size calcium ammonium nitrate particles screened out enter the drum fluidized bed cooler, and qualified products are obtained after cooling;

9) After the sieved large particles of calcium ammonium nitrate are crushed by a roll crusher, they are returned to the drum fluidized bed granulator together with the sieved small particles of calcium ammonium nitrate, and used as crystal seeds for re-granulation.

In the above steps, when the crude calcium nitrate liquid is poured into the continuous filter press, the suitable inlet pressure of the filter press is 0.1-0.3Mpa, the operating temperature is 60-90°C, the pressure less than 0.1Mpa and the operation temperature less than 60°C Any temperature will cause a drop in filtration capacity, and when the pressure is greater than 0.3Mpa and the operating temperature is greater than 90°C, it will increase the energy consumption of the system.

Similarly, the suitable reaction temperature for the neutralization reaction of the filtrate and ammonia gas in the tubular reactor is 70-110°C. When the reaction temperature is lower than 70°C, the reaction speed is too slow, and when it is higher than 110°C, the ammonia gas will escape and the loss will increase.

The operating temperature of the evaporator used for heating and evaporating the calcium ammonium nitrate solution is 150-155°C, and the pressure is 0-0.02Mpa. If the operating temperature is too low or the pressure is too high, the material concentration of the evaporated vapor-liquid mixture will be low, which is not conducive to the expansion and flash evaporation in the evaporative separator. Similarly, if the operating temperature is too high or the pressure is too low, the evaporated vapor will The high concentration of the liquid mixture is also not conducive to expansion and flash evaporation. After the evaporated vapor-liquid mixture enters the evaporation separator, it expands and flashes under the negative pressure of -2kPa to realize gas-liquid separation.

The drum fluidized bed granulator suitable for calcium ammonium nitrate granulation operates at a temperature of 50-90°C. If the temperature is lowered, the area of the fluidized bed needs to be increased, which increases the investment, but the temperature is too high and close to Due to the melting point of calcium ammonium nitrate, it will also cause operational difficulties. The suitable operating pressure in the drum fluidized bed granulator drum is -100～-500Pa, if it is greater than -100Pa, it will easily cause the dust in the equipment to rise outside and pollute the environment. If it is less than -500Pa, it will increase the power consumption of the equipment.

During granulation, the slurry and atomizing air enter the drum fluidized bed granulator at a temperature of 120-140°C and a pressure of 0.2-0.4Mpa. When the temperature is lower than 120°C, it is close to the solidification temperature of the material. It is easy to cause the crystallization of the material and block the nozzle; if the pressure is less than 0.2Mpa, it will directly affect the spray effect of the atomizing air.

Correspondingly, the suitable operating temperature in the drum of the drum fluidized bed cooler is 30-50°C, and the operating pressure is -100--500pa. If the operating temperature in the drum is higher than 50°C, the product will be prone to agglomeration.

A large amount of granulation waste gas produced by the drum fluidized bed granulator and the drum fluidized bed cooler is recovered and dedusted by the supergravity dust collector.

The device for realizing the inventive method comprises:

Two filter presses, one on and one on standby, are used to continuously filter the by-product crude calcium nitrate liquid from the nitrophosphate fertilizer plant;

A filtrate tank for collecting the filtrate filtered by the filter press;

A tubular reactor, where the filtrate from the filtrate tank is passed into it in proportion to the gaseous ammonia for neutralization reaction to generate calcium ammonium nitrate;

At least two neutralization stirring tanks are connected in series behind the tubular reactor in series, and are used to receive the calcium ammonium nitrate solution generated by the reaction of the tubular reactor, and feed gas ammonia to adjust the pH of the calcium ammonium nitrate solution to about 5;

An evaporator for receiving the calcium ammonium nitrate solution from the neutralization tank and evaporating it into a vapor-liquid mixture;

A preheater, installed before the evaporator, is used to heat the calcium ammonium nitrate solution;

An evaporating separator, used to receive the vapor-liquid mixture from the evaporator, and expand and flash to realize gas-liquid separation under negative pressure;

A granulation feed tank, used to collect the evaporated liquid collected at the bottom of the evaporative separator to make it into slurry for granulation;

