Urea hydrolysis system

Abstract

The utility model relates to the field of urea hydrolysis, and particularly discloses a urea hydrolysis system which comprises a urea solution tank, a temperature and pressure reducing device, urea hydrolyzers and urea solution delivery pumps, all the urea hydrolyzers are connected in parallel, and the urea solution delivery pumps correspond to the urea hydrolyzers one by one. A steam outlet of the temperature and pressure reducing device is communicated with a heating steam inlet of the hydrolyzer; a urea solution electric door, a urea solution quick closing door and a urea solution inlet adjusting door are connected in series between the urea solution conveying pump and the hydrolyzer; a heating steam quick closing door and a heating steam inlet adjusting door are connected in series between the temperature and pressure reducing device and the hydrolyzer; and a liquid level detector and a temperature detector are arranged in the hydrolyzer. The urea hydrolysis system disclosed by the utility model can solve the problems that the pressure in the hydrolyzers is easy to influence, so that the pressure of an ammonia steam outlet is unstable, and a squeezing phenomenon exists among a plurality of hydrolyzers which are connected in parallel.

Description

Technical Field

[0001] The utility model relates to the field of urea hydrolysis, and particularly relates to a urea hydrolysis system. Background Art

[0002] The flue gas generated by thermal power generation contains a relatively high content of NO x , and direct emission will cause environmental pollution. Therefore, current thermal power plants need to install denitration devices to treat the NO in the flue gas x before discharging. Ammonia is used as the reducing agent in the denitration device, and urea hydrolysis to produce ammonia has low energy consumption, safe and stable operation, so it is currently a common ammonia production scheme in thermal power plants.

[0003] Thermal power plants usually set up a urea hydrolysis system to produce ammonia. The current urea hydrolysis system is mainly as shown in a urea hydrolysis system for flue gas denitration disclosed in the patent with the application number CN201220032693.9, which is provided with a urea dissolution tank, a urea solution transfer pump, a urea solution storage tank, a urea solution supply pump and a hydrolyzer. The drain outlet of the urea dissolution tank is connected to the inlet of the urea solution transfer pump, the outlet of the urea solution transfer pump is connected to the inlet of the urea solution storage tank, the urea solution storage tank is provided with an outlet and a urea solution return port, the outlet is connected to the inlet of the urea solution supply pump, and the outlet of the urea solution supply pump is respectively connected to the urea solution return port of the urea solution storage tank and the inlet of the hydrolyzer.

[0004] In order to denitrate the flue gas generated by multiple units of the power plant, usually as shown in the optimized dual header system for the finished gas of urea hydrolysis for multi-unit denitration in a thermal power plant disclosed in the patent with the application number 202323392431.0, multiple hydrolyzers are connected in parallel. When the hydrolyzer works, the pressure inside the hydrolyzer needs to be controlled to ensure the load balance of the multiple parallel hydrolyzers and prevent mutual exclusion.

[0005] However, it is found in actual applications that when the solution is introduced into the hydrolyzer, the change in the liquid level will affect the pressure inside the hydrolyzer, resulting in unstable pressure at the ammonia vapor outlet; because the hydrolyzer needs to be heated during operation, the gas inside the hydrolyzer is also heated at this time, and the increase in temperature causes the volume of the gas to increase, so the pressure inside the hydrolyzer will also be affected at this time, resulting in unstable pressure at the ammonia vapor outlet. Summary of the Utility Model

[0006] The purpose of the utility model is to provide a urea hydrolysis system to solve the problem that the pressure inside the hydrolyzer is easily affected, resulting in unstable pressure at the ammonia vapor outlet and causing mutual exclusion between multiple parallel hydrolyzers.

[0007] To achieve the above object, the utility model adopts the following technical solutions: A urea hydrolysis system includes a urea solution tank, a desuperheating and pressure reducing device, at least two urea hydrolyzers, and at least two urea solution delivery pumps. All the urea hydrolyzers are connected in parallel, and the urea solution delivery pumps correspond to the urea hydrolyzers one by one. Moreover, the urea solution delivery pumps connect the outlet of the urea solution tank to the urea solution inlet of the hydrolyzer. The steam outlet of the desuperheating and pressure reducing device is connected to the heating steam inlet of the hydrolyzer. A urea solution motorized valve, a urea solution quick closing valve, and a urea solution inlet regulating valve are connected in series between the urea solution delivery pump and the hydrolyzer; a heating steam quick closing valve and a heating steam inlet regulating valve are connected in series between the desuperheating and pressure reducing device and the hydrolyzer; a liquid level detector and a temperature detector are provided in all the hydrolyzers.

