Method for promoting continuous operation of evaporation and desalination of methylhydrazine evaporator

Abstract

The invention relates to the technical field of methylhydrazine production, and provides a method for reducing the concentration of free alkali NaOH in evaporated liquor to be desalted by adding specific calcium chloride under specific conditions, so that evaporation and desalination can be continuously and stably operated without discharging mother liquor. Used devices comprise a calcium chloride solution preparation system, a monitoring instrument, a feeding system and a separation and removal system. The monitoring instrument comprises a mother liquor alkalinity detector, a mother liquor flow meter, a feeding flow meter and the like; the feeding system comprises a feeding pipeline, a diaphragm pump and the like; the method comprises the steps of calcium chloride solution preparation, linkage setting of flow of a feeding system, mother liquor alkalinity and mother liquor flow, linkage mixing and feeding, separation and removal and the like, the Ca < 2 + > / OH <-> ratio is controlled by reasonably controlling the calcium chloride addition amount and the addition mode, calcium hydroxide precipitates capable of flowing backwards along with feed liquid are generated, the content of free alkali is reduced, and the calcium hydroxide content is increased. And long-time continuous operation can be achieved, and remarkable economic benefits and industrial application value are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of methylhydrazine production, and particularly relates to a method for promoting continuous operation of a methylhydrazine evaporator. BACKGROUND

[0002] Methylhydrazine, also known as monomethylhydrazine, has a molecular formula of CH6N2 and a CAS number of 60-34-4. It is an important chemical raw material and is widely used in many fields such as pesticides and medicines. With the development of the industry, the market demand for methylhydrazine is also increasing. In industrial production, the commonly used synthesis process of methylhydrazine is the chloramine method. This process uses sodium hypochlorite, ammonia and monomethylamine as raw materials, and through a series of reactions, it can finally produce a 2-4% concentration of methylhydrazine aqueous solution. At the same time, about 10% of sodium chloride, as well as excess ammonia and monomethylamine, and a small amount of sodium hydroxide are also produced. The process needs to be followed by a series of complex treatments, including recovery of ammonia and monomethylamine, desalination, dehydration and purification, to finally produce a 40% concentration of methylhydrazine aqueous solution. In the evaporation and desalination process, the sodium hydroxide in the mother liquor will continuously enrich and the concentration will gradually increase, which will cause the scaling of the heater tube and the inner wall of the evaporator, resulting in a significant decrease in heat transfer efficiency, and thus a significant reduction in the evaporation capacity of the evaporator. In order to solve this problem, it is usually necessary to periodically discharge the mother liquor and stop using weak acid water to clean the system. This process not only causes waste of materials, but also reduces the overall operating efficiency of the device. In addition, free alkali NaOH has strong corrosiveness to equipment, especially under high temperature conditions, which can accelerate the corrosion of equipment, thereby significantly shortening the service life of the equipment. More importantly, methylhydrazine has poor thermal stability in a high-temperature alkaline environment and is easily decomposed, which not only leads to the loss of methylhydrazine, but also may have an adverse effect on the safety of the production process and the quality of the product.

[0003] Regarding the problem of scaling in chemical pipelines, existing technologies have also been researched. Chinese invention patent application CN102400167A discloses a chemical cleaning method for scaling in the tubes of an evaporator used in ammonium sulfate production. This method uses chemical cleaning agents during shutdown to remove the calcium and magnesium salts in the scale, thus clearing the blockage. However, it cannot solve the technical problems of free alkali corrosion and methylhydrazine loss in the methylhydrazine evaporation desalination process. The academic paper "The Influence of Crystallized Salts on Evaporation Production" (China Ammonia-Soda, Zhang Bing, 2001, 9:14-15) describes the problem of crystallization and pipe blockage during the evaporation process of solutions containing sodium hydroxide and sodium chloride. This paper argues that most crystallized salts are precipitated due to water vaporization. Crystallized salts precipitated due to flash evaporation partially deposit in the feed pipe, making it rough and accumulating a certain amount of alkali solution. This alkali solution retained in the feed pipe continuously precipitates crystallized salts during flash evaporation when the feed valve is closed, adhering firmly to the pipe wall. The next time material is passed through, the feed liquid will be less effective at flushing it away, and over time, the feed pipe will gradually become clogged. The proposed solution is to minimize the number of elbows, flanges, and valves, thereby reducing pipe resistance and the chance of crystal nuclei adhering. This means ensuring that the precipitated crystals remain suspended in the feed liquid as much as possible, minimizing their adhesion to the pipe wall. While the analysis of the causes in this technical solution is reasonable, it does not completely eliminate the possibility of clogging.