A condenser for cooling and recycling the evaporated gas produced by the evaporation separator;

A rotary drum fluidized bed granulator, slurry, atomizing air, calcium ammonium nitrate seed crystals, and fluidizing gas enter into it at the same time for coating and granulation;

A screening device, including a bucket elevator installed at the discharge port of the drum fluidized bed granulator and a double-deck vibrating screen behind it, are used to screen out calcium ammonium nitrate particles of qualified particle size;

A rotary drum fluidized bed cooler, the sieved calcium ammonium nitrate particles with a qualified particle size enter into it to cool to obtain the product;

A roll crusher for crushing the large particles of calcium ammonium nitrate screened out by the double vibrating screen; and

A return channel is used to send the crushed large granular calcium ammonium nitrate and small granular calcium ammonium nitrate to the rotary drum fluidized bed granulator.

The device of the present invention may also include a supergravity dust collector for recycling and dedusting the granulation waste gas produced by the drum fluidized bed granulator and the drum fluidized bed cooler.

The continuous filter press equipment used in the present invention has low price and large production capacity, and is especially suitable for filtering crude calcium nitrate; the adopted tubular reactor has the advantages of small volume and low energy consumption; the slurry evaporation adopts one-pass evaporation The evaporation efficiency is significantly higher than other types of evaporators.

In particular, the present invention introduces the drum fluidized bed granulation cooling technology into the production and granulation process of calcium ammonium nitrate, and utilizes the nozzles and lifting plates specially arranged in the drum fluidized bed to make the calcium ammonium nitrate slurry pass through the mist After melting, it is sprayed on the curtain of seed crystal particles falling in the drum to form coating granulation. At the same time, according to the characteristics of large heat release of calcium ammonium nitrate crystallization, starting from strengthening the heat transfer intensity, the fluidized bed is used to take away the crystallization. Latent heat and sensible heat, improve cooling efficiency. Since calcium ammonium nitrate particles are coated layer by layer and cooled layer by layer, the sphericity of the produced particles is better, the particle size of the product can be adjusted, the compressive strength is high, it is not easy to agglomerate, and the production efficiency of the granulation equipment is high.

Due to the adoption of the above-mentioned process and production device of the present invention, the production process of calcium ammonium nitrate has low investment, small footprint, low energy consumption, simple operation and superior product performance.

Description of drawings

Fig. 1 is the process flow diagram of producing calcium ammonium nitrate by utilizing nitrophosphate fertilizer by-product calcium nitrate.

Detailed ways

The specific process of producing calcium ammonium nitrate by using calcium nitrate, a by-product of nitrophosphate fertilizer, is shown in Figure 1. It comes from the crude calcium nitrate storage tank of the nitrophosphate fertilizer plant, and the crude calcium nitrate solution with a temperature of 80 ° C is filtered under a pressure of 0.2Mpa. The machine feed pump is driven into the filter press 1, and the present invention is equipped with two filter presses, one is opened and the other is standby for intermittent operation, so as to ensure the realization of continuous filter press. Through the filtration of the filter press 1, about 1% acid-insoluble matter in the thick calcium nitrate solution is filtered out, and the dense phase after the press filtration is returned to the thick calcium nitrate storage tank, and the filtrate flows into the filtrate tank 2 by itself.

If analyze when the acid concentration in the thick calcium nitrate solution in the thick calcium nitrate storage tank surpasses 3.0%, in order to guarantee the molar ratio of product ammonium nitrate calcium approximate 5: 1: 10, need to add appropriate amount of CaCO in the filtrate tank 2 ₃ powders, to neutralize excess nitric acid wherein, the reaction formula is as follows:

The filtrate in the filtrate tank is pumped into the tubular reactor 3 by the filtrate pump, and at the same time, according to the raw material composition content in the filtrate, controlled by the flow ratio regulating valve, the gaseous ammonia is also passed into the tubular reactor 3, so that the gaseous ammonia and Nitric acid in the filtrate is neutralized at a temperature of 70 to 110°C in the tubular reactor 3, and the reaction formula is as follows:

Two neutralization stirring tanks 4 and 5 are sequentially connected at the back of the tubular reactor 3, and the calcium ammonium nitrate solution coming out after the reaction of the tubular reactor 3 enters the neutralization stirring tanks 4 and 5 connected in series, and passes through the pH The value automatic analyzer adjusts the amount of gas ammonia entering the neutralization stirring tank 4, 5, so that the calcium ammonium nitrate solution in the neutralization stirring tank 4, 5 finally reaches a pH value of about 5, and the Ca(NO ₃ ) ₂ in the calcium ammonium nitrate solution :NH ₄ NO ₃ :H ₂ O satisfies the molar ratio relationship of 5:1:10. Due to the exothermic reaction between gaseous ammonia and nitric acid, the temperature of the calcium ammonium nitrate solution in the neutralization stirring tanks 4 and 5 rises to about 80°C.

The calcium ammonium nitrate solution with adjusted pH value in the neutralization mixing tank 4 and 5 overflows and relies on gravity to flow into an evaporating feed tank 6, and then is pumped out by an evaporative feed pump, and a calcium ammonium nitrate solution is injected first. In the heat exchanger 7, it exchanges heat with the hot calcium ammonium nitrate solution at a temperature of about 135° C. from the granulation feeding tank 11, and then enters a preheater 8 to heat and evaporate calcium ammonium nitrate by passing it into the evaporator 9. The condensate of medium-pressure saturated steam after the solution is used as a heat source to further heat the calcium ammonium nitrate solution, so that its temperature rises from 100°C to about 130°C, and finally enters the evaporator 9.

The evaporator 9 uses medium-pressure saturated steam as a heat source. By adjusting the amount of medium-pressure steam, the calcium ammonium nitrate solution is heated to a boiling point of 154°C for evaporation. Expansion and flashing are carried out in the evaporation separator 10, and gas-liquid separation is carried out, and the pressure in the evaporation separator 10 is -2kPa.

After evaporation and separation, the evaporated liquid accumulated at the bottom of the evaporation separator 10 flows into the granulation feeding tank 11. At this time, the molar number composition of the calcium ammonium nitrate solution in the granulation feeding tank 11 is about 5:1:10 , the temperature is around 135°C. Use the granulation feed pump to draw it out, first pass through the ammonium calcium nitrate liquid heat exchanger 7, exchange heat with the cold ammonium nitrate calcium solution from the evaporation feed tank 6, and then reduce the temperature to 122 ° C and send it to the drum flow The bed granulator 12 performs granulation.

The inner wall of the drum of the drum fluidized bed granulator 12 is provided with evenly distributed folded lifting plates, and the center of the drum is provided with a fluidized bed along the axial direction, and the slurry pipe extends into the drum along the axial direction of the drum. , There are multiple nozzles installed on the side of the drum axially perpendicular to the material curtain, and the atomizing air is connected to the nozzle inlet. The ammonium nitrate calcium seed particles from the electronic belt feeding scale are continuously added from the feeding end of the drum. On the one hand, the lifting board copies the granular materials at the bottom of the drum into the fluidized bed. After cooling sufficiently, it is sprayed from the slurry nozzle One side of the direction flows down the overflow port to form a continuous and uniform curtain of calcium ammonium nitrate material, and the other hand gradually moves the granular material from the inlet end to the outlet end. The drum fluidized bed granulator 12 operates at a temperature of 70°C and a pressure of -300pa, and is transported by a granulation feed pump. The calcium ammonium nitrate slurry with a temperature of 122°C and a pressure of 0.35Mpa enters the rotary drum through the slurry pipe. In the drum, at the same time, the atomizing air heated to 122°C by the atomizing gas heater atomizes the calcium ammonium nitrate slurry into droplets at the nozzle of the rotary drum fluidized bed granulator at a pressure of 0.35Mpa, and sprays it on the nitric acid Ammonium calcium granules on the curtain. The droplets collide with the moving particles, coat and solidify on the surface of the particles, and the enlarged calcium ammonium nitrate particles fall to the bottom of the drum, and are copied into the fluidized bed again. The above process is repeated, so that the calcium ammonium nitrate particles advance in a spiral grow gradually in the process. After being pressurized by the granulation blower and filtered by the granulation fluidization air filter, the atmospheric air is passed into the fluidized bed, taking away the latent and sensible heat of crystallization, and cooling the resulting particles.