[0008] The beneficial effects of this solution are as follows:

[0009] 1. Before use, first draw the characteristic curves of each urea solution regulating valve regarding the adjustment valve opening and flow rate according to multiple tests or previous data. According to the characteristic curves, the linear region, sluggish region, and steep slope region of the valve can be distinguished. During implementation, the liquid level detector in this solution can detect the liquid level in the hydrolyzer, limit the stroke range of the urea solution regulating valve according to the actual situation on site. At this time, control the adjustment amount of the urea solution regulating valve in the linear region, avoiding the sluggish region and the steep slope region, so as to achieve linear adjustment. When the liquid level in the hydrolyzer drops to the same height as the heating pipe of the hydrolyzer or is lower than the heating pipe of the hydrolyzer, increasing the opening of the urea solution inlet regulating valve can increase the amount of urea solution entering the urea hydrolysis, effectively raising the liquid level in the hydrolyzer; when the liquid level in the hydrolyzer rises above the heating pipe of the hydrolyzer, close the opening of the urea solution inlet regulating valve to reduce the flow rate of the urea solution entering the urea hydrolyzer, effectively lowering the liquid level in the hydrolyzer; that is, through the set liquid level detector in this solution, the liquid level height in the hydrolyzer can be continuously detected, so as to facilitate continuously adjusting the opening of the urea solution inlet regulating valve according to the liquid level height, thereby continuously adjusting the liquid level height of the urea solution in the hydrolyzer. After testing, the fluctuation of the liquid level after such adjustment is greatly reduced, and when the load is stable, the opening of the urea solution inlet regulating valve can be stabilized within a certain opening range and does not need to fluctuate greatly, effectively improving the control force of the urea hydrolysis reaction, and at the same time avoiding large fluctuations in the pressure in the hydrolyzer, so the pressure at the ammonia steam outlet is basically stable.

[0010] 2. Meanwhile, since each hydrolyzer is equipped with a temperature detector, multiple temperature values can be obtained each time. The median temperature value is used as the temperature reference value, and a deviation value is preset to adjust the temperature in the hydrolyzer where the temperature detector deviates from the deviation value. When the operating temperature of the hydrolyzer is lower than the temperature reference value and the low deviation is greater than the set deviation value, by increasing the opening of the heating steam inlet regulating valve and increasing the amount of heating steam entering the hydrolyzer, the purpose of raising the operating temperature of the hydrolyzer can be achieved. Similarly, when the operating temperature of the hydrolyzer is higher than the temperature reference value and the high deviation is greater than the set deviation value, by reducing the opening of the heating steam inlet regulating valve and reducing the amount of heating steam entering the hydrolyzer, the purpose of lowering the operating temperature of the hydrolyzer can be achieved. It is found in actual tests that by using the above adjustment method, the pressure fluctuation in the hydrolyzer can be controlled within 0.02 MPa, and the temperature deviation during the operation of the hydrolyzer is within 0.5 °C. The temperature deviation value can be set according to the actual situation on site.

[0011] In summary, in this solution, the liquid level detector and temperature detector are set to detect the liquid level height of the urea solution and the temperature in the hydrolyzer respectively, and the liquid level height and temperature can be used as reference factors for adjusting the hydrolyzer at the same time. Compared with not setting temperature as an auxiliary adjustment, single setting of liquid level and pressure independent adjustment, and full stroke operation of the urea solution regulating valve, the urea solution inlet regulating valve in this solution is controlled in the linear region of adjustment, so that the amount of urea solution entering the hydrolyzer is controlled in a linear trend, with stable and steady adjustment. Compared with the 100% amplitude of the urea solution regulating valve, severe fluctuation of the solution flow rate, 100% amplitude of the heating steam regulating valve, and severe fluctuation of the heating steam flow rate before optimization, the operation stability has been greatly improved, the safety has been significantly enhanced, the ability to respond to load changes has been greatly improved, and the loads of the parallel-operated hydrolyzers are balanced, with the temperature deviation controlled within a reasonable range, eliminating the "boiling phenomenon" and "false liquid level" of the urea hydrolyzer, and solving the problems of bursting of the rupture disc caused by too high pressure in a single hydrolyzer and interference between hydrolyzers.

[0012] Furthermore, the number of single hydrolysis temperature detectors is at least three, and all temperature detectors are arranged in sequence along the axial direction of the hydrolyzer, and the axial distance between adjacent temperature detectors is equal.