[0004] Therefore, there is an urgent need to develop a method to enable the methylhydrazine evaporator to continue evaporation and desalination without stopping the machine. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for promoting the continuous operation of a methylhydrazine evaporator for evaporation and desalination by adding an appropriate amount of calcium chloride solution to the mother liquor tank or the pipeline returning the mother liquor to the heater during the evaporation and desalination process. This reduces the concentration of free alkali NaOH in the evaporating liquid to be desalinated, ensuring long-term operation of the evaporation and desalination process while mitigating the corrosion of equipment by free alkali, reducing methylhydrazine loss, and improving production efficiency. This method is particularly suitable for the purification process of methylhydrazine in the production of aerospace propellants, pharmaceutical intermediates, and pesticide intermediates.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for enabling a methylhydrazine evaporator to continuously operate for evaporative desalination includes the following steps:

[0008] (1) Install an alkalinity detector and a flow meter on the mother liquor return pipeline of the methylhydrazine evaporator. The alkalinity of the material in the mother liquor return pipeline is detected in real time by the alkalinity detector, and the flow rate of the mother liquor discharged into the mother liquor return pipeline is detected in real time by the flow meter.

[0009] (2) Preparation of calcium chloride solution: Add water to a container with a stirring device and start the stirring device at the same time. While stirring, add calcium chloride to the water. The amount of calcium chloride added is such that the calcium chloride concentration of the final solution is 30-40 wt.%. The temperature of the liquid is monitored in real time and kept below 50°C. Stir continuously for 25-35 minutes to obtain a clear and transparent calcium chloride solution.

[0010] (3) Linkage setting between feed diaphragm pump and alkalinity detector: Link the feed diaphragm pump with the alkalinity detector in step (1). When the alkalinity detector detects that the alkalinity of the material in the mother liquor return pipeline is higher than the start threshold, the feed diaphragm pump is turned on. When the alkalinity detector detects that the alkalinity of the material in the mother liquor return pipeline is lower than the stop threshold, the feed diaphragm pump is turned off. The start threshold is the alkalinity of the material is 50-120 g / L, and the stop threshold is the alkalinity of the material is 10-50 g / L.

[0011] (4) Linked mixing and feeding: The calcium chloride solution prepared in step (2) is discharged into the mother liquor return pipeline through the feed diaphragm pump in step (3) and then mixed into the heater feed pipeline. The addition and stopping of the calcium chloride solution are realized according to the linkage between the feed diaphragm pump and the alkalinity detector.

[0012] (5) Separation and removal: Calcium chloride reacts with the material in the mother liquor return pipeline during continuous movement to obtain calcium hydroxide precipitate and sodium chloride. The calcium hydroxide precipitate moves backward with the flow of liquid material. When it reaches the centrifuge of the evaporation desalination unit, the centrifuge separates the calcium hydroxide and sodium chloride from the material together.

[0013] Preferably, in step (3), the start-up threshold is an alkalinity of 70-90 g / L (more preferably 80 g / L) and the shutdown threshold is an alkalinity of 25-35 g / L (more preferably 30 g / L).

[0014] Preferably, in step (4), the flow meter set in step (1) is simultaneously associated with the feed diaphragm pump; the flow rate of the calcium chloride solution discharged into the mother liquor return pipeline is L. Cal2 The mother liquor flow rate is monitored in real time by a set flow meter, and meets the L requirement. CaCl2 =L 母 The requirement of ×B÷40.00÷2×110.98÷M÷ρ is to control the flow rate of the calcium chloride solution using a feed diaphragm pump; where L 母 ρ is the mother liquor flow rate, B is the alkalinity in the mother liquor return pipeline, M is the concentration of the calcium chloride solution, and ρ is the density of the calcium chloride solution.

