Safe, efficient and energy-saving ammonium nitrate solution production system

Abstract

The invention discloses a safe, efficient and energy-saving ammonium nitrate solution production system which comprises an efficient tubular reactor, a reactor flash tank and a reflux mixer, the efficient tubular reactor is communicated with the reactor flash tank and the reflux mixer, and an ammonia gas pipe and a nitric acid pipe are connected to the efficient tubular reactor. An adjusting loop is connected among the ammonia gas pipe, the nitric acid pipe and the efficient tubular reactor, the reflux mixer comprises a neutralization washing tower, and the reactor flash tank is further connected with a falling film primary evaporator. Compared with the prior art, the system provided by the invention has the advantage of being capable of safely and efficiently preparing the ammonium nitrate solution in an energy-saving manner by utilizing the pressurized tubular reactor and the MVR evaporator.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of ammonium nitrate solution, and in particular to a production system of a safe, efficient and energy-saving ammonium nitrate solution. Background Art

[0002] With the gradual increase in the safety production needs of ammonium nitrate production enterprises, the State Administration for Market Regulation and the National Standardization Administration jointly issued the "Safety Technical Specifications for Ammonium Nitrate Enterprises" (draft for comments), which requires that when the pH value of the solution in the flash tank (10% ammonium nitrate solution) is less than 1.0, emergency shutdown should be carried out. The main reason is that the ammonium nitrate solution is easy to decompose or even explode when free acid exists in the high-temperature and high-concentration ammonium nitrate solution; the dust content of the exhaust gas is tested in accordance with the national standards "Determination of Particle Matter in Exhaust Gas from Stationary Pollution Sources and Sampling Methods for Gaseous Pollutants" (GB / T16157-1996) and "Technical Specifications for Monitoring Waste Gas from Stationary Pollution Sources" (HJ / T397-2007), which require the ammonium nitrate dust content to be ≤30mg / m, which puts forward higher technical requirements for ammonium nitrate production enterprises.

[0003] In the traditional process, the liquid phase in the reactor flash tank is in a weakly acidic state for a long time, and ammonia is added to increase the pH value during the subsequent concentration process, which poses a certain explosion risk.

[0004] The traditional process uses a pressurized tubular reactor, which is not only simple in structure, easy to operate and adjust, but also can obtain a high-concentration ammonium nitrate solution at one time. It also solves the safety problem of the atmospheric pressure volumetric neutralization reactor and improves the utilization rate of process steam. However, since the reaction is carried out under neutral or acidic conditions, the reactor is severely corroded and has a short service life. In addition, the reaction is operated under the boiling pressure of ammonium nitrate, which produces a large amount of process steam with high pollution. Although a matching process steam washing and treatment system is provided, the process steam is in an overheated state and has a high temperature (195-200°C). In a long-term high-temperature acidic environment, its packing layer uses corrugated metal structured packing, material: S30403 or ceramic structured packing. After a period of normal operation, the lower packing layer of the neutralization washing tower is severely corroded and even collapses as a whole. In addition, the neutralization of ammonia entrained in the process steam and the washing of ammonium nitrate in one washing tower cause fluctuations in operating conditions, resulting in a large excess and fluctuation of pollutants in the process steam condensate, which is extremely unfavorable to the safe production and product quality of the device, and thus affects the production and stability of ammonium nitrate solution.

[0005] Especially when the concentration of nitric acid is lower than 58%, the evaporation condensate (unwashed steam condensate) in the system is in excess. If this part of the excess evaporation condensate is sent to the electrodialysis unit for treatment, the membrane stack will be seriously blocked, the cleaning frequency will increase, and the filter element before entering the membrane stack will also be frequently replaced, resulting in a great consumption of manpower and material costs. Not only does the power consumption increase, but the operating cost also increases accordingly and reduces the service life of the membrane stack. Especially when the concentration of nitric acid is lower than 58%, the evaporation condensate (unwashed steam condensate, ammonia nitrogen content of 350-2100 mg / kg) in the system is in excess. If this part of the excess evaporation condensate is sent to the electrodialysis unit for treatment, the membrane stack will be seriously blocked, the cleaning frequency will increase, and the filter element before entering the membrane stack will also be frequently replaced, resulting in a great consumption of manpower and material costs. Not only does the power consumption increase, but the operating cost also increases accordingly and reduces the service life of the membrane stack. Summary of the invention

[0006] The present invention aims to provide a system for preparing ammonium nitrate solution safely, efficiently and energy-saving by using a pressurized tubular reactor and an MVR evaporator.

