A system and method for preventing product gas from being blocked by urea hydrolysis to produce ammonia

Abstract

The present invention discloses a system and method for preventing blockage of product gas from urea hydrolysis to produce ammonia. This system addresses the technical issues of existing urea hydrolysis product gas systems, which suffer from difficulties in heating, susceptibility to condensation and crystallization, and high risks of system corrosion and pipe blockage. The system comprises a urea hydrolysis reactor equipped with an outlet pipeline connected to a nitrogen generator and a heat exchanger located between the reactor and the nitrogen generator. This system has the advantages of lowering the condensation temperature of the product gas and effectively reducing the risk of system corrosion and blockage.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia production by hydrolysis, and in particular to a system and method for preventing product gas from being blocked during ammonia production by urea hydrolysis. Background Art

[0002] Currently, most thermal power plant flue gas denitrification projects use the selective catalytic reduction (SCR) denitrification process. The reducing agent required for the SCR denitrification reaction is ammonia, which can be obtained from one of three chemical raw materials: liquid ammonia, ammonia water, or urea. Currently, most thermal power plants use the urea hydrolysis process to produce ammonia as the reducing agent for denitrification.

[0003] The chemical equation for the urea hydrolysis reaction is as follows:

[0004]

[0005] The urea hydrolysis process for producing ammonia is based on the principle that a urea solution of a certain concentration, when heated, hydrolyzes to form ammonium carbamate, which then further decomposes to form ammonia and carbon dioxide. The resulting product gas contains water vapor, carbon dioxide, and ammonia. The carbon dioxide and ammonia are products of the urea reaction, while the water vapor comes from the vaporization of unreacted water in the urea solution. When using a 50% urea solution, the volume ratios of the product gas components are: 43.8% water vapor, 18.7% carbon dioxide, and 37.5% ammonia.

[0006] Ammonium carbamate, an intermediate produced during the reaction, is the primary corrosive substance in the urea hydrolysis ammonia production system. Because urea hydrolysis is a reversible reaction, the product gas condenses at low temperatures to produce ammonium carbamate, which corrodes pipes and components. Further water loss leads to urea crystals, which can clog the pipe system.

[0007] Under gaseous conditions, the Gibbs function can be calculated to be less than 0 based on the reaction equilibrium constant, that is, the reaction of ammonium carbamate is a spontaneous decomposition reaction, that is, it is difficult for NH3 and CO2 to generate ammonium carbamate under gas phase conditions.

[0008] When condensed water is generated in the product gas, NH3 and CO2 dissolve in the water. In other words, under liquid phase conditions, NH3 and CO2 react to produce ammonium carbamate. As the temperature decreases, the rate of ammonium carbamate formation increases. Therefore, the key to solving this problem is to prevent the water vapor in the product gas from condensing into water.

[0009] At present, in order to prevent the water vapor in the product gas from condensing into water, the product gas needs to be heated.

[0010] The outlet pressure of the urea hydrolysis ammonia reactor product gas pipeline is 0.35-0.55 MPa. When fed with a 50wt% urea solution, the corresponding product gas condensation temperature is 119.8-131.8°C, requiring a corresponding product gas pipeline heating temperature of at least 130°C. To account for temperature losses in the pipeline, the product gas pipeline heating temperature is required to be controlled between 140°C and 160°C. The main heating methods currently used include steam tracing, steam jacketed piping, and electric heating. Regardless of the heating method used, the high heating temperature places high demands on the quality of the heating and insulation construction.

[0011] When the heating temperature does not meet the requirements, ammonium carbamate is produced due to condensation, which corrodes pipes and components, and places high demands on material selection. Further water loss will form urea crystals, which will block the pipeline system. The entire product gas transmission pipeline needs to be equipped with a purge system.

[0012] In view of the shortcomings of existing technologies, it is necessary to further improve the urea hydrolysis anti-blocking technology. Summary of the Invention

[0013] The technical problem to be solved by the present invention is that the existing urea hydrolysis ammonia production product gas is difficult to heat, is prone to condensation and crystallization, and has a high risk of corrosion and pipe blockage.