[0015] Preferably, in step (4), the ratio of the flow rate of calcium chloride solution discharged into the mother liquor return line to the flow rate of mother liquor in the mother liquor return line is (0.246~0.316) m³. 3 / h:1m 3 / h.

[0016] Preferably, in step (5), calcium chloride reacts with the mother liquor in the mother liquor return pipeline while continuously moving to obtain calcium hydroxide precipitate and sodium chloride. The calcium hydroxide precipitate moves backward with the flow of the mixed liquid and continues to mix with the concentrated evaporation liquid discharged from the evaporator discharge pipe after reaching the evaporator discharge pipe. The mixed concentrated liquid is then separated by the concentrated liquid collection pump. The mixed concentrated liquid is discharged into the thickener through the pipeline and stirred before being discharged into the centrifuge for centrifugation to separate the calcium hydroxide precipitate and supersaturated sodium chloride from the material, obtaining the by-product solid salt. The liquid is discharged back into the mother liquor tank.

[0017] Preferably, in step (5), the liquid that is not separated by the concentrated liquid extraction pump after mixing is mixed with the raw material of the evaporation desalination device by the axial flow pump and then discharged into the heater through the heater feed pipeline. After being heated by the heater, it is discharged into the evaporator for evaporation treatment, and the evaporated gas is discharged for subsequent processing.

[0018] Preferably, the liquid discharged into the mother liquor tank is discharged into the mother liquor return pipeline via a mother liquor pump.

[0019] Preferably, in step (4), for 1m 3 The mother liquor circulation rate is [value missing] / h, and the flow rate of calcium chloride solution in the calcium chloride solution feed line is 0.246–0.316 m³ / h. 3 / h.

[0020] Preferably, in step (2), the water is deionized water; the container is a reaction vessel; and the calcium chloride is industrial grade calcium chloride.

[0021] Preferably, in step (2), the calcium chloride is in the form of flakes or powder, or is anhydrous calcium chloride.

[0022] Preferably, the container is provided with two units. When the first unit is fed with material by the feed diaphragm pump in step (4), the second unit performs the batching in step (2). After all the material in the first unit has been added, the second unit is fed with material by the feed diaphragm pump in step (4) while the first unit performs the batching in step (2), and so on.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention involves adding a specific amount of calcium chloride to the material during the evaporation and desalination process of a methylhydrazine evaporator. Through a specific addition method, the calcium chloride reacts with free alkali to form calcium hydroxide precipitate. However, because the calcium chloride is added to the forward-moving liquid material, and the flow rate is adjusted to ensure the calcium hydroxide precipitate remains suspended in the liquid, the alkalinity of the liquid system is significantly reduced. This mitigates the boiling point increase caused by the increased sodium hydroxide concentration in the liquid. Simultaneously, the effective reduction in the concentration of free NaOH in the evaporator reduces the corrosive effect of this alkaline substance on the equipment. Furthermore, the reduced alkalinity of the liquid greatly improves the stability of methylhydrazine in this environment, reducing decomposition losses under high-temperature alkaline conditions, improving the product quality and yield of methylhydrazine, and achieving efficient recovery of methylhydrazine. This allows the system to operate for extended periods without requiring dedicated shutdown for cleaning.

[0025] 2. By setting specific alkalinity start-up thresholds and specific alkalinity shutdown thresholds, this invention ensures stable alkalinity within the pipeline and the timing for adding calcium chloride solution, thereby improving the continuity and long-term implementation feasibility of this technical solution. Through long-term and arduous research and experimentation, this invention has discovered that crystallization occurs in the feed pipe when the alkalinity exceeds 80 g / L. Before implementing this technology, monitoring the alkalinity of the discharged mother liquor revealed that it reached 120 g / L, necessitating discharge. To achieve stable operation, an alkalinity of 80 g / L was generally selected. Long-term experiments showed that the solubility of calcium hydroxide during evaporation at 80°C under negative pressure is 0.094 g, which translates to an alkalinity of 10 g / L. This means that in the production process of methylhydrazine prepared in this invention, if the alkalinity is below 10 g / L, evaporation and discharge are impossible. Experiments revealed that the optimal alkalinity for the minimum threshold is 30 g / L. Since methylhydrazine is weakly alkaline, maintaining the alkalinity in the pipeline between 30 and 80 g / L (between the shutdown and startup thresholds) facilitates the evaporation of methylhydrazine without its accumulation in the mother liquor. The specific alkalinity shut-off and start-up thresholds are set based on the process of adding calcium chloride solution to methylhydrazine in this invention. Through experiments and principle analysis, it was found that such settings can ensure that there is no need to discharge the mother liquor while ensuring that there is basically no alkaline decomposition loss of methylhydrazine. Thus, by adding calcium chloride within a specific threshold range to form calcium hydroxide precipitate, not only is the free alkali concentration reduced, and precise control of the system alkalinity is achieved, but the stability and controllability of the methylhydrazine evaporation and desalination process are also ensured.