[0007] In order to solve the above technical problems, the technical solution provided by the present invention is: a safe, efficient and energy-saving ammonium nitrate solution production system, comprising an ammonia pipeline, a nitric acid pipeline, a high-efficiency tubular reactor, a reactor flash tank, a neutralization washing tower, and an ammonium nitrate solution tank, wherein the neutralization washing tower is an atomizing washing tower, and the acid inlet of the neutralization washing tower is arranged at the top thereof; a reflux mixer is arranged between the high-efficiency tubular reactor, the reactor flash tank and the neutralization washing tower, an indicating regulating valve is arranged between the neutralization washing tower and the reflux mixer, a flow control valve is also arranged between the ammonia pipeline and the reflux mixer, a venturi scrubber is also connected between the reactor flash tank, the nitric acid pipeline and the neutralization washing tower, and a solution concentration evaporation component is connected between the ammonium nitrate solution tank and the reactor flash tank.

[0008] As an improvement, the solution concentration evaporation component includes a falling film primary evaporator and an evaporation steam compressor, the falling film primary evaporator includes an upper evaporation receiving tank, a first-level falling film primary evaporator, a second-level falling film primary evaporator, and a secondary flash evaporator, the upper evaporation receiving tank, the first-level falling film primary evaporator, the second-level falling film primary evaporator, and the secondary flash evaporator are connected to the ammonium nitrate solution tank in sequence, the air inlet end of the evaporation steam compressor is connected to the upper evaporation receiving tank and the secondary flash evaporator, the output end of the evaporation steam compressor is connected to the second-level falling film primary evaporator, and the air outlet end of the neutralization washing tower is connected to the first-level falling film primary evaporator.

[0009] As an improvement, the output ends of the first-stage falling film primary evaporator and the second-stage falling film primary evaporator are both connected to a process steam condensate tank, and the process steam condensate tank is connected to the acid inlet of the neutralization washing tower.

[0010] As an improvement, the neutralization washing tower includes a spray washing section, a bubble tower plate section, and a fiber demisting section. A washing circulation reflux pump is provided at the bottom of the neutralization washing tower. The washing circulation reflux pump is connected to a reflux mixer, and an indicating regulating valve is connected between the washing circulation reflux pump and the reflux mixer.

[0011] As an improvement, the ammonia pipeline is provided with two branches connected to the pipeline reactor, a flow indicating valve 1 is provided on the ammonia pipeline away from the two branches, a flow indicating valve 2 is provided on the ammonia pipeline between the two branches, the second branch is connected to a reflux mixer, and a flow control valve is provided between the second branch and the reflux mixer.

[0012] Compared with the prior art, the advantages of the present invention are as follows: the ammonium nitrate solution production system not only solves the problem that the pH value of the solution is difficult to stably control during the ammonium nitrate production process, but also completely eliminates the problem that the ammonium nitrate solution contains iron ions due to acid corrosion during the neutralization and washing process due to the elimination of the packing layer of the neutralization and washing tower; the pH value of the flash tank can be accurately controlled by mixing the cooling liquid of the flash tank with ammonia, and the MVR technology (evaporation steam heating and pressurization utilization) is adopted in the ammonium nitrate concentration process to fully improve the quality and pressurize the evaporation steam in the system and use it as a heating source for the second-stage falling film evaporator to replace the use of fresh steam, thereby greatly saving the amount of external steam, and the pollutants in the generated process steam condensate are greatly reduced (30PPm), which can be directly discharged to the process steam condensate treatment system, so that the waste gas emission of the system is almost zero, thereby greatly saving the environmental protection investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a safe, efficient and energy-saving ammonium nitrate solution production system.

[0014] Figure 2 It is a structural diagram of the pH adjustment system.

[0015] Figure 3 This is a schematic diagram of pH adjustment in a neutralization washing tower. DETAILED DESCRIPTION

[0016] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings, wherein the same components are represented by the same reference numerals.

[0017] It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to directions in the drawings, and the words "inside" and "outside" refer to directions toward or away from the geometric center of a specific component, respectively.