The granulated calcium ammonium nitrate is discharged from the outlet of the drum fluidized bed granulator 12, lifted by the bucket elevator 13, and added to the double-layer vibrating screen 14, and the large particles of calcium ammonium nitrate screened out enter the After crushing in the roller crusher 15, the sieved small particles of calcium ammonium nitrate and the small particles of calcium ammonium nitrate crushed by the roller crusher 15 are combined, and then transported to the return hopper by the return belt conveyor, and then to the electronic belt. Feeding scales, after metering, are sent to the drum fluidized bed granulator 12 as calcium ammonium nitrate seed crystal particles.

The finished product of calcium ammonium nitrate with a qualified particle size separated by the double-layer vibrating screen 14 flows into the drum fluidized bed cooler 16 with a temperature of 35°C and a pressure of -300pa, and the cooling air filtered by the cooling air filter and pressurized by the cooling blower Pass in the drum fluidized bed cooler 16, the calcium ammonium nitrate finished product is cooled. The cooled calcium ammonium nitrate finished product flows into the finished product hopper by itself, and then is weighed and packaged by a packaging machine before being put into storage.

The treatment methods for the three wastes generated in the production process are:

The gas-phase secondary steam generated by the evaporation separator 10 enters the condenser 17, condenses and cools under the pressure of 0~-0.02Mpa, makes its temperature drop to 60°C, and flows into the process condensate tank 18 by itself, and the non-condensable gas is directly vented .

The granulation exhaust gas from the drum fluidized bed granulator 12 and the drum fluidized bed cooler 16 first enters the cyclone separator, and the separated fine particles are passed into the underground tank, and the remaining exhaust gas is sucked into the granulation In the induced draft fan, it enters the supergravity dust collector 19 after being pressurized. The dusty air, granulation exhaust gas and acid gas from the filtration and neutralization process discharged by each fan also enter the supergravity dust collector 19, and the process condensate pumped from the process condensate tank 18 also flows in parallel with the above-mentioned tail gas. In the supergravity dust collector 19, after being processed by the supergravity dust collector at a speed of 200 to 400 r/min, the gas-liquid mixture at the outlet is separated by the gas-liquid separator 20, and the solution is sent back to the supergravity dust collector 19 by a circulating pump. Contact with the exhaust gas in parallel, wash off the dust and acid mist, and the exhaust gas is emptied from the top of the gas-liquid separator 20. When the salt content of the process condensate dissolved in the dust (fine material) and acid mist in the exhaust gas reaches 23%, it is discharged into the underground tank.

After being treated by the supergravity dust removal technology, the dust content of all tail gas of the calcium ammonium nitrate unit after treatment is ≤40mg/m ³ , reaching the emission standard.

The fine particles separated by the cyclone separator and the process condensate with a salt content of 23% collected in the underground tank are pumped back to the evaporation feeding tank 6 by the ground tank for further recycling.

Claims (10)