[0026] 3. By using a calcium chloride solution with a concentration of 30-40 wt.% and controlling the preparation temperature below 50℃, this concentration and relatively low temperature of the calcium chloride solution allows for a more complete reaction with the feed solution without causing an overly vigorous reaction. This also ensures compatibility with the set alkalinity range. By rationally controlling the amount and method of calcium chloride addition, the Ca2+ concentration can be controlled. 2+ The OH- ratio is such that it achieves the required OH- for near-complete sedimentation without adding excessive amounts of Ca. 2+ The invention achieves the following effect: By linking the feed diaphragm pump with an alkalinity detector, the alkalinity in the pipeline is controlled in real time within a stable and low range. As the mother liquor continuously accumulates during the evaporation, concentration, and desalination process, the NaOH concentration does not increase. Particulate precipitates are suspended in the feed liquid and then separated by salt separation. In the evaporation and desalination section, the mother liquor in this invention is saturated with sodium chloride. During the evaporation and crystallization process or the cooling crystallization process, the sodium chloride crystals are loose and easier to be washed away by the liquid. In contrast, in existing technologies that do not add calcium chloride, the sodium hydroxide crystals in the solution tend to form scale on the pipe walls and are difficult to wash away. This invention simultaneously converts the sodium hydroxide, which easily forms scale on the pipe walls, into loosely crystalline sodium chloride, thereby further avoiding the opportunity for crystalline salt to adhere to the pipe walls. This effectively increases the evaporation rate of the evaporator, reduces the frequency of maintenance and cleaning, ensures continuous and stable operation, and improves production efficiency. Furthermore, the method of the present invention does not require significant changes to the existing methylhydrazine production process and equipment configuration. Only a small amount of equipment such as a reaction vessel, alkalinity detector, and feed diaphragm pump are needed to achieve technical effects such as reducing scaling and increasing methylhydrazine recovery rate, which greatly improves the economic benefits and practical value of the overall process. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the method for promoting the continuous operation of the methylhydrazine evaporator for evaporation and desalination according to the present invention.

[0028] Figure 2 This is a schematic diagram of the evaporation and desalination process flow of the methylhydrazine evaporator of the present invention.

[0029] Wherein: 101-Evaporator, 102-Heater, 103-Axial flow pump, 104-Concentrate collection pump, 105-Thickener, 106-Centrifuge, 107-Mother liquor tank, 108-Mother liquor pump, 109-First feed diaphragm pump, 110-Second feed diaphragm pump, 111-First calcium chloride batching reactor, 112-Second calcium chloride batching reactor, 113-Stirring shaft, 114-Flow meter, 115-Alkalinity detector; A-Raw material, B-By-product solid salt, C-Deionized water, D-Calcium chloride. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Any equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are within the scope of protection of the present invention.

[0031] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. In this application, when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. Those skilled in the art can determine the specific meaning of the above terms in this disclosure based on the specific circumstances, and they should not be construed as limitations on this disclosure.

[0032] Example 1

[0033] According to Figure 1 The process shown is as follows: Figure 2 The process shown is a method to promote the continuous operation of a methylhydrazine evaporator for evaporation and desalination. The apparatus used includes a calcium chloride solution preparation system, monitoring instruments, a feeding system, and a separation and removal system. The monitoring instruments include an alkalinity detector for real-time monitoring of the material alkalinity in the mother liquor reflux pipeline, a flow meter for monitoring the mother liquor flow rate, and a feed flow meter for monitoring the raw material discharge flow rate. The feeding system includes a feed pipeline and a feed diaphragm pump.