[0013] The beneficial effects of this solution are as follows: Multiple temperature detectors can detect the temperatures at different positions inside the hydrolyzer. Taking the median or average value among them can better judge the temperature inside the hydrolyzer, and it is more reliable when used as the basis for judging whether the temperature inside the hydrolyzer needs to be adjusted. Secondly, multiple temperature detectors work simultaneously. When any one of the temperature detectors is damaged, it can be detected in a timely manner through the significantly different values from the other two temperature sensors. Therefore, it also has the effect of automatically judging bad values, ensuring the normal temperature value, making the measured value closer to the actual temperature inside the hydrolyzer, and thus judging whether the temperature needs to be adjusted more accurately.

[0014] Furthermore, the number of liquid level detectors in each hydrolyzer is at least three.

[0015] The beneficial effects of this solution are as follows: Multiple liquid level detectors can detect the liquid level heights at various parts of the hydrolyzer. Similarly to the temperature detectors, it can better feedback the liquid level height inside the hydrolyzer, and has the effect of automatically judging bad values, ensuring the normal liquid level value. And because it can make the measured value closer to the actual liquid level of the hydrolyzer, it is more accurate to judge whether the urea solution inlet regulating valve needs to be adjusted.

[0016] Furthermore, the liquid level detector is located in the middle of the hydrolyzer and above the heating pipe inside the hydrolyzer.

[0017] The beneficial effects of this solution are as follows: The liquid level detector in this solution is close to the urea solution, and can better detect the liquid level height inside the hydrolyzer.

[0018] Furthermore, a temperature output module is provided. All temperature detectors are electrically connected to the temperature output module, and the temperature output module is used to output the temperature at the median measured by all temperature detectors as the temperature reference value.

[0019] The beneficial effects of this solution are as follows: The temperature output module in this solution can automatically compare the values of the same temperature detector, thereby outputting a more accurate temperature value, without the need for manual recording and judgment, effectively reducing the workload of workers.

[0020] Furthermore, the hydrolyzer is also provided with a urea solution return port. The urea solution return port is communicated with a urea solution storage tank, and a liquid phase return valve is provided between the urea solution storage tank and the urea solution return port.

[0021] The beneficial effects of this solution are as follows: When the hydrolyzer is taken out of service and no longer works, this solution can pass the urea solution inside the hydrolyzer into the urea storage tank through the liquid phase return valve, which can quickly weaken and stop the reaction inside the hydrolyzer, thereby avoiding excessive ammonia waste and potential hazards.

[0022] Furthermore, the ammonia outlet of the hydrolyzer is connected to an ammonia vapor confluence main pipe, and the ammonia outlet of the hydrolyzer is also connected to the urea solution storage tank. A gas-phase reflux valve is provided between the urea solution storage tank and the ammonia vapor outlet of the hydrolyzer.

[0023] The beneficial effect of this solution is that when the hydrolyzer is taken out of service and no longer operates, the reaction inside the hydrolyzer will continue for a period of time. During this process, the ammonia gas generated flows back to the urea solution storage tank through the gas-phase reflux valve, preventing the pressure inside the hydrolyzer from continuously rising and improving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a connection schematic diagram of each part of the urea hydrolysis system in Embodiment 1 of the present invention;

[0025] Figure 2 It is the characteristic curve of the urea solution regulating valve in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following is a more detailed description through specific embodiments:

[0027] The reference numerals in the accompanying drawings of the specification include: hydrolyzer 1, urea solution return port 11, ammonia vapor outlet 12, heating steam inlet 13, urea solution inlet 14, urea solution inlet quick closing valve 2, urea solution regulating valve 21, heating steam quick closing valve 3, heating steam regulating valve 31, liquid-phase reflux valve 4, gas-phase reflux valve 5.

[0028] Embodiment 1

[0029] Embodiment 1 is basically as Figure 1 shown. A urea hydrolysis system includes a urea solution tank, a desuperheating and pressure-reducing device, three urea solution transfer pumps, and three hydrolyzers 1. The three hydrolyzers 1 are arranged in parallel. Each hydrolyzer 1 is provided with a urea solution inlet 14 communicating with the reaction chamber of the hydrolyzer 1, an ammonia vapor outlet 12, and a heating steam inlet 13 communicating with the heating structure of the hydrolyzer 1. The three urea solution transfer pumps correspond to the three hydrolyzers 1 one by one and are used to respectively introduce the urea solution in the urea solution tank into the three hydrolyzers 1. Specifically, in this embodiment, existing urea solution tanks, urea solution transfer pumps, hydrolyzers 1, and desuperheating and pressure-reducing devices are all adopted, and their settings and structures are the same as those in the prior art, so they will not be elaborated in this embodiment.