[0014] The present invention is achieved through the following technical solutions:

[0015] A urea hydrolysis ammonia product gas blocking prevention system includes a urea hydrolysis reactor. The urea hydrolysis reactor is provided with an outlet pipeline. The outlet pipeline is connected to a nitrogen generator and a heat exchanger. The heat exchanger is located between the urea hydrolysis reactor and the nitrogen generator.

[0016] The present invention connects a nitrogen generator to the outlet pipeline of a urea hydrolysis reactor, introduces heated nitrogen into the outlet pipeline and mixes it with the product gas, thereby increasing the chemical components in the outlet pipeline, reducing the volume fraction of water in the original composition, and lowering the condensation temperature of the product gas, thereby reducing the risks of corrosion and crystallization blockage of the entire pipeline system, reducing the requirements for heat and insulation construction, and improving the reliability and stability of the operation of the urea hydrolysis ammonia production system.

[0017] The present invention takes into account the inertness of the gas and the molecular weight of the substance when mixing with the product gas. Nitrogen is an inert gas that is relatively easy to obtain, has a small molecular weight, and is low in cost. Under the premise of adding the same mass of gas, the smaller the molecular weight, the larger the volume share, and the better it can play the role of lowering the recondensation temperature.

[0018] The present invention preferably provides a urea hydrolysis ammonia product gas blocking prevention system, wherein the nitrogen generator is connected to the gas outlet pipeline via a nitrogen supply pipeline, and a first regulating valve, a heat exchanger and a flow controller are provided on the nitrogen supply pipeline. The first regulating valve and the flow controller are electrically connected, and the flow controller detects and controls the opening of the first regulating valve.

[0019] The present invention preferably provides a urea hydrolysis ammonia product gas blocking prevention system, wherein a first regulating valve, a heat exchanger and a flow controller are sequentially arranged on the nitrogen supply pipeline.

[0020] The present invention arranges the heat exchanger between the first regulating valve and the flow controller, which can detect the actual flow of the hot nitrogen coming out of the heat exchanger and pass through the first regulating valve according to the flow, so as to achieve more accurate control.

[0021] The present invention preferably provides a urea hydrolysis ammonia product gas blocking prevention system, wherein a second regulating valve and a pressure display regulating alarm are provided on the gas outlet pipeline, the second regulating valve and the pressure display regulating alarm are electrically connected, the nitrogen supply pipeline is connected between the second regulating valve and the pressure display regulating alarm, the pressure of the product gas is detected by the pressure display regulating alarm and controls the second regulating valve to adjust the pressure.

[0022] The present invention preferably provides a system for preventing product gas from blocking by hydrolyzing urea to produce ammonia, wherein the heat exchanger is a steam heat exchanger.

[0023] A method for preventing blockage of product gas from producing ammonia by urea hydrolysis, comprising the following steps:

[0024] Step 1: heating nitrogen to obtain hot nitrogen;

[0025] Step 2: Mix the hot nitrogen obtained in step 1 with the product gas to reduce the volume fraction of water vapor in the original product gas, thereby reducing the recondensation temperature of the product gas.

[0026] The present invention takes into account that the heating temperature is required to be controlled at 140°C to 160°C, and the quality requirements for heating and insulation construction are high. It is very easy for poor heating to occur, and the product gas condenses and crystallizes to block the pipeline. Therefore, in order to reduce the risk of crystallization and blockage, it is best to lower this heating requirement. Therefore, it is designed to mix hot nitrogen with the product gas to effectively lower the condensation temperature, thereby reducing the heating requirement.

[0027] In a preferred method for preventing blockage of product gas from urea hydrolysis to ammonia according to the present invention, the hot nitrogen in step 2 accounts for 20-30% of the mass of the product gas.

[0028] When 20-30% of hot nitrogen is mixed into the product gas, the condensation temperature of the product gas can be reduced by about 5-6°C.

[0029] The present invention preferably provides a method for preventing blockage of product gas from urea hydrolysis to produce ammonia, wherein the operation steps of step 1 are as follows: nitrogen in a nitrogen generator enters a heat exchanger through a nitrogen supply pipeline for heat exchange to obtain hot nitrogen.

[0030] In a preferred method for preventing blockage of product gas from urea hydrolysis to ammonia of the present invention, the temperature of the hot nitrogen is 140-150°C.