[0034] Includes the following steps:

[0035] (1) Install an alkalinity detector: Install an alkalinity detector and a flow meter on the mother liquor return line of the methylhydrazine evaporator. The alkalinity of the material in the heater feed line is detected in real time by the alkalinity detector, and the flow rate of the mother liquor discharged into the mother liquor return line is detected in real time by the flow meter.

[0036] (2) Preparation of calcium chloride solution: Prepare two 3000L calcium chloride mixing reactors (first calcium chloride mixing reactor and second calcium chloride mixing reactor), and respectively feed the solution into the reactors equipped with stirring components (…). Figure 2 1680 kg of deionized water was added to the calcium chloride batching reactor (with the stirring shaft in the middle), and the stirring component was started at the same time. While stirring, 720 kg of calcium chloride was slowly added to the deionized water. The final concentration of the prepared solution was 30 wt.%. The temperature of the liquid was monitored in real time and kept below 50°C. Stirring was continued for 25 to 35 minutes to obtain a clear and transparent calcium chloride solution.

[0037] (3) Linkage setting between feed diaphragm pump and alkalinity detector: Link the feed diaphragm pump with the alkalinity detector in step (1). When the alkalinity detector detects that the alkalinity of the material in the heater feed line is higher than the start threshold, the feed diaphragm pump is turned on. When the alkalinity detector detects that the alkalinity of the material in the heater feed line is lower than the stop threshold, the feed diaphragm pump is turned off. The start threshold is that the alkalinity of the material is 80 g / L, and the stop threshold is that the alkalinity of the material is 30 g / L.

[0038] (4) Linked Mixing and Feeding: The alkalinity detector detects an alkalinity of 115 g / L in the pipeline, thereby activating the feed diaphragm pump. The flow meter detects a mother liquor flow rate of 10 m³ / L in the mother liquor return pipeline. 3 / h, the calcium chloride solution prepared in step (2) is fed through the diaphragm pump in step (3) at a rate of 3.0m. 3 A flow rate of / h is discharged into the mother liquor return line (meeting L) CaCl2 =L 母 (The requirement is ×B÷40.00÷2×110.98÷M÷ρ). (In other embodiments, a flow meter for calcium chloride can be set to control and monitor the flow rate of the calcium chloride solution). Based on the linkage between the feed diaphragm pump and the alkalinity detector, the addition and stopping of the calcium chloride solution are achieved. After approximately 1 hour, the alkalinity drops to 30 g / L (shutdown threshold), and the feed diaphragm pump is shut down. Then, after approximately 24 hours, the alkalinity rises again to 80 g / L (start-up threshold), and the diaphragm pump automatically starts again, continuing to pump the calcium chloride solution at a flow rate of 2.4 m³ / L. 3 After approximately one hour, the alkalinity drops to 30 g / L, at which point the diaphragm feed pump automatically shuts off. Once the calcium chloride solution in the first calcium chloride batching reactor is depleted, the second calcium chloride batching reactor is used, while the first reactor continues batching. This process repeats until the diaphragm feed pump automatically shuts off again. The unit operated continuously for 330 days without discharging any mother liquor.

[0039] (5) Separation and Removal: Calcium chloride reacts with the material in the mother liquor reflux pipeline during continuous movement, yielding calcium hydroxide precipitate and sodium chloride. The calcium hydroxide precipitate moves downstream with the liquid material, reaching the evaporator discharge pipe where it mixes with the concentrated evaporation liquid discharged from the evaporator. The mixture is then separated by a concentrated liquid collection pump and discharged into a thickener for stirring before being centrifuged to separate the calcium hydroxide precipitate and supersaturated sodium chloride from the material, yielding a byproduct solid salt. The liquid is returned to the mother liquor tank. Part of the material is mixed with the circulating liquid and then mixed with the raw material of the evaporation desalination unit via an axial flow pump. It is then discharged into the heater through the heater feed pipeline, heated by the heater, and then discharged into the evaporator for evaporation. The evaporated gas is discharged for subsequent processing. The liquid discharged into the mother liquor tank is used as mother liquor and is then pumped back into the mother liquor return pipeline. Then, through one of the two calcium chloride batching reactors, calcium chloride solution is discharged into the mother liquor return pipeline in a timely manner according to the linkage between the feed diaphragm pump and the alkalinity detector, thus forming a cycle.