[0030] The urea solution transfer pump connects the outlet of the urea solution tank to the urea solution inlet 14 of the hydrolyzer 1 through a pipeline, and introduces the urea solution in the urea solution tank into the hydrolyzer 1. A urea solution inlet quick closing valve 2 is provided between the urea solution transfer pump and the hydrolyzer 1, and a urea solution inlet regulating valve 21 is connected in series between the urea solution inlet quick closing valve 2 and the hydrolyzer 1.

[0031] The urea solution reflux port 11 is located at the lower part of the hydrolyzer 1. The urea solution reflux port 11 is connected to the urea solution storage tank through a pipeline, and a liquid-phase reflux valve 4 is provided between the urea solution reflux port 11 and the urea solution storage tank. The ammonia vapor outlet 12 is located at the top of the hydrolyzer 1. The ammonia vapor outlet 12 is connected to an ammonia vapor confluence main pipe. The ammonia vapor outlet 12 is also connected to the urea solution storage tank through a pipeline, and a gas-phase reflux valve 5 is provided between the ammonia vapor outlet 12 and the urea solution storage tank.

[0032] The desuperheating and pressure-reducing device is connected to the heating steam inlet 13 through a pipeline, and a heating steam quick shut-off valve 3 is further provided between the desuperheating and pressure-reducing device and the heating steam inlet 13. A heating steam inlet regulating valve 31 is connected in series between the heating steam quick shut-off valve 3 and the desuperheating and pressure-reducing device.

[0033] Three liquid level detectors and three temperature detectors are provided in the hydrolyzer 1. In this embodiment, the liquid level detectors adopt liquid level sensors, and the temperature detectors adopt temperature sensors. The three liquid level detectors are all located in the middle of the hydrolyzer 1 and are slightly higher than the heating pipelines in the hydrolyzer 1. When the liquid level is controlled at a height slightly higher than the heating pipelines, the liquid level detectors in this solution can better detect the liquid level height. At the same time, each liquid level detector is located at a different position in the middle of the hydrolyzer 1. The three temperature detectors are in the reaction chamber of the hydrolyzer 1 and are distributed along the axis of the hydrolyzer 1, and the axial distance between adjacent temperature detectors is equal to measure the temperatures at different positions in the reaction chamber of the hydrolyzer 1 as much as possible.

[0034] Before implementing the urea hydrolysis system in this solution, please refer to Figure 2 and first draw the characteristic curves of each urea solution regulating valve regarding the adjustment valve opening and flow rate through multiple tests or using previous data. Please refer to the characteristic curves of Series 1 in Figure 2 . According to the characteristic curves, the linear region (adjustment valve opening 35 - 65%), the sluggish region (adjustment valve opening less than 35%), and the steep region (adjustment valve opening greater than 65%) of the valve can be distinguished to adjust the opening of the urea solution regulating valve along the linear region.

[0035] After determining the characteristic curves of the opening and flow rate of the urea solution regulating valve, the specific implementation process of the urea hydrolysis system is as follows:

[0036] In this embodiment, the liquid level above the heating pipeline in the hydrolyzer 1 is used as a reference, and a liquid level deviation value is set. When the liquid level in the hydrolyzer 1 is lower than the reference liquid level and the low amount is greater than the deviation value, the opening degree of the heating steam inlet regulating valve 31 is increased, and the opening degree of the urea solution inlet regulating valve is controlled within the nearest linear region to increase the amount of urea solution entering the hydrolyzer 1. Similarly, when the liquid level in the hydrolyzer 1 is higher than the reference liquid level and the high amount is also greater than the deviation value, the opening degree of the urea solution inlet regulating valve is decreased, and it is also controlled within the nearest linear region to reduce the amount of urea solution entering the hydrolyzer 1.