1, utilize the process method of producing calcium ammonium nitrate by-product calcium nitrate of nitrophosphate fertilizer, comprise the following steps: 1) The by-product thick calcium nitrate liquid from the nitrophosphate fertilizer plant is squeezed into the filter press for continuous filtration; 2) the filtrate obtained by filtering is passed into a tubular reactor in proportion to gas ammonia, and a neutralization reaction occurs to generate calcium ammonium nitrate; 3) make the above-mentioned calcium ammonium nitrate solution enter in at least two neutralization stirring tanks connected in series, pass into gas ammonia, adjust the pH=5 left and right of the calcium ammonium nitrate solution; 4) After preheating, the calcium ammonium nitrate solution adjusted in the previous step is introduced into an evaporator, heated to boiling point and evaporated; 5) The evaporated vapor-liquid mixture enters the evaporation separator, where the vapor-liquid mixture expands and flashes to realize gas-liquid separation under negative pressure; 6) Let the evaporated liquid accumulated at the bottom of the evaporation separator flow into the granulation feeding tank by itself, and become a slurry for granulation, and the evaporated gas is recovered after being cooled by the condenser; 7) The slurry from the granulation feeding tank enters the drum fluidized bed granulator together with the atomizing air, calcium ammonium nitrate seed crystals, and fluidization gas. After being atomized by the atomizing air, it is coated on the ammonium nitrate Calcium seed crystal surface is granulated, then cooled and fluidized by fluidizing gas to make calcium ammonium nitrate particles; 8) The calcium ammonium nitrate particles made are lifted to the double-layer vibrating screen through the bucket elevator, and the qualified particle size calcium ammonium nitrate particles screened out enter the drum fluidized bed cooler, and qualified products are obtained after cooling; 9) After the sieved large particles of calcium ammonium nitrate are crushed by a roll crusher, they are returned to the drum fluidized bed granulator together with the sieved small particles of calcium ammonium nitrate, and used as crystal seeds for re-granulation. 2. The process according to claim 1, characterized in that the crude calcium nitrate solution at 60-90°C is injected into the filter press at a pressure of 0.1-0.3Mpa. 3. The process according to claim 1, characterized in that the reaction temperature of the tubular reactor is 70-110°C. 4. The process according to claim 1, characterized in that the operating temperature of the evaporator is 150-155°C and the pressure is 0-0.02Mpa. 5. The process according to claim 1, characterized in that the operating temperature inside the drum of the drum fluidized bed granulator is 50-90°C and the pressure is -100--500pa. 6. The process according to claim 1, characterized in that the slurry and atomizing air enter the drum fluidized bed granulator at a temperature of 120-140°C and a pressure of 0.2-0.4Mpa. 7. The process according to claim 1, characterized in that the operating temperature in the drum of the drum fluidized bed cooler is 30-50°C, and the pressure is -100--500pa. 8. The process according to claim 1, further comprising the following steps: The granulation exhaust gas produced by the drum fluidized bed granulator and the drum fluidized bed cooler is recovered and dedusted by the supergravity dust collector. 9. An apparatus for carrying out the method of claim 1, the apparatus comprising: Two filter presses, one on and one on standby, are used to continuously filter the by-product crude calcium nitrate liquid from the nitrophosphate fertilizer plant; A filtrate tank for collecting the filtrate filtered by the filter press; A tubular reactor, where the filtrate from the filtrate tank is passed into it in proportion to the gaseous ammonia for neutralization reaction to generate calcium ammonium nitrate; At least two neutralization stirring tanks are connected in series behind the tubular reactor in series, and are used to receive the calcium ammonium nitrate solution generated by the reaction of the tubular reactor, and feed gas ammonia to adjust the pH of the calcium ammonium nitrate solution to about 5; An evaporator for receiving the calcium ammonium nitrate solution from the neutralization tank and evaporating it into a vapor-liquid mixture; A preheater, installed before the evaporator, is used to heat the calcium ammonium nitrate solution; An evaporating separator, used to receive the vapor-liquid mixture from the evaporator, and expand and flash to realize gas-liquid separation under negative pressure; A granulation feeding trough, used to collect the evaporated liquid collected at the bottom of the evaporative separator to make it into slurry for granulation; A condenser, used to cool and recover the evaporated gas produced by the evaporation separator; A rotary drum fluidized bed granulator, slurry, atomizing air, calcium ammonium nitrate seed crystals, and fluidizing gas enter into it at the same time for coating and granulation; A screening device, including a bucket elevator installed at the outlet of the drum fluidized bed granulator and a double-deck vibrating screen behind it, are used to screen out calcium ammonium nitrate particles of qualified particle size; A rotary drum fluidized bed cooler, the sieved calcium ammonium nitrate particles with a qualified particle size enter into it to cool to obtain the product; A roll crusher for crushing the large particles of calcium ammonium nitrate screened out by the double vibrating screen; and A return channel is used to send the crushed large granular calcium ammonium nitrate and small granular calcium ammonium nitrate to the rotary drum fluidized bed granulator. 10. The apparatus of claim 9, further comprising: A supergravity dust collector is used to recover and dedust the granulation waste gas produced by the drum fluidized bed granulator and drum fluidized bed cooler.

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