[0031] The present invention preferably provides a method for preventing blockage of product gas from urea hydrolysis to ammonia. In step 2, the flow controller detects and controls the flow of the first regulating valve according to the mass ratio of nitrogen to the product.

[0032] The present invention has the following advantages and beneficial effects:

[0033] 1. The present invention introduces heated nitrogen into the outlet pipeline to mix with the product gas, thereby increasing the chemical components in the outlet pipeline, reducing the volume fraction of water, and lowering the condensation temperature of the product gas, thereby reducing the risk of corrosion and crystallization blockage of the entire pipeline system, and also reducing the requirements for heating and insulation construction, thereby improving the reliability and stability of the urea hydrolysis ammonia production system.

[0034] 2. The present invention can reduce the condensation temperature of the product gas by about 5-6°C by controlling the proportion of the hot nitrogen introduced.

[0035] 3. The nitrogen flow controller of the present invention is arranged after the heat exchanger, and can detect the actual flow of the hot nitrogen coming out of the heat exchanger and pass through the first regulating valve according to the flow, so as to achieve more precise control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0037] Figure 1 This is a schematic structural diagram of the system for preventing product gas from blocking during urea hydrolysis to produce ammonia according to the present invention.

[0038] Names of parts in the attached drawings:

[0039] 1-urea hydrolysis reactor, 2-gas outlet pipeline, 3-nitrogen generator, 4-nitrogen supply pipeline, 5-first regulating valve, 6-heat exchanger, 7-flow controller, 8-second regulating valve, 9-pressure display and regulation alarm. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example 1

[0042] like Figure 1 As shown, a urea hydrolysis ammonia product gas blocking prevention system includes a urea hydrolysis reactor 1, and the urea hydrolysis reactor 1 is provided with an outlet pipeline 2, and the outlet pipeline 2 is connected to a nitrogen generator 3 and a heat exchanger 6, and the heat exchanger 6 is located between the urea hydrolysis reactor 1 and the nitrogen generator 3.

[0043] The present invention connects a nitrogen generator 3 to the outlet pipe 2 of the urea hydrolysis reactor 1, and introduces heated nitrogen into the outlet pipe 2 to mix with the product gas, thereby increasing the chemical components in the outlet pipe 2, reducing the volume fraction of water, and lowering the condensation temperature of the product gas, thereby reducing the risks of corrosion and crystallization blockage of the entire pipeline system, reducing the requirements for heat and insulation construction, and improving the reliability and stability of the operation of the urea hydrolysis ammonia production system.

[0044] The nitrogen generator 3 is connected to the gas outlet pipeline 2 via a nitrogen supply pipeline 4. A first regulating valve 5, a heat exchanger 6 and a flow controller 7 are sequentially provided on the nitrogen supply pipeline 4. The first regulating valve 5 and the flow controller 7 are electrically connected. The flow controller 7 detects and controls the opening of the first regulating valve 5.

[0045] The present invention arranges the heat exchanger 6 between the first regulating valve 5 and the flow controller 7, which can detect the actual flow of the hot nitrogen coming out of the heat exchanger 6 and pass through the first regulating valve 5 according to the flow, so as to achieve more accurate control.

[0046] The gas outlet pipeline 2 is provided with a second regulating valve 8 and a pressure display regulating alarm 9, and the second regulating valve 8 and the pressure display regulating alarm 9 are electrically connected. The nitrogen supply pipeline 4 is connected between the second regulating valve 8 and the pressure display regulating alarm 9. The pressure of the product gas is detected by the pressure display regulating alarm 9 and controls the second regulating valve 8 to adjust the pressure.

[0047] The heat exchanger 6 is a water vapor heat exchanger 6 .

[0048] Example 2

[0049] A method for preventing blockage of product gas from producing ammonia by urea hydrolysis, comprising the following steps:

[0050] Step 1: heating nitrogen to obtain hot nitrogen;

[0051] Step 2: Mix the hot nitrogen obtained in step 1 with the product gas to reduce the volume fraction of water vapor in the original product gas, thereby reducing the recondensation temperature of the product gas.