[0037] The values of the three temperature detectors provided in the same hydrolyzer 1 are averaged, and the average value is used as the temperature value of the hydrolyzer 1. The temperature values of the three hydrolyzers 1 are compared, and the median temperature value is selected as the final temperature adjustment value. The deviation value of the temperature is set to 0.5 °C, and the temperatures in the other two hydrolyzers 1 are adjusted: when the temperature value of the hydrolyzer 1 is lower than the temperature adjustment value and the low amount is greater than the set deviation value, the opening degree of the heating steam inlet regulating valve is increased to increase the heating steam entering the hydrolyzer. Similarly, when the temperature value of the hydrolyzer is higher than the temperature adjustment value and the high amount is greater than the set deviation value, the opening degree of the heating steam inlet regulating valve is decreased to reduce the amount of heating steam entering the hydrolyzer.

[0038] When the hydrolyzer 1 is taken out of service, closing the urea solution quick closing valve 2 and the heating steam quick closing valve 3 can quickly stop the urea solution and heating steam from entering the hydrolyzer 1 respectively, thus facilitating the control of the temperature and liquid level of the hydrolyzer 1. After the hydrolyzer 1 is taken out of service, the solution in the hydrolyzer 1 is stored in the urea solution storage tank through the liquid phase reflux valve 4. The gas phase reflux valve 5 is opened, and the ammonia gas generated after a period of time after taking out of service enters the urea solution storage tank through the gas phase reflux valve 5 for pressure relief. Through tests, the liquid level fluctuation in the hydrolyzer 1 in this embodiment does not exceed 10 mm, and the pressure fluctuation range in the hydrolyzer 1 is less than 0.02 MPa.

[0039] Embodiment 2

[0040] On the basis of Embodiment 1, this embodiment is provided with a controller with a numerical output module. The three temperature detectors in the same hydrolyzer 1 are all electrically connected to the controller, and the numerical output module of the controller outputs the temperature value in the middle position among the three temperature detectors as the temperature value. The adjustment method in this embodiment is the same as that in Embodiment 1, and the difference from Embodiment 1 is that in this embodiment, it is not necessary to manually calculate the average value of the temperature or determine the median value, reducing the workload of workers.

[0041] The above are only embodiments of the present utility model. Specific technical solutions and / or common knowledge such as characteristics that are well-known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present utility model, several deformations and improvements can be made, and these should also be regarded as the protection scope of the present utility model, and these will not affect the implementation effect of the present utility model and the practicality of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A urea hydrolysis system, comprising a urea solution tank, a desuperheating and pressure reducing device, at least two urea hydrolyzers and at least two urea solution delivery pumps. All the urea hydrolyzers are connected in parallel, and the urea solution delivery pumps correspond to the urea hydrolyzers one by one. Moreover, the urea solution delivery pumps connect the outlet of the urea solution tank to the urea solution inlet of the hydrolyzers, and the steam outlet of the desuperheating and pressure reducing device is connected to the heating steam inlet of the hydrolyzers. It is characterized in that: A urea solution electric valve, a quick closing valve for urea solution and a regulating valve for urea solution inlet are connected in series between the urea solution delivery pump and the hydrolyzer; a quick closing valve for heating steam and a regulating valve for heating steam inlet are connected in series between the desuperheating and pressure reducing device and the hydrolyzer; a liquid level detector and a temperature detector are provided in all hydrolyzers.

2. The urea hydrolysis system according to claim 1, wherein: The number of temperature detectors in each hydrolyzer is at least three, and all temperature detectors are sequentially distributed along the axial direction of the hydrolyzer, and the distance between adjacent temperature detectors along the axial direction of the hydrolyzer is equal.

3. The urea hydrolysis system according to claim 2, wherein: The number of liquid level detectors in each hydrolyzer is at least three.

4. The urea hydrolysis system according to claim 3, wherein: The liquid level detector is located in the middle of the hydrolyzer and is higher than the heating tube in the hydrolyzer.

5. A urea hydrolysis system according to any one of claims 2, 3, and 4, characterized in that: A temperature output module is provided, and all temperature detectors are electrically connected to the temperature output module, and the temperature output module is used to output the temperature at the middle position measured by all temperature detectors as a temperature reference value.

6. The urea hydrolysis system according to claim 1, wherein: The hydrolyzer is also provided with a urea solution return port, the urea solution return port is communicated with a urea solution storage tank, and a liquid phase return valve is provided between the urea solution storage tank and the urea solution return port.

7. The urea hydrolysis system according to claim 6, wherein: The ammonia gas outlet of the hydrolyzer is communicated with an ammonia steam converging main pipe, and the ammonia gas outlet of the hydrolyzer is also communicated with the urea solution storage tank, and a gas phase return valve is provided between the urea solution storage tank and the ammonia steam outlet of the hydrolyzer.

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