[0018] It should be noted that when an element is referred to as being "fixed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this article are for illustrative purposes only.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly connected by technicians in the technical field to which the present invention belongs. The terminology used in the specification of the present invention is for the purpose of describing specific embodiments and is not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0020] In order to make the contents of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0021] The invention comprises a high-efficiency tubular reactor, a reactor flash tank, and a reflux mixer. The high-efficiency tubular reactor is communicated with the reactor flash tank and the reflux mixer. The invention also comprises a solution concentration evaporation component, a pH adjustment module, a process steam condensate treatment module, and a process steam washing component composed of a venturi reaction saturator and a washing tower. The washing tower comprises a spray washing section, a bubble plate section, and a fiber demisting section. A washing circulation reflux pump is arranged at the bottom of the washing tower, and the washing circulation reflux pump is connected to the reflux mixer. An ammonia pipe and a nitric acid pipe are connected to the high-efficiency tubular reactor. A regulating loop is arranged between the ammonia pipe, the nitric acid pipe and the high-efficiency tubular reactor. The regulating loop comprises a flow control main loop and a flow control sub-loop which tracks the flow control main loop in a molar ratio of 1:1. The flow control main loop is used as a sub-loop tracking of the flow control sub-loop in a cascade control mode.

[0022] Please refer to the attached Figure 1-2

[0023] Gaseous ammonia and nitric acid mix and react in pipeline reactor R101, releasing heat and producing steam. In flash tank F101, process steam is separated from ammonium nitrate solution, which remains at the bottom with a concentration of at least 87%.

[0024] In order to improve the conversion rate of ammonia and nitric acid, the ratio calculated by using FIC-101 and FIC-102 for single closed-loop ratio adjustment of acid / ammonia is the molar ratio. FIC-101 is the main flow control loop, and the flow control sub-loop FIC-102 tracks the gas ammonia flow at a molar ratio of 1:1. Among them, FIC-101 is the sub-loop tracking of the cascade control method of LIC-101 to achieve the main load control of the ammonium nitrate solution production process.

[0025] Since a small amount of ammonium nitrate will decompose in this process, the gaseous ammonia in the tubular reactor R101 is supplemented with a reaction according to the pH value AIC-101 of the process steam to ensure the pH value of the ammonium nitrate solution and steam.

[0026] The ammonium solution flash tank AIC-102 (pH control loop) serves as the control variable of the controller, which controls the gaseous ammonia in the reflux mixer M101 to be fully mixed with the washing liquid from the neutralization washing tower F102, so that the pH value of the reflux solution entering the reactor flash tank F101 can be timely controlled. Its function is to effectively and fully regulate the free nitric acid escaping from the tubular reactor in the reactor flash tank F101, thereby improving the reaction efficiency and increasing the safety performance.

[0027] The process steam is washed in the neutralization washing tower F102 before use. The process is divided into four parts:

[0028] Feature 1: Direct atomization spray washing method in the spray washing section fundamentally eliminates the corrosion problem of the packing layer of the neutralization washing tower.

[0029] Feature 2: Acid is introduced into the top of the washing tower, which prolongs the contact time of neutralization washing and increases the gas-liquid contact area, which greatly reduces the amount of escaping ammonia. This can reduce the pH value of process steam and increase the pH value of washing liquid (for the AIC104 control loop at the bottom of the neutralization washing tower (F102), the pH of the washing solution of the neutralization washing tower F102 is graded according to its change rate, which greatly reduces the amount of escaping ammonia. This can reduce the pH value of process steam and increase the pH value of washing liquid)).

[0030] Venturi scrubber J101: Circulate the washing liquid from the neutralizing washing pump P101. Calculate the nitric acid required for the supplementary reaction by adding it to the washing liquid. Figure 3 , ammonia is absorbed and neutralized in the acidic washing liquid. At the same time, the superheated process steam is gradually cooled and saturated through washing and plays a role of pre-washing.

[0031] The spray washing section uses a direct atomization spray washing method to fundamentally eliminate the corrosion problem of the neutralization washing tower packing layer (the lower packing layer of the neutralization washing tower has been changed to have serious corrosion or even overall collapse after a period of normal operation. The neutralization washing tower eliminates the packing layer in the original system to fundamentally eliminate the corrosion problem of the packing layer of the neutralization washing tower). Acid is introduced into the top of the washing tower to extend the contact time of neutralization washing and increase the gas-liquid contact area, which greatly reduces the amount of escaping ammonia. This can reduce the pH value of the process steam and increase the pH value of the washing liquid.