[0052] The present invention takes into account that the heating temperature is required to be controlled at 140°C to 160°C, and the quality requirements for heating and insulation construction are high. It is very easy for poor heating to occur, and the product gas condenses and crystallizes to block the pipeline. Therefore, in order to reduce the risk of crystallization and blockage, it is best to lower this heating requirement. Therefore, it is designed to mix hot nitrogen with the product gas to effectively lower the condensation temperature, thereby reducing the heating requirement.

[0053] In step 2, the hot nitrogen accounts for 20% of the mass of the product gas.

[0054] When 20% of hot nitrogen is mixed into the product gas, the condensation temperature of the product gas can be reduced by 5°C.

[0055] The operation steps of step 1 are as follows: the nitrogen in the nitrogen generator 3 enters the heat exchanger 6 through the nitrogen supply pipeline 4 to exchange heat to obtain hot nitrogen.

[0056] The temperature of the hot nitrogen is 140°C.

[0057] In step 2, the flow controller 7 detects and controls the flow of the first regulating valve 5 according to the mass ratio of nitrogen to product.

[0058] Example 3

[0059] The difference between this embodiment and embodiment 2 is that in step 2, the hot nitrogen accounts for 30% of the mass of the product gas, and the temperature of the hot nitrogen is 150° C. When 30% of the hot nitrogen is mixed in, the condensation temperature of the product gas is reduced by 6° C.

[0060] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A urea hydrolysis ammonia product gas blocking prevention system, characterized in that: The invention comprises a urea hydrolysis reactor (1), wherein the urea hydrolysis reactor (1) is provided with an outlet pipeline (2), the outlet pipeline (2) is connected to a nitrogen generator (3) and a heat exchanger (6), and the heat exchanger (6) is located between the urea hydrolysis reactor (1) and the nitrogen generator (3); Hot nitrogen accounts for 20-30% of the product gas mass, and the temperature of the hot nitrogen is 140-150°C; The nitrogen generator (3) is connected to the gas outlet pipeline (2) via a nitrogen supply pipeline (4). A first regulating valve (5), a heat exchanger (6) and a flow controller (7) are provided on the nitrogen supply pipeline (4). The first regulating valve (5) and the flow controller (7) are electrically connected. The flow controller (7) detects and controls the opening of the first regulating valve (5). The gas outlet pipeline (2) is provided with a second regulating valve (8) and a pressure display regulating alarm (9), the second regulating valve (8) and the pressure display regulating alarm (9) are electrically connected, and the nitrogen supply pipeline (4) is connected between the second regulating valve (8) and the pressure display regulating alarm (9); The heat exchanger (6) is a water vapor heat exchanger (6).

2. The urea hydrolysis ammonia product gas blocking prevention system according to claim 1, characterized in that: The nitrogen supply pipeline (4) is provided with a first regulating valve (5), a heat exchanger (6) and a flow controller (7) in sequence.

3. A method for preventing blockage of product gas from urea hydrolysis to ammonia, characterized in that: The system for preventing product gas from blocking by urea hydrolysis to produce ammonia according to any one of claims 1 to 2 comprises the following steps: Step 1: heating nitrogen to obtain hot nitrogen; Step 2: Mix the hot nitrogen obtained in step 1 with the product gas to reduce the volume fraction of water vapor in the original product gas, thereby reducing the recondensation temperature of the product gas.

4. The method for preventing blocking of product gas from urea hydrolysis to ammonia according to claim 3, characterized in that: In step 2, the hot nitrogen accounts for 20-30% of the product gas mass.

5. A method for preventing blockage of product gas from urea hydrolysis to ammonia according to claim 3 or 4, characterized in that: The operation steps of step 1 are as follows: the nitrogen in the nitrogen generator (3) enters the heat exchanger (6) through the nitrogen supply pipeline (4) for heat exchange to obtain hot nitrogen.

6. A method for preventing blocking of product gas from urea hydrolysis to ammonia according to claim 3 or 4, characterized in that: The temperature of the hot nitrogen is 140-150°C.

7. A method for preventing blocking of product gas from urea hydrolysis to ammonia according to claim 3 or 4, characterized in that: In step 2, the flow controller (7) detects and controls the flow of the first regulating valve (5) according to the mass ratio of nitrogen to product.

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