[0040] Comparative Example 1

[0041] This comparative example is used to show a comparison between the existing process without the addition of calcium chloride according to the present invention and Example 1. Comparative Example 1 uses an existing process of the exact same scale as Example 1. The tower is cleaned every 20 days, and the mother liquor is drained once a day on average, with 1 m³ drained each time. 3 Based on a content of 2.2%, the annual loss is 7260 kg of pure methylhydrazine, which is equivalent to 18.15 t of commercial methylhydrazine.

[0042] The yields of methylhydrazine in Example 1 and Comparative Example 1 were determined over a 6-month comparative period, and Table 1 is a comparative data table of the methylhydrazine recovery rates of Example 1 and Comparative Example 1.

[0043] Table 1

[0044] Methylhydrazine yield change wt.% Comparative Example 1 39.20 wt.% Example 1 after 1 month 42.34 wt.% Example 1 after 2 months 43.25 wt.% Example 1 after 3 months 43.23 wt.% Example 1 after 4 months 43.82 wt.% Example 1 after 5 months 43.27 wt.% Example 1 after 6 months 42.95 wt.% Example 1 average per month 43.14 wt.%

[0045] As shown in Table 1, after implementing the calcium chloride addition process of this invention, the yield of methylhydrazine remained at approximately 43 wt.%, while the original process yielded approximately 39 wt.%, representing an increase of 4 percentage points. Considering the loss of discharged mother liquor and the increase in yield, the total cost of Example 1 was reduced by approximately 9% compared to Comparative Example 1.

[0046] Comparative Example 2

[0047] This comparative example illustrates comparative data when calcium chloride was added without setting an addition threshold. Other settings in this comparative example are the same as in Example 1, except that no start-up or shutdown thresholds were set, and calcium chloride solution was continuously discharged into the pipeline. It was found that after 5 hours of addition, 10 tons of 30% calcium chloride solution had been consumed, the alkalinity of the material in the pipeline remained below 10 g / L, and after 8 hours, the amount of methylhydrazine solution continuously extracted decreased from 347 kg / h to 300 kg / h, with a content below 40%, while the concentration of methylhydrazine in the mother liquor increased.

[0048] Comparative Example 3

[0049] This comparative example is used to show comparative data without setting the threshold conditions set by the present invention. The other settings of this comparative example are the same as those of Example 1, except that the alkalinity start threshold is set to 130 g / L. Calcium chloride is added only after the alkalinity reaches 130 g / L. It was found that after 20 days of operation, the evaporation was slow and the evaporator and heater still needed to be stopped and cleaned.

[0050] Comparative Example 4

[0051] This comparative example is used to show comparative data without setting the threshold conditions set by the present invention. The other settings of this comparative example are the same as those of Example 1, except that the alkalinity shut-off threshold is set to 8 g / L. Calcium chloride is only added when the alkalinity is below 8 g / L. It was found that after 7 hours, the amount of methylhydrazine solution continuously extracted decreased from 347 kg / h to 280 kg / h, and the content was below 40%. The concentration of methylhydrazine in the mother liquor increased.