[0032] Spraying all parts F102 lower part: The neutralization washing pump P101 maintains the washing liquid circulation. Make-up water overflows from the tower plate. The washing liquid is maintained slightly alkaline, and a small amount of ammonia is further absorbed and neutralized in the acidic washing liquid. The excess washing liquid returns to the reactor flash tank F101 to cool the ammonium nitrate solution. At the same time, since the washing liquid is a slightly acidic solution, the AIC-102 module performs ammonia replenishment operation on the reflux liquid before returning to the flash tank F101 to further ensure the pH value of the ammonium nitrate solution.

[0033] The trays are divided into: the upper tray is a bubble tray structure, the feed is evaporation condensate, with liquid level control, overflow layer by layer, and each tray has a bubble tray to further wash the process steam. Because there is an acid addition control loop AIC-104 at this washing position, the process steam at the top of the washing tower is acidic.

[0034] High-efficiency demister: The process steam after the tower plate washing still contains a small amount of ammonium nitrate droplets. The droplets are removed by the demister, the separation liquid returns to the tower, and the washed process steam enters the system steam network.

[0035] The dilute ammonium nitrate solution is concentrated in the falling film primary evaporator. The evaporation system is divided into five parts. The high-temperature ammonium nitrate solution first enters the upper evaporation receiving tank F103 for depressurization. The ammonium nitrate solution flashes, and the water vapor goes to the upper part and the solution falls by gravity. It first enters the lower first-level falling film primary evaporator E101 for heating and evaporation. The heating medium is 0.35Mpa washed process steam; then it enters the second-level falling film primary evaporator E102 for heating and evaporation. The heating medium is 0.8Mpa steam upgraded by the evaporation steam compressor; at the same time, most of the ammonium nitrate vapor-liquid mixture flows into F104 through the balance pipe for further flash separation. After the secondary evaporation and secondary flash separation, the solution is concentrated to 96% and flows into the solution tank F105.

[0036] The process saturated water vapor enters the evaporation steam compressor J101 from the primary evaporator F103 and the secondary flash evaporator F104 to heat and pressurize the 0.8MPa process steam, enters the falling film evaporator E102 for evaporation, and finally is separated at the bottom of the primary evaporator E102 and the primary evaporation separator F104. In this way, the waste heat of the process saturated steam can be fully utilized.

[0037] The heated steam condensate is collected in the normal pressure washing evaporation condensate tank F107 and sent to the process steam condensate treatment: electrodialysis system.

[0038] Please refer to the attached Figure 2For the pH adjustment system in production, due to the large volume of the reactor flash tank, it takes a long time for the ammonia mixing effect to be displayed after the reflux liquid is mixed with ammonia in the mixer. In actual production, it takes about 6 to 12 minutes to be displayed. Since the measurement lag time of pH at this position is long, and the concentration relationship expressed by pH is the logarithmic relationship of pH = [H+]10-n, the nonlinear relationship is obvious. For this reason, a pH multi-parameter adjustment loop is specially made for this characteristic. The specific control method is as follows:

[0039] This module is a pH adjustment module; the module function options: whether to use the change rate adjustment K can be selected to be put into or removed.

[0040] When MA=1, it is in automatic state, and when MA=0, it is in manual state;

[0041] The first absolute value refers to the change of the first time difference; the second absolute value refers to the change of the second time difference. The third absolute value refers to the rate of change. When the rate of change is ≥0, it means that the pH fluctuates greatly, and then it is adjusted according to the dual parameters; when the rate of change is <0, it means that the pH tends to be stable and the regulator does not make adjustments for the time being.

[0042] Dual parameter setting, using different parameters to implement control solutions according to the deviation between the measured value and the set value.

[0043] Specific PID parameter settings:

[0044] P1=0.5I1=1.2D1=0

[0045] P2=0.8I2=1.2D2=0

[0046] P3=1.5I3=1.8D3=1.0

[0047] The control capabilities of the above three groups of parameters are gradually enhanced, so that the pH value of the ammonium nitrate solution can be effectively controlled.

[0048] Please refer to the attached Figure 3 , because in the actual production process, the adjustment speed is often slightly slow or the regulating valve is slow to move. The above amino acid ratio relationship is prone to short-term imbalance. Due to the addition of the AIC101 adjustment loop in the original amino acid ratio loop, there is more ammonia and less acid in the process steam; in addition, due to the inherent fluctuation of the gas ammonia flow rate, the nitric acid tracking amount fluctuates slightly. Fluctuations in the pH value of the washing liquid are inevitable. In order to ensure that the excess gas ammonia content FY108 of the steam at the top outlet of the reactor flash tank F101 is calculated in advance and the same molar amount of nitric acid is added to the venturi scrubber J101 at the inlet of the washing tower, a neutralization reaction is carried out in the venturi scrubber to keep the neutralization washing tower under stable pH control.

[0049] Where FY-108 = (FI101) + (FI-103) - (FI102)

[0050] The above formula is calculated on a mol basis.

[0051] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0052] The standard parts used in the present invention can all be purchased from the market, and special-shaped parts can be customized according to the description in the specification and the drawings. The specific connection methods of each part adopt conventional means such as mature bolts, rivets, welding, etc. in the prior art. Machinery, parts and equipment all adopt conventional models in the prior art, and the circuit connection adopts the conventional connection method in the prior art, which will not be described in detail here. The content not described in detail in this specification belongs to the prior art known to professional and technical personnel in this field.

[0053] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A safe, efficient and energy-saving ammonium nitrate solution production system, comprising an ammonia pipeline, a nitric acid pipeline, a high-efficiency tubular reactor, a reactor flash tank, a neutralization washing tower, and an ammonium nitrate solution tank, characterized in that: The neutralization washing tower is an atomization washing tower, and the acid inlet of the neutralization washing tower is arranged at the top thereof. A reflux mixer is arranged between the high-efficiency tubular reactor, the reactor flash tank and the neutralization washing tower. An indicating regulating valve is arranged between the neutralization washing tower and the reflux mixer. A flow control valve is also arranged between the ammonia pipeline and the reflux mixer. A Venturi scrubber is also connected between the reactor flash tank, the nitric acid pipeline and the neutralization washing tower. A solution concentration evaporation component is connected between the ammonium nitrate solution tank and the reactor flash tank.

2. A safe, efficient and energy-saving ammonium nitrate solution production system according to claim 1, characterized in that: The solution concentration evaporation component comprises a falling film primary evaporator and an evaporation steam compressor. The falling film primary evaporator comprises an upper evaporation receiving tank, a first-level falling film primary evaporator, a second-level falling film primary evaporator, and a second flash evaporator. The upper evaporation receiving tank, the first-level falling film primary evaporator, the second-level falling film primary evaporator, and the second flash evaporator are connected to the ammonium nitrate solution tank in sequence. The air inlet end of the evaporation steam compressor is connected to the upper evaporation receiving tank and the second flash evaporator, the output end of the evaporation steam compressor is connected to the second-level falling film primary evaporator, and the air outlet end of the neutralization washing tower is connected to the first-level falling film primary evaporator.

3. A safe, efficient and energy-saving ammonium nitrate solution production system according to claim 2, characterized in that: The output ends of the first-stage falling film primary evaporator and the second-stage falling film primary evaporator are both connected to a process steam condensate tank, and the process steam condensate tank is connected to the acid inlet of the neutralization washing tower.

4. A safe, efficient and energy-saving ammonium nitrate solution production system according to claim 1, characterized in that: The neutralization washing tower comprises a spray washing section, a bubble plate section, and a fiber demisting section. A washing circulation reflux pump is provided at the bottom of the neutralization washing tower. The washing circulation reflux pump is connected to a reflux mixer. An indicating regulating valve is connected between the washing circulation reflux pump and the reflux mixer.

5. A safe, efficient and energy-saving ammonium nitrate solution production system according to claim 1, characterized in that: The ammonia pipeline is provided with two branch pipes connected to the pipeline reactor, a flow indicating valve 1 is connected to the ammonia pipeline away from the two branch pipes, a flow indicating valve 2 is connected to the ammonia pipeline between the two branch pipes, the second branch pipe is connected to the reflux mixer, and the flow control valve is arranged between the second branch pipe and the reflux mixer.

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