[0052] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention may be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for promoting the continuous operation of a methylhydrazine evaporator for evaporation and desalination, characterized in that, Includes the following steps: (1) Install an alkalinity detector and a flow meter on the mother liquor return pipeline of the methylhydrazine evaporator. The alkalinity of the material in the mother liquor return pipeline is detected in real time by the alkalinity detector, and the flow rate of the mother liquor discharged into the mother liquor return pipeline is detected in real time by the flow meter. (2) Add water to a container with a stirring component and start the stirring component at the same time. While stirring, add calcium chloride to the water. The amount of calcium chloride added is such that the concentration of calcium chloride in the final solution is 30-40 wt.%. The temperature of the liquid is monitored in real time and kept below 50°C. Stir continuously for 25-35 minutes to obtain a clear and transparent calcium chloride solution. (3) Associate the feed diaphragm pump with the alkalinity detector in step (1). When the alkalinity detector detects that the alkalinity of the material in the mother liquor return pipeline is higher than the start threshold, the feed diaphragm pump is turned on. When the alkalinity detector detects that the alkalinity of the material in the mother liquor return pipeline is lower than the stop threshold, the feed diaphragm pump is turned off. The start threshold is when the alkalinity of the material is 50-120 g / L, and the stop threshold is when the alkalinity of the material is 10-50 g / L. (4) The calcium chloride solution prepared in step (2) is discharged into the mother liquor return pipeline through the feed diaphragm pump in step (3) and then mixed into the heater feed pipeline. The addition and stopping of the calcium chloride solution are realized according to the linkage between the feed diaphragm pump and the alkalinity detector. (5) Calcium chloride reacts with the mother liquor in the mother liquor return pipeline during continuous travel to obtain calcium hydroxide precipitate and sodium chloride. The calcium hydroxide precipitate moves backward with the flow of the mixed liquid. When it reaches the centrifuge of the evaporation desalination unit, the calcium hydroxide and sodium chloride are separated from the material together by the centrifuge.

2. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (3), the start threshold is the alkalinity of the material being 70-90 g / L, and the stop threshold is the alkalinity of the material being 25-35 g / L.

3. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (4), the flow meter set in step (1) is simultaneously associated with the feed diaphragm pump; the flow rate of the calcium chloride solution discharged into the mother liquor return pipeline is L. Cal2 The mother liquor flow rate is monitored in real time by a set flow meter, and meets the L requirement. CaCl2 =L 母 The requirement of ×B÷40.00÷2×110.98÷M÷ρ is to control the flow rate of the calcium chloride solution using a feed diaphragm pump; where L 母 ρ is the mother liquor flow rate, B is the alkalinity in the mother liquor return pipeline, M is the concentration of the calcium chloride solution, and ρ is the density of the calcium chloride solution.

4. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (4), the ratio of the flow rate of calcium chloride solution discharged into the mother liquor return pipeline to the flow rate of mother liquor in the mother liquor return pipeline is (0.246~0.316) m. 3 / h:1m 3 / h.

5. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (5), calcium chloride reacts with the mother liquor in the mother liquor return pipeline as it continues to move, resulting in calcium hydroxide precipitate and sodium chloride. The calcium hydroxide precipitate moves backward with the flow of the mixed liquid and continues to mix with the concentrated evaporation liquid discharged from the evaporator discharge pipe after reaching the evaporator discharge pipe. Then, the concentrated mixture is separated by the concentrated liquid collection pump. The concentrated mixture is discharged into the thickener through the pipeline and stirred before being discharged into the centrifuge for centrifugation to separate the calcium hydroxide precipitate and supersaturated sodium chloride from the material, resulting in the by-product solid salt. The liquid is discharged back into the mother liquor tank.

6. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 5, characterized in that, In step (5), the liquid that is not separated by the concentrated liquid extraction pump after mixing is mixed with the raw material of the evaporation desalination device by the axial flow pump and then discharged into the heater through the heater feed pipeline. After being heated by the heater, it is discharged into the evaporator for evaporation treatment, and the evaporated gas is discharged for subsequent processing.

7. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 5, characterized in that, The liquid discharged into the mother liquor tank is used as mother liquor and is discharged into the mother liquor return pipeline by the mother liquor pump.

8. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (2), the water is deionized water; the container is a batching reactor; the calcium chloride is industrial grade calcium chloride; in step (1), the alkalinity detector is an online alkalinity detector.

9. The method for promoting continuous operation of a methylhydrazine evaporator for evaporation and desalination according to claim 1, characterized in that, In step (2), the calcium chloride is in the form of flakes or powder, or in the form of dihydrate or anhydrous calcium chloride.

10. The method for continuously operating a methylhydrazine evaporator for evaporation and desalination according to claim 1 or 8, characterized in that, The container is provided with two units. When the first unit is fed with material by the feed diaphragm pump in step (4), the second unit performs the batching in step (2). After all the material in the first unit has been added, the second unit is fed with material by the feed diaphragm pump in step (4) while the first unit performs the batching in step (2), and so on.

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